Abstract:
The present document describes a machine for compacting a ramming paste inside a gap between cathodes of an electrolytic cell. The machine comprises a guiding rod for providing a static pressure in a longitudinal axis which is coincident with the guiding rod; a vibration generator attached to the guiding rod for providing an oscillatory pressure; and a compaction tool attached to one of the guiding rod and the vibration generator for transmitting the static pressure and the oscillatory pressure to the ramming paste inside the gap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional patent application No. 61/858,972 filed on Jul. 26, 2013. 
     
    
     BACKGROUND 
       [0002]    (a) Field 
         [0003]    The subject matter disclosed generally relates to aluminium production. More particularly, the subject matter disclosed relates to machinery used for lining electrolytic cells in the aluminium production industry. 
         [0004]    (b) Related Prior Art 
         [0005]    The aluminium electrolysis process is crucial in the aluminium production industry. It relies on the use of electrolytic cells or pots in which the reduction of alumina occurs. An essential step called pot lining is critical during the construction of the cell. In order to expand the lifespan of the pot, the pot has to be properly lined. The pot lining usually consists of installing different layers of materials, typically bricks, alumina and carbon blocks which isolate the pot shell, which is made of steel, from the harsh conditions, control the heat balance of the pot and contain the molten aluminium and electrolytic bath. 
         [0006]    Cathode blocks are installed side to side on these bricks, and a gap exists between the cathode blocks. The cathode blocks, in combination with anodes suspended in the electrolyte, allow the electrical current to flow, which is at the heart of the electrolysis process. Cathode blocks are usually made of graphite or other form of carbon. 
         [0007]    The cathode needs to be resistant to leaking, because a leakage of molten aluminium or electrolyte bath under the cathode blocks would reduce considerably the lifespan of the pot. Resistance to leaking is obtained by adding a paste called ramming paste to fill the gap between the cathode blocks. The ramming paste is usually made of a carbonaceous substance, most often anthracite. 
         [0008]    Once the ramming paste is injected in the gap between the cathode blocks, it has to be compacted in order to be fully resistant to leaking. A compaction tool known as a pot ramming machine (or pot lining machine) is used for that purpose, using vibrations or mechanical forces to apply a repeated pressure on the surface of the joint between cathode blocks to compact the ramming paste inside the gap. 
         [0009]    The prior art discloses a compaction tool in which the repeated pressure is applied by an arm which follows an arc of circle shaped motion, which is not optimal with regard to the purpose of the movement. 
         [0010]    There is thus a need for a compaction tool that works using a linear motion to produce the repeated pressure on the surface of the joins, therefore applying a force perpendicular to a surface through the entire stroke to achieve a homogeneously compacted joins at every cross section area throughout the entire pot. 
         [0011]    Generally speaking, the vibration generator is tied to an upper structure (usually a gantry) which allows the compaction tool to translate over all the cathode blocks. However, the vibration generator found in the prior art transmits the vibration to this upper structure, thus reducing the lifespan of the whole system and generating maintenance costs. There is also significant noise generation by operating the prior art vibration generators. Among others, the use of a rubber cushion does not allow a sufficient mechanical decoupling between the compaction tool and the upper structure. 
         [0012]    There is thus a need for a compaction module which is designed to reduce the vulnerability of the upper structure to vibration by decoupling the vibrating compaction tool from the upper structure. 
       SUMMARY 
       [0013]    According to an embodiment, there is provided a machine for compacting a ramming paste inside a gap between cathodes of an electrolytic cell. The machine comprises a guiding rod for providing a static pressure in a longitudinal axis which is coincident with the guiding rod; a vibration generator attached to the guiding rod for providing an oscillatory pressure; and a compaction tool attached to one of the guiding rod and the vibration generator for transmitting the static pressure and the oscillatory pressure to the ramming paste inside the gap. 
         [0014]    According to an aspect, the machine further comprises a gantry, wherein the guiding rod is adapted to be attached under the gantry for support. 
         [0015]    According to an aspect, the guiding rod further comprises a vibration isolation device for decoupling vibrations between the vibration generator and the gantry. 
         [0016]    According to an aspect, the machine further comprises a translation frame between the guiding rod and the gantry to enable translation of the guiding rod with respect to the gantry. 
         [0017]    According to an aspect, the vibration generator attached to the guiding rod is located under the guiding rod. 
         [0018]    According to an aspect, the vibration generator attached to the guiding rod is located above the guiding rod. 
