AU2011349108A1

AU2011349108A1 - Control of coating of members

Info

Publication number: AU2011349108A1
Application number: AU2011349108A
Authority: AU
Inventors: David Brawdly HARRISON; Greg Adrian Van Arkel
Original assignee: Australian Tube Mills Pty Ltd
Current assignee: Austube Mills Pty Ltd
Priority date: 2010-12-22
Filing date: 2011-12-19
Publication date: 2013-05-02
Anticipated expiration: 2031-12-19
Also published as: WO2012083345A1; AU2011349108B2; AU2011349108B8; NZ611941A

Abstract

An in-line process is disclosed for galvanising an elongate member with a coating that comprises zinc and aluminium. The aluminium is in a range of 5-20 wt%. The process comprises cleaning and applying a flux that is free from alkali metal to an external surface of the member. The process also comprises drying the flux on the member and pre-heating the member. The process further comprises passing the pre-heated member through a bath comprising the coating of zinc and aluminium and then removing the coated member.

Description

WO 2012/083345 PCT/AU2011/001628 CONTROL OF COATING OF MEMBERS TECHNICAL FIELD An in-line process for continuously coating an elongate member with a Zn/Al 5 coating is disclosed. A coated member resulting from such a process is also disclosed. The member may e.g. be of steel and may take the form of an open section, a closed section, or wire, rod, bar, etc. BACKGROUND ART 10 An in-line galvanising process is known in which a pure zinc coating is applied to a profile section. An example of such an in-line process is shown in AU 708379, and the process of AU 708379 is also observed to increase the yield strength of the formed section (known as the "Duragal effect"). The process of AU 708379 employs a galvanising stage which can be referred to 15 as "oxidising" or "inert" as a reducing atmosphere is not ensured. In the past, this has meant that such processes have not been suitable for use with zinc alloys that comprise amounts of aluminium above 0.3%. Generally, for galvanising with zinc-aluminium alloys, a reducing atmosphere is required. US 4,738,758 discloses a process in which a zinc-aluminium alloy is deposited 20 on a ferrous (e.g. steel) substrate. To prevent surface defects (such as impartial/uneven coverage, black spots and pitting/craters, etc) that can occur when coating with a zinc aluminium alloy, the process introduces an intermediate electrolysis stage in which e.g. a zinc layer is electrolytically deposited onto the steel substrate prior to a flux layer forming. This electrolysis stage, as a matter of course, adds additional complexity and 25 cost into the process. US 6,270,842 discloses a method in which a zinc-aluminium alloy is deposited on a steel material. The method attempts to avoid adverse flux affects (e.g. such as occur in a wet flux system, in which the flux adheres to the galvanised layer; and e.g. such as occur in a dry flux system, in which zinc chloride-based fluxes require thorough 30 drying before galvanising to avoid the aforementioned surface defects, and thus compensatory reagents are thus added to the flux). The method instead introduces a WO 2012/083345 PCT/AU2011/001628 -2 molten flux stage comprising zinc chloride together with alkali metal chlorides and/or alkaline earth metal chlorides and/or alkali metal fluorides. Again, this adds additional complexity and considerable cost into the process. US 7,811,389 discloses a flux for use in a hot dip galvanization process. The 5 flux includes an alkali metal chloride. The alkali metal chlorides are added to improve the fluidity of the flux, to contribute to better melting of the flux on the steel surface, and to bind gaseous aluminium chloride, lessening its influence on pinhole formation and surface roughness. The above references to the background art do not constitute an admission that 10 the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the process as disclosed herein. SUMMARY OF THE DISCLOSURE 15 In a first aspect there is disclosed an in-line process for galvanising an elongate member with a coating that comprises zinc and aluminium. The aluminium is in a range of 5-20 wt%, which is generally considered to be high for an in-line, "oxidising"-type process. The process comprises the steps of: 20 - cleaning and applying a flux that is free from alkali metal to an external surface of the member; - drying the flux on the member and pre-heating the member; - passing the pre-heated member through a bath comprising the coating of zinc and aluminium and then removing the coated member. 