"ELECTRODE SYSTEM"

FIELD OF THE INVENTION

The present invention relates to electric arc furnaces or other electrode systems (eg; Hall Herault), electrodes, combinations of electrodes, assemblies of electrodes all suitable for such furnaces or systems, a system for the protection of graphite electrodes, that are used in high temperature and/or aggressive conditions (e.g.; oxidising conditions of a steelmaking electric arc furnace or a Hall Herault aluminium system).

More particularly, but not exclusively, it relates to electrodes and a system for the protection of graphite or other carbonaceous electrodes by employing a protective gas.

BACKGROUND TO THE INVENTION

An electric arc furnace ("EAF") is a system that heats charged material (for example steel but not limited to steel) by means of an electric arc. Arc furnaces range in size from small units of approximately one ton capacity used in foundries for producing cast iron products, up to about 400 ton units used for secondary steelmaking. Temperatures inside an electric arc furnace can rise to approximately 2000 ⁰ C.

Larger units are generally AC powered with the electric arc is produced by graphite electrodes. The EAF furnace itself usually comprises of a refractory-lined vessel, covered with a retractable roof through which one or more of the graphite electrodes enter the furnace. For a typical AC furnace three graphite or other carbonaceous electrodes are used to create an arc.

For steelmaking the arcing is generally above the melt. The arc forms between the charged material and the electrode or electrode assembly. The charge is heated both by current passing through the charge and by the radiant energy (evolved by of) the arc. For a typical AC furnace three electrodes are used.

The electrodes are usually cylindrical, and typically serially assembled using threaded couplings. As the electrodes wear, new lengths or segments can be added.

The electrodes are preferably automatically raised and lowered by a positioning system, which may use either electric winch hoists or hydraulic cylinders. The regulating system maintains

7 000213

- 2 - an approximately constant current and power input during the melting of the charge, even though scrap may move under the electrodes while it melts.

The furnace is usually built on a tilting platform so that the liquid steel can be poured into another vessel for transport in the steel making process. The operation of tilting the furnace to pour off molten steel is called "tapping". The process may include cleaning the slag door of solidified slag, carrying out any repairs, and inspecting electrodes for damage or lengthening of the electrodes through the addition of new lengths or segments. For a 90-tonne, medium-power furnace, the whole process as a batch process will usually take about 60-70 minutes from the tapping of one charge to the tapping of the next (the tap-to-tap time).

For steelmaking, direct current (DC) are furnaces can also used, with a single electrode in the roof and the current return through a conductive bottom lining or conductive pins in the base. The advantage of DC is lower electrode consumption per ton of steel produced, since only one electrode is used, as well as less electrical harmonics and other similar problems. However, the size of DC arc furnaces is limited by the available electrodes and maximum allowable voltage. Maintenance of the conductive furnace hearth is a bottleneck in extended operation of a DC arc furnace.

Steelmaking EAFs produce many grades of steel, from concrete reinforcing bars and common merchant-quality standard channels, bars and flats to special bar quality grades used for the automotive and oil industry.

A typical steelmaking arc furnace is the source of steel for a mini-mill, which may make bars or strip product. The steelmaking arc furnace is generally charged with scrap steel, though if hot metal from a blast furnace or direct-reduced iron is available economically, these can also be used for steelmaking.

EAFs can also be used for production of non-ferrous alloys, and for production of phosphorus.

A serious problem facing industries employing EAFs is the (deterioration consumption rate) of the electrodes during use. This is due to the aggressive conditions to which they are

subjected in steekαaking. Oxidation of the graphite electrodes takes place readily at the high temperatures and other conditions at which these electrodes are used e.g.; air feed into the EAF.

The bottom tip (e.g.; distal region) of the electrode generates or receives the arc. The electrode is consumed from this end. However (the remainder other parts) of the electrode (e.g.; more proximal region(s) e.g.; flanking regions) also oxidise due to the surrounding oxidising environment. This is sometimes referred to, in steelmaking, as "air burn". This can result in a pencilling of the electrode or worse, a breaking of the electrode further up the electrode. The pencilling effect is where the tip of the electrode gets tapered with use and the distal surface area for arcing and/or of contact with the melting steel decreases. A smaller distal contact area has an adverse effect on the arc and consumption of the electrode and power. This can all lead to an increase in tap-to-tap time as well as cost.

To produce a ton of steel in an electric arc furnace requires on the close order of 400 kilowatt-hours per short ton of electrical energy, or about 44OkWh per metric tonne; the theoretical minimum amount of energy required to melt a tonne of scrap steel is 30OkWh (melting point > ^'■ 1520°/2768°F). Any inefficiency owing to pencilling or excessive electrode usage can marginalise the economics of EAF use for steelmaking.

One way of attempting to protect graphite electrodes of this type is to coat the electrodes with a protective coating to reduce oxidation. Typically prior attempts at solving the problem have centred around depositing or providing refractory coatings onto the major surfaces of the 0 electrode.

Non-exhaustive examples of attempts to reduce consumption rates include: US5,352,523 which discloses a titanium nitride coating obtained by arc spraying titanium in a nitrogen atmosphere; DE 3609359 which gives a coating process of silicon deposition, via plasma spray techniques in a vacuum chamber; US 3,852,107 discloses a thick coating comprising of a matrix ,5 material and of a refractory filler which is electrically non-conductive and can be applied to the graphite electrode only below the electrode clamps.

There are a number of problems with the coating processes. The coatings need to be prepared and applied to the electrodes. This process can be time consuming, costly and inefficient.

The coating can interfere with the steel production process and the arc generation processes arc formation and steel quality.

An alternative method by which electrode protection has been carried out is via impregnation of the interior of the graphite wititi an aqueous solution. For example US4,726,995 discloses contacting the electrode with a liquid composition containing a phosphate-containing compound, a halide-containing compound in a solvent. Again similar disadvantages to those discussed above may result from such procedures.

These types of electrodes are expensive to make as they are of a high quality due to the modifications made to them.

A further alternative method by which electrode protection has been attempted involves the use of an inert gas. Japanese patent abstract JP53119439 discloses providing a hole throughout the centre of the full length of the electrode and a nipple, and supplying nitrogen gas through this bore. The disadvantages of such a system will include that the gas provides limited protection to the electrode. It travels the length of the bore and escapes out through the tip of the electrode rather than diffusing laterally from the bore under pressure (i.e.; effusing) to the side walls of the electrode.

The electrolytic production of aluminium is now known as the Bayer-Hall-Herault process.

In this process, the electrolyte — in this case, bauxite — needs to be molten to allow the passage of the electric current. The melting point of bauxite (aluminium oxide) is very high, in ) excess of 2000 ⁰ C. This means large amounts of energy would be needed to melt it.

Aluminium metal is produced at the negative electrode (cathode) and oxygen gas is liberated at the anode. Both electrodes are made of graphite, and, at the high temperature used in tiie electrolysis, these gradually burn away and have to be continually replaced.

In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

SUMMARY OF THE INVENTION

This is an object to provide an electric arc furnace or other electrode including system (eg; Hall Herault), a method of optimising or reducing electrode usage and/or optimising arc generation, the use of gas effusion to protect surfaces of an electrode or electrode assembly subject

to air burn, an electrode assembly, an electrode, combination of electrodes or assembly of electrodes of, or for, an electric arc furnace or any other system, or a combination or assembly of any such apparatus or of an electrode system -which will at least provide for steel making or other EAF usage a viable option and/or will reduce electrode erosion from surfaces other than those directly involved with the arc.

It is an alternative or further object of the present invention to provide an electrode and related system which reduces the rate of graphite electrode consumption and/or electric power consumption (eg; in an electric arc furnace or a Hall Herault system).

It is an alternative or further object to provide an alternative electrode overcomes or electrode protection system having advantages over the prior art and/ or which at least ameliorates some of the abovementioned disadvantages or which at least provides the public with a useful choice.