         [0019]    According to an aspect, the vibration generator comprises eccentric weights which are enabled for rotating for providing the oscillatory pressure and which are adjustable manually for varying the oscillatory pressure. 
         [0020]    According to an aspect, the vibration generator comprises vibration isolators for allowing an amplitude of motion and for absorbing vibrations. 
         [0021]    According to an aspect, the machine is enabled for pulling up the guiding rod higher than walls of the electrolytic cell for enabling horizontal translation of the guiding rod over another electrolytic cell without lifting the machine in its entirety. 
         [0022]    According to another embodiment, there is provided a guiding rod for compacting a ramming paste inside a gap between cathodes of an electrolytic cell, the cathodes defining a surface. The guiding rod has a weight and comprises a ram, which is coincident with a pushing axis and which can transmit a force along the pushing axis; a barrel surrounding the ram for confining a pressurized fluid in either an upper pressure chamber or a lower pressure chamber within the barrel; a piston for separating the upper pressure chamber and the lower pressure chamber and for providing the force to the ram when the upper pressure chamber and the lower pressure chamber are at different pressures. 
         [0023]    According to an aspect, the pushing axis is vertical regardless of how the surface of the cathodes is inclined. 
         [0024]    According to an aspect, the pushing axis is normal to the surface of the cathodes. 
         [0025]    According to an aspect, the guiding rod further comprises at least one of bushings and bearings around the ram for providing rotatability of the ram around the pushing axis. 
         [0026]    According to another embodiment, there is provided a method for compacting a ramming paste inside a gap between cathodes of an electrolytic cell. The method comprises providing, using a guiding rod, a static pressure in a longitudinal axis which is coincident with the guiding rod; providing an oscillatory pressure at a vibration generator; and transmitting, with a compaction tool, the static pressure and the oscillatory pressure to the ramming paste inside the gap. 
         [0027]    According to an aspect, using a guiding rod comprises using a guiding rod having a weight, wherein providing a static pressure comprises applying the weight of the guiding rod. 
         [0028]    According to an aspect, using a guiding rod comprises using a guiding rod comprising piston, wherein providing a static pressure comprises applying a force with the piston. 
         [0029]    According to an aspect, using a guiding rod further comprises using a guiding rod having a weight, wherein providing a static pressure comprises applying the weight of the guiding rod. 
         [0030]    According to an aspect, providing an oscillatory pressure comprises rotating eccentric weights for generating a vibration and further comprising manually adjusting a position of the eccentric weights to thereby vary the oscillatory pressure. 
         [0031]    According to an aspect, the method further comprises horizontally translating the guiding rod over the cathodes of the electrolytic cell for compacting a ramming paste inside another gap. 
         [0032]    According to an aspect, the method further comprises pulling up the guiding rod higher than walls of the electrolytic cell for enabling horizontal translation of the guiding rod over another electrolytic cell without lifting all mechanical components used in the method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
           [0034]      FIG. 1  is a side view illustrating a pot ramming machine found in the prior art; 
           [0035]      FIGS. 2A to 2C  are perspective views illustrating a pot ramming machine in various contexts according to an embodiment; and 
           [0036]      FIGS. 3A to 3E  are cross sections illustrating the pot ramming machine of  FIGS. 2A to 2C  in various contexts. 
       
    
    
       [0037]    It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
       DETAILED DESCRIPTION 
       [0038]    In embodiments described herein there is disclosed a ramming machine for lining an electrolysis cell, for example an electrolytic cell used in the aluminium production industry. 
       Definitions 
       [0039]    An electrolytic cell, also known as a pot, is a container used in the aluminium production. Among others, the electrolytic cell or pot comprises a pot shell as an envelope, electrodes, a heated electrolytic bath for containing alumina, and molten aluminium produced by the electrolysis. The electrodes comprise an anode suspended in the electrolytic bath and a cathode in the bottom of the shell. 
         [0040]    The cathode is made of carbon that lies in the bottom of the cell. For practical reasons, the cathode usually comprises a plurality of blocks called cathode blocks. 
         [0041]    Having a plurality of cathode blocks creates a gap between each cathode block. The gap width may range between 40 mm and 300 mm, for example. If not properly compacted, the molten aluminium or the electrolytic bath will leak and reach the steel shell, thus deeply damaging this part of the cell, which will stop working. This is why the gap has to be filled with a paste called ramming paste or seam mix. 
         [0042]    The ramming paste is a carbonaceous paste which has a basis of anthracite and uses pitch as a binder. The composition ensures that the paste can achieve its function, but the step of compacting the gap filled by such a substance is quite exhausting for the user/operator and does not give consistent results if performed manually, thus requiring a pot ramming machine (if done manually, a pneumatic compaction tool would be used). 
