GB1569365A - Tube - Google Patents

Description

(54) TUBE (71) We, A/S RAUFOSS AMMUN ISJONSFABRIKKER, a Norwegian Company, of P.O. Box 2, 2831 Raufoss, Norway, do hereby declare the invention for which we pap that a patent may be granted to us.

and the method by which it is to be performed to be particularly described in and by the following statement: - The present invention relates to a tube made of extruded, open profiles which are interconnected along their edges by means of glueing, soldering or the like, to fosm the tube.

More partituistly, but not exclusively, the bRon relates to such tubes adapted for boat exchangers, with longitudinal fins or ribs eluded integrally with the tube wall.

The tube according to the invention may be made of any suitable material. When adapted for heat exchange the material should have good heat conductivity, and aluminium would be weil suited, without being mentioned as a limitation of the scope of the invention.

The most usual method to make finned tubes by extmsion is to extrude the tubes as hollow profiles with fins on one or both sides, making use of a mandrel carried by "bridges" to ftctn the inner surface of the tube. The Abridges" extend radially or are inclined from a tool holder m the press to the inandrel, and the mandrel has a cross section substantially corresponding to the inner cross section of the olbe. By extruding a tube with inner fins the must must have longitadinal slots with substantially the same cross sectional shape as the fins.The slots will have to extend along the entire length of the mandrel, and the depth of the slots will have to correspond to the height of the fins substantially along the entire length Only a slight reduction of the depth might be permitted adjacent the end of the mandrel facing the press piston, because the material to be extruded usually will be able to flow radially inwardly in the slots only to a very small extent. Hence, when the tube is to have long inner fins, i.e. fins which extend tar towards the center of the tube, the slots in the mandrel wilt have to be correspondingly deep, and the mandrel should be only slightly thicker than the diameter of a circle inscribed between the slot bottoms in the portion of the mandrel where the "bridges" are connected.

This portion will be subjected to a high tensional stress caused by the friction between the extruded metal and the mandrel, and there is a danger of fracture in the mandrel. Thus, the depth of the slots (i.e. the radial length of the inner fins in the tube) is limited relative to the main cross sectional dimensions of the tube. Due to the fact that increased cross sectional dimensions (i.e. the diameter of a circular tube) give rise to increased frictional forces because of the increased frictional area, there will also be an absolute limit for the depth of the slots, even if the critical portion of the mandrel has increased cross-sectional dimensions when the tube diameter is increased In the case of tubes of small diameters, the length of the inner fins will be limited by the absolute diameter of the circle inscabed between the slot bottoms.

The limitation mentioned will have the effect that in scrme cases there will not be possible to extrude unitary tubes with at least inner fins having a radial height exceeding a certain limit.

The outer dimensions of the tube, with or without fins to be extruded as a unit is of course limited by the dimensions of the container in the extrusion press.

From these and possibly from other reasons tubes are sometimes made by extruding open profiles, possibly with ribs on at least one side, the profiles being interconnected along their edges by means of gluing, soldering or like to form a tube. This method makes it possible to make extruded tubes with inner fins radially longer than what could be made by extrusion of the tubes as a unit. The method also makes it possible to make tubes having larger outer dimensions that what could be extruded as one unit. The specification of U.S. Patent No. 3,081,824 shows an example of a finned tube made by extrusion of two halves, the halves having fins which, after interconnecting the halves, extend beyond each other. (Figs. 2 and 3 of the patent).

However, according to the specification of this U.S. patent, the interconnection between the profiles is made by joining edges of obtuse or right angled V-shaped cross section, one profile having concave edges forming counterparts to convex edges on the other profile.

These joints, when subjected to forces caused by internal pressure in the tube, are not reliable, because the joining material, such as glue or soldering material, will be subjected to a large component of tensile force. The only way to reduce the tensile stress caused by a certain pressure will then be to increase the wall thickness of the tube, at least in the area of the joint. In most cases, however, such increase of the wall thickness for the only purpose of reducing the tensile stress in the joints in undesirable from more than one reason. Increased thickness means higher material consumption and costs, and local increase of the wall thickness in the joint area may disturb the cross-sectional form undesirably with respect to mounting of end closures at the ends of the tubes or from other reasons.