In an aspect the invention is an electric arc furnace or other electrode system of a kind having advancable electrodes, or electrode assemblies, to generate and/or receive arcing; wherein there is a temperature blindable gas passageway in the electrode(s), or electrode assembly,

Preferably it is an EAF and it is adapted such that a protective gas effuses to a surface subject to air burn reliant on the passageway being more distally blinded than the proximal gas infeed.

In another aspect the invention is a method of optimising or reducing electrode usage and/ or optimising arc generation (eg; in an electric arc furnace), which method comprises or includes the step of using a temperature blindable or a blind gas passageway to provide for sufficient gas pressure to effuse a protective gas to a surface away from the arc subject to "air burn".

In another aspect the invention is the use of gas effusion (i) from a temperature blindable passageway, or a blind passageway, within an electrode or electrode assembly (eg; of an electric arc furnace) (ϋ) to a surface or surfaces of the electrode or electrode assembly subject to air burn.

Preferably said surface is more proximal than the more distal arcing surface(s).

In another aspect the invention is an electrode assembly (eg; of an electric arc furnace or other system) adapted, in use, to effuse a protective gas to its surface(s) liable to air burn more proximal than its (preferably arcing) distal surface (s).

In another aspect the invention is an electrode, combination of electrodes or assembly of electrodes (eg; of, or for, an electric arc furnace or other system) where the or each

electrode has a gas duct able to be pressurised -with a gas feed against each of the progression of duct blinding features as the or each electrode distaUy erodes thereby to effuse gas (i.e.; a protective gas) to a lateral surface or lateral surfaces, more proximal than those being distaUy eroded by or as a result of the arcing.

In another aspect the invention is an electrode, combination of electrodes or assembly of electrodes (eg; of, or for, an electric arc furnace or other system) where the or each electrode has a gas duct able to be pressurised with a gas feed thereby to effuse gas (i.e.; a protective gas) to a surface, in use, liable to air burn.

Preferably the electrode(s) or its components is (are) carbonaceous.

Preferably the or each duct is able to be blinded, thereby to provide for gas back pressure, by a temperature dependent mechanism.

Preferably said temperature dependent mechanism includes a valve and valve seat spaced by an elevated temperature modifiable spacer, able at the elevated temperature(s) to allow valve seating on the valve seat.

^'■ > Preferably said mechanism includes a heat collapsible wire spacer or heat collapsible form

(e.g.; tube).

Preferably said gas duct(s) has (have) been gun drilled.

Preferably the or each electrode has at least two of said mechanisms.

Preferably the or each said mechanism can be screw engaged in said duct. D Preferably each electrode can be serially threaded to a complementary like electrode.

Preferably each electrode is elongate and said duct is axially of the longitudinal axis.

In a further aspect, the invention is, in combination, or in assembly, apparatus suitable for use in a gas passageway of an electrode or electrode assembly (eg; of, or for, an electric arc furnace or other system), the apparatus comprising or including 5 a passageway defining member having a valve seat, ^' a valve member able to seat on or relative to said valve seat to at least substantially occlude said passageway, and a temperature affected spacer to hold said member off said valve seat, wherein elevated temperature collapse of the spacer will have the affect of allowing the )0 occlusion of said passageway by said member under the bias of gravity and/or a gas pressure.

Optionally said passageway defining member has an exterior screw thread (e.g.; preferably is a grub screw with an axial bore and an annular valve seat about one end of the passageway).

Preferably said valve member is a ball.

Preferably said spacer, but not the passageway defining member and the valving member, 5 melts or deforms at between 800°C to 2000°C.

In a further aspect the present invention consist in a method of reducing oxidation of the outside of an electrode comprising feeding a gas into an elongate electrode that includes a number of passages that extend from one end of the electrode to different depths along the body of the electrode through the passage of the electrode that greatest reach into the body except for the passage(s) which may be exposed.

In a further aspect the present invention consist in a method of reducing oxidation of the outside of an electrode comprising measuring the gas pressure of a gas fed into one of a number of passages each extending from a proximal end of an elongate electrode to different depths along the body of the electrode said one passage being the of the greatest reach into the body except for the passage(s) which may be exposed, whereupon a drop in pressure corresponding to an exposure of the one passage at a distal end, the gas flow to said one passage is terminated.

According to a another aspect of the invention there is provided an electrode system comprising a carbonaceous electrode, an inert gas source and a gas conduit means in

! communication with a region of the electrode "the contact region", wherein the contact region is under a positive pressure of inert gas, and wherein the carbonaceous electrode includes a plurality of pores in its structure and at least some of these pores are filled by the inert gas.

Preferably the electrode is an elongate electrode with a distal end and a proximal end and the contact region is at or adjacent to the proximal end.

3 According to another aspect the present invention may broadly be said to consist in an electrode system comprising a plurality of identical electrodes of a porous material, each electrode having a proximal end and distal end and including at least one gas passage extending in the elongate direction from the proximal end at least partially towards said distal end to receive a gas from the proximal end to diffuse through pores of the electrode towards the surface or surfaces of 5 the electrode wherein the plurality of electrodes may be stacked and fastened to each other in a proximal end to distal end manner and gas may be delivered from the proximal end of a first of said electrodes to the body of an electrode stacked therewith.

In a further aspect the present invention consists in an electrode that includes a proximal end and distal end and including at least one gas passage extending in the elongate direction from )0 the proximal end at least partially towards said distal end to receive a gas from the proximal end to diffuse through pores of the electrode towards the surface or surfaces of the electrode wherein the electrode includes a distal end fastening region so that it be stacked and fastened to a like electrode and gas may be delivered from the proximal end of said electrode to the body of an electrode stacked therewith.

Preferably the or each electrode is an elongate electrode with a distal end and a proximal end wherein the gas inflow is effected is at or adjacent to the proximal end.

Preferably the gas is ducted via a conduit having a gas inlet and a cap in contact with the proximal end of the or an electrode.

Preferably the cap engages with the proximal end of the or an electrode by screw thread.

Preferably the electrode is or includes graphite.

Preferably the graphite has been prepared by heat treatment of coke.

Preferably the electrode is elongate and straight in nature.

Preferably the electrode has a rectilinear, elongate direction periphery.

In one embodiment of the invention, at least part, if not all, of the graphite electrode has an outer coating of a protective material capable of reducing the rate of electrode oxidation caused by contact with an aggressive environment.

Preferably the contact region of the electrode includes a recess formed in die proximal end of the electrode. Preferably the cap includes a complementary protuberance engaging with or to locate into the recess.

Preferably the recess and the protuberance are provided with a screw thread and the engagement between the recess and protuberance is by use of the screw thread.

In an alternative embodiment of the invention, at least part, if not all, of the graphite electrode has an outer layer of graphite of reduced porosity.

) Preferably die contact region at the proximal end of the electrode comprises or includes a region of the electrode where any low porosity outer layer has been removed or did not exist.

Preferably the contact region of the electrode includes a recess formed in the proximal end of the electrode, and formed through the outer layer, and the cap includes a complimentary protuberance engaging with the recess. Preferably the recess and the protuberance are provided with a screw thread and the engagement between the recess and protuberance is via the screw thread.

In an alternative embodiment of the invention the electrode includes a thread at its proximal end to receive a cap that has an inlet to receive said gas, said cap defining a captured flow path to deliver gas from said inlet to said electrode. 0 Preferably said cap includes an inlet for each of the passages defined in said electrode and a captured flow path to deliver gas from a respective inlet to a respective passage.

Preferably the or each electrode may be provided with at least one elongate blind passageway extending longitudinally into the electrode from the contact region at the proximal end of the electrode.

00213

- 9 -

In a farther embodiment the invention may broadly be said to consist in a graphite electrode assembly comprising a plurality of straight elongate electrode segments wherein the proximal end of a first segment defines a proximal end of the electrode assembly and wherein at least the distal end of the said first segment includes a longitudinally extending fluid passage extending into the first segment from the proximal end thereof to its distal end to allow fluid communication via said passage between the proximal end of said first segment and the proximal end of a second segment that is fastened with (and preferably to) and longitudinally extending from the first segment.

