Application and development of rubber damping mate

Application and development of rubber damping materials and products for rail transit

Abstract: This paper summarizes the material technology and product application and development of rubber damping products for rail transit

key words: Rail Transit vibration damping rubber products rubber

rubber materials have the following characteristics [1]:

(1) rubber has good damping characteristics, the relative lag value in the elastic range can reach 10 ~ 65%, and the ratio of dynamic and static modulus is about 1.5

(2) the elastic deformation of rubber is much larger than that of metal (up to more than 10000 times), and the elastic modulus is much smaller than that of metal (1/700 to 1/4000)

(3) the sound velocity of rubber is 40 ~ 200m/s, but that of steel is 5000m/s

therefore, it has good shock absorption, sound insulation and cushioning performance [2]. In order to effectively reduce the wheel rail force, improve the running performance of the system, and reduce the system vibration and noise problems of locomotives, vehicles and lines caused by high-speed and heavy load, modern rail transit uses a large number of rubber elastic elements for traction, driving, connection, support, etc., so as to meet the higher requirements of comfort, stability and speed [3]

1. Rubber materials

there are many kinds of rubber used for vibration reduction, and the ones with large amount include: natural rubber (NR), styrene butadiene rubber (SBR), CIS polybutadiene rubber (BR), nitrile rubber (NBR), neoprene (CR), butyl rubber (IR), ethylene propylene rubber (EPDM), etc. Usually, according to different application environments and use requirements, different rubber materials are selected or several rubbers are blended and some modification methods are adopted to improve one or more properties of rubber materials

1.1 blending technology

nr is the most used variety in the field of rubber damping, and many blending studies are based on it. For example, yoshiharu et al. [4] made damping rubber by blending NR and Br. After vulcanization at 150 ℃ for 30min, it was found that the material has good attenuation performance; They also studied the blending of natural rubber and neoprene to make vibration damping rubber. The vulcanization accelerator only promotes the vulcanization of natural rubber rather than the vulcanization of neoprene, so that the vibration damping characteristics of vibration damping rubber are reflected by the neoprene components in the material [5]; Nishiue Takeshi et al. [6] shock absorbers made of natural rubber, cis-1,4-polybutadiene rubber containing unsaturated bonds, metal salts containing OH group organic acids with carbon atoms greater than 4, and some other additives have good durability. The compression set of 22 hours at 70 ℃ and 148 hours at 40 ℃ are 17.0 and 11.7% respectively; In addition to NR, there are also many examples of blending research based on Cr, SBR, EPDM, etc. in addition, the blending research of other materials includes: Toshiaki et al. [7,8] blended rubber material prepared by using the mixture of unvulcanized isoprene styrene block copolymer and vulcanizable brominated p-methyl styrene isobutylene copolymer in the proportion of 80:20 to 25:75. When applied to the damping rubber formula, the material loss factor tan δ Greater than 0.5, and the loss factor Tan is in the range of 30 ℃ to 20 ℃ δ The change of is less than 0.5, so that the material not only has good vibration damping performance, but also has good vibration damping stability. At the same time, the material also has good oxidation resistance and odor oxidation resistance; Masashi et al. [9] the damping rubber material made of brominated vinyl copolymer rubber (BR content 0.2 ~ 5%) and NR and isobutylene rubber has good heat aging resistance, tensile fatigue performance and ozone cracking performance. After 1000 hours of treatment at 90 ℃, the tensile strength remains 62% and the compression set remains 39%; Wangxiaorog et al. [10] used poly (aromatic olefin co maleimide) copolymer with maleated alkyl olefin and alkyl diamine to form polyolefin grafted poly (aromatic olefin co maleimide) copolymer under fully dry conditions. Mixing this material with rubber can prepare high damping materials; Kentaro et al. [11, 12] the insulating rubber material for vibration damping formed by aromatic vinyl monomer and butadiene copolymer has good characteristics of preventing vibration and noise; At the same time, this material also has good flexural fatigue properties; Okada et al. [13] used the rubber blend made of unsaturated copolymer formed by unsaturated ethylene, aromatic olefins and non conjugated olefins in a certain proportion, which makes the vibration damping rubber have good performance in mechanical properties, heat resistance, aging resistance, vibration damping performance, vibration performance disappearance and flex fatigue resistance

1.2 nano modification technology

using a small amount of montmorillonite and carbon black to reinforce natural rubber can improve the comprehensive properties of the material. Table 1 reflects the impact of 10 parts of montmorillonite replacing 10 parts of carbon black on the properties of natural rubber. It can be seen from the table that the hardness of the material decreases, the tensile strength, tensile strength and elongation at break are significantly improved, and the properties of water resistance, oil resistance, heat and oxygen aging resistance, ozone aging resistance and so on are significantly improved. For rubber shock absorbers used in rail transit in the open air, montmorillonite nanocomposite rubber technology shows obvious advantages. Table 1 Effect of montmorillonite on the properties of natural rubber

1.3 carbon black (white carbon black) in situ grafting rubber technology

carbon black and white carbon black are the main reinforcing fillers in vibration damping rubber, but the self polymerization between carbon black and white carbon black particles is large, which is difficult to disperse in the rubber matrix, and because they are strong polar inorganic particles, the interaction between them and non-polar organic substances such as natural rubber is weak, which affects their application effect

the surface of carbon black contains carboxyl, hydroxyl and other functional groups, and the surface of white carbon black also has a large number of hydroxyl functional groups. These highly active groups can be used to improve the effect of carbon black and white carbon black on rubber

carbon black (white carbon black) in-situ grafting rubber technology uses a small molecular coupling agent with amphiphilic chemical activity to make it graft with the surface of carbon black (white carbon black) and rubber macromolecules at the same time in the process of rubber mixing, so that part of the chemical bond force between carbon black (white carbon black) and rubber can be achieved, which can greatly strengthen the interfacial force between carbon black and rubber, and increase the destructive effect of rubber on carbon black (white carbon black) agglomerates, So that the dispersion level is also greatly improved. This can not only significantly improve the constant tensile stress, tensile strength, tear strength and other properties of the vibration damping material, but also significantly reduce the amount of high structural carbon black and improve the structure of the interface. Due to the high chemical interaction strength of the interface, the fatigue heat generation of the material is significantly reduced, the fatigue failure process is postponed, and the bearing performance and service life of elastomer structural materials and products are improved. In addition, it can improve the resistance of rubber to thermal oxygen, ozone and light aging (see Figure 1)

