Abstract:
An arrangement for conveying plates ( 4 ) in particular mother plates with or without a deposited metal layer, in an electrolytic metal refining plant, wherein the plates are intended to be conveyed in the conveyor arrangement ( 25, 50 ) along at least one horizontal conveyor path with the plates orientated generally vertical and equidistant from one another therealong, characterized in that the conveyor arrangement is of the walking beam kind and includes fixed supports ( 28, 54 ) and at least one walking beam ( 30, 62 ) having movable supports ( 31, 67 ), wherein the walking beam is arranged to move in a cyclic pattern, including a lifting movement in which all the plates conveyed along the path are lifted by the movable supports from their fixed supports in a first position, a forward movement in which all plates are advanced simultaneously one step while resting on their movable supports, a lowering movement in which the plates are placed on fixed supports in a new, second position, and a return movement, wherein the length of one step corresponds to the plate spacing (PI; PII) along the path.

Description:
FIELD OF INVENTION 
     The present invention relates to an arrangement for conveying plates, particularly mother plates, with or without deposited metal layers, in a plant for electrolytically refining metals, in which arrangement the plates are intended to be conveyed along at least one horizontal conveyor path while positioned generally vertically and equidistantly in the conveyor path. The invention also relates to a conveyor line which includes two horizontal and mutually perpendicular conveyor paths, wherein an inventive conveyor arrangement is disposed along each conveyor path. 
     DESCRIPTION OF THE BACKGROUND ART 
     In the electrolytic refinement of copper and certain other metals, metal layers are deposited on both sides of so-called mother plates which hang vertically from a horizontal rod, hereinafter called the yoke, having laterally and outwardly projecting parts which form electric contact means for the passage of electric current during the electrolysis process. The plates hang in mutually parallel and equidistant relationship in the tank. Subsequent to the refined metal having been precipitated to a desired thickness onto both sides of the mother plates, the mother plates with their metal layers deposited are moved batch-wise to a plant for further treatment. A primary operation in this plant is to strip the deposited layers from the mother plates. The plates are first advanced along a first horizontal path in the stripping and conditioning plant in their transverse direction. The plates are then transferred to a second path, in which they are conveyed in their longitudinal direction. The actual stripping operation is carried out in this second path. The mother plates are then transferred to a third path which extends parallel with the first path and along which the plates are again advanced in their transverse direction. 
     In the technique used at the present time, this technique having been practised for a very long time, the plates are normally moved along all three horizontal conveyor paths on chain conveyors or other types of endless conveyors. Conventional endless conveyors are also used in other mother plate treatment plants, e.g. plate washing or plate alignment plants, etc. SE 81013427, SE 329011, U.S. Pat. No. 4,577,401 and U.S. Pat. No. 4,069,925 disclose examples of this type of arrangement for conveying mother plates with or without deposited metal layers in conjunction with the pre-treatment or after-treatment of the mother plates in conjunction with the electrolytic refinement of metals. 
     A significant drawback with endless conveyors used in this technical field, normally chain conveyors, is that they are very expensive. This is mainly due to the harsh working environment of the conveyors. For instance, it is necessary to manufacture the chains and also support wheels and other devices from acid-proof steel, at least along parts of the conveyor line. The expensiveness of chain conveyors in this type of plant is also contingent on the necessity to manufacture bearings, bushes and the like from a special material. Another drawback with such conveyors is that they require the provision of separate devices for switching the plates from one conveyor path to another. In the absence of better conveyor arrangements, chain conveyors or other continuously working conveyors are still used in plants of the aforesaid kind in spite of these drawbacks. 
