jm

Vinyl plastisol is PVC resin suspended in a plastisizer. There are thousands of different varieties of PVC resins on the market, hundreds of them suitable for plastisol, and a hundred or so different plastisizers that can be used solo or in combination. In addition there are thousands of additives to change characteristics. That's why they smell different, act differently when you pour them, and have different characteristics after they are cured. The market is very competitive, so the formulas are generally trade secrets. That's also why a favorite might change a little bit because some component of it went off the market or a better/cheaper one came along. Long story short, organic chemists that are worth their salt have very secure jobs. hope this helps. jm

Pardon me... Slush molding makes a shell, the excess uncured milky plastisol is poured out and the remaining is then completely cured. You are proposing cast molding. Here's a short discussion of a way it can be done. Casting / Molding Plastisols The molding process is used in a number of different situations. Floor & bar mats,decorative key chains, toys, bottle cap liners, gaskets, mud flaps, figurines, washers, oil and air filters, etc. The mold curing process may be done by oven or hot plate. Procedure 1. If the mold will be reused, the mold should be coated with a layer of mold release. We recommend our MRV 1000 IPA. Please see instructions for MRV 1000 IPA. 2. Fill the mold cavity with plastisol, add any other parts necessary. 3. The mold and plastisol is then heated by oven or hot plate. When the plastisol reaches 350? to 375? F the mold and part may be taken out of the oven. Caution must be taken with very thick parts- heating should be done gradually in an oven so that the part does not scorch. Approximately 7 minutes per 1/8 " of thickness is required @ 350? to 375? F oven temperature. Parts that are very thick should not be cured with a hot plate. 4. If the mold will be part of the final product, either a primer or a self-adhering type plastisol should be used. Note: Self-Adhering plastisol is commonly used in the process of making automotive air filters with metal end caps.

Silicone caulk won't take the heat. Most tin cured silicones used to make molds are rated at 350* intermittent, which falls well within pouring hot melt into them at up to 400*. There are high temp platinum cured silicones, price similar to the name of the technology, that can take more heat and in fact are used for lead, zinc, and even some lower temp aluminum alloys (a380, for instance) for short runs. I doubt that your molds are made of such a material. The technique you describe is in fact one of the normal ways to make plastisol parts, and is called slush molding. The METAL mold is heated quickly either in a convection oven, or with internal heaters. It is also cooled reasonable quickly with internal cooling coils with circulating mineral oil or something like that. A silicone mold would probably have a cycle time way too long to be useful. Another thing is that old plastic lures are probably machine injected lures. The plastic is forced into the mold under quite a bit of pressure, and a thicker viscosity is actually desirable, as it limits the flash problem. Long story short, they pour thicker. I like to use such material to make master patterns because they are tough, but it is hard to work with, and I heat it up enough so the color usually changes. Patterns don't care, but lures do. The best bet for your gig would be to pour one of the higher quality plastisols available, like M-F supersoft. you can heat it up to the point that it will pour like water, and still not burn. That is probably 50* hotter than you would normally heat it, and might cause some colors to brown out or fade. If you preheat your mold to about 150*, the hot plastic will flow into smaller passages more easily. If the small part is on top, like antennae in a crawdad mold, you need to fill it with one of the glue gun rip-offs like Lurecraft sells. Surface tension in normal plastisol will probably keep it from freely flowing into such a small space. Some who are very steady can pour such things with a small pan, but I shake too much. Start by getting your free pint of supersoft from M-F manufacturing. hope this helps jm

Must be lookin' at the chart from the back side.

If you've tried to oil the raw plaster mold, I don't think you can make anything stick to it. You'll have to make another. For plaster, Use one of the hard ones, I use Ultracal 30, some use Durhams, etc) let it cure cool, even damp for a day or so, bake it bone dry in the oven (250 for an hour or so), then coat it with 2 ton epoxy thinned with a little alcohol. It'll last until you drop it. jm

Senkosam, That's why colors don't do silly things in M-F plastic. jm

Judging from the smoke complaint, and the trouble keeping stuff suspenced, I think you got it a bit hot. M-F cures (turns clear) faster, and is thinner in the liquid state at the same temp as Calhoun. You can pour it a tad bit cooler, or put it through a needle just before it smokes. Interesting thing, M-F supersoft has a tensile strength that is quite a bit higher than the average plastic. (It stretches longer and harder before it breaks.) hope it helps jm

I have a feeling that is what Ghostbaits is calling a Slam Worm. Testimonial..... http://www.ghostbaits.com/home.htm jm

Dave, I used the vacuum setup last night. Here's some pictures. 1. The pump 2. The vacuum jar 3. 100 ml of RTV in a 240 ml cup under vacuum. hope it helps, jm

Sorry, the Grainger link in the last is tied to a session, and will fail. http://www.grainger.com/Grainger/wwg/start.shtml Part Number 3X727 jm

I asked my dentist how she mixes up dental plaster. They have a soft squishy rubber bowl, and a stirring device that vibrates. Between kneading the bowl, and stiring with the vibrator, they get all the bubbles. The vibrating table is a good idea. Schroeder valve, the little thingie in a tire stem that keeps the air in. In refrigeration, we use a flare fitting (5/16" I think) with a schroeder valve built into it. http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611630309&ccitem= I just drilled a hole in the top of a wide mouth canning jar lid, one of those without the threads, you use a ring with it. Then I stuck the extension tube of the schroeder valve through the hole and buttered it up good, inside and out with permatex RTV blue. That's how you connect to it with a standard refrigeration service hose. You don't need the ring, vacuum holds it on good. The vacuum pump is plumbed solid into the refrigerator. You have to cut the tubes to get it out. Then you silver solder one of these fittings to each tube, and that's your pump. If you can leave long enough tubes you could maybe flare it out, or use compression fittings. None of that works for refrigeration, but should be good for the plaster deal. You need to leave the cap on the outlet pipe, just loosened a half turn or so, so it doesn't pump so much air through that it blows the oil out all over the floor, thus irrititating the CFO. (Chief Financial Officer, otherwise known as Sweetheart.) You could probably just use automotive vacuum hose, and slip it over the copper tube at the pump, and one the same size permatexed into the jar lid. Leave plenty of headroom over the product you are putting into the chamber. When the air comes off, it'll "boil" up some. Plaster goes about 30%, but RTV silicone goes at least 100%. Get it into the pump, and your goose is cooked. jm