In one form of this embodiment the distal end of at least the first segment is provided with a protuberance engaging with a recess formed in the proximal end of at least the second segment. Preferably the protuberance and recess are both formed with a screw thread and the engagement is via engagement of the screw threads.

In one form of this embodiment the distal end of at least the first segment is provided with a protuberance engaging with a recess formed in the proximal end of at least the second segment. Preferably the protuberance and recess are both formed with a screw thread and the engagement is via engagement of the screw threads.

Preferably the recess formed in the proximal end of at least the second segment is substantially identical to the recess formed in the proximal end of the electrode.

In an alternative form of this embodiment the first and second electrode segments engage with each other via a connector connected with both the distal end of the first segment and the proximal end of the second segment.

Preferably the distal end of the first electrode segment is provided with a recess connecting with the proximal end of the connector, and the proximal end of the second electrode segment is provided with a recess connecting with the distal end of the connector.

Preferably the distal and proximal ends of the connector are provided with screw threads which engage with complimentary screw threads formed in the recess of the distal end of the first segment and the recess of the proximal end of the second segment.

Preferably the dimensions of the recesses of the distal end of the first segment and the proximal end of the second segment are substantially identical with each other and with the recess in the proximal end of the electrode.

With respect to both forms of this embodiment, preferably the first and second electrode segments are provided with an elongate passageway extending longitudinally into the electrode segment from the contact region of engagement between electrodes and the connector is provided with a passageway extending longitudinally through the length of the connector so located as to be

in direct communication, with the passage of the second segment. Preferably the passageway is temperature blindable.

In an alternative embodiment the electrode has an internal passageway extending from the contact region at the proximal end to the distal end, and the passage includes one or more plugs preventing flow of inert gas from the proximal end to the distal end via the passageway.

Preferably there is a plurality of plugs distributed along the passageway. Preferably the plugs are of a gas permeable and/or porous intumescent material which upon exposure to a swelling temperature, swell to a non-porous and/or non-gas permeable stage.

Preferably the swelling temperature is >500°C; more preferably >1000°C.

In an alternative embodiment the pores of the electrode contain minimal air and are substantially filled with inert gas following evacuation by application of a vacuum and then being placed is under a positive pressure of inert gas for a period of time.

According to a further aspect of the invention there is provided an electrode or electrode segment suitable for one or more embodiments of the above electrode segment.

According to a further aspect of the invention there is provided an electrode connector suitable for one or more embodiments of the above electrode segment.

According to a further aspect of the invention there is provided a cap for an electrode or electrode segment suitable for one or more embodiments of the above electrode segment.

According to a further aspect of the invention there is provided a plug, preferably of i intumescent material, suitable for one or more embodiments of the above electrode segment.

According to a further aspect of the invention there is provided a method for retarding oxidation of a carbonaceous electrode in an aggressive environment comprising the step of contacting the carbonaceous electrode having a plurality of pores with a positive pressure of inert gas so that at least some of these pores are filled by the inert gas.

5 Preferably the step of contacting the electrode with a positive pressure of inert gas is a temporary step prior to introduction to the aggressive environment.

Alternatively the step of contacting the electrode with a positive pressure of inert gas is a continuous process occurring for at least part if not all of the time the electrode is in contact with the aggressive environment.

0 Preferably the electrode takes the form of at least one of the embodiments of electrode system discussed above and the inert gas is substantially continually supplied to the contact region of the electrode.

In a further aspect the present invention may broadly be said to consist in a method for retarding oxidation of a carbonaceous and porous electrode that includes a proximal end and a

$5 distal end and that includes a longitudinally extending passage formed therein from the proximal

T/NZ2007/000213

- 11 - end, the method comprising the steps of introducing into the electrode a positive pressure of inert gas.

In a further aspect the present invention may broadly be said to consist a connector to connect two carbonaceous and porous electrode segments that at least in part define an electrode assembly and that each include a proximal end and a distal end and a longitudinally extending passage formed therein wherein the connector includes at least one fluid passage at least one of which is to establish a fluid communication between the passage of each of the two electrodes.

Preferably the connector engages to each of said electrode segments in a rotational manner (e.g.; by a threaded engagement), wherein the fluid passage of said connector is a manifold that includes an inlet opening to receive gas from the passage of the first segment and an outlet opening the can deliver gas to the passage of the second segment irrespective of the rotational orientation of the first and second segments and/or the connector relative each other.

In a further aspect the present invention may broadly be said to consist in an electrode assembly comprising a first electrode segment that includes a proximal end and a distal end and an elongate direction extending passage that includes an inlet at the proximal end and an outlet at the distal end to facilitate the flow of gas between the proximal end and distal end, a second electrode segment that includes a proximal end and a distal end and an elongate direction extending passage extending between the proximal end and the distal end and that includes an inlet at the proximal end, to facilitate the flow of gas from the proximal end towards the distal end, wherein said first and second electrode segments are rotationally coupled together at the distal end of the first segment and the proximal end of the second segment; and wherein at least one of the outlet of the first segment and the inlet of the second segment are presented non-centrically; and wherein a concentric manifold is provided intermediate of the outlet of the first segment and the inlet of the second segment defining a passage between the outlet of the first segment and the inlet of the second segment for gas flow from said first segment to said second segment irrespective of the rotational orientation of the first segment relative the second segment.

Preferably the concentric manifold is of a diameter and width in the diametric direction to align with both the inlet and the outlet of the second and first segments respectively.

Preferably the outlet is positioned a distance X from the central axis of the first segment and the inlet is positioned a distance X from the central axis of the second segment and the

manifold is a concentric channel positioned at least at a radius X and defined at least one end face of (i) the distal end of the first segment and (ii) the proximal end of the second segment.

Preferably the manifold is defined by one of the first and second segments.

Preferably the manifold is defined by an intermediate member.

Preferably the intermediate member is a connector to connect the two segments together.

Preferably the connector engages to each of said electrode segments in a rotational manner (e.g.; by a threaded engagement), wherein the manifold of said connector is a manifold that includes an inlet opening to receive gas from the passage of the first segment and an outlet opening the can deliver gas to the passage of the second segment irrespective of the rotational orientation of the first and second segments and/or the connector relative each other.

In a further aspect the present invention may broadly be said to consist in an elongate . electrode that includes at least one elongate direction extending passage to allow flow of gas there through.

Preferably there are two passages formed in said electrode.

Preferably the passages extend from one end at least in part towards the other end of the electrode.

Preferably one of the passages passes through the electrode from one end to the other.

Preferably at least one of the passages can at one or both its ends be plugged to seal the passage opening. ) Preferably the plug is threaded into the passage.

Preferably the passage can receive a pig that can travel along the passage.

Preferably the position of the pig is controlled by a cable engaged to the pig that can pull the pig towards the proximal end.

Preferably the pig is a plug that can substantially seal the passage. Preferably the at least one passage contains an intumescent material that swells in size upon an increase in temperature.

Preferably the intumescent material will swell upon being subjected to an increase in temperature to reduce the flow of gas through the passage and towards the eroding end of the electrode at where arcing is, in use, occurring. Preferably the at least one passage contains a temperature activated sinterable material that can sinter upon the reaching of predetermined temperature to reduce the flow of gas towards the eroding end of the electrode at where arcing is, in use, occurring.

In a further aspect the present invention consists in a steel smelter that includes an electrode as herein before described.

T/NZ2007/000213

- 13 -

In a further aspect the present invention consists in a steel smelter that includes an electrode assembly as herein before described.

In a further aspect the present invention consists in a steel smelter that includes an electrode segment as herein before described.

In a further aspect the present invention consists in a steel smelter that includes a connector as herein before described, positioned intermediate of two electrode segments.

In a further aspect the present invention consists in two electrode segments as herein before described connected by a connector as herein before described.

In a further aspect the present invention consists in an electrode assembly as herein before described and a connector as herein before described connecting the two electrode segments of the assembly together. i

Preferably upon the termination gas flow into another (e.g.; the next longest passage) reach of the passages is initiated.

Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

As used herein the term "and/or" means "and" or "or", or both.

As used herein "(s)" following a noun means the plural and/or singular forms of the noun.