Figure 1 Schematic diagram of in-situ graft modification mechanism

2 Rubber damping products

the way of controlling vibration in rail transit is the same as that in other fields [15]:1) reduce the excitation force of vibration source; 2) Separate the vibration from the excitation source (vibration isolation); 3) Ease the vibration of the vibrating body. Rubber damping is mainly used in the latter two aspects

rubber shock absorber has many advantages [1]:1) it can meet the requirements of stiffness in all directions by designing the structure and adjusting the rubber performance; 2) It has both attenuation and energy absorption capabilities, with good vibration reduction effect and easy to cross the resonance zone; 3) The elastic modulus is much smaller than that of metal, which can produce large elastic deformation; 4) There is no sliding part, so there is no wear and easy maintenance; 5) Light weight, easy installation and disassembly

of course, rubber shock absorbers also have some disadvantages: 1) high temperature and low temperature performance is not as good as metal; Oil resistance is not as good as metal; 2) For direct sunlight, it is necessary to cover it with film; 3) The elasticity decreases when it is used for large loads for a long time

2.1 application and development of vibration damping rubber products for rolling stock

rubber shock absorbers for rolling stock are mainly used on bogies, which can be divided into primary suspension device, secondary suspension device, traction suspension device, traction buffer device, etc. according to the installation position [16]

2.1.1 vibration damping rubber products for primary suspension

1) V-shaped spring

V-shaped rubber spring is one of the representative products of primary suspension rubber shock absorber. Compared with metal suspension, it can effectively reduce wear, isolate noise, provide the required vertical, horizontal and vertical stiffness, control horizontal and vertical swing, and provide appropriate traction. Foreign companies such as Dunlop and phonex have mature technologies. Because the V-shaped spring bears circumferential shear and vertical compression deformation, the creep resistance of rubber can become the main symbol to measure the technical level of the product. Zhuzhou Shidai New Material Technology Co., Ltd. conducted a special research on improving the creep resistance of products [17, 18]. The laboratory test results show that the newly developed V-shaped rubber spring has better creep resistance than similar foreign products

Figure 2 V-spring

Table 2 Comparison of static pressure creep of V-spring

2) conical spring

compared with V-spring, the main characteristics of conical spring are as follows: ① cylindrical bushing structure is adopted, and different slot holes can be designed according to the three-dimensional stiffness requirements; ② According to the compression and shear cone theory of rubber spring, adopting the equal stress layer design method and the selected elastic rubber is more conducive to reducing the creep of products; ③ It can provide maximum traction, balance wheel load, and control longitudinal and transverse swing. Therefore, at present, conical springs are mostly used to replace v-springs on newly designed urban rail Metro bogies at home and abroad. The key technology is also the creep resistance, that is, the creep during the service life cannot exceed 20% of the sagging displacement of the product working load. The cone-shaped spring produced by Shidai Xincai company has been tested and calculated by German ContiTech company. The 10-year creep value is less than 5mm, which is only 12% of the working load sagging displacement (see Figure 4)

Figure 3 cone-shaped spring Figure 4 cone-shaped spring 10-year creep value

3) rolling ring rubber spring

rolling ring rubber spring has strong nonlinear characteristics, which can provide different longitudinal and transverse stiffness values required for dynamic performance, It can meet the requirements of vibration reduction and positioning. In the process of vehicle operation, the rubber spring deforms horizontally and vertically, absorbing part of the energy of vehicle vibration. This characteristic is very beneficial to absorbing vehicle high-frequency vibration and reducing noise. The vertical bearing capacity of rolling ring rubber spring is 10 ~ 200kn, and the vertical deflection can reach 60mm, even 132mm. Under the action of lateral load, when the load is equal to 30% - 60% of the maximum vertical load, the lateral displacement can be about 4mm [19,20], and its longitudinal stiffness is about 3 ~ 6 times of the vertical stiffness, while the longitudinal stiffness of other steel springs is close to the rigidity, and its bogie has better curve passing capacity

rolling ring rubber spring was first used on DRRs (doublerubberrollingspring) bogie designed and manufactured by Talbot factory in Germany. At present, DRRs bogie is widely used in freight cars in Germany, Switzerland, Norway, Austria, Denmark, Finland and other countries in Europe. It has the characteristics of small wheel rail effect and good wheel flange wear. Domestic Shidai new material and Southwest Jiaotong University have jointly developed such products, but they have not been popularized and applied

4) liquid composite rubber spring

liquid composite rubber spring shock absorber (referred to as liquid composite spring for short), also known as hydraulic shock absorber, seals fluid with rubber elastomer (usually unfrozen fluid, such as the mixture of ethylene glycol and propylene glycol), and uses the hydraulic support of fluid and rubber to buffer together, which is also a nonlinear shock absorber

Figure 6 metal rubber liquid composite spring

in 1979, the liquid composite rubber spring was first used for vibration damping of Audi car engine, and then it was rapidly promoted, and the cylinder hydraulic engine base and electronic control hydraulic engine base were developed. The technology is increasingly