EP0160882A2 - Apparatus for applying a protective layer to can body seams - Google Patents

Abstract

Device for applying a protective layer to the welded or soldered seam of can bodies with an application roller serving to apply a coating compound within an area covering the seam on the inside (15) of the can body, which also coexists in a central area (9) of its middle part (6) an area width below 60% of the width of the central part (6) has at least one depression (10) and its peripheral surface line (5) has at least one kink point and / or at least two turning points in this central area (9). The device makes it possible for the first time to achieve optimal layer thicknesses of the coating over the weld. To achieve solder seams that are neither too low for the stresses that occur during long-term storage of aggressive liquids, nor too large for the tear resistance stress of the coating that occurs when the edges of the can bodies are flanged. Due to the formation of the application roll, there is an optimal profile of the applied coating layer with the greatest layer thickness immediately above the weld or solder seam, as could not be achieved with any of the previously known application rolls.

Description

The invention relates to a device for applying a protective layer to the weld or solder seam of can bodies with an application roller serving to apply a coating mass within an area covering the seam on the inside of the can body, the two lateral, for supporting the can body on the application roller serving supporting edges and a middle part located between the supporting edges and used to carry and apply the coating mass, which extends from the center of the roll to each of the two roll sides to the last kink or turning point of one representing the roll profile of the application roll and from one to the other roll side peripheral Jacket line extends before the point or area start on the jacket line or, in the absence of such a kink or inflection point, extends to the point or area start in which the can body comes to rest on the support edge assigned to the relevant roll side.

Devices of this type are known for example from CH-PS 624,591, DE-PS 31 34 968 and US-PS 4,361,113. However, for a number of different reasons, some of which were relevant for each of these known devices, these and also all other known devices of the type mentioned at the outset were not yet suitable for providing the weld seams of can bodies with an optimal coating of paint in every respect . And often newer devices of this type, which had been created to overcome defects of previously used devices, brought along with the intended removal of the defects in question new disadvantages, which in turn made it impossible to achieve the goal of optimal varnish coatings in every respect. For these reasons, in the course of time experts had increasingly come to believe that under the conditions prevailing in modern can welding machines, such as the running speeds of the can bodies in the order of 1 m / sec and the resulting speed of the application roll of approx. 500 revolutions / minute as well as at these running speeds with still realizable intervals Between the Sohweiss and painting station, for example, cooling times of only about 1 m, resulting in no more than 1 m and correspondingly high temperatures of the weld seam when applying the paint, it is practically no longer possible to apply a paint coating to the weld seams on the inside of the can body, which also under the most unfavorable circumstances, all the requirements that arise during the further processing of the can bodies and the later use of the cans, such as the necessary resistance to tearing when flanging the edges of the can bodies, complete freedom from pores and permanent resistance to highly aggressive and highly corrosive filling goods, the exclusion of any gas inclusions both within the Lacquer as well as between the lacquer coating and the area covered with it on the inside of the can body as well as the required complete wetting of this area and in particular also the indentations on the weld seam at the moment of application of the varnish and finally the necessary firm adhesion of the varnish to the base would have grown in particular also in the edge areas of the varnish coating, which is why in practice in modern can welding machines, the inside of the weld seam is no longer covered with a varnish coating but with a powder coating applied and then melted and melted by the action of heat plastic particles, which is considerably more expensive than the application of a lacquer coating.

The difficulties which have arisen in the various known devices of the type mentioned at the outset can in part be found directly in the above-mentioned literature references, and in part they will be apparent to the person skilled in the art from the information provided in the individual literature references regarding the main ones there described facilities have been made. One of the main difficulties was originally when the rotation of the application roller was effected in the manner customary for painter's rollers by entraining the roller lying on the surface to be painted during the relative movement between roller and surface, a more uneven in the longitudinal direction of the can bodies and especially at the beginning of each Can hulls too little paint application, which resulted from the fact that the application roll had stopped during the periods in which a previous can hull had already passed the application roll and a spaced can body had not yet reached the application roll (see CH-PS 624.591, p.2, r .Sp., Z.15-26). These and other difficulties that occur with the application roller carried along by the can body, such as the need for a high contact pressure of the application roller on the can body and the resulting coating errors (CH-PS 624.591, p.2, rsp., Z.17-20), the incomplete painting the first can body after each standstill of the welding machine and the necessary sorting out of such incompletely painted can bodies (CH-PS 624.591, p.2, r.Sp., Z.23-26) and the danger of the paint drying when the application roller is at a standstill and the resulting uselessness of the quick-drying paints (CH-PS 624.591, p. 2, r.Sp., Z.20-23,32 / 33), which are very desirable per se, could be reduced by a continuous, regardless of the take-up of the application roll by the can body drive of the application roll can be overcome (CH-PS 624.591, p.2, r.Sp., Z.34-36). The expectations at the time, that with the measure of the continuous drive of the application roll, it was already possible to achieve optimal paint coatings on the weld seams of the can bodies (CH-PS 624.591, p.2, r.Sp., Z.27-32) practical conditions prevailing, much tougher conditions than in laboratory operation, however, not. On the contrary, it was even the case that the continuous drive of the application roll already in the laboratory operation additional means in the form of a specially designed scraper device, which partially encompasses the lateral and lateral surfaces of the application roll (CH-PS 624.591, Claim 4 and 5.3.1. Sp. , Z.54, to r.Sp., Z.30) required in order to throw away excess paint from the application roll and, as a result of this, as a result of the continuous rotation of the application roll, spraying out of paint through the spaces between successively spaced can bodies prevent and also to be able to influence the thickness of the paint application on the weld seam (CH-PS 624.591, p.3, l.Sp., Z.61-63, and r.Sp., Z.19-29). The hoped-for influence on the thickness of the paint application and in particular in practice, however, the expected selectability of the profile of the lacquer layer applied to the weld seam by appropriate choice of the shape of the scraper (CH-PS 624.591, p.3, rsp., lines 19-29) was only in connection with properties of the lacquer layer such as defective adhesion of the lacquer to the base in the edge areas of the lacquer layer as a result of incomplete wetting when applying the lacquer (US Pat. No. 4,361,113, column 2, lines 29-32), which reliably fulfills the main purpose of covering the lacquer Welded seam, i.e. a reliable prevention of any direct contact between aggressive fillings and the metal on the welded seam, and were therefore not acceptable, so that the profile of the lacquer layer applied to the welded seam can in fact be selected with those in CH-PS 624.591 described means was not given. Rather, the complete wetting of the surfaces to be painted with paint, which is indispensable because of the necessary firm adhesion of the paint to the base, required the use of a relatively thin-bodied paint, which in turn only required the application of a relatively thin paint layer with a layer thickness due to the surface tension of the order of 2 to 5 microns, which could not be changed by changing the shape of the stripper in its layer thickness and which, in particular, did not meet the requirements for long-term storage of aggressive filling goods with regard to freedom from pores and resistance to such filling goods sufficient mass was sufficient (US-PS 4,361,113, column 2, Z.25-29 and 32-35). A roller was used as the application roller in the device of the type mentioned at the beginning in CH-PS 624,591, the peripheral dumbbell surface of which has a concave curvature in the central part and an essentially curved portion in the lateral support edges for supporting the can body on the application roller of the can body had an adapted convex curvature (CH-PS 624.591, Claim 7 and S.3, r.Sp., Z.31-35). The middle part of the application roll extended from the middle of the roll to each of the two roll sides with a constant concave curvature up to a kink of the surface line representing the roll profile of the application roll, at which the middle part adjoins the convex edge area assigned to the relevant roll side and forming the supporting edge ( CH-PS 624,591, Fig. 5,6,8). This formation of the application roll was partly due to the special design of the stripping device and the above-mentioned shape of the stripper, which can be changed for the selectability of the profile of the lacquer layer applied to the weld seam (CH-PS 624.591, p.3, r.p. , Z.19-29, and Fig. 8), since at the time it was still assumed that the free space between the application roller and the scraper would correspond approximately to the profile of the lacquer layer applied to the weld seam (CH-PS 624.591, p.3 , r.Sp., Z.24-27), which in practice, however, has already proven to be inaccurate due to the required use of low-viscosity lacquer.

