Replacing the shrink tunnel: stretch-wrap automation explained

Heat-shrink packing works by melting. The pack is sleeved or hooded in polythene, then driven through a tunnel hot enough to take the film past its shrink temperature, where it contracts onto the product. Everything else about the process follows from that one requirement. You need the tunnel, the extraction above it, the floor space it stands on, and the power to hold it at temperature for as long as the line is meant to run.

The costs that surprise people are the ones that do not scale with output. The tunnel has to be brought up to temperature before the first pack goes through, and half an hour of warm-up is not unusual. It then holds that temperature through breaks, through changeovers and through every stoppage upstream. The heat is continuous; the packs are not.

Heat is also not neutral to what is inside. Labels lift, printed sleeves distort, and chilled goods come back out of the tunnel warmer than they went in. On temperature-sensitive lines the tunnel is not only a cost. It is a limit on what you can pack at all.

Stretch film does the same job by a different mechanism. Instead of being shrunk onto the pack by heat, it is elongated as it is applied and then held there by its own recovery and its cling. The tension lives in the film, not in the temperature. Take the heat out of the process and the tunnel, the warm-up and the power draw leave with it.

That is what the AW12 and AW24 systems do at pack level. They wrap individual packs — trays of product, loose bottles gathered into a bundle — in stretch film rather than heat-shrink polythene, cold, at the point the pack is formed. There is no tunnel and no warm-up, so the machine starts when the shift starts.

The published figures for these systems put the draw at around 2 kW against roughly 15 kW for the heat-shrink line they replace, and film consumption at around half. Both are indicative and confirmed at quotation, so they are worth checking against your own line rather than taking on trust.

Three things change immediately. The floor space the tunnel occupied comes back, along with whatever extraction sat above it. The room gets cooler, which matters more than it sounds in a summer warehouse where the packing station is the hottest place in the building. And the first pack of the day goes out at the start of the shift rather than half an hour into it.

The fourth change is subtler and usually worth more. A tunnel wants a steady flow to be efficient, because the energy is spent whether or not packs are moving through it. A cold wrapper does not care. Short runs, frequent changeovers and stop-start demand stop being expensive, which is what makes the switch attractive to lines running many SKUs in small batches.

Cold stretch wrapping suits packs whose job is to be held together and protected in transit: trays, bundles of bottles or cans, multipacks that are broken open at the shelf, cases going into a distribution network. The wrap grips the pack, keeps it square and keeps it clean, and it strips off by hand.

Heat still wins where the sealed skin is the product. A printed shrink sleeve, a tamper-evident closure conformed to an awkward shape, a pack that has to be fully enclosed against water — those are shrink jobs, and pretending otherwise wastes everyone's time. The honest test is to run your own pack both ways and look at what arrives at the far end.

An automated wrapper is only as good as the roll running on it. Narrow-width film on a fast pack wrapper is asked to elongate consistently at speed, cling to itself, hold through handling, and do all of it from a roll that does not need changing every few minutes. Get the film specification wrong and the machine gets blamed for a film problem.

Toreto manufactures narrow-width films for automated vertical wrapping systems, along with printed and plain polythene bundle wrap — printed to your own artwork, or plain and pre-stretched where it is applied by hand. The spec is built to the line rather than pulled off a shelf, which is the same principle the pallet films are built on.

It is worth being blunt about who does what, because packaging suppliers are often vague on it. Toreto works with two machine builders — Matco International on pallet wrapping and strapping, and ATS (Advanced Tooling Systems UK) on filling, capping and robotic packaging. The machines are specified, installed and serviced by the manufacturer's own engineers, not by Toreto.

What Toreto does is manufacture the film that runs on them, and put you in front of the right engineer. If you are costing a tunnel replacement, that separation is useful. You get a machine answer from the people who build the machine and a film answer from the people who convert the film, instead of one supplier guessing at both.