Operators regularly experience down time and increased costs when conventional means for handling and storing coils are used in their process areas. Many industry professionals consider coil storage systems made of wood to be a misuse of valuable natural resources. Further, the wood blocks’ inevitable absorption of oil from the coils can result in costly hazardous-material disposal costs. This paper discusses the manners in which the handling and storage of coils can be made more efficient while reducing the incidence of inner- and outer-wrap damage. The systems discussed herein have been determined by their users to be much safer than the methods they have used in the past. This paper also presents “green” coil storage solutions that are not only constructed of recycled materials, but are also themselves recyclable.
The most commonly used material for keeping steel coils
in place is wood, which normally takes the form of blocks, chocks, stops, pallets, cradles or saddles. Wood is readily available throughout the U.S. and is considered to be relatively inexpensive; however, when viewed in the context of a steel mill, service center or fabrication facility’s total operating life, the use of wood is highly cost-ineffective. Further, the use of wood, which is ultimately discarded in landfills or burned, is considered by many to be a waste of a valuable natural resource. Use of polymeric coil storage systems is now well accepted and continues to gain more and more favor for use by many throughout the U.S. and elsewhere. By using highly engineered materials and complex mathematical calculations, these systems enable safe storage practices and provide a long life, operational efficiency and flexibility, and value to organizations. Perhaps most importantly, polymeric coil storage systems are often made of recycled materials that stay out of the waste stream for 30 years or more. When the storage systems are made from thermoplastics, their components are also recyclable.
Wood Coil Storage Systems i
Initially, and under static load conditions, wood can perform well; however, over time and under impact and other dynamic loads, wood will inevitably splinter (Figure 1) and break (Figure 2) due to its natural, relatively brittle nature. Even when expensive hardwood is used, these blocks provide only short-term solutions. In short, wood is not a long-term solution, as it results in very high life-cycle costs for coil storage operators ii.
Another drawback of using wood as storage blocks is that wood, by its nature, absorbs fluids. As a result, wood will soak up some, but not all, of the oil from the stored coils (Figure 3). This situation not only creates a “slip” safety hazard, but it may also result in expensive block disposal costs in jurisdictions that consider them hazardous waste once “contaminated.”
Operators that are focused on safe practices through good housekeeping have reported significant challenges in maintaining good order when using wood storage blocks.
Figure 4 shows one of the many maintenance issues and “5S” iii challenges caused by wood storage systems.
The use of wood blocks to keep coils in place can also cause safety issues if the blocks are not properly designed, installed and maintained. Vertical forces from the upper coils in double-stacked applications translate to horizontal forces on the lower coils. When the horizontal forces exceed the coefficient of friction between the wood blocks and the floor, the blocks “slide” (Figure 5) resulting in a safety hazard.
Even when the blocks seem securely fastened, the same vertical-to-horizontal dynamic forces can make coils “climb” (Figure 6) over blocks, again creating a significant safety hazard.
Polymeric Coil Storage Systems
Proper coil storage system component design can overcome the issues of block sliding and coil climbing. By creating blocks of appropriate dimensions, a storage system can be implemented that provides efficient and safe conditions. Figure 7 is a graphical representation of how the trigonometric equations were derived to determine appropriate storage block design parameters.iv
Once the appropriate geometry of a storage block is established, its longevity will be based on its material of construction.
Several companies pioneered the use of recycled plastics for molding blocks. Over time, experience and studies of in-field performance of different polymeric formulations have allowed the optimization of compound recipes that provide optimal performance. History has proven that proper selection of the appropriate polymer is critical in ensuring that the blocks provide the physical properties and long life desired by coil storage operators.
A company in Holland has emerged as a leader in the production of various designs of polymeric coil storage systems. This writer has researched the performance of this company’s coil storage systems and found an enviable level of universal satisfaction from their users. Through the use of an ultraviolet-stabilized, polyolefin combination recycled plastic, this Dutch company has developed a diverse product line of coil storage products that is designed to serve various sizes of coils, stacking configurations and weight capacities. Some of the styles of these polymeric block shapes are shown in Figure 8.
