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In machining, the noise and vibration of the hydraulic system directly affect the accuracy of the workpiece.

Noise is a vibration wave from a sound source, in the hydraulic system noise caused by many reasons, such as voltage fluctuation caused by the noise, the noise of the mechanical system, the noise caused by load and the change of flow rate, air enters the noise caused by the cavitation noise, trapped oil and fluid vortex induced etc..

1. hydraulic pump is a major noise source

The noise and vibration of the hydraulic pump can be caused by the change of the network voltage, the change of the load, the pressure fluctuation and the flow pulsation of the power system. The fluctuation of the power grid voltage will cause the flow pulsation of the hydraulic pump, which will cause fluctuation of the pressure of the pump outlet and the pipeline, which is the fluid noise caused by the external flow and pressure fluctuation.

Hydraulic pressure pumps can also produce fluid noise due to pressure shocks in trapped oil areas. Such as the swashplate axial piston pump wheel, the cylinder during rotation in the dead center, the liquid pressure in the piston chamber and discharge chamber through the suction pressure suddenly rose to the moment, oil pressure, have a greater impact pressure. Similarly, pressure shocks occur at the lower dead center, which is the main noise source of the liquid jet pump.

To have the lowest noise of the hydraulic pump, the power grid capacity is large enough; in the choice of hydraulic pump is required to ensure the power and the flow of the premise, try to choose the hydraulic pump speed is low; can also use composite pump, improve the sensitivity of the relief valve, an unloading between the road to reduce noise.

The 2. control valve is another source of noise

The cavitation of the control valve produces fluid noise. This is because the oil flow to flow through the valve, resulting in a high velocity in the throttle, change velocity pressure, when the pressure is lower than atmospheric pressure, dissolved in the oil in the air will be separated, resulting in a large number of bubbles, the noise frequency will be very high.

In addition, in the jet flow, the oil flow rate is uneven and the eddy current occurs, or the noise is also caused by the oil flow is cut off. The solution to this kind of noise is to increase the back pressure at the lower side of the throttling orifice so that it is higher than the boundary value of the air separation pressure, and the method of multistage decompression can be used to prevent cavitation. When the general oil flow passes through the throttling orifice of the control valve, the ratio of the upstream pressure to the downstream pressure shall be 3~6.

The pressure fluctuation of the hydraulic pump causes the valve to resonate so as to increase the noise. In the control valve, especially throttle valve, its throttle opening small, high flow speed, easy to produce vortex, and sometimes the spool, mortar seat, vibration is great. When this happens, replace it with a small gauge valve or throttle it open.

When the directional control valve closes or opens, it will cause vibration and noise due to hydraulic shock. Such as when the solenoid valve is switching rapidly. Hydraulic shock will cause severe fluctuations of the pressure in the pipe and propagate along the pipeline. When it is transmitted to the hydraulic pump and the oil cylinder, it will cause vibration and noise in these links. Reduce this vibration and noise, should be reasonable through the valve and pipeline settings, minimize hydraulic impact.

3. the suction of the hydraulic pump produces noise

The suction phenomenon of a hydraulic pump means that the oil pump is directly sucked into the air or sucked into the oil and mixed with air. This phenomenon not only affects the oil quality, increases the noise, but also affects the volume efficiency of the hydraulic pump, which is not allowed in the hydraulic system. The main reason for this phenomenon is that the oil tank and the oil suction pipe are unreasonable. In order to prevent this phenomenon, the following measures should be adopted:

The design of the tank is reasonable and the volume is large enough. A long oil tank with a partition board can be divided into the oil tank and the fuel tank;

The oil in the tank should be added to the required height, and the oil suction pipe must enter the 3/5 depth of the oil tank;