Abstract:
A drill rod for clearing obstructing material from the interior of a tapping pipe used for evacuation of aluminium from a reduction cell of an aluminium smelter by drilling, wherein the drill rod is flexible, whereby it may drill obstructing material from said tapping pipe, through a bend in the tapping pipe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the cleaning of tapping pipes used in reduction cells of aluminium smelters. 
     2. Prior Art 
     Molten aluminium is tapped from reduction cells in the aluminium smelting industry using vacuum-assisted tapping pipes (also known as tapping siphons or tapping tubes) into either sealed or open crucibles (or ladles). Older-generation tapping pipes, for use with either sealed open crucibles, are usually curved (or otherwise bent) in profile whereas more recent technologies, over the last twenty years or so, normally utilise straight tapping pipes with sealed crucibles. 
     Within the reduction cell (also known as a smelting pot) the molten aluminium is below the molten electrolyte known as bath (which is principally comprised of cryolite). In tapping the aluminium, there is inevitably some pick-up of bath and after several uses a build-up of frozen bath, and some aluminium, is left within the tapping pipes. This renders the tapping pipes ineffective and requires that they be regularly cleaned. 
     Curved tapping pipes have in the past been cleaned using a mechanism known as a pneumatic rattler. This is in the form of a small pneumatic motor with a swiveling head attached to a pneumatic hose, which is fed trough the pipe manually. This is an extremely noisy and dusty operation which is considered unacceptable in today&#39;s smelters. 
     Straight tapping pipes are usually cleaned by automatic tapping pipe cleaning machines which utilise a long straight drill rod with some form of cutter head, rotated by an electric or hydraulic drive, and which is fed forward by an electric, pneumatic or hydraulic mechanism. Some designs of these machines have a longitudinal hole in the centre of the drill rod to allow compressed air to be channelled to the cutter head. This air serves the dual functions of purging debris away from the workface and cooling the cutter head. 
     Problems with automated cleaning of curved pipes have been the requirement to transmit sufficient torque to a cutter head to remove the bath/metal build-up and to be able to channel air to the cutter head. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a drill rod for clearing obstructing material from the interior of a tapping pipe used for evacuation of aluminium from a reduction cell of an aluminium smelter by drilling, wherein the drill rod is flexible, whereby it may drill obstructing material from said tapping pipe, through a bend in the tapping pipe. 
     The invention further provides apparatus for drilling obstructing material from within a tapping pipe of a reduction cell of an aluminium smelter, having: 
     a) means for mounting the pipe substantially fixedly; 
     b) a drilling rod having a cutting head; 
     c) means for rotating the drilling rod for rotating said cutting rod; 
     d) means for axially advancing the drilling rod to cause the cutting head and drilling rod to pass into the interior of the tapping pipe for effecting said drilling, wherein said drilling rod is, over at least a portion thereof adjacent to the cutting head, capable of bending whereby it may, while effecting said cutting, pass through a bend in the tapping pipe. 
     The invention also provides a method for removing material from a tapping pipe comprising passing thereinto a rotating drilling rod having a cutting head whereby to cause the cutting head to clear said obstructing material by drilling, and in which the drilling rod is at least partially bendable, while transmitting cutting torque to the cutting head to accommodate a bend in the pipe. 
