This is the third article in a series of blogs intended to educate users new to flow wrapping as well as to help experienced users looking for a quick reference. It explains the basic calculations used to determine film dimensions to flow wrap a specific product. (Read the other articles in this series Principle of Operation of a Horizontal Flow Wrapper and Sealing Fundamentals of Horizontal Flow Wrapping)
Cut-off Length (package length)
First of all it is important to determine the correct cut-off length. This is especially critical for registered film that incorporates graphics that need to be centred on each package. The diagram and formula below explain how to calculate this distance.
Secondly, you must determine the film web width. Again, one the key inputs for this calculation is the product dimensions. For products with more variable dimensions, such as bakery products, the film width must be increased to allow for bigger variations. This however, creates looser packs with wider finseal areas.
The 5mm (o.2″) can be explained by the distance (including the height and thickness of the deckplates) from the product to the fin seal rollers and some extra film to assure good tracking in the fin seal rollers. Common fin seal roller heights are 6, 9 and 15 mm. Together with the 5mm of film for tracking purposes, this results in finseal widths of 11, 14 and 20 mm respectively.
Use the formulas mentioned in this blog for a starting point only. Testing on your machine with actual product and film is necessary to determine film sizing and cut off.
More explanation on the basic calculations used to determine the film dimensions and flow wrapper configuration can be found in Bosch’s Guide to Flow Wrapping. Feel free to download it under the “Links and Downloads” section on the Pack 101 flow wrapper webpage on the Bosch Packaging website. This guide contains other sections to assist users in initially setting up their wrapper, changing over to new products, or solving problems common in flow wrapper operation.