"PUSHING MACHINE MOVABLE ON RAIL FOR OPERATING INTO THE SLAG HOLE OF STEEL SMELTING ELECTRIC FURNACES"

The present invention relates to a pushing ma¬ chine movable on rail, adapted to operate into the slag hole of electric furnaces for smelting of steel or iron products in general, to be remotely controlled. It is known that the electric furnaces for smelt¬ ing of iron based scraps being directly discharged from the top have a front opening, also called "slag hole" whose threshold or lower step forms the so-called "dam" suitable to keep the molten bath within the furna¬ ce and to be overflown by the slag only, which then is drained at an underlying level through a trap provided on the floor immediately at the outside of the slag hole. The latter also provides the passage for the oxygen lance through which oxygen gas is blown at very high speed directly into the melting zone for refining the melt.

Also some important inconveniences are known, in connection ith the presence of said slag hole and mainly deriving from the top charge of the scrap, which causes the obstruction, at least partial, of the so-called "slag runner" which connects the outer mouth of the hole with the molten bath and must remain unob- structed, in particular to allow the oxygen lance enter¬ ing without obstacles.

On the other hand it is also known that usually it is necessary to await that a cast is over to carry out, before the subsequent one begins, the so-called opera- tion of "slag hole cleaning", in other words removing

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the slag, now cooled, that has deposited on the thre¬ shold of said hole, as well as remaking the "dam". Of course this involves longer standsti ll times between one cast and another, with consequent reduction of the production capacity, since it is impossible to carry out these operations by hand with the electrodes being fed, near high temperatures and with the operators under the danger of being hit by sparks or jets of molten metal. Not only, but the removal of eventually cooled, solid slag, forming an integral block with the underlying step of refractory material (usually dolomi¬ te), resulted in a substantial demolition of the step itself or "dam" and its remaking, with an additional extension of the plant standsti ll time. it has been thought of over coming these inconve¬ niences by using a power shovel that can hold the batch of charged scrap at the inside of the furnace whi le keeping the slag runner free, but the required presence of an operator on board renders extremely dangerous and nearly impossible this solution unless the operator of the mechanical shovel undergoes unlikely performances such as the temporary leaving of the vehicle as the material drops. Simi larly unfeasible results to be the cleaning of the slag hole with active electrodes, when considering the high electric power involved (up to 65 MW) .

Therefore the object of the present invention is that of providing an apparatus capable of carrying out the above-mentioned operations, under a remote control and without the presence of an operator on place. According to the present invention such an appa-

ratus is formed of a pushing machine running into oppo¬ site directions on a rai l length provided in front of the slag hole and having, on a frame mounted on sliding wheels, some of which being driving wheels, an extensi¬ ble arm provided at its fore portion with a front head or shield having a cross-section slightly smaller than the opening of the slag hole, there being provided means for remote controlling the forward or backward movement of the said machine, the extension or the return stroke of said extensible arm, as well as the operation of means for anchoring the machine to the ground, and possibly for swinging the arm in a vertical plane about a pivot provided on the frame itself. According to a preferred embodiment of the machine, the front part of the machine frame may be provided with at least a pair of projections integrally formed with the machine itself for fitting in corresponding seats formed in the masonry structure before the slag hole, practicaLly a retaining wall surrounding and insulating the slag discharge trap.

With the pushing machine according to the pre¬ sent invention, during the scrap charge into the furnace a first series of advantages is obtained, among which the most apparent one is that of preventing the scrap from escaping the slag hole, thus increasing the yield, i.e. the ratio between produced steel and charged scrap. Another important advantage in this stage is that the slag runner, as above defined, is kept free and the scrap drops entirely within the furnace, not on the threshold thereof, where it would be lost, thus reducing even more the yield, and wherefrom it should have to be removed with difficulty once solidifyed, with a

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partial demolition of the threshold itself which then should have to be restored. Furthermore the completely free slag runner means immediate exploitation of the oxygen in the zone where melting occurs, without danger of damaging the lance and anyhow without possible pre¬ sence of scrap between lance and melt bath which would interfere with the oxygen blow, thus reducing its speed and shielding the temperature gradient.

Another series of advantages afforded by the pushing machine according to the present invention is due to the fact that it can be used for cleaning the slag hole and remaking of the dam at about half casting, when for example the electrodes have delivered a prefixed quantity of specific power (such as for example 200 KWh/ton) and are sti ll active. Thus the power deli¬ very is not interrupted and the standsti ll time between two subsequent casts is strongly reduced, whi le the slag overflow level is ensured, as the height of the head shield, being controlled to have the fixed values, keeps automatically constant such a level, thus slag is removed when it is hot, thereby extremely crumbly, without problems of re-bui lding the dam with additional dolomite, all this occurring without any personal intervention, what would clearly involve some risks.

These and other objects, advantages and features of the pushing machine according to the present inven¬ tion wi ll be clearer from the following detai led de¬ scription of a preferred embodiment thereof, given by way of non-limiting example, with reference to the annexed drawings in which:

F_i_g_u_r_e__1 shows a schematic side view of the

pushing machine according to the invention in two diffe¬ rent positions with respect to a smelting electric furnace also schematically shown in cross-section;

M_<ιu_re__2 shows a top plan view of a preferred embodiment of the pushing machine of figure 1; and f gure_3 shows a side view of the pushing machi¬ ne of figure 2;

With reference to the drawings, the pushing ma¬ chine according to the invention essentially comprises a metal frame 1, mounted on four wheels (which could also be of greater number), at least two of which are driving wheels. In the drawings the rear wheels 2, 2' are assumed to be driving, whereas the front ones 2a, 2'a are driven. A geared electric motor 3, having for example a power of about 4HP, directly actuates, through suitable drive mechanisms, a driving axle 3' at the ends of which there are mounted the wheels 2, 2', thus being able to develope a speed of about 20 m/min. The electric feeding of the geared motor 3 is accomplished through an electric cable wound on a reel 13, which is sidely mounted on the frame and is designed to automa¬ tically release the cable by unwinding the same at approaching the machine to the furnace 10 and vice versa re-winding it automatically when the machine is caused to move backwards.

