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jkustel

Pressure Casting Urethane Resin

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Curious who if anyone on here is using a pressure pot to cure their urethane while in the molds. I suppose if you don't have a lot of thin sections or details in your bait then the advantage is a more solid blank that has less bubbles. I'm considering some designs with thin fin sections, etc. and it sounds like curing them under pressure is the way to go to consistently get all the small channels to fill consistently.

I hear of guys running anywhere from 30 to 80 lbs of pressure. The other key as I understand it is that your rtv molds must be cured under pressure as well or they will not withstand the pressure and distort, which makes sense.

Thanks

JK

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I tried it and abandoned the idea. The problem I was experiencing was the extreme compression of the microspheres resulting in too high density and "short shots" after the resin compressed within the funnel. I think you would be better off designing your molds to pour the weak sections first with a stronger resin mixture and then pour the remainder of the bait.

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I hear ya. I'm going to try to get the sections to fill just using small vents and see how it goes. I really don't want to be limited by space (in the pressure pot) on how many molds I can run and/or certainly don't want to have to recalculate all my densities based around another variable like air pressure.....yikes...thanks for the response.....hadn't thought of the density issue.

JK

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There are several alternatives, including some of which that have been used for centuries. The risk you run with too low center of gravity relative to center of buoyancy is the tendency to not track in a vertical plane.

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Also be mindful of your cure time. A lot of the faster cure resins have better strength properties than the slower cure varieties. Either way works jsut depends on your set up and preference

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You might be better pulling the resin through with a vacuum. I posted the technique for plastics, but I see no reason why it shouldn't work for this medium.

Dave

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I have had good success with thinwalled patterns by slightly elevating the last (highest)vented area and using a BIG syringe to inject the resin slowly from the lowest port. Im using filled urethane and the viscosity is pretty high. The fill port and last vent are higher than the cast part, so the runoff cant fall back and create problems with air. I have dowels molded in the halves, and the male ones are vented as well. I suppose that if the design had protrusions out to the side, like fins, you would have to make 90d vents to the top. ??

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