     It is also known to convey mother plates in their transverse direction with the aid walking beam conveyors. In this known technique, the plates hang from longitudinally extending rails on lugs which form electric contact devices on the plates in the electrolysis process. The plates are advanced with the aid of the walking beam conveyors with the platecarried contact lugs resting on said rails. One significant drawback with this method is that the lugs are subjected to a high degree of wear due to sliding on the carrier rails. Another drawback is that the rails do not indicate distinct plate positions as the plates are stepped forwards to new positions. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide an improved conveyor arrangement. More particularly, it is an object of the invention to provide a conveyor arrangement which does not require the use of endless conveyors, such as chain conveyors. A further object is to provide a conveyor arrangement which operates in a manner in which those surfaces which are to conduct current to the plates in the electrolysis process will be subjected to the minimum of wear. Another object of the invention is to provide conveyor arrangements which do not utilize endless conveyors for conveyor the plates in their transverse and longitudinal directions. In those cases in which the plant includes a conveyor line having two or more mutually perpendicular conveyor paths, as is often the case in plants of this kind, and in which the plates are switched from one conveyor path to the other, a further object of the invention is to provide conveyor arrangements which do not require separate devices for switching the plates from one conveyor path to the next conveyor path in said conveyor line. 
     These and other objects can be achieved with a conveyor arrangement in the form of a walking beam conveyor which includes fixed supportive devices and at least one walking beam having movable supportive devices, wherein the walking beam is arranged for movement in a cyclic pattern that includes a lifting movement in which all plates conveyed along the path are lifted by the movable supportive devices from their fixed supports in a first position, a forward advancing movement in which all plates are advanced simultaneously through one step or increment while resting on their movable supports, a lowering movement in which the plates are placed on fixed supports in a new position, and a return movement, wherein the length of the step corresponds to the plate spacing along the path. 
     Further aspects of the invention will be apparent from the following Claims and also from the following detailed description of an exemplifying embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail with reference to the accompanying drawings, in which 
     FIG. 1 illustrates a plant for treating mother plates that have been coated electrolytically with metal layers in an electrolysis process; 
     FIG. 2 is an enlarged view taken on the line II—II in FIG.  1  and shows the initial and terminating parts of a first conveyor path for conveying plates in their transverse direction, and shows an initial part of a second conveyor path at right angles to the first conveyor path, wherein the plates are conveyed in their longitudinal direction in said second conveyor path; 
     FIG. 3 is a view taken on the line III—III in FIG. 2; 
     FIG. 4 is a view taken along the line IV—IV in FIG.  2  and seen from above; 
     FIG. 5 is a view in still larger scale taken on the line V—V in FIG. 4; 
     FIG. 6 illustrates certain parts of the arrangement in the direction of the arrow VI in FIG. 3, in the same scale as in FIG. 5; 
     FIGS. 7A and 7B, collectively referred to as FIG. 7, present a side view taken on the line VII—VII in FIG.  1  and illustrate the first conveyor arrangement, a third conveyor arrangement and the initial and terminating parts of a second conveyor arrangement; 
     FIG. 8 is a view taken on the line VIII—VIII in FIG. 7; 
     FIGS. 9A and 9B are views taken on the line IX—IX in FIG. 7 showing the second conveyor arrangement in two different positions; 
     FIGS. 10A and 10B are views taken on the line IX—IX in FIG. 1, showing the conveyor arrangement in two different advance positions; and 
     FIG. 11 is a perspective view of part of the second conveyor arrangement with its movement devices shown in still larger scale. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Description of the arrangement 
     With reference first to FIG. 1, three conveyor paths are identified generally by reference numerals  1 ,  2  and  3  respectively. The three conveyor paths  1 ,  2  and  3  together form an integrated conveyor line. The conveyor path  1  forms an infeed path for plates generally referenced  4 , these plates being advanced in the direction of the arrow  5  perpendicular to the plane of the plates. The path  2  advances the plates in their longitudinal direction. This conveyor path includes a receiving station  6 , a preparatory stripping station  7 , a separating station  8  where the coating layers  20  (FIGS. 2 and 3) are separated from the mother plates  21 , an inspection station  9  and an offloading station  10 . The plate treatment equipment in stations  7 ,  8  and  9  forms no part of the present invention and will not therefore be described in detail here. This also applies to a washing unit  11  in the first path  1  and to apparatus  12  for treating the bottom edges of the mother plates in the third path  3 . 
