GB2530271A

GB2530271A - Tubes

Info

Publication number: GB2530271A
Application number: GB1416355.4A
Authority: GB
Inventors: Mike Dewhirst
Original assignee: S S TUBE TECHNOLOGY Ltd
Current assignee: S S TUBE TECHNOLOGY Ltd
Priority date: 2014-09-16
Filing date: 2014-09-16
Publication date: 2016-03-23
Anticipated expiration: 2034-09-16
Also published as: GB201416355D0; GB2530271B

Abstract

To form a bend in a primary tube 12 (e.g. an internal combustion engine exhaust), first, a sacrificial tube 10 is temporarily is secured (e.g. welded) to the primary tube 12. Next, a bend is formed using the sacrificial tube 10 to support the primary tube 12 and/or apply a bending load; then the sacrificial tube 10 is separated from at least part of the bend formed in the primary tube 12. Thus, when a bend is needed at the end of the primary tube, the sacrificial tube can be removed from the curved primary tube (rather than wasting expensive primary tube material), e.g. in joining two curved sections together to create two closely spaced bends. A bending die 18 may be used, with a mandrel inserted into the primary tube for support. The sacrificial tube may have a lower yield strength than the primary tube (creating a more uniform wall thickness); may have a lower stiffness and lower cost than the primary tube; and may be reused. The bimetallic tube 10, 12 may also be formed by rolling a bimetallic sheet into a tube.

Description

TUBES

This invention relates to tubes, and in particular to methods for use in the manufacture of tubes including one or more bends.

S

Where tubes are to be manufactured from a metallic material such as steel, it is usual for the tubes to be manufactured by rolling of a sheet of material to form the sheet material into a tube, and for the seam formed as the sheet material is formed into the tube to be, for example, welded. Various finishing processes may then be undertaken.

Where it is required for the tube to include a bend, then a mandrel is introduced into the tube, and a load is applied to the tube to bend the tube, the mandrel serving to provide support to the tube, maintaining the inner diameter of the bent part of the tube substantially equal to that of the remainder of the tube.

The formation of two or more bends in a single tube is difficult, especially if the bends are to be formed adjacent one another and are to be orientated differently to one another or to have a different radius of curvature to one another. Where this is required then it is usual to produce separate tube sections including a respective one of the required bends, and to secure the tube sections to one another in the desired orientation, for example by welding and appropriate finishing, to produce the desired shape of tube.

Where a bend is to be formed in a tube or tube section, it is usual, in order to allow the application of the required loadings to the tube to form the bend in the tube, for the tube to include an unbent section to at least one side of the region of the tube in which the bend is to be formed. Where the tube is to include two or more closely spaced bends, as described hereinbefore, then these straight regions must be removed prior to the connection of the tube sections to one another. Usually, the removed material is then scrapped.

In some applications, for example where the tube is to form part of a high specification exhaust system, then the material of the tube may be of, for example, Inconel, titanium) stainless steel or another relatively expensive metal or alloy. Clearly where the material is expensive then such waste is particularly disadvantageous.

A further disadvantage of the technique outlined hereinbefore for use in the formation of bends in tubes is that usually the wall thickness of the tube to the outer (larger radius of curvature) side of the bend is reduced compared to that to the inner (smaller radius of curvature) side thereof. In some applications such variations in wall thickness may not be acceptable or may be undesirable. Even where non-uniform wall thicknesses are permissible, in order to ensure that no part of the finished tube has a wall thickness less than a predetermined amount, a large part of the tube may be over engineered in the sense that it has a greater wall thickness than is required. Clearly, this impacts upon material costs, weight and the like and so is not desired.

It is an object of the invention to provide a method for use in the formation of a bend in a tube in which at least some of the disadvantages with the arrangements outlined hereinbefore are overcome or are of reduced effect.