The lack of influenceability of the profile of the paint layer applied to the weld seam with the agents described in CH-PS 624.591 due to the required use of low-viscosity paint, and in particular also the insufficient layer thickness of the paint layer over the weld seam for long-term storage of aggressive fillings, which is evident in practice the long-term storage of such aggressive filling goods then led to the proposal evident from DE-PS 31 34 968, which arose when applying the lacquer layer with the means described in CH-PS 624,591 or the corresponding DE-OS 27 28 741 , "to optimally adapt the distribution of the coating mass across the seam to the respective requirements and circumstances (DE-PS 31 34 968, column 1, lines 58-60)", by means of two application rollers arranged one behind the other with such a design that "the application area the one application roll covers the weld or solder seam and two through an annular groove of separate application areas of the other application roller act on the areas on both sides of the weld or solder seam (DE-PS 31 34 968, Claim 1) ", to be overcome. This proposal was based on the consideration that, with the agents described in CH-PS 624.591, a thicker layer of lacquer could also be used to apply a layer of lacquer with a relatively thick layer, which was only due to the lack of adhesion of the lacquer to the base in the edge areas of the Paint layer as a result incomplete wetting of the underlay when applying the lacquer was not acceptable, and that it must therefore be possible to achieve complete wetting and thus firm adhesion of the lacquer to the underlay with two additional application areas that subsequently applied these marginal areas. However, in order to achieve this desired complete wetting, it was necessary to press the lacquer onto the base or to form the two additional application areas with a straight line or slightly convexly curved peripheral surface line, and with this formation of the two additional application areas Then there was the undesirable side effect that the additional application surfaces pressing the paint onto the base simultaneously pressed out the applied paint in a bead-like manner on both sides, thus creating a paint bead on each of the two edges of the overall applied paint layer, which in turn risked the paint layer becoming detached of the base, particularly when storing aggressive filling goods for a long time, since gaps form on the underside of the paint beads, which can be the starting point for a gradual lifting of the paint layer from the base during long-term storage Furthermore, such varnish beads are also undesirable because they can tear when the edges of the can bodies are flanged and such tear points are also the starting points for a gradual detachment of the varnish layer from the base can be in long-term storage. Avoiding the paint beads when applying the paint layer on the weld seam with the device described in DE-PS 31 34 968 was again only possible by using a relatively thin liquid paint, in which the main part of the paint from the first, with relatively high support edges and one Middle part with a straight axially parallel peripheral surface line was applied and the two additional, not provided with supporting edges application areas promoted only relatively little paint and therefore practically no paint pressed out to the sides when pressing the paint on the base, but at least the device was able to DE-PS 31 34 968 uses a somewhat less viscous lacquer and thus also a somewhat larger layer thickness of the lacquer layer above the weld seam of approximately 5 to 8 microns can be achieved, which, however, was still not sufficient for long-term storage of aggressive contents.

In another development described in US Pat. No. 4,361,113, the aim of which was also to achieve greater layer thicknesses of the lacquer layer above the weld seam, this goal was attempted in a purely experimental way by trying out the most varied of application rolls or more precisely by trying out a number of Application rolls with differently designed peripheral lateral surfaces to come closer (US-PS 4,361,113, column 4, Z.11-26). The starting point for this development was again the Application roller already described above in connection with CH-PS 624.591 and shown there in FIGS. 5, 6 and 8, the peripheral lateral surface of which has a concave curvature in the central part and a convex curvature on the two lateral support edges and in which the central part of the application roller extends from the center of the roll after each of the two roll sides to with a constant concave curvature up to a kink point of the peripheral surface line at which the middle part adjoins the support edge having a convex curvature (US Pat. No. 4,361,113, column 4, lines 11-13, and Fig. 2). Starting from this starting point, the experimental development described in US Pat. No. 4,361,113 was first used to investigate whether, by further deepening the central part of this application roll forming the starting point, or by means of a stronger concave curvature in this central part, greater layer thicknesses of the lacquer layer above the weld seam can be achieved ( U.S. Patent 4,361,113, Col. 4, Z.13-19, and Fig. 3A). After this experiment was unsuccessful, an attempt was then made to go the opposite way, i.e. to increase the middle section compared to the job roll forming the starting point, first of all by reducing the concave curvature in this middle section to zero - i.e. to a linear peripheral Surface line in this middle part - and at the same time reduced the width of the support edges to the narrow area of an outer edge (US Pat. No. 4,361,113, Col. 4, Z.21-22, and Fig. 3B), and then by using _j instead an application roll with a concavely curved middle part used those with a convexly curved middle part and also up to an outer edge of reduced width of the supporting edges (US Pat. No. 4,361,113, column 4, lines 22-23, and FIG. 3C), but this opposite path also did not lead to the desired success an acceptable lacquer layer with a greater layer thickness over the weld seam. However, while the two above-mentioned ways of deepening or increasing the middle section along its entire width were from the outset without any prospect of success, the next way followed in this experimental development would be to undulate the peripheral surface line of the application roll (US Pat. No. 4,361,113, Sp .4, Z.23-24, u.Fig.3D) can be accompanied by success with suitable further development, because with this form of the peripheral surface line were two raised supporting edges in the shape of a sinus half-wave and a middle part with three also the shape of one There are depressions with a sinusoidal half wave and two elevations likewise in the form of a sinusoidal half wave, but the uniform waveform of this peripheral surface line, in which the middle region of the middle part formed by the two sinusoidal wave-shaped elevations and the middle sinusoidal wave-shaped depression already 60% of the width of the between the two si took half-wave-shaped supporting edges of the central part of the support roller and furthermore the two supporting edges extended over more than 14% of the total width of the application roller and the central part outside of its central area also two white tere sinusoidal wave-shaped depressions, again precluded success in terms of achieving an acceptable lacquer layer with a greater layer thickness above the weld seam (US Pat. No. 4,361,113, column 4, lines 23-26), and since the causes of success and failure in this of course, just trying out application rolls with differently designed peripheral surface areas could not be recognized (US Pat. No. 4,361,113, column 4, lines 3-7), the failure with the application roll with a wavy peripheral surface line could not give rise to any suggestion for further development along the way in the middle part of the job role convey deepening and elevation peripheral surface line, on the contrary had to distract from such a development. In fact, as part of the further experimental development, the way in which the lacquer densities are applied with layer thicknesses of the order of 200 microns is applied to the weld seam either via various intermediate stages not specified in US Pat. No. 4,361,113 or by chance (US Pat. No. 4,361,113, Col. 4, Z.27-53, and Fig. 4A + B), compared to the application roll shown in FIG. 3D of US Pat. No. 4,361,113, also features exactly the opposite, namely a Elevation in the middle of the middle part, where there is a depression in FIG. 3D, a straight, axially parallel peripheral surface line in the areas of the middle part where the surface line runs sinusoidally in FIG. 3D, and narrow point Support edges, where there are wide sinusoidal half-wave support edges in FIG. 3D. With this shown in Figures 4A and 4B of US-PS 4,361,113 new design of the peripheral surface of the application roller with an acute-angled increase in the middle and at the two lateral ends of the periphery of the application roller (US-PS 4,361,113, column 6, Z .6-9) it was now possible to apply layers of paint with very large layer thicknesses of approx. 180 to 200 microns (US-PS 4,361,113, column 4, line 51 uZ27) to the weld seam, but the intended aim of the application an optimal varnish coating on the weld seams of can bodies was still not achieved. This is because the facts not mentioned in US Pat. No. 4,361,113 that, firstly, layer thicknesses of the lacquer layer of approximately 30 to 60 microns guarantee permanent resistance even to highly aggressive and highly corrosive filling goods and therefore layer thicknesses of 180 to 200 microns are not at all necessary to achieve permanent resistance are necessary and secondly, the wall thicknesses of the can bodies themselves are only between 160 and 220 microns, and with such small wall thicknesses the crack resistance of an approximately equally thick lacquer coating when flanging the edges of the can bodies can no longer be guaranteed with certainty, make it clear that with the in FIGS. 4A and 4B of the application roll shown in US Pat. No. 4,361,113 have apparently not succeeded in layer thicknesses of the lacquer coating over the weld seam in the optimal order of magnitude, So from above. 30 to 60 microns to achieve, but that with this application roller apparently only relatively thick lacquer coatings with a layer thickness of more than 150 microns can be applied.

