Pallet Stretch Wrapper

Overview

A pallet stretch wrapper machine-applies stretch film around a loaded pallet so the load arrives as one stable block instead of shifting cartons. The turntable type is the most common: the pallet sits on a rotating Turntable Assembly disc while a Pre-Stretch Film Carriage climbs and descends a Mast Assembly, laying overlapping film bands from base to top. A semi-automatic machine wraps 20–40 loads per hour and handles pallets up to 2,000 kg and about 2.4 m tall; it replaces hand wrapping wherever a site ships more than roughly 15 pallets a day.

The engineering case for the machine is film economics as much as labour. Stretch film develops its holding force by being elongated, stretched LLDPE pulls back elastically against the load. A person walking around a pallet achieves perhaps 10–20 % stretch; the machine's powered pre-stretch carriage achieves 200–300 %, so 1 m of film off the roll becomes 3–4 m on the load. Film consumption per pallet drops by half to three-quarters, and the film goes on at consistent, programmed tension instead of whatever the operator's arms produced.

How it works

The operator deposits the pallet on the Turntable Disc by forklift (or over the Access Ramp with a hand pallet truck), ties or clamps the film tail, and starts the cycle from the Operator HMI. The Turntable Drive ramps the table up through its Turntable Inverter, soft acceleration matters, because a tall unwrapped load can topple under a hard start. The carriage applies a programmed count of bottom wraps, then the Carriage Lift Drive raises it at a speed that sets the band overlap, typically 50 %. A Load Height Photocell photocell detects the load top so the machine adapts to any pallet height without setup; the carriage applies top wraps and descends. On machines with a Film Clamp and Cut Unit unit, the Hot-Wire Cutter then melts the film through and the Wipe-On Brush presses the tail onto the load, and the table stops at the Home Position Sensor position ready for the next pallet.

Pre-stretch carriage

The carriage is the technical heart of the machine. Film from the Film Roll Spindle passes around two rubber-coated Pre-Stretch Roller drums linked by a fixed Pre-Stretch Gear Set ratio: the downstream roller surface runs 2.5–4 times faster than the upstream one, and the film elongates in the short gap between them. Because the stretch happens between driven rollers rather than between machine and load, the load, even a light or unstable one, never feels the full stretching force, only the separately controlled wrap tension.

That wrap tension is regulated by the Dancer Arm: a spring-loaded roller in the outgoing film path whose deflection feeds back to the Carriage Film Motor speed control. As a rectangular load rotates, film demand surges at each corner and slackens along each face; the dancer absorbs the transient and the motor servo follows it, keeping tension constant within the revolution. Without this loop, corners would see tension spikes that crush light cartons or snap the film.

Structure

The Base Frame is a low weldment, about 80 mm tall, seating a large Slew Ring Bearing ball bearing at the disc centre with perimeter Support Roller cams sharing the eccentric shock of forklift loading. The Mast Column bolts to the base and carries the carriage on Carriage Guide Track tracks, hoisted by a Carriage Lift Chain loop. Total installed power is modest, around 1.5 kW, and most semi-automatic machines run from a single-phase 230 V outlet.

Safety and variants

The hazards are rotation and the descending carriage. A Turntable Skirt closes the gap under the disc edge against foot entrapment, the Mast Guard covers chain pinch points, and a pressure-sensitive Carriage Safety Bumper stops carriage descent on contact with a person or fork. A latching Emergency Stop cuts all motion.

Above the turntable class, rotary-arm wrappers spin the film around a stationary pallet, necessary for very heavy, unstable or liquid loads that should not be rotated, and ring wrappers carry the carriage on a circular ring for fully automatic lines exceeding 100 loads per hour. Below it, robot wrappers drive themselves around oversized or floor-standing loads. All share the same pre-stretch carriage principle; the turntable machine remains the volume seller because it is the cheapest way to put powered pre-stretch to work.