At one time, a J2108B-type off-color monochrome offset printing machine ran out of a strong insulating paint smell during operation, causing abnormal operating conditions. During the shutdown inspection, it was found that the windshield of the main motor (electromagnetic induction motor, JZT-2-51-4, 120 to 1200r/min, 7.5 KW) in the main motor was completely covered by scrap sheets, and the motor was The air outlet is blocked and the surface of the motor casing is extremely hot. The strong paint burnt smell is the high temperature rise of the motor, and the insulation of the motor (especially insulating paint) is heated to a certain extent to stimulate the gas smell. Obviously, if this state continues, the temperature rise of the motor will continue to rise, causing a vicious cycle, the motor will be burned out or will directly affect the life of the motor.
Under the normal load of offset press, how can the main motor produce this abnormal condition? The reason is simple: the fan of the electric motor is blocked by the waste paper from the cold air duct, which affects the heat dissipation of the motor during operation, causing the motor temperature to rise and the abnormal heating.
In order to make our operators understand more clearly and understand why the motor fan is blocked from the cold air duct, it will cause direct damage to the motor. I will introduce some problems related to the temperature rise of the motor during operation of the motor.
As we all know, in the printing and packaging machinery and equipment are generally used motor, motor damage or failure not only increases the repair costs, but also caused equipment defects, a direct impact on the normal production. The main cause of motor damage or failure is due to poor protection and inadequate maintenance.
According to the use of equipment and related data reports, all three-phase asynchronous motor burned out for the following reasons: 1. Bearing fault caused rotor stall or resistance is too large; 2. Insulation aging caused by insulation failure; 3. Due to unbalanced phase or single-phase operation; 4. Dust particles or Other foreign substances cause excessive friction and poor ventilation; 5. Insulation is affected by oil or moisture; 6. Excessive heat causes the coil to burn out.
The life of a motor largely depends on its insulation life. Motor overheating is the most important cause of electrical damage to the motor. When the motor is in operation, all kinds of losses eventually become thermal energy, causing the motor parts to heat up and the temperature to rise. In order to ensure the normal operation of the motor, various insulation grade motors have specified the limit temperature rise. Exceeding this limit temperature rise, the insulation material will accelerate aging. So, in a sense, the life of a motor is its insulation life. In general, every 10°C above the temperature rise limit, life will be reduced by half.
The temperature rise of the motor is not only related to the heat source (various losses) and operating modes inside the motor, but also related to the ability of the surrounding environment of the motor to dissipate heat. The heat dissipation capacity of the motor is determined by the temperature rise of the motor, the size of the heat dissipation surface, and the heat dissipation coefficient of the surface. Like other objects, there are three methods of cooling the motor: convection, conduction, and radiation. The heat dissipation in the motor windings and the iron core is mainly conducted, and the heat dissipation from the stator and rotor surfaces is mainly convection. Therefore, reducing the temperature rise of the motor can enhance the internal heat transfer capability of the motor and the heat dissipation capability of the motor surface. Generally small and medium-sized motors are equipped with a self-cooling fan, so that it blows the surface of the motor at a faster speed and enhances the heat dissipation capability of the motor. Larger-capacity motors, some with independent fan cooling or ducted cooling. Closed-cycle gas cooling for large motors is an effective measure to improve the ventilation cooling system, increase the motor cooling surface, reduce the motor temperature rise and increase the motor capacity. This shows that the running motors (especially small and medium-sized motors equipped with a self-cooled fan) are very important for ventilation and heat dissipation of the fans. Once the air ducts are blocked and the ventilation is poor, the heat dissipation of the motor will be affected. Causes the temperature of the motor to rise too high, which leads to a vicious cycle and the harmful consequences of the motor. Therefore, in the on-site production, the operator should pay attention to civilized production safety (the above-mentioned root cause of the fault is that the operator does not clean up the waste paper produced during offset printing during offset printing as required) and starts the machine. In the meantime, it is necessary to concentrate on energy and achieve "Five Diligence": 1. Look at things: Look at the operation of the machine. 2. Listen: Listen to the sound of the machine. 3. Hard touch: Touch the parts of the machine that are prone to wear and warm up. Is there a significant temperature change? 4. Diligence: There is no scorching of electric appliances, lacquer smell of insulating paint and other strange smells. 5. Diligence check: Check the environment around the machine for any abnormalities, find problems, and eliminate them in time.