US3686421A

US3686421A - Unitized electride holder and arm for electric arc furnace electrodes or the like

Info

Publication number: US3686421A
Application number: US176138A
Authority: US
Inventors: Edgar Wunsche; Alfred H Turner; Lewis H Durdin
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-30
Filing date: 1971-08-30
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: CA957413A; DE2242154A1

Abstract

The disclosed structure comprises a combined electrode holder and supporting arm for holding an electric furnace electrode or the like. The holder includes a clamping device mounted on the outer end of a tubular supporting arm which is preferably made of nonmagnetic stainless steel or some other high strength nonmagnetic material. The clamping device includes a contact member or shoe and means for producing clamping pressure between the contact member and the electrode. The electrical current is supplied to the contact member by a bus tube extending longitudinally within the tubular supporting arm, preferably along the axis thereof. The contact member and the bus tube are made of copper or some other material having high electrical conductivity. Within the tubular supporting arm the bus tube is surrounded by a shielding tube made of copper or some other material having high electrical conductivity. Generally, the shielding tube is electrically insulated from the bus tube and the supporting arm, although an electrical connection between one end of the shielding tube and the corresponding end of the supporting arm is permissible. The shielding tube acts as a magnetic shield around the bus tube and thus prevents the supporting arm from being heated by eddy currents induced in the supporting arm by the magnetic field around the bus tube. The shielding tube confines the magnetic field of the bus tube to the space between the bus tube and the shielding tube.

Description

United States Patent Wunsche et al.

[451 Aug. 22, 1972 [21] Appl. No.: 176,138

[52] US. Cl. ..13/15 [51] Int. Cl ..H05b 7/10, F27d 11/10 [58] Field of Search ..'.l3/l4,15,16

[56] References Cited I UNITED STATES PATENTS 1,856,330 5/1932 Greene 13/16 UX 3,072,732 l/1963 Maloney ..l3/l5 X 3,602,624

Primary Examiner-Roy N. Envall, Jr. Attorney-Burmeister, Palmatier 8L Hamby [57] ABSTRACT The disclosed structure comprises a combined elec- 8/1971 Turner ..l3/l5 trode holder and supporting arm for holding an electric furnace electrode or the like. The holder includes a-clamping device mounted on the outer end of a tubular supporting arm which is preferably made of nonmagnetic stainless steel or some other high strength nonmagnetic material. The clamping device includes a contact member or shoe and means for producing clamping pressure between the contact member and the electrode. The electrical current is supplied to the contact member by a bus tube extending longitudinally within the tubular supporting arm, preferably along the axis thereof. The contact member and the bus tube are made of copper or some other material having high electrical conductivity. Within the tubular supporting arm the bus tube is surrounded by a shielding tube made of copper or some other material having high electrical conductivity. Generally, the shielding tube is electrically insulated from the bus tube and the supporting arm, although an electrical connection between one end of the shielding tube and. the corresponding end of the supporting arm is permissible. The shielding tube acts as a magnetic shield around the bus tube and thus prevents the supporting arm from being heated by eddy currents induced in the supporting arm by the magnetic field around the bus tube. The shielding tube confines the magnetic field of the bus tube to the space between the bus tube and the shielding tube.

19 Claims, 5 Drawing Figures UNITIZED ELECTRIDE HOLDER AND ARM F ELECTRIC ARC FURNACE ELECTRODES OR THE LIKE This invention relates to electrode holders for electric arc furnace electrodes or the like. The electrode holder is preferably combined or unitized with a supporting arm.

One object is to provide a new and improved electrode holder having a contact member or shoe which is supplied with an electrical current by a bus member or tube which extends longitudinally within a tubular supporting arm. In the absence of the present invention, it has been found that a large amount of heat is generated in the tubular supporting arm due to eddy currents induced by the magnetic field around the bus tube.

In accordance with the present invention, such heating of the supporting arm is prevented by surrounding the bus tube with a shielding tube made of a material having a high electrical conductivity. The bus tube is electrically insulated from the shielding tube, although a connection between one end of the bus tube and one end of the shielding tube would be permissible under appropriate conditions. The shielding tube is also preferably insulated from the supporting arm, although a connection between one end of the shielding tube and the corresponding end of the supporting arm is permissible, if the shielding tube is insulated from the bus tube. The shielding tube confines the magnetic field around the bus tube to the space between the bus tube and the shielding tube. Thus, the shielding tube eliminates any mutual inductance or coupling between the bus tube and the supporting arm. The shielding tube also eliminates mutual inductance or coupling between the bus tubes of adjacent electrode holders.

