| 配方類型： |
METALS AND THEIR TREATMENT |
| 配方說明： |
Precision Casting Refractory Mold |
| 配方組成： |
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| 配制方法： |
For precision casting, refractory materials of varying sizes are used to obtain an investment that has maximum strength plus adequate porosity. Fused silica and grog (composed of broken bricks or burnt ground fire clay) are commonly used refractories.
Small amounts of magnesium oxide are pre-blended for even distribution in the finely divided refractory mixture.
Just prior to investment from 3 to 10 volume per cent excess water is added to the completely hydrolyzed solution of ethyl silicate. When the refractory is added, the combination of magnesium oxide and excess water activate and control the gelation of solvent-hydrolyzed ethyl silicate.
A setting time of 40 to 60 minutes has proven successful throughout the industry. This permits thorough mixing, careful filling of the flask, and settling on a vibrating table for at least 20 minutes.
An alcoholic solution of ammonium acetate is a convenient reagent for obtaining rapid gelation. By varying the amount of reagent used, the gelation tim |
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