In the process of customizing silicone rubber products, the product's technology determines its value and sales. At present, liquid injection molding and solid molding processes are more common processing methods, and liquid food-grade silicone is made using platinum catalysts. The product processing technology It can be said that it is the best type at present. For those who understand the processing process of silicone products, as long as they can accept the processing cost, they will basically choose the liquid process. So what advantages does it have?
Liquid silicone has excellent transparency, tear resistance, resilience, yellowing resistance, thermal stability, water resistance, good air permeability, heat aging resistance, and weather resistance. At the same time, the viscosity is moderate, the fluidity is good, and the product is transparent. High sex.
1.Liquid injection molding of silicone rubber
The liquid silicone rubber injection molding method, which started in the 1970s, has gradually become popular. Now, as a molding method of silicone rubber, it has been recognized. First, the commonly used LIMS method will be explained.
If LIMS (liquid silicone rubber injection molding) is explained in one sentence, it is the method of using a pump to transfer the addition-curing liquid silicone rubber to an injection molding machine and curing and molding in the model. From the differences between the two processes and the curing reaction, the advantages of LIMS are:
(1) Saving manpower: The materials transportation, metering, mixing, and injection processes are continuously automated to reduce power consumption.
(2) can improve production efficiency: through rapid curing to shorten the molding cycle.
(3) can improve product quality: no reaction by-products are generated, and no impurities are mixed in.
(4) Suitable for composite molding: Because the material has good fluidity, low molding pressure, and a wide curing temperature range, it can be used for composite molding in addition to insert molding.
2.Latest technical trends of LIMS
At present, not only is the transition from the simple mixing type with the above advantages to the LIMS method, but recently it is actively developing in the following two directions.
(1) Fully automatic molding: no flash, no runner, automatic demoulding
With regard to the fully automated molding process, people have studied from various aspects such as injection machines, molds, materials and so on. It not only saves manpower in process operation, but because it does not produce useless solidified materials, the cost of materials is reduced. From the perspective of environmental protection, this method has also attracted much attention. For the molding of micro-silicone products such as automotive skeleton oil seals, the molding cycle (from injection to the next injection) is required to be within 10s, so that it can be completed in a very short time.
(2) Composite molding: insert molding, binary molding
Because the form of the crosslinking reaction is addition curing, it can be molded at a relatively low temperature. Since no by-products such as peroxide decomposition residues are generated during the cross-linking reaction, it is not necessary to undergo secondary vulcanization in principle. Therefore, it is possible to perform integral molding with resin, and inlay molding by applying a primer material, so that binary molding in which the sealing portion and the skeleton portion are integrated as a whole has also begun to spread.
Silicone rubber products have excellent properties (heat resistance, plug resistance, weather resistance, electrical insulation, flame resistance, etc.). Due to these properties, it is possible to make environmentally friendly molding based on fully automatic molding and integral molding with metal and organic resins.
The material itself is transparent and can be colored, so its application range involves many fields, such as buttons (for computers, mobile phones, etc.), pacifiers for baby bottles, rubber rollers (for copying machines, printers, etc.), pipe joint seals, oil seals and other A variety of automotive accessories, anode caps for television picture tubes, diving equipment, etc.
3.Material for automatic molding without glue edge / no runner
In recent years, in terms of injection molding of liquid silicone rubber, a method known as no edging and no runner molding has become popular. This is a molding method that does not produce useless solidified materials and does not require secondary processing, that is, a molding method that has no injection port, no runners (even if there is no curing), and no waste rubber edges. In order to implement this molding method, the structure of the model and the smoothness of the parting surface, the measurement and discharge accuracy of the injection machine must meet the requirements, and even in terms of materials, it must be a material that is difficult to generate waste rubber edges.
As shown, after the rubber material entering the mold cavity fills the mold cavity, the rubber material flows into the parting surface due to too much rubber material or due to the thermal expansion of the silicone rubber, etc. After curing, it becomes a waste rubber edge. If the parting surface is designed to be narrower, it is difficult to generate waste rubber edges, but at the same time, the air is not easy to be removed, so it becomes the cause of air bubbles in the finished product.
Compared with the previously used materials, the curing curve of this material is a sharp turning state (the time from the beginning of curing to the end of curing is very short). By selecting the proper injection conditions for this type of material, that is, before the material fills the mold cavity, the curing has not yet begun, and the material has good fluidity, and when the material fills the mold cavity, the curing ends immediately, even if there is residual pressure, the material is not Will flow to the parting surface to prevent the formation of waste rubber edges