The invention was therefore based on the object of providing a device of the type mentioned at the outset which is suitable for providing the seams of canned hulls with a varnish coating which is optimal in all respects and which meets all the requirements which arise in the further processing of the can hulls and the later use of the cans such as crack resistance during flaring, resistance to aggressive filling goods, exclusion of gas inclusions in the paint as well as between paint and base and firm adhesion of the paint to the base.

According to the invention, this is achieved in a device of the type mentioned at the outset in that the application roll has at least one recess in a central region of its central part with a region width below 60% of the width of the central part, and the peripheral surface line in this central region has at least one kink point and / or has at least two turning points.

The main advantage of the present device is that with it the optimal layer thicknesses of the lacquer coating over the welding or soldered seam can be obtained without difficulty len, which are neither too low for the stresses that occur during long-term storage of aggressive filling goods, nor too large for the tensile strength stress that occurs when the edges of the can bodies are flanged and, in the case of large layer thicknesses, is above the tear strength of the paint. Another significant advantage of the present device is that the formation of the application roller automatically results in a profile of the applied lacquer layer, which with the greatest layer thickness immediately above the weld or soldered seam and the continuously decreasing layer thickness after the edges of the lacquer coating is too precise meets the requirements that have to be met for an optimal coating due to the existing stresses.

In the case of the present device, the application roll can advantageously be designed such that the central region of the central part thereof has a width of at least 5%, preferably more than 15%, and expediently at most 50% of the width of the central part of the application roll, and that the central part of the Application roll has a width of at least 72%, preferably more than 80%, of the roll width. The best results with regard to the formation of the lacquer coating can be achieved within these design limits.

With regard to the deepening in the middle area of the middle part of the application roll, the following applies direction that the deepest point of the depression expediently from a middle line running between the highest and lowest point of the peripheral surface line parallel to the roll axis, which divides the section of the surface line belonging to the middle part of the application roll into sections located above and below the middle line in such a way that that between the surface line and areas lying on the middle straight line above and below the middle line are of equal size, should have a greater distance than 0.775 times, preferably more than 0.82 times, the distance of the highest point of the peripheral surface line from the middle line. This minimum depth of the recess is necessary, apart from exceptional cases, in order to be able to apply enough coating compound to form a protective layer with a sufficient layer thickness on the welded or soldered seam area on the inside of the can body. The deepest point of the depression should therefore advantageously be at least twice as large, preferably more than four times as large, from the central straight line as the highest point of the peripheral surface line.

It is also of great advantage for the desired formation of the protective layer with the greatest layer thickness above the weld or soldered seam and the layer thickness to be reduced steadily after the edges of the protective layer, if the distance of the peripheral surface line from the inside of the canned body resting on the supporting edges is in Roller axis direction perpendicular direction from the outer ends of the central part to the central region of the central part and preferably continuously up to the same.

In a preferred embodiment of the present device, the application roll has only one recess in the central area of its central part. The application roll can advantageously be designed such that the peripheral surface line in the central region of the central part of the application roll has at least one kink point, preferably located in the middle of the central region, representing an inner edge in the peripheral lateral surface of the application roll, and / or two preferably symmetrically to the center of the middle turning point and / or two at the outer ends of the middle area and preferably also symmetrical to the center thereof, each having an outer edge in the peripheral surface of the applicator roll representing. In a particularly advantageous manner, the peripheral surface line in the central region of the central part of the application roll can have at least one kink point representing an obtuse-angled inner edge in the peripheral surface of the application roll. This preferred embodiment represents the basic form of the present invention which brings with it the general advantages of the invention already mentioned above. Further special advantages can be achieved through the following variants of this basic shape.

In a first advantageous variant of the basic form of the present device, the depression lies between two elevations located within the central region of the central part of the application roll, preferably at least approximately up to the can body. The application roll can expediently be designed such that the peripheral surface line in the central region of the central part of the application roll has at least one kink point, preferably located in the middle of the central region, representing an inner edge in the peripheral lateral surface of the application roll and / or two in the region of the depression and preferably turning points located symmetrically to the center of the middle area and / or at least two in the tip area of the elevations and preferably also located symmetrically to the center of the middle area, each having an outer edge in the peripheral lateral surface of the application roller and / or two outside the area of the depression and preferably also turning points located symmetrically to the center of the central area and / or two outside the area of the depression and preferably at the outer ends of the central area and preferably also symmetrical to the center it has kink points, each of which represents an inner edge in the peripheral lateral surface of the application roll. The peripheral surface line at the deepest point of the depression can be particularly advantageous in that it has an obtuse-angled inner edge in the peripheral surface of the opening have support roller representative kink. The special advantage of this first variant of the basic shape is that it is possible with this variant to apply can coating with different coating diameters to one and the same application roller by applying pressure rollers arranged on the outside of the can body not only to the supporting edges of the application roller but also press on the two projections provided on the same, and the space between the peripheral jacket surface in the middle part of the application roller and the inner wall of the can body remains approximately the same size when the diameter of the manufactured can bodies is changed.

In a second advantageous variant of the basic form of the present device, the application roller has two depressions in the central region of its central part and an elevation located between them, preferably at least approximately up to the can body. The application roll can expediently be designed such that the peripheral surface line in the central area of the central part of the application roll has at least one kink point, preferably located in the middle of the central area, representing an outer edge in the peripheral lateral surface of the application roll and / or two in the area of the elevation and preferably turning points located symmetrically to the center of the central region and / or at least two in the region of the base of the depressions and preferably also located symmetrically to the center of the central area, each representing an inner edge in the peripheral lateral surface of the application roll and / or two outside of the area of the elevation and preferably also located symmetrically to the center of the central area and / or two outside of the area of the Raised and preferably at the outer ends of the central region and preferably also symmetrical to the center of the same, each having an outer edge in the peripheral surface of the application roller has kink points. With particular advantage, the peripheral surface line can each have an inflection point representing an acute-angled inner edge in the peripheral edge surface of the application roller at the deepest points of the depressions. The special advantages of this second variant of the basic shape are that, with this second variant, layer thicknesses of the protective layer over the weld or solder seam can be realized within a range whose upper range limit is clearly above the corresponding upper range limit of the basic shape and its lower range limit is still within of the layer thickness range that can be realized with the basic shape and thus significantly lower than the lower range limit of the layer thickness range that can be achieved with the known protective layer applying protective layers with a thickness of approx. 200 microns, and that in addition with this second variant the same already exists above mentioned advantages as can be achieved with the first variant of the basic shape explained above.

