The Variation of Plastic Pallets Manufacturing Process

Introduction

People are accustomed to using wooden pallets, which appears to be a traditional implement for product handling. Currently, wood pallets stand for 90% of the market. Nevertheless, the pallet market is slowly transforming form wood to plastic usage. Thus, the iconic wooden pallet sustains as an omnipresent authority in storage, transportation, and distribution of manufactured products around the globe. In fact, pre-distinction of wooden pallets has been charged majorly because of their higher costs. Nevertheless, plastic pallets proceed in making infringements due to their reusability, durability, and lightweight character. The current paper will demonstrate the history of plastic pallet usage and the variety of manufacturing processes. Such an approach will be helpful in defining the possibility of innovative tools’ appearance and the future enhancement of processes in making plastic pallets better or more efficient.

Plastic Pallets

Pallets appear to be simple and mere structures, which are being utilized for supporting loads. Nevertheless, their design and manufacturing process appears to be highly sophisticated. Plastic pallets are used to equip a structural foundation for a load and secure it during transportation, handling and storage (Chaudhari, Pathak, & Sharma, 2012, p. 74). Plastic pallets are typically created from high-density polyethylene (HDPE) and polyethylene teraphthalate (PET), due to the fact that these materials are being outlined as thermoplastics, which is resistant to corrosion and weather, making plastic pallets highly durable. Facts demonstrate that pallets can be produced in practically any size and form (Rosato, 2011, p. 43). Despite the fact that plastic pallets have become more widespread, they are still utilized in less than 10 percent of applications, encompassing their inner pools (Rosato, 2011, p. 43). The facts reveal that the manufacturing procedure of a typical 48x40 plastic pallet requires eight times more raw materials, on the contrary to reusable wooden pallet (Chaudhari et al., 2012, p. 74). Moreover, the production process requires five times more energy, and releases more emissions into the water and air, as well as contributes to the higher quantity of waste, in contrast to reusable wooden pallets.

The thermoplastic resin appears to be the predominant plastic utilized in pallets manufacturing, as it softens when energy is added. Thermoplastic resins encompass polyethylene, poly-vinyl, polyesters, polypropylenes, polycarbonate, poly-nylon, and engineered thermoplastics (Chaudhari et al., 2012, p. 75). The facts demonstrate that thermoplastic category of resins appears to be less costly, less challenging in processing and recycling, and more persistent to shocks and impacts, on the contrary to thermosetting resins. Polyethylene appears to be the major thermoplastic raw material that is used in plastic pallets that are manufactured in the U.S., polypropylene stands for the dominant type in Europe (Chaudhari et al., 2012, p. 75). High density of various polyethylene is the most common in plastic pallets, as their properties can be altered drastically by modifications. The major part of plastics is highly solid and strong but appears to be less stiff, which is not the case with wooden ones. Decreased stiffness might restrict the load-carrying capability of plastic. This is a main reason why plastic pallets have not been typically utilized in regards with free-span racking (Rosato, 2011, p. 43). Nevertheless, currently, numerous plastic pallet manufacturers attempt to be executed in order to meet the stiffness necessities. For instance, one current cheap prototype has small I-beams (which are created from a discrepant resin), incarnated in the polyethylene bottom deck (Deng, Shen, Zhu, Wang, & Li, 2010, p. 117). Thus, if a plastic pallet, which costs more to obtain, has to emulate in the market place on a cost-per-usage ground, it should change to a more durable product. In fact, it has to resist the impacts and shocks, in order to become more durable. Nevertheless, if a material is made more impact-resistant, it then requires sacrificing stiffness due to the fact that these two properties are opposed to each other. Plastic appear to be more shock resistant on contrary to wood, but it is less stiff. The main solution for this specific problem stands for composites or consolidating techniques (Rosato, 2011, p. 89). Test and trial are underway on numerous composite materials. A perfect composite should incorporate the material, which is highly persistent and stable to impact and material, which is characterized by stiffness (Zini & Scandola, 2011, p. 1906). This stiffness can be equipped through the usage of carbon, glass, or wood fibers.

