AU688026B2 - Method and apparatus to galvanise metal strip - Google Patents

Description

Method and Apparatus to Galvanise Metal Strip Technical Field The present invention relates to the galvanising of steel articles and more particularly but not exclusively to the galvanising of steel strip.

Background of the Invention The present invention is improvements in or modifications of the galvanising processes described in Australian Patent 425028 (Application 33451/71).

When the processes of the above mentioned Australian patent are employed to galvanise steel strip, there are several disadvantages which are present. Firstly the quality of the coating is such that it cannot be painted to provide a smooth aesthetically pleasing surface. More particularly, when the coating applied to the metal strip solidifies, the "spangles" formed are large and quite visible with definite crystal grain interfaces. These interfaces detract from the appearance of the product when it is painted. It usually requires excessive amounts of undercoat and paint to fill the voids.

15 A still further disadvantage is product damage resulting from relative movement between the steel strip and the roller or rollers employed in the galvanising kettle. In the above mentioned Australian patent, the strip passes between two pairs of rollers immersed S.in a kettle containing molten lead. In units constructed in accordance with the teachings of this Australian patent, there is frequently only employed a single roller about which the 20 strip passes. This roller is also immersed in the lead bath. Relative movement between the roller or rollers and the metal strip destroys the surface finish of the product manufactured. The damage is usually sufficient to have the product discarded as scrap.

A still further disadvantage of the above discussed process is the limited output of the pot. This restriction results from limits in respect of the amount of heat that can be introduced to the coating metals through the pot walls.

Object of the Invention It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

Summary of the Invention There is disclosed herein an apparatus to galvanise steel strip, said apparatus comprising: a pot divided to provide a first zone to receive molten zinc, zinc alloy or zinc alloys, a second zone to contain molten lead, and a third zone to receive molten flux, the zones being arranged along a path along which the strip passes to pass through said third zone, then said second zone to said first zone; and a roller located in said second zone and arranged along said path so that said strip passes about said roller.

(N:\LIBTTJ00074:LMM 2 In a first aspect of the present invention, the apparatus includes a means to produce a reducing flame to heat the strip prior to the strip entering said third zone. Preferably an extraction fan would be provided to withdraw flux fumes from said third zone.

Preferably, the apparatus includes heating means contained in said second zone and arranged along said path to heat the strip prior to the strip being engaged by said roller.

Preferably, the pot includes a pot wall adjacent said roller, and means to heat said pot wall in order to increase the temperature of the lead adjacent said roller.

In a further aspect of the present invention, the apparatus includes water delivery means positioned to deliver water to said strip as it exits from said first zone. Preferably the water contains potassium fluoride.

Brief Description of the Drawing Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawing, wherein: Figure 1 is a schematic sectioned side elevation of an apparatus to galvanise steel 15 strip; Figure 2 is a schematic sectioned side elevation of an alternative preheating device *which may be employed in the apparatus of Figure 1; Figure 3 is a schematic sectioned side elevation of nozzles employed in the apparatus of Figure 1, to cool the strip; Figure 4 is an enlarged schematic side elevation of a portion of the nozzles of Figure 3; and Figure 5 is a schematic plan view of the nozzles of Figure 3.

Detailed Description of the Preferred Embodiment In the accompanying drawing there is schematically depicted an apparatus 10 to 25 galvanise steel strip 11 so as to apply a coating thereto.

The apparatus 10 includes a pot 12 having a side wall or walls 13 and a bottom wall 14. The pot is divided internally by first weir 15 so that the weir 15 cooperates with the S9 side wall 13 to at least partly enclose a first zone 16 to receive molten zinc, a zinc alloy or zinc alloys. The molten zinc has a lower surface 17.

Walls 13 and 14 basically enclose a second zone 19 which contains molten lead.

A second weir 18 encloses a third zone 20 which contains molten flux.

A chute 21 encloses a fourth zone 22 which contains molten aluminium or aluminium alloy.

The flux in the zone 20 has a lower surface 23 while the flux in the zone 22 has a lower surface 24.

Contained in the zone 19 so as to be immersed in the molten lead, is a roller which is supported by means of a stem 26 for rotation about a horizontal axis. The roller is freely rotatable. The bottom wall 14 is provided with a trough 26 to which there is IN:\LIBTT100OO74:LMM

I

directed jets 27 to deliver flame to the trough 26 to raise the temperature of the lead adjacent the roller 26.