In the present device, the application roll can advantageously also be designed such that the peripheral surface line has an at least approximately circular convex course with a preferably larger radius of curvature, at least in the major part of its sections lying between the central region of the central part of the application roll and the outer ends of the central part than half the inside diameter of the can body. The radius of curvature of the circular course should expediently be between 1.25 times and 5 times half the inner diameter of the can body. The advantage of such a design of the application roll is that the above-mentioned advantageous steady increase in the distance of the peripheral surface line from the inside of the can body resting on the supporting edges from the outer ends of the middle part towards the middle region of the middle part closes in for the application the coating composition of optimal shape is realized.

The lateral support edges serving to support the can body on the application roll are expediently increased in relation to the outer ends of the central part of the application roll and preferably border with an obtuse-angled outer edge to the assigned roll side and over each an acute-angled outer edge to the middle part of the application roll. The raised support edges have the advantage that they bring about a relatively sharp delimitation of the outer edges of the protective shrouds or essentially exclude edge smearing. They are mainly provided when the distance of the peripheral surface line from the inside of the can body resting on the supporting edges from the outer ends of the central part of the applicator roll increases relatively weakly towards the central region of the central part. In the case of a relatively large increase in this distance, on the other hand, to achieve a steady decrease in the layer thickness of the protective layer from the center to the edges of the protective layer, it is too often more advantageous if the supporting edges are located lower than the outer ends of the central part of the application roller and preferably with an obtuse angle Adjacent the outer edge to the assigned roll side and with an obtuse-angled outer edge to the middle part of the application roll. In both cases, in order to achieve a good support for the can body and to avoid rapid wear of the supporting edges, it is advantageous if the peripheral surface line in the regions of the supporting edges which serve to support the can body has a convex curvature with a preferably at least approximately half Has inside radius of the can body corresponding radius of curvature.

The present device can be particularly advantageous be further developed in such a way that to influence the layer thickness of the protective layer which forms after the application of the coating composition under the influence of the surface tension of the coating composition, means for cooling the welded or soldered seam area of the can bodies before the application of the coating composition and thus influencing the heating of the applied composition Coating mass through the heated welding or soldered seam area of the can body and thus to influence the surface tension of the applied coating mass are provided, preferably in the form of means for producing a cooling air flow directed from the outside towards the welding or soldering area of the can body. This has the advantage that the layer thickness of the protective layer can be adapted to the requirements placed on the protective layer within a specific layer thickness range which is essentially predetermined by the formation of the peripheral lateral surface of the application roller.

• Fig. 1 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und kreislinienförmigen Verlauf im Mittelteil der Auftragsrolle und einer im Querschnitt dreieckigen Vertiefung im mittleren Bereich des Mittelteiles
• Fig. 2 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und einem Verlauf im Mittelteil der Auftragsrolle mit nach der Mitte zu stetig zunehmender Krümmung und einem den tiefsten Punkt einer Vertiefung bildenden Knickpunkt im mittleren Bereich des Mittelteiles
• Fig. 3 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und kreislinienförmigem Verlauf im Mittelteil der Auftragsrolle und einer im Querschnitt trapezförmigen Vertiefung im mittleren Bereich des Mittel- teiles
• Fig. 4 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und kreislinienförmigem Verlauf im Mittelteil der Auftragsrolle und einer im Querschnitt kalottenförmigen Vertiefung im mittleren Bereich des Mittelteiles
• Fig. 5 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und kreislinienförmigem Verlauf im Mittelteil der Auftragsrolle und einer zwischen zwei Erhöhungen liegenden, im Querschnitt dreieckigen Vertiefung im mittleren Bereich des Mittelteiles
• Fig. 6 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit flachen Stützrändern und einem Verlauf im Mittelteil der Auftragsrolle mit nach der Mitte zu stetig zunehmender Krümmung und einem den tiefsten Punkt einer Vertiefung bildenden Knickpunkt im mittleren Bereich des Mittelteiles
• Fig. 7 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit erhöhten Stützrändern und kreislinienförmigem Verlauf im Mittelteil der Auftragsrolle und zwei im Querschnitt dreieckigen Vertiefungen sowie einer zwischen denselben gelegenen, im Querschnitt trapezförmigen Erhöhung im mittleren Bereich des Mittelteiles
• Fig. 8 die periphere Mantellinie einer Auftragsrolle der vorliegenden Einrichtung mit flachen Stützrändern und einem Verlauf im Mittelteil der Auftragsrolle mit nach dem mittleren Bereich zu stetig zunehmender Krümmung und zwei eine kalottenförmige Vertiefung begrenzenden Wendepunkten an den äusseren Enden des mittleren Bereiches des Mittelteiles
• Fig. 9 ein Beispiel einer mit der vorliegenden Einrichtung auf die Schweissnaht eines Dosenrumpfes aufgetragenen Lackschicht im Querschnitt Fig. 10 und 11 schematische Darstellungen der Vorgänge beim Auftragen des Lackes von der Auftragsrolle auf die Innenseite des Dosenrumpfes und der sich dabei bildenden sogenannten "Lackfahnen" zur Erläuterung der Wirkungsweise der Erfindung.

The invention is explained in more detail below with reference to the figures below, both in terms of its general mode of operation and in some exemplary embodiments. Show it

• Fig. 1 shows the peripheral surface line of an application roll of the present device with raised support edges and circular course on average part of the application roll and a triangular cross-section recess in the central area of the middle part
• Fig. 2 shows the peripheral surface line of an application roll of the present device with raised support edges and a course in the central part of the application roll with a continuously increasing curvature towards the center and a kink point forming the deepest point of a depression in the central region of the central part
• 3 shows the peripheral surface line of an application roll of the present device with raised support edges and a circular shape in the middle part of the application roll and a trapezoidal cross-section in the middle area of the middle part
• Fig. 4 shows the peripheral surface line of an application roll of the present device with raised support edges and circular shape in the middle part of the application roll and a dome-shaped recess in cross section in the central region of the middle part
• Fig. 5 shows the peripheral surface line of an application roll of the present device with raised support edges and circular shape in the middle part of the application roll and one between two elevations lying, triangular cross-section depression in the central region of the central part
• 6 shows the peripheral surface line of an application roll of the present device with flat supporting edges and a course in the middle part of the application roll with a continuously increasing curvature towards the center and a kink point forming the deepest point of a depression in the middle region of the middle part
• Fig. 7 shows the peripheral surface line of an application roll of the present device with raised support edges and circular shape in the middle part of the application roll and two triangular recesses and a trapezoidal cross-section between the same in the central region of the middle part
• 8 shows the peripheral surface line of an application roll of the present device with flat supporting edges and a course in the middle part of the application roll with a continuously increasing curvature towards the central region and two turning points delimiting a dome-shaped depression at the outer ends of the central region of the central part
• 9 shows an example of a cross-section of a lacquer layer applied with the present device to the weld seam of a can body 10 and 11 are schematic representations of the processes during the application of the paint from the application roller to the inside of the can body and the so-called "paint flags" which form in order to explain the mode of operation of the invention.