As used herein the terms "EAF", "tapping", "tap", "air burn" and "pencilling" take or include the meanings previously ascribed thereto.

) As used herein "bHndable" includes the ability to sufficiently halt or slow gas passage such that it effuses laterally of the passageway or duct rather than preferring to move axially therefrom.

As used herein "optimising" includes any improvement beyond the electrode not being protected by a protective gas.

As used herein "protective gas" includes any gas suitable for the purpose whether nitrogen, argon or other inert gas, or mixture(s), and may include combustive or non-inert gases, or mixtures thereof, nonetheless shielding of oxidative erosion of the electrode (s).

The term "comprising" as used in this specification means "consisting at least in part of. When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, I ₅ 1.1, 2, 3, 3.9,

4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7).

The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 shows "penciling" of a conventional EAF graphite or other carbonaceous electrodes as a consequence of oxygen availability, as is desired, in the EAF, i Figure 2 is a schematic of an electrode system of the invention in a generalised form,

Figure 3 is a schematic of one preferred form of the electrode system of the invention,

Figure 4a is a schematic of one embodiment of an interlocking structure of the electrode system of the invention,

Figure 4b is an alternative interlocking structure employing interconnecting nipples of the 0 electrode system of the invention,

Figure 5a is a schematic of one embodiment of an electrode system of the invention where the electrode has an outer coating,

Figure 5b is an alternative embodiment to that shown in Figure 4a,

Figure 6 is a schematic of one embodiment of an electrode system of the invention where '.5 the electrode has an inner passage,

Figure 7a is a schematic of the electrode and nipple of one embodiment of an electrode system where the electrode has an inner passage,

Figure 7b is a schematic showing how the components of Figure 6a interlock to form an overall electrode system of the invention, 0 Figure 8 is a schematic of a further embodiment of the electrode system of the invention with an inner passage and a plug.

Figure 9 is a schematic of the electrode used in the experimental section.

Figure 10 is a side view of the jig used to house the electrode of Figure 9.

Figure U is a schematic of the end pressure plate of the jig of Figure 10.

Figut e 12 is a perspective view of an electrode,

Figure 13is a plan view of the electrode of Figure 12,

Figure 14 is a sectional view through section AA of the electrode shown in Figure 12,

Figure 14A shows a variation to the electrode of Figure 14,

Figure 15 is a perspective view of an electrode in an alternative form to that shown in Figure 11,

Figure 16 is a sectional view through two electrode segments in an assembled configuration wherein the electrode segments are of the kind as shown in Figure 14,

Figure 17 illustrates three segments in an assembled configuration,

Figure 18 illustrates the configuration of Figure 16 but in a partially consumed condition,

Figure 19 illustrates the configuration of Figure 16 but wherein further consumption has occurred and wherein a cap is shown to be engaged with the proximal most electrode segment,

Figure 20 shows part of an electrode segment and a connector for connecting such a segment to a like or similar electrode segment,

Figure 21 is a partially exploded and sectional view of two electrode segments and a cap for delivery of a gas to the electrode assembly,

Figure 22 shows an intermediate connector being used to connect electrode segments in an electrode for an EAF,

Figure 23 shows the variation of the arrangement of Figure 22,

Figure 24 shows still a further variation of the arrangement of Figures 22 and 23, the arrangements of Figures 22 to 24 having already blinded passageways or a blinded passageway in each electrode segment,

Figure 25 shows an electrode or an electrode segment having a passageway there through, and intermissent material being located fully in the passageway with ability to expand or increase in density and/or reduce its porosity when heated,

Figure 26 shows an electrode or electrode segment that includes a peg suspended in the passageway that can be moved upwardly in the passageway as required in order to blind the duct of passageway,

Figure 27 is a diagrammatic view of a preferred embodiment of the present invention where a passageway including grub screw which defines a valve seat has spaced therefrom by a helical or other heat collapsible form, a valving ball,

Figure 28 shows the effect of temperature on the arrangement of Figure 27 whereby under gas pressure and/or gravity the ball seats in the top chamber to the passageway of the grub screw,

Figure 29 shows a different embodiment to that of Figures 27 and 28, where instead of a spring or helical member of for example, a copper conduit able to reduce in size collapses thereby to allow the ball to seal over the entrance of the tube defined or grub screw defined passageway,

Figure 30 is another variation of the arrangement as shown in Figure 29,

Figure 31 is still a further embodiment where a post or like meltable member distances the valving ball from the valve seat,

Figure 32a-f show how progressively an electrode or electrode assembly can be progressively lowered from 32a through 32f thereby to present as the terminal and blinding feature, in serial sequence, each of the arrangements as shown in Figures 27 and 28,

Figure 33 shows a helically threaded electrode segment of a suitable graphite material that is tested in a kiln,

Figure 34 is the electrode segment of Figure 33 when subjected to a kiln with no protection,

Figure 35 compares the electrode segments of Figures 33 and 34 i.e. exposed to the oxidizing conditions and the heated against new,

Figure 36 is a similar comparison to that of Figure 35 but showing, on the left hand side, against a new electrode, on the right hand side, the electrode after testing but where there has been effusing of nitrogen outwardly to the flanking surfaces in order to provide protection,

Figure 37 shows anodes of the Hall Herault process from which it can be seen that the electrodes are not elongate but rather are blocks, such an aluminum smelling process benefiting from the fitting of a nitrogen feed (not shown) into the graphite anode, or a modified anode rod and its connection, thereby to bestow a similar benefit to the electrode mass and/or block as hitherto described with reference to EAFs.

DETAILED DESCRIPTION OF THE INVENTION

The electrode system of the invention comprises a system for imparting protection or a barrier to a graphite or carbon electrode which is employed in aggressive conditions. Typically such an electrode is that used in an electric arc furnace which is often employed in steel making applications. However as would be contemplated by one skilled in the art the electrode system of the invention and the integers which make up this invention are not restricted just to this particular industry nor to an electric arc furnace. There may be other environments which are comparable, or

other industries which would benefit from the use of such an electrode system. Examples include fusion reactors of physical vapour deposition systems.

The aggressive conditions which are present in steel making furnaces, for example, result in deterioration of the electrode.

» Figure 1 shows a typical electrode assembly where electrode segments usually of round periphery are interconnected serially reliant upon nipples.

Figure 1 shows a zone A, a zone B and a zone C. The temperature within the furnace generally increases from zone A to zone C and of course it is the lower distal region of zone 3 which is the arcing surface. Flanking the arcing surface which is generally the hot tip at the bottom

3 of the drawing is a region of zone C subject to pencilling owing to the availability in the EAF of oxygen available to oxidise in the temperatures involved the graphite surface.

By way of example, if the electrode assembly shown in Figure 1 was originally of 600mm diameter and each segment was approximately 2.1 metre long the pencilling primarily appears in the bottom section but nonetheless on the flanking sides of the hot tip. Typically 100mm up from 5 the hot tip the diameter of the electrode will have pencilled down to, for example, about 350mm diameter whilst the hot tip itself, the distal arcing surface, is of a diameter of about 250mm. For the reasons explained elsewhere in this specification this leads to increased electrode wear and/or increased power requirements.

The present invention has in mind one or more passageway down through an assembly as

\0 depicted in Figure 1, whether a common passageway as disclosed in the aforementioned Japanese specification or otherwise which nonetheless, as a result of an ability to blind the passageway above the hot tip has the effect of providing sufficient back pressure to a protective gas flow into the electrode assembly to effuse the protective gas to the flanking surfaces whether of C, B or A. This we have shown to provide for a significant decrease in pencilling of the kind typified in Figure 1. 5 Other advantages arise as well.

The electrode when oxidising can also become more porous. The external surface of the electrode can be eaten away and oxygen/air can also gain access to the internal structure of the electrode through pores and other electrode features. Typically these electrodes are not fully homogeneous. This speeds ups the deterioration of the electrode because the more porous and rough the surface the bigger the surface area.