Plastic Pallets: Manufacturing Processes and Tools

There are numerous different processes, which can be applying to manufacture plastic pallets. All of them appear to have their unique benefits and costs characteristics. Different processes can affect such factors as pallet volume, performance, standardization, and costs.

Injection Molding

The above mentioned facts demonstrate that high performance pallets are typically manufactured through injection molding. An injection molder incorporates a heated barrel with a rotating screw. Colorant and virgin (high quality) plastic are melted together in the barrel, while melted plastic is later being injected into a mold, and pressure is applied (Chaudhari et al., 2012, p. 77). The facts demonstrate that clamping and injection forces appear to be quite high. The major part of injection molding is performed utilizing high-quality or virgin reprocessed resin (Camarinha-Matos & Scherer, 2013, p. 574). The facts show that despite the fact that injection molding is regarded as expensive, it actually appears to be the highest speed procedures, due to the fact that pallets can be manufactured highly quickly when the mold goes to press (Deng et al., 2010, p. 117). Therefore, injection molding is selected for manufacturing plastic pallets when a large quantity of pallets is necessary (Chaudhari et al., 2012, p. 77). The general mass of large or standardized orders stands for injection molded ones. In fact, injection molded pallets provide caliber dimensions and appear to be characterized by high impact resistance from fork tine abuse. This manufacturing process is the idea for producing standard size plastic pallets (Camarinha-Matos & Scherer, 2013, p. 574). If the pallet has to be unique, manufacturers typically reduce to invest in the equipment and tools to produce it, as unique tools will not be used to implement the specific plastic pallets on a regular basis. The facts demonstrate that tools can be changed when orders exceed 50,000 units due to the fact that this quantity allows justifying the investment (Deng et al., 2010, p. 117).

Structural Foam Molding

Structural foam molding stands for another manufacturing process, which is broadly utilized for producing plastic pallets due to the fact that this process is less costly, on the contrary to injection molding which, at the same time, provides practically analogous benefits. Structural foam molding stands for a type of specific low-pressure injection molding. The manufacturing process demonstrates that nitrogen gas and polypropylene or polyethylene plastic pellets are being injected in the mold pocket (Mitchell, Vandeperre, Dvorak, Kosior, Tarverdi, & Cheeseman, 2014, p. 2113). Heat stimulates the blasting agents, which actually transform into a cellular pith with a secure and firm outer surface. This process requires fewer raw materials and helps in creating a plastic with a greater strength-to-load ratio (Chaudhari et al., 2012, p. 77). The facts show that structural foam is produced under lower pressure when comparing it to injection molding. It utilizes gas in the manufacturing procedure, making the inner part of the plastic part appear as porous and not solid. This sponginess provides the possibility to create more rigid platforms, which makes structural foam a perfect solution in furnishing high weight capability in racking. Nevertheless, it results in a trade-off, as the sponginess makes the plastic more sensitive to various damages. Thus, pallets created from structural foam will break into pieces when hit with force. This poses issues for sensitive operations.

Thermoforming

A third manufacturing procedure stands for thermoforming. The most widespread plastic pallet (used during postal services and in numerous supermarkets) stands for thermoformed (Mitchell et al., 2014, p. 2113). This manufacturing process requires two steps. It starts with heating plastic pellets, usually polyethylene, in order to create a superseded plastic sheet of the required thickness. Secondly, one or two sheets are formulated against molds when the air between the sheet and mold is evacuated (Rosato, 2011, p. 43). This method appears to be time consuming, as cycle times are slower, on contrary to previous methods (Chaudhari et al., 2012, p. 77). This procedure appears to be an option, on the contrary to the above-mentioned manufacturing processes. The facts demonstrate that nestable pallet concepts have been evolved, applying the thermoform procedure. On the one hand, malleability and capability to take fork tine abuse appear to be the best benefits of thermoformed plastic (Deng et al., 2010, p. 117). On the other hand, due to the fact that thermoformed plastic appears to be the most flexible one among the previously mentioned, pallets manufactured through this process do not perform well in regards with heavy weight settings. Thermoformed plastic pallets are usually highly durable and lightweight (Deng et al., 2010, p. 117). They appear to be hollow, which makes them susceptible to water retention or in cases when they are punctured and exposed to rain.

