Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1996-10-03
1999-01-26
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148113, H01F 118
Patent
active
058633561
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for producing electric sheets, in particular grain-oriented electric sheets, with an evenly well-adhering glass film and with improved magnetic properties, in which the hot rolled strip which is produced at first and is optionally annealed is cold-rolled up to the end thickness of the cold strip with at least one cold rolling stage, thereafter an annealing separator is applied to the strip which is rolled up to the end thickness, and is dried and thereafter the cold strip thus coated is subjected to high-temperature annealing, with an important component of the annealing separator being a hydrous magnesium oxide (MgO) dispersion and the annealing separator being additionally provided with at least one additive.
During the production of grain-oriented electric sheets a decarburization annealing is carried out after the rolling to end thickness. During this process the carbon is extracted from the material. An oxide layer forms on the strip surface as basic layer whose relevant components are silicon dioxide (SiO.sub.2) and fayalite (Fe.sub.2 SiO.sub.4) . Following the decarburization annealing the strip is coated with a antisticking layer and is subjected to long-term annealing in the coil. The antisticking layer is to prevent, on the one hand, the glueing together of the individual coil windings during the long-term annealing and, on the other hand, to form an insulating layer (glass film) with the basic layer on the strip surface. The antisticking layer substantially consists of magnesium oxide (MgO) . The MgO is slurried in form of a powder in water, applied to the strip and dried. During this process a part of the magnesium oxide reacts with the water to form magnesium hydroxide (Mg(OH).sub.2) . The quantity of water bound to the magnesium hydroxide, relating to the overall oxide powder quantity, is known as annealing loss.
The relevant courses and reactions relating to the insulation between strip surface and antisticking layer during the long-term annealing are summarized below in a simplified way:
______________________________________ Dehydration of the magnesium hydroxide
Mg(OH).sub.2
-- --> MgO + H.sub.2 O
(I)
Formation of glass film
FeSiO.sub.4
+ 2MgO -- --> Mg.sub.2 SiO.sub.4
+ 2FeO (II)
SiO.sub.2
+ 2MgO -- --> Mg.sub.2 SiO.sub.4
(III)
______________________________________
which starts from approx. 350.degree. C. In this respect it is important
for an optimally occurring process, relating both to the insulation as
well as to the formation of the magnetic properties, that the quantity of
the released water remains within certain limits. The water humidifies the
annealing atmosphere which predominantly contains hydrogen and thus
establishes a respective oxidation potential. The annealing atmosphere
must not be too dry because the glass film would be formed too thinly
under such conditions. But it must also not become too humid, because in
such a case there would be too much afteroxidization and the glass film
would have defective places such as local flaking and unfavourable
adherence.
BACKGROUND OF THE INVENTION
In the past a number of additives to the MgO powder were introduced which were to improve the formation of the insulating layer and the magnetic properties of the finished product. These include titanium oxide (TiO.sub.2), boron compounds such as boron oxide (B.sub.2 O.sub.3) or sodium tetraborate (Na.sub.2 B.sub.4 O.sub.7) as well as antimony compounds such as antimony sulphate (Sb.sub.2 (SO.sub.4).sub.3) in combination with a chloride, preferably antimony chloride SbCl.sub.3. The additives used frequently also showed disadvantages in addition to the positive influences on the respective target values, which reduced the product quality. In summary, the processing of such additives is complicated because they partly have to be dissolved in previously heated water. Particularly in the salts of sodium tetraborate and in particular antimony sulphate, which are difficult to dissolve in water, undis
REFERENCES:
patent: 3151000 (1964-09-01), Schmidt et al.
patent: 3151997 (1964-10-01), Harvey
patent: 4909864 (1990-03-01), Inokuti et al.
Bolling Fritz
Dolle Thomas
Gehnen Klaus
Hammer Brigitte
Schrapers Heiner
EBG Gesellschaft fur Elektromagnetische Werkstoffe mbH
Sheehan John
LandOfFree
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