         [0043]    The compaction tool is a solid surface or volume that is used to press on the ramming paste to compact it. 
         [0044]    The process of compacting the ramming paste in the gaps between the cathode blocks is named in various ways, such as: electrolytic cell lining, pot lining, electrolytic cell ramming or pot ramming. The machine used for such performing this task is named in various ways, such as: cell lining machine, pot lining machine, electrolytic cell ramming machine or pot ramming machine. 
         [0045]    Referring now to the drawings, and more particularly to  FIG. 1 , a side view illustrates a pot ramming machine found in the prior art. The bottom of the cell under construction is showed with the plurality of cathode blocks  210 , which are separated by gaps  215 . The prior art compaction tool  100  is shown compacting the ramming paste (not shown) in the gaps  215 . The arc of circle shaped motion  110  of the prior art compaction tool  100  is suggested. 
         [0046]      FIGS. 2A to 2C  are perspective views illustrating the pot ramming machine  200  in use (with the electrolytic cell and with the floor in  FIG. 2A , without the cell and without the floor in  FIG. 2B , and with the electrolytic cell but without the floor in  FIG. 2C ). In an electrolytic cell bottom  218 , the cathode blocks  210  can be seen, separated by the gaps  215 . The compaction tool  340  lies above the gaps  215 , ready for compaction. The compaction tool  340  is maintained by a guiding rod  300  (shown in a simplified view), which is described more thoroughly hereinbelow in relation with  FIGS. 3A to 3E . The guiding rod  300  and compaction tool  340  assembly is suspended over the plurality of cathode blocks  210  using a gantry  350 . The gantry  350  may be replaced by any type of frame or a structure that is known by a person skilled in the art to be able to hold the compaction module  305  in place. The guiding rod  300  and compaction tool  340  assembly is attached to the gantry  350  with a translation frame  352  holding the guiding rod  300 , with the sides of the translation frame  352  lying on the gantry  350 . Rail wheels  354 , attached to the translation frame  352 , allow the translation frame  352  to translate on the gantry  350  in the direction of the beams (or rails) that make up the gantry  350 . The gantry  350  can also translate in another direction on a static rail  220 , using gantry rail wheels  222 . A user  250  may supervise the operation or operate the pot ramming machine  200 . 
         [0047]    With regard to  FIGS. 3A to 3E , there are illustrated cross sections of the pot ramming machine  200  in various orientations or with/without a user  250  or electrolytic cell. The translation frame  352  is shown holding the guiding rod  300  and lying on the gantry  350 , with the use of rail wheels  354  to allow translation of the translation frame  352  on the gantry  350 . The rail wheels  354  could be replaced by any other translation enabling device. A user  250  may operate the pot ramming machine  200 . At the heart of the pot ramming machine  200  is a compaction module  305 , which provides the necessary forces to compress the ramming paste. The compaction module  305  comprises everything from the guiding rod  300  down to the compaction tool  340 . 
         [0048]    The guiding rod  300  is shown in more detail in  FIGS. 3A to 3E . In the embodiment illustrated in  FIG. 3 , the guiding rod  300  is represented as a double rod pneumatic cylinder. In this embodiment, the guiding rod  300  comprises a cylinder barrel  312  forming its outside portion. The cylinder barrel  312  is held by the translation frame  352 . The cylinder barrel  312  comprises an upper pressure chamber  322  and a lower pressure chamber  324 , these two chambers being separated by a piston  320 . A pressurized fluid is confined in either the upper pressure chamber  322  or the lower pressure chamber  324  within the cylinder barrel  312 . In the longitudinal axis  311  of the cylinder barrel  312  is found a ram  310 , also known as a rod. The ram  310  is a double rod in the illustrated embodiment, but may be any other type of ram known by a person skilled in the art to work in this situation. The ram  310  is coincident with the longitudinal axis  311  (aka a pushing axis). The ram  310  may be over-dimensioned to reduce the strain in the materials caused by the side loading if it occurs. At the top of the upper pressure chamber  322 , between the ram  310  and the cylinder barrel  312 , an upper seal  314  seals the upper pressure chamber  322  and an upper bearing  315  allow rotation around the longitudinal axis  311  of the ram  310 . At the bottom of the lower pressure chamber  324 , between the ram  310  and the cylinder barrel  312 , a lower seal  316  seals the lower pressure chamber  324  and a lower bearing  317  allows rotation. 
