WO2012032301A1

WO2012032301A1 - Elongate beam and method for manufacturing elongate beam

Info

Publication number: WO2012032301A1
Application number: PCT/GB2011/001325
Authority: WO
Inventors: Julian M. Allwood; Mark A. Carruth
Original assignee: Cambridge Enterprise Limited
Priority date: 2010-09-10
Filing date: 2011-09-09
Publication date: 2012-03-15

Abstract

Disclosed is a process for manufacturing an elongate steel beam such as an I-beam. Such beams have at least one flange portion and a web portion extending from the flange portion in a depth direction of the web portion. An initial elongate workpiece is provided, the cross sectional shape of the initial elongate workpiece varying with position along the workpiece. The initial elongate workpiece is then rolled so that the variation in cross sectional shape of the initial elongate workpiece is transformed into a corresponding variation in cross sectional shape of the web portion and/or of the flange portion with position along the beam.

Description

ELONGATE BEAM AND METHOD FOR MANUFACTURING ELONGATE BEAM

BACKGROUND TO THE INVENTION Field of the invention

The present invention relates to elongate beams and methods for the manufacture of elongate beams. The invention has particular, but not exclusive, applicability to elongate beams for use in buildings construction.

Related art

Various elongate beams suitable for use in buildings construction are well known. It is particularly well known to use beams formed of steel, in view of this material's high strength and formability into arbitrarily long beams by rolling. Steel beams are typically formed in a shape that increases the efficiency of the beam, by distributing the material of the beam to provide good load-bearing ability and stiffness. Suitable types of beam are typically denoted by a description of the cross-sectional shape of the beam, e.g. I- beam (or H-beam), T-beam, C-beam, etc.

An I-beam has upper and lower flange portions and a web portion integrally formed with the flange portion and extending from the flange portion in a depth direction of the web. The term "depth" is used here since I-beams are typically oriented in use so that the web portion is upright and the upper and lower flange portions are substantially horizontal.

A typical method for manufacturing an I-beam by rolling is set out in Figs. 1 to 10, based on "Manufacturing Processes for Engineering Materials" (5th Edition), by Serope Kalpakjian and Steven R. Schmid, pages 304-305 (1996, published by Prentice Hall). With reference to Figs. 1 and 2, in a first rolling stage a slab (not shown) of uniform thickness and depth (i.e. lateral width) is rolled between shaped rolls 10, 12, rotating about respective rotational axes indicated in Fig. 1 by dash-dot lines. The rolls are shaped in order to provide an elongate workpiece 14 having a cross section resembling a dog bone or dumb bell shape, with a relatively thin longitudinal central part 16 bounded on either side by relatively thick longitudinal edge parts 18, 20. Typically, the workpiece is passed through these rolls multiple times. For each pass, the gap between the rolls is held constant. Fishtail portions at the ends of the workpiece are not shown in any of the drawings.

With reference to Figs. 3 and 4, in a second rolling stage, the workpiece from the first rolling stage is rolled between rolls 30, 32. These rolls have a different shape to the shape of rolls 10, 12, resulting in further reduction in the thickness of the centre 34 of the workpiece, and moving more material from the centre to the relatively thick longitudinal edge parts 36, 38. Typically, the workpiece is passed through these rolls multiple times.

With reference to Figs. 5 and 6, in a third rolling stage, the workpiece from the second rolling stage is rolled between rolls 50, 52 and, oriented perpendicularly to rolls 50, 52, rolls 54, 56. As can be seen from Fig. 6, the result of this third rolling stage is a workpiece 58 that is recognisably similar in shape to an I-beam. Rolls 50, 52 have a stepped profile 51 to roll the central web portion 60 and also the edges 66, 68 of the flange portions 62, 64 of the I-beam. Rolls 54, 56 roll the outer faces of the flange portions 62, 64. With reference to Figs. 7 and 8, in a fourth rolling stage, the workpiece from the third rolling stage is rolled between rolls 70, 72 and, oriented perpendicularly to rolls 70, 72, rolls 74, 76. The fourth rolling stage further evolves the shape, in a similar manner to the third rolling stage. With reference to Figs. 9 and 10, in a fifth rolling stage, the workpiece from the fourth rolling stage is rolled between rolls 90, 92 and, oriented perpendicularly to rolls 90, 92, rolls 94, 96. The main purpose of the fifth rolling stage is to flatten the outer faces of the flange portions using rolls 94, 96. The result of this fifth rolling stage is I-beam 100 having a central web portion 102 and upper 104 and lower 106 flange portions.

