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Author
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Topic: Corrective action for blocked gates
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uncceng
Member Posts: 4
From:Arden, NC USA
Registered: Feb 2005
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posted September 07, 2005 10:50 AM
   
I am having problems with a part that tends to flash in an area that is unacceptable to my customer. The root cause for this unacceptable flash is due to a blocked gate that occurs in the mold itself. To "temporarily" correct this problem, one of the mold technicians will remove the blocked gate by heating up a "poker" and insert the "poker" in the blocked gate. This procedure corrects the problem, however, the correction is short lived. How can I prevent a blocked gate from occurring? Is the material not hot enough so that when the material is melted and injected the gate will not block? The material that is used is an acetyl copolymer. IP: Logged |
Tom C
Moderator Posts: 604
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted September 07, 2005 12:13 PM
Should not the entire mold cavity, gate area and all, be ejected with the part? I would think it impossible to make a quality part where a fozen gate is blown clear by the next shot.Otherwise you need a hot runner system in order to keep the product melted. If the gate area is not being ejected with the part, perhaps the cooling part of the cycle is too short. ------------------
Best Regards, Tom Cunningham Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
Ozducati
Senior Member Posts: 14
From:Brisbane, QLD, Australia
Registered: Apr 2003
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posted September 26, 2005 12:24 AM
Is this gate part of a hotrunner system? If so there are at least two things I can think of off the top of my head that could be the problem.
Could you post as to what type of runner system you are using.IP: Logged |
nathanH
Member Posts: 1
From:logan,ut,USA
Registered: Oct 2005
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posted October 04, 2005 12:42 PM
If you are getting only one gate blocked...Here goes nothing. If it is not the same gate getting blocked each shot, you may have contamination of another material with a higher melting point in your barrel. That will often randomly block a gate. You might have a 'cold slug' blocking it each time. Raising the nozzle temp might help correct that. You might be able to open up the gates a bit to let it shoot through. You might be able to raise the mold temp a bit (in case it is freezing down to much when it enters the mold). Things I would less likely like to do but might work is raising the first injection velocity or pressure. Giving the injection some suck back may help. If the back pressure is too high it could be drooling out of the nozzle and cooling down. There are many things that could be causing it, I can't think of a sure way to know short of trying everything until you find the one that works. If a piece of the sprue is actually breaking off in the gate and not pulling with the rest of it. You may try more (or less) cooling or increasing the draft angle in the gate.
Good Luck
Nate
[This message has been edited by nathanH (edited October 04, 2005).] IP: Logged |
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