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squigster

Need Help With Mold/venting

9 posts in this topic

Hi Guys,

I am having a problem with a mold I have had for a while. It was designed as a one piece mold but my brother is a machinist and I decided to see if he could make it a two piece by adding a plate to it therefore making it a two piece. The problem is that the bait is getting voids in it.

he added vents on the tails and the baits has a vold from the sprue to about 1" down the body in the center of the body.

I figured air was being trapped so I drilled a hole in the top half and repoured now I have two voids, one where it was originally and another right behind the hole I drilled. I dont want to keep experimenting and drilling holes in it and was wandering if someone could possibly shed some light on what may be happening. My first suspicion is the sprue isn't deep enough but that's just a guess. Thanks in Advance. Attached are some pics.

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I am not a machinist or an expert on this topic. It took me a while to figure out from your pics where your plastic flow was. Can he machine another plate from the top? Half the injection port on each side of the mold? If so the venting should be good but you will have to treat it as a hand pour mold topping it off after injection as it cools. It looks like venting is not the problem. The lack of sprue is.

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I think the bubble occurs when you start the pour/injection. The bubble forms behind the inlet and moves rearwards during the pour.

To test this theory, try starting the pour ultra slowly, once the nose is filled, you can speed up.

If this is the case, rounding the underside of the pour spout might work, removing the sharp corner which is causing the bubble. But this is going to make more work trimming the sprue of course.

Dave

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just like hand pouring most molds you do need to top them off as the plastic shrinks, or they will create the bubble in the head that you are getting.

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Ok thanks for the ideas guys. Not sure how to add a bigger sprue though. May have to see if he can make and insert that fits in the holes that is deep.

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Run a trough connecting all the injection or pouring ports. I think your problems will be solved if you have some bulk of excess plastic to draw from.

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you dont necessarily need a bigger sprue, just top it off as is sucks the plastic down, just like you would if you were hand pouring.

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Thanks Guys. I tried adding plastic to the top after pouring but it never gets sucked down. He took the mold yesterday and is going to machine the sprue into a cone shape and make it larger. I hope that solves the problem. I will let you now the results.

Thanks,

Jim

Edited by squigster

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Problem solved! He added a vent to the nose and made a cone "sprue" the depth of the top plate and it sucks the plastic down and it works great! No more air pocket! Thanks for all you opinions! I do appreciate it!

Edited by squigster

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