WO2020088764A1 - Method for producing a grain-oriented flat steel product for electromagnetic applications, flat steel product for electromagnetic applications, and transformer core stack produced from such a flat steel product - Google Patents

Abstract

The invention relates to a method for producing grain-oriented flat steel products for electromagnetic applications (electrical flat steel products), said products reliably having a surface quality which varies within a narrow tolerance window at most and being suitable for a machine-automated stacking process with little complexity. For this purpose, the method according to the invention has the steps of a) providing an electric flat steel product which has an insulating layer on at least one surface, and b) producing a lacquer layer with a thickness of less than 5 μm on the insulating layer. A grain-oriented flat steel product according to the invention accordingly comprises a steel substrate, optionally a forsterite layer produce thereon, an insulating layer which is applied onto the steel substrate or the optionally provided forsterite layer, and a lacquer layer which is applied onto the insulating layer and has a maximum thickness of 5 μm and more than 50 wt.% of which consists of organic components. By virtue of the surface quality produced according to the invention, such flat steel products are suitable in particular for the production of core lamination stacks for transformers.

Description

 Process for the production of a grain-oriented flat steel product for electromagnetic applications, flat steel product for electromagnetic applications and transformer core stack produced from such a flat steel product

The invention relates to a method for producing a grain-oriented flat steel product for electromagnetic applications.

Likewise, the invention relates to a flat steel product for electro-magnetic applications, which is particularly suitable as a base for the production of sheet metal stacks, and a transformer core stack, which is formed from blanks of such a flat electrical steel product.

The flat steel products in question here are

Steel strips or sheets from which parts for electromagnetic systems and the like are manufactured.

Grain-oriented flat steel products of the type in question here, which are also referred to in the technical language and in the present text as "electrical sheets" or "electrical steel flat products", are particularly suitable for uses in which a particularly low magnetic loss is in the foreground and high demands permeability or

Polarization. Such requirements exist in particular for parts for power transformers, distribution transformers and

higher quality small transformers. As explained in detail, for example, in EP 1 025 268 B1, in the course of the manufacture of flat electrical steel products, a steel is first of all made (in% by weight) typically 2.5 to 4.0% Si, 0.010 to 0.100% C, up to 0.150% Mn, up to 0.065% AI and up to 0.0150% N as well as optionally 0.010 to 0.3% Cu, up to 0.060% S, up to 0.100% P, up to 0.2% As, Sn, Sb, Te and Bi, balance iron and unavoidable impurities, to a starting material such as a slab, thin slab or

cast tape, potted. The preliminary material is then subjected to an annealing treatment, if necessary, in order then to be hot-rolled to a hot strip.

After reeling the hot strip obtained in this way and optionally additionally performing annealing as well as completing it also optionally

Descaling or pickling treatment is then cold rolled from the hot strip in one step or several steps, and in the event that several cold rolling steps are carried out, between the

An intermediate annealing can be carried out if necessary in the cold rolling steps. During the decarburization annealing carried out subsequently

usually to avoid magnetic aging of the

The carbon content of the cold strip is significantly reduced.

After the decarburization annealing, an annealing separator, which is typically MgO, is applied to the strip surfaces. The

Annealing separator prevents the turns of a coil wound from the cold strip from welding together during the subsequent high-temperature annealing. During high-temperature annealing, which is typically carried out in a hood furnace under protective gas, a selective texture is created in the cold strip by selective grain growth. Furthermore, a forsterite layer forms on the band surfaces, the

so-called "glass film". In addition, during the

Diffusion processes taking place at high temperature annealing cleaned the steel material. Following the high-temperature annealing, the flat electrical steel product obtained is coated with an insulation layer, thermally straightened and stress-relieved in a final “final annealing”. This final annealing can take place before or after the assembly of the in the

Steel flat product described above is produced to the blanks required for further processing, with a final annealing after the blanks have been cut off in the course of

Additional tensions can be reduced. Electrical steel flat products manufactured in this way are typically 0.15 mm to 0.5 mm thick.

The metallurgical properties of the material, the degrees of deformation of the cold rolling processes set during the production of the flat electrical steel products and the parameters of the heat treatment steps are each coordinated so that targeted recrystallization processes take place. These

Recrystallization processes lead to the "Goss texture" typical of the material, in which the direction of the easiest magnetizability lies in the rolling direction of the finished strips. Accordingly, grain-oriented electrical steel flat products have a strongly anisotropic magnetic behavior.

