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HIGH-DENSITY RACK
Drive-in rack can be configured to store loads four or more deep, creating very dense storage. For example, a drive-in system that stores pallets four high and five deep can hold 20 pallet loads in each bay. In a drive-in system, lift trucks drive into the front of a storage bay, place a load in the designated position then back out. The rack is designed without traditional beams across the bays so lift trucks can maneuver in and out. Instead, pallets rest on rails that run along the inside of the bay, perpendicular to the aisles. Pallets are stored on a last-in/first-out basis. Each bay is typically dedicated to a single product, so drive-in rack is best used for storing large quantities of the same product. They work well where an entire bay of product is moved at once, such as in staging product for shipping.

Drive-through rack is almost the same as drive-in, except that drive-through rack allows lift trucks to enter from either end. This means an aisle is required at both ends of the structure, but it increases access to pallet loads and can be loaded from one end and emptied from the other, enabling first-in/first-out product rotation.

LOW-DENSITY RACK
Single-deep rack (Selective rack), is the most common type used in warehouses and distribution centers. Since loads are stored one pallet deep, this is the lowest density storage of any system, but it allows unimpeded access to every pallet. It can be used in a number of aisle configurations and can be paired with any type of lift truck. Single-deep pallet rack is also the least expensive rack option.

Double-deep rack stores one pallet load behind another in a structure that’s twice as deep as single-deep. This design doubles storage, but it limits access and flexibility. To access the rear pallet load, the front pallet position must be empty. Double handling is necessary unless pallets are stored on a last-in/first-out basis. In most cases, two pallets with the same product are stored in a slot of a double-deep rack, which limits flexibility and requires a deep-reach lift truck to access loads in the rear position.

Which rack is right for your operation? Let’s go back to basics.
Pallet rack systems are a key component of any warehouse or distribution center selecting the right type can keep product organized and maximize cube space from floor to ceiling. More importantly, they are central to getting product out the door.

Basic pallet rack consists of upright steel frames connected by horizontal steel beams and high-rise storage systems can reach 100 feet, but 20 to 25 feet is a typical rack height. Welded frames are more common in the United States and although Bolted construction is more prevalent in Europe it is often used in the United States as well. Beams are usually bolted to frames or interlock using a slotted connection system. Rack components are made of structural steel or roll-formed steel, with roll-formed being the most common in the United States. Structural steel typically costs about 5% to 10% more than roll-formed. Raw materials make up a significant part of the cost of rack so any increase in the price of steel will drive a percentage increase in the cost of the finished rack.

Rack systems can generally be divided into two broad categories: low-density systems that allow easy access to product, or high-density systems that make better use of space but limit access to stored product. Here’s look at what the different systems offer.

pallet, which is loaded from the front, is placed on top of the cart. When the second pallet is loaded, it pushes back the first pallet, exposing the second cart, and so on.

Usually configured two to five pallets deep, these systems offer dense storage. Like flow rack, push-back rack does not require a lift truck to enter the racking structure or require an entire bay to be dedicated to one product. Unlike flow-rack, however, push-back rack manages inventory on a last-in/first-out basis and requires less space than flow-rack because rear access is not necessary.

Pallet Rack Basics

DYNAMIC STORAGE
Gravity flow rackcombines a stationary rack structure with skate wheel or roller conveyor to create a dynamic storage system. Pallets are loaded into the back end of the rack then travel down the slightly inclined lane of conveyor so they can be retrieved from the front of the system.
Flow rack systems provide high-density storage by storing product many pallets deep. Because each layer of flow rack is typically dedicated to a single product, these systems offer less storage flexibility than selective rack but more than drive-in or drive-through. This is a good option for storing dated products because it allows easy rotation of inventory on a first-in/first-out basis. It can be used for picking by the piece, carton or pallet. Carton flow rack that stores individual cartons are also available from many manufacturers. Because there is more engineering involved in creating flow racks, they are more expensive than selective rack.

Push-back rack combines a stationary rack structure with nested carts that move along inclined rails. The first pallet, which is loaded from the front, is placed on top of the cart. When the second pallet is loaded, it pushes back the first pallet, exposing the second cart, and so on.

Usually configured two to five pallets deep, these systems offer dense storage. Like flow rack, push-back rack does not require a lift truck to enter the racking structure or require an entire bay to be dedicated to one product. Unlike flow-rack, however, push-back rack manages inventory on a last-in/first-out basis and requires less space than flow-rack because rear access is not necessary.