Product Bulletin
Furnaces for Electrical Steels
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
Fig 1 Transformer Core Annealing in a
another voltage by use of a transformer or into mechanical
Continuous, Roller Hearth Furnace System
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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.
Fig 2 Bell Furnace for batch processing
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Product Bulletin
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
Fig 3 Roller Hearth Lamination Annealing Furnace
laminations, electrical steels are normally coated for
with Steam Blue System
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
follows 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
Fig 4 Continuous System for Motor Laminations
oxidizing to silicon and long exposures to this oxidizing
condition can undermine the mill anneal finish and cause growth and dimensional difficulties.
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Product Bulletin
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
Continuous Systems equipped with return conveyors and cross transfers
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Product Bulletin
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.
About SECO/WARWICK
The SECO/WARWICK Group is one of the world’s leading manufacturers of heat treatment furnaces and a
technology leader. With our fully equipped research and development facility and cooperation with the leading
academic centers in Europe, we are able to provide innovative solutions not offered anywhere else in the world.
The Group is made up of companies located in five countries on three continents, and we sell our products in 45
countries around the world. We supply furnaces to customers involved with steel, titanium and aluminum
production as well as aluminum recycling, forging, automotive, aerospace, commercial heat treating, HVAC/R,
electronics, wind energy, medical equipment and nuclear industries. Visit our website below for more
information.
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.
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