Warehouse Racking (Storage Racks)

Chapter One – What is a Warehouse Racking System?

Warehouse racking, also known as storage or pallet racking, is a material handling system suitable for mass storage of goods unitized on skids or pallets. It allows efficient utilization of space while providing easy access to stockpiled items for better inventory control. Racks are used by manufacturers for mass storage of mostly non-perishable products when storage space is not enough. Palletized products are usually stacked up to not more than three layers before it becomes unsafe and prone to collapse. A racking system enables manufacturers to store palletized products five to seven stacks high, depending on the height of the facility.

Aside from finished goods handling, racking systems are also used for raw material and parts storage. Selective racking can be designed so that the greatest number of items can be accessed, permitting high variety. Also, some distribution systems favor the use of FIFO or the first-in, first-out method of inventory control. Having a racking system provides access to the oldest items in the warehouse inventory, allowing them to be off-loaded first.

Chapter Two – Benefits of a Racking System

Aside from maximizing storage space, there are other benefits that make warehouse racking feasible. These benefits can be quantified in terms of economic value or savings from leasing additional storage space, less workforce effort, and higher throughput. On the other hand, compliance with safety standards and quality management are other value-adding factors that do not directly translate to savings. Enumerated below are the benefits of a warehouse racking system.

• Efficient storage space utilization: As mentioned earlier, racking takes advantage of the available vertical space that is otherwise unused. Warehouses that are built to contain racks are made with high ceilings to allow racks with higher bays.
• Easy inventory organization: Racks can be addressed easily in comparison to stockpiling. Storing goods with many distinct varieties is virtually impossible with stockpiling without consuming large floor spaces. A type of racking system known as selective racking allows storing different types of goods while keeping the consumed space to a minimum.
  
  

  

  
  

Fewer damaged goods:

The implementation of racking systems was necessary to avoid damage to goods and products. Initially made of wood, racking systems have gradually developed into exceptionally stable metal structures capable of stacking goods several feet into the air with the only limitation being the height of the facility.

Palletization of materials offers an easy and convenient method for organization shipments and receiving supplies. A racking system is a way to place palletized materials in a safe and secure location such that they will not be damaged by mishandling, miscellaneous contact, or falling. Essentially, the metal frame of the racks keeps pallets from shifting and provides a protective barrier. The various designs of racking from two deep designs to excessively tall racking systems makes access to goods easy without disturbing surrounding pallets.

Increased employee productivity:

In a racking system, the location of an empty pallet can easily be found and accessed. This eliminates small unnecessary movements that, in time, stack up to significant losses.

Storage automation:

Adapting a racking system is the first step to warehouse automation. This is achieved by integrating smart conveyor systems and guided forklifts and cranes. This can lead to significant savings in terms of manpower costs and can streamline the business process especially for large distribution centers.

Increased safety:

Warehouse racking is designed to take advantage of storage space, arrange products efficiently, and provide a cataloging system making it easier to pick required items. Safety measures are a necessary part of the efficiency of a warehouse and are an integral part of racking system design. Included as safety measures are sensors and alarms, guard rails, rack end protectors, rack guards, and column guards.

• Guard Rail Systems - Guard rail systems are made of heavy duty rails strategically placed in potentially dangerous areas. The sturdy durable materials of guard rails are designed as protection to avoid accidents and damage to materials.
• Sensors - Sensors are a method of alerting warehouse personnel of dangerous situations. They have a flashing light and audible signal that alerts people in the area regarding forklifts, location of shelving, and the position of stackers.
• Warehouse Software - Warehouse software is used to calculate safety risks and the most productive method for moving products. Its main function is to reduce the number of manual actions by personnel. Additionally, warehousing software determines the most picked items and products and produces a report with proper placement of those goods and the best route to their location.
• Rack End Guards - Rack end guards are designed to protect the bottom of racks. They are bolted to the floor to absorb impacts. Rack end guards are painted safety yellow and have a low contour shape to separate them from column guards.
• Column guards - Warehouse column guards come in a wide assortment of sizes, shapes, and dimensions to be able to meet the needs of different sized racking. As with rack end guards, column guards are floor mounted and painted safety yellow. They erap around three sides of the bottom of the column to protect damage from the pallets, forklifts, and pallet jacks.

Clean and contaminant-free handling:

By having better access, it is easy to clean goods and storage spaces. Better segregation can be achieved to separate goods that can possibly deteriorate or damage adjacent items.

