Newspaper Printing Equipment Management and Maintenance (Chinese)

2) General knowledge of maintenance of printing equipment

The maintenance of the equipment and the maintenance of the equipment are different in content and function. The repair is mainly to find faults, troubleshoot, repair and replace damaged or worn, corroded parts, so that the equipment can operate normally. Equipment repairs are divided into electrical and mechanical parts.

1 General knowledge of electrical maintenance

In the daily printing equipment repair work, the electrical part occupies a large proportion. With the continuous development of printing technology equipment, the degree of automation control is getting higher and higher, and the control system is also more complicated. Therefore, electrical maintenance personnel are required to have a high level of technical skills and quality, and to understand computer principles and operations. For print maintenance electrical personnel, the following points should be noted in daily maintenance work:

a) Carefully read the electrical schematics and related documents of the equipment, and master the electrical principles and control system principles of the equipment in principle. Find out where electrical components are located, how they are routed, and how they are numbered and routed.

b) For machinery and equipment failures, carefully analyze the parts that may have this failure, and look for components and circuits that may cause failures based on electrical schematics, wiring diagrams, etc., and diagnose and eliminate them one by one.

c) In electrical repair, first check the power supply voltage? Whether the current is normal, whether the air pump pressure reaches the standard, whether the hydraulic pressure of the lubrication system meets the standard, etc. If necessary, the load can be disengaged, which is favorable for judging whether the mechanical overload causes electrical failure or protection.

d) The web offset press uses a PC for automatic control, which brings a lot of convenience to troubleshooting electrical faults. Generally, there is a light emitting diode in the control cabinet for fault indication. According to the prompt, the fault location can be found. In more advanced equipment, you can look for prompts on the console display or use a laptop to “talk” with the industrial computer in the control cabinet to find the faulty system? Parts, and then rule out one by one?

e) Frequently encountered electrical faults can be summarized as: fuse damage, contactor, relay contact damage, loose wiring, poor contact, failure of the button, limit switch, safety control system, a certain position control switch is not reset, In the tension control system and the paper break system, some photoelectric detection failures, electromagnetic valve leakage, damage, etc.

f) The motor is the source of power in the printing equipment. The following describes the common faults of the DC motor and the AC motor.

The common faults in DC electric operation are mechanical and electrical. Mechanical failures are mainly manifested as bearing heating, motor vibration, armature colliding with the stator core, and abnormal noise emission. It is generally caused by the rotation of the armature. When checking, manually rotate the armature to observe whether the armature collides with the stator and determine whether the vibration is caused by the motor itself or due to a poor transmission.

The motor is less likely to vibrate due to its own poor balance. Frequently, the concentricity of the transmission is not good enough to cause vibration. This phenomenon can easily cause damage to the motor bearings and even cause deformation of the armature output shaft.

The most common electrical fault of DC motors is the spark between the brush and the commutator. During normal operation, the spark between the brush and the commutator is pale blue, faint and fine, and the contact surface of the brush is smooth and bright. A red-brown oxide film forms on the surface of the commutator.

When the motor is not operating normally, the spark size and color will change. When the fault is slight, the spark will appear yellow-red and bright, and the commutator will have a black surface with burning marks. If the spark is severe, it will spray red and green sparks in a large amount, mixed with flash fire, and accompanied by a buzzing sound. If the machine is not stopped in time, the commutator, brush and brush holder will soon be burnt out.

When the brush position deviates from the geometric centerline, there may be serious sparks when the armature winding is open and short circuited. In addition, brush brands, performance does not match, brush pressure is too large, too small, the brush is not well ground, the contact area is too small and other reasons, will cause failure.

The mechanical failure of an AC three-phase asynchronous motor is basically the same as that of a DC motor. Here is a brief introduction to common electrical faults. First, single-phase operation fault, that is, one phase winding in the three-phase winding of the motor is disconnected. At this time, the motor torque is significantly reduced, the speed is slow, the sound is abnormal, and the time is longer. Severe fever and burnout; Second, the motor has a serious fever, and even issued a paste smell, this failure may be due to the load is too heavy, it may be caused by the power supply voltage is too low, too high.

2 Mechanical maintenance knowledge

Mechanical faults can be generally classified into accidental faults and natural faults. Accidental faults are mostly caused by improper maintenance or adjustments, or violations of operating procedures, and should be avoided as much as possible. Although natural failures are difficult to avoid, they can extend the use and maintenance levels and extend the effective working time of machinery.

There are three main failure modes of mechanical parts: fracture, deformation, and surface failure. The following describes wear, deformation, cleaning methods, and disassembly of printing machine parts.

a) Wear of printing machinery parts

In the working process of the machine, if the size, shape, and surface quality of the relatively moving part surface have changed, it is called wear.

The main causes of wear of parts are friction and molecular attraction. Wear can be divided into abrasive wear, mechanical friction wear and adhesive wear. The reasons that affect the wear of mechanical parts are generally: speed, pressure, lubrication, temperature, materials, processing and cooperation. (to be continued)