25 Such a process can be referred to as a dry flux process in that the film of flux applied to the member is dry before coating. Galvanising fluxes are usually an aqueous solution based on zinc or ammonium chloride, or combinations thereof. Such fluxes may also comprise potassium chloride KCl. It has been discovered that, when KCl is removed from the flux, it is possible to 30 produce an in-line Zn-Al galvanised profile member that is defect free and has a high quality coating appearance at higher line speeds (shorter immersion times) than with a WO 2012/083345 PCT/AU2011/001628 -3 flux that contains KCl (or other alkali metal chloride). In the absence of an alkali metal, such a process does not require compensatory reagents to be added to the flux, such as tin chloride or organic salts, etc. The modified flux also does not require an inert (e.g. nitrogen) or reducing 5 atmosphere to be maintained in the galvanising (coating) stage, with the flux layer preventing oxidation of the member (e.g. a steel profile). In addition, whereas a known or existing flux (such as HCl) is not able to employed with a high Al coating, and in an in-line, oxidising-type process, even if an inert atmosphere is employed (i.e. because the alloy then completely fails to wet the surface), the modified flux of the present 10 disclosure is able to function well at high iron levels. In the process of the first aspect the pre-heating and coating temperatures may also be controlled so that the "Duragal effect" (i.e. improved mechanical properties of the profile section) can be retained. In a more specific form, when the process of the first aspect is to be applied to 15 an open or closed section, the process can comprise the following steps: - shot blasting hot rolled steel strip; - continuously forming the shot-blasted strip into a profile section; - cleaning and applying a flux that is free from alkali metal to an external surface of the section; 20 - drying the flux on the section; - pre-heating the section via an induction heater; - passing the pre-heated section through a flooded trough comprising the coating of zinc and aluminium and then removing the coated section; - quenching, followed by sizing to the final shape. 25 In this more specific form it has been discovered that the combined stages of forming (e.g. roll-forming), pre-heating and metal coating with zinc-aluminium result in an increase in the yield strength of the zinc aluminium coated section (e.g. "Duragal effect" is retained). 30 In a second aspect there is disclosed an in-line process for galvanising an elongate member with a coating that comprises zinc and aluminium. Again, the WO 2012/083345 PCT/AU2011/001628 -4 aluminium is in a range of 5-20 wt%. The process of the second aspect comprises the steps of: - cleaning and applying a flux to an external surface of the member; - drying the flux on the member and pre-heating the member so as not to 5 chemically alter the flux; - passing the pre-heated member through a bath comprising the coating of zinc and aluminium and then removing the coated member. Again, such a process is a dry flux process. It has been discovered that, when pre-heating of the member is controlled so as not to chemically alter the flux, the flux 10 performs optimally in the coating stage of the process with a Zn-Al alloy. In this regard, the flux is ready and able to rapidly release (sublimate) from the member as it enters the bath (e.g. in as little three seconds). Again, and as a result, it is possible to produce an in-line Zn-Al galvanised profile member that is defect free and has a high quality coating appearance, at relatively lower coating weights and thus at a lower cost. 15 In a more specific form, when the process of the second aspect is to be applied to an open or closed section, the process can comprise the steps of: - shot blasting hot rolled steel strip; - continuously forming the shot-blasted strip into a profile section; - cleaning and applying a flux to an external surface of the section; 20 - drying the flux on the section; - induction pre-heating the section so as not to chemically alter the flux; - passing the pre-heated section through a flooded trough comprising the coating of zinc and aluminium and then removing the coated section; - quenching and sizing to final shape. 25 Again, the combined stages of forming (e.g. roll-forming), pre-heating and metal coating with zinc-aluminium result in an increase in the yield strength of the zinc aluminium coated section. In one form, when the member is pre-heated so as not to chemically alter the flux, the pre-heating may be conducted so as not to burn the flux. Thus, the flux, though 30 pre-heated as part of member pre-heating, can retain its essential properties.

