Slipping is one of the common failures of belt conveyors. Once slipping occurs, it is easy to cause material scattering, blockage of feed tube, belt wear and tear, belt breakage and other abnormal phenomena, affecting the normal operation of the belt machine. In this article, we analyze the 9 major causes of slippage and attach the solution measures.

The impact of belt slippage on the belt machine

When the belt is in normal operation, its speed should be the same as the linear speed of the drive pulley surface rotation, and the belt speed should not be lower than 95% of the linear speed of the drive pulley surface. However, in actual operation, due to a variety of reasons, the belt and the drive pulley speed is not synchronized, or drive pulley rotation and the belt does not turn, this phenomenon is known as slippage

After the belt has slipped, it will cause the material to flow back and scatter, and in serious cases, it may cause the belt to wear and tear, burn the motor or even break the belt and other abnormal situations, affecting the safe and stable operation of the belt machine.

Belt machine slippage causes and preventive measures 

1. Insufficient belt tensioning force

If the belt does not have enough tensioning force, between the active pulley and the belt will not produce enough friction driving force, and cannot traction belt and load movement. Belt machine tensioning device usually includes spiral tensioning, hydraulic tensioning, heavy hammer tensioning and car type tensioning several structures. Spiral or hydraulic tensioning device stroke is not enough or improperly adjusted, hammer tensioning and car tensioning device weight is not enough, the mechanism card will cause the belt machine tensioning force is not enough, causing slippage.

Solution measures. 

(1) the use of spiral or hydraulic tensioning structure of the belt machine can be adjusted by tensioning stroke to increase the tensioning force, but sometimes the tensioning stroke has not enough, the belt has a permanent deformation, then the belt can be cut off a section of re-vulcanization.

2) Belt machines with heavy hammer tensioning and carriage tensioning structures can be handled by increasing the weight of the counterweight, or by eliminating the jamming of the mechanism. It should be noted that when increasing the configuration of the tensioning device, add to the belt does not slip can be added, should not add too much, so as not to make the belt withstand unnecessary excessive tensioning force and reduce service life.

2. Severe wear of the drive pulley cover

The drive pulley of the belt machine is generally covered with rubber or cast rubber treatment, the rubber surface will also increase the herringbone or diamond-shaped groove to improve the coefficient of friction, increasing friction. After a long period of operation, the rubber surface of the drive pulley and its grooves can become severely worn, resulting in a lower friction coefficient and reduced friction on the drive pulley surface, causing the belt to slip.

Solution: after this situation, should be taken to re-covering or replacement of the drum method, in the daily inspection, should pay attention to the drive pulley cover rubber check, so as to avoid its wear too large cannot be found in time, resulting in belt slippage affect normal operation.

3. Water, oil, ice and frost on the non-working surface of the belt

Due to natural environmental changes, site ground washing, equipment maintenance and other reasons, in the belt non-working surface adhered to the water, oil, ice, frost and other adhesion with a certain lubricating effect, the belt machine will run in the drive roller surface accumulation, resulting in friction between the roller and the belt significantly reduced, causing slippage.

Solution: In this case, the first thing to do is to determine the source of adhesion and cut off the source. If the source cannot be cut off, some rosin can be scattered on the drum, but be careful not to add by hand, the application of the blower equipment blown into, to avoid personal accidents.

4. Belt machine overload

Due to improper operation or heavy load shutdown, the belt machine carries excessive load in operation, or start the belt machine with load, resulting in overload operation and causing belt slippage.

Solution: In operation, the belt machine current and electronic belt scale should be monitored to control the amount of material to avoid overload operation.

Try to avoid heavy load stopping, so that the belt machine does not exceed its rated load when starting with a heavy load. Belt machine due to other faults after heavy load stop, can be manually cleaned to reduce the starting load.

5. Blockage of the head drop tube

Belt machine falling material tube blockage is not found in time, will cause the head and non-working surface of a large amount of material accumulation, pressure dead belt, causing slippage.

Solution: To prevent this from happening, the duty officer should pay attention to the change of the material on the belt in the belt machine operation, and increase the frequency of checking the material pipe of the head when it becomes sticky, and clean the sticky material of the falling material pipe in time to avoid the occurrence of blockage, even if it cannot be avoided, the amount of blockage should be controlled as far as possible.

6. The conveyor belt is partially scraped and stuck

When a part of the conveyor belt is strongly obstructed, it will cause the belt machine to slip. This situation generally occurs in the belt machine head, tail and tensioning device, for example, the belt machine head, tail tribal material tube card has a foreign body, tail redirection roller does not turn, etc..

Solution: In the operation should strengthen the monitoring of the belt machine current, abnormal changes in the current should immediately stop for inspection, identify the causes and remove obstacles before starting again.

7. Slip speed measuring device failure

The belt machine is generally set up with a slipping speed measuring device, when slipping occurs, it will issue a fault signal and stop the belt machine running.

Slipping speed measuring device is mainly composed of two parts: speed measuring wheel and control box, speed measuring wheel directly in contact with the belt, and driven by the belt to rotate. When there is sticky material on the speed measuring wheel or poor contact with the belt, the device will send a slip signal to stop the belt machine by mistake. In actual operation this situation is more frequent, the control box in the electrical circuit failure will also occasionally send a slip signal.

Solution: In the event of a slip fault in the belt machine and a stoppage, the first thing to do is to check at the site to determine whether the belt machine has slipped. If the slip signal is mistakenly sent by the speed measuring device, it should be checked and dealt with. The general method of handling is to remove the sticky material on the speed measuring wheel, adjust the speed measuring wheel position and exclude the electrical circuit failure.

8. The brake does not open when starting

Belt machine in the start sometimes also because the brake cannot open and skid stop, the reason is that the belt machine drive device by the brake cannot rotate, and at this time the motor circuit has been connected, the site inspection will find that the motor humming, and the belt and its drive device are not action.

9. The angle or friction coefficient between the active pulley and the belt is too small<

Usually the angle between the active pulley and the belt should be no less than 120°, if it is too small, it is easy to cause the belt machine to slip. 

Solution: If the wrap angle between the active pulley and the belt is low and the position of the tensioning pulley is still not effectively increased by adjusting the tensioning pulley, the design may need to be modified. Therefore, these factors should be carefully considered in the preliminary design to ensure the design quality of the belt conveyor. If the problem is only found during assembly and commissioning, it will be very passive to modify the design again. 

In addition, if the coefficient of friction between the main pulley and the belt is too small, it will also cause the belt to slip.

Solution: Carefully observe whether the surface of the active pulley of the conveyor is too smooth, or else use a knurled structure or inlay a layer of rubber before testing. Slipping is one of the common failures of belt machines. If we can standardize the operation, check carefully and maintain carefully, we can control the occurrence of slipping to a large extent. Even after the fault occurs, we can make accurate judgement and deal with it through the above methods, thus ensuring the safe and stable operation of the belt machine system.