AU2787000A - High speed metal joining process - Google Patents

Description

WO 00/51776 PCT/AU00/00147 -1 HIGH SPEED METAL JOINING PROCESS Field of the Invention The present invention relates to a method of joining metal 5 surfaces together. More particularly, but not exclusively, the present invention relates to a high-speed method of joining one or more metal surfaces together by utilising some or all of the residual heat energy retained in metal bars formed in a hot rolling process. 10 Background to the Invention The joining of metal surfaces together can be undertaken using a variety of methods. The most common methods are those which involve melting the contact surfaces of the metals that are to be joined together such that the metal surfaces fuse together and then solidify. 15 Methods for melting the contact surfaces include a wide range of welding methods. In addition hot forging, friction stir-welding, brazing and silver soldering methods, which require that the contact surfaces be hot but not be at their melting temperature, can be used. All these methods require that either the parent metal, or an introduced metal, or 20 both metals, be heated up to either their melting temperature, or close to their melting temperature, prior to the joining taking place. It takes considerable energy to heat up the contact surfaces to their melting temperature. For example, the melting point of carbon steel is in the range of between 13750C and 15000C, depending upon 25 exact steel chemistry, and it should be understood that the steel contact surfaces must be rapidly heated up to this temperature, or close to it, for welding to subsequently occur. Consequently, the faster the welding speed, the greater the energy input required to heat up the contact surfaces. This is a fundamental limitation with all current welding 30 methods. Nevertheless, some welding methods are able to heat up metals very quickly and produce welded contact surfaces at fairly high speeds. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -2 For example, Electric Resistance Welding (ERW) is essentially a hot forging process, where the surfaces are heated up and forced together under pressure. It is commonly used to form pipes and tubes. Small pipes made by this method can be manufactured at speeds of up 5 to 30 metres per minute in Australia and at even higher speeds in other countries. However, for larger diameter pipes the welding speed can be much slower, and is typically of the order of from 2 to 5 metres per minute. Another welding method that can be used is high power laser 10 welding, where welding machines of 20 kW power and greater can weld small contact surfaces at speeds of between 5 and 20 metres per minute, depending upon the thickness of the metals being joined. One of the most commonly employed welding methods used is Metal Inert Gas (MIG) welding which has a typical welding speed for 15 common butt joints in the range of from 0.5 to 1.5 metres per minute. In all of the above methods, it is necessary to first raise the temperature of the contact surfaces, or the temperature of the introduced joining or filler metal, to their respective melting temperatures prior to joining the two surfaces together. This initial 20 raising of the temperature requires energy input and transfer, resulting in time delays. This restricts the speed with which metal surfaces can be joined together and therefore prolongs the time taken in the joining process. Steel contact surfaces can also be joined together using a non 25 ferrous "filler or joining" metal with a lower melting point than steel, for example, by using soldering or brazing techniques. "Soft" soldering uses a tin- or lead-based alloy with a melting point lower than 425C, as the filler metal. "Hard" soldering or silver soldering normally uses alloys of silver, copper and/or nickel as the filler metal and these normally 30 have a melting temperature which is higher than 425 0 C but lower than the melting point of steel (13750C). Brazing is very similar to hard Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -3 soldering except that there is also a slight diffusion of the filler metal into the hot base metal, or a surface alloying of the base and filler metals. Although soldering and brazing methods use non-ferrous filler alloys with a lower melting point than steel, these alloys are almost 5 always weaker than steel, and hence a joint achieved using soldering or brazing methods is weaker than a steel-welded joint. For high strength applications, it is therefore necessary to use welding rather than soldering or brazing methods. Nevertheless, for welding, soldering and brazing methods, it is 10 still necessary to raise the temperature of the contact surfaces or the filler wire to at least the melting point of the filler wire. It would therefore be advantageous to use a joining system which requires no additional heat energy input, or very little additional heat energy input, to melt or join the contact surfaces together. This is 15 particularly relevant for the high speed joining of two half-bars to constitute a hollow bar, as described for example in International Patent Application No. PCT/AU93/00486. By using this manufacturing technique, solid half-bars can be hot rolled at high speed in a rolling mill at the equivalent cost of conventional solid bars and subsequently be 20 joined together to form thick-walled hollow bars. In this way the cost of producing such thick-walled hollow bars, when compared with conventional methods such as the 'pierced billet method', can be substantially reduced. However, presently the two half-bars are joined together initially by aligning the surfaces to be joined and then by 25 welding the surfaces together at high speed along their length. When using this two half-bar manufacturing process with conventional welding techniques such as MIG welding, it is also necessary prior to using this joining method to incorporate a recess