Chapter Three – Selection Factors in Designing a Racking System

Before investing in a racking system, it is important to note several factors to determine the viability of the project. Keep in mind that racks can also cause a space to be less utilized since the frame and its appurtenances take up space. The biggest drawback of a racking system is its difficulty in being modified and reconfigured. To make the most out of the investment, the following are some points to consider.

• Available Storage Space: The first step is to assess how much space is available for constructing storage racks and if the warehouse layout permits such construction. It is important to note that for an existing warehouse, the whole floor area may not be utilized. Racking systems available in the market usually come in standard sizes. Also, the structure of the racking itself takes up storage space. Thus, the desired storage density may not be as expected. In some cases, warehouse features such as walls, partitions, and doors must be modified to accommodate a racking system.
• Vertical Clearance: Aside from the available horizontal space, also assess how much vertical space can be utilized. Available vertical clearance directly influences the storage racking density. Adding one or two layers to an existing three-layer pallet stack can even decrease the storage density due to less utilization of the floor area. Racking systems that take advantage of vertical slopes, such as gravity flow systems, can further decrease the storage density by removing a layer to accommodate the required slope. Moreover, it is important to take note of the required clearances for fire suppression systems and obstructions for airflow. Elevating the stack height may defeat the design features of these systems and may call for modifications that further add to the initial cost of the project.
  
  

  

  
  
• Unitized Load Dimensions: After taking into account the available space and its restrictions, next comes the consideration of the shape and size of the pallets to be stored. The racking system must be designed specifically according to the form of the palletized load. For production lines that produce unitized loads with varying sizes, one may consider the pallet with the largest dimensions. This allows greater flexibility once there is a need to store more of that particular product.
• Load: The frame must be able to support the pallet load by selecting the appropriate material. Most racking systems are made of steel but are created through different manufacturing methods. For lighter loads, cold-rolled steel is sufficient. On the other hand, heavy-duty applications require structural steel that is formed through hot rolling or extrusion.
  
  

  

  
  
• Target Capacity: Knowing the target capacity means determining the target warehouse capacity utilization. Warehouse capacity utilization is an important key performance indicator (KPI) in a business process, especially for logistics and distribution centers. Having too high a capacity has its drawbacks of higher investment and operating costs. Having too low means less room in case of distribution difficulties or overproduction. Also, consider storage space taken by seasonal inventory. Warehouse capacity utilization can substantially increase during the off-seasons.
• Volume of Incoming and Outgoing Goods: This is linked to the target capacity of a storage system. It is important to know the throughput of the manufacturing plant and the rate at which the goods are sold or off-loaded. Aside from these, determine the average duration of seasons with low demand. Usually, manufacturing plants have a minimum throughput or breakeven point. Low storage space can result in halting or lowering the rate of production, which in turn impacts profitability.
• Number of SKUs: A stock keeping unit, or SKU, the number of distinct types of goods. It can also refer to the code or designation given to a specific item for inventory management. Determining the number of SKUs to be stored will help balance between selectivity and storage density of a warehouse racking system. Prioritizing either selectivity or storage density will determine which type of racking system is required.
  
  

  

  
  
• Type of Inventory Accounting Method: Regarding storage racking systems, this can be FIFO (first-in, first-out) or LIFO (last-in, first-out). Inventory cost accounting might not be representative of the physical off-loading of goods. Intuition suggests that the oldest item stored must be taken out first so that there will be no stagnant items that can lose value. However, some businesses use LIFO, which off-loads the most recent goods first. Off-loading from a stockpile of material will usually draw the most recent item added to the pile.
• Investment and Operating Costs: This is perhaps the most important factor for determining the feasibility of using warehouse racking systems. Costs per pallet position typically have range from $50 to $100 for low-density, high-selectivity racking systems and $100 to $250 for high-density, low-selectivity racking systems. For existing warehousing systems that have other options of acquiring additional storage space, such as warehouse extension or leasing storage spaces, it is best to determine the economic benefit of adapting racking systems. The high investment can be offset by savings in operating costs such as decreased manpower, savings from space rentals, etc. Also account for intrinsic benefits such as safety, ergonomics, and compliance with regulatory requirements, which can ultimately affect profitability.

Chapter Four – Different Types of Warehouse Racking Systems

There are several racking designs and configurations suited for a particular application. Storage racks are generally divided into either high-selectivity, low-density or low-selectivity, high-density applications. Racking with high selectivity and low density are selective, double deep, and very narrow aisle racking systems. High-density applications are push-back, drive-in, and pallet flow. Special systems are also possible, which are basically modifications of the previous configurations.