WO 2012/083345 PCT/AU2011/001628 -5 In one form, the flux comprises an acidic zinc chloride flux from which potassium chloride has been removed. For example, the flux may have a pH of less than around 2. This level of acidity serves to keep all solutes in solution, and assists in cleaning the surface of metal oxides and hydroxides. 5 When the flux comprises ammonium chloride therein, the amount of ammonium chloride may be controlled to provide a relatively low ratio compared to zinc chloride. For example, the ratio of ammonium chloride to zinc chloride can be in the range of 1:11 to 1:12. By formulating the flux with a relatively low level of ammonium chloride, the ammonium chloride is observed to remain stable during pre-heating and to also 10 maintain an adequate fluxing action during immersion in the molten zinc aluminium bath. In one form the flux may further comprise BiOCl. For example, the BiOC1 may comprise around 0.08 wt% of the flux concentrate. The addition of BiOC1 to the flux is observed to improve the quality of coating, including by improving wetting by the bath 15 and reducing coating bare spots. The acidic zinc chloride flux can be diluted to form a flux that has a specific gravity ranging from 1.27 to 1.3 (e.g. 30 - 33 Baume), and generally not less than around 1.27. This has been observed to be an optimal density to promote flux release and to minimise surface defects, promote excellent surface finish, etc. 20 In one form, a flux application stage may replace either or both of an existing two-stage pickling procedure employed in an existing in-line galvanising process. In the flux application stage, the flux can be adapted (e.g. made sufficiently acidic of the right viscosity) to also clean the member. In such case, the flux may be applied to the member at a final stage at least of the two-stage pickling procedure. However, the same 25 or a modified flux may be employed in the initial stage, and may function to replace the concentrated pickling acid stage of the existing in-line galvanising process. In one form, the pre-heating may be controlled to heat the surfaces of the member to around 300C and so as not to exceed 330C. This range is time and process speed dependent. In this regard, the range 300 to 330'C represents a maximum 30 operating temperature range for the specific type of in-line galvanising as outlined above. In addition, the zinc chloride-based fluxes employed bum at temperatures WO 2012/083345 PCT/AU2011/001628 -6 greater than 33 0 0 C. It is further noted that this temperature range heats the member sufficiently for the subsequent coating stage (i.e. it better allows the steel substrate to reach galvanising temperature before it exits the coating bath). In one form, molten Zn 12Al may be held in the bath at around 480C and the 5 pre-heated member can then be fully immersed in the bath. In one form, the pre-heating may be controlled (e.g. the temperature may be lowered compared to known pre-heating temperatures) so as not to chemically alter the flux. In addition, the bath temperature may be increased (e.g. correspondingly), and relative to (i.e. in relation to the nature of) the coating composition. When the process is 10 operated in this manner the mechanical properties of the member can be retained (i.e. in a manner akin to the "Duragal effect", as discussed herein). The decrease of the pre heat temperature is, however, controlled so as not to significantly impact on line speeds. In one form, so as to provide for optimal coating quality, the bath may be held in a trough. Further, the pre-heated member may enter and exit the trough through openings 15 defined in opposite ends of the trough. These openings may be matched to the profile of the member. In this regard, the member does not need to enter or exit the molten bath via surface layers of scum, dross, slag, etc. In one form, the process may further comprise the step of rapidly quenching the coated member removed from the bath. This can again preserve (e.g. "freeze") a quality 20 surface finish of the Zn-Al coating on the member thereby allowing higher coating weights to be achieved. In a third aspect there is disclosed a member produced by the process of the first and second aspects, as outlined above. For example, the member may be an open 25 section (e.g. elongate angle, channel, strip etc), or the member may be a welded hollow section, or wire, rod, or bar, etc. In a fourth aspect there is disclosed a bath for an in-line process in which an elongate member is galvanised with a coating that comprises molten zinc and 30 aluminium. The bath comprises a trough that is configured such that the member enters WO 2012/083345 PCT/AU2011/001628 -7 and exits the trough through openings defined in opposite ends of the trough. The openings are matched to the profile of the member. As mentioned above, such a trough configuration provides for optimal coating quality, in that the member does not need to enter or exit the molten bath via surface 5 layers of scum, dross, slag, etc. Such a bath can be use with the process of the first and second aspects, as outlined above. To accommodate such a trough, the bath may further comprise a "kettle" in which the zinc and aluminium is melted, held and supplied in a molten from to the trough. In this regard, the trough may be located in use above the kettle. 10 In a fifth aspect there is disclosed an air wiper for use in an in-line process in which an elongate member is galvanised. The air wiper comprises an elongate polymeric conduit that is positionable in a transverse orientation in relation to the elongate member as it leaves a given stage in the in-line process. The polymeric conduit 15 has a series of spaced air-release slots (e.g. of elongate, slit-like configuration) arranged along its length. Each slot directs air under pressure against the elongate member as it leaves the given stage so as to remove liquid therefrom. Such an air wiper can be employed at the exit of the member from several of the stages of the process of the first and second aspects, as outlined above. The employment 20 of a polymeric conduit resists the corrosive gaseous environment of the in-line process. In one form, the elongate polymeric conduit may be bent intermediate its ends so as to more accurately direct air under pressure against the elongate member as it leaves the given stage. 25 Each of the aspects one to five, as outlined above, can be employed in combination with forming (e.g. roll forming), induction pre-heating and the application of a zinc-aluminium coating to produce a zinc-aluminium coated steel member that exhibits higher yield strength than the parent material (e.g. hot rolled coil or strip) from which it is formed. 30 WO 2012/083345 PCT/AU2011/001628 -8 BRIEF DESCRIPTION OF THE DRAWINGS Notwithstanding any other forms which may fall within the scope of the process as set forth in the Summary, specific embodiments of the process will now be described, by way of example only, with reference to the accompanying drawings in 5 which Figure 1 shows a schematic process flow diagram of a first process embodiment. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to Figure 1, a process flow chart is shown. In the process flow chart a number of differences and improvements over the process of AU 708379 (hereinafter 10 the "existing process" or "Duragal process") are highlighted by shading. In addition, the process flow chart relates to the coating of sections (e.g. open or closed sections), and may be modified when the member is wire, rod or bar. In this regard, the shot blasting may be replaced by grit blasting, and the induction preheating may take place in a reducing (e.g. hydrogen/nitrogen mixed) atmosphere. 