Abstract:
A high pressure shower system for cleaning perforations in a suction roll of a paper-making machine is disclosed. An elongated header pipe is mounted to the outside of the suction box and is fitted with a plurality of spaced high pressure nozzles directed at and in close proximity to the inside surface of the suction roll. The header pipe is driven in a longitudinal reciprocating manner providing complete spray coverage of the suction roll perforations. The water supply conduit to the header passes through the inside of the suction box which has a sealed slot opening to accommodate the reciprocal movement of the header.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a shower system for suction rolls used in papermaking machines. 
     BACKGROUND OF THE INVENTION 
     In paper making machines, suction rolls are commonly used to extract water from the wet paper web before it leaves the felt in the wet forming section of the paper making machine. The suction roll comprises a cylindrical metal shell in which a large number of small evenly spaced holes are formed. The suction roll typically rotates in contact with the felt at web speed and direction. Suction is applied to the inside surface of the roll by means of a suction box. The suction box is an elongated tube inside the suction roll and is fixed against rotation. The suction box has a longitudinal slot which is in sealing engagement with the inside surface of the suction roll. As the rotating inside surface of the suction roll passes over the slot, suction is applied through the holes to assist in de-watering the felt and thereby reduce the water content of the wet paper web. 
     Plugging of the suction roll holes is a commonly encountered problem. The “white water” extracted from the felt contains substantial insoluble components which tend to build up in the suction roll holes. Unless the suction roll is cleaned periodically, this build-up can lead to complete plugging of the suction roll. In such a case, the suction roll must be removed from the paper-making machine and the holes must be manually cleared. This is typically achieved either by manually punching out the obstruction on each hole with a hammer and punch. Given that there are hundreds of thousands of holes in a conventional suction roll, this operation is time consuming and the labour and down-time associated therewith is costly. In addition, such an operation carries with it the risk of damaging the suction roll. 
     There exist a number of known methods and apparatus which are intended to prevent the build-up of deposits during the paper-making operation and thereby avoid or make less frequent the requirement to manually clear the suction roll holes. For example, in U.S. Pat. No. 4,975,150 Yasuda et al. there is disclosed a method of preventing the plugging of a suction roll with makes use of the conventional fan sprays which are conventionally fitted inside the suction roll. These fan sprays apply a coating of white water to the inside surface of the suction roll to improve sealing and reduce friction between the suction box slot opening and the inside surface of the suction roll. While the pressure of the fan head spray is insufficient to dislodge deposits in the suction roll holes, Yasuda et al. disclose the use of maleic acid in the fan spray as an anti-plugging agent. 
     It is also known to provide a dedicated high pressure spray head to clean various perforated elements. For example, in U.S. Pat. No. 5,494,227 Costantini, there is disclosed a shower system having an arcuate array of high pressure spray nozzles mounted for lateral reciprocal movement across a screen which functions to separate pulp by size. Similarly, in U.S. Pat. No. 4,167,440 Falk there is disclosed a high pressure reciprocating spray cleaning apparatus for foraminous elements. 
     It is also known to provide cleaning fluid in a dedicated pressure chamber located inside the suction box for the purpose of cleaning felts. For example, in U.S. Pat. No. 1,840,102 Jespersen, there is disclosed a pressure chamber which extends across the width of the suction roll and applies water under pressure through the suction roll perforations to clean the felt. Similarly, in U.S. Pat. No. 3,190,793 Starke, there is disclosed a pressure chamber employing cleaning fluid subject to high frequency oscillations to clean paper making machine felts. 
     None of these known systems disclose any means to provide a high pressure cleaning fluid into a suction box for cleaning the perforations in a rotating suction roll. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a high pressure shower system for cleaning perforations in a suction roll. The shower system comprises a header pipe extending longitudinally in the annular space between the suction box and the inside surface of said cylinder; a plurality of spray nozzles disposed along said header pipe in close spaced relation with said inside surface, each spray nozzle having a spray axis aligned on a radius of said cylinder; a means for driving said header pipe in longitudinal reciprocating movement; and a means for supplying high pressure fluid to said header pipe for discharge through said nozzles into said perforations. The header pipe is mounted for reciprocal longitudinal movement on brackets fixed to said suction box and the brackets partially encircle the header pipe with the opening in the brackets permitting reciprocal movement of said nozzle without interfering with the spray discharge. The spray nozzles are uniformly disposed along said header pipe at a spacing equal to or less than the stroke length of said longitudinal reciprocal movement. The bracket can includes a wear resistant low friction material in sliding contact with said header pipe. A conduit means is connected to the header pipe and passes into the interior of the suction chamber through an elongated slot in the side of said chamber adjacent to said header pipe and passes out of the suction chamber through an end plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In drawings which illustrate embodiments of the invention, 
     FIG. 1 is an elevational view in part cross-section showing a suction roll fitted with the high pressure shower system of the present invention. 
