Patent Publication Number: US-2022226920-A1

Title: Device and Method for Welding Cylindrical Sections of a Casing

Description:
BACKGROUND 
     The disclosure relates to a device for welding together cylindrical sections of a steel casing, preferably a casing surrounding an electrode mass, preferably to be used in an electric melting furnace, and a method for performing the welding. 
     The embodiments relate to a device of the kind to be used upon joining of cylindrical casings of steel (such as window-, belly band, frame or section casing) in a continuously lowering electrode (the Soderberg electrode) used in electric melting furnaces. More preferred the embodiments are related to a method for welding by using a robot, wherein steel casing sections are welded to each other by using a welding robot. 
     In electric melting furnaces for melting metals, electrodes are used in the process. The electrodes conduct current and a high current intensity is induced which generates heat due to the resistance in the steel melt. The heat is generated by electricity and is necessary to start the metallurgical reactions. 
     The electrodes are often made of carbon and their function is to conduct energy to the reaction zone at the bottom of the furnace. The electrodes should have high mechanical strength, and thus the electrode paste is normally filled into the inside of a cylindrical steel casing. The steel casing is a formwork that holds the electrode paste together, and as the casing gets lowered into the furnace, the casing will get consumed due to the heat, so that a new casing section needs to be added at the top. The electrode paste which follows the casing downwards, will first melt to a liquid phase before it is baked to a solid phase again at the end of the process. In the Soderberg method, the sections are provided with ribs, the ribs being rectangular plates which protrude inwards towards the center of the casing. This helps the casing to conduct electricity better and to hold the baked electrode. 
     In the Soderberg method, the electrodes are lowered into the melt as they are eroded during the melting process. The lowering is made continuous, and electrode mass are added at the top, To hold the electrode mass together, sections of cylindrical pipes (casings) are added around the electrode mass. The steel casings are welded together in sections as the electrodes are lowered into the melting furnace. 
     An attempt has been made to solve this problem, for instance in CN 108436349, but the robot described therein is arranged on a lifting system rather than on the steel casing itself. As the casing moves, the welding will not be correctly positioned, and must be repeated or replaced by manual welding. 
     The welding of the casing sections is at present performed manually. The work environment where the welding is performed may be dangerous and demanding due to heat, smoke, pollution, gas and open current conducting components, among other things. 
     When considering the requirements for personal security and working environment of today, there is obviously a desire for automation and efficiency of such work. 
     The casings are lowered continuously as described above, but they may also move upwards occasionally. The temperature in the furnace must be stable, and therefore the electricity supply through the electrodes must be stable. The resistance is regulated by raising and lowering the electrode tip. In order to decrease the amount of electricity and thus the temperature, the electrode tip is lifted, and to increase the amount of electricity, and thus the temperature, the electrode is lowered. Normally three electrodes are used simultaneously in the same furnace, and the movement of each electrode is not predictable. The movements are not large, but the welding gun must be held steady in relation the casing, even during movements of the casing, in order to position the weld correctly. 
     SUMMARY 
     The disclosed embodiments overcome or at least reduce the effect of one or more of the disadvantages associated with the present technology. Also provided is a device for automating the welding process. Also provided is a device offering full inspection of the welds, preferably both during the welding and afterwards when the welding is complete. The disclosed device may be moveable both in a circumferential and an axial direction in relation to the casing and may be used on both existing and new furnaces. 
     A device for welding cylindrical sections of casings according to the disclosed embodiments, comprises
         a clamping ring configured to surround and attach to a section of the casing, and   a robot provided with a welding gun and at least one joint,       

     wherein the robot is movably attached to the clamping ring by cooperating means. 
     By “clamping ring” it is, in the context of this application, meant a part shaped as a ring which comprises a mechanism for coupling the ring to the casing such that it is attached to and moves with the casing. In a preferred embodiment, the mechanisms comprises a clamping function, such as by adjusting the circumference of the ring to clamp it onto a casing arranged in the center of the ring. When the ring is clamped it surrounds at least the main part of circumference of the casing, and is fastened to it by the clamping. 
