Unitization
Stretch film, also known as stretch wrap or pallet wrap, is one of the most popular unitization materials on the market. By “unitization”, we simply mean the process of bundling and securing several individual packages together, often on a pallet. Other unitization techniques commonly used include shrink wrapping, bagging and strapping. The following outlines the benefits of stretch film over other unitization techniques as well as identifies its weaknesses.
Benefits of Stretch Film
- Less damage to product versus strapping
- Virtually eliminates load crushing by distributing the force of the film over the entire load, without the use of corner boards
- Can take a shock or vibration and still maintain the load in its original unitized configuration
- Material cost per pallet is less than shrink wrapping or strapping
- Equipment is less expensive than shrink wrapping, bagging or automatic strapping equipment
- Provides lower operating and maintenance costs
- Provides a large energy saving over shrink wrapping
- May be produced tinted or opaque for product identification or pilferage prevention
Weaknesses of Stretch Film
- Provides less resistance to moisture than shrink wrap
- Cannot be used to (vertically) compress a pallet load because its primary holding force is in the horizontal direction
Palletization
There are three main causes of compression-loss when palletizing boxes:
Pallet Overhang, Wooden Pallets, and Interlocked Stacking Patterns.
We know, boxes are not rocket science. But, did you know that merely changing the way you stack and palletize your boxes could significantly affect their performance? Incredibly, it has been found that improper palletization can result in boxes losing up to 50% of their compression strength!
Pallet Overhang
The most common culprit of compression-loss is boxes hanging over the edge of the pallet. When this occurs, the two vertical edges of the box not hanging over the pallet edge are primarily supporting the load. In fact, when boxes are stacked on a pallet with as little as ½ inch hanging-over, as much as 30% of their strength is lost! The solution here is to make sure you are using the proper pallet size or the proper palletizing pattern to avoid overhang. You may also want to look at reconfiguring the box dimensions to fit the pallet.
Wooden Pallets
With the space between deckboards on a wooden pallet averaging 1-4 inches, it is common that the bottom of the box is not being entirely supported. This too can cause significant compression losses in the unit load. In fact, up to 15% of compression strength may be destroyed. This may be avoided by choosing pallets with deckboards that are strategically positioned so all of the vertical edges of the box (corners) are being supported. Another option would be to use corrugated pallet liners to cover the bottom of the pallet (pallet deck) to make it a solid surface.
Interlocked Stacking Patterns
This situation can be much like a double-edged sword. Using an interlocked pattern, which rotates each layer on the load, can destroy up to 50% of the compression strength. Palletizing boxes so that they are columnar, or vertically stacked (stacking one box directly on top of the other) is the preferred method. This method, however, makes it difficult to keep the load intact during handling. One solution to this problem is to stabilize the load by using stretch wrap. This can be done by using a stretch wrap machine, or by simply spiral wrapping the load by hand.
Storing & Handling Boxes
Box users make major investments in the development, production and promotion of their products. The boxes they need for shipping represent, on average, less than 1% of the value of their contents. Consequently, if a few boxes are unusable, the loss involved is relatively insignificant, right? Wrong! Remember, without the lowly corrugated box, the product cannot be shipped! Simply stated, unusable boxes can result in unsold products. Therefore, it is worth protecting your inventory of empty corrugated boxes to ensure that:
- The boxes are usable, and don’t end up ready for recycling before they can fulfill their purpose;
- The boxes will run smoothly on automatic setup, filling and closing equipment, avoiding costly jam-ups, repacking and lost time;
- The boxes will stack squarely, avoiding costly accidents during palletization, storage and shipment; and
- The boxes provide the intended protection against damage, leakage or other loss.
Guidelines for proper handling and storage of empty boxes, developed by the Fibre Box Association and the Packaging Machinery Manufacturers Institute, have been summarized and presented below. Following these simple guidelines will maximize the performance and prolong the useful life of your corrugated boxes:
- Store boxes flat from the time they are received until they are ready for use. Damage to
the edges of boxes can occur if they are stored on edge, which can affect runnability on automatic equipment, closure and product protection. - Leave the strapping, bundling or other unitizing device in place until boxes are ready for use.
- Alternate bundle direction, or alternate loose boxes at intervals for greater stability.
- Avoid stacking boxes too high, whether loose or banded, because of slight instability
of stack. Although close, most box styles are not totally flat. The extra thickness
of the tab used at the joint adds a bulge, usually near the centre, giving a tilt to a loose stack of boxes. Alternating directions of bundles when stacking compensates for the
tilt and increases stability. - When building pallet loads of flat boxes, use deck boards to distribute weight evenly.
- Stack boxes only on smooth, clean surfaces.
- Use good materials handling procedures; don’t drop or throw bundles or pallet
loads into place. - Don’t stand, sit or climb on stacked boxes, or place other heavy objects on them. This may crush or distort the flutes in corrugated boxes which will reduce their protective abilities. Any uneven pressure on the flutes can cause crushing or puncture.
- Store boxes off the floor, on pallets or other flat dunnage.
- Store boxes indoors and protect them from overhead moisture. This may require
covering boxes or storing them away from overhead pipes or areas of ceiling condensations. - Avoid temperature and humidity extremes and fluctuations in storage areas. This may require storage away from doorways that are opened frequently. When it is impossible to avoid extremes or fluctuations, bring the boxes to the packing line or another area for a period of time to condition them to a more normal atmosphere before using them. Excessive moisture or water can soften or dissolve the corrugating adhesive, causing delamination; a box that literally falls apart won’t offer much protection. Heat can reduce the moisture content of corrugated boxes, making them brittle. Extreme cold also affects moisture content, making the boxes more fragile.
- Follow “first in, first out” practices in using inventory. Corrugated boxes stored under ideal conditions will remain usable for a long period of time. Less-than-ideal or fluctuating conditions reduce their effectiveness and shorten their useful life. Common sense dictates that old inventory be used before starting on the new.
the edges of boxes can occur if they are stored on edge, which can affect runnability on automatic equipment, closure and product protection.
of stack. Although close, most box styles are not totally flat. The extra thickness
Don’t stand, sit or climb on stacked boxes, or place other heavy objects on them. This may crush or distort the flutes in corrugated boxes which will reduce their protective abilities. Any uneven pressure on the flutes can cause crushing or puncture.
This may requireThe preceding information and illustrations on how to store and handle corrugated boxes are from the Fibre Box Handbook (Fibre Box Association, Rolling Meadows, IL, 1992)