Stretch wrap machines are used in warehouses to secure boxes, bags, or containers on a pallet before shipping or storage. They reduce product damage by applying a controlled layer of plastic film around the load. The system matters because stable pallets move more safely through forklifts, conveyors, trucks, and distribution centers.
It also improves speed and consistency compared with hand wrapping.
A typical machine uses a rotating turntable or rotating arm, a film carriage, and a pre-stretch mechanism to apply tensioned film around the load. The film is stretched before it reaches the pallet, which increases coverage while using less material. Sensors, motors, rollers, and controls coordinate rotation speed, film tension, wrap overlap, and top and bottom reinforcement.
The physics involves torque, friction, tension, elasticity, and center of mass stability.
Key Facts
- Pre-stretch ratio = stretched film length / original film length.
- If a 1.0 m film section is stretched to 2.5 m, the pre-stretch ratio is 2.5:1 or 250%.
- Torque on a turntable is τ = rF, where r is radius and F is tangential force.
- Pallet stability improves when the center of mass stays inside the base of support.
- Film tension is force per strip width in practical settings, often measured as N/cm.
- Wrap overlap percentage = overlap width / film width x 100%.
Vocabulary
- Stretch wrap machine
- A warehouse machine that wraps plastic film around a loaded pallet to hold the load together for handling and transport.
- Pre-stretch
- The process of elongating stretch film before it contacts the pallet so the film can cover more area and apply holding force.
- Film carriage
- The moving assembly that holds the film roll and controls film delivery, tension, and vertical position.
- Turntable
- A rotating platform that spins the pallet while the film carriage moves up and down to wrap the load.
- Load containment force
- The inward force created by stretched film that helps keep the palletized items from shifting.
Common Mistakes to Avoid
- Confusing pre-stretch with overlap is wrong because pre-stretch describes how much the film is elongated, while overlap describes how much one wrap layer covers the previous layer.
- Using too little film tension is wrong because the pallet may look wrapped but still shift during acceleration, braking, or forklift movement.
- Using too much film tension is wrong because it can crush boxes, pull corners inward, or tear the film before the load is secure.
- Ignoring the pallet center of mass is wrong because a tall or uneven load can tip even when the outside is tightly wrapped.
Practice Questions
- 1 A stretch wrap machine stretches 0.80 m of film into 2.00 m before applying it to a pallet. What is the pre-stretch ratio and percent pre-stretch?
- 2 A turntable needs a tangential force of 120 N applied at a radius of 0.75 m to rotate a loaded pallet. What torque is required?
- 3 A pallet has heavy boxes stacked on one side and light boxes on the other side. Explain why stretch wrap alone may not make it safe to move, and describe one loading change that would improve stability.