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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
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Syarat Pasir Cetak
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1.2.1 Definisi Pasir
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.1.1 Macam – macam Pasir Cetak
A. Pasir alami
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B. Pasir Buatan
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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)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.1.2 Bentuk Butiran Pasir
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1.2.1.3 Distribusi Ukuran Butir Cetak
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Tabel 1.2
Tabel Skala Sleeve (ayakan)
Sumber : Heine (1976,p.103)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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)
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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1. Fireclay
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2. Bentonit
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a. Western bentonite
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b. Southern bentonite
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1.2.1.3 Definisi Kadar Air
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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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
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b. Air Bebas
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1.2.1.3.2 Penguapan Kadar Air Pasir Cetak
Penguapan kadar air pasir cetak adalah ........................................................................
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Penguapan rata-rata = 𝑗𝑢𝑚𝑙𝑎ℎ 𝑝𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛
𝑗𝑢𝑚𝑙𝑎ℎ 𝑠𝑝𝑒𝑠𝑖𝑚𝑒𝑛
Laju penguapan kadar air pasir cetak adalah ................................................................
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Laju penguapan = 𝑃𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛 𝑟𝑎𝑡−𝑟𝑎𝑡𝑎
𝑊𝑎𝑘𝑡𝑢
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.1.3.3 Faktor-Faktor Yang Mempengaruhi Penguapan Kadar Air
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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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Sistem pemanasan dengan elemen koil, bodi plat besi
Gambar 1.4 Kompor listrik
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya
2. Timbangan Elektrik
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
Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya
4. Gelas Ukur
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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
Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
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.
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya
2. Timbangan Elektrik
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 = .... %
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
• Pengikat = .... %
• Air = .... %
1.3.3.2 Urutan Kerja Pengujian
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.
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
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2.2.1.1 Permeabilitas
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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)
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Jurusan Mesin Universitas Brawijaya
2.2.1.2 Kekuatan
Kekuatan adalah .............................................................................................................
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Adapun macam-macam kekuatan :
A. Berdasarkan arah gaya (dapat dilihat pada gambar 2.1):
1. Kekuatan Tekan
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2. Kekuatan Geser
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3. Kekuatan Tarik
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Jurusan Mesin Universitas Brawijaya
B. Berdasarkan kadar air:
1. Kekuatan Basah
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2. Kekuatan Kering
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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
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Jurusan Mesin Universitas Brawijaya
b. Kekuatan Kering
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• Pengaruh Kadar Air Terhadap Permeabilitas
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2. Kadar Pengikat
• Pengaruh kadar pengikat terhadap permeabilitas
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• Pengaruh kadar pengikat terhadap kekuatan
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Gambar 2.3 Hubungan kadar lempung dan kekuatan
Sumber: Heine (1976,p.109)
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Jurusan Mesin Universitas Brawijaya
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
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b. Butir Pasir Subangular
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c. Butir Pasir Angular
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d. Butir Pasir Compound
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4. Pemadatan
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Jurusan Mesin Universitas Brawijaya
5. Distribusi Besar Butir Pasir Cetak
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2.2.3 Pengaruh Karakteristik Pasir Cetak Terhadap Hasil Coran
1. Pengaruh Permeabilitas Terhadap Hasil Coran
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2. Pengaruh Kekuatan Pasir Cetak Terhadap Hasil Coran
a. Pengaruh Kekuatan Tekan
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b. Pengaruh Kekuatan Geser
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c. Pengaruh Kekuatan Tarik
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya (2019)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
2. Stopwatch
Alat ini digunakan untuk mengukur waktu sampai 2000 cc udara seperti yang
terlihat pada gambar 2.6.
Gambar 2.6 Stopwatch
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
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
Buatan : Jerman Barat
Fabr : 1725
Gambar 2.7 Permeabilitas meter
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya (2019)
4. Timbangan Elektrik
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.
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Merk : George Fischer
Buatan : Jerman Barat
Gambar 2.8 Permeabilitas meter
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
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).
3. Timbangan Elektrik
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 : ... %
2.3.2.2 Urutan Kerja Pengujian
• Urutan kerja pengujian kekuatan tekan
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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.
4. Putar handwheel secara terus-menerus dengan putaran konstan dan perlahan-
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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.
4. Putar handwheel secara terus-menerus dengan putaran konstan dan perlahan-
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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:
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
3.2.1.2 Macam-Macam Pola
1. Pola Pejal
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
a. Pola Tunggal
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
b. Pola Belahan
..........................................................................................................................
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.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
c. Pola Setengah
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
d. Pola Belahan Banyak
.............................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
e. Pola Penarikan Terpisah
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
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31
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
f. Pola Penarikan Sebagian
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
2. Pola Plat Pasangan
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
3. Pola Cope dan Drag
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
4. Pola Cetakan Sapuan
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
5. Pola Penggeret Dengan Penuntun
.................................................................................................................................
........................................................................................................................................
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........................................................................................................................................
6. Pola Penggeret Dengan Rangka Cetak
.................................................................................................................................
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........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
7. Pola Kerangka A
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
8. Pola Kerangka B
.................................................................................................................................
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........................................................................................................................................
........................................................................................................................................
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
........................................................................................................................................
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........................................................................................................................................
........................................................................................................................................
