LABORATORIUM PENGECORAN...

Laboratorium Pengecoran Logam

Jurusan Mesin Universitas Brawijaya

MODUL PRAKTIKUM

PROSES MANUFAKTUR II

LABORATORIUM PENGECORAN LOGAM

KEMENTRIAN RISET TEKNOLOGI DAN PENDIDIKAN TINGGI

UNIVERSITAS BRAWIJAYA

FAKULTAS TEKNIK

JURUSAN TEKNIK MESIN

MALANG

2020



PL I

PENGUJIAN KOMPOSISI PASIR CETAK

1.1 Tujuan Pengujian

1. Praktikan mengetahui dan memahami komposisi pasir cetak.

2. Praktikan mampu melakukan dan menganalisis hasil pengujian komposisi pasir cetak.

1.2 Dasar Teori

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Syarat Pasir Cetak

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

1.2.1 Definisi Pasir

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................



1.2.1.1 Macam – macam Pasir Cetak

A. Pasir alami

...................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

B. Pasir Buatan

...................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Tabel 1.1

Macam- Macam Pasir

Type of Sand Application Reasons

Natural moulding sand Light castings Permeability is not important and only

good surface finish may be required

Jobbing foundry Only a few castings may be required;

patterns may be of poor quality

Mechanised production of

castings with few cores

There is little influx of sand from cores

Dry sand moulding High permeability is not necessary as

little gas is envloved; patching is easy

Synthetic sand Heavily cored castings At shake-out, large amounts of clay-

free core sand enters moulding sand; regular clay additions are possible

Mechanised production Better hardness and uniform properties

can be obtained

High pressure moulding

Results in good hardness and

permeability, easy stripping, high

strength and toughness in mould

Sumber : Jain (1976,p.63)



1.2.1.2 Bentuk Butiran Pasir

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

1.2.1.3 Distribusi Ukuran Butir Cetak

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Tabel 1.2

Tabel Skala Sleeve (ayakan)

Sumber : Heine (1976,p.103)



Tabel 1.3

Contoh perhitungan distribusi AFS number

Sumber: Heine (1976,p.102)

Tabel 1.3 menunjukkan contoh perhitungan distribusi AFS number yang dapat dicari

dengan rumus berikut:

AFSn = Total Produk

Total Persent Retained =

Σ(Wi x Mi)

Σ Wi.....................................................................(1-1)

Keterangan:

AFSn : Nomor Kehalusan Butir Pasir Cetak Standard AFS

Wi : Berat Pasir Pada Ayakan Ke-i

Mi : Pelipat Dari Tabel

1.2.1.2 Definisi dan Fungsi Kadar Pengikat

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................



airkadar %100awalBerat

akhirBerat -awalBerat PengikatKadar −= ................................... (1-2)

Keterangan:

Kadar Pengikat : Jumlah persentase pengikat yang terdapa pada pasir cetak

Berat awal : berat pasir cetak yang telah bercampur dengan pengikat dan air

(gram) dan dilakukan ditimbang (gram).

Berat akhir : berat pasir cetak yang kadar pengikatnya telah dihilangkan

dengan cara dicuci dengan campuran NaOH (gram),

dikeringkan (gram) dan dilakukan penimbangan (gram).

1.2.1.2.1 Macam - macam Pengikat

Tabel 1.5

Macam-macam pengikat

Sumber : Heine (1976,p.89)

........................................................................................................................................

...............................................................................................................................................



...............................................................................................................................................

...............................................................................................................................................

1. Fireclay

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

2. Bentonit

...................................................................................................................................

..........................................................................................................................................

a. Western bentonite

...............................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

b. Southern bentonite

...............................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

......................................................................................................................................

1.2.1.3 Definisi Kadar Air

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................



...............................................................................................................................................

...............................................................................................................................................

Kadar air (%) = AwalBerat

AkhirBeratAwalBerat − x 100 % .......................................... (1-3)

Keterangan:

Berat awal : berat pasir sebelum dilakukan pemanasan (gram)

Berat akhir : berat pasir setelah dilakukan pemanasan (gram)

1.2.1.3.1 Macam-Macam Air Pada Pasir Cetak

a. Air Terikat

...................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

b. Air Bebas

...................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

1.2.1.3.2 Penguapan Kadar Air Pasir Cetak

Penguapan kadar air pasir cetak adalah ........................................................................

...............................................................................................................................................

...............................................................................................................................................

Penguapan rata-rata = 𝑗𝑢𝑚𝑙𝑎ℎ 𝑝𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛

𝑗𝑢𝑚𝑙𝑎ℎ 𝑠𝑝𝑒𝑠𝑖𝑚𝑒𝑛

Laju penguapan kadar air pasir cetak adalah ................................................................

