All of EDCOR Electronics Corporation's transformers that have steel core lamination are made with M-6 29 Gauge - 0.014" (0.355 mm) Line Orientated Electrical Transformer Steel Lamination, unless the customer specified another core type and is RoHS compliant. This steel is used in audio amplifiers, current, output, power transformers; chokes and saturable reactors; ferro-resonant regulators. The squared hysteresis loop iron-silicon alloy the was expressly developed to provide lower core loss with higher permeability in the rolling direction. Grain oriented laminations are supplied in the stress relief annealed condition. The elementary patterns of the crystals in the material are "oriented", or so arranged that the axis of easiest magnetization is nearly parallel and aligned in the direction of rolling. The alignment is accomplished by special cold-rolling and annealing processes. This gives

1. Lower core losses as a consequence of design.

2. Higher initial permeability.

3. Higher permeability at higher inductions.

4. VA/Temperature relationship is much more stable over a wide range of ambient temperatures.

5. Withstands more severe vibration and shock.

6. Our "EI" lamination s are tested under standards set up by the ASTM A-346.

Core Loss

Epstein-based core loss values for grain oriented steels are usually reported in the 100% with-grain (parallel to the rolling direction) condition. For lamination applications, particularly for E and I configurations, reference should also be made to core loss values with 75% with-grain, 25% cross-grain condition. Maximum core loss limits are shown in the following table.

Permeability

Permeability refers to the relative ease with which a material will accept a magnetic field, compared to air with a permeability of 1. One of the major advantages of laminations that are annealed after stamping is that the highest possible permeability is achieved. This translates into the lowest possible exciting powers (volt-amps per pound) for AC applications.

Typically, minimum peak permeability is 2000 for semi-processed, annealed last grades (measured at 1.5 Tesla, 60 Hertz) for cold rolled and non-oriented silicon grades.

Minimum peak permeability for fully processed grades is significantly less than 2000 and is a function of both gauge and grade.

As a general rule, permeability increases as thickness increases, and decreases with increasing alloy content or higher grades. As a result, some thin high alloy grades; e.g., 29 gauge M19, may exhibit permeability values less than 2000 for semi-processed, and less than 800 for fully processed grades.

The units for permeability are dimensionless because they represent a relative value. Some practices refer to gauss/oersted as the units for permeability.

Saturation induction can be important and can limit overall performance in some applications. As a general rule, saturation induction decreases with increasing alloy content, or grade. For magnetic steels, pure iron has the highest saturation induction (2.3 Tesla). The lowest saturation induction levels (2.10 Tesla) are found in the highest alloy grades M19 and M15, while grain oriented M6 exhibits saturation induction levels of 2.03 Tesla.

Surface roughness is measured by a probe which records and averages the height-to-height variations within a fixed sample length, generally in accordance with ANSI/ASME B46. The average of the surface profile heights is the arithmetic average (AA).

Peak counts can also be used in some applications to describe surface textures and roughness.

Burr Tolerances

Most high quality laminations use tungsten carbide dies with tight tolerances to ensure that all aspects of the punched edges have minimum burrs.

Laminations are usually wired so that all of the burrs follow the same direction, allowing for nesting of laminations and maximum stacking factor without gaps. Assemblers who reverse (rather than rotate) lamination stacks to compensate for gamma should be aware that mismatch of burr directions can lead to gaps in the stack which may be undesirable.

Examples of burr tolerances are shown in the following table.

Stacking Factors

The stacking factor is the ratio of the actual volume of steel in a stack, not including air or insulating materials, compared to the measured dimension of the stack. The stacking factor is affected not only by the surface roughness of the laminations, but also by the pressure applied to the stack and the method of assembly. Examples of typical stacking factors are found in the following table:

Surface Insulation

- Description of Coatings -

The primary function of a coating on a lamination is to provide interlaminar resistance for reduction of stray losses. The resistance of the coating normally depends on both the thickness of the coating and its chemical composition. Variation can be expected in coating resistance primarily due to variation of coating thickness, usually in the range 0.5 to 1.5 microns.

Typically, better performance (higher resistance) coatings are required for higher field strength applications or where elevated temperatures and/or higher efficiencies may be required. Applications using higher frequency (400-1000 Hertz) also usually require higher resistance coatings.

A summary of coating types used for electrical applications based on ASTM A976 is shown in the following table:

C-3 varnish coatings should not be used in conjunction with annealed laminations.

Usually, C-2 and C-5 coatings are considered to be more difficult to weld consistently because of their higher surface resistance and the potential for variations in coating thickness. Special attention to ground current paths, particularly through the edges of the lamination, is recommended when welding laminations with these coatings.

- Steam Blue Oxide -

All of the steel that EDCOR Electronics use has a steam blue oxide on the surfaces and edges. This oxide, often in combination with the rough surface gives an insulating medium to minimize stray losses between laminations. Steam blue oxide is used primarily for fractional, subfractional, and small integral motors, low power, and audio transformers and power supplies.

In addition to its insulating characteristics, steam blue oxide reduces rust and corrosion, and is compatible with a variety of welding processes and secondary powder, epoxy or E-coat processes.

In applications involving high efficiency, high pressure, high power densities or large surface areas, higher value insulating coatings should be used.

Typical Coatings Available for Annealed Laminations (Semi-Processed) Grades -

Basic Design Formulae: