GB2103058A - Furnace electrode clamps - Google Patents

Abstract

A furnace electrode clamp comprises a metallic shell 1 having a part cylindrical inner surface 2 within which a carbon electrode (3) can nest. The inner surface of the shell is provided with axially-extending grooves 5 within which graphite inserts 4 are retained for making electrical contact between the shell and a nested electrode. Each groove is of dovetail-like section which tapers evenly from a maximum width at the top of the clamp to a minimum width at a location towards the base of the clamp. <IMAGE>

Description

SPECIFICATION Furnace electrode clamps This invention relates to furnace electrode clamps 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 through carbon electrodes which are connected through clamps to bus bars carrying the transformer output current. Clamps for carbon electrodes generally comprise a 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 current conducting protective coating, direct contact between the metals of the coating and the clamps 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 of the contact surfaces which reduces the electrical conductivity at the electrode to clamp interface and induces progressive deterioration of performance.

It has been proposed to overcome or mitigate this problem by providing for the contact with the electrode to be made via arcuate section graphite elements set in the inner surface of the clamp.

Such a solution has disadvantages, however, because the graphite is susceptible to oxidation which adversely affects electrical conductivity.

Additionally, such elements are expensive, difficult to machine with the required accuracy, difficult to manoeuvre and assemble which gives rise to extended "down-time" periods when they are replaced. It has been found that 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.

According to one aspect of the present invention, a clamp for a carbon electrode comprises a metallic shell having a partcylindrical inner surface within which the electrode can nest, the inner surface of the shell being provided with axially-extending grooves effective to retain graphite inserts for making electrical contact between the shell and a nested electrode, each groove being of dovetail-like section which tapers, evenly from a maximum mean width at the top of the clamp to a minimum at a location towards the base of the clamp.

In a preferred embodiment of the invention the depth of each groove in the clamp shell is substantially constant along the axial length of the groove and is less than that of the respective insert. Conveniently, a number of such grooves are circumferentially spaced across the cylindrical surface of the clamp shell.

According to the present invention in another aspect, there is provided a furnace electrode clamp comprising a metallic shell and a plurality of graphite inserts mounted on the surface of the shell against which the electrode is clamped, each insert being located and retained within an axially extending groove of dovetail-like section set in the inner surface of the shell whose section tapers evenly between a maximum mean width at the top of the shell and a minimum at a location towards the base of the shell.

The exposed surface of each insert may be provided with a concave portion for engagement with the convex surface of the electrode.

Preferably, the depth of each groove is less than the depth of the respective insert so that the exposed insert end stands proud of the shell inner surface.

According to the present invention in a further aspect, there is provided a graphite insert shaped and dimensioned to be receivable within the shell grooves of the electrode clamp referred to above.

An embodiment of the invention will now be 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 section taken along Il-Il of Figure 1; Figure 3 is a side elevation of the clamp illustrated in Figures 1 and 2; and Figure 4 is a perspective view of an insert used in the clamp illustrated in Figures 1 to 3.

Referring to the drawing, the clamp illustrated comprises a shell 1 of copper, having a part cylindrical inner surface 2 into which a carbon furnace electrode indicated generally by the dotted line 3 can be nested. Water cooling channels may be provided within the shell in a conventional manner.

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 shell 1 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 shell 1, which is conventionally connectable to the appropriate current source, and the electrode 3, is by way of an array of graphite inserts 4 of dovetail-like section. Each insert is retained within a complementary groove 5 provided within the surface 2 of the shell 1 and stands proud of this surface.

As will be seen from Figure 3 of the drawings, the width of each groove and inset tapers evenly from a maximum at the top of the shell, to a minimum at the base. In one particular arrangement, the length of the inserts is slightly less than the axial length of the shell, eg 1 to 2 inches less.

Each insert is machined to form a sliding fit with its co-operating groove and can be provided with a concave surface 6 for engagement with the coated surface of electrode 3.

Turning now to Figure 4, it has been found that an algebraic relationship exists between the angle with each side wall of each insert 4 makes with the insert base (angle Y in Figure 4), and the radial and axial taper angles of the insert (angles X and Z respectively).

Thus, in one arrangement 2 Angle Y=Angle X; and 5 Angle Z=Angle Y.

When assembling the clamp, the inserts 4 are introduced into the upper ends of the grooves 5 and are driven downwardly until they become locked into the positions shown in the drawings. The axial taper causes each insert to push back onto the bottom face of the respective dovetail groove whilst being forced onto the two side retaining faces. This ensures a satisfactory electrical connection between the insert and the clamp shell. Retaining plates may be positioned above and below each insert further'to restrain the insert within the groove. The inserts can readily be removed from the grooves using a minimum of force. 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 shell which is in the form of a half cylinder, the shell 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 (9)

Claims

1. A clamp for a carbon electrode comprising a metallic shell having a part-cylindrical inner surface within which the electrode can nest, the inner surface of the shell being provided with axially-extending grooves effective to retain graphite inserts for making electrical contact between the shell and a nested electrode, each groove being of dovetail-like section which tapers, evenly from a maximum mean width at the top of the clamp to a minimum at a location towards the base of the clamp.

2. A clamp as claimed in Claim 1 or Claim 2 wherein the depth of each groove in the clamp shell is substantially constant along the axial length of the groove and is less than that of the respective insert.

3. A clamp as claimed in Claim 1 or Claim 2 wherein a number of the grooves are circumferentially spaced across the cylindrical surface of the clamp shell.

4. Afurnace electrode clamp comprising a metallic shell and a plurality of graphite inserts mounted on the surface of the shell against which the electrode is clamped, each insert being located and retained within an axially extending groove of dovetail-like section set in the inner surface of the shell whose section tapers evenly between a maximum mean width at the top of the shell and a minimum at a location towards the base of the shell.

5. A clamp as claimed in Claim 4 wherein the exposed surface of each insert is provided with a concave portion for engagement with the convex surface of the electrode.

6. A clamp as claimed in Claim 4 or Claim 5 wherein the depth of each groove is less than the depth of the respective insert so that the exposed insert end stands proud of the shell inner surface.

7. A graphite insert shaped and dimensioned to be receivable within the shell grooves of an electrode clamp as claimed in any one of the preceding claims.

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

9. A graphite insert for use in a furnace electrode clamp substantially as herein described with reference to Figure 4 of the accompanying drawings.