...............................................................................................................................................

Laju penguapan = 𝑃𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛 𝑟𝑎𝑡−𝑟𝑎𝑡𝑎

𝑊𝑎𝑘𝑡𝑢



1.2.1.3.3 Faktor-Faktor Yang Mempengaruhi Penguapan Kadar Air

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

1.3 Pelaksanaan Pengujian

1.3.1 Pengujian Distribusi Besar Butir

1.3.1.1 Alat dan Bahan

Alat yang digunakan dalam pengujian ini adalah:

1. Mesin Pengguncang Rotap

Alat ini digunakan untuk menyaring pasir. Spesifikasi dari alat yang digunakan

adalah:

Jenis : Rotap

Tipe : VS 1

Merk : Retsch

Voltase : 220 V

Daya : 430 Watt

Frekuensi : 50 Hz



Gambar 1.1 Mesin pengguncang rotap

Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas

Brawijaya

2. Timbangan Elektrik

Alat ini digunakan untuk mengukur berat pasir cetak sebelum dan sesudah diukur

kandungan kadar airnya seperti terlihat pada gambar 1.2, berikut spesifikasinya :

Merk : Melter

Frekuensi : 50-60 Hz

Type : PJ 3000

Voltase :100-120V 80mA /200-240V 45Ma

Gambar 1.2 Timbangan Elektrik

Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik

Universitas Brawijaya

3. Cawan

Alat ini digunakan untuk wadah spesimen yang akan di masukan pada moisture

analyzer. Berikut Spesifikasi:

Tipe Produk : Weighing dish



Diameter : 90mm

Kapasitas : 80ml

Gambar 1.3 Cawan

Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik

Universitas Brawijaya

1.3.1.2 Urutan Kerja Pengujian Distribusi Besar Butir Pasir Cetak

1. Ambil pasir cetak sebesar 50 gram sebanyak 3 sampel.

2. Susun ayakan dari bawah ke atas dengan tingkat mesh semakin ke atas semakin besar

meshnya, kemudian letakkan pada mesin pengguncang Rotap.

3. Letakkan spesimen pasir cetak pada ayakan paling atas.

4. Hidupkan mesin pengguncang Rotap selama waktu dan juga frekuensi yang dibutuhkan.

5. Timbang berat pasir yang ada pada masing - masing mesh setelah selesai diayak.

6. Cari harga Sn dari tiap - tiap mesh yang ada dari tabel yang terlampir.

7. Hitung besar nomor kehalusan pasir cetak dalam skala FN maupun AFS.

1.3.2 Pengujian Kadar Pengikat

1.3.2.1 Alat dan Bahan

A. Alat dan bahan yang digunakan dalam pengujian kadar pengikat adalah sebagai berikut:

1. Kompor Listrik

Alat ini digunakan untuk mengeringkan specimen seperti yang terlihat pada

gambar dibawah ini.

Merk : Maspion (tipe 1)

Daya : 300-600 W

Berat :3 Kg

Dimensi (PxLxT) : 24x22x4 (cm)



Sistem pemanasan dengan elemen koil, bodi plat besi

Gambar 1.4 Kompor listrik

Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas

Brawijaya


Alat ini digunakan untuk menimbang spesimen sebelum dan sesudah

dikeringkan. (Untuk spesifikasi dan gambar dapat dilihat pada gambar 1.2 dan

penjelasannya).

3. Panci

Digunakan untuk tempat menghilangkan lempung pada pasir dan untuk

mengeringkan pasir pada kompor listrik. Dengan spesifikasi :

Bahan : Alumunium

Berat :400 g

Diameter : 25 cm

Tinggi :14 cm

Tebal : 1 mm

Gambar 1.5 Panci


Brawijaya

4. Gelas Ukur



Alat ini digunakan untuk mengukur jumlah larutan yang akan ditambahkan pada

pasir cetak. Dengan spesifikasi :

Kapasitas : 250 ml

Tinggi : 32 cm

Diameter : 4 cm

Tebal : 1,5 mm

Bahan : Glass

Gambar 1.6 Gelas ukur


Brawijaya

B. Bahan - bahan yang digunakan.

Bahan yang digunakan untuk pengujian kadar pengikat antara lain :

- Pasir cetak seberat 100 gram

- NaOH 2,5 gram

- Air sebanyak 950 ml

1.3.2.2 Urutan Kerja Pengujian

Urutan kerja pengujian kadar lempung pasir cetak adalah:

1. Timbang pasir cetak seberat 100 gram sebagai spesimen.

2. Larutkan pasir didalam 950 ml air pada panci.

3. Tambahkan NaOH 2,5 % sebanyak 50 ml.

4. Aduk campuran tersebut dan biarkan pesir mengendap selama 5 menit.

5. Buang airnya sebanyak 5/6 dari tinggi permukaan air. Ingatlah jangan sampai ada pasir

yang ikut terbuang.



