Silicone rubber is an inorganic polymer formed by silicon (Si), oxygen (O), carbon (C) and hydrogen (H). The main chemical chain, called the backbone, is formed by silicon and oxygen, which is why it is called siloxane. Carbon and hydrogen can be found in lateral chains as methyl (-CH3), vinyl (-CH=CH2), phenyl (-C6H5, also known as a benzene ring) or other groups (Figure 1). As with all polymers, silicone rubber needs a polymerization process to create the real material from SiOH monomers, which react with Me3SiOSiMe3 (where Me is a metal catalyst) to increase the chain length and with Me3SiO2 to end the chain. As a result of this process, the uncured silicone rubber contains chains with different lengths .
There are numerous methods for producing plastic parts and many will be discussed in this post. Of the various processes, molding and extrusion are the most predominant. The best method will depend on the polymer being used, the part geometry, and the part’s function. The definition of plastic molding is it is a group of manufacturing processes used with a closed tool called a mold, to produce parts. The inside of the mold is in the shape of the part, when the high temperature mold is filled with the molten polymer and closes, the part is formed during the curing. Extrusion is another polymer processing method that can be used to produce plastic parts that are typically linear in shape. The extrusion process also uses hot molten plastic and a heated tool, however the extrusion tool is an open tool, called a die.
When injection molding Liquid Silicone Rubber certain problems can occur that directly affect the quality of the final product, in spite of the great planning that may have gone into material selection, machine, process, and the processing parameters. If these issues are not controlled promptly and properly, they could end up resulting in damage to the machine, mold, and finished product.
Since the introduction of Liquid Silicone Rubber (LSR) in the 1970’s, the optimization of processes and procedures has become increasingly important for achieving higher strength, hardness, flexibility, soft-feel, and durability properties in the end product; reducing lead times and costs.
Liquid injection molding (LIM) is an industrial fabrication process that molds materials into a broad range of components and products. Unlike the standard reaction injection molding process, which relies on pressurized impingement mixing, liquid injection molding uses a mechanical mixing process that focuses mainly on liquid silicone rubber (LSR) and similar elastomeric materials.