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MODUL PRAKTIKUM
PROSES MANUFAKTUR II
LABORATORIUM PENGECORAN LOGAM
KEMENTRIAN RISET TEKNOLOGI DAN PENDIDIKAN TINGGI
UNIVERSITAS BRAWIJAYA
FAKULTAS TEKNIK
JURUSAN TEKNIK MESIN
MALANG
2021
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 mengetahui dan memahami tahapan pengujian komposisi pasir cetak.
3. Praktikan mampu menganalisis hasil pengujian komposisi pasir cetak.
1.2 Dasar Teori
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(Heine, 1976:85)
Syarat-syarat pasir cetak antara lain:
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(Surdia dan Chijiwa, 1975:109-110)
1.2.1 Definisi Pasir
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(Heine, 1987:86)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.1.1. Macam - macam Pasir Cetak
Tabel 1.3
Macam - Macam Pasir
Sumber: Jain (1976:63)
A. Pasir alami
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(Surdia dan Chijiwa, 1975:110)
B. Pasir Buatan
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.1.2 Bentuk Butiran Pasir
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(Jain, 1976:49)
1.2.1.3 Distribusi Besar Butir Pasir Cetak
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Tabel 1.4
Tabel Skala Sieve (Ayakan)
Sumber: Heine (1976:102)
Tabel 1.5
Contoh perhitungan distribusi AFS number
Sumber: Heine (1976:102)
Tabel 1.5 menunjukkan contoh perhitungan distribusi AFS number yang dapat
dicari dengan rumus berikut:
AFSn = Total Produk
Total Persent Retained
= Σ(Wi x Mi) ...............................................................................................
(1-1)
Σ Wi
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Keterangan:
AFSn : Nomor Kehalusan Butir Pasir Cetak Standard AFS
Wi : Berat Pasir Pada Ayakan Ke-i
Mi : Pelipat Dari Tabel
1.2.2 Definisi dan Fungsi Kadar Pengikat
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(Heine, 1976:86)
Kadar pengikat dapat dihitung dengan rumus:
Kadar Pengikat = Berat awal - Berat akhir
100% − Kadar air Berat awal
................................. (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).
(Surdia dan Chijiwa, 1999:121)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.2.1 Macam - Macam Pengikat
Tabel 1.6
Macam - macam pengikat
Sumber : Heine (1976:89)
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(Chastain, 2004:145)
1. Fireclay
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(Chastain, 2004:145)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
2. Bentonit
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(Chastain, 2004:145)
a. Western bentonite
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(Chastain, 2004:145)
b. Southern bentonite
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(Chastain, 2004:145)
1.2.3 Definisi Kadar Air
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(Heine, 2001:88)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Kadar air (%) =
Keterangan:
Berat Awal − Berat Akhir
Berat Awal
x 100 % ................................................... (1-3)
Berat awal : berat pasir cetak sebelum dilakukan pemanasan (termasuk berat pasir, kadar
air, dan kadar pengikat) (gram)
Berat akhir : berat pasir cetak setelah dilakukan pemanasan (termasuk berat pasir dan
kadar pengikat) (gram)
(Surdia dan Chijiwa, 1991:118)
1.2.3.1 Macam-Macam Air Pada Pasir Cetak
a. Air Terikat
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(Heine, 1976:88)
b. Air Bebas
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(Heine, 1976:111)
1.2.3.2 Penguapan Kadar Air Pasir Cetak
Penguapan kadar air pasir cetak adalah .........................................................................
...............................................................................................................................................
Penguapan rata-rata = 𝑗𝑢𝑚𝑙𝑎ℎ 𝑝𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛
……………………………………………………………(1-4)
𝑗𝑢𝑚𝑙𝑎ℎ 𝑠𝑝𝑒𝑠𝑖𝑚𝑒𝑛
Laju penguapan kadar air pasir cetak adalah .................................................................
...............................................................................................................................................
