Abstract:
A supercalender has a top roll, a bottom roll, and a plurality of intermediate rolls. The intermediate rolls are mounted to support frames by pivot arms. The pivot radius defined by the arms is at least about 2½ times the diameter of the largest intermediate roll. Hydraulic load support cylinders are arranged between the intermediate roll bearings and anchor points which are spaced away from the intermediate rolls, to allow greater movement without mechanical interference between hydraulic load support cylinders. The greater length of the pivot arms combined with a greater stroke of the load support cylinders allows the supercalender to accommodate filled rolls which change diameter substantially over their life, as the surface of the rolls is repeatedly turned down to refurbish the roll surface. The calender may be based on an existing calender of the closed A-frame type. One half of each A-frame in the machine direction is removed and a weldment is bolted to the track of each remaining frame along which the bearing housings of the calender rolls formally rode.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to calenders in general, and to supercalenders in particular. 
     A calender, particularly a supercalender, can increase the value of the paper manufactured on a papermaking machine without increasing the cost of fiber, and with only a small increase in energy cost. By improving the surface finish or other attributes of the paper web, the value of the paper is increased without otherwise modifying the papermaking machinery or process. Because of the large fixed costs and high production rates typically involved in paper manufacture, increasing the value of the paper produced can be a particularly advantageous way to increase revenue produced by a papermaking machine. 
     A supercalender is comprised of a stack of rolls, sometimes as many as ten, eleven, or more, which form a plurality of nips through which the paper web is directed. Pressure and often heat are applied to the web as it passes through the nips of the supercalender. A supercalender can impart an improved, or more valuable surface finish, can correct curl, and can improve paper caliper variations. 
     Improving the supercalender has involved controlling the nip force between adjacent rolls by supporting each roll independently of the other rolls in the stack of rolls; the use of crown control rolls, and the use of higher roll temperatures. The use of higher roll temperatures requires an ability to rapidly open a calender stack so that the high-temperature rolls do not overheat opposed compliant rolls when a paper break occurs. 
     Where a plurality of intermediate rolls are mounted between a fixedly mounted, variable-crown upper roll and a movable variable-crown lower roll, one known technique for controlling inter roll nip loading is to mount the intermediate roll bearings on pivot arms. The pivot arms can be supported by support cylinders as disclosed in U.S. Pat. No. 4,901,637 to Hagel et al.; U.S. Pat. No. 5,438,920 to Koivukunnas et al.; U.S. Pat. No. 5,806,415 to Lipponen et al.; and U.S. application Ser. No. 09/303,587 (PCT/FI98/00392), filed May 7, 1998, claiming priority from U.S. provisional application 60/045,871 to Maenpaa et al., which are each incorporated herein by reference. The support cylinders allow control of the nip loading between each of the supercalender rolls. 
     A supercalender may employ rolls of varying diameters and of different types. One type of roll has a polymer roll cover. The resilient roll cover provides a wider nip due to compression of the roll at the nip between rolls. Polymer covered rolls have a relatively long life and require only relatively small reductions in diameter due to refinishing the roll surface during the life of the roll. Smooth metal rolls provide a hard smooth surface against which the paper is compressed. Although metal rolls may be refinished, relatively little material is removed over time. Metal rolls may be heated, typically by hot water, steam or induction heating. Another type of known roll is a filled roll which is comprised of a large number of disks of a material like cotton, flax, or paper. Each disk has a central hole and thousands of individual disks or sheets are stacked up on a metal core and compressed axially at very high pressures. The resulting roll is finished by turning the surface of the roll formed by the compressed disks of fabric or paper. The surface of a filled roll has a relatively short service life requiring frequent machining so that a filled roll decreases substantially in diameter over the life of the roll. 
     Many existing calenders are of the closed frame, or A-frame type, which means the roll bearings at the ends of the individual calender rolls making up the supercalender are held between pairs of vertical frames, which are joined at the top. In these existing calenders, the rolls have bearings which slide on rails between the vertical frames. Nip loading between rolls making up the calender can be controlled only by loading the uppermost roll, which means each successively lower nip has an increased nip loading as the weight of each successive roll adds to the total nip load. 
