US3835233A

US3835233A - Electrode seals for electric-arc furnaces

Info

Publication number: US3835233A
Application number: US00422839A
Authority: US
Inventors: O Prenn
Original assignee: Steel Company of Canada Ltd
Current assignee: Steel Company of Canada Ltd
Priority date: 1973-12-07
Filing date: 1973-12-07
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: BE826227Q

Abstract

This invention provides a seal assembly for use with an electric arc furnace in which a refractory roof covers the furnace proper, and in which at least one electrode passes through the roof. The electrode is supported independently of the roof. The seal assembly includes a main seal ring which closely encircles the electrode, supporting structure capable of carrying the weight of the main ring seal and resting on the periphery of the refractory roof, in order to avoid putting extra weight on the central portion thereof. The supporting structure includes certain pivoting link members which permit lateral mobility of the main ring seal with respect to the refractory roof, and there is also included an adjustable sealing means adapted to close the gap between the main ring seal and the refractory roof. This structure permits the roof to move to some extent in the vertical direction due to thermal expansion, etc., without affecting the main ring seal, and further permits the electrode to undergo certain lateral movements (horizontal) without placing any resultant stress on the roof.

Description

United States Patent [191 Prenn ELECTRODE SEALS FOR ELECTRIC-ARC Primary ExaminerR. N. Envall, Jr. Attorney, Agent, or Firm-Sim & McBumey [111 3,835,233 Sept. 10, 1974 [5 7] ABSTRACT This invention provides a seal assembly for use with an electric arc furnace in which a refractory roof covers the furnace proper, and in which at least one electrode passes through the roof. The electrode is supported independently of the roof. The seal assembly includes a main seal ring which closely encircles the electrode, supporting structure capable of carrying the weight of the main ring seal and resting on the periphery of the refractory roof, in order to avoid putting extra weight on the central portion thereof. The supporting structure includes certain pivoting link members which permit lateral mobility of the main ring seal with respect to the refractory roof, and there is also included an adjustable sealing means adapted to close the gap between the main ring seal and the refractory roof. This structure permits the roof to move to some extent in the vertical direction due to thermal expansion, etc., without affecting the main ring seal, and further permits the electrode to undergo certain lateral movements (horizontal) without placing any resultant stress on the roof.

1] Claims, 5 Drawing Figures ELECTRODE SEALS FOR ELECTRIC-ARC FURNACES DISADVANTAGES OF THE PRIOR ART Conventionally, electric arc furnaces in which electrodes pass downwardly through openings in a refractory furnace roof utilize water-cooled sealing glands around the electrode above the refractory roof, the purpose of which is to close off the portion of the roof opening not occupied by the electrode. It should be understood that the problems associated with the gap between an electrode and the roof opening are persistently met with in this art, because of the fact that the high-temperature gases from within the furnace tend, if they escape along the electrode, to eat away the outer surface of the electrode. Thus, even if it were practical to design the roof opening to have a very close toler-, ance against the outer cylindrical electrode surface at least initially, the slight but gradually increasing escape of furnace gases through whatever gap did remain would gradually increase that gap by eating away the electrode. In practice, it is not feasible to dimension the roof aperture too closely or snugly around the electrode, because the operation of withdrawal and insertion of the electrode through theroof opening (which must take place every time theroof is raised and swung aside to permit the addition of more raw material to the melt) involves very cumbersome equipment, and it would not be possible to avoid binding and dragging of the electrode against the refractory roof during such operation. Binding and dragging of the electrode would tend to break it because graphite is weak in tension, and also would tend to cause some damage to the roof refractories at the electrode opening. For this reason, the openings in refractory roofs for electric arc furnaces are always dimensioned appreciably larger than the nominal size of the electrodes they are to receive, and the problems introduced by this extra gap around the surface of the electrode have been combatted with the provision of annular ring seals closely dimensioned to fit snugly but slideably around the electrode, and intended merely to rest against the edge of the refractory roof around the roof opening. As mentioned before, most such annular ring seals are water-cooled, which requires water lines to and from the annular ring seal.

