Abstract:
A method of differential rewinding includes mounting a plurality of cores on a shaft ( 20 ) formed with a plurality of apertures ( 21 ) containing ceramic balls ( 23 ) urged outwardly into engagement with the cores by means of an inflatable sleeve ( 25 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to a method and apparatus for rewinding and is specifically concerned with differential rewinding. 
     The concept of differential rewinding has been in use for many years and is adopted to accommodate variations in tension or calliper across the web when rewinding material cut from a single roll onto a number of rewind coils. 
     Traditional methods of differential rewinding rely on the rewind cores slipping around a shaft which is being driven at a greater speed than the moving web of material. One arrangement for effecting differential rewinding is shown in FIG. 1 of the accompanying drawings. 
     In FIG. 1, a number of rewind cores  10  are mounted, either directly or via adaptors, on a rewind shaft  11  which is driven at a slight overspeed. Steel friction collars  12  keyed to the rewind shaft  11  are mounted on each side of each rewind core  10  or adaptor, and spacer cores  13  are positioned between adjacent rewind cores  10 . 
     In operation, torque is transmitted to each of the rewind cores  10 , which are free to rotate relative to the rewind shaft  11 , such torque being transmitted frictionally through the steel driving collars  12  which are keyed to the rewind shaft  11  and are loaded axially against the cores  11  and  13  as indicated by the arrows in FIG. 1 by a pneumatic piston and cylinder mechanism. As the pneumatic pressure is increased, the frictional forces and the transmitted torque increases proportionally. This arrangement is such as to allow differential slip to occur permitting each individual strip to be rewound under optimum conditions to form a rewind roll  14 . 
     More recent methods of providing differential rewinding have Involved the use of torque-responsive chucks on a keyed shaft and have improved the effectiveness of the differential system. The chucks each have a bronze bush in the centre with a low coefficient of friction and are assembled with mechanically expanded leaves that grip the cores. 
     The torque-responsive chuck arrangements eliminate the need to remove the spacers and the drive collars from the rewind shaft during reel removal. The chucks retract and release the cores allowing the finished reels to slide over the spacers. The shaft only requires dismantling when the slit pattern is changed to re-positon the chucks. 
     Although the use of torque-responsive chucks provides an improvement over the arrangement shown In FIG. 1, it does have a serious disadvantage in that it involves a reduction in the diameter of the rewind shaft to accommodate the chucks. This results in a dramatic reduction in strength. 
     The objects of the present invention thus Include the provision of an improved method of differential rewinding and the provision of an improved apparatus for differential rewinding which offer significant advantages over the known systems outlined above. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a method of differential rewinding which includes mounting a plurality of cores on a shaft formed with a plurality of apertures containing roller elements urged outwardly into engagement with the cores. 
     According to a second aspect of the invention there is provided a differential rewinding apparatus comprising a shaft on which, in use, a plurality of cores are mounted, a plurality of apertures in the shaft, roller elements in the apertures and means for urging the roller elements outwardly into engagement with the cores. 
     Each of the roller elements is preferably arranged to act between a core and a torque-transfer element formed of a material which has a coefficient of sliding friction with the roller elements lower than the coefficient of sliding friction between the roller elements and the cores. The roller elements will accordingly tend to roll relative to the cores. 
     The cores are preferably formed of cardboard or plastic and the roller elements are preferably ceramic balls, while the torque-transfer elements are preferably in the form of steel cups within which the ceramic balls are seated. 
     The means for urging the roller elements, i.e. the ceramic balls, into engagement with the cores preferably comprises an inflatable sleeve contained within the rewind shaft and so arranged that, when the pressure within the inflatable sleeve is increased, the torque transferred to the cores is increased. 
     The apertures in the rewind shaft are preferably arranged in the form of a multi-start helix so that, when cores of different widths are placed side-by-side on the rewind shaft, the number of roller elements which engage a particular core will depend on the width of the core Thus, as the width of a core is increased, the total torque transmitted to that core will be increased. It will thus be possible to rewind cores of different widths at the same time. 
     Means may be provided for preventing the accumulation of dust between the ceramic balls and the steel cups. Said means preferably comprises means for causing a flow of air out through the apertures in the rewind shaft. 
