GB2117281A

GB2117281A - A process for the production of a pipe having channels in the wall thereof

Info

Publication number: GB2117281A
Application number: GB08308317A
Authority: GB
Inventors: Franz-Josef Holtorf
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1982-03-27
Filing date: 1983-03-25
Publication date: 1983-10-12
Also published as: FR2524110A1; DE3211441A1; GB2117281B; GB8308317D0

Abstract

In a process for the production of a pipe having channels (8) within the wall thereof, which are arranged in the longitudinal direction or at a small angle thereto, a pipe (1) is first produced which has longitudinal grooves (2) on its inner or outer surface. This pipe (1) is slid into or onto a second pipe (3) and the two pipes are joined together by a drawing step in leak-proof fashion. If desired grooves may be formed in both the inner and outer pipes, the grooves co- operating to form the channels (8). Alternatively, ribs (7) may be formed on the surface of one pipe, which enter some of the grooves (2) in the co-operating surface of the other pipe the number of grooves (2) in all cases being a multiple of the number of ribs (7). <IMAGE>

Description

SPECIFICATION A process for the production of a pipe having channels in the wall thereof The present invention relates to a process for the production of a pipe having channels which are arranged in the pipe wall and which run in the longitudinal direction of the pipe or at a small angle thereto.

For heat exchange purposes or for use as burner nozzles, pipes are required which, on the one hand, have a sufficiently thick wall to withstand the internal or external pressure, as the case may be, of the prevailing medium, but in which, on the other hand, the increased wall thickness does not impede or reduce the heat exchange between the media on either side of the wall. For this purpose, pipes have been developed which are provided with longitudinal channels in their walls through which the heat exchange medium is conducted. Hitherto, these longitudinal channels have been produced by the boring of relatively short pipe lengths. However, this method of production is extremely expensive.

It is, therefore, an object of the present invention to provide a process which enables long lengths of pipe which have channels located in the walls to be produced in an economic fashion; and in which the individual channels are separated from one another in pressure-tight manner.

According to the invention, there is provided a process for the production of a pipe having channels within the wall thereof, which run in the longitudinal direction of the pipe, or at a small angle thereto, comprising the steps of forming a pipe having longitudinal grooves or grooves making a small angle to the longitudinal direction, in the inner or outer surface of the pipe, sliding a second pipe having a smaller or larger diameter respectively into or over said first-mentioned pipe, joining the pipes together in leak-proof manner to form a compound pipe by means of a drawing step.

It has been found to be advantageous in many cases to produce longitudinal grooves in equal numbers and at equal spacing into both the outer surface of the smaller pipe and the inner surface of the larger pipe, and to fit the pipes into one another in such a way that the longitudinal grooves are arranged in register one above another and finally to join the pipes to one anothe so as to be leak-proof. In this process, the longitudinal grooves are preferably arranged to be semicircular in cross-section, so that substantially circular longitudinal channels are eventually formed.

In accordance with another embodiment of the invention, longitudinal ribs are formed in the inner surface of the larger pipe and longitudinal grooves are formed in the outer surface of the smaller pipe, the number of longitudinal grooves being a multiple of the number of ribs. The pipes are then fitted together so that at least one longitudinal rib is introduced into a longitudinal groove, whereupon the pipes are joined together so as to form a leak-proof connection. Such a connection can expediently be effected by means of a female die and a mandrel. In addition, it may be desirable to provide the outer surface of the smaller pipe at the contact surfaces, at least in part with a solder layer, and when the pipes have been drawn onto one another to heat the compound pipe so formed to at least the melting point of the solder.In this way, the individual channels are sealed one from another, and the penetration of gases is also prevented. However, it is also possible to subject the pipes which have been drawn one upon another to form a leak-proof connection to a diffusion annealing process, in order to achieve a metallic interconnection of the contact surfaces without the use of added solder. For this purpose, it is advantageous to clean the contact surfaces before they are joined, for example, by mechanically cleaning and/or degreasing both the outer surface of the inner pipe and the inner surface of the outer pipe. This serves to remove residues which could lead to blocking of the small channels after the drawing step.

The invention will now be further described with reference to the drawings, in which: Figure 1 is a schematic cross-sectional view of an inner pipe for use in a process according to the invention; Figure 2 is a similar view of an outer pipe for use in this process; Figure 3 is a schematic side view of drawing means for carrying out the drawing step of the process of the invention; Figure 4 is a schematic cross-sectional view of a further form of composite pipe formed by a process in accordance with the invention; and Figure 5 is a schematic cross-sectional view of yet another form of composite pipe formed by a process in accordance with the invention.

Figure 1 represents a cross-section of a pipe, which may, for example be a copper pipe or a pipe made of a copper alloy having a low content of alloying constituents, which has been provided on its outer surface with grooves 2 running in the longitudinal direction by the use of a suitable annular drawing die which has not been shown.

