MXPA97007999A - A method and an installation to determine the height position of an electr - Google Patents

Abstract

An installation for determining the height position of a vertically movable electrode (2) in an electric arc furnace (1). The installation includes a flexible, elongate element (9), preferably a heavy chain, whose end is attached to a first clamping point on the movable electrode (2). The other end of the chain is attached to a second fixed clamping point. The total weight of those parts of the flexible element that are carried by the movable and fixed clamping points, respectively, would be in response to the vertical movement of the electrode. The installation also includes (6) to detect that part of the total weight supported by the fixed clamping point, to determine the height position of the electrode (2). The invention also relates to a method for determining the height position of a vertically movable electrode

Description

A METHOD AND AN INSTALLATION FOR DETERMINING THE HEIGHT POSITION OF AN ELECTRODE Field of the Invention The present invention relates to a method for determining the height position of a vertically moving electrode in an electric arc furnace, using for this purpose an elongate flexible device, preferably a heavy chain. The invention also relates to an installation for carrying out the method. BACKGROUND OF THE INVENTION Electric arc furnaces typically include one or three electrodes. Three electrodes are used in three phase furnaces with one electrode connected to each phase, considering that only one electrode is used in direct current furnaces. The electrodes are provided with control means that regulate the height of the electrodes in order to maintain an optimum arc between the electrode and the scrap or between the electrode and the molten bath when the scrap reaches this state. A normal work cycle can be divided into three phases. In the first phase, the furnace is filled with scrap and the electrodes are "mined" down through the scrap load while the scrap melts. In the second phase, the scrap surrounding the electrode collapses towards the "mine" and the electrodes must rise again out of contact with the scrap in order to support the electric arcs. The third phase involves stabilizing the electrodes on a lower level above the molten bath in the furnace. The electrodes constantly move up and down to support the electric arcs, particularly during the first two phases. The optimal process control of electric arc furnaces requires knowledge of the furnace wall temperature and also of the vertical movement of the electrodes in the furnace. A good estimate of the casting process for optimal control can be obtained by studying the course of the temperature along with the movements of the electrode. This allows for increased productivity and reduced energy consumption at the same time. Oxygen consumption can also be optimized by this. The continuous detection and recording of the temperature of the wall elements of the oven do not present technical problems. On the other hand, difficulties have been encountered in practice to provide a reliable, cheap and simple method for detecting and indicating the positions of height of the electrodes as a function of time. The electrodes are mounted on electrode arms to which the so-called electrode posts are connected. Previous attempts have been made to record the movements of the electrode posts with the help of associated lines and pulleys and drums to handle the angle indicators or similar devices; in this regard see for example DE-A-2001476 and DE-C2-2651544. However, the environment surrounding the furnaces of this type is extremely severe and problematic and consequently all moving elements will stop working with the passage of time, and the lines used will often break. No unduly thick lines can be used, since they would require the use of pulleys and drums of larger diameters. The use of optical measuring devices has also been proposed. However, such devices increase costs and cause problems as a result of the coatings that are formed on the optical elements with the passage of time. The main object of the present invention is to provide a method and an installation that allows the height position of an electrode in an electric arc furnace to be determined economically, reliably and continuously without the use of rotating elements or optical elements. AU-B-87724/82 describes an installation for determining the height position of an elevator or extraction cage. This installation includes an elongated flexible element that hangs from the movable lifter cage and the position of said cage is determined at different time points, when weighing that part of the flexible element that is carried by the cage. Such an installation can not be used in electric arc furnaces because, among other things, the weight sensing load cell will be located near the furnace in an environment that would make the function of the cell highly unreliable. In addition, it would be necessary to install electronic cables above the furnace, which would result in a number of serious difficulties and increase costs. In addition, the known solution, especially when the flexible element is in the form of a heavy chain, would cause the load cell to be subjected to dynamic stresses in conjunction with the rapid accelerations of the electrode that can be ordered by the electronic control installation, especially when the load cell works to detect the load continuously. In addition to generating mechanical stresses and distensions in the load cell, this would result in erroneous cell signals because the desired electrode position signals would be obscured by signals resulting from these dynamic forces. SUMMARY OF THE INVENTION According to the present invention, a method of the type defined in the first paragraph for determining the position of the height of a vertically movable electrode in an electric arc furnace is characterized in that one end of the flexible element is attached to a first attachment point on the movable electrode or on a part that moves in conjunction with it considering that the other end of said element is attached to a second attachment point in such a way that the total weight of said parts of the The flexible element carried by the movable and the fixed attachment points will vary depending on the vertical movements of the electrode, where the position of height of the electrode is determined by detecting that part of the total weight that is carried by the fixed attachment point. This method thus allows the position of height of an electrode to be determined in a very simple manner without the use of rotating elements and without the influence of dynamic forces resulting from the acceleration of the movement of the electrode. In addition, a weight-determining load cell can be placed in a completely protected place, adequately below the ground. No problems occur with respect to the installation of cables, etc., with this solution. The aforementioned weight is suitably detected continuously and becomes an electronic signal continuously indicating the movement of the electrode. This can be done with the help of a load cell mounted on the attachment point. Other characteristic configurations of the method and of an installation for carrying out the method are made apparent in the following claims. The invention will now be described in more detail in relation to an exemplary embodiment of an inventive installation and also in relation to the accompanying schematic drawing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the reference numeral 1 designates in general an electric arc furnace equipped with an electrode 2. The furnaces are normally operated with alternating current of three phases and include three electrodes, each being controlled separately. Only one electrode has been shown in the schematic drawing, for reasons of simplicity. The electrode 2 is mounted on an electrode arm 3 connected to a movable electrode post 4. In practice, the height position of the electrode 2 is normally determined when determining the position of the post 4, since the post participates in the movement vertical of the electrode. The furnace 1 is initially filled with scrap 5, which is melted with the help of arcs generated between the electrodes 2 and the scrap. The figure shows the electrode 2 in the first phase, in which the electrode is mined towards the scrap as it melts said scrap and forms a hole in it. The movement of the electrode is controlled with the aid of control means which detect the electrode supply current in order to maintain an electric arc between the electrode and the scrap 5. The electrode 2 constantly moves up and down in one direction vertical, although its main movement direction is descending. The scrap surrounding the hole generated by the electrode will normally collapse at a certain point of time. This collapse is exposed to short circuit the electrode and with the same to extinguish the arc, and consequently the electrode rises quickly in order to start a second phase in which the electrode moves down again while the material that is melted It has collapsed into the hole. After completion of this step, a third stabilization phase is started, in which the electrode moves over the molten bath in the furnace to a relatively small area.

