Sealing is a general technology necessary for all industries, not only construction, petrochemical, shipbuilding, machinery manufacturing, energy, transportation, environmental protection and other industries can not do without sealing technology Aviation, aerospace and other cutting-edge industries are also closely related to sealing technology. Sealing technology is widely used in many fields, such as fluid storage, transportation and energy conversion.
The importance of sealing technology the consequences of sealing failure are very serious, the light of leakage, resulting in waste of energy and resources, the heavy will make the operation failure, and even produce fire, explosion, environmental pollution and other consequences endanger personal safety.
With the development of science and technology, the working condition of sealing structure is more severe. As the temperature, pressure and corrosivity of the sealed fluid are greatly increased, the traditional sealing materials such as felt, hemp, asbestos, putty and so on can not meet the use requirements, and are gradually replaced by rubber and other synthetic materials.
Synthetic materials such as rubber are generally macromolecular polymers, in which functional groups with different characteristics (such as chlorine, fluorine, cyano, vinyl, isocyanate, hydroxyl, carboxyl, alkoxy, etc.) become active cross-linking points. Under the action of catalyst, curing agent, or high temperature and high energy radiation, macromolecule changes from linear structure and branched structure to spatial network structure, this process is called curing. Vulcanized rubber or other synthetic materials, macromolecules lose the original mobility, known as a high elastic deformation of the elastomer.
Common Rubber and synthetic materials are: natural rubber, styrene-butadiene, neoprene, butadiene rubber, Ethylene propylene rubber, butyl rubber, polyurethane rubber, acrylate rubber, fluorine rubber, silicone rubber and so on.
6 Performance Indexes For Determining The Quality Of Sealing Materials
1. Tensile Performance
Tensile properties are the most important properties of sealing materials, including tensile strength, constant tensile stress, elongation at break and permanent deformation at break. Tensile strength is the maximum stress at which the specimen is stretched to fracture. Constant elongation stress (modulus of constant elongation) is the stress reached at the specified elongation. Elongation is the deformation of a specimen caused by a specified tensile force. The ratio of the elongation increment to the original length is used. The elongation at break is the elongation at break of the specimen. The tensile permanent deformation is the residual deformation between the marking lines after tensile fracture.
2. Hardness
Hardness of the sealing material resistance to external pressure into the ability, but also one of the basic performance of sealing materials. The hardness of the material is related to other properties to some extent. The higher the hardness, the greater the strength, the lower the elongation, the better the wear resistance, and the worse the low temperature resistance.
3. Compressibility
Due to the viscoelasticity of the rubber material, the pressure will decrease with time, which shows as compressive stress relaxation, and can not return to the original shape after removing the pressure, which shows as compression permanent deformation. In high temperature and oil medium this phenomenon is more obvious, this performance is directly related to the durability of sealing products.
4. Low Temperature Performance
An index used to measure the low temperature characteristics of a rubber seal The following two methods of testing low-temperature performance: 1) low-temperature retraction temperature: the sealing material stretched to a certain length, then fixed, rapid cooling to the freezing temperature below, after reaching equilibrium, loosen the test piece, and at a certain rate of heating, record the style retraction 10% , 30% , 50% and 70% when the temperature is expressed as TR10, TR30, TR50, TR70. The material standard is TR10, which is related to the Brittleness temperature of rubber. Low temperature flexibility: After the sample is frozen to the specified time at the specified low temperature, the sample is bent back and forth according to the specified angle to investigate the sealing ability of the seal after repeated action of dynamic load at low temperature.
5. Oil Or Medium Resistance
In addition to contact with oil-based sealing materials, double esters, silicone oil, in the chemical industry sometimes contact acid, Alkali and other corrosive media. In addition to corrosion in these media, at high temperature will also lead to expansion and strength reduction, hardness reduction; at the same time, the sealing material plasticizer and soluble substances were drawn out, leading to weight reduction, volume reduction, resulting in leakage. In general, at a certain temperature, the change of Mass, volume, strength, elongation and hardness after being immersed in the medium for some time can be used to evaluate the oil resistance or medium resistance of the sealing materials.
6. Ageing Resistance
Sealing materials by oxygen, ozone, heat, light, water, mechanical stress will lead to deterioration of performance, known as the aging of sealing materials. Aging Resistance (also known as weather resistance) can be used after aging style of strength, elongation, hardness changes to show that the smaller the change rate, the better the aging resistance.
Note: weatherability refers to a series of aging phenomena, such as fading, discoloration, cracking, powdering and strength reduction of plastic products due to the influence of external conditions such as sunlight exposure, temperature change, wind and rain. Ultraviolet radiation is one of the key factors to promote plastic aging.
Post time: Jul-28-2021