Slippage is a comprehensive sliding caused by overload, which can be avoided by using the centering distance of the mediation, increasing the tensioning device, and reducing the load. Although slipping can make the transmission fail, it also protects the other parts of the belt drive from damage.
1 . Elastic sliding
The transmission belt is an elastic body, which will be elastically deformed after being pulled. The elastic deformation is different because the tension between the tight side and the loose side is different. As shown in Figure 7-12, when the tight side is wound around the driving wheel at point a, the tensile force is F 1 , and the linear velocity v of the belt is equal to the peripheral speed v 1 of the driving wheel. In the driving wheel, the belt's pulling force is reduced from F 1 to F 2 during the movement from point a to b, and its elastic elongation is also reduced from δ 1 to δ 2 , which indicates that the belt is bypassing the pulley. During the process, the belt is contracted rearward with respect to the wheel (δ 1 - δ 2 ), and a partial relative sliding occurs between the belt and the pulley wheel surface, resulting in a belt speed gradually smaller than the circumferential speed of the driving wheel. Similarly, in the driven wheel, when the belt moves from point c to point d, the pulling force is gradually increased, the belt is gradually elongated, and the relative sliding along the wheel surface is generated, so that the speed v of the belt is gradually larger than the peripheral speed of the driven wheel. v 2 . This sliding between the belt and the pulley due to the elastic deformation of the belt is called elastic sliding of the belt.
The result of the elastic sliding is:
1) The transmission ratio of the belt is unstable;
2) Reduced transmission efficiency;
3) causing wear of the belt and temperature rise of the belt, reducing the life of the belt.
The elastic sliding of the belt is caused by the difference of the pulling force of the belt and the elastic deformation of the belt, and the elastic deformation is related to the elastic modulus of the belt. The belt material with a large elastic modulus can be used to reduce the elastic sliding, but because of the friction type belt transmission It is through the tension difference of the elastic belt to transmit the load, so the elastic sliding is an inherent characteristic of the belt transmission during normal operation, and it is inevitable that it cannot be completely eliminated.
2 . Slip
Under normal conditions, the elastic sliding of the belt does not occur over the entire contact arc. The contact arc can be divided into two parts: a relative sliding (sliding arc) and a non-relative sliding (static arc). The central angles corresponding to the two arcs are called sliding angle and static angle. The static arc is always located at the beginning of the belt winding the main and driven wheels, and the sliding arc is located on the portion of the contact arc that leaves the main and driven wheels. When the belt does not transmit a load, the slip angle is zero. The elastic sliding only occurs on the sliding arc of the belt. As the load increases, the sliding angle gradually increases, and the static angle gradually decreases. When the sliding angle is increased to the wrap angle of the pulley, the limit state is reached and the effective pulling force of the belt drive reaches the maximum (critical) value. If the working load continues to increase, a significant relative slip will occur between the belt and the pulley, i.e., slippage will occur. Since the wrap angle on the big wheel is always larger than the wrap angle on the small wheel, the slip always occurs first on the small reel.