Construction machinery plays an important role in engineering construction. Hydraulic cylinders play an important role in machinery, and it is the key to fault analysis and maintenance of hydraulic cylinders. This paper summarizes and analyzes the faults frequently encountered in mechanical hydraulic cylinders in engineering, and proposes corresponding solutions. Combined with engineering examples, the feasibility of the hydraulic fault repair method is illustrated. Hydraulic cylinder failure analysis Hydraulic system fault diagnosis method Subjective diagnosis method. In actual engineering, equipment for detecting hydraulic systems is often lacking. In this case, the subjective diagnosis can detect the failure of the hydraulic system. Subjective diagnosis is mainly diagnosed by smelling, listening, touching and appearing. The diagnosis is mainly to judge whether the motor and the electromagnet are burnt out and whether the oil pressure has deteriorated. Auscultation is mainly based on the abnormal sound to determine the location of the mechanical failure and the degree of damage. For example: the hydraulic cylinder leaks, the sound is small and long, continuous. Friction sound, the sound is sharp and short, often caused by contact surface grinding burns. Touch is mainly judged by touching the temperature, crack, creep and tightness of the machine. The diagnosis is mainly based on the speed, color, appearance and force.
Parameter measurement diagnostic method. In engineering practice, the performance of the hydraulic system is good or bad, which determines the good or bad of the bad machinery. The parameters that determine the performance of the hydraulic system are mainly pressure, flow, temperature and pump power. By monitoring and troubleshooting these parameters and comparing with the mechanical parameters during normal operation, it is possible to judge the working condition of the system and the location of the situation.
Ferrography diagnostic method. The ferrography diagnostic method is to separate and analyze the oil in the hydraulic cylinder, and derive the shape, color, composition and distribution of the wear particles and the contaminated particles. The information can be used to determine the fault location.
Vibration measurement method. The vibration measurement method is to change the vibration signal of the system by the change of the vibration of the system, thereby judging the fault location of the system.
expert system. Solve system failures with a set of computer intelligence programs that solve problems with computer simulation experts. Troubleshooting and Maintenance Methods The actuator that converts hydraulic energy into mechanical energy in a hydraulic system is a hydraulic cylinder. The fault can be basically summarized as the hydraulic cylinder does not work well, leaks and damage to the cylinder. In the actual project, the phenomenon that the hydraulic cylinder fails and the machine cannot run is not uncommon. Therefore, attention should be paid to the fault diagnosis and maintenance of the hydraulic cylinder.
The hydraulic cylinder failed. 1) The valve plug is stuck or the valve hole is blocked. Maintenance method: Check whether the oil is contaminated, check whether the dirt or colloidal deposits are stuck in the valve core, check whether the valve body is worn or not; 2) the piston rod is stuck with the cylinder tube or the hydraulic cylinder is blocked. Maintenance method: Check if the piston and piston rod seal are too tight, whether it enters dirt and colloidal deposits; 3) The hydraulic system control pressure is too low. Maintenance method: Check the control pressure source to ensure the pressure is adjusted to the system specified value; 4) Enter the air in the hydraulic system. Maintenance method: Check the liquid level of the hydraulic tank, the seals and pipe joints on the suction side of the hydraulic pump, and whether the suction strainer is too dirty. If this is the case, supplement the hydraulic oil, handle the seal and pipe joints, clean or replace the coarse filter; 5) The initial movement of the hydraulic cylinder is slow. Maintenance method: replace the hydraulic oil with better viscosity and temperature performance. At low temperature, it can be heated by the heater or by the machine itself to increase the oil temperature at startup.
The hydraulic cylinder cannot drive the load while it is working. The main performance is that the piston rod is not in position, the thrust is insufficient, the speed is reduced, and the work is unstable. 1) Internal leakage of the hydraulic cylinder. The internal leakage of the hydraulic cylinder is mainly caused by leakage of the hydraulic cylinder block seal, the piston rod and the seal cover seal, and the piston seal are excessively worn. Maintenance method: adjust the speed control valve, do the necessary operation and improvement according to the installation instructions; clean the filter or replace the filter element, hydraulic oil; 2) the hydraulic circuit leaks. Maintenance method: Check and eliminate the leakage of the hydraulic connecting line by operating the reversing valve; 3) The hydraulic oil is bypassed to the tank through the overflow valve. If the overflow valve enters the dirt and the valve plug is closed, the overflow valve is normally opened, and the hydraulic oil will flow back to the fuel tank through the overflow valve bypass, resulting in no oil entering the hydraulic cylinder. If the load is too large, the regulating pressure of the relief valve has reached the maximum rating, but the hydraulic cylinder still does not get the thrust required for continuous operation without action. If the adjustment pressure is low, the pressure is insufficient to reach the required force, and the thrust is insufficient. The relief valve should be checked and adjusted at this time.
