In metalworking, casting is the process of setting molten metallic material in a pre-designed mold. Once the molten metal cools, it becomes a solid metal object in the desired shape. Casting can be achieved with a wide variety of metals, and various materials can be used to form the molds and other equipment. Because casting involves variables, like molten metal materials and mold size, it is important to use the utmost safety precautions during the process and to ensure that trained specialists to operate the molding instruments.
Casting Basics
The basic method of fabricating products by casting is the following ten step process:
1. Pattern development;
2. Mold preparation;
3. Metal melting;
4. Metal pouring;
5. Cooling period;
6. Part removal;
7. Clean up process (removing excess metal from piece, such as risers, etc.);
8. Heat treatment;
9. Optional upgrade treatment;
10. Miscellaneous finalization processes (machining, etc.).
In casting, a mold is used to define the shape desired for the final product. An easy standard example to illustrate this is tin soldiers. Tin soldiers are made with a hollow metal mold that has a mold cavity patterned around the shape of a small soldier. The mold is in two different pieces that, when connected, form the entire pattern. The mold is closed so that the entire pattern is sealed except for a small reservoir area, called a riser, into which molten tin is poured. The mold is set aside for a drying period, and as the tin cools, it solidifies. Once the tin is completely solidified, a fully formed tin soldier is produced. A mold that is filled with molten material is one of the more common casting procedures, but other methods do exist.
There are various types of casting, categorized by the type of mold used. The names used reflect the permanence of the different kinds of molds used: expendable and non-expendable.
● Expendable casting uses sand, plastic, clay or metal molds for the casting process. These molds are discarded after use.
● Non-expendable casting uses molds that are intended for permanent use over long runs. The molds are generally metal, but the method of performing the casting differs greatly from many expendable methods.
These two casting types define the two broadest categories of casting. These types of casting are then categorized by the material used to form the molds:
Expendable Mold Casting Types
● Waste molding involves thin plaster molds used to make clay copies.
● Sand casting uses molds made by bonding sand with polymer or chemicals. These molds are much more durable than other types of expendable casting methods. They allow larger runs made with a single mold.
● Plaster mold castings are slightly less durable than sand molds, plaster molds are composed of gypsum plaster (plaster of Paris) and can be made quickly.
● Shell molding involves resin-treated sand, but they are designed to be thinner than regular sand casting molds. The thinness allows the molds to form more complex geometries and allows highly precise castings.
● Investment casting (or lost-wax casting) uses waxes that have been technologically advanced to be much more stable and durable than typical wax compositions. Investment casting can be used for small or large pieces, and is typically used for castings with complex alloys and geometries.
● Full-mold casting involves molds composed of durable polystyrene foam that is then surrounded by sand, which adheres to the foam’s structure and creates the mold’s shell. When molten metal is poured into the mold, the foam evaporates, allowing the sand to dictate the geometry of the piece.
Non-expendable Mold Casting Types
● Die-casting is a process where a die is formed that features a horizontal pattern. A long stretch of bar stock or other bar metal is fed through the die, which forms the bar, and then each piece is cut off in sections. For instance, a curtain rod might be run through a circular die that will define the circular shape of the curtain.
● Permanent mold casting uses metal to form a mold, so it is a much less expendable form of casting. The metal molds can be reused many times, but are only semi-permanent despite their name. The tin soldier method described above is an example of permanent mold casting.
● Centrifugal casting relies on a large drum turning to create centrifugal force pushing a molten metal into a mold, causing it to fill out the mold geometry. This is beneficial for producing smaller pieces and intricate shapes, like jewelry. Additionally, if the centrifuge is large enough, it can hold many pieces at the same time and complete larger runs.
● Semi-solid metal casting (SSM)is a form of modified die-casting. The process involves using metal that has been softened, usually through heating, to press through the die.
ABOUT KEVA
Keva Casting is a professional casting company that focuses on Construction, Machinery, Automobile, Hardware, Pipeline and many other industries.
We provide top quality products with the best service based on our complete production chain including our own mold design, advanced production techniques, and full management of the supply chain. Keva Casting has two factories located in Zhucheng, China's Shandong province.
We use "shell molding", which is a new technique that has been developed in recent years.This new technique has simplified production procedures and reduced air pollution compared with traditional sand casting and investment casting. Shell making and core making are faster to ensure production in enormous quantities. The dimensions and surface finishing are satisfactory for all kinds of industrial requirements. Besides supplying our own formwork & scaffolding systems, our casting products also supply OEM services in various industries.