brass insert pull-out in Lexan
brass insert pull-out in Lexan
(OP)
Recieved a large delivery of Lexan parts that fail in torque test. There is a small threaded brass insert molded into the housing. The insert acts as a captive nut in the housing, and the housing is clamped onto a mounting bar. This normally takes foot pounds, this shipment didnt even take 10 inch-pounds before the inserts started sliding out.
I assume no dry-out of resin prior to injection. Sure, perhaps a hopper drier, but nothing before. But this is a guess.
Two questions:
1) cause?
2)is there any salvation? Can I dry out the housings (like anneal them) or are do I start from scratch? That puts me behind 3 months if I am lucky..
I assume no dry-out of resin prior to injection. Sure, perhaps a hopper drier, but nothing before. But this is a guess.
Two questions:
1) cause?
2)is there any salvation? Can I dry out the housings (like anneal them) or are do I start from scratch? That puts me behind 3 months if I am lucky..





RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
Chris DeArmitt PhD FRSC CChem
www.phantomplastics.com
Consultant to the plastics industry
RE: brass insert pull-out in Lexan
back in 15-30.
RE: brass insert pull-out in Lexan
Thoughts: weak Lexan due to humid resin, weak Lexan due to poor process control, weak insert adhesion due to cold inserts or oily inserts.Any others?
RE: brass insert pull-out in Lexan
Too low injection temperature so the PC doesn't wet out the metal surface, thereby giving poor adhesion.
Design tests for each hypothesis and you'll soon know the problem.
Chris DeArmitt PhD FRSC CChem
www.phantomplastics.com
Consultant to the plastics industry
RE: brass insert pull-out in Lexan
Thanks to all.
RE: brass insert pull-out in Lexan
Presuming good original design (has this worked OK in the past) possible causes are:-
1) PC degraded due to inadequate drying of pellets.
2) PC resin inferior to previous batches due to low molecular weight.
3) PC grade has mould release chemical added.
4) Mould not fully packed.
5) Inserts not pre-warmed.
6) Inserts contaminated with oil or aromatics.
7) Inserts cleaned with aromatics or chlorinated hydrocarbons and residual solvents causing ESC.
8) Inserts have insufficient undercut or surface texture.
9) The mouldings are a different colour to the original batch or even if the same colour, have a different colour or masterbatch formulation.
10) The moulding machine operator started using a mould release spray or a different spray or a different amount of spray.
Except for insufficient pack all the other causes cannot be corrected in existing parts.
If under packed, it just might be possible to weld under pressure at increase localised pack and better grip the surface, but I very much doubt that can work.
Another costly fix might be to make up a jig to pull the existing inserts then use inserts designed to be applied with ultrasonics. They will have a larger undercut and possibly be barb shaped so they go in easier than they come out. This will depend on the wall thickness where the inserts are located.
I am at a bit of a loss to know why it will take 3 months to get replacement mouldings. Maybe you need another moulder.
Regards
Pat
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RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
If your moulder is in China, maybe you need to visit him for a week to ensure he is doing what is required, when required to fix this, otherwise move the mould.
If you choose to move the mould, the next problem might be actually collecting it on time and in good condition. That might also involve personal supervision and transport organised and paid for by you.
Regards
Pat
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RE: brass insert pull-out in Lexan
RE: brass insert pull-out in Lexan
Strong focus on the wrong insert for the application. High level of stress concentration at insert interface due to wrong insert surface (barbed) and thermal differential. Possible use by molder of mold-release compound. May very well go to post-mold ultrasonic welding. One more try then the tool comes home.
Thank you all for the good insight and experienced opinion.
RE: brass insert pull-out in Lexan