Device and method for dusting smooth or sheet-like products

Information

  • Patent Grant
  • 6447855
  • Patent Number
    6,447,855
  • Date Filed
    Friday, December 8, 2000
    24 years ago
  • Date Issued
    Tuesday, September 10, 2002
    22 years ago
Abstract
The present invention relates to a device and method for dusting smooth or sheet-like products, comprising at least one duster for spraying an air/powder mixture on said products. In order to ensure efficient dusting with no dirt accumulation in the printer or the surrounding area, it is suggested that part of the powder particles be magnetized and means be provided for creating a magnetic field in the powder deposit area so that said powder particles are subjected to a force drawing them towards the product.
Description




BACKGROUND OF THE INVENTION




The present invention relates to a device for dusting stripor sheet-shaped products with which a powder/air mixture is sprayed on the products and to a method for dusting such products.




Such devices and method for dusting are, for example, employed in stacking devices for printed sheets of paper in a sheet-fed offset printing press, so that for drying the printing ink the individual sheets of paper are separated from each other by means of, a powder. In the course of this the problem occurs, that the very fine-grained powder, which is applied to the sheets of paper via an air stream, is only partially deposited on the sheet of paper. Strong air eddy currents occur because of the high conveying speeds of the sheets of paper—apporoximately 15,000 sheets per hour—, so that a large fraction of the powder does not reach and remain on the sheet of paper, but adds to the contamination of the printing press, and of the ambient air. For improving the effectiveness of the dusting it was proposed in accordance with DE-OS 26 46 798 to charge the powder particles and to apply them in the charged state to the sheet of paper. A further device is known from DE-OS 29 46 754, with which the powder to be deposited on the sheet of paper is, in essentially electrically neutral form, dispensed from nozzles and is charged by means of a corona discharge prior to impact on the sheet of paper. This method has the disadvantage that, although the charged powder better adheres to the sheets of paper, it also adheres better to all parts of the press, in particular those that are metallically neutral. The parts of the press are thereby covered with a thick layer of powder in a short time.




For this reason a further device was proposed by DE-OS 33 30 665, in which the powder is electrically neutralized when leaving the nozzle. Although the electrostatic adhesion of powder to metallic parts of the press is prevented, the original problems once more occur, with the very fine-grained powder contaminating large areas of the printing press and the surroundings due to air currents.




The known devices therefore offer only insufficient solutions to the dusting problem, because, in the final analysis, only a small amount of the powder is deposited and remains on the sheet of paper and contamination of the printing press, and of the surroundings, is inadequately prevented. Based on this prior art, it is the object of the invention to provide an improved device and method for dusting moving objects, by means of which the powder can be effectively deposited on the sheets of paper, wherein a contamination of the printing press and the surroundings is reduced.




This object is achieved by a device including means for generating a magnetic field in the deposition area so that a force is exerted on the magnetized powder particle in a direction toward the product, and by a method according to which the powder particles are magnetized prior to impacting the product and are deposited on the product by means of a magnetic force acting on the magnetized powder particles.




A powder/air mixture can be sprayed in a known manner on the sheet of paper by means of the device of the invention, wherein in accordance with the invention the individual powder particles of the powder can be magnetized. Means are furthermore provided for creating a magnetic field in the deposition area of the powder, so that a force in the direction toward the sheet of paper acts on the magnetized powder particles. In this manner, the powder can be better separated from the air carrying it. The magnetic forces are greater than the electrostatic forces of known dusting devices. The known electrostatic forces assist in holding only the powder which has already been deposited on the sheet of paper. But by means of the device of the invention and the corresponding method, the not yet deposited powder can already be effectively influenced by the magnetic forces and can be better separated from the air carrying it.




The flow speed of the powder/air mixture can be increased, as a result of which the powder-carrying air flow is less sensitive to disturbances and therefore the surrounding press elements are less contaminated.