The invention relies upon applying a protective or inert gas (such as but not limited to argon, nitrogen, helium) to a carbonaceous electrode, preferably graphite in such as a way as to impregnate at least in part the electrode and preferably to effuse from its surface. By impregnation we mean that the gas is able to occupy at least some of the pores of such an electrode at the ) expense of entering air or oxygen. One other application of an inert gas to a graphite electrode has been described in Japanese Abstract 53119439. This relied upon a formation of a passageway a sectional view through the entire longitudinal length of the electrode. Gas was admitted to one end of the passageway, travelled the length of the electrode and presumably escaped at the distal end of the electrode. In comparison the subject invention relies upon the gas impregnating the material. This is brought about by communication of the gas with the electrode under positive pressure conductors.

The pressure conditions result in inert gas penetrating a higher percentage of the pores available. It will provide protection to greater regions of the electrode than would occur in the prior art. To the extent there is any pencilling the more the protective gas will reach to and issue from the surfaces to be protected.

The arrangement shown in the Japanese specification aforesaid relies on a flow through of gas where the gas issues axiaUy of the hot tip end of the electrode thereby to billow up and possibly provide some semblance of protection about the hot tip. The present invention however, by reliance upon bliαdable ducts or passageways, or blind ducts or passageways has the ability to effuse gas directly outwardly (Le.; laterally of the electrode axis) thereby to confer a general protective affect over the electrode, and certainly the surfaces of a zone such as C of Figure 1 if the

blind end of the passageway is sufficiently low. Preferably the effusing of the gas is to the full diameter of the electrode. At the very least it is to the surface as it "pencils".

A generalised electrode system 1 is illustrated in Figure 2. The distal end 6 of the electrode 2 will have an arc between the metal bath and the hot tip (distal end). It is the distal end 6 which is subject to deterioration by oxidation from the aggressive conditions. This deterioration gives rise to consumption of the electrode. In the electrode system 1 of the invention the proximal end 7 of the electrode 2 is fitted with a gas tight cap 3 to which some form of entry or conduit 4 is fitted. Inert gas 5 gains entry to the cap 3 via the conduit 4 the inert gas 5 is in communication with the proximal end 7 of the electrode under conditions of positive pressure such that the inert gas 5 will ) penetrate the electrode pores from the proximal end 7. The gas 5 will move its way through the electrode. This allows for greater penetration of the whole electrode 2 and thus greater protection from oxidation.

Figure 3 is an alternative embodiment of the electrode system 1. In addition to the graphite electrode 2 there is provided a recess or socket 23 in the proximal end 7 of the electrode 23 into 5 which a cap 21 will fit with a complimentary and usually engaging (such as by a screw thread) protuberance 22. This arrangement is similar to that of Figure 2 other than the cap 21 being able to be held more securely in place. The inert gas is pressurised at the end and diffuses through the electrode 2.

Figure 4 illustrates two further embodiments of the invention. As is typical in electric arc

,0 furnaces, because of electrode consumption, each electrode is often made up of a plurality of interconnecting segments which can be attached to each other (usually by a screw filling of some type) to allow the electrode to be lengthened. This compensates for the electrode consumption.

Figure 4 illustrates one such embodiment wherein the electrode segments 31 are all formed with a protuberance 32 in the distal end 6 which engages via a screw thread with a recess 33 in the

-5 proximal end 7 of each segment 31. A cap 21 with such a protuberance 32 as discussed in Figure 4 is also used.

Figure 4b illustrates a further embodiment of interconnecting (three) segments differing in that each electrode segment 36 is formed with both a recess 33 in one end and a recess 38 in the other end. These are of substantially identical dimension. These electrode segments 36 are interconnected using a screw threaded nipple 37 which engages with the recesses 33 and 38 via the screw thread (an assembled configuration).

Figure 5a illustrates an alternative embodiment of Figure 2 or Figure 3 wherein the electrode is coated with an outer protective coating 41. Such a coating 41 can be of refractory material such as silicon carbide or zirconia or other materials such as metals, for example copper as would be known in the art. This encourages the inert gas 5 upon admission to the electrode system ) 1 from the proximal end 7 to penetrate further throughout the electrode body without escaping. Such an electrode system may include an inconsistency or discontinuation in the coating 42 for example the base of the distal end of the electrode 6 such that the inert gas which is admitted under pressure to the proximal end 7 is encouraged to flow to the distal end 6. This is the end more susceptible to corrosion. Figure 6 illustrates an alternative embodiment wherein the electrode 51 is 5 fitted or created with an internal passageway 52 which penetrates some but not all of the length of the longitudinal- length of the electrode. The passageway 52 encourages gas 5 to originate at the proximal end 7 of electrode down some of the length, of longitudinal electrode towards the distal end 6.

It should be realised that the electrodes of Figures 5A and 5B and 6 could also form

0 interconnecting segments of electrodes in the same fashion as illustrated in Figures 4A and 4B.

Figure 7 is one such example of this. Figure 7 is a schematic of electrode segments 61 having the internal passageway 62 penetrating at least part of the longitudinal length of the electrode from the proximal end 7 towards the distal end 6. Each electrode segment 61 is formed with a recess 64 in the proximal end 7 and a complimentary recess 63 in the distal end 6. These recesses will engage

£5 with a complimentary nipple 65 which in this embodiment is formed or provided with an internal passageway 66 formed right through. In Figure 7B a plurality of electrode segments 61 are shown

engaged via the complimentary nipples 64. Inert gas 5 is provided in the same way at the cap 21 and will penetrate the system predominantly through the passageway 52 of the first segment diffusing out into the electrode body but also reaching the first nipple 65 and penetrating right through the passage 66 of that first nipple 65 to engage with the passageway 62 of the second electrode segment 61. In this way inert gas 5 is encouraged to penetrate the length of the interconnecting electrode system 1.

Figure 8 illustrates a further alternative embodiment of the electrode system 1 wherein the cap 21 is fitted to an electrode 71 having a bore or passageway 72 formed through the entire elongate length of the electrode system. However a plug 73 is fitted or held in place using a

) mechanical means attached to the top of the furnace which prevents the inert gas from escaping from out the distal end 6 of the electrode 71 via the passageway 72.

Other embodiments of the invention may include the following arrangements:

• A hole is drilled down and through the centre of the electrode and some intumescent material, for example in the form of a plug, is placed down the centre. The nature of

5 intumescent materials is that they which swell as a result of heat exposure thus increasing in volume and decreasing in density. As the region of the electrode containing this material begins to be heated, the material expands and will block the hole at the lower section. This prevents the inert gas escaping through the hole at the bottom of the electrode and will force it into the electrode pores. The intumescent material can be chosen to expand at a

!0 temperature of the melt or at a temperature below the melt, according to desire.

• A hole is drilled down the centre and a powder is placed down this hole which will sinters at the desired temperature thereby blocking the hole. As above, the nature of the powder will be chosen to have sintering at a temperature of interest. Metals could be possible but particularly non-metals such as refractory materials.

5 • A hole is drilled down the middle of all electrodes. A permanent plug will be placed inside the centre of the hole. The plug has a thermocouple embedded inside and hangs down the

centre on a steel cable, as do the wires to the thermocouple. The wire will be fitted to an electrical winding system (or some equivalent) at the top which also has a temperature controller. The controller will wind up the plug at a set point. This will keep the plug at the same distance from the hot end of the electrode. The distance can be varied by changing the set point. The inert gas is then pumped down the centre and the plug will force the gas through the body of the electrode. When an electrode section is added a spare winder and short section of cable will be fitted to the new section. This is lifted up onto the furnace and the old winder is removed and the cable disconnected. The connector is then connected to the new section before it is added. In practice, the dimensions of the electrodes or electrode segments vary considerably depending upon the application and scale. Typical dimensions used in steel making furnaces in New Zealand use interconnecting (via a screw thread) electrode segments of 12 inches outside diameter and 72 inches in length. However this is just one example.

The graphite electrodes we use in our invention are typically prepared from coke. Core is a solid carbonaceous residue derived from low-ash, low sulphur, bituminous coal. Coke typically has a specific gravity of 1.85-1.9 and is highly porous. Coke is usually converted to graphite via the steps of heating to drive off volatiles, extrusion or moulding, and baking to solid carbon. The final step is a step of graphitisation involving heating to 2500 ⁰ C or more.