SUMMARY OF THE INVENTION

The I-beam shown in Fig. 10 has a constant cross-sectional shape along the beam. For example, it has a constant web depth and a constant flange width. The inventors have realised that it would be of interest to develop a steel beam with a a cross sectional shape that varies along the length of the beam, such as web depth that varies along the length of the beam, and/or a flange width that varies along the length of the beam. This allows the beam to be designed efficiently, in order to reduce the weight of the beam for a particular load distribution.

One way to manufacture such a beam would be by cutting individual rolled plates (of constant thickness) to the required shapes and then joining these plates together into a flange(s) and web configuration. Joining could be performed by welding, for example. However, such beams are inconvenient and complex and expensive to manufacture, and the joints between the plates may be weak, or too heavy compared with a corresponding constant web-depth rolled beam.

The present inventors seek to address this problem by developing the present invention. From a processing perspective, the present inventors have found that it is possible to adjust the cross sectional shape of the beam, by controlling the cross-sectional shape of workpieces in the rolling process. For example, the present inventors have found that it is possible to adjust the web depth of an I-beam by control of the rolling process.

Similarly, they have found that it is possible to adjust the flange width of an I-beam. It is known (see the discussion below) to use control of the thickness distribution of the workpiece in a multi-stage rolling process in order to control the lateral width of the final product. However, to the inventors' knowledge, this is only known in the field of plate or sheet metal rolling, where the aim is to produce sheet or plate of constant thickness and constant lateral width. The term "width" is used here since it is conventional to roll sheet or plate using rolls oriented with horizontal rotational axes.

GB-B-2175229 discloses a method for hot rolling metal workpieces. The workpieces are in the form of slabs and are rolled in order to reduce the thickness of lateral edge portions of the slab to a greater extent than the centre of the slab. The result is a rolled workpiece having a longitudinal ridge extending along the centre of the slab. It was advantageously found in GB-B-2175229 that rolling first the lateral edge portions of the slab and then rolling out the thicker central portion allowed the overall lateral width of the slab to be increased in a convenient manner. The result is a finished workpiece of uniform thickness.

EP-A-164265 discloses a similar process to GB-B-2175229, but in EP-A-164265, the slab is first rolled in order to reduce the thickness of a central portion of the slab, leaving longitudinal ridges extending along the workpiece spaced laterally from the central portion. These longitudinal ridges are then rolled out to give a finished workpiece of uniform thickness.

US-A-4,392,371 discloses a method of plate rolling in which a slab is first rolled to increase its lateral width and then rolled longitudinally to a required final thickness. However, this can cause undesirable variations in the thickness of the final rolled workpiece. Such variations in the final rolled workpiece are reduced by careful calculation and control of the thickness distribution of the workpiece during an initial rolling step. This process is disclosed in more detail in Yanazawa et al 1980 [T. Yanazawa et al, "Development of a New Plan View Pattern Control System in Plate Rolling" Kawasaki Steel Technical Report No. 1 , September 1980, pp. 33-46].

US-A-4, 730,475 discloses rolling processes in which the lateral distribution of thickness of the workpiece is controlled in order to control the final lateral width of the workpiece to be constant. The result is a finished workpiece of uniform thickness.

In a first aspect, the present invention provides an elongate beam formed of steel, the beam having at least one flange portion and a web portion integrally formed with the flange portion and extending from the flange portion in a depth direction of the web, wherein the cross sectional shape of the beam varies with position along the beam.

In a second aspect, the present invention provides an elongate beam formed of steel, the beam having at least one flange portion and a web portion integrally formed with the flange portion and extending from the flange portion in a depth direction of the web, wherein:

the depth of the web varies with position along the beam; and/or

the width of the flange varies with position along the beam. In a third aspect, the present invention provides an elongate beam formed of steel, the beam having at least one flange portion and a web portion integrally formed with the flange portion and extending from the flange portion in a depth direction of the web, wherein the width of the flange portion varies with position along the beam. In a fourth aspect, the present invention provides an elongate beam formed of steel, the beam having at least one flange portion and a web portion integrally formed with the flange portion and extending from the flange portion in a depth direction of the web, wherein the depth of the web varies with position along the beam. In a fifth aspect, the present invention provides a process for manufacturing an elongate beam having at least one flange portion and a web portion extending from the flange portion in a depth direction of the web portion, the process including the steps:

providing an initial elongate workpiece wherein the cross sectional shape of the initial elongate workpiece varies with position along the workpiece;

rolling the initial elongate workpiece to provide the at least one flange portion and the web portion, the variation in cross sectional shape of the initial elongate workpiece being transformed into a corresponding variation in cross sectional shape of the web portion and/or of the flange portion with position along the beam.

