By Uffe Steen Kristiansen
Director of Sales, Palletizing & Packaging, Beumer Corp.
For many end-of-line packaging professionals, the choice of a pallet packaging method may not immediately surface as a critical success factor when designing, upgrading or refurbishing a production line or distribution center. While pallet packaging may not be the most alluring aspect of a packaging operation, choosing a pallet packaging method can significantly impact overall profitability, sustainability, and distribution chain performance.
There are three recognized methods available for pallet packaging: conventional spiral stretch wrapping, heat-shrink hooding and stretch hooding. Each method has its advantages and disadvantages depending on the specific application.
Spiral stretch wrapping
Spiral stretch wrapping is the most common method for pallet packaging and provides a low-cost method for securing pallet loads for shipping. The equipment uses cast or blown linear low-density stretch film, which is pre-stretched 60 to 400 percent, depending on equipment type, before being wrapped around the pallet load. There are many manufacturers of spiral stretch-wrapping equipment, and both equipment and film are readily available through a large number of distributors.
The stretch-wrap film can be applied in a variety of patterns depending on the load stability and protection required. A myriad of models are available, from turn-table models—where the operator manually cuts the film and attaches the film tail to the pallet load—to fully automatic rotary-arm, or satellite, models with top-sheet dispenser, automatic film roll change and speeds up to around 100 pallet loads per hour.
While spiral stretch wrapping technology offers a cost-effective pallet packaging solution in some applications, there are drawbacks. Because the film is applied with multiple layers of a relatively narrow overlapping film band, spiral stretch wrapping provides little stability when compared to a hood-style method, as there is insubstantial vertical holding force unitizing the pallet and the load.
For protection against the elements, a top-sheet is often applied to the pallet load. This provides nominal protection, but is practically insufficient for outdoor storage and shipping on open flatbed trucks in inclement weather. Accordingly, the cost of building additional warehouse storage capacity, as well as costs associated with protective tarpaulins for flatbed shipping, must be considered when comparing spiral stretch wrapping with a hood-type method.
The physical properties of stretch-wrap film present challenges that should also be considered when evaluating different pallet packaging methods. Among other things, the overlapping layers of stretch-wrap film tend to trap moisture, and the cling additive in the film attracts dirt and dust. Moreover, relatively low-volume film rolls mean shorter film change intervals, thus reducing machine availability and increasing operating costs. Accurately forecasting and controlling the cost of consumables (stretch-wrap film, in particular) can also be difficult, as individual operators often follow their own preferences in applying stretch-wrap film.
Introduced in the 1960s, heat-shrink hooding is the oldest form of pallet packaging by means of polyethylene film.
Until the advent of newer technology, heat-shrink hooding was the preferred method for optimal stability and pallet load protection. Heat-shrink hooding equipment uses gusseted tubing that is cut and sealed to form a bag. The oversized bag is applied over the pallet load and is then shrunk using heat. The most common heat sources for shrink hooding are natural or liquid propane gas, but other heating methods, such as infrared or electrical "hair dryer-style" heaters, are also used. There are various types of heat-shrink hooding equipment available. Most contemporary approaches to heat-shrink hooding are of the ring type, which allows for a more controlled heat application and provides the all-important bottom shrink that ensures proper pallet and load unitizing.
The heat-shrink hooding method provides good pallet load stability and protection; it works particularly well with loads that have a substantially smaller footprint than the pallet, as the film will shrink tightly around the contours of the pallet and load.
The operating costs of a heat-shrink hooding system are much higher than those of both spiral stretch wrapping and stretch hooding. Because the film bag is shrunk (as opposed to stretched), it must have a larger pre-shrink circumference than the perimeter of the pallet load so that the equipment can apply the bag over the pallet load prior to the application of heat—requiring substantially more film than stretch-hooding. Using significant energy consumption for heating, the heat-shrink hooding method also carries the risk of fire, which can often mean higher insurance premiums to protect against potential losses. Additionally, heat-shrink hooding equipment can be more maintenance-intensive compared to the other two methods.
The fact that most of the performance advantages offered by heat-shrink hooding (such as pallet load stability and protection) are available with the more cost-effective stretch hood technology has all but made obsolete heat-shrink hooding for bagged products.
Introduced in the late 1980s, the stretch hooding method of pallet packaging has, over the past decade, gained significant market share at the expense of heat-shrink hooding and spiral stretch wrapping—not only for bagged products, but also for products in Octabins, cases, pails and other similar primary packaging formats. The principal reason for this is that stretch hooding provides benefits with respect to operating costs, speed, reliability, sustainability and distribution chain performance.
The hood is formed from gusseted tubing, and the height of the pallet load is measured automatically as the pallet enters the machine—ensuring that only the amount of film required for the application is precisely dispensed. Among other operating benefits, energy consumption is low since the film is not heated, and available servo drive technology further reduces energy and maintenance costs.
The quality of today's domestically available, co-extruded stretch-hood films allows for pre-stretch percentages exceeding 80 percent, providing better film yields than what was possible even a few years ago. This performance, combined with film thickness reduction down to 1.6 mils, means that the per-pallet film cost with stretch hooding is competitive with that of spiral stretch wrapping.
Some stretch-hood equipment can also be programmed to allow for application-specific selection of a non-sealed sleeve (for lowest possible film consumption), a closed hood (for optimal load protection and stability) or even an open hood (to avoid moisture condensation for food packaging). Consistently maintaining its tension, stretch-hood film is particularly well-suited for products that, due to their physical properties, tend to settle after being bagged and palletized.
