What Is Prestretch Film?
· A process that allows stretch film to be stretched before being applied.
· The stretch film is prestretched by two rollers. The second rollers rotational speed is quicker than the first, thus stretching the film between them.
Why Use Prestretch Stretch Film?
By stretching the film, the tensile strength of the film increase so that it becomes drastically stronger.
· FILM MEMORY
After the film is stretched it wants to return it to its original form. The more you use this prestretching process, the worst the film memory becomes.
When the stretch film is applied to a load with no force to load, quickly it will be able to detect that the film has tightened due to its memory as it tries to return to it original size.
Stretch film memory is what distinguishes stretch film from other means of packaging unitizing. Settling that can happen during shipment can loosen other methods of unitizing products. Stretch film memory takes up the slack and continues to secure the load during shipment.
· FILM ECONOMIES
Your cost of stretch film is reduced when it is prestreched compared to stretch wrapping a load with film that has not been.
· STRETCH CONSISTENCIES
Using just hand or machine to add tension to stretch film does not provide uniform stretch and is not able to have reliable performance. This type of stretching can lead to intermittent load failures.
How Is Film Prestretched ?
· When film is stretched mechanically between the film carriage rollers due to the gearing ratio and diameter of the rollers it is prestretched.
What Is Post Stretch ?
· The stretch in the film produced by the film tension between the film carriage and the load being wrapped, which is also known as force to load.
· If the film tension is increased the post stretch will be intensified.
Benefits Of Post Stretch
Maximizes load retention of the film.
This "Tension" stretch is generally on the corners of a load, which can cause damage too high.
How To Post Stretch ?
· The amount of film force applied is directly proportional to Post stretch.
· Increase film force and the post stretch will be increase.
What Is Film Force ? (film tension)
· The tension created in stretch film due to the films attempt to return to its original state after having been stretched.
Why Have Film Force ?
· Low film force restrains the film from returning back to its original state.
How To Create Film Force ?
· Film Force is formed by creating tension between the load and the film carriage that can be produced both mechanically and electrically.
· Electrically reducing the speed of the film leaving the carriage compared to what the load requires increases the stretch film force which causes the film to stretch between the load and the carriage.
· Mechanically postpones the dancer arm which measures the speed demand of the load will reduce the film feed leaving the carriage which increases the force.
What Is Film Feed ?
· Provide the stretch film required to wrap a load while keeping the tension of the film constant.
· The carriage must vary the supply of film with the demand of the load while the load revolves.
· A dancer roller reads the demand of the load.
How To Control Film Feed ?
· SENSOR: The stretch wrappers dancer arm rotates a cam shaft which sends a varying signal to the drive board then it sends varying voltage to the motor. The larger the dancer size the larger the output voltage. The larger the output voltage means the faster the film is fed.
· LOWER HANDLING COSTS
Unitizing products with stretch film, greatly decreases handling costs.
· LABOR SAVINGS
Handling of individual boxes is more time consuming than handling a unitized load. Another benefit of unitization packaged goods is the amount of man hours saved in the movement and shipment.
· TRANSPORTATION SAVINGS
Unitizing packaged goods increases the speed at which they are moved, carrier vehicles spend less time at docks. This time saved also offers valuable cost savings.
Reduce the risk of pilferage and theft because packages are in a enclosed load and are complicated to remove. The loss of packaged goods is much easier to keep track of if they are shipped out in unit loads rather than individually, which reduces the occurrences of lost or stolen items.
· MINIMIZE IN PLANT DAMAGE
Stretch Film wrapped goods moved by forklift or pallet jack, are less likely to substain damage than loose boxes carried by hand. Moving a unitized load in a warehouse reduces the risk of product damage.
· MINIMIZE SHIPMENT DAMAGE
It is less likely in shipping that dense and or heavy items will be packed on top of palletized unit loads. You stand a greater chance of not being damaged because of this.
Additional Benefits Of Unitizing
· INVENTORY CONTROL
Unitizing products speeds up control of inventory since large unitized loads can be recognized, counted and managed more easily and individual boxes.
· CUSTOMER SERVICE
Unitizing products and goods for your customers allows them to offload and move goods through their warehouse more efficiently.