In the usual electric furnace, there are several electrodes supported by a corresponding number of electrode holders which are effective to connect the electrodes to the various phases of a multiphase electrical system. The shielding tube minimizes the mutual inductance between the various phases. Such mutual inductance can be troublesome in that it can cause unbalanced conditions with regard to the currents supplied to the electrodes by the various phases. The resulting inequality in the heating produced by the various phases is minimized by the present invention.

The supporting arm is preferably made of nonmagnetic stainless steel or some other high strength nonmagnetic material. The use of a nonmagnetic material obviates the heating that can be produced in a magnetic material by hysteresis effects due to magnetic fields around the electrodes.

Further objects, advantages and features of the present invention will appear from the following description, taken with the accompanying drawings, in which:

FIG. 1 is a longitudinal section taken through a unitized electrode holder and arm, to be described as an illustrative embodiment of the present invention.

FIG. 2 is an outer end view taken as indicated by the line 22 in FIG. 1.

FIG. 3 is a vertical section taken through the arm, generally along the line 33 in FIG. 1.

FIG. 4 is a horizontal longitudinal section taken through the electrode holder and arm.

FIG. 5 is a vertical section taken generally along the line 5--S in FIG. 4. It will be seen that the drawings illustrate a unitized electrode holder and arm 10 for holding a cylindrical electrode 12, which may be of the type employed in an electric arc furnace or the like. The unit 10 comprises a clamping device 14 mounted on the outer end of a supporting arm 16.

The clamping device 14 is generally annular in shape and extends around the electrode 12. The clamping device includes a contact member or shoe 17 for supplying an electrical current to the electrode 12. The contact shoe 17 is made of copper or some other material having high electrical conductivity. It will be seen from FIG. 4 that the contact shoe 17 has a cylindrically curved surface 18 for engaging the electrode 12. Coolant passages 20 are preferably formed in the shoe 17 to provide for the circulation of cooling water or some other fluid coolant. The coolant passages 20 may be drilled or otherwise formed. However, it is particularly advantageous to form the coolant passages in the manner disclosed and claimed in the Turner US. Pat. No. 2,997,51 l, issued Aug. 22, 1961.

The clamping device 14 includes means for producing clamping pressure between the electrode l2 and the contact shoe 17. As shown, the clamping pressure is developed by a movable clamping member or shoe 22 mounted on a clamping band 24 in opposition to the contact shoe 17. However, the contact shoe 17 could also be movable to develop the clamping pressure.

In this case, the force to actuate the clamping shoe 22 is produced by means 26 operable by fluid pressure, such means being illustrated as comprising a piston 28 movable in a cylinder 30 and sealed by a bellows 32. Hydraulic fluid or some other fluid under pressure is supplied to the cylinder 30 by a pipe 34 connected to a passage 36 which leads into the cylinder. The illustrated fluid pressure operated device is arranged to apply the clamping pressure, but the arrangement may also be such that the clamping pressure is applied by a spring and is released by the fluid pressure operated device.

The clamping band 24 is made double walled to provide passages 38 therein for the circulation of water or some other fluid coolant. Coolant passages 40 may also be provided in the clamping shoe 22. As indicated in FIGS. 1 and 2, flexible conduits 42 may be employed to circulate the fluid coolant to and from the clamping shoe 22. Such flexible conduits are preferably made of metal to withstand the heat involved.

The illustrated supporting arm 16 is generally tubular and is preferably made of nonmagnetic stainless steel or some other highstrength nonmagnetic material. The use of nonmagnetic material obviates hysteresis losses in the supporting arm. Preferably, the supporting arm is double walled to provide passages 44 for the circulation of a fluid coolant. As shown to best advantage in FIG. 3, the illustrated supporting arm 16 comprises a rectangular outer wall or tube 46 and a cylindrical inner wall or tube 48.

