Several basic requirements for engineering machinery overhaul:
1. Technical appraisal before overhaul
At present, most of the overhauls of engineering machines are repairs to restore their performance. After the machine has been running for a long time, the aging of all major components and assemblies has reached the limit, so all the machines should be disassembled, cleaned, inspected and repaired. Make its performance meet the factory standards.
Before the overhaul of construction machinery, technical appraisal shall be carried out, which shall be presided over by the technical person in charge of the use unit, management, maintenance and driver's participation shall be carried out, and the pressure, flow, temperature and torque performance of the components before the disassembly shall be tested and reviewed. Data such as technical files and operating records, detailed assessment of fuel and lubricant consumption, and detailed records. It is then compared to the overhaul parameters provided by the original manufacturer to determine if overhaul is required.
The main technical conditions for determining whether a construction machine requires overhaul are:
(1) The engine power performance index drops by more than 20%; the engine oil consumption exceeds the fixed value by more than one time; the engine cylinder pressure does not reach 60% of the specified index when the temperature reaches 45 °C or more.
(2) The main parts of the transmission mechanism are worn to the limit, with yaw, abnormal noise, impact and jitter.
(3) After the steering mechanism wears, the clearance is too large, the operation is unsuccessful; the transmission gear and shaft are seriously worn, the shifting is difficult or the gear is frequently blocked; the brake mechanism is seriously worn, the braking performance is degraded or invalid, and it cannot be adjusted.
(4) The main body of the frame is deformed or cracked; the working device is seriously worn and the operation is unsuccessful; the normal workload cannot be completed, or the operation accuracy is not up to the requirement; the traveling mechanism is seriously worn and cannot work normally.
2. Choice of overhaul method
When the construction machinery enters the factory for overhaul, all parts should be disassembled, measured, inspected and identified, and the wear of each component of the assembly and the cylinder liner and crankshaft of the engine should be tested to obtain the basis for replacement. Generally, the moving parts with large wear need to be replaced; for some inconvenient replacement parts, it is recommended to restore the original design size by welding, thermal spraying, brush plating and chrome plating. If the quality is not guaranteed, the parts to be replaced shall be purchased as required by the original manufacturer or the designated cooperative manufacturer.
Maintenance methods are divided into: repair and replacement of the vehicle. In the vehicle repair method, the parts are sequentially removed from the machine during the repair process, washed, tested, sorted and repaired or replaced, and finally reassembled to achieve a recovery performance repair method. The downtime repair time taken by the vehicle repair method is longer.
To replace the assembly repair method, except to renovate the original frame during the repair process, simply remove the remaining damaged assemblies or accessories and replace them with pre-prepared (or repaired) assemblies or accessories. And then assembled into the repair method of the whole machine. This method can greatly reduce the repair time of downtime, which is beneficial to improve the repair efficiency, reduce the cost and ensure the quality of maintenance. This is also the most popular maintenance method in the US maintenance system, which is of great significance for the use of units to improve the mechanical equipment integrity, utilization and production efficiency.
3. Precautions
(1) Pay attention to the exclusion of safety hazards. During the overhaul, care should be taken to eliminate safety hazards such as adjusting the brake clearance, replacing the worn clutch friction plate and allowing the cab seat to be easily adjusted up and down, and eliminating some of the drivers and maintenance personnel who are likely to cause injury and machine malfunction. Security risks. Strengthen the driver's awareness of labor protection. When conducting experiments on machine hazards, there should be sufficient space and protective facilities around (for example, the excavator engine is prone to disintegration and injury when performing maximum load operation experiments).
(2) Technical performance test after maintenance. The quality of repair of mechanical equipment is the main indicator for measuring the level of maintenance, and it is the key to whether the use unit is satisfied and whether the repair unit can survive and develop. The technical test results of mechanical equipment are based on the "Mechanical Management Code", "Mechanical Quality Standards" and the main technical parameters provided by the original manufacturer. The mechanical equipment after the overhaul shall be tested for technical performance and given an overhaul evaluation. For the mechanical equipment that has been repaired, if the repair quality problem occurs during the correct use, the repairing manufacturer should promptly provide on-site service to solve the problem for the user.
(3) Do a tracking service after overhaul. The maintenance file of the overhaul engineering machinery shall be established, and the repairing unit shall ensure that the repaired construction machinery can reach the specified performance and good use state within a certain period of time. In the event of a general failure within this period, those who can be excluded after adjustment shall be resolved by the user. As a result of large changes. If the parts are damaged, serious oil leakage, water leakage, air leakage and leakage, etc., the main parts must be disassembled for repair, the repairing unit should notify the repairing unit to carry out inspections in a timely manner to reduce downtime and make the overhaul The machine can work as much as possible while in good condition.