     A conventional closed calender cannot rapidly open the nips. Rapid nip opening protects polymer and fiber rolls from damage caused by wads of paper passing through the calender nips. Typically photoeye and web tension sensors detect a paper break and instigate rapid nip opening so that wads of paper formed during a break can pass between calender rolls without damaging them. Existing solutions to rebuilding calenders do allow support of individual rolls by hydraulic pistons which extend between a support frame and the roll bearings. Existing systems, however, do not provide sufficient vertical movement of the roll bearings to accommodate a variety of roll diameters, particularly the ability to accommodate the diameter change of filled rolls over time. 
     A calender or calender rebuild design is needed which can accommodate a wide variety of calender rolls, and facilitate the use of filled rolls by accommodating the substantial change in roll diameter overtime. 
     SUMMARY OF THE INVENTION 
     The calender of this invention may be based on an existing calender of the closed A-frame type. One half of each A-frame in the machine direction is removed and a weldment is bolted to the track of each remaining frame along which the bearing housings of the calender rolls formally rode. Each weldment rests on the calender foundation and consists of two parallel plates which extend in the machine direction 72 inches away from the remaining frames. The lower portion of each weldment has a vertical rail along which the bearing housings of a bottom roll rides. The bottom roll mounted to the bottom bearing is supported by a bottom cylinder which controls the bottom roll&#39;s vertical movement and the opening and closing of the calender roll stack. 
     A top calender roll is fixedly mounted between the weldments. A plurality of intermediate calender rolls are mounted by pivot arms to the weldments, so that each intermediate calender roll is supported on each end by two pivoting arms. Each arm has two plates which extend between the roll end bearing, and extend along either side of the weldment to bearing pins located adjacent to the upstream side of the weldment where the weldment is bolted to the track of the existing frames. 
     The bearing housings of each roll connect the two plates of each arm to form a single integrated pivot arm. The bearing housings incorporate a stop so that each bearing housing on each pair of pivot arms, when pivoting downwardly comes to rest on resilient pads mounted to weldment stops which extend like teeth from the sides of the weldments. The weldment is substantially open ended, opposite the calender rolls. 
     Positioned within the sides of the weldments are pairs of load supporting cylinders which extend between cylinder brackets which span the sides of the weldments and piston mounting brackets which extend from the calender roll bearing housings. The piston mounting brackets are narrower than the weldment and fit within the sides of the weldment and between the weldment stops on which rubber pads are mounted, thus accommodating the stroke of the load supporting cylinders without interference of the supporting weldment. 
     The greater length of the pivot arms combined with the greater stroke of the load support cylinders allows the supercalender to accommodate filled rolls which change diameter substantially over their life, as the surface of the rolls is repeatedly turned down to refurbish the roll surface. 
     It is an object of the present invention to provide a supercalender which can accommodate calender rolls of varying diameter. 
     It is another object of the present invention to provide a supercalender in which greater vertical motion of individual calender rolls is provided for. 
     It is a further object of the present invention to provide a supercalender which can control the nip load on intermediate calender rolls. 
     It is a still further object of the present invention to provide a supercalender in which intermediate rolls are mounted on pivot arms which minimize lateral displacement of the rolls when they are pivoted on the arms. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of the supercalender rebuild of this invention in the closed position. 
     FIG. 2 is a side elevational view of the supercalender rebuild of this invention shown in the open position. 
     FIG. 3 is a broken away side elevational view of the supercalender rebuild of FIG.  1 . 
     FIG. 4 is an exploded isometric view of the supercalender rebuild of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to FIGS. 1-4, wherein like numbers refer to similar parts, a calender  20  is shown in FIGS. 1 and 2. The calender  20  has two spaced apart frames  24  to which weldments  38  are bolted. A top roll  28  is mounted on the weldment  38  for rotation. A bottom roll  26  is mounted for vertical motion on hydraulic pistons  72  and is slidably mounted to the weldment  38 . A plurality of intermediate rolls  34  are placed one above another, so that when the top roll  28 , bottom roll  26  and intermediate rolls  34  are brought together they form calender nips  29  therebetween. 