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........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
c. Penentuan Tambahan Penyelesaian Mesin
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
d. Kemiringan Pola
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3.2.2 Sistem Saluran
3.2.2.1 Pengertian
........................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
35
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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)
.................................................................................................................................
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Pada perhitungan sprue ada 2 persamaan, yaitu choke area dan kontinuitas.
• Choke Area
..........................................................................................................................
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.................................................................................................................................
.................................................................................................................................
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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)
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d. Saluran Masuk (Ingate)
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e. Saluran Penambah (Riser)
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........................................................................................................................................
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
• 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
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c. Core Making
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Macam-macam core making antara lain:
• Green Sand Molding
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• CO2 Process
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39
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
.................................................................................................................................
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3.2.2.3 Macam-Macam Sistem Saluran
1. Saluran Langsung
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2. Saluran Bawah
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3. Saluran Pensil
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4. Saluran Bertingkat
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5. Saluran Terompet
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6. Saluran Cincin
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
7. Saluran Pisah
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8. Saluran Baji
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3.2.3 Pelapis
Pelapis adalah ................................................................................................................
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3.2.3.1 Fungsi Pelapis
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3.2.3.2 Syarat Pelapis
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3.2.3.3 Bahan Pelapis
Pelapis dibagi menjadi 2, yaitu:
1. Lapisan cetakan untuk cetakan pasir basah.
.................................................................................................................................
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........................................................................................................................................
2. Lapisan cetakan untuk pasir kering.
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41
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
........................................................................................................................................
........................................................................................................................................
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.
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
.........................................................................................................................................
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Kelebihan pengecoran logam jika dibandingkan proses manufaktur yang lain adalah:
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44
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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
..........................................................................................................................
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b. Investment Casting
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c. Evaporative Pattern Casting
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2. Permanent Mold Casting
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Macam-macam permanent mold casting adalah :
a. Die Casting (Cetak Tekan)
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45
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Terdapat dua jenis cetak tekan, yaitu:
1. Mesin Cetak Tekan Ruang Panas (Hot Chamber)
...................................................................................................................
..........................................................................................................................
..........................................................................................................................
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2. Mesin Cetak Ruang Dingin (Cold Chamber)
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b. Pengecoran Sentrifugal
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Terdapat tiga jenis centrifugal casting, antara lain:
1. True Centrifugal Casting
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2. Semicentrifugal Casting
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3. Pengecoran Centrifuge
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46
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
c. Squeeze Casting
..........................................................................................................................
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4.2.2 Peleburan
.......................................................................................................................................
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A. Hidrogen Solubility
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B. Tungku Peleburan
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4.2.3 Solidifikasi
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47
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Proses Solidifikasi:
1. Tahapan dalam Pembekuan Logam (Solidifikasi)
.................................................................................................................................
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........................................................................................................................................
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2. Pembentukan Kristal dalam Logam Cair dan Pembentukan Struktur Butir
...........................................................................................................
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3. Macam-macam Solidifikasi
A. Solidifikasi Logam Murni
..........................................................................................................................
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B. Solidifikasi Logam Paduan
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4. Daerah Pembekuan
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48
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
4.2.4 Fluiditas
a. Definisi Fluiditas
.................................................................................................................................
........................................................................................................................................
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........................................................................................................................................
Faktor-faktor yang mempengaruhi fluiditas antara lain:
1. Viskositas
..........................................................................................................................
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.................................................................................................................................
2. Temperatur Penuangan
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3. Komposisi Logam
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4. Permukaan Cetakan
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5. Superheating
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
6. Mode Pembekuan
a. Mode Pembekuan Plane Interface Mode
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b. Mode Pembekuan Jagged Interface Mode
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c. Mode Pembekuan Independent Crystallization Mode
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7. Thermal Properties
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b. Cara Pengujian Fluiditas
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Ada beberapa macam cara pengujian fluiditas, diantaranya :
1. Spiral Mold Test
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2. Vacuum Fluidity Test
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
3. Multiple Channel Fluidity Test Casting
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4.2.5 Cacat Coran
1. Porositas
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2. Shift (Pergeseran)
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3. Dirt and Sand Inclusion (Kotoran dan Inklusi Pasir)
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4. Fin (Sirip)
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5. Shringkage (Penyusutan)
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6. Hot Tears
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7. Gas Defect
Gas defect atau cacat gas dibagi menjadi 2 jenis, yaitu:
a. Pin Holes
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b. Blow Holes
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8. Metal Penetration
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9. Swell
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10. Cold Shot dan Misrun
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Jurusan Mesin Universitas Brawijaya
4.2.6 Inspeksi
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Macam-macam metode pengujian yang sering dilakukan yaitu:
1. Liquid Penetrant Test
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2. Magnetic Particle Inspection
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3. Ultrasonic Test
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4. Eddy Current Test
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5. Radiographic Inspection
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6. Uji Piknometri
Untuk mencari persentase porositas yang terdapat dalam suatu coran digunakan
perbandingan 2 buah densitas, yaitu:
a. True Density
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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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
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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)
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untuk dapat menghitung prosentase porositas dapat dihitung dengan rumus :
% P = (1 − 𝜌𝑠
𝜌𝑡ℎ) × 100% ...............................................................................(4-5)
Dimana :
% P : Persentase porositas
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Jurusan Mesin Universitas Brawijaya
(%) ρs : Apparent density (gr/cm3)
Ρth : True density (gr/cm3)
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