LABORATORIUM PENGECORAN LOGAM

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)



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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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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Tabel 1.4

Tabel Skala Sieve (Ayakan)

Sumber: Heine (1976:102)

Tabel 1.5

Contoh perhitungan distribusi AFS number


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



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).




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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2. Bentonit

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a. Western bentonite

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b. Southern bentonite

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1.2.3 Definisi Kadar Air

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(Heine, 2001:88)



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)


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

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Penguapan rata-rata = 𝑗𝑢𝑚𝑙𝑎ℎ 𝑝𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛

……………………………………………………………(1-4)

𝑗𝑢𝑚𝑙𝑎ℎ 𝑠𝑝𝑒𝑠𝑖𝑚𝑒𝑛

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

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Laju penguapan = 𝑃𝑒𝑛𝑔𝑢𝑎𝑝𝑎𝑛 𝑟𝑎𝑡−𝑟𝑎𝑡𝑎 ………………………………………………………………(1-5)

𝑊𝑎𝑘𝑡𝑢



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



Gambar 1.2 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:

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



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





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



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.



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


Alat ini digunakan untuk menimbang spesimen sebelum dan sesudah dikeringkan.

(Untuk spesifikasi dan gambar dapat dilihat pada gambar 1.2 dan penjelasannya).

3. Cawan

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

B. Bahan yang Digunakan

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

dengan komposisi:

• Pasir Silika = ..... %

• Pengikat = ..... %

• Air = ..... %




Urutan kerja dalam pengujian kadar air adalah sebagai berikut :

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

spesimen.

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

alarm.

3. 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.



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)



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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2. Kekuatan Geser

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3. Kekuatan Tarik

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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 (1980:112)

• Pengaruh kadar air terhadap Kekuatan

a. Kekuatan Basah

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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


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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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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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



Gambar 2.5 Sand rammer


2. Stopwatch

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

terlihat pada gambar 2.6.

Gambar 2.6 Stopwatch


3. Permeabilitas Meter

Alat ini digunakan untuk mengetahui seberapa besar angka permeabilitas dari pasir

cetak yang diuji udara seperti yang terlihat pada gambar 2.7.

Tipe : POU




Fabr 1725

Gambar 2.7 Permeabilitas meter



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.



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


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).


Alat ini digunakan untuk menimbang bahan dan berat spesimen yang akan

digunakan dalam pengujian.

Bahan yang digunakan adalah pasir cetak dengan komposisi

1. Pasir silika : ... %

2. Bentonit : ... %

3. Air : ... %


• Urutan kerja pengujian kekuatan tekan

a. Langkah pengujian tanpa perlakuan panas

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

dengan menggunakan sand rammer (spesimen sebanyak 4 buah).

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

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

sampai rusak.

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

lahan hingga hancur.

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

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

6. Lakukan langkah 1-5 untuk spesimen berikutnya.

b. Langkah pengujian dengan perlakukan panas.

Langkah pengujian sama dengan tanpa perlakuan panas, hanya setelah pasir

cetak dibuat spesimen uji tekan, dilakukan pemanasan dalam dapur pemanas

dengan suhu 275 C selama 45 menit.

• Urutan kerja pengujian kekuatan geser

a. Langkah-langkah pengujian tanpa perlakuan panas

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

geser dengan sand rammer (spesimen sebanyak 4 buah).

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

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

spesimen rusak.


lahan hingga spesimen hancur.



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

tengah pada alat uji geser tersebut.

b. Langkah pengujian dengan perlakuan panas.

Langkah pengujian sama dengan tanpa perlakuan, hanya setelah pasir cetak

dibentuk spesimen uji geser, dilakukan pemanasan dalam dapur pemanasan dengan

suhu 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.


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.



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)



3.2.1.2 Macam-Macam Pola

1. Pola Pejal

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

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

a. Pola Tunggal

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

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

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


b. Pola Belahan

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

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

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

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


c. Pola Setengah

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

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

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

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


d. Pola Belahan Banyak

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

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

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

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


e. Pola Penarikan Terpisah

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

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



33

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

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


f. Pola Penarikan Sebagian

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

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

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

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


2. Pola Plat Pasangan

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

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

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


3. Pola Cope dan Drag

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

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

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


4. Pola Cetakan Sapuan

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

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

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


5. Pola Penggeret Dengan Penuntun

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

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

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



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

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


6. Pola Penggeret Dengan Rangka Cetak

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

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

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

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


7. Pola Kerangka A

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

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

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

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


8. Pola Kerangka B

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

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

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




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

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

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

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

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



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

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

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

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

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


b. Penentuan Tambahan Penyusutan

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

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

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

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

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

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

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

(Heine, 1976:16)

c. Penentuan Tambahan Penyelesaian Mesin

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

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

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

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

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

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

(Heine, 1976:17)

d. Kemiringan Pola

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

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

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

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

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




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)