     The invention also provides rotary device having links coupled together for rotation about a lengthwise device axis, coupling between an adjacent pair of said links being provided by coupling means which couples the adjacent links together for permitting substantially universal movement with respect to each other transversely to said device axis, the coupling means permitting relative displacement between the adjacent links whereby the axial length presented by the adjacent links can be varied between relatively compressed and relatively uncompressed lengths, the coupling means, when the adjacent links are displaced to the condition where the relatively compressed length prevails, at least relatively limiting the degree of said substantially universal movement permitted as between the adjacent links. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention is further described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a side view of an apparatus constructed in accordance with the invention; 
     FIG. 2 is a partially vertically sectioned view of guide tube assembly and flexible drill rod forming parts of the apparatus of FIG. 1, and an aligned tapping pipe; 
     FIG. 3 is a view like FIG. 2 but showing illustrated components in a different condition; 
     FIG. 4 is a view like FIGS. 2 and 3, but showing illustrated components in a still further condition; 
     FIG. 5 is a side view of part of the flexible drill rod forming part of the apparatus of FIG. 1; 
     FIG. 6 is a fragmentary axial cross-section of the part of the flexible drill rod of FIG. 5; 
     FIG. 7 is a diagram illustrating the manner in which control of the apparatus of FIG. 1 is effected; 
     FIG. 8 is a flow diagram illustrating control functions for regulation of motor drive speed in the apparatus of FIG. 1; 
     FIG. 9 is a flow diagram of control functions implemented during a cycle of operation of the apparatus of FIG. 1; 
     FIG. 10 is a further flow diagram illustrating control functions; 
     FIG. 11 is scrap view corresponding to part of FIG. 5, but showing the flexible drill rod in a different condition; 
     FIGS. 12 and 13 are perspective views of two different coupling elements useful in the flexible drill rod  80 ; and 
     FIG. 14 is scrap partly sectional view off the region “A” marked in FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     The apparatus  10  shown in FIG. 1 is formed of two sub-assemblies, a drill rig assembly  12  and a tapping pipe cradle assembly  14 . Assembly  14  comprises a framework  16  which supports a platform  18  at a location somewhat above ground level. Platform  18  has support elements  20 ,  22 ,  24  for supporting the tapping pipe  26  which is to be cleaned. As shown, the tapping pipe  26  is of curved configuration and, for cleaning, it is supported from beneath by two of the elements, elements  22  and  24 , which may, for example, be in the form of “V” blocks, with the element  20  being upwardly extending from the platform  18  but having a downwardly depending and upwardly open hooked upper end  20   a  which hooks over a forward end of the pipe  26 . After positioning in this fashion, hydraulic rams  28 ,  30 ,  35  mounted on the frame  16  are actuated to press against the pipe  26  at spaced locations therealong so that the pipe  26  is securely pressed against the elements  22 , and a lower portion (not shown) of the element  20 . 
     The positioning of the pipe  26  on the cradle assembly  14  may be effected manually by lifting and placing it in position as described or, alternatively, mechanical arrangements able, for example, to position ones of a number of pipes in succession for cleaning may be used. Although the pipe  26  is shown as a detached unit, in some constructions, the pipe  26  is attached permanently to a lid of a crucible which is used for evacuation of aluminium from the reduction cell. In such cases, the framework  16  may be modified to additionally support the lid. 
     The drill rig subassembly  12  comprises a framework  40 , including an elongate sloping bed  42  which extends linearly from a lower location, spaced away from the cradle assembly  14  to a relatively higher location at which it joins to the frame  16  of the cradle assembly  14 . 
     A carriage  44  is mounted for sliding movement lengthwise with respect to the bed  42 , particularly being slidable along lengthwise extending guide bars  46 , carried by the bed  42  and which extend through sliding bearings on the carriage  44 . In FIG. 1, the carriage  44  is shown at a lower position, that is at a location which is furthest away from the cradle assembly  14 . It may, however, be moved up the inclined bed  42 , on bars  46 , to an upper position, at which the carriage  44  is about half-way along the length of the bed  42 . 
     A drive motor  48  is provided on the bed  42 , which rotationally drives a helically grooved drive shaft  45  of a ball screw assembly for effecting movement of the carriage  44  to and between these positions by engagement with a ball screw nut  47  fixed to the carriage  44  and through which the drive shaft  45  passes. 
     The carriage  44  carries a drive motor  50  which may, for example; comprise a hydraulic or electric motor arranged for driving an elongate shaft  52  via a reduction gear assembly  54 . Shaft  52  is mounted by a bearing  56  such that it can rotate axially about an axis extending in the lengthwise direction of the bed  42 , and somewhat above the bed, while being axially immoveable with respect to the carriage  44 . From the bearing  56 , shaft  52  extends through a bearing assembly  58  mounted on the bed  42  and thence into a guide assembly  60 . As shown in FIG. 2, the guide assembly  60  comprises an outer tube  62  and an inner guide tube  64 . The guide assembly  60  is fixed with respect to the bed  42 , being carried by brackets  65 ,  66 . As described later to tube  64  is mounted for axial sliding movement within the tube  62 , from the position shown in FIG. 1 to axially move forward positions. This movement is effected by actuation of a ram  68  fixed to bed  42  by a bracket  70 , and having its piston rod connected to a downwardly depending bracket  72  fixed to the guide tube  64 . 
