EP0224034A1 - Method and arrangement for preventing floating particles from descending, and a heat treatment station in a continuous inner liner installation - Google Patents

Abstract

In order to prevent, for example when internally lining can bodies during the heat treatment of the applied layer following the lining, floating particles or droplets of the lining medium descending onto a surface which is to be kept clean, a gas injection is performed over a large surface of the radiation surface of a heat radiator (51) in that over a large area a nozzle arrangement (55) is provided with nozzle slots (59 and 61). The feeding of gas to the nozzle arrangement (55) occurs by means of a channel (45). In this case, the nozzle arrangement (55) can operate at the same time as a thermal reflector for the radiator (51). <IMAGE>

Description

The present invention relates to a method for preventing the dropping of suspended particles or droplets onto a surface that is to be kept clean in this regard, at least one dimension, an arrangement therefor, an application of the method or the arrangement mentioned to a thermal treatment station for the internal coating of cylindrical bodies, such as can bodies, preferably for the inner coating of their longitudinal weld section and a thermal treatment station on a continuous internal coating system for cylindrical bodies, such as for can bodies.

In powder coating or lacquer coating application techniques, in which, for example, a coating medium is applied in powder form or in the form of droplets or in liquid form to workpieces to be coated, it may be electrostatically assisted to warm up the layer after application in order to fuse the particles or Drying the liquid application to achieve a tight seam. For this purpose, heat sources are provided in the area of the layer produced. By back that can never be completely prevented if coating medium adheres poorly or if the heating zone is immediately adjacent to the coating zone, medium from the coating zone onto the heat sources, such as infrared emitters, causes contamination of the radiating surfaces, baking the coating medium there leads to a hardened crust.

The object of the present invention is to develop a method of the type mentioned in the introduction in such a way that a surface to be kept clean, which is at least one dimension in size, is not contaminated by sinking floating particles or droplets.

This object is achieved in that a gas flow is generated over the surface by gas injection and / or suction over a large area.

A layer of flowing gas is thus generated over the surface to be kept clean, which entrains sinking particles or droplets before the latter have hit the surface to be kept clean. Even if the latter only needs to be blown in a small area to be kept clean in order to prevent precipitation of particles or droplets, this does not lead to a goal in a larger area to be kept clean, because the resulting turbulence would probably result in a small area of precipitation keep clear, but promote this precipitation in adjacent areas.

If the surface to be kept clean is the radiation surface of a heat radiator, the gas flow above this surface gives rise to the problem that the efficiency of the radiator is reduced in that the surface, if no further measures are taken, is cooled by the gas flow.

In order to prevent this, it is proposed in this case that the gas flow be selected in the order of magnitude of the natural convection caused by the heat radiator or that the gas be heated in continuous operation, as by means of the heat radiator itself. The last-mentioned variant is realized by doing this Gas in circulation mode drives through a thermally well-insulated system, if necessary additionally heated there, thereby preventing heat from being removed from the radiator by the gas flow. By applying the flow in the order of magnitude of natural convection, the radiator efficiency loss remains within negligible limits.

For large-area gas injection or extraction at low flow speeds, a problem arises with regard to the design of the blowing or suction nozzles, especially if one takes into account that, for example when using heat radiators, the smallest possible amount of gas should generate the required flow. The proposed, spatially extended nozzles must have small diameters, which initially leads to extensive nozzle slots, but is very difficult to achieve in the required fineness and expansion are. It is therefore further proposed that the injection or suction is carried out at a large number of discrete points arranged in the area of the surface, which is much easier to implement than the formation of the slot nozzles mentioned.

The above-mentioned arrangement for solving the problem is characterized in that in the area of the surface there is at least one channel pressurized with over or under pressure, with an extended nozzle arrangement, preferably with a large number of discrete passages.

The channel results in a largely constant pressure distribution along the nozzle arrangement, so that gas flows out of it, evenly distributed. With the large number of discrete passages, which can be extremely fine, even a small amount of gas results in a sufficient gas flow over the area to be kept clean.