     The plates  4  comprise typical, essentially square mother plates  21  which are coated on both sides thereof with a coating layer  20 . The mother plate  21  is fastened to and hangs from a horizontal rod  22 , hereinafter referred to as the yoke, the two end-parts  23  of which project out beyond the side edges of the plate  21 , these end-parts  23  being referred to as lugs in the following description 
     A first conveyor arrangement for conveying the plates  4  along the first conveyor path  1  is generally referenced  25  in FIGS. 2-4. Fixedly mounted on each long side of a stand  26  is a longitudinally extending rail  27  which carries a longitudinally extending support strip  28  having recesses  29  for accommodating the lugs  23  on the yoke  22 . The spacing PI between the recesses  29  is equal to the spacing between the plates  4  in the electrolysis bath and equal to each walking step of the first conveyor arrangement  25 , as hereinafter described. The strips  28  are formed of a lug-friendly plastic material and form electric contact surfaces in the electrolysis process. The plastic strips  28 , or more specifically the recesses  29 , form fixed supports for the plates  21  in the first conveyor arrangement  25 . The right-hand part of FIG. 2, the left-hand part of FIG.  3  and FIGS. 5 and 6 show the lugs  23  resting on said fixed supports in the recesses  29 . 
     A pair of longitudinally extending, parallel walking beams arranged parallel with and outwardly of respective fixed supports  28  have been generally referenced  30 . Each comprises a plastic strip  31  of the same configuration as the fixed support strip  28 , attached to a metal guide rail  32  having a cross-section in the form of an inverse U. The plastic strip  31  includes recesses  33  which define the movable supports of the conveyor arrangement and which have the same configuration and same spacing as the recesses  29  in the fixed support strip  28 . 
     FIGS. 5 and 6 show a walking beam  30  in its lower position in which the beam rests on a plastic slide rail  34  with the legs of the guide rail  32  embracing the slide rail  34 . This is fixedly connected, in turn, to a robust metal lifting beam  35 . 
     The walking beams  30  are moved vertically by means of vertically acting movement devices. These devices include for each walking beam four first hydraulic lifting cylinders  37  mounted on the stand  26 . The pistons  38  of the lifting cylinders  37  are connected to respective lifting beams  35 . The lifting beam  35  also has a number of horizontal pins  39  which project out pair-wise in respective directions through a fixed generally U-shaped device  40  on a plate  41  on the stand  26 . The U-shaped devices  40  have an inner width equal to the width of the pins  39 , so that the pins  39  are able to slide in said devices  40  as the beam  30  is raised, while preventing longitudinal movement of the beam  35 . The upper part of the generally U-shaped devices has a semi-circular shape that corresponds to the shape of the upper side of the pins  39 . The inner height of the U-shaped devices  40  and the vertical extension of the pins  39  determine the length of stroke of the lifting cylinders  37 , said length being 60 mm in one embodiment. 
     The rear ends of the two walking beams  30  are mutually connected by a transverse beam  42 . A pair of casings  43  in the form of two upstanding rectangular frames are connected to the transverse beam  42  through the medium of pins  44 . The casings  43  accommodate a transverse horizontal pin  45  which is slidably arranged to enable the beams  30 , the transverse beam  42  and the casings  43  to be raised and lowered in relation to the pin  45 , the diameter of which coincides with the inner width of the casings  43 . Furthest to the rear of the stand  26  is a centrally mounted, horizontal hydraulic cylinder  47  having a piston rod  48  which can move horizontally in the symmetry plane  49  of the conveyor path  1 . The piston rod  48  is connected to the pin  45  for horizontal movement of the walking beams  30  through the medium of the casing  43  and the transverse beam  42 , both in a lower position in which the pin  45  is in its highest position relative to the casings  43 , and in an upper position in which the pin  45  is located at the bottom of the uplifted casings  43 . 
     Generally referenced  50  in FIG. 7 is a conveyor arrangement for moving the plates  4  in their longitudinal direction along the next following conveyor path  2 . FIG. 7 also shows end views of the conveyor arrangement  25  in the first conveyor path  1  and a conveyor arrangement  51  in the third conveyor path  3 . This third conveyor arrangement  51  has the same construction as the first conveyor arrangement  25  and will not therefore be described in detail. 
