GB2082028A - Improvements in furnace electrode clamps - Google Patents

Abstract

A furnace electrode clamp comprises a metal shell 2 having a part- cylindrical inner surface 4 within which an electrode 6 can nest. The shell 2 has axially extending grooves 10 which retain graphite inserts 8 for making electrical contact between the shell 2 and the nested electrode 6. The grooves 10 are also part-cylindrical in cross-section to permit relative movement of the inserts 8 within their respective grooves 10 to allow for eccentricity of the electrode 6 and wear of the inserts 8. <IMAGE>

Description

SPECIFICATION Improvements in furnace electrode clamps This invention relates to clamps for graphite electrodes and is particularly although not exclusively, directed to clamps for carbon electrodes which are employed in electric arc furnaces and which have an outer metallic coating.

In electric arc furnaces, power for melting is supplied to the charge by way of consumable carbon electrodes. These are retained in position above the charge by metal clamps which are effective to conduct current to the electrodes from the particular current source employed as well as providing electrode support.

Clamps for carbon electrodes generally comprise a metal body portion of high electrical conductivity usually copper, having a part cylindrical inner surface into which the carbon electrode can be nested, the electrode being held firmly within the body portion by a tensioned band or yoke which embraces the portion of the electrode remaining exposed.

In the case of carbon electrodes provided with a metallic coating, direct contact between the electrode outer surface and the metal of the clamp can produce a eutectic phase which is accompanied by local melting at the operating temperature of the clamp-electrode combination. Local melting does, in turn, produce welding and pitting which reduces the electrical conductivity at the electrode clamp interface and induces progressive deterioration of performance.

It has been proposed to overcome this problem by introducing elements into the part-cylindrical surface of the clamp, so that a graphite-metal interface is produced with the electrode surface coating. However, due to the relatively low electrical conductivity of the graphite, efficient operation of apparatus employing the electrodes requires uniform contact with the electrode coating over the maximum possible area of the graphite insert.

Even with accurate machining of the graphite element contact surfaces, wear of the graphite insert and/or circumferential variation in electrode radius of curvature will degrade uniformity of contact. Uniformity of contact will also degrade as a result of wear of the insert surfaces and it is accordingly one object of the present invention to attempt to overcome the disadvantages.

According to one aspect of the present invention, a clamp for a carbon electrode comprises a metal body portion having a partcylindrical inner surface within which the electrode can nest, the part-cylindrical surface being provided with axially-extending grooves effective to retain graphite inserts for making electrical contact between the body portion and a nested electrode, the grooves and the inserts being shaped to permit relative movement whereby the insert can adjust its position to produce optimum engagement with the outer surface of the electrode.

In a preferred embodiment of the invention the axially extending groove in the body portion of the clamp is also part-cylindrical so as to be able to enclose a graphite insert having a part-cylindrical surface slidably engaging the inner surface of the groove. In this case, the exposed surface of the insert can conveniently be provided with a concave portion for engagement with the convex surface of the electrode; the insert which is moveable within its groove can accordingly rotate to ensure optimum contact with the electrode outer surface, notwithstanding limited eccentricity.

Suitably, each insert has a sector removed at the region of the innermost portion of the groove.

Conveniently, a number of inserts are circumferentially spaced across the cylindrical surface of the clamp body portion, the number of inserts and their dimensions being selected accordng to the electrical conductivity and the current-carrying capacity which is required.

Am embodiment of the invention will now be particularly described by way of example with reference to the accompanying drawings in which: Figure 1 is a top view of a section of a clamp for a carbon graphite electrode.

Figure 2 is a side view of that portion of the clamp of Fig. 1 having a graphite insert within a groove and Figure 3 is a top view of the clamp of Fig.

1 and illustrates members for retaining graphite inserts within their grooves.

Referring to the drawing, the part of the clamp illustrated comprises a body portion (2) of copper, having a part cylindrical inner surface (4) into which a coated carbon furnace electrode indicated generally by the dotted line (6) can be nested. Water cooling channels are indicated generally at 3.

A band or clamping member (not shown) of a type well known in the art is provided to encircle that portion of the surface of the electrode which is exposed by the clamp body portion 2 and is effective both to retain the electrode firmly in position as well as to ensure good electrical contact between the electrode and the clamp.

