Thermal shock test also known as temperature impact test or high and low temperature impact test, is used to assess the product to the ambient temperature of the rapid changes in adaptability, is the equipment design of the identification test and the batch production phase of the routine test, in some cases can also be used for environmental stress screening test. It can be said that the frequency of the application of the hot and cold shock chamber in verifying and improving the environmental adaptability of equipment is only second to the vibration and high temperature test.
1, GJB 150-86 "military equipment environmental test method"
2, GB 2423 "Electrical and electronic products basic environmental test Procedures"
3, U.S. military standard mil-std-810f "Environmental engineering considerations and laboratory tests
In fact, the hot and cold impact test chamber as a tool, the application of the product development at different stages of the purpose is different:
1, the engineering development stage can be used to find the product design and process defects;
2, product stereotypes or design appraisal and batch production stage acceptance decision to provide the basis;
3, as the environmental stress screening application, the aim is to eliminate the early product failure.
Starting temperature requirements
Although the initial temperature of the thermal shock test test is not mentioned or rigidly stipulated in the common cold and hot impact test standard, but this is an issue that must be considered when the test is carried out, since it involves the end of the test at low or high temperatures, which determines whether the product needs to be dried, leading to prolonged test time.
If the test is finished in the Low-temperature standard test products from the thermal shock test chamber (room), should be in the normal experimental atmospheric conditions to recover, until the sample reaches the temperature stability, this operation unavoidably causes the test sample surface to produce the condensation to introduce the temperature to the product influence. Thus altering the nature of the experiment.
In the clause 150 Implementation Guide, it is proposed that in order to eliminate this effect to avoid prolonged recovery and prolonged trial implementation time, the sample can be recovered in a 50 high temperature chamber, and the temperature in the normal room after condensation drying is stable. The implementation guide suggests that the initial impact temperature can be changed to start at a low temperature, so that the results of the test are produced at high temperature to avoid the product from hot and cold shock test chamber condensation. The two test methods have subjected the specimens to six extremes of temperature (three times), three low temperature) and five temperature impact processes, only different impact direction of the times is different, the two tests may achieve the same test results are basically the same, but the latter test method does not need to add drying time, shorten the hot and cold impact test time.
Test Time requirements
1, GJB150.5 stipulates the lower limit 1h, that is, the temperature stability time is less than 1h, must have to 1h, if greater than 1h, then use the time greater than 1h;
2, GB2423.22 to give 10min to 3h of 5 times, with the use of the table according to the temperature and heat shock test box measured product temperatures and stability time, using the most similar to its time or optional time level, directly with its closest time as the holding time;
3, 810F method 503.4 does not specify the specific time or optional time level, directly adopt the product to achieve temperature stability of the time or product in the environment real exposure time.
In the temperature impact test, the most important thing is to build up the stress caused by the uneven expansion and contraction of different materials. The actual thermal shock is most likely to occur outside of the tested product, and the data indicate that it is not necessary to achieve the whole product temperature stability, but the temperature is consistent with the test temperature as long as the tested product looks. This opinion is that although there is a certain truth, implementation is also a certain difficulty, because there is no way to install a lot of sensors on the product surface, in addition to the product parts of the heat transfer capacity is inconsistent, the test products within the adjacent parts of the thermal capacity is also inconsistent, to determine the difficulty.
Temperature change speed of thermal shock test
Temperature change test, in order to set a certain temperature change rate between high temperature and low temperature transition. So there are two kinds of practical applications: for a slow temperature change test, the temperature change rate is <3℃/min (usually the parameters are chosen as 1℃/min), and the temperature change, temperature cycling and temperature alternating test (these three kinds of tests) are also generally applied, and the other is a fast temperature change test, The temperature change rate is ≥3℃/min (usually the parameters are 3℃/min, 4℃/min, 5℃/min, 7℃/min, 10℃/min), and also the rapid temperature change test in general application. The faster the temperature change rate, the more severe the examination.
Thermal shock test temperature variation category
The temperature change class test project has many names: temperature change, temperature cycle, temperature alternating, fast temperature change, temperature impact, hot and cold shock, temperature gradient, grading temperature and so on. And the test methods used in different system standards are different, how to distinguish these pilot projects, how to choose the pilot project, which need to analyze the source of various types of tests and their differences.
Use of hot and cold shock tests
thermal shock chamber for electronic appliances 0 components, automation components, communications components, automotive parts, metal, chemical materials, plastics and other industries, the national defense industry, Aerospace, military industries, BGA, PCB base, electronic chip IC, semiconductor ceramic magnetic and polymer material changes in the physical, testing the material to high, The low temperature of the rally and the product in the heat and contraction of the output of chemical changes or physical damage, can confirm the quality of the product, from the precision IC to the heavy machinery components, no need its ideal test tools.