Common knowledge of equipment shock absorption and isolation
2.1 Characteristics and advantages of rubber shock absorber
Rubber is characterized by both high elastic state and high viscosity state. The elasticity of rubber is generated by the change of the conformation of its curled molecules. The interaction between rubber molecules will hinder the movement of molecular chains, showing viscosity characteristics, so that the stress and strain are often in an unbalanced state. The long chain molecular structure of rubber and the weak secondary force between the molecules make the rubber material show unique viscoelastic properties, so it has good damping, sound insulation and buffering properties. Rubber parts are widely used in vibration isolation and shock absorption, because of their hysteresis, damping and reversible large deformation characteristics. 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 rubber, the more obvious the damping effect. To sum up, the rubber shock absorber made of rubber also has good damping effect. Advantages of rubber shock absorber:
(1) can freely determine the shape, by adjusting the rubber formula components to control the hardness, can meet the requirements of stiffness and strength in all directions;
(2) Large internal friction, good shock absorption effect, conducive to cross the resonance area, attenuation of high-frequency vibration and noise;
(3) The elastic modulus is much smaller than that of metal, which can produce large elastic deformation;
(4) no sliding part, easy maintenance;
(5) small quality, convenient installation and disassembly.
(6) Impact stiffness is higher than static stiffness and dynamic stiffness, which is conducive to impact deformation.
2.2 Main types of rubber shock absorbers are introduced
Rubber shock absorbers are roughly classified as follows according to their functions:
(1) narrow rubber shock absorbers supporting various devices;
(2) rubber buffer for the purpose of absorbing shock;
(3) Rubber springs used as mechanical actuating parts;
(4) dynamic shock absorber to eliminate vibration of specific vibration frequency;
(5) Rubber coupling is also included in the category of rubber shock absorber.
Rubber shock absorbers are narrowly classified by shape as follows:
(1) Compression type This type of rubber shock absorber is mainly used in the direction of compression. Its advantage is that the load bearing capacity is large, but the elastic coefficient of compression direction can not be selected too low.
(2) Shear type This type of rubber shock absorber is mainly used in shear direction. Its load bearing capacity is small, but has the advantage that the elastic coefficient can be selected very small.
(3) Compound is a rubber shock absorber used in the combination direction of compression and shear, with intermediate characteristics of compression type and shear type.
(4) Cylinder type This type of rubber shock absorber can be used for axial vertical, axial, twisting, prying and other directions of vibration reduction. Used for axial vertical and compression type rubber alkali vibrator is similar, its load bearing capacity is generally large, but the elastic coefficient can not be selected too small.
The rubber shock absorber applications according to their classification as follows:
(1) YLJ type rubber damper: YLJ-type rubber mounting is special for roller. According to its load and size can be divided into a variety of different models, respectively for different types of roller;
2) WJ‐type rubber mounting: WJ‐type rubber mounting are versatile rubber shock absorbers. Also known as "universal cushion", with 4 different diameters, different heights of cylindrical boss, upper and lower two cross configuration. It can withstand load in any direction and absorb vibration in any direction. The lateral pressure does not produce sliding. Therefore, there is no need to take measures to prevent the horizontal movement of the machine, saving huge foundation costs. This product is heat and oil resistant, easy to use;
(3) JP-type plate shaped rubber pad: JP-type plate shaped rubber pad. Jp-type plate shaped rubber pad. Its structure for the inside and outside of the metal plate (ring), rubber sandwiched in the middle, to mold production. Available in JP-1, JP-2 and JP-3 models. Used in radios, instruments and instrumentation to protect the whole apparatus from vibration and shock;
(4) J-G type is used for fans, air compressors, freezers, water pumps, precision instruments, meters, machine tools and equipment;
(5) 6JX type is used for ships, vehicles and other power machinery and electronic equipment with high requirements of random vibration and impact isolation;
(6) Type 6WN, type 31, type SH, type E and type EA are used for bulkhead, buffering, anti-impact and noise reduction of engine and ship main engines, machinery and instrument equipment;
(7) XL series, high elasticity rubber coupling, is the first national standard of high elasticity coupling (GB 2496 81) designed and developed from the viewpoints of serialization, standardization and universality, especially with high elasticity (low stiffness, high flexibility). , can reduce the natural vibration frequency of shafting, change the torsional vibration of shafting, so that the diesel engine does not appear dangerous resonance speed, has good damping characteristics, absorb part of the vibration energy; Can absorb and reduce the diesel engine output torque fluctuations; Improve the quality of the power transmission, make up for the shafting installation error;
(8) YXN, XN rubber torsional vibration damper is a new kind of damping element, can overcome the vehicle engine crankshaft torsional vibration of crankshaft system, gear impact, increase parts wear, noise, vibration, and even serious problems, such as crankshaft fracture when resonance. Rubber nozzle is widely used in ship machinery and equipment shock absorption and sound insulation. And viscoelastic damping material, which is a high polymer. With the change of temperature and frequency, its elastic modulus value and loss factor value have great changes. It is a new material for vibration isolation and noise reduction developed at home and abroad, widely used in aviation, aerospace, shipbuilding, automobile, railway, construction, textile and other industries.
