Engineering control of the liquid silicone rubber ...

Thermal curing with conventional rubber molding process, liquid silicone rubber molding process has a time-saving energy efficiency, exempt from the process, finished product rate, comprehensive and low cost, and thus are widely used in electronic appliances, daily chemical products, textile , mold manufacturing and other industries. Dow Corning liquid silicone rubber new 2006 Beijing China International Power Exhibition, Dow Corning Corporation is China's power transmission and distribution industry, launched a series of silicone application technologies and products. China's power market, Dow Corning Corporation, the Regional Manager, Mr. Chu Rong during the show, especially a liquid silicone rubber used in high-voltage hollow insulators "special technical reports. Silicone insulating material because of its hydrophobic and anti-fouling characteristics, can improve the power transmission and distribution systems in the harsh environment of the anti-flashover performance, for the manufacture of low-, high-voltage insulator, hollow bushing, arrester and high voltage insulation coating layer. Compared with ordinary plastic rubber and silicone rubber, liquid silicone rubber has many outstanding advantages and characteristics not easily deformed, such as extreme temperatures, long-term exposure to strong UV radiation is very stable after the installation of the cable attachment link and seal better , which can effectively prevent the surface flashover, etc.. Currently, the Dow Corning liquid silicone rubber cable accessories in the Qinghai-Tibet Railway. An average elevation of the Qinghai-Tibet Railway, the geology is complex and widespread permafrost, the ordinary power cable accessories can not fully meet the special requirements of the railway power grid construction and the environment on the performance of cable equipment. Golmud - Lhasa section cold shrink cable accessories excellent performance it has benefited from the Dow Corning liquid silicone rubber technology and solutions. Implus Footcare high-end orthopedic insoles using the latest generation of GE molding LSR and the LSR Topcoat.     The Laur single-component liquid silicone rubber     The Laur the Silastic company to the market launch of a new liquid silicone rubber. This smooth material application curing technology (EC), to solve some problems in the current two-component liquid silicone rubber. This material can be used as a single system (IP) to cooperate fully with the supply.     Component liquid silicone rubber mixed before use, and that inevitably exist in the local ratio of improper. Two-component system, if the pump is running normally, will have a ratio of inappropriate material. Mixed uneven cycle and physical properties of vulcanization.     Two-component glue the shelf life of more than three days, so when mixing equipment when not in for a long time, you must clean up. Only clean up the improper mixing ratio of A and B components which enable a time, will cause the device to cause the waste of materials. Smooth curing technology material system has a long shelf life, so when mixing equipment for a long time without having to clean up or clean.     Compared with the existing two-component liquid silicone rubber, this new one-component silicone rubber has a similar performance to significantly improve the storage stability. Stored in the warehouse six months later, to test its performance. Compared to the same six months ago, the single-component liquid silicone rubber vulcanization curve and physical properties are almost unchanged. The samples were stored in 71 ° C, the week of testing, proving once again that the stability of this new system.     Smooth curing good stability the same scorch performance benefit to increase the security of the vulcanization process, in the longer filling time. This mold design and mold filling more difficult helpful. Single-component system using liquid silicone rubber curing time than the length of the two-component system, this was mainly due to the scorch time is longer. Smooth curing system cure rate than the number of poor two-component systems.     The material can reach the U.S. Food and Drug Administration (FDA) requirements. Sample rubber the after Sec sulfide, by CFR171.2600 test. The sample passed the rigorous testing of the long-term or repeated contact with food products.     With a longer shelf life, the one-component silicone rubber supply in the way of the whole tie. This reduces the possibility of mixing ratio improper. Supply after a one-component silicone rubber can be colored, you do not the same as the two-component silicone rubber molded front colorants mixed. Therefore, a simple pump to replace the existing mixing and metering equipment.     Liquid silicone rubber injection molding control     Due to the low viscosity of LSR injection molding process, even in the case of low injection pressure, fill flow rate can also be relatively fast. Modern LSR fast curing cycle time is shorter cycle time (in some cases less than 20 seconds), must work together in order to take full advantage of this feature, processing machinery, injection molding and parts transfer systems, etc., as a highly integrated whole operation.     Cold runner molding     Cold runner molding is one of the important processing characteristics of the liquid silicone rubber. There are two basic types of cold runner device used, that is, closed and open systems, their advantages and disadvantages.     Compared with the open system, the most typical characteristics of the closed system in the lower injection pressure, injection molding. Unbalanced shunt device regulation orifice and the materials at different shear thinning fine-tune performance. The disadvantage is that for some given size parts and molds, the equipment required to make additional adjustments.     Open systems is the use of high shear rate in the nozzle or valve, the injection pressure is lowered, the closure. Under normal circumstances, the open cavity filling time is slightly shorter than the closed system. Open systems because of the diversion channel and a smaller nozzle, higher density cavity. Shunt requires the balance of nature, and the rheological properties of the material itself to strictly match. Because of the small size of the flow channel of the open system, it is usually not adjustable orifice, just ordinary valves control the flow and get the best pressure points.     Parting line     Due to the low viscosity of LSR, we must ensure the accuracy of the sub-model line to avoid the flash. Parts of the geometry and parting line location will also affect the stripping process. Slight undercutting in part design, helps ensure that the plastic parts and mold cavity between the solid together.     Shrink     Although liquid silicone rubber injection molding process is not shrinking, but because of the silicone rubber has a high coefficient of thermal expansion, thus stripping, after cooling, usually 2% -3% contraction. Exact data of the contraction depends mainly on the material formulation, but from a processing point of view, when the designer if the idea has considered a number of factors affect the contraction in advance, the final contraction will vary, these factors including the processing temperature, material stripping temperature, cavity pressure.     Exhaust     The best way to exclude the cavity air entrapment in an injection molding cycle, the use of vacuum to the cavity of air entrapment rid of. That is, the design of the parting line to ensure that the mold is closed, the vacuum pump through the mold switch below the fixture cavity vacuum. Once the vacuum level to achieve the expected standard, immediately turn off the mold, injection began. A successful application of the method, efforts to get rid of air The purpose of the adjustment fixture. Maker LSR fill in the fixture, lower to 90% -95% of the cavity, and then the fixture efforts to increase, while avoiding the backlog of liquid silicone rubber overflow, resulting in flash.     Note the entrance     If a cold runner system, set the effective isolation of temperature is very important in the hot cavity cold runner. If the shunt is too hot, the material before the injection began curing, cooling too quickly, it will be from the mold valve area to absorb too much heat, hinder the curing is complete. Closed valve or start sales, general design of 0.5-0.8mm, to ensure that the space of the pin and the flow of materials around. Open system, nozzles and valves are usually smaller (0.2-0.5mm), so you can better control traffic.     In addition, the mold material, structural design, insulation design products, mold release are considered factors.