     The forward end of the shaft  52  is secured to a forwardly and upwardly extending flexible drill rod  80  which extends into guide tube  64  of guide assembly  60 . In the position of the carriage  44  as shown in FIG. 1, and with the guide tube  64  retracted, the forward end of the flexible drill rod  80  is positioned approximately just within the free outer end of the guide tube  64  which, in this condition, projects somewhat from the guide tube  62 . This condition is illustrated in FIG.  2 . 
     The forward end of the flexible drill rod  80  carries an affixed cutting head  92 . The shaft  52 , drill rod  80  and head  92  together form a drilling assembly  35 , which is rotatable as a unit by motor  50 , and which can be moved back and forth with respect to bed  42  by movement of carriage  44  when motor  48  is operated. 
     Shaft  52  and flexible drill rod  80  are hollow, and head  92  has side openings. Air under pressure derived from a source  31  can, in use of the apparatus, be passed into a hollow conduit extending through the shaft  52 , via a rotary coupling incorporated into the bearing  56  to flow into the hollow drill rod  80  and the interior of the head  92 , to exit from the head  92  via the mentioned openings. Flow is controlled by a purge valve solenoid  33 . 
     The pipe  26  has a portion  26   a  adjacent to the assembly  12  and which is somewhat linear and extends, when the pipe  26  is clamped into position as shown, in axial alignment with the guide assembly  60 , including the outer tube  62  and guide tube  64  as well as the flexible drill rod  80 . 
     Cleaning operation begins, by operating motor  50  to cause the shaft  52  and flexible drill rod  80  to be axially rotated, with carriage  44  in the position shown in FIG.  1 . Then the hydraulic ram  68  is extended causing the guide tube  64  to be advanced so that its end engages the end of portion  26   a  of the pipe  26 , and in this case that the internal passageway of the pipe  26  is more-or-less exactly aligned with the internal passageway of the guide tube  64 . This position of the guide tube  64  is illustrated in FIG.  3 . 
     Following engagement of the guide tube  64  with the pipe  26 , motor  48  is actuated to cause the carriage  44  to advance upwards along the bed  42  to cause the forward end of the flexible drill rod  80 , which carries a cutting head  92 , to enter into the internal passageway of the pipe  26  and to drill from this accumulated material such as bath or the like within the pipe  26 . 
     As drilling begins, air from source  31  as passed through the shaft  52 , drill rod  80  and head  92 , exits from the drill head to facilitate drilling and cleaning of drilled material. 
     After drilling has begun, and the head  92  has been advanced a short distance into pipe  26 , to the position shown in FIG. 3, hydraulic ram  68  is actuated to slightly withdraw guide tube  64  into tube  62 . This condition of the guide tube is illustrated in FIG.  4 . By this, there is a clearance gap between the guide tube and pipe  26 , which facilitates the clearance of drilled material from the pipe  26 . That is, drilled material passing back through the pipe  26  may fall through this gap and be cleared from the pipe  26  and guide tube  64 . 
     Because of the flexible nature of the rod  80 , it is possible to advance the head  92  along the interior of the pipe  26  until it passes entirely therethrough, which condition is shown in FIG.  4 . In this process, material cut from the internal passageway of the pipe  26  passes downwardly to be collected in a bin  98 . After cutting is so-effected, the carriage  44  is moved back again to the position shown in FIGS. 1 and 2, and the motor  50  is stopped so as to complete the process. The pipe  26  may then be removed by releasing the clamping by the hydraulic rams  28 ,  30  and  35  and, for example, manually removing the pipe from the platform  18 . At completion, also, the guide tube  64  is moved back to the position shown in FIGS. 1 and 2. 