In the course of the investigations which led to the present invention, it was found that between the weld seam area to which lacquer is applied on the inside of the can body 1 and the parts of the application roller 2 moving away from the can body, as shown schematically in FIGS. 10 and 11 shown, forms a so-called "lacquer flag" 3 or 4, the shape, size and stability of which primarily determine the properties of the lacquer layer that forms, so to speak, the end of the lacquer flag that runs out on the inside of the can body and covers the weld seam area. It was also found that the actual paint application takes place for the most part via this paint flag, or more precisely that the main part of the total amount of paint transferred from the application roller 2 to the inside of the can body 1 is not as previously assumed, for example at the time of contact between the application roller and Inside the can body but rather only afterwards is applied to the inside of the can body using this paint flag. From a physical point of view, the application process takes place in such a way that the inside of the can body is roughly at the point of contact between the application roller and the inside of the can body te is wetted with lacquer and this initially still thin wetting layer adhering firmly to the metal surfaces on the inside of the can body then pulls the lacquer carried by the application roller off the application roller via the lacquer flag. The front of the paint flag has - as indicated by the examples of paint flags 3 and 4 in Figures 10 and 11 - essentially the shape of a hyperbola, the asymptotes of which with a straight line parallel to the axis of the can body on the inside of the can body and a tangent to the application roll at the exit point of the The center of the paint flag on the applicator roller coincide and whose eccentricity, which is a measure of the paint flag length, is determined in the stable state of the paint flag by the surface tension and the toughness of the paint, and by the surface curvatures of the paint flag, especially at the apex of the hyperbola. From the said wetting layer adhering to the inside of the can body, the part of the varnish which is located within the varnish flag between the inside of the can body and the hyperload facing it and a connecting surface between the apex of the hyperbola and a straight line connecting the points of contact between the applicator roller and the inside of the can body is now removed the applicator roll is peeled off on the inside of the can body, while the remaining part of the varnish, which is within the varnish flag between the applicator roll and the hyperload facing it, and the said connection surface between the apex of the hyperbola and the contact points of the application roll and the straight line connecting the inside of the can body, is taken back by the application roll. It follows from this that the amount of the paint applied to the inside of the can body is essentially proportional to the volume of the paint flag and the geometric location of the largest coat of paint is the branch facing the inside of the can body of the hyperbole forming the front of the painted tab, or more precisely the outlet of this hyperload on the inside of the can body . In order to achieve a certain profile of the lacquer coating over the area of the weld seam, it is therefore necessary firstly to keep the volume of the lacquer flag within a certain volume range and secondly to ensure that it is not possible for several parallel lacquer flags to form, but only a single lacquer flag, and that it does always forms the new paint flag in the same place for each can body, for example always in the middle of the application roll if the weld seam is above the center of the application roll. All three of the aforementioned requirements are about solving stability problems that have not even been formulated, let alone solved, so far. In order to be able to keep the volume of a paint flag within a certain volume range, the size of the paint flag must be kept essentially constant, and this can only be achieved if the paint flag, when it is created, also achieves a shape with which this size is reached a stable state in the sense of a mutual all forces acting on the paint flag. The forces acting on a paint color are now essentially the forces caused by the movement of the can body and the rotation of the application roller and transferred to the paint flag by the toughness of the paint, in the sense of an extension of the paint flag and by the surface tension of the paint and the Forces caused by curvature of the surface of the paint flag, of which the forces caused by the convex curvature of the hyperbolic front of the paint flag act in the sense of an extension of the paint flag and the forces caused by the concave curvature of the paint flag cross section act in the sense of shortening the paint flag. So that a stable state occurs at a certain volume or a certain size of the paint flag, the concave curvature of the paint flag cross section at the apex of said hyperbola must be so large that the forces caused thereby, in the sense of shortening the paint flag, act in the sense an extension of the paint flag acting forces, i.e. the forces caused by the movement of the can body and application roller and transferred to the paint flag by the viscosity of the paint and the forces caused by the convex curvature of the hyperbolic front of the paint flag, i.e. the paint flag must be with them Forms simultaneously with the achievement of the specified size, a shape with the size required for the balance of forces reach the concave curvature of the lacquer flag cross-section at the apex of the hyperbola forming the lacquer flag front, so that a stable state is established, and since the shape of the lacquer flag and in particular the width of the flag front determining the size of the concave curvature of the lacquer flag cross-section in the flag front vertex essentially depends on the formation of the peripheral lateral surface of the Depending on the application roll, the volume of a paint flag can only be kept within a certain volume range when using an application roll with a suitably designed peripheral jacket surface and accordingly only achieve a certain desired profile of the coating over the weld seam area with a suitable application roll.

With the previously known application rolls, it was mainly not possible to keep the volume of a lacquer plume within a certain volume range corresponding to the lacquer volume of desirable profiles of the lacquer coating over the area of the weld seam, because the lacquer plugs that formed in the known application rolls were too wide and therefore also had a too wide flag front, so that there was too little curvature of the lacquer flag cross-section at the apex of the hyperbola forming the flag front, which in turn had the consequence that the concave curvature caused by this too little contributed to a shortening of the lacquer flag the for the desirable profiles of the Coatings of paint above the area of the weld seam required for the coat of paint to be too small to cancel out the forces acting in the sense of an extension of the coat of paint.

With the previously known application rolls, this resulted either in an increase in the paint flag up to a length at which the tension increasing with the length of the paint flag acting in the sense of a pulling apart of the paint flag, that caused by the rotating application roller and by the viscosity of the paint the force transferred to the paint flag is generated on the surface of the paint flag, is greater than the surface tension of the paint holding the paint flag surface together, and the paint flag is therefore torn open and then torn to about the point of contact between the application roller and the inside of the can body and then rebuilt again and until the next tear grows and thus oscillates in size similar to a tilting oscillation (as is the case, for example, with the application rolls shown in FIGS. 5, 6 and 8 of CH-PS 624,591 and the application rolls shown in FIGS. 2 and 3A to 3J of US Pat. No. 4,361,113 when using viscous paints was the case) , or there was an increase in the paint flag up to a length at which the aforementioned tension, acting in the sense of a pulling apart of the paint flag, was just a little below the surface tension of the paint holding the paint flag surface together and therefore the working conditions to avoid tearing off Lead paint flag the further increase in this tension beyond the surface tension of the paint had to be observed very precisely and the large paint flag length or the correspondingly large volume of the paint flag associated with this high tension led to a very strong coating of paint on the weld seam area on the inside of the can body (as was the case with the the application roll shown in FIGS. 4A and 4B of US Pat. No. 4,361,113 when using the viscous lacquer specified in this US Pat. and compliance with the other working conditions that can be inferred from this US Pat.

