Abstract:
The invention relates to a service module for factories producing aluminium by fusion electrolysis. The turret ( 9 ) of the inventive service module ( 7 ) is provided with a determined tool set, wherein each tool ( 101, 102, 103 ) is mounted on a telescopic arm ( 111, 112, 113 ) which is fixed to the turret ( 9 ) by a hinge support ( 121, 122, 123 ) which enables said telescopic arm to be perpendicularly movable with respect to a determined hinge point without rotating around the main axis thereof. Said telescopic arms are interconnected by a mechanical connection device ( 200 ) which maintains the relative angular deviation between the perpendicular movements thereof within a given tolerance range. Said invention makes it possible to bring the tools closer without striking each other during the use thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to aluminium production by fused bath electrolysis by the Hall-Heroult process. It is related particularly to pot tending modules used in aluminium production plants. 
       STATE OF THE ART 
       [0002]    Aluminium is produced industrially by fused bath electrolysis in electrolytic cells using the well-known Hall-Heroult process. Plants contain a large number of electrolytic cells arranged in line in buildings called electrolysis halls or rooms and are electrically connected in series using connecting conductors. The cells are usually arranged so as to form two or several parallel lines that are electrically connected to each other by end conductors. 
         [0003]    The operation of an aluminium reduction plant requires work on electrolytic cells, particularly including replacement of spent anodes by new anodes, tapping of liquid metal in cells and tapping or addition of electrolyte. In order to do this work, the most modern plants are equipped with one or several pot tending assemblies including a travelling crane that can be translated above the electrolytic cells, and along series of cells, and one or several pot tending machines each comprising a trolley and a pot tending module provided with handling and working devices (often called “tools”) such as shovels and hoists and that can be moved on the travelling crane. These pot tending assemblies are often called PTA (Pot Tending Assembly) or PTM (Pot Tending Machine). 
         [0004]    Electrolytic cells are arranged to be as close to each other as possible and close to one of the sides of electrolysis halls and the narrowest possible circulation aisle is arranged close to the other side of the halls, so as to optimise the space in the electrolysis halls and to reduce investment costs. This arrangement makes it necessary for the distance between the walls of the electrolysis hall and the limits of the working area of each of the pot tending tools to be as small as possible, particularly to access electrolytic cells. This is called the “tool approach”. The position of cells in the electrolysis hall and the total surface area of the halls resulting from it are very dependent on the volume occupied by pot tending machines and the possibilities of approach and movement of their tools. However, known pot tending modules occupy a large volume that makes it impossible to get close to the sides of electrolysis halls, particularly the lateral sides, and which significantly reduces their movements close to these sides. The volume of the modules may be reduced by moving the tools closer to each other. However, this solution significantly increases risks of damage to the tools during maintenance operations. 
         [0005]    Therefore, the applicant searched for pot tending assemblies capable of avoiding these disadvantages. 
       DESCRIPTION OF THE INVENTION 
       [0006]    An object of the invention is a pot tending module that can be used in a plant for the production of aluminium by fused bath electrolysis and including a frame that can be fixed to a trolley and a turret installed on the frame so as to be able to pivot about a vertical axis A during use and equipped with a plurality of handling and working devices, and characterised in that it comprises a determined set of tools, in that each tool in the said set is mounted on a telescopic arm fixed to the turret through an articulated support that enables pendular movements of the telescopic arm with respect to a determined articulation point while preventing rotation movements of the telescopic arm about a reference axis, called a “principal axis” associated with this telescopic arm, and in that the telescopic arms of the determined set of tools are connected to each other through a mechanical connecting device capable of maintaining the relative angular difference between the pendular movements of the telescopic arms within a determined tolerance range. 
         [0007]    The applicant had the idea of allowing pendular movements of support means of some tools with no rotation to give these tools a positioning freedom which does not change their basic orientation, and to synchronise these pendular movements while limiting the independence of their movement (due to the said determined tolerance range) which prevents them from hitting each other, but without rigidly connecting them to each other. In particular, the said flexibility prevents shocks applied to one of the tools from directly being passed on to other tools in the set. 
         [0008]    Thus, the pot tending module according to the invention can be compact and flexible so that close approaches can be made with tools protected against large accidental forces. The invention avoids the disadvantages of a rigid attachment on the turret, which increases the risks of damage by a false manoeuvre. 