An object of the present invention is to provide a tube having joints between profiles making parts of a tube, wherein the tensile suess in the joined surfaces is considerably lower than in the known joint, particularly when the tube is subjected to intemal pressure.

The present invention consists in a tube made by inter-connecting lengths of extruded, open profiles along their longitudinal edges, by means of glueing, soldering or the like, to form the tube, the profile lengths being joined by overlapping edge portions of substantial equal widths, the thickness of each portion being approximately half the thickness of the tube wall, one peripheral surface of each edge pootion being a direct extension of one tube wall surface, the outer edge of each edge portion being inclined relatively to a plane tangential to the tube wall in the joint area and each edge portion having a transition to the adjoining tube wall which is inclined in the same direction as the outer edge and in such a manner that the angle of the transition is acute.

In order that the invention may be more readily understood an embodiment thereof will now be described, by way of example, with reference to the accompanying drawing, which is an end view of a tube made according to the invention.

The tube shown in the drawing consists of three profiles 1, 2 and 3 interconnected to form a tube of circular cross section, having fins 4, 5 on the inside and the outside, respectively of the tube wall. The interconnected edge portions 6, 7 in each joint may be jointed by glueing, soldering or other suitable means.

The edge portions 6, 7 have overlapping surfaces 8, 9, the major part of which lie parallel to the wall surfaces of the profiles. The outer edges 10 of the edge portions 6, 7 in each joint are inclined relatively to a plane tangential to the tube wall in the joint area (or to a diametral plane), and so are the transitions 11 between the edge portions 6, 7 and the adjoining walls of full thickness. In the embodiment shown, each of the edge portions 6, 7 have a thickness of approximately half the wall thickness of the tube.

The inclined outer edges 10 and transitions 11 have substantially the same direction within each joint, and this direction is such that the angles in the transitions are acute.

This is important, from more than one reason. The outer edge 10 of each edge portion 6, 7 will thus come into engagement with the inclined transitions 11 in such a way that the edge portions 6, 7 in each joint are prevented from being moved radially away from each other. This will contribute to strengthening the joints. Another advantage is that, during glueing, soldering or other treatment of the joints for assembling the tube there may most advantageously be applied an external pressure to the tube, as this will cause the outer edge 10 of each edge portion 6, 7 to be pressed into the acute inner corner of the transition 11 between the neighbouring edge portion and its adjoining wall. This will cause mutual pressure between the main surfaces 8, 9 of the joints, which is advantageous for achieving a perfect joint.

As will be seen from the drawing, the three profiles 1, 2 and 3 in the embodiment shown which might of course be only two or more than three, are all of the same configuration in cross section. Thus, only one type of profile has to be extruded for making one type of tube.

These joints are particularly advantageous with respect to withstanding internal pressure in the tube. The major surfaces of the joints, extending parallel with the wall surfaces, will then mainly be subjected to shear stresses, and may also have a width along the wall periphery which is chosen in accordance with the inner pressure to be present in the tube during use. Thus, the area of the joined surfaces may be freely chosen without affecting the shape of the tube and the wall thickness is not disturbed in the area of the joined surfaces.

Moreover the joined surfaces have a large area without making it necessary to increase the wall thickness in the area of the joint.

Further, the tube can be made from at least two profiles of the same configuration.

It will be apparent that the invention is not limited to tubes with circular cross sections, and the profiles forming the tube do not need to be mutually identical.

WHAT WE CLAIM IS:- 1. A tube made by interconnecting lengths of extruded, open profiles along their

