Headbox apparatus for a papermaking machine

A headbox apparatus for a papermaking machine, said headbox apparatus defining a flow path for stock flowing between an upstream header and a downstream slice lip, said apparatus comprising:

• a plurality of blocks which are anchored within the flow path between the header and the slice lip;
• each block and an adjacent block of said plurality of blocks defining therebetween a flow tube for the flow therethrough of the stock;
• said flow tube having an upstream portion having an upstream and a downstream end;
• said flow tube having a downstream portion having an upstream and a downstream extremity,
• said upstream extremity of said downstream portion extending from said downstream end of said upstream portion;
• said downstream portion of said flow tube having a volume which is greater than a further volume of said upstream portion of said flow tube such that when the stock flows from said upstream portion to said downstream portion of said flow tube, the stock is mixed within said downstream portion;
• said plurality of blocks are fabricated from high density polypropylene;
• each block of said plurality of blocks has a first and a second end;
• each block has a first portion which extends from said first end of said block;
• each block having a second portion which extends from said first portion to said second end of said block;
• said first portion of said block defining a first and a second side, said first and second sides of said first portion being planar, said second side being disposed spaced and parallel relative to said first side;
• said second portion of said block defining a first and a second face;
• said first face of said second portion defining a surface and a further surface;
• said second face of said second portion defining a facing and a further facing;
• said first face being disposed spaced and parallel relative to said second face, said first face and said second face being spaced apart by a distance which is less than a further distance between said first and second sides of said first portion;
• said second portion of said block defining a first rib which is disposed between said surface and said further surface, said first rib extending between said first portion and said second end of said block;
• said second portion of said block defining a second rib which is disposed between said facing and said further facing, said second rib extending between said first portion and said second end of said block;
• said first portion defining a first chamfer which extends between said first side of said first portion and said further surface;
• said first portion defining a second chamfer which extends between said second side of said first portion and said further facing, the arrangement being such that said flow tube is defined between said adjacent blocks so that when stock flows through said upstream portion of said flow tube into said downstream portion of said flow tube, the stock is mixed within said downstream portion, the stock being guided by said second rib of said block and said first rib of said adjacent block such that a first and second vortex are generated within said downstream portion of said flow tube, said first vortex being disposed adjacent to said facing of said block and between said facing of said block and said surface of said adjacent block, said second vortex being disposed adjacent to said further facing of said block and between said further facing of said block and said further surface of said adjacent block so that mixing of said stock within said downstream portion of said flow tube is enhanced;
• said first vortex having a rotational direction which is opposite to a further rotational direction of said second vortex for further enhancing mixing of the stock within said downstream portion of said flow tube;
• said opposite rotational directions of said first and second vortices being predictably achieved by virtue of said first chamfer of said adjacent block and by said second chamfer of said block, said first chamfer of said adjacent block guiding the flow of stock flowing from said upstream portion of said flow tube to generate said first vortex so that said first vortex rotates within said downstream portion of said flow tube in said rotational direction;
• and
• said second chamfer of said block guiding the flow of stock flowing from said upstream portion of said flow tube to generate said second vortex so that said second vortex rotates within said downstream portion of said flow tube in said further rotational direction opposite to said rotational direction so that impact of said first and second vortices on a flow consistency and a velocity uniformity of said stock is reduced.