Off road: tire processors offer their suggestions for getting the most out of tire shredding equipment.

As is often the case in the recycling industry, when designing a processing line for end-of-life tires, it helps to start with the desired end product and work backwards. Although, in the case of tires, the feedstock--passenger tires, off-road (OTR) tires or truck tires--also will affect the type shredders selected.

"The selection of an appropriate shredding system is one of the earliest and most important decisions faced by a tire processor, says Chuck Smith, president of Polymerix Resource Recycling LLC, a tire recycler based in Brownsville, Texas, and operating partner of Synergy Management Group LLC.

Synergy has scrap tire and buffing dust collection operations in Texas and Oklahoma, marketing its products under the Polymerix trade name. The company produces landscape mulch, arena footing and sports fill, among other products.

In addition to the type of material to be processed and the desired level of size reduction, tire recyclers must also consider the volume of material to be processed and the reliability of the equipment they are considering.

WHAT YOU PUT IN. "The type of tires to be processed is the first question which must generally be considered, as there are some tire shredders on the market which will not process anything more robust than a passenger tire," Smith says. "Generally, larger shredders can process anything which can be fed to them; however, many machines (particularly older machines) will not be able to process truck and OTR tires at the same tonnage rates as passenger tires."

Rob Jahries, vice president of Utah Tire Recyclers in Salt Lake City, says that processing OTR tires requires a stronger primary shredder. "Off-road tires need a Barclay or Eldan shredder to knock them down that first step, he says. However, for passenger car tires and truck tires, Jahries says that a Columbus McKinnon (Sarasota, Fla.) shredder would be suitable.

Utah Tire Recyclers makes tire-derived fuel, crumb rubber and alternative daily landfill cover.

The type and number of shredders tire processors use also depends on what they are producing.

WHAT YOU TAKE OUT. "Some applications, such as mono-fill or disposal, require only that the tire no longer be intact," Smith says. "Barclay Roto-Shredder (Stockton, Calif.) makes an excellent primary shredder that will reduce huge volumes of tires to 4.9-inch-wide strips for this type of application. The larger hook-shear-type shredders can also be used for this application."

Smith continues, "The Saturn (Grand Prairie, Texas) and Columbus McKinnon type shredders can also be quite effective at producing chips for further processing as TDF." He adds, "In these applications, how ever, a certain amount of recycling will be required to ensure that all material meets the designated size criteria. Below a nominal size of about 1 inch, most processors will usually be better served by a dedicated granulator than by a shredder."

Smith says that to achieve a greater level of size reduction, some processors will use a step-down approach, installing primary and secondary shredders on their lines. "Other processors might elect to simply pass oversize material back through the shredder as many times as is required to achieve the desired size," he adds.

Jahries says that generally, the smaller the end product, the more equipment a tire processor will need. In addition to shredders, this equipment includes more "exotic" separation equipment to facilitate the separation of the steel and nylon fractions.

"Ancillary equipment required for the production of some sort of chipped product includes a classifier and conveying system," Smith says. "There are many types of both on the market, although vibrating classifiers have proven to be more reliable and require less maintenance than the alternatives."

The use of multiple shredders, granulators and mills that provide progressive size reduction can help recyclefs realize the best throughput from their systems, Jana Nairn of Golden By-Products Inc., Ballico, Calif., says. "Production rates vary greatly depending on specification of feedstock and number of shredders inline."

Golden passes its tires through five machines, the first of which produces a 6-inch particle size. One of the products it markets is Rubber Bark, a colored loose fill material used in play ground and landscaping.

The regular maintenance that a company performs on its size reduction equipment can also affect performance and throughput.

HOW MAINTENANCE FACTORS IN. "The big maintenance issues on most shredders are lubrication, blade sharpening and bearing replacement," Smith says. "If these items are regularly attended to, then the myriad of other problems that can be experienced with a shredder probably won't rear their heads."

Utah Tire Recyclers has established a regular maintenance schedule for its size reduction equipment. Jahries says lubrication is done daily, while cleaning is performed weekly and knife changes are done monthly. He adds that the company's shredder generally will handle 200,000 to 300,000 passenger tire equivalents before requiring blade replacement, while the company's Granutech Grizzly will generally process 5,000 to 10,000 PTEs before the knives need to be replaced.

A variety of variables affect the life of a shredder's wear parts, including the type of tires being processed, the amount of steel passing through the system and the initial hardness of the blades, Smith says.

To aid in processing and to help reduce wear, some tire processors find it beneficial to add some water to their processes. "Although there are alternatives such as hard facing, our experience has been that the best improvement to blade life comes from adding a small amount of water to act as a cutting aid," Smith says.

Jahries agrees, adding that the water helps to increase blade life by reducing the friction and heat produced.

Utah Tire Recyclers monitors its wear part costs closely, he adds. Generally, the company spends a nickel per shredded tire in consumable knife wear, Jahries says.

Tire recyclers can ascertain a system benchmark by running a timed test trial immediately following an overhaul, Smith says. "Daily production records will show a clear trend in output and help the processor determine what the most economical maintenance interval should be. In general, the sharper the blades, the greater your throughput will be," he says.

The reliability of the equipment's manufacturer can also affect machine performance, and all the recyclers interviewed for this feature say that the reputation of the company is important, as is a proven performance record for the equipment in question.

WHY RELIABILITY IS KEY. Nairn says that the history and performance of machines already used in the industry are important factors to consider when purchasing tire shredding equipment.

Smith says that a recycler's choice of shredding equipment should be based on the reliability of the system and the supplier. "Whenever possible, purchase equipment from a reputable vendor that has stocked parts and technical assistance," he says. "Avoid 'home-built,' proprietary and light-duty equipment."

He adds that with the proper maintenance, most shredders will outlast the people who originally purchased them. "This is yet another reason to rely on reputable vendors. The longer the equipment is in service, the harder it will become to identify parts that need to replacement and to maintain factory tolerances without some sort of technical support that knows your machine," Smith says.

Jahries also cites the importance of technical support in shredder selection. "When I'm choosing equipment, I want proven equipment ... companies that have more than one or two pieces in the field working." He adds that companies such as Barclay Roto-Shred; Columbus McKinnon; Granutech-Saturn; Wendt Corp. of Tonawanda, N.Y., which offers the Eldan line of tire processing equipment; and SSI of Wilsonville, Ore., are some of the major suppliers to the tire recycling industry.

As the tire processing industry continues to evolve and markets require the additional refinement of material, equipment providers and tire shredders alike should find ample opportunity to put tire shredders to the test.

The author is managing editor of Recycling Today and can be contacted at [e-mail].