Pallet rack

From wikiMHEDA

Pallet rack is a single or multi-level structural storage system that is utilized to support high stacking of single items or palletized loads.^[1] Also referred to as "pallet racking," it is a material handling storage aid system designed to store materials on pallets (or skids). Although there are many varieties of pallet rack, all types allow for the storage of palletized materials in horizontal rows with multiple levels. All types of pallet rack create some level of increased storage density with the least dense being the least expensive and cost increasing with storage denisity. Selective rack is the least dense at a cost of about $50-$70 per pallet position up to gravity flow pallet rack which can cost $250 -$400 per pallet position. Forklift trucks are usually an integral part of any pallet rack system as they are usually required to place the loaded pallets onto the racks for storage. Pallet racks are an essential and ubiquitous element in most modern warehouses, manufacturing facilities, retail centers, and other storage and distribution facilities.

Contents 1 Selective Pallet Rack Systems 2 Common Components 3 Other Common Types of Pallet Rack 3.1 Drive-in and Drive-Through 3.2 Push-Back 3.3 Pallet Flow 3.4 Double Deep 4 Benefits of Pallet Rack 5 Environments that can Benefit from Pallet Rack Systems 6 References

Selective Pallet Rack Systems

Selective pallet rack is the most common pallet racking system in use today. Selective pallet racks typically come in one of two configurations: a roll formed, or clip-in configuration, and a structural bolt-together configuration.

• Roll formed selective rack is most commonly manufactured in a "teardrop" style. The nickname “teardrop” comes from the fact that the holes on the column of the upright are shaped like a teardrop. Pallets then rest on the horizontal load beams that are held in place by mounting clips. Because the clips on teardrop configurations can be quickly moved, the shelves can be easily adjusted to different heights to accommodate various load sizes. This is convenient for a warehouse that needs to store a wide variety of product sizes.
• Structural pallet rack systems are very similar to roll formed pallet rack systems except the horizontal load beams are attached to the uprights with bolts and have much greater weight-bearing capacity. Also, structural pallet racking can be designed into the structure of the building itself, so that the upright columns are simultaneously used to support the roof of the storage facility, in which case the structural pallet rack uprights replace the storage building’s vertical support I-beams. This system is a rack supported building.
• Very Narrow Aisle (VNA) is the use of selective pallet racking in a tighter configuration to provide maximum space utilization within a storage facility. These systems typically operate in conjunction with wire-guided or rail-guided reach-truck systems. A wire-guided system consists of a wire embedded in the concrete floor that provides tracking for the reach-truck. A rail-guided system consists of angle iron bolted to the floor down the length of each row. Typically, the angle iron is 4” by 3” and ¼” - ⅜” inches thick.

Another advantage of selective pallet rack systems is the easy accessibility they provide to all products at all times. Such accessibility is important if the inventory is rapidly depleted and restocked (called quick turnover). A selective pallet rack system is commonly used in a “big-box” distribution application, as well as in retail store inventory rooms, cold storage applications, wholesale stores, etc.

Common Components

Common components of selective rack include the following:

1. Load beams (also called step beams or box beams).
   • Most Step Beams are roll formed members with a 1⅝” step along the top inside edge. This step is used to hold any load support components such as pallet supports or wire decks.
   • Box Beams have no inset step, instead have four flat sides like a box. All load beams typically mount onto an upright frame column with integral rivets or hooks. Some systems utilize an extra clip or bolt to lock the beam to the upright.
   • Structural Beams are hot formed structural C shapes with connecting clips at either end. Structural load beams are generally used with structural uprights but can be used with standard roll formed uprights. Structural load beams offer heavier weight capacities than step beams or box beams.
2. Upright Frames (also called upright columns or uprights) vary in size and design depending on load requirements, and styles. The most common upright column is produced by roll forming flat coil stock steel into a modified "C" shape with returns. This style is often referred to as open-back roll-formed columns. Holes or slots are punched during manufacturing up and down the column at standard intervals so that the load beams can be mounted into the upright columns. Upright frames can also be constructed utilizing structural C shapes for columns. Structural uprights have an increased weight capacity over roll formed uprights.
3. Diagonal Braces and Horizontal Braces, commonly referred to as upright frame lacing is usually welded between two upright columns to form selective upright frames. The lacing may be bolted to the columns in some cases.
4. Pallet Supports are roll formed channels that are placed front to back between the load beams to support pallets.
5. Wire Decking is commonly used as a safety measure on selective pallet rack to prevent pallets or the products stored on them from falling through the rack structure. Wire mesh decking comes in various thicknesses and mesh dimensions. Wire mesh construction also allows for easy identification of shelf contents and prevents dirt and other debris from accumulating on the shelves because of the holes in the mesh. Most wire mesh decking has U-shaped channel supports, also known as struts, to support the load. With this waterfall decking, the wire mesh extends across the top and down the front of the beam to provide more support, and is more desirable in the marketplace. Reverse waterfall decking can provide containment of a loose product to prevent the product from falling behind the rack system. Lay-in decking rests inside the step of the beam, and wire mesh does not waterfall over the beam. Some types of decking are manufactured with solid metal instead of wire mesh. Even though the solid decking provides a greater distributed weight capacity, it is discouraged by fire inspectors because sprinkler systems cannot spray through the shelves to levels below.
6. Footplates, also known as footpads or baseplates, are at the base of columns and serve as anchors to give the rack more stability: anchor bolts are inserted through the baseplate’s holes to attach the column to the concrete floor. Footplates are made of thicker steel and in some geographic locations, they must be of a certain size and seismic rating. Footpads increase the pallet rack’s overall stability and weight-bearing capacity.
7. Shims are used when the uprights are resting on uneven floors; the shims, equal in size to the base of the uprights, are installed beneath the uprights to level the rack.
8. Row spacers are sometimes used if uprights are arranged in back-to-back rows; the spacers are mounted between adjacent columns to ensure that the rows are kept straight and to give the pallet racks even more strength and steadiness.
9. Wall ties may be used for further support if the uprights are arranged in a row along a wall.
10. Column protectors, also known as post protectors, are protective shields that can be installed around the base of an upright to minimize damage where forklifts might hit the upright. Damage to the base of a column can weaken the entire frame and could cause it to collapse. Column protectors are made of various materials such as polyethylene, ductile iron casting, and other durable materials.
11. Guard rails are installed to increase protection for upright columns and for human safety when platforms or steps are attached to pallet racks.

