kualitas produk coran

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PRODUK CORAN

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  • 10/6/15

    1

    CASTING QUALITY

    Dr. Ir. Dwi Rahmalina, MT

    Casting Quality

    ! Banyak kemungkinan kesalahan yang terjadi selama operasi pengecoran, sehingga menimbulkan cacat produk.

    ! Cacat / defects dapat diklasifikasikan sebagai berikut : ! Cacat umum yang dapat terjadi selama proses

    pengecoran dengan berbagai teknik ! Cacat yang terjadi selama proses pengecoran

    pasir cetak.

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    2

    Benda cor telah selesai mengalami solidifikasi sebelum mengisi seluruh rongga cetakan.

    Cacat Umum: Misrun

    Dua bagian dari aliran logam cair bergabung tetapi tidak terjadi penyatuan sempurna karena premature freezing

    Cacat Umum : Cold Shut

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    3

    Percikan logam terjadi selama penuangan dan menimbulkan bentuk bulatan padat dan terperangkap dalam cetakan.

    Cacat Umum: Cold Shot

    Kerusakan pada bagian permukaan atau cacat dalam yang disebabkan oleh penyusutan selama solidifikasi akibat terbatasnya jumlah logam cair yang tersedia pada bagian akhir pembekuan.

    Cacat Umum: Shrinkage Cavity

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    4

    Rongga gas berbentuk balon yang disebabkan oleh pelepasan gas dari cetakan selama penuangan.

    Cacat Sand Casting : Sand Blow

    Terbentuknya rongga gas kecil pada daerah dekat permukaan.

    Cacat Sand Casting : Pin Holes

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    5

    Jika fluditas dari logam cair terlalu tinggi, maka logam cair akan berpenetrasi ke dalam cetakan pasir atau inti, menghasilkan permukaan cor yang terdiri dari campuran butiran pasir dan logam.

    Cacat Sand Casting : Penetration

    Ketidaksesuaian benda cor pada bagian parting line yang disebabkan oleh displacement relatif dari cope and drag

    Cacat Sand Casting : Mold Shift

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    6

    Metode Inspeksi pada Foundry

    ! Inspeksi Visual untuk mendeteksi cacat yang jelas terlihat seperti misruns, cold shuts, and cacat-cacat permukaan lainnya

    ! Pengukuran dimensi untuk memenuhi syarat toleransi yang diinginkan.

    ! Uji komposisi kimia dan metalurgi, sehubungan dengan kualitas dari cast metal

    ! Uji sifat mekanis " hardness, strength ! Deteksi Cacat " Non Destructive Test (NDT)

    Penggunaan teknik noninvasive untuk menentukan integritas dari material, komponen atau struktur

    atau pengukuran kuantitatif dari beberapa karakteristik produk

    i.e. Inspeksi atau pengukuran tanpa merusak produk.

    Pengertian dari NDT

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    7

    Metode-metode NDT Visual

    Liquid Penetran

    t

    Magnetic Particle

    Eddy Current

    Ultrasonic

    X-ray

    Microwave

    Acoustic Emission

    Thermography

    Laser Interferometry

    Replication

    Flux Leakage

    Acoustic Microscopy

    Magnetic M

    easuremen

    ts

    Tap Testing

    6 Metode NDT yang Umum Digunakan

    Visual Liquid Penetrant

    Magnetic Ultrasonic

    Eddy Current X-ray

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    8

    Metode inspeksi dasar dan umum digunakan.

    Menggunakan Tools : fiberscopes, borescopes,

    magnifying glasses dan mirrors.

    Robotic crawlers permit observation in hazardous or

    tight areas, such as air ducts, reactors, pipelines.

    Portable video inspection unit with zoom allows

    inspection of large tanks and vessels, railroad tank

    cars, sewer lines.

    Inspeksi Visual

    Suatu cai ran dengan karekters i t ik yang t inggi dar i kemampubasahan permukaan (high surface wetting characteristics) diaplikasikan ke permukaan benda kemudiaan didiamkan beberapa saat agar masuk ke surface breaking defects.

    Liquid yg meluap dipindahkan dari permukaan Developer (serbuk) diberikan di permukaan untuk menarik penetrant

    yang terperangkap. Inspeksi Visual sebagai tahao akhir process. Penetrant yg

    biasa digunakan : fluorescent dye and inspkesi dilakukan dibawah sinar UV untuk meningkatkan sensitivitas uji.

    Inspeksi Liquid Penetrant

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    9

    Inspeksi Magnetic Particle

    Benda dimagnetisasi. Finely milled iron particles coated with a dye pigment are then applied to the specimen. These particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity. This indication can be visually detected under proper lighting conditions.