In a sixth aspect, the present invention provides a process for manufacturing an elongate beam having at least one flange portion and a web portion extending from the flange portion in a depth direction of the web, wherein the depth of the web varies with position along the beam, the process including the steps:

a first rolling step to provide an initial elongate workpiece having an initial flange portion and an initial web portion extending from the initial flange portion in a depth direction of the initial web portion, wherein the first rolling step is controlled so that the thickness of the initial web portion varies with position along the initial elongate workpiece

a second rolling step in which the initial elongate workpiece is rolled to reduce the variation in thickness of the initial web portion, thereby providing a variation in depth of the web with position along the beam.

In a seventh aspect, the present invention provides a process for manufacturing an elongate beam having at least one flange portion and a web portion extending from the flange portion in a depth direction of the web, wherein the width of the flange portion varies with position along the beam, the process including the steps:

providing an initial elongate workpiece wherein the thickness of the initial elongate workpiece varies with position along the workpiece; and rolling the initial elongate workpiece to provide the at least one flange portion and the web portion, the variation in cross sectional shape of the initial elongate workpiece being transformed into a variation in width of the flange portion with position along the beam.

It is understood that any of the aspects of the invention may be combined, for example to provide a beam having both a web depth which varies with position along the beam and a flange width which varies with position along the beam. Preferred and/or optional features of the invention will now be set out. These are applicable either singly or in any combination with any aspect of the invention, unless the context demands otherwise.

In the process, it is preferred that the initial elongate workpiece is provided with a deliberate and substantial variation in cross sectional shape with position along the initial elongate workpiece. Accordingly, there is provided a thickness variation in at least one dimension with position along the initial elongate workpiece. In at least one of the subsequent rolling steps, in which rolling takes place so as to reduce the thickness variation with position along the initial elongate workpiece, the variation in thickness is at least partially rolled out in order to transform the initial elongate workpiece thickness variation into a corresponding variation in cross sectional shape of the web portion and/or of the flange portion in a direction orthogonal to the thickness variation with position along the initial elongate workpiece. The flange portion and the web portion typically meet at an intersection region of the beam. Preferably, the web portion extends from the intersection region so that the depth direction of the web portion is substantially perpendicular to the width direction of the flange portion. It is to be noted that, regardless of the orientation of the beam, the thickness direction of the flange portion should be considered in a direction perpendicular to the width direction of the flange portion. Similarly, the thickness direction of the web portion should be considered in a direction perpendicular to the depth direction of the web portion. Preferably, the variation in cross-sectional shape of the web portion with position along the beam is a variation in web depth with position along the beam. Preferably, the variation in cross-sectional shape of the flange portion with position along the beam is a variation in flange width with position along the beam. The integration of the flange portion with the web portion could in theory be achieved by extrusion. However, extrusion of a steel I-beam is not a practical proposition. It could also be done using a metallic rapid prototyping process (e.g. DDM), but this would be impractically slow, and exceptionally expensive. Furthermore, the integration of the flange portion with the web portion could in theory be achieved by machining a slab of material in order to cut away material to form the web portion. This would, however, be very inefficient. In general, the integration of the flange portion and the web portion is achieved by working the shape of the beam from a single starting workpiece. It is expressly considered here that a beam comprising initially separate flange and web portions that are subsequently welded together does not have a web portion integrally formed with the flange portion. Furthermore, a web portion which is cut in order to remove a section of the web portion, the remaining sections being rejoined by welding, is also not considered to be a web portion which is integral and continuously extending between first and second flange portions. It is noted here that in the process of any aspect of the invention, it is not necessary for the first rolling step to be the very first rolling treatment to which the workpiece is subjected. The workpiece may be subjected to previous rolling treatments. g

Where the depth of the web portion varies, preferably, for that beam, the minimum depth of the web portion is d_web and, for that beam, the maximum depth of the web portion is at least 1.1d_web. A typical maximum web depth is, for example, 1.5d_web. Thus, preferably, the maximum web depth is at least 1.5d_Web-

Preferably, the web portion has substantially uniform thickness t_web along the beam. The minimum depth of the web portion may be at least 5t_web-

Where the width of the flange portion varies, preferably, for that beam, the minimum width of the flange portion is w_flan_ge and the maximum width of the flange portion, for that beam is at least 1.1 w_flange- A typical maximum flange width is, for example, 1.5w_flang_e. Thus, preferably, the maximum flange width is at least 1 .5Wfi_ange-

Preferably, the flange portion has substantially uniform thickness t_flange along the beam. The minimum width of the flange portion may be at least 5tfi_ang_e.

