WO1997042354A1

WO1997042354A1 - Galvanising post-treatment apparatus and method

Info

Publication number: WO1997042354A1
Application number: PCT/AU1997/000276
Authority: WO
Inventors: Frank Iain Toomer; Neil John Metcalfe; Kenneth Walter Horne; John Conrad Hansen; Simon Alistair Murie
Original assignee: Industrial Galvanizers Corp Pty Ltd
Current assignee: Industrial Galvanizers Corp Pty Ltd
Priority date: 1996-05-08
Filing date: 1997-05-07
Publication date: 1997-11-13
Anticipated expiration: 1998-11-08
Also published as: AUPN973096A0; ZA973927B

Abstract

An apparatus for treating a galvanised ferrous article following removal of the article from a hot dip galvanising bath comprises a receiving member arranged to receive the galvanised article, rotation means for rotating the receiving member, and a magnet assembly arranged to draw the galvanised article into contact with the receiving member under the influence of a magnetic field.

Description

GALVANISING POST-TREATMENT APPARATUS AND METHOD

TECHNICAL FIELD

The present invention relates to an apparatus and a method for treating a hot dip galvanised ferrous article following removal of the article from a galvanising bath. Throughout the specification the expression "ferrous" is to be understood to embrace iron and alloys of iron such as steel . BACKGROUND ART Hot dip galvanising protects ferrous articles from corrosion by providing a tough metallic zinc envelope which completely covers the surface of the article and seals it from the corrosive action of its environment. When a ferrous article is hot dip galvanised, it is placed in a galvanising bath of a molten galvanising solution. The galvanising solution is typically zinc but the expression "galvanising solution" is to be understood to include alloys of zinc such as GALFAN^Φ (approximately 95% zinc, 5% aluminium and small amounts of rare earth metals) . (GALFAN is a registered trade mark of International Lead Zinc Research Organisation Inc.) . The galvanising solution reacts with the ferrous article to form layers of zinc-iron alloy which contain progressively greater proportions of zinc. The outermost layer is typically metallic zinc which is strongly resistant to corrosive action of normal environments.

Hot dip galvanising has long been practised to prevent corrosion of ferrous articles ranging in size from small articles such as nuts and bolts to very large articles such as bridge beams. In the case of small articles, it is common practice to load a multiplicity of such articles into a basket and dip them at the same time. On removal from the galvanising bath, the basket of now galvanised articles is typically placed in a centrifuge to remove excess zinc from the surface of the articles and thus improve the galvanised coating. DISCLOSURE OF THE INVENTION

In a first aspect, the present invention provides an apparatus for treating a galvanised ferrous article following removal of the article from a hot dip galvanising bath, the apparatus comprising a receiving member arranged to receive the galvanised article, rotation means for rotating the receiving member, and a magnet assembly arranged to draw the galvanised article into contact with the receiving member under the influence of a magnetic field.

In a second aspect, the present invention provides a method for treating a galvanised ferrous article following removal of the article from a hot dip galvanising bath, the method comprising the steps of drawing the galvanised article under the influence of a magnetic field into contact with a rotating receiving member, and ejecting the galvanised article from the rotating receiving member under the influence of centrifugal force.

Ferrous articles are ferromagnetic and hence are capable of being drawn to a magnetic field. Various other metals and alloys including stainless steels, mild steel containing 15% manganese and galvanising solutions are transmissive to magnetic fields and hence a magnetic field can be transmitted through, for example, most stainless steels. According to the present invention, following galvanising, a ferrous article is drawn under the influence of a magnetic field into contact with a rotating receiving member and is subsequently ejected from the rotating receiving member under the influence of centrifugal force to remove excess galvanising solution from the ferrous article. Excess galvanising solution can be removed from the ferrous article at various points during this operation including when the ferrous article makes contact with the rotating receiving member and when the ferrous article is ejected from the rotating receiving member. Following ejection from the rotating receiving member, the ferrous article is preferably slowed, cooled and collected. The present invention thus enables automation of the treatment of a hot dip galvanised article.

The receiving member is preferably a plate of stainless steel or other magnetically transmissive material . The plate may be arranged to rotate in the horizontal plane with recently galvanised articles tipped onto the plate from the basket in which they were galvanised and drawn into contact with a desired position on the plate by the magnetic field. The plate may be arranged to rotate in other planes. Preferably, the plate is arranged to rotate in the vertical plane for use in conjunction with the invention the subject of an Australian provisional patent application no. PN9706 entitled "Galvanising Apparatus and Method" filed by the present applicant on 7 May 1996. The disclosure of application no. PN9706 is incorporated herein by reference.

Application no. PN9706 relates to an invention in which a ferrous article is withdrawn from a hot dip galvanising solution under the influence of a magnetic field. In using the invention the subject of application no. PN9706 in conjunction with the present invention, it is preferred that at the point where movement of the ferrous article ceases to be controlled by the magnetic field withdrawing it from the galvanising solution, it falls under the influence of the magnetic field of the present invention. The ferrous article is thus preferably withdrawn from the galvanising solution and then drawn into contact with the rotating receiving member of the present invention in an essentially continuous movement .

