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Joined: March 01 2008 Location: United States Posts: 1929
Posted: October 06 2009 at 5:41pm | IP Logged
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Joined: December 15 2006 Location: United States Posts: 17
Posted: January 02 2012 at 12:40pm | IP Logged
I have been teaching in schools for some years and some use a water bond sand and others use an oil bond (Petrobond) sand.
The advantage of an oil bond is that once the mold is made it can be set aside for maybe a week until a pour is done. A mold done with a water bond sand is like a giant, tight sponge. It will start losing moisture from the time you are done ramming. After a few days it may have dried out enough that the inside can begin to crumble. If you bump it, it may crumble more. Finally poured and the pour doesn't come out right due to this collapsing.
Oil bond sand won't do that. It can crumble due to impact, but it seems to hold together better. It does not dry out.
As for smoke, during the pour (in my case aluminum and bronze) there is very little. If the mold is left to cool completely (say over night) then upon breaking it out there is also no smoke. If you have to break it out after 30 minutes, there will be lots of smoke. I have broken castings out after 10 minutes on to an iron table. The piece and the sand is so hot that the oil spontaneously combusts. It was not violent, but it was impressive. I would expect almost everyone here doing any pouring is going to do it outside in fair weather.
Mixing sand and oil is easiest with a muller. It is an industrial version of mom's kitchen-aid mixer. It can and is done often with a shovel and something like a mud pan (like those used for mixing mortar). If you want to do it that way, buy a new pan. chipped off mortar in you sand isn't very desirable.
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