     The second conveyor arrangement  50  is mounted in a stand which is generally referenced  52  and which also functions to support other apparatus arranged along the conveyor path  2  for stripping the plates  4 . A plurality of supports  54  are fixedly mounted on the stand  52 . These supports have the form of arms which extend horizontally at right angles from the underside of a longitudinally extending beam  55 . Provided in the outer end is a recess  56  which defines a support for the bottom edge  57  of the plates  4 . Three such fixed supports  54  are provided in each station  6 ,  7 ,  8 ,  9  and  10 . 
     Also provided are lower and upper fixed side supports  58 A,  58 B and  59 A and  59 B respectively. Of these supports, outer side supports  58 A and  59 A extend along all stations with the exception of station  8 , whereas the inner side supports  58 B and  59 B extend only along the stations  7  and  9 . As will be seen from FIG. 2, the receiving station  6  and the offloading station  10  are also provided with inner, upper side supports  61 . So that these side supports  61  will not present an obstacle to the plates  4  as the plates are moved from the first conveyor arrangement  25  to the second conveyor arrangement  50 , the supports have the form of two short, vertical pins which are secured to the stand  52  by angle ties and extend vertically generally in the plane defined by the fixed support strips  28  in the first conveyor arrangement  25 , up over the level of the support strips  28  but not as far as the upper level of the movable support strips  31 , so that the plates can be moved past the side supports  61  with the lugs  23  lifted above said support  61 , when moving the plates from the first conveyor arrangement  25  to the second conveyor arrangement  50  and, after offloading on fixed support devices included in said second conveyor arrangement  50 , are able to lean against the side support  61  in the receiving station  16  via the lugs  23 . The offloading station  10  is provided with a corresponding arrangement. A pair of longitudinally extending, centred side supports  60 A,  60 B are provided at a higher level within the region of the station  7 . 
     One of the walking beams included in the second conveyor arrangement  50  has been generally referenced  62 . The beam is formed of a composite construction including a pair of metal guide rails  65  of inverse U-section, one on each side of the centre line of the conveyor arrangement. The two guide rails or beams  65  are held together by a plurality of horizontal, transverse metal plates  66  disposed along the length of the beam  62 . The guide rails  65  rest on plastic slide rails  70  which are, in turn, connected to a lifting beam  71  which, distinct from the walking beam  62 , extends along the full length of the second conveyor path  2 . The length of the walking beam  62  corresponds to the length of the conveyor path  2  minus “the length of a station”, i.e. the beam is about 20% shorter than the total path length in the illustrated case, in which the stations are five in number. Mounted beneath the lifting beam  71  are three vertical, second hydraulic lifting cylinders  72  in stations  6 ,  8  and  10 . The cylinders  72  are mounted on the stand  52  and each cylinder has a piston rod  73  connected to the underside of the beam  71 . The walking beam  62  is also provided with a pair of vertical end supports  74  for each station, so as to centre the plate in respective treatment station  6 - 10  when necessary and to prevent the plates  4  from moving in their longitudinal directions when resting on the movable support  67  and being stepped forwards by the cyclically repeated feeding movements, which can require relatively powerful acceleration and retardation with each feeding step, depending on the operating speed of the plant as a whole. 
     Extending along part of the walking beam  62  within the regions of the stations  9  and  10  and spaced from said beam  62  is a horizontal rack  64  with outwardly facing teeth. The rear side of the rack  64  is joined to a flat metal rail  63  which, in turn, is connected to the walking beam  62  through the medium of a pair of extended transverse plates  66 A, FIG. 9A, FIG.  9 B and FIG.  11 . The rack  64 , and therewith also the walking beam  62 , can be moved reciprocatingly in a horizontal direction with the aid of a reversible motor  75 , preferably an hydraulic motor whose output shaft functions to drive a pinion wheel  68  around a vertical rotational axle. The pinion wheel  68  engages the teeth on the rack  64 . The pinion wheel  68  has a width (height) such that said wheel will be in engagement with the rack  64  both in the lower position of the walking beam  62 , FIG. 9A, and in the upper position thereof, FIG.  9 B. The motor  75  is attached to a foot  52 B provided in the stand  52 , opposite a stand leg  52 A, between the stations  9  and  10 . 
