What are the six elements of silicone rubber molding and vulcanization?

2021-09-15

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1. Molding temperature: When the formula is fixed, the temperature is the basis for vulcanization. If the temperature is not enough, the rubber compound will not react. If the temperature is too high, the product will be brittle and deformed. Usually lower than 170 degrees, the vulcanization speed is slow and the time must be extended. ; The temperature is higher than 180 degrees, the vulcanization speed is very fast, and the output is high, but it is easy to be dirty, shiny, the product is deformed, the size becomes smaller, the thickness of the thin film exceeds the standard, and the burr becomes brittle.
2. Vulcanization time: The length of the vulcanization time directly affects the quality of the product. The curing time is short, the product is not fully cooked, the deformation is large, it is easy to turn white, and the product is not durable; if the time is too long, the product will be over-sulfurized, the strength and hardness will deteriorate, resulting in brittleness or sticky surface; the relationship between temperature and time must be It is formulated according to the thickness of the product and the type of rubber; thick products must be vulcanized at low temperature for a long time; if it is found that the time is not enough after the mold is released, the product is not cooked and sticks to the mold, and it is difficult to remove the mold and wash the mold, and the mold should be closed again. Vulcanization, which basically sticks the material down. One of the biggest problems in molding is that the employees adjust the machine without permission and cause waste.
3. Machine pressure: refers to the set pressure of the molding vulcanizer, which is controlled by a pressure gauge and a computer. Sufficient pressure can allow the rubber compound to be completely pressed into the mold when the mold is closed, and prevent bubbles from being generated due to a small amount of moisture generated by the rubber compound during vulcanization, and the product bubbles can be controlled with exhaust gas. The hardness of the rubber compound is high and the fluidity is poor, so the selected pressure should be large; if the pressure is too high, it is easy to crush the die edge; the size of the pressure is related to the shape and size of the die, and the pressure should be reduced accordingly to prevent the die and vulcanization. Machine plate deformation. When adjusting the pressure of the vulcanizer, the maximum pressure of the vulcanizer should not exceed the maximum pressure of the vulcanizer, otherwise the machine may be damaged. The empty mold is not pressurized (except for the injection mold), which is an effective measure to protect the mold edge and prolong the life of the mold.
4. Rubber shape: refers to the pre-formed shape of the rubber, which can be a long strip, a small square, or a circle. The thickness, length and width of the rubber must be close to the product. The closer the shape of the rubber is to the shape of the product, the shorter the flow time of the rubber in the mold, the shorter the flow distance, the thinner the burr, and the greater the amount of rubber used. less, the higher the qualified rate of the product;
5. Compound weight: The weight of the compound must be greater than the weight of the product, otherwise there will be a lack of glue. However, the more sizing material is put, the thicker the burrs of the product will be, and the size will become larger. The weight of the compound is directly related to the shape of the compound. How to use the least amount of glue and produce in the most reasonable shape without lack of glue is the embodiment of the technical level of the molding staff. The weight of the rubber compound is enough, but the length is longer than that of the mold, and there will also be a lack of glue; the shape and weight of the rubber compound are suitable, but if it is placed on the wrong side, there will be a situation where one side is thin and one side is missing, and in severe cases, one side will be missing The problem of glue and thick burrs on one side. The shape of the rubber compound is suitable and the total weight is suitable, but the thickness and width of the cut are not uniform, or the glue filling is not uniform, which will also cause a lack of glue. When there is a lack of glue in the product, do not rush to increase the glue material. First, you should take a complete mold including burrs, check the weight, and then see whether the thickness of the product is uniform, and finally decide whether to add material. The technical content and experience of the forming foreman is very important!
6. Operation speed: refers to the operation speed of the vulcanizer when placing the glue and taking the product. Vulcanization is a chemical reaction. The rubber compound will begin to vulcanize when it is placed on the hot mold. For a product with multiple cavities, from the first piece of glue to the last piece of glue, the shorter the time of placing the glue, the better. Clamp the mold immediately, otherwise, various abnormalities such as mold dirty, rubber burning, thick burr, deformation, etc. are likely to occur. When picking up the product, it is easy to blow out the product with pneumatic assistance, but it will reduce the temperature of the mold. If the operation is not skilled, it is most likely that the mold temperature is getting lower and lower, resulting in unfamiliar products and sticking to the mold. Novices are most likely to have this problem. In the production of glossy plastic sheets, the speed of gluing, mold clamping and mold opening has the most obvious impact on the quality of the glossy surface. Why some products with strict appearance requirements choose to hang the mold operation, one of the main principles is also here!