The present invention relates to a structure for cooling the electrode connection in electric arc furnaces; more particularly the invention relates to the cooling of such a connection, whereby the electrodes are respectively comprised of a hollow metallic upper portion, and at least one lower portion is made, e.g., of graphite, and wherein suitable mechanical tension connection of these portions is provided while the electrical connection runs through the front faces of the electrode sections. Moreover, a connector nipple is connected to the lower electrode section, and a connecting element on the upper electrode section receives the nipple.
German printed patent application No. 2,739,483 corresponding to U.S. Pat. No. 4,121,042 generally discloses a compound or combined electrode with an upper section being cooled and made of steel, and a graphite lower section of the type outlined above. The nipple is constructed as a twin cone, and is threaded into the two sections. The nipple is also made of graphite. The main aspect here is that the coolant flow in the upper electrode section is such that the nipple is likewise adequately cooled. Cooling is quite important because particularly in the range of the neck of the nippple connector certain fractures and ruptures can occur which may interfere with the operation of the furnace. As to that particular aspect, the above-identified technology is quite adequate.
However, in practice it was found that the compound or composite electrode construction poses certain difficulties. The mutual disposition of the two electrodes is determined to a higher degree (redundancy) than necessary, i.e., through the cones and the contact front faces of the two electrode parts to be interconnected. If the cone in the upper part is tightened to the nipple, it is quite possible that the contact surfaces, i.e., the axial front ends of the two electrode section are no longer in contact. This means that the electric current which normally flows and is supposed to flow directly across the interface between the two axial front ends of the electrodes will have to flow through the nipple. Moreover, arcing may occur in the gap between the front faces of the electrodes.
In view of the fact that the mutual orientation and disposition of the two electrode parts are in fact subject to redundancy, this kind of construction will not be useable whenever the two electrode sections are in effect interconnected through tension, because this inter-relationship will almost with certainty produce the undesirable gap between the front faces of the electrode sections as outlined above. Moreover, it has to be observed that thermal extensions may occur between the intensively cooled nipple and the adjoining rather warm electrode section made of graphite. As a consequence, the shaft or shank of the nipple part may break, particularly in the thread bottom.
German printed patent application No. 3,144,926 corresponding to U.S. Pat. No. 4,495,624 discloses a graphite electrode which can be form-fittingly connected to the electrode holder of an electrofurnace. This electrode connection structure, however, is in practice always accompanied with very high temperature. This means that the tension rod head can be damaged severely. Also, the connecting piece and, particularly, the tie rod may be severely damaged. The contact-free arrangement of the electrode connection in the interior of the twin wall current conductor tube on the other hand is insufficient for adequate cooling of the connecting area and, particularly, the nipple.