FOR LONGITUDINAL WELDING OF TUBULAR BODY

FIELD OF THE INVENTION

The present invention for longitudinal welding of tubular body provides a method and apparatus for producing parts in particular the production of tubular bodies for tubes, bottles, cans and more, from laminated foil with one or more layers.

PRIOR ART

There is a traditional method [US3388017], where the laminated foil is in the form of tape and is moved by a transporter belt along a mandrel. The foil is formed around the mandrel to overlap the two edges. The bottom surface of the bottom layer of the overlapping edge is in contact with the interior sealing band. The exterior sealing band is in contact with the outer surface of the upper layer of the foil's overlapped edge. The exterior band provides heating, cooling and compression of the foil. This band is heated and the foil in the overlapped area is heated, melted and fused. The band cools down as it moves through the process, which fixes the welding and a tube is produced, which is then cut into tubular bodies.

It is a known device, implementing a method for longitudinal welding of tubular body [US3388017], consisting of a mandrel with longitudinal slot and transport belt for moving the foil. There is an interior sealing band in the slot and exterior sealing band moving on the outside. The laminated foil is formed around the mandrel to obtain longitudinally overlapped edges. The inner surface of the bottom layer is in contact with the interior sealing band. The exterior band is in contact with the outer surface of the upper layer of foil. The exterior band is heating, cooling and pressing the seam. The exterior band is heated by a heating unit above it, and in the next position is cooled by a cooling unit. The produced tube continues on to a cutter unit which cuts it into desired lengths.

The disadvantage of this method and apparatus for longitudinal welding of a tubular body is that the resulting longitudinal seam is of poor quality. To reach the melting point of the plastic layer directly in the contact zone between the layers, it is necessary to overheat the external surface of the upper edge of the foil, which results in an unfavourable appearance of the resulting longitudinal seam. This disadvantage increases with increasing thickness of the foil used.

This method and apparatus is also disadvantaged for the same reasons mentioned above (overheating), in that they are unsuitable for longitudinal welding of foil which has printed images on the outside of the foil. Overheating destroys the image in the welding area as dyes are damaged.

Another disadvantage of this method and apparatus is that they have a complicated construction. The requirements for multifunctional transport belts and sealing bands are technically challenging, they require the use" of special and expensive materials and also have low durability.

The object of the present invention is to create a method and apparatus for longitudinal welding of tubular body providing improved weld quality while reducing waste.

OBJECT AND SUMMARY OF THE INVENTION

The object of the invention is achieved by creating a method for longitudinal welding of a tubular body, where the laminated foil is a tape that moves constantly and is aligned to a mandrel. The laminated foil is formed around the mandrel to overlap the two edges which are subsequently heated, pressed and then cooled under pressure until the weld is formed and finally to produce a tube which can then cut into tubular bodies. Overlapped edges of the foil, during the heating and melting, are maintained at a certain distance from each other creating gap between them, heating and welding is achieved by applying heat in this gap.

The method for longitudinal welding of tubular body can optionally include additional heating under pressure to partially melt the lower layer of longitudinal welded seam on the inner side of the tube and subsequent cooling of the seam.

Apparatus for longitudinal welding of tubular body comprises of a mandrel and transportation system for moving the laminated foil along the mandrel, around which this foil is formed. The apparatus has heating, cooling and pressing units. A cutter is positioned at the end of the cooling zone to cut the tube into desired lengths. The profile of the mandrel, in the heating area of the overlapped edges of the foil, has a step designed to create the cavity between the edges of the foil. This profile, after the heating area, gradually transforms into a plane creating an area for the compression of the seam. The heating unit is a hot air gun with a nozzle supplying hot air into the cavity. The upper side of the foil in the welding area is in contact with the compressing and cooling bar and the bottom end outside the welding area is protected from heating by the lower compressing and cooling bar.

Optionally, the apparatus for longitudinal welding of tubular body can have an extra heating area comprising of a flat metal band with a high frequency inductor placed on top. This inductor also serves as a clamp.

Another option of the apparatus for longitudinal welding of tubular body is that the metal band can be formed to copy the profile of the seam.

The proposed method and apparatus for longitudinal welding of a tubular body have improved the weld quality giving better appearance and less waste.