The hydraulic cylinder piston slips or crawls. Sliding or crawling of the hydraulic cylinder piston will make the hydraulic cylinder unstable. The main reasons are as follows: the internal pressure of the hydraulic cylinder is stagnant. The internal parts of the hydraulic cylinder are improperly assembled, the parts are deformed, the wear or the geometrical tolerances are over-limit, and the movement resistance is too large, so that the piston speed of the hydraulic cylinder changes with the stroke position, and slips or crawls. Most of the reasons are due to poor assembly quality of the parts, scratches on the surface or iron filings from sintering, which increase the resistance and decrease the speed. Treatment method: to ensure the quality of the part configuration, so that the machine is standardized; poor lubrication or excessive machining of the cylinder bore. Because the piston and the cylinder, the guide rail and the piston rod have relative movement, if the lubrication is poor or the cylinder bore is out of tolerance, the wear will be intensified and the linearity of the cylinder center line will be reduced. Thus, when the piston is operated in a hydraulic cylinder, the frictional resistance will be large and small, causing slippage or creeping. Treatment: first repair the hydraulic cylinder, then prepare the piston according to the requirements, repair the piston rod, configure the guide sleeve; hydraulic pump or hydraulic cylinder enters the air. Compressed or expanded air can cause the piston to slip or crawl. Treatment measures: check the hydraulic pump, set up a special exhaust device, and quickly operate the full-stroke and exhaust several times; the quality of the seal is directly related to slip or creep. When the O-ring is used under low pressure, compared with the U-shaped seal, the surface pressure is higher, the difference between the dynamic and static frictional resistance is larger, and slip or creep is easy to occur; the surface pressure of the U-ring is increased with the pressure. However, although the sealing effect is correspondingly improved, the difference between the dynamic and static frictional resistance is also increased, the internal pressure is increased, and the rubber elasticity is affected. As the contact resistance of the lip increases, the sealing ring will tip over and the lip will elongate. It is also easy to cause slippage or creeping, and the support ring can be used to keep it stable in order to prevent it from tipping over. The engineering example analyzes a construction team with a TY220 bulldozer. The total working time is about 9000h. It has been engaged in the earthwork stripping work of the project. At the same time, the early ripper has a small amount of oil leakage. Due to the tight schedule, it has not been treated. After working for 5 hours, the ripper leaked heavily and needed to be replenished frequently. The next day, when the bulldozer was started, the ripper suddenly landed. In response to the above, the maintenance personnel decided to carry out on-site maintenance.
Fault diagnosis: The maintenance personnel use the subjective diagnosis method, and the initial judgment is that the hydraulic cylinder leaks oil. The maintenance personnel removed the hydraulic cylinder and found that the piston rod of the hydraulic cylinder was bent, the cylinder and the piston were worn, and there were more iron filings in the cylinder.
Analysis of the cause: The unevenness of the ripper and the uneven force of the hydraulic cylinder caused the piston rod to bend. The hydraulic cylinder is not properly lubricated. During construction, impurities such as dirt enter the lubrication part, causing abnormal wear, resulting in uneven force on the hydraulic cylinders on both sides. When the bulldozer is constructed, the ripper is subjected to a large mechanical impact due to the influence of the rock. The hydraulic cylinder is not adequately maintained. The operator's operation is not standardized during construction.
Maintenance method: replace the piston and oil seal, correct the piston rod, and brush the piston rod and the inner wall of the hydraulic cylinder.
Summary Engineering analysis shows that the construction machinery should be operated strictly in accordance with the construction manual during construction, and the machinery is well maintained.
The analysis method of hydraulic cylinder failure and the frequently occurring faults are analyzed, and the treatment methods are proposed to improve the reference for future mechanical fault diagnosis and maintenance.
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