Rubber is characterized by both high elasticity and high viscosity. The elasticity of rubber is caused by the change of its curly molecular conformation. The interaction between rubber molecules hinders the movement of molecular chains and shows the viscosity. So that stress and strain are often in an unbalanced state. The long-chain molecular structure of the rubber and the weak secondary force between the molecules make the rubber material exhibit a unique viscoelastic property and thus have good shock absorption, sound insulation and cushioning properties. Rubber components are widely used to isolate vibration and absorb shocks because of their hysteresis, damping, and reversible deformation. In addition, rubber also has hysteresis and internal friction characteristics, they are usually expressed by the loss factor, the greater the loss factor, the more obvious the damping and heat generation of the rubber, the more obvious the damping effect. In summary, the rubber shock absorber made of rubber also has a good shock absorption effect.
Advantages of rubber shock absorbers:
(1) The shape can be freely determined, and the hardness can be controlled by adjusting the rubber formulation components to meet the requirements for rigidity and strength in all directions;
(2) The internal friction is large, and the shock absorption effect is good, which is beneficial to cross the resonance zone and attenuate high-frequency vibration and noise;
(3) The modulus of elasticity is much smaller than that of metal, which can produce a large elastic deformation;
(4) There is no sliding part and it is easy to maintain;
(5) Small quality, easy to install and disassemble.
(6) Impact stiffness is higher than static stiffness and dynamic stiffness, which is beneficial to impact deformation.
2.2 Introduction of main types of rubber shock absorbers
Rubber shock absorbers are classified according to their functions as follows:
(1) a narrow rubber shock absorber that supports various devices;
(2) a rubber bumper for the purpose of absorbing shock;
(3) a rubber spring used as a mechanical actuating member;
(4) A dynamic damper that eliminates vibration of a specific vibration frequency;
(5) Rubber couplings are also included in the category of rubber shock absorbers.
Rubber shock absorbers are classified according to their shape as follows:
(1) Compression type This type is a rubber shock absorber mainly used for the compression direction. The advantage is that the load bearing capacity is large, but the elastic modulus of the compression direction cannot be chosen too low.
(2) Shear type This type is a rubber shock absorber mainly used for the cutting direction. Its load bearing capacity is small, but it has the advantage that the elastic coefficient can be selected to be small.
(3) Composite type is a rubber shock absorber for combination of compression and shear, and has intermediate characteristics of compression type and shear type.
(4) Cylindrical type This type of rubber shock absorber can be used for vibration damping in the vertical direction, axial direction, twisting and distortion of the shaft. Similar to the compression type rubber alkali shaker used for the vertical direction of the shaft, its load bearing capacity is generally large, but the elastic modulus cannot be chosen too small.
Rubber shock absorbers are classified according to their application as follows:
(1) YLJ type rubber shock absorber: YLJ-type rubber mount is a special rubber product for road roller. According to its load and external dimensions, it can be divided into several different models, which are used for different types of road rollers;
(2) WJ type rubber shock absorber: WJ-type rubber mount is a versatile rubber shock absorber. Also known as the "universal pad", it has four cylindrical bosses of different diameters and heights, and the upper and lower sides are arranged crosswise. It can withstand loads in any direction and absorb vibration in any direction. No slippage occurs when subjected to lateral pressure. Therefore, it is not necessary to take measures to prevent the machine from moving horizontally, saving a huge base cost. This product is heat resistant, oil resistant and easy to use;
(3) JP type flat rubber shock absorber: JP-type plate shaped rubber pad One type of rubber shock absorber is a rubber metal product in the form of a flat plate. The structure is an inner and outer metal plate (ring), and the middle is sandwiched with rubber, and is produced by a molding method. It can be divided into three models: JP-1, JP-2 and JP-3. Used in radio, instrumentation and instrumentation to protect its machine from shock and shock;
(4) J G type is used for fans, air compressors, freezers, water pumps, precision instruments, instruments, machine tools;
(5) 6JX type is used for power machinery and electronic equipment with high requirements for random vibration and shock isolation such as ships and vehicles;
(6) 6WN type, 31 type, SH type, E, EA type are used for the main engine, mechanical and instrumentation equipment separator, buffer, anti-shock and noise reduction of diesel locomotives;
(7) XL series, high elastic rubber coupling, is the first national standard (GB 2496 81) series of high elastic coupling designed and developed by serialization, standardization and generalization in China, especially high The elasticity (low stiffness, high flexibility) can reduce the natural vibration frequency of the shafting, change the torsional vibration of the shafting, make the diesel engine not have dangerous resonance speed, have better shock absorption characteristics, absorb part of the vibration energy; absorbable and Reduce the fluctuation of diesel engine output torque; improve power transmission quality and make up for shafting installation error;
(8) YXN, XN rubber torsional vibration damper is a new type of crankshaft damping component, which can overcome the torsional vibration of the crankshaft system of the vehicle engine, gear impact, wear of the machine parts, increased noise, increased vibration, and even the crankshaft during resonance. Serious problems such as breaks. Rubber hoses are widely used in ship machinery and equipment for shock absorption and sound insulation. There is also a viscoelastic damping material, which is a high molecular polymer. There are large changes in the values of the elastic modulus and the loss factor as a function of temperature and frequency. It is a new material for isolation and noise reduction currently developed at home and abroad, and is widely used in aviation, aerospace, shipbuilding, automobile, railway, construction, textile and other industries.
