Modelling the material flow and web tension in the vertical form–fill–seal packaging process

Vertical form–fill–seal (VFFS) machines are widely used to form bags for packaging products such as confectionary and snack food. One critical component of the machine is the forming shoulder, which needs to manipulate, without damage, the packaging material from a flat state into a tube. Some models of the geometry of the shoulder are available and have been used to help with its design and manufacture. However, there currently exists no theoretical basis for determining the geometry of the forming shoulder needed to process particular packaging materials. This paper investigates the application of Euler's theory for material flow around cylinders to the case of forming shoulders used in vertical form–fill–seal systems. It is shown that the theory is indeed applicable, and an inequality relation between the measured coefficient of friction of the material and the forming shoulder parameters is established. It is further shown how this can be used to direct the design of a forming shoulder for a particular application.