The following difficulties tend to be met with when utilizing water-cooled sealing rings as described above.

Firstly, there tends to be frequent arcing from the electrode through the seal and thence to the water line or the refractory roof (which in time may collect a layer of electrically conductive waste materials onits upper surface). Such arcing results in damage and failure of the seals, and is responsible for serious maintenance and production problems.

Secondly, the use of water-cooledrings in the area directly above an extremely high-temperature metal melt always involves the danger of a serious explosion, should the water-cooled ring fall through'a weak or crumbling roof into the molten bath.

When and if there should be any leakage of water from the gland or the water lines, it will constitute a source of hydrogen which is detrimental to the steel making process.

Because the water-cooled seals rest directly against the refractory roof, they place excessive weight against what is always the weakest area of the roof, particularly when the roof has been worn thin over long use. The inherent danger in this situation requires premature roof replacement because of the danger of roof collapse from the excess weight.

Where a water-cooled seal has a given and unchanging internal diameter, the seal it makes with the electrode constantly deteriorates as the escaping furnace gases gradually eat away the outside electrode surface.

OBJECTS OF THIS INVENTION In view of the foregoing disadvantages of conventional practices, it is among the objects of this invention to provide a seal assembly for use with an electric arc furnace which will not place excessive weight on the refractory furnace roof, and yet will provide an efficient seal around the gap between the electrode and the roof opening while permitting lateral mobility of the seal assembly.

It is an object of a preferred form of this invention to allow for a limited amount of vertical roof movement due to thermal contraction and expansion without either placing excessive weight against the roof or losing an effective seal.

GENERAL DESCRIPTION OF THIS INVENTION Accordingly, this invention provides, for use with an electric arc furnace having a refractory roof, and at least one electrode supported independently of said roof and passing through a roof opening larger than the electrode: a seal assembly comprising a main ring seal closely encircling the electrode, support means for supporting the main ring seal above the refractory roof from the periphery thereof, the support means including pivotable link members for permitting lateral mobility of the main ring seal with respect to the refractory roof, and adjustable means for sealing the gap between the main ring seal and the refractory roof.

The support means preferably includes at least three arms extending inwardly above the refractory roof from the periphery thereof, and structure rigidly connecting said arms together.

GENERAL DESCRIPTION OF THE DRAWINGS Two embodiments of this invention are shown in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which:

sembly in the PARTICULAR DESCRIPTION OF THE DRAWINGS Attention is first directed to FIG. 1, in which a refractory roof for an electric arc furnace is shown in partly broken-away perspective. The roof 10 includes an annular outer ring 12 which may be hollow as shown at 14 and which has flat upper and

lower walls

15 and 16, a vertical, cylindrical outer wall 18 and a generally conical inner wall 20 which is downwardly convergent. The refractory roof 10 further includes a refractory dome 22 which spans the full interior of the ring 12, and is somewhat raised toward the centre. The refractory dome 22 is generally constituted by insulative refractory material which, because it is extremely weak in tension,'is constructed in a slightly raised configuration so that all portions of the dome tend to be in compression as a result of the domes weight. The sloping inner wall 20 of the outer ring 12 permits the inwardly rising refractory dome 22 toobtain good purchase or grip against the outer ring 12.

Conventionally, the reason for the outer ring 12 being hollow is to permit it to carry cooling water or other liquid which is fed to and removed from the ring by lines not illustrated.

In the embodiment shown in FIG. 1, the refractory roof has three substantially cylindrical openings 24, of

which only one is visible because-of the roof portion broken away. Through each opening 24 passes an elongated, vertically oriented electrode 26, of which only two have been illustrated in the figure. These electrodes are usually of the consumable type, made primarily of graphite.

A further opening 28 is also provided in the refractory roof shown in FIG. 1, this opening being intended to permit the controlled exhaust of fumes from the inside of the furnace. Suitable exhaust piping (not shown) would normally be provided.

