Shell Mold Casting Advantages, Disadvantages & Process

Shell mold casting, also known as shell molding, is a type of metal casting process that is similar to sand casting. It can be defined as a casting method to cover the molding sand mixed with resin on the metal template with the mold and preheated, heat to melt the resin, form a thin shell, and take it off from the template after baking and hardening to be used as the casting mold, or a casting method of forming a thin shell mold with silica sand or zirconium sand and resin mixture or resin replica sand, forming a thin shell of a certain thickness on the 180 &#; 280 &#; template, and then heating to solidify the thin shell, so as to reach the required temperature and stiffness. 

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Advantages of Shell Mold Casting

Using resin sand to make a thin shell mold or shell core can reduce the amount of molding sand used, the casting parts will get a clear profile and accurate size. 

&#; The process can be done without machining or only a small amount

&#; Economical for large-batch orders 

&#; High dimensional accuracy

&#; Thin-walled, complex parts can be manufactured

&#; Smooth surface of the shell mold cavity

&#; Easy flow of molten metal during the pouring

&#; Good surface finish of castings

&#; Reduced tearing and cracking of casting

&#; Lower labor requirements

Disadvantages of Shell Mold Casting

A drawback of shell molding is the resin-coated sand used in the process is relatively expensive, and the template must be precisely machined, which raises the total cost. In addition, it will also produce a pungent smell when pouring, which to some extent limits the wide application of this method. 

What is the difference between shell mold casting and sand casting?

&#; Shell mold casting has higher dimensional accuracy, higher productivity, and lower requirements of labor. 

&#; Shell molding uses resin-coated sand, which is more expensive than the mixture of raw sand, coal powder, and bentonite used in sand casting, and the resin-coated sand can&#;t be reused. 

&#; The making of shell mold is more complex than sand mold and more costly.

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&#; Shell mold casting requires specific equipment, while sand casting can be done manually as well.

Advantages

Shell molding can be completely automated for mass production.

The high productivity, low labor costs, good surface finishes, and precision of the process can more than pay for itself if it reduces machining costs.

There are few problems due to gases, because of the absence of moisture in the shell, and the little gas that is still present easily escapes through the thin shell. When the metal is poured some of the resin binder burns out on the surface of the shell, which makes shaking out easy.

Complex shapes and fine details can be formed with very good surface finish, high production rate, low labor cost (if automated).

Low tooling cost, Little scrap generated.

Very large parts and complex shapes can be produced.

Many material options.

Low tooling and equipment cost.

Scrap can be recycled.

Short lead time possible.

Disadvantages

The gating system must be part of the pattern because the entire mold is formed from the pattern, which can be expensive.

The resin for the sand is expensive, although not much is required because only a shell is being formed.

High equipment cost.

Poor material strength.

High porosity possible.

Secondary machining often required.

High labor cost if done manually.

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