Laju penguapan = 𝑃𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛 𝑟𝑎𝑡−𝑟𝑎𝑡𝑎 ………………………………………………………………(1-5)
𝑊𝑎𝑘𝑡𝑢
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
1.2.3.3 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 1.2 Mesin pengguncang rotap
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas
Brawijaya
Laboratorium Pengecoran Logam
Jurusan Mesin 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:
Gambar 1.3 Timbangan Elektrik
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas Brawijaya
3. Cawan
Alat ini digunakan untuk wadah spesimen yang akan di gunakan. Berikut
Spesifikasi:
Tipe Produk : Weighing dish
Diameter : 90mm
Kapasitas : 80ml
Gambar 1.4 Cawan
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik
Universitas Brawijaya
Merk : Melter
Frekuensi : 50-60 Hz
Type : PJ 3000
Voltase :100-120V 80mA /200-240V 45Ma
Laboratorium Pengecoran Logam
Jurusan Mesin 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 spesimen 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 1.5 Kompor listrik
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas Brawijaya
Laboratorium Pengecoran Logam
Jurusan Mesin 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 1.6 Panci
Sumber : Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas 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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Gambar 1.7 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 %
- Air sebanyak 950 ml
1.3.2.2 Urutan Kerja Pengujian
Urutan kerja pengujian kadar pengikat pasir cetak adalah:
1. Timbang pasir cetak seberat 100 gram sebagai spesimen.
2. Larutkan 2,5 % NaOH ke dalam 950 ml air pada panci.
3. Masukkan pasir cetak ke dalam larutan NaOH.
4. Aduk campuran tersebut dan biarkan pasir 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 ulangi langkah kerja 4, 5, 6 dan diamkan
selama 5 menit hingga airnya jernih.
7. Panaskan pasir cetak dalam panci dengan kompor listrik pada daya 600W.
8. Aduk pasir hingga kering.
9. Timbang pasir cetak kering dan catat hasilnya.
10. Hitung kadar lempung dengan rumus 1-2.
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 1.8 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 = ..... %
• Pengikat = ..... %
• Air = ..... %
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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. Mengatur temperatur dengan menekan tombol F1 dan tekan F1 kembali untuk
menaikan suhu sampai 110o C kemudian tekan ENTER.
4. Mengatur waktu pemanasan dengan menekan tombol F2 dan tekan tombol F1 untuk
mengatur waktu sampai 10 menit kemudian tekan ENTER.
5. Masukan cawan pertama kedalam alat penentu kelembapan kemudian panaskan pada
suhu sampai 110o C selama 10 menit
6. Tekan ENTER untuk menghilangkan TAR lalu letakkan spesimen 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 mengetahui dan memahami tahapan pengujian karakteristik pasir cetak.
3. Praktikan mampu menganalisis hasil pengujian karakteristik pasir cetak.
2.2 Dasar Teori
2.2.1 Definisi Karakteristik Pasir Cetak
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(Jain, 1999:48)
2.2.1.1 Permeabilitas
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(Heine, 1976:96)
Nilai permeabilitas (P) dapat ditentukan dengan perhitungan :
P = V H ................................................................................................
(2-1)
p AT
Dengan :
P = permeabilitas (ml/cm2 . menit)
V = volume udara (ml)(1ml=cm3)
H = tinggi spesimen (cm)
P = tekanan udara (gr/cm2)(1gr/cm2 = 1cmKa)
A = luas penampang spesimen (cm2)
T = waktu yang diperlukan untuk mengalirkan 1 liter udara (menit) (Suprapto, 2017:87)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
2.2.1.2 Kekuatan
Kekuatan adalah .............................................................................................................
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Adapun macam-macam kekuatan :
A. Berdasarkan arah gaya :
Gambar 2.1 (a) Gaya tekan; (b) Gaya geser; (c) Gaya tarik
Sumber: Beeley (1976:186)
1. Kekuatan Tekan
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......................................................................................................... (Heine, 1976:95)
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
2. Kekuatan Geser
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..................................................................................................... (Heine, 1976:95)
3. Kekuatan Tarik
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..................................................................................................... (Heine, 1976:95)
B. Berdasarkan kadar air :
1. Kekuatan Basah
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
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 (1980:112)
• Pengaruh kadar air terhadap Kekuatan
a. Kekuatan Basah
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Laboratorium Pengecoran Logam
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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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Gambar 2.3 Hubungan kadar lempung dan kekuatan
Sumber: Heine (1976:109)
3. Distribusi Besar Butir Pasir Cetak
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4. 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 (1999:49)
a. Butir Pasir Rounded
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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
b. Butir Pasir Subangular
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c. Butir Pasir Angular
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d. Butir Pasir Compound
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5. Pemadatan
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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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Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
..........................................................................................................................