         [0009]    The determined assembly of tools typically includes at least one tool chosen from among crust shovels, anode handling clamps and crust breakers. 
         [0010]    Another object of the invention is a pot tending machine including a trolley and a pot tending module like that described above. 
         [0011]    Yet another object of the invention is a pot tending assembly for a plant for the production of aluminium by fused bath electrolysis comprising a travelling crane and at least one pot tending machine according to the invention. 
         [0012]    Yet another object of the invention is the use of a pot tending assembly according to the invention for work on electrolytic cells intended for the production of aluminium by fused bath electrolysis. 
     
     
         [0013]    The invention is described in detail below with reference to the attached Figures. 
           [0014]      FIG. 1  illustrates a typical electrolysis hall seen in a sectional view intended for production of aluminium and including a pot tending assembly shown diagrammatically. 
           [0015]      FIG. 2  illustrates a simplified and perspective view of a turret of a pot tending module fitted with standard tools. 
           [0016]      FIG. 3  is a perspective view of one embodiment of the connecting device according to the invention. 
           [0017]      FIG. 4  is an underside view showing one embodiment of the connecting device according to the invention. 
           [0018]      FIG. 5  is a perspective underside view illustrating the turret of a pot tending module according to one embodiment of the invention. 
       
    
    
       [0019]    Aluminium reduction plants intended for aluminium production comprise a liquid aluminium production area that includes one or several electrolysis halls  1 . As illustrated in  FIG. 1 , each electrolysis hall  1  comprises electrolytic cells  2  and at least one “pot tending assembly” or “pot tending machine”  3 . The electrolytic cells  2  are normally arranged in rows or lines, each row or line typically comprising more than a hundred cells. The cells  2  are arranged so as to leave a circulation aisle  31  along the electrolysis hall  1 . The cells  2  include a series of anodes  21  fitted with a metallic rod  22  to be used for attachment and electrical connection of anodes to a metallic anode frame (not illustrated). 
         [0020]    The pot tending assembly  3  is used to carry out operations on cells  2  such as anode changes or filling feed hoppers with ground bath and electrolytic cells with AlF 3 . They can also be used for handling various loads such as pot elements, liquid metal ladles or anodes. The invention relates particularly to pot tending assemblies that can be used for anode changes. 
         [0021]    The pot tending assembly  3  includes a travelling crane  4  that can be translated above and along the electrolytic cells  2 , and a pot tending machine  5  comprising a mobile trolley  6  that can be moved on the travelling crane  4  and a pot tending module  7  equipped with several handling and working devices  10  such as tools (shovels, wrenches, crust breakers, etc.). The travelling crane  4  rests on and travels on running tracks  30 ,  30 ′ arranged parallel to each other and to the principal axis of the hall (and the line of cells). The travelling crane  4  can thus be moved along the electrolysis hall  1 . 
         [0022]    The pot tending module  7  comprises a frame  8 , typically a platform, that can be fixed to a trolley  6  and a turret  9  installed on the frame  8  so that it can pivot about a vertical axis A during use. The turret  9  is usually equipped with a balcony or a control cab  19  containing controls that can be used to manoeuvre the module  7  and the said handling and working devices  10 . The tools are usually all on the same side of the turret  9 , namely the side below the turret during use. 
         [0023]    In the example illustrated in  FIG. 2 , the turret  9  is equipped with a crust shovel  101  an anode handling clamp  102  and a crust breaker  103 . These tools are intended for operations to change anodes in electrolytic cells. In these operations, the crust breaker  103  breaks the alumina and solidified bath crust that usually covers anodes in the cell, the crust shovel  101  is used to clear the place of the anode after the spent anode has been removed, by removal of solid materials (such as pieces of crust and alumina) that are located in it, and the anode handling clamp  102  is used to grip and manipulate anodes by their stem, particularly for the removal of spent anodes from an electrolytic cell and for placement of new anodes in the electrolytic cell. The anode handling clamp  102  may be associated with an anode connectors handling clamp  102   a.    
         [0024]    The turret  9  may also be equipped with other tools, such as a second anode handling clamp  104 , possibly associated with a second anode connector handling clamp  104   a , an alumina or ground bath feed device (not illustrated) including a retractable duct (not illustrated) or a hoist (not illustrated). 
