Arrangement of electrode holders
The present invention relates to an assembly and a method for feeding of electrodes which are used in electro-thermic smelting furnaces. In particular the assembly and the method for feeding of electrodes according to the present invention are intended to be used in conjunction with self-baking electrodes such as conventional &#34;Soederberg&#34; electrodes. 
     For feeding of such electrodes there is a need for feeding means where the possibility for uncontrolled feeding of the electrode is eliminated. The electrode feeding means must further be so simple to produce as possible and it must be easy to perform maintenance work on the electrode feeding means without downtime of the furnace. Further the feeding increment must be easy to adjust and the time interval between each feeding cycle must be easy to regulate. 
     In the known systems for feeding electrode there is usually arranged two holder rings around the electrode, which rings exert radial forces to the electrode. When feeding the electrode the pressure must be released on at least one of the holder rings. Consequently at least 50% of the holding force is lost. When feeding the electrode by this conventional feeding means, the pressure of the first of the holder rings is released and the first ring is moved vertically relative to the second holder ring and the electrode, whereafter the pressure on the first holder ring is reactivated. The pressure on the second holder ring is then released and the electrode is fed down by lowering the first holder ring. When the feeding movement is finished the pressure on the second holder ring is reactivated. 
     It has been discovered that an electrode feeding assembly of this kind imposes relatively large radial forces on the electrode casing and on the electrode itself. With this large radial forces there is a danger for detrimental deformation of the electrode casing and hence of the electrode itself. With the deformation of the electrode casing there is also a danger for totally loosing the holding force imposed on the electrode casing by the holder rings. 
     In the known systems for feeding electrodes, the feeding increments vary too much for every feeding cycle. The feeding increments can therefore not be used as a safe parameter for the electrode consumption. Further with the known systems for feeding electrode the furnace have to be shut down for every kind of maintenance work on the electrode feeding means. 
     In accordance with the present invention the disadvantages and drawbacks of the previously known electrode feeding means has been overcome by means of an electrode feeding assembly comprising a plurality of electrode feeding units which are symmetrically arranged around the periphery of the electrode, which electrode feeding units comprise clamping means that impose a releasable pressure on continuous vertical ribs that extend radially outwards from the electrode casing in such a way that substantially only tangential forces are imposed to the electrode. According to a preferred embodiment of the present invention, each clamping means is formed of two substantially identical, reversed parts which are disposed on each side of the outwardly projecting ribs on the electrode casing. The two halves of the clamping means are hinged on a central member and are pressed together by means of a suitable pressure device. Further the electrode feeding units according to the present invention have means to temporary releasing of the pressure on the clamping means. The means for temporary releasing the pressure on the clamping means is preferentially arranged on that end of the clamping means which is remote from the ribs and the pressure device. 
     The pressure on the clamping means can for example be imposed by one or more springs which are tangentially arranged relatively to the electrode. The springs are preferentially furnished with a bolt and nut, which permits regulation of the clamping force. The central member on which the two halves of the clamping means are hinged, is preferentially the piston of a pneumatic or hydraulic cylinder. 
     In accordance with the present invention there is provided an electrode feeding assembly which assure safe and controlled feeding of the electrode relative to the electrode holder and at the same time completely or partially, contribute to the holding force for the electrode. 
     The cycle for feeding the electrode according to the present invention, is as follows: The pneumatic or hydraulic cylinder for each feeding unit is adjusted to the exact same feeding length. This length is called the feeding increment. The means for temporary releasing the clamping pressure for one of the feeding units is activated. The clamping means is thereby free to be moved relative to the electrode. This is done by activating the pneumatic or hydraulic cylinder. When the clamping means has been moved to its upper position, the means for temporary releasing the clamping pressure is reactivated and the clamping means is again imposing pressure on the ribs. This cycle is done for every electrode feeding unit around the periphery of the electrode with a preset time-delay for the activation of every unit. This means that only the feeding unit which is being moved at a given time does not contribute to the holding force of the electrode. When all electrode feeding units have been moved to their upper position and they all impose holding force to the ribs, the pneumatic or hydraulic cylinders for all th electrode feeding units are deactivated at the same time and the electrode is fed down the preset feeding increment. 
     The feeding increment can be easily and exactly adjusted. The normal feeding increment will be about 3 to 30 mm. The time between each feeding cycle can also be regulated. The time interval between each feeding cycle can for example be regulated from about 10 minutes to about 4 hours. With this possibility for regulation, the feeding can be adjusted to the actual electrode consumption. The electrode feeding assembly and the method for feeding electrode according to the present invention, will give the exact same feeding increment for each feeding cycle and by counting the feeding cycles it is possible to record the electrode consumption at every moment. 
     According to the present invention there is arranged a plurality of electrode feeding units around the periphery of the electrode. If for example six electrode feeding units are arranged, ony 17% of the holding force is lost when the pressure on the clamping means for one of the electrode feeding units is released. When the conventional electrode feeding units with two holder rings are used, at least 50% of the holding force will be lost when feeding the electrode. Further, according to the present invention the force on the ribs can be very high without the risk of deformation of the electrode casing because the clamping units impose substantially only tangential force on the electrode casing. 
