MOULDING DEFECTS 1.PDF

MOULDING DEFECTS AND REMEDIES

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~ HOW MANY KINDS OF DEFECTS ARE THERE?

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~ HOW MANY KINDS OF DEFECTS ARE THERE?

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DEFECTS 1. Sink Marks 2. Streaks 3. Blistering 4. Weld Lines 5. Gloss difference 4

DEFECTS 6. Jetting 7. Record grooves effect 8. Dull spots near gate area 9. Incompletely filled part ( Short shots) 10. Diesel effect 5

DEFECTS 11. Over sprayed parts (Flashes) 12. Stress whitening/Cracking 13. Ejector marks 14. Deformation during demolding 15. Ejection Grooves 6

DEFECTS

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DEFECTS

21. Defects on electroplated parts 22. Broken or ragged film hinge 23. Warpage 24. Fish eye

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DEFECTS

25. Hesitation 26. Over packing 27. Unbalanced flow

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28. Nozzle drool 29. Nozzle freeze – off 30 Nozzle spitting 31. Screw slip

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WHAT ARE THE MAIN FACTORS CAUSING DEFECTS?

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SOME MAIN FACTORS CAUSING DEFECTS

The moulding Machine Mould Operating conditions i.e.. Temperature, pressure, injection speed & time Material. Design of product Management

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! "#$%&# SINK MARKS

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SINK MARKS

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SINK MARKS

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! "#$%&# Sink marks

Sink marks on a cylindrical core with poor temperature control

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! "#$%&# Sink marks appear as depressions on the surface of a molded part. These depressions are typically very small; however they are often quite visible, because they reflect light in different directions to the part.

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CAUSE OF SINK MARKS

Sink marks occur during the cooling process if certain areas of the part are not cooled sufficiently causing them to contract If these contractions are not compensated and the outside wall is not stable enough due to insufficient cooling depressions occur

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Disadvantageous Gating Solidified Peripheral

Moulded part with sink marks (Gating at the thin wall)

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2. STREAKS Streaks are the prominent stretchy marks on the surface of the moldings. CHARRED STREAKS MOISTURE STREAKS AIR STREAKS COLORED STREAKS GLASS FIBER STREAKS

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2.CHARRED STREAKS

Charred streaks due to excessive residence time in the plasticising cylinder 25

2.MOISTURE STREAKS:

Streaks due to excessive moisture content of the granules 26

2.AIR STREAKS:

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2.COLOUR STREAKS:

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6. Reduce residence time in material hopper 7. Reduce injection rate 8. Round sharp edges of transitions. 9. Reduce depth of engraving 10. Provide for venting

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11. Use smaller colour pigments 12. Check solubility of the used die 13. Use shorter glass fiber

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3.BLISTERS

Hollows created on or in the molded part

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3.BLISTERS

Air traps occur when converging flow fronts surround and trap a bubble of air. The trapped air can cause Incomplete filling and packing, Surface blemish in the final part. Air trapped in pockets may compress, heat up and cause burn marks.

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3.BLISTERS

(hollows created on or in the molded part) voids

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3.BLISTERS / BUBBLES

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3.BLISTERS

DELAMINATION

4.Blisters and delamination

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