Thermal shock test

January 12, 2021

At present, engineers have many different opinions on the test of temperature change when formulating standards and implementing standards, and the names of such tests are too many, which leads to some inappropriate use methods in practical applications. In this paper, the temperature change test is interpreted. On the one hand, various test items are analyzed. On the other hand, the appropriate standard items are recommended for reference by engineers.

Temperature change test items have many names: temperature change, temperature cycle, temperature change, rapid temperature change, temperature shock, thermal shock, temperature gradient, and grading temperature. And the test methods applied in the standards of different systems are different. How to distinguish these test items and how to select test items requires analysis of the sources and differences of each type of test.

The test items for this paper are temperature-changing. For the test items such as damp heat, temperature and humidity cycle, etc., the topic will be described later.

1 , temperature change test

1.1 Source

The temperature change tests in various standards are derived from IEC 60068-2-14 Test Method N: Nb in temperature change. Temperature change test at a specific temperature.

1.2 Definition

The temperature change test performs a transition between high temperature and low temperature in order to set a certain temperature change rate. Therefore, there are two types in practical applications: one is a slow temperature change test, and the temperature change rate is <3 °C/min (generally, the standard is often selected as 1 °C/min), which is also the temperature change in general applications. , temperature cycle, temperature alternating test (the three types are one type of test); the other type is a rapid temperature change test, the temperature change rate is ≥ 3 ° C / min (generally, the standard selection parameter is 3 ° C / min, 4 ° C / min, 5 ° C / min, 7 ° C / min, 10 ° C / min), also in the general application of rapid temperature change test. The faster the rate of temperature change, the harsher the assessment.

1.3 Purpose and scope of application

This test is applicable to components, equipment or other products. Simulate changes in temperature with live work for the product, such as rapid changes in ambient temperature while the system/component is operating. If the system/component is at a hot soak temperature (such as a system/component mounted on the engine), the additional transient temperature spikes in the high temperature phase ensure the basic function of the product during this time. In order to prevent the electrothermal diffusion in the system/component from suppressing the low temperature effect of the system/component, the product is turned off during the cooling phase. The failure mode is an electrical fault caused by a temperature change.

Note: This test is not a life test.

1.4 Test methods and parameters

1.4.1 Temperature change test:

ISO 16750-4 5.3.1 temperature change test is recommended for various standards. The specific test procedure is shown in Figure 1 and Figure 2. Figure 1 is applied to non-cabin products. Figure 2 is applied to engine compartment parts because it has an engine. Exhaust heat assessment after flameout, so the limit of high temperature storage was added to the temperature change.

Figure 1 temperature curve

TOB: high temperature limit operating temperature

TUB: low temperature limit operating temperature

Work Category 3.2: Working with 13.5V live

Figure 2 Temperature curve with subsequent heating

TOB: high temperature limit operating temperature

TUB: low temperature limit operating temperature

TNH: After the engine is turned off (parking), the high ambient temperature of zui appears

Work Category 3.2: Working with 13.5V live

1.4.2 Rapid temperature change test:

At present, some of the enterprise standards are found to have such projects, such as GM3172. The specific test methods are shown in Figure 3. These tests are accelerated life test methods and are generally not recommended for use in certification tests.

Figure 3 fast temperature change curve

1.5 Differences and application analysis

For the above two tests, it is recommended to use the ISO 16750-4 5.3.1 temperature change test. Because it is more suitable for the daily use of the product, the rapid temperature change test is applicable to the life acceleration test, and its specific acceleration factor and method. Follow-up manuscript discussion.

1.6 Analysis of important parameters

Characteristics of temperature change test: The product works in the test, the rate of temperature change is constant, the number of cycles is generally set within 30 cycles, and the limit temperature value (so the test is work + storage type test, so the limit value is different according to product usage) There are two options to choose from, see Figure 1 and Figure 2); this is the product performance test (non-life test). The attached table is a recommended parameter for an external company for your reference.

Table 1 Product temperature change test parameters recommendation table

Number of cycles

30

Zui low ambient temperature

Tmin (product low temperature working limit temperature)

Zui high ambient temperature

Tmax (product high temperature working limit temperature)

Temperature change rate

4 ° C / min

Product temperature stabilization time (storage time)

See Table 2

Number of samples

application

Quantity / piece)

Product example

Security class

20

Engine controller, airbag controller, tire pressure monitor

Control class

15

Rain sensor, light sensor, door switch

Portable class

10

CD player, entertainment system

Operating state

See Figure 1, Figure 2

The storage time of the product in the extreme temperature is shown in Table 2.

