Re: Petrobond cores?


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Posted by Lyle Landstrom on August 30, 19100 at 12:23:40:

In Reply to: Petrobond cores? posted by Ken on August 29, 19100 at 15:50:38:

I've made simple cores with petrobond itself. They are delicate and lots of parting compound needs to be used on the corebox - but it works. These were for some novelty lighter holders which looked like brass knuckles but would hold a cigarette lighter. The cores were about 4-5 inches long and had the same cross section as the Bic lighter.

I've used sodium silicate as a binder with c02 blown thru the cores for longer/larger cores. This is made from the same sand as the petrobond (sand only, no petrobond binder). These cores can be remulled with the rest of the petrobond sand. I use about 5% by weight but others have used as little as 3%.

If your getting blowholes, perhaps your using too much binder and the sand isn't pourous enough. Or, you can try to push a wire thru the core lengthwise before baking or curing the core as an extra vent. How much space do you have between the core and the mold (how thick of a casting) Your "egg size bubbles" could be a result of the core sagging in the mold after closing. Perhaps a wire or tube reinforcement would help there as well. The bubbles could also be a result of how your actually configuring the mold. Is it on end or sideways?

Do you have a risor which helps gas escape and shrinkage? The pouring temp and alloy also will contribute to bubbles.

Hope this helps.

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