Compression Molding

Compression molding stands for the fourth tested and genuine manufacturing method of producing the plastic pallets. The process demonstrates that two-piece molds are burdened with material robotically, manually, or via extruders. Therefore, a press stimulates the mold to close, while pressure compels the materials to stow the mold pocket (Rosato, 2011, p. 45). This method allows utilizing discrepant kinds of recycled materials, encompassing rubber, synthetic resins, plastics, and other types of recycled waste products.

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Rotational Molding

The rotational molding procedure originated in the early 1970s (Rosato, 2011, p. 45). This method most commonly utilizes such materials, as linear cross-linked polyethylene and low-density polyethylene (Mitchell et al., 2014, p. 2113). The process starts with loading of powdered or granular plastic material into a shell-looking pocket (Rosato, 2011, p. 45). The mold is heated and has to be rotated in two planes, which are located perpendicularly to each other. This procedure assists in distributing and fusing the material to the mold. The facts show that the molds, in regards with rotational molding, appear to be cheaper, on the contrary to other manufacturing procedures.

Profile Extrusion

The facts demonstrate that profile extruded pallets seriously resemble wooden pallets due to the fact that they are created in an analogous manner. The process requires melting of raw material, which is latter forced via an extruder (Mitchell et al., 2014, p. 2115). Materials should be cooled before they are being cut to lumber–like size and strengthened with screws, nails, heat welds or glue.

History and Enhancements of Plastic Pallets

Plastic pallets date back to the 1960s when they were initially utilized in sanitary applications for raw foods (Rosato, 2011, p. 43). The history demonstrates that the manufacturing processes encountered essential enhancements in regards with design, processing, and materials, which allowed lowering the level of required costs, while making plastic pallets more emulative. The majority of present-day customers are environmentally-conscious, which presupposes that plastic pallet market should shift to the usage of recycled materials (Chaudhari et al., 2012, p. 78). The automotive market pioneered the usage of reusable plastic pallets in 1980 in attempt of minimizing handling spendings and eliminating disposable packaging problems.

Processors of compression and injection molded pallets have shifted to the utilization of more regrind and recycled plastics in order to combat the unchangeable wood prices and elevated resin spendings (Mitchell et al., 2014, p. 2117). The use of recycled materials is the key to better economics, even in regards with structural foam, as it appears to be a “forgiving” procedure accepting materials with discrepant melt indexes (Chaudhari et al., 2012, p. 78). Plastic pallet market also encountered a resurgence of recyclers, in order to equip value-added service. Thus, for example, Greystone Logistics located in Tulsa manages a plastics recycling plant and manufactures injection molds pallets that are generated from 100% recycled resin at a facility in Bettendorf (Deng et al., 2010, p. 119). The facts demonstrate that this company utilizes a proprietary mix of PP and PE from post-consumer and post-industrial streams, which costs approximately 50% less on the contrary to virgin resin (Deng et al., 2010, p. 119). Their pallets are usually grey or black because of their recycle content.

In addition, Greystone’s innovative packable keg pallet appears to have fiberglass rods interposes after molding. The material change to the material blending equips analogous or higher strengths than virgin material usage, while a patented polyethylene grommet results in anti-skid performance (Zini & Scandola, 2011, p. 1906). Solplast Inc, which appears to be a well-known manufacturer of injection molded pallets also utilizes recycled resins, which allows it to enjoy 15% annual growth (Mitchell et al., 2014, p. 2117). In addition, this company has started utilizing a specific low-pressure injection manufacturing technique, which provides a possibility to make heavy-duty monoblock pallets for pharmaceutical, warehouse, beverage, and food usage (Zini & Scandola, 2011, p. 1906). This is a new method, which helps in manufacturing heavier and thicker pallets, characterized by higher impact strength on contrary to traditional high-pressure versions. Nevertheless, this process appears to be slower (10 minutes on contrary to 2 minutes for high-pressure injection), but this actually grants for reduced amount of stress on the material (Deng et al., 2010, p. 119). The performance of the produced materials appears to be greater in contrast to virgin materials, which make these plastic pallets capable of emulating with wooden ones.

