How to improve the service life of conveyor idlers in Mining industry?

Now, the belt conveyors used in high-yield and high-efficiency mines not only use a large amount, but also have a larger and larger rated conveying capacity. In their technical solutions, most of them adopt the direction of increasing the belt speed, which affects the technical performance of the carrying idler.

At present, the belt speed of belt conveyors used in underground coal mines is generally controlled within 7.1m/s (under the condition that the belt width of the conveyor belt is 1800mm~2800mm, the maximum belt speed is 7.1m/s). When the belt speed increases, the speed of the conveyor idler also increases, resulting in an increase in the rotation resistance of the conveyor idler and a decrease in the service life of the idler. According to the DIN 22101-2002 standard, the speed of the conveyor idler should not exceed 600r/min, otherwise the rotation resistance of the conveyor idler will increase sharply and lead to a sharp decrease in service life. Therefore, when the speed of the idler exceeds 600r/min, a larger diameter conveyor idler should be used, which can reduce the speed of the idler.

The conveyor idler is an important accessory of the belt conveyor. Its weight accounts for about 1/3 of the weight of the whole machine. According to the field survey, the service life of the conveyor idlers in coal mines is generally 4000~6000h. The idlers used in the trough of mechanized fully mechanized mining and fully mechanized caving working faces account for about 30% to 50% of the number of damaged conveyor idlers after mining a working face, and the consumption is very large. Belt conveyor shutdown accidents in coal mines. In mining enterprises, 50% of failures are caused by conveyor idler failures. Therefore, it is very important to improve the manufacturing quality of the idler to reduce the energy consumption and operation efficiency of the belt conveyor.

Analysis of Factors Affecting idler Quality

The overall quality of the conveyor idler is determined by the sealing form, processing quality, bearing, bearing house grease, etc. in the structure of the conveyor idler. At present, the new oil-filled idlers used in European and American countries have small running resistance, the bearings are lubricated with thin oil, the belt speed of the conveyor idlers can reach 6~8m/s, and the service life can reach more than 30000h. Therefore, in order to improve the quality of conveyor idlers, it is very important to improve the overall quality of conveyor idlers by improving the sealing structure and lubrication method. At present, the conveyor idler generally adopts the structure of double labyrinth non-contact seal, large clearance KA series special bearing, and 3# lithium-based grease. The main link to improve the quality of the conveyor idler under this structure is the quality of manufacturing and processing and the quality of the main components. The processing technology and equipment accuracy of most conveyor idler manufacturers cannot guarantee the design requirements, resulting in large rotational resistance, high no-load energy consumption, and short service life of the conveyor idler. Therefore, in order to manufacture high-quality idlers, it is necessary to formulate corresponding technological processes, improve the processing technology of conveyor idlers, improve the accuracy of equipment, and manufacture corresponding technological equipment, in order to meet the high speed, high capacity and service life of the belt conveyor. It is necessary to increase the service life of the conveyor idler from 6000h to 20000h even more, so that the number of damaged conveyor idlers can be reduced by 2/3 every year, and the economic benefits are considerable.

The main causes of idler damage and countermeasures

1. Bearing quality

The service life of the conveyor idler mainly depends on the performance of the bearing and seal. If the bearing and seal performance of the conveyor idler are good, the service life of the idler will be greatly extended. The test results show that the friction resistance of the bearing accounts for about 1/4~1/8 of the rotation resistance of the idler. At present, the bearing models used by conveyor idlers are 6204KA, 6205KA, 6305KA, 6306KA and other rolling bearings. Bearing quality determines working life of idler. At present, quite a few manufacturers choose low-priced bearings (about 0.5~1 US dollars) and low-quality bearings to assemble conveyor idlers, and the dimensional accuracy, hardness and clearance of their inner and outer diameters cannot meet the requirements of technical standards. Therefore, it is necessary to purchase reliable bearing products from regular bearing manufacturers, such as: FAG, SKF, HRB (China), NSK, NTN, LYC (China).

2. Quality of bearing house

Poor machining accuracy of the inner hole of the bearing house leads to the circumferential movement of the bearing in the bearing house, which is one of the reasons for damage to the conveyor idler. Stamping bearing house is the most ideal bearing house manufacturing technology at present, because this process uses 3 sets of stamping dies to complete the production of bearing house, with high roundness and small error. The quality of the stamping die determines the quality of the bearing house, which also determines the life of the bearing, and is ultimately related to the service life of the conveyor idler. Therefore, as an conveyor idler manufacturer, it is necessary to follow up the assessment and do management review to ensure that it is a qualified purchase control list, and inspect the purchased bearing housings in strict accordance with the inspection procedures.

3. Welding of bearing house and conveyor idler tube body

The poor welding quality of the bearing house and the pipe body will cause axial disengagement or dust and water immersion into the conveyor idler bearing, resulting in damage to the conveyor idler. Therefore, the welding of the bearing house and the pipe body must be included in the special process and key process in the production process flow chart of the idler, and the operation instruction for this process is specially formulated, and argon or CO2 gas shielded welding should be selected for welding. In the work instruction, parameters such as welding voltage, welding current, gas flow rate, wire feeding speed, and pipe body selection line speed are clearly given. Welding equipment, welding wire materials and welding operators must be verified and calibrated. In summary, the welding of the bearing house and the pipe body should be controlled as a special process point, and the special process operation instruction should be compiled.

4. Grease selection

Improper selection of lubricating grease will cause damage to the bearing, which in turn will lead to damage to the idler. The MT821-2006 coal industry standard clearly requires the selection of 3# lithium-based grease, and all manufacturers must comply with it. Otherwise, the idler will be damaged after several hours of operation. What is emphasized here is: For idler bearings operating at -25°C, special types of low-temperature-resistant aviation grease must be selected.

5.Conveyor idler assembly

Conveyor Idler assembly not only requires the production of special process equipment, but also must be completed on the conveyor idler press machine. Only in this way can the axial specified assembly pressure of the bearing, seal assembly and retaining ring be controlled. It is also required that the constructor must pass the technical training and pass the assembly fitter to operate. In summary, conveyor idler assembly should be controlled as a key process point, and the key process operation instructions should be compiled.

6. Conclusion

The conveyor idler is the main consumable and vulnerable part of the belt conveyor. It has a large quantity and a wide range, and its quality directly affects the normal operation of the conveyor. Therefore, improving the quality of conveyor idlers has a great correlation effect on reducing energy consumption, saving costs, and increasing operational reliability. With the development of conveyors in the direction of long-distance, large-capacity, and high-speed, higher requirements are put forward for idlers in terms of sealing structure, processing quality, bearings, bearing housings, sealing components, and grease. Strict control of process, component quality, and scientific management of the whole process of grease selection can fundamentally improve the quality of conveyor idlers, thereby prolonging the maintenance cycle of the conveyor and ensuring that the belt conveyor can play its due role in high-yield and efficient mines.

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