EP0093083B2 - Process for applying powder in strip form and powder application device - Google Patents

Description

The present invention relates to a powder application method and a powder application device according to the preambles of claims 1 to 4 and 10 and 11.

Methods and devices of the above-mentioned type are e.g. known from DE-A-2 933 841.

The coating of the welded longitudinal seams of can bodies with electrostatically charged powder is known and is mainly used on can bodies. be filled into soft, sensitive goods. Polymer resins are often used as powders. e.g. Epoxy, polyethylene etc. are used, which are conveyed to the weld seam in the finest resolution in an air stream and electrostatically charged shortly before hitting the seam.

When leaving the transport line carrying the powder, the powder is distributed over a wide area in relation to the expansion of the weld seam because the powder is finely distributed by air additionally blown into the spray space and blown against the weld seam as a powder cloud. Parts of the fuselage are thus also coated which do not have to be covered, on the other hand there is a direct weld seam, which often has a sharp edge. rather too little powder to ensure reliable coverage.

DE-A-29 33 641 describes a powder application device in which the powder is separated from the air shortly before reaching the weld seam by centrifugal separation, for example by means of a reversing loop in the transport line and like a liquid at a flat angle approximately parallel to the Seam runs down this. Only then is the powder fluidized again by compressed air supplied through porous walls charged by a row of electrodes also arranged parallel to the seam. Before the final application to the weld seam, together with the air additionally blown through the porous walls of the spray chamber, a powder-air cloud with the finest distribution of the powder particles is formed, which is then attracted to the weld seam and melted onto the weld seam in a subsequent heating device be bound. This device does not allow concentrated application with few powder particles scattering into the surroundings, since the powder flowing onto the weld seam is held by no additional forces except by gravity; a defined distribution of the powder across the seam area is not possible.

Spray heads for powder application devices have become known from Swiss patent specification 803249. which are provided with a plurality of bars and baffles lying transversely to the flow direction of the powder-air mixture. The rods and sheets slow down the powder / air flow and direct it against an outlet slot that is laterally delimited by flexible strips. As a further deflection means, a number of baffles are again provided transversely to this slot. With the help of additional air blown in by glands, the powder / air flow in the rear area of the spray head is additionally supported. The deflecting means and the additional air cause a powder wave with finely distributed powder particles that are blown against the weld seam by the additional air.

The use of various types of baffles for braking and deflecting the air / powder mixture results in a very complicated structure of the spray head, which tends to clog (powder nest). The distribution of the powder achieved by the guiding and braking elements takes place at the expense of a very large throughput of powder and air, which for the most part has to be removed and reprocessed from the suction located outside the can bodies. In addition to the high costs for compressed air and suction air, there are additional costs for the reprocessing and the loss of part of the recycled powder.

Furthermore, a powder application device is already known (US-A-4 205 621), in which a powder-air mixture is directed flat against the weld seam of can bodies through an angle-adjustable nozzle, the nozzle being located in a sealed, delimited area, the a wall is formed by the seam region of a can body, and suction is provided at the end.

In another known device for the electrostatic application of powders (JP-A-54-80 348), an electrostatically charged powder-air mixture is inflated vertically onto the surface to be coated, suction openings being provided in the spray pan next to the feed pipe. A powder cloud, which is a multiple of the diameter of the feed tube, forms between the feed tube and the suction openings.

For the application of relatively thick powder layers on workpieces, it is also known (DE-A-30 01 931) to apply several powder layers in each case with oppositely polarized electrostatic charging fields, because when thicker layers are formed, the deposited powder material is so strongly charged that it arrives the newly arriving ones Powder particles repels, unless a transfer has taken place beforehand. Such a method only makes sense in the production of very thick powder layers, which do not occur when coating the weld seam of can bodies.

Finally, it is already known from a patent brochure "Inside Powder Coating System" by the patent owner to apply a powder-air mixture at a steep angle to the weld seam of can bodies and to suck off air mixed with powder at a distance behind the application point.

All known powder application devices directly or indirectly generate a powder / air cloud in a spray room, which is electrostatically charged in front of or in the spray room and is directed against the seams to be covered, which are guided past the spray room, both as a result of this charging and as a result of the excess pressure and the air currents in the spray room . Despite powerful suction hoods above the spray chamber, many powder parts can settle on the outside of the can body; The majority of the powder parts that are fed into the spray chamber are extracted and have to be cleaned in the reprocessing system.