         [0049]      FIGS. 3A to 3E  also illustrates how the ram  310  and the cylinder barrel  312  are attached to a cylinder base  336 . The cylinder base  336  is also attached from its bottom to the compaction tool  340  vibration generator  330 , located between the cylinder base  336  and the compaction tool  340 . The vibration generator  330  generates pressure oscillations (which are periodic or intermittent) or any other type of vibration. The vibration generator  330  comprises rotatable eccentric weights  334 . The rotatable eccentric weights  334 , when in rotation, cause unbalance in their own rotational movement and generate a mechanical oscillation of a frequency between 30 and 80 Hz, and an amplitude up to 5 mm in the direction of a longitudinal axis  311 . The rotatable eccentric weights  334  are adjustable manually as to their relative position for varying (increasing or decreasing) the oscillatory pressure. The vibration generator  330  further comprises vibration isolators  332  (aka a vibration isolation device) to absorb vibrations and allow amplitude of motion. 
         [0050]    The compaction may have to be done over an inclined surface (e.g. when compacting the peripheral gap between the cathode blocks and the shell). The compaction tool  340  is thus interchangeable to allow the use of an inclined compaction tool (not shown), or a compaction tool  340  adapted for the dimensions of the gaps  215  that are being rammed. The dimensioning of the guiding rod  300  is made to allow compaction when the compaction tool  340  is inclined; it is why the ram  310  is oversized for compacting on a flat surface, as mentioned hereinabove. 
         [0051]    The guiding rod  300  embodied as a pneumatic cylinder, in this example, is able to transmit a static pressure to the compaction tool  340 , or a pressure varying substantially linearly with time, whereas the vibration generator  330  adds an oscillatory movement and pressure. Both these components of the pressure function help the ramming paste to be compacted properly in the gaps  215 . The static pressure is provided in a longitudinal axis  311  which is coincident with the guiding rod  300  (i.e., the longitudinal axis of the guiding rod  300  and the longitudinal axis in which the static pressure is provided are coincident). 
         [0052]    In order to prevent the vibration to be transmitted to the gantry  350 , it is preferable to decrease the pressure in the upper pressure chamber  322  and in the lower pressure chamber  324 . 
         [0053]    For instance, according to an embodiment, the upper pressure chamber  322  and in the lower pressure chamber  324  are both deleted from the design. In this case, there is no need for the piston  320 , and what would stay in the design is a vertically positioned ram acting as the guiding rod  300 , just like the ram  310 . The ram  310  that is used may have a weight that is sufficient to compact the ramming paste, therefore, there is no need for a pneumatically powered ram in such an embodiment. 
         [0054]    According to other embodiments, the guiding rod  300  is a hydraulic cylinder or a single rod cylinder. 
         [0055]    More generally, any type of ram known by a person skilled in the art could work. Preferably, the ram  310  would be a vertically positioned ram, although it is possible to use an inclined ram (not shown) to apply pressure on an inclined surface. In all cases, the movement of the ram  310  is linear and follows the longitudinal axis  311  collinear with the ram  310 . The section of the ram  310  may also have any shape, although a circular shape is preferred if bushings or bearings are to be used to provide rotation. 
         [0056]    The movement of the ram  310  is one-dimensional in the longitudinal axis  311 . It may also rotate around the longitudinal axis  311 . It may therefore achieve its function in a more efficient and simple way than what is found in the prior art (for example what is shown in  FIG. 1 ). 
         [0057]    According to an embodiment, the guiding rod  300  may have enough stroke to allow the pot ramming machine  200  to be entirely pulled above the electrolytic cell walls and thus be transferred on another electrolytic cell under construction with no more equipment than what is described in  FIG. 3 , a feature not found in the known prior art, with the electrolytic cell located under the floor level (the top of the cell under construction is usually flush with the floor level). 
         [0058]    Moreover, it should be noted that the design of the pot ramming machine  200  illustrated in  FIG. 3  has the advantage of reducing the noise and the vibrations transmitted to the gantry  350  by comparison with the prior art. Since the guiding rod  300  lies between the vibration generator  330  and the gantry  350 , its mass is able to absorb the vibration that would be transmitted to the gantry  350 , and since it is free to move vertically (not mechanically connected), the force transmissibility is almost non-existent. Thus the guiding rod  300  helps in reducing the maintenance needs when compared with those of the guiding rods in the prior art. The vibration isolators  332  also contribute to the vibration attenuation. 
         [0059]    While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.