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c. Pengaruh Kekuatan Tarik
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2.3. Pelaksanaan Pengujian
2.3.1. Pengujian Permeabilitas Pasir Cetak
2.3.1.1. Alat dan Bahan
A. Alat-alat yang digunakan
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Gambar 2.5 Sand rammer
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik 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
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
Laboratorium Pengecoran Logam
Jurusan Mesin Universitas Brawijaya
Buatan : Jerman Barat
Fabr 1725
Gambar 2.7 Permeabilitas meter
Sumber: Laboratorium Pengecoran Logam Jurusan Mesin Fakultas Teknik Universitas Brawijaya
4. Timbangan Elektrik
Alat ini digunakan untuk menimbang bahan dan berat spesimen yang akan
digunakan dalam pengujian seperti pada gambar 1.2
B. Bahan-bahan yang digunakan
Bahan yang digunakan untuk pengujian karakteristik pasir cetak antara lain :
- Pasir silika ............ %
- Pengikat ................ %
- Air ......................... %
Dimana 𝜌 air = 1 g/ml =1 g/cc
Maka 200 ml = 200 cc
2.3.1.2. Urutan Kerja Pengujian
1. Panaskan pasir cetak selama 45 menit dengan temperatur 275o C
2. Siapkan 150 gr pasir cetak untuk pengujian ini dengan menggunakan sand rammer.
3. Buka pelindung orifice dan pilihlah salah satu posisi penunjuk skala yang akan
digunakan.
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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. 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.
5. Letakkan tabung spesimen berikut spesimen di dalamnya pada orifice.
6. 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.
7. Catat besar P spesimen pasir cetak dengan tekanan yang terbaca pada skala
permeabilitas meter saat 1000 cc udara yang sudah terlewatkan.
8. Catat waktu yang dibutuhkan untuk mengalirkan udara sebanyak 2000 cc melalui
tabung spesimen pasir cetak yang diuji.
9. Ulangi langkah 1 – 8 sampai spesimen 3 serta catat data P (tekanan).
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
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
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.
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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 275C 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.
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 275C selama 45 menit.
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31
PL III
PERENCANAAN PENGECORAN LOGAM
3.1 Tujuan
1. Praktikan mampu mengetahui, memahami dan mempersiapkan apa saja yang dibutuhkan
dalam perencanaan pengecoran logam.
2. Praktikan dapat merencanakan 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
........................................................................................................................................
...............................................................................................................................................
(Heine, 1976:8)
Pada pemilihan bahan pola perlu memperhatikan faktor – faktor seperti:
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
Material pola yang baik seharusnya:
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Jain, 1979:7)
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Jurusan Mesin Universitas Brawijaya
3.2.1.2 Macam-Macam Pola
1. Pola Pejal
.................................................................................................................................
........................................................................................................................................
a. Pola Tunggal
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
b. Pola Belahan
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
c. Pola Setengah
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
d. Pola Belahan Banyak
.............................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
e. Pola Penarikan Terpisah
..........................................................................................................................
.................................................................................................................................