Selective Racking:

Selective pallet racking has a high SKU count but offers the lowest storage density. Conventional selective pallet racking can be visualized as large shelves that have storage space for a single row of items. The racks can be arranged back-to-back to improve storage density, although they have low storage density because of the space consumed by the aisles. This type is mostly seen in raw materials warehouses, parts storage spaces, and distribution centers where there are many distinct types of products with low volume. Selective pallet racking can be combined with other types to accommodate SKUs with high volumes. Other properties of selective racking are its flexibility between FIFO and LIFO inventory management, the operability of standard forklifts, accessibility for cleaning and inventory accounting, and simple construction that allows for easy reconfiguration. Selective racking has different frame and beam connection designs that are divided into teardrop and slotted racks.

• Teardrop Racks: Teardrop racking is a type of selective racking with modified frame and beam attachments that can be reconfigured and expanded easily without the use of machine tools. Upside down teardrop-shaped holes are punched along the upright frames, where pins attached to the beams are inserted. As the pin falls into the tapered opening, friction secures it in place without requiring additional fasteners. This connection has enough strength to be comparable with permanent joints. Adding heavier loads causes more friction to fix the beam in place. Wire decks are placed above the beams that become shelves for the pallets. Appurtenances such as pallet supports, crossbars, ties, and anchors are added to further strengthen the structure. Teardrop pallet racks are usually produced by roll forming in which metal sheets are cold-rolled into rectangular frames and beams.
  
  

  

  
  
• Slotted Racks: These are sometimes referred to as structural racks. Instead of using upside-down teardrop-shaped holes, slotted racks have a pair of rectangular openings milled along with the upright frame. The frame and beam can be attached by hooks protruding from the beam or by bolts. The main advantage of using slotted racks over teardrop racks are their higher durability and strength. Slotted racks are produced from hot-rolled structural steel, making them more robust than teardrop racks. Higher gauges of sheet metal are used to allow a higher load-bearing capacity. The downside of using slotted racks is their higher cost and weight.
  
  

  

  
  

Double Deep Pallet Racking:

This is a modification of the standard selective racking where instead of using single pallet rows, two rows are used per pallet shelf. This increases the storage capacity of selective racking by 40-60%. This also preserves the advantages seen from the standard selective racking. To operate under FIFO inventory management, the adjacent rows must have the same SKU. This increases the storage density, but selectivity is lowered. The main disadvantage of using this system is the need for specialized forklifts or standard forklifts with double deep handling attachments. This leads to higher operating costs and requires well-trained operators.

Very Narrow Aisle (VNA) Racking:

The concept of this pallet racking is to further improve space utilization of a standard selective while maintaining 100% selectivity. This is done by loading pallets using a fork truck capable of side loading. This eliminates additional space intended for maneuvering the forklift. The aisle space can be minimized by up to 40%. A downside of this type is the need for two sets of equipment for loading and unloading. One is a side-loading fork truck, and the other is a standard forklift for moving products from the palletizing station to the staging area.

Push-back Racking:

This type of racking involves loading the pallet on carts resting on a pair of rails that are available on each push-back lane. These carts are designed to be nested at the front of the aisle. To load a pallet, the forklift pushes against the other pallet, which moves it deeper into the lane. This dynamic racking system allows higher storage density than single or double deep racking. Each lane is one SKU that can be configured three to six pallets deep. Specialized forklifts with deep handling attachments are not needed since the pallet is readily accessible at the front of the lane. The lanes are inclined so that the carts roll towards the aisle. Each lane is a LIFO management since only the most recent pallet is accessible.

Drive-in and Drive-through Racking:

In this type, the pallets rest on a pair of rails that are specifically designed for the pallet dimensions to be loaded. The rails are designed to support the pallet while providing access to the forklift mast and fork as the forklift moves along the bay. Loading is done by driving a forklift into the last open position. Once in position, the pallet is slowly lowered into the rails. After loading, the mast is retracted, and the forklift backs out of the bay. Each bay is dedicated to a single SKU that can be several units deep, making it suitable for high-density storage but with low selectivity. This system is available in two configurations, drive-in and drive-through. In drive-in, the bay has only one access for entrance and exit, allowing for LIFO inventory management. The drive-through, on the other hand, has two access points, one for loading and the other for off-loading. This is used for FIFO inventory management.

