Abstract:
A method for fitting a tubular roll shell ( 2 ) of a roll ( 1 ) in a paper or board machine. In the method, the roll shell ( 2 ) is supported on a stationary roll shaft ( 3 ) by means of hydrostatic slide bearing elements ( 4   a   , 4   b   ; 4   a′,    4   b′;    5   a   , 5   b   ; 5   a′,    5   b ′), acting on the roll shell ( 2 ) in radially opposite directions, at least in the direction of a plane co-directional with a first plane or a plane parallel to a primary loading (F) and in a plane substantially lateral to a plane co-directional with the primary loading (F). The slide bearing elements ( 4   a   , 4   b   , 4   a′,    4   b′,    5   a   , 5   b   , 5   a′,    5   b ′) are loaded hydraulically by means of a pressure fluid. The lateral bearing elements ( 4   a   , 4   b   ; 4   a′,    4   b ′) acting in radially opposite directions have a hydrostatic pressure thereof adjusted by means of a regulator ( 20 ) having feedback connection with the main bearing elements ( 5   a   , 5   b   , 5   a′,    5   b ′) acting in the direction of a plane co-directional with the primary loading (F) to comply at a predetermined ratio with the maximum hydrostatic pressure of the main bearing elements ( 5   a   , 5   b   , 5   a′,    5   b ′) acting on the roll shell ( 2 ). The invention relates further to an apparatus for applying the method.

Description:
FIELD OF THE INVENTION 
   The invention relates to a method for fitting the tubular roll shell of a roll in a paper or board machine with slide bearings, said method comprising supporting the roll shell on a stationary roll shaft by means of hydrostatic slide bearing elements acting on the roll shell in radially opposite directions at least in the direction of a plane co-directional with a primary loading and a plane substantially lateral to the plane co-directional with the primary loading, and said slide bearing elements being loaded hydraulically by means of a pressure fluid. 
   The invention relates also to a roll for applying the inventive method for fitting the tubular roll shell of a roll in a paper or board machine, in which method the roll shell is supportable on a stationary roll shaft by means of hydrostatic slide bearing elements acting on the roll shell in radially opposite directions at least in the direction of a plane co-directional with a primary loading and a plane substantially lateral to the plane co-directional with the primary loading, and said slide bearing elements being loadable hydraulically by means of a pressure fluid. 
   BACKGROUND OF THE INVENTION 
   In current rolls with slide bearings, a roll shell is supported on a roll shaft by means of hydrostatic slide bearing elements acting radially (also axially) on the roll shell and being loaded by means of a hydraulic pressure fluid. Generally, at least two of the slide bearing elements, so-called loading elements, act on the roll shell in directions opposite to each other in the direction of a plane co-directional with a primary loading. At least two of the slide bearing elements, so-called lateral bearing elements, act on the roll shell in a direction lateral to a plane co-directional with the primary loading. This configuration is described in patent publication F1 98320. There, when an external force, for example a force resulting from a nip load, is applied to a roll shell and, thus, to loading elements, a regulator, for example a slide-type valve, mechanically in connection with the loading elements, is used for adjusting the pressure prevailing in the cavity of a slide bearing element closer to a higher loading to surpass the pressure of a loading element acting in the opposite direction so as to offset the external forces. A similar arrangement is implemented for lateral bearing elements, as well. Each slide bearing element is supplied with a constant pressure by way of regulators. 
   It is also prior known to support a roll shell in its middle section for the adjustment of a nip load by means of several, at least two counter zones. For such arrangement, reference can be made to patent publication FI 98554. There, the inner surface of a roll shell is subjected to the action of counter zone elements/chambers set e.g. in two rows, which produce a sum force working in a nip plane in a direction substantially opposite to the force produced by a loading element. 
   However, the above-described arrangement is solely intended to prevent a displacement or stroke of the roll shell relative to the shaft. Heavy bearing loads become a problem in this arrangement. Subjected to such loads, the roll shell tends to turn elliptical as a result of the action of loading elements, even though the roll shell would otherwise remain essentially stationary. If the ellipticity development is not stopped, the stresses in a shell may become so severe that the shell could break as a result of fatigue. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a roll fitted with slide bearings, which is substantially capable of overcoming the foregoing drawbacks. 
