Rubber cushion is characterized by high elasticity and high viscosity. Elasticity of rubber is caused by conformational changes of curled molecules. The interaction between rubber molecules will hinder the movement of molecular chains, thus showing the characteristics of viscous damping, so that stress and strain are often in an unbalanced state.
The curled long-chain molecular structure of rubber and the weak secondary force between molecules; The rubber material exhibits unique viscoelastic properties, thus having good shock absorption, sound insulation and cushioning properties. Rubber parts are widely used to isolate vibration and absorb shock because of their hysteresis, damping and reversible large deformation.
The hysteresis and internal friction characteristics of rubber are usually expressed by loss factor. The greater the loss factor, the more obvious the damping and heat generation of rubber, and the more obvious the damping effect.
The loss factor of rubber material is not only related to the structure of rubber itself, but also to temperature and frequency. At room temperature, the loss factors of natural rubber (NR) and cis-polybutadiene rubber (BR) are small, while the loss factors of styrene-butadiene rubber (SBR), chloroprene rubber (CR), ethylene-propylene rubber (EPR), polyurethane rubber (PU) and silicone rubber are medium, while the loss factors of butyl rubber (HR) and nitrile rubber (NBR) are the largest.
There are generally 5 kinds of rubber materials used for shock absorption, namely NR, SBR and BR are common rubber materials. NBR is used for oil-resistant vulcanizates; CR is used for weather-resistant vulcanizates; IIR for high damping vulcanizates; EPR is used for heat-resistant vulcanizates. Although the loss factor of NR is small, it has the best comprehensive performance, with excellent elasticity, good fatigue resistance, low heat generation, small creep, good adhesion to metal parts, good cold resistance, electrical insulation and processability. Therefore, NR is widely used for shock absorption purposes. When low temperature resistance or weather resistance is required, it can be modified with BR or CR or blended. Nishiue and others shock absorbers made of NR, BR and metal salts of organic acids containing -OH groups with more than 4 carbon atoms have good durability, with compression set of 17.0% and 11.7% at 70℃×22h and 40℃×148h respectively.