Created on:2021-09-24 14:44

Construction machinery_ Construction and construction machinery_ Failure of stabilized soil mixer

Construction machinery_ Construction and construction machinery_ Failure of stabilized soil mixer

The traveling system of wb221 stabilized soil mixer produced by a company is composed of closed hydraulic system (see Figure U), two gear transmission and drive axle. The por valve (pressure compensation servo valve) 4 on the hydraulic system 1 is controlled (fed back) by the working pressure of the traveling system (when moving forward) and the working pressure of the rotor system. When the external load of the machine increases in the mixing operation, the pressure of the traveling system and the rotor working system of the machine increases accordingly. If any of the pressures exceeds the set value of the por valve, The valve core of por valve moves to the right, which will gradually reduce the pressure oil flowing to the servo cylinder 2 of variable displacement piston pump and reduce the displacement of variable displacement piston pump 1, so as to reduce the output power of engine and realize the automatic distribution of power. During the maintenance of the machine, two cases of machine failure were encountered.

U.jpg

(1) Fault I

Due to the improper installation of the pipeline on the machine, the ground clearance of the high-pressure oil pipe of the traveling system is too small, and the pipe burst is caused by friction for a long time. Due to the tight construction period at that time, the user did not purchase the original parts from the manufacturer, but made the oil pipe by himself; Because there is no suitable pipe joint, the original pipe joint is cut and welded on the newly pressed oil pipe. Shortly after the installation of a self-contained high-pressure oil pipe, the machine appeared to have symptoms of walking weakness. Especially after the oil temperature increased, it almost failed to work and there was a lot of foam in the tank.

According to the fault phenomenon and practical experience, the diagnosis is carried out according to the following steps.

(1) observe the vacuum gauge 7 in figure U, whose reading has exceeded the rated value, which indicates that the gear pump is not smooth enough to absorb oil, and then produces foam. It may be that the oil absorption filter 8 is blocked.

② When the oil suction filter and other oil filters on the machine were disassembled, they were seriously blocked, and there were many bright metal particles in the dirt. After checking the hydraulic oil tank, it is found that there are a large number of copper and iron filings, some of which have a particle size of more than 2mm, and there is no oxide layer on the section. It can be seen that some hydraulic components have been seriously worn recently.

③ The measured maximum pressure of the traveling system is only 10MPa, which is far lower than the rated pressure (33mpa), but the pressure of the working system is normal, indicating that the traveling system may have serious leakage. According to experience, the wear degree of the pump is generally much less than that of the pump, and the most easily worn parts in the pump are generally the oil distribution plate and lining plate.

④ Remove the pump and open the pump body. It is found that the oil distribution plate and lining plate have been seriously worn, and individual wear marks are up to 2mm deep. It can be concluded that it is caused by large particle size and hard impurities entering the main system; The coating of oil distribution plate and lining plate has almost been polished and has lost its repair value.

Therefore, the oil distribution plate and lining plate were replaced, the hydraulic system was cleaned again, especially the newly made high-pressure oil pipe, and the full set of filter element and hydraulic oil of the machine were replaced, which worked normally.

Afterwards, the maintenance personnel found the culprit of the fault in the oil suction filter - the welding slag falling into the pipe when welding the pipe joint.

Data show that most faults of hydraulic system are caused by oil pollution, so attention must be paid to prevent oil pollution in use; When making and installing pipelines, pay special attention to prevent dirt from entering the pipeline system.

(2) Fault II

During normal mixing operation, the mixer suddenly heard an abnormal sound, and then the whole machine could not walk, but other parts could work normally. This fault may occur in the mechanical system or in the sub hydraulic system. Because the machine can not walk at all and there is abnormal noise, it can be judged that some parts of the mechanical system are more likely to break, so the mechanical system was checked first.

① Check the pneumatic shift circuit and find that the high-pressure air pipe used in low gear has been washed away (the abnormal sound said by the driver should be the impact sound of air flow when the high-pressure air pipe is disconnected). After the high-pressure gas pipe is installed, the machine still cannot walk; Observing from the peeping viewport, it is found that the shift works normally, but there is no rotation of the internal gear of the transmission when it is in neutral. The above situation is sufficient to indicate that the hydraulic system has failed.

② The measured oil make-up pressure (z2 day) of oil make-up pump 6 is 1.7mpa, which is normal, and the measured control pressure (M1 or M2 port) of servo cylinder 2 is zero; Remove the pressure gauge. When the handle of manual servo valve 3 is pulled to the corresponding maximum position, no hydraulic oil rushes out of the test hose, so it can be preliminarily judged that the manual servo valve or por valve 4 has failed.

③ Remove the manual servo valve and por valve from the variable displacement piston pump. After inspection, the oil circuit of manual servo valve is not blocked, and the valve core works well without abnormality; When the por valve was disassembled, it was found that the end of the main valve core had been broken, and the fracture was at the part with large cross-section change, but no trace of eccentric load was found, so it should be caused by fatigue damage or hydraulic impact. After replacing the por valve, the system returned to normal.

After the fault was solved, what puzzled the maintenance personnel was: Why did the low gear high-pressure gas pipe rush away during normal operation, which would cause the fracture of por valve core? After carefully asking the operator, it turned out that the machine suddenly could not walk during normal operation. Because it was difficult to shift the machine, the driver thought it was not in gear, so the high-pressure air pipe accidentally rushed away during multiple trial shifts.

(3) Summary

The lack of communication between maintenance personnel and operators led to the maintenance personnel mistakenly treating the hydraulic fault as a mechanical fault, thus wasting a lot of time and doing a lot of unnecessary diagnosis work. In fault diagnosis, it is necessary to ask the operator about the situation before and after the fault, analyze the relevant and non relevant factors, especially distinguish false information and grasp the key of the problem, so as to obtain the correct diagnosis result.

Home    Article    Construction machinery_ Construction and construction machinery_ Failure of stabilized soil mixer