The nozzle arrangement preferably comprises a metal structure produced by galvanic application to a negative mold with a large number of pins.

A structure made in this way has neatly defined, closely spaced small passages, and ensures a largely turbulence-free gas inflow or outflow. About 10 to about 60 passages per running centimeter are preferably provided on the nozzle arrangement, preferably with a passage cross cut areas, so that their sum makes up about 40% of the arrangement area.

In order to prevent the lowering of coating particles or droplets onto a longitudinally extended heat radiator at a thermal treatment station of a coating system for workpiece surfaces, it is further proposed that the nozzle arrangement form a channel arranged at a radial distance and coaxial with a longitudinal axis of the radiator.

When designing the nozzle arrangement with a large number of distributed passages, a high degree of versatility is achieved in that passages are selectively covered, such as by adhesive tape or varnish, for the selective keeping of active passage patterns that are extended in line or area. This means that lines with practically the same effect can be kept free of openings with very narrow slit nozzles, the rest are covered.

In the above-mentioned configuration of the arrangement, in connection with longitudinally extended heat radiators, the mentioned galvanic manufacturing technique for the nozzle arrangement is characterized by a further, essential advantage. In contrast to the use of a grid-like mesh as a nozzle arrangement, the aforementioned galvanic production results in an extraordinarily smooth metallic surface, the latter, brought into the area of the radiator, acting as a radiation reflector and, like a rod emits heat radiation that is not emitted towards the workpiece by reflection against the workpiece.

A thermal treatment station according to the invention on a continuous internal coating system for cylindrical bodies, such as for can bodies, has a heat radiator which is longitudinally extended in the direction of travel and is arranged within the interior movement path of the bodies, and the arrangement mentioned above in order to keep the radiator surface clean.

The invention is subsequently explained, for example, using figures.

• Fig. 1 in einer perspektivischen, schematischen Ansicht einer reinzuhaltenden, ausgedehnten Fläche, die erfindungsgemäss vorgesehene grossflächige Gas-Eindüsung bzw. -Absaugung,
• Fig. 2 in einer Darstellung analog zu Fig. 1 mit einer Wärmestrahleroberfläche als reinzuhaltende Fläche, eine erfin­dungsgemässe Düsenanordnung zur Erzeugung der Gasströmung im Umlaufbetrieb,
• Fig. 3 einen perspektivisch dargestellten Aus­schnitt eines erfindungsgemässen Ueber- oder Unterdruckkanals, mit einer feinge­lochten Düsenanordnung, wobei selektiv ein Teil der Lochungen abgedeckt ist,
• Fig. 4 eine schematische Schnittdarstellung durch eine Beschichtungsanlage für die Innenbeschichtung von zylinderförmigen Körpern, wie von Dosenkörpern, mit an­schliessender erfindungsgemässer thermi­scher Behandlungsstation für die Schicht,
• Fig. 5 einen Querschnitt durch eine erfindungs­gemässe thermische Behandlungsstation gemäss Linie V - V von Fig. 4,
• Fig. 6 eine schematische Querschnittdarstellung einer Negativform mit auf bekannte Art und Weise galvanisch abgetragener Me­tallstruktur für die Herstellung einer erfindungsgemässen Düsenanordnung an den Anordnungen gemässen den Fig. 3 bis 5.

Show it:

• 1 is a perspective, schematic view of an extensive surface to be kept clean, the large-area gas injection or extraction provided according to the invention,
• 2 in a representation analogous to FIG. 1 with a heat radiator surface as a surface to be kept clean, a nozzle arrangement according to the invention for generating the gas flow in circulation operation,
• 3 shows a perspective section of an overpressure or vacuum duct according to the invention, with a finely perforated nozzle arrangement, part of the perforations being selectively covered,
• 4 shows a schematic sectional illustration through a coating system for the internal coating of cylindrical bodies, such as can bodies, with a subsequent thermal treatment station for the layer,
• 5 shows a cross section through a thermal treatment station according to the invention along line V-V of FIG. 4,
• 6 shows a schematic cross-sectional representation of a negative mold with a metal structure which has been galvanically removed in a known manner for the production of a nozzle arrangement according to the invention on the arrangements according to FIGS. 3 to 5.

