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Injection Point and Demoulding Analysis of LSR Moulding


Ⅰ. Injection point of LSR molding


Molded LSR adopts a cold runner system. It can maximize the advantages of the rubber material and increase the production efficiency to the highest limit. To process products in this way, there is no need to remove the glue injection channel, thereby reducing the labor intensity of the operation and avoiding a large amount of waste of materials. In many cases, the structure without glue injection can also shorten the operation time.


The rubber injection nozzle is controlled by a needle valve for forwarding flow control. Many manufacturers can use the injection nozzle with an air control switch as standard equipment and set it in various parts of the LSR molding mold. Some mold manufacturers have specially developed an open cold runner system, which is very small and requires multiple injection points (to fill the entire cavity) in an extremely limited mold space. This technology makes it possible to mass-produce high-quality silicone rubber products without separating the glue nozzles.


If a cold runner system is used, an effective temperature interval must be formed between the hot mold cavity and the cold runner. If the runner is too hot, the compound may vulcanize before injection. However, suppose it is cooled too quickly. In that case, it will absorb too much heat from the gate area of the LSR molding die, resulting in incomplete vulcanization.


For products injected with conventional sprues (such as submerged runners and tapered runners), it is advisable to use a small diameter injection port for filling (the diameter of the filling port is usually 0.2mm-0.5mm) for pouring. The low-viscosity LSR compound is the same as the thermoplastic compound. It is essential to balance the runner system. In this way, all the cavities will be evenly filled with the compound. Using simulation software for designing the runner system can greatly simplify the LSR injection molding process and prove its effectiveness through mold filling tests.


Ⅱ. Demoulding of LSR molding


The vulcanized liquid silicone rubber is easy to adhere to the surface of the metal, and the flexibility of the product will make it challenging to demold. The high-temperature tear strength of LSR can make it demoulded under normal conditions. Even if the product is large, it will not be damaged. The most common demolding techniques for LSR silicone molding include demolding template demolding, demolding pin demolding, and pneumatic demolding. Other standard technologies are roller scraping, ejection plate demoulding, and automatic mold control.


When using a demolding system, it must be kept within a high precision range. If the gap between the ejector pin and the guide pin sleeve is too large, or the gap becomes larger due to long-term wear and tear, it may cause glue overflow. The inverted cone or mushroom-shaped top pin is good because it allows a larger contact pressure, which is convenient for improving the sealing performance.


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