     Control of the movements of the various components as shown in FIG. 1 may be effected more-or-less automatically. For example, the motor  48  may be controlled so that the drill rod feed speed is controlled in two modes—high cutting speed for straight sections and low cutting speed for the transition as the cutter head passes through bends. The feed speed may also be controlled via a torque feedback loop from the drill rotation drive motor  50 , such that when the torque increases above a certain preset limit the feed speed is reduced accordingly. Thus, if the torque reaches a critical limit the feed mechanism retracts the drill rod a preset distance and then advances forward again slowly. The control parameters may be set so that the apparatus will retry in this way three times before retracting the drill rod completely. This is usually only necessary if the tapping pipe is blocked with aluminium. 
     The drill rod feed mechanism may incorporate an LVDT (linear variable differential transformer) which detects the position of the drill rod drive assembly, and therefore the movement of the drill rod  80 . If it detects that the drill rod  80  and cutter head  92  are not advancing it initiates the same procedure as outlined above for critical torque 
     When the cutter head has reached the far end of the tapping pipe, which is sensed by the LVDT on the feed mechanism, it is withdrawn until it is completely retracted. As the drill rod  80  is withdrawn compressed air is blown onto it, in the gap between the guide tube and the tapping pipe, to remove any debris which is adhered to the flexible joints in the drill rod  80 . Any carry-over of debris that the air jets fail to remove is collected in a chamber below the rear of the guide tube from where it can be evacuated manually. 
     When the flexible drill rod is completely retracted both the guide tube and the clamps may be automatically retracted. Possible control regimes are described below. 
     FIG. 7 shows some aspects which may be so automatically controlled under the control of central control  100 . This control  100  provides signals to the drive motor  50 , such as to control its speed of operation, to pneumatics for controlling the air flow aforementioned, and to control the clamping operation of the hydraulic rams  28 ,  30 . Control of the motor is facilitated by connecting the motor in the torque feedback arrangement mentioned. The feed screw motor  48  is also controlled from central control  100 . 
     FIG. 8 shows some aspects of control of motor speed during an operation. After initiating operation, at step  120  shown, steps  122 ,  124  are repetitively executed. At step  122  the torque feedback signal from the drive motor  50  is detected. At step  124  the magnitude M of the feedback signal, which is indicative of the magnitude of the applied torque from the motor  50 , is compared with a preset value Ml representing the maximum torque to be applied during operation. In the case that this comparison indicates that the signals are the same, the motor speed control signal is set to maintain motor speed, at the step  126  shown. In the case that the magnitude M exceeds M 1 , motor speed control signal is set to reduce motor speed, at step  128 . In the case where the signal is less than M 1 , the motor control signal is set to increase motor speed at the step  130  shown. In this way, the motor speed may be controlled to maintain efficient cutting. Although not shown in FIG. 8, it is possible to vary the preset M 1  at different stages of the operation, such that, for example, a higher cutting speed is applied at straight sections of the pipe  26  and a lower speed is applied as the cutter is passed through bends in the pipe  26 . Thus, the preset value M 1  may be changed at predetermined points in the cleaning cycle to accomplish this. 
     It is also desirable to control the operation with reference to the movement of the flexible drilling rod  80  through the pipe  26 . FIG. 9 illustrates one method of effecting this, as well as control functions with reference to clamping and operation of the air blast as described. Here, on initiation of operation, and at step  140  as shown, a signal is sent to actuate the hydraulic rams  28  and  30  to initiate clamping, and a signal is sent at step  142  to start operation of the motor  50 . Then signal is sent to actuate the hydraulic ram  68  to extend the guide tube  64  to engage the pipe  26 , at step  142 . At step  144 , signal is sent to start the motors  48 ,  50 . At step  146 , repetitive detection of a position signal S representing the position of the carriage  44 , and thus of the flexible drill rod  80 , is detected. That signal may, for example, be generated by a linear variable differential transformer. At step  148 , repetitive determinations are made as to whether the signal S is indicative that the carriage  44  is at its rest position (ie at the end of a cycle operation). If so, the operation is completed by stopping the motors  48 ,  50  (step  150 ) stopping air blast (step  152 ) releasing the clamping (step  154 ) and retracting the guide tube  64  (step  162 ). If the signal is not indicative of the carriage being at the rest position, repetitive comparisons are made as between the signal S, and a preset value S 1 , where S 1  represents the extreme forward position of the carriage  44  and flexible drill rod  80 . If this comparison indicates that the signal S is less than a preset value S 1 , representing full travel of carriage  44 , the signal S is stored as a stored value S 2 , at step  156 . Then, repetitive comparisons are made (step  158 ) as to whether the stored value S 2  is the same as, or substantially the same as the current value S. If so, motors  48 ,  50  are stopped at step  150 , this corresponding to a case where no movement of the carriage and cutter head  92  is occurring. Although not illustrated, an automatic sequence may then be executed to attempt several times to re-initiate drilling, with the drilling only being finally ceased after, say, three unsuccessful attempts, as mentioned earlier. In the event that the comparison indicates that position signal S has reached the preset signal S 1 , that is that the flexible drill rod  80  has reached its fully extended position, motor control signal is set at step  160  to reverse the motor  48  so as to retract the carriage  44  to its rest position so pulling the flexible drill rod  80  from the pipe  26  and retracting it back into the assembly  60 . A cleaning operation (step  164 ) may likewise be effected. 