         [0025]    The turret  9  of a pot tending module according to the invention is fitted with a determined set of tools  101 ,  102 ,  103 , to which one or several other tools can possibly be added. In the example embodiment illustrated in  FIG. 5 , the determined set of tools consists of the crust shovel  101 , a first anode handling clamp  102  and a crust breaker  103 . 
         [0026]    Each tool in the set is mounted on a telescopic arm  111 ,  112 ,  113  fixed to the turret by an articulated support  121 ,  122 ,  123  that enables pendular movements of the telescopic arm about a determined articulation point P 1 , P 2 , P 3  while preventing rotation movements of the telescopic arm about its principal axis A 1 , A 2 , A 3 . The articulated supports  121 ,  122 ,  123  are typically chosen from among ball joints, universal joints and prestressed springs. Within the framework of the invention, it is advantageous to use universal joints since they are simple. Articulated supports  121 ,  122 ,  123  may be fixed to telescopic arms by any known means such as sleeves  1221 ,  1231 ,  1241  or end pieces  1212 . As illustrated in  FIG. 3 , the articulated supports  121 ,  122 ,  123  may be offset laterally with respect to the principal axis A 1 , A 2 , A 3  of the telescopic arms  111 ,  112 ,  113 . 
         [0027]    The telescopic arms  111 ,  112 ,  113  of the determined set of tools are connected to each other through a mechanical connecting device  200  that can maintain the relative angular difference between the pendular movements of the telescopic arms within a determined tolerance range. The said determined tolerance range is ±10°, in other words the absolute value of the angular difference between the principal axes of any two telescopic arms of the said set remains less than 10°. 
         [0028]    Within the framework of the invention, the term “telescopic arm” means any device comprising at least a first member called the “principal member”  111   a ,  112   a ,  113   a , typically a hollow shaft or an elongated frame, and a second number called a “mobile member”  111   b ,  112   b ,  113   b , typically a rod or a hollow shaft that is free to move with respect to the first member along a determined axis, which is usually parallel to the principal axis of the first member. The first member  111   a ,  112   a ,  113   a  will be fixed to the turret. The tool is fixed to the second member  111   b ,  112   b ,  113   b , and usually to one end of it. In the example embodiments illustrated in  FIGS. 3 to 5 , the telescopic arms comprise a first substantially square hollow shaft  111   a ,  112   a ,  113   a  and a second substantially square hollow shaft  111   b ,  112   b ,  113   b  free to slide inside the first hollow shaft; the principal axis of the first and second hollow shafts coincide. The telescopic arm may comprise one or several complementary intermediate members located between the first and second members and that can slide with respect to these members. 
         [0029]    The principal axis A 1 , A 2 , A 3 , A 4  of the telescopic arms  111 ,  112 ,  113 ,  114  will be substantially vertical during use and typically parallel to the first member of the telescopic arms. The principal axis of the first and second members are usually parallel to each other. 
         [0030]    In one preferred embodiment of the invention, each telescopic arm  111 ,  112 ,  113  is fixed to the corresponding articulated support  121 ,  122 ,  123 , by a first member  111   a ,  112   a ,  113   a , typically at one end of it, and the mechanical connecting device  200  is fixed to the first member  111   a ,  112   a ,  113   a  of each telescopic arm  111 ,  112 ,  113  of the said assembly and is located below the said articulation points P 1 , P 2 , P 3  during use. In the example embodiments illustrated in  FIGS. 3 to 5 , the first member  111   a ,  112   a ,  113   a  of each telescopic arm of the determined assembly is a hollow shaft and the mechanical connecting device  200  is fixed to these hollow shafts. 
         [0031]    The connecting device  200  typically comprises a rigid body  210  connected directly or indirectly to each of the said telescopic arms  111 ,  112 ,  113 . The rigid body  210  is typically made of steel (preferably non-magnetic steel). The device may also include connecting elements  201 ,  202 ,  203  rigidly fixed to the rigid body  210  and intended to facilitate assembly of the device and its installation onto the telescopic arms. 
         [0032]    In one advantageous variant of the invention, the connecting device  200  is fixed to the turret, directly or indirectly, by at least one extendable connecting means  301 ,  302  such as an elastic means and/or an actuator. In one preferred embodiment of this variant, the connecting device  200  is advantageously fixed to a frame  310  fixed to the turret by at least one extendable connecting means  301 ,  302 . The frame  310  is advantageously fixed to a stand  300  fixed to the turret  9 . 
