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TriFactor Home > TriFactor Learning Center > White Papers > Parcel Handling System Design Best Practices, Part 1 – Inbound Unloading and Convey to Sorting Parcel Packages

Parcel Handling System Design Best Practices, Part 1 – Inbound Unloading and Convey to Sorting Parcel Packages

Introduction

Fulfilling bulk orders to brick-and-mortar stores is like stacking blocks: items are packed and shipped in cartons that are easy to see, easy to sort, all the same shape and size.

But with the rise of direct to customer e-commerce, things seem less like Jenga® and more like a jumble.

Instead of only palletizing large boxes onto trucks for route delivery, distribution centers are also turning into piece-picking parcel handlers, fluid-loading mixed shipments—polybags holding a single mascara, bubble mailers carrying baseball mitts, and the lone wheel of cheese nestled into a customized round box—into trailers, vans and other vehicles.

Maximizing throughput of small orders and irregularly shaped packages requires new skills, not to mention different conveyor and sorting equipment.

But those aren’t the only challenges the changing retail landscape has created for the typical distribution center.

For example, as carriers caught onto the e-commerce opportunity, they realized they could optimize the use of cargo area within their trucks—and increase revenue—by charging for the space a parcel takes up, rather than what it weighs. That changed the economics for shippers and drove even more reduction in package sizes; after all, no one wants to pay for a parcel filled with empty air.

There are also more parcel carriers in business now than ever. While more options typically mean greater flexibility and generally lower prices, the trade-off is understanding and complying with multiple carriers’ standards, restrictions, schedules, and manifesting operations. Add in the growing number of local, last-mile delivery services and the task of getting a parcel from point A to point B becomes even more challenging and expensive. According to the Council of Supply Chain Management Professionals (CSCMP), costs associated with last-mile delivery can be more than 25 percent of the total supply chain budget for some companies.

It’s no wonder that some direct-to-consumer businesses are relying on third-party logistics firms to take control of shipping altogether or, at the other end of the spectrum, have taken matters literally into their own hands. It is no secret that Amazon has become their own last mile service provider by setting up parcel delivery stations in metro areas throughout the US and using either their own delivery vans or contracted “Flex” drivers and their personally owned vehicles.

At the very least, though, e-commerce retailers are increasingly investing in material handling systems that can convey and sort a growing variety of parcel package types, making the management of both outbound shipping and returns easier and more accurate.

In this three-part series, TriFactor looks at the nuances of designing a material handling system for parcel packages. First up—the inbound portion of the process: unloading and conveyor to sort.

If it Ships, It Fits: Defining “Parcel Package”

It seems like a simple question: What, exactly, is a parcel package? But the answer is not as straightforward as you might think—and it certainly has changed over the past 25 years ago.

Back in the days before click-and-ship, cardboard cartons and boxes dominated the parcel scene, and for good reason: Boxes are strong, easy to pack and seal, don’t require specialized conveying or loading equipment, and with four flat sides, it isn’t difficult to find a place to affix a shipping label. At the receiving end, they are simple to open, can be stacked for stocking, and—being a paper product— are easy to recycle.

They were perfect for moving goods into the distribution center and for large shipments outbound to a network of stores.

Fast-forward to today, and there are still plenty of paperboard and corrugated cardboard boxes to go around. Although it’s not easy to pinpoint how many boxes are shipped in the U.S. each year, American manufacturers produce about 100 billion annually. That’s big business.

But boxes are big in another way: dimensionally. As the number of direct to consumer orders increased, so did the number of complaints about receiving outsized packages—for example, the pair of candlesticks shipped in a box better suited for table lamp, stuffed with “air pillows” to take up room and provide protection.

In response, retailers have become less dependent on generic boxes and are embracing right-sized alternatives: self-seal bubble envelopes, poly bags, tubes, cylinders, blister packs, basically anything else parcel carriers accept, as long as there’s room for a shipping label and the parcel doesn’t exceed dimension and weight (dim-weight) requirements.

Sure, customers are happier, but the variety often creates a logjam in distribution centers that haven’t updated their processes and equipment, particularly for those relying on traditional box-friendly belt and roller conveyor systems.

The End of the Straight and Narrow?

A staple of distribution logistics, belt and roller conveyors were built for handling full, standard-sized boxes and containers in straight-line succession. And they do a great job of it. Mix in poly bags, padded envelopes, and irregularly shaped cartons, however, and that’s when problems start. Light packages and poly bags can drag against vertical belt rails or get caught under them, resulting in damaged product or equipment jams. The same issues can occur when belted or roller curves are used to change direction of the conveyor path rather than a spiral chute due to the many small catch points the belted and roller curves inherently have.

Ironically, although these parcels often require individual handling, they flow in bulk rather than as individual units. Envelopes are piled up on boxes that are piled up on poly bags or more envelopes. As such, the weight capacity requirements for the conveyor system must increase to up to 50 pounds per foot of conveyor in order to accommodate the possibility of stacked or nestled parcels being conveyed at any given time. Additionally, roller conveyors, even those with tight roller centers, do not perform well in a bulk flow environment making the typical conveyance method a slider bed with belting that is heavy gage (10 gage or 12 gage formed steel). Motor drives can be up to 15 or 20 HP and the drive pulleys can be as large as 16” in diameter. High volume of bulk flow parcels translates to heavy duty conveyor.

