Selection Factors of Rubber Seal Compound Factory Suppliers Manufacturers Quotes

Selection Factors of Rubber Seal Compound

When choosing rubber seals, the first properties to be considered include tensile strength, constant tensile stress, elongation, elongation at break, permanent deformation at break and stress-strain curve. We call it tensile strength. The tensile strength is the maximum tensile stress when the specimen is stretched to fracture. The tensile stress (modulus of elongation) is the stress (modulus) reached when the elongation is specified. The elongation is the deformation of the specimen caused by tensile stress, expressed as a percentage of the increment of elongation to the original length. Elongation at break is elongation at break. The permanent deformation is the residual deformation of the gauge part after tensile fracture.

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Then we consider the basic properties of rubber seals hardness.  Hardness means the ability of rubber to resist external pressure intrusion. The hardness of rubber is related to some other properties to a certain extent. For example, the harder the rubber is, the stronger the strength, the lower the elongation, the better the wear resistance, and the worse the low temperature resistance. High hardness rubber can resist extrusion failure under high pressure. Therefore, suitable hardness should be selected according to the working characteristics of parts.

We know that rubber seals are often compressed, so we have to consider the compressibility of rubber seals. Because of the viscoelasticity of rubber, the compressive stress of rubber decreases with time after compression, which shows that the compressive stress relaxes; after removing the pressure, the original shape can not be restored, which shows compressive permanent deformation. These phenomena are more significant in high temperature and oil medium.  They will affect the sealing performance of seals and are one of the important properties of sealing compounds.

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The brittleness temperature, which is the highest temperature at which the specimen breaks under a certain impact force at low temperature, can be used to compare the low-temperature properties of different rubber compounds. However, the brittleness temperature of rubber does not indicate the lowest working temperature of rubber parts, especially in oil medium, because the working state of rubber parts is different from the test conditions. Secondly, the low temperature retraction temperature is that the specimen is stretched to a certain length at room temperature, then fixed, rapidly cooled to below freezing temperature, then released after reaching the temperature balance, and warmed up at a certain speed, recording the temperature when the specimen retracts 10%, 30%, 50% and 70%, expressed as TR10, TR30, TR50 and TR70, respectively. . In the material standard, TR10 is generally used as an index, which is similar to the brittleness temperature of rubber. Another way to indicate the low temperature performance of rubber is to determine its cold resistance coefficient. Generally, the specimen is compressed to a certain amount of deformation at room temperature, and then frozen at a prescribed low temperature, then unloaded for its recovery at low temperature, recovery and compression ratio is called compression cold resistance coefficient. The greater the coefficient, the better the cold resistance of rubber.

Rubber seals have a harsh living environment, most of which are found in fuel, lubricating oil, hydraulic oil and other systems, so often contact with a variety of oils, naturally it needs to have oil resistance. Rubber in the oil medium, especially at higher temperatures, will lead to expansion, softening and reduction of strength and hardness. At the same time, plasticizers or soluble substances in rubber may be leached by oil, resulting in weight loss, volume reduction, resulting in leakage. Therefore, the oil resistance of rubber is an important property of rubber compound working in oil medium. Generally, the weight, volume, strength, elongation and hardness of the oil are measured after soaking for a certain period of time at a certain temperature. Sometimes it can also be expressed by the oil resistance coefficient, that is, the ratio of strength or elongation to the original strength or elongation after immersion in the medium.

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The above is a brief introduction of the main properties that should be considered in rubber seals.

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