In addition to energy losses, that also plays a role in transformers

Noise matters. This is based on a physical effect known as magnetostriction and is caused by the

Properties of the electrical steel core material used influenced.

It is known that the applied to an electrical steel flat product

Insulation layer can help to minimize the magnetic loss of grain-oriented electrical steel flat products. Thus, the insulation layer can transfer considerable tensile stresses to the base material in the burned-in state, which, as described for example in EP 2 022 874 A1, can be up to 0.8 kg / mm ² , which corresponds to tensile stresses of up to approximately 8 MPa. The tensile stresses transmitted by the insulation coating not only improve the magnetic loss values of the respective flat electrical steel product, but also reduce the magnetostriction, which in turn has a positive effect on the noise behavior of a transformer manufactured using such flat electrical steel product.

An insulation layer showing these effects and a process for its production are described, for example, in DE 22 47 269 C3, according to which insulation layers with layer densities of up to 4 g / m ² can be achieved. It is also explained there that the tensile stresses transmitted from the insulation layer to the steel substrate are the result of different thermal expansion coefficients of the insulation layer and the

Are steel base material.

The main components of the insulation solution used according to DE 22 47 269 C3 to produce the insulation layer are aluminum phosphate and silicon dioxide, the latter also being able to be added in colloidal form. Another component of insulation coatings is common

Chromic acid anhydride (chromium trioxide) or chromic acid, the content of this constituent, which is questionable with regard to its effects on the environment, being able to be minimized if the other ingredients of the insulation solution are selected appropriately (DE 10 2008 008 781 A1, EP 2 022 874 A1).

Common to the above-mentioned known insulation layers is that they are first applied to the surface of the flat electrical steel product to be coated, which may already have been coated with a glass film, then the thickness of the insulation layer is adjusted, for example with the aid of squeezing rollers, and finally the insulation layer is baked in an oven . The baking temperature is typically approx. 850 ° C. In this context, it is also known from DE10 2010 038 038 A1 that the adhesion and the layer thickness of the insulation layer can be significantly increased by repeating the application and baking of the insulation layer at least twice. The operation of transformers, which are based on transformer cores made from such insulation-coated flat electrical steel products, results in significantly reduced numbers

Noise emissions.

Regardless of whether the insulation layer by one or more

performed coating and baking, the insulation layer obtained and produced in the manner described above is the result of a large number of chemical reactions and phase changes at different temperatures. These processes, which determine the properties of the insulation layer, are not least chemical

Composition of the steel base material of the electrical steel flat product depending. As a result of the tolerances in the composition of the steel substrate that have to be accepted in large-scale production, this leads to variations in the coating in color and surface roughness of the insulation layer on the flat electrical steel product.

Such variations have so far been uncritical from a technological point of view.

In particular, fluctuations in the roughness could be tolerated within a relatively wide tolerance range, since the individual sheets separated from the flat electrical steel product are still typically stacked by hand, for example in the manufacture of transformer cores

be placed on top of each other. This manual production method allows deviations in handling or stackability, which result from the different surface roughness and the resultant

result in different friction behavior, can be easily compensated for without the production process being disturbed or delayed. Such compensation of inhomogeneities in the surface properties of sheet metal blanks, which are made up of flat electrical steel products coated with an insulation layer of the type explained above, can be achieved, if at all, only with considerable effort in the case of machine stacking on an industrial scale.

Against this background, the task has arisen of specifying a process for the production of grain-oriented flat steel products for electromagnetic applications (“electrical flat steel products”), which reliably varies within a narrow tolerance window at most

 Have surface quality and are therefore suitable for example for an uncomplicated, machine-automatic stacking.

Likewise, a grain-oriented flat steel product for electromagnetic applications should be specified, the surface quality of which varies within a narrow tolerance window, so that, from blanks of such an flat electrical steel product, stacks which are particularly suitable for the production of transformer-core stacks can be automatically and automatically formed are.

With regard to the method, the invention has achieved this object in that at least the work steps specified in claim 1 are carried out in the production of a grain-oriented flat steel product. It goes without saying that the process steps which are not mentioned here and which are usually carried out for the person skilled in the art in the production of flat steel products of the type in question here are also additionally carried out in the process according to the invention if there is a need for this.

A grain-oriented solution to the above task

Flat steel product has at least the features listed in claim 16. Advantageous refinements of the invention are specified in the dependent claims and are explained in detail below, like the general inventive concept.

