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Post by Bsud on Mar 26, 2018 19:42:07 GMT -5
My question is could someone help me out here. My molds are turning out parts that are different sizes. It doesn't make any sense to me why my part pattern size is 0.62 thickness but I demold some that's thinner than that? Also I get some thats wider also. Am I missing something here? I use alumifoam to pour my molds. TIA
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Post by Brian on Mar 28, 2018 20:52:03 GMT -5
... I cant comment on alumifoam as I don't use it. I cast 1/25 scale car parts...small stuff, but must be correctly proportioned to scale. I use HS-2 ...been know to pick up some HS-3 from the brick & mortar stores as well from time to time. I have had the same issues in the past...either w/ brand X's sub par RTV Silicone or with HS-3 (at times if I am not careful.) What it sounds like to me, if the pour is too thin, then too much pressure is being applied to the mold if it's a multipart mold...if its a single part mold, then it could be collapsing in on its self due to the weight of the RTV is more than the free standing mold can support without distortion. Just the opposite for the "wider" sizes....not enough pressure being applied to a multipart mold or the resin is creating hydraulic pressure with in the mold forcing it to expand. I switched over to HS-2 from HS-3 due to it making a firmer mold that can with stand more pressure when used in a multi part mold(pressure holding the mold pieces together) yet still has the flex I need for under cuts and etc. |
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Post by Bsud on Mar 28, 2018 21:30:31 GMT -5
Thank you for the response. I do use a two sided mold to mold two halves together. So what do you think I should try doung?
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Post by Brian on Mar 30, 2018 17:14:34 GMT -5
What is the size of your mold? With the 2 halves together what is the height,width, length ...I am going to assume that the 2 halves are pretty close to being equal halves.....size will make a difference as far as how I answer the question....larger mold vs. smaller mold
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Post by Bsud on Mar 31, 2018 22:04:32 GMT -5
They are not big, like 4"x 3"x 2" that's with the two halves together
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Post by carol - Alumilite Corp on Apr 3, 2018 10:08:38 GMT -5
Bsud,
When you are using a tin cure silicone there is moderate shrinkage, the larger the mold the more shrinkage you may incur. The linear shrinkage on the HS series is .3%. Some shrinkage in tin cures can take place up to 72 hours after cure. If you are needing no shrinkage or have close tolerance that you must adhere to it would be best to use a platinum cure silicone. The Trans40 and Plat55 are essentially nil for shrinkage and the Plat 10-25-40 are <.1%.
Regards,
Carol
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