"DRUM MANUFACTURE"

BACKGROUND TO THE INVENTION

THIS invention relates to drum manufacture. In particular, the invention relates to a method and production line for manufacturing steel drums, typically of 21Ot capacity.

It is recognised that empty steel drums are expensive to transport because of the space which they occupy. Thus the cost of steel drums can be high if they are manufactured at a site remote from that at which they are to be filled. To reduce the transportation cost, it has been proposed, in the case of the so-called Sirco drum, to produce drum kits having three separate components, namely a tubular body, a top end and a bottom end. The kits are supplied to the customer who then assembles the drums as required.

Conventionally the body of the kit is formed by rolling a flat, pre-painted steel sheet to a round cylindrical form. Company identification logos and/or other markings are typically screen-printed on the flat pre-painted sheet before it is rolled. The free edges of the round cylindrical form are then welded to one another.

A problem which arises in the use of the Sirco system is that the weld is unsightly and destroys the continuity of the originally applied paintwork, often necessitating a localised touch-up of the paint. This is particularly problematical in situations where the body is painted different colours in different regions along its length, for instance where a central region of the body is to be one colour or carries screen-printed markings and end regions are to be another colour. The end result is invariably unsightly. In situations where one surface of the initial flat sheet is precoated with a rust inhibitor or other treatment, the further problem which arises is that the protection provided by the internal coat is discontinuous at the weld, leading to the possibility of localised internal corrosion in this region if a subsequent step to coat the weld line is not undertaken.

To address these problems it has been proposed by the present applicant in WO2004/067204 to stiffen each drum body temporarily, after the welding step, and to apply external paint to the body in a roller spray booth while it is so stiffened. In the preferred method described in this document, temporary stiffening is achieved by means of stiffening rings inserted manually into one or both ends of the cylindrical body. After the external painting step, the rings are removed from the end(s) and the body may proceed, after external paint curing, to a screen printing station if external screen printing is in fact required. At the screen printing station, the body is again temporarily stiffened, possibly by means of similar stiffening rings, while the external screen printing is carried out.

The specification of WO2004/067204 describes a number of advantages which come about through the use of these temporary stiffening techniques. However from the point of view of efficiency and speed on a drum production line it is perceived that the temporary stiffening techniques described in WO2004/067204 are somewhat less than optimal and may require manual intervention. It is also considered that the drum body production line described in this document is somewhat less than optimal from a speed and efficiency point of view.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a method of manufacturing drums on a production line, the method comprising the steps of: rolling flat, unpainted steel sheets to cylindrical forms; welding free edges of the forms to one another to produce cylindrical bodies; transporting the cylindrical bodies stepwise and with their axes upright through an external painting and internal treatment booth;

in the external painting and internal treatment booth, initially depositing each body at each of one or more roller spray stations with the lower end of the body locating on a circular array of rollers which stiffen the body, rotating the rollers to cause the body to rotate while paint is sprayed onto its external surface, thereafter depositing the body at an internal coating station at which the internal surface of the body is coated with an appropriate treatment, and moving the externally painted and internally coated bodies out of the external painting and internal treatment booth and through a single curing oven in which curing of the paint and internal coating takes place.

In the preferred method the bodies are transported stepwise through the external painting and internal treatment booth by means of a walking beam conveyor. Typically the walking beam conveyor operates to lift each body in turn, move it forwardly and deposit it with its lower end locating on the circular array of rollers at a roller spray station, further operates to lift each body in turn off the rollers at a roller spray station, move it forwardly and deposit it at the internal coating station and further operates to lift each body in turn and move it forwardly from the internal coating station onto a further conveyor which moves the body to the curing oven.

The method may include the steps of transporting the bodies through a screen printing station and, at the screen printing station, temporarily stiffening the bodies, screen printing the external surfaces of the bodies and destiffening the bodies.

Still further the method may comprise the steps of transporting the bodies to a nesting station and, at the nesting station, deforming a plurality of bodies and nesting them one inside the other, or alternatively of transporting the bodies to a final assembly station and, at the final assembly station, fastening drum ends to the ends of the body to form fully assembled drums.