Preferably, the flange portion has a width (e.g. in a direction parallel to the thickness direction of the web portion) of at least 5t_web. Where the width of the flange portion varies, the flange portion may have a width of at least 5t_web at at least one position along the beam. Furthermore, preferably the flange portion has a thickness (e.g. in a direction parallel to the depth direction of the web portion) of at least 0.5t_web. In some

circumstances, the thickness may be referred to as flange depth, as it is measured in a direction parallel to the depth direction of the web portion. Preferably, two flange portions are provided, bounding the web portion at the limits of the depth of the web portion. It will be understood that the features of the flange portion described herein, including the variable flange width feature of any aspect, may apply to one or more, for example each, flange portion. The elongate beam may be one of an I-beam, a C-beam, a T-beam and an L-beam. An I-beam (also called an H-beam in some countries) is most preferred.

Preferably, the length of the beam is at least 1 m. Preferably, the width of the flange portion is at least 5 cm. Preferably, the thickness of the web portion is at least 3 mm.

Preferably, the beam is formed of steel.

Where a beam with a web depth which varies with position along the beam is formed, preferably the method comprises:

a second rolling step in which the initial elongate workpiece is rolled to reduce the variation in thickness of the initial web portion, thereby providing a variation in depth of the web with position along the beam. Preferably, in the process, in the first rolling step, the depth of the initial web portion is substantially constant along the initial elongate workpiece.

The process may include a further rolling step, intermediate the first and second rolling steps, in which the initial web portion is selectively rolled to reduce the variation in thickness of a selected part of the initial web portion extending along the initial elongate workpiece, thereby providing an intermediate elongate workpiece having an intermediate web portion with a remaining non-selected part of the intermediate web portion retaining a greater variation in thickness than the selected part of the intermediate web portion. Preferably, in the second rolling step, the non-selected part of the intermediate web portion is then rolled and the development of the depth of the elongate beam is unconstrained in at least one direction.

In the further rolling step, development of the depth of the elongate beam may be constrained by at least one roll.

In the further rolling step, the selected part of the initial web portion may be a strip located proximal the flange portion. Where there is a second flange portion, the selected part of the initial web portion may be longitudinal strips located proximal each flange portion, leaving a central, longitudinally extended non-selected part of the intermediate web portion having a greater variation in thickness than the selected part of the intermediate web portion.

After the further rolling step but before the second rolling step, preferably the thickness of the selected part of the intermediate web portion is substantially constant. This allows the second rolling step to concentrate only on rolling out the thickness of the non- selected part of the intermediate web portion, without problems associated with trying to ensure uniform thickness in the web portion proximal the flange portion. After the second rolling step, preferably the thickness of the web portion is substantially equal to the thickness of the selected part of the intermediate web portion after the further rolling step but before the second rolling step.

Where a beam with a flange width which varies with position along the beam is formed, preferably the method comprises:

a first rolling step in which the initial elongate workpiece is rolled to provide an intermediate elongate workpiece having at least one intermediate flange portion having a width direction and an intermediate web portion extending from the flange portion in a depth direction of the web portion, wherein the thickness of the intermediate flange portion varies with position along the intermediate elongate workpiece; and

a second rolling step in which the intermediate elongate workpiece is rolled to reduce the variation in thickness of the intermediate flange portion, thereby providing a variation in width of the flange with position along the beam.

In the second rolling step, the development of the width of the flange portion may be constrained by at least one roll. However, preferably development of the width of the flange portion is unconstrained. The width of the intermediate flange portion may be substantially constant along the intermediate elongate workpiece.

Preferably the initial elongate workpiece is formed by an initial rolling step, carried ourt prior to the first rolling step, wherein the rolling is controlled so that the depth of the initial elongate workpiece varies with position along the initial elongate workpiece.

Further preferred (or simply optional) features of the invention are set out below.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention are described below, with reference to the accompanying drawings, briefly described here:

Figs. 1-10 illustrate a known I-beam rolling process.

Fig. 11 shows a schematic view of an I-beam according to an embodiment of the invention.