The clamping band 24 is welded or otherwise secured to the outer end of the supporting arm 16, as will be evident from FIG. 4. The contact shoe 17 is also suitably mounted on the outer end of the supporting arm 16. As shown, a mounting plate or member 50 is mounted on the arm 16 to back up the contact shoe 17.

Means are preferably provided to insulate the contact shoe 17 from the supporting arm 16 and the clamping band 24. As shown in FIGS. 1 and 4, thin members 52 of electrically insulating material are provided for this purpose.

Electrical current to energize the contact shoe 17 is supplied to the shoe by a bus tube or member 54, extending within the hollow tubular supporting arm 16. This location of the bus tube provides a highly compact construction. It will be seen that the bus tube 54 extends longitudinally within the supporting arm 16 and has a portion 56 which projects beyond the inner end of the supporting arm. A connecting member 58 is secured to the projecting portion 56 and is adapted to be connected to one or more flexible cables leading to a source of electrical current. The bus tube 54 and the connecting member 58 are made of copper or some other material having a high electrical conductivity.

The bus member 54 could be solid, but is preferably tubular to provide a passage 60 therein for the circulation of cooling water or some other fluid coolant. The passage 60 is preferably employed to carry the fluid coolant to or from the contact shoe 17. An additional pipe or tube 62 is preferably provided to complete the circuit for the circulation of the fluid coolant to and from the contact shoe 17. As shown, the coolant pipe 62 is coaxially disposed within the bus tube 54. Preferably, the bus tube 54 is axially disposed within the supporting arm 16.

In accordance with the present invention, a shielding tube 64 is provided around the bus tube 54 and within the tubular supporting arm 16. The shielding tube 64 is made of copper or some other material having a high electrical conductivity. Other examples of such highly conductive materials are silver and high conductivity aluminum. The bus tube 54 and the shielding tube 64 are preferably cylindrical and coaxial. The high conductivity shielding tube acts as an effective magnetic shield around the bus tube 54 so that the magnetic field around the bus tube is confined to the space between the bus tube 54 and the shielding tube 64. Thus, the shielding tube 64 eliminates electromagnetic induction or coupling between the bus tube 54 and the tubular supporting arm 16. In the absence of the shielding tube 64, such electromagnetic induction generates eddy currents of a very considerable magnitude in the metal walls of the supporting arm 16. These eddy currents cause heating of the supporting arm so that a great deal of energy is wasted. Moreover, the heating may be so great as to be destructive.

The shielding action of the highly conductive tube 64 is due to the circulating currents which are induced in the shielding tube by the magnetic field around the bus tube 54. Because of the high conductivity of the shielding tube 64, the heat produced by these circulating currents is small and is easily dissipated by the cooling water or other fluid coolant.

The shielding tube 64 is preferably insulated from the bus tube 54, although a connection at one end would be permissible. As shown, the shielding tube 64 is electrically insulated from the bus tube 54 at both ends and at intermediate points. At the end of the shielding tube 64 adjacent the contact shoe 17, the shielding tube is electrically insulated from the contact shoe and the bus tube 54 by a thin insulating-layer or member 66. At the opposite or inner end of the supporting arm 16. the shielding tube 64 is insulated by an annular supporting member or insulator 68 made of a heat resistant insulating material. It will be seen that the shielding tube 64 is fitted into a bore 70 in the insulator 68. Another bore 72 is formed in the insulator 68 to receive a collar 74 moved around the projecting end portion 56 of the bus tube 54. The insulator 68 is bolted or otherwise secured to the supporting arm 16. I

The shielding tube 64 is also preferably insulated from the tubular supporting arm 16, although an electrical connection at one end is permissible. In this case, the projecting end of the shielding tube 64, adjacent the insulator 68, is electrically isolated from the supporting arm 16 by electrical insulating member 76. At the end of the illustrated shielding tube 64 adjacent the contact shoe 17 the shielding tube 64 is connected to the supporting arm 16 by a collar 78 which acts as a spacer between the shielding tube 64 and the inner wall 48 of the tubular supporting arm 16.

The highly conductive shielding tube 64 substantially eliminates any electromagnetic coupling between the bus tube 54 and the supporting arm 16 so that the current in the bus tube does not induce currents in the supporting arm. Thus, the heating that would be caused by such induced currents is eliminated.

