Forming screen with unperforated longitudinal strips, a machine having the forming screen and method of producing a fibrous web

A forming screen for a machine for producing a fibrous web, the forming screen comprising:

• a perforated substrate having a form of a continuous web extending in a longitudinal direction, a first lateral edge and a second lateral edge opposite said first lateral edge;
• a perforated useful region disposed between said first lateral edge and said second lateral edge, and on said perforated useful region the fibrous web to be produced is formed when the forming screen is used and said perforated useful region is spaced from said first lateral edge and said second lateral edge;
• a first edge strip disposed between said first lateral edge and said perforated useful region and a second edge strip disposed between said second lateral edge and said perforated useful region, wherein said first edge strip and said second edge strip are also perforated;
• an unperforated first separating strip extending in the longitudinal direction being disposed between said first edge strip and said perforated useful region and/or an unperforated second separating strip extending in the longitudinal direction being disposed between said second edge strip and said perforated useful region, wherein said unperforated first separating strip and/or said unperforated second separating strip has or have a width of between 1 mm and 8 mm;
• and
• an upper side facing the fibrous web and a lower side facing away from the fibrous web, wherein the perforated useful region having a plurality of through-channels formed therein and extending through said perforated substrate and connecting said upper side to said lower side, wherein said through-channels are non-cylindrical and have a cross-sectional area decreasing along a thickness direction of said perforated substrate from said upper side to a central region of said perforated substrate disposed between said upper side and said lower side, wherein an upper edge of at least one of said plurality of through-channels is in direct contact with an upper edge of at least one other adjacent through-channel of said plurality of through-channels such that said upper edge of said at least one of said plurality of through-channels does not lie in a plane.