The high quality of today's films means that a single film hood format can, within certain limitations, be used to stretch-hood multiple pallet sizes. However, it is important to analyze the net financial benefit of a one-size-fits-all approach, as the total film cost will be lower if each pallet size has a dedicated film hood format.
Unlike spiral stretch wrapping, stretch hooding provides ready evidence of tampering, as it is not possible to remove a product from the pallet without tearing the film. The smooth film surface also provides for easier loading and unloading of trailers. With spiral stretch wrapping, the friction between the films on two pallet loads can cause tears and film tails to come undone, compromising the integrity of the pallet load.
For products sold at retail outlets, such as home centers, the clear, one-layer, stretch-hood film provides much better product recognition at point-of-sale than multi-layer spiral stretch-wrap film does. It is also possible to print advertising or handling instructions on the stretch-hood film. A side benefit is that stretch-hood film allows for easy bar-code scanning, virtually eliminating misreads and associated remedial costs.
Addressing current trends in sustainability, recent advancements in stretch-hood technology have reduced film usage per-pallet-load, while simultaneously offering more intuitive user interfaces, reduced energy consumption, smaller machine footprints, and throughputs exceeding 150 pallet loads per hour. Modular designs also allow for faster and less costly installation. In addition, the use of intuitive graphic user interface screens helps with ease of operation and troubleshooting.
Cost of ownership
Properly evaluating the choice of a pallet packaging method goes far beyond comparing equipment acquisition costs. Several factors can significantly impact the cost of ownership and, consequently, the return on investment.
• Equipment cost: Spiral stretch wrapping equipment is available in multiple speed ranges and varying degrees of automation. With prices ranging from below $10,000 for semi-automatic low-speed models to $120,000 or more for high-speed rotary-arm or satellite models, there is generally a spiral stretch wrapping model for every budget.
Heat-shrink hooding equipment also comes in both semi- and fully automatic models. The price range is generally between $50,000 for semi-automatic models (where the operator applies a pre-made shrink bag over the pallet load) and $200,000+ for fully automatic, high-speed models.
The price of stretch-hooding equipment has come down over the past couple of years due to increased competition and the development of simpler equipment. Prices range from roughly $140,000 for single-format equipment to $200,000+ for multi-format equipment. For high-output facilities, it is important to realize that one single stretch-hood machine can replace multiple spiral stretch-wrap machines due to the higher achievable speeds.
• Film cost: If protection and stability are secondary, the film cost for spiral stretch wrapping a pallet load can be low because of minimal film thickness and comparatively high pre-stretch percentage. Where protection and stability are critical, however, multiple layers of stretch-wrap film must be applied for stability, and a top-sheet added for protection. This can greatly increase film cost per pallet.
Heat-shrink hooding is significantly more expensive in film cost per pallet than either of the other two methods because of the need to oversize the film hood prior to shrinking. The film cost per pallet for shrink hooding can easily exceed that of stretch hooding by 40 percent or more. Substantial energy costs associated with heat-shrink hooding also add to the cost-disadvantage of this method.
For stretch-hood film, recent developments have enabled the use of much thinner films with significantly higher pre-stretch percentages than was previously possible. This makes stretch hooding competitive with spiral stretch wrapping in terms of film cost per pallet load for applications where moderate load stability and protection is required.
• Labor and maintenance cost: Spiral stretch wrapping equipment is simple to operate and maintain. Semi-automatic models, in particular, require little training for operation. Maintenance costs, however, tend to be on the high side because of the quantity of moving components. The drawback of spiral stretch-wrap equipment is that the relatively low-volume film rolls require frequent replacement at higher throughputs. Some manufacturers do offer an automatic film change option; however, this can be an expensive option, adding complexity to the equipment.
Having to replace the film roll at short intervals reduces line availability and increases direct labor costs. The resulting costs from outdoor storage, or measures to protect from the weather, can be significant and must be included in a total cost-of-ownership analysis.
Heat-shrink hooding equipment is moderately maintenance-intensive in comparison with spiral stretch wrapping and stretch hooding, as heat-shrink hooding involves more wear parts that require replacement at regular intervals.
The least labor-intensive method of pallet packaging is stretch hooding. The film roll can be up to 39-inches in diameter, easily allowing for 10 times longer film change intervals and increasing line availability. The roll change is a simple procedure typically taking no more than 10 minutes to return the machine to production. Unlike stretch wrapping, adjustments to machine settings are rarely necessary, thus ensuring consistent high-quality packaging results. Moreover, with fewer wear parts than stretch-wrap machines, stretch-hooding equipment requires little maintenance, and five-sided pallet protection eliminates the need for protective tarps.
Making the choice
Making the right choice of pallet packaging method involves a thorough analysis of many factors that influence not only the daily operating costs, but also the entire distribution chain performance. When product leaves the production facility, it is at its highest value-added state and should arrive at the customer's facility in the same condition.
For low-throughput applications, where stability and protection are secondary to initial acquisition cost, spiral stretch wrapping provides an attractive option. When production line efficiency, protection against the elements, load stability and product recognition at the point-of-sale are important criteria, then stretch hooding may be a better solution in overall packaging performance and total value of ownership.
View a video of stretch-hood machine at http://youtu.be/tH0Y7qX0hbQ
Source: Beumer Corp.