GB2176980A - Cooling furnace electrodes - Google Patents

Abstract

An improved method by adapting a cooling jacket 5 to a graphite electrode 7 in an electric furnace, which incorporates cooling means, so that conventional graphite electrodes can be used and cooled sufficiently to permit satisfactory use. The cooling means may be tubes carrying coolant, which is preferably water. The tubes may be arranged in multiple formation around the circumference of the electrode and may be fed with coolant in an up and down formation to achieve a forced cooling circuit. The tubes may be carried on rings for example split rings with a connecting link, which expands and contracts appropriately. Operation may be by hydraulic or other means but preferably by controlled use of the pressure of the coolant itself. <IMAGE>

Description

SPECIFICATION An electrode cooling system for graphite electrodes This invention relates to cooling jacketforgraphite electrodes, such as for example, those used in electric arcfurnaces or other type of electric furnaces for melting or refining processes.

The surface of a graphite electrode which is exposed to the heat from the melt tends to be consumed during use as a result of oxidation. This consumption ofthe graphite in a lateral direction leads to early wearofthe electrode and consequent need for its replacement.

Reduction ofthe temperature of the electrode can extend its useful lifetime and reduce the electrode surface exposed to oxidation, and systemsforcooling the electrodes of electric furnaces during a melting or refining process are already known but are not entirely satisfactory. The difficulty arises in applying cooling to a graphite electrode. One known system uses a liquid cooled metal shaft, to which a short graphite electrode is attached. This system has the disadvantage of being expensive, as the handling and preparation required to connect the graphite electrode to the metal shaft involves several additional operations during the melting process.

We have now discovered that the problems associated with this use of the metal shafts can be overcome by using a cooling jacket which can be clamped to the conventional graphite electrode. This enables conventional graphite electrodes to be used and cooled, with the result that additional handling and separate preparation ofthe electrodes is not required. Also, the need for making expensive modifications to the fur- nace is avoided.

Thus according to our invention we overcome those problems by providing a cooling jacket, clamped to the circumference ofthe graphite electrode during operation.

Preferably, the jacket is made so that it can be expanded and contracted. Expanding thejacketthen allows an electrode to be inserted within the jacket or removed from it, orforthe position of the electrode to be adjusted (for example by lowering it further into the furnace); contracting the jacket it will equalize the different tolerances of the graphite electrode diameters and also guarantee an adequate heat transfer.

The cooling means comprises ducts to form the jacket, through which coolant can circulate and conduct the heat from the electrode.

The most preferred arrangement is a series of mul tipletubes set around a support ring in a substantially vertical direction relative to an electrode. This enables coolant to be fed up and down the tube system from the cooler outer end to the hot lower end within the furnace and back again.

The jacket and its component tubes and ringmembers may be made of any convenient material which has therequisite strength and heat conductivity. Thus it can be made of metal, preferably such as steel or copper.

The jacket may be fabricated by any means which is convenient and will provide the assembly with adequate strength and resistance to the heat ofthefur- nace.

The coolant, supplied under pressure, is circulated through the cooling means so that it conducts the heat from the electrode and is then returns to a cooling zone where it can lose its heat before it is recirculated again.

The coolant may be of any conventional fluid. It is preferably water, but gas (for example air) may be used if desired. The temperature ofthe coolant may as is conventionally used.

The ducting ortubing of the jacket and the flow rate and the velocity of the coolant is designed to achieve an uniform heat transmission over the whole cooling area.

The jacket should be held as close to the graphite electrode surface while in operation as is conveniently practicable, so that sufficient transfer of the heatto the coolant is achieved.

The expandableform can be achieved in a variety of ways, but we prefer two use a form in which a cluster of tubes is adapted to surround an electrode and is secured bya ring memberatornearits upperend.At the lower end which is the heated end within the furnace a ring member is adapted to provide the required expanding and contracting action. The rings may be operated bythesame ordifferentexpandingi contracting means.

Oneform ofthe ring membercomprisesa band disposed around the ducts or tubes and adapted to tighten around them when the assembly is required to contract on to the electrode. The operation ofthis band may be by any conventional means, for exam ple a hydraulically, pneumatically or electrical iy oper- ated lever or plunger which can be operated to move the band between the loosened (expanded) and tightened (contracted) positions. This is very convenient foruseatthe upperend of the jacket.

Another form of ring member comprises a split ring with its ends joined buy a link member which can be moved to expand or contract the size of the ring member. This may be operated by any convenient means, for example hydraulicalty, pneumatically or mechanically. An especially preferred form, however, is that in which the pressure of the coolantwithin the cooling tubes is used to actuate the link member. This may be done by arranging thatthe iink memberis connected to a plunger within a cylinder and thatthe link member is moved when a predetermined press ure ofthe coolant is reached.

This operation by the coolant pressure is preferably such that the expanding of the sleeve or its ring memberoccurs when the pressure is increased above some pre-set limit, which is itself above the normal working pressure ofthe coolant. Then when the electrode needs to be replaced or adjusted the coolant pressure can be temporarily increased, for example by a restrictorvalve in the coolant return, thereby actuating the plunger and causing the link memberto move the split ring member and expand it.

The expanding/contracting mechanism may be spring loaded or biased so that it tends to return to the desired position when actuating forces are released.

Such spring mechanisms are well known as such, but should be made of materials which are satisfactorily resistant to the conditions of use (especially heat).

One way of protecting them is to site them within the cooling system ofthe jacket so as to minimise exposure to the heat ofthe furnace.

The jacket ofthe present invention may be supported on a conventional arm adapted to the furnace to hold the electrode in position.

