Shrink Bundler Product

Overview

Shrink bundling is the technique of grouping multiple beverage cans or bottles together (4, 6, 12, or 24-packs), wrapping them tightly in polyethylene film, and heat-shrinking the film to create a compact, stable unit ready for case-packing and shipping. This is the standard in beverage packaging worldwide: soft-drink, beer, juice, and water bottles all leave the bottling line as shrink bundles.

The inline shrink bundler automates the entire process: bottles or cans arrive in single-file from an upstream line (filler/seamer/caser), are mechanically grouped into stacks (using pushers and gates), wrapped in polyethylene film, sealed, heat-shrunk in a tunnel, cooled, and discharged as finished bundles. Speeds of 50–150 bundles per minute are typical for modern machines, with throughput adjustable via VFD-controlled conveyor speeds and precisely timed solenoid gates.

How it works

Grouping and stacking: Bottles or cans arrive single-file on the main conveyor at 0.5–2 m/min. A pneumatic pusher arm (solenoid-actuated) periodically pushes bottles sideways to collect them into groups of 4, 6, 8, 12, or 24, depending on the target bundle size. This grouping is done on a platform with mechanical stops or gates that hold the group in place. For a 12-pack, the pusher cycles 12 times, pushing one bottle per cycle until 12 are grouped; then the group is released to the wrapping station.

Film wrapping: The grouped bundle is positioned on a wrapping platform. Film is fed from a motorized unwind spindle and, either with a rotating table underneath the bottles or a spiral guide above, is wrapped around the bundle. The film is unwound under controlled tension (10–20 N) to prevent sagging or tearing. One complete wrap (or a double-wrap for larger bundles) covers the group; the overlapping film edges meet at one side.

Sealing: At the overlap, a hot-sealing bar (electrically heated to 200–250 °C or ultrasonically driven) presses both film layers together for 0.5–2 seconds, creating a watertight seam. The seal is the only closure; there are no clips, tapes, or additional fasteners. A cutting blade (hot or ultrasonic) simultaneously cuts the film cleanly, disconnecting the bundle wrap from the continuous film supply.

Shrinking: The wrapped but still-loose bundle is conveyed into a hot-air or steam tunnel maintained at 100–130 °C. As the polyethylene film heats, its polymer chains relax and the film shrinks 15–30% in all directions, conforming tightly to the bundle. The shrinkage also pulls the seal tight and firms up the bond. Residence time in the tunnel is 20–60 seconds, depending on line speed and film thickness.

Cooling: After exiting the tunnel, the bundle is still warm (~50–60 °C) and the film is soft. A short cooling section (with passive air or optional fan cooling) allows the film to set and harden, stabilizing the bundle shape. By the time the bundle exits, it is rigid and ready for labeling or case-packing.

Polyethylene film and shrink properties

Film types:

• Low-density polyethylene (LDPE): 15–25% shrinkage, 12–25 micron, compliant and durable. Most common for beverage bundling.
• Linear low-density polyethylene (LLDPE): Similar shrinkage, higher puncture resistance, better for rough handling.
• Oriented polypropylene (OPP): 5–10% shrinkage, clearer appearance, stiffer. Used for premium or transparent wraps.

Shrinkage control: Shrinkage is controlled by:

• Tunnel temperature (higher temperature = more shrinkage, but risk of film puncturing or bottles softening).
• Residence time (longer time = more complete shrinkage, but slower throughput).
• Film thickness (thicker film shrinks slower, thinner film faster).
• Film width relative to bundle size (tighter wrap = tighter shrinkage).

Optimal tunnel setpoint is 110–120 °C for LDPE with 20–40 second residence time, achieving 20–25% shrinkage and a professional finish.

Synchronization and timing

The shrink bundler is entirely mechanical and pneumatic-controlled, with synchronization driven by an encoder on the main conveyor and a PLC:

1. Grouping gate closes: When the encoder pulse reaches position (e.g., every 6 bottle-pitches for a 6-pack), the stop gate closes, halting bottles.
2. Pusher activates: Solenoid opens air to the grouping pusher. The pusher cycles 6 times (one bottle per cycle) until the group is complete.
3. Gate releases: Group is released to the wrap station.
4. Film unwind triggers: Servo or stepper motor unwinds film at the correct speed and tension.
5. Sealer fires: After wrapping, a solenoid or timer triggers the sealing bar to close and cut.
6. Tunnel conveyor advances: Bundle enters tunnel for predetermined dwell time.
7. Cycle repeats: Next group enters the grouping position.

Total cycle time is 3–6 seconds per bundle, depending on bundle size and settings.

Common film and wrapping issues

Torn or wrinkled film: Causes: excessive unwind tension, incorrect guide-bar alignment, or obstruction catching the film. Remedies: reduce tension to 15 N, re-align guide bars, inspect for debris.

Poor seal: Causes: sealing bar temperature <190 °C, dwell time too short (<0.5 sec), or moisture/dust on film. Remedies: increase sealing temperature to 210–230 °C, extend seal dwell, clean film path.

Insufficient shrinkage: Causes: tunnel temperature <105 °C, residence time <15 sec, or film too thick (>25 micron). Remedies: raise tunnel temperature to 115 °C, slow conveyor speed (increase dwell), switch to thinner film.

Loose bundles post-shrink: Causes: film slipped during sealing or seal was incomplete. Remedies: verify seal temperature and dwell time, inspect sealing bar flatness (replace if worn or warped).

Throughput and energy

At 100 bundles/minute (typical 6-packs at standard speed):

• Power: 15–20 kW continuous (motors, heater, controls).
• Film consumption: ~0.5–0.8 kg per bundle (depending on wrap coverage and film thickness).
• Cost per bundle: $0.10–$0.25 in film and energy.

An 8-hour shift at 100 bundles/min produces ~48,000 bundles, consuming ~30–40 kg of film (cost ~$3–$8) and ~100–150 kWh of energy (cost ~$5–$8 at $0.05/kWh).

Hygienic design and washdown

In beverage plants, the shrink bundler is typically in a semi-open area and can be hosed down weekly. Stainless steel components (conveyor, tunnel chamber) are standard; solenoids and electrical boxes are mounted away from spray zones or protected by enclosures. Film path is kept clear of standing water by sloped surfaces and drain holes. Air compressor and heater intake are filtered to prevent contamination.