Detection and use of old construction machinery to delay the aging of equipment

4. Adjustment and repair methods

Adjustment of the engine throttle

For instance, the diesel engine installed on a truck crane, after long-term use, sometimes shows a slow acceleration when operating the throttle on the vehicle, failing to reach the maximum speed and maximum power. At this point, it is necessary to inspect and adjust the entire transmission chain of the foot pedal on the vehicle. This job requires two people. One person gets on the vehicle and operates the accelerator pedal, while the other observes the movement of the speed control lever at the fuel injection pump. Although the operator in the cab of a crane that has been in use for many years has pushed the accelerator pedal to the limit position, in reality, the speed control lever of the diesel fuel injection pump sometimes still cannot reach the limit position. Because the speed control lever is located in a part of the entire machine that is not easily observable by the operator, its idle stroke is often overlooked. Therefore, it is necessary to observe it for a longer time and try it several times. The reasons for this situation are, first, the dimensional chain of the transmission system of the diesel engine throttle has changed, resulting in excessive accumulation of idle travel in the middle. The second reason is that some fasteners on the transmission devices, such as set screws, are loose. At this point, the throttle transmission dimension chain should be checked step by step. When the throttle is fully depressed on the vehicle, the speed control lever must also reach the limit. The clearance on the throttle transmission chain should be retained as required and tightened and adjusted according to the specific conditions of each piece of equipment.

(2) Repair of gear pumps

Gear pump wear mainly occurs on the inner surface of the pump casing, the tooth top and the tooth thickness. The repair method is: apply a layer of metal coating liquid to the worn area on the inner surface of the pump casing to restore its original size. For gears, electroplating can be applied to the tooth top and tooth thickness areas to restore the dimensions of the tooth thickness and tooth top. Bushings are generally replaced but not repaired. When replacing a new bushing, it is necessary to pay attention to its axial length and leave no space. Precise measurements can be made on several used gear pumps of the same model. Then, gears and pump bodies with relatively light wear can be selected for recombination and assembly, and tests can be conducted on the test bench.

(3) Repair of plunger pumps

The wear of a plunger pump mainly occurs on the surface of the plunger and the holes where the rotor fits the plunger. Repair method: Reconfigure the plunger according to the measured size of the worn plunger hole. The material, heat treatment process, outer diameter size and surface roughness of the new plunger must all meet the relevant technical requirements. Before assembly, the new plunger and mating holes can be ground. In addition, the plungers and rotor plunger holes with less wear can also be selected from several used plunger pumps of the same model for recombination and assembly. Generally speaking, the fit clearance between the old plunger and the hole should not exceed 35μm. When the wear reaches 45μm, it should be scrapped.

(4) Repair of the control valve

The new valve stem should be reconfigured according to the measured size of the worn valve stem hole. The material, heat treatment process, dimensions of each part and surface roughness of the new valve stem must all ensure compliance with relevant technical requirements. Before assembly, it is best to grind the new valve stem and the valve stem hole on the valve plate (it is best to turn a process mandshaft for grinding). If the conditions are not available, the new valve stem can also be ground. At the same time, the elastic force of the positioning spring of the control valve and each return spring in the pressure adjustment device should be tested to see if it meets the requirements. The repair method can also be determined based on the degree of wear of the valve stem holes on each type of valve plate. If there are multiple old valves of the same model, they can be inspected and adjusted among several. The repaired valve should be tested on a test bench. Alternatively, it can be placed flat, with kerosene filled in the two holes on top, and the speed of oil leakage measured with a stopwatch to determine the sealing degree of the valve.

(5) Repair of hydraulic cylinders

The causes of internal and external leakage in hydraulic cylinders: First, the surface of the piston rod (or plunger) is severely worn or has grooves pulled out. It can be repaired by electroplating or metal brush plating. The second issue is the wear on the inner surface of the guide sleeve. As the guide sleeve is inexpensive, it is usually replaced. The third issue is that the hydraulic cylinder body itself is severely worn or has deep grooves pulled out, or there are cavitation areas on the inner wall of the cylinder body. This can also be repaired by brush plating process. The fourth point is that the sealing gasket on the piston is worn out. At this time, it can be replaced. Internal leakage and external leakage can both cause the hydraulic cylinder to automatically retract. There are three inspection methods for the hydraulic cylinder installed on the vehicle: The first is to use a dial indicator. Attach the magnetic indicator base to the piston rod of the hydraulic cylinder, and press the pointer against the end face of the cylinder barrel. Observe the change value of the pointer before and after the engine is turned off for 15 minutes (including the following two methods), which is the retraction amount of the hydraulic cylinder. The second method is to stick a piece of paper on the extended piston rod with grease and measure the change in the distance from the upper end of the paper to the end of the hydraulic cylinder, which is also the retraction of the hydraulic cylinder. The third method is to lock a rubber plate that can be released and locked onto the piston rod, and the measurement method is the same as that of using a paper sheet. The above-mentioned detection method is also a way to determine whether the hydraulic cylinder is leaking internally and to what extent. Based on the measured retraction of the hydraulic cylinder, the wear degree of the seal on the piston and the service life of the equipment can be accurately calculated. If the service life is very short, it can be determined that the seal was damaged due to improper assembly methods. This is very useful for correcting incorrect assembly methods and judging the degree of internal leakage in hydraulic cylinders.

(6) Clean the hydraulic system and filter the hydraulic oil

Hydraulic oil contamination is the main factor causing malfunctions in construction machinery, accounting for approximately 80%. Therefore, regular inspections of hydraulic oil must be carried out. When conditions are poor, a 120-mesh filter screen can be used for filtration. At the same time, the oil tank and the entire hydraulic system should be cleaned regularly, or the oil should be changed regularly.

(7) Adjustment and repair of various operation and control devices

The operation and control devices include various handles, buttons, accelerator pedals, etc. For the handles that are prone to loosening, regular checks should be conducted to see the extent of their damage, and the locking devices should be readjusted or tightened. Severely worn parts can be welded and repaired or replaced. For electrical switches or buttons, the contact state of the contacts can be adjusted or new parts can be replaced.