Surface sinks in small polyurethane (TPU) washer 3

[Hawker1]

First time user of a C60A10W polyurathane. Parts are
three sizes .38, .25 & .18 dia. x .05 thick. Surface
must flate an free of sinks. These are vacum seals.
Processor has try a range of injection speeds & pressures
and temps suggested by supplier.

 

[Pud]

Is it dry prior to moulding?

Tool venting?

Too much shear heat being put into material (e.g too high back pressure/too high screw surface speed?)

Rgds


Harry

 

[patprimmer]

If it sinks, pack it in harder by using:

More injection pressure

More hold up pressure

More hold up time

larger gates, runners, sprues etc

Is the ring check valve sealing

Is there enough injection stroke to reliably close the ring check

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dwightdixon]

The usual problem is too small gates. Urethane takes gates at least 1/2 the thickness of the thickest part of the molded part. Fill moderately fast and keep the hold pressure at 50% of the peak injection pressure. Make sure your cushion is holding. You may have a leak in the check ring valve. Cut the part in half and you will likely find some shrink voids.