15 For example, in the case of wire coating, the improved features of the present process can be used to implement a single stage dipping wire coating process. The improved flux compositions as disclosed herein can also provide a ductile microstructure in the coating (i.e. where the alloy layer is sub-micron and the coating essentially consists of a metallic overlay). Further, the improved features of the present 20 process can be incorporated into the process known as the "SunWyre" method. Thus, the following description should also be interpreted as generally being applicable to the coating of wire, rod and bar. Further, when the member is an open section vacuum wiping may be employed, and when the member is a closed section air wiping may be employed, as also 25 explained herein. Process Overview In overview, and as shown in the process flow chart of Figure 1, members in the form of profile sections are formed (e.g. roll-formed) from hot rolled strip then re 30 coated in Zn 12A1 0.1Si alloy prior to further forming. The process as applied to sections does not require an inert or reducing atmosphere and hence is considerably WO 2012/083345 PCT/AU2011/001628 -9 simplified in comparison to existing Zn-Al processes. The process also does not require complex pre-treatment stages such as electrolytic deposition of e.g. Zn onto the strip, or use of a molten flux, use of alkali metal in the flux, etc. The zinc alloy to be coated comprises 12% Al and 0.1% Si by weight, referred 5 to herein as "Zn 12Al". The resultant coated product is able to replace and substitute for known profile sections coated with a pure zinc coating (e.g. that were previously coated in accordance with the process of AU 708379; such products being referred to as the "Duragal range"). The Zn 12A1 coating has improved corrosion resistance over zinc coatings of the same coating weight. In addition, the so-called "Duragal Effect", where 10 the mechanical properties of the steel substrate are enhanced by the forming and galvanising steps, is able to retained with the operating parameters and new bath chemistry employed in the present process. Strip Feed - Stages 1 & 2 is In the process of Figure 1, hot rolled strip is employed. The minimum grade strip feed is equivalent to at least TF300 or, more typically, TF400 hot rolled coil. The "TF" refers to hot rolled strip that is suitable for production of hollow sections (i.e. with TF shorthand for Tube Form). The number 300 (or 400) refers hot rolled strip with nominal minimum yield strength of 300 MPa (or 400 MPa) for production of hollow 20 sections. In stage 1 of Figure 1 strip is slit from an HRME (Hot Rolled Mill Edge) coil feedstock. The slit strip is passed to a coil joining stage (end-to-end welding) and accumulation stage 2. By way of contrast, if coating of rod, bar or wire were being implemented using 25 the present process, the rod or bar feed would be hot rolled from e.g. a high carbon steel, whereas the wire feed would be cold drawn or cold rolled from e.g. either a high or low carbon steel. Surface Cleaning - Stage 3 30 In stage 3 of the process of Figure 1, surface cleaning, such as shot blasting of the hot roll coil is performed to class 2.5 of AS 1627 (class 2.5 corresponds to "near WO 2012/083345 PCT/AU2011/001628 - 10 white metal" blast cleanliness). Where the as-received strip is pickled hot roll coil shot blasting is sufficient. Alternatively, if pickled and oiled hot rolled coil is used it must first be degreased (e.g. using a permanganate or alkali solution) prior to flux application. Air wiping after cleaning is such that no or minimum residual 5 permanganate/alkali is carried over to the later flux stage, so as not to contaminate the flux chemistry. As mentioned above, for wire, rod or bar, the shot blasting can be replaced by grit blasting. Forming - Stage 4 10 In stage 4 of the process of Figure 1, the shot-blasted/degreased strip is now formed into its basic open profile. This is performed by a series of rolls. Alternatively, for closed section the strip may be seam welded to form a hollow section of various profile (round, square, rectangular, etc). 15 Chemical Pre-Treatment - Stage 5 In stage 5 of the process of Figure 1, a first modification to known in-line "oxidising" or "inert" processes takes place. In this stage, the normal pickling of the shot blasted profile section in a 10-14% HCl solution is replaced. Instead, alternative chemical pre-treatment options are employed, namely a single-step flux procedure or a 20 pickling/single-step flux procedure. Each of these stages can from part of the "cleaning" of the profile section. Single-step Flux Procedure An acidic flux is heated (e.g. to around between 50-60C) using an immersion heater, and is applied to the surface via fan sprays in the second compartment of the 25 tank. Alternatively, the flux may be applied at ambient temperatures. The flux is a specially prepared flux, developed to facilitate coating with a Zn-Al alloy in an "oxidising" procedure, and is described in greater detail in Example 2. Because the flux needs to be dry before it is heated above 1 00 0 C (Stage 6), it is heated in the flux tank to between 50-60C, using an immersion heater. The flux is applied to an appropriate 30 thickness (e.g. around 10 microns or less), with thickness being controlled by wiping at the flux tank exit. In the case of an open section, the section passes through a vacuum WO 2012/083345 PCT/AU2011/001628 - 11 wipe apparatus employing a vacuum in the range of from 3 up to 10 kPa. The vacuum wipe is located at the entry end of the induction heaters (described below with reference to Stage 6). In the case of a closed section, the section passes through an air wipe apparatus. 5 Pickling in Conjunction with a Single-step Flux Procedure In Step 1. Pickling of the shot blasted profile section is typically carried out in 10-14% HCl solution in a pickling tank/vessel. The acid is applied to the surface via fan sprays to blast residual scale from the surface. Wiping (e.g. vacuum or air wiping) of the pickled profile section is employed to prevent carryover of acid to the rinse tank. 10 In Step 2. The flux of Example 2 is applied to the clean surface of the profile section via fan sprays. The flux replaces the usual dilute (4% HCl) pickling stage of the existing process. Again, the flux may be applied at ambient temperatures, or is heated in the flux tank to between 50-60 0 C, using an immersion heater and is applied to a thickness of around 10 microns or less, controlled by wiping (e.g. vacuum or air 15 wiping) at the flux tank exit. As mentioned in Example 3, the vacuum and air wiping apparatus between each of the steps have been redesigned to provide uniform controllable wet film thickness with no bare spots. 20 Drying & Induction Pre-heat - Stage 6 In stage 6 of the process of Figure 1, the distance between the final stage flux application tank/compartment and the drying stage is increased, to aid with flux drying on the profile section. The first bank of induction heaters provided final drying of the profile section and is controlled to prevent boiling of the flux. 25 In stage 6 of the process of Figure 1, a second modification to the known in-line "oxidising" or "inert" processes takes place. As previously, induction pre-heat of the profile section is required prior to coating. However, due to the new and different flux composition required for an inline, oxidising Zn-Al process, the profile section surface temperature needs to be more carefully controlled. In the case of wire, rod or bar a 30 reducing atmosphere (e.g. mixed H 2

