Centrifugal Casting|Types, Applications|Echofast

Centrifugal casting, also commonly known as spin casting, is a metal casting technique that works by using rotation’s centrifugal forces to distribute the molten metal into the mold cavities. The metal is then solidified, resulting in the desired shape of the finished product. This technology is closely connected with rotational speeds and pouring rates, which depend on the material being used and the design specifications. The process is considered to be cost-effective for creating near-net shape, and cylindrical components with a central axis of rotation.

Casting process schematic (Source: Kubota)

The process of centrifugal casting can be generalized into the following list of steps:

The mold wall is coated with refractory material, which is typically ceramic coating. In the true centrifugal casting process, the mold is preheated and the ceramic slurry is applied while spinning. Then, the mold comes to the stage of drying and baking. Cleaning the mold surface before applying the refractory coating is required to remain excellent surface finish and the integrity of the cast part.
The molten metal is poured directly into the mold through a spout, and there is no need for a gating system.
The mold can be rotated in the process of pouring the molten material or after the pouring. Generally, the rate of rotation is between 300 to 3000 RPM.
The centrifugal forces induced by the rotation of the mold push the molten material toward the cavity’s outside wall.
The mold continues to spin until the molten metal solidifies.
After the casting has solidified, the mold is removed and opened. The final casting is then removed.

Centrifugal casting can be divided into three types, namely centrifuging, semi-centrifugal casting , and true centrifugal casting.

Centrifuging process illustration. Image Credit:
https://engineeringproductdesign.com/knowledge-base/centrifugal-casting/

1.Centrifuging

In centrifuging, mold cavities of any shape are positioned at a specific distance from the axis of
spin. The molten metal is forced into the mold cavity through the sprue and the runner to create
the desired shape. Similar to true centrifugal casting, the properties of the castings can change
with distance from the spin axis. Centrifuging boasts some advantages. This technique is ideal
for creating relatively intricate, thin-walled and small parts with good surface finish. It is most
common for small components like jewelry, small bushes, and sleeves. The desired part can be
manufactured with fewer casting-related flaws. This is because impurities are near the axis due
to the low density. In other words, they are far away from the part. There is no need for
post-processing. In spite of these advantages, this method also has some drawbacks. It is not
suitable for all the alloys, which is indicative of the limited material options. Additional machining
is required for the sprue and runner.

Semi-centrifugal casting illustration. Image Credit:
https://engineeringproductdesign.com/knowledge-base/centrifugal-casting/

2.Semi-Centrifugal Casting

Semi-centrifugal casting is used to create solid castings rather than tubular casts under the
influence of the centrifugal force. The following is an illustrated example of semi-centrifugal
casting. The molds are configured with a riser at the rotation axis,contributing to the flow of
molten metal.Parts made by semi-centrifugal casting boast higher density in their exterior regions
than at the centre of the rotating axis. The rotational symmetry produced by this process makes
it ideal for objects such as pulleys, spoked wheels, gear blanks,nozzles and brass bush. The
casting centre can be removed, further removing the lowest-density part of the cast. There are
some factors that affect the overall quality of the casting, including the rotational speed,
component diameter, pouring temperature, pouring speed, and others.

Centrifuging process illustration. Image Credit:
https://engineeringproductdesign.com/knowledge-base/centrifugal-casting/

3.True Centrifugal Casting

Molten metal is poured into a rotating mold without the need for gating mechanisms in the true centrifugal casting process. The process can be performed using both vertical as well as horizontal rotation. The vertical rotation is usually used to cast smaller parts. In contrast, horizontal rotation is more popular, which is usually used to cast longer parts. The horizontal method is very useful for producing tubular parts such as tubes, pipes, bushes and rings. The quality of the final product is affected by the revolving speed of the horizontal true centrifugal casting.Molds are made of steel, iron, or graphite, and a refractory lining is applied to extend
life. The surfaces of the molds are designed to accommodate various external styles for pipe casting. Products made by true centrifugal casting are highly dense. This process has many advantages, including high density, excellent outer surface finish, great mechanical strength,
low equipment and labor cost, and the creation of minimal scrap. The true centrifugal casting process has some disadvantages as well. The technique has limited alloy options, and it is limited to cylindrical parts. The casting inner surface diameter is not accurate. Substantial initial investment is required in the process, and the lead time can be long.

1.Stainless Steel

2.Nickel Alloys

3.Copper

4.Cast Iron

5.Aluminum

6.Steel

Centrifugal casting has a variety of applications across multiple industries.

Industrial

Bushings

Engine cylinder liners

Rings

Brake drums

Water supply lines

Sewage pipes

Street lamp posts

Large pipes like gas pipes

Medical

Intricate medical implants like hip replacements and dental crowns

Automotive

Cylinder liners

Pistons

Pipes

Tubes

Cylinders

Aerospace

Rocket nozzles for aerospace propulsion systems

Jet engine compressor cases

1.What is the difference between centrifugal casting and investment casting？

Investment casting uses disposable ceramic dies or molds, whereas centrifugal casting utilizes durable and reusable dies. Though both of them can be used to produce
high-quality and well-formed parts, the processes are different in that centrifugal casting utilizes centrifugal force.

2.How to reduce porosity in centrifugal casting?

Choose the right material.

Optimize the mold design.

Control the casting parameters.

Perform post-casting treatments.

Test and inspect the cast product, etc.

3.How much does centrifugal casting cost?

Centrifugal casting is regarded as a relatively inexpensive process with a total investment requirement no more than $20,000. It is much more affordable than investment casting, which usually costs millions.