Designing with Rubber

“Moulding is the term given to the processes of shaping or forming different raw materials like rubber, metal or glass using a special shape called a mould,” says an expert from a rubber moulding company, Camberley Rubber. He continues, “The mould acts like a container to hold a molten material while it solidifies. These are typically made of steel as this is a long-lasting material and reduces wear and tear.”

What is Rubber Moulding?

Rubber moulding is the process that creates usable rubber materials from elastomers or untreated rubbers. Elastomers are naturally occurring polymers with elastic qualities, this means that they return to their original form after pressure has been released. This gives them plenty of uses in industrial applications and domestic use as well.

Rubber material selection

There are many different rubber compounds and each has its own set of special uses. A thorough selection process will help to choose the correct option for each use. The following pointers will help make the best selection which will lead to the best performance in the long run.

• What will primary function be? Will it absorb energy or transmit fluids? Will it seal off fluids?
• What is the cost for materials?
• Is this an interior part or exterior?
• Are there temperature requirements?
• Will the rubber be exposed to chemical compounds?
• Are there any regulatory requirements?

Rubber moulding process

Injection Moulding

In this process, hot molten rubber is injected into a mould cavity at high pressure. The molten rubber is allowed to sit in the injection barrel in a molten state. This is one of the most proficient approaches to making a wide variety of rubber products.

Injection Process

• The incurred rubber materials will be fed into the injection barrel in a long strip.
• The uncured rubber is then heated with an auger screw under closely controlled temperatures. Once the rubber has reached the correct temperatures, the screw can be retracted.
• Once the auger screw has moved back, the rubber materials can be injected into the mould cavities at high pressure from an injection press.
• The auger screw then moves forward when the mould has been closed under high pressures and this forces rubber into the mould.
• The auger then turns and refills the injection cavity while more rubber is heated for the next injection.
• This part can be removed and the mould opened and the injection ready for the next mould to be filled.

Advantages of Injection Moulding

1. Fast production
2. Flexibility in colour and material
3. Minimum wastage of material
4. Labour cost is low
5. Design flexibility

Disadvantages of Injection Moulding

1. Initial cost of equipment is very high
2. Difficult to project total costs
3. Many parts of design are restricted

Compression Moulding

Perhaps the most simplistic approach to the moulding process is to take the rubber materials and place them in the mould cavity directly. This will cause the rubber to take the shape of the mould once it has been closed. Compressions moulds can be very different in size and shape.

Compression process

The uncured rubber materials are placed in a mould which is placed under high pressure from a hydraulic system. Once the mould is reopened the rubber product can be removed. The excess rubber also called flash can be trimmed away from the outside. Compression moulding is used to produce products with a medium hardness. Flash created in this process is greatly reduced.

Advantages of Compression Moulding

1. Low cost for tooling
2. Good option for small productions
3. Good for large projects
4. Materials don’t use sprues, runners and gates.

Disadvantages of Compression Moulding

1. Simple technique but cost of labour is high
2. High material waste
3. Slow process time
4. Compression moulding
5. Moulds can be easily damaged

It is always important to look at the requirements of the operations thoroughly to be sure you can choose the most suitable approach for the desired product.