/N

2 ) may be employed.

WO 2012/083345 PCT/AU2011/001628 - 12 In the process of Figure 1, the induction pre-heat is preferably controlled to heat the surfaces of the profile section to around 300C and so as not to exceed 330'C, because the new and different flux composition burns at greater than 330C. This operating temperature is outside the normal operating window for previous fluxes. This 5 range is noted to be time and process speed dependent, with the range 300 to 330"C representing a maximum operating temperature range for the specific type of in-line galvanising as outlined in Metallic Coating - Stage 7. The pre-heating temperature is controlled (typically lowered compared to known pre-heating temperatures) so as not to burn or chemically alter the flux. 10 However, the bath temperature is correspondingly increased (see Metallic Coating Stage 7), and so as to suit the particular coating composition. When the process is operated in this manner the "Duragal effect" (i.e. improved mechanical properties of the profile section) can be retained. Accurate temperature monitoring and control is therefore employed, so as not to 15 significantly impact on line speeds. Metallic Coating - Stage 7 In stage 7 of the process of Figure 1, the now preheated profile section is coated with the new Zn 12A1 coating composition. In this regard, the preheated profile section 20 leaves the induction heater and enters a flooded trough filled with molten Zn 12AI held at around 480'C and is fully immersed therein. The Zn 12A1 alloy (also containing 0.1% Si) bath melts at 443'C, considerably higher than existing zinc only baths. In stage 7 of the process of Figure 1, a third modification to the known in-line "oxidising" and "inert" processes is made. Zn 12AI alloy is corrosive to existing A1006 25 Lycoplate. All steel items in contact with the molten alloy are thus upgraded to 316L stainless steel, as per Example 4. Troughs, pump wells, pump impellers and end plates are also upgraded to 316L stainless steel. Pump wells are constructed from 316L pipe to save on machining costs. The heat capacity of the galvanising furnace system is controlled and modified to maintain the desirable bath temperature of~480C while 30 restricting the lower thermal conductivity of 316L compared to low carbon steel.

WO 2012/083345 PCT/AU2011/001628 - 13 A further modification to the known processes includes increasing the bath trough length. In this regard, the bath is extended towards the entry end by approximately 750mm from bath entry point to increase immersion time of the profile section in the bath. This also assists flux release. 5 Advantageously, with the new flux employed, an inert (e.g. nitrogen) atmosphere under the galvanising hood is no longer required, as the flux layer prevents oxidation of the steel profile section. Advantageously, bottom dross does not form in the Zn 12AI bath, so bottom drossing is no longer required. Drossing is a function of bath chemistry and, because 10 aluminium preferentially reacts with iron over zinc, the resulting by-product (dross) has a lower density than dross formed in an aluminium-free (e.g. zinc only) bath. Modified Fume Extraction In stage 7 of the process of Figure 1, a further modification to the known 15 process includes changing the fume extraction. The new flux includes ammonium chloride which "fumes-off' as the profile section enters the bath. In stage 7, the two stage extraction system is redesigned, as per Example 5. Some gas flow is still required to vent fumes from the galvanizing bath, affected by fan forced dust extraction. 20 Coating Control - Stage 8 After exiting the bath, the now coated section passes through a so-called "Blow Ring", which is an air knife with an annular orifice that is used to control the coating mass. The coating comprises a liquid metal overlay (same chemistry as the bath). The liquid metal overlay subsequently solidifies in the quench tank Stage 9 with 25 a two-phase microstructure. On galvanised sections, the Blow Ring controls the coating thickness of the metal overlay, while the iron zinc alloy layer is determined by the immersion time of the steel in the zinc bath. Therefore, for the same applied wiping force, a Zn 12AI coating has a thinner overall coating than a galvanised coating made under the same conditions. This is because the Zn 12AI coating effectively has no alloy 30 layer thickness (<1 micron), and zinc iron alloy layer growth is inhibited by aluminium (and silicon).