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33
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
f. Pola Penarikan Sebagian
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:57)
2. Pola Plat Pasangan
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:58)
3. Pola Cope dan Drag
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:58)
4. Pola Cetakan Sapuan
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:58)
5. Pola Penggeret Dengan Penuntun
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
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Jurusan Mesin Universitas Brawijaya
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:58)
6. Pola Penggeret Dengan Rangka Cetak
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:59)
7. Pola Kerangka A
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:59)
8. Pola Kerangka B
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:59)
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35
3.2.1.3 Bahan Pola
Tabel 3.1
Karakteristik dari bahan pola Rating
Characteristic 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 (1989:303)
Keterangan:
E = Excellent
G = Good
F = Fair
P = Poor
........................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
3.2.1.4 Perencanaan Pembuatan Pola
a. Penentuan Cope dan Drag
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
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Jurusan Mesin Universitas Brawijaya
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:51)
b. Penentuan Tambahan Penyusutan
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Heine, 1976:16)
c. Penentuan Tambahan Penyelesaian Mesin
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Heine, 1976:17)
d. Kemiringan Pola
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1986:53)
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37
3.2.2 Sistem Saluran
3.2.2.1 Pengertian
........................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
3.2.2.2 Bagian-Bagian Sistem Saluran
Gambar 3.15 Sistem saluran
Sumber: Surdia dan Chijiwa (1996:65)
a. Cawan Tuang (Pourin Basin)
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Jain, 2003:126)
b. Saluran Turun (Sprue)
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Jain, 2003:127)
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Jurusan Mesin Universitas Brawijaya
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
....................................................................................................... (3-3) 𝑅𝑎
A = 𝑚 .................................................................................... (3-4)
d X t X C√2 X g x h
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 (kg⁄ 3) m
t = waktu penuangan (s)
c = discharge coefficient
g = percepatan gravitasi (m⁄s2)
h = tinggi sprue efektif (m)
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√
39
• 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)
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)
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:67)
d. Saluran Masuk (Ingate)
...............................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:68)
e. Saluran Penambah (Riser)
.................................................................................................................................
........................................................................................................................................
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Jurusan Mesin Universitas Brawijaya
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:68)
• Hukum Chorinov
T𝑅𝑖𝑠𝑒𝑟 = 1,25 TProduk ..................................................................... (3-7) V1
2 V2 2
( ⁄A1) 𝑅𝑖𝑠𝑒𝑟 = 1,25 ( ⁄A2
) ......................................................... (3-8)
dengan :
V1 = volume riser
A1 = luas area riser
V2 = volume produk
A2 = luas area produk
Sumber: De Garmo (1997:354)
f. Dam dan Trap
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Surdia dan Chijiwa, 1996:65)
c. Core Making
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
Macam-macam core making antara lain:
• Green Sand Molding
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
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Jurusan Mesin Universitas Brawijaya
41
• CO2 Process
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Surdia dan Chijiwa, 1996:126)
3.2.2.3 Macam-Macam Sistem Saluran
1. Saluran Langsung
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
2. Saluran Bawah
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
3. Saluran Pensil
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
4. Saluran Bertingkat
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
5. Saluran Terompet
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
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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
........................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
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3.2.3.3 Bahan Pelapis
Pelapis dibagi menjadi 2, yaitu:
1. Lapisan cetakan untuk cetakan pasir basah.
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
2. Lapisan cetakan untuk pasir kering.
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
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.
Bahan yang digunakan adalah pasir cetak dengan komposisi pasir silika, bentonit,
dan air serta:
1. Pasir silika halus
2. Grafit
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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
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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.
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45
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
........................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Surdia dan Chijiwa, 1986:1)
Kelebihan pengecoran logam jika dibandingkan proses manufaktur yang lain adalah:
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
(Heine, 1976:1)
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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
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Kalpakjian, 2009:309)
b. Investment Casting
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Kalpakjian, 2009:317)
c. Evaporative Pattern Casting
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Kalpakjian, 2009:271)
2. Permanent Mold Casting
.................................................................................................................................
........................................................................................................................................
........................................................................................................................................
........................................................................................................................................
(Heine, 1976:285)
Macam-macam permanent mold casting adalah :
a. Die Casting (Cetak Tekan)
..........................................................................................................................
.................................................................................................................................
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47
.................................................................................................................................
.................................................................................................................................
(Groover, 2010:239)
Terdapat dua jenis cetak tekan, yaitu:
1. Mesin Cetak Tekan Ruang Panas (Hot Chamber)
...................................................................................................................
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:239)
2. Mesin Cetak Ruang Dingin (Cold Chamber)
...................................................................................................................