A grain-oriented flat steel product according to the invention can be produced by a method according to the invention and is suitable

in particular for the production of transformer core sheet metal stacks, which are formed by stacking blanks of a flat electrical steel product according to the invention.

In the inventive method for producing a grain-oriented flat steel product for electromagnetic applications with his

Processing optimized surface condition is accordingly a) providing an electrical steel flat product having at least one surface thereof an insulating layer, and generates b) on the insulating layer is a maximum of 5 mi ^h, in particular less than 5 gm, thick resist layer.

The flat electrical steel product provided in step a) can be produced in a conventional manner, for example by using the method known in the prior art explained at the outset.

According to the invention, a lacquer layer is now applied to the insulation layer provided by the flat electrical steel product provided. Their thickness is dimensioned such that they only marginally influence the spacing of sheet metal blanks obtained from an electrical steel flat product according to the invention in a stack and, as a result, the dimensions and magnetic properties of a transformer core formed by such a stack. This is especially true if the thickness of the Lacquer layer is less than 5 gm, in particular at most 2 gm or at most 1 gm. A lacquer layer applied according to the invention typically has a minimum thickness of 0.5 gm.

Surprisingly, it has been shown that the inventive

applied varnish the static friction coefficient on the with the

Painted insulation layer against the

Frictional properties of an unpainted insulation layer can be shifted into an optimal value range for automatic handling.

A grain-oriented flat steel product according to the invention for

Accordingly, electromagnetic applications ("electrical steel flat product") encompasses

 - a steel substrate,

 - optionally a forsterite layer produced on the steel substrate,

 - An insulation layer applied to the steel substrate or the optionally available forsterite layer

 and

- A layer of lacquer applied to the insulation layer, the maximum

5 gm, in particular less than 5 gm, is thick and is composed of more than 50% by weight of organic components.

The lacquer layer provided according to the invention for modifying the rubbing properties of the surface of a flat electrical steel product can be applied to the surface in question in any manner known from the prior art for this purpose. Conventional roll coaters or squeegees are suitable for this, with which the paint used in each case is suitable

Layer thickness, if necessary by applying two or more passes. For painting the electrical steel flat product on both sides, a coater can be used, which only has one side at a time Coating steel flat product, the electric steel flat product to be painted can be run twice over the same system, where necessary it is turned between the two runs. If two coaters of this type are available, these can be run through in succession in order to apply the lacquer layer one after the other on both sides of the flat electrical steel product.

The production of the lacquer layer carried out in step b) of the method according to the invention then comprises the steps b.1) which are usually carried out in the prior art for this purpose. Applying a solvent-free lacquer as a wet film to the surface of the insulation layer,

b.2.1) drying the paint applied to the surface,

and or

b.2.2) curing of the paint applied to the surface.

The invention is based on the knowledge that, based on a conventional coating system designed for the coating of stainless steel sheets, the surface properties of flat electrical steel products of the type in question can be influenced in a simple and favorable manner.

Since the paint provided for the application to the surface at a temperature of 20 ° C has a Brookfield viscosity of less than 5000 mPas with a spindle 3, a wet film of particularly uniform distribution and thickness can be applied to the insulation layer.

A suitable formulation for the purposes of the invention

Lacquers applied according to the invention contain at least the following

Components (in% by weight) A: 40-90% by weight of at least one oligomeric linear or branched epoxy, polyester, polyether and / or polyurethane (meth) acrylate,

B: 5-60% by weight of at least one monofunctional (meth) acrylate or a di-, tri- or poly (meth) acrylate compound, which is in each case liquid at 20 ° C.

Already by the application of a lacquer composed in this way to the insulation layer of the flat steel product, optimized friction properties are produced on the surface of a flat steel product according to the invention for further processing.

The starting point for the lacquer layer produced according to the invention can be the solution-free coating agent proposed in DE 101 44 531 B4 for producing an anti-fingerprint coating, which can be cured by irradiation with ultraviolet light. The content of DE 101 44 531 B4 is hereby incorporated into the present application by reference to the invention.

As with regard to the optimization of the

Surface quality has been particularly advantageous here

emphasized when the paint applied according to the invention as a further component

C: 15-40% by weight of at least one particulate pigment.

In this embodiment of the invention, which is particularly important in practice, the coating agent known from DE 101 44 531 B4 is mixed with an organic or inorganic UV pigment preparation, by the addition of which the desired setting of that according to the invention is added painted surface existing friction properties is made particularly effective.