In order to explain the method according to the invention, FIG. 1 shows an extended surface 1, above which floating particles 3 or floating droplets are present and which, due to their own weight G, lower against surface 1. According to the invention is to prevent these floating particles on the Impact area 1 to be kept clean, burn there for example, harden, stick or in some other way form undesirable surface contamination, large-area gas injection or extraction, as shown by the arrows 5, may also be realized, as shown in dashed lines a turbulence lifting the particles 3. Due to the large-area gas flow, a flowing gas layer 7 is formed over the surface 1, which prevents the suspended particles 3 from lowering onto the surface 1. It must be ensured that the gas injection or extraction takes place along the surface 1 in such a way that as little turbulence as possible arises, relative to the expansion of the surface 1, which would drive the particles 3 against the surface 1 in certain areas, which is just to be prevented.

2, the surface 1 ′ to be kept clean is formed by the heat radiating surface of a schematically illustrated heat radiator 9 with a heating coil 11 through which current flows. Such a heat radiator 9 per se causes natural convection K by the gas heated above the radiator 9 rising in a known manner. If floating particles 3 are to be prevented from sinking onto the radiating surface 1 'by realizing a large-area gas flow over this surface 1' according to the invention, it must also be prevented that the efficiency of the radiator 9 is caused by this gas flow is unreasonably reduced, the radiant surface 1 'is cooled too much by the gas flow. As shown schematically in FIG. 2, this is realized in that both sides of the radiating surface 1 'and in its immediate area, each with elongated nozzles 13, acting as slot nozzles, are provided, one of which is used for gas injection, the other for gas extraction, whereby a gas flow over the surface 1 'is realized. To prevent heat from being extracted from the radiation area of the surface 1 ′ by the gas flow of the gas 5, the gas 5 is circulated through a line system 15, with a schematically illustrated pump 17, the line system being thermally well insulated from the environment and / or, as entered schematically at 19, the gas is additionally heated, as with a heating coil, in such a way that the temperature gradient between the radiating surface 1 ′ and the flowing gas layer becomes negligible. Instead of or in addition to the circulating operation, the amount of heat dissipated by the gas flow can be kept to negligible values by keeping the amount of gas flowing over the area 1 ′ per unit time as low as possible. This requires the formation of very narrow nozzles 13, which act as slot nozzles, and the blowing or sucking sides are acted upon with relatively small overpressures or underpressures ± Δp.

Such elongated, very narrow nozzles are relatively expensive to manufacture. A simple possibility of realizing such nozzle structures acting as slot nozzles is shown in FIG. 3. An overpressure or vacuum channel 21 is formed in its longitudinal extent by three walls 23. The fourth longitudinal wall, which forms an actual nozzle wall 25, consists of a structure with a large number of closely spaced small, discrete passages 27. The desired nozzle contour on the nozzle wall 25 is covered by covering unnecessary passages 27 with adhesive tape, lacquer, silicone, rubber or by any other means another material that is suitable for this purpose is realized, generally by covers 29 and only the passages 27 _{a are left} free, which define the desired nozzle contour, as shown in FIG. 3, the desired narrow nozzle slot. Such a nozzle wall section or the structure used for this purpose is preferably, and as shown schematically in FIG. 6, galvanically produced by removing a metal layer 35 on a negative mold 31 with a large number of pins 33 lying close together. This creates an extremely smooth layer 35 with a very fine, dense pattern of the opening formed by the pins 33. However, other manufacturing processes can also be used, such as the use of lasers to produce the passages in a smooth, at most thin, material phase. The nozzle wall section is preferably formed with approximately 10 to approximately 60 passages 27 per running centimeter, the openings of which are dimensioned such that they make up approximately 40% of the nozzle wall surface. The flat metal surface realized in this way structure 35, as will be described below, has great advantages, particularly when used with heat radiators.

