Injection moulding basics

Injection moulding is one of the most effective methods of producing moulded rubber parts. It is a manufacturing technique that involves injecting material into a closed mould to create pieces. Injection moulding may be done with a variety of materials like metals, plastics, glassware, thermoset elastomers, and polymers. It's crucial to design the parts to be manufactured through injection moulding carefully. Key considerations are the material to be used for the component, the intended form and characteristics of the part, the material and design of the mould, and the moulding machine's qualities.

How injection moulding works

In injection moulding, a ribbon-like strip of uncured rubber is fed into a rotating screw, pulled into the injection unit, pre-heated and plasticised, and then injected into a mould cavity. Here the rubber is held under high pressure and temperatures to vulcanise. When curing is complete, the moulded rubber part is ejected from the mould.

Advantages of injection moulding

  • Lower unit costs
  • Injection moulding rubber is an ideal process for:
    • Producing high volumes of small to medium size parts
    • Large shot weights
    • Achieving medium-to-high dimensional tolerances
    • Manufacturing parts that require colour consistency or overall uniformity
  • In addition, injection moulding reduces cure times because the rubber is pre-heated
  • The injection moulding process results in reduced material waste

Disadvantages of injection moulding

  • The machinery used for injection moulding is often more expensive than other moulding tools
  • Small part runs can be costly
  • Long set-up lead times
  • Part design restrictions

Injection moulded troubleshooting

Countless quality control issues can arise from manufacturing injection moulded rubber. There are five common injection moulding problems:

  1. Short shot: The incomplete filling of a mould cavity, which results in an incomplete part.
  2. Shrinkage: Occasionally, the moulded rubber part comes out smaller than the cavity it was produced in.
  3. Excess flashing: Rubber material can leak along the mould’s parting line. This flashing can affect the part’s surface and sealing abilities.
  4. Warpage: The intended shape of the rubber part can become distorted during the cooling process.
  5. Brittleness: Shorter molecular chain lengths can impair the physical integrity of a rubber part, making it brittle and prone to cracks or breakages.

Contact Specialized Mouldings for details

Injection moulding is just one of several moulding techniques used in the market. To discuss custom rubber moulding for your specific application, please get in touch with a representative from Specialized Mouldings South Africa today.