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What supports the physical strength of silicone rubber seals?

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What supports the physical strength of silicone rubber seals?

Date of release:2019-06-27 Author: Click:

Relationship between formulation and various physical properties: all kinds of silicone rubber products have their specific useful properties and process requirements. In order to meet its physical properties, it is necessary to choose suitable polymer and coordination agent for rational formula design. Firstly, it is necessary to understand the relationship between formula design and physical properties of silicone sulfide rubber. The physical properties of vulcanized silicone rubber are closely related to the design of the formula.

Tensile strength

Tensile strength enables silica gel products to resist the root limit ability of tensile damage. It is an important index of silicone rubber products. The life of many silicone rubbers is directly related to tensile strength. Such as the conveyor belt cover rubber, silicone rubber shock absorber durability is increased with the increase of tensile strength. The tensile strength is related to the structure of silicone rubber. Therefore, when the external force is greater than the intermolecular interaction, the sliding between molecules will occur and the material will be destroyed. On the contrary, if the molecular weight is large, the intermolecular force increases, the cohesion of the glue increases, and the chain segment is not easy to slide when stretched, then the damage degree of the material is small. All the other factors that affect the intermolecular forces have an effect on the tensile strength. For example, NR/CR/CSM has crystalline substituents on the main chain, which greatly increases the valence between molecules and the tensile strength. That is one of the main reasons for the good self-reinforcing properties of silicone rubber. The tensile strength of silicone rubber increases with the increase of crystallinity. Tensile strength is also related to temperature. Tensile strength at high temperature is much lower than that at room temperature. Tensile strength is related to the root crosslinking density. As the crosslinking density increases, the tensile strength increases. After the maximum value is reached, the crosslinking density continues to increase, and the tensile strength decreases significantly. The tensile strength of silicone vulcanized rubber decreases with the increase of crosslinking energy. Natural silicone rubber, which can produce tensile crystallization, breaks the weak bond at the early stage, which is beneficial to the oriented crystallization of main health, so it has a higher tensile strength. Through vulcanization system, using the sulfur vulcanization, the choice and promoter DM/M/D can also improve the tensile strength and (except carbon black reinforcing, because carbon black thermogenesis), the relationship between tensile strength and filling agent and reinforcing agent is one of the important factors that affect the tensile strength, the smaller the diameter of packing material, the bigger the specific surface area, the larger the surface active reinforcing performance, the better.

Tear strength

The tear of silicone rubber is caused by the rapid expansion of crack or crack in the material under stress. Tear strength is not directly related to tensile strength. In many cases tearing is not proportional to stretching. In general, crystalline silicon rubber is stronger than amorphous silicon rubber in tearing. Tear strength depends on temperature. In addition to the natural silicone rubber, the tear strength decreases significantly at high temperature. The tearing strength of silicon rubber filled with carbon black and white carbon black was improved obviously. Tear strength is related to vulcanization system. Sulfurous bonds have a higher tearing strength. High sulfur content high tear strength. However, excessive sulfur content significantly reduces the tear strength. The use of flatness promoter is beneficial to improve the tear strength. The tearing strength is related to the filling system. Various reinforcing fillings, such as carbon black, white carbon black, white yanhua and zinc oxide, can obtain higher tearing strength. Some coupling agents such as laurane can improve tear strength. Usually the addition of a softener decreases the tear strength. Such as paraffin oil will make the tear strength of styrene-butadiene gum is very adverse. Aromatic oils, on the other hand, do not change much.

Constant tensile stress and hardness

Constant tensile stress and hardness are important indexes of material stiffness, and they are the forces required by vulcanized rubber to produce certain deformation, which are related to large tensile deformation. The higher the molecular weight of silicone rubber, the greater the effective stress of crosslinking. The crosslinking density of silicone rubber with small molecular weight can be increased appropriately in order to obtain the specified constant tensile stress. Any structural factor that increases intermolecular forces. Can improve the vulcanized rubber mesh resistance deformation ability. The stress at constant extension has great influence on crosslinking density. No matter it is pure rubber or reinforced vulcanized rubber, with the increase of crosslinking density, the constant tensile stress and hardness also increase linearly. Usually through the vulcanizing agent, accelerator, assistant vulcanizing agent, active agent and other varieties of regulation to achieve. The promotion of sulfur content has a significant effect on increasing the stress at constant extension. It is beneficial to increase the stress of fixed extension. The filler can improve the stress and hardness of the product. The higher the reinforcing performance, the higher the hardness, the higher the constant stretching stress. With the increase of hardness, the constant tensile stress increases with the increase of filling. On the contrary, with the increase of softener, the hardness decreases and the stress decreases. In addition to the addition of reinforcing agent and alkyl phenolic resin hardness up to 95 degrees, high styrene resin. Using resin RS, accelerator H and the hardness of the system can reach 85 degrees.

Wear resistance

Abrasion resistance is characterized by the ability of silica gel products to resist material loss due to surface damage under the action of friction. Is closely related to the service life of silicone rubber mechanical properties. It takes the form of;

1. Wear and tear, continuous cutting and rubbing of sharp rough material on the surface during friction. As a result, the contact points on the silicone rubber surface are cut and pulled into tiny particles, which fall off from the silicone rubber surface and form a abrasion strength which is directly proportional to the pressure and inversely proportional to the tensile strength. As resilience increases, it decreases.