According to another aspect of the invention there is provided a steel drum production line comprising: rolling means for rolling flat, unpainted steel sheets to cylindrical forms, welding means for welding free edges of the forms to one another to produce cylindrical bodies, an external painting and internal treatment booth, the booth including one or more roller spray stations, a circular array of rollers at each roller spray station, paint spray means at each roller spray station and an internal coating station, transport means for transporting the bodies through the booth, the transport means being operable to deposit each body initially at each of the roller spray stations with a lower end of the body locating on the array of rollers such that the rollers stiffen the body, the rollers being rotatable to cause the body to rotate and the paint spray means being operable to spray paint onto an external surface of the rotating body, the transport means further being operable to deposit each body thereafter at the internal coating station for coating of an internal surface of the body with an appropriate treatment, a curing oven, and moving means for moving the externally painted and internally coated bodies out of the external painting and internal treatment booth and through the curing oven for curing of the paint and internal coating.

The preferred production line comprising both a nesting station and a final assembly station, means at the nesting station for deforming the bodies and nesting a plurality of bodies one inside the other, means at the final assembly station for fastening drum ends to the ends of the body to form fully assembled drums, and means operable selectively to deliver the bodies either to the nesting station or to the final assembly station.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 diagrammatically illustrates the steps carried out in the drum manufacturing method of the invention;

Figure 2 shows a plan view of a production line employing the method of the invention;

Figure 3 diagrammatically illustrates the manner which drum bodies are transported stepwise through the external painting and internal treatment station.

DETAILED DESCRIPTION OF THE DRAWINGS

In the description which follows, the same reference numerals are used, throughout the various Figures, where possible, to designate corresponding items of equipment.

The method and production line of the invention commences with flat, rectangular mild steel sheets 10 which are cut from sheet material by means of a guillotine 11 (Figure 2). Each sheet 10 is then rolled in turn to a cylindrical form 12 by a conventional sheet rolling machine 13 (Figure 2). The free edges 14 of the cylindrical forms 12 are then welded to one another along weld lines 16 at a welding station 17 (Figure 2), to form round cylindrical bodies 18. In practice on the production line seen in Figure 2, each form 12 is first spot welded by a spot welder 17.1 to establish the cylindrical shape and the full seam weld is then made by a seam welder 17.2.

As shown in Figure 2, the bodies are oriented horizontally and are deposited on a conveyor 19. At a position 20 the bodies are upended, i.e. tilted upright such that their axes are vertical. At a position 21 , the bodies are picked up one by one by a walking beam conveyor 22 which transports them sequentially and incrementally through an internal painting and internal coating booth 23. The walking beam conveyor 22 is described below in more detail.

In the booth 23, the walking beam conveyor 22 transports each body 18 laterally in turn to an external spray painting position 24 (Figure 1) and sets them down. At this position there is an array of four rollers 25 arranged in a circle. Each roller is independently rotatable about a vertical axis and, as shown in the enlargement in Figure 2, has a frustoconical upper surface 25.1 , a cylindrical surface 25.2 and a lower flange 25.3. The upper surface 25.4 of the flange has a slight downward inclination relative to the horizontal. The conically sloping surfaces 25.1 receive the lower edge of the body 18 and guide it over the cylindrical surfaces 25.2 onto the flange surface 25.4. The rollers are carefully positioned such that their surfaces 25.2 make firm contact with the internal surface of the body 18.

As soon as the body 18 is seated on the rollers 25 in the manner described above, the rollers are driven in rotation about their own, individual axes 25.5. Frictional contact between the roller surfaces 25.2 and the internal surface of the body causes the body itself to rotate about its own, vertical axis.

The rollers 25 simultaneously serve two important functions. Firstly, they rigidity and stiffen the body 18 which, without such stiffening, would have very little rigidity and be unsuitable for external roller spray painting. Secondly, the rollers cause the body to rotate about its axis through the frictional interaction described above.

At the station 24 a roller spraying operation is carried out. Stationary paint spray heads 26 spray paint onto the external surface of the body 18 as it

rotates. In Figure 1 it will be noted that the spray heads 26 are arranged to spray paint externally onto the body 18 so as to form two painted bands 27 with a vacant band 28 between them.