   In order to achieve this, a method of the invention is principally characterized in that the hydrostatic pressure of lateral bearing elements acting in radially opposite directions on a roll shell in a direction substantially lateral to a plane co-directional with primary loading is adjusted by means of a regulator having feedback connection from the main bearing elements acting in the direction of a plane co-directional with primary loading to comply at a predetermined ratio with the maximum hydrostatic pressure of the main bearing elements acting on the roll shell. 
   On the other hand, a roll for applying the method is characterized in that the hydrostatic pressure of lateral bearing elements acting in radially opposite directions on a roll shell in a direction substantially lateral to a plane co-directional with primary loading is adjustable by means of a regulator having feedback connection from the main bearing elements acting in the direction of a plane co-directional with primary loading to comply at a predetermined ratio with the maximum hydrostatic pressure of the main bearing elements acting on the roll shell. 
   The invention provides substantial benefits over prior art slide bearing assemblies. The discussed slide bearing assembly enables a roll shell not to become elliptical or its degree of ellipticity will be just slight compared with slide bearing assemblies of the prior art. This is possible in such a way that, in addition to the delivery of a constant pressure, each lateral bearing element is supplied, if necessary, with a pressure proportional at a certain ratio to the maximum pressure prevailing in the cavities of slide bearing elements acting in the direction of a plane co-directional with primary loading. This in turn is accomplished in such a way that the regulator receives a control signal either mechano-hydraulically or electrically from the maximum pressure prevailing in the cavity of any of the foregoing slide bearing elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example with reference made to the accompanying drawings, in which: 
       FIG. 1  shows a slide bearing assembly for a roll of the invention in a schematic end view. 
       FIG. 2  shows a regulator according to the embodiment of  FIG. 1  in a schematic structural view. 
       FIG. 3  shows a second embodiment of the invention in a schematic end view. 
       FIG. 4  shows a third embodiment of the invention in a schematic end view. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows schematically one preferred embodiment of the invention, in which the roil is designated with reference numeral  1 . The roil  1  includes a stationary shaft  3 , around which is mounted a shell  2  of the roll  1 . The roll shell  2  is supported on the shaft  3  by means of hydrostatic slide bearing elements  4   a ,  4   b  and  5   a ,  5   b  acting on an inner surface of the roll shell  2  in radially opposite directions. The slide bearing elements  5   a  and  5   b  or main bearing elements are mounted on the shaft  3  in the direction of a plane which is co-directional with a primary loading F. The slide bearing elements  4   a  and  4   b  or lateral bearing elements are set in the direction of a plane which is lateral to the plane co-directional with the primary loading F. It is obvious that main bearing elements as well as lateral bearing elements can be mounted on the shaft in higher numbers, e.g. as twin elements or in groups of three. 
   The supply of a hydrostatic pressure fluid to the main bearing elements  5   a  and  5   b  is prior known. In other words, for example the loading F developed by a counter roll  15  upon the roll shell  2  strives to move the roll shell  2  as well as the main bearing elements  5   a  and  5   b  relative to the shaft  3 . Thus a valve  6 , fitted mechanically in connection with the element  5   a , can be used for adjusting in cavities  50  and  51  the pressure of a hydraulic pressure fluid delivered through a constant pressure feed line P P  as well as feed lines  7 ,  7 ′ as required, such that the roll shell  2  remains substantially stationary in the direction of a plane co-directional with the loading F. 
   The lateral bearing element  4   a  is provided with separate feed lines P and  13 . Between the feed fines P and  13  is arranged a regulator  20 . The lateral bearing element  4   b  is also provided with a separate regulator  28 , which is supplied with a hydraulic pressure fluid along a constant pressure feed line P S , and by way of the regulator  28  further into a cavity  41  of the lateral bearing  4   b.    
   The regulator  20  has its construction depicted schematically in  FIG. 2 . The regulator  20  comprises a mechano-hydraulic slide valve, which is functionally similar to a pressure recovery valve, having a constant pressure on the inlet side, the pressure ratio between the control side and the outlet side being constant. The valve  20  includes a cylindrical space  21 , which is smaller at a first end than at a second end in terms of its diameter. The cylindrical space  21  is provided with a valve stem  22  for a lengthwise movement in the space  21 . The valve stem  22  is fitted with two slides  23  and  24  for dividing the cylindrical space  21  for three isolated smaller spaces  21   a ,  21   b ,  21   c . The first slide  23  is mounted on the end of the valve stem  22  in the diametrically smaller cylindrical space  21   a . The second slide  24  is fitted in connection with the valve stem  22  in the diametrically larger cylindrical space  21   b ,  21   c . The valve stem  22  has its second end provided with an actual regulator element  25  which, as the valve stem  22  is reciprocating, opens and closes a constant pressure feed line P which is in communication with the valve  20 . 
