Development and prospect of rubber synchronous belt

The Synchronous Belt is a new type of transmission belt developed by combining the advantages of belt transmission, chain transmission and gear transmission. Since the synchronous belt is driven by meshing the tooth surface with the pulley, there is no slippage between the belt and the pulley during the transmission process, and synchronous transmission is presented. Compared with the V-belt (V-belt), the synchronous belt is light and thin, with high strength, accurate transmission ratio, high transmission efficiency, large transmission power range and high transmission speed. Compared with chain and gear transmission, synchronous belt transmission has stable transmission, small impact, no lubrication, no pollution, and low noise. Due to the many advantages of synchronous belt drive, it has developed very rapidly. It has been widely used in textile machinery, automobile, tobacco machinery, food machinery, light industry, chemical industry, computer and general machinery.

1. Synchronous belt rubber
Early Synchronous Belts were made of cast polyurethane rubber, which has the advantages of general liquid rubber and does not require equipment such as rubber mixing and calendering. The process is simple and easy to form. The centrifugal casting method can produce light conveyor belts with precision and complex shapes. . However, due to the poor heat resistance and water resistance of polyurethane glue, it becomes sticky at about 80cI=, it is easy to hydrolyze in a humid environment, and the strength drops seriously, and because the Timing Belt produced by the casting method cannot be placed on the tooth bread cloth, although the polyurethane itself is durable Abrasive, but still inferior to neoprene straps covered in abrasion-resistant nylon. Therefore, polyurethane belts are only used in low-speed and light-load transmissions of office machinery, home appliances, projectors, etc., and cannot be used in automobiles and general industrial transmissions. Following polyurethane rubber, neoprene is mainly used in the manufacture of synchronous belts, which has excellent tensile properties and dynamic fatigue properties, and also has excellent weathering resistance, oil resistance, flame retardancy and outstanding adhesive properties. However, the disadvantages of chloroprene rubber are poor storage stability and poor process performance, easy to scorch and roll sticking, and poor heat resistance is the biggest weakness as a material for making synchronous belts. The operating temperature range of chloroprene rubber synchronous belts is -30cI=~ 120cI=. Modern mechanical transmission is developing in the direction of miniaturization, light weight, and high efficiency. In particular, automobile engines have higher requirements for speed, power, and heat resistance. Neoprene rubber can hardly meet the new requirements when its performance is maximized.
The synchronous belt made of hydrogenated nitrile rubber (HNBR) developed in the mid-1970s can basically meet the requirements of modern mechanical transmission. Compared with chloroprene rubber, hydrogenated nitrile rubber has excellent high temperature resistance (175°C) and low temperature resistance (-40°C), excellent physical and mechanical properties and high elasticity, ozone resistance, flex cracking resistance, Oil resistance, wear resistance, and good processing performance similar to nitrile rubber. Therefore, rubber for synchronous belts is gradually developing towards hydrogenated nitrile rubber. For the timing belt used in special occasions, different rubber varieties are selected according to the requirements of the environmental conditions of use, such as chlorosulfonated polyethylene rubber, chlorohydrin rubber, ethylene propylene rubber, polyurea elastomer or its combination.

2. Skeleton material for synchronous belt
For the polyurethane timing belts produced in the early years, the skeleton material is generally copper-plated steel wire, because this kind of skeleton material commonly used in tires and rubber hoses has high strength and sufficient supply. However, the synchronous belt made of steel wire as the skeleton material has a large elongation after use, and the pitch of the synchronous belt is elongated, resulting in poor meshing with the pulley, resulting in tooth jumping, and the belt is quickly damaged. Analyzing the reason, it may be that the initial modulus of the steel wire is small, and the tensile deformation is relatively large during operation. Other disadvantages of the steel wire are that it is not well bonded to the rubber and is easy to be pulled out; the steel wire is easy to rust in a humid environment and is easy to debond from the rubber; the unevenness and twist of the steel wire also often cause the tape to deform or deviate. These factors have accelerated the damage of the synchronous belt. Since the skeleton material made of steel wire cannot meet the application requirements of the synchronous belt, a new skeleton material must be found. With the development of industrial technology, the improvement of drawing, twisting, post-processing and other processes in glass fiber manufacturing has produced glass fiber rope with good performance, which has high tensile strength, high modulus, and good heat resistance. , Good dimensional stability, small elongation, easier to bond with rubber than steel wire, etc. Compared with the steel wire synchronous belt, the glass fiber rope synchronous belt can work under any weather conditions and will not rust under wet conditions. In order to improve the flex resistance of glass fiber rope and the adhesive performance with rubber, glass fiber rope is impregnated with butadiene, styrene, butadiene pyridine terpolymer latex or a blend with neoprene latex J. Synchronous belts made of glass fiber ropes can basically meet the requirements of current automobiles and general industrial transmissions. But glass fiber rope also has many disadvantages, such as brittleness, intolerance to twists and turns, and poor stability to impact loads, which often lead to a reduction in the reliability of the synchronous belt. There have also been people who tried to make the tensile body material of the synchronous belt with polyester, carbon fiber cord, etc., but the effect was not good.
