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Soft Plastics Troubleshooting

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I'm wondering if someone could help me troubleshoot the following problem when pouring soft baits with tentacles and or other appendages (see attached). I've noticed some inconsistency in how my baits are turning out. Some baits turn out perfectly whereas others have arms (especially those closest to the head) that are shorter than they should be.

I'm curious to know if any of you have experienced similar problems and solutions that you may have found. Thanks in advance for your help!

IMG_20210102_174701033.jpg

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 When that happens to me, I try three things.  First, I try holding pressure on my injector for a five count.  If that doesn't help, I try heating my plastic a little hotter.  If I still have a problem, I'll increase the venting to each appendage.

Usually one or two, or all of those steps works.

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On 1/7/2021 at 3:00 PM, SlowFISH said:

Can you upload picture of the mold?  We can probably provide some additional help.... but Marks points are best place to start.  Depending on mold type (material) there are a couple options to open up venting if necessary.

J.

I have a Lurecraft 6.25 Diamond Tail Injection Aluminum Mold that I am having problems with bubbles as well. From searching all the threads it seems the only thing I havent done is increase the venting. Would you have any tips on exactly how to do that? I will attach a pic of the mold. The vent lines are at the bottom, but they are only on 1 side of the mold. This picture does not show them very well.

I have reached out to Lurecraft, but no answer yet.

mold link: https://www.lurecraft.com/625-Diamond-Tail-Injection-Mold-8-Cav-2-Pc-Allum/productinfo/5XLU-17345/

5XLU-17345.jpg

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The lines from the tail of the worm on the right side of the picture (side with the bolts) are the vents.  Take the corner of the tip of a flat blade screwdriver that fits in the vent and scratch them just a tiny bit deeper.   You're just scratching, not gouging.  It doesn't take much.

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I'd say you've found part of the problem yourself. Inject your plastic faster.

It seems like your baits are cooling too fast in the mold. Keep the pressure on while shooting.Preheat the mold as well. And open your vent lines a tiny bit.

BTW...I like that mold,Most of the others I've seen like that are flat on one side. Don't like that. Your mold looks round and ribbed completely around. Is that true? If so I may end up getting that mold.

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Another thought ..... all of the cavities are on a horizontal plane when injecting the hot plastic into the mold cavities and entrapping air causing bubbles in the top of the ribs . You could try propping up the tail side of the mold on a piece of wood 3/4" so the cavities are running up hill towards the tail . This way the hot plastic will force the air out through the vent in the tip of the tail as the cavity fills . Air is thinner than plastic and flows through the vent faster .

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12 hours ago, Tiderunner said:

 

BTW...I like that mold,Most of the others I've seen like that are flat on one side. Don't like that. Your mold looks round and ribbed completely around. Is that true? If so I may end up getting that mold.

Yes that’s exactly how they are. I have 3 molds from Lurecraft. A Diamond tail, Curly tail, and stick bait. All are completely round. No flat sides. 

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19 hours ago, bryanmc said:

The lines from the tail of the worm on the right side of the picture (side with the bolts) are the vents.  Take the corner of the tip of a flat blade screwdriver that fits in the vent and scratch them just a tiny bit deeper.   You're just scratching, not gouging.  It doesn't take much.

Awesome. Thank you very much. The stick bait molds I have from them have vent lines on both pieces and I never have problems. I will try and open them up tonight. 

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7 hours ago, jigmeister said:

Another thought ..... all of the cavities are on a horizontal plane when injecting the hot plastic into the mold cavities and entrapping air causing bubbles in the top of the ribs . You could try propping up the tail side of the mold on a piece of wood 3/4" so the cavities are running up hill towards the tail . This way the hot plastic will force the air out through the vent in the tip of the tail as the cavity fills . Air is thinner than plastic and flows through the vent faster .

Jigmeister has some good advice here.... and the others who pointed to inj speed.... you'll need to play with a few things but air is getting caught in each rib which is common with molds like this.  Tilting the mold (tail up) might help that air push out.... along with injection speed should help.

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10 hours ago, jigmeister said:

Another thought ..... all of the cavities are on a horizontal plane when injecting the hot plastic into the mold cavities and entrapping air causing bubbles in the top of the ribs . You could try propping up the tail side of the mold on a piece of wood 3/4" so the cavities are running up hill towards the tail . This way the hot plastic will force the air out through the vent in the tip of the tail as the cavity fills . Air is thinner than plastic and flows through the vent faster .

I inject the opposite way. Though we both use the same principle. I use a vise for my molds, and always angle them slightly downward away from the injection port. Been doing that for years after trial and error. The hottest plastic then runs down to the furthest point first.

I can see your point though. Your way puts the vents on top so the mold can for lack of better word. burps itself as the mold fills.

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Tried opening the vent a little more. It feels larger than the rest. Held decent pressure for a solid 10 seconds. And the same cavity does the same thing. You can see the bubbles all the way on that one side. Should I try to make some vents perpendicular to that cavity along that side?

B4F808E9-64B7-4FB0-AE9C-79A07555D670.jpeg

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10 hours ago, Les Young said:

Are you checking the temp of your plastic after heating? I had a mold form a  maker do that & i sent him a message about it & he had me actually measure the temp & it was 400*. I backed off the heat a few seconds & no more problems.

I’ve shot it at every temp from 280-345. Same problem on the same cavity every time. 

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Try this just for grins.  Next time you shoot the mold, put a bait in the top cavity before you close and shoot it.  Because the port looks so shallow I'm wondering if if you're getting a little air in the top cavity while it cools.   Be sure to keep the sprue topped off after you inject when you try this.

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19 minutes ago, bryanmc said:

Try this just for grins.  Next time you shoot the mold, put a bait in the top cavity before you close and shoot it.  Because the port looks so shallow I'm wondering if if you're getting a little air in the top cavity while it cools.   Be sure to keep the sprue topped off after you inject when you try this.

The pics with baits help... Bryan's suggestion is a good one... and now seeing it's just the top bait and the bubbles are pretty much down the entire bait on the top side - try putting 1 or 2 small c clamps on top edge of that mold in addition to what you are already using to clamp it.  You might not be getting a perfect/tight seal and sucking a little air in when it cools. 

All my molds are made of resin and they warp/bend when they get to hot.... sometimes I don't get a good seal between the mold haves and have an issue like this.

But to answer an earlier question as well... if all else fails - you could try to vent each rib up top - but I'd exhaust every option first before you start messing with your mold.  IF you do decide to vent it - I'd start with a VERY TINY vents... maybe just use a utility knife scratch a tiny vent then hit the surface with some 800 grit and paper to flatten out any distortion of the metal  - you really don't need much for air to escape.

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