Manufacturing Process-Centrifugal Casting & Rotational Molds
Centrifugal Casting & Manufacturing Techniques
Centrifugal Casting Process
Centrifugal casting fits under the general category of casting as a manufacturing process and utilities a permanent mould.
Typically this process is used for the production of long, hollow components that do not need cores for their production. The molten metal is fed into a copper or sand lined cylindrical steel mould which is rotated about its longest axis. The effect of the rotation is to throw the molten metal outwards so that it coats the inside of the tubular mould.
The process is suited for metals but does not include refractory or reactive metals. On occasion a water cooling system is adopted to speed up solidification periods, but this obviously increases tooling costs.
- Equipment is usually simple and low cost, although water cooling can push costs up as can the adoption of the copper lined moulds
- Setting up time is quick and easy
- No waste material 100% utilization
- High quality outer surface
- Good control over metallurgical structure
- Requires further post casting machining, usually considered as a stock material production process
- Inclusions and porosity tend to migrate to the inner surface and may need to be machined out
- Only really suited to the production of hollow cylinders
Centrifrugal Casting Process, an Introduction
Manufacturing Processes - Rotational Moulding
A similar manufacturing process to centrifugal casting is rotational moulding. This is another permanent mould process that has been developed over the years after it was originally used for the manufacture of artillery shells.
The modern day use of rotational moulding is for the production of thermoplastic components such as containers or similar hollow articles that require uniform thin sections.
A measured amount of polymer is introduced to the mould in the form of a powder or slurry. The mould is closed and then initially fed into a heated chamber whilst spinning around 2 or more axes. Once the polymer takes the shape of the mould it is fed out of the oven and through a cooling chamber which usually sprays water and or blows cool air onto the the mould to cool it. Once cool the product is removed from the mould, rotation is maintained through the heating and cooling cycles to ensure the uniform coating of the inside of the mould with the plastic.
- Low mould and equipment costs
- No waste material, 100% utilization
- Dedicated tooling, but low cost
- Poor mechanical properties due to low molecular mass
Process improvements include the measurement of the air temperature in the mould so that accurate heating periods can be applied ensuring the plastic is neither over exposed or under exposed during the heating cycle. A possible further change to the process may be the use of pressure to accelerate coalescence of the polymer particles. It also aids the cooling stage because the moulding stays in contact with the mould until completely cooled ready for removal. There are some health and safey factors to take into account however before full adoption of pressurized systems.
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