6. Tambahkan airnya hingga seperti semula dan ulangilangkah kerja 4, 5, 6 dan diamkan

selama 5 menit hingga airnya jernih.

7. Panaskan pasir cetak dalam panci dengan kompor listrik pada suhu 110°C - 110°C.

8. Aduk pasir hingga kering.

9. Timbang pasir cetak kering dan catat hasilnya.

10. Hitung kadar lempung dengan rumus 1-3 :

airkadar %100awalBerat

akhirBerat -awalBerat PengikatKadar −= rata-rata



1.3.3 Pengujian Kadar Air

1.3.3.1 Alat Dan Bahan

A. Alat yang Digunakan

1. Moisture Analyzer

Alat ini digunakan untuk mengukur kandungan kadar air pasir cetak seperti yang

terlihat pada gambar 1.1. Spesifikasi alat :

Merk

: Saitorius

Voltase : 100-120/220-290 VAC

Model : MA 30

Frekuensi : 50-60 Hz

Arus : 3,3 A / 1,6 A

Gambar 1.7 Moisture Analyzer


Brawijaya


Alat ini digunakan untuk menimbang spesimen sebelum dan sesudah

dikeringkan. (Untuk spesifikasi dan gambar dapat dilihat pada gambar 1.2 dan

penjelasannya).

3. Cawan

Alat ini digunakan untuk menampung pasir silika. Bisa dilihat pada gambar 1.3

B. Bahan yang Digunakan

Bahan yang digunakan dalam pengujian ini adalah pasir cetak sebanyak ….. gr,

dengan komposisi:

• Pasir Silika = .... %



• Pengikat = .... %

• Air = .... %


Urutan kerja dalam pengujian kadar air adalah sebagai berikut :

1. Ambil pasir cetak kemudian timbanglah seberat 25 gram sebanyak 3 buah sebagai

spesimen.

2. Nyalakan Moisture Analyzer dengan menekan tombol ON/OFF sampai terdengar

bunyi alarm.

3. Masukan cawan pertama kedalam alat penentu kelembapan kemudian panaskan

pada suhu sampai 110o C selama 10 menit

4. Mengatur temperatur dengan menekan tombol F1 dan tekan F1 kembali untuk

menaikan suhu sampai 110o C kemudian tekan ENTER.

5. Mengatur waktu pemanasan dengan menekan tombol F2 dan tekan tombol F1

untuk mengatur waktu sampai 10 menit kemudian tekan ENTER.

6. Tekan ENTER untuk menghilangkan TAR lalu letakkan specimen di dalam cawan.

7. Tutup penutup Moisture Analyzer lalu tekan ENTER untuk mengeksekusinya.

8. Catat kandungan kadar air yang terbaca pada alat pengukur tiap menitnya.

9. Setelah terdengar alarm, ukurlah berat akhir pasir cetak setelah dikeringkan dengan

menekan tombol CF.

10. Ulangi langkah 3 – 9 untuk cawan berikutnya.



PL II

PENGUJIAN KARAKTERISTIK PASIR CETAK

2.1 Tujuan Pengujian Karakteristik Pasir Cetak

1. Praktikan mengetahui dan memahami karakteristik pasir cetak.

2. Praktikan mampu melakukan dan menganalisis hasil pengujian karakteristik pasir

cetak

2.2 Dasar Teori

2.2.1 Definisi Karakteristik Pasir Cetak

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

2.2.1.1 Permeabilitas

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Nilai permeabilitas (P) dapat ditentukan dengan perhitungan :

TAp

HV P

= ………………………………………………………………………….(2-1)

Dengan :

P = permeabilitas (ml/cm2 . menit)

V = volume udara (ml)(1ml=cm3)

H = tinggi spesimen (cm)

P = tekanan udara (1gr/cm2)(1gr/cm2 = 1cmKa)

A = luas penampang spesimen (cm2)

T = waktu yang diperlukan untuk mengalirkan 1 liter udara (menit)



2.2.1.2 Kekuatan

Kekuatan adalah .............................................................................................................

...............................................................................................................................................

............................................................................................................................................... .

Adapun macam-macam kekuatan :

A. Berdasarkan arah gaya (dapat dilihat pada gambar 2.1):

1. Kekuatan Tekan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Kekuatan Geser

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

3. Kekuatan Tarik

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................



