6, test requirements

Start temperature requirements

Although the general cold and hot shock test standards for the starting temperature of the hot and cold shock test is not mentioned or not made mandatory, but this is the test must be considered when carrying out, because it involves whether the test is to end at low temperature or high temperature state, thus determining whether the product needs to be dried, resulting in extended test time.

If the test ends at the end of the low temperature standard test product from the cold and hot impact test box (chamber), should be restored under normal test atmospheric conditions until the sample to reach the temperature stability, this operation will inevitably make the test sample surface condensation introduction temperature effect on the product. This changes the nature of the experiment.

In the GBJ 150 implementation guide, in order to eliminate this effect to avoid prolonged recovery of the test implementation time, the sample can be recovered in a high temperature box of 50, until the condensation dry before reaching temperature stability at room temperature. The implementation guide suggests that the starting impact temperature can be changed, starting from low temperature test, so that the test results at high temperature to avoid the product out of the hot and cold impact test box condensation. The two test methods have subjected the test sample to withstand six extreme temperature (three high temperatures, three low temperatures) and five temperature impact process, but the number of different impact directions is different, the two tests may achieve the same test effect, but the latter test method does not need to add drying time, shorten the cold and hot impact test time.

Test time requirements

(1) GJB150.5 provides for a lower limit of 1h, that is, the temperature stabilization time is less than 1h, there must be 1h;

(2) GB2423.22 gives 10min to 3h 5 time levels, the same use table according to the hot and cold impact test box measured product temperature stability time, the use of its closest time or optional time rating, directly using its closest time as the holding time;

(3) 810F method 503.4 does not specify a specific time or optional time rating, directly using copper drain heat shrink tube to achieve temperature stability time or copper drain heat shrink tube in the environment of the real exposure time.

In the temperature impact test, the most important is to establish the stress caused by the inconsistency of heat expansion and cold shrinkage of different materials. The actual thermal impact is most likely to occur on the outside of the copper discharge shrink tube under test, the relevant information indicates that the temperature of the whole product need not be achieved, but as long as the temperature of the copper drain shrink tube is the same as the test temperature. Although there is some truth, there are some difficulties in implementation, because it is not possible to install many sensors on the surface of the copper drain heat shrink tube, in addition to the copper drain heat shrink tube parts of the heat transfer capacity is not consistent, the test copper drain heat shrink tube internal adjacent components heat capacity is not consistent, it is difficult to determine.

铜排热缩管冷热冲击测试

1、热收缩材料：以可塑性线型高聚物或高聚物合金为基材，用高能辐照方法或化学方法使聚合物分子 链部分交联成为网状结构获得弹性“记忆效应”，经加热扩张至特定尺寸后冷却定型，使 用时加热到适当温度后自行收缩到扩张前的形状和尺寸，这种材料称为热收缩材料。

2、热收缩套管：将上述高聚物或高聚物合金通过挤出成型得到规定尺寸的管状中间产品，辐照（或化学）交联后加热扩张，冷却定型得到的具有一定尺寸的管状产品成为热收缩套管。

3、铜排热缩管冷热冲击试验的定义

冷热冲击试验又名温度冲击试验或高低温冲击试验，是用于考核铜排热缩管对周围环境温度急剧变化的适应性，是批产阶段的例行试验中不可缺少的试验，在有些情况下也可以用于环境应力筛选试验。可以说冷热冲击试验箱在验证和提高铜排热缩管的环境适应性方面应用的频度仅次于振动与高低温试验。

4、常见的执行标准

   （1）GJB 150-86《军用设备环境试验方法》

   （2）GB 2423《电工电子产品基本环境试验规程》

   （3）美军标MIL－STD－810F《环境工程考虑和实验室试验》

5、冷热冲击试验的目的

   实际上冷热冲击试验箱作为一种工具，应用在产品研制的不同阶段时的目的是不同的：

  （1）工程研制阶段可用于发现铜排热缩管的设计和工艺缺陷；

  （2）铜排热缩管定型或设计鉴定和批产阶段验收决策提供依据；

  （3）作为环境应力筛选应用时，目的是剔除铜排热缩管的早期故障。

   因此在编写研制过程不同阶段的环境试验大纲或筛选大纲，试验报告或筛选报告时，就将冷热冲击试验的试验目的具体化，不宜表达含糊或笼统。

6、试验要求

起始温度要求

   虽然一般的冷热冲击试验标准中对冷热冲击试验的起始温度不予提及或不做硬性规定，但这却是试验进行时必须考虑的问题，因为涉及到试验是结束在低温还是高温状态，从而决定了是否需要对产品进行烘干，导致延长试验时间。

   如果试验结束在低温标准受试产品从冷热冲击试验箱（室）内取出后，应在正常的试验大气条件下进行恢复，直到样品到到达温度稳定，这一操作难免使试验样品表面产生凝露引入温度对产品的影响。从而改变试验的性质。

   在GBJ 150实施指南中提出，为了消除这一影响避免长时间恢复延长试验实施时间，可将样品在50的高温箱中恢复，待凝露干后再在常温中达到温度稳定。实施指南中提出可改变起始冲击温度，从低温开始试验，以使试验结果在高温避免产品出冷热冲击试验箱产生凝露。两种试验方法却使受试样品经受六次极端温度（三次高温，三次低温）作用及五次温度冲击过程，只是不同冲击方向的次数有所不同，这两种试验可能达到的试验效果是基本相同的，但后一种试验方法无需加烘干时间，缩短了冷热冲击试验时间。

试验时间要求

   （1）GJB150.5规定了下限1h，即温度稳定时间小于1h，必有要1h；若大于1h，则用该大于1h的时间；

   （2）GB2423.22中给出10min到3h的5个时间等级，同使用表根据冷热冲击试验箱测得的产品温度稳定时间，采用与其最相近的时间或可选时间等级，直接采用与其最相近的时间作为保持时间；

   （3）810F方法503.4中则不规定具体时间或可选时间等级，直接采用铜排热缩管达到温度稳定的时间或铜排热缩管在环境中真实暴露时间。

   在温度冲击试验中，最为关键的是建立起不同材料热胀冷缩不一致造成的应力。实际热冲击最可能发生在受试铜排热缩管的外部，有关资料指出不必达到整个产品温度稳定，而只要受试铜排热缩管外表而温度与试验温度一致就行。这一意见是虽有一定道理，实施起来也有一定困难，因为不可能在铜排热缩管表面安装许多传感器，此外铜排热缩管各部分传热能力不一致，受试铜排热缩管内部邻近部件热容量也不一致，确定起来有难度。