     FIG. 2 is a transverse cross-sectional view of a suction roll suction roll fitted with the high pressure shower system of the present invention. 
     FIG. 3 is a plan view showing the spray header and the associated bracket and sealing details of the present invention. 
     FIG. 4 is a transverse cross-sectional view of the bracket and spray header of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown in part cross-section, suction roll  2  is an elongated cylinder having stainless steel cylindrical wall  3  and rubber surface  4  bonded to its outer surface. 
     Perforations  6  are drilled radially through wall  3  and rubber surface  4  in a close set uniform pattern over substantially the entire surface. In conventional papermaking machines, suction roll  2  can be 33 feet wide and 36 inches in diameter with cylindrical wall  3  being about 2½ inches thick. Suction roll  2  is mounted for rotation about its horizontal longitudinal axis. Each end of suction roll  2  is supported for rotation in end assembly  8  at each end, one of which is shown in FIG.  1 . 
     As shown in FIG. 2, suction box  20  is positioned longitudinally along the central axis within suction roll  2  and is fixed against rotation at each end to bearing end assembly  8 . Vacuum is applied to suction chamber  24  within suction box  20  by means of an appropriate suction line (not shown) which passes through fixed end wall  26  of end assembly  8 . In conventional installations, a vacuum of from about 18 to 23 inches Hg is common. 
     Walls  32  of suction box  20  are spaced approximately 6 inches inside cylindrical wall  3  of suction roll  2 . Suction chamber  24  has slots  28 ,  30  formed longitudinally through walls  32 . Flanges  36  are project radially outward on either side of slots  28 ,  30  and carry on their radially outer surfaces elastomeric seals  34  in sliding contact with the inside surface  38  of rotating suction roll  2 . Vacuum in suction chamber  24  is applied to the inside surface  38  of suction roll  2  through slots  28 ,  30  and draws water from the felt (not shown) in contact with the rubber surface  4  of suction roll  2  through perforations  6  into suction chamber  24  and out through the suction line. 
     In order to reduce friction between elastomeric seals  34  and inside surface  38  of suction roll  2 , to improve the vacuum seal there between and to clean out accumulated debris, suction box  20  is fitted with a plurality of fan spray heads  42  which direct water under low pressure against the inside surface  38  of suction roll  2 . Fan spray heads  42  are mounted at uniform intervals along a header pipe (not shown) which extends longitudinally along the outside of suction box  20 . The spacing interval and spray pattern are such as to provide a relatively uniform application of water to inside surface  38  along the length of suction roll  2 . A suitable source of low pressure water (not shown) is piped through fixed end wall  26  of end assembly  8  and is connected to header pipe  43  through wall  32 . 
     Thus far described, the suction roll arrangement is conventional. In operation, fibres, fillers and other particulate matter present in the white water extracted from the felt tends over time to plug perforations  6  in suction roll  2 . Eventually, the perforations become plugged to such an extent that suction roll  2  must be removed from the papermaking machine and each perforation must be manually cleared, typically by a laborious hammer and punch operation. In accordance with the present invention, there is provided a high pressure spray shower which operates to continuously clean the perforations  6  in suction roll  2  and greatly reduce or eliminate the requirement for manual cleaning. 
     Referring again to FIG. 1, the high pressure spray shower of the present invention includes header pipe  60  which is mounted longitudinally along the outside of suction box  20 . Header pipe  60  is fitted with a plurality of spray nozzles  62  evenly spaced along its length. Spray nozzles  62  are in close proximity (approx. ¾ to 1 inch) to the inside surface  38  of suction roll  2  and are aligned to direct a needle like jet of fluid in a radial direction into the bore of suction roll perforations  6  as they rotate past the nozzle. Spray nozzles  62  are preferably formed of stainless steel and drilled with a 0.040 inch orifice. 
