WO2012083345A1 - Dispositif de commande pour le revêtement d'éléments - Google Patents

Dispositif de commande pour le revêtement d'éléments Download PDF

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Publication number
WO2012083345A1
WO2012083345A1 PCT/AU2011/001628 AU2011001628W WO2012083345A1 WO 2012083345 A1 WO2012083345 A1 WO 2012083345A1 AU 2011001628 W AU2011001628 W AU 2011001628W WO 2012083345 A1 WO2012083345 A1 WO 2012083345A1
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WO
WIPO (PCT)
Prior art keywords
flux
coating
bath
aluminium
zinc
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PCT/AU2011/001628
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English (en)
Inventor
David Brawdly HARRISON
Original Assignee
Australian Tube Mills Pty Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2010905596A external-priority patent/AU2010905596A0/en
Application filed by Australian Tube Mills Pty Limited filed Critical Australian Tube Mills Pty Limited
Priority to NZ611941A priority Critical patent/NZ611941A/en
Priority to AU2011349108A priority patent/AU2011349108B8/en
Publication of WO2012083345A1 publication Critical patent/WO2012083345A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips

Definitions

  • An in-line process for continuously coating an elongate member with a Zn/Al 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.
  • 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").
  • AU 708379 employs a galvanising stage which can be referred to 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 on a ferrous (e.g. steel) substrate.
  • 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 adds additional complexity and 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 drying before galvanising to avoid the aforementioned surface defects, and thus compensatory reagents are thus added to the flux).
  • the method instead introduces a 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 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.
  • 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:
  • 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 - KC1. It has been discovered that, when KG is removed from the flux, 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 higher line speeds (shorter immersion times) than with a 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 atmosphere to be maintained in the galvanising (coating) stage, with the flux layer preventing oxidation of the member (e.g. a steel profile).
  • an inert e.g. nitrogen
  • reducing atmosphere e.g. a known or existing flux
  • the modified flux of the present disclosure is able to function well at high iron levels.
  • 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.
  • the process of the first aspect when the process of the first aspect is to be applied to an open or closed section, the process can comprise the following steps:
  • aluminium is in a range of 5-20 wt%.
  • the process of the second aspect comprises the steps of:
  • the process of the second aspect when the process of the second aspect is to be applied to an open or closed section, the process can comprise the steps of:
  • the pre-heating 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.
  • the flux though pre-heated as part of member pre-heating, can retain its essential properties.
  • the flux comprises an acidic zinc chloride flux from which potassium chloride has been removed.
  • 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.
  • the amount of ammonium chloride may be controlled to provide a relatively low ratio compared to zinc chloride.
  • the ratio of ammonium chloride to zinc chloride can be in the range of 1 : 11 to 1 : 12.
  • the flux may further comprise BiOCl.
  • the BiOCl may comprise around 0.08 wt% of the flux concentrate. The addition of BiOCl to the flux is observed to improve the quality of coating, including by improving wetting by the bath 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.
  • a flux application stage may replace either or both of an existing two-stage pickling procedure employed in an existing in-line galvanising process.
  • the flux can be adapted (e.g. made sufficiently acidic of the right viscosity) to also clean the member.
  • the flux may be applied to the member at a final stage at least of the two-stage pickling procedure.
  • the same 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.
  • the pre-heating may be controlled to heat the surfaces of the member to around 300°C and so as not to exceed 330°C.
  • This range is time and process speed dependent.
  • the range 300 to 330°C represents a maximum operating temperature range for the specific type of in-line galvanising as outlined above.
  • the zinc chloride-based fluxes employed burn at temperatures greater than 330°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).
  • molten Zn 12A1 may be held in the bath at around 480°C and the pre-heated member can then be fully immersed in the bath.
  • 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.
  • the bath temperature may be increased (e.g. correspondingly), and relative to (i.e. in relation to the nature of) the coating composition.
  • the decrease of the preheat temperature is, however, controlled so as not to significantly impact on line speeds.
  • the bath may be held in a trough.
  • the pre-heated member may enter and exit the trough through openings 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.
  • 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 surface finish of the Zn-Al coating on the member thereby allowing higher coating weights to be achieved.
  • the member may be an open section (e.g. elongate angle, channel, strip etc), or the member may be a welded hollow section, or wire, rod, or bar, etc.
  • 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 comprises a trough that is configured such that the member enters and exits the trough through openings defined in opposite ends of the trough. The openings are matched to the profile of the member.
  • Such a bath can be use with the process of the first and second aspects, as outlined above.
  • 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.
  • the trough may be located in use above the kettle.
  • 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 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 of a polymeric conduit resists the corrosive gaseous environment of the in-line process.
  • 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.
  • forming e.g. roll forming
  • induction pre-heating e.g. induction pre-heating
  • the application of a zinc-aluminium coating e.g. 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.
  • 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.
  • 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.
  • 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
  • the coating i.e. where the alloy layer is sub-micron and the coating essentially consists of a metallic overlay.
  • the improved features of the present process can be incorporated into the process known as the "SunWyre" method.
  • the following description should also be interpreted as generally being applicable to the coating of wire, rod and bar.
  • members in the form of profile sections are formed (e.g. roll-formed) from hot rolled strip then re- coated in Zn 12A1 0.1 Si alloy prior to further forming.
  • the process as applied to sections does not require an inert or reducing atmosphere and hence is considerably 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 to herein as "Zn 12A1".
  • 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.
  • the so-called “Duragal Effect” where 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.
  • 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 MP a) for production of hollow sections.
