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Extreme Mold Lock - Expert Input Needed

Extreme Mold Lock - Expert Input Needed

Extreme Mold Lock - Expert Input Needed

(OP)
Hello. I am quite a situation and I want to see if my molder isn't giving me the run around. I am in a dire situation and need feedback to see if I should find a new molder or take him at his word. I have searched and made calls and cannot get a definitive answer. I might just be using the wrong terminology but I need any feedback

I have a large mold that makes a large cooler holder. It has ran thousand and thousands of parts (some smooth and some issues - part of the reason I found a new "better" molder. My current molder has made successful parts on the last run but this time it started out with extreme mold lock (mold will not open) the molder took full responsibility and says he has spent a few days separating the mold (3 days). He said he used too much pressure and too long of a shot. Has anyone seen such a case or is this complete bs? They have the mold separated and are polishing it now.

Has anyone seen such a case where the mold locks up this bad from the described situation? Material is polycarb. Any feedback would be highly appreciated and will most likely guide how I move forward. Thanks in advance.

RE: Extreme Mold Lock - Expert Input Needed

What kind of mold, is it a typical 2 plate style? Did it lock up with a full shot and then unable to open or eject (and subsequently solidify in situ)? Does it have side pulls, slides, cams, lifters, pecker pins, any other mechanical reason that could contribute? Is it a hydraulic ram or toggle type machine?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Extreme Mold Lock - Expert Input Needed

(OP)
It is a basic one cavity mold around 4'000 pounds. Has 12 push pins. The reason i have been told it locked up was because it had too much pressure and too long of a shot time. The mold has locked up before but not to the point where it had to be removed from the machine and separated and now it has to be re polished. Have you ever heard of this type of extreme lock up? I was told it was an extreme lock up. The molder has a lot of experience. I am not sure what to make of the situation. The draft of the mold is borderline.

RE: Extreme Mold Lock - Expert Input Needed

There are many possible causes. Did it lock up with a full shot and then unable to open or eject (and subsequently solidify in situ)? Is it a hydraulic ram or toggle type machine? How deep is the part, assuming it's a tray-like part and do you have any air poppets to help break the vacuum on ejection?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Extreme Mold Lock - Expert Input Needed

(OP)
It was explained to me that the mold was completely locked up. I know there are hoses that go around it but I am pretty sure that is for temp. I was told the pressure was too much for too long, so I would assume that it was complete. Its approx 12" deep with borderline draft. I know nothing is impossible but how likely is this scenario? Especially when this molder was able to run this part successfully in the past? What would be the advantages of the molder changing running successful procedures to higher pressure and running the shot time longer? Why would they do that?

RE: Extreme Mold Lock - Expert Input Needed

12 inches deep with minimal draft could be very challenging. It's difficult to speculate further based on available information. Insufficient or lack of mold release, air poppets or vacuum breakers to overcome the suction effect of the part being ejected, undersized machine for the tool and surface area, and a host of other possibilities. But to answer your question, it is not beyond imagination that a tool could become stuck together. Too much pack and hold (pressure) isn't going to help particularly if the draft is insufficient to begin with.

It would be worthwhile to sit down and have a serious meeting with the molder to discuss precisely what they believed happened, and to document acceptable molding parameters, and to establish first of all if their equipment is appropriate for that tool and capable of the consistency and performance necessary.

If your molder is a long established enterprise and you've done your due diligence before moving your tool to them (refrences and all that), it's worth to give them the benefit of the doubt and work with them. Your best suppliers will be the ones that have worked through really difficult situations with you and there has been enough mutual trust involved to arrive at a real solution.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Extreme Mold Lock - Expert Input Needed

(OP)
I really really appreciate your feedback and help. This alleviates a lot of my stress I had by second guessing my molder. I was not trying to start making any accusations at all without talking to someone as knowledgeable as yourself. I would have been back to square one without your input. Thank you again. Thank you so much! You would not believe how much your feedback has helped me. Hopefully I can pay it forward one day. Thank you thank you thank you!

RE: Extreme Mold Lock - Expert Input Needed

What is "borderline draft"? 2-3° per side is what PC likes.
Yes, you can get a tool to lock if part is over packed. PC is a very "draggy"* material, adding to the problem.

Many years ago we used to make 12" long sundae cups out of SAN.It was like moulding 2 x Morse tapers. Slight over packing and it was stuck. Our solution was to put an oil heater on the tool at about 150°C to soften the parts. Made quite a bang when the tool finally opened!

*Technical term - high friction and soft

www.tynevalleyplastics.co.uk

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