Varnish is a type of liquid coating material, composed of resin that is capable of drying into a hard transparent film. While varnish is commonly associated with woodworking for the means of protecting surfaces and improving their appearance, insulating varnish is also quite useful for electrical applications. For devices such as motors, transformers, generators, sensors, and various other apparatuses that rely on electromagnetic induction for their functionality, insulating varnish and impregnating resins serve to protect and enhance electrical insulation and structural integrity.
For a standard transformer, as an example, coil windings will feature electrical wires that are coated with a thermosetting resin or insulating varnish for the means of protecting such assemblies from electrical shorting. Additionally, the transformer assembly itself may also be sealed with a resin to protect the system from various environmental hazards such as moisture and dirt. When applying insulating varnish and resins to electrical equipment, their application results in crosslinked materials which will boast high strength, stability, and durability.
In order to apply insulating varnish electrical materials and resins for sealing electrical components, there are a few methods that may be used. Generally, the most popular methods available are potting, casting, and encapsulation. Potting is a method in which the device is loaded with a pot and then filled with liquid potting. Due to the pot loading the device, it becomes a part of the assembly itself. Potting is typically reserved for high production conditions and is the most popular method of the three. Casting is a method that is quite similar to potting, albeit the molding case is removed from the assembly once encapsulation and curing is finalized. Encapsulation is the final common method which consists of having a device dipped into a resin. Also known as a “dip coating”, such methods prove quite popular and result in a thick coating that encases the assembly.
While varying methods may be used to achieve a certain type of insulating varnish electrical assembly, there are also a few common insulating resins that are often used for such procedures. Epoxy resists are quite common due to their high strength and low shrinkage when cured. Additionally, they also provide optimal strength and resistance against chemicals and environmental conditions, making them a robust choice. While most epoxies come in the form of two-part resins that are cured at room temperature, there are also various thermally cured or thermoset one-part epoxies. For their application, epoxy resins are commonly used as casting resistance materials, laminating resins, encapsulates, electrical conductors, structural bonding adhesives, and more.
Phenolic and formaldehyde are also common resins, coming in the form of molding compounds or adhesives that are capable of withstanding high heat with their resistance. While such resins can be made from a variety of materials, the most durable versions are made from chemicals of the phenol group and formaldehyde. Phenolic resins also may come in a variety of states such as liquid, powder, and film forms. With their high dielectric properties, strong resistances, and strong bonds, such resins are commonly used for a variety of applications.
Polyurethane resins are the final primary material, offering assemblies high flexibility, durability, and impact resistance. Formed through a reaction between an isocyanate component with polyols or other components, such resins then complete their curing with air evaporation, heat application, or a catalyst. When choosing polyurethane resins, it is important that the insulating varnish will provide a long service life. If conductivity rises due to degradation or improper insulation, damage can quickly ensue.
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