Types of Rubber Moulding and their Advantages and Disadvantages

Designing with Rubber
“Molding” is a process used in manufacturing industries in which raw materials like plastic, rubber, metal or glass are given different shapes using a mould. A mould is a container in which liquid raw material is poured in which turns into solid. They are made up of steel to avoid quick wear and tear.

What is Rubber Moulding?
Rubber moulding is a process of creating a usable rubber product from elastomers or untreated rubber. An elastomer is a natural polymer having elastic properties i.e. they return into their original shape on applying pressure. So they are widely used in different industries not only because they are malleable, but they can also have multiple utilities in domestic and industrial sectors.

Rubber material selection
There are different types of rubber compounds; each differs from one another.  The selection process helps us in choosing the correct compound. Following things should be kept in mind which further helps in achieving the best performance levels.
  • Main function of the part that is: will it absorb or transmit energy or fluid? Seal the fluid
  • Material cost per part
  • Location of the part: Inside or outside
  • Temperature requirements
  • Exposure to chemicals
  • Physical property and regulatory requirements 
Rubber molding process

Injection Molding

It is a process in which heated rubber material or compound is injected into the mold cavity under high pressure. The material in its molten state is kept inside the injection barrel. Injection molding is the most proficient way of creating the molded rubber products.

Injection Process

  • The uncured rubber material in the form of continuous strip is fed into the injection barrel.
  • Then it is warmed by an auger screw in a temperature controlled barrel. The auger screw is pulled backwards once the rubber material accumulates in front of it.
  • Once the auger screw moves backwards the rubber material is injected into the mold cavities by an injection press.
  • The auger screw is then pushed forward when the mold is closed under high pressure forcing the material into the mold cavities.
  • The auger screw turns again to refill the injection barrel when the material is cured in the heated mould. The part can be removed once the mould opens and the injection press is ready for the next shot.
Advantages of Injection molding
  • Fast production
  • Minimum wastage of material
  • Design flexibility
  • Labor cost is low
  • Flexibility in color and material
Disadvantages of Injection molding
  • Initial tooling cost is high
  • Difficult accurate costing
  • Restricted part designs 
Compression Molding
It is the simplest form of molding process in which the compound or rubber material is placed in the mold cavity directly and it takes the shape of the cavity once the mold is closed. The compression moulds differ in size and shape.

Compression process

Uncured compound or rubber material is placed in the mold which is closed under hydraulic pressure. The part can be removed once the mold opens up. The excess rubber or flash is trimmed from the part. Compression molding is mostly done for compounds with medium hardness. The flash created in the rubber moulding process is reduced in this process.

Advantages of Compression Molding
  • Low tooling cost
  • Best for small production
  • Good for big parts
  • Material doesn’t have to pass through gates, sprues or runners
Disadvantages of Compression Molding
  • Production technique is simple but labor cost is high
  • High wastage of material
  • Process time is slow
  • Compression molding process is not suitable for complex moulds
  • Increase in rejection rate because of contamination
  • Tough to control flash
  • Molds can be damaged
It is important to look into all the requirements of a product while choosing the most suitable production solution as each process has its own advantages and disadvantages.

If you still want to more info about rubber moulding, then please stay this link and get more details on rubber molds. 
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