Views: 10 Author: Site Editor Publish Time: 2025-07-25 Origin: Site
Motors are fundamental components of a wide range of industrial, commercial and household appliances. To ensure the life and reliability of motors, high-quality insulation materials are required to prevent failures caused by electrical, mechanical and thermal stresses. The insulation performance of motor windings is a key factor in determining motor reliability, life and operational safety. Among the many factors that affect insulation, the varnishing and curing effects of windings play a decisive role. Appropriate varnishing can fill the gaps and micropores inside the windings, making the windings tightly combined, and enhancing insulation performance, heat resistance and mechanical strength. On the contrary, poor varnishing may lead to insulation breakdown, increased temperature rise, and even motor failure.
This process not only enhances electrical insulation performance, but also significantly affects the mechanical stability, heat resistance and overall efficiency of the motor. Therefore, it is crucial to improve the varnishing effect.
There are two main types of impregnating varnishes: solvent - based varnishes and solvent - free varnishes.
· Solvent - based Varnishes: These varnishes contain a certain amount of solvents, which can adjust the viscosity of the varnish. They have good fluidity and permeability, but the solvents may volatilize during the drying process, which may affect the environment and the health of operators.
· Solvent - free Varnishes: As the name suggests, these varnishes do not contain solvents. They have the advantages of high solid content, low VOC (volatile organic compound) emissions, and good environmental performance. However, their viscosity is usually relatively high, and special equipment or processes may be required for impregnation.
The following table compares the main properties of solvent - based and solvent - free impregnating varnishes:
Property | Solvent - based Varnish | Solvent - free Varnish |
Viscosity Adjustment | Relatively easy (by adding solvents) | Difficult (usually need to adjust temperature or use special equipment) |
Environmental Impact | Higher VOC emissions | Lower VOC emissions |
Solid Content | Generally lower (affected by solvent content) | Higher |
Permeability | Good (due to lower viscosity) | Relatively poor (higher viscosity) |
· Viscosity: Viscosity is a key factor affecting varnish penetration and paint amount. Lower viscosity is conducive to varnish penetration into the winding gap, but too low viscosity may result in insufficient paint. On the other hand, although higher viscosity can improve filling performance, it may reduce penetration. Therefore, the appropriate viscosity should be determined based on the winding size and winding gap. For example, for windings with smaller gaps, a lower viscosity varnish may be more suitable to ensure sufficient penetration.
· Solid Content: For solvent - based varnishes, the solid content is an important indicator. A higher solid content means that after the solvent volatilizes, a thicker and more continuous 漆膜 can be formed. International standards recommend high - solid - content and low - viscosity varnishes. In China, the solid content of insulating varnishes is generally not less than 45%. For solvent - free varnishes, the curing volatile content is usually used to represent, and the curing volatile content of general - purpose solvent - free varnishes should not exceed 15%.
· Drying Time and Curing Temperature: Drying time and curing temperature affect production efficiency and energy consumption. In order to save energy and increase efficiency, it is recommended to use insulating varnish with fast drying speed and low curing temperature. However, the drying and curing process must also ensure that the paint film is fully cured to form a good paint film. For example, some advanced insulating varnishes can be cured at a lower temperature (such as 120-150℃) in a shorter time (such as 1-2 hours), which is conducive to reducing production costs and improving production efficiency.
· Electrical and Chemical Properties: The impregnating varnish must have excellent electrical properties, such as high breakdown strength and volume resistivity, to ensure the insulation performance of the windings. It should also have good chemical stability, being resistant to moisture, heat, oil, and other factors. For example, in a high - humidity environment, the varnish should have good moisture resistance to prevent the insulation performance from deteriorating.
The structure of the motor winding, including the number of turns, coil arrangement and the gap between windings, has a significant impact on the impregnation effect. Windings with compact structures and small gaps are more difficult to impregnate, and the impregnation varnish needs to penetrate into narrower spaces. For example, in some high-performance motors, the windings may be designed as a multi-layer structure, which requires the impregnation varnish to have excellent permeability to ensure that all layers are fully impregnated.
Before impregnation, the windings must be thoroughly cleaned to remove contaminants such as oil, dust and metal debris that may affect the adhesion and insulation properties of the impregnation varnish. Pre-treatment processes such as degreasing, rust removal and drying should be strictly followed. For example, ultrasonic cleaning can be used to remove stubborn contaminants on the surface of the windings, and then the windings can be dried in a clean and dry environment to ensure that there is no residual moisture.
