I made a wood mold to make my foam cores. It makes a curved, 1/2 in sheet of foam 30 in x 18 in, so it needs to release easy. I am using 5 lb polyurethane foam. First try I used super 77 to stick down clear plastic sheeting and no release agents. That was my most successful attempt yet, it stuck to it but I got it out in one piece. only downfall was the plastic sheeting had a bunch of ripples in it so I tried strechalon 500 so it would work in smoother with some watershield to release it and it stuck. I also tried black plastic sheeting which releases great free rise but under pressure in the mold sticks, even with wax or watershield. I will eventually figure it out but if anyone has a great solution for my next try that would be awesome!
Where I buy Pu foam they also have a release agent for it, for making foam preforms. The mould should be smooth and non porous though.
I think the heat from the foam is melting the plastic sheeting and bonding to it. I am still surprised it stuck to the strechelon 200, its max temp is 250 F. How hot does foam get during cure? I wish i could get a hold of some Tooltec from Airtech in small quantity. Im thinking of using thin sheet metal to go over the wood. This is mold is just R&D so I can easily cut different shapes until I get a good design down then I will make a more permanent mold.
I think the foam also changes size (shrinks) as it cures - you mix the foam and lay it out, then it sticks to the plastic. But then it shrinks and pulls in the plastic causing the ripples. I noticed the same thing working with polyester resin, my gut tells me it’s not so much a heat problem.
I’m curious - did you get any attempt with plastic sheet that didn’t ripple?
Even if it’s just a test mould, I’d say that painting it in 2k (won’t be chemically reactive) would the be the easiest bet, save all these dramas you’re having.
I applied the clear plastic sheeting with the oven on and door open and stretched it while I was laying it down. After curing it had no ripples but still partly stuck. I got sick of release films so I went to the home depot and picked up galvanized sheet metal and stuck it down with super 77 which worked surprisingly good, almost a little too good I had the first part crooked and it was difficult to straighten out. For the 45 degree areas I used scraps of tooltec from work. I sealed it and watershielded it and it released excellent.
Thanks mugget for the 2k paint idea it will be good for future applications.
Now the only problem I’m having is the foam is really brittle, it may be because it is only 5 lb foam for the 1/2 in sheet. But on other failed attempts the foam seemed more plasticity and durable which makes me think the foam is degrading and close to expiration (about a month and a half away). So I was thinking add more foam to get the density up. Also the foam dispenser could be high on the part B the Isocyanate, low on part A resin still within calibration and just switch high on A low on B.