Method and apparatus for top sealing woven bags

Abstract

A system is provided for filling and sealing bags and is especially useful with woven polybags formed of thermoplastic material. The system includes a plastic welder having a folding device for folding over a portion of the filled bag which is sealed by a welding tip and pinch rollers. The welding tip may be moved between welding and non-welding positions based on a bag sensor or timer. A contact prevention member prevents the welding tip from contacting and damaging a coating on a portion of the bag. The system is configured to form a substantial seam without using hot melt adhesive.

1 . A plastic welding system comprising:
 a folding device configured for folding over a top section of a bag as the bag moves in a downstream direction;   a downstream end of the folding device; and   a welding tip adjacent and downstream of the downstream end of the folding device.   
     
     
         2 . The system of  claim 1  further comprising a fully folded section of the folding device configured so that the top of the bag is fully folded from a downstream end of the bag to an upstream end of the bag when the bag is within the fully folded section. 
     
     
         3 . The system of  claim 1  wherein the folding device adjacent the downstream end includes a substantially vertical front guide, a substantially vertical rear guide and a substantially vertical intermediate guide between the front and rear guides; the front and intermediate guides define therebetween a substantially vertical front space; the rear and intermediate guides define therebetween a substantially vertical rear space; and the welding tip is directly downstream of the intermediate guide. 
     
     
         4 . The system of  claim 3  further comprising
 a bottom of the intermediate guide; and 
 a bag-engaging contact prevention member which is adjacent the downstream end of the folding device and extends rearwardly beyond the intermediate guide and lower than the bottom of the intermediate guide so that the contact prevention member is adapted to push rearward a sub-seam portion of the bag immediately below the top section of the bag so that the welding tip does not contact the sub-seam portion, the top section including a folded over overlapping portion and an overlapped portion which is overlapped by the overlapping portion. 
 
     
     
         5 . The system of  claim 1  further comprising
 a rear surface of the welding tip; 
 a bag-engaging contact prevention member which is adjacent the welding tip and extends rearwardly beyond the rear surface of the welding tip so that the contact prevention member is adapted to push rearward a sub-seam portion of the bag immediately below the top section of the bag so that the welding tip does not contact the sub-seam portion. 
 
     
     
         6 . The system of  claim 1  further comprising
 a sensor positioned to sense a bag as the bag moves downstream; and 
 a controller which is in communication with the sensor and controls movement of the welding tip. 
 
     
     
         7 . The system of  claim 6  wherein the controller controls the welding tip to move from a non-welding position to a welding position in response to a signal from the sensor. 
     
     
         8 . The system of  claim 6  further comprising a timer; wherein the controller is programmed to control the welding tip to move from a welding position to a non-welding position in response to a signal from the timer indicative of passage of a specified time period. 
     
     
         9 . The system of  claim 8  wherein the controller is programmed to control the welding tip to move from the welding position to the non-welding position in response to the signal from the timer absent a signal from the sensor indicative of sensing a bag at the sensing location within the specified time period. 
     
     
         10 . The system of  claim 1  further comprising
 a timer; and 
 a controller which is in communication with the timer and controls movement of the welding tip. 
 
     
     
         11 . The system of  claim 10  wherein the controller is programmed to control the welding tip to move from a welding position to a non-welding position in response to a signal from the timer indicative of passage of a specified time period. 
     
     
         12 . The system of  claim 1  further comprising a pair of pinch rollers downstream of the welding tip. 
     
     
         13 . The system of  claim 12  further comprising a cooling device positioned for cooling the pinch rollers. 
     
     
         14 . The system of  claim 13  further comprising a source of compressed air in fluid communication with the cooling device. 
     
     
         15 . The system of  claim 13  wherein the cooling device is configured for directing airflow toward the pinch rollers. 
     
     
         16 . The system of  claim 1  further comprising a bag-filling assembly upstream of the folding device. 
     
     
         17 . The system of  claim 1  further comprising
 a conveyor having a conveyor surface which is movable in the downstream direction and adapted to carry bags in the downstream direction; 
 a pair of rotatable pinch rollers adapted for pinching therebetween an upper portion of a bag which moves in the downstream direction on the conveyor surface; and 
 a synchronizing mechanism operatively connected to the conveyor and pinch rollers to control a downstream movement rate of the conveyor surface and a rotation rate of the pinch rollers in a synchronized manner so that a bottom of the bag and the upper portion of the bag move downstream at respective rates which are substantially identical. 
 
     
     
         18 . The system of  claim 1  further comprising
 a conveyor having a conveyor surface which is movable in the downstream direction and adapted to carry bags in the downstream direction; 
 a pair of revolvable pinch belts adapted for pinching therebetween an upper portion of a bag which moves in the downstream direction on the conveyor surface; and 
 a synchronizing mechanism operatively connected to the conveyor and pinch belts to control a downstream movement rate of the conveyor surface and a revolution rate of the pinch belts in a synchronized manner so that a bottom of the bag and the upper portion of the bag move downstream at respective rates which are substantially identical. 
 
     
     
         19 . A plastic welding system comprising:
 a folding device configured for folding over a section of a bag as the bag moves in a downstream direction;   a welding tip adjacent the folding device;   a timer; and   a controller which is in communication with the timer and controls movement of the welding tip.   
     
     
         20 . A method comprising the steps of:
 filling a woven polybag formed of a thermoplastic material with a fill material; and   welding an open end of the bag to form a welded seam to close the bag with the fill material therein without using in the welded seam a hot melt adhesive which is distinct from the thermoplastic material.