1. From the materials used in the transmission belt, rubber has developed from natural rubber to synthetic rubber, and further extended to special synthetic rubber CSM and HNBR: the skeleton materials have expanded from cotton fiber to rayon, polyester, nylon, glass fiber, steel wire and aramid fiber, as shown in Table 2. Products. In order to improve the durability of V-belts, cut V-belts have appeared since the 1960s, and their sides are not covered with cloth, so they have excellent bending fatigue resistance and have replaced most of the subcontracted V-belts.
On the other hand, after 1980s, V-shaped flat belts with flat belts and V-shaped belts developed rapidly. Because of its excellent performance and large increase in output, it has partially replaced cutting V-belt. Then in the United States, Japan and other countries, a wedge-shaped V-belt appeared. Because of its thin thickness, large contact area with pulleys and good bending performance, this belt can be used on small pulleys, thus making great contributions to miniaturization and energy saving of transmission devices.
In addition, the principle that the back of the transmission belt can also be driven is used, for example, in automobile fans, AC motors, power control systems, air conditioners and the like. The serpentine driving mode of a transmission belt has attracted attention from all walks of life, and its application scope is expanding day by day. The representative products of this multi-faceted, multi-directional and multi-machine transmission are hexagonal belt and round belt.
The latest product of transmission belt is toothed belt, also known as synchronous belt. It combines the advantages of gear, chain and belt transmission device, and has the characteristics of high transmission efficiency, accurate transmission ratio, low noise, energy saving and convenient maintenance. Although many patents appeared on its transmission principle as early as 1900, it didn't start industrialization until half a century later, and finally became the leading transmission product of precision machinery since the 1980s. In particular, high-precision microstrip made of saturated nitrile rubber and polyurethane elastomer has entered the high-tech field. The biggest difference between toothed belt and traditional transmission belt is synchronization and silence. Therefore, it is the most respected environmental protection product today. In recent years, after the teeth of toothed belt are changed from square teeth to round teeth, the transmission force is further increased and the development prospect is extremely broad.
Due to the different characteristics of different mechanical requirements, the prices of various transmission belts are quite different, so the transmission belts will develop in the direction of diversification of structure and materials in the future, and their uses and specifications will also be increasingly diversified. The ratio of V-belt, toothed belt and flat belt in transmission belt will generally change up and down within the range of 6: 3: 1. See Table 4 for the types of drive belts required by various industrial machinery and equipment.
(1) rubber and elastomer
V-belts were originally NR or NR/SBR mixtures. Nowadays, chloroprene rubber has been widely used for its excellent heat resistance, wear resistance, bending resistance and oil resistance. This trend will continue in the future until a new rubber variety with more balanced comprehensive physical properties is found.
When cutting V-belts and V-flat belts, CR reinforced by short fibers will expand, and the lateral compression and longitudinal bending of the belt will be realized through the directional reinforcement of short fibers in the transverse direction of the belt. There will be more HNBRV flat belts for transmission belts with strict requirements on heat resistance. CR was originally used in toothed belt, and it is still an ideal material, and will continue to be widely used in general industrial transmission in the future. For toothed belts that need heat resistance and durability, a large number of special heat-resistant and oil-resistant rubbers, such as CSM and HNBR, should be used. Because of its excellent performance, this kind of rubber is very expensive, which is several times higher than the existing products. However, with the technical progress of automobile industry and the deterioration of environment, especially HNBR will become the leading material of toothed belt in the future. Polyurethane elastomer is the most ideal material for small and miniature toothed belts. Especially in precision machinery, there is no other material to replace toothed belt. In the future, the varieties, specifications and uses will expand rapidly, and the development prospect is extremely broad. Flat belts used to be rubber. With the appearance of thin flat belt, polyurethane and nylon sheets have become the key development direction.
⑵ skeleton material
The skeleton material of the transmission belt has been improved, and the skeleton of the V-belt determines the strength and life of the belt. Cotton thread was used in the early strengthening layer, and then strong artificial silk thread was used. Due to the disadvantage of large elongation, polyester rope with high strength, small elongation, good heat resistance and bending resistance has been widely used in the world since 1970s. In 1980s, modified polyester rope with high elongation and low shrinkage appeared, which became the mainstream of V-shaped skeleton materials. For variable speed belts and V-belts for agricultural machinery that require high load transmission and impact resistance, some have begun to use aramid fibers. The reinforcing layer of toothed belt has been used for a long time to reduce its strength, and at the same time, it is suitable for high-speed rotary transmission because of its large specific gravity, and has been basically eliminated. Due to the expansion problem, polyester cord is rarely used in products requiring high dimensional accuracy. At present, it is considered that the best skeleton material is glass fiber, which can make the elongation of meshing transmission small and the linear expansion coefficient moderate, but it has not been widely used because of its shortcomings such as bending fatigue. In the future, aramid fiber with higher strength and better bending performance may partially replace glass fiber and squeeze into the ranks of the best skeleton materials for toothed belts. At present, a kind of twisted polyester toughened monofilament skeleton has appeared on the market. This skeleton material is gradually recognized by everyone because of its relatively low price, high strength, good flexibility and long service life.
(3) outsourcing protective cloth
Cotton canvas has always been the main protective cloth for V-belts, and it still remains in this state. For some parts that require good wear resistance and bending resistance, cotton blended canvas and even synthetic fiber canvas are also used. Outsourcing protective cloth will continue to maintain this trend in the future. In order to protect the teeth and core wires, the toothed belt mainly uses high-strength synthetic fibers, usually nylon canvas, and the future direction is to further refine it.