B. Berdasarkan kadar air:

1. Kekuatan Basah

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Kekuatan Kering

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2.2.2 Faktor – faktor yang Mempengaruhi Karakteristik Pasir Cetak

1. Kadar Air

Gambar 2.2 Grafik pengaruh air dan bentonit pada pasir

Sumber: Surdia dan Chijiwa (1980,p.112)

• Pengaruh kadar air terhadap kekuatan

a. Kekuatan Basah

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................



b. Kekuatan Kering

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

• Pengaruh Kadar Air Terhadap Permeabilitas

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Kadar Pengikat

• Pengaruh kadar pengikat terhadap permeabilitas

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

• Pengaruh kadar pengikat terhadap kekuatan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

Gambar 2.3 Hubungan kadar lempung dan kekuatan

Sumber: Heine (1976,p.109)



3. Bentuk Butir Pasir Cetak

Dari bentuk butirannya, butir pasir dibagi menjadi 4 yaitu butir pasir bulat, butir

pasir sebagian bersudut, butir pasir bersudut, dan butir pasir compound.

(a) (b) (c) (d)

Gambar 2.4 Ukuran dan dimensi butiran pasir cetak (a) compounded (b) angular (c)

subangular (d) rounded

Sumber: Jain (1999,p.49)

a. Butir Pasir Rounded

..........................................................................................................................

.................................................................................................................................

b. Butir Pasir Subangular

..........................................................................................................................

.................................................................................................................................

c. Butir Pasir Angular

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

d. Butir Pasir Compound

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

4. Pemadatan

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................



5. Distribusi Besar Butir Pasir Cetak

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2.2.3 Pengaruh Karakteristik Pasir Cetak Terhadap Hasil Coran

1. Pengaruh Permeabilitas Terhadap Hasil Coran

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Pengaruh Kekuatan Pasir Cetak Terhadap Hasil Coran

a. Pengaruh Kekuatan Tekan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

b. Pengaruh Kekuatan Geser

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

c. Pengaruh Kekuatan Tarik

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................



2.3. Pelaksanaan Pengujian

2.3.1. Pengujian Permeabilitas Pasir Cetak

2.3.1.1. Alat dan Bahan

1. Sand Rammer

Alat ini digunakan untuk menumbuk pasir cetak menjadi bentuk spesimen yang

dikehendaki yaitu panjang 5,08 cm dan diameter 2 in (luas penampang = 20,268 cm2).

Dapat dilihat pada gambar 2.6.

Tipe : POU

Merk : George Fisher

Fabr : 2054

Buatan : Jerman Barat

Gambar 2.5 Sand rammer


Brawijaya (2019)



2. Stopwatch

Alat ini digunakan untuk mengukur waktu sampai 2000 cc udara seperti yang

terlihat pada gambar 2.6.

Gambar 2.6 Stopwatch


Brawijaya (2019)

3. Permeabilitas Meter

Alat ini digunakan untuk mengetahui seberapa besar angka permeabilitas dari

pasir cetak yang diuji udara seperti yang terlihat pada gambar 2.7.

Tipe : POU


Fabr : 1725

Gambar 2.7 Permeabilitas meter




Brawijaya (2019)


Alat ini digunakan untuk menimbang bahan dan berat spesimen yang akan

digunakan dalam pengujian seperti pada gambar pl1.

2.3.1.2. Urutan Kerja Pengujian

1. Siapkan 150 gr pasir cetak untuk pengujian ini dengan menggunakan sand rammer.

2. Panaskan pasir cetak selama 45 menit dengan temperatur 275o C

3. Buka pelindung orifice dan pilihlah salah satu posisi penunjuk skala yang akan

digunakan.

a. Skala biru untuk skala orifice 0,5 mm P = 0 – 50 cm3/menit

b. Skala merah untuk skala orifice 1,5 mm P = 0 – 500 cm3/menit

• Skala P dibaca dari skala merah bagian luar dari pengukuran tekanan.

• Skala paling dalam menunjukkan tekanan dinamis antara orifice dan

spesimen dalam mm kolom air.

4. Isi tabung dengan air secukupnya.

5. Memutar kran pada posisi B dan angkat tabung udara ke atas secara perlahan – lahan

hingga angka nol terlihat tepat pada batas tabung bawah lalu kunci pada posisi E.

6. Letakkan tabung spesimen berikut spesimen di dalamnya pada orifice.

7. Putar kran pada posisi A bersamaan mulai menghitung waktu dengan stopwatch saat

udara dialirkan ke spesimen pasir cetak. Hal ini ditandai dengan tabung udara mulai

turun ke bawah.

8. Catat besar P spesimen pasir cetak dengan tekanan yang terbaca pada skala

permeabilitas meter saat 1000 cc udara yang sudah terlewatkan.

9. Catat waktu yang dibutuhkan untuk mengalirkan udara sebanyak 2000 cc melalui

tabung spesimen pasir cetak yang diuji.

