March 8, 2008

Manufacture - Aluminum Tube

Collapsible aluminum tubes are made in tin, lead, tin-lead alloys, lead coated with tin, aluminum and certain thermoplastics such as polythene and polyvinyl chloride. Aluminum is now the most commonly used material for metal tubes and polythene tubes. There are a number of problems to be solved before plastic tubes can be used as widely as metal tubes. Briefly some of the problems still to be overcome are the collapsibility of plastic tube, their permeability with regard to moisture and essential oils, and the migration of plasticizers, especially where PVC is used.

Collapsible aluminum tube production may be divided into two main processes, mechanical fabrication and treatment of the tube surface. Mechanical fabrication of aluminum tubes involves five stages of processing. Most of these are carried out automatically on a mass produced flow line basis with manual handling reduced to a minimum. Aluminum of 99.7 percent purity is cast, rolled to a predetermined thickness and blanked to provide cylindrical pieces of metal of a defined diameter. These pieces of metal, generally referred to the desired metallurgical state for fabricating. The slugs are then lubricated and, by a process of impact extrusion, the lubricated slugs are converted in a specially designed press to the tube shape, with a shoulder and nozzle. The tubes are transferred from the press to an automatic machining lathe, where they are trimmed to the correct length, a thread rolled or cut on the nozzle portion, and the external surface of the tube shoulder machined to give a decorative pattern if desired.

The five stages of processing provide tubes of the desired dimensions. The severe impact-extrusion forces involved in the transformation of slug to tube do, however, leave the tube in a work hardened state. To provide the flexibility or collapsibility associated with these containers, they are annealed at temperatures not far removed from the melting point of the metal itself. This stage in the processing removed from the melting point of lubricant used in the extrusions process; it anneals the tube and so provides collapsibility. Moreover the high temperatures involved sterilize the tube completely. Surface treatment of the tube with a protective lacquer (if this feature is desired), followed by a high temperature storing period. This external enameled surface can then be printed in from one to four colors, as desired, on offset printing machines. A surface stoving period dies the ink and sets the enamel coating. Tubes coming off the processing line at this stage require only a cap or closure to be fitted to the nozzle before packing into suitable boxes or cartoon for dispatch.

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