The modern distribution center is like a superhighway for processing products. The idea is to get items from Point A to Point B as quickly and efficiently as possible. Except in a distribution center, there is also a Point C, Point D, Point E, and so on.

An automated sortation system is the most efficient tool DCs have for moving ordered products to their designated points within the system. Think of it as the exit ramp that leads to the secondary roads and streets of the facility including the gateway to the customer – the shipping dock. The type of sortation system chosen for open goods and cartons – crossbelt, tilt tray, sliding shoe, pop-up diverters, and pusher systems – depends greatly on the product and volume being processed, giving each its own sweet spot in DC operations.

Crossbelt sorters are excellent at directing a large number of items to many destinations. These are typically the fastest sorters, able to divert over 300 units per minute based on size.

Crossbelts are built in a circular track surrounding multiple destinations. These destinations are typically accumulation chutes, but can also be additional diverts or shelving. Crossbelt systems feature a series of small powered belts installed perpendicular to the track. Induction can be automatic or manual. When a product reaches its destination, the belt powers on, sliding the product across the track and to its destination.

An advantage of crossbelts is that they provide a positive discharge - the belt physically moves the product while other systems, such as tilt trays, rely on gravity. Because of this, crossbelts are suited to sorting small or lightweight items such as books, videotapes, and compact discs. Most systems limit product weights to about 60 pounds.

Another benefit of crossbelts is that they offer bi-directional discharge, meaning that the belt can divert product left or right. Some new quad systems also divide each cell into four belt units with two of the belts running parallel to each other. This allows large products to ride on all four belts at once or for each to act independently. Such systems provide versatility along with high throughputs while occupying a relatively small footprint.

Tilt tray systems are kin to crossbelts in that they have a similar design and sort in the same basic manner. Often the decision to choose between crossbelt or tilt tray is based on preference. Tilt trays are high-speed, high-volume sorters able to perform from 200-300 diverts a minute depending on system size. Facilities that do a large amount of batch picking often use tilt trays to break the batches down to individual orders.

Like crossbelts, a typical system consists of a train of trays that runs along a circular track. Products are inducted onto the trays by hand or by automatic conveyor. The trays, typically polished wood, are designed to hold a wide range of products. Chutes are aligned along the perimeter of the track. The trays pass under a scanner upon induction which reads a bar code on the item. This tells the management system what product is on that tray. It then travels around the track and as it approaches the destination chute selected by the management system, the tray tilts, sliding the product down into an accumulation and packing area. They can also sort bi-directionally.

Tilt tray systems are often used for shipping duties by companies with high-volume outputs, such as parcel handlers. The trays in this application sort parcels and flats, feeding outbound shipping lanes.

Tilt trays, like crossbelts, are more complicated systems that require a higher amount of maintenance than lower-volume sorting devices.

Many companies choose sliding shoe sorters for their versatility and ability to sort just about any size or shape of carton. These sorters consist of a long conveying apparatus with small rectangular blocks known as shoes situated to one side of the conveyor. As a carton riding on the conveyor reaches its assigned divert destination, a series of the shoes slides across from one side to the other, gently pushing the carton along with them and diverting it down a chute or onto another conveyor line.

Sliding shoe sorters are for mid-range sorting, both in throughput and cost. These highly reliable systems can sort up to 200 cartons per minute with most operating around 120 per minute. Unlike tilt trays and crossbelt sorters, sliding shoes are not suited for single piece items unless they are placed into totes or already boxed.

Galyan's Trading Post, a retail chain offering sporting goods, fitness equipment, and camping gear, recently installed a very large sliding shoe sorter in its facility near Indianapolis (Hytrol Conveyor). The 500-foot unit sorts parcels for shipping to its current 22 stores via 31 diverts.

"A sliding shoe sorter was selected because we have such a variety of cartons in our DC – 300,000 SKUs including odd size items such golf bags and fisherman's hip waders," says Don Richards, director of distribution. "We chose the sliding shoe because of our high throughput demands. It is designed to eventually support 71 stores."

An advantage of sliding shoe sorters is that products do not have to be justified to a particular side as is the case with other sorters, such as push diverters. Accumulation, however, must be performed to produce the proper amount of spacing between cartons for the shoes to operate properly.

Sliding shoes are used in a variety of operations – shipping, receiving, kitting, and diversion to order-filling lanes. Many facilities use the same sorter for a number of tasks, with some diverts assigned to receiving and others to shipping duties.

Pop-up systems comprise the most widely used method of sorting in both manufacturing and distribution environments. The advantage of pop-up diverters is that they can be placed just about anywhere that goods flow along a conveyor, making them highly flexible. Many are used to divert products to shipping lanes. Others are used to sort items for assembly at workstations or for directing products to pallet build or storage areas. Cartons retain their orientation, as they gently transfer from one conveyor line to another.

Pop-up systems also comprise a low-cost solution, with a typical system of 8-10 diverts running around $50,000. Since there are few moving parts, maintenance is usually low.

There are several major types. The most common systems feature a series of wheels set at an angle within the middle of a conveyor. As a carton to be diverted approaches, the wheels pop up. The carton hits the angled wheels and is diverted.

Some systems use pop-up rollers or belts instead of wheels. Others use steerable wheels or directional swivels that turn as the product is sorted, allowing a higher angle of divert without the need to greatly slow down the parcel. Some of these are designed to divert to either side of the conveyor.

Similar to sliding shoe systems, items must be able to ride a conveyor or be placed into totes to operate with pop-up systems. The angle of divert greatly affects speed. Systems with a smaller divert angle of 30 degrees can sort 100 cartons per minute. Right angle transfers of 90 degrees typically handle about 60 cartons each minute.

Similar to pop-up sorters, push diverters are positioned in-line on a conveying system. As a product approaches its divert point, an arm or pusher slides out and moves the carton to its new destination lane. Some systems are designed so that the pusher impacts the carton. Others are made to sweep the carton as it contacts the pusher. And still more are made with swing arms that move out over a conveyor so that when the carton arrives it encounters the obstacle and turns to a divert lane.

Push systems are relatively simple and require little maintenance. Like their pop-up cousins, pushers are considered lower-level sorting. That does not mean, however, that they cannot be used for extensive sorting applications.

Chicago's O'Hare Airport uses push diverters to sort 15,000 bags a day in its International Terminal.

"We chose push diverter sorting based on the very limited space we had," says executive director Jack Ranttila. "For the type of product we are handling, it was a logical technology to use."

The O'Hare system (Sandvik Sorting Systems) is sandwiched between the ticket counter and the main lobby and has only 14 feet of height clearance. Push systems, like the one at O'Hare, are well suited to close-quarter demands as most can be designed to cover a wide range of divert angles – typically from 20 degrees to 45 degrees. A more severe angle can also be attained, but to do so requires that the carton slow down.

Pushers can typically handle a higher volume than pop-up diverters, often performing 150 diverts a minute. Because of the nature of the system, there is some impacting of cartons as the divert takes place. Therefore, fragile items are not well suited to this type of system. With proper edge alignment and accumulation upstream, the impact can be greatly reduced. Orientation is usually not maintained, especially where pushers divert to a chute.

Push diverters can handle a wide range of products and are often used for sorting large and heavy cartons. As with sliding shoe and pop-up sorters, items need to be conveyable to work with a push system.

These systems are used extensively in baggage handling and parcel and postal sorting. Within distribution facilities they commonly serve shipping, receiving, and returns processing.