It's a classic materials handling challenge. How do you most effectively move individual items, totes, cases, pallet loads and even odd-shaped product from point A to point B in the warehouse or distribution center?

Quite often the answer is going to be conveyors. But now comes the tricky part. Which type of conveyor, from skatewheel and live roller to sliding bed, provides the best combination of throughput, return on investment and ease of handling?

Finding that balance is exactly what Rick Weeden and his team at Williams-Sonoma focused on when planning a new distribution center two years ago. A critical consideration for system designers, says director of retail distribution Weeden, was to find conveyors that would be able to transport the retailer's many shapes and sizes of cooking products and housewares.

In its previous DC, Williams-Sonoma (see MMH December, 2001) relied on automatic guided vehicles (AGVs) and lots of manual handling to move larger, non-conveyable items. By moving from 20-inch wide conveyors to 36-inch live-roller units in the new DC and installing pallet conveyors in critical areas, nearly 75% of items that had been non-conveyable in the old facility now ride the conveyors and can be processed faster. The AGVs are also no longer needed.

"We are now able to convey everything here from salt and pepper shakers to large side chairs," explains Weeden.

At Verizon's Westfield, Ind., warehouse, Steve Morris, manager of project implementation, was faced with the same considerations as Weeden.

"We first looked at our load data to see what we were conveying as we designed our system," says Morris. "The more uniform the load unit, the more efficient the conveyor system can be. The smaller the variances, the less frequent the jams," he adds.

Verizon sought a solution that would provide high system throughput and reliability. The project team chose to place most items that would ride the conveyors into a standard tote, then designed the system to match the tote, selecting live roller and belt conveyors for most of the facility's needs.

The result is an award winning DC in Westfield (See MMH February, 2001) to service technicians in the field, retail stores and home customers.

In other words, a good starting point in any conveyor selection process is an analysis of what will travel on the conveyors. This should take into account the weight, size variance, stability, consistency and the bottom surface of the items that will be conveyed. Those details, in turn, will have a direct impact on the productivity of the finished system.

With that in mind, here's a rundown of the most common types of conveyors, how they operate and what they do best.

Skatewheel conveyors use a series of small metal or aluminum wheels aligned in rows. These units are non-powered and rely on gravity for conveying. They are ideal for moving cartons, sacks and bags down an incline. They are also used in shipping areas to convey products down specific lanes for loading into outbound trucks.

Skatewheel systems are typically inexpensive, easy to maintain and are often portable. Some systems are expandable, similar to an accordion.

Since it is often difficult to control items on skatewheels because there are no motors to move loads along, they are not suitable to all applications. Their use is typically limited to short runs and areas that are easily accessible. Skatewheels are commonly used for the end of conveyor runs, divert spurs and as loaders.

Belt conveyors are among the most commonly used devices in facilities and cost-effectively convey a wide range of products. They are ideal for general transport of light- and medium-weight items in just about any location of the building. Maintenance costs are low too.

The belt rests upon a constructed bed. Motors slide the belt along, which in turn moves the products resting upon it. With a large amount of surface area contacted between belt and product, these conveyors produce sufficient friction to make them ideal for transporting items along inclines or declines and for conveying odd-shaped items.

Sliding bed conveyors are suited for unstable loads that travel at low speeds. They are often located at load stations and assembly stations. These systems typically convey products on an unpainted metal surface that slides along a bed. Since the bed is solid, there is a large amount of surface contact area, making these conveyors ideal for odd-shaped items and small items that are not placed into totes.

Live roller conveyors are also a common fixture in distribution centers and manufacturing facilities. These systems feature a series of elongated rollers mounted across the conveying bed. The roller sizes can vary, depending on product. Belts, chains, or line shafts power the rollers.

Belt drives provide the most positive contact and usually require less maintenance. They typically offer the lowest overall cost of roller systems. Chain systems are more complex. Line shaft systems allow for quick changes in flow and are often chosen for systems that will involve right angle transfers and diverts. Line shaft units also tend to be quieter.

Live roller systems are well suited to a wide range of product conveying. Many facilities with a varied product mix choose live rollers. They can handle heavy loads and are also ideal for dirty or harsh conditions. Products can easily merge into these systems as well as divert to other lines. They are also used to accumulate product.

One drawback to live roller conveyors is that products must have a solid bottom and sufficient weight to ride properly on the rollers. Loose articles can easily fall between rollers, therefore it is recommended that items be either boxed or placed into totes.

Systems that include work-in-process or require a buffer often use accumulating conveyors. Accumulation backs up and stages selected product without impeding workflow elsewhere.

They are commonly used at workstations or for preparing product before it enters a sortation system. Accumulation systems consist of rollers or belts that power and stop automatically to provide spacing between cartons as directed by either photo eyes or sensing rollers.

Accumulating conveyors are more expensive and require additional controls and motors than many other systems, but the benefits in flexibility outweigh the added costs when applied properly.

Click on this icon to read about how to test systems once installed.

Click on this icon to read about other considerations in selecting conveyors.