Glue and molds

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Jim Burr

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Having a great pressure pot now and boxes of worthless wood:biggrin: I was going to make some single use molds from corrigated plastic sign material and hot glue. BUT...I'm using PR. My question is...will the curing temp of PR cause the glue to fail? I will move to Alumilite in time, but budget restrains:mad: dictate I use up the gallon of PR I have first.
Thanks for the help:biggrin:
 
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You might want to test the corrugated sign material as well. It might not react well to the PR either. Just a suggestion I have no idea.

Make a small mold and test it out. Put that in a box that will contain any leaks or failures though. No need making your put suffer.

Let us know.
 
Ta Da!! Sucess!! I did two molds for my first WW casting. One was corrigated sign material...about $7 at Lowes for a 26x26 blank sheet. Cut it with scissors and then Hot glued the inside all around. Wrapped in 2 layers of foil to contain any spills.
The second was cutting board. But I didn't have any screws the right size, so, you guessed it...hot glue and two layers of foil. I popped the blanks in, did a 3 color pour and set them in pot at 40psi over night. Opened it up this morning. Some minor leaking from the mold but the foil contained it. Looks like the glue held fine!
Might make it easier to make molds for those odd pieces that we all get now and then.
 
They both did Billy...I didn't get real careful about my gluing. The amount of material that leaked was about 10-15 drops. Two things I will change; use my 3/8" sticks rather than my 1/4" and pay more attention to the gluing process.
 
Got any pics of the molds? I'm about to make some cutting board molds, and hot glue sounds like a good idea. PR gets hot, but I doubt it gets hot enough to melt hot glue. And based on your results, that seems to be true.

So, how did the WW blanks turn out?
 
Hot glue will not permanently hold cutting board (poly) molds together. The only way to do it permanently is to use a special glue and process or welding. Polyethelene is basically a very high density wax, that is why it releases so well which also causes most all adhesives to fail.

This is from experience and information from a close friend who is a retired chemical engineer. He was the VP of Quality Control and Processes for Exxon's plastics division world wide before he retired. The main product he worked with was polyethelene, the stuff the white cutting boards are made from!
 
MesquiteMan said:
Hot glue will not permanently hold cutting board (poly) molds together. The only way to do it permanently is to use a special glue and process or welding. Polyethelene is basically a very high density wax, that is why it releases so well which also causes most all adhesives to fail.
Click to expand...

Yup...this was just a test kinda thing and no small amount of impatience on my part:rolleyes::wink:. For standard size, regular use molds, Curtis does a WW cast tutorial that I follow. For the oddball size or "crap...I can't find my mold" the sign material worked very well. Once I get home...I'll be getting the proper size screws for my cutting board molds.
Bob, the WW casting came out great!!:biggrin:, No air bubbles and what looks like good adheasion. When I get home next week, I'll be doing more of the sign material and paying attention to my gluing...but the foil will still be used! Pic's later.
 
Plain old cardboad works well for the one off molds also. I have done that many times. Simply hot glue or tape it together and cast away. After the casting is done, simply cut the cardboard off on the saw and you are good to go!
 
Here's what I found that might be a possibility.

Adhesives Structural Adhesives-Shop 3M

This says it bonds to polypropylene, polyethylene and other LSE plastics.
But if I was going to spend that much, I might just be better off to buy a pre-made mold.

However, for my purposes, I'm thinking hot glue all the sides but one. Then use screws to keep the sides in place. I'm hope the hot glue will be able to keep the mold from leaking. Then for the side that is removed, just use plumbers putty.
 
BSea said:
However, for my purposes, I'm thinking hot glue all the sides but one. Then use screws to keep the sides in place. I'm hope the hot glue will be able to keep the mold from leaking. Then for the side that is removed, just use plumbers putty.
Click to expand...

If you are already using screws, as long as you pull them up nice and tight, your molds will not leak, even with nothing in there. The very first time you run the mold it might leak a tiny bit but the resin will then fill in any gaps and it will no longer leak. I have 30-40 cutting board molds made this way and none leak. If you are worried about it, you can also just use the plumber's putty before you screw it together. This will fill any small gaps as well. I don't mess with this because I am able to pull them up nice and tight and not have any issues. The same with the part that you remove to get the blanks out. I don't use any putty. It just depends on how well you build your molds.
 
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