DE2657952B2 - Electrode string for electric arc furnace - Google Patents

Description

It has now been proposed, within an electrode connection with a first and a second electrode portion each connected to the End faces is provided with an internally threaded box, and with an externally threaded box provided, the end faces of the electrode sections connecting nipple stress concentrations within the entire connection as a result avoid or reduce the depth of the box thread and / or the nipple thread in the The area of the thread run-outs of the box thread and / or nipple thread is made smaller than that Thread depth in the range of half the thread length (DE-OS 25 55 688). However, this measure is sufficient do not provide a complete solution to the problem identified.

The object of the invention is therefore to design the electrode connection so that another Reduction of the tensions in the transition area from the thread to the box bottom is achieved so that there destruction of the electrode string and thus costly operational interruptions and electrode losses be avoided.

This object is achieved in that the undercut in the thread of the Box is formed at least one thread with a reduced cross-section, whose ζ ir The thread flank pointing towards the box opening is cut at an angle in the undercut, which is equal to or greater than a right angle.

This ensures that the box thread nitvi more due to the burden of the corresponding The nipple thread can break out, as the obtuse or, in the extreme case, 90 ° angle λ creates a has a much wider residual cross-section.

If the lowering of the cross-section through a large angle <x covers several turns of the box thread, it is also achieved that here only the tip of the nipple thread transmits loading forces to the box thread. This enables elastic yielding of the nipple thread. Due to both advantages, box cracks are no longer to be expected at this point with the usual overloads.

According to an advantageous embodiment of the proposed invention, the undercut can be rotationally symmetrical to the longitudinal axis of the electrode and parallel to the bottom of the box or helically with the The pitch of the box thread run by at least 360 °. Furthermore, it has become dependent on the The elasticity and strength of different electrode and nipple materials have proven to be advantageous Undercut - seen in cross section - in the area of the lowered thread turn with a straight, curved or angled course. Furthermore, the box can also be like this be designed that the undercut - seen in cross section - adjoining the area of the lowered thread has a curved course to which another straight one Connect the area and then the transition curve to the bottom of the box. As radii of curvature Either a single radii or several merging radii of different sizes come in Question.

The invention is explained in more detail below by means of the exemplary embodiments shown in the drawing explained. In the drawing shows

F i g. 1 shows the load and tension

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state of the box in the bottom of the box,

Fig. 2 is a sectional view of a box thread with conventional undercut,

F i g. 2a shows a section of the thread run-out of the conventional undercut from FIG a corresponding part of the acting nipple,

F i g. 3 a sectional view of the box thread with the undercut according to the invention with an annular and parallel to the bottom of the box,

3a shows a section of the undercut of F i g. 3, with part of the acting nipple,

F i g. 4 shows a sectional view of the box thread with the undercut according to the invention with a helical Course, according to the thread pitch.

The in F i g. 1 is valid for all electrode connections shown in the drawing, in which a nipple 2 is screwed into an electrode box 1. It is important that the quality to keep the sketched stress levels as low as possible.

In a known electrode connection, FIG. 2 shows how the decreasing residual cross-section 5 of the thread forms an acute angle α through the conventional undercut 4 in the thread run-out 3 and thus the thread height h ' and the thread width b' are equally shortened. The associated section of the thread run-out 3 in FIG. 2a illustrates how, when the nipple 2 expands, the residual cross-section 5 and the thread 6 of the box thread are loaded by the engaging nipple thread 7 of the nipple thread.

If one takes into account that the material of the electrode is very coarse-grained and brittle, then it can be seen that on the one hand through the nipple passage 7 squeezing into the thread gap 8 there is a risk of breaking out of the remaining cross-section 5 of the box 1, wherein, as shown at 9, a crack is formed, the one has a strong notch effect and can therefore result in the box wall tearing off. On the other hand, can the nipple passage 7 over the entire width of its flank 10 and with the full, available to him standing force also on the next thread 6 of the box 1, so that from here to Undercut 4 a sharp change in load occurs.

The novel, in F i g. 3 of the undercut 4 of the thread of the box 1 shown, the cross-sections 5 and 6 of the thread run-out 3 are shortened in such a way that one or more thread flanks 11 pointing to the box opening are cut at an angle of> 90 °, i.e. usually at a blunt one Winkei. The corresponding excerpt in FIG. 3a shows the shape of the cross sections 5 and 6 of the box thread and their loading by the nipple passage 7 even more clearly. The advantage achieved by this construction is that the residual cross-section 5 of the box thread, which is encumbered by the pressing nipple passage 7, can no longer break out, since it retains a much larger thread width b due to the obtuse angle λ, and thus no longer runs the risk of tearing open the box exists at this point.

In addition, since the nipple duct 7 is only closest to one another over part of the width of its flank 10, shortened residual cross-section 6 of the box thread is supported, elastic yielding under load of the nipple passage 7 reached. This means that

at least the last nipple passage 7 in terms of him possible power transmission is not yet maximally stressed, so that there is no such strong change in load to the undercut 4 as this is the case with conventional shaping. s

As a result, the material stresses present in the bottom of the box in the area of the undercut 4 including the area of the shortened thread cross-sections 5 and 6 largely reduced. The in the F i g. 3 and 3 a shown undercut 4 is ring-shaped and ι ο parallel to the box bottom 12 and can be with a produce simple form steel on a lathe.

