GB2202552A

GB2202552A - Coating elongated carbon articles by spraying

Info

Publication number: GB2202552A
Application number: GB08805185A
Authority: GB
Inventors: Kalervo Pietilainen; Bertil Holmgren
Original assignee: COATED ELECTRODES International
Current assignee: COATED ELECTRODES International
Priority date: 1987-03-06
Filing date: 1988-03-04
Publication date: 1988-09-28
Also published as: GB8805185D0; GB8705271D0

Abstract

Apparatus for applying protective coating to an elongate carbon article e.g. an electrode for use in electric arc steel-making includes a carriage 1 suspended from a track 30 located above the carriage, a headstock and tailstock 19, 20 mounted on the carriage between which a carbon article to be coated can be supported, means 21, 21 being provided for imparting rotation through the headstock and/or tailstock 19, 20 to effect controlled rotation of the carbon article supported therebetween and a fixed coating station 3 including one or more spray devices operable to apply a coating of oxidation resistant material to the surface of the supported carbon article. The carriage is driven along the overhead track such that, in operation, the surface of the rotating article passes in close proximity to the coating station. <IMAGE>

Description

Coating Carbon Articles This invention relates to apparatus for and a method of applying a coating of protective material to the surface of an elongate carbon article. More especially, but not exclusively, the invention concerns the coating of graphite electrodes to protect them against oxidation.

Protecting graphite electrodes for use in, for example, electric arc steelmaking by coating the electrode surface with one or more layers of molten aluminium and/or aluminium alloys is well known. In one particular coating process, sequentially applied layers of molten aluminium and aluminium alloy are subjected to an electric-arc treatment by means of a side electrode which describes a helical path with respect to the surface of the coated electrode..

During the coating process, a DC current of between 1,000 and 2,000 amperes is supplied to the body of the electrode to be coated.

Hitherto, machines employed for this and similar coating processes have generally consisted of a lathetype machine which includes fixed and loose headstock and tailstock spindles between which the electrode is supported for rotation with its longitudinal axis generally horizontal. Rotation is imparted by means of a DC or AC motor coupled through a gearbox to the fixed headstock spindle. Positioned to one side of the electrode to be coated is a slide rest which is moved lengthwise of the electrode by means of a lead-screw driven by a separate DC motor or mechanically from the rotation gearbox. The slide rest carries the various coating, arc treatment and grinding devices used during the coating process.

Both types of machine referred to above suffer from the disadvantage that both the slide rest and the electrode need to be driven to achieve the required coating, the former in the longitudinal sense generally parallel to the electrode axis and the latter in a rotational sense. In addition to the complications which arise because of the need to impose these independent drives, it is evident that advantages accrue from an arrangement in which the various coating, arc treatment and grinding stages could be effected at a static location.

Other disadvantages inherent in known machines are principally a consequence of the manner in which the electrodes to be coated are supported. In many known machines, numerous steps and procedures are required to mount or remove electrodes from the machine leading to inefficient use of time and increased expense.

The present invention sets out in one aspect to provide a coating machine which overcomes, or at least alleviates the aforementioned disadvantages.

According to the present invention in one aspect there is provided apparatus for applying a protective coating to an elongate carbon article, which apparatus comprises a carriage suspended from a track located above the carriage, a headstock and tailstock mounted on the carriage between which a carbon article to be coated can be supported, means for imparting rotation through the headstock and/or tailstock to effect controlled rotation of the carbon article supported therebetween, a fixed coating station including one or more spray devices operable to apply a coating of oxidation resistant material to the surface of the supported carbon article, and means operable to drive the carriage along the overhead track such that, in operation, the surface of the rotating article passes in close proximity to the coating station.

The drive-means for the carriage may comprise a motorised chain-drive or a motorised rack and pinion mechanism.

In another aspect, the present invention provides a method of applying a protective coating of oxidation resistant material to the periphery of an elongate carbon article, which method comprises the steps of causing the article to rotate about it's longitudinal axis and to traverse a path which lies in close proximity to a coating station at which oxidation resistant material is applied to the periphery of the article to protect the same.

