Explain the key points of liquid silica gel mold processing and production
As shown in the figure, it is a liquid silica gel injection mold. The molding product is a medical liquid silica gel airbag product. The characteristics of the mold are as follows:
1. The product is high-precision injection molding of silica gel airbag for medical use, and the hardness of the product is 45 degrees
2. The mold adopts 6 groups of electric heating and independent control to ensure uniform mold temperature;
3. Vacuum pumping technology is adopted to accelerate the discharge of air in the mold cavity to prevent gas trapping, lack of glue and poor performance;
4. The runner system adopts the technology of cold runner + latent hot runner
5. The parting surface is sealed with rubber rings to prevent air from entering the mold cavity during vacuum pumping
Overview of liquid silica gel injection molding:
1. Liquid silica gel
Liquid silicone rubber is a kind of flexible thermosetting material with non toxicity, heat resistance and high recovery. Its sulfur change behavior is mainly characterized by low viscosity, rapid curing, shear thinning and high coefficient of thermal expansion.
LSR is a double liquid rapid vulcanization material with platinum as catalyst. It can be produced by injection molding, mass, rapid vulcanization and repetitive machinery.
Its products have good thermal stability, cold resistance, physiological inertia, excellent electrical insulation performance, and will not produce toxic substances during combustion. Therefore, it has been widely used in the production and design of medical products, baby products, automobile manufacturing, food industry and electronic products, diving products, kitchen appliances and precision waterproof seals, and has become an irreplaceable material.
2. Injection molding characteristics of liquid silica gel:
Liquid silicone rubber is divided into a glue and B glue. The ratio of the two is controlled to be 1:1 by the quantitative device, and then fully mixed through the static mixer, pumped into the barrel of the injection molding machine, and then carried out injection molding production.
Due to the low viscosity of liquid silicone rubber, the backflow and leakage of materials should be considered in the processing process. Therefore, there are high requirements for the check ring of the screw to ensure that the amount of liquid silicone injected into the mold is accurate and there will be no sharp edge. There are high requirements for the sealing position of the mold. The typical exhaust slot is generally 1 ~ 3mm wide and 0.o04 ~ o.oo5 mm deep. It is best to install a vacuum structure in the mold to ensure that the air in the mold cavity is discharged in time.
It is required to adjust the appropriate fluidization time and mold temperature for the process parameters to ensure that the product can be completely cured and free from deformation. Generally, it is not necessary to maintain the pressure, but it is required to set the material quantity accurately.
3. Characteristics of liquid silica gel mold
In mold design, there are generally the following forms:
1) Hot runner
It is a waste of materials, simple design and low cost. It is mostly used for large products.
2) Cold runner with needle valve
It can realize automation and short cycle.
3) Cold runner without needle valve
Due to the high expansion coefficient of LSR, it will expand during heating and shrink slightly during cooling, so the parts cannot maintain accurate side distance in the mold. Therefore, the cold runner can be used for processing. The LSR should maintain low temperature and fluidity. The cold runner adopts a closed system. In the injection cycle, the closed system uses “glue sealing needle” or “needle valve” in each runner to control the accurate measurement of LSR materials. Due to the remarkable thermal expansion characteristics of silicone rubber, the shrinkage is 2 ~ 4% (vulcanization temperature is 150 ℃), and silicone rubber has the characteristics of compression deformation. Baby Straw Training Cup For Toddler Kids is made of silicone material.
1) To avoid turbulence and spray, use a small glue injection port.
2) Use needle or wing glue injection port
3) Use T-type guide bolt
Instead of the cylindrical guide bolt, the air blowing method shall be adopted during demoulding, and the thermal insulation layer / plate shall be added.
4) Do not use antirust agent / oil containing polymerization inhibitor. Generally, toluene, xylene, etc. can be used
In addition, the solidified LSR is easy to stick to the metal surface. The most common demoulding technologies include ejector pin ejection and air pushing.