Non Grain Oriented Electrical Steel Strip NO Grades

NO grades are non-grain-oriented (NGO) electrical steel strip products with isotropic magnetic properties, designed for rotating machines and high-frequency applications. Because the steel has no preferred rolling direction, it can be stamped into stator and rotor laminations of any orientation, which is why almost all motor cores are built from NGO material. The NO series adds very thin gauges starting at 0.10 mm, giving low eddy-current loss at 400 Hz and above, so these grades are suited to high-speed motors, automotive drives and industrial appliances.

What Are NO Grades of Non-Grain-Oriented Electrical Steel?

Non-grain-oriented electrical steel is an iron-silicon alloy processed so that its magnetic properties are similar in all directions. Grades are identified by the NO prefix followed by the nominal thickness and a loss number: for example, NO20-13 is 0.20 mm nominal thickness with a maximum core loss of 13 W/kg at 1.0 T and 400 Hz. The designation system lets a designer compare grades directly by thickness and loss performance.

Because of their good permeability and low core loss, NO grades are ideal for high-frequency applications. A very low nominal thickness starting at 0.10 mm contributes directly to this: thinner laminations shorten eddy-current paths, and since eddy-current loss rises with the square of thickness, the reduction in loss at 400, 700 and 1000 Hz is substantial. All NO grades can be combined with bonding varnish or traditional insulating varnishes, and an HS (high-strength) variation is available with especially high yield strength for high-speed rotors.

Why Thin Strip Matters at High Frequency

Core loss in electrical steel has two components: hysteresis loss, which depends on the material and flux density, and eddy-current loss, which depends on lamination thickness and frequency. At power frequency (50/60 Hz), 0.35 mm and 0.50 mm strips are common. At 400 Hz and above, eddy-current loss dominates, so the strip must be thin: the NO series goes down to 0.10 mm (0.004 in), which keeps eddy-current loss small even at 1000 Hz. The result is significantly higher machine output for the same energy input, and lower temperature rise in the stator and rotor.

NO Grade Specification Table

Core loss is guaranteed at 1.0 T and 400, 700 and 1000 Hz; mechanical properties are minimum values for yield and tensile strength; A80 is the elongation on 80 mm gauge length; and thickness tolerance is given in millimeters.

Customized sizes are available. The HS (high-strength) variants of these grades provide higher yield strength for rotors that must resist centrifugal stress at high speed.

Surface Insulation and Processing

NO strip is supplied with an insulating coating that withstands the stress-relief annealing often applied after punching. Bonding varnish grades can be laminated into rigid core stacks without additional joining, which improves the mechanical integrity of the stator and rotor while keeping eddy-current losses low. Traditional insulating varnishes are available where inter-laminar resistance and punching performance are the main concerns. The coating system is selected according to the annealing temperature and the application.

Typical Applications

Stators for automotive drive motors: thin NO grades from 0.10 mm give high power density, excellent permeability and low core loss in medium- to high-speed electric drive systems.

Rotors for industrial appliances: high-speed motors in vacuum cleaners, food processors and garden tools benefit from the low eddy-current loss and light weight of thin high-strength NO grades.

High-frequency generators and motors operating at 400 Hz and above for aerospace and marine systems.

Reluctance machines and other rotating equipment where isotropic magnetic properties are required.

Frequently Asked Questions

Q: What does the NO grade designation mean?
NO identifies non-grain-oriented strip. The first number is the nominal thickness in hundredths of a millimeter, and the second number is the maximum core loss in W/kg at 1.0 T and 400 Hz. For example, NO20-13 is 0.20 mm thick with a maximum loss of 13 W/kg at 1.0 T/400 Hz.

Q: Why are thin grades needed for high-frequency motors?
Eddy-current loss increases with the square of lamination thickness and with frequency. At 400–1000 Hz, thin strip (0.10–0.27 mm) keeps eddy-current loss small, so the motor runs cooler and delivers more output for the same input.

Q: What is the difference between grain-oriented and non-grain-oriented steel?
Grain-oriented steel has excellent magnetic properties in one direction (the rolling direction) and is used for transformer cores. Non-grain-oriented steel has uniform properties in all directions, so it can be stamped into motor laminations with flux in any direction.

Q: What is an HS grade?
An HS (high-strength) grade is a NO grade with increased yield strength, achieved through alloying and processing. It is used for rotors and stators that experience high centrifugal or mechanical stress, such as high-speed motors.

Q: Can NO strip be used with bonding varnish?
Yes. Bonding varnish grades allow laminations to be bonded into a rigid stack during annealing, improving core rigidity and reducing noise and vibration in the finished motor, while maintaining low inter-laminar loss.

Q: How do I choose the correct NO grade for a motor or generator?
Base the choice on the design flux density and operating frequency, the acceptable core loss and the required stacking factor, and then on the process route: punching, laser cutting, welding, bonding varnish or final annealing each place different demands on coating and mechanical properties. Quote the motor rating, lamination geometry and strip width to the supplier so the grade and coating can be matched to the intended process.