Following is a description of stack wrapper machines used in a pretzel packaging application:
Larger pretzels are typically consumed singly while small pretzels are served in multiples. While it is fairly common seeing small pretzels packed loose into Quattro, Doy or Pillow packs, wrapping stacked large pretzels is rather difficult due to their very uneven and irregular shape.
Overcoming this obstacle with traditional horizontal continuous flow wrappers has proved to be a difficult task. New stack wrapper machines provide a solution.
The packing process can be briefly described as follows:
- The loose pretzels are taken by two double-arm pick-and-place machines (supplied by Schubert GmbH) at the exit of the freezer line and get stacked in piles of 3 pretzels each on our conveyor provided with a modular polyprop belt with two lanes of 145 x 132mm pockets with step-by-step movement, the last part being inclined by 5° up in order to let the product rest on the back flight and remain stacked.
- A short cross conveyor then meshes with the aforementioned conveyor to take the products over at 90° to the incoming direction.
- Two servo driven pistons push the six stacks of pretzels upwards through the 5° angled rectangular shaped forming tube equipped with a central dividing plate to prevent friction between the two rows of pretzel in order to let the product keep the correct position all the way to the finished bag. A light vacuum is applied by the pistons while travelling forward so as to help the film shrink around the product.
- The very short film carriage is placed underneath the forming set thus making the machine footprint as compact as possible.
- The wrapping film, pulled by two vacuum belts, is longitudinally fin-sealed by a servo driven rotating sealing band with a vertical adjustment to fit the easy-opening tear tape along the back seal.
- A pneumatic sliding plate holds the pack in a position parallel to the tube axis and tilts down by 15° to drop it on to the downstream conveyor.