Since the magnetic force leads to better separation of the powder particles from the air carrying them as well as to a more effective deposition of the powder on the sheet of paper, the amount of powder used can be reduced.




Advantageous embodiments of the device in accordance with the invention are the subject the dependent claims.




Permanent or electromagnets can be used for generating the magnetic field. Electromagnets are preferred, since they can be switched off, for example, for cleaning the printing press, and can therefore be better cleaned of adhering powder.




In an advantageous manner the magnet is arranged in such a way that the product can be passed through between one pole and the spray nozzle, so that the sheet of paper to be dusted can be conveyed directly over one pole of the magnet, so that the strongest possible magnetic field prevails in the deposition area of the powder.




In an embodiment of the invention in which the magnet has a U-profile whose legs form poles which extend transverse to the transport direction and across the width of the product, it is assured that an even magnetic force acts on the powder over the entire width of the sheet of paper.




An embodiment of the invention comprises means including a plurality of electromagnets arranged parallel and transversely to the transport direction. This permits adaptation of the magnetic field to various paper widths by activating only the magnets covered by the sheet of paper to be dusted.




In accordance with another embodiment one pole of the magnet(s) is preferably arranged in the deposition area of the powder, since the greatest strength of the magnetic field prevails in the pole area. The other pole is preferably arranged downstream in the conveying direction, so that the non-deposited powder once more experiences a force in the direction toward the sheet of paper at that location. The efficiency of deposition is thereby increased.




The sheets of paper are transported past the spraying nozzle by conveying means. So that the conveying means do not interfere with the magnetic field, they preferably primarily consist of a non-magnetizable material, for example plastic. A gripper element, by means of which the sheet is grasped at its front end for conveying, is however made of a magnetizable material. In this manner, strong magnetic fields are generated at the front edge of the sheet, so that the deposition of powder is assisted by the magnetic force in this area, which would otherwise only be insufficiently dusted with powder by means of known devices.




The magnetizable powder can consist of covered or coated iron particles, or of powder particles having covering iron particles on their surface. Iron is ferromagnetic and therefore strongly magnetizable. The iron particles should be covered or coated, so that the iron cannot oxidize and leave unwanted spots on the sheet of paper.




The invention will be explained in detail in what follows by means of an exemplary embodiment, making reference to the drawings.











BRIEF DESCRIPTION OF THE DRAWING





FIG. 1

shows a greatly schematized side view of a device in accordance with the invention;





FIG. 2

shows a plan view along the line II—II of

FIG. 1

;





FIG. 3

shows a view as in

FIG. 1

of a further embodiment;





FIG. 4

shows a view as in

FIG. 2

of the further embodiment of the invention according to

FIG. 3

;





FIG. 5

shows a plan view as in

FIG. 1

of a further embodiment;





FIG. 6

shows an embodiment of the invention with conveying means for a sheet of paper.











DESCRIPTION OF THE PREFERRED EMBODIMENT




A device


10


in accordance with the invention, represented in the drawings, has a spray bar


14


arranged transversely to a conveying direction


12


, which has spray nozzles


16


, by means of which a powder/air mixture, represented by dashed lines


18


, can be sprayed over the width of the product to be sprayed, a sheet of paper


20


in the exemplary embodiment shown. For spraying, the sheet of paper


20


is pulled past the spray nozzles


16


in the conveying direction


12


by means of suitable conveying means


38


.




The powder consists of individual magnetizable powder particles, which preferably consist of covered or coated iron particles. In an alternative embodiment the powder particles consist of known materials, for example starch or calcium carbonate, and have covering iron particles on their surface.




The device


10


furthermore comprises means


22


, with which a magnetic field represented by dotted lines


23


can be generated in the deposition area


24


of the powder, i.e. on the surface of the sheet of paper


20


. The powder particles entering the magnetic field are magnetized by the magnetic field


23


. The magnetic field is generated in such a way that a magnetic force acts on the powder particles in the direction toward the sheet of paper


20


.




