IL206755A - Method and system for electrostatic painting of a rolled tin sheet - Google Patents

Description

METHOD AND SYSTEM FOR ELECTROSTATIC PAINTING OF A ROLLED TIN SHEET BACKGROUND OF THE INVENTION Field of the invention The invention is in the field of painting metal articles, and in particular deals with electrostatic painting of a long tin sheet.

Description of related art Electrostatic painting or powder coating is used for painting metal articles. Atomized particles are being charged electrically, thus repelling each other as they exit a spray nozzle and covering evenly the metal article. The metal article is grounded and the charged particles are attracted to the surface of the metal part evenly. After painting, the part is baked to convert the powder into a type of plastic.

Before painting, the metallic surface is treated by cleaning materials which remove dirt and process the metallic surface for absorbing the powder. To this aim, the metal articles are transferred from a bath to bath, using levers for heavy articles.

Painting rolled tin sheets is especially challenging, and in the prior art rolled tin sheets are wet painted rather than painted by electrostatic painting, as electrostatic painting failed to get uniform surface coverage.

Thus, it is an object of the current invention to provide a method and system for electrostatic painting of rolled tin sheets uniformly. Also, it is an objective of the current invention to save area of the plant floor.

BRIEF SUMMARY OF THE INVENTION It is provided a system for painting a long foldable sheet moving from a sheet source to a sheet destination. The system includes liquid baths for pre-treating the long foldable sheet, means for guiding the long foldable sheet within the liquid baths, such that the long foldable sheet fully bends within the liquid baths, means for uniform painting of the treated sheet, and ovens for drying the painted sheet.

In some embodiments, the sheet source is a sheet drum. Rollers disposed near edges of the liquid baths are used to guide the long sheet at entrances and at exits of the liquid baths. Rollers disposed within the liquid bath are used to guide bending of the long sheet inside the liquid bath. Pairs of rollers disposed close to the liquid baths receive the treated sheet in between and extract excess pre-treating liquid out of the treated sheet.

In some embodiments, the long foldable sheet is an aluminum tin sheet.

In some embodiments,, the width of the long foldable sheet is between 500 and 700 mm, and its thickness is between 0.5 and 1.1 mm.

In some embodiments, several electrostatic painting guns paint the long sheet uniformly.

In some embodiments, the oven includes a helical guiding structure for forcing air flow therein in a substantially helical duct. The maximal air temperature is between 250°C and 280°C.

It is provided a method for painting a long foldable sheet moving from a sheet source to a sheet destination using a system including pre-treating liquid baths, means for guiding the sheet within the liquid baths, means for uniform painting of the sheet, and drying ovens. The method includes guiding the long foldable sheet into the liquid baths for pre-treatment, fully bending the long sheet inside the liquid baths, painting sides of the treated sheet, and applying flowing hot air inside the ovens for drying the painted sheet.

In some embodiments, the method further includes drawing the long sheet from a sheet drum, using rollers to guide the long sheet at entrances and exits of the liquid baths, bending of the long sheet inside the liquid bath, and guiding the sheet in between a pair of rollers for extracting excess pre-treating liquid off the treated sheet.

In some embodiments, the method includes forcing air flow in the oven through a substantially helical duct, at a maximal air temperature between 250°C and 280°C.

In some embodiments, the method further includes wrapping the dried sheet around a receiving sheet drum.

BRIEF DESCRIPTION OF THE DRAWINGS The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to system organization and method of operation, together with features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings in which: Fig. 1 is a schematic drawing of a first parLof a system for painting a long foldable sheet.

Fig. 2 is a schematic drawing of a second part of a system for painting the long sheet. Fig. 3 depicts several electrostatic guns painting lower and upper sides of the long sheet.

Fig. 4 is a flow chart of a method for painting the long foldable sheet.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in terms of specific example embodiments. It is to be understood that the invention is not limited to the example embodiments disclosed. It should also be understood that not every feature of the methods and systems handling the described system or devices is necessary to implement the invention as claimed in any particular one of the appended claims. Various elements and features of devices are described to fully enable the invention. It should also be understood that throughout this disclosure, where a method is shown or described, the steps of the method may be performed in any order or simultaneously, unless it is clear from the context that one step depends on another being performed first.

Before explaining several embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The systems, methods, and examples provided herein are illustrative only and not intended to be limiting.

In the description and claims of the present application, each of the verbs "comprise", "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of .the. verb.

A system for painting an aluminum tin sheet 5 moving from a raw sheet drum 10 to a painted sheet drum(not shown) is illustrated in Figs. 1 ,2 and 3. The system includes liquid baths 12a,12b,12c, and 12d for pre-treating tin sheet 5, bending rollers 14 and 16 for guiding the long foldable sheet within the liquid baths, electrostatic painting guns 18 and 19 for uniform painting of the treated sheet, oven 22 for drying sheet 5 before painting, and ovens 24 and 26 for drying sheet 5 after painting.

In some embodiments, the width of the sheet is between 500 and 700 mm. Its thickness is between 0.5 and 1.1 mm. Its length is 1000-2000m, preferably 1400-1600m.

For drawing sheet 5 from drum 10, an electric motor (not shown) rotates drum . Edge rollers 28 are used to guide the long sheet at entrances and exits of the liquid baths 12a,12b, 12c and 12d. Pairs of rollers 30 disposed close to liquid baths 12a, 12b, 12c and 12d receive the treated sheet 5 in between and extract excess pre-treating liquid out of treated sheet 5. Before painting, treated sheet 5 is further dried in oven 22.

Bending sheet 5 within liquid baths 12a, 12b, 12c, 12d saves a lot of plant floor area, and allows the sheet to stay more time within each bath.