Graphite electrodes prepared by such a process do not exhibit the same properties as naturally occurring graphite. One important characteristic which differs is the density. The theoretical graphite density is between 2.09 - 2.23 gem ^"3 . In out experience, graphite electrodes prepared by such a process having a varying density, typically in the range of 1.6 - 1.7 gem ^"3 . This is due to the porous structure. We find that electrodes prepared by such a process typically have an outer surface or "skin" or region which is of slightly greater density than the bulk. This inherent skin means that the porosity and density profile will change as you profile through an electrode from one side to the other. Indeed some ways electrodes of this nature could be similar to the

electrode illustrated in Figures 5a and 5b which employ a foreign coating layer. It will also have a similar function to the outer foreign layer covering the gas from the inlet down through the electrode body. The embodiment of Figure 5b can be created by machining away or otherwise destroying the outer skin in one region, such as at the distal end 6.

Other implications of this outer skin may be prior to fitting the cap at the proximal end of an electrode or electrode system, part of this skin will be destroyed to allow the gas to penetrate the electrode or electrode segment more readily.

In practise, in embodiments such as that illustrated in Figure 3 and others where the screw thread process 23 is created, this recess will have broken through this skin. The gas in such I scenarios is more likely to penetrate the electrode better from the recessed part of the proximal end than the non-recessed part.

The gas used in the electrode system of the invention preferably is an inert gas which conveys some protection to the graphite of the electrode from oxidation. In some ways this gas could be viewed as permeating the pores of the electrode to form a barrier about the electrode. 5 Preferred gases would include argon, helium and nitrogen. In practice nitrogen is more likely to be used as it is cheaper. Again a preferred form of the invention may include where the gas has been dried and/ or oxygen removed. In practice it is likely that commercially available nitrogen will be employed directly.

Whilst the preferred form of the electrode system of the invention uses a generally

0 continuous supply of gas under pressure, it is possible also to subject the electrodes or electrode segments to vacuum conditions to evacuate the pores, and then flush the electrode through with an inert gas to substantially fill at least some of the pores. This embodiment is likely not to be effective as other forms but is within the scope of the invention. -

Where, in the specification, we have referred to pores or porosity in the graphite structure, -5 ^' we mean apertures or vacancies in the structure due to the laminar hexagonal structure of graphite.

However we also include other pores or void which are likely to be larger and are due to the method by which the graphite electrodes have been prepared. In our experience, in addition to the skin at the surface the intention of the electrodes may show inhomogeneous texture. There are often region of greater porosity and greater weakness. Such regions are more susceptible to oxidation as the melt is able to penetrate more easily. However an advantage of this system lies in that these regions, due to their greater porosity, are more likely to admit the inert gas and so be imparted with greater protection.

We will now describe embodiments of Figures 12 onwards.

With reference to Figure 12 there is shown an electrode 101. The electrode 101 is ) preferably a graphite electrode and is of a composition that may commonly be used in steel or other metal smelting applications. The electrode 101 may for example be a graphite electrode. It may be uncoated or otherwise treated or coated to create a physical shield about its perimeter.

As illustrated herein the electrode may be substantially of a cylindrical shape having a substantially circular cross section as shown in Figure 13. It extends generally in the longitudinal 5 direction LL between its proximal end 104 and distal end 105. Alternatively the electrode may be of a non-circular cross section. The electrode 101 may also not be of a constant cross sectional shape over its length between its distal ends 104 and 105. It is preferably rectilinear in its outward shape.

The distal end 105 is the end of the electrode that is positioned proximate the bath of 0 material during the smelting process. The proximal end 104 is that end of the electrode that is proximate more the electrode support equipment such as the grips that hold and support and control the positioning of the electrode relative the bath of material.

At or near the proximal end 104, the electrode has been adapted to receive a flow of gas.

The electrode 101 as for example shown in Figure 14 includes a passage 106 extending from the

5 proximal end 104 of the electrode 101 towards the distal end 105 of the electrode. The passage

106 may be located to extend along at least part of the central axis XX of the electrode 101 that extends parallel to the longitudinal direction LL. It may instead extend in an off-axis location.

The passage 106 may either be a through hole or a blind hole. In Figure 13, the passage

106 is illustrated to be a blind hole and terminates within the body of the electrode 103 short of the i0 distal end 105. The passage 106 is preferably a through hole or blind hole but may alternatively be defined by a more porous or less dense zone of the material of the electrode 101 or other material.

In a most preferred form the passage 106 is a hole (whether blind or through).

The passage 106 includes a gas inlet 107 at or proximate the proximal end 104. A gas can be introduced into the passage 106 via the inlet 107 and thereby be injected into the electrode 101. The electrode 101 having a certain degree of porosity (and likely to have a varying degree of porosity across its width at any given cross section along its length) will result in any gas introduced into the passage 106 via the inlet 107 from diffusing in the body of the electrode and towards its surface or surfaces 110. The diffusion of gas to the surface will establish a shield or partial shield about the electrode 110. Such shielding should improve the consumption characteristics of the electrode.

The end 112 of the passage 106 that is distal from its inlet 107 preferably terminates short ) of the distal end 105. The passage 106 may have a length H that is shorter than the distance between the proximal end 104 and distal end 105 prior to use of the electrode.

Gas that is introduced under pressure will thereby be encouraged to diffuse outward towards the surface or surfaces 110. This will be accomplished not just from the end 112 of the passage 106 but along its entire length of the passage 106 between the inlet 107 and end 112. S The primary consumption of the electrode occurs at the distal end 105. ^" When consumption reaches a point where the end 112 becomes exposed to the surrounding atmosphere, a gas flow pressure change can be detected. Such can trigger the termination of the gas flow at that point in time in order to stop gas flow out through the exposed end. From then on, shielding may not be provided by the gas.

0 A variation to the electrode shown with reference to Figures 12 to 14 is for example shown in Figure 14A wherein the electrode 101 includes a plurality of passages 106, 106A and 106B. Each of these passages has an end terminating at a different distance from the proximal end 104. Consumption of the electrode will result in the passage 106 becoming first exposed whereupon delivery of gas to this passage 106 can be terminated and switched or continued for flow to the passage 106A. When the electrode is consumed so that the passage 106A becomes exposed, its gas supply can be terminated and switched or continued for delivery of gas to the passage 106B. This allows for a gas to be delivered and diffused along substantially die entire length of the electrode regardless of the state of consumption.

With reference to Figures 15 and 16 there is shown a variation to the electrode described 0 with reference to Figures 12 to 14A. Electrodes in certain industries consist of electrode segments that are assembled in an axial direction with each other to establish an elongate electrode assembly.

With reference to Figure 16, there is shown two electrode segments 114 and 115. The assembly 116 of these two electrode segments defines a proximal end 104 and distal end 105. The proximal end electrode 114 defines at its proximal end the inlet 107 to the passage 106. The 5 passage 106 is in fluid communication with the passage 206 of the distal end segment 115. The

segment 114 has the passage 106 passing through the body of the electrode segment and defines an outlet 119 at the end at which the segment 114 is engaged to the segment 115. This allows for a passage of gas through the segment 115.

The segment 114 may be engaged to the segment 115 by the use of a connector region 122. The connector region 122 may consist of a nipple 123 of the proximal electrode segment 4 and a recess 124 of the segment 115. Each of the segments 114 and 115 are preferably of the same shape and as such can allow for any number of electrodes to be "stacked" onto each other in the axial direction. With reference to Figure 16, it can be seen that the segment 115 includes a nipple 123 for its engagement to a like electrode segment.

) The connector region 122 may alternatively be defined by a separate element such as a connector 129 as for example shown with reference to Figure 21. The connector region 122 and/or the use of the connector 129 as shown in Figure 21 facilitates the connection of electrode segments by a threading engagement. Rotation of one segment relative to the other in one direction will result in the electrodes threadingly engaging together. Rotation in the opposite 5 direction will threadingly disengage the electrodes. A tapered thread connector may be used to establish a good connection between the two electrodes.