The magnetic field which draws the galvanised article into contact with the rotating plate is preferably a static magnetic field generated by a bar electromagnet located on the side of the plate remote from the direction in which the ferrous article(s) is/are drawn to the plate with the axis of the core of the electromagnet substantially normal to the face of the plate.

The plate is preferably mounted on a shaft and is preferably caused to rotate by action of a variable electric motor driving the shaft. The strength of the magnetic field is preferably variable by varying the current supplied to the electromagnet from a variable magnet controller.

The strength of the magnetic field and the speed of rotation of the plate are preferably matched such that the ferrous article(s) contacts the plate at an area substantially aligned with the axis of the core of the electromagnet with the ferrous article then moving with respect to the plate whilst substantially retaining its position with respect to the core of the magnet until means for removing the influence of the magnetic field cause the ferrous article to move with the plate and be ejected from the plate under the influence of centrifugal force. The means for removing magnetic influence may comprise momentarily reducing the strength of the magnetic field but preferably, it comprises an aberration in the surface of the plate such as an upstanding barrier.

Following ejection from the plate the galvanised ferrous articles which have been removed of excess galvanising solution are preferably slowed and cooled.

Slowing and cooling of the galvanised article(s) may be achieved by one or more of the following techniques.

The galvanised article(s) may be ejected through a magnetic field of progressively decreasing strength which slows the galvanised article(s) . The galvanised article (s) may be ejected through one or more curtains of water or the like which slow and cool the galvanised articles. The galvanised article(s) may be ejected into a barrier such as a rubber blanket which slows the galvanised article(s). The galvanised article(s) may be ejected into a vessel of cooling solution such as water which cools the galvanised article(s). It is sometimes desirable to remove excess galvanising solution from a hot dip galvanised article in the absence of atmospheric oxygen, particularly where the

_Φ galvanising solution is GALFAN . The apparatus of the present invention may be arranged to be encased in or covered by a shroud to operate in an inert gas atmosphere such as nitrogen or a reducing atmosphere such as nitrogen/hydrogen.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of an embodiment of the present invention,

Figure 2 is an end elevation of the embodiment of

Figure 1, Figure 3 is a schematic plan of the plate of Figures

1 and 2 and downstream processing apparatus, and

Figure 4 is a schematic side elevation of Figure 3.

Referring firstly to Figures 1 and 2 , the apparatus 10 comprises a receiving member in the form of a plate 12, rotation means in the form of a variable speed electric motor 14 connected to plate 12 by a shaft 16, and a magnet assembly 18. The plate 12, electric motor 14, shaft 16 and magnet assembly 18 are mounted on a stainless steel frame 19 so as not to transmit the magnetic field generated by magnet assembly 18 to the electric motor 14 with consequential adverse affect on the operation of electric motor 14.

The magnet assembly 18 comprises a bar electromagnet

20 having a core 21 which is rectangular in cross- section. The electromagnet 20 has a magnetic coil which is supplied current from a variable 240V DC power supply. When current is applied to the electromagnet 20 a strong magnetic field is induced which draws ferrous articles in the direction of the arrow marked A in Figure 1. Electromagnets of the kind described above can generate magnetic fields equivalent to 0-150,000 ampere turns.

The plate 12 is formed from stainless steel so as to be transmissive of the magnetic field generated by the electromagnet 20. As illustrated, the plate 12 is circular, 12mm thick and has a diameter of 1,250mm but it is to be appreciated that it may be larger or smaller and may be of a different shape. The centre of the plate 12 is mounted to shaft 16 which is driven by variable speed electric motor 14. The electric motor 14 spins the plate 12 (counter-clockwise as viewed in Figure 2) at speeds in the range of 0-500rpm but it is to be appreciated that variations of the design could achieve rotation of the plate 12 at speeds in excess of 500rpm if necessary. It is also to be appreciated that the apparatus 10 could be configured to facilitate clockwise rotation of the plate 12. The plate 12 rotates in the vertical plane and its rear face 22 is located close to the front face of the core 21 of the magnet 20 so that maximum magnetic field is transmitted through the plate 12. The core 21 is positioned between the centre and the rim of the plate 12 with the axis of the core 21 located closer to the rim than the centre of plate 12. The front face 24 of the plate 12 is formed with a centrally located stainless steel shroud 26 which prevents galvanised ferrous articles from moving towards the centre of plate 12. Four arms 28 (not illustrated in Figure 1) formed from stainless steel angle radiate from the shroud 26. It is to be appreciated that the number of such arms 28 can be varied.

