Equipment Focus: Conveyors

Moving scrap throughout your plant is what conveyors do best. Here’s a look at the latest features to help keep these belts rolling safely and productively.

By Lynn R. Novelli

Conveyors are an efficient, versatile, and durable means of moving high volumes of scrap through the recycling process. Though the basic concept of how conveyors operate hasn’t changed all that much in 50 years, today’s conveyors do offer some new features that improve production and operational safety. If you’re looking to purchase a new conveyor or retrofit an older one, it’s worth reviewing the types of conveyors and special features available.
   A Thomas Register search of conveyor manufacturers turns up more than 700 companies, though only a handful of those firms specialize in conveyors for the scrap industry. Finding a company that knows the industry can be a starting point for selecting a vendor, suggests Marlin Bills, president of Osborn Engineering Inc. (Tulsa, Okla.). “Scrap is a unique niche market,” he notes. “The conveyor manufacturer needs to understand the scrap-specific stresses on the system and design to avoid problems.”
   After weeding out the vendors who don’t know the scrap industry, customer service is the next important consideration. “You want a vendor who’ll respect the end user’s needs,” says Mike McLemore, president of Central Manufacturing Co. Inc. (Grove-land, Ill.). “The first challenge for the conveyor manufacturer is offering a solution that considers the customer’s budget, site, and environment, beyond just the load.”
   All of the leading conveyor manufacturers note that they operate on a design/build approach so that virtually every conveyor sold is a custom system. In fact, McLemore likes to say that the model number for every conveyor his company sells is its stock number, thus emphasizing the custom nature of the business.
   While conveyors are based on a simple concept—a motorized belt and a system of pulleys and idlers—the purchase decision can be complex. “A conveyor that’s going to be in daily service in a scrap business must be heavy duty, efficient in terms of the tonnage per hour it can handle, and designed and built in such a way to allow for the company’s future production growth,” says Kent Graves, president of U.S. Conveyor Technologies Manufacturing Inc. (Mackinaw, Ill.).
   Manufacturers report that ferrous and nonferrous scrap recyclers typically rely on two main conveyor configurations: an infeed conveyor to feed their processing equipment and, depending on the equipment, one or more outfeed—also called offtake, takeaway, or downstream—conveyors to carry the processed scrap away from the processing equipment for separation, further processing, storage, or shipment.
   Given that brief overview, here’s a closer look at the state-of-the-art in scrap-related conveyors today.

