EP0093083A2 - Process for applying powder in strip form and powder application device - Google Patents

Abstract

One or more layers of meltable powder are applied to the weld seam (12) of can bodies (4). The powder is fed through lines (15, 115) at an obtuse angle up to the weld seam (12) and applied directly. Several lines (15, 115) can be arranged one behind the other so that the powder can be applied in several layers. The subsequent layers each overlap the ones below, so that the most sensitive area, the seam (12), has the most powder. The spray head (6) consists of a slit-shaped opening (13), the width of which increases towards the rear. A can body with a protective layer applied to the weld seam, which is much thicker in the area of the seam than in the neighboring areas.

Description

The present invention relates to a powder application method and a powder application device according to the preambles of claims 1 and 8 and a can body according to the preamble of claim 19.

The coating of the welded longitudinal seams of can bodies with electrostatically charged powder is known and is predominantly used on can bodies in which sensitive filling goods are filled. Polymer resins, e.g. Epoxy, polyethylene and others 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 in relation to the expansion the weld seam wide area. Parts of the fuselage are thus also coated, which would not have to be covered, but on the other hand, the weld seam, which often has a sharp edge, has less powder to lie on to ensure reliable coverage.

A method is known from US Pat. No. 3,713,862, with which a defined narrow and uniform powder application strip is applied to the outside of the seam with the aid of the lateral areas of the seam-covering tape.

Coating the inside of the seam is not possible in this way because the slotted masking tape is not covered by the welded, i.e. closed hulls can be performed. Furthermore, uniform powder application over the entire coverage area is not advisable. If enough powder is applied to reliably cover the welding edges of the seam, there is too much material in the side areas, which is uneconomical given the high prices for powder. If the application thickness is kept low, the seam is poorly covered.

German Offenlegungsschrift No. 29 33 641 describes a powder application device in which the lateral powder scattering by partial separation of the air from the powder shortly before (the exit) prevent the powder from escaping from the spray head. Shortly before reaching the seam, the powder is separated from the air by centrifugal separation, for example with a reversing loop in the transport line, and sprayed approximately parallel to the seam into a spray room, where it is charged by a row of electrodes also arranged parallel to the seam. The introduced parallel to the flow of powder also in the spraying air flow mixes there forced läufi ^g again with the powder and generating a powder / air cloud. This device hardly enables a concentrated application with a few powder particles scattering into the environment; a defined distribution of the powder across the seam area is not possible.

In the further development of the aforementioned DE-OS 29 43 641 for an upward application (European patent application No. 54757), the spray chamber consists of a porous material. Gas or air is blown into the spray space through this porous material in order to blow the powder particles introduced essentially parallel to the weld seam against the seam area. A defined order that only covers the very narrow seam area is excluded with this arrangement. This inevitably leads to large powder consumption.

From the Swiss patent specification 603'249 spray heads for powder application devices have become known, which with a A large number of bars and baffles lying transversely to the flow direction of the powder / air mixture are provided. The bars 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 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 nests). 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 by the suction and reprocessed. 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.

All known powder application devices directly or indirectly produce a powder / air cloud in a spray room, which is electrostatically charged 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.

The object of the present invention is to provide a device which overcomes the disadvantages of the known devices.

In particular, it is an object of the invention to reliably cover the sensitive central seam area with a thick layer; the outer areas, however, should only be coated as far as is absolutely necessary.

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.

Another object of the invention is to design the device in such a way that it can be arranged as close as possible to the welding machine.

According to the invention, these objects are achieved in accordance with the characteristics of claims 1 and 8.

Further advantageous embodiments can be found in the subclaims.

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.

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

Another advantage of the invention is that by moving the powder feed lines close to the weld seam, it is possible to work with a small amount of air and less pressure, so that less powder excess has to be reprocessed and, in addition, few powder particles are flung next to the seam area. Furthermore, a concentrated application of the powder without static charge on the seam is also possible.

Another advantage of the invention is that the powder layer thickness can be metered well across the seam due to the arrangement of two feed lines lying next to one another.

Another advantage of the invention is that the helical routing of the lines largely prevents the occurrence of blockages.

Another advantage of the invention is that the suction can be used to easily remove the excess powder from the application zone in addition to the outlet openings. Since this powder is not contaminated, it does not need to be cleaned.

Another advantage of the invention is that the powder / air flow can be divided without interference in the cone-shaped space.

Another advantage of the invention is that, thanks to modest dimensions, the device can be provided directly on the welding machine, which, thanks to the short transport path from the welding point to the device, makes it possible to position the seam to the spray head exactly, and thereby the powder on the the weld still adheres to the hot seam and can be applied exactly to it.

A further advantage of the invention is that the additional heating of the seam area or the keeping of the same at the same time makes it possible to apply powder with little or no charging. In many cases, the powder's frictional charge in the supply lines is sufficient to ensure sufficient adhesion to the hot seam.

