Compression moulding is a manufacturing process that is used to create various rubber components and products across multiple industries, delivering consistent results.
In short, it can be defined as the transformation of raw rubber compound, typically in the form of blanks or formed pellets, into finished goods. The raw rubber compound is placed directly within the mould cavity, which is then closed and subject to intense heat and pressure (typically between 150 °C and 200 °C).
Today, we at AV Industrial Products are taking a closer look at this manufacturing technique. We want to understand why it is popular and what, exactly, the advantages of the compression moulding process are.
Understanding the Compression Moulding Process
The process of compression moulding starts with the selection of suitable materials, such as Natural Rubber Compounds and Synthetic compounds such as Chloroprene and EPDM.
In the form of “blanks”, these rubber compounds are placed into the pre-heated mould cavity. Depending on the production volume, and size of the component, it is possible to utilise either a single cavity mould or a multi cavity mould (sometimes with over 50 cavities).
For rubber to metal bonded components, the metal parts are also placed directly into the cavity of the mould, after being pretreated and having an adhesive coating applied.
The mould is placed in a compression moulding press, where the mould is forced closed and pressure is then applied which forces the material to conform to the shape of the mould.
This technique is renowned for creating efficient, precise and consistent results, allowing manufacturers to develop an array of quality products. Common examples include:
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Anti Vibration Components
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Customer rubber moulded items
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Rubber to Metal Bonded components
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Vehicle and Equipment parts
Key Components and Considerations
The mould which is typically used consists of two halves with a cavity, in the shape of the component, machined into the mould.
The mould’s material, design and surface finish will impact the quality and finish of the product significantly. As such, manufacturers relying on compression mouldingare meticulous in selecting the correct mould. For high production volumes the steel moulds can be case hardened to increase wear and hence longevity of the mould surface.
Temperature and pressure, as stated, are instrumental in the process. The compression moulding machine will be digitally controlled in terms of temperature, pressure, and time period. This helps the material reach the correct temperature for curing. Depending on the material type, formulation and product size, the temperature required will change.
Controlled pressure is also vital, as it allows for the proper distribution of material in the mould cavity and also aids the rubber to metal bonding process. With both of these things, the end result is consistent and structurally sound.
Materials Suitable for Compression Moulding
Natural Rubbers (NR)
Natural rubber is often used in industry, and particularly within the anti-vibration industry. This is due to its high resilience properties, low compression set and ease of processing.
Synthetic Rubbers
Synthetic Rubbers such as Chloroprene, EPDM and Nitrile, are often used in place of natural rubber where mechanical properties such as resistance to Oil, Fuel and Ozone/UV are required. They often are not as resilient as NR, and can have a higher cost basis, and therefore should only be used where NR is not suitable.
Plastic and Metals
Most rubbers can be bonded to plastics and metals, allowing complex shapes and products to be achieved, such as the mounting plate for an anti-vibration mounting. Often a 2 part adhesive is applied to the metal or plastic which cures during the moulding process.
Advantages of Compression Molding
There are a number of advantages to be gained from the compression moulding process. These include:
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Cost effective for large scale operations, compared to other moulding techniques
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High production rates with multiple cavities able to fit a single mould
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Low cost tooling compared to other types of rubber moulding
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High degree of customisation with the process able to facilitate complex shapes and varying thicknesses
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Excellent levels of strength and structural stability achieved
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Suitable for a wide range of demanding applications
Conclusion
In conclusion, this is a versatile manufacturing technique that is used in applications across various industries.
For those looking to produce quality and complex components, with strength and durability, compression mouldingis a fantastic solution.
If you believe that you would benefit from this process in your organisation, we would like to hear from you. As an anti vibration expert, we can work with you to create compliant and quality mould prototypes.
