Push Back Rack
Push-back rack provides last-in-first-out (LIFO), deep-lane (typically two to five pallets deep) storage by employing a slightly inclined, rail-guided, nested carrier for each pallet load. As a load is placed into storage, its weight and the force of the putaway vehicle push the other loads in the lane back into the lane to make room for the additional load. As a load is removed from the front of a storage lane, the weight of the remaining loads (automatically with gravity) advances the remaining loads toward the rack face.
The name "push-back" comes directly from the loading process. The system is named for the distinct action where a new pallet being loaded into the lane literally pushes back the pallets that are already stored there.
1. Push Back Rack Operations
Loading pallets into a push-back lane is a straightforward, repetitive process:
a. First Pallet In: A forklift operator places the first pallet onto the top carrier in an empty lane. This carrier sits at the very front of the lane, right on the aisle.
b. The "Push": When the operator brings the second pallet, they line it up with the lane and simply push the load against the first/front pallet in the lane. The force from the forklift and the weight of the new load cause the first/front pallet to gently move back into the lane on its carrier.
c. Repeat: This process is repeated for each subsequent pallet. As a new pallet is loaded, it pushes the entire line of existing pallets back one position.
Retrieving a pallet is even simpler, as gravity does most of the work:
a. First Pallet Out: The forklift operator gently lifts and removes the front pallet from the lane.
b. Automatic Advancement: Because the rails are slightly inclined, the moment the front pallet is removed, the weight of the rear pallets automatically advances them forward, advancing the entire lane of pallets to the rack face.
c. Ready for Picking: This action brings the next pallet in line to the front of the rack, making it immediately available for picking. This means every lane always has a pallet ready to go.
2. Push Back Rack Advantages
The main benefit of push back rack is its high storage density achieved without sacrificing direct rack face access from the main aisle. By combining density and accessibility, push-back racking offers several storage benefits, especially when compared to other common storage systems, including (a) Rack Face Selectivity, (b) Storage Density, (c) Conventional Lift Truck Accessibility, (d) Elimination of Vertical Honeycombing,
a. Rack Face Selectivity. Because each deep lane can be dedicated to a different SKU (Stock Keeping Unit), push-back offers a great balance between high density and product variety. Every SKU/lane has a load that is immediately accessible along the aisle.
b. Storage Density. By storing pallets up to seven deep, push-back systems dramatically increase pallet storage capacity in the same footprint compared to single-deep or double-deep pallet racks.
c. Conventional Lift Truck Accessibility. Since all of the putaway and retrieval takes place at the rack face, there is no need for special lift truck attachments as is the case with double-deep rack.
d. Elimination of Vertical Honeycombing. The design of push back rack eliminates the need for operators to drive inside the rack structure, preventing vertical honeycombing, improving safety, and improving productivity.
3. Disadvantages of Push Back Rack
There are three main disadvantages of push back rack – last-in-first-out inventory rotation, rack face congestion, and horizontal honeycombing.
a. Last-in-First-Out (LIFO). Push-back racking is a LIFO (Last-In, First-Out) system. This means that the last pallet placed into a lane will be the first one to be removed. This LIFO rotation makes push back rack unsuitable for products that require strict FIFO (First-In, First-Out) rotation, such as perishable goods with expiration dates.
b. Rack Face Congestion. A primary disadvantage of a push-back system is the potential for aisle congestion. Because the mechanical design of push back requires both picking and restocking to occur at the same side of the rack, congestion may occur in a storage aisle, especially if there are fast moving products housed in the aisle.
c. Horizontal Honeycombing. In the nested, LIFO design of push back rack, for any products that have only one or two pallets on hand housed in push back rack block the storage capacity behind them. Rear storage locations are blocked, wasting the storage capacity of that lane. Therefore, the system is mechanically optimized for SKUs with at least two pallets on-hand.
4. Push Back Rack Cost
RightChain™ always recommends that direct quotes be obtained from push back rack suppliers in order to know exactly what a given push back rack installation may cost. That said, RightChain™ has had quotes ranging from $150 to in excess of $400 per pallet position. The cost is justified against the occupancy cost savings that may accrue from increases in storage density.
For example, if a push back rack installation of 500 pallets is being considered and the cost per pallet position is $300, then the entire installation would have an initial investment cost of 500 pallet positions x $300 per pallet position = $150,000. If the installation yields a footprint reduction of 2,000 square feet, and the unit occupancy cost is $20 per square foot per year, then the annual savings in occupancy cost would be 3,000 square feet x $20 per square foot per year = $60,000 per year. The payback on that potential investment would be $150,000 / $60,000 per year = 2.5 years.
5. Push Back Rack Applications
Push back rack is best applied for medium moving products with multiple pallets on hand that do not require strict FIFO rotation in facilities with relatively high occupancy costs. Push back rack is not appropriate for products with only a single pallet on hand because the single pallet would block access to several pallet storage locations. Push-back rack works effectively and efficiently for medium to fast-moving SKUs with three to ten pallets on-hand where FIFO rotation is not required.