     In the Soderberg method described above, cylindrical sections are welded to each other, at the site of the melting furnace. The first (also referred to as lower) section is continuously lowered into the furnace, and a second (also referred to as upper) section is lifted on top of the first section and the sections are welded to each other. The casings may have ribs on the inside, and if this is the case, then the ribs must also be welded to each other. This is normally performed by moving the welding gun into the inside of the casing through a number of openings or windows in the casing. These windows are closed by welding a patch over the window when the ribs are welded. 
     In the following, the embodiments are described having the clamping ring attached to the first section of the casing, and then the robot will be directing upwards from the ring during welding. However, the clamping ring may also be attached to the second section before welding, and in such a case the robot will be hanging from the clamping ring, and being directed downwards to weld the connection between the sections. 
     In order to perform the welding, a clamping ring of a device according to the disclosure may be clamped to the first section, which is lowered into the furnace. 
     Once the second section is arranged in position, the robot is suitably positioned and may weld the sections together. The clamping ring and robot must be removed from the first section before the whole of the first section is lowered into the furnace. 
     In one embodiment, the clamping ring can be configured as a complete closed ring which has an initial diameter that is larger than that of the casing sections. The ring can be placed over the casing to surround it and a clamping mechanism activated to hold the ring in place at the desired height. The clamping mechanism can comprise one or more extendible legs or clamping elements configured to move into engagement with the outer surface of the casing section when extended to fix the clamping ring to the casing.” 
     In another embodiment, the clamping ring is a broken ring having two ends, and the releasing and clamping may occur by adjusting the distance of the ends, and thus the circumference of the ring. In this embodiment the ring must be lifted over the upper part of the casing in order to be removed or added to the casing. 
     In yet another embodiment, the ring comprises two, three or more parts hinged to each other to at pivotable joints. The release may then be performed by pivoting one or more of the parts away from the casing, and the clamping may occur by attaching the parts to each other, and possibly adjusting the distance between the different parts. The attachment and adjusting of the ends or parts of the ring may be performed by one of a mechanic, hydraulic or pneumatic mechanism. The clamping must be sufficiently strong to carry the weight of the robot and to follow the movements of the casing. 
     The robot of the disclosed device, is provided with a welding gun to perform the welding between the first casing, and the second casing arranged on top of the first casing. The robot is provided with a welding gun to perform the welding between the first casing to which the clamping ring is attached, and the second casing which is arranged on top of the first casing. In order to perform the welding sufficiently accurately, the robot has at least one joint to enable movement of the welding gun towards and away from the casing. Joints may be configured to cause rotation about an axis such that movement of each joint causes movement of the welding gun in a  2 D plane. Two such joints may be present. In a preferred embodiment, three such joints are present and the axes of rotation of the joints are orthogonal. The welding gun may be moved in any direction by moving the gun using one or a combination of the three joints. 
     When for instance ribs on the inside of the casing should be welded, as described above, the robot must move through windows in the casing, and once inside the window, the welding gun should be able to move in all directions. Based on such needs, the robot may be provided with more than three joints, possibly six or even seven joints or more, to be able to direct the welding gun at the position to be welded. The optimal number of joints will be obvious to a skilled person once the type of casing, clamping ring and welding gun are known. 
     The movement of the robot may preferably be controlled by a controller, more preferably a remote controller. In an even more preferred embodiment, the movement or movements of the robot are preprogramed in a computer, and an operator is required to only initiate different sub-programs, such as for instance a “welding ribs” sub-program, a “welding circumference of the casing” sub-program and possibly a “welding patches” sub-program. 
     In a preferred embodiment, the robot comprises a camera directed towards the tip of the welding gun in order to monitor the casing being welded. The camera may also be used before the welding starts, in order to position the robot and welding gun precisely. In a preferred embodiment the direction of the camera may be remotely adjusted if an operator desires to inspect surrounding parts of the casing. In yet another preferred embodiment, the movement of the robot is adjusted according to the image viewed through the camera, in order to position the welding gun correctly for welding. 
