Thread Content
The drum is the main rotating component of a belt conveyor, and its casting quality, welding quality, material chemical composition, and mechanical properties are all related to the overall quality of the drum. If the drum is damaged while in operation, it will prevent the conveyor from functioning properly; in severe cases, cracks in the drum can tear the conveyor belt, leading to serious accidents and economic losses. To ensure the external and internal quality of the drum, key controls can be implemented from the following aspects. I. Selection of materials for drum components: The material and thickness of the drum lining must meet **standard requirements** to ensure that the dimensions and mechanical properties are satisfactory. To produce high-quality products, it is necessary to lay a solid foundation from the start. The drum hubs (cast steel components) must be free of any casting defects after processing. At a certain power plant, the coal conveyor belt had to be shut down for maintenance and replacement due to cracks in the drum hubs, resulting in losses of hundreds of thousands of yuan per day. In actual production, our company strictly adheres to the requirements of the national standards JB/T5000.3, JB/T5000.4, and JB/T5000.5; moreover, each joint is subjected to ultrasonic testing, with methods and parameters that comply with the requirements specified in GB10595-2009. II. Requirements for drum processing: To ensure that the allowable value of static imbalance of the drum meets the precision grade G40 specified by national standards, it is necessary to improve the accuracy of its manufacturing during the processing stage. Strict control must be exercised over the processing techniques and workflow; a reasonable workflow and processing techniques are essential to ensure high-quality products. The following processes require strict control. (1) For rolling the tube sheet, a mandrel cushion must be used before rolling; the radius of this mandrel cushion should be close to the inner radius of the tube sheet. The length of the arc formed during rolling should be at least 1/8 of the circumference. At point R on the edge of the tube sheet (see Figure a), a 120° arc template should be used for inspection, and no gap larger than 0.3 mm is allowed. Measures should also be taken to prevent dents during welding. Spot weld when the rolled gap reaches 2-3 mm; the weld length is 10-15 mm, with a spacing of 300-400 mm. After the drum skin is rolled into a circular shape, the roundness error should not exceed 1 mm, in order to meet the requirements regarding the outer diameter of the drum and to ensure that the drum skin achieves the desired minimum wall thickness after processing. (II) Processing of the drum’s socket: The processing steps for manufacturing the socket have strict requirements (illustrated using a cast-welded socket as an example). During machining, the non-vent surface should be used as the reference plane; alignment is done by using the outer circle of the adapter. The vent surface, the outer circle, and the inner hole are first rough-machined, after which the non-vent surface is machined using the vent surface as the reference plane, and a welding groove is created on this surface. Since casting defects tend to occur at the risers of castings, controlling the manufacturing process can effectively reduce the quality issues caused by such defects. In the process of manufacturing drums, our company has changed from traditional manufacturing methods; areas on the drum that previously did not require processing are now processed as well, with a roughness level of Ra25. The overall processing of the receiving part reduces the likelihood of asymmetrical structural shapes, thereby lowering the static imbalance of the drum. (III) For the processing of the drum cylinder, in order to ensure the accuracy of the outer circle and the inner hole, the outer circle of the cylinder shell is first used as a radial alignment reference for boring the hub hole. To ensure that the hub holes at both ends are concentric, attention is paid to aligning the inner holes; a dial indicator is mounted on the boring bar, and alignment is carried out using the inner hole from the rough machining stage as a reference, with the accuracy required to be less than 0.5. Sufficient movement of the dial indicator is used to achieve axial alignment. When boring the hub hole at the other end, the same alignment procedures must be strictly followed. To turn the outer circumference of the cylinder, process equipment is used to align things around the center line of the two hub holes, ensuring that the installation center is concentric with the rotation center of the cylinder. After processing, check the minimum wall thickness and wall thickness variation of the drum. During measurement, in order to more accurately reflect the wall thickness variations across the entire drum, for cast-welded drum disks, four lines are drawn at intervals of 90° starting from a point 100 mm away from the circumferential seam, with a 50-mm offset from the longitudinal seam; at each of these lines, four points are measured evenly to determine the wall thickness variation. The minimum value obtained should be greater than the minimum allowable wall thickness, and the difference between values should be less than the specified limit for wall thickness variations. III. Welding Assurance for Drum Quality (1) Welding of the drum shell: CO2 gas shielded welding or submerged arc automatic welding can be used for this purpose. Depending on the diameter of the cylinder, the single-sided welding with double-sided formation method can be used (first weld one side, then use carbon arc gouging to clean the root on the opposite side before welding). (II) Welding of the drum shell and the flange (illustrated specifically using heavy-duty drums) Heavy-duty drums are welded using CO2 gas shielded welding or submerged arc automatic welding. Type A (see Figure b) uses CO2 gas shielded welding for the root pass, followed by submerged arc automatic welding. Type B (see Figure c) uses CO2 gas shielded welding in combination with submerged arc automatic welding: first, CO2 gas shielded welding is used to weld at the inner opening of the drum; after grinding the outer surface, CO2 gas shielded welding is used to seal the bottom; finally, submerged arc automatic welding is employed to give it its final shape. A proper welding process **improves the quality of the welds and the reliability of the welded areas. After simplification welding, the welds must be subjected to ultrasonic testing to ensure welding quality. IV. Matching of drum heat treatment processes: Throughout the entire part processing process (including heat treatment), close coordination between machining processes and heat treatment processes is an important guarantee for improving product quality. Therefore, more attention should be paid to pre-heat treatment and establishing the proper role of heat treatment processes within the machining process. In drum manufacturing, proper arrangement of heat treatment is very important. (1) Before rounding the cylinder shell, annealing is required to eliminate welding stresses. During annealing, the temperature rise rate should not exceed 150°C; the material is heated to 600–650°C and held there for 2 hours, after which it is cooled slowly to 150°C and then air-cooled. After taking such measures, both the structure and properties of the material are improved. (2) The cylinder should be annealed after welding to relieve welding stresses, thereby preventing cracks in the welds. In short, only by formulating a reasonable heat treatment process can the mechanical properties of parts be optimized, thereby enabling the production of high-quality conveyor machinery. In summary, during the production of drums, it is essential to implement strict control over all stages of the manufacturing process. Ensuring strict quality control at each stage and addressing issues as they arise during production is the fundamental way to reduce the on-site failure rate of belt conveyor drums.