BRIEF DESCRIPTION OF THE DRAWINGS

- FIG.1 is a global view of the apparatus

- FIG.2 is a cross section of the apparatus in the heating area (A-A)

- FIG.3 is a cross section of the apparatus in the welding area (B-B) - FIG.4 is a global view of the apparatus with optional additional heating and compression

- FIG.5 is a cross section of the apparatus in the area of additional heating and compression with a flat plate (C-C)

- FIG.6 is a cross section of the apparatus in the area of additional heating and compression with a profiled plate (C-C)

EXAMPLE IMPLEMENTATION AND OPERATION OF INVENTION

The invention can be described in more detail by the use of an example implementation of the method and apparatus for longitudinal welding of tubular body.

The apparatus for the longitudinal welding of tubular body in FIG.l, FIG.2 and FIG.3 comprises of a mandrel 1 , transport system (not shown in the drawings) for moving the laminated foil 2 along the mandrel 1 around which the foil 2 is formed. There is a heating unit 3, cooling and compressing Unit. After the welding area there is a cutter to cut the tube into tubular bodies. The profile of the mandrel 1 in the heating area of the overlapped edges 7 and 8 of the foil 2 has a step 5 to form a cavity 6 between edges 7 and 8 of the foil 2. This profile after the heating zone gradually transforms into the plane 9. This forms a compression area between mandrel 1 and compressing/cooling bar 10. The heating unit 3 is a nozzle supplying hot air into the cavity 6. Over the foil edge 7 is placed the compressing/cooling bar 10 having cooling channel 1 1, and over the second edge 8 - compressing/cooling bar 12 having cooling channel 13.

FIG. 4 and FIG. 5 show the apparatus for longitudinal welding of tubular body, which has been optionally fitted with an additional heating area. This is installed after the initial working area, where a metal band 14 is fixed onto the surface of the mandrel 1 and above it is positioned a high frequency inductor 15, which also generates compression on the seam. In FIG. 6 of the apparatus for longitudinal welding of tubular body, metal band 14 has a stepped profile which copies the profile of the seam.

The method and apparatus for longitudinal welding of a tubular body works as follows:

The foil 2 by means of a transport mechanism (not shown in the figures) moves at a relatively constant speed through the unit. Forming elements (not shown in the figures) are placed in the path of the foil 2 so that the foil 2 forms around the mandrel 1. Further, one edge 7 of the foil 2 passes under a compressing/cooling bar 10, and the other edge 8 under compressing/cooling bar 12. The step 5 in the mandrel 1 prevents contact between the edges 7 and 8 of the foil 2 and forms a cavity 6. Air, heated to a suitable temperature, is supplied into the cavity 6 by means of the nozzle 3 so by the time a section of foil 2 passes through the heating area the temperature of the edges 7 and 8 of the foil 2 that will come into contact with each other will be high enough to melt them. Melting is limited to the parts of the foil 2 which are not in contact with the compressing/cooling bars 10 and 12 and the mandrel 1. As the foil 2 moves along the mandrel 1 , the edges 7 and 8 follow the change in the profile of the mandrel 1 transforming it into a flat plane 9, edge 8 of the foil 2 is lifted up pressing it to edge 7 and the two edges 7 and 8 are then pressed together and cooled by compressing/cooling bar 10. The compression action forces molten material from both edges 7 and 8 of the foil 2 to be mixed and fused together then gradually cooled by the cooling bar until it reaches a temperature lower than the melting point. After the seam has been welded the tube goes through the cutter 4, which cuts it into the desired lengths.

A metal band 14 is used when additional heating has been installed. It is fitted under the inductor 16 and runs on top of the mandrel 1. When applying high frequency voltage to the inductor 16, the metal band 14 is heated and transmits the heat energy to the foil 2. The foil 2 is partially melted in the area in contact with the metal band 14. As a result of the pressure applied by the inductor 16 to the foil 2 the molten material of the foil 2 flows to the side and the overall thickness of the seam is reduced. As the foil 2 moves from the area with the metal band 14 and contacts with the mandrel 1, which is not heated, the molten section of the foil 2 is cooled and sets. The metal band 14 can have an optional step, which helps to heat and melt an additional part of the foil 2 in contact with the already melted foil 2. After welding has been completed, the foil 2 goes in the cutter 4 which cuts it into the desired lengths.