After the roller spraying operation, the walking beam conveyor lifts the body 18 off the rollers 25 and moves it sideways through an incremental step to another roller spraying station 29 where a paint spray head 30 sprays paint onto the vacant band 28 after the body has been located over further rollers 31 which operate in the same way as the rollers 25.

It will be understood that the spray heads 26 will typically spray paint of one colour onto the body in the bands 27 and that the spray head 30 will spray paint of a different colour onto the body in the band 28. The colour scheme which is sprayed onto the body will in each case be determined by the requirements of the eventual customer. In some instances, the requirement may be for a single colour only, in which case the spray heads 26 will perform all required painting and the spray head 30 is not actuated at all.

It will also be understood that as one body 18 is moved from one station 24 to the next station 29, another body 18 is picked up and moved to the station 24 by the walking beam conveyor. Thus the bodies proceed through the spray booth one by one and in a stepwise or incremental fashion.

After spraying has taken place at the station 29, the body 18 is lifted off the rollers 31 by the walking beam conveyor 22 and is moved laterally to a station 32 at which the internal surface of the body can be coated with a rust inhibitor or other corrosion resistant or other treatment. At this station, the body is located on guides 33 which position it correctly in relation to an internal spray head apparatus 34. The guides 33 may have a shape similar to the rollers 25, 31 but they do not need to be rotatable. The apparatus 34 is moved vertically relative to the interior of the body and its spray heads 34.1 are rotated to spray the relevant treatment onto the internal surface of the body.

Although only one internal coating station is illustrated in Figure 1 , there may in fact be two or more such stations at which different or further internal coatings are applied.

Figure 3 shows a diagrammatic side view of the walking beam conveyor 22. This includes a first, stationary beam structure 70 including laterally spaced apart, elongate beams 72 (only one visible) and a second, movable beam structure 74 including laterally spaced apart, elongate beams 76 (only one visible) which are parallel to the beams 72.

The conveyor 22 includes a drive (not shown) for the beam structure 74 which moves that structure cyclically relative to the beam structure 70 from an initial position illustrated by solid lines in the case of the beam structure 70 and dashed lines in the case of the beam structure 74. In this initial position, the beams 76 of the beam structure 74 lie alongside the beams 72 of the beam structure 70 but extend longitudinally beyond those beams as indicated by the numeral 76.1. The beam structures are connected to one another by a linkage (not shown).

In the initial, forward stroke of the cycle the drive lifts the beam structure 74 relative to the beam structure 70 and displaces it, to the right as illustrated, along an arcuate path 78 which again positions the beams of the structure alongside the beams of the structure 70. Thereafter in a second, return stroke of the cycle, the drive shifts the beam structure 74 laterally to the left to the initial position again, in this case without lifting it relative to the beam structure 70.

In operation, the end portions 76.1 of the beams 76 initially locate beneath the lower end of an upended drum body 18 at the position 21. During the forward stroke the drum body 18 is lifted and displaced laterally along the arcuate path as described above, and is moved into the booth 23. Here it is deposited at the position 24 on the rollers 25, which are mounted on the beams 72 of the beam structure 70. The drive now shifts the beam structure 74 to the left again on the return stroke in order to locate beneath

the next drum body 18. The rollers 25 are simultaneously rotated to rotate the drum body 18 while paint is sprayed externally onto it by the roller spraying operation described above.

The cycle is repeated continuously. On each forward stroke, the walking beam conveyor moves a new drum body to the position 24 for paint application. At the same time, it lifts the previous body from the position 24 and moves it to the right, to the position 29 where, if necessary, the next external paint application step is carried out. On the next forward stroke, the body is lifted off the rollers 25 at the station 29 and is again moved one step to the right, in this case to the station 32, and so forth. Thus the walking beam conveyor advances the drum bodies stepwise from the position 21 and successively to the positions 24, 29, 32 as well as any further internal coating stations which may be provided in the booth 23.

After internal coating with the appropriate treatment(s), the walking beam conveyor transports the body out of the booth 23 and onto another conveyor 35 which takes the bodies to an oven 36 (Figure 2). As indicated by the numeral 32.1 in Figure 2, there may be a separate, additional internal treatment booth situated outside the booth 23 to apply a subsequent internal coating to the drum bodies during their movement on the conveyor 35.