In a further aspect the invention provides a method for causing a coating of a protective material to be applied to the surface of an elongate carbon article, the method including the step of clamping the article between rotatable spindles of members dependent from a support structure positioned above a line passing through the axis of the spindle.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 is a plan view from above of coating apparatus in accordance with the invention; and Figure 2 is a side elevational view partly in section of the coating apparatus illustrated in Figure 1.

The coating machine illustrated in the drawings includes a wheeled carriage 1 by which an electrode 2 (shown in broken line) to be coated can be moved past a fixed coating station 3. The machine is housed within a sound absorbing booth 4 from which fume is extracted through a stack 5. The area of the stack inlet can be varied through operation of a flapvalve. The booth 4 is open at one end to the extent necessary to enable the electrode to enter and leave the booth.

The carriage 1 comprises an outer frame-member including elongate side members 6 each joined at one end by a bridging member 7. Bearing housings 8 are secured to the upper face of each side member 6 and support front and rear axles 9 of the wheels 10 of the carriage. Supported between the side members 6 of the outer frame-member is an inner carriage section 11 including elongate side members 12 each joined at one end to a bridging member 13. Support for the inner carriage member 11 is provided by cross-pieces 14 secured to the upper and lower faces of the side members 12. The cross-pieces 14 overlie the upper and lower faces of the side members 6 of the outer framemember but are not secured thereto.

The bridging members 7, 13 are connected through a pneumatically operated piston 15 sliding within a cylinder 16 connected to a source of air under pressure. As illustrated the piston 15 is connected to bridging member 13 and the cylinder 16 to bridging member 7. Through selective control of air to the cylinder 16, the piston 15 operates to move the inner carriage member 10 with respect to the side members 6 to vary the distance between the bridging members 7, 13.

Dependent from the bridging members 7, 13 are electrode support members 17, 18 respectively. Each electrode support member 17, 18 is insulated from the ajoining carriage member and carries an externally conical head or tail stock spindle 19, 20 between which the electrode 2 is clamped during the coating process. The headstock spindle 19 is coupled through a gearbox 21 to a DC or AC electric motor 22 which operates to impart rotational motion to the electrode 2. The support member 17 for the loose tailstock spindle 20 includes an earth connection 23.

Connections of the positive and negative poles of the DC source to the electrode are effected by contact rings 24, 25 coupled to the spindles 19, 20 respectively in any conventional manner. The mergers 17, 18 which support the spindles 19, 20 are electrically insulated from the carriage by insulation material 26.

DC current of between 1,000 and 5,000 amperes is supplied to the contact rings 24, 25 from a flexible copper lead 27 caged within an articulated insulated sheath 28 which seats within a suitably shaped ledge 29 extending along the length of the booth 4.

The wheels 10 of carriage 1 track over rails 30 which extend along the full length of the coating machine. The rails 30 are supported at the required height by means of structural members (not shown).

The carriage 1 is driven along the rails 30 by a pinion 31 driven through an endless chain 32 connected to the drive spindle of a DC motor 33. The pinion 31 co-operates with a rack 34 carried by the outer framemember of the carriage 1. The ledge 29 is positioned below and to one side of one of the rails 30 and the length of the flexible copper lead 27 is such that it effectively folds and unfolds within the sheath 28 as the carriage traverses forwards and backwards along the rails 30. Alignment of the carriage 1 with respect to the rails 30 is assisted by guide-wheels 35 carried by the side members 6 of the outer frame of the carriage.

The fixed electrode coating and treatment station 3 is positioned below and to one side of the electrode 2. The station 3 has a series of treating tools and coating appliances, including a device for cleaning an electrode surface, one or several heads for electric arc treatment of the surface, spraying devices for applying aluminium, aluminium alloys and graphite particles onto the electrode surface, and a grinding device. Each of the tools and coating appliances are connected to electrical switching and material feeding devices. Thus, the electric arc treatment head includes an automatic system for maintaining the current and voltage of the arc substantially constant.

