Thermal Shock Chamber: Introduction, Classification, Operating Mechani

1. What is Thermal shock

Thermal shock is the abrupt temperature variation from cold to hot and vice versa, causing different parts of an object to deform in various directions. This differential deformation can be understood in terms of expansion or contraction. At certain points, it may exceed the material's tolerance, leading to the formation of cracks.

2. Types of thermal shock chambers

Currently, there are many manufacturers in the market producing thermal shock chambers with different designs and costs. However, the common feature of these chambers is that they operate on a specific principle: rapidly increasing or decreasing the temperature of the test sample to assess the material's durability.

In reality, there are various types of thermal shock chambers with different designs and operating principles depending on the testing requirements and international standards to be met. Therefore, thermal shock chambers also have many different classification methods.

Based on the Environment Inside the Test Chamber: There are two common environments: air and liquid. Based on this, thermal shock testing chambers are classified into structures including single-zone, two-zone, and three-zone designs.

Additionally, in some cases, vibrating systems are designed inside the thermal shock chambers to assess the reliability of the samples being tested.

2.1. Thermal shock testing in an air environment (Air to Air) – Common type

With this type, air is heated or cooled directly inside the sample chamber (1-zone and 2-zone types). Alternatively, cold and hot air can be blown into the sample chamber using a fan from a different area (3-zone type).

Typically, to generate hot air, various types of resistive heaters are used to heat the air. Meanwhile, common refrigerants used for cooling include R23, R32, R401, R507, etc. In cases requiring rapid cooling for a short duration, liquid nitrogen is often used.

For testing in an air environment, the temperature range of these chambers typically falls between -80°C to +200°C.

2.2. Thermal shock testing in a liquid environment (Liquid to Liquid) – Less common type

The distinctive feature of this type of chamber is that instead of supplying hot or cold air to the test chamber, the test chamber is immersed in a specialized hot or cold liquid. This type of chamber is often used to apply very intense thermal shocks to test samples, with rapid testing times and optimized resistance to sample deformation.

However, the usage cost is relatively high, especially with challenges in preserving specialized liquid, as it tends to evaporate, leading to significant loss. Additionally, the sample size for this type of chamber is limited in terms of both weight and test chamber volume compared to basic types.

2.3. Two-zone and three-zone thermal shock chambers

Commonly used worldwide are two-zone and three-zone chambers. With a three-zone chamber, three areas are independently placed in three zones, and the test chamber has a mechanical mechanism that can move between hot and cold zones. The position of the zones can be customized by manufacturers to be either vertically or horizontally oriented.

For the two-zone chamber type, the test area has an operational mechanism similar to an elevator that can move from the hot zone to the cold zone and vice versa. The duration of this movement is typically within 10 seconds.

Meanwhile, the three-zone thermal shock chamber includes a hot zone, an intermediate zone, and a cold zone. The main difference is that, for the three-zone type, the sample is fixed in the intermediate zone, while for the two-zone type, the sample will move to change the environment.

During the testing process, air in the hot and cold zones is heated and cooled to a temperature set as per requirements.

When the temperature in the hot zone reaches and stabilizes at the set value, the door of the hot chamber will automatically open to blow hot air into the intermediate chamber where the sample is placed. It will take a certain amount of time to maintain the temperature at a stable value according to the set parameters. After the testing time in the hot environment is completed, the door of the hot zone that contacts the intermediate zone will close. Subsequently, the door of the cold zone will open to blow cold air into the intermediate zone where the test sample is located. At that point, it will also take some time (5-10 minutes) to maintain the temperature at a value set by the parameters.

After completing the testing time in the cold environment, it marks the end of a cycle. The system can automatically repeat with different cycles according to user requirements.

2.4. Single-zone thermal shock chambers

This type is less common. It has only one test zone, and this zone is fixed. Because there is only one zone, the rapid temperature changes demand a fast heating and cooling rate for the chamber. Typically, these chambers cool rapidly using nitrogen gas and heat by directly blowing hot air into the zone. The advantage of this chamber is its compact size.

Next is the air heating and cooling system. All types of thermal shock chambers are equipped with circulating fans in the test chamber, aiming to create an air stream to evenly distribute the temperature within the chamber. Hot air is typically generated by burning high-power resistors (similar to how heaters operate), while cold air is usually produced using a compressor (similar to air conditioners, refrigerators). The zones for generating hot and cold air operate independently.

3. The basic operating principle of the thermal shock chamber

Initially, the test sample is placed in the test zone, and at this point, the temperature of the test zone is the ambient temperature.

Next, we choose to raise the sample to a high (or low) temperature threshold by supplying hot or cold air to the test zone through the operational mechanism of the three types of chambers mentioned above.

Then, maintain that threshold temperature for a certain period to ensure the temperature inside different parts of the test sample reaches uniformity. Afterward, the test zone will move from the hot zone to the cold zone (or vice versa) for chambers with two or three chambers. For single-zone chambers, the system reverses the heat supply (stops heating and starts cooling or vice versa). In the new temperature environment, the test sample continues to be maintained for a specified period as required.

Thus, the thermal shock chamber completes one cycle, and typically a test program will repeat the cycle n times as needed.

The entire process is controlled through the control panel.