2. Fatigue wear, the vulcanized rubber surface in contact with the friction surface is subjected to periodic compression, shearing, stretching and other deformation effects in the repeated process, making the silicone rubber surface fatigue, and gradually produce micro cracks in it. The development of these cracks causes microscopic peeling of the material surface. The fatigue wear increased with the increase of elastic modulus and pressure, and increased with the decrease of tensile strength and fatigue performance.

Roller friction, silicone rubber under the smooth surface contact, due to the effect of friction force, vulcanized rubber surface uneven place deformation, and was torn damage, become the fall off surface. The wear resistance is related to the main mechanical properties of vulcanized rubber. When designing the formula, try to balance the relationship between various properties. Relationship between wear resistance and analysing, the largest in general NBR > BR > SSBR > SBR (EPDM) > NR (IIR) > > IR CR abrasion resistance is associated with vulcanization system, appropriate to increase the degree of crosslinking 徎 can improve the wear resistance. The more single sulfur bond, the better wear resistance, this is the semi-effective vulcanization system wear resistance is the best reason. The wear resistance of CZ as the first accelerator is better than that of other promoters, and the optimal amount of reinforcing agent will improve the wear resistance to a certain extent. Wear resistance can be minimized by the proper use of softener. Such as natural gum, styrene-butadiene gum with aromatic oil. Effective use of antiaging agents can prevent fatigue and aging. Increasing the dispersion of carbon black can improve the wear resistance. The wear resistance can be greatly improved by using the surface treatment agent of cinnamane. Rubber and plastic blends are used to improve wear resistance, such as the use of ding qing and PVC, made of textile leather. With buqing and three - yuan nylon and with buqing and phenolic resin. Add solid lubricant and anti-wear material. For example, adding graphite, molybdenum disulfide, silicon nitride and carbon fiber into the silicone rubber material of buqinjiao can reduce the friction coefficient of vulcanized rubber and improve its wear resistance.

Fatigue and fatigue damage.

Vulcanized rubber under the action of alternating stress, the structure and properties of the material change phenomenon called fatigue. With the fatigue of 徎, causing damage to the material of the phenomenon called fatigue damage.

1. Influence of silicone rubber structure, good fatigue resistance of silicone rubber with low glass transition temperature. Silicone rubber with polar groups has poor fatigue resistance. Silicone rubber with large groups or side groups in its molecules has poor fatigue resistance and structured sequence. It is easy to crystallize and has poor fatigue resistance.

2. Influence of silicone rubber vulcanization system. The vulcanization system with single sulfur bond has the smallest fatigue performance and good fatigue resistance. Therefore, the amount of crosslinking agent should be reduced as much as possible.

3. The influence of filler: the less the reinforcing performance, the less the influence of filler, and the larger the dosage of filler, the greater the influence, and the less the use of filler.

4. To soften the influence of the system, choose the non-viscous softener with low softening point as far as possible; The dosage of softener is a few more as far as possible, contrary high viscosity softener unfavorable and multi-purpose, be like the fatigue resistance of pine tar is poor, the fatigue resistance of fat kind plasticizer is good.

Six, elastic

The most valuable property of silicone rubber is elasticity. High elasticity comes from the movement of silicone rubber molecules, which is completely caused by the conformation change of crimped molecules. The interaction between the silicone rubber molecules can impede the movement of the molecular segments, showing viscosity or viscosity. So the properties of silicone rubber are both elastic and sticky. The factors affecting elasticity include deformation size, action time, temperature, etc. When the interaction between molecules of silicone rubber increases and the molecular chain has high regularity, it is easy to produce tensile crystallization, which is conducive to the improvement of strength and high elasticity. In general silicone rubber, natural, butadiene rubber elasticity is the best, followed by bujing, chloroprene. Butyl benzene is inferior to butyl. Elasticity is related to the crosslinking density. With the increase of crosslinking density, the elasticity of vulcanized rubber increases and reaches the maximum value. A proper increase in fluidization is beneficial to elasticity. The combination of sulfur and CZ, and the combination of sulfur and D in the high elastic fit have higher resilience and less hysteresis loss. The elasticity is related to the filling system, and increasing the gum content is the most direct and effective way to improve the elasticity. The relationship between elasticity and softener. Softener is related to the miscibility of silicone rubber. Such as natural, butyl, butyl and stone wax oil, better than naphthenic oil. Buqing and DOP are better than naphthenes and aromatic oils. Generally speaking, plasticizer will reduce the elasticity of silicone rubber, plasticizer should be used as little as possible.

Elongation at break (elongation)

Elongation at break is related to tensile strength. Only when the tensile strength is high enough to ensure that it is not damaged during deformation can the elongation be high. Generally, with the increase of the constant tensile stress and hardness, the elongation of fracture decreases, and the greater resilience and the smaller permanent deformation, the greater elongation of fracture. Different silicone rubber, its elongation at breaking is different, natural rubber with a rubber content of more than 80%, its elongation at breaking can reach 1000%. Such as butyl silicone rubber. Elongation decreases with the increase of crosslinking density. Manufacturing high fixed extension products, vulcanization degree should not be too high, you can slightly less sulfur or reduce the amount of vulcanizing agent. Increasing the dosage of filler can reduce the elongation at tearing. The higher the structure of the reinforcing agent, the lower the elongation at tearing.

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