Band sealer for closing bags

A sealing machine for closing and sealing polyethylene bags by welding together film laminae forming the ends of the bags, comprising:

• an elongate frame,
• a bag top conveyor on the frame and including a pair of horizontally oriented endless conveyor chains in side by side relation with each other and defining elongate bag conveying runs confronting each other and cooperating with each other to receive, grip, carry, and discharge the ends of the bags in upright condition,
• a pair of endless heating bands and a pair of endless cooling bands, the heating and cooling bands being disposed adjacent the receiving and discharge ends, respectively, of the conveying runs, said bands having heat transfer runs extending along the conveying runs and engaging and confining the film laminae of the bag, the heat transfer runs of the heating bands being straight and parallel and lying flush against each other from end to end, the heat transfer runs of the cooling bands also being straight and parallel and lying flush against each other from end to end,
• mounting means including wheels on the frame and mounting such heating and cooling bands in spaced and end to end relation with each other, the adjacent ends of the heat transfer runs in the heating bands and also in the cooling bands, being offset with respect to each other in a direction along the runs, the band mounting wheels being similarly offset whereby adjacent band mounting wheels have their respective points of tangency to the respective bands spaced from each other in the direction of said heat transfer runs,
• heat generating and absorbing means adjacent the heating and cooling bands respectively, and including a pair of rigid stationary heating bars on opposite sides of the heat transfer runs of the heating bands and also including a pair of rigid stationary cooling bars on opposite sides of the heat transfer runs of the cooling bands, each of said heating bars and cooling bars having a plurality of heat transfer elements slidable thereon and engaging the flat side of the adjacent band, said heat transfer elements being movable toward and away from the bands and being obliquely tiltable about axes extending transversely of the bands and generally parallel to the flat sides of the adjacent band, electric heaters on said heating bars and generating heat therefor, said cooling bars having cooling fluid passage means therein to provide for dissipation of heat, and
• springs urging said heat transfer elements toward the heat transfer runs of the adjacent bands and being yieldable under influence of the film laminae passing between the bands to allow outward movement of the heat transfer elements with separation of the bands and oblique tilting of such heat transfer elements to conform to the localized orientation of the bands as the bags pass therebetween, said springs producing return of the transverse movement and oblique orientation of the heat transfer elements to maintain the heat transfer elements in flush engagement with the bands and to return the bands to lie flush against each other subsequent to passage of the bag from the heat transfer runs.