1、 Technical appraisal
At present, most of the major overhauls of engineering machines are to restore their performance. After a long period of operation, the aging of main components and assemblies has reached the limit. Therefore, all the machines should be disassembled, cleaned, inspected and repaired to make their performance reach the standard at the time of delivery.
Before the overhaul of construction machinery, the technical appraisal shall be conducted, which shall be presided over by the technical director of the user unit and attended by the management, maintenance and driving personnel. The performance of each part of the machine such as pressure, flow, temperature and torque before disassembly shall be tested, the technical archives and operation records shall be reviewed, the consumption of fuel and lubricating oil shall be assessed in detail, and detailed records shall be made. Then compare with the relevant overhaul parameters provided by the original manufacturer to determine whether overhaul is required.
The main technical conditions for determining whether the construction machinery needs overhaul are:
(1) The engine power performance index decreases by more than 20%; the oil consumption exceeds more than twice the rated value; the engine cylinder pressure cannot reach 60% of the specified index when the temperature reaches more than 45 ℃.
(2) The wear of the main parts of the transmission mechanism reaches the limit, with phenomena such as deflection, abnormal sound, impact and shaking.
(3) The clearance of the steering mechanism is too large after wear, and the operation fails: the transmission gear and shaft are seriously worn, and it is difficult to shift or often skip the gear:
The braking mechanism is seriously worn, the braking performance is degraded or invalid, and cannot be adjusted.
(4) The main body of the frame is deformed or cracked; The working device is seriously worn and the operation fails: the normal workload cannot be completed, or the operation accuracy cannot meet the requirements: the traveling mechanism is seriously worn and cannot work normally.
2、 Selection of methods
During the overhaul of construction machinery in the factory, each part shall be disassembled, measured, inspected and identified in groups, and the wear of each component of each assembly and the cylinder liner and crankshaft of the engine shall be detected, so as to obtain the basis for replacement. Generally, the moving parts with large wear need to be replaced; For some parts that are inconvenient to be replaced, the original design size should be restored by welding repair, thermal spraying, brush plating and chromium plating. If the quality is not guaranteed, the parts to be replaced shall be purchased from the original manufacturer or the designated cooperative manufacturer as required.
The maintenance methods are divided into on-site repair and assembly replacement repair. On vehicle repair method is a repair method in which parts are removed from the machine in turn during the repair process, cleaned, tested, classified, repaired or replaced, and finally reassembled to restore performance. The on vehicle repair method takes up a long downtime for repair.
The assembly replacement excavator repair method is a repair method in which, in addition to renovating the original frame, all the damaged assemblies or accessories need to be removed, replaced with the assemblies or accessories prepared (or repaired) in advance, and then assembled into the whole machine.
This method can greatly reduce the repair time of shutdown, improve the repair efficiency, reduce the cost and ensure the maintenance quality. This is also the most popular maintenance method in the American maintenance system, which is of great significance for users to improve the intactness rate, utilization rate and production efficiency of mechanical equipment.