Referring now to Fig. 2, in oven 24 an air blower 32 forces air flow in the direction of moving sheet 5, while air sink 34 draws the air outside oven 24. The maximal air temperature in oven 24 is between 250°C and 280°C. Preferably, heaters installed within oven 24 heat the air. Alternatively or in combination, the air is heated outside oven 24 and is introduced into oven 24 as hot air. To save energy, the air emitted by air sink 34 is flowing back in a duct (not shown) to air pump 32.

Preferably, oven 24 includes a helical guiding structure 36 for forcing air flow in a helical duct, thus providing more uniform and more intensive drying of the painted sheet. Structure 36 has a raised helical rib with edge 38, much like a thread made for receiving an imaginary huge screw.

Referring now to Fig. 3, it illustrates an exemplary electrostatic painting system 50, which includes a container 52 for containing painting powder, a plurality of flexible pipes 54 and 56, and electrostatic guns 18 and 20 for painting the upper side and bottom side of sheet 5, respectively. The angular spread of the emitted painting materia] is broad enough to provide uniform painting of sheet 5.

Preferably, guns 18 and 20 are mounted on holders(not shown) oscillating in either the sheet propagating direction or in the lateral direction, which is perpendicular to the propagating direction, to facilitate more uniformity of painting. Guns 18 and 20, or their holders, are supported by respective bridges 58 and 60, which are secured to the floor by bases 62.

A method 100 for painting a long tin sheet moving from a sheet drum 10 to a receiving sheet drum is depicted in the flow chart of Fig. 4. The method includes a step 110 of drawing the long sheet of a sheet drum 10, and a step 120 of guiding long foldable sheet 5 into liquid baths 12a,12b,12c, and 12d using rollers 28. The method further includes a step 130 of fully bending sheet 5 inside liquid baths 12a,12b,12c, and 12d, a step 140 of guiding the sheet in between pairs of rollers 30 for extracting excess pre-treating liquid off the treated sheet, a step 150 of electrostaticaly painting sides of treated sheet 5, and a step 160 of guiding sheet 5 into ovens 24 and 26. Finally, the method further includes a step 170 of applying flowing hot air inside oven 24 for drying the painted sheet, and a step 180 of wrapping the dried painted sheet 5 around a receiving sheet drum. .

In some embodiments, the method includes forcing air flow in the oven through a substantially helical duct 36, at a maximal air temperature between 250°C and 280°C.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. In particular, the present invention is not limited in any way by the examples described.

Claims (20)

3447/7-10 CLAIMS:

1. A system for painting a long foldable sheet moving from a sheet source to a sheet destination, the system comprising: a) one or more liquid baths for pre-treating the long foldable sheet; 5 b) means for guiding said long foldable sheet within at least one liquid bath such that said long foldable sheet fully bending within said at least one liquid bath; c) means for painting of the treated sheet; and d) one or more ovens for drying the painted sheet. 10

2. The system of claim 1 wherein the sheet source is a sheet drum.

3. The system of claim 1 wherein the system includes one or more rollers disposed near an edge of a liquid bath, for guiding the long sheet at entrance or exit of said liquid bath. 1 5

4. The system of claim I wherein at least one roller disposed inside a liquid bath is used to guide bending of the long sheet inside said liquid bath.

5. The system of claim 1 wherein the system further includes at least one pair of 20 rollers disposed close to at least one liquid bath, the rollers adapted for receiving the treated sheet in between and extracting excess pre-treating liquid out of said treated sheet.

6. The system of claim 1 wherein the long foldable sheet is an aluminum tin sheet. 25

7. The system of claim 1 wherein the width of the long foldable sheet is between 500 and 700 mm.

8. The system of claim 1 wherein the thickness of the long foldable sheet is between 30 0.5 and 3.1 mm.

9. The system of claim 1 wherein two or more electrostatic painting guns paint the long sheet. 3447/7-10

10. The system of claim 1 wherein at least one oven includes a helical guiding structure for forcing air flow therein in a substantially helical duct.

11. 1 1. The system of claim 1 wherein the maximal air temperature in at least one oven is between 250°C and 280°C.

12. A method for painting a long foldable sheet moving from a sheet source to a sheet destination using a system including one or more pre-treating liquid baths, means for guiding the sheet within at least one liquid bath, means for painting the sheet, and one or more ovens, the method comprising: a) guiding the long foldable sheet into at least one of the liquid baths for pre- treatment; b) fully bending the long sheet inside at least one liquid bath; c) painting at least one side of the treated sheet; and d) applying flowing hot air inside at least one oven for drying the painted sheet.

13. The method of claim 12 wherein the method further includes drawing the long sheet of a sheet drum.

14. The method of claim 12 wherein at least one roller is disposed near an edge of a liquid bath and the method further includes guiding the long sheet at entrance or exit of said liquid bath using the roller.

15. The method of claim 12 wherein at least one roller is disposed inside a liquid bath and the method further includes guiding the bending of the long sheet inside said liquid bath.

16. The method of claim 12 wherein the method further includes guiding the sheet in between two rollers disposed close to at least one liquid bath for extracting excess pre-treating liquid off the treated sheet. 3447/7-10

17. The method of claim 12 wherein the painting is electrostatic painting.

18. The method of claim 12 wherein the method includes forcing air flow in at least one oven through a substantially helical duct.

19. The method of claim 12 wherein the method includes forcing hot air flow over the painted sheet at a maximal air temperature between 250°C and 280°C.

20. The method of claim 12 wherein the method further includes wrapping the dried sheet around a receiving sheet drum.