Method and apparatus for covering areas of damaged protective coating, and a transport system

The invention relates first of all to a method for covering areas of damaged protective coating on containers or the like, in which, according to the invention, protective coating material is stamped on to the zone in which the damaged areas occur. The invention also describes an apparatus for carrying out the method in which a carrier unit is provided for stamping protective coating material on to the damaged area. Apparatus is provided for positioning the carrier unit with respect to the container.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to methods and apparatus for manufacturing metal containers in general, and to methods and apparatus for providing a protective coating to an area of the metal containers in particular.

2. Background Information

In the manufacture of metal containers such as small tubs of 0.5 liter to several liters capacity, lugs are provided on either side of the container body as anchor points for the carrying handle. These lugs are attached to the bodies preferably by welding or by some other method of fixing after the bodies have been resistance spot welded; this, however, means that the protective coating or covering applied to the sheet metal prior to fabrication of the containers is damaged and/or that bare metal is left exposed after the attachment process. These areas of damaged coating or bare metal then have to be given a protective coating to prevent corrosion by, or contamination of, the product contained. The invention can of course be applied to any situation where unprotected areas of the kind described above are to be covered with a coating for similar reasons.

In principle, methods which suggest themselves for covering the areas of damaged protective coating or of bare metal are those used to produce large areas of protective coatings on bare metal. In one such method, can seams are coated by a wet lacquering process in which a lacquer is applied to the surface to be coated. Disadvantages of this known method are the long drying times and the solvent vapors given off in the drying phase, necessitating the increasing use, for environmental reasons, of special extraction systems.

In another known method for covering welded can seams which have been exposed by the welding process, electrically charged coating powder is sprayed between lateral shields on to the weld seam, which is carried continuously past the spraying unit and is therefore “endless”, while excess coating powder which accumulates in the shields is continuously extracted. The powder which has been sprayed on is then heated in heating lines, which can be up to 20 meters long, and is thereby cured. This known method, which is sometimes also used in the manufacture of welded tub bodies (to cover the exposed body seam) is, as has been said, continuous, that is to say endless, and is not suitable for treating small areas. Moreover, it is likely that the intact, already coated surface of the containers would be contaminated, which would necessitate subsequent cleaning, or heating of the entire internal surface of the container in order to bind the pulverulent coating material.

Lastly, there is the option of sticking a foil with protective coating material over the damaged areas. This known procedure utilizes an additional substance, namely an adhesive suited to the purpose, and this should be avoided if possible, to avoid further contamination and spoiling of the product contained. For containers intended to be filled with a food product, for example, this would mean that the foodstuff compatibility of the adhesive would have to be proved and/or approval obtained from such authorities as the FDA in the USA, which is a time-consuming and expensive process. In any event, the adhesive would still need to be pronounced completely safe for the individual product to be contained, not least in view of the shelf life of up to several years expected of metal packaging.

The amount of material absorbed in the process of restoring the covering layer is also relevant, as such containers may be manufactured in large numbers, with the result that the consumption of material (in addition to the capital costs) is a critical factor for the production line.

Accordingly the problem which lies at the basis of the present invention is to specify a method and an apparatus which are capable of performing the task with a minimum amount of additional coating material.

This problem is solved by a method for covering areas of damaged protective coating on containers or the like, characterized in that protective coating material is stamped on to the zone in which the areas to be coated occur. Advantageous configurations of the invention, an apparatus for carrying out the method and a transport system are indicated in further claims.

The invention has the following advantages. Because material is applied only in the region where bare or damaged areas occur, and there is no longer any need for surplus powder to be removed, it becomes possible to cover such areas at small cost in terms of coating material. Furthermore, there is no contamination of the container and no giving off of noxious solvent vapors, as it is possible to work with materials that are already recognized and accepted as appropriate, notwithstanding the fact that the methods used hitherto in the can industry (where lugs may be unknown) basically cannot be applied to the solution of the present problem.

These and other objects, features and advantages of the present invention will become apparent in light of the detailed description of the invention, and the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a lug20which essentially consists of a cylindrical body which has a cover with a hole21at one end and a foot22extending away from the longitudinal axis of the

body at the other end. Weld points, formed e.g. by the spot welding process, are indicated at23.

