The cleanliness of hydraulic oil in hydraulic system with servo Yan high precision and high response control exceeds the standard
The cleanliness of hydraulic oil in hydraulic system with servo Yan high precision and high response control exceeds the standard
Viscosity and cleanliness grade are the two most important indexes of hydraulic oil. The selection of viscosity is mainly based on the ambient temperature and working temperature of the hydraulic system, which is generally determined before the equipment is put into use, while the cleanliness grade needs to be tested regularly and corresponding measures can be taken to ensure it. Single large particles in hydraulic oil directly affect the flexibility of hydraulic components, while small particles will cause wear. Keeping the cleanliness of hydraulic oil in a reasonable range can greatly reduce the occurrence of operation faults and improve the service life of the equipment.
Implement predictive maintenance based on equipment condition monitoring, and regularly detect the solid particle size of hydraulic oil. If it exceeds the standard, take corresponding treatment measures for hydraulic systems under different working conditions.
For hydraulic systems with servo control, the cleanliness grade of hydraulic oil is usually nasl638 grade 6 or higher. However, in the implementation of condition monitoring, it is found that the cleanliness level of the system is nasl638 level 9, which exceeds the standard required by the equipment. This equipment is a safety collision test system. In the hydraulic system, the servo control cylinder is used to simulate the actual impact collision. In actual work, the hydraulic system is in pressure maintaining standby mode for most of the time, and the oil cylinder will act only in case of collision. The manufacturer of the hydraulic power unit is the company. The oil tank volume is 300L. Dr constant pressure swashplate variable piston pump is adopted. The displacement is set at 80L / min and vg46 mineral oil is used. When the hydraulic system is in the pressure maintaining standby state, the oil pump is in the "zero displacement" working state, that is, after reaching the set pressure of the oil pump, the swashplate angle changes, so that the oil pump hardly discharges oil and maintains the constant pressure. See Fig. 5 for oil pump.
The motor oil pump is vertically placed and works in the oil tank, which can not only reduce the working noise of the oil pump, but also use the hydraulic oil in the oil tank to cool the oil pump, so as to prolong the service life of the oil pump. Since the oil pump is placed in the oil tank, the pressure cut-off of the pressure shut-off valve (DR) is realized by connecting the overflow valve remotely controlled at port x (see Fig. 6), which is located at the bottom of the pressure gauge next to the control cabinet of the hydraulic power unit. In order to avoid excessive instantaneous load of the motor when the oil pump is started, the normally closed DBW electromagnetic overflow valve is powered on in time delay to switch the high pressure, that is, when the oil pump is just started, the solenoid valve coil is not powered, the pilot valve of the overflow valve cannot establish pressure, the main valve of the overflow valve is open, so that the P port of the oil pump is connected to the oil tank, the oil pump can be started at low pressure, and the starting load of the motor is very low. After a delay of tens of seconds, the solenoid valve coil is powered on, and the pilot valve establishes pressure. Since the set pressure of the overflow valve is higher than the cut-off pressure of the oil pump pressure shut-off valve, the main valve of the overflow valve is closed, and the oil pump is in "zero displacement" after reaching the set pressure to maintain the working state of constant pressure. The DBW electromagnetic overflow valve is located under the pressure gauge next to the hydraulic power unit control cabinet, and the principle is shown in Figure 6.
The system adopts oil return filter, with filtering accuracy of 10 µ m, allowable flow ≤ 250L / min, bypass check valve and electrical blockage alarm function (see Figure 7).
The main reason why the cleanliness exceeds the standard is that the hydraulic oil filtration of the equipment is not sufficient in the process of daily use. Use the DBW electromagnetic overflow valve of the equipment to temporarily interrupt the delayed power on of the solenoid valve in the control program of the hydraulic power unit, or directly unplug the coil plug of the solenoid valve to keep the main valve in the "short circuit" state, so that the hydraulic oil at the outlet of the oil pump can flow back to the oil tank after being filtered by the oil return filter through the overflow valve. At the same time, because the filter itself has the blocking alarm function, In case of blockage, the alarm will be given immediately, and there will be no case where the bypass valve is opened for useless work. The filtering effect is very ideal. After 2h, the cleanliness reaches nasl638 grade V, and the solid particles > 10 µ m are almost completely filtered out.