  • 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.
  • 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.
  • 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 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
  • Air wiping after cleaning is such that no or minimum residual
  • permanganate/alkali is carried over to the later flux stage, so as not to contaminate the flux chemistry.
  • the shot blasting can be replaced by grit blasting.
  • 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).
  • stage 5 of the process of Figure 1 a first modification to known in-line "oxidising” or “inert” processes takes place.
  • the normal pickling of the shot blasted profile section in a 10-14% HC1 solution is replaced.
  • alternative chemical pre-treatment options are employed, namely a single-step flux procedure or a pickling/single-step flux procedure.
  • An acidic flux is heated (e.g. to around between 50-60°C) using an immersion heater, and is applied to the surface via fan sprays in the second compartment of the tank.
  • 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
  • Example 2 Because the flux needs to be dry before it is heated above 100°C (Stage 6), it is heated in the flux tank to between 50-60°C, using an immersion heater. The flux is applied to an appropriate thickness (e.g. around 10 microns or less), with thickness being controlled by wiping at the flux tank exit.
  • the section In the case of an open section, the section passes through a vacuum 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.
  • 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
  • Step 2 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
  • 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.
  • the flux may be applied at ambient temperatures, or is heated in the flux tank to between 50-60°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 wiping) at the flux tank exit.
  • 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.
  • stage 6 of the process of Figure 1 a second modification to the known in-line
  • the pre-heating temperature is controlled (typically lowered compared to known pre-heating temperatures) so as not to burn or chemically alter the flux.
  • the bath temperature is correspondingly increased (see Metallic Coating - Stage 7), and so as to suit the particular coating composition.
  • the "Duragal effect” i.e. improved mechanical properties of the profile section
  • the now preheated profile section is coated with the new Zn 12A1 coating composition.
  • the preheated profile section leaves the induction heater and enters a flooded trough filled with molten Zn 12A1 held at around 480°C and is fully immersed therein.
  • the Zn 12 Al alloy (also containing 0.1% Si) bath melts at 443°C, considerably higher than existing zinc only baths.
  • stage 7 of the process of Figure 1 a third modification to the known in-line "oxidising” and “inert” processes is made.
  • Zn 12A1 alloy is corrosive to existing A1006 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 ⁇ 480°C while restricting the lower thermal conductivity of 316L compared to low carbon steel.
  • 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
  • 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.
  • bottom dross does not form in the Zn 12A1 bath, so bottom drossing is no longer required.
  • Drossing is a function of bath chemistry and, because 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.
  • stage 7 of the process of Figure 1 a further modification to the known process includes changing the fume extraction.
  • the new flux includes ammonium chloride which "fumes-off ' as the profile section enters the bath.
  • 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.
  • 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 a two-phase microstructure.
  • 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 12A1 coating has a thinner overall coating than a galvanised coating made under the same conditions. This is because the Zn 12A1 coating effectively has no alloy layer thickness ( ⁇ 1 micron), and zinc iron alloy layer growth is inhibited by aluminium
  • a further modification to the known process includes providing an extension to the quench entry.
  • This extension can achieve 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 coating.
  • Shaping and sizing stage 10 of the process of Figure 1 is a two-stage operation.
  • the solidified coated profile section is now further roll-formed to provide it with a specific desired profile.
  • Stage 11 of the process of Figure 1 shows a passivation stage directed to a zinc- aluminium coating.
  • 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.
  • 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.
  • 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
  • G-Flux 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.
  • 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.
  • 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.
  • a number of G flux formulations comprised bismuth oxychloride - BiOCl, at a level of around 0.08 wt% of the flux.
  • the BiOCl 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.
  • the flux was dried before being heated above 100°C.
  • 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 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.
  • the vacuum wipers between each of the steps were redesigned to provide a uniform controllable wet film thickness with no bare spots on 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).
  • 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 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.
  • the new material was also expected to have a longer bath life than existing bath materials in the existing process.
  • 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.
  • the pre-heated section was able to enter and 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.
  • the two stage hood fume extractor and "dog-box" dust collector were replaced with a single fume dust collector hood.
  • the process produced less ash, less entrained metal and more fume.
  • 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 entered the molten Zn-Al bath, as well as oxides displaced from the bath surface.
  • An R2 Rating refers to the durability requirements for lintels set out in AS/NZS 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.
  • the Zn-Al coating as produced herein achieved an R3 rating - equivalent corrosion resistance to a 600 g/m coating (batch hot dipped galvanized) and at a lower coating thickness (250 g/m 2 external Znl2Al coating of a low thickness e.g. -40 microns). This made such lintels suitable for areas with higher salt deposition rates, up 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.
  • the in-line Zn-Al galvanising process was able to operate 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).
  • the in-line Zn-Al galvanising process was able to maintain the mill speeds of existing galvanising processes.
  • a 250 g/m external Znl2Al coating was also observed to be ductile and able to be mandrel bent without disbanding (unlike a 600 g/m2 zinc coating - e.g. batch hot dipped galvanized).
  • a 250 g/m 2 external 12A1 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 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 external 12A1 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).
  • 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 after installation).
  • 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 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 Znl2Al 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 mechanical properties of standard grades of steel.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Coating With Molten Metal (AREA)