         [0033]    Advantageously, the connecting device  200  comprises:
       a first extendable connecting means  301  that runs along a first strain axis C 1  at rest and that is connected directly or indirectly to the said frame  310 , at one end, and to a first telescopic arm  111 , at the other end;   a second extendable connecting means  302  that runs along a second strain axis C 2  at rest, perpendicular to the first strain axis C 1  at rest and is directly or indirectly connected to the said frame  310 , at one end, and to a second telescopic arm  112 , at the other end.       
 
         [0036]    The said first and second extendable connecting means  301 ,  302  are typically connected to the said first and second telescopic arms  111 ,  112  respectively through connecting elements  201 ,  202 . 
         [0037]    In this embodiment, the connecting device  200  advantageously also comprises a rigid body  210  and the said connecting elements  201 ,  202  are also connected to the rigid body  210 . 
         [0038]    Preferably, the said rigid body  210  is also directly or indirectly connected to a third telescopic arm  113 . This connection is typically made by a connecting element  203 . The connection of the device with three separate telescopic arms produces a statically determinable system in which it can be guaranteed flatness of the rigid connecting points  2012 ,  2022 ,  2032  in the rigid body  210 . 
         [0039]    The said extendable connecting means  301 ,  302  are typically chosen from among elastic means (such as springs and prestressed springs), actuators (such as pneumatic, hydraulic or mechanical jacks) and combinations of them. The use of prestressed springs that only enable displacements starting from a predetermined excitation force threshold, can efficiently maintain the said angular difference within the said tolerance range. The use of pneumatic or hydraulic jacks provides a means of giving deliberate movements to the tools and possibly automatically controlling these movements. According to the invention, the elastic means can be used alone or in combination with an actuator (typically placed parallel to the elastic means); similarly, the actuator can be used alone or in combination with an elastic means (typically placed parallel to the actuator). 
         [0040]    The extendable connecting means  301 ,  302  enable a limited movement of telescopic arms intended to keep the relative angular difference between the pendular movements of the telescopic arms within the said determined tolerance range. 
         [0041]      FIGS. 3 to 5  illustrate a preferred embodiment of the invention. In this embodiment, the device comprises a frame  310  fixed to the turret  9  through a stand  300  and a rigid body  210  connected to three telescopic arms  111 ,  112 ,  113  through connecting elements  201 ,  202 ,  203  each having a first articulated connecting point  2011 ,  2021 ,  2031  fixed to the telescopic arms  111 ,  112 ,  113  and a rigid connecting point  2012 ,  2022 ,  2032  fixed to the rigid body  210 . The rigid body  210  is connected to the frame  310  by springs  301 ,  302  perpendicular to each other, that are fixed to the rigid body through first and second connecting elements  201 ,  202  each of which has a second articulated connecting point  2013 ,  2023 . The springs may be replaced by actuators or may be combined with actuators. As illustrated in  FIG. 4 , the device may include one or several complementary connecting rods  201  a between the connecting elements and the telescopic arms, connected through articulated connecting points  2011   a ,  2011   b  and intended to facilitate assembly of the device on the telescopic arms. 
         [0042]    The turret  9  may comprise at least one complementary telescopic arm  114  fixed to the turret  9  through an articulated support  124  and a connecting means between this telescopic arm and one of the other three telescopic arms  111 ,  112 ,  113  or between this telescopic arm and the connecting device  200 . The said connecting means may be elastic (such as a spring) or articulated (such as a connecting rod). Preferably, the articulated support  124  enables pendular movements of the telescopic arm with respect to a determined articulation point P 4  while preventing rotation movements of the telescopic arm about its principal axis A 4 . 
         [0043]    The connecting device  200  can limit the amplitude of pendular movements of the telescopic arms. Thus, the tools can be arranged closer to each other without any risk that they will collide during use. 
         [0044]    It is advantageously possible to associate the connecting device  200  with an inclination detection system fixed onto one of the telescopic arms or to a displacement detector placed on one of the elastic systems (in other words on the said springs or actuators) so that the displacements of the telescopic arms can be known and the motor power supply causing displacement of the tools can be switched off if necessary. 
         [0045]    The pot tending module  7  according to the invention may include a walkway fixed to the said frame  310 .