GB2079891A - Aluminium tube - Google Patents

Abstract

The invention relates to aluminium tubes rolled from strip metal. Known rolled tubes of this type are difficult and expensive to produce with small diameters and/or with sufficient resistance to working pressures. According to the invention, the rolled aluminium strip forms at least two layers (3, 4) in the wall of the tube, one layer (3) being offset to the thickness of the strip to join another radially adjacent layer (4), the adjacent layers (3, 4) being soldered on their entire surfaces <IMAGE>

Description

SPECIFICATION Aluminium tube roll-formed from a strip The invention relates to tubes particularly those formed from rolling an aluminium strip about a longitudinal axis.

The strip from which a known tube of this type is manufactured has the width of the tube circumference. When the strip is roll-formed into a tube, the contact point of the edges of the strip is welded. Because of the welding seam formed thereby, the tube has to be carefully and expensively tested if it is to be suitable for high pressure loads. For production reasons, only a relatively large minimum diameter can be obtained, so that to produce tubes of a smaller diameter, several process steps in a drawing device are necessary, which is also expensive.

Extruded; i.e. seamless, aluminium tubes have even greater minimum diameters. This involves even greater expenditure in terms of drawing and annealing, to produce small diameter tubes.

The manufacture of rolled two-layer tubes from a copper-plated steel strip is already known. These tubes have the trade name "Bundy-tube", and are produced with a minimum diameter of approximately 3 mm, without a drawing process being necessary. The two layers of such tubes are soldered together as described in German Patent No: 19 62 760.

The present invention seeks to provide for the creation of an aluminium tube of the type indicated in the introduction, which can have a comparatively small minimum diameter, in which drawing processes are either entirely superfluous or only a single process is necessary, for the production of tubes with a small or very small diameter.

According to the invention, in a tube formed by rolling an aluminium strip about a longitudinal axis, the rolled strip forms at least two layers in the wall of the tube and the strip is offset to the thickness of the strip where it ceases to be part of one layer and starts to be part of a radially adjacent layer, such radially adjacent layers being soldered on their entire juxtaposed surfaces.

Tubes according to the invention are able to be produced already having a very small diameter, and capable of fulfilling high demands as regards compression strength.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing wherein:~ Figure 1 shows a perspective view of the end of an aluminium tube according to the invention, with the space between the layers of metal lamination in the tube cross-section greatly exaggerated; and Figure 2 shows a cross-section of the strip used for the manufacture of the tube according to Figure 1.

As shown in the drawing, a strip 1 with an approximate width twice the tube circumference 7tD with sharpened edges 2 can be rolled in a contour moulding machine around its longitudinal axis into a tube cross-section, such that the finished contour of the tube with wall thickness s has two layers 3 and 4. The changeover 5 of the two coils of the strip is offset to wall thickness s/2. The geometric shape of this changeover is identical to the geometric shape of the changeover in the cross-section of the known Bundy-type.

The strip of aluminium is provided with a plating 6 on half its width, corresponding to the dimension 7tD, which consists of a solder material as described in German Patent No: 19 62 760. On heating the strip, rolled into the tube crosssection, under protective gas up to the soldering temperature, a flux-free, even soldering takes place on the annular clearance 7 interrupted at changeover 5. The free surfaces of the tube are solderless.

1. A tube formed by rolling an aluminium strip about a longitudinal axis, wherein the rolled strip forms at least two layers in the wall of the tube and the strip is offset to the thickness of the strip where it ceases to be part of one layer and starts to be part of a radially adjacent layer, such radially adjacent layers being soldered on their entire juxtaposed surfaces.

2. A tube according to Claim 1, in which the wall thereof has two layers of aluminium, and wherein the strip, which is flat before rolling, is plated on half its width with a fiux-free solderable solder, the other half being unplated.

3. A tube formed by rolling an aluminium strip substantially as described herein with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Aluminium tube roll-formed from a strip The invention relates to tubes particularly those formed from rolling an aluminium strip about a longitudinal axis. The strip from which a known tube of this type is manufactured has the width of the tube circumference. When the strip is roll-formed into a tube, the contact point of the edges of the strip is welded. Because of the welding seam formed thereby, the tube has to be carefully and expensively tested if it is to be suitable for high pressure loads. For production reasons, only a relatively large minimum diameter can be obtained, so that to produce tubes of a smaller diameter, several process steps in a drawing device are necessary, which is also expensive. Extruded; i.e. seamless, aluminium tubes have even greater minimum diameters. This involves even greater expenditure in terms of drawing and annealing, to produce small diameter tubes. The manufacture of rolled two-layer tubes from a copper-plated steel strip is already known. These tubes have the trade name "Bundy-tube", and are produced with a minimum diameter of approximately 3 mm, without a drawing process being necessary. The two layers of such tubes are soldered together as described in German Patent No: 19 62 760. The present invention seeks to provide for the creation of an aluminium tube of the type indicated in the introduction, which can have a comparatively small minimum diameter, in which drawing processes are either entirely superfluous or only a single process is necessary, for the production of tubes with a small or very small diameter. According to the invention, in a tube formed by rolling an aluminium strip about a longitudinal axis, the rolled strip forms at least two layers in the wall of the tube and the strip is offset to the thickness of the strip where it ceases to be part of one layer and starts to be part of a radially adjacent layer, such radially adjacent layers being soldered on their entire juxtaposed surfaces. Tubes according to the invention are able to be produced already having a very small diameter, and capable of fulfilling high demands as regards compression strength. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawing wherein:~ Figure 1 shows a perspective view of the end of an aluminium tube according to the invention, with the space between the layers of metal lamination in the tube cross-section greatly exaggerated; and Figure 2 shows a cross-section of the strip used for the manufacture of the tube according to Figure 1. As shown in the drawing, a strip 1 with an approximate width twice the tube circumference 7tD with sharpened edges 2 can be rolled in a contour moulding machine around its longitudinal axis into a tube cross-section, such that the finished contour of the tube with wall thickness s has two layers 3 and 4. The changeover 5 of the two coils of the strip is offset to wall thickness s/2. The geometric shape of this changeover is identical to the geometric shape of the changeover in the cross-section of the known Bundy-type. The strip of aluminium is provided with a plating 6 on half its width, corresponding to the dimension 7tD, which consists of a solder material as described in German Patent No: 19 62 760. On heating the strip, rolled into the tube crosssection, under protective gas up to the soldering temperature, a flux-free, even soldering takes place on the annular clearance 7 interrupted at changeover 5. The free surfaces of the tube are solderless. CLAIMS

1. A tube formed by rolling an aluminium strip about a longitudinal axis, wherein the rolled strip forms at least two layers in the wall of the tube and the strip is offset to the thickness of the strip where it ceases to be part of one layer and starts to be part of a radially adjacent layer, such radially adjacent layers being soldered on their entire juxtaposed surfaces.

2. A tube according to Claim 1, in which the wall thereof has two layers of aluminium, and wherein the strip, which is flat before rolling, is plated on half its width with a fiux-free solderable solder, the other half being unplated.

3. A tube formed by rolling an aluminium strip substantially as described herein with reference to the accompanying drawing.