In the case of the in FIG. 4 is the undercut 4 when milling the box thread getting produced. This creates immediately above! 5 the box bottom 12 an additional helical edge 13, which, however, for the durability of the Box 1 is not disadvantageous, since the higher material stresses on the area of the shortened Thread cross-sections 5 and 6 are limited. F i g. 4 also shows the possibility of the undercut 4 to give a curved course in the area of the shortened thread cross-sections 5 and 1 and the curvature, Execute with continuously changing radii. This curvature can be applied directly to the bottom of the box run in, but also merge into another angled or straight area, to which di Transitional curvature to the box bottom 12 hi connects.

In the drawing figures it is not shown that the undercut in the area of the shortened thread The cross sections also have an angled course and / or have a stepped jump can be without thereby adversely affecting the voltage conditions for the box In addition, it is not shown that the Hänterschp.eä tion - seen in cross section - then to the area of a shortening the thread of the box has a curved course, to which another straight area and then the over Connect the aisle curve to the bottom of the box.

For this purpose 3 sheets of drawings

Claims (10)

1 claims: 1. Electrode strand made of carbon electrodes and connecting nipples for electric arc furnaces, where there is an undercut between the thread of the electrode boxes and the box bottom of the thread is provided up to at least the outer thread diameter, thereby characterized in that through the undercut (4) in the thread of the box (1) at least one thread (6, 5) with a lowered cross-section is formed whose thread flank (11) pointing towards the box opening the undercut is cut at an angle (<x) that is equal to or greater than a right-hand angle Angle is 2. Electrode string according to claim 1, characterized in that the undercut (4) runs rotationally symmetrical to the longitudinal axis of the electrode and parallel to the box bottom (12) (Fig. 3,3a). 3. Electrode string according to claim 1, characterized in that the undercut (4) helically with the pitch of the box thread by at least 360 ° and centric to the The longitudinal axis of the electrode runs (FIG. 4). 4. Electrode string according to one of claims 1 to 3, characterized in that the undercut (4) - seen in cross section - in the area of the lowered thread (6, 5) a has a straight course (Fig. 3, 3a). 5. Electrode string according to one of claims 1 to 3, characterized in that the undercut (4) - seen in cross section - one in the area of the lowered thread (5) has a curved course (FIG. 4). 6. Electrode string according to one of claims 1 to 3, characterized in that the undercut (4) - seen in cross section - one in the area of the lowered thread has angled course. 7. Electrode string according to one of claims 4 to 6, characterized in that the undercut (4) adjoining the area of the lowered thread turn - seen in cross section - has a curved course which merges directly into the box bottom (12). 8. Electrode string according to one of claims 4 to 6, characterized in that the undercut (4) adjoining the area of the lowered thread turn - seen in cross section - has a curved course, to which another straight area and then the transition curve connects to the bottom of the box. 9. Electrode string according to one of claims 5, 7 and 8, characterized in that the undercut (4) has curvatures in different areas, each provided with a single radius. 10. Electrode string according to one of claims 5, 7 and 8, characterized in that the undercut (4) is in different areas Has curvatures, each provided with mutually merging radii of different sizes are. The invention relates to an electrode string formed from carbon electrodes and connecting nipples for electric arc furnaces, where between the thread of the electrode boxes and the Box bottom an undercut of the thread up to at least the outer thread diameter is provided (DE-AS 22 34 411). Carbon electrodes are to be understood here as electrodes that are made of both graphitized and ίο consist of non-graphitized carbon material. In electrode strands of this type, the undercut of the box thread has the purpose of high To avoid material loads in the area between the thread and the bottom of the electrode box. These loads result from mechanical and thermal effects, especially during use in the hot melting furnace and also when the hot electrodes are pulled out of the furnace after the melt has been tapped. Mechanical effects arise on the one hand from the frequency of the electrical current flowing through it, which causes the electrodes to vibrate strongly, and on the other hand from the fact that the electrodes are subject to vertical and lateral loading forces, which are caused by reciprocal shock-like contacts between the electrode strand and not yet melted lumps of metal or scrap will. Thermal effects and the resulting loads arise from different material expansions, especially when the nipple has a higher thermal expansion across the longitudinal axis of the electrode than the electrode box, e.g. B. when rapidly cooling the box outside of the oven.
Due to the expansion forces D between the nipple and the electrode box and due to the vertical forces Kund 'possible transverse forces Q , the following material stresses in particular result in the area of the box bottom, which are shown in FIG. 1 are shown, namely circumferential stress O ₁ * caused by the expansion of the ■ to box, bending stress Ob and shear stress τ, also caused by the widening of the box and the simultaneous non-widening of the rigid box bottom, as well as tensile stress σ »caused by those nipple forces that act on the inclined thread flanks in the direction of the box opening. With these tensions, additional high notch tensions σ * arise in the transition area to the box bottom and in particular in the adjacent first thread turns of the box that are loaded by the nipple. For this reason, there is a risk of the box wall tearing open, as a result of which the electrode strand attached by the screw connection can fall off. There are known thread undercuts according to DIN 76, which compared to a simple thread run-out cause a noticeable reduction in the notch stresses in the bottom of the box in that the Undercut acts like a so-called relief notch on the sharp thread notches one that the material of the electrode is very coarse-grained and brittle, then this is Undercut has not yet achieved a sufficient solution to the problem because of the existing stresses due to the thread cross-section, which tapers in height and width in the thread run-out, no matter how large may be that they break out of the thread and thus to tear and subsequent breakage of the Lead threaded box.