ABSTRACT: The crosslinking principle, classification, formulation, process and equipment of silane crosslinked polyethylene insulators for wires and cables are briefly described. Some characteristics of silane naturally crosslinked polyethylene insulators in application and use and factors affecting their crosslinking status are also introduced.
Key words: silane crosslinking; natural crosslinking; polyethylene; insulation; wire and cable
Silane crosslinked polyethylene cable material as insulation material for low-voltage power cables has been widely used in China's wire and cable industry. Compared with peroxide cross-linking and irradiation cross-linking, this material has the advantages of simple manufacturing equipment, convenient operation and low comprehensive cost. It has become the leading insulating material for low-voltage cross-linked cables.
1. Crosslinking Principle of Silane Crosslinked Cable Material
There are two main processes in the preparation of silane crosslinked polyethylene: grafting and crosslinking. In the process of grafting, free radicals were produced by the free initiator and pyrolysis free radicals, which lost H atom on tertiary carbon atom. The free radicals reacted with vinylsilane - CH = CH2 group to form a grafted polymer containing trioxysilyl group. During the crosslinking process, the grafted polymer was hydrolyzed to produce silanol under the action of water, and - OH condensed with the adjacent Si - O - H group to form Si - O - Si bond, which resulted in crosslinking between polymer macromolecules.
2. Silane Crosslinked Cable Material and Its Cable Production Mode
As you know, the production of silane cross-linked cable materials and their cables can be divided into two steps and one step. The difference between two-step method and one-step method is where the silane grafting process takes place. The grafting process is carried out in two-step method at the cable material manufacturer and in one-step method at the cable manufacturer. At present, the two-step silane crosslinked polyethylene insulation material with the largest market share in China consists of so-called A and B materials. A material is Polyethylene Grafted with silane and B material is catalyst master material. Its weight ratio is generally A:B = 95:5. A material and B material are made by cable material factory and sold in cable factory. After mixing A material and B material proportionally before using, cable factory can extrude them in ordinary extruder. Cable insulation cores are then crosslinked in warm water or steam.