Re: Petro bond sand


Bramblebush ForumsFAQ

Posted by bruce paul fink on October 15, 19100 at 09:39:16:

In Reply to: Re: Petro bond sand posted by Sonny Jeffers on October 14, 19100 at 22:10:12:

Petro bond sand will work with most metals including aluminum or cast iron. Of course you get a 'sand' surface finish. Not necessarily bad but not to the degree of finger print surface quality of a plaster based investment or even harder surface ceramic shell mold.

Two of the advantage differences of sand molds is the elimination of a burnout to remove the model, and the greater porosity of the sand so it can partially vent right through the mold body itself. This is also a great time and energy saver.

But it also has the disadvantage of needing the model to be such that you can lift it out, thus no real undercuts and all sides with slight draft tapers for the model removal. An exception to this is when the model is a styrofoam item that burns out as the metal goes in. Never one of my favorites but certainly good under some model or production conditions.

As far as using a mold more than once (unless you are getting into very expensive and sometimes water cooled metal molds for production) it is much easier to make a model that can be used more than once and to still discard each used investment, or to reprocess the used investment for reuse.

The closest I ever got to that was to make a urethane rubber positive model with all parting planes and sprues, cup and vents as part of it, and then to cast individual investments one at a time for each half. Let each side set up and remove just one half at a time and recast the remaining side or portion. Then remove the first investment segment and keep recasting in a rotation. This makes a series of investment pieces that will reassemble perfectly (use alignment key ways in the model) before casting and that do NOT have any interior model left in to require a burnout for that part.

I did a series of 18 for 6 different models that way for a total of 108 bronze castings that were each about 7 lb.

The investment was a plaster based one but only needed a shorter 700 degree burnout for the mechanical and chemical water removal. The models still exist and many more could be done if needed since the urethane rubber models show no wear at all.

Hope this is clear enough. A picture is worth a thousand words but no pic here. bpfink

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