Motor requirements for insulating paint

The insulation process is involved in the motor from coil winding to assembly of finished products, and motor insulation has always been an important link in motor production. According to the production experience, once the motor insulation structure is determined, the electromagnetic wire, outgoing wire, shaft insulation, slot insulation, turn to turn insulation, terminal block and other components, if properly selected, will generally have fewer failures. In the process of insulation treatment, due to improper selection of insulating paint or unstable quality of insulating paint, or failure to strictly operate according to the insulation treatment process, there are generally many problems, and the specific manifestations are diverse. Some problems are not easy to find at that time, and they do not occur until the whole machine is installed or the goods arrive at the customer, which will bring great losses to the enterprise. Therefore, designers, technologists and operators of insulation treatment process should pay enough attention to this link when selecting materials and operating processes. The requirements for insulating paint of motor can refer to the following requirements.

(1) Electrical performance

For the motor, it mainly refers to the electrical strength (E) and insulation resistance coefficient of the paint（ ρ v、 ρ s) Two indicators. For these two indicators, the insulating paints produced in China can meet the requirements.

(2) Mechanical properties

As far as the motor is concerned, it is subject to vibration force, cold and hot impact force, and rotating centrifugal force, and the instantaneous temperature rises. Therefore, it requires good adhesion of insulating paint. Especially under high temperature (such as 155 ℃ or 200 ℃), the adhesive force should be strong, the thermal deformation temperature of the material itself should be high, and it can maintain sufficient impact strength and toughness under high temperature, so as to ensure that the motor can work safely under intense mechanical stress and has a long life.

Permeability is very important in impregnating varnish. Lacquer impregnated coils with poor permeability are very easy to cause no paint in the deep, which will not improve the performance of other insulating materials in the deep, and will easily cause weaknesses, thus causing breakdown or shortening the life. Generally speaking, paints with excessive polymerization (i.e., viscosity increases when viewed with naked eyes) or inappropriate solvents have poor permeability. For some requirements of high slot full rate, enamelled wire with small diameter (such as Φ 0.20mm or less) is required to have good permeability to the paint.

(3) Thermal performance

When the electric tools are working, the polymer materials will be cracked, hydrolyzed and oxidized with the temperature rising, which will make the materials hard and brittle, as well as crack and other phenomena, leading to the reduction of insulation resistance, electrical breakdown strength, mechanical strength, and the increase of stress and deformation. Therefore, it is of great significance to improve the heat resistance of insulating materials to ensure the safe operation of motors and improve motor power.

There are many methods to evaluate the thermal properties of paint films, such as thermoelasticity, temperature index, etc. Among them, the temperature index is recommended by the International Electrotechnical Commission to indicate the long-term heat resistance of insulating materials, and the specific level is expressed in figures. The water-soluble insulating paint at the earth edge has passed the heat resistance test at 180 ℃ for 30 hours, and the paint film is not powdery and cracked.

(4) Physical properties

It is required that the viscosity is moderate to facilitate penetration and proper paint amount; The solid content should be large, and the proportion and volatilization of the solvent should be reduced as much as possible; Low water absorption; Light color; The paint film has good cold and heat shock resistance.

(5) Chemical properties

Due to different application occasions of insulating paint, it is necessary to consider the resistance to humid and hot weather, solvent resistance and compatibility with other insulating materials.

(6) Process performance

As the insulating paint is not the final product, it needs to dip the stator and rotor in the motor manufacturing process, and then solidify to play its due role in the motor. Due to the large production volume of electric tools, it is required that the curing speed should be fast when impregnating rotors and stators, so as to ensure fast production. The curing speed and the storage period (service life) of paint are a pair of contradictions. If the curing speed is fast, the storage period (service life) must be short. If the storage period (service life) is long, the curing speed must be slow. Because it is required that the insulating paint has a long service life and good permeability after being prepared, but it also needs less loss, so it will not have harmful effects on other materials such as copper wire.

(7) Rationality and advancement of technology and economy

Electric tools are similar to household appliances in large quantity and wide range. The cost of materials directly affects the price of products. Therefore, in order to ensure that the product has a certain progressiveness index, economy must be considered, otherwise the product will lack competitiveness due to its high price.

(8) Environmental requirements

In recent years, the European Union has proposed RoHS directives to restrict the use of harmful chemicals for the electric tool materials exported to China, and required them to be enforced.

RoHS directive is implemented from July 1, 2006 (EU TTI Group decided to advance it to December 31, 2005), which means that the content of the following six hazardous substances in the products of new electronic and electrical equipment put on the EU market should meet the following requirements:

Cd<100ppm

Pb<1000ppm

Hg<1000ppm

Cr6+(hexavalent chromium)<1000ppm

PBB<1000ppm

PBDE<1000ppm