A first object of the invention is to achieve more reliable coverage of the sensitive central seam area with less powder.

This object is solved by the features of claims 1 or 2.

Surprisingly, by dividing the powder / air flow in the spray opening over several zones, which can have different application widths, more reliable coverage of the sensitive central seam area can be achieved with less powder.

Another advantage of the invention is that by dividing the powder / air flow over several lines, the application thickness can be varied in the individual areas.

Another object of the invention is to apply the powder conveyed into an air stream to the seam area with a small proportion of conveying air.

This object is achieved by the features of claims 3 or 4 or 10 or 11.

By entering the powder / air flow at a steep angle to the weld seam, it is now possible to apply the powder particles directly to the weld seam without additional introduction of compressed air. As a result, the powder particles reach the weld seam without redirection thanks to the kinetic energy drawn from the transport air. The extraction of air within the spray chamber next to the mouth of the powder feed line effectively counteracts scattering (cloud formation) of the powder particles on the flight to the weld seam.

• Figur 1 eine schematische Darstellung einer Pulverauftragsvorrichtung an einer Dosenrumpf Längsnaht-Schweissmaschine,
• Figur 2 einen Längsschnitt durch eine Sprüh-vorrichtung,
• Figuren 3/4 eine Draufsicht auf eine Sprühvorrichtung gemäss Figur 2,
• Figur 5 einen Längsschnitt durch eine weitere Ausführungsform der Sprühvorrichtung,
• Figur 6 eine Draufsicht auf die Sprühvorrichtung gemäss Figur 5.
• Figuren 7, 8, 9 einen Querschnitt der Leitungen längs Linie VII-VII, resp. VIII-VIII, resp. IX-IX in Figur 5 und
• Figur 10 eine Draufsicht auf die Sprühvorrichtung.

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

• FIG. 1 shows a schematic illustration of a powder application device on a can body longitudinal seam welding machine,
• FIG. 2 shows a longitudinal section through a spray device,
• FIGS. 3/4 a top view of a spray device according to FIG. 2,
• FIG. 5 shows a longitudinal section through a further embodiment of the spray device,
• FIG. 6 shows a top view of the spray device according to FIG. 5.
• Figures 7, 8, 9 a cross section of the lines along line VII-VII, respectively. VIII-VIII, resp. IX-IX in Figure 5 and
• Figure 10 is a plan view of the spray device.

The powder preparation, the reprocessing and the melting of the powder into a homogeneous layer on the seam are not the subject of this invention and are therefore only described to the extent necessary for understanding the invention.

1 shows schematically a known seam welding machine 1 with the electrode rollers 2, 3, some freshly welded can bodies 4, the powder application device 5 with the spray head 6, the external suction 7 and the combined processing and reprocessing system 8 and a known heating device 9 for melting the Powder shown on the seam. An electrical system for generating the high voltage for charging the powder is shown symbolically and is designated by reference number 10.

The spray head 6 is shown on an enlarged scale in FIG. 2 as a longitudinal section. In addition, a can body 4 located above the spray head 6 is shown, which passes the spray head 6 from left to right (arrow A). The upper cut surface 11 through the can 4 runs exactly through the weld seam 12 of the fuselage 4 and lies above the spray opening 13. Four feed lines 15 for a powder / air mixture open, inclined to the horizontal, into the room 14. Another, larger in cross section Line 16 opens into the head space 17 at the end of the spray head 6. The line 16 is connected to a suction system that leads to the processing system 8.

The lines 15 begin in a cone-shaped space 18, in which the powder / air mixture from the main line 19 is divided between the lines 15 if more than two lines 15 are provided.

Needle-shaped electrodes 20 can protrude into the conical ring-shaped space 18. They are coaxial with the lines 15 leading away from the space 18. They are connected to the high-voltage source 10 via an annular copper electrode 21 and a line 22.

Depending on the size of the can body diameter, the space available does not allow all cables 15 in the lower half of the spray head 6 parallel to each other. With a can diameter of less than 65 mm, the lines 15, as shown in FIG. 2, are preferably led away from the conical ring-shaped space 18 in a helical manner.

