Sheet forming unit for producing a material web and method for operating the sheet forming unit

A sheet forming unit for a paper machine, the sheet forming unit comprising:

• a headbox for outputting a suspension jet;
• an inner fabric forming a loop;
• an outer fabric forming a loop, said inner fabric loop and said outer fabric loop forming a gap for receiving said suspension jet;
• a forming element arranged within said inner fabric loop, said inner fabric loop and said outer fabric loop jointly wrapping around said forming element at least partially in a wraparound region;
• a plurality of guide rolls arranged within said outer fabric loop;
• a white-water box for receiving white water accumulating in a region of said forming element, said white-water box being arranged in said outer fabric loop;
• a machine-wide guide element which is at least one of:
• a) arranged in said wraparound region within said outer fabric loop such that white water is formed into a jet and is directed into said white water box such that a contact surface is formed between said suspension jet and a space formed by said outer fabric loop, a length of said contact surface viewed in a direction of travel being greater than 100 millimeters (mm), wherein a gap is formed between said guide element and said forming element, a progression of said guide element essentially following a contour of said forming element and said progression of said guide element is selected such that said gap viewed in a direction of travel exhibits a divergent progression;
• and
• b) in a region of at least one of said plurality of guide rolls of said outer fabric a machine wide guide apparatus is provided outside said space formed by said outer fabric loop, said guide apparatus forming a converging gap with said outer fabric in a direction of movement.