In order on the one hand to achieve the optionally desired high pigment content of the lacquer layer applied to a flat electrical steel product according to the invention and on the other hand to hold a sufficient amount of hardening components in the lacquer applied according to the invention, this can be done in the course of the method according to the invention

applied lacquer to more than 50 wt .-%, in particular more than

60 wt .-%, consist of organic components.

For curing, the lacquer layer can be thermal or actinic radiation, such as UV radiation or, in a manner known per se

Exposed to electron radiation, the use of coating systems curing by UV radiation having proven particularly useful.

In the event that the organic constituents of the lacquer can be hardened under actinic radiation, the lacquer can contain, as a hardenable component, an acrylate resin that can be hardened by radiation.

For this purpose, it is advantageous if, based on the sum of its organic constituents, the lacquer is composed at least partially, preferably predominantly, of an acrylate resin.

Here is a combination of multifunctional urethane acrylate,

difunctional epoxy acrylate as well as mono-, di- and trifunctional

Reactive thinners, such as monofunctional (meth) acrylate or di-, tri- or poly (meth) acrylate compounds, are inexpensive to achieve a high surface hardness while the highly pigmented coating dries out. For this purpose, an acrylate combination, in which the aforementioned different UV acrylates each have a third, has proven particularly useful. The volume shrinkage of the applied lacquer layer is to be adjusted in a manner known per se so that the adhesion of the lacquer layer to the

Insulation layer of the provided electrical steel flat product is not impaired in the course of drying and hardening.

The lacquer applied in accordance with the invention may further contain the following component:

D: 0.1-20% by weight containing at least one acidic group

 (Meth) acrylate compound,

Finally, in the lacquer applied according to the invention, the following can also be used as a component:

E: up to 10% by weight of one or more additives may be present.

Extensive examples of components A, B, D and E are given in DE 101 44 531 B4, which has already been referred to above. Those mentioned in DE 101 44 531 B4 for components A, B, D and E.

Preferred ranges apply equally to the lacquer used according to the present invention.

The covering of the substrate formed by the insulation layer of the flat electrical steel product provided by the lacquer layer produced thereon according to the invention can be ensured particularly effectively by the pigments optionally added to the lacquer applied according to the invention.

One or more pigments selected from the group of “carbon black, graphite, molybdenum sulfide, talc, iron oxide black or titanium dioxide pigments” are particularly suitable as optionally added component C. Carbon black, graphite and molybdenum sulfide in particular are substances which, according to the knowledge of the invention, are suitable for reducing the sliding friction behavior of a surface of an insulation layer present on an electrical steel flat product. Soot and graphite particles have been found to be particularly suitable for adjusting the frictional properties of the surface of a flat steel product according to the invention. In contrast, talc, iron oxide black or titanium dioxide pigments contribute to a particularly good hiding power based on the property of these pigments to absorb light.

In the event that the total proportion of the particulate pigments optionally present in the lacquer includes both pigments selected from a first group "carbon black, graphite, molybdenum sulfide" and pigments selected from a second group "talc, iron oxide black and titanium dioxide", , it is advantageous if the relative proportion of pigments of the first group is preferably at least 5% by weight, in particular at least 8% by weight or 10% by weight, in each case based on the total proportion of the particulate pigments, one being optimal effect of the pigments of the first group with relative, ie related to the total amount of pigments in the paint

Contained from 8 to 20 wt .-% result.

At the same time, based on the total proportion of the particulate pigments contained in the lacquer, the proportion of the pigments of the first group should not exceed 40% by weight, in order to avoid disadvantageous flow properties of the lacquer and to ensure optimal wetting and optimal behavior in the

To ensure curing of the paint. In order to ensure appropriate contents, at least 0.5-10% by weight of a pigment selected from the group "carbon black, graphite or molybdenum sulfide", based on the paint formulation, can be present as component C in the paint applied according to the invention.

In order to achieve this effect reliably with the very small layer thickness specified according to the invention, the method according to the invention applied coating formulation in total at least 10% by weight,

in particular at least 15% by weight of pigments. This high

The pigment content ensures that any unevenness on the surface of the insulation layer is covered in such a way that an optimally flat and therefore smooth surface with a low coefficient of friction m _{H is} obtained. Pigment contents of at least 15% by weight, in particular at least 20% by weight, have proven to be particularly expedient with regard to the setting of the static friction behavior of the surface provided with a lacquer coating in the manner according to the invention. At

Containing a total of more than 40% by weight of pigments, however, there was no further improvement with regard to the stackability and the covering of the substrate of the flat electrical steel products coated according to the invention or blanks obtained therefrom, whereas the processability of the paint formulation is significantly more difficult, so that this content as the upper limit for the levels of pigments in the invention

applied paint has been determined.

