Method and apparatus for continuous production of bags from thermoplastic film

A method for continuous production of bags from thermoplastic film in the form of a continuous longitudinally advanced two layer web with the film layers continuously joined along one longitudinal edge of the web wherein said web has a cross-section such that the number of film layers in one portion is greater than in the thickness of the remainder of said cross-section, from the leading end of which web bags are successively made by transverse seam welding and severance carried out at substantially equally spaced locations on the web, the steps which comprise:

• feeding said web tangentially onto the outer surface of a continuously rotating welding drum provided with a plurality of welding anvils extending parallel to the drum axis of rotation and spaced substantially equally about its circumference by a distance (X) greater than the width (Y) of the bags to be formed;
• effecting a preliminary seal of said film layers along a portion of a path transverse to the direction of travel of the web, wherein said web has a cross-section such that the number of film layers in said portion of said transverse path is greater than in the thickness of the remainder of said cross-section by bringing a heating bar into contact with said portion of the web located over one of said anvils and maintaining said contact during a predetermined length of travel of said web in contact with said drum circumference;
• thereafter simultaneously welding and severing said web along the whole of said path traversing said web inclusive of said preliminary seal;
• and
• after completion of the welding and severing step, pulling back the newly formed leading edge of said web relative to rotation of said drum by a distance on said drum circumference substantially equal to X minus Y in the direction opposite to that of rotation of the drum.

Apparatus for fabrication of bags by transverse seam welding and severance from the leading edge of a longitudinally advanced web having at least two layers of thermoplastic film and having the film layers continuously joined along one longitudinal edge of the web wherein said web has a cross-section such that the number of film layers in one portion is greater than in the thickness of the remainder of said cross-section, said apparatus comprising:

• a frame and a welding drum mounted therein;
• said drum having a plurality of elongated welding anvil elements extending parallel to the axis of rotation of said drum and spaced substantially equally about its circumference thereof each anvil element being resiliently mounted in said drum and movable radially toward and away from said drum axis and biased outwardly to a normal position slightly above the drum surface;
• means for continuously rotating said drum;
• web feeding and positioning means spaced from said drum for directing said web tangentially on to the surface of said drum;
• means to retain said web on said drum surface after it has been received thereon;
• preliminary sealing means comprising means for bringing a heating bar into contact with a portion of said web located over one of said anvils, for moving said heating bar continuously through a path which includes an arc conforming to the contour of the surface of said drum and synchronously with said anvil during rotation of said drum and retained web through a predetermined distance and for removing said heating bar from contact with said web;
• means for bringing a welding bar into seam welding and severance contact with the full width of said web and underlying anvil in registration with the location of prior contact with said heating bar and for removing said welding bar from contact with said web after completion of said seam welding and severance;
• web pull-back means located adjacent to said web prior to said preliminary sealing means;
• actuating means for causing said web pull-back means to engage said web and apply tension thereto sufficient to pull back the web relative to rotation of said welding drum by a predetermined distance in the direction opposite that of rotation of said drum after said web welding bar has been removed from contact with said web;
• and
• means for coordinating the rotation of said drum and the movements of said heating bar, said welding bar and said web pull-back means in mutually timed relationship.

A method for production of bags from thermoplastic film in the form of a continuous longitudinally advanced web having at least two layers with the film layers continuously joined along one longitudinal edge of the web wherein said web has a cross-section such that the thickness at least in one portion of the web is greater than the thickness of another portion of said web, from the leading end of which web bags are successively made by transverse seam welding and severance carried out at substantially equally spaced locations on the web, the steps comprising:

• feeding said web tangentially onto the outer surface of a continuously rotating welding drum provided with a plurality of welding anvils extending parallel to the rotational axis of said drum and spaced equally about its circumference;
• effecting a preliminary seal during a predetermined length of travel of said web on said drum along one portion of a path transverse to the direction of travel of the web, wherein said one portion has a cross-section greater in the thickness than another portion of said cross-section of the web;
• and
• thereafter simultaneously welding and severing said web along the whole of said transverse path inclusive of said preliminary seal.

Apparatus for fabrication of bags by transverse seam welding and severance from the leading edge of a longitudinally advanced web having at least two layers of thermoplastic film and having the film layers continuously joined along one longitudinal edge of the web wherein said web has a cross-section such that the number of film layers in one portion is greater than in thickness of the remainder of said cross-section, said apparatus comprising:

• a frame and a welding drum mounted therein;
• said drum having a plurality of elongated welding anvil elements extending parallel to the axis of rotation of said drum and spaced substantially equally about its circumference thereof each anvil element being resiliently mounted in said drum and movable radially toward and away from said drum axis and biased outwardly to a normal position slightly above the drum surface;
• means for continuously rotating said drum;
• web feeding and positioning means spaced from said drum for directing said web tangentially onto the surface of said drum;
• means to retain said web on said drum surface after it has been received thereon;
• preliminary sealing means comprising means for bringing a heating bar into contact with a portion of said web, for moving said heating bar synchronously with said anvil during rotation of said drum and retained web through a predetermined distance and for removing said heating bar from contact with said web, wherein said heating bar is mounted on an endless flexible drive member supported on sprockets and provided with drive means to move said belt continuously in a path which includes an arc conforming to the contour of the surface of said welding drum and spaced therefrom a distance such that the heating bar is brought into contact with said web and underlying anvil at the beginning of said arc and moves in synchronism with said web and anvil thereby maintaining said contact while transversing said arc;
• means for bringing a welding bar into seam welding and severance contact with the full width of said web and underlying anvil in registration with the location of prior contact with said heating bar and for removing said welding bar from contact with said web after completion of said seam welding and severance;
• web pull-back means located adjacent to said web prior to said preliminary sealing means;
• actuating means for causing said web pull-back means to engage said web and apply tension thereto sufficient to pull back the web relative to rotation of said welding drum by a predetermined distance in the direction opposite that of rotation of said drum after said welding bar has been removed from contact with said web;
• and
• means for coordinating the rotation of said drum and the movements of said heating bar, said welding bar and said web pull-back means in mutually timed relationship.