WO 2012/083345 PCT/AU2011/001628 - 14 Quenching - Stage 9 In stage 9 of the process of Figure 1, a further modification to the known process includes providing an extension to the quench entry. This extension can achieve 5 high coating weights (above 200 g/m 2 ). The extension involves providing a water spray to the top surface of the tube and a box to contain the water. This extension promotes the early solidification of the liquid metal overlay in order to achieve a uniform coating thickness distribution around the circumference of the section. More specifically, the more rapid quench provides a finer microstructure in the resultant cooled, solidified 10 coating. Shaping & Sizing - Stage 10 Shaping and sizing stage 10 of the process of Figure 1 is a two-stage operation. In this regard, the solidified coated profile section is now further roll-formed to provide 15 it with a specific desired profile. Surface Protection - Stage 11 Stage 11 of the process of Figure 1 shows a passivation stage directed to a zinc aluminium coating. 20 Passivation of the zinc-aluminium coating provides short-term protection against wet-storage-staining and to prevent early darkening of the alloy surface. An existing silane passivation treatment and application system may be employed and in practice is observed to inhibit darkening of the alloy surface. Alternative inhibitors can be employed as appropriate including trivalent chromium, chromate, zirconium, etc. 25 Cut-off & Bundling - Stages 12 & 13 In the process of Figure 1, stage 12 cut-off of the surface passivated continuous length, and stage 13 bundling of the discrete cut-off length were as per existing processes. 30 WO 2012/083345 PCT/AU2011/001628 - 15 Examples Non-limiting Examples will now be provided to further illustrate certain of the stages of the process as outlined above. Example 1 -Development of Flux 5 A new flux was developed for the process. The flux properties were optimised towards enabling the flux to be sprayed onto the profile section (e.g. "cold" such as at ambient temperature). The new flux was also observed to facilitate coating with a Zn-Al alloy in an "oxidising" coating environment. The flux was applied to the profile section 10 immediately prior to process stage 6 Drying & Pre-heating. The flux (known as "G-Flux") was specified to contain no potassium chloride KCl. It was surprisingly discovered in trials that, absent KCl, the flux resulted in faster flux release times. This in turn allowed shorter immersion times and/or faster line speeds. 15 The G-Flux comprised an acidified zinc chloride solution together with some ammonium chloride, inhibitors and wetting agents (e.g. bismuth / cadmium / cerium / lanthanum oxychlorides). The flux pH was observed to be less than 2, with this level of acidity serving to keep all solutes in solution, and assisting in cleaning the profile section surface of metal oxides and hydroxides. 20 When the G-flux contained ammonium chloride, the amount of ammonium chloride was controlled to provide a relatively low ratio compared to zinc chloride (e.g. in the range of 1:11 to 1:12). This relatively low level of ammonium chloride was observed to remain stable during pre-heating whilst still maintaining an adequate fluxing action during immersion in the molten zinc aluminium bath. 25 A number of G flux formulations comprised bismuth oxychloride - BiOCl, at a level of around 0.08 wt% of the flux. The BiOCI was observed to improve the quality of the coating, including by improving wetting by the bath and reducing coating bare spots. The G-Flux was applied to the clean surface of the profile section via fan sprays. 30 The flux was dried before being heated above 100C.

WO 2012/083345 PCT/AU2011/001628 - 16 The G-flux (carrying the trade name Thermaprep-G) was supplied as a concentrate and was diluted to a specific gravity in the range of 1.27 to 1.3 (or 30-33 Baume) prior to use. It was noted that an SG lower than around 1.27 could lead to surface defects. Flux concentration was checked using a hydrometer, as it was 5 important not to over-dilute the flux. The flux was applied to a thickness of around 10 microns. Thickness was controlled by the final air wiping at the flux tank exit. Example 2 - Vacuum Wipe Apparatus Redesign For open sections, the vacuum wipers between each of the steps were redesigned to provide a uniform controllable wet film thickness with no bare spots on 10 the open profile section. A fan was used instead of a vacuum pump and the vacuum wipe operated up to a vacuum ranging from around 3 to 10 kPa (e.g. around 9kPa). Example 3 - Air Wipe Apparatus Redesign For closed sections, the air wipers between each of the steps were redesigned to provide a uniform controllable wet film thickness with no bare spots on the profile 15 section. The existing air wipers comprised a bent perforated stainless steel pipe, which was prone to corrosion under the process conditions. The new air wipes comprised plastic pipe manifolds with slots instead of holes. These were observed to more evenly distribute air, and were corrosion resistant. Example 4 - New Bath Design 20 All bath materials in contact with the Zn 12A1 alloy were replaced with 316L stainless steel. Experimental procedure revealed that the corrosion rate of 316L in Zn 12AI was only 0.511 mm/year. However, it was also noted that 316L stainless steel has a higher coefficient of thermal expansion and lesser thermal conductivity than A1006 Lycoplate. Thus, finite element analysis was employed to validate the bath design. The 25 current bath design was thus modelled in 316L at 480C. This analysis resulted in a recommendation to reduce bath wall thickness from 50 to 40mm. Bath life was modelled and expected to exceed 20 years. It was also noted that, in situations where a higher mechanical strength was required, the 316L could be specified with 316H mechanical properties. The new material was also expected to have a longer bath life 30 than existing bath materials in the existing process.

