Causes and mechanical analysis of belt deviation of belt conveyor

Belt conveyor is the main equipment of conveying system, and its safe and stable operation directly affects the supply of raw materials. The deviation of the belt  is the most common fault of the belt conveyor , and its timely and accurate treatment is the guarantee of its safe and stable operation. There are many phenomena and causes of deviation, and different adjustment methods should be adopted according to different phenomena and causes of deviation, in order to effectively solve the problem. This paper is based on many years of field practice, from the user's point of view, using the mechanics principle to analyze and explain the causes of such failures and treatment methods.

1. The verticality error between the installation position of the carring idlerand the center line of the conveyor is large, resulting in the belt running to a deviation at the carring section . When the belt runs forward, it gives the roller a forward traction force Fq, which is decomposed into a component force Fz that makes the roller rotate and a lateral component force Fc that makes the roller axial movement. Since the roller fixed by the idler frame cannot move axially, it will inevitably produce a reaction force Fy to the belt, which makes the blet move to the other side, resulting in deviation.

After making clear about the force condition of deviation of carrying idler after installation , it is not difficult to understand the reasons for the belt deviation, the adjustment method is also clear,The first method is to process long holes on both sides of the idler set for adjustment .The specific method is that which side the belt is offset, and the side of the idler should move forward in the direction of the belt, or the other side should move back . If the belt runs off in the upward direction, the lower position of the idler  should move to the left, and the upper position of the idler should move to the right.

The second method is to install the aligning idlers, aligning idlers have a variety of types, such as intermediate shaft type, four-link type, vertical roller type, etc. The principle is to block or idler rotation in the horizontal plane direction to block or generate transverse thrust to make the belt automatically centripetal to achieve the purpose of adjusting the deviation of the belt, and its stress situation is the same as that of the carrying idler . Generally, this method is more reasonable when the total length of the belt conveyor is short or when the belt conveyor is running in both directions, because the short belt conveyor is more likely to run off and is not easy to adjust. This method at the long belt conveyor is better not to be used , because the use of aligning idler will have a certain impact on the service life of the belt.

2. The axis of the head driving pulleyor tail returningpulley is not perpendicular to the center line of the conveyor, which cause the belt to run off at the head drum or tail reversing drum. When the pulley is deviating, the tightness of the belt on both sides of the pulley is inconsistent, and the traction force Fq received along the width direction is inconsistent, which becomes an increasing or decreasing trend, which will make the belt attach a moving force Fy in the decreasing direction, resulting in the belt running away from the loose side, that is, the so-called "running loose but not running tight".

The adjustment method is as follows: for the head pulley, if the belt runs off to the right side of the pulley, the right pillow block should move forward.If the belt runs off to the left side of the roller, the left pillow block should move forward, and the corresponding left pillow block can also be moved back or the right pillow block is moved back. The adjustment method of the tail pulley is exactly the opposite of the head pulley. After repeated adjustments until the belt is adjusted to the ideal position. It is best to install the idler accurately before adjusting the drive or returning pulley

Third, the mismachining tolerence of the outer surface of the pulley, adhesive material or the uneven wear cause the diameter to be different, and the belt will run off to the side with the larger diameter. That is the so-called "run big not run small". Its force condition: the tractive force Fq of the belt forms a moving component force Fy towards the large diameter side, in the action of component force Fy, the belt will produce deviation. For this situation, the solution is to clean up the sticky material on surface of the drum,  the lagging surface with mismachining tolrence and uneven wear must be replaced and re-processed rubber lagging.

Fourth, the transfer point at the material dropping position is not straight to cause the belt deviation. the transfer point of the material at the material dropping position on the belt deviation has a very large impact, especially two conveyors projection at the horizontal ground has been vertical, impact will be much larger. Usually the relative height of the two belts above and below at the transfer point should be considered. The lower the relative height, the greater the horizontal velocity component of the material, the greater the lateral impact Fc on the lower belt, and the material is also difficult to center. The material on the cross section of the belt is deflected, and the horizontal component of the impact force Fc Fy eventually causes the belt to run off. If the material goes to the right, the belt goes to the left, and vice versa.

For the deviation in this case, the relative height of the two conveyors should be increased as much as possible during the design process. The form and size of the upper and lower funnels and guide chutes of belt conveyors with space restrictions should be carefully considered. Generally, the width of the guide chutes should be about three-fifths of the width of the belt. In order to reduce or avoid the deviation of the belt, the baffle plate can be added to block the material and change the direction and position of the material.

Fifth. The problems of the belt itself. such as the use of the belt for a long time, aging deformation, edge wear, or the center of the remade joint is not straight after the belt is damaged, which will make the tension on the two sides of the belt inconsistent and lead to deviation. In this case, the whole length of the belt will run to one side, and the maximum running out is at the wrong joint. The only way to deal with it is to re-make the rubber joint with the wrong center, and replace the aging deformation of the belt.

Sixth, the tension device of conveyor can not makes enouth tension force to the belt. the belt does not deviate without load or a small amount of load , when the load is slightly large there will be deviation phenomenon. The tension device is an effective device to ensure that the belt always maintains enough tension force. If the tension force is not enough, the stability of the belt is very poor, the greater the impact of external interference, and the phenomenon of slipping will occur in serious cases. For belt conveyors using weight tension devices, counterweights can be added to solve the problem, but too much should not be added, so as not to make the belt bear unnecessary excessive tension and reduce the service life of the belt. For belt conveyors using spiral or hydraulic tension, the tension stroke can be adjusted to increase the tension force. However, sometimes the tension stroke is not enough and the belt is permanently deformed, at which time a section of the belt can be cut off and re-bonded.

Seventh, for the belt conveyor with design of a concave , such as the radius of curvature of the concave section is too small, if there is no material on the belt when starting, the belt will spring up at the concave section, in the case of strong wind weather will also blow the belt off, therefore, it is best to add a pressure belt wheel at the concave section of the belt conveyor to avoid the belt spring or be blown off by the wind.