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RTV rubber mold/Resin casting question.
fhvn4d
#159
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Massachusetts, United States
Joined: April 07, 2008
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Posted: Tuesday, March 08, 2016 - 11:17 PM UTC
Thought I would post a question to the masses who do their own mold making and casting in resin. I have been a faithful user of Micro Marks 300 quick mold making A&B 1-1 and have enjoyed the molds it makes. I have also used their 1-1 resin to cast and have have alot of problems with bubbles forming no matter how much effort I make to not agitate it. I use a brush to make sure the bubbles are initially not against any edges of the mold, but they seem to just develop out of thin air... I have tried vibrating the molds and no luck really.. I guess my question is what do you all out there do and what do you use to make your castings.




matt
Staff MemberCampaigns Administrator
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New York, United States
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Posted: Wednesday, March 09, 2016 - 12:02 AM UTC
Pressure cast. I use a "paint pot" with a valve/ quick connect to my compressor, and a gauge on the other port.
It's much cheaper than a Vacuum pump setup for home casting.
krow113
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British Columbia, Canada
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Posted: Wednesday, March 09, 2016 - 12:20 AM UTC
Yes pressure casting may help. vacuuming the material before the pourccan help as well, a simple rig can be made for use with a home vacuum. Check casting supply sites for ideas, and watch the pressure , and the working time of the material. Your items don't look that bad.Even the best get bubbles...

fhvn4d
#159
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Massachusetts, United States
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Posted: Wednesday, March 09, 2016 - 04:46 AM UTC
could you guys expand on what you suggested??? what pressure should I operate it at ? how do you get your molds in there with wet casting agent in it without making a mess? I use stuff that takes about 30 minutes to set and is cured in 2-4 hours. I always wondered if slower curing stuff would be better too. what resins do you guys use?
krow113
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British Columbia, Canada
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Posted: Wednesday, March 09, 2016 - 05:15 AM UTC

Quoted Text

could you guys expand on what you suggested??? what pressure should I operate it at ? how do you get your molds in there with wet casting agent in it without making a mess? I use stuff that takes about 30 minutes to set and is cured in 2-4 hours. I always wondered if slower curing stuff would be better too. what resins do you guys use?



Pressure will be determined by your testing.
If you cant move your mould from the table to the pressure pot without a mess you got problems with the mould. I pour into the mould while it is in my pressure pot. 30 mins is slow enough.
Smooth-On is what I use.
matt
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New York, United States
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Posted: Wednesday, March 09, 2016 - 06:51 AM UTC
I use Smooth On mold max rtv and smooth cast resins
junglejim
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Alberta, Canada
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Posted: Wednesday, March 09, 2016 - 07:44 AM UTC
Another Smooth-On user. Try brushing some talcum powder/baby powder in your molds before you pour, just sprinkle a bit in, tap your mold around so it gets in all the areas and blow it out, this cuts down on the surface tension and helps the resin flow better. I also use a pressure pot, both for vacuuming the rubber when making the molds, and pressuring the resin when casting. About 35-40 psi will be enough to crush them bubbles.

Jim
panzer67
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Nuevo Leon, Mexico
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Posted: Friday, March 11, 2016 - 09:17 AM UTC
smooth on works great ( you must use the lowest viscosity resin and the curing time more large as 2 hours to assure the bubbles will eliminate ...)

smooth works great to me
astursimmer
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Baden-Württemberg, Germany
Joined: July 22, 2015
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Posted: Friday, March 11, 2016 - 12:54 PM UTC
Hi Brian,
I did years ago a lot of resin casting. Like you I used a tool to fill the small corners in the mold (tipically the rivets) before pouring the rest. Bubbles were never a problem. Few months ago I did some new castings but could get only a resing with a shorter pot life. I tried to shake it less, as I had less pot time, and I got bubbles and even some areas where the resin was not completely cured, probably due to insufficient mixing. I mean, perhaps your less shaking is counterproductive.
On the other hand in my older trials I also did sudder bubbles with the resin batches older than one year. Bubbles development in the mould while hardening, and more volume contraction. Check your resin shelf life if possible.
Hope that helps.
Nacho