Help, Can't get multi-piece molds vacuum tight

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#1

So I have a 3 piece mold that I can’t seem to get vacuum tight. I have been trying to use some liquid (bathroom)sealant along the flanges and around the bolt holes but I can never get it to stay vacuum tight. been letting it dry overnight etc I’m running out of ideas and patience… any suggestions? (the flanges fit very snug and there is not any appreciable gap, but I manage to get some weeping leaks once pulling vacuum?

I’m considering trying some pva on the faces of the flange and then bolting it all together and then filling the part line with some more pva just for that extra little protection…

the mold is all semi-permed so I haven’t been using a silicone based liquid sealant since the silicone doesn’t release from the surface…

Any help would be greatly appreciated.

#2

I doubt pva would help.
if its being really stuborn, you could always double bag it.
ie. one bag on the flange for the infusion and another envelope style bag. that should cure ya

#3

the mold is very large…not sure if I could envelope it, but the bagging over the flange area might work.

I gave it another shot with the sealant. This time I put 3 seperate lines of sealant running the length of the mold, hopefully that will work better, we’ll see…

#4

Hmm…depending on the flange mating, how about a thin sheet of rubber/silicone. Fully cured stuff, not liquid/caulk based.

#5

you could try a gasket maker material stuff also :cool:

#6

I have seen molds actual leak thru the mold surface.

Bondline showed me a trick using carbon paper vacuum bagged in the mold, pull a vacuum and then spray the back of the mold with ammonia. The fumes will turn the carbon paper purple…then it is the mold itself.

Several companies have latex or other spary on’s for the back to seal them up too.

#7

Thanks for the tips guys…

That liquid gasket idea is great, I have some of that lying around too! I’ll see how it releases from a semi permed surface.

#8

im gonna vacuum bag a 3 piece mold on the weekend as well. im gonna use the vacuum tape on the flanges and if it doesnt work, i’ll bag it around the flanges (and the bolt holes)

#9

pulled vacuum today, it’s still pulling as we speak and has been for about 12 hours, not the slightest leak. I just made sure to put 3 beads of sealant on the flanges, let it cure for an extra day and also had a heat lamp on the flanges for a short while. It sure did the trick!

I will post pics of the final product in a few days! She’s a big’un!:smiley:

#10

Yep, I have had two molds do this to me. For a temporary fix i used some sticky bag tape on the outer surface of the mold. sometimes you can run your finger over that area and hear the leak stop/start again.