The main drive of rapier loom-belt drive
(1) Classification Belt transmission can be divided into friction transmission and meshing transmission according to the transmission principle. Friction transmission is a transmission belt that is placed on the driving pulley and the driven pulley with a certain tension, and relies on the friction generated between the transmission belt and the pulley surface to transmit the friction. The meshing transmission relies on the meshing of the teeth on the surface of the synchronous belt and the tooth grooves on the synchronous pulley to transmit gear. Therefore, mesh transmission can achieve the same fixed transmission ratio as chain transmission or gear transmission. In addition, according to the differences in materials and cross-sectional shapes of the transmission belts, common transmission belts can be roughly classified as follows:
Characteristics of several commonly used belts: 1. General flat belts Generally, flat belts have greater tensile strength and good moisture resistance , the center moment is large, the price is cheap, but the transmission ratio is small and the efficiency is low. It can be transmitted in cross, semi-cross and guide wheel angles, and the transmission power can reach 500kW. The transmission ratio is generally less than 7, and the belt speed is 15~30m/s. 2. General V-shaped belt General V-shaped belt is a transmission belt with a trapezoidal cross-section. It is widely used in fabric machinery. See Figure 1-41. Its two sides are working surfaces, which are in contact with the pulley groove and have the function of wedges. Therefore, the friction force is about half greater than that of the flat belt, and the traction capacity is also improved. In addition, compared with flat belts, it also has the following advantages: it can reduce the wrapping angle on the pulley; it can increase the transmission ratio; it has small initial tension; it can reduce the outer size. However, the height of the V-shaped belt is much greater than the thickness of the flat belt, which is detrimental to its bending on the pulley and mechanical efficiency during transmission. Generally, the maximum transmission ratio of V-shaped belt in open transmission is i≤7; when equipped with a tensioner, it can reach i≤10. Generally, the agreed number of flexures of V-belts is 40 times/s; the transmission efficiency is about 0.85~0.95; the maximum transmission power can reach 700kW; V-belt transmission is a friction transmission, so the transmission ratio cannot be very accurate, and the slip rate is about 2 %the following. The belt speed is 20~30m/s, and the optimal belt speed is 20m/s. 3. Narrow V-shaped belt As shown in Figure 1-42, the narrow V-shaped belt is a new type of V-shaped belt developed on the basis of the general V-shaped belt. Compared with the general V-shaped belt, its width is reduced by about 1 /4, so the lateral stiffness is relatively large; the top surface of the belt is arched, so that the strong layer remains on a plane after being loaded and the force is uniform; in addition, the position of the strong layer is slightly higher than that of the general V-shaped belt, making the neutral The linear shift, coupled with the concave curves on both sides of the belt, increases the contact area between the belt and the groove surface of the pulley when it bends on the pulley, and increases the flexibility. Therefore, the ability of the narrow V-shaped belt to transmit power is greater than that of the ordinary V-shaped belt. The belt is much higher.