Going In
Selecting the right infeed conveyor depends on the production rate desired—that is, the tonnage per hour, says Marlin Bills. This factor is the primary influence for the design of the conveyor’s mainframe and supports as well as the motor and drive selection, he notes.
   Also in the mix are factors unique to each scrap recycling facility, such as the angle of incline, whether the conveyor needs to be above or below grade, and the distance to be covered, manufacturers say.
   Infeed conveyors in the U.S. ferrous scrap industry almost always feature a steel-belt construction, notes Kent Graves. Often, the belt is described as having a “Cat-track” design because it resembles the crawler tracks of Caterpillar excavators. That term can be used generically, however, though many conveyor manufacturers actually do use all Caterpillar-built components, including the idlers and belts, Graves says. Overall, “made in the U.S.A.” still carries weight with conveyor manufacturers, according to Mike McLemore, who says that the leading ones prefer to purchase their system components, including steel, from U.S. suppliers. Offshore products are definitely available and often cheaper, but few conveyor companies have incorporated them into their systems, states Graves.
   According to McLemore, the hydraulic track belt conveyor has become a scrap industry standard for its productivity and reliability. This type of heavy-duty belt is designed to carry the mix of ferrous scrap that makes up the bulk of feedstock for shredders in the United States.
   n Europe, where vehicles tend to be of lighter-gauge construction, piano-hinge belt conveyors dominate the infeed conveyor market, explains another conveyor maker. That design hasn’t made serious inroads into the U.S. market in part because piano-hinge belts are generally considered suitable only for light-duty applications.
   The conveyor’s steel frame is almost always custom-designed based on the recycling system configuration and, hence, can vary widely, manufacturers note. For heavy-duty scrap applications, the open frame is the sturdiest design with legs set on either 20-foot centers for standard construction or 50-foot centers for truss construction, explains Marlin Bills.
   Drive assemblies for conveyors are basic and heavy duty, though there usually are at least a couple of choices available. Most manufacturers still offer the option of electromechanical or hydraulic drives. Hydraulics are by far the more common choice in the scrap industry because they allow for variable speed control and stop/start operation under full load torque, says Kent Graves. A shear pin sprocket assembly provides overload protection for the drive and chain while a drive clutch with ball detent is designed to slip in overloaded conditions and reset for normal operation when the overload is corrected.
   Beyond the basics of belts, frames, and drives, a number of bells and whistles are also available to customize conveyors for specific applications, simplify maintenance, increase productivity, or achieve various combinations of these three.
   For example, consider conveyor location. Though some scrap recyclers—such as shredder operators—prefer their infeed conveyors constructed above grade, conveyors can be installed at or below grade to make it easier to feed scrap onto the belt, says Marlin Bills. While operational efficiency is the same above or below grade, he claims, operating a conveyor in a below-grade pit increases maintenance time and costs related to cleaning out the pit. Still, for some recyclers, below-grade installations may make sense, Bills says.
   Some of the newer innovations in conveyor design are meant to simplify maintenance. Cat rollers are sealed and self-lubricating, but drive components still need to be lubricated. Fortunately, an automatic lubrication system for the chain drive will cut maintenance costs and extend chain life. 
   To reduce downtime and increase production, speed sensors, amp sensors, and motion sensors that sense belt tracking are all available options. For the most high-tech approach, the entire conveyor operation can be computer-controlled and monitored with a CRT screen readout for the operator, notes Kent Graves. 
   The general trend in infeed conveyors—for shredders, at least—is to feed them with multiple loading cranes to allow for higher production, Graves points out. Megashredders operating at 6,000 hp require a steady stream of feedstock, more than a crane and tiltbed can handle, he explains. So it’s not uncommon for scrap facilities running a megashredder to have two cranes feeding a wide-bed infeed conveyor and two more cranes in the scrap heap feeding those cranes. This configuration allows for maximum efficiency in loading material onto the conveyor, he notes.

