Furnaces for Electrical Steels

Coatings | Lamination Annealing | Typical Cycles

SECO/WARWICK manufactures a wide variety of custom furnace systems for transformer core annealing, lamination annealing, bluing and amorphous metal processes.

For batch or continuous operations, SECO/WARWICK provides quality roller hearth, pusher, mesh belt, bell and elevator furnace systems with PC/PLC control systems that provide precision temperature control and process flexibility.

Characteristics of Electrical Steels

The conversion of electrical energy from one voltage to another voltage by use of a transformer or into mechanical energy by use of a motor requires establishment of a strong concentrated magnetic field. This concentration and strength is obtained by the use of ferro-magnetic steel containing silicon or steels which have had carbon content reduced to less than .01%.

Decarburized steel has the approximate magnetic qualities of AISI M36 steel containing up to 1-1/2% silicon, and is generally applied in fractional and small integral horsepower motors. Silicon steels are used primarily in high efficiency equipment with grain oriented silicon steels being used in the highest efficiency equipment.

Grain growth is generally promoted in all classes of electrical steels to improve magnetic qualities by reducing the number of grain boundaries. The magnetic qualities of various steels are determined by

Epstein tests on samples tested for energy loss and permeability.

Electrical Steels

The performance of a steel in an electro-magnetic circuit is measured by eddy current and hysteresis losses, and permeability. All of these parameters are affected by the heat treatment given to the steel during the course of its fabrication into a magnetic structure. The presence of carbon sulphur, oxygen and nitrogen in the steel increase eddy current and hysteresis losses while lowering permeability. Carbon is by far the most harmful element, and heat treatment is therefore aimed at reducing carbon levels.

In-processing annealing, in addition to removing strains set up by cold working, also reduces carbon levels by carrying out the annealing cycle in a decarburizing atmosphere. Hysteresis losses are decreased and permeability is increased. Carbon levels can be reduced from .08% to less than .01% in AISI1008 steel. Eddy current losses vary with lamination thickness and lamination coatings. For most 60 hertz applications 24 gauge (.024”) has optimum stamping qualities consistent with acceptable eddy current losses.

Coatings

To reduce or minimize eddy current losses between laminations, electrical steels are normally coated for increase of inter-laminar resistance. These coatings may be organic, in-organic or a coating of magnetite (Fe3O4).

Organic and inorganic coatings are generally applied with rolls and then baked to remove a volatile vehicle. Magnetite (Fe₃O₄) is applied by exposing the lamination to a high dew point exothermic atmosphere or a super heated steam atmosphere for a period of up to one hour at a temperature of 950˚F.  This coating greatly increases resistance between laminations and provides a high resistance to rust and corrosion.

Lamination Annealing

Batch or continuous annealing of stamped laminations follow a cycle employing a rich exothermic atmosphere with soaking time for decarburization and grain growth. Cooling cycles are also controlled to obtain optimum magnetic qualities. All stamping oils must be removed before the steel is introduced to the annealing chamber.

Transformer Core Annealing

When wound transformer cores are annealed, dew point is critical as oxygen compounds such as water vapor are oxidizing to silicon and long exposures to this oxidizing condition can undermine the mill anneal finish and cause growth and dimensional difficulties.

Amorphous Metal

Amorphous Metal is a relatively new material for use in electrical devices. The main advantage is that it has no grain boundary as there is in grain oriented silicon steels. Therefore it transforms energy much more efficiently than silicon steel.

Typical Cycles

Industrial Services

A wide range of services are available for our equipment. These include rebuild projects, field service, spare parts, equipment supply, control and combustion upgrades, and fabrication services. As a result of these services, we have provided our customers improved performance, lower emissions, better efficiency and enhanced product temperature uniformity.

The latest design, materials, and equipment specifications should be obtained from the company before any reliance is placed on this standard bulletin since changes may occur due to product improvement. E-mail info@secowarwick.com for more information and a quote.

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