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Vertical Form/Fill/Seal 101: Key Considerations

As the name implies, vertical form/fill/seal (vf/f/s) machines form, fill, and seal packages in a vertical orientation.

Weighpack Form Fill Seal Machine

The machines convert films and other flexible substrates into bags and similar packages. The machines are used in a variety of industries, for diverse products with diverse requirements. There are similarities among users, though. The products, like liquids, powders, granulates, grains, and certain bulk items, all have flow properties.

Despite their seemingly do-all nature, vf/f/s machines are not stand-alone operations. They must be integrated into a production line, between upstream and downstream operations. The integration imposes decisions in aiming for the optimal fit. A reasonable start is an understanding of certain basics about vf/f/s machines, in the sequence of the three functions.

Forming. A roll of substrate is placed onto an unwinding roll. The substrate is pulled up, and then around and over rollers, to a forming collar and around a forming tube. The substate is formed into a package, the width of which is determined by the shape and size of the tube. The length of the package is determined by the programed distance in which side-positioned drive belts pull downward.

Filling. Positioned above the vf/f/s machine is a feeding (also called dosing or weighing) station. It drops product into the forming tube and into a package that has been given back and bottom seals (described in the next section). Dry product typically travels on an incline conveyor up to the feeding station. Liquids are pumped.

Sealing. First, vertical jaws seal the back of the package along its length. There are two types of vertical seals: overlap (or lap) and fin (or fold-over). They differ in how the inner and outer surfaces of the substrate are sealed together. An overlap seal is inner-to-outer and a fin seal is inner-to-inner. The difference in seal width, and therefore material usage, is negligible, and neither seal is inherently stronger. The choice depends on the substrate. For example, an outer surface that’s not readily heat-sealable is not compatible with an overlap seal.

Next, horizontal jaws seal the bottom of the package and, after the previously described filling is performed, seal the top of the package. The top seal is cut crosswise, allowing the separated package to fall onto a collection surface, such as a conveyor. After the cut, a portion of the top seal remains and becomes the bottom seal of the next package.

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