The electric arc spraying devices also include automatic systems for maintaining constant voltage dependent upon the rate at which wire is fed to the spray devices.

The operation of the illustrated coating machine will now be described. The electrode 2 to be coated is initially positioned on a lifting table 36 positioned at the entry end of the booth 4. The height of the table 6 can be varied through operation of hydraulic or pneumatic cylinders and is controlled through a controller 37 to ensure that the height of the electrode above the ground corresponds to the level of the spindles 19, 20. The carriage 1 is traversed over the table and the pneumatic piston 15 operated to move the inner carriage member away from the bridging member 7 of the outer frame of the carriage so that the electrode can be located between the support members 17, 18 and clamped between the spindles 19, 20 by operation of the piston 15 to draw the inner carriage member towards the bridging member 7.Once clamped in position, the electrode is moved by the carriage to the position indicated in Figures 1 and 2 of the drawings. The electrode is then rotated by means of the motor 22 and the carriage moved slowly towards and past the coating and treatment station 3 by means of the driven pinion 31 meshing with the rack 34. As the carriage moves, so the flexible copper lead 27 folds and unfolds within the ledge 29. The various heads and spray-coating devices present at the station 3 therefore effectively describe a helical path with respect to the passing electrode surface.

On completion of the electrode traverse the chaindrive may be reversed so that a second coating and treatment can be applied to the electrode surface.

Once the coating procedure has been completed the electrode is again supported by the lifting table, the head and tailstock spindles moved apart by means of the piston 15 and the coated electrode thereby released for further processing.

It is to be understood that the foregoing is merely exemplary of one coating machine in accordance the invention and that various modification may be made thereto without departing from the true scope of the invention. Thus drive to the carriage may be effected by means of a motorised rack and pinion instead of the chain-drive described above.

Claims

CLAIMS:

1 Apparatus for applying a protective coating to an elongate carbon article, which apparatus comprises a carriage suspended from a track located above the carriage, a headstock and tailstock mounted on the carriage between which a carbon article to be coated can be supported, means for imparting rotation through the headstock and/or tailstock to effect controlled rotation of the carbon article supported therebetween, a fixed coating station including one or more spray devices operable to apply a coating of oxidation resistant material to the surface of the supported carbon article, and means operable to drive the carriage along the overhead track such that, in operation, the surface of the rotating article passes in close proximity to the coating station.

2 Apparatus as cla-imed in claim 1 further comprising a sound absorbing booth which encloses the carriage and coating station and which includes fume extraction means.

3 Apparatus as claimed in claim 1 or claim 2 wherein the carriage comprises inner and outer carriage sections, one such section being movable selectively relative to the other such section to vary the distance therebetween.

4 Apparatus as claimed in claim 1 wherein the drivemeans for the carriage comprises a motorised chain-drive.

5 Apparatus as claimed in claim 1 wherein the drivemeans for the carriage comprises a motorised rack and pinion mechanism.

6 A method of applying a protective coating of oxidation resistant material to the periphery of an elongate carbon article, which method comprises the steps of causing the article to rotate about it's longitudinal axis and to traverse a path which lies in close proximity to a coating station at which oxidation resistant material is applied to the periphery of the article to protect the same.

7 A method for causing a coating of a protective material to be applied to the surface of an elongate carbon article, the method including the step of clamping the article between rotatable spindles of members dependent from a support structure positioned above a line passing through the axes of the spindles.

8 A method as claimed in claim 7 wherein the elongate carbon electrode comprises an electrode for use in an electric arc furnace, and wherein the electrode is supported by a carriage suspended from a track located about the carriage, the carriage being movable along the overhead track such that the surface of the rotating electrode passes in close proximity to fixed coating stations.

9 Apparatus for applying a protective coating to an elongate carbon article substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.