US2093390A

US2093390A - Means and method of making electrode joints

Info

Publication number: US2093390A
Application number: US758245A
Authority: US
Inventors: Lewis B Wyckoff
Original assignee: Union Carbide and Carbon Corp
Current assignee: Union Carbide Corp
Priority date: 1934-12-19
Filing date: 1934-12-19
Publication date: 1937-09-14
Anticipated expiration: 1954-09-14

Description

[CROSS REFERENCE EXAMIQER I L. B. WYCKOF F MEANS AND METHOD OF MAKING ELECTRODE Filed Dec. 19, 1934 Sept. 14, 1937.

JOINTS INVEN TOR.

LEW/S B. WYCKOFF ATTORNEY.

Patented Sept. 14, 1937 UNITED STATES MEANS AND METHOD OF MAKING ELEC- TRODE JOINTS Application December 19, 1934, Serial No. 758,245

11 Claims. (Cw) I 2,? '7 a f; 7

The invention pertains to joints in electrically conductive articles composed at least in part of carbon or a carbonaceous material, and more particularly to a means and method of making joints in carbon electrodes such as those used in electric furnaces.

When such electrodes are used in electric furnaces they are gradually consumed, and in order to provide continuous operation and also prevent electrode waste, new electrodes are joined to the old ones when they are partially consumed. A common method of joining such electrodes is to provide each end of each electrode with a threaded recess to receive a correspondingly threaded carbonaceous connecting pin, but such joints are not satisfactory because the electrical resistance is higher than that of an equal length of solid electrode. This high resistance is due to the fact that the contact area of the joint may be less than the cross sectional area of the electrode, and also to the fact that the contact area is not continuous but is made up of a large number of point contacts.

Many expedients have been proposed to lower the resistance of such joints, such as filling the spaces between the contact surfaces with a Joint compound composed of acarbonaceous material such as carbon or graphite, or both, and a liquid binder such as glucose, molasses, or dextrln. Such compounds have no cementing qualities but are simply fillers, which are only loosely held in the joint after it has been heated. These filled joints are not entirely satisfactory for the reason that when a joint is heated, cracks develop around the recessed. ends of the electrodes and due to the lack of cementing quality of the compound, portions drop off. Also, failures and breakage of the joints areoften occasioned by the electrical resistance of the contact in the joint which causes local overheating and partial oxidation of the electrode or connecting pin. Furthermore, there is an energy loss as well due tothe resistivity of the electrode joints which detracts from the overall emciency of the electric furnace. 5

Therefore, one object of the invention is to provide electrically conductive carbonaceous articles such as carbon electrodes with joints .ductive crystals penetrating and interlocking with the contact faces so that portions of the F l J I abutting ends of two electrodes or e1ectrode seccontact faces of the electrodes and also between bide frn i i n g materia l may be employed sucH aTs 45 silica, silicon or any other suitable siliceous mate- PATENT OFFICE electrodes around the joints will not become separated even though they become cracked into many pieces.

. Another object is to provide a process of making such joints wherein an electrically conductive 5 carbide is formed in the joints by which the mechanical strength is materially increased and the electrical resistivity is materially reduced over joints employed heretofore.

Another object is to provide a joint compound for making such joints composed of materials capable of combining into an electrically conductive carbide under the influence of suitable heat, and also having suflicient resistance to the passage of the normal amount of current employed with such electrodes to cause the generation of suflicient heat to form this carbide in these joints.

These and other objects and novel features of the invention will be more fully explained in the following specification and the accompanying illustration which is a longitudinal sectional view of an electrode Joint of the type described.

The invention, which may be employed in electrically conductive joints in carbonaceous materials of various kinds, may be embodied in joints between the abutting ends of carbon electrodes A and B of the type used in continuously operated electric furnaces. Such electrodes may be of any suitable form such as cylindrical, and each end may be provided with a threaded recess III in which a correspondingly threaded connecting pin 0 fits in the aligned recesses of the tions. The process of forming my improved joint between such electrodes consists in providing a filling of an electrically conductive carbide forming material in the spaces between the abutting the electrodes and the connecting pin, and then 40 heating the joint to a temperature suiilcient to form an electrically conductive carbide in the joint.

In making the joint any suitable silicon carrial, ams carbide forming material may be applied in any suitable way such as by mixing the material with a suitable binder or adhesive such as La asse se ii ami tseta and t applyingth mixt to the contact faces of the electrodes and connecting pin before they are assembled. The siliceous material may be of any '7 suitable fineness but a material is preferred that y will pass through a screen of 30 mesh per inch or 5;

a II

ing material 2 aoeasoo finer. and preferably, a su mciently fiuid binder is employed to form a thin slurry or compound having a consistency suitable for the size and type of joint to which it is applied. In general, the application of a layer of such compound from 55 inch to V inch in thickness is satisfactory, and a somewhat thinner layer may be applied to the threaded surfaces than to the plane surfaces on the ends of the electrode and connecting pin.

After the compound has been applied to the contact faces of the Joint the electrodes may be assembled while the compound is still in a semifiuid condition so that. even distribution over the abutting contact faces will be effected when the electrode assembly is screwed together or otherwise assembled. A preferred form of the new joint compound that gives excellent results may be made by combining a well known commercial joint compound with a substantially equal weight of such as flour of silica, re e silicon or any other suitable Emceous m commercial Joint compound may be composed of graphite with some carbonaceous binder such as mglucose, molasses, or tar. Other binders may be meme-n am silicate. Any commercial Joint compoun n ng any binder that is satisfactory in this type of Joint when the carbide forming material is not employed is satisfactory when it is employed, and although any form of silicon bearing material is satisfactory, ordinary commercial comminuted silica, silicon or any other suitable siliceous material is preferred for purpose of economy.