2.3.2. Pengujian Kekuatan Pasir Cetak

2.3.2.1 Alat Dan Bahan

1. Universal strenght machine

Alat ini digunakan untuk menguji kekuatan pasir cetak udara seperti yang terlihat

pada gambar 2.8.



Merk : George Fischer


Gambar 2.8 Permeabilitas meter


Brawijaya

2. Sand Rammer

Alat ini digunakan untuk menumbuk pasir cetak menjadi bentuk spesimen yang

dikehendaki yaitu panjang 5 cm dan diameter 2in (luas penampang = 20,268 cm2).


Alat ini digunakan untuk menimbang bahan dan berat spesimen yang akan

digunakan dalam pengujian.

Bahan yang digunakan adalah pasir cetak dengan komposisi

1. Pasir silika : ... %

2. Bentonit : ... %

3. Air : ... %


• Urutan kerja pengujian kekuatan tekan



a. Langkah pengujian tanpa perlakuan panas

1. Ambil campuran pasir cetak seberat 150 gram, lalu buat spesimen uji tekan

dengan menggunakan sand rammer (spesimen sebanyak 4 buah).

2. Pasang kepala uji tekan pasir cetak pada alat uji kekuatan pasir cetak.

3. Letakkan spesimen pada kepala uji tekan pasir cetak secara hati-hati jangan

sampai rusak.

4. Putar handwheel secara terus-menerus dengan putaran konstan dan perlahan-

lahan hingga hancur.

5. Baca dan catat besar kekuatan tekan pasir cetak tersebut (lengkap dengan

satuannya) pada skala paling luar yang terdapat pada alat uji tekan pasir

cetak.

6. Lakukan langkah 1-5 untuk spesimen berikutnya.

b. Langkah pengujian dengan perlakukan panas.

Langkah pengujian sama dengan tanpa perlakuan panas, hanya setelah pasir

cetak dibuat spesimen uji tekan, dilakukan pemanasan dalam dapur pemanas

dengan suhu 275 C selama 45 menit.

• Urutan kerja pengujian kekuatan geser

a. Langkah-langkah pengujian tanpa perlakuan panas

1. Ambil campuran pasir cetak seberat 150 gram, kemudian buat spesimen uji

geser dengan sand rammer (spesimen sebanyak 4 buah).

2. Pasang kepala uji geser pasir cetak pada alat uji kekuatan geser pasir cetak.

3. Letakkan spesimen pada kepala uji geser secara hati-hati jangan sampai

spesimen rusak.


lahan hingga spesimen hancur.

5. Baca dan catat besar kekuatan tekan pasir cetak tersebut pada skala yang di

tengah pada alat uji geser tersebut.

b. Langkah pengujian dengan perlakuan panas.

Langkah pengujian sama dengan tanpa perlakuan, hanya setelah pasir cetak

dibentuk spesimen uji geser, dilakukan pemanasan dalam dapur pemanasan

dengan suhu 275 C selama 45 menit.

• Urutan kerja pengujian kekuatan tarik pasir cetak

a. Langkah-langkah pengujian tanpa perlakuan panas



1. Ambil campuran pasir cetak seberat 125 gram, lalu buat spesimen uji tarik

dengan menggunakan sand rammer (spesimen sebanyak 4 buah).

2. Pasang kepala uji tarik pasir cetak pada alat uji kekuatan pasir cetak

3. Letakkan spesimen pada kepala uji tarik pasir cetak secara hati-hati jangan

sampai rusak.


lahan hingga spesimen hancur.

5. Baca dan catat besar kekuatan tarik pasir cetak tersebut (lengkap dengan

satuannya) pada skala paling dalam yang terdapat pada alat uji tarik pasir

cetak.

6. Lakukan langkah 1-5 untuk spesimen berikutnya.

b. Langkah pengujian dengan perlakuan panas.

Langkah pengujian sama dengan tanpa perlakuan, hanya setelah pasir cetak

dibentuk spesimen uji tarik, dilakukan pemanasan dalam dapur pemanasan dengan

suhu 275 C selama 45 menit.

29



PL III

PERENCANAAN PENGECORAN LOGAM

3.1 Tujuan

1. Praktikan mampu memahami dan mempersiapkan apa saja yang dibutuhkan dalam

perencanaan pengecoran logam.

2. Praktikan dapat merencanakan cetakan pasir, sistem saluran dan pola.

3. Praktikan dapat membuat cetakan pasir.

4. Praktikan mampu memecahkan masalah - masalah dalam perencanaan pengecoran

logam.

3.2 Dasar Teori

3.2.1 Pola

3.2.1.1 Pengertian Pola

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Pada pemilihan bahan pola perlu memperhatikan faktor – faktor seperti:

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Material pola yang baik seharusnya:

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................



