problem with injection mould

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problem with injection mould

Postby bassfanatic » Sun Aug 27, 2017 7:25 pm

need a little help from someone here as im having a problem with my injection mould first is that all the plastic doesn't fill the mould when I inject it or if im lucky that it does im getting dents on my soft plastics but the first problem is my main one any help please need to sort this asap
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Re: problem with injection mould

Postby aka anglinarcher » Mon Aug 28, 2017 12:16 pm

If you can take a picture and save it on the cloud, then attach a link, then we can see it. This will help a lot, but I will take an educated guess.

First problem, plastic doesn't fill the mold when you inject it. It sound like you don't have vents to let the air out ahead of the plastic. When you inject it forms a seal and to get the room available for the plastic you need air escape vents. The big guys that inject plastic call this sprues and it is trimmed off after the items cools. Small items may need only very tiny vents but larger items will need either more or larger vents. If your mold are silicone, just use a razor knife to cut some small channels. If your mold is VAC 50, you will need to do it with a Dremel tool.

The second problem tells me you are probably injecting a larger item. Denting after the pour is the result of the plastic shrinking as it cools. One way to deal with this is to create a mold with a reservoir from which the cooling plastic can draw. At about 2:35 into the following video you will see the plastic reservoir that leads to each of the lures which helps provide a place to draw from. ... yPhoto/23/

In the following video, it is an open pour design, but you can still see the extra reservoir on top to allow for the cooling plastic to draw. ... yPhoto/37/

If the dents are not too large, you can often eliminate them by holding pressure on your injector a few seconds longer at the end of the pour.

I hope I have made this clear, and good luck on your pour/injection.
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Re: problem with injection mould

Postby bassfanatic » Wed Aug 30, 2017 5:38 am

I actually do have vents on my moulds but I do get cooling in my injector so im wondering is the same happening in my mould ive a vac 50 made mould can I pre heat this
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Re: problem with injection mould

Postby dahlberg » Thu Aug 31, 2017 7:57 am

Yes, for sure pre heat your mold. I would guess this, along with heating the injector will take care of your issues.
good luck with your project!
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Re: problem with injection mould

Postby bassfanatic » Mon Sep 11, 2017 10:18 am

ive heated both and i still have the smame problem although not as bad ,im sure its to do with the temp of the plastic i thought i might be overheating so poured it at a coolerl temp and the dents are smaller ,the other prob i think i have is the vents are too small but i made a bigger mold and i dont have the problem with that at all
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Re: problem with injection mould

Postby Mike - Alumilite » Mon Sep 18, 2017 6:49 am

You got it. Whenever you have shrink or an indent in your lure ... you need to make a bigger reservoir to allow the material in the lure cavity to cool before the reservoir. Shrinkage always draws from the last place to cool. Therefore, if we have a larger reservoir, it will draw the shrink from the reservoir and not the lure cavity.

On some very large lures I pour where it would add a lot of mold making material necessary to cast a huge reservoir, I simply scrape out the cooled Alumisol out of the reservoir at about the 5-10 minute point and pour brand new hot Alumisol into it. This basically keeps super hot and liquid soft plastic in the reservoir longer which the material shrinks out of.

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