Cracks During Casting

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baker4456

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Joined
May 2, 2008
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Location
Garland, Tx, USA.
I have had a couple of castings that come out of the pressure pot with a crack. I thought at first it was an air pocket but it looks like some one cut it with a real thin knife. Has any one had this happen or know why it happened? Can I fix it with thin CA? I'm not sure I can get the CA to go into the crack. Spent a lot of time prepairing the tubes for this casting and don't want to scrap it. Help!!!!:confused:
 
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Cracks..? The only thing I can think of is a temp problem. If there's too much of a
difference between the temp of the mold and the resin, I can see potential problem,
but nothing else really comes to mind.

If you can get thin CA into it, that might work. It should 'wick' into the crack .. let
gravity be your friend, too. Don't worry about it getting on the surface, you can
sand/polish it up to a matching gloss anyway..
 
Don't know about repairing sorry. Curious was it PR or Alumilite?

My first PR cast was a photograph and when I pulled it out of the pot it was cracked down the middle where the photo was.

Dunno why tho.


Manny
 
my understanding is that too much heat can cause cracking. like too much catalyst. pressure should not cause cracking unless the tube gave way after the PR hardened. don't see that happening though.
 
The only time i remember a casting crack like you describe is when I used a long piece (10 inch) of PVC pipe for the mold, I may have also used too much catalyst which creates the heat. I never tried it again or had one crack that I remember.
 
Heat causes PR to have fissures or even crack. Yes, I've had this happen. The heat builds up in the center of the blank and the only escape for the heat is through the exposed surface. I had several cracks or fissures when I was casting in blocks that used 16 ounces of resin. I now cast in the silicone rubber molds made by gadget and cast pen blank size casts. I use 3 drops of MEKP per ounce of PR and the results are great. But, I only cast snake skins and computer labels...no colors, dyes or powders.
Do a good turn daily!
Don

baker4456 said:
I have had a couple of castings that come out of the pressure pot with a crack. I thought at first it was an air pocket but it looks like some one cut it with a real thin knife. Has any one had this happen or know why it happened? Can I fix it with thin CA? I'm not sure I can get the CA to go into the crack. Spent a lot of time prepairing the tubes for this casting and don't want to scrap it. Help!!!!:confused:
Click to expand...
 
I know how you feel after spending time preparing the casting and then have the block crack. Welcome to the wacky world of casting. You can try to repair it with thin CA. It's worth a try. I started casting using 8 drops of catalyst per ounce and quickly started backing off and have settled with 3 drops and it works for me. I also start with resin warmed to about 140 degrees...but I've not always done that and 3 drops worked when I was not heating the resin.

You might try casting in layers...maybe 3 layers of 5 ounces each....6 ounces on the last layer to get the 16 oz required. I have cast in two layers...pour the first layer and when the PR starts gelling I place the prepared tube into it. It is sticky enough that the tube will stick. Then I cast the second layer. The seam becomes invisible after the block has cured.
Do a good turn daily!
Don

baker4456 said:
Don,
I had about 16oz in plastic tupperware. It poured about 1" thick and I used ~80 drops of catalyst.
Click to expand...
 
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