Fig. 12 illustrates schematically the development of variable web depth by rolling.

Figs. 13-28 illustrate a process according to a preferred embodiment of the invention. Fig. 13 shows a first rolling stage.

Fig. 14 shows a perspective view of the workpiece resulting from the first rolling stage. Fig. 15 shows a second rolling stage.

Fig. 16 shows an end view of the workpiece resulting from the second rolling stage.

Fig. 17 shows a perspective view of the workpiece resulting from the second rolling stage. Fig. 18 shows a third rolling stage.

Fig. 19 shows an end view of the workpiece resulting from the third rolling stage.

Fig. 20 shows a perspective view of the workpiece resulting from the third rolling stage. Fig. 21 shows a fourth rolling stage.

Fig. 22 shows an end view of the workpiece resulting from the fourth rolling stage.

Fig. 23 shows a perspective view of the workpiece resulting from the fourth rolling stage. Fig. 24 shows a final rolling stage.

Fig. 25 shows an end view of the beam resulting from the final rolling stage.

Fig. 26 shows a top view of the beam resulting from the final rolling stage.

Fig. 27 shows a side view of the beam resulting from the final rolling stage.

Fig. 28 shows a perspective view of the beam resulting from the final rolling stage.

Fig. 29 shows an example load case examined is for a simply supported 2m span beam, carrying a uniform distributed load of 100kN/m.

Figs. 30-33 show a modified process according to a preferred embodiment of the invention.

Fig. 30 shows a first rolling stage.

Fig. 31 shows a perspective view of an intermediate elongate workpiece.

Fig. 32 shows a second rolling stage.

Fig. 33 shows a perspective view of the beam resulting from the second rolling stage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS. AND FURTHER OPTIONAL FEATURES OF THE INVENTION

In the preferred embodiments, the formation of an I-beam for use in buildings

construction will be considered. However, other beam formats, such as L-beam, T-beam, C-beam, etc., can be formed in a corresponding manner. Fig. 11 shows a schematic view of an I-beam 200 having a web portion 202 with upper 204 and lower 206 flange portions. The web portion has a depth that varies with distance along the longitudinal direction of the I-beam. Such a configuration can reduce the required weight of an I-beam for a specific load distribution.

An I-beam with varying web depth can be produced by rolling. Briefly stated, the process provides a workpiece having a constant web depth but variable web thickness with longitudinal position along the workpiece. Subsequently subjecting this workpiece to rolling to roll out the variations in web thickness (i.e. to provide uniform web thickness) causes flow of the material in the web. Provided that the depth development of the web is suitably unconstrained, this allows the provision of variable web depth. This is illustrated schematically in Fig. 12, showing opposing rolls 210, 212. The rollgap 214 between rolls 210, 212 is held constant. Where the workpiece 216 has a web thickness that is greater than the rollgap 214, material will flow in the web to increase the web depth.

A preferred process for producing a beam having a web depth which varies with position along the beam, will now be described in greater detail, with reference to Fig. 13-28. Note that in each rolling stage, it is possible to pass the workpiece through the rolls only one time. However, for some or all of the rolling stages, it is preferred to pass the workpiece through the rolls multiple times, in order to avoid forming defects in the material. In Fig. 13, opposed rolls 300, 302 are provided. Rolls 300, 302 are rotatable about respective axes 304, 306. A further set of rolls 308, 310 is provided, orthogonal to rolls 300, 302. In use, the roll gap between rolls 300, 302 is variable by adjusting the distance D1 between rolling axes 304, 306. Starting with a workpiece of rectangular cross section that this constant along the length of the workpiece, rolling of the workpiece can be performed whilst the distance D1 is varied during a single (and, optionally, subsequent) rolling passes. The roll gap between rolls 308, 310 is held constant.

The result of this is a workpiece 312 as illustrated in Fig. 14. Workpiece 312 has a constant depth d1 but a thickness t1 which varies along the length of the workpiece, according to the control of D1 during the rolling stage.

The next stage of the rolling process is shown in Figs. 15-17 and corresponds to the rolling stage shown in Figs. 1 and 2.

In Fig. 15, rolls 320, 322 are used to roll the workpiece resulting from the previous rolling stage shown in Figs 13 and 14. The shape of the rolls 320, 322 is similar to that of rolls 10, 12 in Fig. 1 , in that the rolls are shaped in order to provide a workpiece 324 having a cross section resembling a dog bone or dumb bell shape. However, in the rolling stage shown in Fig. 15, the roll gap is varied as the workpiece passes through the rollers, by control of D2. Fig. 16 shows an end view of workpiece 324. Fig. 17 shows a perspective view of workpiece 324.

