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The surface finish of your cast components depends greatly on the type and quality of sand used in the casting process. The sand’s manipulation and makeup are vital considerations.”


trapping gases within that would have seeped out of more porous sands. Tis can cause porosity and other gas defects in the finished casting. Te surface area of the sand used also increases with


finer grains. Tis too presents a trade-off—more resin is required to coat the sand mixture when the surface area is increased. Tis can equate to a rise in cost that may be passed on to the buyer. Resins and coatings can improve casting surface


quality with the use of almost any type of sand. Resins, such as phenolic urethane, can smooth out casting sur- faces and provide some refractory properties. Generally, resin-coated sands are used for applications that require exceptional surface finish.


Shell sands produce some of the best surface finishes in the sand casting arena because they tend to combine the highest hot strength and resin level with the finest grain of any chemical sand. Lower cost sand also


includes more impurities, including foreign elements that


compromise the flowability of the sand. To com- bat these contaminants, which can change the way region-specific sand compacts, metalcasters can use a coating that fills in the gaps that result on the mold and core faces. Such a coating will cause particles to be transferred to the surface via a zircon conductor. Of course, this means moving toward materials that are harder to source.


Considerations During Casting Even if you know what kind of surface finish you


require, how do you find the right metalcaster to deliver it? According to Jiten Shah, president, Product


The sand mold’s method of compaction is one variable in determining the final surface finish of a casting.


44 | METAL CASTING DESIGN & PURCHASING | Jan/Feb 2016


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