With regard to the reactivity, the viscosity, the chemical resistance and the resistance to hot oil of the hardened lacquer applied according to the invention and the pigment wetting during the application of the lacquer, it is favorable if that formed from the content% A of component A and the content% B of component B. Weight ratio% A:% B 1: 1 to 3: 1,

in particular 5: 4 to 5: 2.

The varnish applied according to the invention is preferably solvent-free in order to avoid the formation of pores and other surface defects in the varnish layer due to volatile constituents which outgass upon application, during drying or during curing. Solvent-free in the sense of the present invention means that in the lacquer applied according to the invention the sum of the contents of volatile organic compounds with a boiling temperature at 1 atm (1,01325 bar) of less than 100 ° C. is less than 5% by weight, in particular less than 1% by weight or optimally less than 0.5% by weight. The coating layer is typically applied at temperatures of up to 90 ° C, so that the operational safety of the

The method according to the invention is advantageous if the flat electrical steel product to be coated has a temperature of at least 60 ° C., in particular at least 80 ° C., for the application of the lacquer, the

Temperature of the flat electrical steel product should not exceed 120 ° C, especially not more than 100 ° C, to have a negative impact on the

Avoid creating an optimally even layer.

The thickness of the lacquer layer applied according to the invention can be determined using

Magnetic induction can be determined according to ISO 2178.

In accordance with the above provisions, a grain-oriented flat steel product according to the invention for electromagnetic applications comprises

 - a steel substrate,

 - optionally a forsterite layer produced on the steel substrate,

 - An insulation layer applied to the steel substrate or the optionally available forsterite layer

 and

 - A layer of lacquer applied to the insulation layer, the maximum

5 pm, in particular less than 5 miti, thick and composed of more than 50 wt .-% of organic constituents.

A grain-oriented electrical sheet coated with a lacquer layer in the manner according to the invention typically has a static friction coefficient m _H of 0.20-0.35 on the free surface of the lacquer layer. This makes flat steel products according to the invention optimally suitable for automated stack formation with blanks which are divided from flat steel products according to the invention. The sliding friction is already significantly reduced by the presence of the hardened lacquer containing components A and B, so that the stacking of the blanks is facilitated. The pigments of the first groups of the optionally added component C reduce the coefficient of sliding friction

in addition, are therefore preferred, as already described, and help to ensure that the coefficient of static friction which is favorable for further processing is reliably established. An optimum working window for the formulation with regard to the applicability and the covering capacity and for setting the desired sliding friction coefficient, based on the lacquer layer, is in the range of 15-40% by weight of a pigment selected from the group "carbon black (carbon black), graphite, molybdenum sulfide, talc , Iron oxide black and titanium dioxide ”.

As already mentioned above, the pigment particles according to the invention are optionally present in the lacquer applied to the steel substrate of the flat steel product to form the lacquer layer with particle diameters of <5 pm, with particle diameters of at least 0.05 pm in practice with regard to the effectiveness and distribution of the particles have proven particularly effective, and with particle diameters of at most 2 pm, in particular at most 1 pm, the effect achieved by the optional presence of the particles sets in particularly reliably.

A particularly effective effect of the presence of the pigments in the

Lacquer layer according to the invention results if the proportion of the particulate pigment based on the lacquer layer is at least 20% by weight.

The desired particle size of the pigment content optionally present in the lacquer applied according to the invention of less than 5 pm is during the

Trituration of the total pigment content with component (B) of the lacquer, possibly with components (A) and (B) of the lacquer, set as a grindometer value according to Hegman in accordance with DIN 53203. A lacquer layer applied according to the invention on the insulation layer of a flat electrical steel product contains a binder based on acrylates and / or urethanes, preferably based on acrylates, the proportion of acrylates in the lacquer coating preferably being at least 80% by weight based on the sum of the contents organic components of the lacquer coating is.

The steel substrate of an electrical steel flat product according to the invention consists of steel alloys typical of electrical steel flat products. The steel substrate can thus be produced from a steel which consists of (in% by weight) 1.5-6.0% Si, optionally further elements and, due to the production process, unavoidable

Contamination in total contents of at most 4.0% and the rest consists of iron. An example of such an alloy is a steel which consists of (in% by weight) 1.5-4.0% Si, 0.02-0.20% Cr, 0.01-0.35% Cu, 0 , 03 - 0.20% Sn, 0.03 - 0.30% Mn, 0.01 - 0.03% P, balance iron and unavoidable impurities.