     Header pipe  60  is mounted for reciprocating motion along its longitudinal axis to the outside wall  32  of suction box  20  by means of brackets  64 . As best shown in FIGS. 3 and 4, brackets  64  comprise stand-off  68 , collar  70  and bearing sleeve  72 . Header pipe  60  is slidably received in bearing sleeve  72  which is formed of a suitable wear resistant low friction material such as Teflon™ to facilitate the reciprocating movement. Bearing sleeve  72  and collar  70  only partially encircle header pipe  60  so as not to obstruct or interfere with the reciprocating movement or the spray of nozzles  62 . 
     Header pipe  60  is connected to supply pipe  66  through elongated slot  68  in wall  32  of suction box  20 . Supply pipe  66  passes through pressure seal  65  in fixed end wall  26  of bearing end assembly  8  and is connected to a source of high pressure water (approx. 350 psi) through flexible high pressure feed hose  67 . 
     Oscillator  80  is fixed to bearing end assembly  8  and is of a conventional hydraulic design. Stroke rod  82  is connected to supply pipe  66  by link arm  84 . Stroke rod  82  is driven in a reciprocating linear action by oscillator  80  which causes supply pipe  66  to move in a reciprocating manner through pressure seal  65 . Elongated slot  68 , pressure seal  65  and flexible high pressure feed hose  67  permit supply pipe  66  to move reciprocally and act as a fixed link to drive header pipe  60  along its longitudinal axis. Angle brace  69  can be used to strengthen corner  70  of supply pipe  66 . 
     The spacing between spray nozzles  62  is fixed at slightly less than the stroke length of oscillator  80 . This provides at least some overlap in the areas covered by adjacent spray nozzles at the limits of their reciprocal motion thus ensuring that all perforations will be exposed to the high pressure spray. For example, with an oscillator having a stroke length of about 6¼ inches, a centre spacing of about 6 inches between spray nozzles  62  is suitable. 
     In order to ensure proper operation of suction roll  2 , it is necessary to limit the loss of vacuum in suction box  20  through elongated slot  68  To achieve this, sealing plate  90  is fixed to supply pipe  66  and closely overlies elongated slot  68 . Gasket  92  is fixed to suction box  20  around elongated slot  68 , for example by way of countersunk bolts. Gasket  92  is advantageously formed of a thin sheet of a suitable wear resistant low friction material such as Teflon™. When vacuum is applied inside suction box  20 , sealing plate  90  is drawn into sealing engagement with gasket  92  to reduce vacuum loss. In addition, the low friction nature of gasket  92  facilitates the reciprocating sliding movement of sealing plate  90  over gasket  92  and reduces stress on oscillator  80  and supply pipe  66 . It has been found in practice that gasket  92  can suitably be formed from a sheet of ½ inch thick Teflon™ and extend about 1-2 inches beyond the edges of elongated slot  68 . Sealing plate  90  can suitably be formed from ⅛ inch thick stainless steel plate of a generally rectangular configuration and of sufficient length to maintain coverage of gasket  92  at opposite limits of stroke. 
     In operation, contaminants in the high pressure spray water tends to accumulate in the ends of header pipe  60  and plug the spray nozzles  62  adjacent the ends. In a preferred embodiment of the present invention, the ends of header pipe  60  are connected to the interior of suction box  20  by flexible bleed lines  100 . Bleed lines  100  are flexible high pressure hydraulic lines of a suitably small diameter, (e,g, ⅜ inch). Bleed lines  100  are attached to high pressure fittings  101  which are threaded into a drilled orifice (e.g., ⅛ inch) in each end cap  102  which closes off the end of header pipe  60  and into a drilled orifice (e.g., ⅜ inch) in wall  32  of suction box  20 . Bleed lines  100  are of sufficient length to flexibly accommodate the entire stroke length of header pipe  60 . The flow of high pressure fluid through bleed line  100  carries contaminant build-up out of the ends of header pipe  60  into suction box  20 , thereby avoiding plugging of the spray nozzles  62  located adjacent the ends of header pipe  60 . 
     While the above description includes the use of fan spray heads  42  to lubricate the elastomeric seals  34  and inside surface  38  of suction roll  2 , the high pressure spray shower of the present invention itself provides lubrication to the and permits the fan spray heads  42  to be eliminated, if desired. 
     While the present invention has been described with reference to the embodiment shown in the drawings, it will be understood that many variations are possible and come within the scope of the claims set out below.