1 Accident overview
The drag chain belt of the quay bridge trolley numbered QC01 at the container terminal of Guangzhou Nansha Port deviated, causing serious edge tearing, wear and deformation of the belt, and the extrusion of the belt side caused the deformation and arching of the cable pressing code (see Figure 1 (a)). According to the on-site inspection, it was determined that the accident was caused by the belt slotting on the guide plate (see Figure 1 (b)) and scraping with the side plate of the tensioning bracket.
2 Cause analysis
2.1 Whether the drag chain belt has quality problems
The quality problem of the drag chain belt may lead to a deviation accident. For example, the uneven tension inside the belt causes the imbalance of tension on both sides, leading to the deviation of the belt. In fact, as a flexible part, the internal tension of the belt cannot be absolutely balanced, and the deviation phenomenon cannot be avoided, but as long as it is controlled within a certain range, it will not affect the normal operation of the equipment. The drag chain belt of QC01 quayside trolley bears the tension through the lining of aluminum alloy plate, which can more ensure the internal tension balance than the ordinary non-metal belt. Therefore, it is determined that the deviation accident is not caused by the quality problem of the drag chain belt itself.
2.2 Whether the drag chain belt conveying system has defects
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 tensioner are all factors to be considered in determining the cause of the deviation accident.
The alignment difference between the belt traction point and the belt bracket may cause the belt to deviate during operation. Since the traction point of the drag chain belt is located in the trolley and the rear auxiliary trolley, the lateral deviation of the trolley and the rear auxiliary trolley during operation may cause the belt traction point to be misaligned with the belt bracket. The trolley track of QC01 quayside bridge is a welded track with poor straightness. The trolley is prone to lateral deviation during operation, which is an important reason for the drag chain belt deviation.
The large straightness deviation of the belt bracket may also cause the belt to run away during operation. QC01 quay bridge is produced by Zhenhua Port Machinery Co., Ltd., with guaranteed installation quality and strict inspection. Generally, the belt deviation will not be caused by the straightness of the belt bracket.
The height of the belt groove on the belt guide plate determines whether the belt is easy to fall out of the groove in case of deviation. The height of the belt groove on the belt guide plate of QC01 quayside bridge trolley is too small, which is easy to cause the drag chain belt to deviate.
The reliability of the belt tensioner determines whether the belt can maintain tension when the tension changes. During the inspection, it was found that the belt tensioner of QC01 quay bridge trolley was not reliable. In the static state, the tension spring should have extended and pulled the belt guide plate backward to keep the belt tensioned, but in fact, the tension spring is still in the compression state in the static state. The vibration generated when the trolley is running (especially when passing the front and rear axle hinge points) causes the traction head to shake, causing the belt to jump and relax instantaneously. Due to the failure of the tensioning device to tension the belt in time, and the belt slotting under the action of the lateral force transmitted by the traction head, the tension on both sides of the belt is unbalanced, which leads to the belt and the side plate of the tensioning bracket being scraped. It can be seen that the poor reliability of the belt tensioner is the main reason for the deviation of the drag chain belt.
3 Solutions
In order to prevent the drag chain belt deviation accident from happening again, the drag chain system shall be rectified from the following aspects:
(1) The upper and lower surfaces of the belt are smooth before the transformation (see Figure 2), and it is easy to run off and out of groove during operation; After the transformation, the drag chain belt is added with stiffeners (see Figure 3) to ensure the straightness in operation.
(2) Before the transformation, the surface of the guide plate is smooth, and the belt is easy to fall off the groove; After the transformation, the guide plate is provided with grooves, so as to cooperate with the belt stiffener to run on the guide plate and prevent the belt from slotting on the guide plate.
(3) Before the transformation, the idler is cylindrical, and the belt runs in a straight line by the protruding part of the edge; After the transformation, the idler has grooves (see Figure 4), so as to cooperate with the belt stiffener to run on the idler and prevent the belt from running.
4 Implementation effect
After the modification of the trolley drag chain belt conveying system, the quay bridge did not have a drag chain belt deviation accident during its operation. Practice has proved that the solution is practical and effective.
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2023-02-17