Project Introduction:

High and low temperature testing is the abbreviation for high temperature testing and low temperature testing. The purpose of the test is to determine the adaptability of products for storage, transportation, and use under high or low temperature climate environmental conditions. The severity of the test depends on the temperature and exposure duration at high or low temperatures.

Comparative Analysis of Test Methods:

1. Non-dissipating and Dissipating Samples

When testing under natural air conditions, after the sample temperature stabilizes, if the temperature at the hottest point on the surface remains more than 5°C above the surrounding ambient temperature, it is considered a dissipating sample; if it is equal to or less than 5°C, it is a non-dissipating sample. All non-operational storage and transportation tests are non-dissipating tests. During operational testing, if the temperature rise is less than 5°C after stabilization, it is also considered a non-dissipating test. For example, after a type test for an electric fan, if the temperature rise on all accessible external surfaces does not exceed 20°C, it is considered a dissipating test.

2. Temperature Shock Test and Temperature Ramp Test

When the test chamber temperature reaches the specified temperature, immediately placing the sample into the chamber for testing is called a temperature shock test. Placing the sample into the chamber at room temperature and then gradually raising or lowering the chamber temperature to the specified test temperature is called a temperature ramp test.

Generally, if it is known that temperature shock does not cause other harmful effects on the sample, a temperature shock test should be used to save time; otherwise, a temperature ramp test should be used.

3. Natural Air Circulation Test and Forced Air Circulation Test

For non-dissipating tests, forced air circulation can improve heat exchange efficiency. The higher the air circulation speed, the higher the heat exchange efficiency. Therefore, for such forced tests, an air circulation speed ≥2 m/s is recommended. For dissipating tests, a natural air circulation test is preferred. If natural air circulation does not meet test requirements, forced air circulation should be used.

Application Scope:

High and low temperature testing primarily targets electrical, electronic products, their components, and other materials. The test severity depends on the temperature and duration. High and low temperatures may cause products to overheat, affecting safety and reliability, or even causing damage, such as:

· Due to different expansion coefficients of materials, leading to bonding and migration between materials.

· Altering material properties.

· Degrading electrical performance of components.

· Reducing the elasticity or mechanical strength of elastic elements, shortening product lifespan.

· Accelerating degradation and aging of polymer and insulating materials, shortening product lifespan.

· Reducing elasticity of flexible materials like rubber, causing cracking.

· Increasing brittleness of metals and plastics, leading to fractures or cracks.

· Making materials brittle, such as plastics and steel prone to brittle fracture at low temperatures, rubber materials hardening, elasticity decreasing, etc.

Basic Requirements for Products After High and Low Temperature Testing:

Product quality after high and low temperature testing is generally inspected according to requirements specified in product technical conditions or agreements. For example, the impact of high temperature on motor performance includes increased resistance of conductive materials, leading to current changes, and for precision motors, affecting accuracy. Therefore, after high temperature testing, insulation resistance should be measured inside the chamber, with values not less than 5 MΩ, and other motor performances should also be tested. Generally, if products meet the following basic requirements after temperature testing, they are considered compliant with high and low temperature requirements.

(1) No surface damage, deformation, or other defects. For coated surfaces, there should be no peeling, blistering, or discoloration.

(2) For plastic parts, no cracks, bubbles, or deformation.

(3) Rubber products show no aging, adhesion, softening, or cracking.

(4) No flow at soldered joints.

(5) Product performance data and structural functions meet technical condition requirements, with no other defects hindering normal operation.

Reference standards: GB/T 2423.1, GB/T 2423.2, IEC 60068-2-1, IEC 60068-2-2, EN 60068-2-1, EN 60068-2-2, etc.

Test parameters for high temperature testing: Test temperature, test duration, heating rate.

Performance impacts of high temperature testing: Material thermal aging, cracking, discoloration, softening, melting, expansion, or functional failure.