Radiation crosslinked wire and cable
Writer: Sterilization Time: 2020-10-23 Browse: 626 ℃
Radiation crosslinked wire and cable
After radiation crosslinking, the insulation layer of wires and cables based on polyethylene and polyvinyl chloride can improve the temperature resistance grade and mechanical strength, and reduce the environmental stress cracking. It is widely used in communication, aircraft, automobile, spaceship, computer and television products.
The modification of radiation crosslinking of wire and cable insulation is determined by its crosslinking density. The crosslinking density of insulation can be controlled by adjusting irradiation dose, and the modification and improvement of materials can be further controlled. The main performance changes include: changes in electrical properties (discussed in detail in several papers); changes in dielectric constant, dielectric loss tangent and dielectric strength caused by radiation (which are related to the stable structure and accumulation of radiation products produced by irradiation); radiation crosslinking leads to the increase of mechanical strength, cold flow and creep resistance, and elastic mode The important changes of insulation caused by radiation are the changes of heat resistance, solvent resistance and cracking resistance.
1. The selection and formulation design of insulation materials for wires and cables are the basis of radiation crosslinking wire and cable modification. It determines the basic properties of insulating materials, processing technology and the feasibility of radiation processing.
2. Extrusion molding of wires and cables, forming the basic structure of cables, depends on the processing technology of polymer materials and cable process conditions. Processing determines the intrinsic phase structure of polymer, which in turn restricts the chemical reaction and structural transformation in the next process radiation processing.
3. After the electron beam (EB) radiation processing of electron accelerator, the insulating material will be transformed from linear polymer into three-dimensional network structure, and its crosslinking degree and uniformity are closely related to the transmission device under the electron beam of the accelerator. Adverse side effects are often accompanied by radiation oxidation, thermal effect and electrostatic effect. The generation of these effects is related to the electron energy (penetration depth), irradiation dose required, dose rate, transmission process and mode, as well as the dose and formula composition of polymer insulation crosslinking. Radiation processing is the key to the success or failure of wires and cables. The efficiency and results of radiation processing depend on the morphology of additives and polymers.
4. The comprehensive performance test of the product includes:
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(1) Determination of crosslinking degree. Because the heat resistance and solvent resistance of wires and cables are closely related to the crosslinking degree of insulation. Generally, there are two methods to characterize the crosslinking degree of insulation of wires and cables
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a) the content of gel was determined to be greater than 75%.
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b) Under the specified conditions, the thermal elongation and residual deformation rate are not more than 175% and the residual deformation rate is less than 4%.
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(2) Mechanical property test. Including the tensile strength, usually greater than 12.5mpa; elongation at break > 200%.
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(3) Aging life. According to the working temperature of insulated wires and cables, the state condition is selected (such as working temperature of 125 ℃, aging temperature of 158 ± 2 ℃, cycle of 168h), and the retention percentage of strength and elongation after aging is greater than 75%.
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(4) Electrical performance. Volume resistivity, dielectric strength, dielectric constant, dielectric loss, partial discharge.
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(5) Other related performance tests.
Polymers used for wire and cable insulation are multicomponent mixtures. The cross-linking reaction between macromolecules mainly occurs in irradiation processing, but the consumption and conversion of different additives in materials can not be ignored, which slows down the cross-linking reaction process or produces other adverse side reactions. Therefore, the particularity of radiation chemical reaction must be fully considered.
In order to ensure the various properties of the products after radiation processing, it is very important for the manufacturing process of insulating materials and the uniformity of blending and additives dispersion. The electrical defects of polymer insulation are mainly caused by structural defects and impurities. The uneven dispersion of sensitizers, antioxidants, flame retardants, fillers and processing aids leads to the increase of charge carriers and the reduction of volume resistance. EB Radiation processing produces radiation damage in polymer materials. The higher the dose, the more defects, the greater the impact on electrical properties.
