What is Pre-Stretch?

It is the controlled process of stretching the film before it is applied to the load.

Pre-stretch Gears

How does Pre-Stretch work?

The film passes between two rollers (primary and secondary) and a series of pinch rollers on the film carriage. The primary roller pulls film off of the film roll and into the film carriage at a controlled speed.

Wulftec pre-stretch
Film Flow
Pre-stretch
Area
Primary
Roller
Secondary
Roller

Due to the difference in the diameter of the rollers and the ratio of the gearing driving the rollers, the secondary roller turns at a faster speed than the primary roller, so the film is stretched between the two.

 

Why use Pre-Stretch?

  1. PRE-STRETCH FILM MEMORY
    2.
    • Once it is stretched the film try’s to return to its initial form. This is called the memory of the film.
    • It is this film memory that helps differentiate pre-stretch film from other methods of unitizing; it pulls back tightening on the load to better contain the product.
    • Minutes after the film is applied to the load, even with little or no film tension, the tightening action of the films memory can be seen.
    • Settling that can occur during shipment tends to loosen other methods of unitizing, whereas film memory continues to secure the load.
  2. STRENGTH
    • As you stretch the film, the tensile strength of the film is increased.
    • Depending on the ratio of the pre-stretch gearing, the tensile strength of the film can be increased up to twice as much as unstretched film.
  3. SIGNIFICANT SAVINGS
    • Pre-stretching film drastically reduces the cost of consumables (film) compared to wrapping a load with unstretched film, such as hand wrapping.
    • Machine payback can be as quickly as 6 months.