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injection molding machine circuit failure maintenance case analysis

TIME:2020-12-05 Share

This is a failure phenomenon of a LISONG injection molding machine. The phenomenon is that the machine alarms: "The safety relay has not been reset, please reopen the safety door".

At first thought it was caused by not closing the safety door. But it is no problem to double check the safety door before and after the switch. Check the travel switches and emergency stop switches of the front and rear safety doors one by one. All contacts are operating well, and there is no disconnection or poor contact.

injection molding machine

Consider starting from the safety relay in the alarm. This is a Pilz safety relay, model piIz PNOZ x2.8p.

The A1 and A2 ports of this type of safety relay are connected to ±24ⅴ DC power supply; s21, s22, s11, and s12 are connected to the normally closed contact of the emergency stop switch; the reset button is connected between s12 and s34 (if manual reset is not required, automatic To reset, just short s12 and s34).
injection molding machine
When the safety door is opened and closed once in the manual state, the safety relay and the two intermediate relay indicators next to it will light up, and there is no alarm display on the computer display. But as long as the action is taken, a fault alarm will appear, and the indicator lights of the three relays will not light up at the same time. The ±24ⅴ DC power supply on the A1 and A2 ports of the safety relay comes from one of the v+ and v- terminals on the DC power box.

The test found that when there is no alarm on the display, the voltage between the two sets of v+ and v- on the DC power box is ±24ⅴ.

When the computer alarms "safety relay is not reset, please reopen the safety door", the multimeter detects that the DC voltage connected to the A1 and A2 ports of the safety relay is only about 5v, while the voltage of the other set of v+ and v- ports on the power box It is still normal at ±24v.

This discovery brings me one step closer to troubleshooting, which shows that the group of power supply voltage changes has a short circuit fault.

After careful investigation, the group of power cords used to connect the solenoid valve for the blower function was short-circuited. As a result, the output voltage of the power supply box becomes lower. However, the safety relay cannot work normally when the power supply voltage is insufficient, so the above alarm fault occurs. After separating and insulating short-circuited wires. Troubleshooting, the injection molding machine is operating normally.

For more information about the failure of the injection molding machine, please pay attention to the LISONG machine.
 

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