Headbox tube bank apparatus and method of directing flow therethrough

A headbox tube bank apparatus for the flow therethrough of stock in a papermaking machine, said apparatus comprising:

• a tube bank frame for rigidly supporting the tube bank, said frame defining a plurality of openings;
• a plurality of tubes cooperating with said frame such that each tube of said plurality of tubes extends through and is supported by an opening of said plurality of openings;
• each tube of said plurality of tubes having an upstream and a downstream portion, the arrangement being such that the stock flows through said tube from said upstream to said downstream portion;
• said upstream portion defining an internal crossmachine direction section of substantially circular configuration for maximizing the velocity of the stock through said tube;
• said downstream portion having a first and a second end, said downstream portion converging towards said second end thereof;
• said first end of said downstream portion defining an internal cross-machine direction section of substantially circular configuration greater than the cross-machine direction circular section of the upstream portion and being connected to said upstream portion;
• and
• said second end of said downstream portion defining a downstream orifice having a flow area in a cross-machine direction which is of substantially flattened rectangular configuration for progressively increasing the uniformity, stability, cleanliness, and for lowering the turbulence of the stock during flow thereof through said downstream portion, said downstream portion being an integral continuous element.