Redfish 452 Posted January 3, 2015 Report Share Posted January 3, 2015 I am new to the forum and have greatly benefitted so far by reading, reading, reading.......... I have been pouring my own swim baits in one piece (open top molds). I recently made a 2 piece injection mold and have had limited success so far. I inject the plastic and upon removing the bait, I find a slight depression in the side of the bait, The depression is not due to a bubble ( it has no sharp edges like a bubble) but looks as if the side of the bait just sunk inward after cooling. has anyone seen this problem before? Any suggestions? Quote Link to comment Share on other sites More sharing options...
Basseducer Posted January 3, 2015 Report Share Posted January 3, 2015 Redfish, That is due to shrinkage, As the plastic cools it shrinks. That is common with large body baits. One thing to try is to hold pressure for a few seconds before taking the injector away. Quote Link to comment Share on other sites More sharing options...
Bassinfool Posted January 3, 2015 Report Share Posted January 3, 2015 Commonly refered to as denying. It's caused by the bait needing more hot plastic where there is none available. Like suggested, try holding pressure for a few seconds. Also try shooting the bait at a lower temp so it isn't starving for more hot plastic. Also, welcome to the forum. Glad to have you aboard! Good luck with it, let us know if you fix your problem. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Thanks for the advice, I will try again tomorrow. Quote Link to comment Share on other sites More sharing options...
Bassinfool Posted January 3, 2015 Report Share Posted January 3, 2015 That should read denting by the way. Autocorrect on cell phones, got to love it. Quote Link to comment Share on other sites More sharing options...
gone2long Posted January 3, 2015 Report Share Posted January 3, 2015 Yep also do you have a large enough sprue and topping off this will allow for some additional plastic to be drawn in during curing. Quote Link to comment Share on other sites More sharing options...
smallmouthaholic Posted January 3, 2015 Report Share Posted January 3, 2015 Design ,venting and the ability of the mold to draw liquid plastic through a small opening into a larger one before the larger cavity starts to cool all contribute to denting. Check you plastic temp and keep in close to 310 to 325- inject slowly so the air can escape the mold. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Any suggestions on the best type of thermometers? Infrared? Quote Link to comment Share on other sites More sharing options...
Bassinfool Posted January 3, 2015 Report Share Posted January 3, 2015 I would go for a digital probe type thermometer over the infrared simply for the fact you need to measure the middle of the cup of plastic and not just the top. I have both a digital and some cheap candy thermometers the fiance uses and both work well for me. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Thank you. Will get one. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Regarding the sprue? Is that where you insert the tip of the injector? If so, I made it to fit the injector tip which is about 5/8 inch. Quote Link to comment Share on other sites More sharing options...
gone2long Posted January 3, 2015 Report Share Posted January 3, 2015 Regarding the sprue? Is that where you insert the tip of the injector? If so, I made it to fit the injector tip which is about 5/8 inch. Yes they are around 1/2 - 5/8 inch deep and should be topped off after injecting. the gate is the hole in-between the sprue and either the bait for single cavity or the runner for multi cavity. If your gate is to small it may have difficulty drawing plastic through before the plastic cures. Quote Link to comment Share on other sites More sharing options...
gone2long Posted January 3, 2015 Report Share Posted January 3, 2015 http://faculty.ferris.edu/hillm/myweb7/runners/balanced%20h%20runner.bmp Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Thank you very much for your input. The dents are major in respect to the position. They are in the forward position of the bait body and make it hard to insert the jig head in that the body is no longer full in the location where the keeper portion of the jig head falls. I will try to send a pic of the mold halves. Also, FYI, the mold is made out of a fairly hard RTV material. I am sure this makes somewhat of a difference in curing time as opposed to a milled aluminum mold. Quote Link to comment Share on other sites More sharing options...
gone2long Posted January 3, 2015 Report Share Posted January 3, 2015 Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Yes, I would certainly be willing to make a new mold. In fact, my goal was to eventually make a multi cavity mold. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Sorry this took so long. I had to figure out how to send a pic. Quote Link to comment Share on other sites More sharing options...
gone2long Posted January 3, 2015 Report Share Posted January 3, 2015 The vent at the gate would make me suspect a problem as if the mold fills the pressure is released at that vent and not allowing it to pressure the mold cavity. Quote Link to comment Share on other sites More sharing options...
Baitjunkys Posted January 3, 2015 Report Share Posted January 3, 2015 I assume i put to many vents in my molds... with the proper gate you cant have to many vents. I have yet to cut a mold that dont shoot perfect. I have begun venting the gate/bait line recently. Keeps them pesky air bubbles from collecting in the head... Im still a amatuer tho. And surely you pros got it down to a science. 1 Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 I can easily plug the gate vent and give it a shot. No pun intended. Someone suggested keeping the injector pressured a little longer. How long? Minutes? Quote Link to comment Share on other sites More sharing options...
smallmouthaholic Posted January 3, 2015 Report Share Posted January 3, 2015 I'll repeat myself which I've not read again. Lower and monitor your injecting,plastisol temp from 280 - 315 degrees.A heated injector makes this very easy to accomplish injecting @ lower temperatures. You must top off the mold immediately after injecting S-L-O-W-L-Y.( to let the air escape) Excessively hot plastic shrinks faster as it cools requiring more and some times continuously topping-off until the plastic stops receding (drawn into the mold) . The suggestion to use a immersion probe to check plastic temperatures is spot on. I imagine you're using a microwave to heat your plastic which can very easily reach plastic temps. of 375-400 degrees. Quote Link to comment Share on other sites More sharing options...
DaveMc1 Posted January 3, 2015 Report Share Posted January 3, 2015 Sorry but the issue you have is the gate (narrow area between the injection port and the cavity is too small. the cavity needs to be almost touching the injection port. what is happening is that narrow section is freezing off not allowing the bait to draw fresh hot plastic as it cools and contracts, causing the dents you are describing. regardless if your temp is 300 or 350, you should be able to shoot this bait with no issue other than having to top it off because your reserve reservoir is smaller. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 Thanks for all the advice. I purchased a digital thermometer and will enlarge the injection port. Down here in LA we are under tornado watches and extremely bad rains as I type so I will have to wait till the weather clears as I am working outside under a carport. Quote Link to comment Share on other sites More sharing options...
Redfish 452 Posted January 3, 2015 Author Report Share Posted January 3, 2015 By "heated injector" are you referring to an injector that has been heated or an electrified injector that heats and maintains the temp you want by itself? If so, where does one get this type injector? Quote Link to comment Share on other sites More sharing options...
smallmouthaholic Posted January 3, 2015 Report Share Posted January 3, 2015 By "heated injector" are you referring to an injector that has been heated or an electrified injector that heats and maintains the temp you want by itself? If so, where does one get this type injector? Ultra-molds makes a heated injector stand( heated via plug-in electricity) that holds both their newer medium and large injector. They are single injectors and make a tremendous difference when shooting small batches out of a microwaved cup of plastisol.I also use a dual heated injector when shooting laminates from their Shooting Star System. Quote Link to comment Share on other sites More sharing options...
