mc37 Posted February 10, 2016 Report Share Posted February 10, 2016 I'm new to making my own soft plastics. I have a new large rtv silicone single cavity mold that i'm having trouble getting all the air out of for a complete casting of a lure. Starting to feel defeated since I've been trying different things. I've preheated my injector and the mold itself. I've added extra vents near the highest point and the most problematic point as well. I've even just added a vibrating table to the mix. I cant quite figure this one out. I've been reading about using Jet Dry diluted with water as a pretreatment for the mold to relieve surface tenson... thoughts? Am I running out of options? surely someone will be able to determine my problem from the pics any help will be greatly appreciated! Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted February 10, 2016 Report Share Posted February 10, 2016 Images of the open mold would be more useful, showing the pour hole and vent positions. Dave Quote Link to comment Share on other sites More sharing options...
mark poulson Posted February 10, 2016 Report Share Posted February 10, 2016 I am just a hobby pourer, but I wouldn't use anything with water in it on my molds. I use spray PAM, and shoot at 325 degrees max. for most of my molds. The hotter the plastic, the more it shrinks. For a big bodied bait, I would hold pressure for 15+- seconds, because the plastic is so thick it can shrink as it cools. I would also start with 310 degree plastic. Quote Link to comment Share on other sites More sharing options...
archery1 Posted February 10, 2016 Report Share Posted February 10, 2016 (edited) yes ..with thick bodied baits the plastic really shrinks when it cools . try lower temps ,holding pressure and make sure u top mold off alot. I would never use anything with water in it around hot plastic. It is not a good idea Edited February 10, 2016 by archery1 Quote Link to comment Share on other sites More sharing options...
DaveMc1 Posted February 10, 2016 Report Share Posted February 10, 2016 yes ..with thick bodied baits the plastic really shrinks when it cools . try lower temps ,holding pressure and make sure u top mold off alot. I would never use anything with water in it around hot plastic. It is not a good idea He is dealing with actual bubbles in the plastic, If he had denting issues I'd say that this (or more importantly revising the injection port to hold more reserve plastic and opening the gate) would solve the issue. Quote Link to comment Share on other sites More sharing options...
gone2long Posted February 10, 2016 Report Share Posted February 10, 2016 By the looks of that last pic I would say your injecting air into the mold meaning your sucking air into the injector do you purge your injector prior to shooting? And as others have stated stay away from the water that's never a good combination. Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 10, 2016 Author Report Share Posted February 10, 2016 Of course I wouldn't be adding hot plastic to a wet mold. I was thinking the jet dry may have an effect even after the mold is dried. I have been injecting a touch over 400 degrees so I'm gonna give 310 a try tonight. Coming down in temp I would definitely want to open the gate a bit more than it is. Quote Link to comment Share on other sites More sharing options...
edgecrusher Posted February 10, 2016 Report Share Posted February 10, 2016 I reckon you do not have enough plastic in the sprue to allow the mold to suck the plastic in as it cools, I reckon if you remade the mold as a vertical pour with a long straight wide sprue you may fair better, hell with a design like that you might even be able to pour straight down a sprue hole without an injector (if you went vert pour) and get a full bait. 1 Quote Link to comment Share on other sites More sharing options...
DaveMc1 Posted February 10, 2016 Report Share Posted February 10, 2016 A hand pour straight down the nose will do better than injecting it from the side like that. The way it is laid out is asking for bubble problems. even injecting straight down the nose would probably work better. Quote Link to comment Share on other sites More sharing options...
gone2long Posted February 10, 2016 Report Share Posted February 10, 2016 Man that is one big bait did you ever weigh that beast? Those last pics didn't give that away! Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 11, 2016 Author Report Share Posted February 11, 2016 Man that is one big bait did you ever weigh that beast? Those last pics didn't give that away! It's taking around 7oz plastic to fill it. Haven't got a full bait to weigh yet. I'm about to put some of y'all's tips to work. Going to try injecting 310 degrees first before I go converting the mold into a vertical pour. I designed it horizontally because I wanted gravity to help me make the belly a different color but I guess I could've made a better injector entry. I'll post later with results. Thanks a bunch guys. Quote Link to comment Share on other sites More sharing options...
mark poulson Posted February 11, 2016 Report Share Posted February 11, 2016 It's taking around 7oz plastic to fill it. Haven't got a full bait to weigh yet. I'm about to put some of y'all's tips to work. Going to try injecting 310 degrees first before I go converting the mold into a vertical pour. I designed it horizontally because I wanted gravity to help me make the belly a different color but I guess I could've made a better injector entry. I'll post later with results. Thanks a bunch guys. I agree that having a vertical sprue will help, but you could try something else first. Since you made the mold in two parts, you can try hand pouring the bottom half while it's open, then closing it and injecting the other color into the top half with the sprue on top, like you have it. Quote Link to comment Share on other sites More sharing options...