This pipe 1 is subjected to a cleaning process and is then introduced into an outer pipe 3 (shown in Figure 2) of larger internal diameter which has been produced in a separate operating step. This pipe 3 may also expediently consist of copper or a low-alloying constituent copper alloy, but the material need not necessarily be identical with the material of the smaller pipe 1. The inner surface of the pipe 3 should also be cleaned. After the assembly of the pipes 1 and 3 one inside the other, the pipes are drawn so as to be leak-proof.

As shown in Figure 3, this is expediently effected by means of a female die 4 and a mandrel 5. The mandrel 5 is first introduced into the pipe 1, and the pipes 1 and 3 are provided with a common drawing device. This drawing device is led through the die 4, and by means of a tensioning device which acts upon the drawing device, the pipes 1 and 3 are drawn together through the die 4 so as to produce a leak-proof connection between them.

In order to achieve a particularly reliable sealiny of the longitudinal grooves and longitudinal channels 2 one from another, those areas 6 of the surface of the pipe 1 which are located between the channels 2 may be provided with a layer of solder, for example, in the form of paste, powder or film.

After having been drawn, the compound pipe is then subjected to an annealing process in which the temperature used is greater than the melting point of the solder layer.

Figures 4 and 5 illustrate further examples of pipes which have been produced by the process of the invention and are suitable for use as burner nozzles in autogenous welding devices. As shown, the inner pipe 1 possesses twelve longitudinal grooves 2 which are formed in the outer surface thereof as previously described by means of a die.

The outer pipe 3 has six internal longitudinal ribs 7 which enter every other longitudinal groove 2. The longitudinal ribs 7 are produced on the inner wall of the pipe 3 in known manner by means of a suitable mandrel. The remaining grooves 2 into which the ribs 7 do not enter, co-operate with the inner wall of the pipe 3 to form channels in the wall of the composite pipe. In Figure 5, the inner pipe 1 again possesses twelve longitudinal grooves 2, in its inner wall, whilst the outer pipe 3 carries both longitudinal grooves 8 and ribs 7 on its inner surface. When the pipes 1 and 3 are assembled together, the six ribs 7 are introduced into six of the grooves 2, whilst the grooves 8 form circular channels with the other remaining grooves 2.

It will be appreciated that, while for clarity, reference has been made to longitudinal channels, these can equally be channels making a small angle to the longitudinal direction of the pipes, the grooves and, when used, ribs on the pipe surfaces making the same small angle to the longitudinal direction as the channels to be formed.

Claims

1. A process for the production of a pipe having channels within the wall thereof, which run in the longitudinal direction of the pipe, or at a small angle thereto, comprising the steps of forming a pipe having longitudinal grooves or grooves making a small angle to the longitudinal direction, in the inner or outer surface of the pipe, sliding a second pipe having a smaller or larger diameter respectively, into or over said first-mentioned pipe, joining the pipes together in leak-proof manner to form a compound pipe by means of a drawing step.

2. A process as claimed in Claim 1, wherein said longitudinal grooves are formed in equal numbers and at equal intervals in both the outer surface of the smaller pipe and the inner surface of the larger pipe, and the pipes are so assembled prior to drawing, that the longitudinal grooves in the two pipes are in register, whereby said channels are formed when the pipes are joined to one another in leak-proof fashion.

3. A process as claimed in Claim 1, wherein longitudinal ribs are formed on the inner surface of the larger pipe, and longitudinal grooves are formed in the outer surface of the smaller pipe or vice versa, the number of longitudinal grooves being a multiple of the number of ribs, and the pipes are then fitted into one another so that at least one longitudinal rib is introduced into a longitudinal groove, whereby when the pipes are joined to one another in leak-proof manner, the remaining grooves co-operate with the surface of the other pipe to form channels within the wall of the compound pipe formed.

4. A process as claimed in any one of the preceding Claims, wherein said pipes are joined to one another by drawing using a female die and a mandrel.

5. A process as claimed in any one of the preceding Claims, wherein the outer surface of the smaller pipe is at least partially provided with a layer of solder at the contact surfaces with the larger pipe, and that, after the pipes have been drawn, the compound pipe so formed is heated at least to the melting point of the solder.

6. A process as claimed in any one of the preceding Claims, wherein both the outer surface of the smaller pipe and the inner surface of the larger pipe are cleaned prior to assembly of the pipes.

7. A process for the production of a pipe having longitudinal channels, or channels making a small angle to the longitudinal direction of the pipe, within the wall thereof, substantially as hereinbefore described with reference to the drawings.

8. A pipe having longitudinal channels, or channels making a small angle within the longitudinal direction of the pipe, within the wall thereof, produced by a process as claimed in any one of Claims 1 to 7.