1. Characteristics of liquid silicone

Liquid silicone rubber is a non-toxic, heat-resistant, and highly resilient flexible thermosetting material. Its rheological behavior is mainly characterized by low viscosity, rapid curing, shear thinning, and high coefficient of thermal expansion. LSR is a dual liquid rapid vulcanization material using platinum as a catalyst, which can be produced through injection molding, mass production, rapid vulcanization, and repetitive mechanical production. Its products exhibit good thermal stability, cold resistance, excellent electrical insulation performance, and will not produce toxic substances during combustion. Therefore, in the production design of health products, cars, baby products, medical supplies, diving products, kitchen utensils, and seals, etc

Becoming an irreplaceable material.

2. Forming process

LSR is a two component liquid material, divided into A and B components. The mixer works by fully mixing A and B components in an accurate 1:1 ratio. Due to the colored design of some products, they are equipped with a color pump unit and a color measurement section. After the A+B components, additives, colors, etc. are fully mixed, they enter the plasticizing system. This plasticizing screw has both homogenization and mixing functions. The mixture is injected into a hot mold through the screw, and the silicone undergoes a curing reaction at a mold temperature of 170-200 ℃. When using a cold runner system, it is worth noting that the runner should be cold enough. To avoid glue leakage, the needle valve is installed on the surface of the mold components. After the glue injection is completed, the needle valve immediately closes the injection nozzle.

2.1 The feeding system can be selected in the following forms: 1) Bidirectional pump

The feeding system can be moved up and down, which can maintain pressure well. Due to the connection between pumps A and B and synchronous hydraulic pneumatic control, this type of feeding system is more reliable and accurate.

2) The one-way pump is a universal type that can only be used for single feed

3) Synchronous single pump with check valve

4) The metering cylinder system is mainly used in conjunction with individual pumps

2.2 Key components of liquid silicone rubber injection molding machine

1) Due to the low viscosity of LSR, it is necessary to consider material reflux and glue leakage during the processing, so sealing the screw is necessary.

2) To prevent LSR from solidifying, a needle valve nozzle should be used.

3) Mixing and metering components of components A and B

2.3 Mold design In mold design, there are generally several forms:

1) Hot runner is a waste of materials, simple in design and low in cost, and is mostly used for large products.

2) The cold flow channel with needle valve can achieve automation and short cycle.

3) Cold flow channel without needle valve

Due to the high coefficient of expansion of LSR, it expands during heating but contracts slightly during cooling, making it difficult for the component to maintain accurate side distance in the mold. So cold runner processing can be used, and LSR should maintain low temperature and fluidity. The cold runner adopts a closed system, and in the injection cycle, the closed system uses "sealing needles" or "needle valves" in each runner to control the accurate measurement of LSR material.

Due to the significant thermal expansion characteristics of silicone rubber, the shrinkage rate is 2-4% (vulcanization temperature is 150 ℃), and silicone rubber has the characteristic of compression deformation