In the kind of electric arc furnace to which this invention is applicable, the electrodes 26 are suspended by means (not shown) located above the furnace and capable of downwardly inserting and upwardly withdrawing the three electrodes through the openings 24. Such electrode controlling and supporting means forms no part of this invention.

Shown in FIG. 1 is a seal assembly shown generally at 30, which is seen to include three main ring seals 32,

each adaptedclosely to encircle one of the electrodes 26 at a location above the refractory roof 10. The seal assembly further includes support means shown generally at 34 for supporting the main ring seals 32 above the refractory roof 10 from the outer ring 12. More specifically, and with particular reference to FIG. 1, the support means 34 includes three

arms

36, 37 and 38 extending inwardly and slightly upwardly from the outer ring 12, spaced above the refractory dome 22. An incomplete loop structure 40, which may be madeas shown by welding five hollow cylindrical steel sections together in the general configuration of a portion of a hexagon, rigidly connects the three

arms

36, 37 and 38 together, while lying outwardly of the three electrodes 26. The reason for leaving the loop structure 40 incom- 4 plete has todo with the tremendous electrical currents that wouldbe induced in a closedloop structure of electrically conductive material by the rapidly changing magnetic field around the electrodes 26 when these are connected to a 3-phase source. Because it is not essential to construct the loop structure 40 from electrically conductive material, the fact thatthe loop structure is incomplete does not form an essential part of this invention. The incomplete section provides space forthe exhaust snorkel.

The same difficulty with induced electric currents would arise if the

arms

36, 37 and 38 were merely continued on to join at a single apex centrally of the three electrodes 26, and this is why such a connection is not utilized in theembodiment shown. Again, by constructing the

arms

36, 37 and 38 from non-conductive material, the problem associated with induced electric current would be obviated.

Each of the

arms

36 and 37 has at its outer extremity a foot member 42 which is slideably received within an upwardly open C-shaped guide member 44 fixed by welding or other suitable manner to the outer ring 12 of the refractory roof 10. Each foot member 42 is fixed to an upwardly extending rod member 46, which is adapted to be received in a cylindrical bushing member 47 at the end of the

respective arms

36, 37. The bushing'member 47 in the particular embodiment shown has a liner 48 which may be of teflon or other lowfriction material. The liner 48 includes upper and lower annular portions and a central cylindrical portion lying between the rod member 46 and the insulating bushing member 47. The liner 48 is also electrically insulative.

Each rod member 46 has a diametral slot adapted to receive a tightening wedge member 50 as shown.

The other arm 38, in the particular embodiment shown, is bifurcated into two branches 52 to clear the roof-lifting eaves (not shown) each terminating in a bushing member 54. The bushing members 54 are also adapted to be received over respective rod members 56 and to be locked thereto by means of wedge members 57. The rod members 56 extend upwardly from disclike bases 58 secured, as by welding, to the outer ring The arm 37, as illustrated in FIG. 1, has an inner, horizontally projecting portion 60 which terminates in a cleavis structure 62 which includes two vertical pivot pins 63. Extending from and pivoted to each pin 63 is a link member 64 (both clearly shown in FIG. 3), and each link member 64 supports at its free end an upwardly extending slide pin 66 (only one visible in FIG. 1). v

The arm 36 also includes a horizontally extending portion 68 which terminates in a cleavis structure 70 which also supports two pivot pins 72. Extending from and pivoted to each pivot pin 72 is a link member 73, each of which supports a further pivot pin 74 at its free end.

tending from the further pivot pin 86 is another link member 88 which has at its free end an upwardly extending slide pin 90. Pivoted to and extending from the pivot pin 83 is a link member 92 which supports at its free end an upwardly extending slide pin 94.