A situation that calls for the solution of the above-mentioned problems according to the invention arises in the thermal treatment of the coating of workpieces. Such coatings are often carried out by injecting powder or liquid particles against the workpieces to be coated, this coating is often supported electrostatically and after the workpieces have been provided with the powder or the liquid coating medium, the latter is thermally treated, ie heated. This thermal treatment can in principle be carried out in such a way that thermal radiation sources are provided on the side of the workpieces facing away from the coating, with which the workpieces are heated, which leads to the desired effect with regard to the coating medium just applied. However, with this technology, the heat of the emitters is poorly used by using a large part of the heat to warm up the workpieces: depending on the material, volume or treatment time of the workpieces, the heat emitters provided must be designed for significantly higher outputs than the thermal ones Effect on the coating medium would actually be necessary. However, the above-mentioned emitters are now arranged on the same workpiece side that is also coated and As close as possible to the area in which the coating medium is applied to the workpieces, solid or liquid particles falling back from the workpieces and / or injected medium particles or droplets penetrating into the thermal treatment zone from the coating zone, if they striking the radiating surfaces of the emitters, by hardening, burning, etc. a layer that is sometimes difficult to remove. On the other hand, the arrangement of the heat radiators on the coated workpiece side would allow a drastic reduction in the radiator output. This is now possible using the present invention. The coating technology mentioned is also used for the internal coating of cylindrical bodies, such as can bodies, for can production, in particular for the food industry.

As shown schematically in FIG. 4, in continuous production, can bodies 37 are moved over a cantilever arm by means of transport, not shown here and not essential in the context of the present invention, the cylindrical bodies 37, also not shown in FIG. 4, only by shaping sheets, then welding the longitudinal edges, are created, whereupon the welded, cylindrical bodies 37 are guided along the arm 39 via a coating station 41. As shown schematically in Fig. 4, at the coating station 41 by a feed line device 43 a coating medium in the form of solid particles or droplets, gas-driven, injected and adhered to the inner wall of the body 37, often supported by electrostatic forces, on the inner wall of the body 37. The electrostatic forces are created by applying a high electric field between the mouth area the feed line 43 and the bodies 37 realized. A suction station 46 sucks off the coating medium emerging in the direction F flowing towards the body 37. In particular, the weld seam part of the body 37 is coated in this way. Following the coating station 41, a thermal treatment station 44 designed in accordance with the invention is now provided, which, as shown in FIG. 4, comprises a heat radiator 51, which is elongated in the direction F and arranged on the arm 39 and which now serves as the coating medium in the manner described above -Extremely exposed to pollution. On the other hand, the arrangement of the heat radiator 51 directly in the area of the previously applied coating enables an optimal utilization, ie an optimal efficiency of the heat radiator 51

5 shows a cross-sectional view through the thermal treatment station 44 according to the invention. A groove 45 is incorporated in the protruding arm 39, immediately below the part of the cylindrical one provided with the coating 47 Body 37 with its weld seam 49, the bodies 37 being moved with the transport means, not shown, such as chain drives etc., at a distance with respect to the arm 39 over the latter. A heat radiator, such as an infrared rod radiator 51, is arranged in the channel 45, for example an infrared radiator with a quartz tube, such as manufactured by Heraeus. The groove 45 has a collar 53 projecting against a plane of symmetry E placed through the area of the weld seam 49, on which a nozzle wall 55, preferably of the structure shown and described with reference to FIG. 3, is arranged. The nozzle wall 55 comprises the radiator 51 coaxially. The trough 45 with the nozzle wall 55 thus acts as a channel, analogously to the channel 21 from FIG. 3, which is supplied with pressure, for example, by overpressure + Δp via a line arrangement 57. As shown in FIG. 5, passages 27 _{a which} remain active are left open by means of covers 29 and define, for example, two lateral and a lower longitudinally elongated slot nozzle 59 and 61, respectively. This results in a large-area gas flow 63 around the radiator 51, as indicated by the arrows, and coating medium 3 falling back from the body 37 or penetrating from the coating zone 41 of FIG. 4 into the thermal treatment zone 43 is prevented from falling onto the surface of the radiator 51, which, by baking, results in the thermal yield of the radiator being difficult to remove 51 would lead to impairing pollution layer.