In recent years, aramid fiber cords have been used as the skeleton material of the synchronous belt. Compared with other commonly used skeleton materials, aramid fiber has the following advantages: the density is only 1/5 of steel wire and 1/2 of glass fiber; under the same weight, its strength is 8 times that of steel wire, 3 times that of glass fiber, and its modulus is It is about twice that of steel wire and glass fiber; under the same volume, the strength of aramid fiber is about 50% higher than that of steel wire and glass fiber, and its modulus is smaller than that of steel wire, but slightly higher than that of glass fiber. However, the elongation at break of aramid is higher than that of steel wire and slightly higher than that of glass fiber. The performance of aramid fiber is mainly determined by its high crystallization and high orientation macromolecular structure. All the indicators of tensile performance, bending performance and torsion performance of aramid fiber are higher than those of traditional synchronous belt skeleton materials. Centrifugal forces and vibrations during belt operation are particularly advantageous. The high modulus, low elongation and low creep of aramid endow the synchronous belt with good dimensional stability and no elongation during use. Aramid fiber is resistant to high temperature, the maximum operating temperature can reach 240°C, and its strength hardly decreases after 500 hours at 160°C, so it is a good material for making synchronous belts. Now people have used aramid 1414 as a skeleton material for synchronous belts.
In addition, Dow Chemical Company in the United States also uses synthetic fibers such as polyimide (P84) fibers and polybenzimidazole (PBI) fibers on timing belts, but due to price reasons, they have not yet been promoted. It is expected that the above-mentioned aramid fiber and these two fibers will become the main materials for the skeleton material of the synchronous belt in the future.
3. The wrapping layer of the synchronous belt
In order to protect the tooth rubber of the synchronous belt from wear and tear, a layer of wear-resistant nylon deformed gauze is covered on the tooth surface of the synchronous belt. The weft elongation of the fabric is required to be large (>130%), and the warp strength should be high, generally above 2.8 kN/5 em, to meet the needs of the production process. The cloth made of nylon raw silk for clothing is easily damaged during the operation of the synchronous belt. It must be woven with industrial nylon raw silk. It has high tensile strength, wear resistance and tear resistance. However, the heat resistance of nylon is poor, and it begins to deteriorate after 50 hours at 120°C, and its strength drops by 30% to 70% by 400 hours. Under the vulcanization condition of the synchronous belt at 180°C for 30 min, the general strength drops by about 15%, while the nylon cloth added with chlorine or spandex in order to increase the elongation drops by about 50% under this condition, which seriously affects the synchronous belt. service life. Polyester and aramid have good heat resistance, and the strength drops within 10% at 120°C for 400 h, which is suitable for the requirements of timing belts. Therefore, there is a tendency for polyester or aramid fabrics to replace nylon fabrics as tooth bread cloths.
In order to better protect the timing belt tooth rubber, the British patent provides a double-layer nylon tooth covering cloth, which is suitable for the timing belt of automobile engines. The outer layer of cloth plays the role of anti-wear, and the inner layer of cloth plays the role of anti-shear The middle rubber layer is the buffer layer. The U.S. patent provides another new type of fabric tooth wrap, that is, the warp yarn of the fabric is made of a crimped synthetic fiber, or a core yarn with elastic yarn (spandex) wrapped around it with a crimped synthetic fiber. The new type of yarn is formed; the weft yarn is composed of twisted yarns of synthetic staple fibers, especially twisted yarns of meta-aramid staple fibers. The surface has a lot of fluff, which is suitable for the manufacture of automobile synchronous belts and other synchronous belts with strict usage requirements. The tooth-wrapped cloth can improve the service life of the belt and effectively control the transmission noise.