Other Common Types of Pallet Rack

Some of the most common types of pallet rack systems used include:

Drive-in and Drive-Through

Drive-in and drive-through rack (sometimes spelled drive-thru) are storage rack configurations that allow the forklift to drive directly into the lane of stacked rows (called a bay). The difference between a drive-in and a drive-thru pallet rack system is simply whether the bays have an entry at only one end, or at both ends. Drive-in rack systems use a common entry and exit, while drive-thru systems have entry points at either end of the bay. Because a drive-in racking system has only one entrance, it uses what is called a LIFO (last in, first out) storage method. With only one entrance, the last pallet put into a row is necessarily the first one to be taken out. A drive-thru storage system, with two different entry points, can also use a FIFO (first in, first out) storage method. With a FIFO system, pallets are loaded in one end and are pushed back to the other end, where they are then at the front of the row on the opposite side. The first pallet put into such a row is the first one taken out at the other end. This system is advantageous for material with an expiration date or wherever shelf life is a major concern.

Push-Back

Push-back pallet rack systems are designed around the principle of organizing space by depth rather than width. This depth arrangement greatly reduces aisle space and increases storage density. In this configuration, each bay can be up to six pallets deep; each pallet stored on wheeled carts that fit onto rails. The rails are slightly angled toward the load/unload side of the rack in order to take advantage of gravity, saving enormous amounts of energy for moving heavy pallets. When a forklift sets the pallet onto the cart, it drives forward and causes the pallet to bump the next pallet, causing the entire row of pallets to roll backwards. When removing a pallet from the front position the remaining pallets immediately stage themselves forward so that the next available pallet can be accessed. Push back rack is a LIFO (last in, first out) storage system.

Pallet Flow

Pallet flow rack systems are high density pallet storage systems that utilize depth to increase capacity. This system uses a slightly inclined rail with rollers that allow pallets to move easily along the sloped plane. These systems are also called gravity flow or dynamic flow systems. The pallet flow system often has complex motion and braking systems to control the speed of the moving pallet. Pallet Flow racking systems are either a FIFO (first in, first out) or a LIFO (last in, first out) storage system. If the system is loaded from the back and unloaded from the front, its FIFO; if the system is loaded and unloaded from the front its a LIFO system. Some disadvantages of high density pallet storage systems are; less access to all stock at any given moment (although if the stored product is all the same, it should not matter), and the expense of such systems. Selective pallet rack systems are considerably less expensive per pallet position than their higher density counterparts. In most medium to large facilities, however, high density pallet rack systems are essential, since they provide the efficiency of time and high cost facility space is better optimized.^[2]

Double Deep

Double Deep systems are single selective pallet racks that have been adapted. Double deep pallet racks provide greater utilization of warehouse space due to the density of the loads stored and narrow aisle design of the double deep pallet rack. On a cost-per-pallet basis, a double deep pallet rack system is significantly more cost effective than conventional selective pallet racks.^[3] A reach truck or lift truck with a double mast may be used to access a double deep rack.

Benefits of Pallet Rack

• Maximized space utilization.
• Improved SKU management.
• Increased throughput and flow.
• More efficient picking abilities with less chance of errors.
• Less on-hand inventory and more inventory turns.
• Improved on-time product delivery by consolidating orders with less errors.
• Increased product protection.
• Reduced labor costs.
• Improved safety.
• Improved facility layout and appearance.
• Improved ergonomics and reduced worker fatigue.

Environments that can Benefit from Pallet Rack Systems

• Manufacturing Environments – housing of raw materials and components to storing product inventory or finished goods.
• Distribution/Warehouse Environments – systems available for simple pallet storage or complex order picking systems.
• Retail Stores – displaying and storing product.
• Archive & Record Storage – utilizes existing space for maximum record storage^[4].

References

1. http://www.mhia.org/learning/glossary
2. Mark Juelich, American Warehouse Systems
3. Engineered Products, Pallet Rack