GB2145432A - Improvements in metal coating and marking processes - Google Patents

Abstract

During manufacture, a metal bar, billet or bloom or the like prior to being conveyed past a coating apparatus is first treated at a preparation station where a rotary tool (20) having a multiplicity of heat, wear and impact resistant bodies (22) contacts the metal and chips off or abrades away the oxide or scale film leaving clean, bare metal. The adjacent coating station then immediately applies the desired coating onto the bare metal. The coating can take the form of identifying symbols created e.g. by a spray or jet-type printing head. Cleaning and coating can be performed on the metal when it is cold, red hot or at some intermediate temperature. <IMAGE>

Description

SPECIFICATION Improvements in metal coating and marking processes The present invention relates to improvements in coating processes, such as are used to apply certain coatings to metal substrates which are, or have been, at high temperatures. The temperature levels are so elevated that the substrates carry an oxide film, or scale, of appreciable thickness. Not uncommonly, such an oxidised layer is rather weak and may well flake off, taking with it a coating applied thereto.

The particular coating process with which we are mainly concerned is used to apply identifying markings onto metal products in the course of their manufacture in foundry or mill. Composition and treatment history are well known to affect the properties of metals, e.g. steels, significantly. Permanent marking is of great importance since different steels are not readily distinguishable just by visual inspection. It may well be necessary to mark a steel product very soon after it has issued from a continuous casting machine. Obviously, the metal will then be very hot, e.g. at 1000"--1200"C or higher. There may be other occasions when the metal to be marked is or has bcen as hot as this, e.g. following hot rolling or forging.Whether the marking is applied to the metal when hot, or after cooling to ambient temperature, it will have a thick layer of oxide thereon ("mill scale" in steel-making terminology).

The need to mark readily oxidisable metal products is not, of course, confined to the ferrous metallurgical industry.

In view of the tendency for oxide or scale to flake off, identification markings or indicia should be applied to the clean metal per se, so the oxide or scale should first be removed.

Several scale removal methods have been tried. In one method, a high pressure water jet is directed at the scale. This works reasonably adequately when the metal product is hot. Considerable amounts of steam are produced and the method is thus potentially risky to workers. Wire brushing has been tried, but is impractical. The brushes which are costly to replacc wear or melt away unduly quickly in contact with hot metal. Yet another method proposes playing an oxy-acetylcne fiame over the oxidised substrate. Thermal shock would presumably be responsible for attacking the oxide layer in large measure. This approach might seem simple, but the cost in terms of gas consumption is unacceptably high.Moreover, the ever increasing degree of automation in metal production plants calls for automated operations, and descaling equipment employing such burners would be prohibitively expensive to build.

Once the scale has been detached in some way, the indicia must be quickly applied to the metal surface, before significant re-oxidation products accumulate.

There are several indicia-depositing techniques available. One employs a jet-type dot printer, in which a high temperature resisting ink or paint is projected in a controlled manner onto the descaled area. Somewhat similar methods involve jetting a fusible powder onto the substrate or evaporating a suitable metal such as aluminium onto the substrate. Indicia can be generated by spraying inks, paints, fusible powders or metals through stencils onto the substrate. Stencil-cutting and spray marking machines are available for this purpose. Impression marking is another technique available.

By the use of a suitable marking material, oxidation of the metal underlying the applied indicia will be inhibited. The indicia will then be capable of standing out visibly against the surrounding background. Corrosion of thc underlying metal can be similarly inhibited by the indicia, so markings should remain visible after extended storage in stockyards. The permanence of the indicia will, however, ultimately depend on the efficacy of the scale removal method used before the indicia are applied.

The present invention aims to provide an improved metal coating method, wherein the coating is for instance in the form of indicia, said method incorporating a more efficacious oxide or scale-removing technique than hitherto available and which, above all, is inexpensive to perform. The invention also aims to provide apparatus capable of accomplishing the method.

According to the present invention, there is provided a method of providing metals covered by oxide or scale with permanent coatings e.g. in the form of identification markings, wherein a metal article is first presented to a surface preparation station and then to a coating station for receipt of the coating, and at the first station its oxide or scale covering is stipped therefrom by a flaying tool which comprises rapidly moving bodies of heat, wear and impact resistant material.

The invention also provides apparatus for providing metals covered by oxide or scale with permanent coatings e.g. in the form of identification markings, comprising a surface preparation station and an adjacent coating station to which a metal article for coating is presented in turn, the first station employing a flaying tool for stripping the oxide or scale covering from the article, the tool comprising rapidly moving bodies of heat, wear and impact resistant material.

The oxide or scale covering is flayed from the metal article by fragmenting and detaching it due to impact, where the covering is itself weak and is weakly bonded to the underlying metal, by abrading it, or both.

The present invention will now be described in more details, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 somewhat diagrammatically shows apparatus according to the invention in perspective, and Fig. 2 shows a flaying tool employed in the apparatus shown in Fig. 1.

The apparatus 10 is for applying identifying symbols or indicia to a metal article 11 such as a slab, billet, bloom, continuously cast strand or milled sheet or strip. The apparatus comprises two adjacent stations past which the moving article 11 is conveyed. The first station 1 2 encountered by the article 11 is a surface preparation station which flays oxide or scale from that part of the article to receive indicia. The second station 1 4 is a printing station for applying the indicia to the deoxidised or de-scaled surface.

The illustrated printing station 1 4 has a jettype dot printer head 1 5 but other types of printer can be substituted. Such printers as spray an ink or paint through a stencil can be used, for instance. For forming the indicia, inks, paints, fusible powders and sprayed metals can be used. The chosen material should survive high temperatures since the article may be red hot at the time of applying the indicia to it or at a later stage in its processing.

