Coating apparatus – Solid applicator contacting work – With work-handling or work-supporting
Reexamination Certificate
1999-07-21
2001-08-21
Edwards, Laura (Department: 1734)
Coating apparatus
Solid applicator contacting work
With work-handling or work-supporting
C118S212000, C118S227000, C118S236000, C118S249000, C118S253000, C118S261000, C118S262000
Reexamination Certificate
active
06277196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to coating apparatus for applying a coating of an insulating lacquer to steel strip, especially electrical steel strip. The invention also relates to methods of applying coatings using this apparatus, and to steel strip coated thereby.
2. Description of Related Art
It is known to coat non-oriented electrical steel strip on one or both surfaces with an insulation lacquer in order to improve the performance of the strip when employed, for example, in a magnetic core of an electrical machine; insulation coatings on electrical steel laminations reduce the eddy currents in a stack and hence reduce power losses in the steel.
Certain applications for steel require coatings which are essentially organic in nature and exhibit only reasonably good punchability characteristics. Such coatings, however, exhibit good welding properties. Conversely, other coatings comprise inorganic additives and exhibit excellent welding characteristics but behave poorly when punched. Therefore the coating chosen has to be a compromise to suit the final application required.
U.S. Pat. No. 4,288,492 discloses an electrical steel sheet coated with an insulating lacquer of an organic polymeric material. The thickness of the lacquer coating is less than 10 microns, typically between 1 and 8 microns. U.S. Pat. No. 4,288,492 does not disclose the method by which the coating is applied, other than by reference to the employment of a roll coater. Conventional roll coaters generally comprise a grooved roller which rotates in contact with the surface of a sheet to be coated and applies a controlled pressure thereto. Coatings applied by such rolls tend to be uneven and the grooved rollers themselves are susceptible to damage and blockage because of pick-up resulting in subsequent poor coating of the electrical steel surface. U.S. Pat. No. 4,288,492 also discloses the step of curing the applied coating with ultraviolet rays or electron beams.
It is extremely difficult with conventional electric steel coatings to produce the very thin coatings of uniform thickness required because of the rheology of the applied coating.
In order to be suitable for some methods of application such as the multiple-step kneading roll method, coatings require the lubricity imparted by organic additives. However, high organic solvent based coatings have many disadvantages such as inflammability, the need for expensive after burners for burning off solvent vapour and the need to remove volatile organic compounds.
Other methods of coating such as the pick-up roll method are limited to low speed coating because it is impossible to pick up high viscosity liquids onto the pick-up roll. This method has further disadvantages, for example, the thickness of the resulting coating becomes irregular if there are any variations in the coating speed.
A system for applying coatings to substrates using a roller having an engraved surface is shown in “Raster- und Haschurenwalzen hergestellt mittels Lasertechnik” in COATING 12/95, St. Gallen CH, and means for heating the substrate and apparatus to lower the viscosity of the lacquer is shown in U.S. Pat. No. 4,949,667.
SUMMARY OF THE INVENTION
The applicants have now established that by means of this invention a relatively thin coating of an organic or organic/inorganic high viscosity insulating lacquer of uniform thickness can be applied consistently at high speeds, to one or both surfaces of electrical steel strip moving continuously between, for example, an uncoiler and a coiler, without the addition of thinning agents to the coating lacquer.
According to the present invention in one aspect there is provided apparatus for applying a coating of an insulation lacquer to a moving surface of a steel strip, the apparatus comprising a rotatable metering roller whose surface defines a multiplicity of cells, a reservoir connected to receive controlled quantities of organic or organic/inorganic insulating lacquer from a source of such lacquer, means for controlling the temperature of the lacquer resident in the reservoir, means for immersing a part of the roller surface in a bath of insulating lacquer resident in the reservoir to cause insulating lacquer to enter the cells of the roller surface, means for wiping excess lacquer from the roller surface means for imparting rotation to the roller, a rotatable applicator roll having a substantially plain surface free of grooves or other indentations, means for rotating the applicator roll with its surface in contact with the surface of the lacquer carrying metering roller or an intermediate lacquer carrying transfer roller whereby lacquer present in the cells of the metering roller is transferred to the surface of the applicator roll, and means for moving the surface to be coated continuously past and in contact with the applicator roll to apply a continuous uniform coating of lacquer to that surface, and means for controlling the temperature of the lacquer in the reservoir before it is transferred to the metering roller.
One or more intermediate transfer rollers may be positioned between the lacquer carrying roller and the applicator roller.
A set of smoothing rollers may be positioned downstream of the applicator roll, the smoothing rollers applying limited pressure to the lacquer coated strip.
The strip is preferably a strip of non-oriented electrical steel.
The lacquer is preferably heated to between 40° C. and 50° C.
The lacquer may be UV curable, a drying chamber including UV lamps being positioned downstream of the applicator roll to cure the applied coating.
REFERENCES:
patent: Re. 31695 (1984-10-01), Zink
patent: 3568636 (1971-03-01), Lockwood
patent: 3987750 (1976-10-01), Knapke
patent: 4231318 (1980-11-01), Zink
patent: 4288492 (1981-09-01), Hiromae et al.
patent: 4354449 (1982-10-01), Zink
patent: 4378390 (1983-03-01), Yoshida et al.
patent: 4485132 (1984-11-01), Furuzono et al.
patent: 4949667 (1990-08-01), Yoshida et al.
patent: 5336529 (1994-08-01), Schafer
patent: 5755883 (1998-05-01), Kinose et al.
“Raster-und haschurenwalzen hergestellt mittels Lasertechnik”, Coating, No. 12, 1995, St. Gallen, CH., pp. 482-485.
Beckley Philip
Snell David
Woodman Gwilym Leslie
Blank Rome Comisky & McCauley LLP
Edwards Laura
European Electrical Steels
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