The next stage of the rolling process is shown in Figs. 18-20 and corresponds to the rolling stage shown in Figs. 3 and 4. Again, the roll gap between rolls 330, 332 is varied by control of D3 in order to provide workpiece 334, shown in end view in Fig. 19 and in perspective view in Fig. 20, having a web portion 336 with constant depth d3 but varying thickness t3 along the length of the workpiece. The next stage of the rolling process is shown in Figs. 21 -23 and has no equivalent rolling stage in the process illustrated in Figs. 1 -10, although is similar in some respects to the rolling stage shown in Figs. 5 and 6. The workpiece is passed through opposed rolls 350, 352 and opposed rolls 354, 356 (orthogonally disposed compared with rolls 350, 352). In this stage, the roll gap between rolls 350 and 352 is held constant during each rolling pass of the workpiece. Similarly, the roll gap between rolls 354 and 356 is held constant during each rolling pass of the workpiece. Rolls 350, 352 have annular projections 358, 360 disposed axially adjacent a central channel 362. Annular projections 358, 360 are located in order to reduce the thickness of the web portion of the wok piece only in regions close to the flange portions. Rolls 354, 356 flatten the outer surfaces of the flange portions and prevent the overall depth of the workpiece from varying along the length of the workpiece.

The result of this rolling stage is shown in Figs. 22 and 23. Fig. 22 shows an end view of the workpiece 364 and Fig. 23 shows a perspective view of the workpiece 364. Web portion 366 has peripheral longitudinal regions 368, 370 of relatively small, constant thickness and a central longitudinal region 372 of relatively large but variable thickness t4. Note that the depth d4 of web portion 366 is constant, with the result that the flanges 374, 374 are parallel.

The final stage of the rolling process is shown in Figs. 24-28. In Fig. 24, rolls 400, 402 oppose each other and, at least for the final pass of the workpiece, have a constant roll gap. The roll gap can also be held constant for previous (i.e. non-final) passes of the workpiece, but this is not considered to be essential. The rolls 400, 402 are shaped in order to fit between flanges 374 and 376 of the workpiece 364 from the previous rolling stage, in order to roll out the thickness variations of the workpiece. In this embodiment, there is no constraint on the flanges in Fig. 24, and thus the web can increase in depth in each direction parallel to the rolling surface of each roll 400, 402. In other embodiments, one of the flanges may be constrained, in order to provide depth development of the web in one direction only (e.g. in order to form a beam having one planar and one curved flange, as in Fig. 11 ). The result of the final rolling stage is shown by the views of the resultant beam 410 in Fig. 25 (end view), Fig. 26 (top view), Fig. 27 (side view) and Fig. 28 (perspective view). In these drawings, the web 412 has a varying depth d5 along the length of the beam, but a constant thickness t5. Consequently, the flanges 414, 416 are curved along the length of the beam.

Summarising the preferred process, it can be seen that the rolling process proceeds initially in the same manner as a conventional I-beam production process, using a set of different shaped rolls to gradually produce an l-shaped cross-section. However, the size of the roll gap is varied along the length of the beam, with (in the illustrated embodiment) a larger roll gap towards the lengthwise centre of the beam and a narrower gap at the lengthwise ends of the beam. This produces a workpiece with a web of variable thickness, but uniform depth. When the web thickness is then reduced, the material flows in a manner similar to that shown in Fig. 12. In areas of increased thickness, there is a larger outward flow of material, so the flanges are moved further apart.

Consequently, a workpiece of variable web thickness can be converted into a beam of variable web depth. The advantage of a variable web depth beam is that it allows the beam geometry to be optimized for a particular application. Calculations have shown that an optimized beam may be around one third lighter than a conventional beam, giving a significant overall material saving. Although such a beam could, in theory, be produced by other means, it is advantageous to produce the beam by hot rolling as existing manufacturing technology can be used, and a high output volume can be achieved. Industrially practical alternative methods would rely on cutting and welding, which would be more labour intensive, more expensive, and may produce an inferior product. The economic benefit to the producer is considerable. The present inventors have carried out experimental work on a mini rolling mill, using modelling clay (Plasticine™). Modelling clay provides a good model for hot steel, the results show that it is possible to produce an l-section beam with a variable web depth. This proof of principle demonstrated by the inventors indicates that similar results would be obtained on a hot steel rolling mill.