• Figur 1 eine schematische Darstellung einer Pulverauftragsvorrichtung an einer Dosenrumpf-Längsnaht-Schweissmaschine,
• Figur 2 einen Längsschnitt durch eine Sprühvorrichtung,
• 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 Draufischt 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 top fish on 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.

FIG. 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 one Known heating device 9 shown for melting the powder 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 in Fig. 2 on an enlarged scale 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 to the lines 15 leading out of 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 conditions do not allow all the lines 15 to be routed in parallel in the lower half of the spray head 6. 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 a light grid, represents the weld seam 12. The unpainted cutouts 27 close immediately adjacent to it on, further out the protective lacquer 28 already applied to the can plates in a flat state.

The approximate width ratios of the weld seam 12 and the regions 27 adjacent to it, also 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 essentially at right angles to the can surface or to the seam 12 and at a very short distance from the same. The distance between that The line end and the weld seam 12 are 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. Easily replaceable end pieces 315 are preferably 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, by the remaining free path to 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 can be at the end of the feed line 19, of course, also 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 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, which are longitudinally welded between the welding rollers 2 and 3 and carried by a transport system 29, reach the powder application device 5 Spray head opening 13 a narrow, only just covering the welding seam 12, applied powder strips. 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 the adhesion is achieved by gluing at 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 supplied in the air stream through line 19. After the division 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 is the (powder / air flow)

Powder / air flow led directly 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 subsequent 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 (19)

1. A method for applying a strip-like powder layer on the weld seam of can bodies, characterized in that the powder is applied directly in succession in two or more, at least partially overlapping layers. 2. The method according to claim 1, characterized in that the width of the following overlapping layers increases / decreases. 3. A method for applying a strip-like powder layer on the weld seam of can bodies, the. Powder, carried by an air stream, being conveyed to a slit-shaped spray opening of a spray head lying opposite the weld seam and being applied from there to the can bodies passed by the transport device at the opening , characterized in that the powder is brought from a line (15, 115) close to the weld seam (12) and is applied there at an obtuse angle to the weld seam. 4. The method according to claim 3, characterized in that the powder at substantially right angles to the Weld seam (12) is brought up and applied to the weld seam (12) from a distance of between 2 and 5 mm. 5. The method according to any one of claims 3 and 4, characterized in that the powder is applied in the immediate vicinity of the welding point (the welding rollers (2, 3)) as long as the temperature of the weld seam (12) is higher than the melting temperature of the powder. 6. The method according to any one of claims 3 and 4, characterized in that the temperature of the weld seam (12) and the immediately adjacent areas (27) is heated by a heat source above the melting temperature of the powder, or is kept above the melting temperature. 7. The method according to any one of claims 3 and 4, characterized in that the air carrying the powder and the excess powder not adhering to the weld seam is sucked off between the lines (15, 115) and / or in the head space (17). 8. Powder application device for applying a strip-shaped powder layer on the longitudinal seam of can bodies with a powder carried by an air stream in the seam area distributed, a slit-shaped opening having spray head as well as a transport device for conveying the carcasses along the opening, characterized in that the powder of the slit-shaped Oeffnun ^g (13) of the spray head (6) through an opening into the opening (13) line (15,115) which line (15, 115) leads at an obtuse angle up to the weld seam (12) so that the powder leaving the line (15, 115) strikes the weld seam at an obtuse angle. 9. The device according to claim 8, characterized in that the line (15) is assigned a flap (215) which is adjustable for metering the amount of powder. 10. The device according to claim 8, characterized in that the line (115) opens substantially at right angles to the weld seam in the opening (13), and that the line (115) at a distance of 2 to 5 mm from the weld seam (12) ends. 11. The device according to claim 8, characterized in that a plurality, seen in the transport direction of the hulls, leads (15, 115) arranged in series opens into the opening (13). 12. The device according to claim 11, characterized in that the opening (13) consists of a narrow zone (25) and an adjoining wider zone (26). 13. The apparatus according to claim 12, characterized in that the cross sections of the line mouths in the narrow zone (25) less than in the wider zone. (26) are. 14. The apparatus according to claim 12, characterized in that in the wider zone (26) two lines (115) open side by side in the opening (13). 15. The apparatus according to claim 11, characterized in that the lines (15) are guided helically to the outlet opening (13). 16. The apparatus according to claim 8, characterized in that the powder is electrostatically charged in the cone-shaped distribution space (18) before entering the lines (15, 115). 17. Device according to one of claims 8 to 16, characterized in that the application of the powder by profile belts lying to the side of the opening (13) and rotating in the transport direction are limited. 18. Device according to one of claims 8 to 16, characterized in that on the side of the opening (13) sealing elements (23), e.g. Rubber or brush strips are provided. 19.Can fuselage with a welded longitudinal seam and a protective layer lying on the seam area, which has been produced by fusing or crosslinking a powder applied with an air stream, characterized in that the protective layer in the immediate vicinity of the bead forming the weld seam (12) has a substantially larger one Thickness than in the adjacent edge zones (27).

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