   A control pressure for the valve stem  22  is introduced above the slide  23  into the cylindrical space  21   a  by way of feed lines or transit paths  8 ,  8 ′ and  10 . The feed line  8  is in communication with the cavity  50  of the main bearing element  5   a  for bringing a pressure signal along the feed line  8  to a shuttle valve  9 . Furthermore, the feed line  8 ′ is in communication with the cavity  51  of the main bearing element  5   b  for bringing a pressure signal along the feed line  8 ′ to the shuttle valve  9 . By virtue of the shuttle valve&#39;s  9  action, a higher-pressure signal can be delivered along a feed line  10  to the valve  20 . For example, when the counter roll  15  applies a loading force on the roll shell  2 , the cavity  50  of the main bearing element  5   a  by virtue of the action of the valve  6  develops a higher hydrostatic pressure than the cavity  51  of the main bearing element  5   b . The hydrostatic pressure working within the main bearing element  5   a  becomes so high that the roll shell  2  tends to “stretch” in the direction of a plane co-directional with the primary loading F, and to “flatten” in the direction of a plane lateral to the above-mentioned plane. Consequently, the feed line  8  carries a higher active pressure than the feed line  8 ′, as a result of which, by virtue of the shuttle valve&#39;s  9  action, the cylindrical space  21   a  carries a control pressure consistent with the maximum hydrostatic pressure prevailing in the cavity  50 , thus having an effect on the action of the valve  20  and the slide  23 , and hence, on the action of the valve stem  22 . 
   Upon receiving a control signal along the feed line  10  on the top surface of the slide  23 , the valve  20  will be essentially subjected to a force F 1 =P max /A 1 , wherein P max  represents a pressure consistent with the maximum hydrostatic pressure prevailing in the cavity  50  of the main bearing element  5   a  or in the cavity  51  of the main bearing element  5   b , and A, represents a surface area of the slide  23 . When the force F, is more powerful than a counterforce F, produced by a counter spring  26  present in the valve  20 , the valve stem  22  makes a move as the valve  24  compresses the spring  26 . At the same time, the regulator element  25 , accompanying the valve stem  22  in its movement, shifts to a position to open a flow path from the constant pressure feed line P to the regulator  20 , and thence further to a feed line  13  which is in communication with the cavity of the lateral bearing  4   a.    
   The opening of a flow path results in an increase or development of pressure in the space  21   c  above the slide  24 , which in turn produces a force F 2 =P 2 /A 2  which is counteractive with respect to the force F, and contributes to the actions of the valve stem  22  and in which P 2  represents a pressure working in the space  21   c  of the valve  20  on the slide  24 , and A 2  represents a surface area of the slide  24 . 
   The valve stem  22 , along with its slides  23  and  24 , searches for its position until the forces F 1  and F 2  attain an equal rate. Compared to the forces F 1  and F 2 , the force F S  of the spring  26  is substantially insignificant and, thus, need not be accounted for. In a balanced condition, the pressure P max  prevailing in the space  21   a  above the slide  23  in relation to the pressure P 2  prevailing in the space  21   c  above the slide  24  is always proportional to a ratio between the surface areas A 1  and A 2 . Hence, a pressure prevailing in the feed line  13  between the valve  20  and the cavity  40  and in the cavity  40  is equal to that prevailing in the valve space  21   c . As the control pressure P max  changes, there will also be a change, as the valve stem  22 , and hence the slide  24 , are moving, in the pressure P 2  of a pressure fluid acting in the space  21   c  in accordance with the above-mentioned area ratio. Preferably, the area ratio is defined in such a way that P 2  is about 0.5–0.8 times with respect to P max . However, the multiplier can be lower or higher as necessary. 
   When the valve  20  is closed, a holding pressure of the lateral bearing element  4   a  as well as lubrication between the lateral bearing element  4   a  and an inner surface of the roll shell  2  are secured by means of a separate feed line, fitted with a pressure reducer valve  12  and connected to the feed line  13  which is in communication with the cavity  40 . 