     Mounted on the plates  66  are posts  53  which carry movable supports  67 . The posts  53  extend from the respective plates  66  to an extent such as to terminate at a distance from the outer ends of the fixed supports  54 , wherein the movable supports  67  extend inwardly from respective posts  53  towards, and slightly beyond the centre line of the conveyor arrangement, at a level beneath or above the fixed supports  54 , depending on the positions of the movable supports  67  in the working cycle. Two such supports  67  are provided for each plate  4 . These supports include recesses  69  for accommodating the bottom plate edges  57 , in correspondence with the fixed supports  54 . 
     In order to prevent the lifting beam  71  from being subjected to longitudinally acting forces as the walling beam  62  slides on the slide rail  70 , locking means are provided analogously with that described above with reference to the first conveyor arrangement. These locking means include lower and upper female members  76 ,  77 , fixed on the stand  52  and provided with holes  78 ,  79  having vertical centre lines. The locking means also include vertical male members  80 ,  81  which are mounted on the lifting beam  71  with the aid of bracket means  82  so as to be coaxial with the holes  78 ,  79 . When the lifting beam  71 , and therewith the walking beam  62 , is located in its lower position, the male members  80  are received in the lower female member  78 , and when the lifting beam  71  and the walking beam  62  are located in their respective upper positions, FIG. 10B, the male members  81  are received in the upper female member  79 . The distance or spacing between the female members  76  and  77  also determines the length of stroke of the lifting cylinders, which in the illustrated case is 110 mm, i.e. greater than the corresponding length of stroke in the first conveyor arrangement. 
     In addition to the aforedescribed equipment, the conveyor arrangements also include hydraulic equipment pressure sources, hydraulic lines, etc., and also proportional valves coacting with the horizontally acting hydraulic cylinders to dampen acceleration and retardation forces in a known manner. Also included is a microprocessor which controls the functions of all hydraulic cylinders and also the motor  75  when the motor is an hydraulic motor. Corresponding electrical control means are provided when the motor is an electric motor. 
     Description of the method of operation 
     The manner in which the first conveyor arrangement  25  operates in conveying the plates  4  along the first conveyor path  1  will be described first. The conveyor arrangement  25  is loaded with plate batches  4  from the electrolysis tanks with the aid of a crane. The plates  4  are placed in the rear section of the conveyor arrangement  24 , this section being assumed to be empty. The spacing between the plates  4  as they are taken from the electrolysis tank is kept constant until the plates have been placed on the fixed supports  28  with the lugs  23  resting in the recesses  29 . The walking beams  30  are in their lower, rearward positions at this point. 
     Conveying of the plates  4  with the aid of the conveyor arrangement  25  is initiated by raising the lifting beams  35  to their upper positions with the aid of the lifting cylinders  37 , wherewith the pins  39  slide in the U-shaped members  40  until the upper cylindrical surface of the pins  39  contacts the inner end surface of the U-shaped members  40 . The length of stroke of the lifting cylinders  37  and the upper and lower positions of the walking beam  30  are thus determined by the length of the U-shaped members  40  and by the end stops formed by the upper rounded end of said member  40  and the respective plate  41  to which the U-shaped members  40  are attached. During the lifting movement, in which the pins  39  slide in the U-shaped members, the movable supports—the plastic strips  31 —engage the lugs  23  outside the fixed supports  28  and lift the plates  4  so as to move the yoke  22  out of contact with the fixed supports  28 . 
     The walking beams  30  are then stepped forwards by the hydraulic cylinder  47 , wherewith the guide rail  32  slides on the slide rail  34 . The step length PI coincides with the spacing between the plates  4  in the conveyor arrangement. 
     Horizontal frictional forces acting in the feed direction on the slide rail  34 , and therewith on the lifting beam  35 , are taken-up by the U-shaped members  40 , and thereby by the stand  26  by transference from the pins  39 , therewith preventing these forces from being transmitted to the piston rods  38  of the lifting cylinders  37 . 
     Subsequent to the walking beams  30  having been stepped forwards one step, the lifting beams  35 , and therewith also the walking beams  30 , are again lowered until the pins  39  in the U-shaped members  40  engage the plate  41 . The plates are again seated in recesses  29  in the fixed supports  28  during this lowering movement, FIG. 6, although in new advanced positions. 