     The quality of welding is crucial for a continuous operation of the melting furnace, and therefore the possibility to inspect the quality of the welds may be necessary. In a preferred embodiment, the camera takes a picture of the area to be welded both before and after welding. The weld is inspected according to a given standard, and if the welding is not accurate a signal is provided to the operator. All pictures or videos taken can be saved for documentation. 
     The welding gun of the device may be any suitable welding gun, and the possibilities in terms of which welding gun to use will be obvious to a skilled person. In a preferred embodiment the welding gun has a long neck, possibly including one or more bends, and possibly being a goose neck, to provide easier access to the welding positions. Normally the welding gun needs welding wire, which can be supplied from a wire coil by a wire feeder. 
     The robot is movably attached to the clamping ring by cooperating means. The cooperating means provides attachment to prevent unintended removal of the robot, as well as to allow movement of the robot along the clamping ring. In this way the robot may move around the casing in a circular track to weld the casings together along their whole circumference. Depending on the clamping ring, the cooperating means attaching the robot to the ring, and the robot itself, the robot may not need to move completely around the circumference of the casings, but the welding gun must be able to move along the complete circumference. 
     The cooperating means may for instance comprise cooperating elements of the clamping ring and a counterpart on the robot, such as a feather and tongue joint, and the movement may be provided by rotating wheels and a motor. In a preferred embodiment, the cooperating means comprises mechanical, pneumatic, hydraulic or magnetic counterparts engaging each other. In a more preferred embodiment, the clamping ring and a part of the robot are further provided with teeth or similar to constitute a pair of gear rims, wherein the robot moves along the clamping ring when the gear rims engage each other. The gear rim of the robot may preferably be a driving gear wheel which engages with teeth on the gear of the clamping ring. The means to move the robot along the clamping ring may be powered by a motor arranged on the robot, or the clamping ring. The cooperating means may also be any combination of the means mentioned above. 
     In an alternative embodiment, the robot comprises an extra unit for welding patches. The extra unit is arranged to pick up patches from a storage, arrange a patch over a window of the casing, and hold the patch in place until the welding gun has fastened it to the casing. The extra unit may be removed from the patch following or during the completion of the welding of the patch to the casing. 
     In a preferred embodiment, the robot is arranged on a carriage, and the carriage is attached to, and moveable along the clamping ring. When a carriage is used, the above described cooperating means for attachment and movement comprises cooperation between elements of the carriage and clamping ring, rather than clamping ring and robot. In this embodiment the carriage may further include a motor to move the carriage, and thus the robot, along the clamping ring. The carriage may further carry other equipment such as patches to be welded onto the casing to close openings used to weld ribs on the inside as described above, and welding wire in a wire coil, one or more wire feeders and/or similar additional components. 
     The welding wire, welding coil, wire feeder, patches, motor and other parts may also be arranged outside of the clamping ring, for instance on a deck of the furnace, and supplied to the robot by lines and cables. Depending on the particular circumstances, the robot may be arranged to move around the casing a number of times, or only one round before it must return in the opposite direction. The latter may be advantageous when lines and cables are running to the robot from outside of the clamping ring. 
     With the disclosed embodiments, there is provided a robotized solution for performing the welding process between the steel casings, by means of robotized operations. 
     On the steel casing there is fixed an adjustable and moveable clamping ring with cogs or teeth, following the movement of the casing. On this gear rim or ring of cogs, there is provided a carriage with guiding means and a motor with a cog wheel, or toothed wheel in engagement with the cogs or teeth of the gear rim. By means of motor and toothed wheel the carriage may be driven around the steel casing in a circular track. A robot having a number of arms and joints with axis control is arranged on the carriage. The robot is provided with a welding gun being controlled by the movements of the robot, which guides the welding gun in the desired track according to the welding operation. 
     To position the welding gun correctly, a camera is arranged on the arm holding the welding gun, and the camera communicates with the robot in such a way that the robot may be in an optimal position for the welding process. 