Located above the weir 18 is a canopy 28 enclosing a space 29. The canopy 28 contains flux vapours so the vapours are basically restricted so as to be contained within the space 29, Communicating with the space 29 is an exhaust fan to inhibit flux vapours exiting through the aperture 30 through which the strip 11 passes, Located above the third zone 20 are nozzles 31 which produce a "reducing" flame to pre-heat the strip 11 prior to it entering zone The strip 11 is further heated by means of heating elements 32 arranged adjacent the strip 11 prior to engaging the roller A duct 33 is provided along which molten aluminium is passed to the lower zones of the molten lead contained within the zone 19. The conduit 33 communicates with the zone 22 so as to receive the molten lead therefrom.

The strip 11, upon passing through at least a portion of the zone 16, engages a pair of spaced rollers 34 which remove excess material from the strip 11. The rollers 34 aid in maintaining an even coating on the strip 11.

As the strip 11 leaves the zone 16, it passes water nozzle assembly 35 which delivers water spray to impact against the hot strip 11. The water is caused to evaporate rapidly. The evaporating water rapidly removes heat from the strip 11 and causes the "spangle" size of the coating material to be reduced considerably.

In operation of the above described apparatus 10, the strip 11 prior to being delivered to the apparatus 10 is cleaned by "pickling" in acid. It is then subsequently water rinsed. It is important at this stage that the strip be of a very high standard in respect of being free from oil (rolling or rust preventative oil). The strip then enters the apparatus 10 and is heated by the nozzles 31 to approximately 1 100'C. The reducing flame aids in maintaining cleanliness of the strip for delivery to the molten flux contained in the zone 20. The extraction fan removing the flux vapours also aids in maintaining cleanliness of the strip, particularly with regard to pre-heating of the strip immediately adjacent the zone The strip 11 passes through the flux zone 20 and then past the heating elements 32.

The heating elements 32, while heating the strip 31, also heat the surrounding lead to reduce the viscosity thereof and therefore the drag on the roller 25, Similarly heating of the trough 26 also raises the temperature of the lead and therefore reduces its viscosity.

By reducing the viscosity there is less drag on the roller 25 and therefore the frictional forces required to drive the roller 25 are reduced. This in turn will reduce the incidence of relative movement between the strip 11 and the roller 25, It is also proposed to have the roller 25 manufactured so as to have a diameter in the vicinity of 500-900mm, depending on the thickness of the strip.

INALIBTTIOOO74:LMM 4 After leaving the zone 19, the strip passes through the zone 16 for coating. Excess material is removed via the rollers 34, and as the strip exits the zone 16, water from the assembly 35 rapidly cools the strip in order to produce a high quality coating.

In Figure 2, there is schematically depicted the pot 12 of Figure 1. In this embodiment, there is provided an alternative preheating assembly 36. The preheating assembly 36 aids in raising the temperature of the strip 11 prior to it entering the pot 12.

In this respect it should be appreciated that the output of the pot 12 is restricted by the amount of heat which can be transmitted to the coating material in the pot 12. The output is therefore increased by preheating the strip 11 prior to entering the pot 12.

The assembly 36 includes a gas furnace 37 which would typically produce gas temperatures in the vicinity of 1100°C. This will rapidly heat the strip 11 and will assist in removing the milling oil from the surface of the strip 11. This improves the galvanising process. Direct flame impingement on the strip 11 will assist both strip heating and surface cleaning. The flame is a reducing flame to permit oxidizing of the strip surface while in the furnace 37. As the strip leaves the end of the furnace 37, it will oxidize rapidly if exposed to air and sinc, it is at an elevated temperature. To eliminate o°° this, a shroud 38 surrounds the strip 11, through which shroud 38 flue gases pass by being delivered thereto via a duct 39. The duct 39 extends from the upper end of the .oeooi S: furnace 37 to the lower end of the shroud 38, Gas and air would be delivered to the S 20 furnace 37 to ensure that a reducing flame is provided. By having flue gases delivered to the shroud 38, an inner gas flow surrounds the strip 11.

In Figures 3 to 5, there is schematically depicted the water nozzle assembly The nozzle assembly 35 includes a plurality of nozzles arranged in two sets 36 and 37. The sets 36 and 37 are on opposite sides of the strip 11 and are of substantially the gO•• same construction and arrangement. The nozzles 36 and 37 are arranged in a "V" configuration as best seen in Figure 5. Compressed air is delivered to each nozzle 36 and S 37 by means of a duct 38. Water is also delivered to each nozzle 36 and 37 by means of a duct 39. If so required chemicals may be added to the water to enhance the surface finish being produced. Typically potassium fluoride is added to the water. For example 2-5 by weight of potassium fluoride could be added to the water.

