Impregnation is a highly specialized and critical step in the motor manufacturing process. The special nature of this process lies in its contact with flammable and explosive chemicals, posing significant safety hazards and environmental challenges.
Speaking of the key aspects of the impregnation process, let's first review the content discussed in recent issues of MS . MS . has covered a great deal of topics related to motor insulation, such as insulation being the lifeblood of a motor, insulation systems for special-purpose motors, and the impact of insulation on motor temperature rise, almost to the point of exhaustion. Therefore, it's easy to understand why winding impregnation is so crucial for a motor, and why motor manufacturers are always willing to invest heavily in continuously upgrading and improving their motor impregnation equipment.
MS . Can meticulously compared the appearance of disassembled stator windings from well-known domestic and international motor manufacturers. Some windings had a thick layer of varnish, while others appeared remarkably thin, due to differences in manufacturing processes and equipment among manufacturers. While colleagues held differing opinions on which was superior based on appearance, their analyses from various perspectives deeply impressed MS . Can. After all, without physical dissection, no opinion can be definitively confirmed to be accurate; only when the varnish is sufficiently densely filled between the winding gaps can a product be considered of superior quality.
In short, the impregnation effect directly affects the reliability of the motor's core component—the winding. The impregnation varnish and its processing equipment are essential hardware conditions for ensuring advanced motor manufacturing standards. To allow everyone to participate in the discussion of the effects of insulating impregnation varnish and winding impregnation, Ms. Can will first share some of her views and insights today, hoping to explore and research this specific technical topic in greater depth.
Edge impregnation paint
Insulating varnish is one of the main insulating materials for motors, primarily used to impregnate the stator and rotor windings. It is available in solvent-free and solvent-based versions. The varnish fills the air gaps between the conductors and the core in the stator and rotor windings and core slots. Because varnish has better thermal conductivity than air, it effectively reduces motor temperature rise and extends motor lifespan.
Impregnation and drying
Impregnation and drying involves penetrating and filling the gaps between the motor coils with insulating varnish and then heating and drying it. Through impregnation and drying, the motor coils solidify into a unified whole, reducing and eliminating mutual movement and improving the overall performance of the motor, as well as its resistance to moisture and chemical contamination. The impregnation and drying process is particularly critical and important for the performance of the motor.
VPI impregnation process
VPI impregnation is an abbreviation for Vacuum Pressure Impregnating, a process that consists of two stages: vacuuming and pressurized impregnation. Many motor manufacturers currently use VPI impregnation. VPI treatment ensures thorough penetration of the varnish and removes air from the windings, effectively improving the motor's electrical strength, mechanical properties, thermal conductivity, and protective performance.
Factors affecting the effect of impregnation paint
(1) Surface requirements of the parts to be impregnated. A clean and dry surface of the parts is conducive to the wetting of the paint. If the parts to be impregnated have grease and dirt, the surface will not be conducive to the wetting of the paint, and will also cause varying degrees of contamination to the impregnating paint. In particular, powdery debris inside the iron core may cause fatal electrical failures in the windings.
(2) Characteristics of the impregnation varnish itself. The wettability of the impregnation varnish is closely related to the quality of the components after impregnation. If the varnish has excellent wettability, it can ensure that the fine gaps are completely filled. Otherwise, it is necessary to overcome the inherent repulsive force between the liquid and solid insulation surfaces through pressure, which will affect the insulation treatment effect. VPI equipment has this capability and can perfectly achieve the fullness of winding impregnation.
Wettability is the degree to which a liquid wets a solid surface, expressed by the wetting angle. The wetting angle is the angle between the tangent to the liquid phase at the point of contact between the two phases and the tangent to the solid surface. A smaller wetting angle indicates better wetting; a larger wetting angle indicates worse wetting. A wetting liquid has a concave surface in a capillary tube, while a non-wetting liquid has a convex surface. Here, it specifically refers to the ideal effect of good contact and bonding between the impregnating paint and the object being impregnated.
(3) Adhesives for composite insulation materials. The compatibility between the adhesives and the compatible impregnating varnishes in the composite materials used for motor winding processing is particularly important. If the two are incompatible, it will affect the spreadability and wetting effect of the varnish on the surface of the solid material.
(4) Viscosity of impregnating varnish. When the viscosity of the varnish increases, its surface tension also increases, which will reduce the wettability of the varnish and affect its penetration ability.
The effect of temperature on impregnation and its effect evaluation
● Temperature and the penetrating power and wetting ability of impregnating paint
Under the same impregnation conditions, varnish with lower viscosity easily penetrates and wets the surface of the insulating material being impregnated, while varnish with higher viscosity is less likely to penetrate and wet. As the temperature increases, the viscosity of the impregnating varnish decreases. Therefore, in actual insulation treatment, selecting the appropriate impregnation temperature is crucial to achieving satisfactory insulation treatment results.
●Temperature and the filling capacity of impregnating varnish
The filling capacity of impregnating varnish depends primarily on its solids content. Therefore, a high solids content is generally required for good filling properties. Since impregnating varnishes from the same batch have the same solids content, with a fixed solids content, higher temperatures result in lower viscosity and a lower solids content per unit volume; conversely, lower temperatures result in a higher solids content per unit volume.
●Factors affecting the wettability of impregnating varnish
1) A clean and dry surface of the component is conducive to impregnation, while grease and dirt are detrimental to impregnation; 2) The characteristics of the impregnation varnish itself; 3) The compatibility between the adhesive of the insulating material wrapping the component and the impregnation varnish; 4) The viscosity of the impregnation varnish; 5) Temperature.
● Evaluation of impregnation and drying effects
Many motor manufacturers evaluate the varnishing effect by the amount of varnish applied, but Ms. Can believes that if the varnish is too sticky, its penetration ability will be poor, and the final effect will be to form a thick shell on the winding surface, without actually achieving a curing effect; conversely, if the varnish is too thin, its penetration will be good, but it will not be easy to coat the winding, and it will also not achieve a curing effect.
For this reason, different motor manufacturers attach great importance to this process. However, different motor manufacturers will also examine and verify the process parameters such as pre-drying, impregnation and drying based on their own products, equipment and materials. Simply adopting existing methods may not truly meet the quality requirements of their own products.