5, a large area of the radiator 51 acts against the arm 39 and would in itself heat the latter and not the coating 47. The efficiency of the emitter 51 is now increased, however, in that the nozzle wall 55 is formed with a smooth, reflective surface directed against the emitter 51, as a result of which the nozzle wall 55 also performs the functions of a reflector in addition to its injection task. Such a reflective, smooth surface is, as already mentioned above, realized by using a galvanically produced nozzle structure 35, as described with reference to FIG. 6, as the nozzle wall 55.

Claims (13)

1. A method for preventing the lowering of suspended particles or droplets (3) on an area (1; 1 '; 55) which is to be kept clean in this regard and is at least one dimension long, characterized in that the area is injected over a large area by gas injection and / or suction (5) generates a gas flow. 2. The method, preferably according to at least one of the claims, as claimed in claim 1, wherein the surface to be kept clean is the radiation surface (1 '; 51) of a heat radiator, characterized in that the gas flow is selected in the order of magnitude of the natural convection caused by the heat radiator or the gas is heated in continuous operation, as by means of the heat radiator (1 ') itself. 3. The method, preferably according to at least one of the claims, as claimed in claim 1 or 2, characterized in that the injection and / or suction is carried out on a plurality of discrete points (27; 27 _a ) arranged in the area of the surface. 4. Arrangement for preventing the lowering of suspended particles or droplets onto a surface which is to be kept clean in this regard and is at least one dimension wide, characterized in that in the region of the surface (1; 1 '; 51) at least one surface or vacuum (± Δp) acted upon channel (21; 45) is provided with an extended nozzle arrangement (27; 27 _a ; 13). 5. Arrangement, preferably according to at least one of the claims, as claimed in claim 4, characterized in that the nozzle arrangement comprises a plurality of discrete passages (27; 27 _a ). 6. Arrangement, preferably according to at least one of the claims, as according to one of claims 4 or 5, characterized in that the nozzle arrangement (25; 55) is a metal structure (35) produced by galvanic application to a negative mold with a plurality of pins (33) ) includes. 7. Arrangement, preferably according to at least one of the claims, as according to one of claims 4 to 6, characterized in that the nozzle arrangement (25; 55) has approximately 10 to approximately 60 discrete passages (27; 27 _a ) per running centimeter. 8. Arrangement, preferably according to at least one of the claims, as claimed in claim 7, characterized in that the sum of the passage cross-sectional areas makes up 30-50% of the nozzle arrangement area. 9. Arrangement, preferably according to at least one of the claims, such as according to one of claims 4 to 8 for preventing the lowering of coating particles or droplets to a longitudinally extended Heat radiator (55) at a thermal treatment station of a coating system for workpiece surfaces (37), characterized in that the nozzle arrangement (55) forms a groove arranged at a radial distance and coaxial with a longitudinal axis of the heater, preferably also as a reflector. 10. Arrangement, preferably according to at least one of the claims, such as according to one of claims 4 to 9, characterized in that passages of the nozzle arrangement (55) are selectively covered (29), such as by adhesive tape or paint or other cover material, for the selective keeping of active orifice patterns (27 _a ) of the nozzle arrangement (55) which are extended in line or area. 11. Application of the method according to at least one of claims 1 to 3 or the arrangement according to at least one of claims 4 to 10 at a thermal treatment station for the internal coating of cylindrical bodies (37), such as can bodies, preferably for the internal coating of their longitudinal weld seam part (49 ). 12. Thermal treatment station on a continuous internal coating system for cylindrical bodies (37), such as for can bodies, characterized in that a heat radiator (51) is provided which is longitudinally extended in the direction of passage and arranged within the interior movement path of the body, and an arrangement according to at least one of the claims 4 to 10 to keep the emitter surface clean. 13. Application of the method, according to at least one of claims 1 to 3, or the arrangement, according to at least one of claims 4 to 10, for keeping a heat-radiating surface clean.

Images