2.3 Main application fields of rubber shock absorbers
2.3.1 Rubber shock absorber With the development of social economy, domestic and foreign automobile models are quite frequent, the automobile industry is facing a period of rapid change, the characteristics of development is to ensure driving safety, riding comfort, high-speed driving and luxury under the premise of further improve the service life of automobiles. Damping products are used to control the vibration and noise of the automobile and improve its handling stability. They are generally placed in the automobile engine frame, pressure rod device, suspension bushing, center bearing bracket, bump limiter and torsional vibration shock absorber and other parts to improve the safety and comfort of the automobile. Damping products can be divided into bracket, bushing, cushioning and damping four categories, the main requirements of shock absorption, heat resistance and good fatigue resistance. Automotive damping rubber products include engine bearings, suspension components, rubber spring, rubber air spring and collision rubber protective parts. In recent years, in order to improve the safety, comfort and maneuverability of automobiles, the variety and number of automobile damping rubber products are increasing, such as a car on the number of damping rubber products has reached 50 ~ 60 pieces. Rubber shock absorbers for engine and transmission operating systems are used to insulate the vibration of the source. Multi-lateral coupling and damping clutch are adopted in the damping part of transmission. The shock absorber used on the front and rear suspension device should not only bear the weight of the car body, but also make the car body not transfer the up and down vibration of the wheel, restrain the irregular movement of the unsprung mass, transfer power and braking force. The rubber buffer is one of the important shock absorbers of the car body. Its structure is a rubber layer sandwiched between two metal plates. The purpose of the buffer is achieved by the shear deformation of the rubber. Recently, the cylinder buffer filled with nitrogen and co-existing with shock absorber oil has been developed, which is characterized by improving the load capacity of the buffer (up to 20MPa), good shock absorption effect and prolonging its service life. NR and SBR are the main rubber materials used in automobile rubber shock absorbers. In order to improve the heat resistance of shock absorbing products, IR, IIR,CR,EPDM and so on have been used as the main material. Thermoplastic elastomers will also be used in some shock absorbers, such as body and chassis shock absorbers. For example, Zhejiang Haimen Rubber Factory has developed NR /CR and spring seat shock absorber for car chassis with good effect.
2.3.2 Rubber damping products for railway locomotive and railway sleeper cushion According to statistics, there are about 10,000 kinds of rubber materials and parts used in domestic railway and locomotive, and the consumption of rubber is about 10 kt/a. With the increase of the speed of railway locomotive, the dynamic effect of the line increases sharply, causing the line, the wheel and the locomotive walking part of the components produce intense wear, railway locomotive parts of the shock resistance requirements are more and more high, rubber shock absorber application is more and more popular, so the application of rubber products in the locomotive variety and number. Damping rubber products on railway locomotive mainly include central supporting rubber pile, axle box tie rod rubber spring body, side bearing rubber pile, motor suspension rubber pad, elastic wheel, elastic gear, rubber air spring, transmission device bow rubber block and rubber ball hinge, coupler rubber buffer, etc. The rubber shock absorber used in locomotive is mainly used to withstand compressive stress, shear stress and torsional moment, as well as to withstand the combined action of two or more stresses at the same time. With the rapid development of railway construction in our country, railway sleeper is gradually changed from sleeper to concrete sleeper. Although the service life of the sleeper is extended and the stability of the track frame structure is improved after the replacement, the elasticity of the track is decreased significantly, which causes the buffer of the track to the wheel-rail impact to become worse. In order to improve the cushioning performance of concrete sleeper, reduce the impact force of sleeper on the road bed and increase the insulation, elastic polymers are used at home and abroad to solve the elastic problem of concrete sleeper track. Rubber sleeper pad is used for rail and concrete sleeper between or under the elastic pad (in addition to soft soil rubber sleeper pad, laminated wood rail and plastic sleeper pad, etc.), rubber sleeper pad with its unique elasticity and good insulation properties and is widely used in railway lines. According to different uses, concrete sleeper rubber pad is generally divided into pillow (under the rail) pad and pillow pad 2 types. Rubber sleeper cushion due to long-term exposure in the atmosphere and placed under the pillow, constantly subjected to the shock and impact of the locomotive, so it requires good natural aging resistance, heat resistance, cold resistance and good elasticity and cushioning, shock absorption performance, in addition to better wear resistance, electrical insulation, compression and shear resistance. The most important thing in formula design is to consider the durability of materials and low cost. Commonly used main materials include NR, SBR,BR,CR, EPDM, etc.
