1. Characteristics of liquid silica gel:
Liquid silica gel is a non-toxic, heat-resistant and highly resilient flexible thermosetting material, and its rheological behavior is mainly characterized by low viscosity, rapid curing, shear thinning and high thermal expansion coefficient. Its products show good thermal stability, cold resistance, excellent electrical insulation performance, and will not produce toxic substances when burning; Therefore, it has become an irreplaceable material in the production design of health products, automobiles, silicone bottles, medical supplies, diving supplies, silicone kitchenware and silicone mats.
second, molding process:
liquid silica gel is a two-component liquid material, which is divided into component A and component B. The mixer works to fully mix component A and component B in an accurate ratio of 1:1. Because some products are colored, they are equipped with color pump set and color metering part. A+B components, additives, colors, etc. are fully mixed and then enter the plasticizing system. This plasticizing screw has the functions of homogenization and mixing at the same time. The mixture is injected into a hot mold through the screw, and the silica gel is cured at the mold temperature of 17 ~ 2℃. 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, and the needle valve immediately closes the nozzle when the glue injection is completed.
3. The following forms can be selected for the feeding system:
1. Two-way pump: it can move up and down to feed, which can keep the pressure well. Because the A and B pumps are connected and synchronously controlled by hydraulic and pneumatic, this form of feeding system is more reliable and accurate.
2. One-way pump is a general type, which can only feed one item.
3. For synchronous single pump with check valve, the metering cylinder system is mainly used in conjunction with the single pump.
4. Key components of liquid silicone rubber injection molding machine:
Due to the low viscosity of liquid silicone rubber, the backflow and leakage of the material should be considered during the processing, so it is necessary to seal the screw; Liquid silica gel has a high expansion coefficient, which will expand when heated, but shrink slightly when cooled, so the parts can not keep accurate side margins in the mold. Therefore, cold runner processing can be adopted, liquid silica gel should maintain a low temperature and fluidity, and the cold runner adopts a closed system. In the injection cycle, the closed system adopts a "rubber sealing needle" or a "needle valve" in each runner to control the accurate measurement of LSR materials. Because silicone rubber has obvious thermal expansion characteristics, the shrinkage rate is 2 ~ 4% (curing temperature is 15℃), and silicone rubber has the characteristics of compression deformation.
5. Attention should be paid to the following aspects in mold design:
1. In order to avoid turbulence and spray, use a small glue injection port.
2. Use needle-shaped or wing-shaped glue injection ports.
3. T-shaped guide pin is used instead of cylindrical guide pin, and an air gun is used for demoulding, and heat insulation layer/plate is added.
4. Do not use rust inhibitor/oil containing polymerization inhibitor, but generally use toluene, xylene, etc.