The joint formed and assembled as described may be heated in any suitable way to form the carbide in the Joint, and the degree of heat applied may vary with the type of carbide forming material employed. As silicon carbide fo at a temperature of approximately 1700 C., the joint described above may be heated to this temperature or above and the heat may be applied by a separate furnace, by the furnace in which the electrode is used, or by passing a suitable electric current through the joint.

When the joint is employed in electrodes for continuously operated electric furnaces, the current passing through the electrode during normal operation of the furnace may provide the heat for forming the carbide, and it is one of the features of the invention that the joint compound described produces sufficient resistance in the joint to cause suflicient localized heating to form electrically conductive carbides in the joint by interaction of the siliceous carbide forming materials with the carbon of the electrode or joint compound. After the carbide forming reactions are completed the electrode Joint quickly cools to substantially the temperature of the rest of the electrode and the joint is characterized by its low electrical resistance and high ,mechanicai' strength. The siliceous material introduced into the joints just described performs a double function, in that it provides a high initial resistance in the joint which builds up sufllcient temperature to form silicon carbide, and also supplies the sili- Therefore, the contact faces are not only held against relative parallel movement, but they are also held against separation by the interlocking action of these penetrating crystals. Thus, portions of the recessed end of the electrodes are prevented from falling away even though the ends become cracked into many pieces.

The low electrical conductivity of the joints are due to the large area of contact afforded by the large number of conductive silicon carbide crys-' tals formed in the joint and also by the orientation of the crystals. It is known that silicon carbide crystals have greater conductivity along one axis than along another, and it is .believed that when silicon carbide crystals form under-the conditions described above. by the heat developed from the resistance to an electric current passing through the joint, they are oriented in such a direction as to carry the current across the joint along their most conductive axes. Also, the formation of these crystals in' the joint provides many additional paths for the current to follow over those existing before the crystals formed, as they fill spaces that were originally void. This. is believed to be the reason why the temperature at the Joint drops appreciably after the crystals form even though the current through the Joint is continued, thus indicating that the Joint has a s L'The method of making joints of low elec-"' trical resistivity between continuous type electric furnace carbonaceous electrodes which consists in coating the interface between contiguous electrodes with a material of the group consisting of silica and silicon: and passing an electric current through said material to form a carbide of silicon along said interface.

2. The method of making joints of low electrical resistivity and high mechanical strength for continuous type electric furnace carbonaceous electrodes which comprises thesteps of forming a threaded recess in a face of each of two contiguous electrodes; coating said recesses and said faces with a material of the group consisting of silicon and silica ,mixed with a binder; securing together said electrodes in face-to-face relationship by means of a connecting member threaded into each of said recesses; and passing an electric current through said electrodes, said connecting member, and said material to form a layer consisting of a carbide of silicon between said faces and between thethreads of said recesses and the threads of said connecting member.

3. A method of mahng joints in carbon electrodes comprising the steps of coating thecontact faces of such a Joint with a semi-fluid mixture composed of a carbonaceous material,

and a substantially equal weight of comminuted silicon said carbonaceous material including graphite and abinder; assembling said Joint while said mixture is in a semi-fluid condition; and then heating said mixture by passing suiiicient electric burrent through said joint to form electrically acoasoo face of each of said contiguous electrode members:

conductive silicon carbide in said Joint and thereby reduce the resistance thereof.

4. A continuous type electric furnace electrode comprising at least two carbonaceous electrode members having contiguous surfaces, and a material of the group consisting of silicon and silica, and a binder, disposed between, and covering a substantial portion of said contiguous surfaces.

5. An electric furnace electrode comprisingcoaxially aligned carbonaceous electrode members having opposed end faces, and a layer consisting of a carbide of silicon between and united to said faces and providing a mechanically strong joint of low electrical resistivity between said members.

6. An electric furnace electrode comprising coaxially aligned carbonaceous electrode members having opposed end faces; anda layer consisting of a carbide of silicon between and united to said faces, said layer being formed from a binder mixed with a material of the group consisting of silicon and silica.

'1. An electric furnace electrode comprising coaxially aligned carbonaceous electrode members having opposed end faces and a central threaded recess in each of said faces: a threaded pin fitting in both recesses and cooperating with the threads therein to secure said members together; and a mechanically strong joint of low electrical resistivity between said faces and between such threads, said joint comprising a layer including a carbide of silicon between and united to said faces and said threads.

8. A continuous type electric furnace electrode comprising at least two contiguous carbonaceous electrode members: a threaded recess formed in a means threaded into each of said recesses and connecting said contiguous electrodes in faceto-face relationship: and a material of the group consisting of silicon and silica, mixed with a binder. disposed between and in'contact with said means, said threaded recesses and the opposed faces of said contiguous electrode members.

9. An electric furnace electrode comprising coaxially aligned carbonaceous electrode members having opposed end faces and a central threaded recess in each of said facaz: a layer, comprising a binder and a material of the group consisting of silicon and silica, between and contacting said faces and also coating the threads in such recesses; and a threaded pin fitting in both recesses and cooperating with the threads therein to secure said members together and to compress said layer between said faces and the cooperating threads, the construction being such that said layer is converted to a carbide of silicon upon passing an appropriate electric current therethrough.

10. A joint compound for continuous type electric furnace carbonaceous electrodes comprising a binder and a material of the group consisting of silicon and silica.

11. A compound-for use in forming joints between the abutting faces of carbon electrodes comprising a mixture of a carbonaceous material including graphite and a binder, and comminuted silicon, in which the weight of the silicon is substantially equal to the weight of the other ingredients.

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