Electrical contact between the body portion (2), which is conventionally connectable to the appropriate current source, and the electrode (6) is by way of an array of part cylindrical graphite inserts (8). Each insert (8), which extends substantially over the whole axial length of the clamp, is retained within a partcylindrical groove (10) provided within the surface (4) of the body portion (2).

Each insert (8) is machined to form a sliding fit with its co-operating groove and can be provided with a concave surface (12) for en gagement with the metallic coated surface of electrode (6).

With an electrode offered up to the array of inserts (8) each insert can rotate within its groove to assume an angular position ensuring that the concave surface (12) produces the best possible mate with the corresponding region of the electrode surface. In this way limited eccentricity of the electrode surface or wear of the inserts can be accommodated without unduly reducing the area of contact at the interface.

Each insert (8) has a sector removed from that portion lying at the base of its groove (10) so that when the clamp is tightened limited movement of the insert can occur to permit firmer engagement with the groove wall and increase electrical conductivity at the insert-groove interface to a maximum.

As illustrated in Fig. 1 each insert is partly retained in position by being enclosed beyond its major diameter in its corresponding groove 10 provided in the body portion of the clamp.

Figs. 2 and 3 illustrate the manner in which each insert is further retained within its corresponding groove to prevent axial movement and also to prevent excessive radial movement in the case where enclosure by the groove beyond the major diameter of the insert cannot be provided.

As shown in Figs. 2 and 3 each axial end of the insert is provided with a recess 1 3. The upper recess is arranged to engage a spur 14 cast integrally with the clamp body portion 2 or on a retaining plate while the lower recess is, as more particularly shown in Fig. 3, arranged for engagement by a removable spur provided on one of two retaining plates 18 and 20 screw fitted to top and/or bottom of the base of the clamp body portion. The abutting surfaces of the recesses and spurs are such that on securement of the plates 18 and 20 the inserts are drawn into the grooves to improve retention.

As can be seen from the drawings graphite inserts can be removed and replaced by unscrewing the retaining plates 18 and 20.

In an alternative embodiment the recesses 1 3 in the inserts may be replaced by projections which engage with co-operating recesses in the retaining plates 18, 20, and in the clamp body portion.

It will be appreciated that while the invention has been particularly described with reference to a coated graphite electrode it is equally applicable to uncoated electrodes whether intended for arc furnace operation or for any other application.

It will also be appreciated that while the clamp of the invention has been described with reference to a body portion which is in the form of a half cylinder, the body portion may be in the form of a full cylinder with a slightly eccentric bore to permit the electrode to be inserted into and withdrawn from the engaging relationship with the part cylindrical surface. In this case the electrode may be retained in the position where it makes contact with the inserts by applied pressure.

Claims (8)

1. A clamp for a carbon electrode comprising a metal body portion having a partcylindrical inner surface within which the electrode can nest, the part-cylindrical surface being provided with axially-extending grooves effective to retain graphite inserts for making electrical contact between the body portion and a nested electrode, the grooves and the inserts beng shaped to permit relative movement whereby the insert can adjust its position to produce optimum engagement with the outer surface of the electrode.

2. A clamp in Claim 1 wherein each axially extending groove is also part-cylindrical in cross-section so as to be able to enclose a graphite insert having a part-cylindrical surface slidably engaging the inner surface of the groove.

3. A clamp as claimed in Claim 2 wherein the exposed surface of the insert is provided with a concave portion for engagement with a convex surface of the electrode.

4. A clamp as claimed in Claim 2 or Claim 3 wherein each insert is rotatable within its respective groove.

5. A clamp as claimed in any one of Claims 2 to 4 wherein each insert has a sector removed at the region of the innermost portion of the groove.

6. A clamp as claimed in any one of Claims 2 to 5 wherein the inserts are evenly spaced around the cylindrical surface of the clamp body portion.

7. A furnace electrode clamp comprising a metallic body portion and a plurality of graphite inserts mounted on the inner surface of said body portion, against which an electrode can be clamped.

8. A furnace electrode clamp substantially as herein described with reference to Figs. 1, 2 and 3 of the accompanying drawings.