Table 2 Relationship between product weight and temperature immersion time

Product weight (kg)

Immersion time (holding time min)

<0.34

20

0.34-0.68

30

0.68-0.91

40

0.91-1.36

50

1.36-4.53

75

>4.53

To be defined

As can be seen from Fig. 4 and Fig. 5, the components with relatively simple structure and the whole machine with fewer components and components are generally selected for 5 cycles. The structure is more complicated, and the whole machine with more components and parts used can select most of the fault causes by exposing 10 cycles. For equipment, complete machines and instruments with higher reliability, it is sometimes possible to choose between 20 and 30 cycles.

Figure 4 Selection of different equipment cycles

Figure 5 Selection of different equipment cycles

2 , thermal shock test

2.1 Source

The thermal shock tests in various standards are derived from IEC 60068-2-14 Test Method N: Na in temperature change. Rapid temperature change test in a specific time.

2.2 Definition

The rapid temperature change is performed within a specific time. The conversion time is generally set to manual 2 to 3 minutes, automatic less than 30 seconds, and small test pieces less than 10 seconds. The temperature shock test in common terms is also a thermal shock test.

2.3 Purpose and scope of application

This is an accelerated test that simulates a large number of slow temperature cycles in a vehicle. Corresponding to the actual vehicle temperature cycle, acceleration is possible with a faster rate of temperature change and a wider range of temperature variations. The failure mode is material cracking or seal failure due to aging and different temperature expansion coefficients. This test will result in mechanical defects (cracks) that do not require live work.

2.4 Test methods and parameters

2.4.1 Thermal shock test (gas):

There are two ways to achieve this, one is manual conversion, the product is converted between the high temperature box and the low temperature box; the other is the impact test box, the temperature is converted by the circulation damper of the switch hot and cold room or the like. The upper temperature limit and the lower temperature limit are the storage limit temperature values ​​of the product. See Figure 6 for the specific method.

Figure 6 temperature shock curve

2.4.1 Thermal shock test (liquid):

This test is derived from IEC 60068-2-14 Test Method N: Nc in temperature change. The realization method is a basket type, and the product is placed in a hanging basket and immersed in different temperature liquids as required. It is applicable to glass-? seals and similar products, so the project will not be evaluated in electrical products.

2.5 Differences and application analysis

In the above two test items, it is recommended to use IEC 60068-2-14, Na for testing. This test item belongs to the test of accelerated test products. IEC 60068-2-14, Na and ISO 16750-4 5.3.2 The recommended number of cycles in the thermal shock test is 5, and there are too few practical applications. The parameters of Table 3 are recommended.

It is stated here that the number of cycles required for thermal shock in IEC 60068-2-14, ISO 16750-4, MIL-STD-810F and GJB150 is within 5 cycles, because the three types of standards for this test Defined as: Determines whether equipment can withstand rapid changes in its ambient temperature without physical damage or performance degradation. The simulated situation is: the air transportation of the product, the aviation investment, and the transfer of other products from different temperature zones. Therefore, in order to assess such conditions, the test execution is a sample storage test. The product does not work during the test. The number of temperature shocks of the product is based on the number of times the product will actually be used. Such test items are a kind of product reliability. .

From the above analysis, we can know that for our automotive products, when we carry out this standard, because the simulation conditions of our assessment are different, the parameters need to be changed. The main variation parameters are: the number of cycles is increased (as applied to automotive electrical products for accelerated aging test) Therefore, the number of cycles generally exceeds 100).

2.6 Analysis of important parameters

There are several important parameters to consider in this test: cycle number, temperature conversion time, temperature hold time, temperature limit value (so the test is a storage type test, so the limit value is the storage limit temperature value). The reference parameter settings are shown in Table 3. The specific number of cycles is an empirical value calculated by the acceleration model, which is not detailed here.