     The working cycle of the first conveyor arrangement  25  is thereafter completed by returning the walking beams to their rear starting positions, said beams now being free from load. The plates  4  are advanced stepwise by the first conveyor arrangement  25  in this way until they reach the forward end of the conveyor path  1 . 
     The manner in which the plates  4  are transferred from the first conveyor path  25  to the second conveyor path  50  will now be explained with reference to FIG.  2 . It is assumed that the receiving station  6  is empty and that the movable supports  67  in the second conveyor arrangement  50  are located in their lower, rear positions or are moved back to adopt these positions prior to terminating transfer of the plates. It is also assumed that a plate  4 A to be transferred has been lifted-up by the waking beam  30 , being suspended by on the lugs  23  accommodated in recesses  33 . The walking beam  30  is advanced forwards from this position through a step length PI, wherein the plate, referenced  4 A′ in this position in FIG. 2, hangs immediately above the recesses  56  in the fixed supports  54  in the receiving station  6  on a level at which the lower edge  57  of the plates is positioned above the upper level of the movable supports  67 . Any tendency of the plate  4 A′ to swing as the walking beam  30  is braked is taken-up and quickly dampened by the lower, outer side support  58 A. During this transfer movement, the plate  4 A- 4 A′ passes between the upper, rear side support  61  in the receiving station  6 , at the same time as the lugs  23  pass over said side support  61 . The walking beam  30  is then lowered, as described above with regard to the working cycle of said beam, such as to cause the bottom edge  57  of the plate  4 A′ to rest in the recess  56  on the fixed supports  54  in the receiving station. This takes place before the walking beam  30  has reached its bottom position. The lugs  23  are thus released from the recesses  33  in the movable supports  31  of the walking beam  30  during the final phase of the lowering movement of the beam  30 . The waking beams  30  are then drawn back by said first hydraulic cylinder  47 . It will be understood that a plurality of plates  4  are advanced one step in the conveyor arrangement  25  in accordance with the aforegoing, in parallel with transferring the plate  4 A- 4 A′ to the next conveyor arrangement  50  in line. It should also be mentioned that the movable supports  67  in the second conveyor arrangement  50  may be located in their upper positions (shown in broken lines in FIG. 2) during the first phase of the transfer operation, but that they are lowered to their lower positions immediately prior to the walking beams  30  being lowered and the plate  4 A′ removed from the fixed supports  54  in the receiving station  6 . 
     The side support  59 A prevents the thus offloaded plate  4 A′ from falling forwards in the receiving station  6 , while the side supports  61  prevent the plate from falling backwards. The first-mentioned side support  59 A acts directly on the plate  4 A′, whereas the rear side supports  61  act on the lugs  23 . 
     A working cycle of the second conveyor arrangement  50  will now be described. It is assumed that a plate  4 A′ is present in the receiving station  6  and that the offloading station  10  is empty or at least one possible plate in the offloading station has been transferred to the third conveyor arrangement  51 . It is also assumed that the walking beam  62  is located in its rear position, FIG.  7 . The working cycle is begun with the second lifting cylinder  72  raising the lifting beam  71  and therewith the walking beam  62  from a lower position determined by the lower female members  76 , to an upper position determined by the upper female member  77 . Thus, the extent of this lifting movement is defined by the distance between said members  76  and  77 . At the same time, the lower male members  80  move out of engagement with the lower female members  76  and, at the end of the lifting movement, the upper male members  81  engage in the hole  79  in the upper female member  77 . This lifting movement brings the movable supports  67  into contact with the bottom edge of respective plates  4 A′,  4 . This upward movement then continues so that the plates  4 A′,  4  are lifted from the fixed supports  54  with the aid of the movable supports  67 . The teeth on the rack  64  slide against and in engagement with the teeth on the pinion wheel  68  during the whole of this lifting movement. 
