What are the basic requirements for major overhauls of construction machinery?

Technical appraisal before major overhaul

At present, most major overhauls of engineering machines are aimed at restoring their performance. After a long period of operation, the aging of all major components and assemblies of the machine has reached its limit. Therefore, the entire machine should be disassembled, cleaned, inspected and repaired to bring its performance back to the standard at the time of factory delivery.

Before major overhauls of construction machinery, technical appraisals must be conducted, presided over by the technical director of the user unit, with the participation of management, maintenance and driving personnel. The performance of each component of the machine, such as pressure, flow, temperature and torque, should be tested before disassembly, and technical files and operation records should be reviewed. The consumption of fuel and lubricating oil should be thoroughly evaluated, and detailed records should be kept. Then compare the parameters related to major overhauls provided by the original manufacturer to determine whether a major overhaul is needed.

The main technical conditions for determining whether construction machinery needs major overhauls are:

The power performance indicators of the engine have dropped by more than 20%. The consumption of engine oil exceeds the rated value by more than double. The cylinder pressure of the engine fails to reach 60% of the specified index when measured at a temperature above 45℃.

⑵ The main parts of the transmission mechanism have worn to the limit, with phenomena such as wobbling, abnormal noise, impact and vibration.

⑶ When the steering mechanism wears out, the clearance becomes too large and the operation malfunctions. The gears and shafts of the transmission are severely worn, making gear shifting difficult or frequently skipping gears. The braking mechanism is severely worn, the braking performance declines or fails, and it cannot be adjusted.

⑷ Deformation or cracking of the main body of the frame; The working device is severely worn and the operation malfunctions. Unable to complete the normal workload or the operation accuracy does not meet the requirements; The walking mechanism is severely worn and cannot work properly.

2. Selection of major overhaul methods

When construction machinery is brought into the factory for major overhauls, each part should be disassembled, measured, inspected and appraised in groups. Wear tests should also be conducted on each component of each assembly and the cylinder liner, crankshaft, etc. of the engine to obtain the basis for whether to replace them. Generally, moving parts with significant wear need to be replaced. For some components that are not easy to replace, it is advisable to restore their original design dimensions by processes such as welding repair, thermal spraying, brush plating and chromium plating. If the quality is not guaranteed, the parts that need to be replaced should be purchased as spare parts from the original manufacturer or the designated cooperative manufacturer as required.

The maintenance methods are divided into: vehicle repair and assembly replacement repair. The vehicle repair method involves removing parts from the machine one by one during the repair process, followed by cleaning, inspection, classification, repair or replacement, and finally reassembly to restore its performance. The vehicle repair method takes up a relatively long time of downtime for repair.

The replacement assembly repair method refers to the repair process where, in addition to overhauling the original frame, all the damaged assemblies or accessories are removed and replaced with those that have been prepared (or repaired) in advance, and then the entire machine is assembled. This method can significantly reduce the downtime for repair, which is conducive to improving repair efficiency, lowering costs and ensuring maintenance quality. This is also the most popular maintenance method in the American maintenance system, which is of great significance for the user units to improve the integrity rate, utilization rate and production efficiency of mechanical equipment.

3. Precautions

Pay attention to eliminating potential safety hazards. During the major overhaul, it is necessary to pay attention to eliminating potential safety hazards, such as adjusting the clearance of the brake, replacing the worn clutch friction plates, making the driver's seat in the cab adjustable up and down conveniently, and eliminating some safety hazards that may cause injuries to drivers and maintenance personnel and machine malfunctions. Enhance the labor protection awareness of drivers. When conducting experiments on the dangers of machines, sufficient space and protective facilities should be left around (for example, the engine of an excavator is prone to disassembly and injury during the maximum load operation test).

(2) Technical performance tests after maintenance should be conducted. The repair quality of mechanical equipment is the main indicator for measuring the level of maintenance and is the key to whether the user units are satisfied and whether the repair units can survive and develop. The testing basis for the technical performance of mechanical equipment is the "Mechanical Management Specification", the "Mechanical Quality Standard", and the main technical parameters provided by the original manufacturer. After major overhauls, mechanical equipment should undergo technical performance tests and receive a major overhaul evaluation. For the mechanical equipment that has been repaired and left the factory, if any repair quality problems occur during correct use, the maintenance manufacturer should provide on-site service in a timely manner to solve the problems for users.

⑶ Provide good follow-up services after major overhauls. Establish maintenance files for major overhauled construction machinery, and the repair units should ensure within a certain period that the repaired construction machinery can reach the specified performance and good working condition. If a general malfunction occurs within this period and can be eliminated after adjustment, it shall be resolved by the user unit itself. In case of significant changes. When the machine parts are damaged, such as severe oil, water, gas or electricity leakage, and the main components must be disassembled for repair, the sending unit for repair should notify the repair unit to conduct a joint inspection and repair in a timely manner to reduce downtime and ensure that the machine after major repair can operate in as good a condition as possible.