In both cases, i.e. both with an oscillating lacquer plume and with the lacquer plume with a length that is only slightly below the stability limit, the tests which were carried out in connection with the present invention for control purposes also resulted, which were already explained at the beginning with reference to the relevant literature references Defects of the lacquer coatings over the weld seam, i.e. with application rolls as in FIGS. 5, 6 and 8 of CH-PS 624.591 and in FIGS. 2 and 3A to 3D of US Pat. No. 4,361,113 when using viscous lacquers as a result of the oscillating lacquer flag, incomplete wetting in the edge areas of the lacquer layer, which is caused by the fact that at the moment the lacquer flag is torn, a relatively large amount of lacquer similar to a large lacquer drop and then during the formation of the new lacquer flag due to the beginning still ge wrestle volume, only a small amount of lacquer is applied, and with an application roller as in FIGS. 4A and 4B of US Pat. No. 4,361,113, when using the viscous lacquer specified there, a very large layer thickness of the lacquer coating due to the large lacquer flag length and the correspondingly large volume of the lacquer flag and consequently insufficient crack resistance when flanging the edges of the can body.

Also as part of these tests, a control test was carried out to clarify whether the deficiencies mentioned were caused by the use of less viscous paints and a corresponding reduction in those caused by the movement of the can body and the rotation of the application roller and transferred to the paint flag by the toughness of the paint Letting go of forces did not lead to the achievement of stable instead of oscillating paint flags or to the achievement of more stable conditions with paint flag lengths that were significantly below the stability limit, but rather to the emergence of a new stability problem, in that most of the known application rolls now had not just one but several parallel ones , in the transverse direction formed lacquer flags connected to one another up to part of their total length, the flag lengths of which were generally not stable and of the same size but instead varied depending on the cross connections of the lacquer flags edges and therefore to an extremely un even paint application on the inside of the can body. The newly emerging stability problem is confusing insofar as the occurrence of several interconnected paint flags under the same working conditions can theoretically result in an infinite number of different stable states, while in the case of only one paint flag under the given working conditions there is theoretically only one only stable condition exists, and for this reason alone and because of the practically resulting unevenness of the paint application on the inside of the can body when several parallel paint flags appear, which was also found in the control test, another condition for the achievement of a certain profile of the paint coating over the weld seam area had to be prevented an appearance of several parallel paint flags.

In particular, in the control experiment, in particular when using application rolls provided with pronounced elevations in the peripheral lateral surface, a strong tendency to form several parallel paint plumes was found. Such a tendency was particularly noticeable in the application roll shown in FIG. 3D of US Pat. No. 4,361,113 with a wavy peripheral jacket surface, when using it up to four parallel paint flags, ie one paint flag per elevation of their four half-wave elevations peripheral lateral surface, could also be observed, but also the application rolls shown in FIGS. 3A and 2 of this US-PS and in particular also the application roll forming the subject of this US-PS, shown in FIGS. 4A and 4B, showed such a tendency. This tendency to form up to three parallel paint plumes in the application roller according to FIGS. 4A and 4B of US Pat. No. 4,361,113 in the case of the use of less viscous varnishes should also have been the reason why, with this application roller, uniform varnish coatings only with viscous varnish and the resultant very large layer thicknesses of the lacquer coatings resulting from this application roll, while smaller layer thicknesses lying within the optimal range for lacquer coatings above the weld seam due to the tendency to form several parallel lacquer plugs in this application roller when using less viscous lacquers and the resulting non-uniformity of the paint application on the inside of the can body could not be achieved. Likewise, the pronounced tendency towards the formation of several paint flags observed in the application roll according to FIG. 3D of US Pat. No. 4,361,113 may also be the reason for the unsuitability of this application roll for achieving uniform paint coatings over the area of the weld seam.

From the results of the aforementioned control test was to be concluded that the cause of the formation of several parallel paint plumes are the centrifugal forces acting on the paint carried by the application roll, that in the case of not too viscous paints within the paint carried by the application roll, a paint flow in the direction of the parts furthest away from the roll axis of the peripheral surface and which therefore lead to the fact that the paint carried by the application roller moves due to the rotation of the application roller after the increases or more precisely to the higher parts of the peripheral surface line of the application roller and from the highest places it then peels off in the form of lacquer flags after the lacquer collected above it at the highest points to form a kind of lacquer mountains has come into contact with the inside of the can body and has thus triggered the detachment of these lacquer flags.

This knowledge of the cause of the formation of several parallel paint flags can now be used to meet the above-mentioned condition to be observed in order to achieve desirable profiles and, in particular, suitable layer thicknesses of the paint coating over the weld seam area, to keep the paint flag volume within a certain volume range and for this purpose the paint flag width and thus also the width of the flag front and the resulting, the paint flags length and thus the concave curvature of the paint flag cross-section at the apex of the hyperbole forming the paint flag front, which determines the volume of the paint flag: if the peripheral lateral surface of the application roll is designed in such a way that the peripheral surface line of the application roll or more precisely the distance from the roll axis in the middle part the application roll rises to a central area of the central part and are located in this central area or at the limits of the same maxima of the peripheral surface line, then this formation leads to the fact that the paint carried by the application roll due to the rotation of the application roll at these maxima peripheral coat line accumulates and after the contact of this paint accumulated on the maxima of the peripheral coat line with the inside of the can body, these paint maxima detach from these maxima, which, however, with a sufficiently small distance between these maxima from one another or with a sufficiently small Narrow width of the middle region mentioned merge into a single, relatively narrow lacquer flag, that is to say, one can, as it were, by producing a plurality of parallel, closely spaced and therefore fusing lacquer flags to obtain the desired only relatively narrow lacquer flag, the flag volume of which corresponds to the desired profile and desired layer thickness of the lacquer coatings over the weld seam area and which also always due to the fixation of their position by the above maxima of the peripheral surface line The same place arises and is therefore formed immediately above the weld seam on the inside of the can body for each can body that passes through the painting device.

The following is essential for the formation of an application roll which is suitable for applying a protective layer to the weld or solder seam of can bodies and which provides optimal coatings within an area covering the seam on the inside of the can bodies:

The peripheral surface line of the application roll or its distance from the roll axis should have at least two relatively close to each other and expediently approximately equal maxima in the middle part of the application roll. In a central area of the middle part of the application roll, at the outer limits of which or within these maxima, there must be at least one depression of the peripheral surface of the application roll or at least a minimum of the distance of the peripheral surface line of the application roll from the roll axis. In addition, the two maxima closest to the outer limits of the central region of the middle part of the application roll or coinciding therewith in the direction of the outer ends of the middle part of the application roll must also be part of the peripheral lateral surface of the application roll Connect the ren ends of the middle part to the decreasing distance of the peripheral surface line of the application roll from the roll axle.

Within the two areas of the middle part of the application roll, which range from the outer ends of the middle part to the nearest, located within the middle area of the middle part of the application roll or at its outer limit, the distance of the peripheral surface line of the application roll from the The roller axis is expediently to be smaller than at the associated maximum and larger than or at least as large as at the assigned outer end of the middle part of the application roll and preferably to increase continuously from each of the two outer ends of the middle part after the assigned nearest maximum. This training promotes the desired movement of the paint in the direction of the two maxima.

In the areas of the supporting edges adjoining the middle part of the application roll, the peripheral surface line of the application roll should expediently have smaller distances from the roll axis than at the two maxima closest to the outer limits of the middle area of the application roll or coinciding therewith. In addition, the points in the support edge areas with the greatest distance from the roller axis should suitably only a little have a larger and advantageously at least almost the same distance from the roller axis as the outer ends of the central part of the application roller. This configuration can prevent paint flags from forming on the supporting edges.

With regard to the above-mentioned deepening in the middle area of the middle part of the application roll, it should be noted that the maxima mentioned in the middle area or at the outer limits thereof should be sufficiently pronounced to enable or promote the formation of the desired paint flags at these points What a certain minimum depth or a certain minimum volume of the depression requires, but that on the other hand the lacquer volume within the depression and thus also the volume or depth of the depression must not be too large, so that the resulting paint colors do not come from the inside the volume of paint flowing in from the recess is pushed apart but rather pushed together by the volume of paint flowing in from the outside, so that they merge in the desired manner into a single paint flag.