The spray opening 13 can have sealing elements 23 in the form of rubber or bristle strips on the side. These serve to seal or laterally limit the emerging powder to the can body 4.

The head space 17 is closed towards the can 4 with a lid 24.

The top view in FIG. 3 shows that the opening 13 in the spray head 6 has two zones 25 and 26 of different widths. On the input side, seen in the transport direction (arrow A) of the can bodies 4, the slot zone 25 is narrower than the slot zone 26 on the output side.

On the input side, a can 4 running in via the spray head 6 is visible in FIG. The central part, drawn in light grid, represents the weld seam 12. The unpainted recesses 27 adjoin directly adjacent to it, further away the protective lacquer 28 already applied to the can sheets in a flat state.

The approximate width ratios of the weld seam 12 and the regions 27 adjacent to it, which also have to be covered, and the slot zones 25 and 26 of the opening 13 can be seen from this illustration. The narrow zone 25 is slightly wider than the seam 12, the wider zone 26 exceeds the overall width of the seam 12 and the recesses 27.

In another embodiment of the opening 13 (FIG. 4), the cross section of the opening 13 widens continuously from the inlet-side to the outlet-side end of the spray head 6. The supply of the powder / air mixture, however, remains the same, as shown in FIG. 2, distributed over a plurality of lines 15.

Of course, a smaller or a larger number can also be provided instead of the four lines 15 shown, for example.

In a further embodiment of the invention, the lines 115 carrying the powder / air flow open substantially at right angles to the can surface or to the seam 12 and at a very short distance from the same. The distance between the line end and the weld seam 12 is in the range from 2 to 5 mm, preferably approximately 2.5 m. The opening cross section of the mouths of the lines 115 can be round or angular; however, the lines 115 can also be guided twice and in particular lie next to one another at the wide point 26 of the opening 13. Preferably, easily replaceable end pieces 315 are attached to the lines 115. In addition to the suction line 16 opening into the head space 17, further lines 116 can be provided before and after each line 115. These lines 116 preferably open to the base of funnel-shaped depressions 117, which are located between the powder lines 115. The suction lines 116 are connected to the processing system 8 via the suction line 16. (Figures 5/6).

To the side of the spray opening 13, sealing elements 23 or moving plastic belts can protect the areas next to the seam 12 from the deposit of powder particles. In the embodiment according to FIGS. 5 and 6, these covers can also be dispensed with, in particular if the lines 115 open very close to the weld seam 12 and consequently the powder / air flow can also escape at a very low speed in order to cover the remaining free path up to Overcome seam 12. Powder particles which do not reach the seam or which loosen again are immediately removed from the spray opening through line 116.

If the spray head 6 is designed with only two lines 15, 115, the distribution of the powder / air stream at the end of the feed line 19 can of course also be carried out via a y-shaped splitting of the line 19. The electrodes 20 can then preferably lie in the legs of the Y.

Particularly when applying the powder, in which the greater part of the transport air flows parallel to the powder stream, the formation of the powder stream when it emerges from the lines 15, 115 is important. The cross sections according to FIGS. 7, 8, 9 and according to FIG. 10 show an embodiment of the lines 15, 115 which let the powder emerge vertically as a band-shaped stream, or at least at an obtuse angle to the seam. The initially round cross section of the powder lines 15, 115 has, starting at the arcuate part of the line 15, 115 below the outlet opening, a rectangular cross section which continues to the outlet opening. The powder particles floating in the air flow in the horizontally lying section of the line 15, 115 are distributed over the flat outer radius and slide upwards where they leave the line 15, 115 as a narrow band standing transversely to the weld seam.

From the welding machine 1, the can bodies 4 welded longitudinally between the welding rolls 2 and 3, carried by a transport system 29, reach the powder application device 5. Initially, a narrow powder strip, which just covers the welding seam 12, is applied from the narrow zone 25 of the spray head opening 13. When passing through the wider zone 26, the powder is applied in an area which not only includes the weld seam 12 but also the adjacent areas 27. The already covered seam area 12 is again coated with powder.