To ensurethatthe cooling jacket is atthesame potential as the graphite electrode, it is preferred to provide insulation material to insulate the jacket elec tricallyfrom the main electrode support arm.

With the cooling jacket around the graphite electrode it is possible to use uncoated and,orsmaller electrodes, which leads to further reduction in the electrode consumption costs.

The invention is illustrated but not limited bythe accompanying drawings, in which Figure lisa vertical section showing a melting furnace and the cooling jacket, clamped to a graphite electrode.

Figure2 is a cross section through a graphite elec trodewith a clamped tubular cooling jacket and the upperclamping arrangement around it.

Figure 3 shows a view, in partsections of the expandable/contractable cooled lower ring and the vertical cooling tubes leading to it.

In figure 1 there is shown an electric melting furnace 1 which includes a cover 2 and ports 3 to allow a graphite electrode 7 to pass through.

The expandable/contractable cooling jacket 5 shown as a series of multiple tubes, is supported by the upper ring 8 which is via clamps 11 attached to a conventional electrode holding arm 6.

The uppersupport ring 8 is fabricated as a hollow tube which suspends the cooling jacket 5 when ex pandedforreplacementorlowering the electrode7.

Atthe same time this support ring 8 will bathe main coolantfeed and return connectionforthe cooling jacket 5 and the expandable/contractable lower ring member9.

)n figure 2 there is shown the graphite electrode7 and the vertical cooling tubes ofthe jacket 5 clamped to the electrode 7. A band 13, reliably arranged around the tubes of the jacketS, is connected to a spring loaded cylinder 12 and with the counter block 15, connected to a plunger 14, a tight connection of the jacketS to the circumference ofthe graphite electrode 7 can be achieved which is necessary for a sufficient heat transmission.

In figure 3 there is shown the expandable/contractable lower cooling ring member9.Thetwo risertubes 16 provide the necessary connections forthe pressurized coolantfeed and return from the support ring 8, figure 1.

The expanding action ofthe ring member9 can be achieved byan integrated spring loaded plunger 14.

Furthermore the ring member will expand thever- tical cooling tubes of the jacket 5 which is necessary when the graphite electrode 7 has to be replaced or adjusted. This can be achieved by small brackets 17, welded to the circumference of the lower ring mem bet9, but not exceeding the overall dimensions ofthe cooling jacketS.

In operation the tubes ofthe jacket5 are tightly clamped to the graphite electrode 7. On the upper end ofthejacket5 this can be achieved with a spring loaded cylinder 12 and an attached band 13 as well as a counter block 15 on the lower end ofthe cooling jacket 5 the biased ring member 9 will keep the vertical tubes 5 tightto the circumference ofthe electrode 7.

Ifthe graphite electrode 7 has to be replaced or adjusted the operation coolant pressure will be increased which expandsthe biased lower ring mem ber 9, actuated by a plunger 14 and also enlarges the diameter ofthe lower part ofthe cooling tube 5.

The cylinder 12 on the upper part of the cooling jacket will be actuated which enables the precontracted vertical cooling tubes ofthe jacket 5 to expand and the graphite electrode is free to move.

This procedure can be repeated as often as required.

Claims (17)

1. Ajacketforthe use to place around the circumference of a graphite electrode in an electric furnace and having cooling means incorporated in it.

2. Ajacketas claimed in Claim 1 wherein means are provided for expanding and contracting the jacket diameterforthe purpose of movement or adjustment of an electrode within it ortho equalize the tolerances in the electrode diameter.

3. Ajacketascaimed in Claim 1 or2whereinthe cooling means comprises ducts through which a coolant can circulate.

4. Ajacket as claimed in Claim 3 wherein the ducts are in theform oftubeswhich extend through the roof and are held in position close to the electrode during use.

5. A jacket as claimed in Claim 4 wherein a series of multiple tubes is set around the jacket in a substan tiallyvertical direction relative to the electrode and so asto surround an electrode within the jacket.

6. A jacket as claimed in Claim 5 wherein the mul- tiple tubes are fed in a continuous up and down forced cooling circulation with the supply of the coolant.

7. A jacket as claimed in Claim or 6 wherein the upper and/or lower ends of the multiple tubes are connected by return elbows to build a continuous cooling circuit.

8. Ajacketas claimed in any of Claims 1 to 7 wherein a cluster of tubes is adapted to surround an electrode surface and is secured by ring members at or near its ends, and the ring members are adapted to provide the required expanding and contracting actions.

9. Ajacket as claimed in Claim 8 wherein one or more of the ring members comprises a band disposed around the ducts ortubes and adapted to tighten around them when the assembly is required to contract on to the electrode.

10. A jacket as claimed in Claim 8 or9 wherein one or more ofthe ring members comprises a split ring with its ends joined by a link member which can be moved to expand orcontractthe size of the ring member.

11. A jacket as claimed in Claim 10 wherein the pressure of the coolant within the cooling tubes is used to actuate the link member.

12. A jacket as claimed in Claim 11 wherein the link member is moved when a predetermined press ureofthecoolantwill be increased.

13. Ajacketasclaimed in Claim 10 oral wherein the link member is moved to expand the jacketwhen the pressure ofthe coolant is increased above a pre set limit which is itselfabove the normal working pressure ofthe coolant.

14. Ajacket substantially as described herein with reference to Figures 1 to 3 ofthe accompanying drawings.

15. An improved electric furnace having at least one jacket as claimed in any of Claims 1 to 14.

16. A method of cooling a graphite electrode in an electric furnace, using a jacket as claimed in any of Claims 1 to 14.

17. A method of cooling graphite electrodes in an electric furnace, as claimed in Claim 16, wherein the coolant used is water.