Conveyor basics
Here's both a refresher and an update on the wheel, belt, roller and chain conveyor commonly used to transport products through industrial facilities.
By Corinne Kator, Associate Editor -- Modern Materials Handling, 12/1/2007
- Non-powered conveyor
- Powered package-handling conveyor
- Powered pallet-handling conveyor
- Over-sized conveyor
Visit a modern distribution center or manufacturing facility and you're likely to find miles of different kinds of conveyor moving cartons, totes, pallets, components, work-in-process and finished goods from one area of the facility to another.
Conveyor has been a staple in materials handling for decades. It's available in many styles and is used in countless applications. In this article, Modern spotlights some of the most common conveyor types:
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Non-powered skatewheel and roller conveyor
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Powered belt and roller conveyor used in handling packages and other small products
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Powered chain and roller conveyor used in handling pallet loads of goods
Non-powered conveyor
The simplest form of conveyor—non-powered conveyor—uses the natural forces of inertia and/or gravity to keep products in motion.
Portable sections of non-powered conveyor are often used for loading packages into the back of an over-the-road truck. Non-powered conveyor can also serve as takeaway conveyor for cartons coming out of an automated sorter, and it's often used in workstations and in pick modules where employees complete their tasks and then push their work along to the next zone or station.
The two most common types of non-powered conveyor are skatewheel and roller.
Skatewheel conveyor
Little energy is needed to turn the small wheels of a skatewheel conveyor, and that makes skatewheel good at maintaining the speed of a product, says Tim Kraus, conveyor product manager for FKI Logistex (877-935-4564, www.fkilogistex.com). Because each wheel turns independently, he adds, skatewheel conveyor is also a good choice for the curved sections of a conveyor line.
Roller conveyor
Non-powered roller conveyor is commonly used for workstations and pick modules because it provides a better working surface and is often less expensive than skatewheel conveyor. It's also good at slowing the inertia of products coming out of a high-speed sorter.
Powered package-handling conveyor
When it comes to moving packages and other relatively small items, two styles of conveyor dominate the market: belt conveyor and roller conveyor.
Traditionally, says Ken Ruehrdanz, market development manager at Dematic (877-725-7500, www.dematic.us), belt conveyor has been used for transporting products, while roller conveyor has been used for accumulating products. Recent advances in technology, however, are blurring that line.
Belt conveyor
In traditional belt conveyor, an AC motor drives a pulley that then turns a long, looped belt. The belt can be made of a variety of materials, depending on the items it's intended to convey. Underneath the belt sits either a bed of non-powered rollers or a sheet of metal known as a slider bed.
Traditional belt conveyor is a simple, time-tested technology. It's less expensive than powered roller conveyor, it provides a more stable conveying surface, and it can convey a wider variety of products, says Ruehrdanz. Poly bags, envelopes and electronics are examples of products handled easily by belt conveyor that are often too small or too light to be conveyed directly on rollers.
Roller conveyor
Despite the advantages of belt conveyor, many of today's distribution centers are filled with roller conveyor, says John Kuhn, director of conveyor products at FKI Logistex, because roller conveyor allows accumulation of products.
“Accumulation is basically a way to make the conveyor store product for a determined amount of time,” he says. The product can then be released into, for example, an automated sorter or palletizer.
Roller conveyor falls into a number of different categories, depending on the way the rollers are driven. The four most common categories are line-shaft, chain-driven, belt-driven and motorized roller.
Line-shaft conveyor
In a section of line-shaft conveyor, a long metal shaft runs below the bed of rollers. Rubber o-rings connect the rollers to the shaft so that when the motor turns the shaft, the shaft turns the rollers.
Line-shaft conveyor is the least expensive form of roller conveyor, says Kuhn. But its sales are declining, he adds, because of safety concerns and high maintenance requirements and because line-shaft conveyor is not good at accumulation.
Chain-driven roller
Chain-driven roller conveyor, on the other hand, provides excellent accumulation, says Kuhn. This type of conveyor is driven by a metal chain (usually covered with a rubber or plastic pad) that runs beneath the roller bed, perpendicular to the rollers. As a motor moves the chain, the chain moves the rollers.