• Die peripheren Mantellinien 5 der Auftragsrollen in den Figuren 1 bis 8 weisen im Mittelteil 6 der Auftragsrolle zwei nahe beieinander liegende gleichhohe Maxima 7 und 8 auf, die an den äusseren Grenzen des mittleren Bereiches 9 des Mittelteiles 6 der Auftragsrolle (Fig.1-4 u.6-8) oder innerhalb des mittleren Bereiches 9 (Fig.5) liegen und zwischen denen eine Vertiefung 10 (Fig.1-6 u.8) oder zwei Vertiefungen 10' und 10" mit einer zwischen denselben gelegenen Erhöhung 11 (Fig.7) liegen. Innerhalb der beiden Bereiche 12 und 13 des Mittelteiles 6 der Auftragsrolle, die von den äusseren Enden des Mittelteiles 6 bis zum mittleren Bereich 9 des Mittelteiles 6 reichen, steigt der Abstand der peripheren Mantellinie 5 der Auftragsrolle von jedem der beiden äusseren Enden des Mittelteiles 6 nach den zugeordneten nächstgelegenen Maxima 7 bzw. 8 zu fortlaufend an. In den Bereichen der Stützränder 14 hat die periphere Mantellinie 5 der Auftragsrolle geringere Abstände von der Rollenachse als an den beiden Maxima 7 und 8. Auf den Stützrändern 14 liegt die in den Figuren 1 bis 8 gestrichelt angedeutete Dosenrumpfinnenwand 15 auf. Die Stützränder 14 sind mit einer an die Dosenrumpfinnenwand 15 angepassten Krümmung konvex gekrümmt. Die Stellen der Stützränder 14 mit dem grössten Abstand von der Rollenachse haben bei den in den Figuren 1 bis 5 und 7 dargestellten Auftragsrollen einen um ca. 0,1 mm grösseren Abstand von der Rollenachse als die äusseren Enden des Mittelteiles 6 der Auftragsrolle und bei den in den Figuren 6 und 8 dargestellten

The application rolls shown as exemplary embodiments in FIGS. 1 to 8 with their peripheral surface lines fulfill all the conditions specified above as essential for an optimal coating of paint over the area of the weld seam, enabling the formation of such application rolls:

• The peripheral surface lines 5 of the application rolls in FIGS. 1 to 8 have two equally high maxima 7 and 8 in the middle part 6 of the application roll, which are located at the outer limits of the central region 9 of the middle part 6 of the application roll (FIGS. 1-4 and .6-8) or within the central area 9 (Fig.5) and between which a depression 10 (Fig.1-6 and 8) or two depressions 10 'and 10 "with an elevation 11 located between them (Fig .7) Within the two areas 12 and 13 of the middle part 6 of the application roll, which extend from the outer ends of the middle part 6 to the middle area 9 of the middle part 6, the distance of the peripheral surface line 5 of the application roll from each of the two outer ones increases Ends of the middle part 6 too continuously according to the assigned nearest maxima 7 or 8. In the areas of the support edges 14, the peripheral surface line 5 of the application roll has smaller distances from the roll axis than at de n two maxima 7 and 8. The inner side of the can body 15, indicated by dashed lines in FIGS. 1 to 8, lies on the supporting edges 14. The support edges 14 are convexly curved with a curvature adapted to the inner wall 15 of the can body. The locations of the support edges 14 with the greatest distance from the roller axis are at a distance of approximately 0.1 mm from the roller axis in the application rollers shown in FIGS. 1 to 5 and 7 than the outer ends of the middle part 6 of the application roller and at shown in Figures 6 and 8

Application rollers the same distance from the roller axis as these outer ends of the middle part 6. The depth of the depressions 10 or 10 'and 10 "compared to the maxima 7 and 8 is approximately in the application rollers with relatively wide depressions in Figures 1, 3 and 4 0.2 mm, in the case of application rolls with somewhat narrower depressions in FIGS. 2, 6 and 8, approximately 0.4 mm and in the case of application rolls which are provided with elevations in the central region 9 of the middle part 6 that reach up to the inside of the can body, The distance between the maxima 7 and 8 from the inside of the can body is approximately 0.3 mm for all application rolls shown in FIGS. 1 to 4 and 6 to 8.

With the application rollers shown in FIGS. 1 to 4 and 6 to 8 with their peripheral surface lines, lacquer coatings could be applied over the weld seam area with a layer thickness over the weld seam of up to approximately 60 microns. Even larger layer thicknesses of up to 80 or 100 microns can be achieved with the application rollers in FIGS. 5 and 7, but there is generally no great need for layer thicknesses above 60 microns. In all of the application rolls shown, there are varnish coatings over the weld seam area of a width corresponding approximately to the width of the application rolls of approx. 10 mm with the greatest layer thickness in the middle of the coating and thus directly above the weld seam and after the edges of the coating, the layer to be reduced thickness. The distribution of the layer thickness in the transverse direction of the coating can still be influenced to a certain extent by more or less strong cooling of the can bodies on their way from the welding station to the painting device by means of a cooling air flow directed from outside to the weld seam of the can bodies, since the applied paint is from the not yet cooled weld seam is heated and the surface tension of the varnish decreases with increasing warming, so that strong cooling of the can bodies can achieve a high surface tension of the applied varnish, which tries to pull the varnish surface smooth and thereby to some extent to compensate for the Layer thicknesses in the immediate vicinity of the weld seam ensures.

An example of a lacquer coating that was applied with the application roller shown in FIG. 1 is shown in cross section in FIG. 9. The lacquer coating was applied to the weld seam on the inside of a can body made of 0.2 mm thick sheet metal. The application roll used had a width of 10 mm and a peripheral surface line as in FIG. 1 with 0.5 mm wide support edges 14, an increase of the support edges 14 over the outer ends of the middle part 6 of 0.1 mm, a circular course of the peripheral Surface line 5 in the areas 12 and 13 with convex curvature and a radius of curvature of 120 mm, a depth of the ver Indentation 10 compared to the maxima 7 and 8 of 0.2 mm, a distance of the deepest point of the indentation 10 from the inside of the can body of approximately 0.5 mm and an angle of 160 ° between the two surfaces delimiting the indentation 10. A lacquer with a white color known commercially under the name "Grace Pillnay A 4699-S-77" was used as the lacquer. The result was the following layer thickness distribution in FIG. 9 in the transverse direction of the coating (from left to right in FIG. 9): a layer thickness of 14 microns at a distance of 2 mm from the center of the weld seam, and a layer thickness of at a distance of 1 mm from the center of the weld seam 20 microns, a layer thickness of 50 microns at a distance of 0.5 mm from the center of the weld seam, a layer thickness of 40 microns above the center of the weld, a layer thickness of 20 microns at a distance of 0.5 mm from the center of the weld and a distance of 1.5 mm from the center of the weld seam a layer thickness of 10 microns.