     For maintenance work on the electrode feeding units at least one unit can be removed without need for furnace downtime and without any risk for uncontrolled feeding of the electrode as only 17% of the holding force of the electrode feeding assembly is lost when one of the electrode feeding units is removed. 
     Furthermore the electrode feeding assembly according to the present invention can be used for electrodes with highly different diameters. The feeding units are small and occupies a small volume. The height of the feeding units according to the present invention is about 400 mm, whereas the conventional feeding systems have a height of up to 4000 mm. 
    
    
     Further features and advantages of the present invention will be seen from the description of the drawings wherein; 
     FIG. 1 shows a top view of an electrode with electrode casing and six electrode feeding units, one of the electrode feeding units being shown in detail; 
     FIG. 2 shows a vertical front elevation of one of the electrode feeding units according to the present invention; and 
     FIG. 3 shows a top view of one of the electrode feeding units. 
    
    
     FIG. 1 shows a top view of an electrode casing 5 with continuous, vertical ribs 6 extending radially outwardly from the electrode casing 5. According to the embodiment of the present invention shown on FIG. 1, the electrode casing comprises six ribs 6 extending outwardly from the electrode casing 5. To each rib there is arranged one electrode feeding unit 1. This implies that according to the embodiment of the invention shown on FIG. 1, there is arranged a total of six electrode feeding units 1. The feeding units will be described below in connection with FIGS. 2 and 3. 
     FIGS. 2 and 3 show a preferred embodiment of the electrode feeding unit 1 according to the present invention. The electrode feeding unit 1 comprises lifting/lowering means 8 and clamping means 2. The clamping means 2 is formed of two substantially identical, reversed units which are hinged around a vertical member 3. 
     The clamping means 2 is intended to engage with the ribs 6 extending outwardly from the electrode casing. To press the clamping means 2 against the ribs 6, the electrode feeding unit 1 is furnished with a suitably spring-loaded device 4. The spring-loaded device 4 preferably consists of a helical or a disc spring and a bolt and nut 11. The spring-loaded device 4 is arranged on the clamping means 2 on the same side of the member 3 as the ribs 6. The spring-loaded device 4 is preferably adjustable. According to the embodiment of the present invention shown on FIGS. 2 and 3 the spring-loaded device 4 can be adjusted by tightening or loosening the bolt and nut 11. 
     The clamping means 2 is on the end remote from the ribs 6 and the spring-loaded device 4 furnished with means for temperorary releasing the pressure exerted by the spring-loaded device 4. According to the embodiment of the present invention shown on FIGS. 2 and 3 the means for temporary releasing the pressure exerted on the ribs is a pneumatic or hydraulic cylinder 7. The piston 10 of the cylinder 7 is at its outer end mounted to one of the two halves of the clamping means 4. When the piston 10 goes into the cylinder 7 the two halves of the clamping means 4 will rotate in opposite direction about the member 3 and hence the pressure exerted on the rib 6 by the clamping means 2 will be released. Since the clamping means 3 is free to rotate about the member 3, the clamping means 4 will be self-adjustable in relation to the rib 6. 
     According to a prefered embodiment of the present invention the member 3 is a part of the lifting and lowering means 8. The lifting and lowering means 8 is preferably a pneumatic or hydraulic cylinder 8, and the member 3 is the piston of the cylinder 8. The cylinder 8 is mounted on a frame 9 which in turn can be mounted either on the electrode holder casing or on a suspension frame (not shown). Alternatively, the frame 9 can be mounted on a furnace floor (not shown). In the normal position the piston 3 of the lifting and lowering means 8 is in its lower position and the clamping means 2 exerts full pressure to the rib 6. The feeding cyclus is as follows: The cylinder 7 for one of the feeding units is activated and the piston 10 moves into the cylinder. The pressure on the rib exerted by the clamping means 2 is then released and the electrode feeding unit is free to move in vertical direction. The lifting and lowering cylinder 8 is then activated and the clamping means 2 moves upwards as the piston 3 moves out of the cylinder 8. When the piston 3 is in its upper position, the cylinder 7 is deactivated and the pressure exerted on the rib 6 by the clamping means 2 is restored. This cycle is done for every electrode unit 1 around the pheriphery of the electrode, but with a preset time-delay between the cycle for each electrode feeding unit 1. In this way there is only one electrode feeding unit at a time that is not exerting pressure on the ribs 6. When all the electrode feeding units 1 have been lifted to their upper position and they all exert pressure to their ribs, the cylinders 8 for all of the electrode feeding units is deactivated at the same time and the electrode is fed down. 
     Even if the embodiment of the present invention shown on the figures have six electrode feeding units, it should be obvious that the electrode feeding assembly according to the present invention can have at least two such units and also more than six, for example 8.