The following calculations are to determine the weight savings which can be achieved by using an optimized beam with a varying web depth. The load case examined is for a simply supported 2m span beam, carrying a uniform distributed load of 100kN/m, as shown in Fig. 29.

Typically, steel I-beams are purchased directly from a steel supplier, e.g. Corus in the UK. The beams available from Corus are published in a table of standard universal beam sections which lists the different geometries which are available. If the beam geometry is restricted to those available in these tables, then a value can be obtained for the mass of a standard beam which is suitable for the load case given above and shown in Fig. 29.

If it were possible to choose any flange/web dimensions, rather than just those available in the standard table, then it is possible to reduce the mass of the beam required for the load case given above and shown in Fig. 29. However, such a the beam would still have constant web depth.

The three values listed below are for (1) an optimized beam with variable web depth (2) a straight beam with constant web depth but with no restrictions placed on flange/web thickness, and (3) a standard section straight I-beam taken from the tables published by Corus.

1. Mass of Optimized, Variable Web Depth Beam: 30kg

2. Mass of Straight l-Beam: 35kg 3. Mass of Standard Section l-Beam, taken from tables: 46kg

Therefore the variable web depth beam is 35% lighter than a standard section beam, and around 15% lighter than a non-standard straight beam.

A preferred process for producing a beam of variable flange width will now be described in greater detail, with reference to Figs. 30-33. Note that in each rolling stage, it is possible to pass the workpiece through the rolls only one time. However, for some or all of the rolling stages, it is preferred to pass the workpiece through the rolls multiple times, in order to avoid forming defects in the material.

A workpiece 312 as illustrated in Fig. 14 is produced, by a process as described above with reference to Fig. 13. The next stage of the rolling process is shown in Figs. 30 and 31 , and corresponds to the rolling stage shown in Figs. 1 and 2. Rolls 500, 502 are used to roll the workpiece resulting from the previous rolling stage shown in Figs. 13 and 14. The shape of the rolls 500, 502 is similar to that of the rolls 10,12 in Fig. 1 , in that the rolls are shaped in order to provide a workpiece 504 having a cross-section resembling a dog bone or dumb bell shape. It will be understood that as the workpiece is rolled between the rolls 500,502, the thickness of the forming flanges 506,508 is not constrained. Accordingly, at points along the length of the workpiece 312 resulting from the previous rolling stage where the thickness is larger, on rolling between the rolls 500, 502, excess material flows to form thicker portions of the forming flanges 506,508.

The resulting workpiece 504 is shown in Fig. 31. It will be seen that the flanges 506, 508 have a constant width w6 but a thickness t6 which varies with position along the workpiece. Further intermediate rolling stages may be carried out, before and/or after the rolling stage described with reference to Figs. 30 and 31 , for example in order further shape the workpiece, e.g. to reduce the thickness of the web, or to provide a web with a depth which varies with position along the beam.

The final stage of the rolling process is shown in Fig. 32. In this stage, an arrangement of two outer rolls 600 and 602, and four inner rolls 604, 606, 608 and 610 is used. The workpiece 614 is shown in rolling position, and has two flange portions 612 and 616. At least for the final pass of the workpiece, there is a constant roll gap D4 between the two outer rolls 600 and 602. Similarly, at least for the final pass of the workpiece, there is a constant roll gap between outer roll 600 and inner rolls 604 and 608, and between outer roll 602 and inner rolls 606 and 610. The roll gaps can be kept constant for previous (i.e. non-final) passes of the workpiece, but this is not considered to be essential. In this way, as flange 612 passes between outer roll 600 and two inner rolls 604 and 608, the thickness variation of the flange is rolled out. Thus, the flange width can increase in each direction parallel to the rolling surface of each roll 600, 604 and 608. Similarly, as flange 616 passes between outer roll 602 and two inner rolls 606 and 610, the thickness variation of the flange is rolled out. Thus, the flange width can increase in each direction parallel to the rolling surface of each roll 602, 606 and 610.

The resulting beam 614 is shown in Fig. 33. It can be seen that the beam 614 has two flanges 612, 626 which both have constant thickness t7. Both of the flanges 612 and 616 have a width w7 which varies with position along the beam. These embodiments have been described by way of example. Modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person on reading this disclosure and as such are within the scope of the present invention.