Finally, it should also be pointed out that the present device for applying a protective layer to the welded or soldered seam of can bodies, apart from the application roll, can be constructed in the same way as is described, for example, in OH-PS 624,591 or US Pat. No. 4,361,113 , ie an application roll according to the present invention can be easily used in such a known device and leads in connection with such a known device to the success achieved with the present invention. It is unnecessary is therefore a further detailed explanation of the structure and operation of these known devices in connection with the present invention. It would be noted only that it is of advantage, the up _t ragsrollen according to the present invention corresponding to the given already in the CH-PS 624 591 excitation (p.3, r.Sp., Z.49-51) with a next to the application roller arranged Kotor, expediently to drive an electric motor. Furthermore, the stripping device provided for stripping the paint should be expediently designed such that, in the application rollers according to the present invention, the paint is completely stripped from the support edges 14 (which can be achieved by a scraper lying almost on the support edges 14), so that each Possibility of forming paint flags on the support edges 14 to be excluded.

Claims (23)

1.Device for applying a protective layer to the welded or soldered seam of can bodies with an application roller serving to apply a coating composition within an area covering the seam on the inside of the can body, the two lateral support edges serving to support the can body on the application roller and one between the supporting edges, which serves to carry and apply the coating composition, which extends from the center of the roll after each of the two roll sides to the last break or turning point of a peripheral coat line that represents the roll profile of the application roll and runs from one to the other roll side in front of the The point or area begins on the surface line or, in the absence of such a kink or inflection point, extends to the point or area in which the can body comes to rest on the support edge assigned to the relevant roll side, characterized that the application roll has at least one recess in a central region of its central part with a region width that is less than 60% of the width of the central part, and that the peripheral surface line has at least one kink point and / or at least two turning points in this central region. 2. Device according to claim 1, characterized in that the central region of the central part of the application roll has a width of at least 5%, preferably more than 15%, and two-dimensionally at most 50% of the width of the central part of the application roll. 3. Device according to claim 1 or 2, characterized in that the central part of the application roll has a width of at least 72%, preferably of over 80%, of the roll width. 4. Device according to one of claims 1 to 3, characterized in that the deepest point of the recess from a between the highest and lowest point of the peripheral surface line parallel to the roller axis center line that the part of the application roll belonging to the section of the surface line so in above and Sub-sections located below the middle line divides that the areas lying between the surface line and the middle line are equal in size above and below the middle line, a greater distance than 0.775 times, preferably than 0.82 times, the distance from the highest point of the peripheral surface line from that has straight lines. 5. Device according to claim 4, characterized in that the deepest point of the depression of the middle straight line is preferably at least twice as large is more than four times the distance from the highest point of the peripheral surface line. 6. Device according to one of claims 1 to 5, characterized in that the distance of the peripheral surface line from the inside of the can body resting on the supporting edges in the direction perpendicular to the roll axis direction from the outer ends of the central part to the central region of the central part and preferably up to the same rises continuously. 7. Device according to one of claims 1 to 6, characterized in that the application roller has only one recess in the central region of its central part. 8. Device according to claim 7, characterized in that the peripheral surface line in the central region of the central part of the application roll has at least one preferably in the middle of the central region, an inner edge in the peripheral lateral surface of the application roll and / or two preferably symmetrical to the center of the middle area and / or two kink points located at the outer ends of the middle area and preferably likewise symmetrically to the center thereof, each representing an outer edge in the peripheral surface of the application roll. 9. Device according to claim 7 or 8, characterized in that the peripheral surface line in the central region of the central part of the application roll has at least one blunt point representing an obtuse-angled inner edge in the peripheral surface of the application roll. 10. Device according to one of claims 1 to 6, characterized in that the recess lies between two elevations located within the central region of the central part of the application roller, preferably at least approximately up to the can body. 11. The device according to claim 10, characterized in that the peripheral surface line in the central region of the central part of the application roll at least one preferably located in the middle of the central region, an inner edge in the peripheral lateral surface of the application roll and / or two in the region of the recess and preferably inflection points located symmetrically to the center of the central region and / or at least two in the tip region of the elevations and preferably likewise symmetrically to the center of the central region, each having an outer edge in the peripheral lateral surface of the application roller and / or two outside the region of the depression and preferably also point of inflection and / or symmetrical to the center of the central area has two kink points located outside the region of the depression and preferably at the outer ends of the central region and preferably likewise symmetrically to the center thereof, each representing an inner edge in the peripheral lateral surface of the application roller. 12. The device according to claim 10 or 11, characterized in that the peripheral surface line at the deepest point of the recess has a blunt point representing an obtuse-angled inner edge in the peripheral surface of the application roller. 13. Device according to one of claims 1 to 6, characterized in that the application roller in the central region of its central part has two depressions and an elevation located between them, preferably at least approximately up to the can body. 14. The device according to claim 13, characterized in that the peripheral surface line in the central region of the central part of the application roll at least one preferably located in the middle of the central region, an outer edge in the peripheral lateral surface of the application roll and / or two in the region of the elevation and preferably turning points located symmetrically to the center of the central region and / or at least two in the region of the base of the depressions and preferably also located symmetrically to the center of the central area, each representing an inner edge in the peripheral lateral surface of the application roll and / or two outside of the area of the elevation and preferably also located symmetrically to the center of the central area and / or two outside of the area of the Raised and preferably at the outer ends of the central region and preferably also symmetrical to the center of the same, each having an outer edge in the peripheral surface of the application roller has kink points. 15. The device according to claim 13 or 14, characterized in that the peripheral surface line at the deepest points of the depressions each has an acute-angled inner edge in the peripheral surface of the applicator roll representing a kink point. 16. Device according to one of claims 1 to 15, characterized in that the peripheral surface line has an at least approximately circular convex shape with a preferably larger radius of curvature at least in the predominant part of its sections lying between the central region of the central part of the application roller and the outer ends of the central part than half the inside diameter of the can body. 17. The device according to claim 16, characterized in that the radius of curvature of the circular course is between 1.25 times and 5 times half the inner diameter of the can body. 18. Device according to one of claims 1 to 17, characterized in that the supporting edges are raised relative to the outer ends of the central part of the application roll and preferably adjoin the associated roll side with an obtuse-angled outer edge and each have an acute-angled outer edge on the central part of the application roll . 19. Device according to one of claims 1 to 17, characterized in that the supporting edges are located lower than the outer ends of the central part of the application roll and preferably with an obtuse-angled outer edge on the associated roll side and with an obtuse-angled outer edge on the central part of the application roll adjoin. 20. Device according to claim 18 or 19, characterized in that the peripheral surface line in the regions of the support edges serving to support the can body on the application roll has a convex curvature with a radius of curvature which preferably corresponds to at least approximately half the inner diameter of the can body. 21. Device according to one of claims 1 to 20, characterized characterized in that in order to influence the layer thickness of the protective layer which forms after the application of the coating composition under the influence of the surface tension of the coating composition, means for cooling the welding or soldered seam area of the can bodies prior to application of the coating composition and thus for influencing the heating of the applied coating composition - or soldered seam area of the can body and thus for influencing the surface tension of the applied coating mass are provided, preferably in the form of means for producing a cooling air stream directed from the outside onto the welded or soldered seam area of the can body. 22. Device according to one of claims 1 to 21, characterized in that the distance of the peripheral surface line of the application roll from the roll axis in the areas which extend from the outer ends of the central part of the application roll to the central region of the central part is smaller than the assigned boundary of the central region and greater than or at least the same size as at the associated outer end of the central part and preferably increases continuously from each of these two outer ends after the assigned boundary of the central region. 23. Device according to one of claims 1 to 22, characterized in that the peripheral surface line of the application roll in the areas of the support edges has smaller distances from the roll axis than at the two boundaries of the central area of the central part of the application roll.

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