You may think a conveyor’s primary job is moving material from point to point throughout a processing system. In truth, a conveyor is much more than a means of conveyance. This equipment plays a critical role in helping to prepare material for the next step in a processing system.
“The ferrous and nonferrous industry requires that we prepare the material for each step along the way, not just transport it,” says Kent Graves, the founder of U.S. Conveyor Technologies, Mackinaw, Illinois.
While he says the aggregate industry uses conveyors to quickly transport piles of rock, preferring the material to be condensed in the center of the belt, in the scrap industry, “moving material in a uniform size and flow across the full width of a belt is of utmost importance.”
The uniform flow of the material helps downstream sorting equipment function most efficiently, improving recovery and purity.
While conveying equipment takes many forms, including belt, screw, vibratory, magnetic and air, Graves says the primary purpose of such equipment is to collect, move, spread and meter material among specialized processing and sorting machines.
Graves formed U.S. Conveyor in 1988. At that time, the company specialized in designing and building equipment and conveying systems for the scrap recycling industry, automotive manufacturers and the aquaculture industry. By 1998, U.S. Conveyor was focused solely on serving the recycling industries, integrating, designing, building and installing complete systems and upgrades. U.S. Conveyor also partners with Spaleck USA, Loudon, New Hampshire, to provide screening solutions.
In the interview that follows, Graves shares his perspective on conveyors and what goes into designing an efficient processing system.
Recycling Today (RT): How critical is properly specifying a conveying system to the efficient functioning of a scrap yard? How can the wrong conveyor affect shredder and downstream sorting operations?
Kent Graves (KG): Picking a conveyor for a picking line, be it robotic or hand sort, requires a specialized conveyor. It must have automated or manual speed controls for different material and flow rates. Material must be spread across the entire width with low burden depth and be able to be reached from all sides.
This process with hand pickers present must meet and exceed all safety standards.
Sometimes moving material from Step A to Step B is performed by other equipment than a conveyor, like trommels or screeners that separate and size material along the way. The goal of designing a system is to do the most in preparation of the material along its route within the confines of the system.
RT: What are the biggest missteps related to conveying systems that you’ve seen in the scrap processing facilities that you’ve visited?
KG: Trying to fit a system into too small of space, ending up with a difficult-to-maintain and less productive process.
RT: What factors do you take into account when designing conveying systems for a scrap yard?
KG: The design of a system starts with its intended purpose, what process equipment is to be integrated and what results are expected. To do this, we will engineer the mass flow rates into each process based on the customer’s tons-per-hour requirement and then develop a plan with the correct number and size of equipment required. This design and drawing process is constantly reviewed with the customer until a system meets the intended use and budget.
When replacing pieces of equipment in an existing system, like trommels, batch feeders or shredder infeeds, we use the above process but also laser scan the existing layout so that we can insert a plug-and-play item to ensure a perfect fit and seamless integration.
RT:What factors do you consider when determining the angle or length of a conveyor for a specific application?
KG: This is always a moving target. In a perfect world, no conveyor should exceed 20 degrees. Using speed, moisture content, type, size, burden depth of material along with the footprint, a calculation can be made as to the orientation and angle that best suits the purpose.
A number of times in existing systems or compressed footprints, we must exceed the 20-degree standard, and specialized equipment, such as bent or high incline conveyors, must be designed into the process.
RT: Are you seeing a move toward the use of modular conveyor systems in scrap yards? What advantages are associated with modular systems?
KG: U.S. Conveyor has spent years in development of modular conveyors. They have become our most popular conveyor. This is because separation technology within the system is constantly changing. Our conveyors generally outlast these changes and can be reconfigured very inexpensively to accommodate new technology, which can save large amounts of money compared with replacing the conveyors.
RT: Are reversing conveyors growing in popularity? What do they offer to scrap yards in terms of versatility?
KG: Yes, customers are demanding more flexibility and redundancy from their systems, and reversing conveyors are a great tool to accomplish this. Reversing conveyors offer a reliable method of moving material to different operations or bunkers with just a push of a button. Reversing conveyors take the place of flop gates or other less-reliable methods of diverting material flow and can reduce the total amount of conveyors needed. Reversing conveyors can bring you online or offline quickly without shutting down the system. They offer a means to introduce new material to a downstream, giving redundancy and capacity when needed.
RT: What kind of belt options are available, and which offer the most durability in scrap applications?
KG: Conveyors in the ferrous system must hold up to years of extreme abuse from shred, unshredables, pokers and heavy oil- and acid-laced ASR (auto shredder residue). This requires heavy frames, mine-duty components and MOR (moderately oil-resistant) belts.
The nonferrous side still requires a robust conveyor frame along with various choices for belts. These include flat belts with scrapers, cross-rigid belts for bent conveyors and belts with various cleat designs for steep inclines.
RT: In terms of maintenance, what is critical to the ongoing functioning of a conveyor system?
KG: Extremes in cold and heat during the different seasons can affect tracking, [and] the amount of buildup on all the equipment must be monitored.
Conveyors in general must be put on a daily maintenance schedule of at least visual inspections and on a weekly or monthly schedule for grease and wear parts review, such as scrapers. Keeping a clean facility with a consistent maintenance program will make your systems last years longer.