Referring now to FIGS. 1, 2 and 3, it will be seen that each main ring seal 32 includes an outer cylindrical support wall 96, preferably of steel, surrounding and supporting an inner ring 97 of refractory material. The inner ring has a central cylindrical opening adapted snugly to receive the electrode 26. The outer support wall 96 of each main ring seal 32 has two antipodally extending appendages in the form of flanges 98, each of which has an opening adapted slidingly to receive one of the upwardly extending slide pins. Thus, the nearer main ring seal 32 in FIG. 1 is pivotally connected to a slide pin 78 and a slide pin 94. The main ring seal 32 directly in back of the one just described in FIG. 1 is pivotally connected to a slide pin 66 and a slide pin 90. The third main ring seal 32 is pivotally connected to a slide pin 78 and a slide pin 66. I It will now be particularly evident; in FIG. 3'that each main ring seal 32 has one of its flanges pivoted to a stationary pin through a single link member, and has the other of its flanges pivoted to a stationary pin through a double linkage. This single and double linkage arrangement for each main ring seal provides a limited amount of lateral mobility for the main ringseal, which permits it to move to some extent with :respect to the refractory roof l0, and thereby accommodate some shifting of its respective electrode 26.

Turning now to FIG. 2, it will be seen that the particular vertical position of the slide pin 78 is arranged in such a way that the main ring seal 32 is ordinarily maintained spaced above the refractory dome 22. Because the refractory dome 22 tends to move up and down with thermal expansion and contraction, and because it is very important to close off the gap 99 between the opening 24 and the electrode 26, there is further provided an annular roof seal 100 which encircles the lower part 102 of the support wall 96, the lower part 102 being of cylindrical configuration. The annular roof seal 100 is sized to permit a snug but'slideable telescoping movement with respect to the lower part 102 of the support wall 96, and is intended normally to rest against the refractory dome 22 as shown in FIG. 2. The weight of the annularroof seal 100 is much less than that of the main ring seal 32, and does not consitute an excessive loading for the refractory dome 22.

In the preferred embodiment shown in FIG. 2, the annular roof seal 100 has a conical, upwardly convergent inner surface 104, and an upper inner edge 106 which is specifically sized snugly to receive the part 102. As seen in FIG. 2, the annular roof seal 100 has a lower wall 107, an upper wall 108, and a plurality of peripherally spaced partitions Each annular roof seal 100 also includes two antipodally spaced shafts 112 secured to the upper wall 108 and adapted to pass through suitably located apertures in the flanges 98. For example, the shafts 112 may be simple bolt shafts with their head ends welded or otherwise secured to the upper wall 108. Each shaft 112 extends upwardly through its respective flange 98 and has above the flange an expanded portion incapable of passing through its respective aperture, for example a double nut locking arrangement as seen in FIG. 2. With this arrangement, the telescoping movement of the an- 110 to give it added strength.

nular roof seal with respect to the main seal ring 32 is limited in the downward direction because of the double nuts 114 and is limited in the upward direction by mechanical interference between the annular roof seal 100 and the support wall 96 just beneath the flange 98. As seen in FIG. 2, the support wall 96 has a step 116 which would mechanically interfere with the annular roof seal 100. The step 116 is not essential to the invention, and in its absence the annular roof seal 100 would have mechanical interference with the flanges 98. V

A pennannular rod element 118 is adapted to fit snugly and resiliently about the lower part 102 of the support wall 96, but such that it can fall downwardly with respect to the support wall 96 under gravity. It is sized in such a way that it tightly embraces the part 102. Because it is permitted to fall under gravity, the rod element 118 will settle against the annular roof seal 100 just above the upper edge 106, whereby any small gap remaining between the annular roof seal 100 and the lower part 102 of the support wall 96 will be blocked.

Further as seen in FIG. 2, the pivot pin 72 is prevented from electrical contact with the link member 73 by means of two low-friction, insulative half-bushings 120 which fit between the pivot pin 72 and the knuckle 122 which forms part of the link member 73.

All of the pivot pins of the three cleavis structures fixed to the three

arms

36, 37 and 38 are electrically insulated from their respective link members in the same manner.