     The calender  20  may be constructed as a rebuild where the rolls  26 ,  28 ,  34  of an existing calender, and portions of the frame  24  of an existing calender are used in the construction of a new calender  20 . Because of the considerable cost of the calender rolls generally, and particularly of the bottom roll  26  and the top roll  28  which will normally be variable-crown rolls, reuse of the calender rolls will save considerable cost. Reuse of the part of the frame  24  saves the cost and time of constructing a new frame and foundation. 
     In a supercalender, where a plurality of intermediate calender rolls are positioned between a lower variable-crown roll and a upper variable crown roll, the nip loading uniformity could be controlled by the variable-crown rolls, except for the fact that the rolls extended beyond the paper engaging nip, and relatively heavy roll bearings are cantilevered off the ends of the rolls. In addition, in a conventional supercalender each successive nip must have a higher linear nip load because each roll must support the weight of all the rolls position above it. 
     The weight of the bearings and the unsupported portions of the rolls cause a downward deflection of the roll ends. Mounting the roll bearings to arms which are supported by hydraulic loading cylinders allows the weight of the unsupported portion of the rolls plus the bearing housings to be supported. As explained more fully in U.S. patent application Ser. No. 09/303,587 (PCT/FI98/00392), the loading angle which defines the linear loading of intermediate rolls can also be controlled by the use of hydraulic loading cylinders which are mounted to support the arms to which the roll bearings are mounted. 
     Referring to FIGS. 1 and 2, the calender  20  provides the benefit of using hydraulic loading cylinders  30  to support the bearing housings  32  of the intermediate rolls  34  which are mounted on the arms  36 . The roll support arms  36  are mounted to a weldment  38  by pivots  39 . The weldment  38  is bolted to an existing calender frame  24 , as shown in FIG.  4 . The loading cylinders  30  are arranged so that the extension of the pistons  46  do not interfere with the mounting of the loading cylinder  30  of the next higher intermediate roll  34 , as shown in FIG.  1 . The bearing housings  32  of each intermediate roll have piston mounting brackets  42  which extend towards and partly between the sides  44  of the weldment  38 , as shown in FIGS. 3 and 4. Hydraulic loading cylinders  30  is comprised of the piston  46  which is mounted to the piston mounting bracket  42  and a hydraulic cylinder  48  which is mounted between lower support cylinder brackets  50  which are mounted between the two spaced apart vertical walls  44  of the weldment  38 . 
     The lower support cylinder brackets  50  are mounted below the piston mounting brackets  42  and spaced inwardly towards the pivots  39  which mount the arms  36 . The position and arrangement of the hydraulic loading cylinders  30 , and the way in which they are substantially contained within the weldment  38  allows greater extension of the hydraulic loading cylinder pistons  46 , without the interference between cylinders inherent in the prior art. The greater extension of the hydraulic loading cylinder pistons  46  allows greater vertical movement of the intermediate rolls  34 . Greater movement of the intermediate rolls  34  allows the supercalender to accommodate fiber rolls which decrease in diameter substantially over their useful life. Greater vertical movement also facilitates substituting different intermediate rolls as may be required by a particular grade of paper. 
     Referring to FIGS. 2 and 3, a rebuilt calender  20  is constructed by tearing down an existing closed calender A-frame (not shown) to leave a single frame  24  consisting of the up machine direction portion of the A-frame of the pre-existing calender, on both the front frame  24  and back (not shown) of the pre-existing calender. The front frame  24  has a track  54  along which previously the bearing housings of the intermediate rolls rode. The weldment  38  has a protruding land  56  which fits within the sides  58  of the track  54 . Bolts  60  mount the weldment  38  to the track  54  of the front frame  24 . The weldment  38  extends over the foundation previously occupied by the portion of the A-frame which was removed. 
