The cycle times of film-processing machines have been constantly increased since the beginning of their development. The intermittent working method especially in longitudinal sealing on bag forming, filling and sealing machines represented a restriction in performance which made it necessary to develop new continuous working methods. Regardless of the speed, it is possible to produce sealing seam of any length using a relatively short band length.
The working principle corresponds to the impulse sealing method described above. While the cycle is executed at a “fixed point” between fixed sealing bars with a heating up and cooling down process, in the continuous method the film passes through heated-up and cooled-down areas. Depending on the film type different design types are used in praxis:
The film layers are in contact with circulating bands. The film layers are pressed together from the inside by a heated and a cold jaw pair. The circulating bands are driven at the same speed at which the film is transported. Consequently, no relative motion exists between the band and the film. The jaw pairs move along the inside of the band and must therefore be made of an appropriate material. With this device all sealing films can be fused. The jaw pairs and especially the circulating bands are wear parts, as they are exposed to continuous abrasion.
Hot air sealing
In this design type the heat is transmitted by heated air, i.e. it is contactless. The cooling zone is formed by a cold air nozzle. The mere contact of the film layer will be sufficient to perform a sealing. The system is almost free from wear and thus very easy to maintain. However, the working speed decreases as the film thickness increases. This is due to the limited heat transmission by way of hot air.