Attention is now directed to FIGS. 4 and 5 which show an optional additional sealing means for closing the gap at the top of each of the main ring seals between the main ring seal and its respective electrode 26. In the embodiment shown in FIGS. 4 and 5, the support wall 96 surrounds the plurality of gravity seals 124, each of which is swingable about a horizontal pivot pin 126 which in turn is anchored to the main ring seal by means of upstanding tabs 128. Each gravity seal 124 supports an arcuate sealing edge 130, and all of the arcuate sealing edges together are sized to snugly and substantially completely surround the outer periphery of the electrode 26. As can be seen in FIG. 5, each gravity seal 124 has a part-cylindrical portion 132 which, when the arcuate sealing edge 130 rests against the electrode 26, is in disequilibrium, and tends to seek equilibrium by pressing the arcuate sealing edge 130 against the electrode 26.

While the embodiment shown in FIGS. 1 and 3 and described above has each main ring seal 32 connected by means of a single link at one side and a double link at the other side, it will be appreciated that the same lateral mobility can be obtained by providing two double links for each of the main ring seals. A single and a double link for each main ring seal is the minimum amount of linkage necessary to provide lateral mobiltry.

It will further be understood that, while the main ring seals 32 described above consist of refractory material, the advantages of the structure of this invention will be equally apparent if the main ring seals were to be water-filled glands of the type in conventional use. Because the peripherally based support structure for the main ring seals is completely independent of the refractory dome 22, and is not imperilled by collapse of that dome, there is no risk that such water-filled glands or sealing rings would fall into the high-temperature melt.

What I claim is:

1'. For use with an electric arc furnace having a refractory roof, and at least one electrode supported independently of said roof and passing through a roof opening larger than the electrode, a seal assembly comprising:

a main ring seal closely encircling said electrode,

support means for supporting the main ring seal above the refractory roof from the periphery thereof, the support means including pivotable link members for permitting lateral mobility of the main ring seal with respect to the refractory roof,

and adjustable means for sealing the gap between the main ring seal and the refractory roof.

2. The invention claimed in claim 1, in which said support means includes at least three arms extending inwardly above the refractory roof from the periphery thereof and structure rigidly connecting said arms together, said main ring seal having two pivot attachment appendages extending substantially antipodally theredate thermal contraction and expansion.

6. The combination claimed in claim 5, in which said other two arms include at their outer ends a foot member adapted to slide in an upwardly open C-shaped guide member fixed to the roof periphery which restrains vertical and lateral movement of the foot member but permits radial movement thereof with respect to the furnace.

7. The combination claimed in claim 4, in which, for each main ring seal, said single link is pivoted to its respective arm through a non-conductive mounting arrangement, and in which each appendage of each main ring seal has an aperture adapted to register slidingly over an upwardly projecting pin supported by the respective link member, whereby each main seal ring may be raised upwardly with respectto its respective from, said link members including a single link pivotally connected between one appendage and one of said arms, and a double link pivotally connected between the other appendage and another of said arms.

3. In combination: an electric arc furnace having a refractory roof and three electrodes supported in triangular relationship independently of said roof, each electrode passing through a roof opening larger than itself, and a seal assembly which includes:

a. three main ring seals closely encircling the three electrodes, I

b. support means for supporting the main-ring seals from the periphery of the refractory roof, the support means including pivotable link members adapted to permit limited lateral adjustability of the three main ring seals with respect to the roof.

4. The combination claimed in claim 3, in which the support means includes three arms extending inwardly above the refractory roof from the periphery thereof, each arm being generally positioned between a different pair of electrodes, a broken loop structure rigidly connecting said arms together and lying outwardly of the electrodes, each main ring seal having two antipodal, pivot attachment appendages, said link members including, for each main ring seal: a single link pivotally connected between one appendage and the arm on one side of the main ring seal, and a double link pivotally connected between the other appendage and the arm on the other side of the main ring seal, all link members being capable of pivotal movement in the horizontal plane only.