Moreover, the shielding tube 64 substantially eliminates any electromagnetic induction between the bus tubes of adjacent supporting arms in the usual type of electric furnace, utilizing several supporting arms to hold the various electrodes of a multiphase electrical system. The elimination of electromagnetic coupling between the bus tubes of the various phases eliminates the troubles that can be caused by such coupling. Thus, such coupling between phases can upset the balance that should exist between the phase currents. When this balance is upset, the heat generated by the electrodes of the various phases is rendered unequal. The shielding tube of the present invention eliminates or greatly reduces such inequalities.

It will be seen that a space 80 is provided between the shielding tube 64 and the inner wall 48 of the supporting arm 16. Cooling water or some other fluid coolant is preferably circulated through the space 80. Cooling water can also be circulated through the space 82 between the bus tube 54 and the shielding tube 64, but this is not usually necessary and may cause losses due to currents induced in the water by the intense magnetic field in this space.

With the shielding tube of the present invention, there is no heating of the supporting arm due to currents induced by the bus tube. Thus, the supporting arm is protected against damage due to excessive heatmg.

The positioning of the bus tube within the supporting arm provides a highly compact construction which makes it possible to group the electrodes of the various phases around a'pitch circle of smaller diameter. The more compact construction reduces the mechanical stresses in the structure and also reduces the cost of maintenance.

We claim:

1. Electrode holder means for an electric furnace electrode or the like,

comprising an annular clamping device adapted to be mounted around the electrode,

said clamping device including a contact member for making an electrical contact with the electrode,

said contact member being made of a material having high electrical conductivity,

said clamping device including means for developing clamping pressure between the electrode and said contact member,

a hollow generally tubular supporting arm mechanically connected to said clamping device to afford support for the electrode and the clamping device,

a bus member electrically connected to said contact member and extending longitudinally within said hollow generally tubular supporting arm to transmit electrical current to said contact member,

said bus member being made of a material having high electrical conductivity,

a shielding tube extending around said bus member and disposed longitudinally within said hollow generally tubular supporting arm,

said shielding tube being made of a non-magnetic material having high electrical conductivity the conductivity of at least comparable to high conductivity aluminum to provide a magnetic shield between said bus member and said supporting arm,

said arm thereby being protected against heating due to eddy currents induced by the current in said bus member,

and insulating means providing electrical insulation between at least one end of said bus member and the corresponding end of said shielding tube while also providing electrical insulation between at least one end of said shielding tube and the corresponding end of said supporting arm.

2. Electrode holder means according to claim 1,

in which said contact member, said bus member and said shielding tube are made of copper.

3. Electrode holder means according to claim 1,

in which said bus member is made of copper.

4. Electrode holder means according to claim 1,

in which shielding tube is made of copper.

5. Electrode holder means according to claim 1,

in which said shielding tube is made of aluminum having high electrical conductivity.

6. Electrode holder means according to claim 1,

in which said supporting arm is made of high strength nonmagnetic material.

7. Electrode holder means according to claim 1,

in which said supporting arm is made of nonmagnetic stainless steel.

8. Electrode holder means according to claim 1,

in which said insulating means includes an insulator mounted on said supporting arm and affording support for one end of said bus member and the corresponding end of said shielding tube.

9. Electrode holder means according to claim 1,

in which said insulating means includes means affording electrical insulation between said contact member and said supporting arm.

10. Electrode holder means according to claim 1,

including means for circulating a fluid coolant through said clamping device, said contact member, said bus member, and said supporting arm.

1 l. Electrode holder means according to claim 1,

in which said clamping device includes means for exerting clamping force against the electrode in opposition to said contact member.

12. Electrode holder means accordi g to claim 1, in which said clamping device "16 udes a clamping member for engaging the electrode in opposition to said contact member,

' and means for developing a clamping force against said clamping member to produce clamping pressure between said clamping member and said electrode and also between said electrode and said contact member.

13. Electrode holder means according to claim 1,

in which said clamping device includes a clamping member movable against said electrode in opposition to said contact member,

and fluid pressure actuated means for developing clamping force against said clamping member to develop clamping pressure between said clamping member and said electrode and also between said electrode and said contact member.

