Abstract:
Apparatus for sealing a cylindrical roll with respect to a trough in which the roll is disposed is disclosed, the apparatus comprising an end seal applied to the end surface of the cylindrical roll, a longitudinally extending seal applied to the barrel-shaped outer surface of the cylindrical roll, and a spring for dynamically urging the end seal against the end surface of the cylindrical roll and against the longitudinally extending seal.

Description:
FIELD OF INVENTION 
   The present invention relates to the de-watering material suspensions with the aid of press rolls, and more particularly to a sealing arrangement located between a press roll and a trough or pit that partially surrounds the roll. 
   BACKGROUND OF THE INVENTION 
   As will be apparent from Swedish Patent Nos. 503,010 and 509,519, such press rolls are at present sealed by means of an end seal that connects with the end surface of the roll, wherein a longitudinally extending seal in the form of a flexible element is pressed against the cylindrical surface of the roll. 
   It is generally difficult to seal around a corner of a rotating press roll, because the roll is moveable in two directions. Firstly, the roll moves axially as a result of thermal expansion, and secondly it moves radially as a result of variation in the clearance between rolls. Sealing against the roll end is achieved with the end seal and with the seal that extends longitudinally along the roll, both of these seals being pressurised and “floating” with the roll in a direction that is normal to the sealing surface. Sealing around the corner of a roll is effected with the aid of a static seal that seals against the longitudinally extending seal on the one hand and against the end seal on the other hand. 
   The static seal tends not to follow the sealing surface, and is therefore mounted with a given clearance in relation thereto. This clearance can result in leakage if excessively large and in wear of the sealing surface if excessively small. 
   One object of the present invention is to provide a seal at an edge of a moveable roll that will solve the aforesaid problems, and then in particular with regard to a roll of a roll press for de-watering material suspensions. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, this and other objects have now been realized by the invention of apparatus for sealing a cylindrical roll with respect to a trough in which the cylindrical roll is partially disposed, the cylindrical roll including an end surface and a barrel-shaped outer surface, the apparatus comprising an end seal applied to the end surface of the cylindrical roll, a longitudinally extending seal applied to the barrel-shaped outer surface of the cylindrical roll, and urging means for dynamically urging the end seal against the end surface of the cylindrical roll and against the longitudinally extending seal. Preferably, the cylindrical roll comprises a press roll for dewatering material suspensions. 
   In accordance with one embodiment of the apparatus of the present invention, the urging means comprises a spring. Preferably, the spring comprises a leaf spring, and the end seal includes an oblique surface, the leaf spring being applied against the oblique surface, whereby a predetermined force distribution is obtained between the end surface of the cylindrical roll and the longitudinally extending seal. In another embodiment, the spring exerts a predetermined spring force, and 60% of the predetermined spring force is exerted against the end surface of the cylindrical roll and 40% of the predetermined spring force is exerted against the longitudinally extending seal. 
   In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a guide plate for the end seal and a seat for the end seal, whereby the end seal can move only in a single plane thereby. Preferably, both the end seal and the longitudinally extending seal are adapted solely for movement in the single plane. In a preferred embodiment, the end seal includes a wedge-like surface and the longitudinally extending seal includes a corresponding wedge-like surface adapted for coacting with the wedge-like surface of the end seal, thereby forming a lip on the longitudinally extending seal facing outwardly from the trough. 
   In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a piston-cylinder mechanism for applying the longitudinally extending seal to the periphery of the cylindrical roll. 
   The present invention includes a dynamically spring biased edge seal that follows the sealing surface in two directions and which seals against both the end seal and the longitudinally extending seal. 
   The edge seal includes an oblique surface against which a spring acts, wherein the slope of that surface can be chosen for appropriate force distribution of one force component acting on the sealing surface and the other force component acting on the longitudinal seal. For example, the spring may be caused to exert up to about 60% of its force on the sealing surface and up to about 40% of its force on the longitudinal seal. 