Table 3 Recommended parameters for thermal shock test parameters

Number of cycles

500 (engine compartment), 100 (other parts)

Zui low ambient temperature

Tmin (product low temperature storage limit temperature)

Zui high ambient temperature

Tmax (product high temperature storage limit temperature)

Conversion time

≤30s

Product temperature stabilization time (storage time)

See Table 2

Number of samples

5

Working status

Not working

3 , temperature gradient test

3.1 Source

The temperature gradient tests in various standards are derived from the 5.2 temperature gradient test in ISO 16750-4.

3.2 Definition

Change the temperature according to a certain rate, generally take 5 °C / min, and perform function detection when the temperature is stable. The grading temperature test in common terms is also a temperature gradient test.

3.3 Purpose and scope of application

Used to check for possible failures in mechanical and electrical installations in local areas where the operating temperature is small.

3.4 Test methods and parameters

Place the product in a temperature chamber, reduce the temperature gradient from 20 °C to Tmin (low temperature limit operating temperature) at 5 °C / min, then raise the temperature gradient from Tmin to Trnax (high temperature limit operating temperature) at 5 ° C / min, each step Wait until the product reaches a new temperature. Whenever the product reaches a new temperature, the product's working mode is tested according to the product's large working voltage and zui's small working voltage. The product is turned off during the temperature adjustment process. At each temperature point between Tmin and Tmax, the product should maintain normal function, ie the functional state should be in normal operation during and after the test. The number of cycles is generally set to 5, which is the product performance evaluation project. The specific implementation method is shown in Figure 7.

t time, min.

T temperature, °C.

Figure 7 temperature gradient curve

3.5 Differences and application analysis

In the actual application of this test, temperature changes can be used instead. The difference between temperature changes is very small: high temperature working limit temperature, low temperature working limit temperature, product live working in test, temperature change rate and other important parameters are similar, the difference is temperature In the change test, there is a high temperature residual heat storage temperature limit test, and the temperature gradient test is only the working limit temperature test, so the temperature change test actually includes the effect of the temperature gradient, and it is recommended to cancel the test of such test items.

3.6 Analysis of important parameters

There are several important parameters to consider in this test: the limit temperature (so the test is a work type test, so the limit value is the product working limit temperature value), the temperature change rate, and the number of cycles.

4 , equipment requirements

4.1 Wind speed requirements

All kinds of temperature change test standards have requirements for the wind speed in the temperature change test chamber, and both require less than or equal to 2m/S. This requirement is to ensure that the test product is not subjected to excessive airflow during the test, resulting in excessive heat transfer from actual use. A certain wind speed in the test box is conducive to the rapid and uniform temperature inside the box, and if the wind speed is too large, the heat exchange of the test product by the wind surface is greater than the back surface, and the actual heat conduction phenomenon is not generated inside the product.

4.2 Absolute humidity requirements

There is no requirement for humidity in MIL-STD-810F. This is based on the use of products made of general materials, and the effect of humidity on the temperature impact test is not significant. In 810F, it is pointed out that when testing porous porous materials (such as fiber materials), moisture is easy to penetrate into the product, and expansion after freezing at low temperatures may cause material damage. It is recommended to control the humidity of the test chamber when testing. Generally, the absolute humidity in the box is required to be less than or equal to 20 g/m.

4.3 Requirements for test chamber air temperature recovery time

GJB150.5 (with MIL-STD-810 C/D) and GB2423.22 (with IEC 60068-2-14) have the same requirements for this requirement, which are less than or equal to the test time (referring to the time when the product reaches temperature stability). 10%, while 810F is clearly less than or equal to 5 min. The purpose of this requirement is to require the test chamber to have a large heat sink to ensure that the test product is truly subjected to an environment with sudden temperature shock.

4.4 Difference between box wall temperature and test temperature

The requirements for the difference between the wall temperature and the test temperature are also specified in various standards. This is to avoid excessive radiant heating effect caused by the large temperature difference between the two, which causes the temperature of the test product to be uneven. General provisions: ≤ 3% (high temperature), ≤ 8% (low temperature).

From the above analysis, the difference and source of each temperature change test item and the requirements for the test equipment can be known. In practical applications, we recommend that you use the temperature change test project (ISO 16750-4 5.3.1 temperature change test) and the thermal shock test (ISO 16750-4 5.3.2 thermal shock test, the recommended number of test cycles is shown in Table 3) .

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