     In an alternative embodiment, the clamping ring and/or the robot is provided with hoisting means to move the clamping ring axially along the casing to hoist the robot into position for welding. In a preferred embodiment, a distal end of these means may be arranged to engage or attach to the upper end of a casing, and thereafter hoist the clamping ring. The hoisting means may be one or more bars protruding from the ring, and extending axially along the casing, wherein the upper end is arranged for engaging the upper edge of the casing section. The bars are preferably telescopic, and even more preferably are controlled remotely, wherein the ring may be hoisted once the upper ends are attached to the casing by retracting the bars. 
     The bars may also be a part of the casing, wherein the clamping ring is provided with hosting means engaging the bars to move the ring axially along the casing. The hoisting means are preferably mechanical, pneumatic, hydraulic or magnetic means, such as hydraulically driven telescopic bars, or gear rims. 
     In an alternative embodiment, the hoisting means are wires, ropes, chains or similar which can be attached to an upper part of the second casing manually, and the clamping ring comprises a winch or similar to hoist the ring and thereby the robot into position. 
     When using embodiments comprising hoisting means, once the welding between a first and second casing is completed, the clamping ring may be released and hoisted by the hoisting means to position the robot to weld the two next casings, at which point it can be reattached to the casing in its new position. In this way the clamping ring must only be released, not be removed from the casing, and the amount of manually work is reduced to a minimum. 
     In one aspect, the welding process starts by mounting the carriage, robot and equipment at a starting point. Then a sequences starts, whereby the robot takes pictures to define a precise position before the welding process starts. 
     The welding gun is preferably supplied with power and gas through cables and tubes connected to a welding generator. In one embodiment the robot and welding gun are also arranged to weld on the inside of a cylindrical steel casing. This welding operation is performed through openings which are closed by robot welding after the welding operation on the inside is completed. 
     Once the welding operations are finished, the welding robot may be detached and moved to the next steel casing. 
     In one aspect, the embodiments relate to a device for welding of cylindrical sections of steel casing surrounding electrode mass of a continuously lowering electrode in an electric melting furnace. The welding of connections is performed with a robot, holding a welding gun, mounted on a carriage arranged on a gear rim fastened to the steel casing and with the motor with gear engagement to the gear rim. 
     In a preferred embodiment, the device further comprises a camera to position the welding gun, the camera is arranged at the welding gun. 
     In yet another aspect, the disclosed embodiments relate to a device for welding of cylindrical sections of steel casings in an electric melting furnace wherein a robot is connected to a carriage in engagement with a gear rim connected to the steel casing. The robot is provided with a welding gun for welding the weld between sections of the casing. The welding gun is preferably provided with a camera to position the welding process. The robot has a number of moveable axes being controlled by a robot axis controller. 
     In another aspect, the embodiments relate to a method for welding together cylindrical sections of casing using the device described above. The method comprises the steps of 
     a) positioning and clamping the clamping ring at the correct position, 
     b) moving the robot along the clamping ring to the correct position for welding, c) welding the sections to each other by the welding gun of the robot, and d) releasing the clamping ring. 
     The steps may be repeated separately or in order until the sections are sufficiently welded. 
     In an alternative embodiment of the method, when the casings have windows and ribs to be welded on the inside, the method further comprises the step of welding a patch over the window. 
     In an alternative embodiment of the method, when the robot comprises a camera, the method further comprises the step of taking and processing pictures as well as repositioning the clamping ring and/or robot. 
     When the robot comprises a camera, the method may comprise the step of repositioning the robot and/or the clamping ring based on, or in response to the pictures taken by the camera. Further, the method may also comprise the step of comparing the pictures taken by the camera to a given standard, and then giving a signal to an operator if the pictures taken deviate from the standard beyond a given limit. Pictures of the weld can, for example, be compared to pictures of an ideal weld and certain properties of the two images, such as the thickness or consistency of the welds, can be determined using image processing techniques and compared to decide whether the current weld falls within required limits. The pictures taken may be transferred for saving and documentation, such as to a data storage device. 
     In an alternative embodiment of the method, when the device comprises hoisting means, the method further comprises the step of attaching the hoisting means to the casing, and further possibly the step of extending and retracting the hoisting means. 