As mentioned in the introduction, a clear understanding of the melting process can be obtained by studying the course of electrode movement along with the temperature course in the kiln wall elements, so that the melting process can be controlled optimally and can, for example, make a decision as to when additional scrap should be loaded into the furnace. According to the present invention, a heavy chain 9 or the like, for this purpose, is attached between the lower end of the movable electrode post 4 and a fixedly mounted load cell 6. The load cell is assembled in a manner conveniently below ground level, in order to protect both against heat and against dust and also from the scrap that falls into the furnace as the furnace fills. The load cell is connected to a unit 8 for displaying and recording the signal obtained through a conductor or cable 7. The load cell 6 supplies a signal corresponding to the force exerted by the chain 9 on the cell. This force varies between a maximum value when the electrode 2 and the electrode post 4 are located in their lowermost positions, and a smaller value when said electrode and electrode post are located in their higher positions. Thus, in a particular case, this force exerted by the chain in the first position corresponds to the weight of the entire chain 9, considering that the force exerted in the second position corresponds to half the weight of the chain. The load cell 6 continuously converts this force into an electrical signal, which is sent to the unit 8 through the conductor 7. The unit 8 displays the movement of the electrode as a function of time and the curve thus produced is studied together with the course taken by the temperature in the wall elements of the furnace, to control the melting process. In order to obtain correct measurement values in a continuous detection process, it is important that the load cell is suspended from the fixed clamping point and not from the movable clamping point, since in the latter case the load cell would be influenced by the dynamic forces caused by the accelerating movements of the electrode and therefore would provide false signals. The installation described above can be installed at a low cost and has a very reliable function, among other things because it does not contain rotating elements. In addition, it can be placed in a well protected position. It will be understood that the above described and illustrated installation constitutes only a preferred embodiment of the invention that can be modified in several aspects within the scope of the following claims. For example, the chain may hang from the attachment point against a collection means, for example, in the form of a fixed surface on which a portion of the chain is collected and which corresponds thereto to the fixed attachment point before mentioned. The length of the chain collected on the collector surface will depend on the position of the electrode and its vertical movement, allowing the movements of the electrode to be determined by the weight of this length of chain collected. The chain can be replaced with some other heavy flexible element and the load cell can be replaced with other means capable of determining the pulling force acting on the fixed point of attachment of the chain.

Claims (5)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. A method for determining the height position of an electrode moving vertically in an electric arc furnace, with the aid of a flexible, elongate element, preferably a heavy chain, characterized in that one end of the flexible element is clamped to a first clamping point located on the movable electrode or on a part moving along with it, holding the other end of the element to a second fixed clamping point, such that those parts of the total weight of the flexible element supported by points respective movable and fixed clamps will vary in response to vertical movements of the electrode; and detect that part of the total weight supported by the fixed clamping point to determine the height position of the electrode. A method according to claim 1, characterized in that said weight is continuously detected and the detected weight is converted into an electrical signal that continuously indicates the movement of the electrode. 3. An installation for determining the height position of an electrode (2) moving vertically in an electric arc furnace (1), with the help of a flexible, elongate element (9), preferably a heavy chain, characterized in that one end of the flexible element is attached to a first attachment point located on the movable electrode (2) or on a part (4) that moves together with it, and the other end of said element is attached to a second point of contact. fixed clamping, in such a way that the total weight of those parts of the flexible element (9) that are transported by the movable and fixed clamping point respectively will vary in response to the vertical movement of the electrode; and that a medium is provided (6) to detect that part of the total weight supported by the fixed clamping point to determine the height position of the electrode (2). 4. An installation according to claim 3, characterized in that said means includes a load cell (6) that continually detects said weight and converts the detected weight into an electrical signal that continuously indicates the movement of the electrode. An installation according to claim 4, characterized in that one end of the flexible element (9) is fastened to the lower end of an electrode post (4) connected to the electrode (2); and in which the load cell (6) is mounted adjacent to the fixed clamping point.