WO 2012/083345 PCT/AU2011/001628 - 17 The bath trough was suspended above a larger bath (kettle). The kettle melted and supplied molten zinc and aluminium to the trough. Openings were formed in opposite ends of the trough, with the shape and configuration of the openings being matched to the profile of the section. Thus, the pre-heated section was able to enter and 5 exit the trough through the openings so as to be immediately immersed, with molten Zn-Al spilling into the underlying kettle. The outside walls of the trough were painted with boron nitride paint. The use of folded corners (as opposed to welded joints) was maximised in the trough design and, as necessary, the bath trough could incorporate flanges and stiffeners. 10 Example 5 - Fume Extractor Redesign Release of the new flux during bath immersion was observed to result in increased fuming above the galvanizing trough. The immersion caused the flux to release (i.e. to sublimate). It was discovered that this process occurred in just 3 seconds. The hood fume extraction was revised accordingly. 15 In this regard, the two stage hood fume extractor and "dog-box" dust collector were replaced with a single fume dust collector hood. With the new flux, the process produced less ash, less entrained metal and more fume. Hence, the size of the fume hood was increased, the air velocities were increased, and the dust collector was redesigned to capture ammonium chloride particles that fumed-off as the profile section 20 entered the molten Zn-Al bath, as well as oxides displaced from the bath surface. Example 6 - Discussion of Outcomes In was noted that the existing "Duragal Plus" galvanised lintel produced in the existing Duragal process could only achieve an R2 Rating, as the in-line galvanising process cannot produce a 600 g/m2 zinc coating (Duragal coatings ~300 g/m 2 zinc 25 coating). A 600 g/m2 pure zinc coating weight is required for a zinc galvanised coating to achieve an R3 rating. This makes the Duragal Plus lintel suitable only for areas with low salt deposition rates (e.g. for use in construction in zones 10km or greater from breaking surf). (An R2 Rating refers to the durability requirements for lintels set out in AS/NZS 30 2699.3 - Built-in components for masonry and shelf angles. AS/NZS 2699.3 classifies durability using an R rating system, which is based on airborne salt deposition rates.) WO 2012/083345 PCT/AU2011/001628 - 18 The Zn-Al coating as produced herein achieved an R3 rating - equivalent corrosion resistance to a 600 g/m 2 coating (batch hot dipped galvanized) and at a lower coating thickness (250 g/m 2 external Zn12Al coating of a low thickness e.g. -40 microns). This made such lintels suitable for areas with higher salt deposition rates, up 5 to 1 km from breaking surf. The in-line Zn-Al galvanising process also improved the tensile properties of the steel substrate, allowing the use of strip with lower tensile strength or thinner gauge compared to hot rolled products. If used for a Zn bath, the in-line Zn-Al galvanising process was able to operate 10 at increased mill speeds (for a 50x50x4 angle profile - 85 m/min; c.f. existing process 75 m/min; for a 100x50x4 channel profile - 70 m/min; c.f. existing process 55 m/min). For a Zn-Al bath, the in-line Zn-Al galvanising process was able to maintain the mill speeds of existing galvanising processes. A 250 g/m 2 external Zn12Al coating was also observed to be ductile and able to 15 be mandrel bent without disbanding (unlike a 600 g/m2 zinc coating - e.g. batch hot dipped galvanized). A 250 g/m 2 external 12Al coating was observed to be smoother than a 600 g/m 2 coating (batch hot dipped galvanized) and to not contain ash or flux inclusions. It was also better suited to powder coating. This was because the coating was thinner and the 20 coating process was such that the coated substrate was able to exit the bath through a flow of molten metal (unlike batch galvanising where the galvanised section has to be withdrawn from the bath through any by-products on the bath surface). A 250 g/m 2 external 12AI coating was observed to be easier to weld, due to the thinner coat, with lesser fuming, than a 600 g/m 2 coating (batch hot dipped galvanized). 25 In-line galvanising was noted to have a lower cost base than batch galvanising. In-line galvanising did not detrimentally affect mechanical properties or shape of the galvanised item like batch galvanising can. In-line galvanized lintels were less prone to handling damage than painted lintels (painted lintels are lintels painted with a protective coating prior to delivery to the building site; most residential lintels are then painted 30 after installation).

WO 2012/083345 PCT/AU2011/001628 - 19 Articles can be distorted during batch galvanising because, at the galvanizing bath temperatures, the yield strength of steel is lowered by approximately 50%. If the adjacent steel is not at the same temperature, and if any stresses exist, the weaker area will be subject to movement by the stronger area. The continuous, in-line process was 5 observed to correct distortions (in the sizing process). Batch galvanised coatings have a significant zinc iron alloy layer. This part of the coating is brittle, and the coating may crack or delaminate during bending. The Zn 1 2Al coating was ductile and was able to be bent over a tighter radius than a batch galvanised coating. Hot dip galvanizing was also observed to have no effect on the 10 mechanical properties of standard grades of steel. In summary, in the modified process as outlined above, it was possible to produce an in-line galvanised product with improved external corrosion resistance, with better processing attributes than similar batch hot dipped zinc galvanised members, with a defect free and a high quality (e.g. satin-like; no spangle) coating appearance, at low 15 coating weights and thus at a lower cost. Whilst a number of specific process embodiments have been described, it should be appreciated that the process may be embodied in other forms. In the claims which follow, and in the preceding description, except where the 20 context requires otherwise due to express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the process.

Claims

1. An in-line process for galvanising an elongate member with a coating that comprises zinc and aluminium, the aluminium being in a range of 5-20 wt%, the process comprising the steps of: 5 - cleaning and applying a flux that is free from alkali metal to an external surface of the member; - drying the flux on the member and pre-heating the member; - passing the pre-heated member through a bath comprising the coating of zinc and aluminium and then removing the coated member. 10

2. A process as claimed in claim 1 wherein the member is pre-heated so as not to chemically alter the flux.

3. A process as claimed in claim 1 or 2 wherein the member is pre-heated so as 15 not to burn the flux.

4. A process as claimed in any one of the preceding claims wherein the flux comprises an acidic zinc chloride flux from which potassium chloride has been removed. 20

5. A process as claimed in claim 4 wherein the flux has a pH of less than around 2.

6. A process as claimed in claim 4 or 5 wherein, when the flux comprises 25 ammonium chloride therein, the amount of ammonium chloride is controlled to provide a relatively low ratio compared to zinc chloride.