Abstract

L'invention divulgue un procédé en ligne pour galvaniser un élément allongé grâce à un revêtement qui comprend du zinc et de l'aluminium. L'aluminium se situe dans la plage de 5-20% en poids. Le procédé comprend le nettoyage et l'application d'un flux qui est exempt de métal alcalin sur une surface externe de l'élément. Le procédé comprend également le séchage du flux sur l'élément et le préchauffage de l'élément. Le procédé comprend en outre le passage de l'élément préchauffé à travers un bain comprenant le revêtement de zinc et d'aluminium puis l'enlèvement de l'élément revêtu.
PCT/AU2011/001628 2010-12-22 2011-12-19 Dispositif de commande pour le revêtement d'éléments WO2012083345A1 (fr)

Priority Applications (2)

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NZ611941A NZ611941A (en) 2010-12-22 2011-12-19 Control of coating of members
AU2011349108A AU2011349108B8 (en) 2010-12-22 2011-12-19 Control of coating of members

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AU2010905596A AU2010905596A0 (en) 2010-12-22 Control of coating sections
AU2010905596 2010-12-22

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WO2012083345A1 true WO2012083345A1 (fr) 2012-06-28

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106939398A (zh) * 2017-05-04 2017-07-11 西安泰力松新材料股份有限公司 一种金属丝镀锡工艺及其镀锡装置
CN107179749A (zh) * 2016-03-11 2017-09-19 宝山钢铁股份有限公司 热镀锌产品全流程质量控制方法
WO2020173586A1 (fr) * 2019-02-25 2020-09-03 Fontaine Holdings Nv Procédé pour le zingage, en particulier la galvanisation à chaud, de produits en fer et en acier
CN113046673A (zh) * 2021-03-11 2021-06-29 江苏中远稀土新材料有限公司 一种用于钢制电缆桥架的耐蚀性稀土多元合金镀层

Citations (4)

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Publication number Priority date Publication date Assignee Title
US3696503A (en) * 1969-10-28 1972-10-10 Allied Tube & Conduit Corp Method for continuously galvanizing steel strip
US4738758A (en) * 1985-05-07 1988-04-19 International Lead Zinc Research Organization, Inc. Process for continuous deposition of a zinc-aluminum coating on a ferrous product, by immersion in a bath of molten metal
US6270842B1 (en) * 1998-08-20 2001-08-07 Azuma Kogyo Co., Ltd. Method of galvanizing with molten zinc-aluminum alloy
US7811389B2 (en) * 2005-12-20 2010-10-12 Teck Metals Ltd. Flux and process for hot dip galvanization

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3696503A (en) * 1969-10-28 1972-10-10 Allied Tube & Conduit Corp Method for continuously galvanizing steel strip
US4738758A (en) * 1985-05-07 1988-04-19 International Lead Zinc Research Organization, Inc. Process for continuous deposition of a zinc-aluminum coating on a ferrous product, by immersion in a bath of molten metal
US6270842B1 (en) * 1998-08-20 2001-08-07 Azuma Kogyo Co., Ltd. Method of galvanizing with molten zinc-aluminum alloy
US7811389B2 (en) * 2005-12-20 2010-10-12 Teck Metals Ltd. Flux and process for hot dip galvanization

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107179749A (zh) * 2016-03-11 2017-09-19 宝山钢铁股份有限公司 热镀锌产品全流程质量控制方法
CN107179749B (zh) * 2016-03-11 2019-10-15 宝钢湛江钢铁有限公司 热镀锌产品全流程质量控制方法
CN106939398A (zh) * 2017-05-04 2017-07-11 西安泰力松新材料股份有限公司 一种金属丝镀锡工艺及其镀锡装置
WO2020173586A1 (fr) * 2019-02-25 2020-09-03 Fontaine Holdings Nv Procédé pour le zingage, en particulier la galvanisation à chaud, de produits en fer et en acier
CN113046673A (zh) * 2021-03-11 2021-06-29 江苏中远稀土新材料有限公司 一种用于钢制电缆桥架的耐蚀性稀土多元合金镀层

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AU2011349108B8 (en) 2015-10-01
AU2011349108A1 (en) 2013-05-02
AU2011349108B2 (en) 2015-09-17
NZ611941A (en) 2014-12-24

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