2.3 Main applications of rubber shock absorbers
2.3.1 Rubber shock absorber for automobiles
With the development of social economy, the transformation of domestic and foreign cars is quite frequent, and the automobile industry is facing a period of rapid change. The development is characterized by ensuring driving safety, ride comfort, high speed and luxury. To further improve the service life of the car. Shock Absorbing Products are used to control the vibration and noise of automobiles and improve their steering stability. They are generally placed in automobile engine frames, pressure bar devices, suspension bushings, center bearing brackets, bump limiters and torsional vibration dampers. To improve the safety and comfort of the car. Shock-absorbing products can be divided into four categories: brackets, bushings, cushioning and damping. The main requirements are shock absorption, heat resistance and fatigue resistance. Automotive shock absorbing rubber products include engine mounts, suspension members, rubber springs, rubber air springs, and impact rubber guards. In recent years, in order to improve the safety, comfort and operability of automobiles, the variety and quantity of shock-absorbing rubber products for automobiles have been increasing. For example, the number of shock-absorbing rubber products in a car has reached 50 to 60 pieces.
The rubber shock absorbers for the engine and transmission operating system are used to isolate the vibration of the source. The transmission part is shock-absorbing with a polygonal coupling and a damping clutch. The shock absorbers used on the front and rear suspension devices not only bear the weight of the car body, but also prevent the car body from transmitting the up and down vibration of the wheel, suppressing the irregular movement of the unsprung mass, and transmitting the power and braking force. The rubber bumper is one of the important shock absorbers of the car body. Its structural form is that a rubber layer is sandwiched between two metal plates, and the shear deformation of the rubber is used for buffering purposes. Recently, a cylindrical buffer that is filled with nitrogen and coexists with shock absorber oil has been developed, which is characterized by an increase in the load capacity of the shock absorber (up to 20 MPa), a good shock absorption effect, and an extended service life. The rubber materials used in rubber shock absorbers for automobiles are mainly NR and SBR. In order to improve the heat resistance of shock absorbing articles, IR, IIR, CR, EPDM, etc. have been used as host materials. Thermoplastic elastomers will also be used in partially shock absorbing articles such as shock absorbers for body and chassis. For example, Zhejiang Haimen Rubber Factory adopted NR /CR and developed a car spring seat shock absorber with good effect.
2.3.2 Rubber shock absorbers for railway locomotives and railway sleeper pads
According to statistics, there are more than 10,000 kinds of rubber materials and components used in domestic railways and locomotives, and the consumption of rubber is about 10 kt/a. With the increase of the speed of railway locomotives, the dynamic effect on the line increases sharply, causing severe wear on the components of the lines, tires and locomotives. The requirements for seismic resistance of railway locomotives are getting higher and higher. Rubber shock absorbers The application is becoming more and more popular, so the variety and quantity of shock absorbing rubber products on the locomotive are increasing. The shock absorbing rubber products on the railway locomotive mainly include a central supporting rubber pile body, an axle box pull rod rubber spring body, a side bearing rubber pile, a motor suspension rubber pad, an elastic wheel, an elastic gear, a rubber air spring, a bow rubber block of the transmission device, and Rubber ball joints, coupler rubber bumpers, etc. The rubber shock absorber applied to the locomotive is mainly used to withstand compressive stress, shear stress and torsional moment, and to withstand two or more stress combinations at the same time.
With the rapid development of railway construction in China, railway sleepers have also been gradually changed from sleepers to concrete sleepers. After the change, although the service life of the sleeper is prolonged, the stability of the track frame structure is improved, but the elasticity of the track is significantly reduced, resulting in a deterioration of the buffering effect of the track on the wheel-rail impact. In order to improve the cushioning performance of the concrete sleeper, reduce the impact force of the sleeper on the track bed, and increase the insulation, elastic polymers are used at home and abroad to solve the elastic problem of the concrete sleeper track. Rubber sleeper pads are elastic pads for use between or under the rails and concrete sleepers (in addition to soft soil rubber sleeper pads, laminated wood rails and plastic sleeper mats, etc.), rubber sleeper pads with their unique elasticity and good insulation Performance is widely used on railway lines.
