Which Moulding Process Should You Use?

When choosing the type of rubber moulding process that you need for your application, there are several factors you need to consider. Some of these factors are:

•The size and the geometry of the part
•The weight of that part
•The material that is needed
•The volume of the parts needed

Moulding with rubber compression is the most traditional method of moulding rubber. It is an ideal method for low and medium volumes of production. It is extremely useful when moulding gaskets, seals, or O-rings. It is also good for large or bulky items.

Which Moulding Process Should You Use?

Rubber moulding is widely used because it is efficient and economical for a wide array of different products. It is one of the best methods for low production volumes or for medium and large parts. When using higher-cost materials, rubber mouldings can save a great deal of money.

Compression Moulding

Compression moulding can be quite cost-effective if the following factors are taken into account:

•The quantity to be made is low
•The items have a rubber-to-metal bonding application
•Extreme material hardness is necessary
•Large Parts required

Rubber Transfer Moulding

This type of moulding has the advantages of both injection moulding and compression moulding.The latter is one of the easier methods of moulding. This type is best for parts that have multiple cavities or other intricate workings that need a closed mould that will bond rubber to metal parts. If the geometry of the part could cause cavities in the mould to trap air, it is also a good method. Some advantages include:

• A need for fewer and simpler pre-forms – one pre-form fills many cavities
• Tighter dimensional tolerance control -the mould is closed and will not allow a material to spill out of the cavity parting line
•Geometry remains more precise and parting lines thinner and less noticeable

Injection Moulding

Rubber injection moulding was an offshoot of the early 1960s plastics industry but it originally had some issues with temperature and pressure. Plastics cool when the rubber moulding is heated and rubber injection moulding requires much more pressure per square inch. Once these issues were conquered it became one of the best methods for industrial use. There are three types of rubber injection moulding:

Organic Rubber Injection

This starts with an efficient material that is prepared by mixing it and then stripping it and placing it in a continuous screw. This charges a barrel when needed with a pre-measured amount of material. When the mould closes, the material is injected into the cavities and cured. Benefits of this include:

• Eliminating an operator’s placement of pre-forms
• The material is pre-heated before going into cavities thereby decreasing the material’s viscosity.
• A quicker cycle time than compression and transfer mouldings

Liquid Injection Molding (LIM) or LSR Mixture Injection

These are processes where two-part liquid silicone are delivered into a static mixture in a fixed ration. The LSR mixture blends with platinum cure and is fed to the injection unit where it goes through a runner and gate until it cures in the closed mould. Once the cycle ends, the parts are removed or ejected and a new cycle begins. LIM Moulding benefits are:

• Contamination is limited with an automated closed-loop system
• Flash-less parts
• Optimized cycles
• LIM is ideal for the medical product industry
• High-quality components with complex shapes can be repeated in mass quantities and still be done in a cost-effective way.

Thermoplastic Rubber or TPR Injection

This form of moulding makes use of thermoplastic elastometers or TPEs. These have similar properties and characteristics of rubber, but they are processed like plastics are. The benefits of choosing TPE over thermoplastic rubber include:

• Simplified processing because there is no mixing or vulcanization needed
• More cost-effectiveness because walls are thinner and have lower density
• TPEs can be coloured
• The remains are always recyclable scraps and parts