     Reference throughout the specification to “one embodiment” or “an embodiment” “one aspect” or “an aspect” means that a particular feature, structure, or characteristic described in connection with an embodiment and/or aspect is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment”, or “in one aspect” or “in an aspect” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with the help of the enclosed Figures, showing a preferred embodiment of a device according to the invention. 
         FIG. 1  shows a welding robot arranged and ready for assignments, 
         FIG. 2  shows detail of a welding robot mounted on a carriage and gear rim, 
         FIG. 3  shows another embodiment of a clamping ring with a carriage and robot seen from above, 
         FIG. 4  shows another embodiment of a clamping ring with a carriage and robot seen perspective from above, and 
         FIG. 5  shows details of the carriage shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The different parts of the figures are not necessarily to scale in relation to each other, as the diagram is merely for illustrating the invention. 
     The following description of an exemplary embodiment refers to the drawing, and the following detailed description is not meant or intended to limit the invention. 
     In the Figures, reference number  1  refers to a melting furnace having electrodes  2  being lowered into the melt  3 . The electrodes consist of electrode mass which is added from the top 4 as the electrodes  2  are lowered continuously. To hold the electrode mass cylindrical sections of steel casing  12  are added with welded connections  8  between the sections. The steel casings  12  are provided with internal ribs  5  and holes  14  for access to enable welding of the connection  8 . 
     For welding the connection  8  a robot  6  is being used, which is arranged on a carriage  25  driven by an electromotor  26  and connected to a gear rim  9  with gear wheel and guiding means  10  on both sides of the cogging, in such a way that the carriage  25  may be driven in a circular track around the casing  12 . 
     The robot  6  is connected to the carriage  25  through the adapter  23 , and may be rotated around axis  21 . The joint  27  may be rotated around axis  22  and is connected to the arm  28 , which is connected through the joint  30  rotatable around axis  24  to the arm  29  and the joint  31  rotatable around axis  36 . The joint  31  is rotatable around axis  35  and is connected to the welding gun  32 . A camera  33  is arranged close behind the welding gun  32  and provides for photographing of the welding area, in such a way that the welding gun may be positioned correctly. 
     Welding of the inside of the casing may be provided through the gap/opening  14  which afterwards are closed by welding by the robot. As shown, the axis  21  is perpendicular to axes  23  and  24 , axis  36  is perpendicular to axes  24  and  35   
     The welding gun  32  and robot  6  receive power and gas through cables and tubes  40  connected to a welding apparatus  41 . 
     Arranging the welding robot  6  in position for welding is performed manually by means of remote control from a panel  51  which is operated by a person  50  located on a deck  7  over the melting furnace  1 . 
     In the Figures a device is shown for welding cylindrical sections of a casing  12 . The device comprises a clamping ring, shown as a gear rim  9  and a guide  10  in  FIGS. 1 and 2 , and as a three parted ring in  FIGS. 3 and 4 . In other embodiments, the ring may be divided into two more than three parts. The device further comprises a robot  6  attached to the clamping ring by cooperating means, shown as a gear rim on the clamping ring and another gear rim on the carriage  25  in  FIGS. 1-3 . The gear rim on the carriage is driven by a motor  26 , causing the carriage to move along the clamping ring. 
     In the embodiment shown in  FIGS. 1 and 2 , cables  40  run from the robot and carriage to a welding apparatus  41  on the deck, and thus the robot can only rotate one time around the casing  12  before changing direction to return to the starting point, in order to avoid stretch on the cables. Alternatively, the welding apparatus must be moved according to the movement of the carriage. 
       FIGS. 3 and 4  show details of a second and third embodiment of the clamping ring  100 . The ring comprises three parts  100   a ,  100   b ,  100   c , wherein the parts are hinged to each other by way of two hinges  101 , in such a way that the clamping ring has two ends  102 . A bar  103  is arranged between the two ends  102 , being fixed to one end, and attached to a tightening system  104  on the other end. In the shown embodiment the tightening system is only indicated by a circle, but it may be any suitable hydraulic, pneumatic or mechanical system configured to clamp the ring around the section, by reducing the distance between the ends of the ring. 
