6. Test Requirements
Initial temperature requirement
Although the starting temperature of cold and hot shock test is not mentioned or rigidly stipulated in the general standard of cold and hot shock test, it is a problem that must be considered when the test is carried out, because it involves the end of the test at low or high temperature, which determines whether the product needs to be dried, leading to prolonged test time.
If the test product is removed from the cold and hot shock chamber at the end of the test, it should be restored under normal test atmosphere until the sample reaches a stable temperature. This operation will inevitably cause the influence of condensation introduction temperature on the surface of the test sample. This changes the nature of the test.
In the GBJ 150 implementation guidelines, in order to eliminate this effect and avoid prolonging the implementation time of the test, the sample can be recovered in 50 high temperature chambers, and the temperature can be stabilized at room temperature after dew drying. In the implementation guidelines, it is proposed that the initial impact temperature can be changed to start the test at low temperature, so that the test results can be avoided from condensation in the cold and hot shock test box at high temperature. The two test methods make the sample undergo six times of extreme temperature (three times of high temperature, three times of low temperature) and five times of temperature shock process, but the number of times of different impact directions is different. The two test methods may achieve the same test effect, but the latter test method does not need additional drying time and shortens the cold and hot shock test time.
Test time requirement
(1) GJB150.5 prescribes a lower limit of 1 hour, that is, the time of temperature stabilization is less than 1 hour, it must be 1 hour; if it is more than 1 hour, it should be more than 1 hour.
(2) In GB2423.22, five time grades of 10 minutes to 3 hours are given. The product temperature stabilization time measured by the table according to the cold and hot shock test box is the closest time or the optional time grade, and the closest time is directly used as the retention time.
(3) In method 503.4 of 810F, there is no specific time or optional time grade. The time when the temperature is stable or the real exposure time of the copper heat shrinkage tube in the environment is directly adopted.
In the temperature impact test, the key is to establish the stress caused by the inconsistency of thermal expansion and contraction of different materials. The actual thermal shock is most likely to occur outside the copper heat-shrinkage tube under test. It is pointed out that the temperature of the whole product does not need to be stable, as long as the appearance of the copper heat-shrinkage tube under test and the temperature is consistent with the test temperature. Although there is some truth in this opinion, it is also difficult to implement because it is impossible to install many sensors on the surface of the copper heat-shrinkage tube. In addition, the heat transfer capacity of each part of the copper heat-shrinkage tube is inconsistent, and the heat capacity of the adjacent parts inside the copper heat-shrinkage tube is also inconsistent, so it is difficult to determine.