1. Accident Overview
The drag chain belt of the quay bridge trolley with the container terminal number QC01 at Guangzhou Nansha Port deviated, causing severe tearing, wear, and deformation of the belt. The compression on the side of the belt caused deformation and arching of the cable compression code (see Figure 1 (a)). After on-site inspection, it was determined that the accident was caused by the belt falling out of groove on the guide plate (see Figure 1 (b)) and scraping with the side plate of the tensioning bracket.
(a) Belt deviation damage (b)The belt is in the groove on the guide plate
Figure 1 Damage to the drag chain belt of the quay bridge trolley
2. Cause analysis
2.1 Is there a quality issue with the drag chain belt
The quality issue of the drag chain belt may lead to deviation accidents, such as uneven internal tension of the belt causing uneven tension on both sides, leading to belt deviation. In fact, as a flexible component, the internal tension of the belt cannot be absolutely balanced, and the phenomenon of deviation cannot be avoided. However, as long as it is controlled within a certain range, it does not affect the normal operation of the equipment. The drag chain belt of the QC01 shore bridge trolley bears tension through an aluminum alloy plate lining, which ensures better internal tension balance compared to ordinary non-metallic belts. Therefore, it is determined that the deviation accident is not caused by the quality problem of the drag chain belt itself.
2.2 Are there any defects in the drag chain belt conveyor system
The alignment between the belt traction point and the belt bracket, the straightness of the belt bracket, the height of the belt groove on the belt guide plate, and the reliability of the belt tensioning device are all factors that need to be considered to determine the cause of the deviation accident.
The difference in alignment between the belt traction point and the belt bracket may cause the belt to deviate during operation. Due to the fact that the traction point of the drag chain belt is located on the trolley and rear auxiliary trolley, the lateral deviation of the trolley and rear auxiliary trolley during operation may cause the belt traction point to be misaligned with the belt bracket. The trolley track of QC01 shore bridge is a welded track with poor straightness, and the trolley is prone to lateral deviation during operation, which is an important reason for the deviation of the drag chain belt.
The large straightness deviation of the belt bracket may also cause the belt to deviate during operation. The QC01 shore bridge is produced by Zhenhua Port Machinery, with guaranteed installation quality and strict inspection. Generally, the belt will not deviate due to straightness issues with the belt bracket.
The height of the belt groove on the belt guide plate determines whether the belt is easily dislodged in case of deviation. The height of the belt groove on the belt guide plate of the QC01 shore bridge trolley is too small, which can easily cause the drag chain belt to deviate.
The reliability of the belt tensioning device determines whether the belt can maintain tension when the tension changes. During the inspection, it was found that the reliability of the belt tensioning device of the QC01 shore bridge trolley is not high. Under static conditions, the tension spring should have extended and pulled the belt guide back to maintain tension, but in reality, the tension spring is still in a compressed state under static conditions. The vibration generated during the operation of the car (especially when passing through the hinge points of the front and rear axles) causes the traction head to shake, causing the belt to jump and instantly relax. Due to the inability of the tensioning device to tension the belt in a timely manner, coupled with the belt being dislocated under the lateral force transmitted by the traction head, the tension on both sides of the belt is unbalanced, leading to more and more deviation during continuous operation, resulting in scraping and grinding between the belt and the side plate of the tensioning bracket. It can be seen that the poor reliability of the belt tensioning device is the main reason for the deviation of the drag chain belt.
3 Solutions
In order to prevent the occurrence of a deviation accident of the drag chain belt from happening again, the drag chain system should be rectified from the following aspects:
(1) Before the renovation, the upper and lower surfaces of the belt were smooth (see Figure 2), making it prone to deviation and slotting during operation; After the renovation, the drag chain belt will be reinforced with ribs (see Figure 3) to ensure straightness during operation.
Figure 2: Smooth upper and lower surfaces of the belt before renovation
Figure 3: Adding reinforcing ribs to the drag chain belt after renovation
(2) Before the renovation, the surface of the guide plate was smooth and the belt was prone to slotting; After the transformation, the guide plate is equipped with grooves to cooperate with the belt reinforcement ribs to run on the guide plate and prevent the belt from falling off the groove on the guide plate.
(3) Before the transformation, the supporting roller was cylindrical, and the protruding part on the edge ensured the straight running of the belt; After the transformation, the roller is equipped with grooves (see Figure 4) to cooperate with the belt reinforcement ribs to run on the roller and prevent belt deviation.
Figure 4: After modification, the groove of the idler belt
4 Implementation effect
After the renovation of the trolley drag chain belt conveyor system, the quay bridge did not experience any deviation accidents of the drag chain belt during operation. Practice has proven that the solution is practical and effective.
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2023-05-09