Filling and Sealing Packaged Foods
Practical Action
Hot-wire sealers have a metal wire that is heated to red heat to simultaneously form a seal and
cut the film, whereas a bar sealer holds the two films in place between heated jaws until the seal
is formed. In the impulse sealer, films are clamped between two cold jaws. The jaws are then
heated to fuse the films and they remain in place until the seal cools and sets.
Fig. 11. Band sealer for plastic film
Photo from Peter Fellows
Rotary (or band) sealers (Fig. 11) are used for higher filling speeds. They have continuous belts that
pass the mouth of a sachet or bag between heated rollers, and the two sides of the film are welded
together. The seal may then pass through cooling belts that clamp it until the seal sets.
Form-fill-seal (FFS) equipment
FFS equipment has different forms: vertical form-fill-seal, known as ‘transwrap’ or ‘flow pack’,
and horizontal form-fill-seal known as ‘pillow pack’ or ‘flow wrap’. The machines use a roll of
film, which they form into a tube, seal one end, fill the food and then seal the other end in a
continuous operation. All types of FFS equipment are very expensive, require a source of
compressed air and skilled maintenance technicians, and are therefore not likely to be affordable
by small-scale processors.
Shrink-wrapping and stretch-wrapping
Low-density polyethylene (see Technical Brief: Packaging Materials for Foods) is a film that
shrinks in two directions when it is heated by either hot air or a radiant heater. Shrink-wrapped
bottles, jars etc. are replacing cardboard distribution boxes in many countries (Fig. 12).
Fig. 12. Shrink-wrapped bottles and jars
Photo from Aqua Technology Inc
In stretch-wrapping, polyethylene or polyvinyl chloride film is wrapped under tension around
boxes on a pallet. The equipment is simple and low-cost (Fig. 13). Shrink-wrapping can also be
used to manually wrap individual pieces of food (e.g. cheese) or to form the lid of plastic trays.
Fig. 13. Stretch-wrapping cartons
Photo from Advance Lifts)
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