· Dipping Tank: This is the most basic paint dipping equipment, which is simple and easy to operate, but the paint dipping effect has certain limitations, especially for windings with complex structures or small gaps, the paint liquid may not be able to fully penetrate into the winding, ultimately resulting in uneven paint dipping.
· VPI (Vacuum Pressure Impregnation) Equipment: As mentioned in the reference content, VPI equipment is an important process equipment for the production of electrical equipment such as high-voltage motors and transformers. It can create a vacuum environment to remove air and moisture from the windings, and then apply pressure to ensure that the paint liquid fully penetrates into the windings. VPI equipment can significantly improve the varnishing effect, but it also has high requirements for equipment investment and operation.
· Vacuum Degree and Holding Time: The vacuum degree is usually set between 50 - 100 Pa, and the holding time is about 10 - 30 minutes. A higher vacuum degree and appropriate holding time can more effectively remove air and moisture from the windings, creating favorable conditions for the penetration of the varnish. For example, in the production of high - voltage motor windings, a vacuum degree of 60 Pa and a holding time of 20 minutes may be used to ensure that the windings are fully degassed.
· Pressure and Holding Time: After the vacuum process, pressure is applied, usually in the range of 0.3 - 0.8 MPa, and the holding time is 20 - 60 minutes. The pressure helps to drive the varnish into the windings and ensure that the varnish fills all the gaps. Different types of windings and varnishes may require different pressure and holding time settings. For example, for windings with large gaps, a lower pressure may be sufficient, while for windings with small gaps, a higher pressure may be needed.
· Temperature Control During Impregnation: The temperature of the varnish and the windings during impregnation also affects the impregnation effect. Generally, the temperature is controlled between 40 - 80 °C. An appropriate temperature can reduce the viscosity of the varnish, improving its permeability, while also preventing the varnish from curing too quickly. For example, when using a solvent - free varnish with high viscosity, increasing the temperature to 60 °C can effectively reduce its viscosity and improve the impregnation effect.
· Oven Drying: This is the most common drying method. The windings are placed in an oven, and the temperature is gradually increased to the curing temperature of the varnish. The drying process needs to be carefully controlled to ensure uniform heating of the windings. For example, a rotating oven can be used to ensure that the windings are heated evenly during the drying process, preventing local overheating or under - curing.
· Infrared Drying: Infrared drying uses infrared radiation to heat the windings. It has the advantages of fast heating speed and uniform heating. However, the equipment cost is relatively high, and the control of the drying process requires certain technical expertise.
The curing temperature and time depend on the type of impregnation varnish. Generally, the curing temperature is 120-200℃ and the curing time is 1-4 hours. Inappropriate curing temperature and time will lead to incomplete curing of the impregnation varnish, resulting in reduced insulation performance and mechanical strength. For example, for a certain solvent-free impregnation varnish, in order to ensure complete curing, the curing temperature can be set to 150℃ and the curing time can be set to 2 hours.
Impregnation is a process of filling the gaps and micropores in the motor windings with an impregnating varnish. This not only improves the insulation performance but also enhances the mechanical strength and thermal conductivity of the windings. The impregnating varnish, after curing, forms a continuous and smooth film on the surface of the windings, binding them into a rigid whole.
Aspects of Significance | Details |
Insulation Performance | A proper impregnation process can effectively prevent the ingress of moisture, dust and other contaminants, thereby improving the electrical insulation performance of the winding and avoiding electrical breakdown and short circuit failures during motor operation. |
Temperature Rise | A good impregnation process can improve the thermal conductivity of the winding, thereby dissipating heat more effectively, reducing the temperature rise of the motor, and helping to improve motor efficiency and extend its service life. |
Mechanical Strength | After curing, the impregnation varnish can provide additional mechanical support for the winding, reduce the impact of mechanical vibration and centrifugal force during motor operation, and help prevent the winding from loosening and deformation. |
VPI is widely adopted for high-voltage motors and precision windings due to its superior penetration and film-forming properties. The optimized process flow is as follows:
· Pre-treatment: Clean windings to remove oil, dust, and oxides using solvents or ultrasonic cleaning.
Pre-dry windings at 90–100°C for 3–5 hours to reduce moisture content below 0.5%.
· Vacuum Stage: Place windings in a sealed chamber and apply vacuum (-0.095 to -0.1 MPa) for 30–60 minutes to extract air from gaps and micropores.
· Impregnation: Introduce varnish into the chamber until windings are fully submerged, maintaining vacuum for an additional 15–30 minutes to enhance penetration.
· Pressure Application: Release vacuum and apply external pressure (0.3–0.5 MPa) for 20–40 minutes to force varnish deeper into gaps.