These systems, depending on their particular type, have been designed to withstand up to as much as 100 tons and to accommodate three-high stacking without the need for chains. Third party testing has confirmed that these polymer systems provide physical properties that are highly resistant to splintering, breaking or crushing (Figure 9). Further, the polyolefin polymer used in these systems does not absorb oil and therefore does not create long-term environmental concerns. Perhaps most importantly, these polymer systems are 100% recyclable. As such, even beyond the 30-year design life of their polymeric parts, they will not need to be deposited in a landfill!
A relatively new modular system, called RollStop1, has become that of choice for many coil storage operators globally. It is made of the advanced polymer material described above, which employs an easy-to-install design with four simple components (Figure 10).
The RollStop system is assembled on two rails that run the length of each storage row, which maintain their parallel placement through the use of regularly positioned spacers. The rails are supplied in lengths of approximately 13 feet and are joined, end-to-end, using a specially designed threaded connector. The polymeric blocks, whose placement can be changed at any time based on the diameter of the stored coils, are placed over the rails, four blocks per coil (Figure 12). The blocks secure themselves to the rails via the specially designed “mating rib pattern,” eliminating the need for separate mechanical fasteners or heavy steel c-channel assemblies.
Long-term Global “Green” Contributions of Polymeric Coil Storage Systems
The material used in polymeric coil storage systems is made of recycled components. Interestingly, one of the inputs used by the Dutch system molder comes from a plastic used in the growing of tulips, a practice for which Holland is well known. This material, which would likely otherwise be buried in a landfill, adds to the strength and long life of the storage blocks.
Because these coil storage systems are designed to have 30-year lives, material that normally would be recycled or thrown away is taken out of the waste disposal and recycling system for a long period of time. Reports are that a plastic water bottle winds through the recycle loop once every eight to 18 months. As shown in Figure 12, the recycling process requires collection, sorting, washing, grinding and decontamination in order to transform the plastic bottles into a usable material before the recycled plastics are sent to a molder to manufacture new bottles. This process is costly, time consuming and often an inefficient use of energy; however, when compared to disposing of the plastic bottles in a landfill, recycling is preferred in most cultures.
By using recycled plastics in the molding of polymeric coil storage systems, these materials are removed from the waste stream for at least 30 years. The equivalent weight of 500,000 16-oz. plastic water bottles is used to make a typical polymeric storage system for 100 floor-level coils. Clearly, the manufacture of polymeric coil storage systems salvages millions of tons of plastic that otherwise would be destined for the continuous waste recycling loop or, even worse, for landfills like that shown in Figure 13.
The use of polymeric systems relieves the plastic recycling and landfill processes of millions of tons of plastic each year, thus contributing to popular “green” initiatives. More importantly, recycled polymeric systems often greatly enhance the operational efficiencies at a coil storage facility. Proper design of storage blocks ensures that coils can be placed securely and safely over the design life of the system. Specific benefits of the use of the polymeric storage systems include:
- Improved safety
- Clean, modular design
- Simple installation
- Rugged, polymeric components
- No chains that damage coils
- Increased floor space utilization
- No wooden components that split, break or absorb oil
- Easy to store and move
i Baach, Michael; Detweiler, Stephan; Nebehay, Leonard. “Safe, Economical Coil Storage: A Case Study,” The Philpott Rubber Company, 2008.
ii Baach, Michael, “Implementing a Safe, Economical Coil Storage Program: A Total Cost of Ownership Perspective,” FMA MetalForm Conference 2009
iii “5S” A workplace organization methodology that uses a list of five Japanese words – seiri, seiton, seiso, seiketsu and shitsuke. Transliterated or translated into English, they all start with the letter S: sorting, straightening, systematic cleaning, standardizing, and sustaining. The list describes how items are stored and how the new order is maintained. The decision making process usually comes from a dialogue about standardization which builds a clear understanding among employees of how work should be done. It also instills ownership of the process in each employee, Original author and publish date unknown.
iv Esselbrugge, Martin. “Safety and Reduced Damage in the Coil Store,” Steel Metal Industries, April 1998