4. Application of synchronous belt
Synchronous belt is a new type of conveyor belt introduced by Uniroyal Company of the United States in 1940. It is first applied to the synchronous transmission of sewing machines and bobbins, which eliminates the shortcomings of ordinary transmission. Due to the many advantages of synchronous belt transmission, by the 1970s, foreign synchronous belts had been greatly developed, and the scope of use had been expanded to various fields using V-belts, chains and gear transmissions. Synchronous belts are widely used in new textile machinery, automobiles, tobacco machinery, machine tools, food machinery, petrochemical machinery, printing and dyeing machinery, computers, medical machinery and other mechanical transmissions. For example, in textile machinery, there are rapier looms, air-jet looms, water-jet looms, drawing frames, worsted frames, roving frames, twisting machines, doffing machines, circular knitting machines, cord twisting machines, ribbons, etc. Synchronous belts are used in machines, wool spinning equipment, chemical fiber equipment and other machinery. Most of the existing foreign and new brands of automobile engines with a displacement below 3 000 ml use synchronous belt drive, which is almost 100% used in 13 countries, 80% used in Europe, and 40% used in the United States. Such as Vauxhall, Seat, Talbo in the UK, BMW, Opel, AudiNsu, Volkswa in Germany. gen, Fiat, Laneia, Sofim of Italy, Mitsu of 13 books. bishi, Nissan, Toyota, Daihatsu, Mazda, France's Cri. Models such as troen, Renault and Fo in the United States all use timing belts.
Even small diesel engines, pumps and air compressors are incorporating timing belts in new machinery. At present, the production volume of synchronous belts in advanced countries is close to that of V-belts, and the application fields are still expanding.
5. Production status of timing belt
At present, the famous foreign manufacturers of synchronous belts include: Italian Pirelli Company, German Berstof Company, Japanese Samsung Bando and Unita Company, American Uniroyal Company and British Denlop Gates Company, etc. In foreign countries, the production volume of synchronous belts in advanced countries is very large. According to information, the annual output of 13 synchronous belts is nearly 80,000, with sales of about 20.5 billion 13 yuan. The products have many specifications, high quality, and a high export rate.
my country began to produce polyurethane timing belts in the 1960s. However, due to the poor heat resistance and water resistance of the material, as well as the reasons for the process, design and use, the working life is stable, and it cannot fully meet the high speed and large speed of imported and domestic equipment. power transmission requirements. Since the 1980s, with the introduction of a large number of foreign technologies and equipment, as well as the needs of domestic mechanical design and manufacturing departments for the adoption of synchronous belts and technical transformation work, the demand for synchronous belts has become more and more urgent, and the consumption is increasing. Spend a lot of foreign exchange on imported timing belts. For this reason, my country began to introduce the neoprene synchronous belt production line of the Federal German Scholz Company in 1984.
my country's self-developed neoprene synchronous belt manufacturers mainly include: Jiangsu Zhongsheng Transmission Technology Co., Ltd., Ningbo Cixi Synchronous Belt Factory, Ningbo Chaochuan Synchronous Belt Co., Ltd., Hanzhong City Synchronous Belt Factory and Zibo Fengxiang Rubber Products Co., Ltd., etc. several.
The synchronous belt started relatively late in our country, but it has developed rapidly and has formed a production scale, but it faces many problems. Synchronous belts are energy-saving products with good economic and social benefits. In order to vigorously develop the synchronous belt industry in my country, on the one hand, we must do a good job in publicity and promotion to expand the application range of synchronous belts; on the other hand, we must further improve the quality of synchronous belts and replace imported products. product. High-quality synchronous belts require high-quality textile reinforcement materials. We should use high-performance fibers to develop and produce cords and wraps suitable for synchronous belts to promote the development of synchronous belts.