7. A process as claimed in any one of the preceding claims wherein the flux further comprises BiOCl. 30 WO 2012/083345 PCT/AU2011/001628 - 21

8. A process as claimed in claim 7 wherein the BiOCl comprises around 0.08 wt% of the flux.

9. A process as claimed in any one of the preceding claims wherein the flux has 5 a specific gravity in the range of 1.27 to 1.3.

10. A process as claimed in any one of the preceding claims wherein a flux application stage replaces either or both of an existing two-stage pickling procedure in an in-line galvanising process. 10

11. A process as claimed in claim 10 wherein the flux is applied to the member at a final stage of the two-stage pickling procedure.

12. A process as claimed in claim 10 or 11 wherein, in the flux application 15 stage, the flux is adapted to also clean the member.

13. A process as claimed in any one of the preceding claims wherein the pre heating is controlled to heat the surfaces of the member to around 300 0 C and so as not to exceed 330 0 C. 20

14. A as claimed in any one of the preceding claims wherein molten Zn 12Al is held in the bath at around 480"C and the pre-heated member is fully immersed in the bath. 25

15. A process as claimed in any one of the preceding claims wherein the pre heating is controlled so as not to chemically alter the flux, whereas the bath temperature is increased relative to the coating composition.

16. A process as claimed in any one of the preceding claims wherein the bath is 30 held in a trough, and the pre-heated member enters and exits the trough through WO 2012/083345 PCT/AU2011/001628 - 22 openings defined in opposite ends of the trough, the openings being matched to the profile of the member.

17. A process as claimed in any one of the preceding claims further comprising 5 the step of rapidly quenching the coated member removed from the bath.

18. An in-line process for galvanising an elongate section with a coating that comprises zinc and aluminium, the aluminium being in a range of 5-20 wt%, the process comprising the steps: 10 - shot blasting hot rolled steel strip; - continuously forming the shot-blasted strip into a profile section; - cleaning and applying a flux that is free from alkali metal to an external surface of the section; - drying the flux on the section; 15 - pre-heating the section via an induction heater; - passing the pre-heated section through a flooded trough comprising the coating of zinc and aluminium and then removing the coated section; - quenching, followed by sizing to the final shape. 20

19. A process as claimed in claim 18 that is otherwise as defined in any one of the claims 1 to 17.

20. An in-line process for galvanising an elongate member with a coating that comprises zinc and aluminium, the aluminium being in a range of 5-20 wt%, the 25 process comprising the steps of: - cleaning and applying a flux to an external surface of the member; - drying the flux on the member and pre-heating the member so as not to chemically alter the flux; - passing the pre-heated member through a bath comprising the coating of zinc 30 and aluminium and then removing the coated member. WO 2012/083345 PCT/AU2011/001628 - 23

21. A process as claimed in claim 20 wherein the member is pre-heated so as not to burn the flux.

22. An in-line process for galvanising an elongate section with a coating that 5 comprises zinc and aluminium, the aluminium being in a range of 5-20 wt%, the process comprising the steps: - shot blasting hot rolled steel strip; - continuously forming the shot-blasted strip into a profile section; - cleaning and applying a flux to an external surface of the section; 10 - drying the flux on the section; - induction pre-heating the section so as not to chemically alter the flux; - passing the pre-heated section through a flooded trough comprising the coating of zinc and aluminium and then removing the coated section; - quenching and sizing to final shape. 15

23. A process as claimed in any one of claims 20 to 22 that is otherwise as defined in any one of the claims 1 to 17.

24. A member produced by the process as claimed in any one of the preceding 20 claims.

25. A bath for an in-line process in which an elongate member is galvanised with a coating that comprises molten zinc and aluminium, the bath comprising a trough that is configured such that the member enters and exits the trough through openings 25 defined in opposite ends of the trough, the openings being matched to the profile of the member.

26. A bath as claimed in claim 25 wherein the bath further comprises a kettle for melting and supplying molten zinc and aluminium to the trough, and wherein the trough 30 is located in use above the kettle. WO 2012/083345 PCT/AU2011/001628 - 24

27. A bath for use with the process as claimed in any one of claims 1 to 22.

28. An air wiper for use in an in-line process in which an elongate member is galvanised, the air wiper comprising an elongate polymeric conduit that is positionable 5 in a transverse orientation in relation to the elongate member as it leaves a given stage in the in-line process, the polymeric conduit having a series of spaced air-release slots arranged along its length, each for directing air under pressure against the elongate member as it leaves the given stage so as to remove liquid therefrom. 10

29. An air wiper as claimed in claim 28 wherein the elongate polymeric conduit is bent intermediate its ends so as to more accurately direct air under pressure against the elongate member as it leaves the given stage.

30. An air wiper as claimed in claim 28 or 29 for use with the process or bath as 15 claimed in any one of claims 1 to 26.