     The method and apparatus of the present invention are such that it is not necessary to fit spacers between adjacent cores. Any slit widths can accordingly be accommodated without resetting so that the present invention will enable the machine downtime to be decreased by up to 30% while improving the rewind shaft strength and achieving a dramatic increase in the reel quality. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1, as mentioned above, shows a traditional form of differential rewinding apparatus, 
     FIG. 2 is a partly broken away plan view of a differential rewind shaft assembly in accordance with the present invention, 
     FIG. 3 is a transverse sectional view of the shaft assembly of FIG. 2, 
     FIG. 4 is a longitudinal sectional view of one end of the shaft assembly of FIG. 2, 
     FIG. 5 is a longitudinal sectional view of an intermediate portion of the shaft assembly of FIG. 2, 
     FIG. 6 is a longitudinal sectional view of the other end of the shaft assembly of FIG. 2, and 
     FIG. 7 is a view corresponding to FIG. 4 but showing an alternative form of differential rewind shaft fitted with a cleaning assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The shaft assembly shown in FIGS. 2 to  6  includes a high quality steel tube  20  which is turned to a diameter of 0.8 mm. less than the internal diameters of the cores onto which the rolls of paper or other flexible materials are to be rewound. A large number of apertures  21  are machined in the steel tube  20 , the apertures  21  being arranged in the form of a three-start helix so that, as shown in FIG. 2, there is a repeated pattern comprising three apertures  21 A spaced apart 120° contained in a first common plane, three apertures  21 B in a second common plane offset 40° from the apertures  21 A in the first common plane, and three apertures  21 C in a third common plane offset 40° from the apertures  21 B in the second common plane. 
     Each of the apertures  21  is counterbored and, in the completed assembly, each aperture  21  contains a steel support cup  22 , a ceramic ball  23  and a brass retaining ring  24 , all of which are fitted from the outside of the shaft assembly. 
     A rubber bladder or sleeve  25  mounted on a tubular steel cartridge  26  is mounted within the bore of the steel tube  20 . the rubber bladder  25  being attached to the steel cartridge  26  by means of hose clips  27 . The cartridge  26  is secured at its ends to mounting elements  28  and  29  fixed to the steel tube  20  so that the steel cartridge  25  and the rubber bladder  25  will rotate in unison with the steel tube  20 . 
     A compressed air supply (not shown) is connected to the shaft assembly through a rotary union and into one end of the shaft assembly expanding the rubber bladder  25  so as to cause the ceramic balls  23  to protrude through the retaining rings  24  and against the inside surfaces of the cardboard rewind cores (not shown). 
     The steel support cups  22  transmit the force exerted by the bladder  25  to the balls  23 . The coefficient of sliding friction between the ceramic material and steel is lower than that between the ceramic material and cardboard The balls  23  will thus slide preferentially relative to the steel support cups  22  and will rotate against the inside surfaces of the cores. 
     The higher the air pressure within the rubber bladder  25 , the greater the frictional forces acting between the steel cups  22  and the ceramic balls  23  which, in turn, increases the torque transmitted to the individual cores. The total torque transmitted to a particular core will depend on the number of balls  23  which it engages, i.e. on the width of the core. 
     The rotational speed of the shaft assembly is greater than that of the rewind cores causing them to slip around the tube  20 . The action of the balls  23  pressed against the inside surfaces of the cores causes small grooves to appear immediately around the bores of the cardboard cores. The ceramic balls  23  will be located in these small grooves preventing any axial displacement of the cardboard cores relative to the shaft assembly and guaranteeing a good edge profile on the rewinding reels. 
     The shaft assembly is such that spacers between the cores are not required and it can accommodate any slit widths without resetting. The use of the shaft assembly and the method of differential rewinding of the present invention will therefore decrease the machine downtime by up to 30%, and possibly more, while improving the shaft strength and dramatically improving the reel quality. 
     Turning next to FIG. 7, this shows the apparatus of FIGS. 2 to  6  fitted with a cleaning system. It includes a manual spool valve  30  at the end of the shaft assembly at which the supply of compressed air Is connected. The manual spool valve  30  is shown in FIG. 7 in its cleaning position but is normally in its running position displaced upwardly from that shown in FIG.  7 . 
     When in its running positions the spool valve  30  provides communication between an inlet passage  31  and an air feed passage  32  connected to the interior of the bladder  25 . When in its cleaning position, the spool valve  30  provides communication between the inlet passage  31  and an air feed passage  33  which communicates with the space between the steel tube  20  and the bladder  25 . 
     The mode of operation of the system shown in FIG. 7 is as follows: 
     a) when the shaft assembly has finished running and is stationary the air is expelled from the bladder  25 , 
     b) the operator then pushes the spool valve  30  into the cleaning position, i.e. as shown In FIG. 7, and operates a push button on the control desk controlling the differential rewinding operation. This then supplies the inlet passage  31  with a pre-set cleaning pressure for a set amount of time, and 
     c) the air passes into the air feed passage  33  and exits through the apertures  21 , purging the balls  23  and cups  22  of dust and dirt. 
     The operator then removes the reels from the steel tube  20  and inserts the new cores on to the shaft. The set amount of time at cleaning pressure has finished and the operator switches the manual spool valve  30  back into the run position, ready for the next cycle. 
     It will be appreciated that this sequence of operations is tied in to the machine sequencing to ensure that, every time the shaft is unloaded and then loaded, the ceramic balls  23  and the stainless steel seats  24  are cleaned.