Belt-driven roller
Belt-driven roller conveyor works on the same principle, but it's a belt rather than a chain that runs beneath the rollers. Belt driven roller is also a good accumulator. It's quieter than chain-driven roller, says Kuhn, and requires less maintenance because there's no chain to oil.
Motorized roller
Motorized roller (also known as internal motor or motor-driven roller) conveyor is the newest roller technology. A section of motorized roller conveyor is divided into small zones. At least one roller in each zone has an internal motor that turns the roller. The rollers in each zone are connected to each other by rubber o-rings so that the turning of the motorized roller turns all the rollers in the zone.
The motors used in motorized roller are usually 24-volt DC motors. These motors use less energy than the motors used to drive other forms of roller conveyor, says Kuhn, and they provide less torque, making them safer, too.
Because each zone of rollers is powered independently, the zones can be configured to run only when a package is present. This “on-demand” feature, says Kuhn, increases energy savings even further and decreases noise.
Motorized roller isn't as fast as the other forms of roller conveyor, he adds, but it offers better product control and is easier to maintain. The upfront cost of motorized roller is higher than that of other forms, but, says Kuhn, “as the usage goes up, price of the components is coming down.”
Segmented belt conveyor
The invention of motorized roller conveyor led to the development of a second kind of belt conveyor known as segmented belt conveyor. A section of segmented belt conveyor is essentially a section of motorized roller conveyor with a few feet of belting wrapped around each zone of rollers.
Segmented belt conveyor, says Dematic's Ruehrdanz, combines the accumulating power of roller conveyor with the stability of belt conveyor, resulting in excellent carton control.
Powered pallet-handling conveyor
Pallet-handling conveyor is often used in conjunction with automatic palletizers or automated storage and retrieval systems. There are two basic types of pallet-handling conveyor: chain conveyor and roller conveyor. Both can handle heavy loads up to about 4,000 pounds, says Phil Kaffenberger, vice president of engineering at HK Systems (800-457-9783, www.hksystems.com), and both are relatively slow, typically handling just four pallet loads per minute.
Chain conveyor
Chain conveyor is a simple technology that uses motors to turn two, three or four strands of heavy-duty chain. The pallets ride directly on the chain. Chain conveyor is less expensive than roller conveyor, says Kaffenberger, but it's best suited for captive systems where pallets are a uniform size and can be counted on to be in good condition.
Pallet-handling roller conveyor
Pallet-handling roller conveyor looks like the roller conveyor used for handling packages, but the rollers are wider and thicker. Most pallet-handling roller conveyor is chain-driven, says Kaffenberger, because that drive method is the “toughest and hardiest.”
Chain-driven pallet conveyor works differently from chain-driven package conveyor. Instead of running beneath the rollers, the chain runs along one side of the roller bed. Each roller is connected to the chain with a sprocket. The conveyor is divided into small segments, and each segment has its own AC induction motor, says Kaffenberger. This segmentation, he says, allows for better control and allows some accumulation of pallets.
Internal DC motors haven't yet been used to drive pallet-handling rollers, he says, but that technology may be coming soon.
Over-sized conveyor
Many manufacturing plants need to convey items that are too big and heavy for pallet conveyor. The heavy-duty conveyors designed to carry these loads are often driven by chains embedded in the floor or ceiling of the facility.
One of the simplest of these conveyors is towline. A towline conveyor consists of a chain buried in a channel in the floor, a wheeled cart sitting on the floor above the chain, and a tow pin that attaches the cart to the chain. As the chain advances, so does the cart.
Towline conveyor can handle loads up to 70,000 pounds. Its most common use today, says Bill Casey of SI Systems (800-523-9464, www.sihs.com), is in vehicle manufacturing where low-profile carts carry the frames of all sizes of vehicles—from lawnmowers to bulldozers—through the assembly process.
Another conveyor popular on vehicle assembly lines is overhead power-and-free conveyor. Watch for Modern to address the basics of overhead conveyor next year.
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