According to the present invention there is provided a method for use in the formation of a bend in a tube comprising the steps of: securing a length of a sacrificial tube material to a length of primary tube material in which the bend is to be formed; forming a bend in the primary tube material, using the sacrificial tube material to support the primary tube material and/or apply a bending load thereto; and separating the sacrificial tube material from at least part of the bend formed in the primary tube material.

The step of forming a bend in the primary tube material conveniently comprises locating a mandrel therein prior to the application of the bending load thereto.

The sacrificial tube may be of, for example, a relatively low cost material. By the use of such a relatively low cost material it will be appreciated that cost savings can be made. Depending upon the nature of the sacrificial tube material, it may be possible for the sacrificial tube material to be used several times, for example for use in the formation of bends in two or more different lengths of primary material.

The sacrificial tube material may conveniently be of lower yield strength than the primary tube material. In such an arrangement, during the formation of the bend less reduction in the wall thickness of the outer side (greater radius of curvature) part of the bend may occur than in traditional arrangements. Accordingly, the method may be of benefit in applications in which there is a requirement for the tube to be of uniform or substantially uniform wall thickness.

Even where uniform wall thickness is not itself a requirement, by the use of the method tubes can be formed in which the minimum wall thickness is well controlled without needing to form other parts of the tube with a relatively large wall thickness, and so materials savings can be made resulting in cost savings and weight reductions can be made.

The invention further relates to a tube manufactured using the method set out hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 3 are diagrammatic views illustrating stages in the method for use in the manufacture of tubes in accordance with an embodiment of the invention; Figures 4 and 5 are comparisons of a conventional bend formed in a tube with a bend formed in a tube using the technique described with reference to Figures 1 to 3; and Figure 6 is a graph illustrating the stress-strain relationships for the materials used in the tube of FigureS.

Referring firstly to Figures ito 3 of the accompanying drawings, a method of forming a bend in S a tube comprises securing a length or section 10 of a sacrificial or reclaimed material tube to an end of a section 12 of a primary material tube in which a bend is to be formed to form a composite, bi metallic tube 14 so that the sections of sacrificial material and primary material are arranged end-to-end. By way of example, the primary material may comprise an Inconel, titanium or stainless steel material, but it will be appreciated that the invention is not restricted in this regard. Typically the securing operation will be achieved by welding an end of a preformed tube of the sacrificial material to an end of a tube of the primary material of substantially the same diameter. Clearly this requires the materials of the sections 10, 12 to be compatible to being welded to one another. Whilst welding is the currently preferred securing technique, it will be appreciated that the tubes could be secured to one another using other techniques. Furthermore, othertechniques for forming the bimetallic tube are possible. By way of example, sheets of suitable materials could be secured to one another prior to being rolled to form the material into a tubular form.

After formation of the bi metallic tube 14, a mandrel 16 is introduced into the section 12 of the tube 14 of the primary material, and the tube 14 is positioned into a die 18. The die 18 comprises pressure, clamp, wiping and bend sections as is conventional. As the die 18 is of conventional form, its nature and operation will not be described herein in further detail. The die 18 and mandrel 16 serve to hold the section 12 of the tube 14 of the primary material whilst a bending load is applied by another part of the die 18 to the section 10 of the tube 14 of the sacrificial material, the load serving to form a bend in the tube 14. The bend is formed in the part of the tube 14 of the primary material, as illustrated in Figure 3.

Whilst Figures ito 3 illustrate the formation of a90 degree bend in a tube, it will be appreciated that the invention is not restricted in this regard. Likewise, the nature of the die 18 is not of relevance to the invention, and a number of alternative dies or bending processes may be used without departing from the scope of the invention as defined by the appended claims.