In principle, the invention is suitable for use on all grain-oriented flat steel products which are provided with an insulation layer. Such

Insulation layers are applied in particular to grain-oriented flat electrical steel products, for which the application of a

paint layer according to the invention has proven to be particularly useful.

The insulation layer of flat electrical steel products of the type according to the invention is obtained and produced in a conventional manner, as described, for example, in the publications cited at the beginning. So there is

Insulation layer composed of the components silicon dioxide, a phosphate and a metal oxide, the insulation layer being predominantly amorphous.

A transformer sheet metal stack according to the invention consists of blanks which are divided from flat electrical steel products according to the invention and

are stacked on top of each other. The blanks are connected to one another in a manner known per se by appropriate clamping means, the clamping forces effective for stacking and for the non-positive connections being oriented in accordance with the surface normals established on the surfaces of the blanks. All blanks are at least on one side, preferably on both sides, in the area of the surface of another

The surface coming into contact with the blank is provided with a lacquer coating according to the invention which is composed of more than 50% by weight, preferably more than 60% by weight, of organic constituents and is applied in a layer thickness which is spaced apart along the Stacking of immediately adjacent electrical steel sections (in each case defined as the sum of the layer thicknesses of the lacquer coatings on the facing surfaces of immediately adjacent electrical steel sections and measured in each case by means of magnetic induction according to ISO 2178) results in less than 5 pm, preferably less than 2 pm, the coefficient of static friction of the surface of one blank provided with the lacquer layer is greater than or equal to 0.20 and less than or equal to 0.35.

The lacquer layer applied according to the invention does not transmit tensile stress to the insulation layer covered by it or to the steel substrate carrying the insulation layer, but only serves to adjust the sliding behavior on the top of the insulation layer.

The coefficient of static friction n of the paints coated according to the invention

Surface can be determined in the manner customary in the prior art. For this purpose, a stack of three blanks each with the same surface is formed and stretched between two blocks, each of which is aligned by a normal to and against the respectively assigned surface of the blanks

Compressive force F _N of 0.3 MPa. The respective outer blanks are loaded with a tensile force FR directed in the same direction, while the blank in the middle is loaded with a tensile force FR which is oriented in the opposite direction but is of the same size as that exerted on the other two blanks Traction FR. The tensile forces FR are continuously increased until the blanks are relative to one another move. The value of the pulling force reached at this point is called F _{R rriax} . The static friction coefficient m _H can then be determined as follows:

F _R max = M _H x F _{N *} MH = F _{R ma} x / F _N where F _N = 0.3 MPa

If soot particles are used as particles (component C) in the lacquer applied according to the invention, a coating according to the invention can also be clearly characterized using the analysis method "Fourier-Transformed Infrared Spectroscopy" (FTIR). In this case, this provides peaks that can be clearly assigned to the soot particles, since they are not overlaid by the peaks of other constituents.

To show this, a Bruker Tensor 27 and a Harrick "Praying Mantis" DRIFT cell were used. The DRIFT (Diffuse Reflectance Infrared Fourier Transformation) process is the conventional ATR process

In this case, consider (Attenuated Total Reflection) because it not only captures the outer skin, but the entire paint layer down to the

Insulation coating recorded and thus enables full characterization.

In the spectrum obtained by the DRIFT method, two peaks could be determined that describe the effect of the soot particles. The peak of the soot (carbon black) is 731 cm ¹ . It has a certain width so that the peak integral int (peak carbon black) of 690 cm ¹ to 760 cm ^{1 is} formed for quantification.

The acrylate peak at 1740 cm ¹ serves as the reference peak. Here, the integral int (peak acrylate) is integrated over the range from 1690 cm ¹ to 1780 cm ¹ .

The respective peak integrals can be determined using the OPUS VERSION 7.2 device software offered by Bruker Corporation, Billerica, USA, subtracting the baseline. The quotient Q is formed from the peak integrals int (peak carbon black) and int (peak acrylate):

 Q = int (peak carbon black) / int (peak acrylate)

Only integrals that are positive are taken into account. If there are negative integrals, the respective coating does not meet the requirements of the invention.

Flat electrical steel products according to the invention are characterized by quotients Q, to which applies

0.1 <Q <3.0.

Flat steel products according to the invention which meet these requirements reliably have a target according to the invention

Stiction coefficient PH from 0.20 to 0.35.