     Of course, more complex regimes man above-described may be utilised. As mentioned, it has been found advantageous, for example, to slightly retract the guide tube  64  from the pipe  26  after commencement of drilling, in order to provide a clearance space for the ejection of material cut by the cutting head. In that case, a comparison may be made of the signal S as mentioned with a farther preset S 3  to send a signal to effect operation of the cylinder  68  for so moving the guide tube  64  when that comparison shows that the cutting head has moved a desired predetermined distance into the pipe  26 , so as to effect slight reverse movement of the guide tube  64 . 
     During retraction, compressed air may continue to be blown into the guide tube  64  so as to blow debris accumulated on the drilling rod from this for removal, as the drilling rod is retracted into guide tube. The debris may be removed at the lowermost end of the tube  64 , that is the end furthest away from the unit  14 , and caught in a hopper  82   
     FIG. 10 summarises the steps mentioned in FIG. 9, and also indicates further respective steps  193  of determining if the end of travel of the carriage  144  has been detected. If no travel is detected on three successive detections speed of motor  50  is reduced, motor  48  is reversed and an air blast is activated (step  148 ). If there is no movement of motors  48 ,  50  (step  150 ) the system stops and an alarm is raised. If no carriage motion is detected on two successive detections, motor  48  is first activated in reverse and then forwardly (step  175 ,  179 ). 
     The flexible drill rod  80  may be formed of a plurality of lengthwise spaced interconnected links  180  which define, in the axially extending condition of the drill rod, a substantially continuous cylindrical outer surface, but which nonetheless permit some degree of universal flexibility as between adjacent links. FIG. 5 shows the drill rod  80  as being formed of a plurality of such links  180 . Each link has a central generally cylindrical portion  182 , and first and second pairs of lugs  184 ,  186  extending to opposite axial sides thereof. The pair of lugs  184  extend in generally parallel relationship as do the lugs  186 . Viewed axially, however, the lugs  184  are displaced with respect to the periphery of the link  180  by 90°. The pair of lugs  184  has aligned openings  188  and the pair of lugs  186  has a similarly arranged aligned openings  190 . A common transverse axis of the openings  190 , which passes through the longitudinal axis of the link  180  is arranged, accordingly, at 90° to a common transverse axis of the openings  188 , which axis likewise extends through the lengthwise axis of the link  180 . The links  180  are arranged so that lugs  184  extend in one axial directional sense and lugs  186  in the opposite directional sense, with respect to the lengthwise axis of the rod  80 , with the transverse axes of the openings  190  in one link  180  being at the same lengthwise location along the length of the rod as the transverse axis of the openings  188  of the adjacent link  180 , and with those axes being at 90° to each other. As best shown in FIG. 6, a somewhat cubical coupling element  192  is positioned within a generally cubical space bounded by each pair of lugs  184  of one link  180  and the lugs  186  of the adjacent such link. Coupling elements  192  have openings  196  in four peripheral faces, and locking pins  194  extend through the openings  188 ,  190  of the adjacent lugs so as to pass into openings  196  so as to pivotally connect lugs  184 ,  186  with the coupling elements  192 . By this means, universal movement as between the adjacent pairs of links  180  is possible, about the transverse axes as mentioned. The pins  194  may be secured to the lugs  184 ,  186 , such as by welding. 
