Filling Machines for Ice Pack Lines: Piston, Peristaltic and Gravity Compared

A gel filling line fails in ways a water line never does. The pump that filled 40 pouches a minute with water will fill 25 with gel, drift ±4% on weight, and leave strings of polymer across the seal bar. Buyers usually blame the SAP when the real problem is a filler sized for a different fluid.

Three fillers, three failure modes

Piston fillers handle gel well because they displace volume rather than relying on flow. Expect ±1% on a 500 g fill, 20–40 pouches a minute on a four-head machine, and a clean cut-off at the nozzle if the gel is shear-thinning. The failure mode is wear: abrasive SAP particles score the cylinder bore, and after 6–10 months you see weight drift. Specify a ceramic or hard-chrome bore and a piston seal rated for food contact.

Peristaltic fillers never touch the product, which is why small producers like them. Accuracy is ±2%, throughput 10–25 pouches a minute, and the tube is a consumable at $4–8 replaced every 100–200 hours. They handle 1–2% gels without shearing the polymer, which matters if you hydrate in line.

Gravity and overflow fillers are the fast option at 60–80 pouches a minute, but they rely on the product being uniform. A gel that has been sitting in the hopper for an hour stratifies, and the last 10% of the batch fills light. Use them only with continuous recirculation and a hopper agitator at 20–30 rpm, and check weights every 15 minutes rather than every shift.

What gel does to a filler that water does not

Gel is shear-thinning and slightly elastic. It climbs a rotating shaft, it holds air, and it does not level itself in the pouch. Air entrainment is the expensive one: 3% entrained air means 3% less mass in every pack and a compressible cushion that changes your headspace calculation. Fill from the bottom through a nozzle that stays submerged, and deaerate the batch in a vacuum tank at -0.6 bar for 10 minutes before filling, or let it stand 30 minutes after hydration.

Temperature matters too. Gel at 15°C flows about twice as fast as gel at 8°C, so a line started cold will overfill. Hold the batch at 20–25°C, and if you hydrate on site, remember that a 0.8% solution needs 4–6 hours to reach full viscosity — filling at hour one gives you a thin product that settles in the pouch and leaves a water ring at the top.

Nozzle, deaeration and the dry band

Use a 12–16 mm nozzle for a 0.8% gel; anything under 10 mm builds back pressure and causes stringing. Fit a positive cut-off — a snuff-back or a mechanical pinch — because a dripping nozzle puts gel exactly where the seal needs to be dry. Leave a 15 mm dry band between the fill line and the seal, and set the sealer to 145–155°C at 0.3 MPa for 1.0–1.2 s on 90 micron PE. If you fill above 40°C, add a air knife at the neck; condensation inside the film does the same damage as a spill.

Matching the filler to your batch size. Under 2,000 packs a day, a peristaltic bench filler pays back in weeks and leaves capital for film quality. Between 2,000 and 15,000, a four-head piston machine is the sensible middle. Above that, go inline: hydrate in a 2,000 L jacketed tank, recirculate, and fill on a rotary gravity machine with in-line checkweighing that rejects outside ±1.5%. Whatever you buy, run it for a week with your actual gel before you sign; a machine that fills water neatly can still string, drip and aerate on a 1.2% formulation.

Formulation and filler have to be chosen together — a highly shear-thinning SAP for gel packs fills cleanly on a piston machine at 25 pouches a minute where a high-swell grade strings and drips.