Failure phenomenon and cause analysis of the hotte

2022-08-21
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Mechanical failure phenomenon and cause analysis

friendly answer from mechanical experts

check the internal leakage of boom cylinder. In the simplest way, it puts forward strong mass reduction requirements for aircraft design; Another method is to raise the boom and see if it has obvious free fall. If the drop is obvious, disassemble the oil cylinder for inspection, and replace the sealing ring if it is worn

during maintenance, find out the cause of the fault from the following three points and improve the system:

(1) check the internal leakage of the boom cylinder. The simplest way is to raise the boom and see if it has obvious free fall. If the drop is obvious, disassemble the oil cylinder for inspection, and replace the sealing ring if it is worn

(2) check the control valve. First, clean the safety valve and check whether the valve core is worn. If worn, replace it. If there is still no change after the installation of the safety valve, then check the wear of the control valve spool. The gap service limit is generally 0.06mm, and it should be replaced if it is seriously worn

(3) measure the pressure of the hydraulic pump. If the pressure is low, adjust it. If the pressure still cannot be adjusted, it indicates that the hydraulic pump is seriously worn

generally speaking, the main reasons why the boom cannot be lifted with load are:

a. the hydraulic pump is seriously worn. Serious leakage in the pump during low-speed operation; When running at high speed, the pump pressure increases slightly, but due to the wear and internal leakage of the pump, the volumetric efficiency decreases significantly, and it is difficult to reach the rated pressure. The long-term operation of the hydraulic pump intensifies the wear and tear, and the oil temperature rises, resulting in the wear of hydraulic components and the aging and damage of seals, loss of sealing capacity, deterioration of hydraulic oil, and finally failure

b. the selection of hydraulic components is unreasonable. The specification of boom cylinder is 70/40 non-standard series, and the seals are also non-standard parts. The manufacturing cost is high and the replacement of seals is inconvenient. The small cylinder diameter of boom cylinder will inevitably make the set pressure of the system high

c. the design of hydraulic system is unreasonable. It can be seen from Figure 1 that the control valve and the full hydraulic steering gear are single pump in series, the set pressure of the safety valve is 16MPa, and the rated working pressure of the hydraulic pump is also 16MPa. The hydraulic pump often works under full load or overload (high pressure) for a long time, and the system has hydraulic impact, and the oil is not changed for a long time. The hydraulic oil is polluted, which intensifies the wear of the hydraulic pump, so that the pump shell of the hydraulic pump bursts (such faults have been found later)

improvement and effect

stop in place (L) improve the hydraulic system design. After many demonstrations, the advanced new system of priority valve and load sensing full hydraulic steering gear is finally adopted to solve the problems of difficult manufacturing and poor accuracy of the lead screw lifting device of the tension testing machine. According to the Steering requirements, the flow can be distributed preferentially. No matter the size of the load and the speed of the steering wheel, it can ensure sufficient oil supply, and the rest can be supplied to the working device circuit, so as to eliminate the loss of success rate caused by excessive oil supply in the steering circuit, improve the system efficiency, and reduce the working pressure of the hydraulic pump

(2) optimize the design of boom cylinder and hydraulic pump to reduce the working pressure of the system. Through optimization calculation, the boom cylinder adopts the standard series 80/4. The displacement of the hydraulic pump is increased from 10 large-span and anti-seismic building steel ml/r to 14ml/r, and the set pressure of the system is 14MPa, which meets the lifting force and speed requirements of the boom cylinder

(3) pay attention to the correct use and maintenance of the loader during use, add or replace hydraulic oil regularly, maintain the cleanliness of hydraulic oil, and strengthen daily inspection and maintenance

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