Coming Out
While some scrap processing equipment—such as balers—generally don’t feature downstream conveyors, other types of processing machinery do, with automobile shredders having one of the most conveyor-intensive downstream systems.
   As processed scrap emerges from the shredder, it travels along a vibratory or oscillating conveyor and onto a transfer conveyor to the magnetic separation unit or air classifier. Iron and steel scrap are usually deposited on one or more picking conveyors, with the final, clean scrap fed onto an elevated radial stacking conveyor for stockpiling or loading for transport.
   The mixed nonferrous and nonmetallic fraction heads off on another conveyor line, generally through a trommel screen or other type of separator, that feeds the material onto specialized conveyors related to the eddy-current separation system. After the nonferrous is recovered, a final conveyor carries the remaining shredder fluff to a storage site or containers for disposal. 
   Like their infeed counterparts, most outfeed or downstream systems are custom-designed to meet the recycler’s needs. Regardless of their design, function, or position in the downstream process, outfeed conveyors are basically a rubber-belt design.
   According to conveyor producers, the material and the rate of feed determine the length of the conveyor at each downstream processing stage. Production and efficiency depend on the ability to process high volumes rapidly, which may require a longer run and a higher horsepower motor. 
   Durability of the belt is one factor that can affect outfeed efficiency, says Bills. Oil, abrasive materials, and load torque impose high stress on rubber conveyor belts, so it’s important that all belts in the outfeed conveyor system are oil-resistant and that the entire assembly, including the belt, is rugged enough to withstand stress and abnormal shock loads, he suggests. To reduce belt maintenance, some manufacturers offer rubber disc return idlers on their flat-belt conveyors that reduce the accumulation of dirt and grease on the underside. 
   Belt width also comes into play in determining conveyor efficiency. Belts up to 7 feet wide have reportedly become common for outfeed conveyors in the scrap industry. The slider-belt design using a flat pan will prevent material from sagging between rollers during transport, though this design has a higher friction coefficient that needs to be calculated into production efficiency, manufacturers note.
   One of the latest innovations in downstream conveyors is the ergonomically designed picking conveyor. On this model, the return is below picking-floor level, allowing pickers to sit at the conveyor facing the belt, like sitting at a desk, instead of having to sit sideways. This position reduces neck, arm, and back strain for the workers, says Marlin Bills.
   Troughing conveyors can be useful to funnel processed material to the center, says Kent Graves. These units are constructed with flared sides to minimize material jamming or backups to the shredder gate.
   Impact bars or idlers at the loading station will absorb stresses on the belt and keep production moving, according to Bills. 
  As for radial stacking conveyors, conveyor manufacturers will configure the system based on the processor’s offloading requirements, Bills says. This is determined by the recycler’s final transportation and/or container plan (such as railcar, truck, roll-offs, or hoppers) and available stockpile space.
   An automated discharge system with load sensors on conveyors and discharge chutes can control loading or discharging material by hydraulically raising and lowering the stacker to keep loading height low to reduce dirt and maximize efficiency.

Staying Safe
“Though conveyors are one of the most benign-looking pieces of equipment in the scrap yard, they’re really one of the most dangerous,” states Marlin Bills. 
   Many of the innovations in conveyor design are driven by an increased recognition of their potential hazards. Product safety is paramount for conveyor manufacturers whose primary market is the scrap industry, says Mike McLemore, who asserts that “the product should exceed government standards when possible.”
   Conveyor manufacturers strive to make their products safe by equipping them with guards, fences, signage, and shut-off mechanisms. Safety pull switches and cables that bring the conveyor to an immediate stop in the event of an emergency are now standard on many conveyor systems, while chains, belt drives, and gear motors are covered to meet OSHA and ANSI regulations, manufacturers note. 
   Also, raised protective side panels are standard on most conveyors to prevent accidental contact. In addition, optional handrails and fences are highly recommended as an added precaution.
   Manufacturers also recognize that the return side of a conveyor can be as hazardous as the top load-bearing side. The newest enhancement to address this risk is a covered return belt that prevents a worker from getting caught in the belt while passing underneath, Bills notes. On conveyors that don’t have this feature, a protective fence or guard is an easy and relatively inexpensive way to enhance safety, he adds.
   At a minimum, all potential nip points or entrapments should be shielded, safety signage should be standard, and fences and walkways should automatically be part of the design, says McLemore. As a rule, “avoid any inviting hazard in design and construction, and make the conveyor safe and accessible to service,” he suggests.
   All safety procedures should be spelled out in the equipment manual, McLemore notes, adding that it’s still “the employer’s responsibility to train personnel in safe operation and maintenance procedures.”
   Over the years, equipment purchasers have increased their awareness of safety issues, he says. “These days, customers are very sensitive to the fact that manufacturers must provide a product that meets all safety requirements. We’re likely to see safety specs written right into the RFQ.” • 

Editor’s Note: ReMA offers a training video titled Working Safe & Smart Around Conveyors that reviews the dangers of conveyors in scrap recycling operations and offers suggestions on preventing conveyor accidents. The video, available in English and Spanish, costs $75 for ReMA members, $150 for nonmembers. To order, call 202/737-1770, or visit ISRI’s online Bookstore at www.isri.org.

Lynn R. Novelli is a writer based in Russell, Ohio.