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)



√

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)

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

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

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

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


d. Saluran Masuk (Ingate)

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

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

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

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

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


e. Saluran Penambah (Riser)

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

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



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

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


• 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

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

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

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


c. Core Making

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

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

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

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

Macam-macam core making antara lain:

• Green Sand Molding

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

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

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

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

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



41

• CO2 Process

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

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

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

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

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

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

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

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


3.2.2.3 Macam-Macam Sistem Saluran

1. Saluran Langsung

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

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

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

2. Saluran Bawah

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

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

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

3. Saluran Pensil

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

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

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

4. Saluran Bertingkat

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

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

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

5. Saluran Terompet

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

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

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



6. Saluran Cincin

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

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

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

7. Saluran Pisah

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

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

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

8. Saluran Baji

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

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

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

3.2.3 Pelapis

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

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

3.2.3.1 Fungsi Pelapis

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

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

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

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

3.2.3.2 Syarat Pelapis

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

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

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

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



43

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



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


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.



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

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

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

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

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

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


Kelebihan pengecoran logam jika dibandingkan proses manufaktur yang lain adalah:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(Heine, 1976:1)



46

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

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

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

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


c. Evaporative Pattern Casting

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

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

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


2. Permanent Mold Casting

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

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

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

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

(Heine, 1976:285)

Macam-macam permanent mold casting adalah :

a. Die Casting (Cetak Tekan)

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

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



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

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

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



48

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

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

(Groover, 2010:244)

3. Pengecoran Centrifuge

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

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

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

(Groover, 2010:245)

c. Squeeze Casting

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

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

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


4.2.2 Peleburan

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

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

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

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

A. Hidrogen Solubility

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

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

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

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

(Beeley, 2001:256)

B. Tungku Peleburan

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

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

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



49

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

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

4.2.3 Solidifikasi

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

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

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

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

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

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

(Smith, 2001:122)

Proses Solidifikasi:

1. Tahapan dalam Pembekuan Logam (Solidifikasi)

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

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

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

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

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

2. Pembentukan Kristal dalam Logam Cair dan Pembentukan Struktur Butir

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

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

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

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

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

3. Macam-macam Solidifikasi

A. Solidifikasi Logam Murni

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

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

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

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

(Groover, 2010:214)



50

B. Solidifikasi Logam Paduan

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

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

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

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

(Groover, 2010:215)

4. Daerah Pembekuan

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

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

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

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

(Groover, 2010:216)

4.2.4 Fluiditas

a. Definisi Fluiditas

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

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

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

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

Faktor-faktor yang mempengaruhi fluiditas antara lain:

1. Viskositas

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

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

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

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

2. Temperatur Penuangan

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

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

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

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

3. Komposisi Logam

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

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



51

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

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

4. Permukaan Cetakan

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

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

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

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

5. Superheating

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

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

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

(Beeley, 2001:112)

6. Mode Pembekuan

a. Mode Pembekuan Plane Interface Mode

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

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

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

(Beeley, 2001:21)

b. Mode Pembekuan Jagged Interface Mode

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

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

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

(Beeley, 2001:21)

c. Mode Pembekuan Independent Crystallization Mode

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

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

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

(Beeley, 2001:21)

7. Thermal Properties

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

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



52

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

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

(Sundari, 2011:4)

b. Cara Pengujian Fluiditas

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

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

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

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

Ada beberapa macam cara pengujian fluiditas, diantaranya :

1. Spiral Mold Test

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

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

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

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

(Beeley, 2001:17)

2. Vacuum Fluidity Test

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

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

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

(Beeley, 2001:18)

3. Multiple Channel Fluidity Test Casting

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

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

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

(Beeley, 2001:23)

4.2.5 Cacat Coran

1. Porositas

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

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

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




53

2. Shift (Pergeseran)

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

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

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


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

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

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

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

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


4. Fin (Sirip)

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

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

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

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

5. Shrinkage (Penyusutan)

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

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

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

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

6. Hot Tears

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

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

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

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




54

7. Gas Defect

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

a. Pin Holes

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

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

(Jain, 1976:197)

b. Blow Holes

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

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

(Jain, 1976:197)

8. Metal Penetration

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

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

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


9. Swell

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

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

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


10. Cold Shot dan Misrun

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

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

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

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

(Groover, 2010:249)

4.2.6 Inspeksi

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

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

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

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



55

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)

LABORATORIUM PENGECORAN LOGAM

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