These key questions can help narrow the applicable sortation options to begin understanding the rough cost. However, there are many other questions that should be answered before making a final selection. In fact, if the solution provider does not spend as much or more time up-front understanding the operational requirements needed to design the system, then there’s a very good chance the system will not perform as expected. With so many considerations, how does one choose the proper type of sorter?
Once you have determined your goals, needs and system requirements, it’s time to analyze what type of sortation system will best satisfy your company’s needs. There are a number of sortation systems available, depending on what you wish to accomplish and they are based on high, medium and low throughput rate.
At this point, it should be noted that with the global push towards “green” solutions, the rising cost of electricity and the anticipated carbon reduction legislation, it is prudent to consider a low-voltage, 24 volt DC (VDC) sortation system. This is where the marketplace is heading due to energy, ergonomics, safety, maintainability, modularity, floor space utilization and noise concerns. Plus, they are rapidly becoming very cost competitive with standard AC voltage technology. Their throughput rate typically falls within the medium category.
HIGH-THROUGHPUT SORTERS—GREATER THAN 60 PPM
1. Sliding Shoe Sorter (rate range: 70 to 200 Product Sorts Per Minute (PPM) targeted range)*
The high initial investment and additional required sound dampening may deter some operations from selecting a sliding shoe sorter. However, it works well when handling high volume and a variety of product sizes since it is a push type rather than a pull type. The product is conveyed on a series of closely linked “slats” that are generally constructed of hollow-extruded, 3- to 4-inch-wide aluminum tubes.
The flat surface and closely linked slats have very little open gap between them, which make them excellent for handling a variety of different sized products. Upon each slat is a “shoe” that wraps around the slat so it slides easily and always remains attached to the same slat. When the moving product is near its intended divert destination, multiple shoes slide and push the product down a chute or a conveyor section known as a spur.
Because of the product’s high speed (400 to 600 feet per minute or more), the spur is usually a gravity-sensitive design to minimize product rotating, which causes jams in the throat of the spur. This also provides a tertiary advantage of minimal maintenance and no electrical power required for the spurs. Minimal maintenance does not come without preventative inspections to the sorter.
2. Cross-Belt Or Tilt-Tray Sorter (rate range: 60-plus PPM; maximum rate varies depending on number of induction locations)
These sorters are usually chosen for retail and postal distribution centers because they can handle a wide variety of products from CDs and Ziploc bagged products to large/heavy postal bags. Since these systems also have the highest initial costs, this usually limits them to large applications with specifications that are impossible to accomplish with a conventional sorter.
Operations calling for a cross-belt or tilt-tray sorter benefit from the availability of multiple induction points. Cross-belts and tilt-trays circulate in a horizontal loop by running on a single rail system. The difference is that a cross-belt has short individual conveyor sections oriented 90 degrees to the direction of travel. When the cross-belt arrives at the desired divert location, the conveyor runs either left or right to discharge the item. The width of the cross-belt will vary based upon maximum product size, but they are typically less than 20 inches wide, meaning they are usually specified for smaller items that are difficult to handle.
A tilt-tray is very similar to a cross-belt, except product is inducted onto a concave or box-shaped tray. When the tray arrives at the desired divert location, it tilts either left or right to discharge the item. The width of the tilt-tray will also vary based on maximum product size. However, these sorters are generally specified for larger/heavier items since it is quicker, easier and less costly to pneumatically/electrically tilt a tray than to start a conveyor from a dead stop under a heavy load. The sorter typically discharges to chutes due to cost savings when used with a high number of divert locations.