into each elongate member to accommodate the weld fill. When using this process with laser welding, 30 a recess for weld filler metal is not required. Surprisingly, the present inventor has found that the welding process previously required to join two metal bars can now be Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -4 circumvented by instead utilising the heat energy retained in the bars, from the hot rolling process employed in the formation thereof, to join the longitudinal edges of the two bars together. The heat energy retained within the bar/s has been found to be sufficient to join the 5 edges of the same or indeed of two or more different bars, by pressing the edges together whilst the bar/s are still in the rolling mill. What is also significant is that such a joining process can take place at not less than the speed of the hot rolling process, thereby reducing the time previously taken for such metal surfaces to be joined. Therefore, such 10 a joining process has the advantage of eliminating the requirement to transport the bars past welding heads for the welding process to take place, thus speeding up the manufacturing and production process of hollow bars. The present inventor has further found that the joining process 15 can also be achieved by feeding a strip of an appropriate alloy, by means of a feeder mechanism, between the at least two edges to be joined, followed by pressing the at least two edges against the alloy strip. The heat energy retained within the elongate member from the hot rolling process has been found to be sufficient to cause the alloy 20 strip to melt and form a brazed joint. Once the alloy strip comes into contact with the hot surface, the alloy melts and fuses to the hot metal surface. This melting of the alloy strip has the advantage that the surface tension in the alloy causes it to flow towards any cracks or grooves in the elongate members, thus substantially strengthening both 25 the join and the elongate members themselves. The alloy is subsequently solidified on cooling by passing the joined elongate members through a series of water sprays. The join formed by employing the alloy strip was found to be surprisingly stronger than expected and was found to be sufficiently strong for the use of the 30 hollow bar as a rock bolt, for example. A major advantage of the present invention is that, if the contact surfaces are joined together using a welding process when the bars are Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -5 hot (for example, above 8000C), then the effects of a welding Heat Affected Zone (HAZ) and centre-line cracking within the weld are minimised. This occurs because the welding or joining process is undertaken when the temperature of the bars is high (approximately 5 8000C or above). This temperature is generally higher than the austenising temperature of most carbon steels and therefore the equivalent weld metal in the fusion zone found in conventional welding techniques and the surrounding base metal in the HAZ will be fully annealed. The detrimental effects of HAZ and centre-line cracking in 10 conventional welding are caused principally by rapid cooling of the weld metal and this will not occur if the welding or joining takes place when the base metal in the bar itself is hot. Most steel and metal bars are produced in some type of rolling mill. In particular steel bars, rods, flats and other longitudinal steel 15 sections are commonly produced in a hot rolling mill. The hot rolling process involves taking a billet of steel (typically 12m long by 127mm by 127mm) and heating it up in a furnace to a temperature of between 9000C and 12000C. It is clearly much easier to "deform" or "shape" steel when it is hot rather than when it is cold. When the billet has 20 reached the required temperature, the billet is then taken out of the furnace and passed through a series of rolling stands. These rolling stands are pairs of large rollers, which sequentially reduce the size of the billet down to the shape and size of the final product. A rolling mill may typically have from 10 to 20 rolling stands. 25 The reduction in size of the billet from one rolling stand to another is restricted to within certain limits. However each time the billet passes through a rolling stand, the cross-sectional area of the billet reduces, but the length increases to maintain constant volume. Consequently, the speed of the billet increases each time it passes 30 through a rolling stand. When a billet enters the first rolling stand, it is typically moving at a speed of less than 0.5 metres per second. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -6 However, when the billet leaves the last rolling stand it is typically moving at from 8 to 13 metres per second. During the time the billet leaves the heating furnace until it passes through the last rolling stand, it loses some heat and the 5 temperature drops slightly. The temperature may typically drop from say 11000C to 12000C in the furnace, to approximately 8000C to 10000C at the last rolling stand, although the hot rolling process itself tends to input energy into the bar and maintain the temperature of the billet. When the billet leaves the last rolling stand it is normally formed 10 into the shape and size of the final product, such as a bar or rod. The only additional manufacturing processes performed after the final rolling stand are normally controlled cooling processes, such as passing the bar through a water spray or water bath to rapidly cool the bar to increase surface strength and hardness. These cooling processes 15 would typically rapidly cool the surface of the bar to from 6000C to 7000C. It is therefore evident that products produced using the hot rolling process have a considerable amount of retained heat energy after the final bar, rod or section is formed. This heat energy is normally allowed 20 to dissipate and is therefore wasted. The process described in the present invention utilises this existing heat energy thereby creating a far more energy-efficient and cost-effective process for the production of hollow bars, rods or sections. 