14. Electrode holder means according to claim 1,

in which said bus member extends from said contact member and through the entire length of said supporting arm,

said bus member having means projecting beyond the end of said supporting arm and including means for connecting the bus member to a source of electrical current,

said shielding tube extending around said bus member within said supporting arm.

15. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are coaxial.

l6. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are generally cylindrical and coaxial.

l7. Electrode holder means according to claim 1,

in which said bus member and said shielding tube are coaxial with said supporting arm.

18. Electrode holder means according to claim 1,

in which said bus member is in the form of a tube.

19. Electrode holder means according to claim 1,

in which said bus member is in the form of a generally cylindrical tube coaxial with said shielding tube.

Claims

1. Electrode holder means for an electric furnace electrode or the like, comprising an annular clamping device adapted to be mounted around the electrode, said clamping device including a contact member for making an electrical contact with the electrode, said contact member being made of a material having high electrical conductivity, said clamping device including means for developing clamping pressure between the electrode and said contact member, a hollow generally tubular supporting arm mechanically connected to said clamping device to afford support for the electrode and the clamping device, a bus member electrically connected to said contact member and extending longitudinally within said hollow generally tubular supporting arm to transmit electrical current to said contact member, said bus member bEing made of a material having high electrical conductivity, a shielding tube extending around said bus member and disposed longitudinally within said hollow generally tubular supporting arm, said shielding tube being made of a non-magnetic material having high electrical conductivity the conductivity of at least comparable to high conductivity aluminum to provide a magnetic shield between said bus member and said supporting arm, said arm thereby being protected against heating due to eddy currents induced by the current in said bus member, and insulating means providing electrical insulation between at least one end of said bus member and the corresponding end of said shielding tube while also providing electrical insulation between at least one end of said shielding tube and the corresponding end of said supporting arm.

2. Electrode holder means according to claim 1, in which said contact member, said bus member and said shielding tube are made of copper.

3. Electrode holder means according to claim 1, in which said bus member is made of copper.

4. Electrode holder means according to claim 1, in which shielding tube is made of copper.

5. Electrode holder means according to claim 1, in which said shielding tube is made of aluminum having high electrical conductivity.

6. Electrode holder means according to claim 1, in which said supporting arm is made of high strength nonmagnetic material.

7. Electrode holder means according to claim 1, in which said supporting arm is made of nonmagnetic stainless steel.

8. Electrode holder means according to claim 1, in which said insulating means includes an insulator mounted on said supporting arm and affording support for one end of said bus member and the corresponding end of said shielding tube.

9. Electrode holder means according to claim 1, in which said insulating means includes means affording electrical insulation between said contact member and said supporting arm.

10. Electrode holder means according to claim 1, including means for circulating a fluid coolant through said clamping device, said contact member, said bus member, and said supporting arm.

11. Electrode holder means according to claim 1, in which said clamping device includes means for exerting clamping force against the electrode in opposition to said contact member.

12. Electrode holder means according to claim 1, in which said clamping device includes a clamping member for engaging the electrode in opposition to said contact member, and means for developing a clamping force against said clamping member to produce clamping pressure between said clamping member and said electrode and also between said electrode and said contact member.

13. Electrode holder means according to claim 1, in which said clamping device includes a clamping member movable against said electrode in opposition to said contact member, and fluid pressure actuated means for developing clamping force against said clamping member to develop clamping pressure between said clamping member and said electrode and also between said electrode and said contact member.

14. Electrode holder means according to claim 1, in which said bus member extends from said contact member and through the entire length of said supporting arm, said bus member having means projecting beyond the end of said supporting arm and including means for connecting the bus member to a source of electrical current, said shielding tube extending around said bus member within said supporting arm.

15. Electrode holder means according to claim 1, in which said bus member and said shielding tube are coaxial.

16. Electrode holder means according to claim 1, in which said bus member and said shielding tube are generally cylindrical and coaxial.

17. Electrode holder means according to claim 1, in which said bus member and said shielding tube are coaxial with said supporting arm.

18. Electrode holder means according to claim 1, in which said bus member is in the form of a tube.

19. Electrode holder means according to claim 1, in which said bus member is in the form of a generally cylindrical tube coaxial with said shielding tube.