     When the ring is to be arranged around a casing section, the parts  100   a ,  100   b  and  100   c  are pivoted to enclose the casing  12 , and the bar  103  is inserted into the tightening system  104 . Then the system  104  tightens the ring by reducing the distance between the ends  102  of the ring  100  until the ring is clamped onto the casing sufficiently to carry the load of the robot  6  and/or carriage  25  while following any movement of the casing. If the ring is to be removed from the casing, the steps are repeated in reversed order. 
     In embodiments wherein parts of the ring can not be pivoted in relation to each other, the ring may for instance be lifted above and lowered onto the casing. Once arranged around the casing, it may be tightened as described above. 
     In the embodiments of the clamping ring shown in  FIGS. 3 and 4 , the ring has a thickness T in radial direction and a length L in axial direction, and further an upper  105  and lower  108  peripheral flange, at a distance from the inner edge  106  of the clamping ring being configured to be in contact with the casing. The flanges  106 ,  108  are parallel to the casing and create an upward facing shelf  107 , and a downward facing self (not shown). The carriage is attached to the clamping ring by elements  110  enclosing the upper and lower peripheral flange, and wheels running along the upper and/or lower flange. 
     In the embodiment shown in  FIG. 3 , the clamping ring  100  is provided with a gear rim  9  on the peripheral flange  105 , the gear rim is arranged radially, and facing inwards towards the casing. The carriage is provided with a corresponding gear wheel (not shown) engaging the gear rim  9 . The gear wheel on the carriage is a driving gear wheel, and is driven by a motor (not shown). 
     In the embodiment shown in  FIGS. 4 and 5 , the carriage is provided with wheels  120  being parallel to the shelf  107 , wherein the wheels engage the peripheral flange  105 , and as the wheels rotate, the carriage will move along the clamping ring. 
     In the embodiment shown in  FIG. 5 , the elements  110  which attaches the carriage  25  to the flange  105 / 108 , comprises a first plate  110   a  protruding from the carriage  25  towards the casing, and a second plate  110   b  protruding from a distal end of the first plate towards the shelf  107 . Once the carriage is attached to the clamping ring, the free end of the second plate  110   b  is close to the shelf, and thus the two plates  110   a ,  110   b  enclose the upper  105  respectively lower  108  peripheral flange. The wheels  120  providing movement along the ring  100 , is attached to the upper plate  110   a , and is driven by a motor (not shown). A similar structure may be present to enclose the lower flange  108 . Alternatively, only the upper flange  105  may be present, with the carriage supported by elements  110  extending around the upper flange and further supported against the outward facing surface of the clamping ring by means of a wheel or another supporting element. 
     In an example not shown in the Figures, the lower peripheral flange  108  may also be provided with a gear rim, or the carriage may be provided with wheels engaging the lower flange. 
     When the embodiments shown are to be used to weld cylindrical sections of a casing, the method comprises the following steps
         positioning the clamping ring  100  in relation to the windows of the casing and/or the connection between two adjacent casings sections,   bringing the ends  101  of the ring  100  towards each other in order to tighten the ring,   moving the carriage  25  along the ring  100 , to position the robot correctly at the site of welding, the carriage being moved by powering the driving wheels on the carriage,   welding the sections of the casing, and possibly the ribs  5  of the sections together, while moving the carriage along the ring, and by moving the arms  28 ,  29  and joints  27 ,  30 ,  31  of the robot,   releasing the clamping ring from the casing by bringing the ends  101  apart from each other, in order to reposition the ring at a new welding site.       

     If the ring is not arranged on the casing before the method is to be used, then the ring  100  must be positioned around the casing previously to the first step. 
     The examples above are given to illustrate the invention, and should not be used to interpret the following claims in a limited manner. The scope of the invention is not limited by the examples given above. Modifications and amendments of the invention, being obvious to a skilled person, are also included in the scope of the invention.