Three Key Points for LSR to Achieve Precision Injection Molding

Do you know what is the LSR? It is called as the Liquid Silicone Rubber. There are many differences between LSR and traditional thermoplastic rubber processing, which increases the processing difficulty. LSR is quite different from traditional thermoplastic material processing in terms of shrinkage, demoulding, mold materials, cold runner system, temperature control, etc., making LSR more difficult to process than ordinary thermoplastic rubber.

The waterproof silicone gasket of smartphones is mostly secondary molded on the original metal or plastic accessories. At the same time, the gasket volume is smaller than the commonly used, and it has higher requirements for compatibility with the casing and accessories. It requires the use of more precise injection molding technology.
The key to achieving precision injection molding of LSR is as follows:

(1) Full mixing of LSR
1. Accurate mixing rate: LSR is a two-component raw material of A and B . Before injection molding, it must be fully mixed in an accurate rate of 1 : 1 . If it is a colored LSR product, the color paste ratio must also be accurately controlled.
2. Mixer: Static mixer is a key component in injection molding. Only after the A and B are fully evenly mixed in the static mixer can the LSR injected into the mold be completely vulcanized and molded.

(2) Sealing and temperature control of injection molding machine components
1. Due to the low viscosity of LSR, to consider the backflow and leakage of the material, the screw must be sealed.
2. Since the mold is heated during the LSR molding process, in order to prevent LSR solidification, nozzle with a water-cooled structure can be used to ensure that the temperature is low enough.

(3) Finished product control during injection molding
1. Parting line: Considering the position and accuracy of the parting line in advance. It helps to avoid air entrainment and welding to avoid burrs.
2. Shrinkage: Although LSR does not shrink during injection molding, due to its extremely high thermal expansion coefficient, it usually shrinks by 2% to 3% after demolding and cooling.
3. Gate position: The actual product shrinkage rate needs to be considered.
4. Vacuuming: When designing the parting line, the mod must be airtight. The vacuum pump evacuates all cavities through the clamp under the mold switch.
5. Demoulding: Generally, it can use the demoulding technology of stripper plates, ejector pins and air ejector, or manual demoulding.
6. Mold temperature: LSR is vulcanized molding during heating, so the temperature inside the mold must be evenly distributed. The temperature difference is controlled within +/-10℃.