Discussion on the manufacturing process of traditional motors - varnishing technology

The manufacturing process of traditional motors is a very mature process. There is no secret. As long as the right process route is selected, there will generally be no major problems. What is currently being pursued is to improve in the direction of lean production and how to meet the company's pursuit of profits through better methods.

Industrial motors have different materials and processes according to different voltages. They are generally divided into low-voltage motors and medium- and high-voltage motors. Motors below 1140V can be classified as low-voltage motors, while motors above this voltage belong to the category of medium- and high-voltage motors.

01 Varnishing - an important process to extend insulation life

The insulation life of low-voltage motors has been finalized when selecting materials and completing winding, unwinding and binding. Unlike general perceptions, the varnishing process does not increase the insulation life. The main purpose of this process is to extend the insulation life of the motor.

The insulation life of low-voltage motors is mainly determined by the insulation layer of the conductor. When each major process is passed, the insulation strength is reduced by about 30%~40%. At present, the enameled wire can generally reach an insulation strength of 8 to 10 kilovolts during the withstand voltage test, but there is still a certain probability of insulation breakdown during the withstand voltage test before all the processes of varnishing. Because after winding, unwinding and binding, these three major processes, each time the insulation strength is reduced by about 35%, the original 8kV insulation strength will drop to about 2.2kV, which is very close to the voltage of the withstand voltage test, so there is a certain probability of insulation breakdown.

If you want to improve the yield of production, you must start with the protection of the enameled wire in these processes to minimize the loss rate of insulation strength and finally achieve the highest possible insulation strength before varnishing. The life of the motor will be relatively improved.

In recent years, due to the progress of the insulating paint of the enameled wire, the enameled wire with nanomaterials can generally extend the insulation life very well. But it only extends the insulation life, not immortality, it still has a life limit. The loss of insulating materials is a one-way subtraction, which will only get closer and closer to the end, and will not self-repair. The enameled wire with nanomaterials only prolongs the damage path in the insulation layer to achieve the effect of extending the life.

The process of varnishing is classified as a key process in the production process of low-voltage motors. The purpose of this process is to improve the insulation life. A good varnishing effect will make the motor life much longer, but it does not increase the insulation life, but delays the end of life.

02 How does the effect of varnishing affect the insulation life of the motor?

The life of the insulation is a one-way subtraction. Any abnormality will shorten the insulation life, and there is no possibility of repair. It will only get shorter and shorter during the operation time of the motor. During the operation of the motor, due to the magnetic field, if we can see the state of the stator winding head during the operation of the motor, we will find that the size of the winding head will change with the operation of the magnetic field, and friction will occur between the electromagnetic wires during this change. In the wire slot of the stator core, the gap between the electromagnetic wires will rub against each other with the vibration of the motor during the operation of the motor. Long-term friction will cause the insulation layer to be lost, and the effect of partial discharge will occur in advance, and finally cause the insulation failure between the electromagnetic wires to form an inter-turn short circuit. This is also the reason why most motors that have been running for a long time fail, which is the origin of inter-turn short circuit. A stator with poor varnishing effect cannot fix the winding head and the electromagnetic wire in the slot, allowing movement (looseness) between the electromagnetic wires, which will cause friction between the electromagnetic wires, accelerate the loss of the insulation layer, and ultimately accelerate the end of the insulation life. A stator with good varnishing effect will integrate as many electromagnetic wires as possible through the paint, minimize the friction between the electromagnetic wires, and thus extend the life of the motor, but in any case, the friction between the electromagnetic wires is objectively present and it is impossible to completely eliminate it (because the current process cannot guarantee that there is no gap between the electromagnetic wires, it is just a matter of more or less). Therefore, the insulation life after varnishing will not exceed the original insulation life.

03 How to choose a suitable varnishing process?

How to choose the appropriate process? At present, the varnishing process of industrial low-voltage motors is divided into several categories, immersion, vacuum varnishing, vacuum + pressurized varnishing and dripping. Everything has two sides, and good and bad places coexist. Each process has its merits and relatively weak points, which depends on the purpose of the enterprise.

At present, the stators of industrial low-voltage motors with a frame size less than 160 are generally immersed in the process. This is because the size of this type of motor is large. The immersion varnishing process allows a high degree of automation, such as continuous immersion equipment, which can meet the company's production requirements. At the same time, this type of motor has a low unit price and requires a cost-effective process to maintain.

The vacuum varnishing and vacuum + pressure varnishing processes cannot achieve a highly automated production mode due to the structure of the vacuum tank body, which requires feeding and discharging actions. They are generally used on motors with certain value, such as motors with a frame size greater than 160 and explosion-proof motors. Some equipment claims to be able to complete vacuum varnishing with high automation, but if you look closely at the relevant parameters, you will find that there is a big difference in the vacuum degree that can be achieved with tank-type equipment. At best, it can only be called a micro-negative pressure equipment. This type of process is more expensive than immersion varnishing, but the varnishing effect is better. The national standard clearly requires that the varnishing of explosion-proof motors must be vacuum varnishing.

The dripping varnishing process is a relatively complex process, especially for larger stators, which can only be done one by one, with lower efficiency, but the best effect. The stator is required to rotate continuously throughout the entire process to avoid the problem of paint leakage. All the insulating paint that enters the stator will eventually remain on the stator, including the amount of paint on the winding head, which is much greater than any other varnishing process, and can reach a weight increase of nearly 8% relative to the original weight.

In some applications, different varnishing processes are even used crosswise to ensure sufficient paint. This depends on the application and process requirements of the motor. Of course, the cost of good process requirements will also rise exponentially, which requires the company to determine whether to invest so much based on the positioning of its products.