3.2.1.2 Macam-Macam Pola

1. Pola Pejal

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

a. Pola Tunggal

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

b. Pola Belahan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

c. Pola Setengah

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

d. Pola Belahan Banyak

.............................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

e. Pola Penarikan Terpisah

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

31



f. Pola Penarikan Sebagian

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Pola Plat Pasangan

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3. Pola Cope dan Drag

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

4. Pola Cetakan Sapuan

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

5. Pola Penggeret Dengan Penuntun

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

6. Pola Penggeret Dengan Rangka Cetak

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................



7. Pola Kerangka A

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

8. Pola Kerangka B

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3.2.1.3 Bahan Pola

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Tabel 3.1

Karakteristik dari bahan pola

Characteristic

Rating

Wood Aluminum Steel Plastic Cast Iron

Machinability E G F G G

Wear Resistance P G E F E

Strength F G E G G

Weight E G P G P

Repairability E P G F G

Resistance to:

Corrosion E E P E P

Swelling P E E E E

Sumber: Kalpakjian (1989,p.303)

33



Keterangan:

E = Excellent

G = Good

F = Fair

P = Poor

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

3.2.1.4 Perencanaan Pembuatan Pola

a. Penentuan Cope dan Drag

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

b. Penentuan Tambahan Penyusutan

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................



c. Penentuan Tambahan Penyelesaian Mesin

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

d. Kemiringan Pola

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3.2.2 Sistem Saluran

3.2.2.1 Pengertian

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

35



3.2.2.2 Bagian-Bagian Sistem Saluran

Gambar 3.15 Sistem saluran

Sumber: Surdia dan Chijiwa (1996,p.65)

a. Cawan Tuang (Pourin Basin)

...............................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

b. Saluran Turun (Sprue)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

Pada perhitungan sprue ada 2 persamaan, yaitu choke area dan kontinuitas.

• Choke Area

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................



Tabel 3.1

Nilai konstan (b) untuk ketebalan Casting berbeda

Ketebalan Dinding Di bawah 6 mm Antara 6-12 mm Di atas 12 mm

Constanta b 0.99 0.87 0.47

Sumber: Victor Anjo (2013)

𝑅 = 𝑏√𝑊 ................................................................................................ (3-1)

𝑅𝑎 =𝑅

𝐾 .𝐶 ................................................................................................. (3-2)

𝑡 =𝑊

𝑅𝑎 ....................................................................................................... (3-3)

A =𝑚

d x t x c√2 x g x h .................................................................................... (3-4)

dengan :

R = pouring rate (kg/s)

A = choke area

W = massa yang dituang (kg)

Ra = pouring rate yang disesuaikan (kg/s)

K = fluiditas logam

C = efek gesekan dengan nilai 0,85-0,90 untuk sprue yang meruncing dalam sistem

gating.

d = massa jenis logam (kgm3⁄ )

t = waktu penuangan (s)

c = faktor efisiensi

g = percepatan gravitasi (ms2⁄ )

h = tinggi sprue efektif (m)

• Persamaan Kontinuitas

Digunakan untuk .............................................................................................

.................................................................................................................................

.................................................................................................................................

Q = AatasVatas = AbawahVbawah ............................................................... (3-4)

√2 x g x hatas x Aatas = √2 x g x hbawah x Abawah ............................................ (3-5)

Aatas = √hbawah

hatas x Abawah ............................................................ (3-6)

37



dengan :

Q : Kecepatan aliran volume

Aatas : Luas penampang bagian atas coran

Vatas : Kecepatan aliran

Abawah : Luas penampang bagian bawah coran

Vbawah : Kecepatan aliran

c. Saluran Pengalir (Runner)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

d. Saluran Masuk (Ingate)

...............................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

e. Saluran Penambah (Riser)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................



• Hukum Chorinov

T𝑅𝑖𝑠𝑒𝑟 = 1,25 TProduk ............................................................................. (3-7)

(V1

A1⁄ )

2

𝑅𝑖𝑠𝑒𝑟 = 1,25 (V2

A2⁄ )

2

......................................................... (3-8)

dengan :

V1 = volume riser

A1 = luas area riser

V2 = volume produk

A2 = luas area produk

Sumber: De Garmo (1997,p.354)

f. Dam dan Trap

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

c. Core Making

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

Macam-macam core making antara lain:

• Green Sand Molding

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

• CO2 Process

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

39



.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

3.2.2.3 Macam-Macam Sistem Saluran

1. Saluran Langsung

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Saluran Bawah

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3. Saluran Pensil

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

4. Saluran Bertingkat

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

5. Saluran Terompet

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

6. Saluran Cincin

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................