25 Summary of the Invention According to the present invention there is provided a process for the high speed joining of opposed metal surfaces, said process including the step of utilising heat energy retained in the metal to fuse 30 said surfaces together. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -7 Preferably the metal surfaces comprise at least one surface of a first elongate member and a further surface of the same first elongate member or at least one surface of a further elongate member. Preferably the joining process takes place in a hot rolling mill. 5 Preferably the joining process further includes the step of pressing the hot surfaces together. Preferably, each metal surface comprises a longitudinal edge of the elongate member. Typically the joining process is carried out at a speed which is not less than that of the production of the hot rolling process. 10 Preferably the or each elongate member is selected from a metal strip or a solid metal half-bar or a single hinged bar that can be deformed or folded into the shape of a hollow bar. Preferably the surface is a longitudinal edge of the metal strip or the solid metal half bar or a single hinged bar. Preferably further the fusing of the pair of 15 surfaces is facilitated by subsequently pressing the surfaces together to form a hollow bar. Preferably the metal of the strip or bar is selected from the group of steel, stainless steel or other steel alloy. More preferably the metal is high strength steel and may contain small quantities of nickel, 20 chromium, vanadium or molybdenum. Preferably the joining process is a combination of utilising the heat energy retained in the metal surface from the hot rolling mill, together with a conventional joining method. Preferably the conventional joining method is selected from hot forging, conventional 25 welding, laser welding or brazing, but is in no way limited to these methods. More preferably the conventional joining method is applied immediately after the longitudinal bar shape has substantially been formed in a hot rolling mill and is typically joined at or after the last rolling stand. 30 In a preferred embodiment of the invention, the high speed joining process further includes the step of incorporating an alloy into the join between the opposed metal surfaces, prior to fusing the Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -8 surfaces together. Preferably, the surfaces are fused together by pressing in a hot rolling mill. Preferably the alloy is fed by a feeder means between the metal surfaces to be joined. Typically, the alloy feeder means is a coil feeder 5 consisting of a coil of alloy strip of, for example, 30 millimetres wide by 0.5 to 1 millimetre thick and 500 metres long. The alloy strip is typically fed by a series of drive rollers and guide boxes that would begin to feed the alloy strip between the two half-bars at the same speed as the rolling mill, i.e. 8 to 10 metres per second. Preferably the feeder means 10 is situated proximate to the hot rolling mill or forms part of the hot rolling mill. Preferably the alloy is in the form of a strip. Preferably further the alloy comprises a brazing filler metal. Preferably the filler metal is selected from an alloy of copper and silver which would be suitable for use on ferrous or non-ferrous metals. Most preferably the filler metal 15 has a melting point in the range between 6000C and 12000C. Preferably the hollow bar is a threaded rock bolt or a drill rod. Preferably when the hollow bar comprises a rock bolt, the filler metal is selected from an alloy having a melting point of about 8500C. Preferably when the hollow bar comprises a drill rod, the joining method 20 would typically comprise high speed welding or forging or by using a filler metal with a relatively high tensile strength and with a consequently higher melting temperature. Preferably as soon as the alloy has melted and has "wetted" the contact surfaces of the half-bars, the joining process further includes 25 the step of passing the bar through a series of water sprays/baths to cool and solidify the alloy. Preferably the alloy strip includes an alloy strip, which is coated with the appropriate fluxes, whereby oxidation of the opposed metal surfaces is reduced. Preferably the joining process is carried out in an inert gas atmosphere, whereby oxidation and scale 30 formation is reduced. Preferably the joining process to form the hollow bar further includes the steps of cropping; descaling to remove scale and oxide; Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -9 and spraying the bar with water to remove any oxide layer formed on the bar during the joining process. Preferably when the joining process used is a hot rolled forging process, the shape of the contact faces is designed to cause disruption 5 or shear of any surface scale or oxide so formed. More preferably, the shape of the contact faces is selected from a tongue and groove combination or off-set chamfered faces. These faces come into contact with each other causing initial shearing or disruption of the oxide layer while further closure results in additional removal of the scale or oxide 10 layer prior to the surfaces being fully joined. The scope of the present invention also extends to a hollow bar formed by the joining process according to the present invention. Throughout this specification the word "bar" refers to any elongate member and includes bars, rods, sections, flats, rounds, 15 angles, half-bars, but is not limited to these in any way. Where the specification refers to an "elongate member", it is to be understood that the invention includes all such variations and modifications of an elongate member and includes billets, bars, rods, flats, sections, tubes, pipes or wires, but is not limited to these. 