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Max-Cast, Inc.
P.O. Box 662
Kalona, Iowa 52247

tel: 1-8_00-728-933_9
local: (319) 65_6-5365
M-F, 8:30am-5:00pm


For casting iron, bronze, and aluminum there are two basic molding techniques: sand and investment casting. These are waste mold systems; in other words, the mold is broken with each casting. Since the high heat of the metal destroys the surface of the mold, they cannot be reused.

There are many different binder systems for sand molds. They bond the sand grains together well enough to allow metal to be poured into the mold and have the mold cavity hold its shape until the metal solidifies. The simplest is a clay-water bond known as greensand. Other "bakeable" binders use molasses or flour. No-bake binders with chemical resins are also utilized. Generally, sand castings require a pattern on which sand mixed with binder is rammed and carefully removed. The pattern must, therefore, be draftable without undercuts (horizontal protrusions or depressions) which will prevent the mold from being pulled from the pattern. Piece molds can be pulled off more complex patterns to avoid undercuts and cores can be used to make bulky pieces hollow for weight saving and to avoid metal shrinkage problems. Patterns which will have many molds taken off them can be made of wood, aluminum or plastic. Some undercuts can be tolerated if flexible rubber patterns are used. Sand casting is usually less expensive than investment casting. Where surface texture does not have to be as highly detailed, it may be the best bet. Many larger pieces are done with the grosser sections done in sand molds while the highly detailed parts such as head, hands, and feet are investment cast.

A variation of sand casting incorporates the investment casting concept of "investing" the pattern in the mold. Polystyrene foam carvings and/or assemblages maybe invested: rammed-up in sand along with a pour cup and lots of vents. The molten metal can be poured through the cup directly into the styrofoam pattern, vaporizing the foam out the vents and replacing it with metal.

Investment casting utilizes the same principle. The pattern is invested in the mold. With lost wax casting, the wax pattern is melted and/or burned out of the mold before the metal is poured in and while the mold is still very hot. It is generally best to make a rubber mold and cast wax patterns from it rather than to invest the one and only original. This practice leaves no reference for the casting/finishing stages. Plus it leaves no "safety net" if the original does not cast correctly. The liability of failure is actually greater since fabricated waxes tend to be weaker than cast ones. Some strength and durability is required of the wax when applying the refractory molding materials. A rubber mold also makes editions possible. An additional benefit of this method is found in the fact that the foundry can store your rubber mold and produce more waxes and metal castings when needed.

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