   Furthermore,  FIG. 1  visualizes a valve assembly for the lateral bearing element  4   b  acting on the roll shell  2  in a radially opposite direction for supplying a hydraulic pressure fluid to the lateral bearing element  4   b . The lateral bearing element  4   b  is in a mechanical connection by way of a spindle rod  29  with a slide  28   a  of a valve  28 . Thus, as a result of the action of the lateral bearing element  4   a , the roll shell  2  shifts to the right according to  FIG. 1  for a contact with the lateral bearing element  4   b , which uses the spindle rod  29  to drive the slide  28   a  of the valve  28  out of its position in front of a port  28   b . Thus, the feed line P S  is provided with a clear flow path through the valve  28  into the cavity  41  of the lateral bearing element  4   b . The element  4   b , and thus the slide  28   a , travels a short distance until the port  28   b  opens sufficiently for pressures in both cavities  40  and  41  of the lateral bearing elements  4   a  and  4   b  to become equal for holding the roll shell  2  in lateral direction substantially stationary and for preventing a lateral flattening of the roll shell  2 . 
     FIG. 3  illustrates a second embodiment of the invention. A shaft  3  is provided with two main bearing elements  5   a ,  5   a ′, set at a distance from each other in a direction radial with respect to the direction of a plane substantially co-directional with a primary loading F, and acting on the inner surface of a roll shell  2 . Respectively, the shaft  3  is provided with two main bearing elements  5   b ,  5   b ′ acting on the inner surface of the roll shell  2  in radially opposite directions. The shaft  3  is further provided with lateral bearing elements  4   a  and  4   b , acting in radially opposite directions on the inner surface of the roll shell  2  in a direction lateral to a plane co-directional with the primary loading F. 
   The supply of a hydraulic pressure fluid to the main bearing elements  5   a ,  5   a ′ and  5   b ,  5   b ′ is prior known in its basic principles and only briefly reviewed here. The hydraulic pressure fluid is brought along a feed line P P  to a valve  6 , whereby the pressure fluid is delivered further along lines  7  and  7 ′ into cavities  50  and  51  of the elements  5   a  and  5   b ′ and still further along feed lines  30  and  32  into respective cavities  50  and  51  of the elements  5   a ′ and  5   b . The pressure fluid is also brought along feed lines P and  13  to a valve  42 , whereby the hydraulic pressure fluid is delivered along lines  31  and  31 ′ into cavities  40  and  41  of the elements  4   a  and  4   b.    
   Between the feed lines P and  13  is fitted an electrically controlled regulator  20 , for example an electrically controlled valve, which is prior known regarding its design and operation. As in the previous embodiment, a control signal for the regulator  20  is consistent with the maximum pressure prevailing in the cavities  50  or  51  of the main bearing elements  5   a ,  5   a ′ or  5   b ,  5   b ′. The control signal is produced e.g. by fitting the cavities  50  and  51  with pressure detectors  52  and  53 . The pressure-consistent electrical signal received therefrom is carried along an electrical transit path  8 ,  8 ′ to a signal reversing switch  9 ′. The switch  9 ′ is intended to distinguish from the two signals received from the transit path  8 ,  8 ′ the one that is consistent with the higher pressure, and to transmit it further along a transit path  10  to the regulator  20 . The regulator  20  opens or closes in compliance with the pressure-consistent signal received in the regulator  20 , such that the pressure fluid supplied through the feed line  13  and the valve  42  and prevailing in the cavities  40  and  41  has a pressure which is about 0.5–0.8 times the maximum hydrostatic pressure prevailing in the cavities  50  and  51  of the main bearing elements  5   a ,  5   a ′ or  5   b ,  5   b ′. However, this multiplier can be lower or higher, even higher than 1. 
     FIG. 4  shows yet another, a third embodiment of the invention. As compared to the second embodiment, a single lateral bearing element is replaced with two radially spaced-apart pairs of lateral bearing elements  4   a ,  4   a ′ and  4   b ,  4   b ′. The elements  4   a  and  4   a ′ are in communication with each other by way of a feed line  33  used for supplying a pressure fluid from a cavity  40  of the element  4   a  into a respective cavity  40  of the element  4   a . The elements  4   b  and  4   b ′ are similarly in communication with each other by way of a feed line  34 . Another difference between this arrangement and the previous one is that the regulator  20  is functionally a pressure-controlled mechano-hydraulic valve similar to the one described in connection with the first embodiment. The pressure regulation of a pressure fluid delivered to a regulator  42  is naturally implementable also electrically, as set forth in connection of the second embodiment. The number of slide bearing elements can also be varied as necessary.