Liquid Silicone Rubber Injection Molding

Liquid Silicone Rubber Injection Molding design

Thermoset liquid silicone rubber (LSR) liquid injection molding structure is similar to thermoplastic rubber molding structure on the whole, but there is still difference between both of them.
LSR material usually has a lower viscosity, contributing a short time for injection molding, so it is, even under a fairly low injection pressure. A good venting device plays an important role in mould for avoiding air entrapment.
Besides, LSR materials don’t shrink in molding like the thermoplastic rubber do and they usually tend to expand with heat while shrinks slightly with cold. Therefore the liquid silicone rubber products won’t stay in molding convexity as expected but in cavity with larger surface area.   `   

Liquid Silicone Rubber Injection Molding Shrinkage
LSR shrinkage doesn’t exist in the molding but exist after demolding during the following cooling process. As for the shrinkage, it depends on the rubber formula to a certain extent. However, in terms of moulding, shrinkage may be influenced by several facts, including mold temperature, rubber temperature at demolding, pressure in the cavity and consequent rubber materials compression.       
 
Liquid Silicone Rubber Injection Molding Parting Line
Locating the parting line is one of the steps before designing the liquid silicone rubber injection molding. Venting is realized through the grooves on parting line. The only way for groove is located in the area where injection rubber finally reaches, which helps to avoid air entrapment in the mold and reduce the loss of strength at welding.            

 
Liquid Silicone Rubber Injection Molding Venting
With LSR injection, the air entrapment in cavities will be compressed when molding encloses and then expelled through the venting grooves. If the air entrapment don’t be expelled entirely, the LSR products will be finished along the white edge.
 

Liquid Silicone Rubber Injection Molding Injection Point
Cold runner system should be adopted at LSR moulding, which can maximize the LSR advantages and productivity. Besides, this processing method can avoid removing sprue, increasing labor and sometimes a large amount of  materials waste.