In operation of the above described nozzle assembly 35, the air pressure is adjusted as well as the distance the nozzles are from the strip. Typically, the nozzles are spaced 75-120mm from the strip and each of the nozzles 36 and 37 are spaced from their adjacent nozzles by approximately 75mm. Preferably, the nozzle assembly 35 is placed just before the zinc would normally freeze in air. This adjustment is used to optimise surface finish and typically the nozzle assembly 35 would be positioned between 700mm and 3,700mm above the coating control jets 40 which may be used in conjunction with or as an alternative to the rollers 34, Preferably the assembly 35 would be designed for rapid removal from the coating line by being mounted on wheels and supported on a steel support structure. Preferably it IN:\LBr100074:LMM

I

B

would be laterally movable relative to the strip 11, or be completely removable by overhead crane.

4 *4 a a a a a a. 4 a.

a a. a aa a 4a 4* a a a a a a a IN~kLIBTT]00074:LMM

Claims (11)

1. An apparatus to galvanise steel strip, said apparatus comprising: a pot divided to provide a first zone to receive molten zinc, zinc alloy or zinc alloys, a second zone to contain molten lead, and a third zone to receive molten flux, the zones being arranged along a path along which the strip passes to pass through said third zone, then said second zone to said first zone; a roller located in said second zone and arranged along said path so that said strip passes about said roller; and means to produce a reducing flame to heat the strip prior to the strip entering said third zone.

2. The apparatus of claim 1, wherein the means to produce a reducing flame is a furnace.

3. The apparatus of claim 2, wherein said furnace has an entry portion through which the strip enters the furnace, and an exit portion through which the strip leaves the furnace, and said apparatus further includes a shroud to surround the strip as it leaves the rir furnace, the shroud extending to adjacent the third zone, and duct means to deliver exhaust gases from said furnace to said shroud so that the strip passing therethrough is surrounded by an inert gas.

4. The apparatus of claim 1, 2 or 3, further including extraction means to S 20 withdraw flux fumes from said third zone.

The apparatus of any one of claims 1 to 4, wherein said pot has a pot wall adjacent said roller, and said apparatus further includes means to heat said pot wall in order to increase the temperature of lead adjacent said roller.

6. The apparatus of any one of claims 1 to 5, further including means in said second zone between said first zone and said roller, to heat lead adjacent the strip.

7. An apparatus to galvanize steel strip, said appartus comprising: a pot divided to provide a first zone to receive molten zinc, zinc alloy or zinc alloys, o a second zone to contain molten lead and a third zone to receive molten flux, the zones being arranged along a path along which the strip passes to pass through said third zone, then said second zone to said first zone; a roller located in said second zone arranged along said path so that said strip passes about said roller; and water delivery means positioned to deliver water to said strip as it exits from said first zone.

8. The apparatus of claim 7, wherein said water delivery means is a plurality of water nozzles, the nozzles being arranged in two sets, with the sets being located on opposite sides of said path so that opposite sides of the strip receive water sprayed from the nozzles. [N\LIBTTJOOO74:LMM I

9. The apparatus of claim 8, wherein the nozzles of said first set and the nozzles in said second set are each arranged in a configuration with the nozzles of each set being arranged in two lines which converge in the direction of travel of the strip.

The apparatus of claim 7, 8 or 9, wherein said water delivery means includes means to deliver air under pressure to said nozzles to aid in spraying the water on the strip.

11. An apparatus to galvanize steel strip, substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 1 and 2 as modified by Figure 3. Dated 25 May, 1995 -Versen-lntemationa--(Aust-Pty--td- Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON &onx /nkr\Q-hefonal Ausa P- S o. -0 S fee: *C C C IN:\LIBlTT00074:LMM I Method and Apparatus to Galvanise Metal Strip Abstract An apparatus (10) to galvanise steel strip (11) so as to apply to a coating thereto. The apparatus (10) includes a pot (12) within which there is located a roller (25) about which the strip (11) passes. Prior to entering the pot the strip (11) is preheated by nozzles (31) applying to the strip (11) a "reducing" flame. When the strip (11) leaves the pot water is applied to the strip (11) by a nozzle assembly Figure 1 a.e. *a a o |N:\LIBTT)00074:LMM -I