On the frame 1 there is centrally mounted an extensible arm formed of two coaxial tubes 5, 5a, here shown as having a square cross-section, which however could have any different cross-section shape, at the end of the inner one, designated 5a, there is integrally provided a metal head or shaped shield 6 that forms

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the actual tool of the apparatus. The tube 5a of smaller cross-section slides within the outer tube 5 as it is fixed, preferably at its end zone near to the head 6, as better shown in figure 3, to a central piston rod of a piston-c linder 15 having the cylinder fixedly mounted to the outer tube 5 of the extensible arm. It preferably shows stiffening ribs 12 spaced along the length and is supported on the frame 1 through a cradle formed of two vertical brackets or lugs 11, 11 ' between which a pin 17 is mounted. About pin 17 two holed flanges 21 can rotate, which are fixed to the outer tube 5 and consequently the extensible arm. In a rear side zone of tube 5, its outer surface is also fixed to the piston rod, preferably having a fork shape 19, of another cylinder 16 which is vertically mounted on the frame 1. Both cylinders are operated by a pressurized fluid means such as air or preferably oil, in the latter case there being provided a hydraulic system formed of a tank 7 and a pomp-motor unit 4 also fixedly mounted on the frame 1 of the machine and fed by an electric cable, other than that for feeding the geared motor 3. Both cables are independently wound on the reel 13 and through remote controls (not shown), preferably doubled in a control deck and in an emergency push-button panel hanging on the sliding floor of the machine, the forward and backward movements or the stop of the machine itself are controlled, as well as of forward, backward, upward and downward movements of the extensible arm. Sti ll with reference to figures 2 and 3 there are preferably provided, near the rear wheels 2, 2",

anchoring means to the ground, mounted in the central zone of the frame 1 at a distance therebetween equal to about the distance between the wheels and formed of two vertical posts 8 longitudinally movable with reci¬ procating movements as being actuated by a driving cylinder 18. The stroke of posts 8 is such as to reach downwards a position lower than that of contact rai l-wheels, thereby the posts can firmly fit into seats formed in the rai ls themselves or the surrounding floor so that the pushing machine is anchored during its operating manoeuvres, in particular during the forward movement of the extensible arm with shield 6, thus avoiding that by reaction the frame 1 can move backward and the push onto the scrap to be kept within the furnace may fai l. The cylinders 18 wi ll be prefera¬ bly fed through the same hydraulic system comprising the pump 4 and tank 7 upon controls that are also of the remote-type, different from those provided for operating the extensible arm. This anchoring means can of course show any other different embodiment known in the a rt .

Finally the pushing machine according to the invention will be preferably provided with front hori¬ zontal studs 9, 9' mounted on bumper plates 23, 23' fixedly mounted onto the frame and positioned before the front wheels 2a, 2'a to shield them from impacts. The two front studs 9, 9' are designed to fit into corresponding holes (not shown) formed in metal seats, such as rai l sections, embedded in the structure 20 or retaining wall placed before the threshold of the slag hole, against such a wall the pushing machine being

blocked at the end of its forward stroke. Thus it is avoided that the machine may undergo a ti lting moment during the operation of cleaning and remaking of the dam or in general when the arm 5, 5a is swinging in the vertical p lane .

From the foregoing it is clear the operation of the pushing machine according to the present invention, which wi ll be moved forward, with shield 6 completely retracted, unti l reaching its stroke end where the anti-ti lt ing studs 9 are fitted into the seats of struc¬ ture 20, whereafter the anchoring posts 8, 8' are lowe¬ red and the machine is ready for its action through extension of the inner arm 5a to carry the head shield 6 near the melting bath, thus ensuring that the slag runner 10a is kept clear of scrap during the subse¬ quent charge. Possible manoeuvres of movement can be carried out also in vertical direction, when it is required to push to the inside of furnace 10 pieces of scrap which may assume undesired positions. As the charge is over and melting is at beginning, the machine can move backward to allow the introduction of the oxygen lance through the runner 10a, for the direct action of refining onto the molten product. The lance, whose direction is controlled from outside, is not sub ect to the risks of damages since the runner is free and the oxygen, flowing at a speed that can be even supersonic, is blown in ti ll the inside of the molten bath .

Subsequently, at about half casting, when the electrodes have delivered a prefixed quantity of energy, e.g. 200 KWh/ton, as measured at the control deck

the oxygen lance is withdrawn and the pushing machine is caused to move forward again to perform the cleaning and the dam re-bui lding operations, thus ensuring the overflow level of the slag being constant. This opera¬ tion, carried out with subsequent forward and backward movements of the movable arm, with possible displacement also in the vertical plane to augment the mechanical action on the slag itself, occurs easi ly upon remote control of an operator who is however able to observe the working area. It wi ll be noticed that when working in these conditions, the slag is at high temperature, thereby is crumbly and easi ly removable from the underly¬ ing layer of dolomite or other refractory material which does not require demolitions and subsequent re-bui lding. Mention has been already made before about the advantages in terms of time, of operating in this stage without prolonging the waiting time between two subsequent casts.