Keep it moving
The key to smooth-running conveyor operations is keeping everything in motion. That's where sortation systems come in.
To understand the role sortation systems play in the DC, it might help to picture the tangle of railcars and tracks in a busy rail switchyard. Though the average switchyard may look like an exercise in chaos, it's anything but. As the trains roll in, track switches swiftly marshal the incoming railcars and route them to the proper spurs or sidetracks, clearing the way for new arrivals. Much like the switches that keep cars moving at busy rail intersections, sortation systems direct the traffic flow in today's conveyorized DCs. Whatever their type—pop-up, tilt tray, cross-belt, bomb bay—it's the sorters that keep the operation humming, rounding up the Star Wars action figures, flannel shirts, tubes of lipstick and whatever else comes hurtling down the conveyor belts and directing them to hundreds of possible destinations.
In their role as traffic cops for the DC, sortation systems direct products from one conveyor line to another. They can be as simple as a single divert that sends cartons to a processing station or as complex as a system of hundreds of destination chutes arrayed around a high-speed tilt tray or crossbelt track. (See the accompanying box for a description of the most common types of sortation systems and their applications.)
Of course, nowhere is it written that a DC can only use one type of sortation system; many facilities have successfully integrated multiple types of sorters into their operations. One such operation is the Blair Co., a retailer that markets apparel and home dÈcor items. Blair uses a variety of sorting systems in its 875,000-square-foot distribution center complex in Warren, Pa. (the DC actually consists of two adjacent buildings connected by a conveyor bridge). The company ships 50,000 units each day using two crossbelt sorters, a sliding shoe sorter and several pop-up diverters, all from Siemens Logistics and Assembly Systems.
Most items are picked in batches from storage locations and picking areas in the first building. The pop-up sorters located among the conveyor lines are used primarily to divert items to stations where tasks like product personalization and monogramming are carried out.
Once all of the value-added processes are completed, items are conveyed to the second building, where they pass through the sliding shoe sorter, which performs multiple tasks. Some items may pass through this sorter more than once during their journey through the building, being diverted to a different processing area each time. For example, the sorter may first send items picked for multi-line orders to one of the crossbelt sorters for order consolidation. The sliding shoe sorter also diverts single line orders to a bagging area. Once bagged, these are sent back through the sorter again, this time to be diverted to packing stations. Some cartons also pass through the same sorter an additional time to be diverted to sealing machines.
The crossbelt sorters serve as the heart of the distribution system at Blair's DC. The first crossbelt sorter breaks down bulk-picked items into individual orders for packing. This unit replaced a tilt-tray system that was previously installed at the facility. Since crossbelts use a moving belt to divert items, this sorter occupies less space than the old tilt-tray unit, yet still contains a whopping 500 destination chutes.
"This crossbelt sorter sorts on three-foot center lines," explains Tim Harlan, director of operations for fulfillment. "The tilt tray could not sort on that short interval. We were able to reduce the footprint and save money." Harlan adds that the sorter is capable of processing 182,000 items over two shifts each day.
Products for about 10 orders (each order averages just over two units) are sorted into each of the sorter's chutes. A worker situated at the bottom of the chute manually removes items from the chute and packs them into shipping cartons. Many of these cartons will pass through the sliding shoe sorter again for sealing.
The second crossbelt sorter serves shipping needs. Once packed and sealed, all cartons enter this crossbelt shipping sorter at five automatic induction points. This shipping unit sorts items to about 45 destinations, depending on weight and how they will ship. Most products are shipped via the U.S. Postal Service. About 21 of the sorter's destination chutes are assigned to bulk mail centers. These items are gathered and then placed on a truck for delivery to postal sorting facilities in distant cities. (By shipping directly to the bulk mail centers, Blair saves greatly on postal costs.) Other diverts are used for very small items (items weighing under one pound) that are gathered into Gaylord boxes for later processing by the Postal Service, and a few additional lanes are reserved for orders handled by UPS.
"It is unusual to use a crossbelt for shipping," Harlan admits. "We could have gone with a tilt-tray system there," he says, but because the company was already operating a crossbelt in the pack area, it opted to install another cross-belt so that it could consolidate its sorter parts inventory.
Others lean toward tilt trays
The Blair Co. may have chosen crossbelts, but it's equally common for companies that place a premium on high speeds to opt for the tilt tray model. One such company is eToys Direct. This direct-to-consumer toy retailer has two large Beumer tilt-tray systems at its distribution center in Blairs, Va. The facility also has a sliding shoe sorter from FKI Logistex that is used during high-volume periods to send products to staging lanes where they are held for later processing.
The first tilt-tray sorter at eToys Direct consists of 495 trays and is used for assigning batch-picked pieces to individual orders. As totes of batched items approach the sorter, items are removed at 12 induction stations and manually placed onto sorter trays. Scanners read the tray numbers and determine which of the 400 chutes arrayed on each side of the track should receive each item. As the tray approaches the proper chute, the tray tilts and the product falls into the chute. Up to seven orders are accumulated into each chute. A worker then manually divides the gathered items into individual order totes, which then are conveyed to a value-added station (like a gift wrapping center) if needed before being sent on to packing stations. Orders average 3.6 items.
Cartons of packed orders next head to the second tilt-tray unit, which handles shipping tasks. This sorter has 525 trays and feeds 18 shipping lanes. It has a rated capability of performing 8,760 tilts per hour and provides accuracies above 99.8 percent.
So far, at least, it appears that the tilt trays have not only met, but exceeded expectations. "On our best day last year, we shipped 48,000 cartons," reports Kenneth Scruggs, eToys Direct's facilities manager. "And [we] could have handled even more."
About the Author
David Maloney has been a journalist for more than 35 years and is currently the editorial director for DC Velocity and Supply Chain Quarterly magazines. In this role, he is responsible for the editorial content of both brands of Agile Business Media. Dave joined DC Velocity in April of 2004. Prior to that, he was a senior editor for Modern Materials Handling magazine. Dave also has extensive experience as a broadcast journalist. Before writing for supply chain publications, he was a journalist, television producer and director in Pittsburgh. Dave combines a background of reporting on logistics with his video production experience to bring new opportunities to DC Velocity readers, including web videos highlighting top distribution and logistics facilities, webcasts and other cross-media projects. He continues to live and work in the Pittsburgh area.
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