A hard to find fault 0

2022-06-17
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An undetectable fault

a fault occurred in our js2102 offset press. The phenomenon is that the automatic lifting limit switch frequently sends out the paper lifting signal, and the conical motor is also frequently started, but the rise of the main paper stack is very small, sometimes even does not move

press the on or down button by hand, but the motor can rise or fall normally. Use an ammeter to measure that the three-phase working current of the motor is normal. Through the analysis of the fault, the possibility of problems in the motor, mechanical transmission mechanism, AC contactor, thermal relay and insurance is eliminated, and the idea of finding problems in the automatic lifting control circuit is determined. There are two electrical control elements in the automatic lifting control circuit: one is the limit switch installed on the specific function structure of the external wall insulation material testing machine of the presser foot machine; First, what are the methods of opening and maintaining the tension machine controlled by the limit? It is an electronic time delay relay installed on the wall panel of the machine to determine the working time of the motor. First check the limit switch on the presser foot. After the power is cut off and removed, press the ram by hand to hear the sound of the internal contacts on and off, and use the resistance block of a multimeter to detect, proving that the switch is obviously damaged. Use a new limit switch for commissioning, and the fault remains the same. Is it caused by too short delay of electronic time delay relay? After the delay adjustment and test run, the failure is not eliminated. The progress of plastic granulator technology is closely related to the development of the whole national economy. After further analysis, it is considered that the problem should also be in the automatic rising control circuit. The automatic lifting limit switch works only after it is touched by the screw on the presser foot. Therefore, the reason must be found out whether the action of the presser foot mechanism is correct. Test the machine. When the paper presser foot is pressed down with the rotation of the machine, try to help it with a little force by hand to make the screw touch the eye position switch more reliably. At this time, the motor returns to normal, and the rising of the raw paper stack is also powerful immediately. Once the hand is not used to help, the fault occurs again. This fully proves that the fault is not only caused by the damage of the limit switch, but also caused by the insufficient force of the presser foot when pressing down. Temporary emergency measures: fix a 20cm long bicycle inner tube on both sides of the presser foot mechanism, and press the middle part on the presser foot. The elasticity of the rubber makes the presser foot increase a certain force when pressing. Try the machine again, and the fault is finally eliminated

later, it was found that the gap between the long universal shaft on the presser foot mechanism and its universal drive sleeve was worn too much, resulting in the paper presser foot not acting in place during pressing. This is really a difficult fault to find out

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