Headbox of a paper machine or equivalent

Abstract

The invention relates to a headbox of a paper machine or equivalent. The headbox comprises in its connection cleaning tubes ( 11 a 1 , 11 a 2 . . . ), by means of which stock is separated into accept and reject, the accept being passed forward in the headbox and further onto a forming wire (H 1 ).

1 . A headbox ( 10 ) of a paper machine or equivalent, characterized in that it comprises in its connection cleaning tubes ( 11   a   1 ,  11   a   2  . . . ), by means of which stock is separated into accept and reject, the accept being passed forward in the headbox and further onto a forming wire (H 1 ).  
     
     
         2 . A headbox as claimed in  claim 1 , characterized in that the headbox ( 10 ) comprises the cleaning tubes ( 11   a   1 ,  11   a   2  . . . ) of a first step (PuI) of a hydrocyclone installation ( 11 ).  
     
     
         3 . A headbox as claimed in the preceding claim, characterized in that the cleaning tubes ( 11   a   1 ,  11   a   2  . . . ) are situated one upon the other and adjacent to one another in the headbox of the paper machine such that at least a stock flow (L 1 ) from a stock inlet header (J 1 ) is passed into each cleaning tube, the accept being passed centrally within the cleaning tubes out of each cleaning tube, advantageously to an intermediate chamber ( 30 ) of the headbox and further to a turbulence generator ( 31 ) and further to a slice cone ( 32 ) and further onto the wire (H 1 ).  
     
     
         4 . A headbox as claimed in any one of the preceding claims, characterized in that each cleaning tube ( 11   a   1 ,  11   a   2  . . . ) comprises a flow duct (a 1 , a 2  . . . ) for the stock from the stock inlet header (J 1 ) and advantageously also a flow duct (e 1 , e 2  . . . ) for dilution water from a dilution water inlet header (J 2 ), and that the cleaning tube ( 11   a   1 ,  11   a   2  . . . ) comprises an internal inner sleeve ( 34 ) inside an outer tube ( 33 ), and that the reject is passed out of the end of the outer tube ( 33 ) and the accept is passed through a flow duct (f 1 ) situated centrally inside the inner sleeve ( 34 ) forwards in the headbox.  
     
     
         5 . A headbox as claimed in the preceding claim, characterized in that the dilution water is passed to an inlet end (C 1 ) of each cleaning tube ( 11   a   1 ), which inlet end is situated in the adjacency of the inner sleeve ( 34 ), and that the reject is passed from an end (C 2 ) of the cleaning tube opposite to the above-mentioned end (C 1 ) further to a reject inlet header (J 3 ) and further to a second step (PuII) of the hydrocyclone installation ( 11 ).  
     
     
         6 . A headbox as claimed in any one of the preceding claims, characterized in that the dilution water inlet header (J 2 ) comprises in its connection control valves (V 3 ), by means of which the dilution flow is regulated into each cleaning tube ( 11   a   1 ,  11   a   2  . . . ).  
     
     
         7 . A headbox as claimed in any one of the preceding claims, characterized in that each cleaning tube ( 11   a   1 ,  11   a   2  . . . ) comprises an outer tube ( 33 ), which comprises, at least over part of its length, a conical portion to produce a spiraling flow inside the outer tube ( 33 ) of the cleaning tube ( 11   a   1 ,  11   a   2  . . . ).  
     
     
         8 . A headbox as claimed in any one of the preceding claims, characterized in that both the stock inlet header (J 1 ) and the dilution water inlet header (J 2 ) taper towards their ends and comprise a duct ( 26 ) for a circulation flow back to a thick stock duct ( 22 ) to the suction side of a pump (P 2 ).  
     
     
         9 . A headbox as claimed in any one of the preceding claims, characterized in that a duct ( 27 ) connected to the reject inlet header (J 3 ) is provided with a valve (V 1 ), which regulates the reject flow to the second step (PUII) of the hydrocyclone installation ( 11 ).  
     
     
         10 . A headbox as claimed in any one of the preceding claims, characterized in that the dilution headbox (J 2 ) comprises a duct ( 28 ) for a circulation flow, which duct comprises a valve (V 2 ) for regulating the dilution circulation flow to the duct ( 27 ) leading from the reject inlet header (J 3 ).  
     
     
         11 . A headbox as claimed in any one of the preceding claims, characterized in that there is a duct ( 16 ) for a dilution circulation ( 14 ) from a wire section, in which connection dilution water is pumped by means of a pump (P 1 ) through a screen ( 15 ) further to the duct  16  and further to the dilution inlet header (J 2 ).  
     
     
         12 . A headbox as claimed in  claim 1 , characterized in that hydrocyclone cleaning is arranged to form the last process stage of the short circulation before the forming of a slice jet taking place in the headbox, and there are two or more flow ducts from the hydrocyclone cleaning to the headbox proper.  
     
     
         13 . A headbox as claimed in  claim 1 , characterized in that a dilution flow (L 2 ) and a stock flow (L 1 ) are combined before passing them to the cleaning tubes ( 11   a   1 ,  11   a   2  . . . ).