Non Oriented Grade Varnish Improves Steel Punchability and Interlaminar Insulation

Non-oriented grade electric steel varnishes are meant to enhance the operation of fully processed electrical steel. The main objective is to improve the steel punchability and provide interlaminar insulation. Each type has its own particular characteristics such as punchability effect, insulation level, weldability, temperature resistance, and corrosion protection. That is why material use determines the optimum varnish to be used. Every varnish is developed to be environment-friendly, chromium-free and hydrosoluble.

The C3 type varnish has a base of synthetic resins that creates a product possessing excellent lubrication properties needed for punching. The coated sheet can even be punched without any additional lubricant. The resin chemical composition has certain advantages such as strong adhesion and high elasticity. The C3 varnish is well suited for automatic stacking processes. A standard gauge can be anywhere from 1 to 4 µm per side. A coat thickness of 3 µm assures an optimum interlaminar insulation, whereas a thickness less than 1 µm has the advantage of improved weldability.

The C5 type varnish is pigmented, created with pigments, mineral products and thermostable resins. In the case of the EC 5N varnish, the amount and type of mineral products used is selected to create a coating that provides sustained temperature resistance during periods of prolonged thermal treatment. This is particularly important to situations where stress-relief annealing is needed after punching. The C5 varnish composition is created to maintain dielectrical properties during the course of damaged copper winding repair. In addition, the coating mineral part provides a high degree of thermal conductivity. The mineral product and resin combination strikes the right balance between weldability and corrosion protection. A typical gauge is from 1 to 4 µm per side. As opposed to the EC-5-N, the EC-5-P uses a greater amount of organic components to achieve a higher rate of punchability, while simultaneously maintaining good weldability. A standard gauge is between 1 to 2 µm per side.

The C6 type varnish is also pigmented, and is particularly recommended for high-power rotating machines because of its high electric insulation. The mineral elements are chosen to prioritise punching oil retention and reduce punching tool wear. The varnish rigidity is also enhanced and this reduces dimensional changes when under high pressure or temperature. The C6 varnish is well suited to contractor use as it reduces noise while permitting a high flutter frequency. A standard gauge is around 4 to 10 µm per side. The C6 varnish can be obtained in a formaldehyde-free version.

All these coatings are useful for pole sheets in cold rolled variants, fully processed grades, and in a diverse variety of electrical appliances including transformers, contactors and rotating machines. The raw materials utilised have a chemical composition in both cured varnish and liquid state that does not need specific protective measures while processing coated steel or while using the coating in any desired application.

Nikhil Kaitwade

With over 8 years of experience in market research and consulting industry, Nikhil has worked on more than 250 research assignments pertaining to chemicals, materials and energy sector. He has worked directly with about 35 reputed companies as lead consultant for plant expansion, product positioning, capacity factor analysis, new market/segment exploration, export market opportunity evaluation and sourcing strategies.