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:241)
b. Pengecoran Sentrifugal
...................................................................................................................
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:242)
Terdapat tiga jenis centrifugal casting, antara lain:
1. True Centrifugal Casting
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:243)
2. Semicentrifugal Casting
...................................................................................................................
..........................................................................................................................
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48
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:244)
3. Pengecoran Centrifuge
...................................................................................................................
..........................................................................................................................
..........................................................................................................................
(Groover, 2010:245)
c. Squeeze Casting
..........................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Kalpakjian, 2009:283)
4.2.2 Peleburan
.......................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
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A. Hidrogen Solubility
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(Beeley, 2001:256)
B. Tungku Peleburan
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4.2.3 Solidifikasi
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(Smith, 2001:122)
Proses Solidifikasi:
1. Tahapan dalam Pembekuan Logam (Solidifikasi)
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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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(Groover, 2010:214)
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B. Solidifikasi Logam Paduan
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(Groover, 2010:215)
4. Daerah Pembekuan
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(Groover, 2010:216)
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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(Beeley, 2001:112)
6. Mode Pembekuan
a. Mode Pembekuan Plane Interface Mode
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(Beeley, 2001:21)
b. Mode Pembekuan Jagged Interface Mode
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(Beeley, 2001:21)
c. Mode Pembekuan Independent Crystallization Mode
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(Beeley, 2001:21)
7. Thermal Properties
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(Sundari, 2011:4)
b. Cara Pengujian Fluiditas
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Ada beberapa macam cara pengujian fluiditas, diantaranya :
1. Spiral Mold Test
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(Beeley, 2001:17)
2. Vacuum Fluidity Test
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(Beeley, 2001:18)
3. Multiple Channel Fluidity Test Casting
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(Beeley, 2001:23)
4.2.5 Cacat Coran
1. Porositas
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(Surdia dan Chijiwa, 2013:214)
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2. Shift (Pergeseran)
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(Surdia dan Chijiwa, 2013:214)
3. Dirt and Sand Inclusion (Kotoran dan Inklusi Pasir)
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(Surdia dan Chijiwa, 2013:215)
4. Fin (Sirip)
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5. Shrinkage (Penyusutan)
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6. Hot Tears
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(Kalpakjian, 2009:249)
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7. Gas Defect
Gas defect atau cacat gas dibagi menjadi 2 jenis, yaitu:
a. Pin Holes
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(Jain, 1976:197)
b. Blow Holes
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(Jain, 1976:197)
8. Metal Penetration
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(Surdia dan Chijiwa, 2013:214)
9. Swell
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(Surdia dan Chijiwa, 2013:214)
10. Cold Shot dan Misrun
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(Groover, 2010:249)
4.2.6 Inspeksi
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Macam-macam metode pengujian yang sering dilakukan yaitu:
1. Liquid Penetrant Test
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(De Garmo, 2008:247)
2. Magnetic Particle Inspection
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(De Garmo, 2008:248)
3. Ultrasonic Test
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(De Garmo, 2008:251)
4. Eddy Current Test
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(De Garmo, 2008:309)
5. Radiographic Inspection
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(De Garmo, 2008:310)
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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Untuk memperoleh nilai true density dapat dicari dengan menggunakan persamaan
yang ada pada standar ASTME 252-84, yaitu:
𝜌 = 100 ........................................................................ (4-3)
𝑡ℎ (
% 𝐴𝑙 % 𝐶𝑢 % 𝐹𝑒 [
Dengan :
𝜌𝐴𝑙 )+ (
𝜌𝐶𝑢 )+(
𝜌𝐹𝑒 )+𝑒𝑡𝑐]
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 ..........................................................................................(4-4)
(𝑤𝑠−(𝑤𝑠𝑏− 𝑤𝑏))
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:
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% P = (1 − 𝜌𝑠 ) × 100% ............................................................................ (4-5) 𝜌𝑡ℎ
Dimana :
% P : Persentase porositas
(%) ρs : Apparent density (gr/cm3)
Ρth : True density (gr/cm3)
Recommended