    Magnetic Particle Crack Indications

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    10

    Radiography Menggunakan radiasi yg mempunyai energi lebih

    tinggi (shorter wavelength) dari gelombang electromagnetic seperti cahaya yg terlihat.

    Radiasi dapat berasal dari X-ray generator atau sumber radiasi lain.

    High Electrical Potential

    Electrons - +

    X-ray Generator or Radioactive Source Creates Radiation

    Exposure Recording Device

    Radiation Penetrate the Sample

    Film Radiography

    Top view of developed film

    X-ray film

    The part is placed between the radiation source and a piece of film.

    The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation.

    = more exposure

    = less exposure

    The film darkness (density) will vary with the amount of

    radiation reaching the film through the test object.

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    11

    Radiographic Images

    Conductive material

    Coil Coil's magnetic field

    Eddy currents

    Eddy current's magnetic field

    Eddy Current Testing

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    12

    Eddy Current Testing

    Pengujian arus Eddy sesuai untuk mendeteksi retak pada permukaan serta dapat digunakan untuk membuat konduktivitas listrik dan

    pengukuran ketebalan lapisan. Here a small surface probe is scanned over the part surface in an attempt to detect a crack.

    Gelombang suara berfrekuensi tinggi diberikan ke material dan direfleksikan kembali dari cacat atau permukaan.

    Reflected sound energy is displayed versus time, and inspector can

    visualize a cross section of the specimen showing the depth of features that reflect sound.

    f

    plate crack

    0 2 4 6 8 10

    initial pulse

    crack echo

    back surface echo

    Oscilloscope, or flaw detector screen

    Ultrasonic Inspection (Pulse-Echo)

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    13

    Ultrasonic Imaging

    Gray scale image produced using the sound reflected from the front

    surface of the coin

    Gray scale image produced using the sound reflected from the back surface of the coin (inspected from heads side)

    High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled

    scanning system.

    Inspeksi of Raw Products

    !Forgings, !Castings, !Extrusions, !etc.

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    14

    !Cracking !Corrosion !Erosion/Wear !Heat Damage !etc.

    Inspeksi untuk In-Service Damage

    Power Plant Inspection

    Probe Signals produced by

    various amounts of corrosion thinning.

    Periodically, power plants are shutdown for inspection.

    Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion

    damage.

    Pipe with damage

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    15

    Wire Rope Inspection

    Electromagnetic devices and visual inspections are used to find broken wires and other

    damage to the wire rope that is used in chairlifts, cranes and

    other lifting devices.

    Storage Tank Inspection

    Robotic crawlers use ultrasound to inspect

    the walls of large above ground tanks for signs of thinning

    due to corrosion.

    Cameras on long

    articulating arms are used

    to inspect underground storage tanks for damage.

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    16

    ! Simpel dari segi Geometri: ! Although casting can be used to produce

    complex part geometries, simplifying the part design usually improves castability

    ! Avoiding unnecessary complexities: ! Simplifies moldmaking ! Reduces the need for cores ! Improves the strength of the casting

    Pertimbangan dalam Desain Produk

    ! Sudut pada benda cor: ! Sharp corners and angles should be avoided,

    since they are sources of stress concentrations and may cause hot tearing and cracks

    ! Generous fillets should be designed on inside corners and sharp edges should be blended

    Pertimbangan dalam Desain Produk

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    17

    ! Draft Guidelines: ! In expendable mold casting, draft facilitates

    removal of pattern from mold ! Draft = 1 for sand casting

    ! In permanent mold casting, purpose is to aid in removal of the part from the mold ! Draft = 2 to 3 for permanent mold processes

    ! Similar tapers should be allowed if solid cores are used

    Pertimbangan dalam Desain Produk

    Draft

    ! Minor changes in part design can reduce need for coring

    Figure 11.25 Design change to eliminate the need for using a core: (a) original design, and (b) redesign.

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    18

    ! Toleransi Dimensi dan Penyelesaian Permukaan : Significant differences in dimensional accuracies and finishes can be achieved in castings, depending on process:

    ! Poor dimensional accuracies and finish for sand casting

    ! Good dimensional accuracies and finish for die casting and investment casting

    Pertimbangan dalam Desain Produk

    Pertimbangan dalam Desain Produk

    ! Allowances pada Proses Pemesinan: ! Almost all sand castings must be machined to

    achieve the required dimensions and part features

    ! Additional material, called the machining allowance, is left on the casting in those surfaces where machining is necessary

    ! Typical machining allowances for sand castings are around 1.5 and 3 mm (1/16 and 1/4 in)