     The walking beam  62  is then advanced one step with the aid of the motor  75  through the medium of the pinion wheel  68  and rack  64 , wherewith the movable supports  67  pass over the fixed supports  54 , FIG.  9 B. The step length is equal to the spacing PII between the plates along said second conveyor path  2 . Similar to the case in the first conveyor arrangement  25 , acceleration and retardation forces are dampened by proportional valves in the hydraulic lines (not shown) supplying the motor  75 , which in this case is an hydraulic motor. Corresponding electrical control means are used when the motor is an electric motor. This essentially prevents the plates from sliding on their movable supports  54 . The plates are able to lean against the upper side supports  59 A,  59 B during horizontal movements of the plates, while the lower side supports  58 A and  58 B prevent the plates  4  leaving the recesses  69 . It will be understood that only the mother plates  21  are advanced beyond the terminating stations  9  and  10 , whereas the metal coatings  20  stripped from the plates are recovered in a manner not applicable to the present invention. 
     The transfer of horizontal frictional forces acting on the lifting beam  71  during said horizontal movement to the piston rod  73  of the lifting cylinders  72  is prevented by virtue of the engagement of the upper male members  81 , FIG. 9B, with the upper female members  77 , which in turn are attached to the stand  52 . Thus, the horizontal frictional forces acting on the lifting beam  71  are transferred to the stand  52  via the bracket means  82 , the male members  81  and the upper female members  77  during said forward movement, FIG. 9B, and by the bracket means  82 , the lower male members  80  and the lower female members  76  during the return movement, as described below. 
     Subsequent to having moved the plates  4 A′,  4  one step forwards through the step length PII, the lifting beam  71 , and therewith the walking beam  62 , is lowered to its lower position determined by the lower female members  76 , wherein the plates are deposited in their new positions into the recesses  56  on new fixed supports  54 . Any plate or plates that has or have slipped in the recesses  64  despite damping of the acceleration and retardation forces with the aid of said proportional valves will be centered in the station with the aid of the end supports  74  during this lowering movement of the lifting beam. Although this should be evident from FIG.  7  and also from the above description of the equipment, it will also be mentioned here that the fixed supports  54  and the movable supports  67  in all stations  6 - 10  are placed in different positions as seen in the longitudinal direction of the conveying arrangement  50  when the walking beam  62  has adopted one of its two stationary positions during the working cycle. 
     The movable supports  67  are empty during the return movement and therewith pass beneath the fixed supports  54 , FIG. 9A, which now support plates resting in the recesses  56 . During this return movement, the horizontal frictional forces acting on the lifting beam  71  are taken-up via the bracket means  82  and the lower male members  80  and transferred to the lower female members  76  and therewith to the stand  52 . Return of the walking beam  62  to its second position signifies completion of the working cycle of the second conveyor arrangement  50 . Forward movement of the walking beam  62  during the aforedescribed working cycle results in the deposition of a plate in the outfeed station  10 . Prior to subsequent lowering of the walking beam  62  to its lower position, walking beams included in the third conveyor arrangement  51  have been moved beneath the projections  23  on the plate in the offloading station  10 , so that the plate, designated  4 A″ in FIG. 7, is placed on the walking beams in the third conveyor arrangement  51  as lowering of the walking beam  62  in the second conveyor arrangement  2  continues. In other respects, the third conveyor arrangement  51  in the conveyor path  3  operates in a similar manner to that described with reference to the first conveyor arrangement  25  although “in reverse” and moves the plate away from the offloading station  10  during the next phase of the working cycle. 
     The working cycles of the three conveyor arrangements, of which the working cycles of the conveyor arrangements  25  and  50  have been described in detail above, are controlled by a microprocessor. Programming of the microprocessor is determined by a number of parameters, among other things by the treatment to which the plates are to be subjected in the stations  7 ,  8  and  9  along said second conveyor path  2 . 
     The microprocessor is also programmed to feed a plate  4 A,  4 A′ into the receiving station  6  in parallel with the outfeed of a plate from the outfeed station  10 . The microprocessor is also programmed so that a new plate  4 ,  4 A′ will not be fed into the receiving station  6  until the station is empty and another plate, more specifically a mother plate  21 , has been advanced to the outfeed station  10 . It will be understood that the working cycles of the three conveyor arrangements  25 ,  50  and  51  are synchronized with one another, although this does not mean that the individual parts of the working cycles are carried out synchronously but are rather phase displaced relative to one another.