FIG. 2Ashows the body24of a container to which a lug20according toFIG. 1has been attached. The welding process has left areas of damaged protective coating, indicated at25, on the inside of the container. These damaged areas25correspond to the weld points on the foot22of the lug20, and preferably lie in a circle, spaced apart at regular intervals, as shown inFIG. 2B. The problem of the invention is to repair the areas of damaged protective coating so that corrosion of the tub wall, and contamination of the product contained, cannot occur.

Two lugs20are provided on each container, and are located opposite each other on the outside of the container in the region of the container's upper rim. A carrying handle can be joined in a known manner to the lugs20, and thus to the container, by the hole21. The invention is of course not limited to the attachment of lugs of this type, and can be adopted in any situation where a connection has to be made with other parts, such as tear-off tabs or similar, leaving areas needing to be covered with a protective layer.

FIG. 3shows one embodiment of apparatus according to the invention for coating areas of damaged protective coating located on the inside of a container1which has been provided with lugs2. In one way of carrying out the invention, the damaged areas are coated by stamping pulverulent coating material on to the zone susceptible to damage. Pulverulent coating material is applied by means of a carrier unit12, preferably a so-called “stamp pad”, which is pressed on to the affected area by means of a pusher unit11, causing coating material to be transferred on to the body of the container1. Transfer of coating material is assisted if the temperature of the container1, and/or of the region to which the coating powder is to be applied, is higher than that of the carrier unit12. A heating element4, which will be described presently, is provided for this purpose.

After every stamping of coating powder on to the zones subject to damage, the carrier unit12has to be recharged with powder. This is done by means of a rotatably mounted transfer unit9which is driven by an angular gear10and which preferably has a number of carrier units12with corresponding pusher units11arranged on it. Then, one carrier unit12can be picking up coating material while another carrier unit12is stamping coating material on to the container1. Yet another carrier unit12can be preheated during the same time interval by means of the above-mentioned heating element4in order that, in the ensuing step, it will be able to pick up coating material which has been prepared on a turntable3in a manner which will be described presently, the carrier unit12again being actuated by means of the corresponding pusher unit11to effect such pick-up of material.

As can be seen fromFIG. 3, with optimum handling it is possible for the damaged areas25of both lugs2welded to the same container1to be provided with coating material. To accomplish this, an additional transfer unit9of similar construction to the one which has been described, and preferably driven by the same angular gear10, is provided. This means that perfectly synchronized coating of the damaged areas at the two lugs2is assured, or in other words that the two symmetrically arranged transfer units9work in unison on either side of the container1. Each transfer unit is rotatably mounted and holds four carrier units12i.e. stamps made of silicone. The carrier units12are displaced axially by the corresponding pusher unit11at every working step. In a first step, the carrier unit12is pressed on to the heating element4and preheated so that in the next step it will be able to pick up the prepared coating powder from the turntable3as a result of light adhesion due to heating. In the next step, the carrier unit12with the powder adhering to it is lightly vacuumed to remove any loose powder particles. This results in greater cleanliness in the container1. In the final step, the carrier unit12with the coating powder adhering to it is stamped on to the damaged areas.

To avoid having to move the angular gear10and the two transfer units9up and down, the containers1to be coated can be raised by means of an elevating platform6to enable the carrier units12to stamp coating powder on to the damaged areas.

As has already been mentioned, the pulverulent coating material to be stamped on to the damaged areas is removed from the rotatably mounted turntable3by the carrier unit12concerned. This turntable3forms part of a batching unit31which also has other components and which will now be further described with reference toFIG. 4.

FIG. 4shows the batching unit31in a perspective view. In addition to the preferably horizontal turntable3, which has recesses14that are about to be explained and which is preferably rotatable about a vertical axis17and capable of being driven in such rotation by a drive unit13(FIG. 3), a bin8for pulverulent coating material and a cleaning unit16are provided.

The recesses14are filled with coating powder, which runs out from the bottom of the bin8, up to the level of the top of the turntable3. For this purpose a wiper18, for example in the form of a strip, is provided behind the bin8, viewed in the direction of rotation of the turntable3. InFIG. 4, the reference numeral15denotes the transfer position in which a carrier unit12(FIG. 3) picks up as nearly as possible all the coating material contained in the recess14.

Transfer is assisted by heating the carrier unit12concerned, or the surface thereof, by means of the heating element4before pick-up takes place.

