What is Compression Moulding?
Compression moulding is one of several moulding processes. It is the use of compression (force) and heat to shape a raw material e.g. hydraulic and pneumatic seals by using a metal mould. The raw material is heated in the mould until pliable while the mould is closed for a specified period. Upon removal it is quite common that the moulded product to contain excess materials, normally called flashing, which has extruded while being heated and compressed in the mould. Flashing is removed by an experienced cleaning team to maintain the exact measurement of the product manufactured
Compression Moulding Basics
The following factors are considered when using a compression moulding method:
- Raw Material
- Shape (mould)
- Pressure applied
- Curing Time
Two types of raw plastics materials are most often used for compression molding:
- Thermoset plastics – Four kinds of thermosets are polyurethane, unsaturated polyesters, phenolic and silicones
- Thermoplastics – Four common types are polyethylene, polypropylene, polystyrene, and acrylics.
Thermoset plastics and thermo plastics are unique to the compression method of moulding. Thermoset plastics refer to pliable plastics, e.g. hydraulic seals that once heated and set to a shape may not be changed. Thermo plastics harden as a result of being heated to liquid state and then cooled and can be reheated and cooled as much as necessary.
The amount of heat required to produce the desired product vary.
Time is also a factor. Material, pressure, thickness of the part is some of factors which will determine how much time the part will need to be in the mould. Thermoplastics will require that part is cooled will be rigid before extracting.
It is important to ensure that no matter what material is used, the material fills the crevices in the mould to ensure the most even distribution which will result in a perfect product.
The process of compression moulding begins with:
- The material is placed into the mould.
- The product is heated until somewhat soft and pliable.
- A hydraulic tool presses the material against the mould.
- Once the material is hardened and has taken shape of the mould it is ejected
- The final products will require additional work, such as cutting away the flashing
- Other products will be ready immediately upon leaving the mould.
Advantages of Compression Moulding
Compression molding is one of the least expensive ways to mass-produce products due to its cost-effectiveness and efficiency. This method is highly efficient, leaving little material or energy to waste.
Future of Compression Moulding
As many products are still made using raw materials, compression molding is likely to remain in widespread use among those seeking to make products like hydraulic seals and polyurethane products. What is possible in the near future is that moulds will be manufactured without flashing when creating the product.
Computers and technology in the future will probably make it possible to mould with less manual labour required. It would not be far-fetched to say that in the future an assembly line may handle all aspects of the compression molding process from measuring and filling the model to removing the product and flash (if necessary) without human interference.