According to the drawing specifications, the clearance between the hole on the web and the hub is 0.106 mm, but the actual fit clearance measures 1.3 mm. This clearly indicates that the hole on the web is oversized, and the roller is not concentric with the shaft. During operation, the hub and the web move relative to each other in the circumferential direction, causing the connecting bolts to experience significant shear stress over time. Initially, the bolts loosen and retract. As the retraction continues, some bolts eventually fail due to shearing. Once all the bolts are cut, the drum shaft becomes disengaged, leading to damage of the drum and a complete shutdown of the belt conveyor system.
To address this issue, two treatment methods were implemented. The first method involves aligning the roller shaft on a lathe to ensure it is concentric. It also aims to achieve the required clearance between the plate hole and the hub as specified in the drawing. To prevent bolt loosening, two positioning pins are installed at 120-degree intervals between the web and the hub. These pins serve two purposes: they ensure proper alignment during assembly and restrict any relative movement between the web and the hub during operation. Additionally, three positioning keys are welded onto the web plate, and corresponding keyways are milled into the hub. When assembling, these keys are matched with the keyways to maintain consistent clearance and prevent any relative motion between the hub and the web. Furthermore, the original M24 coupling bolts were upgraded to M30 bolts to increase their strength and durability.
The second method involves aligning the gap between the web and the hub on a lathe, then welding them together as a single unit to eliminate any relative movement. To avoid scrapping the entire drum, the drum shaft can be pressed out and reassembled easily. The roller shaft was modified by removing the shoulder on both ends, allowing for easier removal and installation. Since the hub is welded to the web, axial re-synchronization is no longer possible. Therefore, one end of the hub is first welded, followed by the installation of the shaft, and then the other end of the hub is welded. This approach helps reduce assembly difficulties and ensures better alignment of the key and keyway.
Although both methods involve multiple processing steps, the second method presents challenges in assembly, particularly in aligning the keys and keyways. However, after evaluating the economic benefits, the improved drums were successfully installed in 18 centralized transportation lanes of the Mi Village Mine and 18041 transportation lanes. The results were excellent, with no issues reported. After the improvement, a single drive roller can last for at least one year or longer. This means that two rollers can be saved annually, and each roller saves approximately 1.14 million yuan, resulting in a total saving of 2.14 million yuan per year. This calculation does not include additional costs such as downtime, labor, and material expenses during replacement. With a total of 12 belt conveyors in the mine, only one drum needs to be rebuilt each year, saving about 28.18 million yuan annually.
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