The means


22


can include at least one permanent magnet. In a first embodiment of the invention, the means include an electromagnet


26


(FIG.


1


), which is arranged in such a way that the sheet of paper can be passed through between at least one pole


28


and the spray nozzles


16


.




Preferably both poles


28


and


30


of the electromagnet


26


are arranged underneath a sheet guidance panel


32


guiding the sheet of paper


20


(FIG.


1


). The sheet of paper


20


is securely guided by this and the contamination of the electromagnet


26


is prevented.




In the exemplary embodiment represented in

FIGS. 1 and 2

, the electromagnet


26


is formed by a U-profile, whose U-legs form the poles


28


and


30


, and which extends transversely to the conveying direction


12


, across the width of the product. Therefore the poles


28


and


30


extend over the entire width of the sheet of paper


20


. A coil


31


, through which current flows, generates the magnetic field in the iron core of the magnet


26


.




In the further exemplary embodiment represented in

FIGS. 3 and 4

, a plurality of electromagnets


34


has been arranged, parallel and in a row, transverse to the conveying direction


12


, through whose respective coils


36


the current flows in the same direction, so that like poles are adjacent to each other, transverse to the conveying direction


12


. It is then possible, corresponding to the width of the sheets of paper, to turn off individual electromagnets, so that contamination of the printing press outside the width of the sheets of paper is prevented.




The magnet(s) is/are preferable arranged as shown in FIG.


5


. In this case the one pole


28


is located directly in the deposition area


24


of the powder, and the other pole


30


downstream in the conveying direction


12


.




In the exemplary embodiment shown in

FIG. 6

, the device in accordance with the invention has conveying means


38


, having gripper elements


40


, with which the sheet of paper


20


is grasped at its front edge


42


for transport.




So that the magnetic field


23


is not disturbed by the massive conveying means


38


with its a gripper element


40


, the conveying means


38


has a portion made of a non-magnetizable material, for example plastic. The gripper element


40


is advantageously made of a magnetizable material, since in that case, its free edge


44


becomes a magnetic pole when the conveying means


38


moves over the magnet


26


and the gripper element


40


is magnetized. By means of this, more powder is deposited in the area of the front edge


44


of the sheet of paper


20


.



