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Why do insulators use silicone rubber?

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Starting from the second half of the 19th century, the only insulating materials suitable for high voltage when erecting transmission lines were ceramics and glass. In the 1940s, due to the advent of polymer materials, ceramics and glass were no longer the preferred insulator materials, and European and American countries began to study polymer insulators. Subsequently, the physical and electrical properties, long-term reliability, and optimal shape of electrical insulators were studied, and the productivity has also been continuously improved.

Among the polymer materials that can replace ceramics and glass, silicone rubber has had practical performance since the 1960s, standing out among several polymers. Silicon rubber insulators have more advantages than ceramic insulators. Firstly, it is lightweight, easy to operate, and safe; In addition, ceramic insulators often suffer from breakage, which can be damaged by an impact. Silicone rubber insulators can withstand mechanical impacts such as vehicle collisions with power poles.

Although other polymer materials also have the advantages described above, only silicone rubber will not cause too much pollution to the environment. Polymer insulators are waterproof, so there is no leakage and surface arcing caused by water droplets falling. Silicone rubber insulators recover their water resistance faster than other polymer insulators, and are a durable material that can be used for a long time in harsh environments.

Characteristics of silicone rubber:
The main chain of silicone rubber is composed of siloxane (Si O) chains. Due to the significant difference between the negative electrical properties of Si and O on this bond, which are 1.8 and 3.5 respectively, it has ionic bond properties. In this way, the bond energy of Si-O is higher than that of C-C (see Table 1). In addition, ① due to the properties of the main chain ionic bonds, the ionic properties of the side chain methyl C-H are weakened and are not susceptible to attack by other molecules, so their chemical stability is good; ② Since Si does not form double or triple bonds, it is difficult to form a starting point for the decomposition of the main chain (due to this reason, the Si-C bond is quite stable), resulting in a more stable main chain of silicone rubber.

Characteristics of silicone rubber:
Heat and cold resistance; Waterproofness; Electrical performance; Weather resistance; Permanent deformation

Classification of silicone rubber:
Silicone rubber can be divided into solid and liquid types based on its properties before vulcanization, and can also be divided into three types based on the vulcanization mechanism: peroxide vulcanization, addition reaction vulcanization, and condensation reaction vulcanization. The difference between solid and liquid silicone rubbers is the molecular weight of polysiloxanes. Solid silicone rubber can be vulcanized using either peroxide vulcanization or addition reactions, commonly referred to as high-temperature vulcanized rubber (HTV) or heat vulcanized rubber (HCR). Although liquid silicone rubber materials vulcanized by addition reactions can also be vulcanized at room temperature, they are known as liquid silicone rubber (LSR), low-temperature vulcanized rubber (LTV), and two-component room temperature vulcanized rubber (RTV) due to different molding methods and vulcanization temperatures. When manufacturing polymer insulators, injection molding and pouring molding methods are commonly used.

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