What Is Pre-stretch Film?Pre-stretched film is made with a process that allows film to be stretched before it is applied. The stretch film is pre-stretched by two rollers. The second roller’s rotational speed is quicker than the first, thus stretching the film between them.
How Is Film Pre-stretched?When film is stretched mechanically between the film carriage rollers due to the gearing ratio and diameter of the rollers. it is pre-stretched.
Why Use Pre-stretch Stretch Film?
- Strength: By stretching the film, the tensile strength of the film increases 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 pre-stretching 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 pre-stretched compared to stretch wrapping a load with film that has not been pre-stretched.
- 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.
What Is Post Stretch Film?Post stretch is the stretch in the film created by the film tension between the film carriage and the load being wrapped, which is also known as force to load. In post stretch film, if the film tension is increased, the post stretch will be intensified.
How To Post Stretch?The amount of film force applied is directly proportional to post stretch. Increase film force and the post stretch will also increase.
Benefits of Post Stretch Film?Pros: Maximizes load retention of the film. Cons: This “tension” stretch is generally on the corners of a load, which can cause damage too high.
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. [/one_half]
Why Have Film Force?Low film force restrains the film from returning back to its original state. [/one_half_last]
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?
- Using a 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.
Cost ReductionLowers handling costs: By unitizing products with stretch film you handling costs greatly decrease. Savings in labor: 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. The time saved also offers valuable cost savings.
Additional Benefits Of UnitizingInventory 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.
- 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 plant damage by using stretch film. Stretch Film wrapped goods moved by forklift or pallet jack, are less likely to sustain damage than loose boxes carried by hand. Moving a unitized load in a warehouse reduces the risk of product damage.
- Minimize your shipment damages with the proper use of stretch film. 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.
Should I be using Metallocene?
- Only if it works and is cost competitive.
- A film labeled Metallocene can have any were from 5% to 100% Metallocene.
- Metallocene can improve some properties and decrease others.
- It depends on how the Metallocene is used and what the other layers consist of. There are a as many different ways to use Metallocene as there are different types of film on the market.
- The bottom line is your concern should be focused on how the film performs in your specific application. Being sold on film composition or structure can be a game of “Smoke & Mirrors”.
Should I be using 7 Layer film?
- Only if it works.
- Being 7-layer doesn’t mean that the film will perform better in your application.
- Some 7-layer films can use the same material in all 7 layers. It depends on the materials used, the quality of the manufacturing technique and equipment design.
- Once again the concern for the film user should be does the film work day-in-day-out in my application at the lowest possible cost.
Will switching down a gauge save money?
- Every situation is different and you may get more benefit from increasing the gauge.
- Some applications require faster cycle times.
- Some applications are only concerned with cost per roll.
- There are many hidden costs to down gauging:
- Cycle times- Actually increasing the gauge and decreasing the amount of wraps can increase cycle times and decrease costs per load. Increasing wrapping time per stretch wrapper.
- Film breaking- Lighter gauge films are more likely to have film breaks, either from machine variations, edge damage during handling or film defects. Automated plants have very low tolerance for any type of film breakage, labor costs must be considered in when choosing gauge of the film.
- Load integrity- Thorough testing should be completed before considering changing to a lower gauge. Remember the old saying “Do not believe anything you hear and only half of what you see”. Load retention can change over time, which will affect your package, either during transit or in your customers’ warehouse.
Should I be using one-sided cling films?
- One-sided cling films cover a broad range of slip and cling properties.
- High slip films are usually films that allow the wrapped load to slide against each other, even with a lot of force applied.
- Most one-sided cling stretch films do not have high slip, but will prevent pallets from sticking together. This will satisfy a majority of end users.
- If you require your wrapped pallet or product to slide against other wrapped products than a “High Slip” film would be best for your application.
- If you are only concerned with pallet not sticking together, than a common one-side cling film would work well.
- Most applications do not need two-sided cling films a standard one-side cling film will work well.
- Some stretch wrappers rotate backwards and can put the slip side against the stretch rollers, causing the film not to stretch. And resulting in poor yields.
Do I need a UVI film?
- UVI additives can be expensive.
- If you plan to store the film outside for any length of time, you need a UVI film.
- Most UVI films will last for an average of 3-6 months. It requires high concentrations of UVI to guarantee a film to last 12 months, which can increase the cost significantly.
- A UVI Film that will last 9 months from September to May, could only last 3 months during June, July and August.
- A UVI film that will last 6-9 months in Canada, may only last 3 months in Florida.
- Some UVI’s can protect the product, but they have limited use and will only last for a short period of time. The best protection for the product is an opaque film or bag.
How can I decide if my film breaks are caused by the equipment or the film?
- One clue may be the pattern of film breaks, if there seems to be a pattern associated with the breaking it is more than likely is the machine causing the breaking.
- Tearing from the edge could be rough handling of the rolls either during transit or during use.
- Film breaks caused by imperfections tend to be random and not related to any position or timing of the wrapping cycle.
- Breaking occurring in the same place repeatedly on different rolls would indicate a machine problem.
- Even slight changes in machine settings can dramatically affect the performance of the stretch film. For example, small adjustments to the force setting can change the force on the film by 100%, causing damage to the load and film breaks.