After the coating powder is picked up, the turntable3goes on turning. When it reaches the cleaning unit16, at the entry to which a brush16ais provided, any coating material remaining in the recess14is removed.

The configuration of the recesses14, and hence of the coating patches actually applied, is such that consumption of coating material can be kept to a minimum and yet is sufficient to ensure that the damaged areas—together with a certain margin—are reliably covered. Moreover, the thickness of the coating applied is set by the depth of the recesses14.

In keeping with the arrangement of weld points assumed here and in view of the criteria mentioned above, the chosen form for the recesses14is that of a ring.

The method of handling the containers1is shown schematically inFIG. 5, in which individual process steps, each corresponding to one segment of cycle time, are numbered52to58. The same steps and numbers also appear inFIG. 6.

Referring toFIG. 5, a container1, which has already been provided with a bottom, lugs2, and a handle, is transferred to the coating unit7, that is to say it is initially placed in position52. Here the lugs2are aligned to ensure that the coating material will be stamped in the right place. By a pendulum step process which will be described presently, the containers1are individually transported to the next position53,56in order that the target zones can be heated with a heating unit30, designed as an induction heater, hot air blower, or infra-red radiator. For a more homogeneous contact with the powder adhering to the transfer unit12, the container1is preferably heated from the inside. In one embodiment of the invention, the containers1are lifted vertically by means of an elevating platform6, to avoid having to move the heating units30. Hot air or infrared radiation can be brought to bear from both sides, and can be used simultaneously if desired. The container1—if need be after pausing in a waiting position W—is then transferred to position54, where coating material in powder form is applied, preferably in the manner described with reference toFIGS. 3 and 4. Here again the container1is raised, to avoid having to move the batching unit31and transfer units9together with their angular gear10(FIG. 3). Finally, in position55,57, heating again takes place: by means of heating units30, the temperature of at least the zones subject to damage is raised, preferably to the melting point of tin. Depending on the melting point of the protective coating material employed, the requisite temperatures will lie e.g. between 150 and 240° Celsius.

FIG. 6shows a transport system according to the invention in which the positions52to58which have been described with reference toFIG. 5are realized in an arrangement that is compact and allows for rigidly imposed transport cycle times. The application of coating takes place in a production line for the containers concerned which may extend from the cutting-up of sheet-metal blanks to form the containers to the filling and closure of the containers, so that the transport cycle is preordained. With the aid of a rotary manipulator60the containers1can be preheated in tandem, one being heated while the other is being transported and vice versa.

To heat a container, the container is transferred, by means of suction cups62or the like forming part of the rotary manipulator60, from position52to position53, where it is parked. In the next step of the cycle, the next container arriving in position52is picked up and transferred to position56. During this transfer phase, the container parked in position53stays where it is. Not until a container has been parked in position56is the container in position53picked up again, and transferred by rotation of the manipulator60to position54, where for example the stamping-on of coating powder as described with reference toFIGS. 3 and 4takes place. The second rotary manipulator61is used in a similar way.

In this way, the heating phase is extended without affecting the fundamental cycle time. If baking is necessary following application of the coating powder, a second rotary manipulator61, connected in series, will be required, again giving the heating unit30(FIG. 5) an extended dwell time.

The method according to the invention and the transport system according to the invention are particularly suited for mechanized and continuous operation in a production line, as has already been stated. Over 80 cycles per minute can be achieved. Consumption costs can be kept to a minimum by the precise nature of the batching. With the method according to the invention, contamination of the container with loose powder does not occur, as any loose powder will stay stuck to the carrier units.

In another embodiment of the invention, instead of using stamping pads as carrier units these are formed as a solid bar of protective coating material. Shortly before being stamped on to the damaged areas, the bar end is melted and/or the target zones are preheated to a temperature above the melting point of the coating material. This involves only minor modifications of the apparatus according to the invention. For instance the batching unit in the form described is no longer required. But the essence of the inventive idea still remains.

In one embodiment of the apparatus according to the invention, a foil tape which is cut up into blanks is used instead of powder. These blanks are then picked up by the transfer unit and applied to the inner wall of the container in the same way as a prepared ring of powder. The apparatus can remain essentially unchanged, the only difference being that the bin8will then be dispensing foil blanks instead of powder on to the turntable3. An expert will be capable of making the necessary modifications without needing further instruction.