At the heart of the surface preparation station is a rotary flaying tool 20. The tool has a central shaft 21 and a multiplicity of balls 22 attached thereto by radial arms 23. The arms are flexible so as to give, and are wire, fibre or plastics bristles. The arms 23 support the balls at their free ends, and here there is one ball per arm. The balls are made from heat, wear and impact resistant material and can be made of corundum, the carbides or silicon, tungsten or boron, and the like. The tool is rotated such that the balls move at high speed to rap or abrade the surface oxide or scale efficiently from the article 11. To rotate the tool 20 a pneumatic, hydraulic or electric motor is provided (not visible in the drawings). Finding the best speed of rotation of the tool 20 is a matter of trial and error and speeds not higher than 1000 RPM or so are contemplated.

The tool 20 and its motor are mounted on a carrier arm 25 supported by a crossed-slideway system 26. The mounting on carrier arm 25 is such that the tool 20 is positionable in a vertical direction, and its position in a horizontal plane is variable by the slideway system 26. Pneumatic, hydraulic, electric or cam-type actuators with suitable controls are provided to position the tool in the three mutually perpendicular directions relative to the moving article 11. Conveniently, the said mounting permits the tool and motor to be positionally adjustable about a vertical axis. A guard 28 shields the tool motor and the tool and protects bystanders from flying grit, sparks and so on. Means can be provided to flood the tool 20 with a coolant which can be gaseous or liquid; if the latter then it can be a lubricant too.

The coating station 14 and in particular the head 1 5 are movable in at least two directions (in the horizontal plane), thanks to a second crossed-slideway system 30. The positioning of head 1 5 is controlled and effected in a manner similar to the positioning of the tool 20.

Overall control of the apparatus 10 will be governed by means of detectors which sense the approach of the article 11 and its precise path of movement or position. Signals from the detectors can be applied to a microprocessor responsible for moving the tool and printing head into their operative positions relative to the article and for operating them in proper synchronism.

In operation, the tool 20 is advanced towards the article 11 such that its balls 22 can make contact with the surface of the moving article. As the tool rotates, the rapidly moving balls fragment and detach, and/or abrade away, the oxide or scale covering. A patch of clean, bare metal is cleared, long enough to receive the identifying symbols. The latter are then applied almost immediately, and before substantial re-oxidation of the metal can occur, by the closely adjacent printing head 1 5.

The procedure can be performed on red-hot metal articles or on articles which have cooled to ambient temperature or some intermediate temperature. For some coating materials, the metal substrate may have to be at 300on or more.

As described above, the article is prepared and marked while in motion. In principle the article could be prepared and marked while stationary, relative motion between it, the tool 20 and the head 1 5 being gained by operation of the slideway systems 26, 30.

The identifying symbols can conveniently be machine-readable, and they need not be alpha-numeric. Bar or stripe coded indicia could be applied by the head 1 5.

If desired, a further station can be interposed between stations 1 2 and 14, for spraying a primer coating onto the metal article 11 before it receives its indicia. Such a primer coating will be applied to reduce or eliminate oxidation or rusting of the area containing the indicia.

Rather than prepare just a relatively small area of the article, the tool could de-oxidise and descale a substantial area. Then, if the prepared surface is primed, there is provision for indicia to be applied thereto at different stages in the processing of the article.

The flaying tool could be used to de-oxidise and descale the entire face of thc article. The station 14 could then be used to deposit a protective coating over the whole of that surface. The invention is thus not limited exclusively to providing coatings actually in the form of indicia but extends to full-surface coating.

The flaying tool 20 is not overly costly and is expected to be serviceable for use when applying identification symbols to several tens of steel bars, billets, blooms etc. The expense per article in terms of tool costs is expected to be minimal, therefore.

Claims (11)

1. A method of providing metals covered by oxide or scale with permanent coatings e.g. in the form of identification markings, wherein a metal article is first presented to a surface preparation station and then to a coating station for receipt of the coating, and at the first station its oxide or scale covering is stripped therefrom by a flaying tool which comprises rapidly moving bodies of heat, wear and impact resistant material.

2. A method according to claim 1, wherein said bodies are rotated into contact with the article and are each supported on the end of a flexible arm so as to perform a flailing action.

3. A method according to claim 1 or claim 2, wherein said bodies are balls of heat and wear resistant material selected from alumina and the carbides of silicon, tungsten and boron.

4. A method according to claim 1, 2 or 3, wherein the metal article is flayed and coated while at a temperature in excess of 300"C.

5. A method according to claim 1, 2, 3 or 4, wherein the metal article is flayed and coated while moving past the respective stations.

6. A method of coating oxide or scale covered metals, e.g. to provide identification markings thereon, substantially as herein described with reference to the accompanying drawings.

7. Apparatus for providing metals covered by oxide or scale with permanent coatings e.g. in the form of identification markings, comprising a surface preparation station and an adjacent coating station to which a metal article for coating is presented in turn, the first station employing a flaying tool for stripping the oxide or scale covering from the article, the tool comprising rapidly moving bodies of heat, wear and impact resistant material.

8. Apparatus according to claim 7, wherein the tool is rotationally driven and each of said bodies is supported from a shaft of the tool at the end of a flexible arm so as to perform a flailing action on the article.

9. Apparatus according to claim 7 or claim 8, wherein said bodies are balls of heat and wear resistant material selected from alumina and the carbides of silicon, tungsten and boron.

10. Apparatus according to claim 7, 8 or 9, wherein the coating station comprises an ink, paint or powder sprayer.

11. Apparatus according to claim 7, 8 or 9, wherein the coating station comprises a stencil and spray printer or a jet type printer for applying a coating in the form of alphanumeric symbols.

1 2. Apparatus for coating oxide or scale covered metals, substantially as herein described with reference to and as shown in the accompanying drawings.