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. However, according to the specification of this U.S. patent, the interconnection between the profiles is made by joining edges of obtuse or right angled V-shaped cross section, one profile having concave edges forming counterparts to convex edges on the other profile. These joints, when subjected to forces caused by internal pressure in the tube, are not reliable, because the joining material, such as glue or soldering material, will be subjected to a large component of tensile force. The only way to reduce the tensile stress caused by a certain pressure will then be to increase the wall thickness of the tube, at least in the area of the joint. In most cases, however, such increase of the wall thickness for the only purpose of reducing the tensile stress in the joints in undesirable from more than one reason. Increased thickness means higher material consumption and costs, and local increase of the wall thickness in the joint area may disturb the cross-sectional form undesirably with respect to mounting of end closures at the ends of the tubes or from other reasons. An object of the present invention is to provide a tube having joints between profiles making parts of a tube, wherein the tensile suess in the joined surfaces is considerably lower than in the known joint, particularly when the tube is subjected to intemal pressure. The present invention consists in a tube made by inter-connecting lengths of extruded, open profiles along their longitudinal edges, by means of glueing, soldering or the like, to form the tube, the profile lengths being joined by overlapping edge portions of substantial equal widths, the thickness of each portion being approximately half the thickness of the tube wall, one peripheral surface of each edge pootion being a direct extension of one tube wall surface, the outer edge of each edge portion being inclined relatively to a plane tangential to the tube wall in the joint area and each edge portion having a transition to the adjoining tube wall which is inclined in the same direction as the outer edge and in such a manner that the angle of the transition is acute. In order that the invention may be more readily understood an embodiment thereof will now be described, by way of example, with reference to the accompanying drawing, which is an end view of a tube made according to the invention. The tube shown in the drawing consists of three profiles 1, 2 and 3 interconnected to form a tube of circular cross section, having fins 4, 5 on the inside and the outside, respectively of the tube wall. The interconnected edge portions 6, 7 in each joint may be jointed by glueing, soldering or other suitable means. The edge portions 6, 7 have overlapping surfaces 8, 9, the major part of which lie parallel to the wall surfaces of the profiles. The outer edges 10 of the edge portions 6, 7 in each joint are inclined relatively to a plane tangential to the tube wall in the joint area (or to a diametral plane), and so are the transitions 11 between the edge portions 6, 7 and the adjoining walls of full thickness. In the embodiment shown, each of the edge portions 6, 7 have a thickness of approximately half the wall thickness of the tube. The inclined outer edges 10 and transitions 11 have substantially the same direction within each joint, and this direction is such that the angles in the transitions are acute. This is important, from more than one reason. The outer edge 10 of each edge portion 6, 7 will thus come into engagement with the inclined transitions 11 in such a way that the edge portions 6, 7 in each joint are prevented from being moved radially away from each other. This will contribute to strengthening the joints. Another advantage is that, during glueing, soldering or other treatment of the joints for assembling the tube there may most advantageously be applied an external pressure to the tube, as this will cause the outer edge 10 of each edge portion 6, 7 to be pressed into the acute inner corner of the transition 11 between the neighbouring edge portion and its adjoining wall. This will cause mutual pressure between the main surfaces 8, 9 of the joints, which is advantageous for achieving a perfect joint. As will be seen from the drawing, the three profiles 1, 2 and 3 in the embodiment shown which might of course be only two or more than three, are all of the same configuration in cross section. Thus, only one type of profile has to be extruded for making one type of tube. These joints are particularly advantageous with respect to withstanding internal pressure in the tube. The major surfaces of the joints, extending parallel with the wall surfaces, will then mainly be subjected to shear stresses, and may also have a width along the wall periphery which is chosen in accordance with the inner pressure to be present in the tube during use. Thus, the area of the joined surfaces may be freely chosen without affecting the shape of the tube and the wall thickness is not disturbed in the area of the joined surfaces. Moreover the joined surfaces have a large area without making it necessary to increase the wall thickness in the area of the joint. Further, the tube can be made from at least two profiles of the same configuration. It will be apparent that the invention is not limited to tubes with circular cross sections, and the profiles forming the tube do not need to be mutually identical. WHAT WE CLAIM IS:-

1. A tube made by interconnecting lengths of extruded, open profiles along their

longitudinal edges, by means of glueing, soldering or the like, to form the tube, the profile lengths being joined by overlapping edge portions of substantially equal widths, the thickness of each portion being approxi inately half the thickness of the tube wall, one peripheral surface of each edge portion being a direct extension of one tube wall surface, the outer edge of each edge portion being inclined relatively to a plane tangential to the tube wall in the joint area and each edge portion having a transition to the adjoining tube wall which is inclined in the same direction as the outer edge and in such a manner that the angle of the transition is acute.

2. A tube as claimed in claim 1, wherein each profile length has one edge portion located radially outside the middle of the tube wall and one edge portion located radially inside the middle of the tube wall, whereby the profile lengths are of uniform configuration.

3. A tube made by interconnecting lengths of extruded, open profiles along their longitudinal edges, substantially as hereinbefore described with reference to the accompanying drawings.