The invention is explained in more detail below on the basis of exemplary embodiments. Show it:

1 shows a spectrum determined by DRIFT of a flat electrical steel product provided according to the invention;

2 shows a spectrum determined by DRIFT of a flat electrical steel product not provided according to the invention with a lacquer layer.

To demonstrate the effect of the invention, samples of in

provided conventionally produced grain-oriented electrical steel flat products, the steel substrate each consisted of one of the steels A - D, the composition of which is given in Table 1.

The electrical steel flat product samples were also conventionally coated with a 0.5-3 μm thick insulation layer, which consisted of a Forsterite (Mg ₂ Si0 ₄ ) layer and an overlying layer of a silica / silicate glass, which optionally contained up to 10 wt .-% Cr.

A part of the samples has been coated with a lacquer layer in accordance with the requirements of the invention, while another part of the samples has been lacquer-coated for comparison, but with outside the

Lacquer formulations according to the invention. A third part of the samples also remained uncoated for comparison.

For the paint coating, the samples were first pretreated alkaline or acidic for surface cleaning. Spray degreasing at 60 ° C has proven itself here.

To improve the adhesion and for a more even application of the paint coating, the samples were also heated before coating, with temperatures of 80 - 100 ° C being found to be optimal.

The respective coating layer was applied to the samples heated in this way using a conventional three-roller coater, in which the

Rubberization of the application roller had a hardness of at least 80 Shore A.

For the paint coating, a paint was provided which, as component A, contained 33% by weight urethane acrylate with a viscosity of 1800-2200 mPas (at 60 ° C) and 33% by weight epoxy acrylate with a viscosity of 2500-3500 mPas (at 60 ° C) and as component B contained 34% by weight alkoxylated triacrylate with a viscosity of 50-100 mPas (at 25 ° C). The overall formulation had a viscosity of 500 - 800 mPas at 25 ° C. The viscosities were determined using a spindle 3 according to Brookfield.

The pigments (component C) iron oxide black, titanium dioxide and soot particles are each in the form of a pigment preparation with component B and an im Grindometers according to Hegman (DIN 53203) determined particle diameters of less than 5 pm were provided and were formulated accordingly. With a constant proportion of iron oxide black (14% by weight) and titanium dioxide (3.75% by weight), only the proportion of soot particles was varied.

The varnish layer was cured with commercially available UV lamps for 1 to 5 seconds, with the entire radiation spectrum being from 250 nm to 450 nm

was used and a high UVC content was particularly advantageous

turned out.

Table 2 shows the steel of the steel substrate of the electrical flat steel product sample used in each case, the soot content R in the lacquer layer, the quotient Q - as far as can be determined - the static friction m _H for the tests carried out

Temperature T of the sample during the coating and the thickness D of the lacquer layer are given. Table 2 also shows whether the respective example is according to the invention.

The tests show that the coefficient of static friction m _{H increases}

different steel analyzes of the steel substrate of the samples has changed very little at most, so that the setting of the

Stiction of friction m _H on the surface of the sample can be done very precisely.

Outside the specifications according to the invention, the additives in the lacquer layer (here carbon black) are significantly larger, so that the reproducibility is restricted.

1 shows the result of a DRIFT examination of the paint coating of the flat electrical steel product sample obtained in test A1 according to the invention, which sample contained a soot particle content R of 2.2% by weight in the paint coating. The peak for the carbon black soot particles is 731 cm ¹ , while the associated peak integral int (peak carbon black) extends over the range 690 cm ¹ to 760 cm ¹ and in the example shown in FIG. 1 has a value of 8, 3 has reached.

The acrylate peak serving as the reference peak is 1740 cm ¹ , the associated integral int (peak acrylate) extending over the range from 1690 cm ¹ to 1780 cm ¹ and having a value of 55.9 in the example shown in FIG. 1 .

In the example according to the invention shown in FIG. 1, the quotient Q was thus

Q = int (peak carbon black) / int (peak acrylate) = 8.3 / 55.9 = 0.15 for a static friction coefficient m _H of 0.31 determined for the sample obtained in test A1 and corresponding to the requirements of the invention.

In the electrical steel flat product sample obtained in test A2 not according to the invention, the peak integral int (peak carbon black) determined over the range 690 cm ¹ to 760 cm ^{1 was} 1.55 and that determined over the range from 1690 cm ¹ to 1780 cm ¹ Integral int (peak acrylate) 67.80. This gave a quotient Q of 1.55 / 67.80 = 0.02 with a static friction coefficient p _H of 0.15 which is outside the scope of the invention.