The adhesion of the powder to the can 4 is achieved in a known manner either by electrostatically charging the powder particles on the electrodes 20 or by friction on the feed lines 15, the can 4 having an opposite charge, or adhesion is achieved by gluing to the temperature of the weld seam 12, which is still hot or kept hot by a heat source (not heated) and exceeds the melting temperature of the powder.

The powder is fed in the air stream through line 19. After the distribution in the conical space 18 or in the y-shaped end of line 19 into one or a plurality of lines 15 and the static charge, the (powder / air stream) becomes direct and without further baffles through the slot 13 to the can seam 12 and the areas 27. With the help of the sealing elements 23, the order can be limited exactly to the width of the slot opening 19. The powder parts not adhering to the can 4 and the transport air are fed through the suction line 16 out of the head space 17 and / or the funnel-shaped depressions 117, the powder particles emerging between the following cans 4 are removed by the suction 7 and fed back to the processing plant. After the powder has been applied via the spray head 6, the can bodies are guided along a heat source or heater 9 so that the powder melts and forms a well-adhering coating on the can seam 12.

The method and the device described above for covering the inner seam can of course be used analogously for the outer seam covering. Of course, the method described can also be used to apply the powder to an underlying seam.

Claims (24)

1. Method of applying a strip-like powder layer to the welded seam (12) of can bodies (4), wherein the powder, carrier by an air stream, is conveyed to a spray chamber (14), which is situated opposite the welded seam (12) and has a slot-like spray aperture (13) in a spray head (6), is electrostatically charged and is applied to the welded seams (12) of the can bodies (4), which are conveyed past the aperture (13) by a conveyor device (29), characterised in that the powder within the spray chamber (14) is applied in direct succession in two or more strip-like layers which at least partially cover one another, the width of the layer following the first layer being greater that the width of the first layer.
2. Method of applying a strip-like powder layer to the welded seam (12) of can bodies (4), wherein the powder, carried by an air stream, is conveyed to a spray chamber (14), which is situated opposite the welded seam (12) and has a slot-like spray aperture (13) in a spray head (6), is electrostatically charged and is applied to the welded seams (12) of the can bodies (4), which are conveyed past the aperture (13)by a coveyor device (29), characterised in that the powder within the spray chamber (14) is applied in direct succession in two or more strip-like layers which at least partially cover one another, the width of the layer following the first layer being smaller than the width of the first layer.
3. Method of applying a strip-like powder layer to the welded seam (12) of can bodies (4), wherein the powder, carried by an air streain, is conveyed to a spray chamber (14), which is situated opposite the welded seam (12) and has a slot-like spray aperture (13) in a spray head (6), the powder is electrostatically charged and is applied to the welded seams (12) of the can bodies (4), which are conveyed past the aperture (13) by a conveyor device (29), the powder being applied through a line (15) at an angle to the welded seam (12), through the spray chamber (14) and the slot-like spray aperture (13) to the welded seam (12), and powder emerging outwardly between the successive can bodies (4) is discharged by a suction means (7), characterised in that the powder is guided by a line (15,115) to the vinicity of the welded seam (12) and is substantially applied in the form of a band-like stream at a steep angle relative to the welded seam (12) from the line which extends into the spray aperture (13) opposite the welded seam (12), and in that simultaneously air is additionally drawn by suction from the air stream, which introduces the powder into the spray chamber (14), adjacent the opening of the powder-and-air line (15).
4. Method of applying a strip-like powder layer to the welded seam (12) of can bodies (4) wherein the powder, carried by an air steam, is conveyed to a spray chamber (14), which is situated opposite the welded seam (12) and has a slot-like spray aperture (13) in a spray head (14), the powder is electrostatically charged and is applied to the welded seams (12) of the can bodies (4), which are conveyed past the aperture (13) by a conveyor device (29), characterised in that the powder is conveyed from a line (115), which extends into the spray aperture (13) opposite the welded seam (12) substantially in the form of a bandlike stream , to the vicinity of the welded seam (12) and is applied to the welded seam (12) substantially at a right angled and in that simultaneously air is additionally drawn by suction from the air stream, which introduces the powder into the spray chamber (14), adjacent the opening of the powder-and-air line (115).
