Patent Application
20240408637
The invention relates to an apparatus and a method for the continuous manufacturing of steel strips coated with a homogenous varnish layer for electrical applications.
The terminology “electrical applications” relates to the use of steel strips to manufacture goods having specific magnetic properties, e.g. stator and rotor of electric motors, transformers and turbines of windmills. Steel for electrical applications are also known as electrical steel and generally comprises 0 to 6 weight percent of silicon. The electrical steels can be divided into two categories: the non-oriented steel and the oriented steel.
The electrical steels are usually coated with a varnish to insulate the steel in order to prevent the flow of electricity and to reduce the eddy current. This varnish is generally a water-based solution comprising 25 to 75 weight percent of resin and 5 to 15 weight percent of solvent (such as alcohol) and a balance consisting of water. The varnishing process comprises at least two steps: a first one where the varnish is coated in the form of a wet film and a second one where the varnish is cured to get a reticulated dry film. The thickness of the wet film is generally from 1.5 to 15 μm in order to have a dry film thickness from 0.8 to 5 μm.
In the manufacturing process, the varnishing takes place after an annealing. Depending on the line architecture, the varnishing section can be coupled with the annealing furnace or not. The fact that the varnish section is coupled or not with an annealing furnace impacts the line speed. Furthermore, the varnish needs to be reticulated in a drying step at the peak metal temperature (PMT) which also limits the maximal speed line. Consequently, the line speed can vary from 30 to 300 m·min−1.
U.S. Pat. No. 6,277,196 aims at coating a thin uniform layer of an insulating lacquer consistently at high speeds on an electrical steel strip. This apparatus comprises an engraved pick-up roll and an applicator roll having a substantially plain surface free of grooves or other indentations.
EP 3 143 179 discloses a process and an equipment to uniformly coat a packaging steel with a passivation layer. This apparatus comprises a chamber doctor blade, a coating roll and an applicator roll.
A purpose of this invention is to provide an apparatus and a method permitting to uniformly varnish an electrical steel strip for a wide range of line speeds. Consequently, the varnish layer on the steel should not present any pattern. Indeed, most of the coating apparatus for electrical steel are coupled with an annealing furnace leading to variation of the line speed.
The present invention provides a coating apparatus 1 for the continuous manufacturing of steel strips S coated with a varnish for electrical applications comprising a tank 2, a coating roll 3 and an applicator roll 4 wherein:
The present invention also provides a method for the continuous manufacturing of steel strip coated with a varnish, carried out by an apparatus as described above,
Other characteristics and advantages will become apparent from the following description of the invention.
The invention, as represented in
In the embodiment illustrated in
One embodiment of the left part 1A of the coating apparatus 1 is illustrated in
As illustrated in
The wiping device makes it possible to ensure that the coating roll 3 is coated with the necessary quantity of solution to be deposited to obtain the required wet varnish thickness. This wiping device is preferably equipped with doctor blade. This device can be made up of two blades, for example, the first blade being located at the point where the coating roll 3 enters the tank 2 and makes it possible to remove residual varnish solution remaining from the preceding passage of the coating roll 3 through the tank 2, and the second blade being located at the point where the roll coating roll 3 exits the tank 2, and makes it possible to remove the excess solution. The blades can be made, for example of plastic, stainless steel or carbon fibre. The device can also be a single blade, for example, a blade made of stainless steel, located at the point where the coating roll 3 exits the tank 2.
As illustrated in
This varnish solution has a viscosity from 2.5×10−2 Pa·s at 20° C. to 4.0×10−1 Pa·s at 20° C. In a first example, the solution comprises dry extract between 30-50 weight percent composed of acrylic resin and phosphate pigments, co-solvent (alcohol) 5-10 weight percent and a balance consisting of water. In another example, the solution comprises dry extract of 40-60 weight percent being a mix of polyurethane resin and aluminium and silicon oxide, co-solvent (alcohol) 5-10 weight percent and a balance consisting of water.
The coating roll 3 is a roll coated by a ceramic whose surface is engraved. More precisely, the coating roll 3 is engraved with any patterns or cell structures. For example, the pattern can be a 60° or 30° or 70° hexagonal cells, line pattern, cobra pattern. The cells of the coating roll are filled with varnish solution. The surface of the coating roll can be made of ceramic. The cells of the coating roll can be etched with the aid of a laser or mechanical tooling.
Even though the coating roll is engraved with a pattern, the coating roll is configured to homogeneously transfer the varnish onto the applicator roll. It means that no pattern is transferred to the applicator roll. Consequently, the varnish thickness is homogeneous in the width direction.
In a first preferred embodiment, the coating roll 3 has a plurality of 60° hexagonally shaped cells, the line count of which is between 50 and 200 lines per centimetre, and the volume of which is from 5×10−6 to 6×10−5 m3 per square meter of roll surface, and preferably from 1×10−6 to 5×10−5 m3 per square meter of roll surface.
In second preferred embodiment, the coating roll 3 has a cobra pattern with a cell volume from 1×10−5 to 8×10−5 m3 per m2 of roll surface.