5. The combination claimed in claim 4, in which one of said arms is adapted to be fixed to said roof periphery and the other two arms are adapted to be slideably supported by said roof periphery, thereby to accommolink members at least to a limited extent without disengagement therefrom. I

8. For use with an electric arc furnace having a refractory roof, and at least one electrode supported independently of said roof and passing through a roof opening larger than the electrode, a seal assembly comprising:

a main ring seal closely encircling said electrode and having at least part of its outer surface of cylindrical configuration;

support means for supporting the main ring seal above and independently of the central portion of the refractory roof for at least limited lateral mobility with respect to the refractory roof,

and an annular roof seal encircling said part for snug but slideable telescoping movement with respect thereto, the annular roof seal resting on the refractory roof.

9. The invention claimed in claim 8, in which the annular roof seal has a conical, upwardly convergent inner surface, and a circular upper inner edge snugly embracing said part of the main ring seal.

10. The invention claimed in claim 8, in which the annular roof seal has a plurality of spaced-apart shafts extending slidingly through apertures defined by the main seal ring, the shafts being parallel with the axis of said part and having expanded portions remote from the annular roof seal preventing disengagement of the shafts from the apertures, whereby the telescoping movement of the annular roof seal with respect to the main seal ring is limited in both directions.

11. The invention claimed in claim 8, which further comprises a plurality of gravity seal elements each having an arcuate sealing edge adapted to move toward the outer surface of the electrode under gravity and away from said outer surface against gravity, the gravity seal elements being mounted above the main ring seal and being adapted to cooperate to define a closed sealing loop against said outersurface, thereby to limit escape of gases from the furnace between the main sealing ring and the electrode.

Claims

1. For use with an electric arc furnace having a refractory roof, and at least one electrode supported independently of said roof and passing through a roof opening larger than the electrode, a seal assembly comprising: a main ring seal closely encircling said electrode, support means for supporting the main ring seal above the refractory roof from the periphery thereof, the support means including pivotable link members for permitting lateral mobility of the main ring seal with respect to the refractory roof, and adjustable means for sealing the gap between the main ring seal and the refractory roof.

2. The invention claimed in claim 1, in which said support means includes at least three arms extending inwardly above the refractory roof from the periphery thereof and structure rigidly connecting said arms together, said main ring seal having two pivot attachment appendages extending substantially antipodally therefrom, said link members including a single link pivotally connected between one appendage and one of said arms, and a double link pivotally connected between the other appendage and another of said arms.

3. In combination: an electric arc furnace having a refractory roof and three electrodes supported in triangular relationship independently of said roof, each electrode passing through a roof opening larger than itself, and a seal assembly which includes: a. three main ring seals closely encircling the three electrodes, b. support means for supporting the main ring seals from the periphery of the refractory roof, the support means including pivotable link members adapted to permit limited lateral adjustability of the three main ring seals with respect to the roof.

5. The combination claimed in claim 4, in which one of said arms is adapted to be fixed to said roof periphery and the other two arms are adapted to be slideably supported by said roof periphery, thereby to accommodate thermal contraction and expansion.

7. The combination claimed in claim 4, in which, for each main ring seal, said single link is pivoted to its respective arm through a non-conductive mounting arrangement, and in which each appendage of each main ring seal has an aperture adapted to register slidingly over an upwardly projecting pin supported by the respective link member, whereby each main seal ring may be raised upwardly with respect to its respective link members at least to a limited extent without disengagement therefrom.

8. For use with an electric arc furnace having a refractory roof, and at least one electrode supported independently of said roof and passing through a roof opening larger than the electrode, a seal assembly comprising: a main ring seal closely encircling said electrode and having at least part of its outer surface of cylindrical configuration; support means for supporting the main ring seal above and independently of the central portion of the refractory roof for at least limited lateral mobility with respect to the refractory roof, and an annular roof seal encircling said part for snug but slideable telescoping movement with respect thereto, the annular roof seal resting on the refractory roof.

11. The invention claimed in claim 8, which further comprises a plurality of gravity seal elements each having an arcuate sealing edge adapted to move toward the outer surface of the electrode under gravity and away from said outer surface against gravity, the gravity seal elements being mounted above the main ring seal and being adapted to cooperate to define a closed sealing loop against said outer surface, thereby to limit escape of gases from the furnace between the main sealing ring and the electrode.