A preferred embodiment of an apparatus for applying blanks will be described with reference toFIGS. 7 to 10.

FIG. 7shows the preferred embodiment of the invention in a partly cutaway view perpendicularly to the transport direction of the containers1. The containers1are transported in a series of steps; before the application of foil (and if a heating device—which will be explained later (FIG.9)—is used, before reaching the heating device), the containers1are aligned so that the point of application is in register with the position of the lugs2. Preferably, the containers1are aligned so that the lugs2are located laterally when viewed in the transport direction.

Foil100is supplied from a reel107located in a hot box112under the transport system for the containers1. In the case of the apparatus illustrated inFIG. 7, the foil tape100is double-wound on the reel107. This makes it possible by means of suitable deflection pulleys102to104to convey the foil100to the transfer unit in a simple manner, as follows: the foil tape is fed by means of a tape feed unit and tape holder109which are operated alternately, and the foil100is cut into the desired shapes by means of a punch108and transferred to the transfer unit9fitted with carrier units12. Here the carrier units12preferably consist of so-called “stamp pads” which pick up the foil blanks by suction. These stamp pads have holes at suitable points which communicate with a chamber connected in turn to a low-power vacuum pump.

InFIG. 7the transfer unit9has been drawn in two positions. In the upper position, the carrier unit12is charged with a blank of foil material. A container1with areas of damaged protective coating in the region of the lugs2has been prepared and placed in position underneath the transfer unit9. The transfer unit9is then moved to the second, i.e. lower, position by means of a pneumatic or hydraulic cylinder111. A further, horizontally mounted cylinder presses the carrier units12charged with blanks radially outwards at the same level as the lugs2, so that the blanks are applied to the areas of damaged protective coating. Prior to the application of the blanks, the container1is heated, in a manner which will be described presently, to a temperature affording ideal conditions for joining the foil material to the interior of the container.

Polyamide-12 (also known under the trade name NYLON), polyamide-6 and polyester have all proved suitable as foil material, especially polyamide-12. In the case of the last mentioned product, the containers1and/or their interiors in the region of the lugs2are preferably heated to a temperature of approx. 160° Celsius. This ensures perfect bonding of the foil material to the inner wall of the container.

At the same time, the hot box112containing the reel107of foil tape is heated to a temperature of approx. 80° Celsius. This prepares the foil material for the application process. Any water droplets which may have been deposited on the tape are evaporated by this warming process before the foil is applied. This will effectively prevent flaking.

In a further embodiment of the apparatus according to the invention, shown inFIG. 8A, a skid113is substituted for the hot box112. The foil tape is guided along this skid113, which is heated to approximately 100° Celsius. This again prevents water droplets from being deposited on the foil tape, and evaporates any water droplets which may be present.

FIG. 8Bshows an alternative embodiment to the skid113shown inFIG. 8A. The foil tape is guided through a hot-air tunnel114which performs the functions stated above.

FIG. 9shows an arrangement for three-stage heating of the areas of damaged coating on the interior of the containers1, which are advanced in steps in the direction of the arrow120by means of a transport system (not shown inFIG. 9). During the stages when the containers are at rest, hot air supply lines124,125,126are positioned in the open topped containers over the damaged areas. In synchronization with the advance of the containers1in the direction120, a drive unit121is triggered so that the supply lines124,125,126do not come into contact with the containers1. The drive unit121is coupled with the heat supply lines124,125,126by drive belts122and swiveling axes127,128,129. The heat supply lines124,125,126are supplied with hot air via a heating air duct123, in which they are pivotally mounted.

With the proposed heating device, there is no need to vary the transport cycle for the containers1even if the heating operation has to be performed in a number of cycles. Also, the amount of movement of the heating assemblies is minimal.

InFIG. 10B, round blanks151are produced by means of a punch108(FIG. 7A). A strip of waste155is left over.

Lastly,FIG. 10Cshows the preferred type of blank. By means of the punch108(FIG. 7A), blanks152are produced that are circular except for two straight segments. The intermediate pieces156that are left over as waste are extracted by means of an extraction device110.

The invention can be used to advantage in other applications besides the covering of areas of damaged protective coating on containers. The invention is highly suitable for covering areas on components of any description.

Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and the scope of the invention.