Vibration phenomena and elimination strategies of Y27 double-action hydraulic press

Double-action hydraulic press has low energy consumption, high efficiency and novel style. Equipped with safety protection device, automatic counting function, two-speed control of movable beam: no-load fast, work-in slow speed against the mold, stretching. The main cylinder and press side cylinder have lower limit protection, and the upper and lower limit stroke position setting is simple, convenient and fast.

ⅠStructure features

●The double-action hydraulic press is mainly used for thin plate stretching, bending, forming, etc. It can also be used for plastic pressing, cold extrusion bending, molding correction and press fitting. The double-action hydraulic press's crimping cylinder can be used as a buffer device, and it can also be used for falling material and punching, and the working pressure of each cavity can be adjusted separately under the pressure regulated by the system. In order to ensure the quality of drawing and crimping, the crimping cylinder is equipped with a pressure-holding system.

●The working pressure, pressing speed and stroke of the double-action hydraulic press can be adjusted within the specified range according to the needs. The double-action hydraulic press has independent power mechanism and electrical system, and adopts centralized control by push button, which can realize three operation modes: manual, semi-automatic and automatic. In the semi-automatic and automatic operation mode, it can be divided into three working states of ejecting cylinder without ejecting, positive stretching and reverse stretching, and two pressing modes of constant pressure and constant range can be realized.

Ⅱ The causes of vibration and elimination strategy

●Generation of vibration

When the inner slider goes down quickly during work and changes to slow speed before contacting with the workpiece, the liquid-filled valve suddenly generates violent shock vibration, which continuously causes the pipe to resonate and make a loud noise. Inside the slider down once to hit a burst, if not lifted in time will be due to oil strike (water hammer) phenomenon which leads to pipe rupture and machine damage. First of all, check the source of vibration parts, the impact sound is issued from the filling valve outward, after checking the internal structure of the filling valve parts have not found any signs of damage, so the following analysis.

●Hydraulic system analysis

1. Oil strike (water hammer) phenomenon analysis

The two tanks of the double-action hydraulic press are installed on the top left and right sides of the machine body, and the inlet of the filling valve is at the same level as the bottom of the tank, and the oil in the tank has a fixed pressure transfer to the output (outside the filling valve). When the slider goes down quickly by its own weight, the filling valve is sucked open by negative pressure, and the oil in the tank flows into the upper chamber of the main cylinder at the speed of Vt through the pipe.

When the slider goes down fast to slow speed, the filling valve suddenly closes. In this instant, the flow rate of the inlet of the filling valve suddenly changes to 0. The external (output) fluid suddenly loses the kinetic energy of the negative pressure suction, and the flow energy is intercepted, causing the pressure at the output end to rise sharply and ram the valve. The pressure at the input end (tank) is transmitted at the speed of sound, and the oil in the pipeline loses its flow speed, because the fixed pressure in the tank is smaller than the pressure transmitted, the backflow of oil forces the pressure at the input end to drop, and is transmitted to the output end in turn at the speed of sound, so that the pressure outside the filling valve suddenly changes from high pressure to low pressure, and the low pressure is transmitted to the input end at the speed of sound. The pipe produces a violent pressure oscillation sound.

2.The moment the filling valve is hit by high pressure, the main cylinder upper chamber pressure is low reason

The speed of the slider going down by its own weight is an important parameter, the slider overcomes the frictional resistance of each cylinder sealing device to get more ideal downward speed, and at the same time in the slider fast downward to slow speed when the liquid filling valve is closed after the main cylinder upper cavity suction sufficient oil. The pressure generated is larger than the outside of the filling valve, to meet these conditions, the filling valve will be firmly pressed, the output end and then a sudden increase in pressure can not push the filling valve, so there will be no vibration.

The piston seal part of the slider is loosened due to wear in the long-term movement, which causes the slider to go down faster by its own weight, and thus the vacuum phenomenon occurs in the upper chamber of the main cylinder, resulting in low pressure and slowing down the pressure rise in the upper chamber of the main cylinder.

●Elimination strategy

1.In order to smoothly eliminate the shock vibration during the liquid filling process, first of all, readjust the inner ram to open the liquid filling valve during the return journey in advance and hysteresis conditions, so as not to be disturbed when eliminating the vibration.

2.Adjust the speed of the inner slider downward. Liquid-filled valve into the oil speed and its overflow area is directly related to the flow rate at the inlet of the valve and the slider weight downward speed proportional to.

3.Adjust the main oil pump oil supply. In order to eliminate vibration , it has sufficient conditions, and in the servo control system to make additional adjustments, so that the inner ram stretching speed increased slightly. This strengthens the pressure of the upper chamber of the main cylinder after the filling valve is closed is much greater than the pressure outside the filling valve, so that the filling valve has no possibility of vibration.