7. Saluran Pisah

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

8. Saluran Baji

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3.2.3 Pelapis

Pelapis adalah ................................................................................................................

...............................................................................................................................................

3.2.3.1 Fungsi Pelapis

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

3.2.3.2 Syarat Pelapis

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

3.2.3.3 Bahan Pelapis

Pelapis dibagi menjadi 2, yaitu:

1. Lapisan cetakan untuk cetakan pasir basah.

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Lapisan cetakan untuk pasir kering.

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

41



........................................................................................................................................

........................................................................................................................................

3.4 Urutan Kerja Pembuatan Cetakan Pasir

3.4.1 Alat dan Bahan

Alat-alat yang digunakan utuk membuat cetakan pasir adalah:

1. Rangka Cetak ( Cope dan Drag )

Alat ini digunakan sebagai tempat untuk membuat cetakan pasir.

2. Pola

Alat ini digunakan untuk membuat bentuk/rongga cetakan benda kerja yang

sudah diberi penambahan toleransi.

3. Saluran Masuk dan Riser

Alat ini digunakan sebagai tempat mengalirya logam cair dalam cetakan.

4. Papan Datar

Alat ini digunakan untuk tempat alas dalam membuat cetakan.

5. Kamera

Alat ini digunakan sebagai dokumentasi.

6. Mal Gambar

………………………………………….

7. Penggaris

………………………………………

Bahan yang digunakan adalah pasir cetak dengan komposisi pasir silika, bentonit,

dan air serta:

1. Pasir silika halus

2. Grafit

3.4.2 Urutan Kerja

Langkah - langkah dalam pembuatan cetakan adalah :

1. Aduk pasir cetak dengan komposisi tertentu dengan tangan agar campurannya merata.

2. Taburi pola dengan grafit secara merata.

3. Letakkan mal gambar diatas papan datar, kemudian letakkan drag dalam posisi

terbalik, lalu letakkan pola sesuai dengan mal gambar.

4. Masukkan pasir cetak dan padatkan hingga rata dan padat memenuhi drag. Ratakan

permukaan pasir cetak bagian atas dengan penggaris.



5. Balik drag kemudian taburi dengan pasir silika halus agar permukaan pisah pada pasir

cetak tidak lengket, kemudian ratakan dengan kuas secara hati – hati.

6. Letakkan cope diatas drag, kemudian posisikan pola sesuai dengan pola sebelumnya.

7. Isi cope dengan pasir cetak, padatkan hingga cope terisi penuh lalu ratakan permukaan

dengan penggaris. Selama pemadatan jangan sampai pola berubah posisinya.

8. Setelah cope dan drag terisi penuh, angkat cope dari drag secara hati - hati, kemudian

cabut polanya. Apabila masih terjadi kerusakan, maka tempatkan kembali pola ke

posisi semula dan isi bagian – bagian yang rusak tersebut dengan pasir cetak.

9. Apabila pola telah selesai dicabut, letakkan kembali semua cope diatas drag,

kemudian cetakan yang sudah jadi tersebut letakkan ditempat yang aman dan datar.

43



PL IV

PENUANGAN LOGAM DAN INSPEKSI

4.1 Tujuan

1. Praktikan mengetahui dan memahami pengecoran logam

2. Praktikan mengetahui dan memahami macam cacat coran dan inspeksi

3. Praktikan mampu melakukan inspeksi dan menganalisis hasil coran

4.2 Dasar Teori

4.2.1 Pengecoran Logam

.........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Kelebihan pengecoran logam jika dibandingkan proses manufaktur yang lain adalah:

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

44



Dalam pengecoran logam, dibagi menjadi dua berdasarkan pada cetakan pengecoran, yaitu

:

1. Expandable Mold Casting

Expandable mold casting adalah ............................................................................

........................................................................................................................................ .

Macam – macamnya yaitu:

a. Sand Casting

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

b. Investment Casting

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

c. Evaporative Pattern Casting

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Permanent Mold Casting

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

Macam-macam permanent mold casting adalah :

a. Die Casting (Cetak Tekan)

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

45



Terdapat dua jenis cetak tekan, yaitu:

1. Mesin Cetak Tekan Ruang Panas (Hot Chamber)

...................................................................................................................

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

2. Mesin Cetak Ruang Dingin (Cold Chamber)

................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

b. Pengecoran Sentrifugal

...................................................................................................................

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

Terdapat tiga jenis centrifugal casting, antara lain:

1. True Centrifugal Casting

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

2. Semicentrifugal Casting

...................................................................................................................

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

3. Pengecoran Centrifuge

...................................................................................................................

