Created on:2021-06-25 09:07

Troubleshooting of hydraulic system of AZ560 injection molding machine

Troubleshooting of hydraulic system of AZ560 injection molding machine

(1) A2560 injection molding machine

Injection molding machine is a multi-stage pressure and flow control system. In order to ensure that the injection molding machine works accurately and effectively according to the process requirements (certain pressure, speed, time, temperature) and action sequence, the electro-hydraulic proportional control system is widely used in modern injection molding machines. The common small injection molding machine is a constant displacement pump with electro-hydraulic proportional valve control system, which is suitable for the occasion of low power; The injection molding machine with higher power is proportional volume control. The hydraulic system of AZ560 injection molding machine is a typical variable displacement pump control system with compound regulation of flow and pressure.

AZ560 injection molding machine is composed of two independent injection molding machines and a rotary table with 16 sets of molds. One injection molding machine injects the upper and the other injects the sole. Each rotation of the rotary table produces 16 pairs of imitation leather boots. The hydraulic pump of injection molding machine adopts Rexroth V4 variable double vane pump, one of which is F-type control mode, the other is C-type control mode. F-type control mode can control flow and pressure, C-type control mode is constant pressure control with manual pressure regulation.

(2) Performance characteristics of Rexroth V4 variable vane pump

Rexroth V4 variable vane pump adopts double vane structure. The blades are arranged radially in the rotor slot. The oil is distributed in one direction, and the floating side plate is used to compensate the axial clearance, so as to obtain higher volumetric efficiency. The working pressure of the pump is 0 ~ 16MPa, and the best adjustable pressure is 4 ~ 16MPa. The circular stator ring is located between the large and small positioning pistons, and the third contact point of the stator ring is the height adjustment screw. The large positioning piston is supported by a soft spring, and its effective area is twice that of the small positioning piston. The thrust of the spring is enough to overcome all kinds of friction when the pressure is zero to push the stator to the maximum eccentric position, so the pump can output the maximum flow when starting. The bearing adopts sliding bearing with dynamic pressure lubrication, which has strong bearing capacity. The pump is also equipped with automatic exhaust valve. This special structure enables it to form a more flexible control mode, such as C, D, W, e, u, F, V control mode, etc.

Figure B is the schematic diagram of F-type control mode of Rexroth V4 variable vane pump, and figure C is the flow and pressure characteristic curve of F-type control mode of V4 variable vane pump. In Figure B, serial number 1 is the V4 variable vane pump body, control valves 2 and 3 are installed on the pump body, proportional pressure valve 4, proportional throttle valve 5 and relief valve 6 are external superimposed control valves, and relief valve 6 is used as safety valve.

When the pressure P of the hydraulic circuit is greater than the set pressure of the proportional pressure valve 4, the valve 4 opens and overflows, and the oil pressure on the left side of the control valve 3 unloads. Under the action of the oil pressure, the control valve 3 overcomes the set force of the spring and turns to the right position. At this time, the large piston of the V4 variable displacement pump unloads, the displacement decreases, the holding pressure no longer rises, and the flow of the pump can only maintain internal leakage, The pressure set by proportional pressure valve 4 is the shut-off pressure of V4 variable pump.

CDE.jpg

When the proportional pressure valve 4 is continuously adjusted, the flow and pressure characteristic curve of figure D can be obtained.

When V4 variable displacement pump is working, when the spring force on the left side of control valve 2 is set, the pressure difference between the inlet and outlet of proportional throttle valve 5 is determined by the spring force, and there is a corresponding value. No matter what causes the pressure difference to increase or decrease, control valve 2 will maintain the corresponding value of the pressure difference between the inlet and outlet of proportional throttle valve 5 by controlling the displacement of hydraulic pump to decrease or increase. Therefore, under the condition of constant pressure difference between inlet and outlet, changing the opening of proportional throttle valve 5 will pass through the corresponding flow, which is the output flow of V4 variable displacement pump, and the characteristic curve is shown in Figure E. When the flow and pressure of V4 variable displacement pump are controlled by compound proportion at the same time, the flow and pressure characteristic curve is the same as that in Figure C.

(3) Failure analysis of a2560 injection molding machine

① Phenomenon I does not feed, motor does not turn, but can be injected.

From this phenomenon, the hydraulic pump P1 to establish working pressure P3 is not a problem, so we should focus on the electromagnetic valve ev21. On the surface, the push rod of the solenoid valve can push, but in fact, the spool of the solenoid valve has been stuck, and it can work normally after cleaning and adjustment.

② Phenomenon II hydraulic pump P1 can not establish working pressure.

Check relief valve 3, 4, 5, 9 and solenoid valve ev30 in Figure F first. If all are normal, remove the control valves 2 and 3 on the hydraulic pump PL body (see Fig. b). If the oil passage is blocked, pump P1 will return to normal after cleaning. Sometimes it may be that the oil distribution plate of the hydraulic pump has been scratched. In this case, if the scratch is not deep, one layer can be worn off, and the shell on the pump body can be worn off at the same time, so as to ensure the end clearance. After reassembly, push the large positioning piston of pump P1 with a driver to check whether the stator ring inside can move flexibly. If it can't move, the end cover is too tight. You can measure the error with a micrometer. If the error is small, a tracing paper can be clamped on this side of the end cover. In addition, the most fatal defect of V4 variable vane pump is its poor anti pollution ability and easy to damage the sliding bearing. If the sliding bearing is seriously damaged, it must be replaced and the system oil must be kept clean.

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