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Gravity Casting

Gravity Casting


During casting, a manufacturer pours liquid or plastic material into a mold and allows it to harden into the shape of the cavity. Parts producers often rely upon this process to create components from molten metals. Casting may involve the use of either disposable or reusable molds. Gravity casting today works well in conjunction with the use of permanent molds.

 

About Permanent Mold Casting

During permanent mold casting, a manufacturer employs a "permanent" mold. While this structure won't endure indefinitely, it typically permits extended re-use before requiring replacement. Unlike a disposable mold, it survives the casting process. Permanent molds today typically consist of stainless steel, graphite or other durable constituents.

Take a moment to consider four types of popular casting processes which may utilize permanent molds. Some manufacturers focus upon one of these methods, while others rely on several different casting processes:

Gravity Casting

During gravity casting, in its simplest form a manufacturer pours molten material into a well-lubricated mold from an access point at the top. Gravity causes the liquid to spread into the lower levels of the mold where it hardens as it cools into a new shape conforming with the mold cavity.

"Slush" Casting

This casting method does not necessarily require the use of extremely high temperatures; the term "slush casting" sometimes refers to a casting process allowing manufacturers to create a variety of low cost lightweight, hollow items. For instance, in the past companies used slush casting to generate ornately detailed toy figurines, jewelry, ornaments and masks. Reportedly, a manufacturer pours molten material into a mold and then allows partial cooling and solidification before removing the remaining liquid. This process leaves a solid shell coating the surface of the mold. The resulting cast product will possess an interior hollow cavity or depression.

Low-Pressure Casting

Pressure casting closely resembles gravity casting, except a manufacturer applies pressure to assist the distribution of molten material through the mold cavity. The use of a pressurized chamber and compressor may enable the filling of molds with resin, rubber or even metal to ensure more reliable distribution of casting material inside complexly shaped molds, for example. The preferred method selected for creating pressure depends upon the raw material.

"Vacuum" Casting

Manufacturers have developed a wide variety of different types of vacuum casting technologies for use with plastic and metal raw materials. (Some authorities refer to the use of a vacuum to fill a mold as "vacuum assisted" casting.) The manufacturer rigidly controls the casting environment to maintain a vacuum in order to help fill a mold uniformly during this form of casting. The difference in the atmospheric pressure gradient maintained inside a mold and around molten metal permits vacuum assisted mold filling, allowing manufacturers greater control over this step (especially with respect to the speed of mold filling) than gravity casting permits. Vacuums also play an important role in maintaining the shape of the mold itself in some commercial casting processes.

 

Gravity Casting: Materials And Applications

Metal part manufacturers who perform traditional gravity casting typically invest significant tooling in the creation of well-designed permanent molds. The manufacturer lubricates the mold surface thoroughly to reduce sticking. Then molten raw material enters the mold from an opening or gate at the top; gravity permits the complete filling of every cavity within the mold. After cooling, the manufacturer removes the cast part. Today, the process of gravity die casting has largely surpassed conventional gravity casting in high-volume manufacturing settings.

The diversity of gravity casting today permits the use of many different materials during this process. Additionally, this form of casting has obtained widespread applications.

Materials

Gravity casting works well with permanent molds filled through a gate or other opening located at the top of the mold. Although the raw materials used in casting impact the selection of mold-making constituents, today manufacturers frequently create permanent molds from stainless steel, gray cast iron, graphite or other durable materials.

Manufacturers in the past have used gravity casting to create metal parts from virtually every commercially important metal or metal alloy. Due to the high temperatures required to melt ferrous metals and metal alloys, however, this process often relies upon raw materials within lower melting point ranges, such as lead, zinc and tin.

Applications

Applications for gravity cast components occur in every industrial sector today. It permits the creation of jewelry, tools, consumer goods, gears, wheels, pipes and housings. Manufacturers may create many different types and sizes of parts using gravity casting.

 

Advantages of Gravity Casting

Gravity casting permits manufacturers to create items with excellent surface details reliably. Gravity casting may result in the creation of reasonably uniform products. It works best with simple shapes which permit casting within a single-part mold, but will also permit the creation of some complex forms. Blacksmiths, artists and other "low tech" manufacturers utilize basic gravity casting conveniently.


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