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Brief description of injection molding process of silicone injection molding machine

by:FUHONG     2021-06-01
1. The characteristics of liquid silica gel. Liquid silica gel is a two-liquid fast vulcanizing material with platinum as a catalyst. The product is characterized by good thermal stability, cold resistance, excellent electrical insulation performance, and no toxic substances will be produced during combustion. Silicone injection molding machine, liquid silicone injection molding machine, adopts injection molding method, mass, rapid vulcanization, and repetitive mechanical production. Liquid silica gel is a non-toxic, heat-resistant, flexible thermosetting material with high resilience. The rheological behavior is mainly manifested as low viscosity, fast curing, shear thinning and high thermal expansion coefficient. It has become an irreplaceable material in the production design of health products, automobiles, baby products, medical products, diving products, kitchen utensils, and seals. 2. The molding process. LSR is a two-component liquid material, consisting of component A and component B, which are mixed thoroughly in a precise ratio of 1:1. Some products are colored designs. A+B components, additives, colors, etc. enter the plasticizing system after being fully mixed. The plasticizing screw of the silicone injection molding machine and the liquid silicone injection molding machine have the functions of homogenization and mixing at the same time. The mixture is injected into the hot mold through a screw, and the silica gel undergoes a curing reaction at a mold temperature of 170-200°C. 1. The feeding system 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. Mainly used in conjunction with a single pump 2. The key component of the 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 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, generally have the following forms. ①. Hot runner, waste of materials, simple design, low cost, mostly used for large products. ②. The cold runner with needle valve can realize automation and short cycle. ③. Cold runner without needle valve. LSR has a high coefficient of expansion, which 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 low temperature and fluidity. The cold runner adopts a closed system. In the injection cycle, the closed system uses a sealing needle or needle valve in each runner to control the LSR Accurate measurement of materials. Because silicone rubber has significant thermal expansion characteristics, the shrinkage rate is 2--4% (vulcanization temperature is 150 ℃), and silicone rubber has the characteristics of deformation under pressure. 4. After the analysis of LSR flow and vulcanization, the following aspects should be paid attention to in the design of silicone injection molding machine and liquid silicone injection molding machine. To avoid turbulence and jetting, use a small injection port. Use needle-shaped or wing-shaped injection ports. Use T-shaped guide bolts instead of cylindrical guide bolts. When demolding, use an air gun and add heat insulation layer/board. Do not use rust inhibitors or oils containing polymerization inhibitors, generally toluene, xylene, etc. can be used. The cured LSR is easy to stick to the metal surface. Common demolding techniques include ejector pin ejection and air ejection. From the above information, it can be seen that the main problems solved by silicone injection molding are its mixing and metering parts, as well as the silicone injection molding machine, the sealing of the screw of the liquid silicone injection molding machine, the design of the mold, and the liquid silicone is controlled to a ratio of 1:1 by a quantitative device. After injection of the material tube, injection molding production is carried out. Recommended reading: Description of condition control in injection molding process of vertical disc injection molding machine JTT-850R.
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