In use, the plate 12 is rotated by supplying current to electric motor 14 and a magnetic field is transmitted through plate 12 by supplying current to electromagnet 20. Following hot dip galvanising, galvanised ferrous articles are drawn to plate 12 at an area coinciding with the centre of the transmitted magnetic field and are retained in contact with plate 12 by the magnetic field. The action of the galvanised ferrous article striking plate 12 removes a proportion of the excess galvanising solution on the ferrous article. Following impact of the ferrous article on plate 12, the ferrous article is subject to three different forces, namely gravitational force, attraction to the magnetic field, and the tendency to move with plate 12. The strength of the magnetic field and the speed of rotation of the plate 12 are such that the ferrous article effectively slides over the plate 12 rotating beneath it and remains in an effectively constant location with respect to the core 21 of the electromagnet 20 until it is met by one of the arms 28. At this point, the ferrous article commences moving with the plate 12 with the affect of the magnetic force diminishing as the ferrous article moves with the plate 12 over the corner of the core 21 until the ferrous article is free of the magnetic field and subject to gravitational and centrifugal forces. The result is that the ferrous article is ejected from the rim of the plate in a substantially vertical plane where it is available to be collected and cooled. In being ejected from the plate 12, some of the remaining excess galvanising solution on the ferrous article may be removed by an inertial action. The lines of ejection of a series of articles from plate 12 are sufficiently close to facilitate collection of the articles.

Referring now to Figures 3 and 4, the ferrous articles are ejected from the plate 12 in the direction of arrow B (see Figure 3) and into shrouding structure 30 having a roof 32 and side walls 34 and 36. The ferrous articles then strike inclined barrier 38, possibly after having bounced off the inside of roof 32 or side walls 34 or 36, and move under the influence of gravity down barrier 38 until they land on stainless steel conveyor belt 40 having an upper run 42 moving in the direction of arrow C (see Figure 4) . Excess galvanising solution removed from the ferrous articles on striking barrier 38 and excess galvanising solution ejected into shrouding structure 30 similarly land on upper run 42. The ferrous articles and excess galvanising solution then move along the upper run 42 below the lower edge 44 of barrier 38 until they pass beneath transverse magnetic separator 46. The magnetic separator 46 comprises a bar electromagnet 48 mounted inside stainless steel conveyor belt 50 which has an upper run 52 moving in the direction of arrow D (see Figure 3) . Galvanising solution is non¬ magnetic and hence the excess galvanising solution travelling on upper run 42 is not attracted to electromagnet 48 and continues along upper run 42 beneath magnetic separator 46 until it follows the path of arrow E (see Figure 4) into collection bin 54 from which it is available for subsequent re-use. Being magnetic, the galvanised ferrous articles are lifted from upper run 42 into contact with the lower run 56 of conveyor belt 50 as they travel along upper run 42 beneath magnetic separator 46. The conveyor belt 50 is formed with a series of transversely mounted stainless steel arms (not shown) . Following contact with lower run 56, the galvanised ferrous articles are transported to upper run 52 where they move in the direction of arrow D and are removed from the conveyor belt 50 during subsequent movement from upper run 52 to lower run 56. Following removal from conveyor belt 50 the galvanised ferrous articles are available for further processing such as quenching.

Claims

1. An apparatus for treating a galvanised ferrous article following removal of the article from a hot dip galvanising bath, the apparatus comprising a receiving member arranged to receive the galvanised article, rotation means for rotating the receiving member, and a magnet assembly arranged to draw the galvanised article into contact with the receiving member under the influence of a magnetic field.

2. An apparatus as claimed in claim 1 wherein the receiving member is a plate having a front face for receiving the galvanised article and a rear plate remote from the front face.

3. An apparatus as claimed in claim 2 wherein the front face of the plate has an upstanding arm which extends from a central portion of the front face of the plate to an edge of the front face of the plate.

4. An apparatus as claimed in claim 3 wherein the plate has a plurality of upstanding arms.

5. An apparatus as claimed in claim 3 or claim 4 wherein the plate is a circular plate and the plate and the arms are formed from stainless steel.

6. An apparatus as claimed in any one of the preceding claims wherein the receiving member is arranged to be rotated in the vertical plane by the rotation means.

7. An apparatus as claimed in any one of the preceding claims wherein the rotation means comprises a variable speed electric motor arranged to drive a shaft mounted to the receiving member.

8. An apparatus as claimed in any one of claims 2-7 wherein the magnet assembly comprises a bar electromagnet having a core adjacent the rear face of the plate with the axis of the core being substantially normal to the rear face of the plate.

9. An apparatus as claimed in any one of the preceding claims further comprising means for slowing galvanised ferrous articles ejected from the receiving member.

10. An apparatus as claimed in claim 9 wherein the means for slowing comprises a shrouding structure having an internal barrier into which the galvanised ferrous articles are arranged to be ejected from the receiving member.

11. A method for treating a galvanised ferrous article following removal of the article from a hot dip galvanising bath, the method comprising the steps of drawing the galvanised article under the influence of a magnetic field into contact with a rotating receiving member, and ejecting the galvanised article from the rotating receiving member under the influence of centrifugal force.

12. A method as claimed in claim 11 wherein the ferrous article is removed from the hot dip galvanising bath under the influence of a second magnetic field and then drawn into contact with the rotating receiving member under the influence of the magnetic field in a substantially continuous movement.

13. A method as claimed in claim 11 which utilises an apparatus as claimed in any one of claims 1-10.

14. A galvanised ferrous article treated by a method as claimed in any one of claims 11-13.