- save costs and reduce environmental footprint
The packaging industry is growing steadily. One of the key driver is the increasing need for packaging material. With more stringent hygiene regulations in the European food sector and changing consumer profiles, smaller packaging units are required. The number of single households, especially in large cities, continues to rise at a fast rate, which means that consumers purchase smaller quantities.
To save resources, i.e. material, as well as energy costs in the production process, measures are put in place to boost product quality while increasing the efficiency of production plants. The integration of web monitoring systems in the operating production process is a prime example of such measures. Linear array cameras, for instance, scan every square centimetre of the product to ensure that material containing inclusions or folds is rejected and not delivered to the customer.
Roll misalignment produces rejects
Figure 1 shows examples of such folds in plastic foils. On closer examination of these longitudinal folds it appears that they follow a particular direction. On the left (Fig. 1) the folds follow a downward direction in the plane of projection. On the right, the direction is clearly upward. This is the result of a force perpendicular to the actual production direction, causing the web to move up or down and creating folds. But where can such a force come from and, more importantly, how can it be avoided?
A common aspect of all web handling installations is that the materials are guided over numerous rolls throughout the production process. Therefore, all forces generally occurring as part of the process are generated by the rolls. Figure 2 shows how misalignment of the rolls can lead to transverse forces perpendicular to the production direction.
The schematic depiction of a roll (Fig. 2) that is not perpendicular to the production process illustrates how the transverse force comes about as a result of the incorrect distribution of forces. This transverse force causes distortion of the material web, shown here by the rhombus pattern. Figure 1 (right side) shows the same effect in a real situation, with the folds also having an irregular rhombus pattern.
In addition to the unwanted folds, the longitudinal sides are also asymmetrical, as shown by the red and green lines. Although it does not directly disrupt the film manufacturing process itself, it does cause problems in the subsequent processing steps. Due to asymmetrical winding of the film, it prevents straight running of the web.
Good machine alignment, and roll alignment in particular, is essential to achieve maximum efficiency of the production in the packaging industry. With modern production machines running faster with larger working widths, this has even become a key requirement. The rise in speed and working widths increases the risk of folds and the production of rejects.
Good roll alignment throughout the entire installation requires a complete measurement of all the rolls involved in the web handling process. Until recently, this was a very difficult task, since only optical and mechanical procedures were available. Both methods are very time consuming and take up a great deal of space in the machines. Due to structural reasons, it is often not possible to get the required direct line of sight from one roll to the next. Today, PARALIGN provides an inertial measurement system that allows roll parallelism measurements in a fraction of the time needed by conventional measurement methods.