Constraints influencing the design of forming shoulders and the use of exact geometry

This paper considers the design of the forming shoulder, which is a crucial part of a vertical form, fill and seal machine used for packing small discrete items. As with other forms of packaging machine, the basic design has evolved over a number of years and is based on a number of empirical design rules, whose application can be time consuming and costly. To address this issue, the aim of this paper is to investigate the effects of machine-material interaction and the parameters of the design that influence these effects. In particular, the geometry of the shoulder is considered and means for defining its complex form discussed, together with the design issues related to the performance of the machine in terms of web tension and its ability to track correctly. In industrial practice, a modified form of the geometry is used to encourage better tracking, even though this increases web tension. An experimental investigation with exact shoulders has shown that they have better tracking properties than conventional ones and that they can deal successfully with a wider range of materials. It has also been found that a different approach to the design of the shoulder is possible, concentrating initially on web tension rather than tracking. As an exact shoulder can handle a wider range of materials, it is also found that it is possible to design machines in which fewer change parts are required. (c) 2007 Journal of Mechanical Engineering. All rights reserved.