In the most preferred form the electrode segments 114 and 115 are engaged directly to each other. A jointing compound or other means of sealing between the interface of the two segments may be used. However alternatively an intermediate element such as for example the connector

0 130 shown with reference to Figure 20 may be positioned interposed between the two electrode segments.

As a result of the threaded engagement of the two electrodes, and unless the passage 106 extends along the central axis XX of each of the electrode segments, alignment between the two passages 106 and 206 in the example shown with reference to Figure 16, will be an issue. 5 Accordingly one or both of the electrode segments at their interface regions with an adjacent electrode, may include a manifold 139. The manifold 139 as for example shown with reference to Figure 15 is preferably an arcuate or circular slot or groove formed at the end of the electrode segment with its centre on the axis XX. In the example shown with reference to Figure 16, the outlet 119 will always be in fluid communication with the passage 206 because of its radial )0 positioning from the central axis XX, to correspond with the same radial position of the concentric manifold 139. Regardless of the rotational orientation about the rotational axis XX of the segment 114 with the segment 115, the outlet 119 will always be in fluid communication with the manifold 139.

In the example shown with reference to Figure 16 the segment 114 and 115 include off axis 5 conduits 106 and 206. The provision of the manifold by one or both of the segments 114 and 115

at their interface region can allow for fluid communication to occur for gas entering the inlet 107 with the outlet 163 irrespective of the relative rotation or orientation of the segments 114 and 115.

With reference to Figure 17 there is shown a variation to that described with reference to Figure 14A wherein a plurality of passages are provided through one, some or all of the segments 114, 115 and any intermediate segments such as segment 118.

Each of the passages 306, 406 and 506 are defined by passage segments in two or three of the electrode segments 114, 115 and 118 as shown in Figure 17. The passage 306 extends from an inlet 107 through segment 114 and partially into segment 118. The passage 506 consists of passage segments extending through the electrode segment 114 and 118 and partially into segment 115. ) The passage 406 extends through all of the segments 114, 115 and 118. The passage 406 extends along the rotational axis XX and therefore it does not utilise a manifold for establishing fluid communication between its inlet and distal end/outlet. Passages 306 and 506 are positioned radially outwardly from the rotational axis XX and accordingly manifolds are provided by the segments to establish fluid communication between the passage segments. Further segments may 5 be stacked onto the three segments as shown and are provided to allow passages to be established, each terminating at a different distance from the proximal end 104 of such an electrode assembly.

Gas may be delivered to each of the passages that have a sealed end during use of the electrode. Alternatively gas may only be supplied to one of the passages being that passage that has the largest reach through the electrode assembly other than the passage that is open at the distal 0 end of the electrode assembly.

In the example as shown with reference to Figure 17 it is preferably passage 506 and in addition and optionally, also passage 306 that is pressurised by the delivery of gas to the electrode at the proximal end 104. Passage 406 given that it is exposed at its distal end, will not have a gas supplied thereto as such a gas will pass substantially through the passage 106 and out through its ,5 distal end opening without significant diffusion of gas occurring towards the surface or surfaces 110 of the electrode assembly.

With reference to Figure 18, a partially consumed electrode assembly 116 is illustrated wherein the distal end 105 has been partially consumed. Passage 506 is illustrated to be pressurised by a gas introduced at the distal end 104. It can be seen that the manifolds 538 and 539 are also O flooded with gas. Whilst in Figure 18 the segments of the passage 506 are shown to be in alignment, such need not necessarily be so where a manifold such as that as herein described is utilised.

With reference to Figure 19, further consumption is shown to have occurred to the electrode as shown with reference to Figure 18. The passage 506 has become exposed at the distal

end 105. In the condition shown with reference to Figure 19, the passage 306 is now the passage that receives the gas.

With reference to Figure 18 where both the passage 506 and 306 remain closed at its distal end, it is preferably that only the passage with the greatest reach into the electrode assembly is pressurised. However in an alternative form, both or all of the closed passages may be simultaneously pressurised.

The introduction of gas into the electrode assembly 116 preferably occurs at the distal end 104 via an end cap 186. With reference to Figure 8 for multiple passages through the electrode assembly the end cap will include partitions and independently controlled gas inlets 108 for each of the passages extending through or partially into the electrode assembly 116. Upon the exposure of a distal end of a passage at the distal end 105 of the electrode, a pressure drop can be detected by the system of the present invention that can consequently result in a termination of the gas supply to such a passage. Accordingly control valves and pressure sensors" are preferably included in the system of the present invention for such purposes.

Where a blind hole is to be provided to an electrode or electrode segment, such may be provided firstly by drilling or establishing a through hole through the electrode or electrode segment and then plugging it from the distal end of the through hole to establish a blind hole. Other variations and combinations of electrodes and electrode segments with holes and through holes may establish the desired effects by the present invention. For example a hole may be established down the centre of each electrode segment and the top end of each hole is threaded to take a plug. Another hole may be established along side the centre hole, and is of a depth determined by the distance from the cap to a certain distance to the sill. An end cap is fitted and the centre hole may be pressurised with a gas passing through the top electrode and into the blind hole of the second electrode. When an electrode is added an operator may place a plug in the centre hole before adding a new electrode. This will prevent the gas from going all the way through the second electrode and only down the partial hole. This offers the advantage that the electrodes may be identical.

Figures 22 to 24 show a sequence of stacking of electrodes of this configuration. A plug 265 may be used to plug one of the passages by an operator as a stacking from the top end of the new segments occurs. In Figure 22 the electrode B is shown to have one of its passages plugged. When both the passages of the electrode B are exposed as shown in Figure 23 gas supply may be terminated to deliver gas to the electrode B and may be switched to the blind hole passage of electrode A. When a new electrode such as electrode C is to be stacked as shown in Figure 24, it can continue to deliver gas to electrode A to its blind hole until electrode B and electrode A are

consumed to a particular state to expose the blind hole of electrode A whereupon the gas applied to the blind hole of electrode A will be terminated and switched to the blind hole of electrode C.

With reference to Figure 25 there is shown an electrode or electrode segment that has a through hole extending therethrough. The through hole is preferably filled with an intumescent material. The material that may be used will have a tendency to expand or increase in density and/or porosity when exposed to heat. Maximum heat exposure of the electrode is predominantly occurring at its distal end the selection of the intumescent material is such as to ensure that an effective plugging of the distal end of the through bore occurs. The intumescent material will however allow for gas to migrate down the through bore towards the plugged end to allow for ) distribution of gas along the electrode body. The material may alternatively be a material that has a tendency to sinter and when exposed to the desired temperature will sinter to effectively block the passage at or proximate the distal end.

Whilst in the electrode segment variation of the present invention a particular number of holes are shown in the accompanying drawings, it will be appreciated by a person skilled in the art

5 that any number of holes or passages may be established in the electrode segments in order to establish delivery of gas to different depths of the electrode body. The present invention may also extend to a number of holes being established to the same depth in order to facilitate delivery of a gas to an even depth and at equispaced intervals about the central axis of the electrode segment.

For example nine holes may be drilled around the section between the distal end and the proximal

0 end. Three holes may pass all the way through, three holes may extend for example 60 percent and three holes may pass only 30 percent through the electrode.

With reference to Figure 26, there is shown an electrode or electrode segment that includes a pig 267. The pig may have a thermo couple embedded inside and is suspended or located down the hole of the electrode segment. The pig 267 is engaged by a cable 268 that can pull the pig ,5 through the hole. .A winding system 269 may be used to control the position of the pig within the electrode or electrode segment. The winding system may be controlled as a result of feedback of temperature of the thermo couple so that the pig may be set substantially at the same distance from the eroding end of the electrode. The cable may extend through multiple electrode segments and the pig may transfer from segment to segment as segments are consumed. When an electrode )0 section is added a spare winder and short section of cable can be fitted to the new section. This is lifted up onto the furnace and the old winder may be removed and the cable disconnected. The connector is then connected to the next section before it is added. The pig is preferably plug shaped.

