What is the effect of high temperature and low temperature on the reliability of products?
Influence of high and low temperature on product reliability
Effect of low temperature on products
·The elasticity of flexible materials such as rubber is reduced and cracks occur;
·The brittleness of metals and plastics increases, leading to fracture or crack;
·Due to the different shrinkage coefficient of materials, when the temperature change rate is large, it will cause the moving parts to be stuck or not rotate properly;
·When the viscosity of the lubricant increases or solidifies, the friction force between the moving parts increases, resulting in sluggish action or even stop working;
·The electrical parameters of components change, which affects the electrical performance of products;
·Freezing or frosting causes damage to product structure or dampness, etc.
Low temperature environmental effect
·Harden and embrittle the material.
·The different shrinkage characteristics of different materials make the parts stuck.
·Loss of lubrication due to increased viscosity of the lubricant.
·Electrical changes (such as resistance, capacitance, etc.).
·Changes in the function of transformers and electromechanical components.
·The impact base hardens.
·Rupture of explosives, such as ammonium nitrate.
·To crack and embrittle the test piece and change the impact strength and reduce the strength
·Static fatigue occurs in glass.
·To condense and freeze water.
·Reduce dexterity, hearing and vision.
·Change the combustion rate.
Effect of high temperature on products
Due to the different expansion coefficients of various materials, the adhesion and migration between materials are caused;
·The loss of lubricant or the decrease of lubrication performance increase the wear between moving parts;
·Deformation of sealing packing, gasket, seal, bearing and rotating shaft;
·Mechanical failure or complete failure due to adhesion;
·Changes in electrical parameters of components affect the electrical performance of products
·Overheating of transformer and electromechanical components;
·Combustion or explosion caused by flammable or explosive materials;
·The internal pressure of the seal increases and causes the fracture;
·Aging, discoloration, blistering, cracking or cracking of organic materials;
·The insulating properties of insulating materials are reduced.
High temperature environmental effect
·The different expansion characteristics of different materials make the parts stuck.
·The loss of viscosity of lubricant leads to the loss of lubricant and the loss of lubrication of contact.
·Change the dimensions of the test piece in whole or in part.
·Mechanical or total failure caused by package, gasket, seal, bearing and main shaft becoming skew, stuck and failure.
·The gasket is permanently deformed (colloidal).
·Deterioration of air tightness.
·The resistance changes.
·The stability of the circuit changes with the temperature gradient and the different expansion characteristics of the material.
·Overheating of transformers and electromechanical components.
·Change the function / non function margin of relay and magnetic and hot start components.
·Reduce operating life.
·The crystal structure inside the solid material is separated.
·High pressure is generated inside the sealed test piece.
·Speed up the combustion of explosives and propellers.
·The shell of explosive casting expands.
·The explosive dissolves and seeps.
·Deterioration and fracture of organic materials.
Effect of temperature change on products
·The electrical properties of components are decreased due to the falling off of coating layer, cracking of potting material and sealing compound, even cracking of sealing shell and leakage of filler;
·For products made of different materials, when the temperature changes, the products are heated unevenly, resulting in product deformation, cracking of sealed products, breakage of glass or glassware and optical instruments, etc;
·A large temperature difference will cause condensation or frosting on the surface of the product at low temperature, and evaporation or melting at high temperature. Such repeated effects will lead to and accelerate the corrosion of the product.
Environmental effect of temperature change
·Broken glass and optical equipment.
·The movable parts are stuck or loose.
·The structure is separated.
·Electronic or mechanical failure due to rapid condensation or freezing.
·To break in a granular or striated form.
·Different shrinkage or expansion characteristics of different materials.
·Deformation or fracture of components.
·Cracking of surface coating.
·Air leakage from the sealed cabin.
Application Comparison of various test methods in high and low temperature test chamber
I. heat dissipation test sample with and without forced air test
In the high and low temperature test chamber industry, the method to ensure the fluctuation of uniformity is to adopt the air circulation mode. The motor drives the fan to generate the air circulation to form the wind speed flow direction. The test without forced air circulation is a kind of test simulating the influence of free air conditions, which is more suitable for the test of heat dissipation test samples. The test with forced air circulation is difficult without forced air circulation Or when the specified test conditions cannot be guaranteed, two methods of forced air can be used: 1 and 2. Method 1 is used when the test chamber is large enough to meet the test requirements without forced air circulation. However, when the specified low temperature cannot be maintained without forced air circulation in the chamber, the cooling or heating requirements of the high and low temperature test chamber adopt forced air circulation.
II. Non thermal test samples and thermal test samples
During the condition test, when the temperature of the test sample is stable and measured under the free air condition, the hottest spot temperature on the test sample surface is more than 5 degrees higher than the ambient air temperature, which is considered as heat dissipation; otherwise, it is non heat dissipation test sample. If there is no electricity or no load during the storage test and test period, the test sample is non heat dissipation test sample, and low temperature test is adopted for the test Test method.
III. non thermal test samples
Temperature gradual change test of high and low temperature test chamber (the former is rapid temperature change test chamber and the latter is high and low temperature test chamber)
① temperature gradual change test: first put the test sample with room temperature into the test box with the same room temperature, and then start the cold source to cool the temperature in the box gradually to the specified test temperature. If the test sample is too large or too heavy, or because of the complex functional test wiring, the test shall also be used when it cannot be put into the low-temperature box without frosting during the sudden change test;
② temperature sudden change test: first adjust the temperature of the test chamber to the specified test temperature, and then put it into the test sample with room temperature. This test method is applicable to the time when the known temperature sudden change does not produce operation on the test sample.
Eight selection points of high and low temperature test chamber
1. Whether the user is selecting high and low temperature test chamber or other test equipment, the temperature conditions specified in the test requirements shall be met;
2. To ensure the temperature uniformity in the test area of the test chamber, the forced air circulation or non forced air circulation can be selected according to the heat dissipation of the sample;
3. The heating or cooling system device of the high and low temperature test chamber shall have no effect on the sample
4. The test chamber shall be convenient for placing samples with relevant sample racks, and the mechanical properties of the sample racks shall not be changed due to the change of high and low temperature;
5. The high and low temperature test chamber shall be provided with protective measures. For example: there are observation windows and lighting, with power phase failure, over temperature protection, all kinds of alarm devices;
6. Whether there is remote monitoring function according to the requirements of customers;
7. It is required to install automatic counter, indicator light, recording equipment, automatic shutdown and other instruments and devices, and have good recording and display functions during the implementation of the cycle test of the test chamber;
8. According to the sample temperature, there are two measurement methods: upwind and downwind sensor. The position and control method of temperature and humidity control sensor in the high and low temperature test chamber can be selected, and the appropriate equipment can be selected according to the product test requirements of customers.