Method and apparatus for forming a web

Claim 1

A method of forming a web having a predetermined grammage profile in its transverse direction comprising the steps of introducing a composite flow of particulate material suspended in air into the distribution chamber of a forming head, depositing said particulate material onto the upper surface of a horizontal air permeable belt moving through said distribution chamber to form a web, applying suction from the underside of said belt through a plurality of suction sections positioned below the distribution chamber of the forming head and oriented in substantially parallel relation to one another and to the longitudinal direction of said belt, also applying suction through a plurality of suction sections positioned downstream of said forming head, measuring the profile of the web downstream of said distribution chamber, comparing the measurements of the profile with predetermined set points, generating a control signal indicative of any difference between said profile measurements and said predetermined set points, and controlling the amount of suction applied in predetermined suction sections, including the amount of suction applied at the longitudinal edge portions of the web, in response to said control signal so as to correct deviations from the predetermined grammage profile across the web and to form a web having a higher grammage at said longitudinal edge portions than the grammage in the central region of the web.

Claim 2

A method of forming a web having a predetermined grammage profile in its transverse direction comprising the steps of introducing a composite flow of particulate material suspended in air into the distribution chamber of a forming head, depositing said particulate material onto the upper surface of a horizontal air permeable belt moving through said distribution chamber to form a web, applying suction from the underside of said belt through a plurality of suction sections positioned below the distribution chamber of the forming head and oriented in substantially parallel relation to one another and to the longitudinal direction of said belt, also applying suction through a plurality of suction sections positioned downstream of said forming head, measuring the profile of the web downstream of said distribution chamber, comparing the measurements of the profile with predetermined set points, generating a control signal indicative of any difference between said profile measurements and said predetermined set points, and controlling the amount of suction applied in predetermined suction sections, including the amount of suction applied at the longitudinal edge portions of the web, in response to said control signal so as to correct deviations from the predetermined grammage profile across the web and to form a web having a higher grammage at said longitudinal edge portions than the grammage in the central region of the web.

Claim 3

An apparatus for forming a web having a predetermined grammage profile in its transverse direction comprising a forming head including a distribution chamber, means for introducing a composite flow of particulate material suspended in air into a distribution chamber, a horizontal air permeable belt mounted for movement through said distribution chamber and for receiving the particulate material on the upper surface of said belt so as to form a web, suction means positioned on the underside of said belt at a plurality of spaced-apart locations along the path of travel of said belt and comprising a plurality of suction sections positioned in substantially parallel relation to adjacent suction sections and to the longitudinal direction of said belt for applying suction from the underside of said belt, web sensor means positioned downstream of said distribution chamber for measuring the profile of the web, means for comparing the measurements of the profile of the web with predetermined set points and for generating control signals resulting from said comparison, and suction control means responsive to said control signals for adjusting the suction applied in predetermined suction sections including the amount of suction applied at the longitudinal edge portions of the web so as to obtain a predetermined grammage profile across the web.

Claim 4

An apparatus for forming a web having a predetermined grammage profile in its transverse direction comprising a forming head including a distribution chamber, means for introducing a composite flow of particulate material suspended in air into a distribution chamber, a horizontal air permeable belt mounted for movement through said distribution chamber and for receiving the particulate material on the upper surface of said belt so as to form a web, suction means positioned on the underside of said belt at a plurality of spaced-apart locations along the path of travel of said belt and comprising a plurality of suction sections positioned in substantially parallel relation to adjacent suction sections and to the longitudinal direction of said belt for applying suction from the underside of said belt, web sensor means positioned downstream of said distribution chamber for measuring the profile of the web, means for comparing the measurements of the profile of the web with predetermined set points and for generating control signals resulting from said comparison, and suction control means responsive to said control signals for adjusting the suction applied in predetermined suction sections including the amount of suction applied at the longitudinal edge portions of the web so as to obtain a predetermined grammage profile across the web.