20 Where the specification refers to an "alloy strip" or to a "metal strip" or to a "filler wire", it is to be understood that the invention includes all such variations and modifications of a "strip" or "wire" or "rod", but is not limited to these and includes one or many "strips", "wires" or "rods. 25 Description of the Drawings Figure 1: Formation of a Hollow Bar either by using two separate Half-Bars, or by forming a Billet around a Central Hole. 30 Figure 2: Forming a Pipe or Tube by forming a Flat around a Central Hole. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -10 Figure 3: High Speed Hot Rolling Joining Processes using a Hot Rolling Mill. Figure 4: Cross Sections showing the detailed Process of Formation of a Hollow Bar by inserting an Alloy 5 Strip between two separate Half-Bars. Detailed Description of the Invention The invention is further described by means of the following non limiting examples. 10 The hollow bar which is the product of the process of the invention can be formed by using either two separate half-bars or by forming a billet around a central hole as shown by the various process stages in Figure 1. The cross-section of billet when it is in the heating furnace can be seen in Figure 1(a). The billet is then passed through a 15 rolling mill and shaped as shown in Figure 1(b). The process of the present invention can be illustrated as shown in Figures 1(c) to 2(f). After subsequent rolling, the billet is formed into a "dog bone" shape (Figure 1(c)). Further rolling and forming of the "dog bone" billet produces a single bar in the shape of two half-bars (Figure 1(d)). One 20 half of the billet is then formed to bring at least one contact surface in contact with another contact surface (Figure 1(e)). An alloy strip is then inserted between at least one pair of contact surfaces prior to the contact surfaces being finally brought together (Figure 1(f)). An alternative process is as shown in Figures 1(g) to 1(j), where 25 the billet is split into two separate bars (Figure 1(g)) which are then rolled in parallel to each other. The two separate bars are then formed into two half-bars by subsequent rolling (Figure 1(h)) which are then are brought together and aligned to form the correct finished bar shape (Figure 1(i)). The half-bars may be joined by inserting an alloy strip to 30 braze half-bars together (Figure 1(j)), or be forged or welded together. Another aspect of the invention relates to the forming of a pipe or a tube by forming a "flat" around a central hole. This process is Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -11 illustrated in Figures 2(a) to 2(f). Initially, the billet is of square cross section when it is introduced into the heating furnace (Figure 2(a)). The billet is then placed in the rolling mill where it becomes of circular cross section (Figure 2(b)). After subsequent rolling, the billet is converted to 5. a rectangular cross-section (Figure 2(c)). Further rolling and forming produces a "flat" (Figure 2(d)). The surface of the "flat" includes both a smooth surface or a "deformed" surface with ridges to increase surface friction. The "flat" is formed into a shape where one longitudinal contact surface can be brought together with another longitudinal contact 10 surface (Figure 2(e)). The longitudinal surfaces so formed could either be welded together or alternatively the "flat" is similarly formed into a circular shape as shown above, but an alloy strip is inserted between the contact surfaces prior to the contact surfaces being finally brought together (Figure 2(f)). 15 The detailed process of the formation of a hollow bar by inserting an alloy strip between two separate half-bars is as illustrated in Figures 4(a) to 4(f). Initially, the billet is substantially formed into the shape of two half-bars although the two halves still form one bar (Figure 4(a)). The billet is then split into two separate half-bars separated by a small 20 gap (Figure 4(b)). An alloy strip is positioned between the two half-bars (Figure 4(c)), with the two half-bars positioned such that they can be moved without damaging the alloy strip (Figure 4(d)). The two half-bars are then brought back into alignment with the alloy strip positioned between them (Figure 4(e)) and then lightly squeezed between a pair or 25 multiple pairs of rollers where the heat from the two hot half-bars causes the alloy strip to melt and fuse with the surface metal of the contact surfaces (Figure 4(f)). Continued heating of the alloy strip from the two hot half-bars causes the alloy strip in the central hole to thereby coat the internal surface of the central hole (Figure 4(g)). The 30 assembled hollow bar is passed through a series of water sprays and allowed to cool, thus solidifying the alloy strip and forming a complete brazed hollow bar (Figure 4(h)). Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -12 In some applications, it may be desirable to join two bars, rods or sections together along one or more surface/s. Alternatively, it may be desirable to join two or more surfaces together within the same bar, rod or section. 5 Bars can be produced using a hot rolling process. It is also possible to produce more than one bar at a time, using a hot rolling process, by splitting the billet in one of the rolling stands and then subsequently rolling and forming more than one bar at a time through the remaining rolling stands. In this manner it is possible to produce 10 two bars simultaneously, as is commonly done with existing technology. This "billet splitting" method of production has two major advantages. Firstly, it effectively increases the rate of reduction of the size of the billet and means that fewer rolling stands are required to produce that particular size of bar and, secondly, it doubles the rate of 15 production. However, in some applications it may be desirable to rejoin the billet together again. For example, if the rolling mill contains 15 rolling stands, a billet could typically be split into two separate bars at about rolling stand number 12. If the two separate bars are formed at this 20 stage and shaped in the final few rolling stands, it is possible to rejoin the two separate bars along one or more longitudinal surface at or after the final rolling stand. Alternatively, one or more longitudinal surfaces within the same bar could be joined together at or after the final rolling stand. 