Problem getting blanks out

Signed-In Members Don't See This Ad
micharms

micharms

Member
Joined
Nov 8, 2004
Messages
681
Location
Port Elgin, Ontario, Canada.
I've been pouring bottlestopper blanks using pvc pipe as the mould. I've sprayed with Pam and am still having problems getting the blanks out of the pipe. A dowel and a mini sledge finally knocked them out. The other problem is that there are remnants of the PR left behind. How do I make it easier to get the blanks out and how do I clean the pipe to get rid of the leftovers?

When I originally started pouring these I tried the pill bottle route but had even worse luck with those.

Thanks
Michael
 
Signed-In Members Don't See This Ad
Michael,

This is NOT what you want to hear, but that's the way we started making blanks, too.

NEVER DID figure out how to get them out. And, if you hit them with a dowel, you may develop internal cracks that will show up when you turn them.

Sorry I can't help, but maybe you feel better if you know it's not just YOU!!
 
I have to agree with Seawolf here... Seems like it would be far simpler to just turn off the PVC. In the long run, to me it would be far easier to just "lose" the cost of the PVC and less risk of internal cracking like Ed was talking about.
 
Just out of curiosity, how long are you letting the pr cure before you remove from your mold? I find that it shrinks somewhat as time passes, like the next day,
and is easier to remove later, rather than sooner.
I have sometimes rapped the mold all around the outside with a mallet to help release it, too.
It's pretty obvious the pam is not working 100% by the fact you have remnats left behind (they're stuck!!).
I might try a different lubricant if I were you.
There is a commercial aerosol mold release made for plastic injection molding, brand name Stoner. It might help you, I would ask before buying it, though.
I'm sure some of the casting guru's will chime in shortly.
 
What type of PVC are you using? It has to be schedule 40. It should shrink and release without any problem without a release agent. I've re-used the PVC for over a hundred casts and still no problem.
Another thought... are you sure it's PR and not a urethane resin?
 
Last edited:
I was about to ask about the urethane, too. It won't shrink nearly as much
as the PR. But PR will shrink and it will harden. So .. if you're leaving PR behind,
and it isn't shrinking, then I'd agree with johnnycnc .. it might be too soon to
de-mold.

Vaseline mixed with mineral spirits (90% spirits) works well as a release. You can
gently warm it and put it in a spray bottle. ( 2 for $1 at Walmart) Shake it up and
spray it on.
 
Typical mold treatment would be to clean and polish the mold as much as possible, and then treat with PVA (polyvinylacetate) - a mold release agent.

Another worthwhile ploy is to cut a slot in the PVC pipe. Clamp it closed (or tape over the slot) before casting. When you want to remove the blank, unclamp (or untape), stick a screwdriver in the slot and twist to pry it open. This breaks the mold free of the blank and it should drop out.
 
Thanks for all the suggestions. It is PR and I left it for an extra day before trying to get the blanks out. I even heated everything in a small convection oven we have discarded to make sure the cure was complete.

I'll clean up the PVC before the next cast and try the vaseline/mineral spirits solution. I think I'll also try the slot in the pipe. I had thought about doing that but just never got around to it.

For some of the pipe the first time it was used it worked like a charm so that is what has me a bit frustrated with this.

The way the weather is going up here there isn't much casting time left as I do it in my garage.

I guess I'll just keep on pluggin' - er casting away:confused:

Michael
 
I agree w/ those who say that the PR should shrink enough to make removal easy.


Here's another thing to try. But don't do it with PR that's not totally cured.

Put them in the freezer.

Lately I've been using steel tubing for my alumilite molds. Not exactly smooth on the inside- far from it w/ a welded seam. Real pain to get the blanks to release since alumilite doesn't shrink much. Out of frustration I tried sticking them in the freezer. I still have to use a hammer and dowel to pop them out, but it's overcoming minor drag rather than a major battle.

Not-totally cured PR? Don't even think about putting it in the freezer unless you want any food in there to smell/taste like PR. DAMHIKT.
 
Using a plastic for the mold seems like asking for trouble. Solvents will attack almost anything. Nalgene might be an exception.
But, if you are going to use it, try a real mold release product. Machinist supply houses have it. Gun shops have it for use by those who cast bullets. On-line, try Midway Arms or Brownell's.
 
You must log in or register to reply here.
Back
Top Bottom