Liquid silicone (LSR) products are molded in this way

Its products have good thermal stability, cold resistance, excellent electrical insulation performance, good elasticity, water and moisture resistance, acid and alkali resistance and other chemical substances will not produce toxic substances when burning.

Forming process

LSR is A two-component liquid material, which is divided into A component and B component. The mixer works to completely mix component A and component B in an exact 1:1 ratio. Since some products are colored, they are equipped with a color pump group and a color metering section. A+B components. Additives. The colors are completely mixed and then enter the plasticizing system.

The plasticizing screw has the functions of homogenization and mixing. The mixture is injected into the hot mold through the screw, and the silicone gel solidifies at the 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 part and the needle valve closes the nozzle immediately.

1. Feeding system.

The following forms can be selected:

1) Two-way pump

Because the A.B pump is connected and synchronized, it can move up and down to feed and maintain pressure.

Hydropneumatic control, so this form of feed system is more reliable and accurate.

2) One-way pump

General type, only single feed.

3) Synchronous single pump with check valve.

4) Measuring cylinder system.

Mainly used for single pump.

2. Key components of Liquid silicone rubber injection molding machine.

1) Due to the low viscosity of LSR, the backflow and leakage of the material must be considered during the processing, so the screws must be sealed.

2) Needle valve nozzles are used to prevent LSR from curing.

3) Mixing of A.B components. Measure the parts.

3. Mold design.

In mold design, there are generally the following forms:

1) Hot runner

Material waste, simple design, low cost, mostly used in large products.

2) Cold runner with needle valve.

Can be automated, short cycle.

3) Cold runner without needle valve.

Due to the high expansion coefficient of LSR, it will expand during heating, but there will be a slight contraction during cooling, so the parts can not maintain accurate side spacing in the mold. Therefore, the cold runner can be processed. The LSR should maintain a low temperature and fluidity. The cold runner adopts a closed system. During the injection cycle, the closure system uses an accurate measurement of the LSR material with a sealing needle or needle valve. Silicone rubber has obvious heating expansion characteristics, shrinkage rate of 2%~4% (vulcanization temperature of 150℃), silicone rubber has the characteristics of compression deformation.

Therefore, the design of the mold should pay attention to the following aspects:

1) Use small injection port to avoid turbulence and jet;

2) Use needle-like or wing-like injection mouth;

3) Replace the cylindrical guide pin with a T-shaped guide pin, and add insulation layer/plate with an air gun when demoulding;

4) Do not use anti-rust agents/oil containing retardants, generally can use toluene, xylene and so on.

LSR vulcanization was analyzed.

1) The vulcanization reaction of liquid silicone rubber requires a certain reaction time;

2) Ideal flow, diameter 2mm, flow distance 170cm or more;

3) The minimum thickness is 1/1000mm;

4) Too high mold temperature will lead to vulcanization and hinder flow;

5) Laminar flow can avoid bubbles;

6) High-speed injection will cause turbulence;

7) The viscosity of the material will change the flow pattern;

8) Turbulence causes white spots.

Guangzhou S-guangyu Machinery & Equipment Co.,Ltd is a professional liquid silicone rubber(LSR) Injection molding machine manufacturers in China since 2010.We have got more than one hundred patents and serve for more than thousands of customers .if you want to learn more about our machines,please visit our web www.lsrexpert-better.com or contact us:86-13902294163.