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

46



c. Squeeze Casting

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

4.2.2 Peleburan

.......................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

A. Hidrogen Solubility

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

B. Tungku Peleburan

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

4.2.3 Solidifikasi

........................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

47



Proses Solidifikasi:

1. Tahapan dalam Pembekuan Logam (Solidifikasi)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Pembentukan Kristal dalam Logam Cair dan Pembentukan Struktur Butir

...........................................................................................................

.................................................................................................................

.................................................................................................................

.................................................................................................................

.................................................................................................................

3. Macam-macam Solidifikasi

A. Solidifikasi Logam Murni

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

B. Solidifikasi Logam Paduan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

4. Daerah Pembekuan

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

48



4.2.4 Fluiditas

a. Definisi Fluiditas

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

Faktor-faktor yang mempengaruhi fluiditas antara lain:

1. Viskositas

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Temperatur Penuangan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

3. Komposisi Logam

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

4. Permukaan Cetakan

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

5. Superheating

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

49



6. Mode Pembekuan

a. Mode Pembekuan Plane Interface Mode

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

b. Mode Pembekuan Jagged Interface Mode

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

c. Mode Pembekuan Independent Crystallization Mode

..........................................................................................................................

..........................................................................................................................

..........................................................................................................................

7. Thermal Properties

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

b. Cara Pengujian Fluiditas

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

Ada beberapa macam cara pengujian fluiditas, diantaranya :

1. Spiral Mold Test

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

2. Vacuum Fluidity Test

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

50



3. Multiple Channel Fluidity Test Casting

..........................................................................................................................

.................................................................................................................................

.................................................................................................................................

4.2.5 Cacat Coran

1. Porositas

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Shift (Pergeseran)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3. Dirt and Sand Inclusion (Kotoran dan Inklusi Pasir)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

4. Fin (Sirip)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

5. Shringkage (Penyusutan)

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

51



6. Hot Tears

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

7. Gas Defect

Gas defect atau cacat gas dibagi menjadi 2 jenis, yaitu:

a. Pin Holes

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

b. Blow Holes

.................................................................................................................................

.................................................................................................................................

.................................................................................................................................

8. Metal Penetration

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

9. Swell

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

10. Cold Shot dan Misrun

.................................................................................................................................

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

52



4.2.6 Inspeksi

.......................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

...............................................................................................................................................

Macam-macam metode pengujian yang sering dilakukan yaitu:

1. Liquid Penetrant Test

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

2. Magnetic Particle Inspection

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

3. Ultrasonic Test

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

4. Eddy Current Test

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

5. Radiographic Inspection

........................................................................................................................................

........................................................................................................................................

........................................................................................................................................

6. Uji Piknometri

Untuk mencari persentase porositas yang terdapat dalam suatu coran digunakan

perbandingan 2 buah densitas, yaitu:

a. True Density

.............................................................................................................................

....................................................................................................................................

....................................................................................................................................

53



...................................................................................................................................

Untuk memperoleh nilai true density dapat dicari dengan menggunakan persamaan

yang ada pada standar ASTME 252-84, yaitu:

𝜌𝑡ℎ = 100

[(% 𝐴𝑙

𝜌𝐴𝑙)+ (

% 𝐶𝑢

𝜌𝐶𝑢)+(

% 𝐹𝑒

𝜌𝐹𝑒)+𝑒𝑡𝑐]

........................................................................ (4-3)

Dengan :

𝜌𝑡ℎ : True density (gr/cm2)

𝜌𝐴𝑙 𝜌𝐶𝑢 𝜌𝐹𝑒 etc : Densitas unsur (gr/cm3)

% 𝑙 %𝐶𝑢 %𝐹𝑒 etc : Presentase berat unsur

b. Apparent Density

............................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

Untuk perhitungan apparent density, menggunakan persamaan sesuai karakter

struktur ASTMB3H-93 sebagai berikut:

𝜌𝑠 = 𝜌𝑤 𝑤𝑠

(𝑤𝑠−(𝑤𝑠𝑏− 𝑤𝑏))

..........................................................................................(4-4)

Dengan :

ρs : Apparent density (gr/cm3)

ρw : Density air (gr/cm3)

ws : Berat sample udara (gr)

wsb : Berat sample dan keranjang didalam air (gr)

wb : Berat keranjang (gr)

...................................................................................................................................

...................................................................................................................................

untuk dapat menghitung prosentase porositas dapat dihitung dengan rumus :

% P = (1 − 𝜌𝑠

𝜌𝑡ℎ) × 100% ...............................................................................(4-5)

Dimana :

% P : Persentase porositas

54



(%) ρs : Apparent density (gr/cm3)

Ρth : True density (gr/cm3)

LABORATORIUM PENGECORAN...

Documents

Transcript of LABORATORIUM PENGECORAN...