     The weldment has a back  62  and two sides  44  and downstream edges  64  which are thicker than the sides  44  and support one pair of triangular teeth  66  for each intermediate roll  34 . The triangular teeth  66  have upwardly facing surfaces  67  on which are mounted resilient pads  70  and which form stops, which support the intermediate rolls  34 , when the calender  20  is in the open position, as shown in FIG.  2 . Corresponding teeth  68  are formed on the bearing housings  32  of the intermediate rolls  34 . As shown in FIG. 2, when the calender  20  stack is opened by moving the bottom roll  26  down by means of the bottom roll support cylinder  72 , the intermediate rolls  34  come to rest on the upwardly facing surfaces  67  and resilient pads  70  of the triangular teeth  66  which engage the bearing housing teeth  68 . As shown in FIG. 3, the bearing housing of the bottom roll  26  slides along a track  74  formed on lower portions  76  of the weldment  38 . 
     A gap  78  is formed between the downstream edges  64 , of the weldment  38 . The gap opens into the interior  80  of the weldment  38 . In contradistinction to the prior art, where the hydraulic load cylinders are mounted substantially along the downstream edges of the calender support, the hydraulic loading cylinders  30  of the calender  20  are mounted substantially within the interior  80  of the weldment  38 . The downstream edges  64  of the weldment sides  44  may be tied together for increased stiffness by short bars  81  which extend between the weldment sides  44 . The short bars  81  are positioned to avoid interference with the hydraulic load cylinders  30 . Assembly of the calender  20  is facilitated by access openings  82  which facilitate positioning pairs of opposed bracket parts which form the lower support cylinder brackets  50  which are mounted to the sides  44  of the weldment with bolts  86 . 
     The access openings  82  also facilitate positioning the lower portions  88  of the hydraulic cylinders  48  within the grooves  90  in the bracket parts  50 . The bracket parts  50  may also be joined by through bolts (not shown) which tie the weldment sides  44  together. In addition, the lower portions  88  of the hydraulic cylinders  48  may be held within the brackets by keys  93  which prevent the hydraulic cylinders  48  from being inadvertently lifted out of the grooves  90 . The pivotal arms  36  are mounted over the pivots  39  which extend outwardly of the weldment sides  44 , closely spaced from the back  62  of the weldment  38 . Pivot brackets  92  overlie the arms  36  and the pivots  39  to provide stronger support to the pivots  39 . The pivot arms  36  are bolted by bolts  94  to ductile cast iron bearing housings  32 , on which the piston mounting brackets  42  are integrally formed. 
     During assembly, the bearing housings  32  with attached hydraulic load cylinders  30  are bolted to the pivot arms  36 . The bottom of the roll support cylinder  72  may then be positioned the lower portions  88  through access openings  82  so the lower portions  88  ride with in the grooves  90  of the bracket parts  50 . The intermediate rolls  34 , as shown in FIG. 3, are mounted by bearings  102  within the bearing housings  32 . Referring to FIGS. 1 and 2, an inside flyroll  104  is mounted to the inside part  99  of the pivot arm  36 . Alternatively, an outboard flyroll  100  is mounted to a bracket on the bearing housing  32 . 
     The top roll  28  is fixedly mounted, as shown in FIGS. 1 and 2, to the weldment  38 . All loading of the calender stack is performed by the bottom roll  26  which, as previously described, slides along the track  74  formed on lower portions  76  of the weldment  38 . The calender stack can be rapidly opened, as shown in FIG. 2, by moving the bottom roll  26  downwardly and allowing the pivot arm  36  to come to rest on the upwardly facing surfaces  67  of the teeth  66 . In the open position, gaps of at least about 0.19 inches are formed between each intermediate roll and the preceding roll. 
     In combination with a greater stroke of the hydraulic loading cylinders  30 , the pivot arms will have a correspondingly greater swing radius between the axis  106  of the intermediate the rolls  34 , and a pivot axis defined by the pivots  39 . Pivoting the arms  36  results in not only vertical movement of the intermediate rolls, but a small horizontal or machine direction motion so that the individual intermediate rolls may not be positioned precisely above, or precisely below another intermediate roll  34  or the top roll  28  or bottom roll  26 . To the extent any intermediate roll  34  forms a nip which is offset from a calender plane  107  extending between the axis  108  of the top roll  28  and the axis  110  of the bottom roll  26 , lateral forces will be developed in the pivot pins  39 . The lateral forces are related to the amount of lateral offset of the intermediate roll  34  axis  106 . These lateral offsets are minimized by positioning the pivot pins  39  and the stops formed by the upwardly facing surfaces  67  to position each intermediate roll so that the intermediate roll axes  106  are initially positioned to the right as viewed in FIGS. 1 and 2 of the calender plane  107  extending between the axes  108 ,  110  of the top and bottom rolls. The pivot arms  36  are arranged so that the intermediate roll axes  106  cross the plane  107  twice, thus reducing the total angular displacement of the intermediate roll axes  106 , away from the calender plane  107 , by a factor of four, and the lateral displacement by more than a factor of ten. 
