1. Tensile properties of valve sealing materials
Tensile properties are the first properties to be considered for sealing materials, including: tensile strength, modulus stress, elongation at break and permanent deformation at break. Tensile strength is the maximum stress at which a specimen is stretched to fracture. Constant elongation stress (Constant elongation modulus) is the stress achieved at a specified elongation. Elongation is the deformation caused by the specimen being subjected to a specified tensile force, and is expressed as the ratio of the increment of elongation to the original length. Elongation at break is the elongation of the specimen when it breaks. Tensile set is the residual deformation between the marked lines after tensile fracture of the specimen.
2. Valve sealing material hardness
The hardness of the valve sealing material indicates the ability of the sealing material to resist external pressure, and it is also one of the basic properties of the sealing material. The hardness of the material is related to other properties to a certain extent. The higher the hardness, the greater the strength, the smaller the elongation, the better the wear resistance, and the worse the low temperature resistance.
3. Compression performance of valve sealing material
Valve rubber seals are usually in a compressed state. Due to the viscoelasticity of the rubber material, the pressure will decrease with time when compressed, showing compression stress relaxation; after removing the pressure, it cannot return to its original shape, showing compression permanent deformation. This phenomenon is more obvious in high temperature and oil medium, and this performance is directly related to the durability of the sealing ability of the sealing product.
4. Low temperature performance of valve sealing material
The index used to measure the low-temperature characteristics of rubber seals. Two methods of testing low-temperature performance are introduced below: Low-temperature retraction temperature: Stretch the sealing material to a certain length, then fix it, cool it rapidly below the freezing temperature, and release it after reaching equilibrium Test piece, and heat up at a certain speed, record the temperature when the sample shrinks 10%, 30%, 50% and 70%, expressed as TR10, TR30, TR50, TR70 respectively. The material standard is based on TR10, which is related to the brittle temperature of rubber. Low-temperature flexibility: After the sample is frozen at a specified low temperature for a specified time, it is bent back and forth at a specified angle to investigate the sealing ability of the seal after repeated dynamic loads at low temperatures.
5. Oil resistance or medium resistance of valve sealing material
In addition to contacting petroleum-based, diester, and silicate oils, valve sealing materials are sometimes exposed to corrosive media such as acids and alkalis in the chemical industry. In addition to being corroded in these media, it will also cause expansion, strength reduction, and hardness reduction at high temperatures; at the same time, the plasticizer and soluble substances in the sealing material will be drawn out, resulting in weight loss, volume shrinkage, and leakage. Generally, at a certain temperature, after soaking in the medium for a certain period of time, the changes in mass, volume, strength, elongation, and hardness are measured to evaluate the oil resistance or medium resistance of the sealing material.
6. Aging resistance of valve sealing materials
The performance of valve sealing materials will deteriorate after being subjected to oxygen, ozone, heat, light, moisture, and mechanical stress, which is called the aging of sealing materials. Aging resistance (also known as weather resistance) can be expressed by the changes in strength, elongation, and hardness of the style after aging. The smaller the rate of change, the better the aging resistance.
Note: Weather resistance refers to a series of aging phenomena such as fading, discoloration, cracking, chalking and strength reduction of plastic products due to the influence of external conditions such as sunlight, temperature changes, and wind and rain. Among them, ultraviolet rays Irradiation is a key factor in promoting the aging of plastics.
