Impregnation varnish is used to impregnate electrical coils and windings to fill the gaps therein, so that the wires of the coils and the wires and other insulating materials are bonded together to improve the electrical strength, mechanical properties, thermal conductivity and protective properties of the electrical coil insulation. Ms. Can will have a brief discussion with you about impregnation varnish today, hoping to help with process quality control.
1 Basic requirements for electrical coil impregnation varnish
● Low viscosity and high solid content to ensure good permeability and paint hanging amount;
● Good stability during storage and use;
● Good curing and drying characteristics, fast curing, low temperature, good internal drying;
● High bonding strength, so that electrical equipment can withstand higher speed and mechanical force impact;
● Compatible with other component materials;
● Good environmental performance.
2 Classification and characteristics of impregnation varnish
● Solvent impregnation varnish. Solvent impregnation varnish contains solvent, and its solid content (mass fraction) is usually between 40% and 70%. Solvent impregnation varnish with a solid content greater than 70% is called low-solvent impregnation varnish, also called high-solid impregnation varnish.
Solvent impregnation varnish has good storage stability, good permeability and film-forming properties, and is relatively cheap, but the dipping and baking time is long, and the residual solvent will cause gaps in the impregnated material. The volatile solvent also causes environmental pollution and waste, and its use is limited. It is mainly used for impregnation of low-voltage motors and electrical windings.
Solvent-free impregnation varnish is usually impregnated by immersion, and vacuum pressure impregnation and dripping can also be used.
Solvent-free impregnation varnish cures quickly, has a short dipping and baking time, has no air gap in the impregnated insulation, has good integrity, and has high electrical and mechanical properties. Solvent-free impregnation varnish has been widely promoted and applied to replace solvent-free impregnation varnish in high-voltage generators, motors, large-scale, fast-beat production lines, and certain special motors and electrical appliances. However, the storage period of solvent-free impregnation varnish is short. Solvent-free impregnation varnish can be impregnated by immersion, continuous immersion, rolling immersion, dripping immersion and vacuum pressure immersion.
3 Precautions for the use of impregnation varnish
●Quality management of impregnation varnish during use. Solvent-free paint is a polymerizable resin composition. Various types of solvent-free impregnating paints will self-polymerize to varying degrees during storage and use. Improper management will accelerate this self-polymerization. Once the solvent-free paint in the impregnation equipment produces gel, it will quickly solidify and become scrapped within 1 to 2 days, causing major accidents and losses. Therefore, the quality of the solvent-free impregnating paint in use must be strictly managed, and measures must be taken to ensure the quality stability of the paint.
(1) Regularly track and monitor the quality of the impregnating paint in use. The inspection items and inspection cycles can be formulated according to the impregnating paint used, the impregnating process equipment and the production tasks. The inspection items generally include density, density, gel time, moisture content and active diluent content. If the quality index of the paint exceeds the upper limit of the internal control index, new paint or other measures should be taken immediately to adjust it.
(2) Prevent moisture and other impurities from entering the impregnating paint. Whether epoxy or polyester solvent-free impregnating paint is very sensitive to moisture. A small amount of moisture entering the system will cause the viscosity of the paint to rise rapidly. Moisture and impurities should be prevented from entering the paint during the transportation, storage and use of the impregnating paint. The water, air and low molecular volatiles mixed in the paint can be removed by vacuuming and paint layer degassing devices, and the paint liquid can be filtered by filtering devices. The sediment in the paint is regularly filtered out to keep the resin pure.
(3) Correctly select the impregnation temperature so that the viscosity of the paint reaches the specified value. This can be selected based on the viscosity-temperature curve of the paint, while considering the difference between cold-dip workpieces and hot-dip workpieces. If the dipping temperature is too high, it will have an adverse effect on the viscosity stability of the paint; if the dipping temperature is too low, the viscosity will be high and the dipping effect will be poor.
(4) Regularly circulate and stir the paint liquid to keep the temperature of the paint liquid in the paint tank and pipeline as low as possible to prevent the paint liquid in the pipeline from self-gelling and solidifying, which will block the paint pipeline.
(5) Add new paint regularly. The adding cycle and amount depend on the production task and the nature of the paint. By adding new paint under normal production tasks, the impregnation paint in the tank can usually be used stably for a long time.
(6) Low temperature storage reduces the self-polymerization speed of the paint. The storage temperature can be controlled below 10°C. For long-term unused or conditional occasions, the storage temperature should be even lower, such as -5°C.
For solvent impregnation paint, the focus is to regularly check the density and viscosity of the paint to keep it within the control range.
● The effect of impurities on the curing of unsaturated polyester impregnation paint. Practice has shown that materials such as copper and phenols have a delayed effect on the curing of unsaturated polyester impregnation paint. Some other materials, such as rubber and oily enameled wire, will be dissolved or swollen by the styrene active monomer in the impregnation paint, making the surface of the impregnated workpiece sticky.
● Compatibility issues. Compatibility tests should be carried out to ensure that the impregnation paint is fully compatible with other constituent materials in the insulation system.
●Baking process issues. Solvent-based impregnation varnishes contain a large amount of solvents. Generally, two or more impregnation, baking and gradual temperature increase baking processes are used to prevent pinholes or gaps in the paint film and improve the performance and life of coil insulation. The baking process of solvent-free impregnation varnishes should be careful to prevent excessive glue flow. Rotary baking can effectively reduce glue flow.
●Environmental pollution issues. Appropriate measures should be taken to control the solvent vapor and styrene emitted during the impregnation and baking process within the specified allowable content range.
Post time: Aug-15-2024