In the example shown with reference to Figure 21 wherein a central passage is provided for 5 an electrode or two or more electrode segments, the end cap 186 may not include the same

partitions as those defined with reference to the end cap shown in Figure 19. A single inlet for gas may be defined by the end cap 108 for introduction of gas into the electrode or electrode assembly.

Where an intermediate connector 129 is used for connecting electrode segments, the connector may include a passage or passages for the purposes of creating a fluid connection between the passages of the electrode segments. This is for example shown in Figure 22.

As an alternative to one or each of the electrode segments defining a manifold for establishing a connection for flow of gas between electrode segments alternatively a connector such as a the connector 130 may provide such features. In the example as shown with reference to Figure 20, the electrode segment 614 does not define such manifolds but alternatively the ) manifolds 739 are provided by the intermediate connector 130. Also in the example as shown with reference to Figure 21, the connector will separate contact of adjacent electrode segments from each other.

Figures 27 to 31 show arrangements where a copper mass as a spring form 100 can collapse and indeed assist in melding the ball shown in Figures 27 and 28 onto the grub screw valve seat

3 thereby to sufficiently occlude the passageway through the engaged grub screw through the electrode so as to enable pressure to be sufficient to effuse out through the electrode. The copper tubes and copper post shown in Figures 29 to 31 are viable alternatives to the spring form 100.

Figures 29 through 31 show how a copper tube under a cover (as in Figure 29) can support the valve (in this case a ball) away from the valve seat, Figure 30 likewise, and Figure 31 shows, for 0 example, a copper post holding the ball distances from the grub screw provided valve seat.

By way of example about three bars of pressure of nitrogen as a protective gas can be fed at, for example, 1OL/ minute into the electrode. Whilst nitrogen is preferred argon and/or mixtures of nitrogen and argon are also the preferred.

With copper melting at, for example, about 1084°C it can be seen that in the circumstances ,5 as shown progressively through Figures 32A through 32F, different assemblies serially provide the blinding function to ensure gas issuance outwardly of the electrode or electrode assembly.

To summarise various systems will now be discussed.

System 1: An end cap is placed over the end of the electrode and is held in place by a threaded section screwing into the end socket of the electrode. The Nitrogen is pressurised on the 0 end and diffuses through the body. It is hoped that the Nitrogen can find its way to the tip area.

System 2: A coating is placed over the surface of the electrode so can not escape from the surface until the coating is burned off. The Nitrogen will be forced to travel down the body further

giving better protection further down. The end cap and other parts of the system are the same as system 1.

System 3: A hole is drilled down all the electrodes to approximately 75% of the length. A hole is also drilled through the centre of each nipple and into the opposite end just to pass through any skin. The length of this hole is determined by the distance from the clamp to the sill height of each particular EAF. An end cap is placed on the end of the electrode which applies Nitrogen pressure to the end of the hole. The gas diffuses through the body from the hole but it also diffuses from the end of the hole into the nipple cavity of the next electrode. Advantages are that all electrodes are the same. The disadvantage is that Nitrogen flow in the second section is low. System 4: A hole is drilled down the centre of each electrode and the top end is threaded to take a plug. Another hole is drilled along side this at a depth determined by the distance from the clamp to the sill as in system one. An end cap is fitted and the centre hole is pressurised with N and the gas passes through the top electrode and into the partial hole in the second. When an electrode is added the operator places a plug in the thread in the centre hole before adding a new electrode. This stops the Nitrogen from going all the way through the second electrode and only down the partial hole. The advantage of this system is that all electrodes are the same. The disadvantages are that it can only get through two sections.

System 5: Several holes are drilled down the electrode in different positions and depths.

The holes are matched up by grooves in the end on the electrode so the gas can pass around the groove and into the corresponding hole in the next section. This system allows to have combinations of 2,3 or 4 holes and the electrodes would have to be added to the furnace in the correct sequence. The end cap will have to be positioned/setup to put the gas into the correct hole.

The advantage of this system is that it will allow the N to flow at any depth in the electrode. The disadvantage is several different types of electrode are required and the gas has to be set onto the correct hole on the top electrode.

System 6: Several holes are drilled down each electrode and these are matched up on the ends by grooves as per system five. The pressure is applied to the end with an intelligent device that can detect a pressure drop if the hole goOes all the way through. The system will shut off the glow on that hole and open the flow on the next hole.

System 7: This would be the same as system 5 but the holes are matched up by placing a disc in between each section to make the holes connect up.

System 8: A hole is drilled down the centre of all electrodes and a plug is held in one position in the centre to prevent the gas from passing out the end of the electrode. The plug is maintained in the same position via a mechanical means on a tube which is attached to the top of ) the furnace.

EXPERIMENTAL

In order to confirm that the gas will permeate through the graphite electrode a standard electrode, as used in one of the local mills, was purchased for some initial trials. A drawing of the electrode is shown in Figure 9.

A jig 90 was developed, as shown in Figures 10 and 11, so that trial pressures of air 95 could be applied to one end of the electrode in order to determine how far down the length of the electrode the gas could travel with time. Two connecting rods 91 were used to construct the jig 90. Spraying the electrode surface with soapy water marked the movement of the air through the electrode. Wherever the air was allowed to escape from die surface a large amount of foaming could be observed. This was used as an indication of the extent of travel of the air through the electrode.

As shown in Figure 11, the pressure plate 92 with holes 93 to for the connecting rods 91, was designed so that the air pressure could be applied at pressures ranging from V2 to 4 bar over three different areas (3 different O-rings).

The initial trial consisted of applying Vz bar pressure over an area encompassed by a 450 mm diameter o-rϊng. This meant that the pressure was applied to the majority of the electrode face and the threaded recess 33. When the outside surface of the electrode was sprayed with the soapy water the foaming indicated an air penetration of 500 mm length. When the jig was rearranged so that the 150 mm diameter area was applied at the same pressure, the gas front moved down to approximately 650 mm. No further advance of the gas could be detected even after the pressure was sustained for 2hours of testing.

Increasing the pressure of the gas in Vi bar steps up to a maximum pressure of 3 bar showed some improvement in the depth of penetration but not to the extent expected.

A lO mm diameter hole, 500 mm deep, was drilled length wise into the electrode and again the air was applied using the 150 mm pressure plate. The soap test showed that this increased the penetration of the air front to approx 800 mm. The depth of the hole was extended to approx 900 mm and the experiment repeated. Once again the gas front advanced and by the time that the hole had been increased to 1200 mm the whole of the electrode became permeated with air. ) Part of a second section of electrode was screwed onto the graphite plug 37, as shown in

Figure 12, and the air was again applied using the 150 mm pressure plate. After applying the pressure for 30 minutes there was no ingress of air into the second electrode. When a hole was drilled through the graphite plug and the pressure again applied to the combined electrodes, foaming was detected in the second electrode. When a further central passage was drilled in the second electrode it aided the movement of the gas front as it had done in the first electrode. Experimental Conclusions

We have had different degrees of success at impregnating a carbon electrode with a gas.

The depth of penetration of the gas is dependent on the area of the electrode face exposed to the pressure and to a lesser extent the actual pressure of the gas. It also depends on the nature of the surface of the electrode and whether or not there is an outer layer. The depth of penetration of gas is increased by drilling a hole into the electrode and filling with gas from this hole. It has also been

shown that this ingress of gas can be transferred to a second electrode provided the graphite plug and the second electrode are drilled so as to continue the channel.

As indicated earlier by reference to Figure 37 whilst a description has been given in respect of EAF circumstances where such protective gas effusion is of benefit, Figure 37 shows in an aluminum electrode system used in the Hall Herault process. The concept here would be just to fit a nitrogen feed into the graphite anode or modify the anode rod and its connection methods so that the gas can be fed into the anode via the rod. This would be easy for the operators to just connect the gas feed to the rod when they place the anode in the cell.

An advantage of the present invention is that a lower grade of electrode or an electrode that has not been subject to post processing may be used.

Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth.

Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or improvements may be made without departing from the scope or spirit of the invention.

In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognise that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.