In a third preferred embodiment, the coating roll 3 has a quadrangular pattern with a cell volume from 1×10−5 to 4×10−5 m3 per m2 of roll surface.
After passage through the tank 2, the surface of the coating roll 3 coated with varnish solution comes into contact with the applicator roll 4. The coating roll 3 can rotate either in the clockwise direction or in the opposite direction. The applicator roll 4 is preferably itself driven in a direction of rotation that is opposite to the one of the coating roll 3.
The applicator roll 4, or at least its surface, is preferably made of a material that makes possible an optimum transfer of the solution, i.e. a transfer that minimizes the losses of solution due, for example, to absorption by the material of which the roll or its surface is made, or on the contrary by excessive slippage of the solution over the surface of the roll. This material can also exhibit resistance to chemical corrosion resistance as well as to mechanical wear. Preferably, the applicator roll 3 is made of elastomer. In a first preferred example, the applicator roll is made of chlorosulfonated polyethylene. In a second preferred embodiment, the applicator roll is made of polyurethane.
The applicator roll is configured to homogeneously coat said steel strip in the width direction. Consequently, there is no varnish pattern on the resulting coated strip. In order to achieve such a homogeneous coating, the applicator roll surface is a substantially plain surface free of grooves or other indentations.
Preferably, the applicator roll 3 has a roughness Ra from 0.5 μm to 3.5 μm. If the applicator roll roughness Ra is greater than 3.5 μm, inhomogeneity of the coated varnish can appear. Even more preferably, said applicator roll has a roughness Ra from 0.6 to 1.5 μm.
The applicator roll has a shore A hardness from 40 to 60. The hardness can be measured following the ASTM D2240 standard.
If the shore A hardness is below 40, then the lifespan of the applicator roll is severely reduced due to the coating process. Preferably, the applicator roll 3 has a shore A hardness of at least 45, such a minimal hardness provides a better lifespan and still provide a good deformation of the roll leading to an uniform coating.
If the shore A hardness is greater than 60, the maximum varnish wet thickness is too limited, especially for smaller line speed. Preferably, the applicator roll 3 has a shore A hardness of at most 55.
Indeed, in
It can be observed that for a coating roll according to the invention, the maximum wet thickness that can be coated is of at least 15 m for a speed line of at least 30 m·min−1.
Consequently, the claimed range of hardness for the applicator roll offers a wide range of varnish coating wet thickness while assuring a sufficient durability.
The invention also relates to a method for the continuous manufacturing of steel strips coated with a varnish, carried out by means of an apparatus as previously described,
Preferably, said steel strip is an electrical steel strip. Even more preferably, said steel strip is a non-oriented electrical steel strip. Said non-oriented electrical steel strip preferably comprises from 1.5 to 4 weight percent of silicon.
Preferably, the steel strip is running at a speed from 30 to 500 m·min−1. Even more preferably, the steel strip is running at a speed from 30 to 300 m·min−1.
The contact pressure between the coating roll 3 and the applicator roll 4 must be sufficient to transfer the varnish solution from the coating roll to the applicator roll, although it must not be so great that it causes splashing which can result in losses of solution and therefore a non-optimal transfer of the solution. This pressure between said two rolls can be applied, for example, with the aid of a cylinder mounted on the coating roll 3. The total force FRR applied to the coating roll 3 is preferably from 500 to 3000 N per meter of width of the strip.
Following this contact, the applicator roll 4 is coated with the wet varnish solution which is to be deposited on the strip S.
The contact pressure between the applicator roll 4 and the strip must not be too great, at the risk of wiping off too much of the wet varnish solution film deposited, nor too low, at the risk of insufficiently wetting the strip with the solution. Moreover, a minimum pressure must be exerted by the roll on the strip to compensate for potential flatness defects in the latter. This pressure between the applicator roll 4 and the strip S can be applied, for example, with the aid of at least one cylinder mounted on the applicator roll. The total force FTB applied to the applicator roll 4 is preferably from 2000 to 6000 N per meter of width of the strip.
The speed of rotation of the applicator roll 4 and of the coating roll 3 can be synchronized with the speed of displacement of the strip.
In one embodiment of the invention, the thickness of the wet varnish thickness deposited is measured with the aid of the thickness-measuring device 6.
In addition, or in an additional embodiment of the invention, the speed of rotation of the coating roll 3 can be controlled by the control unit 9 illustrated in
The thickness can be measured, for example, with the aid of an electromagnetic radiation gauge. These gauges are preferably installed as close as possible to the coating apparatus 1 because the moisture evaporates from the film very quickly, which can cause a significant variation in the measurements.
Following the step of the deposition of the wet varnish layer, the strip is subjected to a drying step. This drying step is carried out with the aid of a drying unit 5.
Preferably, following this drying phase, the thickness of the varnish layer deposited is from 0.8 μm to 5 μm after drying.
This drying unit 5 is, for example, a drying tunnel equipped with nozzles that spray air in the direction of the coated strip at a temperature between 12° and 350° C. The drying unit can also be an inductor increasing the temperature of the strip to a PMT preferably between 220° C. and 290° C.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/059204 | Oct 2021 | WO | international |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/059551 | 10/6/2022 | WO |
