Technology and application of heat shrinkable cable accessories

Principle of Heat shrinking

Heat shrinkable materials, also known as polymer shape memory materials, are mainly new polymer functional materials with "memory effect" by making the crystalline or semi-crystalline linear polymer structure become three-dimensional network structure after high-energy ray irradiation or chemical crosslinking. Crosslinked polymer elastic between the high elastic state, applying the external force can stretch or expansion, colleagues quenching, maintain the state material though the expansion deformation has memory effect, the temperature above the melting point, deformation immediately eliminate, immediately return to its original shape, this principle can be used to produce the expansion ratio is big, easy to control product quality products.

With different purposes of, the requirements for the performance of the heat shrinkable products also each are not identical, with a single polymer materials has been difficult to meet the practical requirements of the application, it is must to study the formula of heat shrinkable products, with polymer alloy and all kinds of function can make successful material such as fillers and additives, in order to meet the requirements of actual use.

Chemical Formulation

Mainly composed of substrate alloy and additives, the main raw materials are polyethylene, ethylene - ethyl acetate, propylene - acetate, silicone rubber, EPDM rubber, nitrile rubber, antioxidant, anti-aging agent, stabilizer, lubricant, plasticizer, acetylene carbon black and other components. Cable accessories are mainly used to restore the performance of the cable body and terminal connection, so the accessory materials have the requirements of conductivity, stress control, insulation, oil resistance, etc. 

At the same time, it is also considered that in the field of power distribution, parts and pipes are used to seal cable connections and terminals. When the sealing materials are used outdoors, the influence of the environment on the materials must be considered, and the infiltration of moisture between the heat shrinkable pipe fitting and the cable surface must be prevented.

Radiation Crosslinking

After the radiation of high energy rays α, β and γ, the linear structure of polymer materials becomes a three-dimensional network structure, which has the memory effect. Radiation dose and control is one of the key processing technologies of heat shrinkable materials. Choosing the appropriate degree of cross-linking can make it have both small residual deformation and better mechanical properties. 

If the dosage is too large, the elongation is small, the product is stiff, difficult to expand and the yield is low. If the dose is too small, the permanent deformation is too large, and the heat shrinkable material shrinks to its original size. In the process of irradiation, high-energy rays make crosslinked polymer molecular chain, while another blow off the molecular bonds, in reaction to the phenomenon, fill in the right amount of antioxidants, prevent or reduce the radiation of high-energy radiation damage to the molecule to achieve the best effect of crosslinking, the crosslinking degree show platform effect on certain irradiation dose area, to set a wide range of irradiation processing. 

The precise control of product performance provides a guarantee, but also ensures the stability of product quality, Radiation cross-linking is the key to the processing of heat shrinkable materials. The degree of cross-linking not only affects the processing technology of production, but also affects the effect of use. For example, the problem of shrinkage cracking should not only consider the environmental stress cracking, but also the thermal stress cracking of materials.