This technique is used to form precision engineered components and pieces where it’s necessary to incorporate a rubber-to-metal bonded section. It’s mainly used in high-volume production settings, and there are many benefits to the technique.
Rubber injection moulding is the ideal technique for precision applications requiring high-volume turnout with tight tolerances. Compared to other processes, it has a high degree of automation, a fast rubber cure time and controllable waste from production.
The types of components that most suit the injection moulding process are those that require a high degree of repeatability and precision. Once the mould is made, components with complex or intricate detail can reliably be reproduced thousands of times with little error.
All processes have downsides and uses that are not suitable for the technique. For injection moulding, it is the high startup costs that can make it less accessible for products that do not require a high volume of repeats. There is also the issue of what material or elastomer and cure system is required as not all are suitable for injection moulding.
How it works
The rubber injection moulding requires a bit of initial setup. An illustration of the equipment and description of the process can be found at https://www.researchgate.net/publication/326408379_Understanding_of_Rubber_Injection_Moulding_Understanding_of_Rubber_Injection_Moulding. The injection mould must be created for the desired product. Once that has been done and loaded into the system, a rubber ribbon of the correct material is fed into a part of the machine known as the rotating screw. This rotating screw then carries the rubber ribbon into the injection unit to deliver a controlled amount of material to it.
Once the rubber ribbon has been pulled into the injection unit, it is plasticised (softened) at a specific temperature for that material. When the rubber has reached the appropriate temperature, it can be injected into the mould cavity through something called a runner and gate system. Runners carry the rubber and gates hold it in place under high pressure at an elevated temperature. This process allows the rubber to cure and be vulcanised. It is necessary to test the material to determine the ideal cure time, pressure and temperature. Once the material has cured, it can be removed from the mould cavities and the next cycle can begin.