Glideb8 Posted September 2, 2020 Report Share Posted September 2, 2020 Hey there, I've made several injection molds for a swimbait that I've designed(along with a creature bait mold) and I keep having this problem no matter what I'm trying. I tried pushing plastic fast, slow, medium, holding pressure, keeping the injector in the injection hole until I see all air bubbles pop out of the vent holes, then I top off the injection hole, etc. I keep getting an air pocket close to where I'm injecting the plastic from my injector. I have a 6oz injector now, so running out of plastic isn't the issue. I've included a crude diagram to show what I'm talking about. The diagram shows a side view of the mold. What I also did was make vent holes coming directly from the eye sockets after I discovered the air pocket after doing 3-4 injections. The plastic does come out of the vent holes, but the air pocket still remains. I get a complete injection sometimes, but when that does happen, I get some weird deformity on the top of the head to where it looks like the plastic was sucked in a little. Thanks in advance! Quote Link to comment Share on other sites More sharing options...
Apdriver Posted September 2, 2020 Report Share Posted September 2, 2020 (edited) If we could get a pic of your bait, that would be helpful. The weird deformity suck is a dent. I also suspect the air pocket is caused by the plastic cooling and contracting. That causes the dent. It is also causing the air pocket in the nose which is because your runner is too small. Here’s what happens. As the plastic cools and contracts, it needs a place to draw extra non-hardened plastic from. That’s why you see large runners on some molds. If this runner is closed off by hardened plastic before the bait has cooled and drawn what it needs, it will collapse and dent. If the runner is too small, as the bait draws from it it will suck air instead of hot plastic and makes the bubble. So how to stop all this nonsense...shoot at cooler temps. Typically 305 or so but you may get cooler than that but things start getting problematic if you get too cool. When you shoot, hold pressure for a ten, fifteen count. If that doesn’t work maybe longer. Experiment....Also, after you finish injecting pour more hot plastic in the injection port as it draws plastic. Do this once or twice. One other option is a sprue extender that extends the runners length. Can be homemade with copper tube or store bought. Edited September 3, 2020 by Apdriver 1 Quote Link to comment Share on other sites More sharing options...
Glideb8 Posted September 3, 2020 Author Report Share Posted September 3, 2020 I know the dent is from the plastic cooling, but I couldn't figure out why it was happening. I'll try the cooler temp, but I was also going to try to just pour it into the mold to see what happens. My only concern with just pouring is that the fins won't be formed. I figured the runner might be the issue, but the thing is, the nose of the bait is about the width of the circumference of the runner, which is 1/4". I actually cut some of the mold out to make the runner a bit larger. I don't want the nose of the bait to looked hacked up when I have to cut the sprue off and eventually sell them. Of course the injection hole is the standard 5/8". Right now the runner is about 1/4" high and the sprue hole is about 1/2" high. Thanks for the help and I'll report back! Quote Link to comment Share on other sites More sharing options...
McLuvin175 Posted September 3, 2020 Report Share Posted September 3, 2020 Another tip that may help is to de-mold much sooner than you are now. If you can interrupt the contraction that occurs leading to dents you can prevent the dent. Even if the interior is still molten as long as you can handle the bait place it in a bath of water to finalize cooling. Relaxing the bait in water allows for even contraction/shrinkage. Additionally the use of mold release may help as well breaking the surface tension the mold creates on the surface of the bait. 1 Quote Link to comment Share on other sites More sharing options...
Glideb8 Posted September 3, 2020 Author Report Share Posted September 3, 2020 2 hours ago, McLuvin175 said: Another tip that may help is to de-mold much sooner than you are now. If you can interrupt the contraction that occurs leading to dents you can prevent the dent. Even if the interior is still molten as long as you can handle the bait place it in a bath of water to finalize cooling. Relaxing the bait in water allows for even contraction/shrinkage. Additionally the use of mold release may help as well breaking the surface tension the mold creates on the surface of the bait. Thanks for the tip. Quote Link to comment Share on other sites More sharing options...