 Figures in% by weight, the rest in each case iron and production-related inevitable impurities which have no influence on the properties of the steel substrate

Table 1

 *) no fertilization of Q because at least one peak integral was negative

Table 2

Claims

PATENT CLAIMS 1. A method for producing a grain-oriented flat steel product for electromagnetic applications with a surface texture optimized for its further processing, in which a) an electric flat steel product is provided which has an insulation layer on at least one of its surfaces, and b) a thickness of at most 5 pm on the insulation layer Paint layer  is produced. 2. The method according to claim 1, characterized in that the generation of the lacquer layer (step b))  b.1) the application of a lacquer as a wet film on the surface of the  Insulation layer,  b.2.1) drying the lacquer applied to the surface and / or b.2.2) includes curing the paint applied to the surface. 3. The method according to claim 1 or 2, characterized in that the paint provided for application to the surface at a temperature of 20 ° C has a Brookfield viscosity with a spindle 3 of less than 5000 mPas. 4. The method according to any one of the preceding claims, characterized  characterized in that the paint consists of more than 50 wt .-% of organic components. 5. The method according to any one of the preceding claims, characterized  characterized in that for curing the paint applied to the surface of a thermal or actinic radiation  is exposed. 6. The method according to claim 5, characterized in that the lacquer contains as a curable component a radiation-curable acrylate resin. 7. The method according to any one of the preceding claims, characterized  marked that the paint contains the following components:  A: 40-90% by weight of at least one oligomeric linear or  branched epoxy, polyester, polyether and / or polyurethane (meth) acrylate, B: 5-60% by weight of at least one monofunctional (meth) acrylate or a di, tri or poly (meth) acrylate compound, which is in each case liquid at 20 ° C. 8. The method according to claim 7, characterized in that the lacquer further contains the following component:  C: 15-40% by weight of at least one particulate pigment. 9. The method according to claim 8, characterized in that component C is at least one pigment selected from the group "carbon black, graphite, molybdenum sulfide, talc, iron oxide black and titanium dioxide". 10. The method according to claim 9, characterized in that the proportion of pigments selected from the group "carbon black, graphite or molybdenum sulfide" based on the total content of component C is at least 5-40 wt .-%. 11. The method according to any one of claims 7 to 10, d a d u r c h  characterized that the paint also contains the following components:  D: 0.1-20% by weight containing at least one acidic group  (Meth) acrylate compound. 12. The method according to any one of claims 7 to 11, characterized  characterized that the paint also contains the following components:  E: up to 10% by weight of one or more additives. 13. The method according to any one of claims 7 to 11, characterized characterized that the paint is solvent-free. 14. The method according to claim 13, characterized in that the sum of the contents of volatile organic compounds with a boiling temperature at 1 atm (1, 01325 bar) of less than 100 ° C in the lacquer is less than 5 wt .-%. 15. The method according to any one of claims 7 to 14, characterized  characterized that from the% A of the  Component A and the content% B of component B formed  Weight ratio% A:% B is 1: 1 to 3: 1. 16. Grain oriented steel flat product for electromagnetic applications, the  - a steel substrate,  - optionally a forsterite layer produced on the steel substrate,  - An insulation layer applied to the steel substrate or the optionally available forsterite layer  and  - Includes a layer of lacquer applied to the insulation layer, the  is at most 5 pm thick and is composed of more than 50% by weight of organic components. 17. Flat steel product according to claim 16, characterized in that there is a on the free surface of the lacquer layer Has coefficient of static friction m _H of 0.20-0.35. 18. Flat steel product according to claim 16 or 17, characterized characterized in that the lacquer layer 2-20 vol .-% of a Pigments selected from the group "carbon black, graphite, molybdenum sulfide, talc, iron oxide black and titanium dioxide" with a medium  Contains particle diameter of <5 pHm. 19. Flat steel product according to one of claims 16-18, characterized  characterized in that the steel substrate is produced from a steel which consists of (in% by weight) 1, 5 - 6.0% Si, optionally further elements and production-related unavoidable impurities in total contents of at most 4.0% and as the rest is made of iron. 20. Flat steel product according to one of claims 16-19, characterized  characterized in that the insulation layer from the  Components silicon dioxide, a phosphate and a metal oxide, the insulation layer being predominantly amorphous. 21. A transformer core sheet stack formed by stacking blanks of a grain-oriented flat steel product procured according to one of claims 16-20.