Hot bar welding is a technique that is mainly used to join thermoplastic films, i.e. materials having a thickness of less than 0.5mm. The technique is based on the principle that if two thermoplastic films are pressed against a heated metal bar, they will soften and a joint can be made between them. Since the technique relies on the conduction of heat through one of the films, this limits the thickness of material that can be welded. Sometimes two heated bars are employed, one either side of the films, and this has the effect of reducing the welding time.
The equipment comprises one or two metal bars, which are generally electrically heated. One of the bars is hinged to allow the placement and removal of the thermoplastic films, and the weld pressure is applied mechanically by the operator or via pneumatic cylinders. A coating of PTFE is often applied to the bars to prevent softened or molten thermoplastic from adhering to them.
Hot bar welding can be a rapid process with typical weld times in the order of 1-3 seconds. Hot bar welding has found application in a number of industrial sectors, but is most widely used in the packaging industry for sealing bags and films made from thermoplastics.