   The edge seal is preferably adapted to lie flat against the end surface of the end seal and includes a wedge-shaped surface that co-acts with a corresponding wedge-shaped surface on the longitudinal seal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in more detail with reference to the following detailed description, which in turn refers to the accompanying drawings, in which 
       FIG. 1  is a side, elevational, partial, cross-sectional view of a conventional roll press, 
       FIG. 2  is a side, elevational, partial sectional view of an inventive seal in accordance with the present invention, and 
       FIG. 3  is a top, elevational, cross-sectional view of the seal according to the present invention. 
   

   DETAILED DESCRIPTION 
   The conventional roll press illustrated in  FIG. 1  includes two cylindrical rotatable, liquid permeable press rolls  10  whose barrel shaped surfaces are comprised of perforated sheet metal welded to a roll body. The rolls are received partially in a trough  12  such as to form spaces  13  between the rolls and the inner surface of the pit. These spaces  13  communicate with pulp suspension inlets  14 . The press rolls  10  form therebetween a press nip  15 . The spaces  13  are sealed from the surroundings by means of seals  16  acting against the barrel surfaces of the rolls  10  and end seals which act against the end walls of the rolls. The pulp web present in the roll nip  15  functions as a seal between the rolls. Doctor arrangements  18  are positioned downstream of the nip for removing from the barrel surfaces of the rolls the pulp web accompanying the rolls from the roll nip  15 . The seal  16  between the trough  12  and the barrel surface of each roll  10  extends along the full length of the roll. 
     FIG. 2  is a sectional view of the inventive sealing arrangement, where the barrel surface  109  of a press roll  110  to be sealed is shown schematically with a peripheral line. The space  113  to be sealed comprises the internal volume of a trough  114  similar to that shown in  FIG. 1 . The sealing arrangement includes an end seal  115  which is placed in sealing abutment with the end wall of the roll. The end seal  115  is terminated with a flat end surface  117  with which a flat side  120  of an edge seal  119  abuts. 
   The edge seal  119  is adapted to move in a plane at right angles to the end wall of the roll and parallel with the end surface  117 , as shown by the double-headed arrow in that Figure. Movement of the edge seal to this plane is controlled positively (forcibly guided) by virtue of the movement that takes place between a guide plate  121  and a seating  122 . Sealing of the space  113  against the roll periphery is effected with the aid of a longitudinally extending seal  123  which is mounted in the trough  114  for movement into contact with the barrel surface  109  in the same plane as that in which edge seal  119  moves. The longitudinally extending seal  123  is adapted to be pressed against the barrel surface with the aid of a piston-cylinder device  125  which exerts pressure against the seal when a pressure medium is pressurised in a limited volume  127  in which the piston is intended to move. That part of the longitudinally extending seal  123  which faces towards the barrel surface includes a lip  129  which is formed by a longitudinally extending wedge-like surface  131  on the seal. The oblique surface of the seal  123  abuts with a corresponding wedge-like surface  131 ′ on the edge seal  119 . 
     FIG. 3  is a schematic view from above of the edge seal  119 , the longitudinally extending seal  123  and the end seal  115 , indicated in broken lines beneath the edge seal  119 , and shows that these sealing devices mutually co-act through the medium of the possible directions of movements shown by the double headed arrows in the Figure. In this regard, the edge seal  119  is provided with an oblique surface  133  against which a leaf spring  135  acts dynamically. The leaf spring is mounted on the outside of the trough  114 , so that the spring can be adjusted into optimal abutment with and optimal tension against the edge seal and so that it can follow dynamically the longitudinal movements of the roll and the movements of the longitudinally extending seal. As a result of the spring force acting on the oblique surface, the edge seal is pressed against the end wall  137  of the roll  110  and also against the longitudinally extending seal  123 , as indicated by the two upper double-headed arrows in the figure. The longitudinally extending seal  123 , with its lip  129 , is moveable towards and away from the roll  110  respectively, as indicated by the lowermost double-headed arrow in that figure. As will be seen from the figure, the longitudinally extending seal  123  extends along the full length of the roll  110  and slightly beyond the roll, so as to overlap the edge seal  119  and co-act with its wedge-like surface  131 ′. 
   This has been described above with reference to  FIGS. 2 and 3  a sealing arrangement at one corner of a roll press. It will be understood, however, that in reality a roll press according to  FIG. 1  will require a sealing arrangement at all four corners of the press. 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.