LSR Injection Molding Process Introduction

LSR is a two-component liquid material, divided into A component and B component. The work of the mixer fully mixes the A component and the B component in a precise 1:1 ratio. And because some of the products are of colored design, it is equipped with a color pump set and a color metering part. The A+B components, additives, colors, etc. enter the plasticizing system after being fully mixed.

This plasticizing screw has the functions of homogenization and mixing at the same time. The mixture is injected into the hot mold through the screw, and the silica gel undergoes a curing reaction at a mold temperature of 170-200°C. When using a cold runner system, it is worth noting that the runner should be cold enough. In order to avoid glue leakage, the needle valve is installed on the surface of the mold part. When the glue injection is completed, the needle valve immediately closes the injection nozzle.

1. Feeding system

You can choose the following forms:

1) Bidirectional pump

The feed can be moved up and down, and the pressure can be maintained well. Because the A and B pumps are connected and synchronized by hydraulic and pneumatic control, this type of feeding system is more reliable and accurate.

2) One-way pump

It is a universal type and can only be fed in a single item.

3) Synchronous single pump with check valve

4) Measuring cylinder system

It is mainly used in conjunction with a single pump.

2. Key components of liquid silicone rubber injection molding machine

1) Due to the low viscosity of LSR, the reflow and leakage of the material must be considered during the processing, so the sealing of the screw is necessary.

2) In order to prevent the LSR from solidifying, a needle valve nozzle should be used.

3) Mixing and metering parts of A and B components.

3. Mold design

In mold design, there are generally the following forms:

1) Hot runner

Relatively wasteful materials, simple design, low cost, and mostly used for large products.

2) Cold runner with needle valve

It can be automated and the cycle is short.

3) Cold runner without needle valve

Due to the high expansion coefficient of LSR, it expands when heated, but shrinks slightly when cooled, so the parts cannot maintain precise side margins in the mold. Therefore, cold runner processing can be used. LSR should maintain a lower temperature and fluidity. The cold runner adopts a closed system. In the injection cycle, the closed system uses a "sealing needle" or a "needle valve" in each runner. "To control the accurate measurement of LSR materials.

Because silicone rubber has significant thermal expansion characteristics, the shrinkage rate is 2% to 4% (vulcanization temperature is 150 ℃), and silicone rubber has the characteristics of deformation under pressure.