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Poor welds Flow marks Poor finish

Brittleness

Warping

more cavities cavity mould Material too cold Injection pressure too low Inadequate venting Dirty cavity surface Mould temperature too low Excessive use of mould surface lubricant Material cold Mould cold Material degraded(Yellow specks) Contamination Excessive regrind Moulded in stresses due to: on multi-

(a) Material cold

(b) (b)

Overpacking

in

vicinity of gate

Silver streaking

Part ejected too hot Material cold Mould cold Condensation of moisture on mould Entrapped vapour

Polymer

dripping

from Degradation

nozzle when mould is in the open position

overheating; becomes to

o

due to polymer

fluid

and

Burn marks

develops gas Nozzle too hot Improper venting

Gv:

Increase heating Increase injection pressure Give enough venting Clean Increase mould temperature Use of mould surface lubricant not recommended Increase heating Increase mould temperature Decrease heating Check cylinder and hopper

Reduce regrind

percentage

of

  • (a)

    Increase heating

  • (b)

    (b) Check feed. Reduce injection pressure and heating. Reduce injection time.

Increase cooling time Increase heating Increase mould temperature Dry and heat mould

Pre-dry material Reduce temperatures Purge cylinder

Reduce heat to nozzle

Clean vents

20

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