Rubber injection molding is an ideal process to produce precision rubber molded components and rubber-to-metal bonded products.  This process is selected for rubber parts that require high volumes, tight tolerances, over-molding, or precision applications. Rubber injection molding delivers speed and precision not found in other rubber manufacturing processes.  Furthermore, rubber injection molding is an optimal manufacturing process for products specified with rubber compounds that have quicker rubber cure times. Efficiency is gained by a higher level of automation, strict control over flash, and reduced waste from scrap parts.

Rely on Qualiform’s technical staff’s experience with rubber injection molding to help our customers determine if injection molding is the correct process for their product application and material property requirements.

Rubber Injection Molding Process Description

The process of injection molding rubber starts with bulk mixing the rubber compounds, aka stock.  The stock is then stripped into continuous strips approximately 1.25″ wide & .375″. The strips of uncured rubber stock are then fed from a hopper into the rubber molding injection equipment via a conveyance channel.

A large auger-type screw moves the stock into a barrel that holds a specific amount of rubber stock.  As it turns and moves through the channel into the injection unit, the material is heated.  As the rubber stock is heated, it plasticizes to a target temperature.  The plasticized rubber material is then injected into a heated mold cavity held under high pressure.  A runner and gate system is used similarly to the plastic injection molding process.  The temperature and pressure activate the cure of the rubber compound, vulcanizing it.  Once the rubber reaches and required level of cure, it is allowed to cool and reach a solid state within the mold. The molds open and parts are removed or ejected ready for the next cycle.

Rubber injection molding began in the mid-1960s as a spin-off from the plastic injection molding process.  The difference in this rubber molding service process is that rubber is cured under significantly more pressure per square inch of the mold’s cavity surface.

Advantages of the Rubber Injection Molding

• A highly efficient process
• Can be fully automated with automatic material feeding
• Provide high precision rubber molded products
• Superior process for consistency and repeatability
• Allows for molding of complex geometry
• Ideal over-molding of inserts, overmolded components and rubber to metal bonding
• Eliminate preforms and preform labor cost
• Flashless molding / flashless tooling / eliminating secondary trimming
• Rapid cavity filling
• Reduced cycle time
• Minimal material waste

Disadvantages of Rubber Injection Molding

• Higher start-up/shutdown costs
• Suited for high volume applications
• Not all elastomers are suitable