archery1 Posted February 11, 2016 Report Share Posted February 11, 2016 i misunderstood that he had bibbles in plastic..sorry dave Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 11, 2016 Author Report Share Posted February 11, 2016 I agree that having a vertical sprue will help, but you could try something else first. Since you made the mold in two parts, you can try hand pouring the bottom half while it's open, then closing it and injecting the other color into the top half with the sprue on top, like you have it. Yes sir, that is what I was after when I designed the mold horizontally. Now I'm just desperate for a complete bait regardless of color! Lol Quote Link to comment Share on other sites More sharing options...
djs Posted February 11, 2016 Report Share Posted February 11, 2016 Needs more vents in the top portion of the mold and vent the ends of the tail Quote Link to comment Share on other sites More sharing options...
Frank Posted February 11, 2016 Report Share Posted February 11, 2016 It's taking around 7oz plastic to fill it. Haven't got a full bait to weigh yet. I'm about to put some of y'all's tips to work. Going to try injecting 310 degrees first before I go converting the mold into a vertical pour. I designed it horizontally because I wanted gravity to help me make the belly a different color but I guess I could've made a better injector entry. I'll post later with results. Thanks a bunch guys. What injector are you using to get 7oz of usable plastic? Quote Link to comment Share on other sites More sharing options...
JRammit Posted February 11, 2016 Report Share Posted February 11, 2016 (edited) I use to make all my molds horizontal, i had the same problems you are having with many of them.... I learned that the horizontal molds work fine for small (crappie size) or long/slender baits (worms), but are a nightmare for bigger thicker baits Vertical is your solution for an injection mold of that caliber... If you want a simple 2 color bait, an open hand pour mold is the sure shot.... You can slightly round over the flat side by carefully "over filling" the mold, causing a "dome effect" Edited February 11, 2016 by JRammit 1 Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 11, 2016 Author Report Share Posted February 11, 2016 What injector are you using to get 7oz of usable plastic? I have a 10oz injector from bass tackle Quote Link to comment Share on other sites More sharing options...
Bogbaits Posted February 11, 2016 Report Share Posted February 11, 2016 I have had the same problem with a large Frog mold I have,10 inches long and the frog weights 8 ounces,The only way I could make it work was to pour each side of the bait with the mold open then close it and inject the center,on such large baits you end up pushing the internal air that's in the molds,not even sure you could vent it properly as it takes a large injector,maybe if you were machine injecting you could vent it properly,anyway this way works for me Quote Link to comment Share on other sites More sharing options...
Frank Posted February 11, 2016 Report Share Posted February 11, 2016 I have a 10oz injector from bass tackle I have one of those too. Try and warm it up a lot. Just the mass of aluminium will cause large bubbles in the injector as it takes some time to fill and it starts to solidify fast. On your mold having parts of the bait that are above the filling point lets air get trapped. Nose pour would be better with either nose up or down with a real long sprue to help feed the bait while it cools. Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 13, 2016 Author Report Share Posted February 13, 2016 On your mold having parts of the bait that are above the filling point lets air get trapped. I think that's exactly why I had so much trouble. So I've plugged the vent holes and I've began converting it to pour in to the nose. I had to make an alternate vent on the nose to help the pour flow a little better. I ended up using the injector on my second try and got a better result. Getting closer to a complete bait 1 Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 13, 2016 Author Report Share Posted February 13, 2016 About to try again Quote Link to comment Share on other sites More sharing options...
Bozo Posted February 14, 2016 Report Share Posted February 14, 2016 you will never elevate this problem with this size bait unless you pour the belly then close the mold and pour through a "new' top or back area sprue gate that is deep enough to allow the natural contraction of the cooling plastic to take place in the pour sprue/gate area of the the bait,which would happen outside of the cavity area if it were the highest part of the back side of the mold. the reason is that most of the contraction will happen where the heat dissipates last. Hope this makes sense to you 1 Quote Link to comment Share on other sites More sharing options...
fishon-son Posted February 14, 2016 Report Share Posted February 14, 2016 wow thats a big bait...maybe shoot the belly first then the rest after it cools..but a top pour for sure will do it....if you can find a alumimum funnel and use it for a sprue extender that may work just for the extra pressure pushing down to hold the plastic in place..also some one said 310/325 deg....400 wow thats hot you maybe boiling the plastic at that heat.... 1 Quote Link to comment Share on other sites More sharing options...
mc37 Posted February 14, 2016 Author Report Share Posted February 14, 2016 Yes I was heating it up to 400 because I didn't have anything to pre heat my injector and it was freezing up too fast on me. I've since started with a warm injector, dropped plastic to 345 and got a full bait this afternoon. Minor denting on the nose but by far the best casting I've had yet and FINALLY a useable bait! Gonna try again tomorrow with a temp closer to 325. 1 Quote Link to comment Share on other sites More sharing options...