     The calender  20  achieves an ability to accommodate greater vertical movement in a calender where the rolls are mounted to pivot arms, by using the arms which in proportion to the diameter of the intermediate rolls, are substantially longer, so that intermediate roll diameter is about 40 percent or less of the pivot radius defined between the intermediate roll axis  106 , and the pivots  39 , and by placing the hydraulic loading cylinders  30  in the overlapping diagonal arrangement as shown in FIGS. 1 and 2 so that greater extension of the hydraulic loading cylinders  30  is possible without interference between cylinders. In the prior art, hydraulic loading cylinders are positioned substantially in a vertical line, and thus each loading cylinder could only extend until it came into interference with the loading cylinder immediately above. 
     The calender  20 , as shown in FIGS. 1 and 2, has a top roll diameter which begins life with a diameter of 34.28 inches, and a bottom roll which begins life with a diameter of 42 inches. The intermediate rolls, depending on roll type, vary between 32 inches for filled rolls, 28.8 in. for polymer rolls, and 24.7 inches for thermal rolls. The rolls will decrease in diameter, in a manner known in the art, due to periodic resurfacing by a turning down of the roll diameters, with the amount of roll diameter reduction being dependent on the roll type. FIG. 2 shows the calender  20  in the open position with maximum diameter rolls, and the rolls resting on stops formed by the surfaces  67  of the triangular teeth  66 . FIG. 1 shows the calender  20  in a closed position with minimum diameter rolls. The total vertical motion of the bottom roll axes is thirty inches between FIG.  1  and FIG.  2 . The pivot radius defined between the intermediate roll axes  106  and the center of the pivots  39  is eighty inches. For the lowermost intermediate roll  114 , which has a maximum angular motion of about 17 degrees, and a maximum vertical motion of the roll axes of about twenty-four inches, or about 30 percent of the pivot radius. The roll has a maximum horizontal displacement of the roll axes of about 0.45 inches from the calender plane  107 , which is less than one percent of the pivot radius, with the actual displacement of the nip formed between the lowermost intermediate roll  114  and the bottom roll  26 , or the roll immediately above being displaced about a maximum of 0.41 inches from the calender plane  107  and it is this last displacement which controls the amount of lateral loads developed at the pivot arm  36  pivots  39 . 
     The intermediate roll  34  immediately above the lowermost intermediate roll  114  has a smaller vertical motion, approximately twenty-one and one half inches or slightly more than twenty-five percent of the pivot radius and proportionately less horizontal displacement. Less vertical motion is required of the intermediate rolls  34  as the top roll  28  is approached, so that the horizontal motion can be to less than one percent of the pivot radius, without necessarily causing the axis of the intermediate rolls  34  to pass twice through the calender plane  107 . The calender plane  107  could be tilted with respect to the vertical, in which case the horizontal and vertical displacements are measured as parallel and perpendicular to the calender plane. 
     It should be understood that the calender rolls  26 ,  28 ,  34  are supported on either end by mirror image frames, arms, and load support cylinders. The rolls having a typical cross machine direction width which is greater than the width of the paper web being calendered which, for an on-machine calender, may be several hundred inches wide. 
     It should be understood that the calender  20  may be constructed as a rebuild calender or as a new calender. 
     It should be understood that in the claims the term support frame refers to the structure to which the pivot arms are mounted, whether that is a weldment, a weldment plus an existing frame, or simply a frame, however constructed, which supports the pivot arms. 
     It should be understood that in the claims the terms support cylinders includes hydraulic cylinders, pneumatic cylinders, electric actuators, air rides/air bags, and other types of actuator. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.