The bodies are moved through the oven 36 in side by side pairs on a further conveyor 37. The oven 36, which may be gas-fired, cures the external paint and internal treatment(s) applied in the spray booth 23 and, possibly, at the booth 32.1.

After passage through the oven 37 the bodies 18 accumulate in a slack or accumulation zone 38 from which a conveyor 39 transports them to subsequent stations in the production line.

Where alphanumerics and/or graphics are to be screen printed on the exterior of the bodies 18, they are arranged with their axes horizontal and

are passed through a screen printing station 40. At this stage the bodies still lack rigidity. For this reason, stiffening cones 41 (Figure 1) are inserted automatically, by appropriate drive arrangements, into the ends of the body. The stiffened body can now be rotated about its horizontal axis while a screen printing head 40.1 applies the relevant alphanumerics and/or graphics to the external surface thereof.

It will be understood that temporary stiffening of the body is necessary at this stage, in view of the pressure applied to the body by the screen printing head, to maintain the round cylindricality of the body as it is rotated. After screen printing the stiffening cones 41 are withdrawn automatically.

The bodies are then passed through an infra-red curing station 42 at which bodies which have been screen printed are subjected to infra red irradiation to cure the screen printing ink. Irradiation may be carried out by infra red lamps supported by an openable and closable frame. The frame is closed about each drum requiring curing and the lamps are energized for a period of time necessary to achieve adequate curing. Typically the infra red curing station 42 is only actuated for bodies which have actually been screen printed.

The production line is now operated selectively in such a way that the bodies 18 are either taken by a conveyor 43 to a nesting station 44, or by a conveyor 45 to a conveyor 46 which transports them through a final assembly line 47.

Each body taken to the nesting station 44 is deformed to a kidney shape and is slipped lengthwise into another similarly deformed body as illustrated in Figure 1. This is achieved, with the axis of the body horizontal, by pressing downwardly on the top of the body, preferably in the vicinity of the weld line 16 which is arranged uppermost, in a press. As shown in Figure 1 , a substantial number of bodies, each deformed to a kidney shape, can be nested one inside the other for compact transportation.

The nesting procedure is performed in situations where drums are to be transported to a remote locality in a knock down or kit form. The nested bodies are transported to their destination along with the required number of drum ends, i.e. tops and bottoms. At that destination, final assembly can take place.

Where fully assembled drums are to be produced, the bodies 18 pass, in the final assembly line 47, sequentially through a flange and curl station 48 at which flanges are formed at the ends of each body, a bead expanding station 49 at which beads are formed in the body to reinforce it, a corrugator 50 at which strengthening corrugations or ribs are formed in the cylindrical wall of the body, an end feeding station 51 at which drum ends are fed into position and seaming stations 52 and 53 at which a sealing compound is injected at the flange location and the flanges are seamed over the ends in a seam rolling operation. Finally, the drums are passed through a leak testing station 54 at which they are tested for possible leakage. Thereafter the assembled drums 55 are taken by a conveyor 56 to a storage location for eventual supply to customers, or directly to a loading station at which they are loaded onto trucks or other transporters.

It will be understood that the production line seen in Figure 2 can be operated selectively to produce drum bodies which are to be supplied in knock down, nested form as well as fully assembled drums. All production steps in the line are the same up to branching of the conveyors 43, 45. It will also be understood that the production line will be operated batchwise to produce either drum bodies for supply in knock down form or fully assembled drums.

A number of the production line steps and items of equipment described above are similar to those described in WO2004/067204. There are however some important and advantageous differences.

One important difference is the use of a combined external painting and internal treatment booth, with a walking beam conveyor to transport the

drum bodies through the booth and, thereafter, the use of a single curing oven to cure both the external paint and internal treatment coat. It is perceived that these features will enhance the efficiency and speed of the production line. It is also believed that the fact that the external painting is carried out before internal coating is advantageous compared to initial internal treatment and subsequent painting, in that it avoids the necessity to apply external paint over possibly uncured overspray which may occur during internal coating.

The production line described above is also advantageous in that the same line is used selectively to produce both nestable drum bodies and fully assembled drums, with all drum bodies being made in exactly same way. Where both nestable drum bodies and assembled drums are to be produced, this avoids the necessity for two separate production lines.