Compression molding also appears to be well positioned in the pallet market, as it is capable of handling the procedure transformations to the recycled materials usage. The changed composite technology utilizes the range of 500-4000-ton vertical compression units, in order to manufacture automotive, distribution, and grocery pallets, which are typically created of copolymer and homopolymer PP recycled resins. The proprietary manufacturing procedure incorporates superseding a molten “log” or “billet”, which has to be immediately transmitted to the compression press (Chaudhari et al., 2012, p. 78). The facts show that this high-output procedure appears to be as fast as high-pressure injection, but unit cost is 25% lower, on the contrary to structural foam and 40% lower than thermoforming.

Compression molding also allows using a proprietary high-output procedure with low-cost tooling pallets. This is an innovative manufacturing process that is applied in Granville Composite Products, and can be outlined as “thermo-kinetic molding”, specifically designed for recycled resins (Zini & Scandola, 2011, p. 1913). This method allows manufacturing press bed sizes of up to 9 x 6 ft, which actually opens up the new market opportunities in a form of bagged cement that is presently dominated by wooden pallets (Zini & Scandola, 2011, p. 1913).

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Future Developments for Improved Utilization and Efficiency

Plastic pallet industry requires the development of innovative structural designs, which can help in lowering weight and costs. The facts demonstrate that structural-foam and injection molded pallets can appear in more complex one- and two-piece designs, conjoined with snap-fits and metal fastening and should incorporate nylon or steel consolidations in order to equip edge-racking capacity (Rosato, 2011, p. 47). Currently, the major part of injection molded pallets are produced of HDPE, but appears that it is better to utilized PP, as it can result in greater stiffness. The experiments demonstrate that a PP impact copolymer appears to be greater flex modulus, on the contrary to HDPE (Chaudhari et al., 2012, p. 79). In addition, pallet injection molders can be turned to multi-platen presses, as it can elevate the performance and productivity, while consistent valve gating provides enhanced efficiencies, and the usage of electric screw drives can improve the overall cycle time. The enhancement of structural foam manufacturing process can be executed through the usage of bigger machines (up to 1000-ton) with multi-nozzle technology, which might result in a greater output and the possibility to produce plastic pool pallets (Chaudhari et al., 2012, p. 79). Moreover, current developments demonstrate that execution of structural-foam machines with a two-platen clamp can result in faster cycles and lower costs.

In addition, it is also important to concentrate on the introduction of innovative lines of structural-foam machines, which can be dedicated to short-size pallet making, as it can help in enhancing the overall capacity and output (Zini & Scandola, 2011, p. 1913). The experiments and trials show that these implements might cost up to 40% less, on the contrary to the current general-intention machines, while providing better productivity and cycle time due to the robots utilization.

Conclusion

The current paper demonstrates that despite the fact that wooden pallets dominate the market, plastic pallets are progressively accelerating and become more and more competitive. The plastic pallet industry utilizes a broad variety of manufacturing processes, including injection molding, thermoforming, structural foam molding, compression molding, rotational molding, etc. All of them have the vivid advantages and disadvantages in regards to cost, persistence, and stiffness. Nevertheless, the increase of plastic pallets industry appears to be phenomenal, especially in regards with the last decade. The majority of currently manufactured plastic pallets are being produced from recycled thermoplastics. The research vividly demonstrates that inclusion of waste materials into plastic pallets lowers the burden on landfills and lead to solid value addition. Innovative changes in materials, design, and manufacturing processes appear to have a remarkable impact on the thermal and mechanical characteristics of the composition. The possible future innovations can help the plastic pallet industry in seizing the market and disrupt the popularity of wooden pallets, which currently dominate, having approximately 90% of the market shares. Introduction of new tools and machinery can provide solid enhancements in stiffness and resistance, together with variations in size and uniqueness of application.   

Recommendation for Further Studies

The review and analysis of plastic pallets revealed that there is a possibility to enhance the effectiveness and performance profile of plastic pallets with a help of composite materials. Thus, a perfect composite has to be highly persistent and stable to impact the materials characterized by stiffness, which can be equipped through the usage of carbon, glass, or wood fibers.

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