25 Since the single or multiple bars passing through the rolling stands are hot, typically at 9000C to 10000C, it is relatively easy to form and shape them into the desired size, configuration and position. It is therefore possible to align the contact surfaces into their correct position at the end of the rolling mill. 30 By way of example, one billet of steel can be formed around a central hole (Figures 1(d) to 1(f)), or alternatively, two half-bars can be produced simultaneously in a hot rolling mill (Figures 1(g) to 1(i), and Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -13 also Figure 4). If the two half-bars are then brought together at or after the final rolling stand, it is possible to join them together using one of several different process as described below. The two half-bars can be joined together by a brazing-type 5 process. An alloy strip is inserted between the two half-bars (Figures 1(f), 1(j), 2(f), 3(a), and Figure 4) and the two half-bars are lightly squeezed together onto the alloy strip (Figure 4(f)). The heat from the half-bars melts the alloy strip and joins the two half-bars together (Figure 4(g)). The alloy strip is inserted between the two half-bars at 10 the same speed as the bars are moving through the mill at the point at which they contact. In addition, as soon as the alloy has melted and has "wetted" the contact surfaces of the half-bars, the bar can be passed through a water spray bath to cool and solidify the alloy. The alloy strip can be coated with the appropriate fluxes and oxidation of the 15 contact surfaces can be reduced. In addition, the hot bars could also be surrounded by an inert gas to reduce oxidation and scale formation. The two half-bars can be joined together by a forging-type process. The two half-bars are brought together preferably over a mandrel. The two half-bars are then squeezed together at high pressure and are 20 forged together. The mandrel may be made from a suitable material and is preferably water-cooled (Figure 3(b)). The two half-bars can be joined together by a welding-type process, where the welding would occur immediately after the last rolling stand to minimise oxidation and to maximise the temperature of the bar for welding (Figure 3(b)). 25 In the aspect of the high speed welding or joining of pipes, as discussed above, the typical fastest welding or joining speeds are up to 30 metres per minute for small diameter pipes. Steel pipes or tubes are normally produced by rolling a flat strip of steel into a circular shape, such that the two edges of the flat strip of steel are in contact with each 30 other. These two edges are then joined together by Electric Resistance Welding (ERW). Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -14 The ERW process heats the contact edges up to just below the melting point of the steel and the two edges are pushed and fused together. At the start of this process, the steel strip is normally at ambient air temperature, and although some heat energy is input into 5 the strip due to the pipe-forming process, most of the energy to heat the steel comes from the ERW process. It is one aspect of this present invention that the steel strip be produced in a hot rolling mill and that it subsequently be formed into a circular shape and joined together when the steel strip still retains some 10 residual heat from the hot rolling process (Figure 2). For example, if the steel strip was to be welded together when the residual heat of the steel strip was for example, 900C, then the additional heat energy required to join the steel edges together would be reduced. The speed of production could therefore be substantially increased. 15 In addition, if the steel strip was to be formed into a circular shape, for a pipe at, say 900 0 C, rather than at 30 0 C, then it is possible to form a much smaller radius of curvature in the pipe for a given wall thickness. Moreover, the outside surface of the steel strip can be hot rolled with a deformed profile, for applications where increasing the 20 surface friction of the pipe or tube is important (Figure 2(d) as a smooth flat). It is also possible to form the steel strip into a circular shape, again at say 900 0 C, leaving a small gap between the two edges (Figure 2(e))and then introduce a thin strip of metal into this gap (Figure 2(f)). If 25 this metal strip is made from an alloy with a lower melting point than the hot steel pipe, the heat from the steel pipe can be used to substantially melt the alloy strip and join the edges together. The speed of production of pipes could therefore be substantially increased. Alternatively, the joining processes described above could also 30 be used to join one or more longitudinal surfaces in a single hinged bar. The bar could be deformed about its hinge point and one or more Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -15 longitudinal surfaces could be joined together by using one of several different processes as described above. Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as 5 specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof. Those skilled in the art will also appreciate that the invention described herein is susceptible to variations and modifications other 10 than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions, and compounds referred to or indicated in this specification, unless specifically excluded, individually or collectively, and any and all combinations of any two or 15 more of said steps or features. Substitute Sheet (Rule 26) RO/AU