On the Receiving End

The reign of the square cardboard box might be over, but the good news is that with a few updates, distribution centers can bring their operations and into the 21st century. Packaging has evolved with the times, but so have parcel handling best practices and equipment options. Of particular note: The telescopic belted conveyor, which can be installed at dock doors to make parcel handling easier, more accurate, and more efficient.

Designed to bridge the actual gap between the distribution center’s conveyor system and the truck dock, telescopic belted conveyors reach inside the vehicle, expanding all the way to the front of a 53-foot trailer. Associates work from the back of the vehicle to the front, unloading, scanning, and placing one item at a time onto the telescopic belt. Because operators don’t need to carry products manually, telescopic belt conveyors can effectively accelerate the inbound unloading process. Additionally, designating multiple doors for telescopic belt conveyors makes it possible to unload multiple trucks at the same time.

Immediately downstream of the dockplate, telescopic conveyors are married up to a longitudinally ribbed incline belt conveyor for moving parcels up elevations to one long and wide collector belt. This main unloader collector belt operates at a normal speed about three times faster than the incline belt, swiftly pulling the packages off and reducing jams at the 90-degree transitions. A platform supporting the unloader collector belt provides underside clearance for normal forklift operations and personnel traffic.

Spiral or Incline? Finding the Best Convey to Sort Route

Of course, telescopic conveyors aren’t the only way to step up parcel handling operations. Advances in convey to sort technology are also helping distribution centers maintain high productivity, even when handling inconsistent parcel shapes and sizes. Determining the optimal conveyor path from the unloader collection belt to the sorting equipment isn’t necessarily a simple task: it has to consider both the best route and how to transition between elevation changes.

In most parcel stations or sort centers, the location of the sorting area is not a straight-line path from the unloading area. Therefore, changes in direction must be designed into the conveyor system. As mentioned earlier, in bulk flow parcel applications, a standard belt or roller curve conveyor will cause more harm than good. Therefore, changes in direction are accomplished through UHMW lined spiral chutes that can turn packages smoothly 30, 60, 90 or 180 degrees. These spiral chutes not only change direction, but they are declining, which obviously uses the natural force of gravity as the means for the smooth flow of packages while changing the direction of flow.

Although these spiral chutes are the most effective way to change direction, it doesn’t necessarily mean that they are perfect and without design challenges.

First, the more spiral chutes in the conveyor path, the more places there are for parcels to get caught up and jam the equipment. Even the smallest of catch points at transitions from the belt conveyor discharge tail to the infeed of the spiral chute will snag a stray piece of plastic from a loose poly-bag conveying along the side of the conveyor. Once that happens, the possibility of a build up of packages increases.

Second, the higher the degree of direction change for the spiral chute, the higher the conveyor feeding it must be: for example, in the case of a 60” wide spiral chute with a 90-degree right hand turn, the discharge end of the belt conveyor upstream of the spiral chute will have to be 45 inches higher elevation than the infeed of the belt conveyor downstream of that spiral chute. Similarly, if the change of direction must be only 30 degrees, then the elevation difference between the infeed to the discharge only needs to be 15 inches.

Due to the challenges that these elevation changes create when changing direction, and because the addition of each spiral chute increases the possibility of catch points, a significant amount of thought and creativity must be applied in order to best locate the sort area in relation to the unloading area.

In addition to these nuances when designing the parcel conveyor system from unloading and conveying to the sort area, there are a few other tidbits of best practices to consider:

• Stay below 12-degree pitch on inclines. The only exception is the unloader inclines, which will be higher pitch, but will use longitudinally ribbed belts and are loaded by associates inside the truck using the telescopic unloaders. Therefore, the parcels are singulated and not stacked one on top of another. Once those inclines discharge parcels onto the large and wide common collector belt, the flow of packages becomes a bulk situation and not singulated. So, in order to reduce the possibility of packages sliding backwards on inclines, limit the angle to 12 degrees maximum.

• Don’t discharge parcels onto an inclining belt. Instead, a better strategy is to discharge onto a horizontal section of the belt and then use a two-pulley hitch about 5’ to 10’ downstream of the infeed section in order to start the incline. This will keep packages from tumbling backwards and causing jams at the infeed section.

• At the discharge end of incline belts, use noseovers to bring the conveyor to horizontal, which will close the gap between the discharging tail pulley and the infeed of the next conveyor or chute. This reduces or eliminates catch points and possible jams.

• To avoid wearing down tail pulley bearings, design the discharge location from a straight or spiral chute so it’s 12” to 18” downstream of the tail section. The impact of the parcels will be felt by the slider bed section, which is just dumb steel, as opposed to the tail pulley, which has rotating parts or precision parts, such as bearings. Better to beat up the flat steel than wear down axles, bearings, collars, sleeves, bushings, fasteners, etc.

• At the locations where packages are being discharged, design to have the bed sections as 10-gauge steel. All other downstream bed sections can be 12-gauge, which is still heavy duty. The 10-gauge steel at these impact areas will keep the conveyor from vibrating and resonating along the downstream rigidly connected bed sections.

• Constant vibration can cause fasteners to back out and other mechanical issues. So the thicker steel will minimize this possibility.

Improving productivity while handling small packages can be a tall order but understanding best practices and innovations in parcel conveyance design can stack the odds in your favor.

A system integrator can optimize a material handling solution that’s right for your business, helping you adapt to today’s growing retail model while continuing to serve your traditional base effectively.

Next time: Parcel Handling System Design Best Practices, Part 2 – Manual and Auto Sorting Parcel Packages