The length error of narrow V-shaped belts is about 1/2 to 1/3 smaller than that of ordinary V-shaped belts. Therefore, when multiple narrow V-shaped belts are used for transmission, the force on each transmission belt is relatively uniform, and the service life of the belt can be extended. Increased by about 2 times. The width and diameter of the narrow V-belt pulley can be reduced, and the cost is 20% to 40% lower than that of the general V-belt. It can completely replace the general V-belt. Narrow V-shaped belt is suitable for high-speed transmission, the belt speed can reach 20~25m/s, and the limit is 40~50m/s; it is also suitable for low-speed transmission. The transmission efficiency of narrow V-shaped belt is 90% to 97%. In summary, the narrow V-shaped belt has many advantages. Therefore, in recent years, it has been increasingly used in the transmission of general machinery and cloth machinery. It is estimated that there will be a trend to replace the general V-shaped belt in the future. 4. Combined V-shaped belt As shown in Figure 1-43, the combined V-shaped belt is an extension of the narrow V-shaped belt. Each V-shaped belt has the same length and good integrity; each belt is stressed evenly, has large lateral stiffness, and runs smoothly, eliminating the vibration of a single belt; it has high load-bearing capacity and long life; it is suitable for pulsating loads and impact vibrations Occasionally, it is very suitable for parallel shaft transmission vertical to the ground. The pulley size is required to be arranged with high accuracy. At present, there are only 2 to 5 joint groups. Belt speed 20~30m/s. 5. Multi-V belt As shown in Figure 1-44, the multi-V belt is also called a laminated V-belt. It is a new type of transmission belt. It is an annular belt with several longitudinal triangular wedges on the lower belly of the flat belt base. The wedge surface is the working surface. In recent years, it has been widely used. In cloth machinery, it is generally used in equipment that requires a large number of V-shaped belts and high impact force. Poly-V belt has the advantages of both flat belt and V-shaped belt. Compared with flat belt, it has the same flexibility, but it will not fall off from the pulley during operation. It can be applied to high speed, and the speed ratio can reach 1:10. Compared with ordinary V-shaped belts, poly-V belts have the following advantages:
(1) Large transmission capacity. Due to the good contact between the V-belt and the pulley, the load is evenly distributed between the working surfaces, so its load-bearing capacity is high. When the width of the poly-V belt is the same as that of the general V-belt, the transmission power of the poly-V belt can be increased by 30% to 50%. That is to say, when transmitting the same power, the diameter and width of the wheel can be reduced by adopting the poly-V belt, and the structure Compact and cost-reduced. (2) The phenomenon of uneven belt lengths when multiple belts are driven is eliminated. Therefore, in the event of instantaneous overload, the multi-V belt can still not slip and continue to transmit with high efficiency. Generally, the width of the V-shaped belt has manufacturing errors along the circumference of the belt, causing changes in the transmission ratio and causing vibration. However, the multi-ribbed belt does not have such shortcomings. It vibrates less, generates less heat, and operates smoothly. (3) Small elongation and long service life. The poly-V belt, like the synchronous belt, uses steel wire rope or polyester wire rope with small elongation, high tensile and fatigue resistance as the strong layer, and is covered with rubber or polyurethane. Especially polyurethane V-ribbed belts, due to their light specific gravity, high strength, good oil resistance and wear resistance, high friction coefficient, and better transmission performance. 6. Synchronous belt Synchronous belt transmission has begun to exist in the 1940s. Due to its various unique advantages, it is widely used in the modern machinery industry, and its varieties and specifications have also made new progress. In recent years, synchronous belt drive has been increasingly used in cloth machinery, such as worsted spinning machines, air-jet looms, rapier looms, and water-jet looms.It is used in looms, ribbon looms and other equipment. Synchronous belt transmission has the following characteristics: (1) The transmission is precise and there is no slipping. Synchronous belt transmission is a meshing transmission. During transmission, the teeth of the synchronous belt mesh with the tooth grooves of the pulley. The transmission is relatively accurate and there is no slippage. (2) Suitable for high-speed operation. Modern machines require high speed and can operate continuously for a long time. The synchronous belt can meet this requirement, and its maximum speed can reach 80m/s. (3) Easy maintenance. It is not metal-to-metal contact, so there is no need to add lubricant to keep the machine clean. At the same time, the synchronous belt will not stretch during use, so it does not need to be adjusted after the initial tension is given. It is suitable for use in locations that are inaccessible to people or inconvenient to operate. (4) Compact structure. The synchronous belt has high strength, light weight, thin belt thickness, good flexibility, suitable for high speeds and smaller pulley diameters, and has a compact transmission structure. (5) High transmission efficiency. Synchronous belt drive is not a friction drive and does not require a large initial tension, so it can reduce the stress on the bearing. The synchronous belt is light in weight, has good meshing performance, and generates little heat during operation, so the transmission efficiency is high, up to 98% to 99%. (6) Low impact. The synchronous belt does not have the phenomenon of the chain line jumping up and down during chain transmission, so the transmission is smooth and the impact is small, and it can be used for forward and reverse and precise transmission. (7) It can reduce the weight of the transmission mechanism. Use synchronous belt transmission, but use aluminum alloy or plastic pulleys. Therefore, when transmitting the same power, the use of synchronous belts can reduce the weight of the transmission mechanism. (8) Large speed ratio and wide load range. The transmission ratio of synchronous belt transmission can be as high as 12 to 20, and it can be used in transmissions ranging from a few watts to hundreds of kilowatts. (9) Low noise. Timing belt drives are less noisy than gear or chain drives. According to the tooth shape classification, synchronous belts can be divided into two categories: trapezoidal tooth synchronous belts and arc tooth synchronous belts. See Figure 1-45 and Figure 1-46. Compared with the trapezoidal tooth synchronous belt, the arc tooth synchronous belt has smaller tooth root stress concentration, longer life, and the transmission power is 1.2 to 2 times higher than the trapezoidal tooth.
