Liquid silicone injection molding is a very efficient and accurate production method for high quality silicone rubber components. Of the many factors to control for in production, speed is one of the most important. The speed at which silicone is injected into a hot mold must be precisely metered to ensure that a defect-free and dimensionally accurate part is produced.
Silicone rubber has a relatively low viscosity and fast cure rate, which makes it a great material for injection molding. Cycle times are faster than all other methods, depending on part thickness. Mold shrinkage can be controlled with the speed and pressure of injection and are lower than other molding methods. Mold designs, including gate location and quantities, also depict at which speed and pressure silicone can be injected.
A number of curing agents can be added to the raw material to ensure proper curing. The most common agent for silicone rubber compounds are organic peroxides or liquid platinum, which decompose to form free radicals that react with the pendant organic groups on the silicone polymer. The result is a permanent crosslink between the polymer chains, the number and distribution of which influences the final physical property profile of the cured rubber.
The speed at which silicone is injected depends on the other key variables in silicone molding. Speed of injection can be defined as the inches per second of injection flow. The heat of the mold and the pressure used to inject are the other factors that coincide when producing silicone rubber. The heat is important, depending on the geometry of the part produced.
Large parts at high heats need to be injected at high speeds to fill the cavity before curing begins. Larger parts at low heat need to be injected slowly to avoid air being trapped in the cavity during injection. Smaller parts with simple shapes can be injected at high pressures and speeds without ill effects, reducing cycle times and production cost. Parts with deep cavities are the most complex to mold, requiring the speed to be intensely monitored and controlled to completely fill the part without trapping air.
At SiTECH, we utilize advanced silicone injection molding technology and machinery to accurately control for heat, speed and pressure. We offer many value added services to help lower your overall production cost, including screen printing, abrasion resistant coatings and printed circuit board assembly among other services. For all your silicone rubber needs, trust SiTECH to provide the highest quality silicone components available.