5. Method according to claim 4, characterised in that the powder is applied to the welded seam (12) from a distance of between 2 and 5 mm.
6. Method according to one of claims 3 and 4, characterised in that the powder is applied in the direct vicinity of the welding point (the welding rollers (2, 3)), as long as the temperature of the welded seam (12) is higher than the melting temperature of the powder.
7. Method according to one of claims 3 and 4, characterised in that the welded seam (12) and directly adjacent regions (27) are heated by a heat source to above the melting temperature of the powder or, respectively, are kept above the melting temperature.
8. Method according to one of claims 1 to 4, characterised in that powder, which does not adhere to the welded seam (12), as well as air from the air stream, are drawn by suction in the can conveying direction near the opening of the line or lines (15, 115).
9. Method according to one of the preceding claims, characterised in that the air carrying the powder and the excess powder not adhering to the welded seam (12) are discharged by suction upstream and/or downstream of the line or lines (15, 115) at the bottom of the spray chamber (14).
10. Powder applying device for applying a strip-like powder layer to the welded seam (12) of can bodies (4), comprising a spray head (6) with with means for electrostatic charge, a spray chamber (14) and a slot-like spray aperture (13) as well as a conveyor device (29) for conveying the welded seam (12) of the can bodies (4) longitudinally of the aperture (13), and a powder feed line (15) and a suction means (7) for discharging the powder which emerges outwardly between the can bodies (4), which succeed one another with a spacing therebetween, characterised in that the powder feed line (15) discharges at the base of the spray chamber (14,17) opposite the spray aperture (13) into the spray chamber (14, 17) at a steep angles relative to the aperture (13) and in that a suction line (16) additionally discharges into the spray chamber (14, 17) adjacent the line (15).
11. Device for applying a strip-like powder layer to the welded seam (12) of can bodies (4), comprising a spray head (6) with with means for electrostatic charge, a spray chamber (14) and a slot-like spray aperture (13) as well as a conveyor device (29) for conveying the welded seam (12) of the can bodies (4) longitudinally of the aperture (13), and a powder feed line (115) and a suction means (7) for discharging the powder which emerges outwardly between the can bodies (4) which succeed one another with a spacing therebetween, characterised in that the powder feed line (115) discliarges into the chamber (14, 17) in the vicinity of the spray aperture (13) substantially at a right angle to the spray aperture (13), and in that a suction line (116) additionally discharges into the spray chamber (14, 17) adjacent the line (115).
12. Device according to one of claims 10 or 11, characterised in that the suction line (116) discharges into the base of a funnel-shaped recess (117) at the bottom of the chamber (14) of the aperture (13).
13. Device according to one of claims 10, 11 or 12, characterised in that the suction line (116) is connected to a processing plant (8) via a central suction line (16).
14. Device according to claim 11, characterised in that the line (115) terminates at a distance of 2 to 5 mm from the spray aperture (13).
15. Device according to one of claims 10 or 11, characterised in that a plurality of lines (15, 115),which are arranged in series when viewed in the conveying direction of the cans, extend into the chamber (14) of the aperture (13).
16. Device according to claim 15, characterised in that the spray aperture (13) comprises a narrow zone (25) and a subsequent, wider zone (26).
17. Device according to claim 15, characterised in that the cross-sections of the line openings in the narrow zone (25) are smaller than in the wider zone (26).
18. Device according to claim 15, characterised in that two lines (115) extend adjacent one another into the spray aperture (13) in the wider zone (26).
19. Device according to claim 15, characterised in that the lines (15) extend helically relative to the aperture (13).
20. Device according to one of claims 10 to 19, characterised in that the application of the powder is limited by profile belts which are situated laterally of the spray aperture (13) and rotate in the conveying direction.
21. Device according to one of claims 10 to 19, characterised in that sealing means (23), e.g. rubber or brush strips, are provided laterally of the spray aperture (13).
22. Device according to one of claims 10 to 21, characterised in that a head chamber (17) is connected with the end of the spray aperture (13) within the chamber (14) the suction line (16) extending into said head chamber.
23. Device according to claim 22, characterised in that a slot-like gap exists between the head chamber (17) closed off by the cover (24) at its upper end, and the can (4).
24. Device according to one of claims 10 or 11, characterised in that the line (15, 115) has a rectangular or segmental cross-section upstream of the outlet aperture.

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