2.3.3 Rubber shock absorbers for Bridges In bridge engineering, supports should be set at both ends of the span of beam Bridges. The main function of the support is to transfer all the load (including dead load and live load) on the bridge span structure to the pier reliably, and to bear the horizontal displacement and Angle deformation of the end of the bridge span structure due to the action of the load; The second is to adapt to changes in temperature and humidity caused by expansion and contraction. The bridge support has two kinds of fixed and movable support, the former is to fix the position of the bridge structure on the pier, can make the end of the bridge structure rotate freely and can not move; The latter not only enables the end fulcrum to rotate freely but also requires it to move for its own use, bearing the expansion and displacement caused by factors such as temperature, concrete shrinkage and load of the bridge span structure. Foreign countries began to use rubber bearings in the late 1950s, to the 1960s has been used in many countries in the world. Compared with other rigid supports, the bridge rubber bearing not only has reliable performance, but also has the advantages of simple structure, sufficient material source and easy processing and manufacturing. Because rubber bearing can adapt to the deformation of the superstructure of wide bridge, curved bridge and oblique bridge in all directions, it is not only widely used in small and medium span highway bridge, urban bridge and railway bridge, but also widely used in large span bridge. At present, three types of ordinary plate, PTFE plate and box rubber bearing are widely used in bridge engineering. The selection principle of rubber main material for bridge rubber bearing is that NR, CR, EPDM, IIR and chlorinated IIR are basically selected on the premise of meeting the engineering performance requirements and combined with the requirements of environmental conditions. The manufacturing process of bridge rubber bearing is multi-purpose molding. The production process is rubber after plasticizing and compound according to the formula to make compound, parking, back refining and calendering out of the film, cut into a certain specification of semi-finished film. Semi-finished product molding in the plate vulcanization machine pressure vulcanization, vulcanization process should pay attention to avoid the uneven thickness of the finished product and the movement of the steel plate. In the bridge rubber bearing, the lead rubber bearing is made by filling lead vertically in the middle of the ordinary damping rubber bearing. First, the purpose of filling lead is to improve the energy absorption effect of the support and ensure that the support has moderate damping; The other 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. As the leading product, the isolation system composed of this rubber bearing has been widely used in large and medium-sized Bridges abroad, and has achieved good results. High damping rubber bearing is made of high damping rubber material. High damping rubber can be obtained by adding graphite into NR or synthetic rubber. The damping characteristics of the material can be adjusted according to the amount of graphite. Like lead core damping rubber bearing, high damping rubber bearing has the functions of both isolator and damper, and can be used independently in isolation system.
2.3.4 Rubber Shock absorbers for Construction engineering Due to unavoidable natural disasters such as earthquakes, the construction of buildings and structures resistant to strong earthquakes is an important subject in the field of construction engineering. At the same time, the increasing traffic density leads to greater vibration transmission and noise pollution, and the isolation of vibration and noise in civil buildings has become an urgent problem to be solved. Since 1966, the United States took the lead in the use of insulation in Abani building, and Japan, France, New Zealand and our country successively are for the position of the fixed bridge span structure on the pier, which can make the bridge span use the isolation rubber bearing in some important buildings. Free rotation without movement at the end of the present structure; The latter not only makes the end of the foundation isolation building, more than 80% of the building using laminated rubber isolation bearing system. Laminated rubber bearing is not only widely used in bridge construction engineering, but also has been used in the base of the building, which is used to isolate the source, earthquake protection and the isolation of water buildings. These structures have been shown to withstand strong earthquakes, such as in Los Angeles, USA, in January 1994
In the Los Angeles earthquake and the Kobe earthquake in January 1995, the buildings with laminated rubber bearing system showed excellent anti-earthquake effect, not only the buildings did not fall down, but also the internal facilities were not damaged. Therefore, in recent years, laminated isolation rubber bearing is more widely used at home and abroad. At present, hundreds of buildings in our country have used laminated rubber bearing for earthquake isolation. Many test results show that the use of rubber bearing isolation engineering can not only reduce the damage to the superstructure, but also relax the height limit and safe distance of the building. Because the outer surface of the vibration isolation rubber bearing is a thick rubber layer, the steel plate and the adhesive rubber layer will not decline due to the influence of the environment, and its service life can reach more than 95a. The durability and fire resistance of rubber bearing have been proved by many tests and examples to meet the requirements of the design life of buildings. In addition, the isolation rubber bearing is also widely used in the isolation of buildings along roads, railways, subways and water structures. Niu Jinlong et al from Donghai Engineering Design Institute of the Navy studied the basic methods and principles of energy dissipation and shock absorption of the top floor with rubber bearings in building construction, theoretically analyzed the damping effect of this energy dissipation and shock absorption method, and demonstrated the good damping effect of this method in building construction through model tests and engineering examples. Its damping effect is generally in 10% ~ 40%, energy dissipation damping can not only be used for seismic fortification of old houses, but also can be used for shock absorption of new houses; Not only can be used for multi-layer, but also can be used for high-rise, especially the use of insulation layer shock absorption, can be used as one of the building of multiple lines of defense, and will not affect the use of the function of the house, is a more ideal shock absorption method. Zheng Wenbo et al. studied the development trend of the damping rubber bearing and its application in the damping of buildings and pointed out that the damping rubber bearing tends to be compatible with the setting of multiple types of damping bearings in the structure, the rubber selection develops to the combination of multiple rubber types, and the selection of adhesives emphasizes the particularity and pertinence. The product becomes a new type of laminated rubber structural parts, it and air spring composed of three dimensional system damping parts have better shock-proof effect.