As shown in Figure 4, in a bend formed in a tube using a traditional method, the wall thickness of an outer part of the bend, ie that part of the bend of greatest radius of curvature, denoted in Figure 4 as t-outl will be smaller than the nominal wall thickness of an unbent part of the tube, whilst that of the inner part of the bend, denoted as t-inl is of greater wall thickness than the nominal wall thickness. These variations in wall thickness are most pronounced at the end of the bend where the bend is integrally formed with the straight section, deformation of the free end of the tube (as denoted by the line 20 in Figure 4) resulting in less variation in the wall thickness at this part of the bend. If these variations in wall thickness are not taken into account then there is a significant risk that if the tube section bent in this manner is used in a high temperature application such as in an internal combustion engine exhaust system the relatively thin wall thickness regions of the tube may not be capable of withstanding the temperatures and stresses experienced in use, and so there is an increased risk of failure of an exhaust manufactured using the tube if the effect of these variations is not sufficiently accounted for.

In comparison, as shown in Figure 5, in a tube manufactured in accordance with the method described hereinbefore, by appropriate selection of the material of the sacrificial section 10 to be of a lower yield strength and, potentially, a lower stiffness than the material of the primary section 12, when the bend is formed in the tube 14, deformation of the material of the sacrificial section 10 to reduce its wall thickness will occur in preference to the corresponding deformation of the material of the primary section 12. Some of the stresses induced during the bending process are transferred into the straight, sacrificial section 10, leading to a combination of wall thickness change and shearing of the tube material. As shown in Figures, this results in a change in the shape of the joint or connection between the sections 10, 12 as denoted by the line 22, similar to the change in shape denoted by the line 20 at the free end of the tube 14, and less reduction in the wall thickness of the bend formed in the primary section 12. Accordingly, once the bend has been formed and the required bend is cut from the primary section 12, it will be appreciated that the wall thickness of the primary section will be of good uniformity and stresses within the bend will be relatively uniformly distributed. The thickness t-inl will be substantially equal to the thickness t-outl. As a result, the risk of a failure when the bend is used in part of, for example, an exhaust system as mentioned hereinbefore is considerably reduced.

Furthermore, where the primary material is of expensive form, wastage of the expensive primary material is reduced, enhancing manufacturing efficiency.

As the bend section of tube is of good wall thickness uniformity, there is less need to use oversize S material thicknesses in the tube to ensure that a minimum wall thickness is attained.

Figure 6 illustrates the stress-strain relationships of the materials used in the arrangement of Figure 5, line 24 illustrating the characteristics of the primary material and line 26 illustrating the characteristics of the sacrificial material, showing that the sacrificial material has a lower yield strength and lower stiffness than the primary material, but having a higher failure stress than the yield stress of the primary material.

Whilst in the description hereinbefore the sacrificial material section 10 is of reduced yield strength to assist in the formation of a bend of substantially uniform wall thickness, where wall thickness is not of concern but there is a need to avoid wastage of expensive materials, then it may be desired to use the method of the invention but without requiring the sacrificial material to be of reduced yield strength simply to allow the use of a relatively low cost material for the sacrificial material section instead of using a more expensive material in this region. By way of example) the sacrificial section may be of a material with similar or better room temperature mechanical properties than the primary section. If little deformation of the sacrificial material section occurs in use then it may be possible for the sacrificial material section to be reused in such arrangements.

Whilst the description hereinbefore is of specific example embodiments of the invention it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS: 1. A method for use in the formation of a bend in a tube comprising the steps of: securing a length of a sacrificial tube material to a length of primary tube material in S which the bend is to be formed; forming a bend in the primary tube material, using the sacrificial tube material to support the primary tube material and/or apply a bending load thereto; and separating the sacrificial tube material from at least part of the bend formed in the primary tube material.
2. A method according to Claim 1, wherein the step of forming a bend in the primary tube material comprises locating a mandrel therein prior to the application of the bending load thereto.
3. A method according to Claim 1 or Claim 2, wherein the sacrificial tube material is of a lower cost than the primary tube material.
4. A method according to any of the preceding claims, wherein the sacrificial tube material to capable of being reused in the method.
5. A method according to Claim 1 or Claim 2, wherein the sacrificial tube material is of lower yield strength than the primary tube material.
6. A method according to ClaimS, wherein the sacrificial tube material is of lower stiffness that the primary tube material.
7. A tube manufactured using the method of any of Claims ito 6.