With the stuff I use, I measure the water and the powder, then add the powder slowly to the water. It will form a little heap over the water, and slowly take up the moisture. I wait patiently 2 minutes, then I begin to carefully stir it. If the powder isn't lumpy, it'll stir into a smooth mass pretty quickly. Then after that I cheat and vacuum de-gass it. Put up a picture of the Senko Toads. jm

Just my 2 cents worth, A pot heats the plastic just on the bottom, or on the bottom and sides. Microwaves focus the heat about an inch into the plastic, effectively doubling the amount of plastic actually being heated. The kink in this rope is the fact that the plastisol is a pretty good insulator, and thus tries to block the travel of heat through it. The first blast in the microwave cures about half of the plastic, mostly in the middle, leaving a milky ring and bottom. Stirring it up includes the millk. Second blast cures almost all of it, except a thin film of milk against the glass. Another stir, and maybe a few more seconds, and it's good to go. Same scenario in a pan on a stove takes at least twice as long, maybe more. A pot ususally automates the stirring, but it still takes time. Another factor is the fact that if plastisol is held at high heat for a long time, some ingredients evaporate, (the smell, and the smoke) changing the characteristics of the plastic, usually for the worse. Nuking it gets it to the mold as quick as possible. jm

Question: Whats the best way to rid the top layer of bubbles? Hi, When you pour in the plaster, pour it slowly beside the bait, then tease it toward the bait so that it finds it's own level, rising up the bait like the tide. That pushes the bubbles off the top and to the surface, or lost somewhere where they're harmless. I vacuum de-gas the plaster before I pour it to remove most of the bubbles. Tapping the table near the mold and/or the container you're pouring from helps to bring the bubbles to the top. Anticipating your question, the vacuum is from an old refrigeration compressor, and the vacuum chamber is a fruit jar with a Schroeder valve permatexed into the top. I like to use clear polyester casting resin for molds. You can see the bubbles and tease them out with a toothpick. I don't think you can make a usable 2 part mold with it, though, because it shrinks a couple of percent. They make Epoxy mold casting materials for just this sort of thing, namely vacuum forming molds for plastic. It's about $150 a gallon, and hell to use. The main difference is that the resin is high temp, which I don't think is necessary, and it's filled with aluminum, which gives it some of the characteristics of aluminum. I'm working on formulating an inexpensive casting epoxy, either finding a filled resin that works, or filling a standard casting resin with aluminum or aluminum trihydrate. I'll post it when I get something done. For sure it'll cost at least twice the polyester price.

Kamakazee, I like the bags too. Could we get some information on them? jm

That explains the awful smell, too. Getting that power bait stuff on your hands could wreck your marriage. jm

Silicone is expensive, but it is made for just this sort of problem. jm

Hi, I remelt scrap for things like mold impressions, where I could use a little harder plastic and color doesn't make any difference. I decided to use up some old commercial "dead" worms, and got something in the batch that smelled like dead fish, bubbled incessantly, and wouldn't quit bubbling till I burned the batch. I ain't got time for this. Next time I'll use my own scrap only, and add new plastic and hardener till I get the tool plastic I need. In the good old days, when every plastisol was vinyl resin and DOP, you could use them. Now there are about a hundred different plasticizers, and about a gazillion resins, along with many other additives and flavors. You can't know what you are getting if you try to reuse it. The "3X" totally uncompatible superplastics further complicate the issue. If your time is worth anything at all, just buy new plastic and pour good worms with minimum effort every time. jm

Borderbasser, First things first, you have to take care of the CFO. jm

To manufacture a hollow something, like a ball, from plastisol, the general technique is to put uncured plastisol inside a hollow mold, then heat and rotate the mold on all 3 axis until it turns to plastic, then cool it down while maintaining the rotation, then open and extract the molding. It's called rotational molding, or rotomolding. jm

Cheap trick to get it to the top. Still looking for an answer. thanks jm

Del, Plastisol does not have any volatile (at 200C) components whatsoever. If it bubbles, then there is something foreign in it. Water is common, but it could be almost anything, like a solvent for instance. jm

Plastic hardness is measured in a scale called Shore A durometer. The soft stuff we like to pour is in the range of 4 to 10. Plastic hardener is nothing more than a harder formula, probably about shore A 60, which is about the softness of plastic plier handle covers. If the "hardener" is 60, one cup per gallon would raise the durometer about 4 points. If it is 30, it would raise it about 2 points. Plastic softener is plain plasticizer. Hope this helps. jm

Epoxy is about twice as expensive as polyester resin, but has some advantages. I think shrinkage is nill, and many get as hard as shore D 60, which is like a billiard ball. If you could make a 2 piece mold out of epoxy, it would be much cheaper than CNC aluminum. (sorry Del ) I like to experiment, but I find that reinventing the wheel can be cost prohibitive, thus I post the question. thanks jm

Has anybody here made 2 piece molds from epoxy? jm