7. Wide V-shaped belt As shown in Figure 1-47. The wide V-shaped belt has good flexibility, heat resistance and lateral pressure resistance. It is widely used in continuously variable transmission mechanisms. For example, the Hunter-type warp let-off mechanism commonly used in rapier looms adopts a wide V-shaped belt type continuously variable speed for its continuously variable speed part. Wide V-shaped belt has the following characteristics: (1) The width of the belt is large, and the ratio of bandwidth to belt height is generally 2 to 4. (2) The speed change range is larger, up to 3 to 6. The wider the belt, the smaller the wedge angle, the wider the speed change range; when using a wide band with a small wedge angle, the speed change range can reach 9 to 12. (3) The wedge angle of the belt is small, between 22° and 40°. (4) It has sufficient lateral stiffness to avoid “collapse” and torsion. (5) Have sufficient longitudinal flexibility. (6) The elongation of the belt is small. The wide V-shaped belt also relies on friction to transmit power, so there is also elastic sliding loss, and the transmission ratio cannot be very accurate. 8. Toothed V-shaped belt As shown in Figure 1-48. The load-bearing layer of the toothed V-belt is a rope core structure, and the inner surface is made of a V-shaped belt with evenly distributed transverse teeth. It has good heat dissipation, good adhesion to the wheel groove, and is a V-shaped belt with good flexibility.
(2) Belt tensioning and installation Appropriate tensioning of the transmission belt so that the transmission belt has a certain pre-tightening force is an important factor for the normal operation of the belt drive. If the pre-tightening force is insufficient, the belt will slip on the pulley, which will reduce the ability and efficiency of transmitting loads, wear the working surface of the belt, cause the small pulley to heat up rapidly, and sometimes cause the belt to vibrate. The synchronous belt will also skip teeth due to poor meshing, or even fall off the pulley. Excessive preload force will reduce the life of the belt, increase the load on the shaft and bearings, and intensify the heating and wear of the bearings. For belt drives, the distance between shafts should generally be adjustable to facilitate tensioning and replacement of the drive belt. Tensioning methods include: (1) Move a pulley to change the distance between shafts, usually by adjusting the position of the motor. (2) Use a position-adjustable tensioning wheel for adjustment. (3) Change the belt length. For flat belts with joints, the belt length is often cut off regularly to tighten the belt. Method of measuring tension: Apply a pressure F perpendicular to the belt at the midpoint of the length S between the tangent points of the belt and the two pulleys, causing it to produce deflection D, as shown in Figure 1-49, you can get the belt’s Tension T, the relationship between these factors is as follows:
(2) When multiple belts are driven, in order to balance the load on each belt, the matching tolerance of the belts should not be greater than the agreed-upon value. (3) The axes of each pulley should be parallel to each other, and the corresponding V-shaped groove symmetry planes of each pulley should coincide. (4) Before installing the belt into the wheel groove, the center moment should be adjusted first, and it should not be forced into it. (5) The center distance should be adjusted so that the belt tension is appropriate, and the required initial tension can be controlled according to the above method.
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