Low temperature control mode of high and low temperature damp heat test chamber: the refrigeration cycle adopts air cooling or water cooling cycle, which is composed of two isothermal processes and two adiabatic processes. The process is as follows: the refrigerant is adiabatically compressed to a higher pressure by the compressor, which consumes work and increases the exhaust temperature, After that, the refrigerant carries out isothermal heat exchange with the surrounding media through the condenser to transfer heat to the surrounding media.
It is applicable to the inspection of various performance indexes of aerospace products, information electronic instruments and meters, materials, electricians, electronic products, various electronic components under high temperature, low temperature or damp heat environment.
What is the role and significance of high and low temperature test?
Degradable plastics exposed to thermal environment may undergo a variety of physical and chemical changes. The length of exposure time and temperature determine the degree and type of change. High temperature and short exposure period are usually enough to shorten the induction period of oxidative degradable plastics, which will lead to the consumption of antioxidants and plasticizers. Physical properties such as tensile strength, impact strength, elongation and modulus may change during the induction period; However, these changes are usually not due to the decrease of molecular weight, but only a response with temperature, such as the increase of crystallinity or the decrease of volatiles, or both.
In general, short-term exposure of plastics to high temperature will release volatile substances, such as water, solvents or plasticizers; Reduce molding stress; Improve the curing of thermosetting plastics; Improve crystallinity; And change the color of plasticizer or colorant or both. Generally, progressive shrinkage will occur with the reduction of volatiles or further polymerization. Some plastics, such as PVC, may change due to the loss of plasticizer or the fracture surface of polymer molecular chain. Polypropylene and its copolymers tend to become very brittle when molecules degrade, while polyethylene softens before tensile strength and elongation decrease and embrittlement. Therefore, it is very necessary to study the performance of components and equipment such as plastics, rubber, paints and varnishes, polymer materials and circuit boards at high temperature.
High and low temperature test is a method used to determine the adaptability of products to storage, transportation and use in high temperature climate environment. The severity of the test depends on the temperature of the high temperature and the duration of exposure. The high and low temperature test of polymer materials such as plastics, rubber, paint and varnish mainly includes hot air aging, heat resistance test, heat resistance measurement, etc. Hot air accelerated aging refers to that the sample is exposed at a higher temperature than the rubber service environment, in order to obtain the natural aging effect of rubber in a short time. Heat resistance test refers to the test in which the sample is exposed to the same temperature change as the rubber service environment.
The high and low temperature test mainly covers electrical and electronic products, as well as their raw devices and other materials. The severity of the test depends on the high and low temperature temperature and test duration. High and low temperature may overheat the product, affect the safety and reliability of use, and even damage, such as:
·Due to the different expansion coefficients of various materials, the bonding and migration between materials are caused
·Change material properties
·Reduce the electrical performance of components
·The elastic or mechanical properties of elastic elements reduce the strength and shorten the service life of products
·Accelerate the deterioration and aging process of polymer materials and insulating materials and shorten the service life of products.
·The elasticity of flexible materials such as rubber decreases and breaks;
·The brittleness of metals and plastics increases, resulting in cracking or cracks;
·Make materials brittle, such as plastic and steel are prone to embrittlement damage at low temperature, the hardness of rubber materials increases and the elasticity decreases.
Therefore, high and low temperature test is of great significance, and it is also very important!
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