Dynamic storage
If you can't beat the laws of gravity in a distribution center, use them to your advantage with dynamic storage.
By Allison Manning, Associate Editor -- Modern Materials Handling, 1/1/2009
Depending on the number of SKUs passing through your distribution center, a dynamic storage option can help keep them moving. Dynamic storage, including gravity flow and push back rack, uses gravity to shift cartons or pallets down toward the receiving point.
Sure, for a warehouse with thousands of SKUs, simply putting an item statically on a shelf can work fine. But for a manufacturing plant or distribution center with only a few SKUs but huge throughput on those items, a more efficient storage system is necessary. Depending on what you're storing, a carton flow, pallet flow, push back or high density system might be what you need, especially if you're looking to save space.
GRAVITY FLOW RACKS
Carton flow
Gravity flow racks can handle both cartons and pallets, depending on what's needed. In fact, carton or case flow systems are elemental to many operations, says Don Derewecki, president of Gross & Associates|TranSystems (732-636-2666). The systems are used to index individual cartons to a pick face.
Carton flow rack is normally used in picking systems or smaller case systems, and in pick-to-belt operations, according to Dick DeFoe, Steel King's national account manager for dynamic storage (www.steelking.com, 800-826-0203). For production parts picking, most manufacturers find that small plastic totes weighing less than 35 pounds are a great fit for flow rack handling and presentation, according to Keith Soderlund, Creform's vice president of sales (www.creform.com, 800-839-8823).
At medical equipment company MEDRAD, installing Creform's flow racks at each worker's station saved labor and time, smoothing out the flow of parts and components into the assembly areas. The moveable flow racks provided storage and efficient feeding of items for packing. Packaging times were reduced by more than 3 minutes for some products.
Soderlund says some gravity flow racks include error proofing systems, which ensure that the correct parts are being pulled. “This is becoming increasingly important on assembly lines with mixed model production,” he says. “Repairing the mistake of choosing the wrong part can be very expensive and time consuming.”
Pallet flow
When multiple pallets with the same SKU need to be stored, pallet flow racks can help organize your building.
Pallet flow storage is an alternative when equipping a new building amidst rising capital and operating costs, “Generally, what they're looking for is more space in their warehouse without having to add on or put in a new addition,” DeFoe says.
Because gravity flow operates as a first in, first out (FIFO) process, they are commonly used in industries managing in perishable goods. A dairy supplier may place pallets filled with gallons of milk in a gravity flow rack, ensuring that no pallet is neglected or sits on a shelf too long.
“Everything has a lifespan on it,” DeFoe adds. “They have to turn the stock over and get the freshest out.”
Gravity flow systems index individual cases to a pick face.
In the dairy section in a grocery store, a worker can stock gallons of milk from the refrigerated storage room, allowing the product to slide down the incline, while a customer picks from the front. It works the same in a warehouse. One lift truck can load pallets for storage, while another on the other side can take them out.
Frazier Industrial president Carlos Oliver (www.frazier.com, 800-614-4162) says flow racks are big in food and grocery applications because of the density, selectivity and durability requirements. In other industries, such as retail, the density isn't needed because of the high SKU counts and low number of pallets per SKU.
Push back racks
With only one access point, push back racking operates as a first in last out (FILO) system. In a standing refrigerator with only one access point, loading bottles of soda is a push back operation. As each bottle of soda is added, the one added previous is pushed back. When a bottle is taken out, the rest behind it slide forward to the point of entry.
The denser your product, the more likely you are to choose push back over gravity flow.
“Where your ratios are more than eight pallets per SKU to 15 pallets per SKU, those are more in line with the use of push back,” Oliver says.
With push back, an open aisle on the opposite end is unnecessary for loading, says DeFoe, allowing the racking to be pushed directly against the wall, saving space. But it has to be an item that doesn't require first in first out, such as a fast moving or nonperishable product. And only one access point means it's impossible to load and unload at the same time, as can be done with gravity flow rack.
Push back racking is limited as to how many pallets deep it can be, DeFoe says. “It takes a strong lift truck to push pallets back uphill,” he said.
High-density pallet storage systems are a good choice where space is at a premium.
HIGH-DENSITY SYSTEMS
Dynamic storage is a mature technology. But there have been innovations, from battery powered carts to better wheel and track systems.
Some SKUs have dozens of pallets, more than can be handled by a push back rack or gravity flow system, and stacking pallets too deep with either system can be unproductive and unsafe. High density systems marry drive-in and push back racking.
One product that addresses this issue is a battery cart on which the pallet sits, with power carrying the pallet along a rail, rather than it relying on gravity. All the lift truck needs to do is deliver the pallet to the cart, with no pushing necessary. Ray Chase, executive vice president at Konstant (www.konstant.com, 847-364-2400), calls this racking his company developed a “poor man's AS/RS system,” suitable for an environment where people are more comfortable working with mechanical systems.
This double-sided system, called the Pallet Runner, operates between 10 and 30 pallets deep, but can do projects with single pallet selectivity up to 60 pallets deep and five pallets high.
Chase says that in the supply chain, manufacturers and those at the first step of distribution had a very small SKU set that might represent a huge portion of the volume. The companies handled the product in pallet loads, but had between 50 and 100 of the same pallet repeated. Push back wasn't getting the job done.
“Many in the industry will be 10 deep, but you can't find a fork truck that can push 10 pallets back,” Chase says. “Six deep is about it for a fork truck to push back.”
One bread company uses this kind of high-density storage to handle freshly baked loaves. On one side of the system is the bakery where the loaves are prepared and placed into the system. The general warehouse is on the other side. Similar applications are used for the beverage industry. “Anything where it's just a lot of the same item,” Chase says.
High-density systems are a good choice in areas where space is at a premium, such as a freezer or refrigerator, Derewecki says. The high cost of cooling that part of the warehouse demands more efficient storage. Chase says his company has seen significant success in frozen applications, down to -22 degrees Fahrenheit.
When multiple pallets of the same SKU need to be stored, pallet flow racks can help organize a building.
SAFETY
Too steep of an incline or lack of proper braking, and that pallet you loaded on the other side will pick up major speed. Suppliers are working to eliminate the incline, or pitch, needed to use gravity in a push back rack or pallet flow. Less pitch means less forward force on the lowest pallets, and less wear and tear on the lift trucks needed to push the pallets back. Chase says his company has gotten its push back pitch down to 3/16-inch, while the industry standard is between a 1/2 and 7/16-inch.
Braking is also an issue. When he entered the business 30 years ago, DeFoe says there was only one braking option on flow rack: skate wheels. These wheels didn't brake so much as just act as slowing mechanisms for the pallets. “If you loaded a pallet 20 deep and didn't have brakes, it would pick up speed,” DeFoe says.
Now, improved braking devices include more plastic, high impact wheels, rather than steel, accommodating different weights. Some can slow down pallets weighing up to 25,000 pounds. One system guides pallets down the line one at a time, keeping them captured within the lane, rather than allowing one to slide down on its own with gravity. The pallet stays in place until the system indexes it forward. “There's no live pressure on the products,” LoadBank International president and CEO Doug Hughes (www.loadbank.com, 800-458-9010) said of his company's SafeLANE—an alternative to centrifugal braking systems, brake roll, and other gravity pallet handling systems.
Skate wheels in a flow rack system act as a slowing mechanism for pallet loads.
Dynamic storage
09/30/1999Keeping business green
04/30/2001How pallet loads stack up
10/31/2004Gravity flow rack boosts throughput 30%
10/01/2006
View All On-Demand Webcasts