Claims

1 . A process for manufacturing an elongate beam having at least one flange portion and a web portion extending from the flange portion in a depth direction of the web portion, the process including the steps:

(i) providing an initial elongate workpiece wherein the cross sectional shape of the initial elongate workpiece varies with position along the workpiece;

(ii) rolling the initial elongate workpiece to provide the at least one flange portion and the web portion, the variation in cross sectional shape of the initial elongate workpiece being transformed into a corresponding variation in cross sectional shape of the web portion and/or of the flange portion with position along the beam.

2. A process according to claim 1 wherein the variation in cross-sectional shape of the web portion with position along the beam is a variation in web depth with position along the beam, and/or wherein the variation in cross-sectional shape of the flange portion with position along the beam is a variation in flange width with position along the beam.

3. A process according to claim 1 or claim 2, for manufacturing an elongate beam wherein the depth of the web varies with position along the beam, wherein the method comprises:

a first rolling step to provide an initial elongate workpiece having an initial flange portion and an initial web portion extending from the initial flange portion in a depth direction of the initial web portion, wherein the first rolling step is controlled so that the thickness of the initial web portion varies with position along the initial elongate workpiece; and

4. A process according to claim 3 wherein, in the first rolling step, the depth of the initial web portion is substantially constant along the initial elongate workpiece.

5. A process according to claim 3 or claim 4 including a further rolling step, intermediate the first and second rolling steps, in which the initial web portion is selectively rolled to reduce the variation in thickness of a selected part of the initial web portion extending along the initial elongate workpiece, thereby providing an intermediate elongate workpiece having an intermediate web portion with a remaining non-selected part of the intermediate web portion retaining a greater variation in thickness than the selected part of the intermediate web portion.

6. A process according to claim 5 wherein in the second rolling step, the non- selected part of the intermediate web portion is rolled and the development of the depth of the elongate beam is unconstrained in at least one direction.

7. A process according to claim 5 or claim 6 wherein in the intermediate rolling step, development of the depth of the elongate beam is constrained by at least one roll.

8. A process according to any one of claims 5 to 7 wherein, in the further rolling step, the selected part of the initial web portion is a strip located proximal the flange portion.

9. A process according to any one of claims 5 to 8 wherein, in the further rolling step, the selected part of the initial web portion comprises longitudinal strips located proximal each flange portion, leaving a central, longitudinally extended non-selected part of the intermediate web portion having a greater variation in thickness than the selected part of the intermediate web portion.

10. A process according to any one of claims 5 to 9 wherein, after the further rolling step but before the second rolling step, the thickness of the selected part of the intermediate web portion is substantially constant.

11. A process according to claim 10 wherein, after the second rolling step, the thickness of the web portion is substantially equal to the thickness of the selected part of the intermediate web portion after the further rolling step but before the second rolling step.

12. A process according to claim 1 or claim 2 for manufacturing an elongate beam wherein the width of the flange varies with position along the beam, wherein the method comprises:

13. A process according to claim 12 wherein the width of the intermediate flange portion is substantially constant along the intermediate elongate workpiece.

14. A process according to claim 12 or claim 13 wherein the initial elongate workpiece is formed by an initial rolling step in which the rolling is controlled so that the depth of the initial elongate workpiece varies with position along the initial elongate workpiece.

15. An elongate beam formed of steel, the beam having a first flange portion, a web portion, and optionally a second flange portion, wherein the web portion is integrally formed with the first flange portion, and with the second flange portion if present, the web portion itself being integral and continuously extending from the first flange portion in a depth direction of the web to the second flange portion, if present, wherein the cross sectional shape of the beam varies with position along the beam.

16. An elongate beam according to claim 15 wherein the depth of the web varies with position along the beam.

17. An elongate beam according to claim 16 wherein the minimum depth of the web is d_web and the maximum depth of the web is at least 1.1d_web

18. An elongate beam according to any one of claims 15 to 17 wherein the web has substantially uniform thickness along the beam.

19. An elongate beam according to any one of claims 15 to 18 wherein the width of the first and/or second flange portion varies with position along the beam.

20. An elongate beam according to claim 19 wherein the minimum width of the first and/or second flange portion is Wnange and the maximum width of the first and/or second flange portion is at least 1.1w_flange.

21. An elongate beam according to claim 19 or claim 20 wherein the first and/or second flange has substantially uniform thickness along the beam.

22. An elongate beam according to any one claims 15 to 21 wherein the beam is one of an I-beam, an H-beam, a C-beam, a T-beam and an L-beam.