Patent Publication Number: US-6905575-B2

Title: Arrangement for the web threading of a multi-roll calender

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   This application is a U.S. national stage application of International Application No. PCT/FI01/00585, filed Jun. 20, 2001, and claims priority on Finnish Application No. 20001965 filed Sep. 6, 2000, the disclosures of both of which applications are incorporated by reference herein. 

   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The invention relates to an arrangement for the web threading of a multi-roll calender of a paper/board or finishing/converting machine, which calender comprises a number of rolls formed into a roll stack, and a number of lift-out rolls, which are arranged in such a way that the web being treated travels from one calender nip to another via a lift-out roll. 
   With paper machines, the trend has for long been to close open transfers in order to improve runnability. As a result of online calendering, the first open transfers are between the dryer section of the paper machine and the calender, and in the set of rolls of the calender. 
   Nowadays it is known that many web breaks take place precisely at the calender. These can be eliminated quite efficiently by closing the web threadings inside the calender and between the dryer section and the calender. Closing the web threading before and after the calender is not in any way extraordinary. The problem is instead how to accomplish functional closing of the web threading in the set of calender rolls. 
   The web threadings of the calender will in future have to be closed due to, among other things, higher running speeds, whereby the loads on the web will increase due to the optimisation of draws, or in general to improve time efficiency. 
   One solution for closing the web threading of a calender is disclosed in the publication U.S. Pat. No. 4,552,620. In it, the belt used for closing the web threading is looped through the calender nips (see appended FIG.  1 ). The paper web travels through each nip between the belt and the roll. The web is not supported in a completely satisfactory manner when it travels through the calender. The situation can be somewhat improved by applying the known solution to a calender of the above-mentioned type which is equipped with lift-out rolls. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide a reliable arrangement for closing the web threading of a multi-roll calender. 
   The solution relating to the invention is characterised in that between the calender roll and the lift-out roll, the web being treated is supported by means of at least one closing member not extending through the nip, which closing member is formed by a belt, wire or metal wire, which is arranged to travel via two or more guide rolls. 
   In one embodiment of the invention this has been implemented in such a way that a first closing member picks the web up from the surface of the calender roll, and a second closing member transfers the web onto the surface of the next calender roll. 
   In another embodiment of the invention this has been implemented in such a way that the closing member picks the web up from the surface of a calender roll and returns the web onto the surface of the same calender roll, from where the web is conveyed to the next nip along the surface of the calender roll. In such a case, the most preferable arrangement is such that the closing member comprises at least three guide rolls located at the vertexes of a polygon, and in addition at least one guide roll formed into a lift-out roll and arranged inside the area limited by the vertexes of the said polygon. 
   The invention is described in greater detail in the following, with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows diagrammatically a calender in which is used closed web threading according to the prior art. 
       FIG. 2  shows diagrammatically a multi-roll calender in which is used closed web threading according to a first embodiment of the invention. 
       FIG. 3  shows diagrammatically a multi-roll calender in which is used closed web threading according to a second embodiment of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2 and 3  show an arrangement according to the invention for closing the web threading of the multi-roll calender  1  of a paper/board or finishing/converting machine. The calender  1  comprises a number of rolls  2 ,  3  formed into a roll stack, and a number of lift-out rolls  4 , which are arranged in such a way that the web W being treated travels from one calender  1  nip N to another via a lift-out roll  4 . 
     FIG. 1  shows a prior art solution which was already referred to in the introduction to the specification. 
   In the solution according to  FIGS. 2 and 3 , the calender  1  comprises alternately a hard metal roll  3  and a soft fibre or polymer roll  2 . The drive may take place, for example, by means of one roll, whereby power transmission to the other rolls takes place by means of frictional forces, or each roll has its own drive. Since the properties of paper develop better on the hard roll side of the nip, a so-called turning nip, which has two soft rolls  2  positioned in succession, is used near the centre of the calender. In this way, also the other side of the paper is treated against the hard rolls  3  at the end part of the calender. 
   Between the calender  1  roll  2 ,  3  and the lift-out roll  4 , the web W being treated is supported by means of at least one closing member  5 ,  5 ′ (FIG.  2 ),  6  ( FIG. 3 ) not extending through the nip N. The closing member is formed by a belt, wire or metal wire  7 , which is arranged to travel via two or more guide rolls  4 ,  8 . The closing member  5 ,  5 ′,  6  forms its own endless cycle. 
   In the embodiment according to  FIG. 2 , the first closing member  5  picks the web W up from the surface of the calender  1  roll  2  or  3 , and the second closing member  5 ′ transfers the web onto the surface of the next calender roll. The grip on the web W is turned between the first and second closing members  5 ,  5 ′. The guide roll of the closing member  5 ′ marked by reference numeral  4  forms a lift-out roll. The closing member  5 ,  5 ′ does not pass through the nip N, but the web W is picked up from either a polymer roll  2  or a metal roll  3  onto an underpressurized, full-width wire or corresponding closing member  7 . Supported by the wire, the web W undergoes the turn of the grip and is transferred onto the surface of the next roll by means of another underpressurized transfer system. The transfer of the web W is ensured by means of an adhesion difference or an overpressure zone. On the other hand, web tension will effect this transfer automatically. The web W is conveyed to the next nip N along the surface of the roll. Between the first and second suction transfer systems can be used underpressures of different magnitudes, which ensures the changeover of the grip from one system to the other. 
   The drives of the calender rolls operate the closing member, or the members have their own drives. If power is transmitted from the roll to the wire closing system, this contact may have a positive effect in that it heats the web. 
   The amount of evaporation of the calender can be limited by means of the closing member and air conditioning. 
   The closing member makes threading possible without having any separate devices in the stack. Gradually progressing threading also becomes possible. In addition, threading may be of full width. 
   In the solution relating to  FIG. 3 , the closing member  6  picks the web W up from the surface of the calender  1  roll  2  or  3 , and returns the web W onto the surface of the same roll, from where the web is conveyed to the next nip N along the surface of the calender roll. 
   In this solution, the closing member  6  comprises at least three guide rolls  8  located at the vertexes of a polygon, and in addition at least one guide roll  4  formed into a lift-out roll and arranged inside the area limited by the vertexes of the said polygon. 
   In the solutions relating to  FIGS. 2 and 3 , the web W is conveyed to the nip N along the surface of the calender  1  roll  2 ,  3 . At least one guide roll  8  of the closing member  5 ,  5 ′,  6  presses the closing means  7  of the closing member against the calender  1  roll  2 ,  3 . 
   The closing member  5 ,  5 ′,  6  is arranged to be underpressurized to ensure the transfer.