Claims (20)

1. A process for the high speed joining of opposed metal surfaces, said process including the step of utilising heat energy 5 retained in the metal to fuse said surfaces together.

2. A process according to claim 1, wherein the metal surfaces comprise at least one surface of a first elongate member and a further surface of the same first elongate member or at least one surface of a further elongate member. 10

3. A process according to claim 1 or claim 2, wherein the joining process takes place in a hot rolling mill.

4. A process according to claim 3, wherein the joining process further includes the step of pressing the hot surfaces together.

5. A process according to claim 4, wherein the or each metal 15 surface comprises a longitudinal edge of the or each elongate member.

6. A process according to claim 5, wherein the or each elongate member is selected from a metal strip, a solid metal half-bar or a single hinged bar that can be deformed or folded into the shape of a hollow bar. 20

7. A process according to claim 6, wherein the or each surface is a longitudinal edge of the metal strip or the solid metal half bar or the single hinged bar.

8. A process according to claim 7, wherein the fusing of the opposed surfaces is facilitated by subsequently pressing the surfaces 25 together to form a hollow bar.

9. A process according to claim 8, wherein the joining process is a combination of utilising the heat energy retained in the metal surface from a hot rolling mill together with a conventional joining method. 30

10. A process according to claim 9, wherein the conventional joining method is applied immediately after an elongate member has substantially been formed in the hot rolling mill. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -17

11. A process according to any one of claims 1 to 10, wherein the high speed joining process further includes the step of incorporating an alloy into the join between the opposed metal surfaces, prior to fusing the surfaces together. 5

12. A process according to claim 11, wherein the alloy in the form of a strip is fed by a feeder means between the metal surfaces to be joined.

13. A process according to claim 11 or claim 12, wherein the alloy comprises a brazing filler metal. 10

14. A process according to any one of claims 11 to 13, wherein the joining process further includes the step of passing the or each elongate member through a series of water sprays/baths to cool and solidify the alloy as soon as the alloy has melted and has "wetted" the opposed surfaces.

15 15. A process according to claim 14, wherein the alloy strip includes a coated alloy strip.

16. A process according to any one of claims 1 to 15, wherein the joining process is carried out in an inert gas atmosphere, whereby oxidation and scale formation of the opposed metal surfaces is reduced. 20

17. A process according to any one of claims 1 to 16, wherein the joining process is to form a hollow bar and further includes the steps of: (i) cropping; (ii) descaling to remove scale and oxide; and 25 (iii) spraying the bar with water to remove any oxide layer formed on the bar during the joining process.

18. A hollow bar formed by the joining process according to claim 17.

19. A process for the high speed joining of opposed metal 30 surfaces substantially as hereinbefore described with reference to any one of the accompanying drawings. Substitute Sheet (Rule 26) RO/AU WO 00/51776 PCT/AU00/00147 -18

20. Use of the process of any one of claims 1 to 17, substantially as hereinbefore described. Substitute Sheet (Rule 26) RO/AU