Pallet racks are the standard storage rack used in most warehouses and manufacturing plants. They are sized to fit a standard skid. Standard skids are 45″ by 48″ and pallet racks are designed to accommodate the 48″ length of the skid, with a small overhang. In most cases this works out to a width of about 54″. Fabricated out of steel, pallet racks are sturdy enough to handle most skid weights. The spacing of the vertical beams can be adjusted to meet different loading requirements. Pallet racks are sometimes called “selective racks,” since each pallet is accessible by a forklift. Where the forklift picks up the skid is called the “pick face.” The more skids that have a pick face, or can be accessed by the forklift without moving anything out of the way, the more selective the rack is.
The shelves, or load beams, on a pallet rack are adjustable to virtually any height, with holes in the uprights every few inches. Roll-formed pallet racks are designed so that the load beams clip into these holes, without any further attachment necessary. For large weight carrying capacity, structural pallet racking is bolted together, instead of snapped.
Double deep racks are racks designed to store two pallets or skids in each aisle. In the simplest scenario, a double deep rack is just two standard pallet racks beside each other. However, true double deep racks are engineered to be less expensive than two pallet racks, since fewer uprights and cross members are required.
With double deep racks, only the first pallet is accessible by a standard fork lift or reach truck. The second pallet is located behind the first pallet and can only be removed with an extended reach forklift.
While double deep racks make greater use of space, there are some tradeoffs. FIFO is harder to manage since not all the pallets are accessible. Additionally, the required extended reach forklift is more specialized, requiring wider aisles and slower pick times.
Very narrow aisle racking refers to a specific warehouse layout with narrow forklift aisles. Usually standard pallet racks are used, but the aisles are reduced to the absolute minimum required for a reach truck. Due to the reduced aisle widths, more space can be used for racks and product storage. Very Narrow Aisle Racking makes efficient use of storage space, with each pallet being accessible (lots of pick faces!), but only specialized reach trucks can be used, since the forklift will not be able to turn around. Often, VNA racking is used for pick racks, where the product removed is not a full skid and the operator is raised up on a platform to select small boxes or parts.
Drive in racks are designed to allow a fork lift to drive directly into the rack to get to the next pallet of product. The pallets are set on rails that guide the skids in each lane as they are being moved with the forklift. Drive in racks should be used to store lots of similar product, since the ones at the back are not accessible. Skids are stored according to Last in First Out principles, since selectivity is low. In order to access the top levels of the rack, all the pallets in front and below have to be removed so that the forklift can drive in.
This system is conceptually similar to just stacking all the pallets on top of each other, except each pallet is supported by the rack. The rack prevents crushing of the pallets underneath.
Similar to drive in racks, drive through racks store pallets very closely together. Pallets are stored on rails, so forklifts can drive into the racking system to retrieve skids just like drive in racks. With drive through racks, however, the pallets can be accessed from both ends by a forklift, enabling first in first out processing. Due to the increased storage density, most pallets will still be inaccessible without removing the outer ones first.
In a push back rack, pallets are stored on moving carts which travel on an angled incline. Unlike a double deep rack or drive in rack, the forklift doesn’t have to stretch or drive in to reach the farther pallets. The carts use gravity to roll down the incline, so they are always presentable on the pick face to a standard forklift. When loading a push back rack, the forklift driver lines up the new pallet with the stored pallets and pushes the stored load back, creating a space for the new pallet. Push back racks are typically used against a wall, where FIFO doesn’t need to be maintained.
Pallet flow racks use gravity to direct the skids to one end of a gradually angled rack. Inclined rollers allow the skids to flow freely, while retarders ensure heavy skids don’t flow too fast. Pallet flow racks are commonly used when FIFO needs to be followed, since they can be loaded on one end and unloaded from the other. Warehouse flow is optimized when replenishment and retrieval do not interfere with each other.
Pallet flow racks are also often used as conveyors in manufacturing facilities to convey pallets from one area to another.
Retail fixture racks are simply pallet racks that are used in a retail environment, like a big box store. Most industrial warehouses only care about how well a storage rack functions, but in a retail environment the rack is visible to consumers and contains special features for displaying product.
Retail fixture racks are more customized for smaller pallets, or less than full pallets. As well, they integrate different styles of dividers, product display shelving and tool holders directly into the storage system.
Cantilever racks consist of a main vertical support structure with beam “arms” stretching out horizontally. These cantilever arms are used to hold rigid product that comes in lengths like pipes, steel beams or wood. No skids or pallets are necessary, since the product rests directly on the arms of the rack.
Each cantilever rack needs to be designed based on the weight and type of product being stored. The length and spacing of each cantilever is critical to prevent deflection of the load. Often cantilever racks are placed against a wall, where the wall can be used to provide additional support. For heavier loads, however, the cantilever rack should be designed to support loads independent of bracing to a building structure.
Carton flow racking is a rack with rollers to flow boxed product out in one direction using gravity. Just like pallet flow racking, angled rollers convey product to one end of the rack. Carton flow racks are loaded from one side and unloaded from the other side. These are ideal for maintaining FIFO, since the oldest loaded product will always be available at the front to be picked.
Carton flow racks are designed to handle small boxes or cartons that are less than a skid in size. The flow racks consist of free moving rollers or wheels on a slight incline, and boxes roll down the incline to be picked from the other side. Since picking and loading are on opposite sides of the racks, carton flow racks create a very efficient flow in the aisles with minimal interference and cross traffic between operators.
Pick racks are designed for small components that don’t require a forklift to move. Usually an operator will be picking one or two of these components each time, so the box or bin stays on the rack. In most cases pick racks use removable bins full of individual components. When located at ground level they are easily accessible to an operator on a walking or tugger route. In large distribution centers, pick racks can be stacked vertically, with the operator using a work platform to travel up and down, picking the parts required for each order. Pick racks are useful when you have thousands of skus and each order consists of several sku numbers that need to be found.
Warehouse shelving comes in many shapes and sizes. Shelving is designed to hold product, cartons or boxes that are smaller than a pallet. For pallet-sized product, some variation of pallet rack would be used. Boltless shelving is optimal since it can easily be configured to accommodate different sized cartons, but heavy duty shelving generally needs to be bolted together to support larger weights.
Shelving, like pick racks, is designed to store product that is hand picked. Smaller than pallets, boxes have different lengths and widths requiring versatile shelving units. If a platform is used to lift the operator, shelving can be as high as the ceiling of the warehouse, as long as it’s supported properly.
A mezzanine is neither a rack nor a shelf. Industrial mezzanines are large structural steel platforms with stairs and a solid floor where product is stored. On the mezzanine, people can use pump trucks to move pallets, or hand pick from shelving. Sometimes entire rooms or offices are built on mezzanines. Forklifts are still required to lift pallets up to the mezzanine, or people can bring up boxes up the stairs, one and a time. Depending on local codes, the area under a mezzanine requires lighting and fire protection, increasing the cost of installing a mezzanine.
The pallet runner system is a proprietary system developed by Konstant. Pallets are stored on rails similar to those in a drive through rack. However, the forklift doesn’t drive into the rack to move pallets. A motorized pallet is placed in the rack lane and travels below the stored skids. It positions itself below a skid, then lifts the skid off of the rail and moves it forward or backward. The motorized pallet moves the skids to the end where the forklift can remove them. A driver can load a pallet runner into a rack and it will do all the shuffling back and forth, carrying the pallets to the other side, while the forklift continues to load or unload from the front face. It’s an interesting system that allows the pallets to move automatically while the forklift is busy doing something else.