     As shown in FIGS. 5 and 12, the openings  196  in each coupling element  192  are elongate in the axial direction of the flexible drill rod  80 , so that relative movement between the links  180  and the coupling elements, and thus between adjacent links  180  is possible, with the pins  194  being variably positionable within the openings  196 . In the condition shown in FIG. 5, the pins are displaced relatively rearwardly in the openings  196 . FIG. 11 shows a condition where the links  180  are moved apart in the axial direction of the flexible drill rod until the pins  194  approach forward ends of openings  196 . By this arrangement when axial compressive force is applied to the flexible drill rod it assumes the condition shown in FIG. 5, but is otherwise free to assume the condition shown in FIG.  11 . In the compressed condition rear transverse surfaces  209  of the links  180  are firmly pressed against forward transverse surfaces  207  of the following links  180 . Surfaces  207  are between the keys  184  of the links. In this compressed condition, the links are substantially locked as a rigid unit so that the flexible drill rod  80  is rendered to a rigid linear configuration. When, however, the links are in the extended condition of FIG. 11, the flexible drill rod is capable of bending via its universal joints, as provided by the coupling elements  192  and interconnecting pins  194 . That is, the links are capable of universal movement with respect to each other. The degree of permitted movement is, however, limited by bringing together of incline end surfaces  211  of the links  180  with the adjacent surfaces  207 , at limit bending positions of adjacent links  180 . 
     As shown in FIG. 5, the links  180  and coupling elements  192  have respective openings  200 ,  202  therethrough, and these are axially aligned so as to provide an inner axial passageway extending opening through the rod  80  and which may receive a flexible compressed air conduit  216  for directing compressed air to the head  92  as previously mentioned. This air conduit may communicate with another conduit in an aligned passageway in shaft  52  which extends back to a location adjacent bearing  56  on carriage  48 . The bearing may include a rotary coupling for admission of air into the conduit  216 . 
     The head  92  may be of the form as shown, having a somewhat conical configuration with cutting teeth  204  thereon. The head may have openings  206  through which air delivered from the drill rod  80  exits. 
     The drill rod  80  may be connected to shaft  52  in any convenient way, such as by mating screw threads  219 , 221  (FIG.  11 ). 
     The flexible drill rod  80  may be of various different styles depending on the profile of the tapping pipe. It is generally desirable to form the drill rod as a series of flexible joints with holes drilled axially through each of the components known as universals and journals, as above described. Through these holes a conduit is, as described, passed from one end of the flexible drill rod to the other for the purpose of conveying compressed air to the cutter head. 
     It will be appreciated that, since the flexible rod  80  is variable in length, the end of the conduit  216  should not be fixed with respect to shaft  52 . As shown in FIG. 14, the end of the conduit  216  which is enclosed within the end of the shaft  52  may be attached to a fitting  235  which incorporates an externally sealing O-ring seal  237 . The fitting  235 , which acts as a piston, is free to move backwards and forwards within a chamber machined  239  into the end of the straight drill rod. This ensures that the opposite end of the conduit remains engaged with the cutter head. 
     The described forming of coupling elements  192  of the flexible drill rod with elongate openings  196  to receive the pins  194  allows it to better bend where required and act as a solid drill rod if pushed together in a straight configuration. This may be used for tapping pipes  26  which have two straight lengths with an angular bend between. However, FIG. 13 shows an alternative coupling element  250  having round openings  252  instead of the elongate openings  196 . In this case, movement of the links  180  and coupling elements  250  the flexible drill rod is substantially precluded, so the flexible drill rod has more limited bending capacity. 
     The style of flexible drill rod described in FIGS. 5 and 6 is particularly useful for tapping pipes with several bends or with a continuous or near-continuous curvature. 
     The universals, journals and pins may be manufactured from alloy steel and are heat-treated to achieve high strength and, in the case of the universals, good wearing characteristics. 
     Of course, the apparatus  10  may be varied to accommodate particular forms of pipe  26 . For example, the bed  42  need not necessarily by inclined. 
     The described arrangement has been advanced merely by way of explanation any many modifications may be made thereto without departing from the spirit and scope of the invention which includes every novel feature and combination of novel features herein disclosed.