GB2191432A

GB2191432A - Method of manufacturing containers

Info

Publication number: GB2191432A
Application number: GB08713901A
Authority: GB
Inventors: John Ian Bucklow; Ian Maxwell; Terence Arthur Turner
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1986-06-13
Filing date: 1987-06-15
Publication date: 1987-12-16
Anticipated expiration: 2007-06-15
Also published as: GB8614394D0; GB8713901D0; GB2191432B

Abstract

A can body 15 is made by continuously extruding a tube 12 of metal, expanding the diameter of the tube to reduce the wall thickness and work-harden the wall, and cutting the tube into required lengths. These lengths are then flanged 17 and can ends 18 are fitted. The extrusion apparatus may be of the friction-feed type. <IMAGE>

Description

SPECIFICATION Method of manufacturing containers The invention relates to a method of manufacturing metal containers and relates in particular to a method of manufacturing beverage or food cans of the type having a cylindrical body closed at either end by a can end fixed by double seaming.

For many years can bodies have been made by cutting a rectangular blank from sheet metal, folding the blank to a cylinder and joining the adjacent edges by interlocked folding or welding. Such cans are expensive because the sheet material is costly to produce. Further, the side seam may require further treatments such as coating with lacquer.

The present invention provides a method of manufacturing metal containers in which the container body is continuously extruded rather than formed from a blank. In order to manufacture containers economically it is important that they have a very low wall thickness. In order to provide containers having a wall thickness which is less than the minimum wall thickness at which a tube can successfully be extruded for a given diameter, the method of the present invention includes the step of expanding the diameter of the extruded tube to reduce the wall thickness. This step also helps to work-harden the material of the container.

According to the present invention there is provided a method of manufacturing metal containers comprising the steps of: a) continuously extruding a tube of material; b) expanding the diameter of the tube; c) cutting the tube into required lengths.

The continuous extrusion may be carried out on a machine such as is described in British Patent 1370894 (UKAEA) for example. The benefits of using continuous extrusion machines is that the feedstock is in a cheaper form because less work has been done on it.

For example, the feedstock may be scrap. Further, scrap arising from the continuous extrusion process is itself amenable to recycling at modest costs.

Suitable metals include commercially pure aluminium and its alloys, steel, copper and its alloys.

Embodiments of the invention are described below with reference to the accompanying drawings in which: FIGURE 1 is a diagramatic view showing container bodies being formed from a continously extruded tube; FIGURE 2 shows an alternative embodiment of the extrusion machine used in Figure 1; and FIGURE 3 shows a detail on an enlarged scale of a yet further embodiment of extrusion machine suitable for use in the invention.

In a first form of the invention, metal can bodies are formed from the tube 12 extruded from a continuous extrusion machine 1. The extrusion machine 1 comprises a rotating wheel 2 having a peripheral groove 3 formed therein and a shoe member 4 closing a segment of the groove and having an abutment 5 which projects into the groove.

Feed material in the form of aluminium rods 6 is passed between a guide roller 7 and the wheel 2 to enter and be entrained within the groove 3. Frictional engagement drags the rod into the gap between the shoe member 4 and the wheel 2 until it is forced against the abutment 5. The abutment 5 deflects the material through an orifice 8 into a cavity 9 which becomes filled with pressurised material. The frictional work done in forcing the material around the wheel 2 and into the cavity 9 raises the temperature of the material and increases its plasticity. From the cavity 9, material is extruded through a bridge die comprising a first portion 10 which defines the interior surface of the extrudate and a second portion 11 which defines the exterior surface of the extrudate.The die is held in the shoe 4 and defines an annular orifice that shapes the extruded material into the form of a tube 12.

A flying shear apparatus 13 indicated by arrows, cuts the extruded tube to desired lengths 14. Each cut length of tube 14 is then expanded to a desired diameter and reduced wall thickness required for a can body 15. Expansion of the cut lengths of tube may be carried out by any suitable means such as, for example, mechanical plug boring, expansion by electromagnetic force, expansion by means of pneumatic or hydraulic pressure, or by expansion of a mandrel within the tube. If desired a central portion of a can body may be further expanded to create a can body having a central portion of larger diameter than the terminal portions thereof.

After the length of tube has been expanded to a required diameter the terminal margins are reduced to form shoulders 17 which are subsequently provided with flanges 18 which permit fixing of can ends by double seaming.

The can maker usually seams on one can end and the packer seams on the other end after the can has been filled.

Optionally, the edges of cut lengths of tube can be trimmed after the expansion stage.

Figure 2 shows an alternative embodiment in which a continuous extrusion machine is supplied with feed material in the form of powder, fragments, pellets or chopped wire etc. A ceramic wheel 13 indicated by arrows travels with the tube as it is cut to desired lengths.

The extruded tube may be cut to can body lengths either before or after it has been expanded to the desired diameter. If required the expanded tube may be pulled through a drawing die to correct the wall thickness and possibly improve straightness.

Figure 3 shows an alternative extrusion machine wherein twin wheels 2 are provided to force feed material 6 into a chamber 9 from which a tube 12 is extruded at a tangent to the wheels 2. A replaceable mandrel 20 cooperates with a die 21 to define an annulus through which the plastic material is extruded.

Apparatus as shown in Figure 3 is particularly advantageous where it is required to expand the extruded tube by means of pneumatic or hydraulic pressure. In this case, the mandrel 20 may be provided with a through bore 22 which can connect the inside of the extruded tube to a source of pneumatic or hydraulic pressure. In this case the extruded tube, extruded with a diameter of less than 50 mm may be expanded within a cooled and lubricated supporting block (not shown) to a diameter of about 65mm. Relatively long sections of expanded tube may be formed by pinching and welding the extruded tube as it emerges from the die, to close off the end of the tube, and inflating the tube through the port 22 as it is extruded. Lengths of expanded tube formed in this way can be subsequently cut to can body lengths by any suitable means.

The extrusion of metal tubes having thin walls becomes progressively more difficult as the diameter of the extruded tube is increased. Naturally it is a requirement of economics that the walls of metal cans are as thin as possible whilst still having the necessary strength characteristics. Commonly wall ironed beverage cans may have a wall thickness of about 0.1-0.2 mm.

In one preferred range of the present invention, a metal tube is extruded at a diameter of about 25 mm and a wall thickness of about 0.5-1.0mm and is subsequently expanded to a a diameter of about 65mm and a wall thickness of about 0.2-0.4mm.

Claims

1. A method of manufacturing metal containers comprising the steps of: a) continuously extruding a tube of material; b) expanding the diameter of the tube; c) cutting the tube into required lengths.

2. A method as claimed in claim 1 wherein the tube is cut into lengths before its diameter is expanded.

3. A method according to claim 1 wherein the tube is cut into lengths after its diameter is expanded.

4. A method according to any preceding claim further comprising the steps of forming a reduced shoulder at the marginal end of each length of tube and subsequently providing a radial flange at each end of the tube.

5. A method according to any preceding claim wherein the expansion of the tube is carried out by means of pneumatic or hydrau iic pressure.

6. A method of manufacturing a container substantially as described herein with reference to any one of the accompanying drawings.