Claims
  • 1. A method for dusting strip- or sheet-shaped products, the method comprising the steps of:a) disposing at least one spray nozzle at a substantial separation from the product to define a gap; b) spraying a powder/air mixture on the product at a deposition area, wherein said powder can be magnetized, said powder spreading in said gap to generate a deposition area having a size substantially greater than an output diameter of said spray nozzle; c) conveying the product past said spray nozzle in a transport direction; and d) disposing a magnet means below the product, said magnet means having a first pole disposed below the product proximate said disposition area, and a second pole disposed below the product downstream of said first pole in said transport direction to generate a magnetic field in a region of said gap between said spray nozzle and the product, said magnetic field exercising a downward force on said powder along said transport direction between said first and said second poles.
  • 2. A device for dusting strip- or sheet-shaped products, the device comprising:at least one spray nozzle for spraying a powder/air mixture on the product at a deposition area, wherein said powder can be magnetized, said spray nozzle disposed at a substantial separation from the product to define a gap through which said powder spreads to cover said deposition area, said deposition area having a size which is substantially larger than an output diameter of said spray nozzle; means for conveying the product past said spray nozzle in a transport direction; and magnet means having a first pole and a second pole, said first pole disposed below the product proximate said deposition area, and said second pole disposed below the product downstream of said first pole in said transport direction, wherein said magnet means generates a magnetic field in a region of said gap between said spray nozzle and the product, said magnetic field exercising a downward force on said powder along said transport direction between said first and said second poles.
  • 3. The device of claim 2, wherein said magnet means comprises at least one permanent magnet.
  • 4. The device of claim 2, wherein said magnet comprises at least one electromagnet.
  • 5. The device of claim 2, wherein said magnet means comprises a magnet with a U-profile, whose U-legs form said first and said second poles, said first and said second poles extending transversely to said transport direction of the product over a width of the product.
  • 6. A device for dusting strip- or sheet-shaped products, the device comprising:at least one spray nozzle for spraying a powder/air mixture on the product at a deposition area, wherein said powder can be magnetized, said spray nozzle disposed at a substantial separation from the product to define a gap through which said powder spreads to cover said deposition area, said deposition area having a size which is substantially greater than an output diameter of said spray nozzle; means for conveying the product past said spray nozzle in a transport direction; and a plurality of electromagnets which are arranged parallel and next to each other, transversely to said transport direction of the product, each electromagnet having a first pole and a second pole, said first-pole disposed below the product proximate said deposition area, and said second pole disposed below the product downstream of said first pole in said transport direction, wherein said plurality of electromagnets generate a magnetic field in a region of said gap between said spray nozzle and the product, said magnetic field exercising a downward force on said powder along said transport direction between said first and said second poles.
  • 7. The device of claim 2, wherein said conveying means is disposed on a same side of the product as said spray nozzle, said conveying means comprising a first member made of a non-magnetizable material and a second member made of a magnetizable material, said second member defining a gripper element cooperating with the product to grasp the product at a front edge thereof.
  • 8. The device of claim 7, wherein said powder is covered or coated with iron particles.
  • 9. The device of claim 7, wherein said powder comprises powder particles having covering iron particles on their surface.
  • 10. A device for dusting strip- or sheet-shaped products, the device comprising:at least one spray nozzle for spraying a powder/air mixture on the product at a deposition area, wherein said powder can be magnetized, said spray nozzle disposed at a substantial separation from the product to define a gap through which said powder spreads to generate a deposition area having a size which is substantially greater than an output diameter of said spray nozzle; and magnet means having a first pole and a second pole, said first pole disposed below the product proximate said deposition area, and said second pole disposed below the product downstream of said first pole in said transport direction, wherein said magnet means generates a magnetic field in a region of said gap between said spray nozzle and the product, said magnetic field exercising a downward force on said powder along said transport direction between said first and said second poles, said magnet means having a magnet with a U-profile whose U-legs form said first and said second pole and which extend transversely to a conveying direction of the product over a width of the product.
  • 11. A device for dusting strip- or sheet-shaped products, the device comprising:at least one spray nozzle for spraying a powder/air mixture on the product at a deposition area, wherein said powder can be magnetized, said spray nozzle disposed at a substantial separation from the product to define a gap through which said powder spreads to generate a deposition area having a size which is substantially greater than an output diameter of said spray nozzle; and permanent magnet means having a first pole and a second pole, said first pole disposed below the product proximate said deposition area, and said second pole disposed below the product downstream of said first pole in said transport direction, wherein said permanent magnet means generates a magnetic field in a region of said gap between said spray nozzle and the product, said magnetic field exercising a downward force on said powder along said transport direction between said first and said second poles.
Priority Claims (1)
Number Date Country Kind
196 35 830 Sep 1996 DE
Parent Case Info

This application is a continuation of application Ser. No. 09/147,768 filed Mar. 4, 1999 now abandoned, which is a 371 of PCT/EP97/043 94 filed on Aug. 13, 1997 the complete disclosure of which is hereby incorporated by reference.

US Referenced Citations (4)
Number Name Date Kind
2027087 Buckner Jan 1936 A
4156036 Lennon et al. May 1979 A
4475979 Idstein et al. Oct 1984 A
4598870 Schloz Jul 1986 A
Foreign Referenced Citations (2)
Number Date Country
58-31773 Feb 1983 JP
64-24796 Jan 1989 JP
Continuations (1)
Number Date Country
Parent 09/147768 US
Child 09/731825 US