Depending on the application, the concrete sleeper rubber pad is generally divided into two types: the upper (under the rail) pad and the under the pillow. Due to the long-term exposure to the atmosphere and under the pillow, the rubber sleeper pad is constantly subjected to the vibration and impact of the locomotive. Therefore, it is required to have good resistance to natural aging, heat, cold and good elasticity and cushioning and shock absorption. Also have better wear resistance, electrical insulation, compression and shear resistance. The most important thing in formula design is to consider the durability and cost of the material. Commonly used main materials are NR, SBR, BR, CR, EPDM, and the like.
2.3.3 Rubber shock absorber for bridge
In the bridge project, the support of the beam bridge bridge is required at both ends. The main function of the support is to reliably transfer all the loads on the bridge span (including dead load and live load) to the pier, and to withstand the horizontal displacement and corner deformation of the bridge span due to the load; It is adapted to the expansion and contraction caused by changes in temperature and humidity. The bridge support has two kinds of fixed and movable supports. The former is to fix the position of the bridge structure on the pier, so that the end of the bridge span can be freely rotated and cannot move; the latter not only enables the end support to rotate freely but also requires energy. Self-use movement, bearing the expansion and contraction caused by factors such as temperature, concrete shrinkage and load.
Foreign countries began to use rubber bearings in the late 1950s. By the 1960s, there were many countries in the world. Compared with other rigid supports, bridge rubber bearings not only have reliable working performance, but also have the advantages of simple structure, sufficient material source and easy processing and manufacturing. Because the rubber bearing can adapt to the deformation of the upper structure of the wide bridge, the curved bridge and the oblique bridge in all directions, it is widely used not only in small and medium-sized highway bridges, urban bridges and railway bridges, but also in large spans. The bridge is also used in large quantities. At present, three types of common plate type, PTFE plate type and box type rubber bearing are widely used in bridge engineering. The principle of selecting the rubber main material of the bridge rubber bearing is to select NR, CR, EPDM, IIR and chlorinated IIR according to the requirements of the environmental conditions on the premise of meeting the engineering performance requirements. The manufacturing process of the bridge rubber bearing is mostly molded. The production process is that the rubber is plasticized and then mixed with the compounding agent to form a rubber compound. After being parked, refining and calendering, the film is cut into a semi-finished film of a certain specification. After the semi-finished product is installed, it is vulcanized and vulcanized on the flat vulcanizing machine. The vulcanization process should pay attention to avoid uneven thickness and movement of the steel plate.
In the bridge rubber bearing, the lead rubber bearing is made by vertically filling the lead in the middle of the ordinary damping damping rubber bearing. The purpose of filling lead is to improve the energy absorption effect of the support and ensure proper damping of the support; the second is to increase the early stiffness of the support, which is beneficial to control the wind response and resist the micro-vibration of the foundation. The isolation system consisting of this rubber bearing has been widely used in large and medium-sized bridges abroad and has achieved good results. The high damping rubber bearing is made of high damping rubber material. The high damping rubber can be obtained by incorporating graphite into NR or synthetic rubber, and the damping properties of the material can be adjusted according to the amount of graphite incorporated. Like the lead-damped damping rubber bearing, the high-damping damping rubber bearing has both a vibration isolator and a damper, which can be used independently in the isolation system.
2.3.4 Rubber shock absorbers for construction projects
Buildings and structures resistant to strong earthquakes are an important issue in the field of construction engineering due to unavoidable natural disasters such as earthquakes. At the same time, the increasing traffic density leads to greater vibration transmission and noise pollution, and the vibration and noise isolation of civil engineering buildings has become an urgent problem to be solved.
Since 1966, the United States has taken the lead in the use of the Abani Building. Japan, France, New Zealand and China have also been positioned to fix the bridge span on the pier, allowing the bridge to be used in some important buildings. Support. At the end of the current structure, it is free to rotate and cannot move; the latter not only makes the base-isolated building with more than 80% of the buildings constructed with a laminated rubber isolation bearing system for earthquake resistance. Laminated rubber bearings are widely used not only in bridge construction projects, but also in the base of buildings to isolate seismic sources, seismic protection and seismic isolation of water structures. Practices have shown that these buildings with isolated rubber bearings can withstand strong earthquake tests, such as the large earthquake in Los Angeles in January 1994 and the Kobe earthquake in Japan in January 1995. The buildings in the system show excellent seismic performance, not only the building is not down, but the internal facilities are not destroyed. Therefore, in recent years, laminated isolation rubber bearings have been widely used at home and abroad. At present, hundreds of buildings in China have used laminated isolation rubber bearings. Many test results show that the seismic isolation of the rubber bearing can not only reduce the damage to the superstructure, but also the height limit and safety distance of the building can be appropriately relaxed. Since the outer surface of the isolated rubber bearing is a thick rubber layer, the steel plate and the adhesive rubber layer are not degraded by the influence of the environment, and the service life can reach 95a or more. The durability and flame resistance of rubber bearings have been proven by many tests and examples to fully meet the design life requirements of buildings.