· Drainage and Curing: Remove excess varnish and cure windings in an oven. Curing parameters depend on varnish type (e.g., 150°C for 4 hours for polyesterimide varnish).
For low-voltage motors or non-critical applications where VPI is unavailable, conventional dipping processes can be optimized through:
· Multi-stage Dipping: Repeat dipping 2–3 times with intermediate drying to compensate for insufficient penetration.
· Varnish Agitation: Stir varnish continuously during dipping to maintain uniform viscosity and prevent sedimentation.
· Controlled Drainage: Tilt windings at a 45° angle during drainage to reduce paint accumulation at the bottom, ensuring uniform film thickness.
Curing is the final step that determines varnish hardness, adhesion, and insulation performance. Key optimizations include:
· Gradient Temperature Curing: Increase temperature in stages (e.g., 80°C for 1 hour → 120°C for 2 hours → 150°C for 3 hours) to avoid rapid solvent evaporation, which causes bubbles.
· Uniform Airflow in Ovens: Install fans and baffles to ensure consistent temperature distribution (±5°C) across all parts of the winding.
· Post-curing Inspection: Measure curing degree using differential scanning calorimetry (DSC) to ensure no uncured regions remain.
· Technical Training: Provide regular technical training for workers engaged in the impregnation process, including the principles of impregnation, operation of equipment, and control of process parameters. Improve their technical level and operation skills.
· Quality Awareness Training: Strengthen the quality awareness training of workers, make them understand the importance of the impregnation process for motor performance and quality, and encourage them to actively participate in quality control.
· Based on Motor Type and Application Environment: Different types of motors and application environments have different requirements for impregnating varnishes. For example, in a high - temperature environment (such as in a boiler fan motor), a high - temperature - resistant varnish should be selected; in a humid environment (such as in a marine motor), a varnish with good moisture resistance should be chosen.
· Considering Production Cost and Efficiency: While high - performance varnishes may provide better impregnation effects, they also often come with higher costs. Therefore, a balance should be struck between performance and cost. For example, in mass - produced general - purpose motors, a cost - effective solvent - based varnish may be selected, while in high - end motors with strict performance requirements, a solvent - free varnish with excellent performance may be preferred.
· Improving Winding Structure: For windings that are difficult to impregnate, the winding structure can be optimized. For example, increasing the gap between the windings appropriately or changing the arrangement of the coils can improve the permeability of the varnish.
· Strengthening Cleaning and Pretreatment: Establish a strict cleaning and pretreatment process to ensure that the windings are free from contaminants. Use advanced cleaning equipment and processes, such as ultrasonic cleaning and high - pressure air blowing, to improve the cleaning effect.
· For Small - batch Production or Laboratory Use: If the production volume is small or for laboratory research, a combination of dipping tank and appropriate process control can be used. Although the impregnation effect may not be as good as that of VPI equipment, it can meet the basic requirements at a lower cost.
· For Mass Production: VPI equipment should be used as much as possible to ensure a high - quality impregnation effect. At the same time, the VPI equipment should be regularly maintained and calibrated to ensure its stable operation.
· Temperature Uniformity: Whether using oven drying or other drying methods, ensure uniform heating of the windings. Use temperature sensors to monitor the temperature of different parts of the windings during the drying process and adjust the heating method in a timely manner.
· Curing Curve Optimization: Develop an appropriate curing curve according to the type of varnish and the characteristics of the windings. The curing curve should include the heating rate, holding time at each temperature stage, and cooling rate to ensure complete curing of the varnish and good performance of the windings.
Effective impregnation of motor windings is crucial to improving motor performance. The vacuum pressure impregnation (VPI) process has significant advantages over traditional methods, can achieve uniform penetration of paint, and greatly optimize the insulation effect.
To achieve high-quality impregnation, multi-dimensional efforts are needed: select suitable impregnation paint, optimize winding design and pretreatment, accurately control VPI parameters, strictly control the drying and curing process, and establish a full-process quality control system.
Although the initial investment of VPI equipment is high, the long-term benefits are outstanding - it can improve motor efficiency, reduce failure rate, extend life, and significantly reduce overall costs, especially to meet the needs of industrial and commercial fields for high-reliability motors, while helping the industry to develop in the direction of high efficiency and environmental protection.
In the future, with the upgrading of motor technology, impregnation technology needs to continue to innovate, including the application of intelligent equipment and the research and development of new materials. Manufacturers can only gain an advantage in competition and support high-quality development of the industry if they master core processes and persist in innovation.