Pallet Flow (Gravity Flow) Storage:

This design employs roller beds that move the pallets into the last open position. The lane has two openings similar to a drive-through racking, one at the front and one at the rear. The pallet is loaded at the rear side. After loading, the pallet rolls along the lane towards the front side. This is achieved by having the lane inclined at the rear. Off-loading is done on the front side of the racks. Pallet flow, like drive-in and drive-through racking, is suitable for high volume, low SKU number applications. In terms of inventory management, this system is suitable for FIFO. It has the same storage density as a drive-through but not as much as drive-in racking since it uses two lanes. This dynamic system is better than drive-in and drive-through since it is not prone to damage from forklifts that can lead to collapse.

Cantilever Racking:

This type is ideal for storing long products such as roofing materials, pipes, tubes, and lumber. It is composed of upright columns with cantilever arms on one or both sides. Vertical clearances between the arms can be adjusted depending on the bulkiness of the product. The angles can also be adjusted to help with load retention. Unlike standard selective racking, cantilever racks do not have upright frames at the front that obstruct loading. Aside from storing long products, it can also store irregularly shaped items such as appliances and furniture.

Carton Flow:

The principle is similar to pallet flow racking. This type also has two access points, one for loading and the other for off-loading. Manual loading and off-loading can be done without the need for forklifts. This is ideal for high volume piece-pick applications such as in cold storages and food racks. Carton flow lanes can accommodate non-standard size items.

Mobile Racking:

This type involves moving a whole rack assembly laterally to create an aisle space. Moving the rack is usually accomplished by driving it using electric motors. Smaller racks can also be mechanically or manually operated through pushing or pulling or by rotating handwheels with a high ratio. This type is a high-density storage system with high selectivity. However, access is not readily available as the racks need to be moved first for access. This is suitable for warehouses with low traffic.

High-Bay Racking:

As the name suggests, this type takes advantage of having high bays. They are most suitable for automated distribution centers for high density, high selectivity, and high throughput storage. The racks can be single, double, or in some instances, multi-deep rows. Automatic cranes with telescopic forks or order-picking trucks stabilized by rails and supports move along the aisle. The crane picks up a pallet from the conveyor system and places it on its designated rack. Due to the complexity and high cost of this system, it is only viable for warehousing that hedges profits on efficient storage.

Chrome Wire Racking:

Chrome wire shelving is highly versatile and inexpensive with the same strength as stainless steel. It has a clean finished look and can be used to store a wide assortment of items with a durability capable of holding trays, cartons, boxes, and storage containers.

• Strength - Chrome plated wire shelves can hold up to 800 LBS when the shelves are under four feet tall. A standard four shelf unit can hold up to 3,200 lbs of products while shelves over four feet can hold 600 lbs.
• Light Reflection and Penetration - Unlike standard gray metal shelving, chrome plated wire reflects light, which can brighten a storage area. Since the shelves are made of wire and not solid, light passes through the shelves to make it easier to identify stored items.
• Sprinkler Effectiveness - In the case of a fire, the chrome plated wire shelving allows water penetration to the floor, a feature that is positively viewed by fire marshals.
• Mobility - Chrome plated wire shelving can be turned into mobile shelving by adding casters.

Special Shelving:

Epoxy coated shelving, which can be gray, black, or green, is ideal for humid and wet environments. Some types of epoxy shelving can have an antimicrobial agent to prevent the buildup of bacteria, which is important for shelving used in the food industry and healthcare.

Automated Storage and Retrieval Systems (ASRS):

ASRS systems use software, computers, and robotics to make handling, storage, and picking smoother and more efficient. They can be adjusted and customized to fit any size warehousing system and are dependent on various technologies to automatically complete warehousing tasks.

There are several different types of ASRS systems that are capable of being configured to meet every type of warehousing need. The most common systems are:

• Unit Load ASRS - are used for large cases or pallets including loads that weigh several thousand pounds. They have fixed and movable aisle cranes.
• Mini-load ASRS - are smaller versions of unit load ASRSs and are used for lighter loads. They have shuttles and cranes designed for narrow aisles.
• Horizontal Carousels - Horizontal carousels are a form of sorting device used with small parts and products. They can be activated by a computer program or an electronic switch.

• Vertical Carousels - Vertical carousels operate like horizontal carousels and have the same activation mechanisms but complete their function vertically rather than horizontally.

• Vertical Lift Modules (VLM) - VLMs place or pick items from trays. They are the most flexible of the automated inventory methods and adjust when the inventory changes. Each tray is capable of holding a ton of parts. VLMs have two columns of trays for picking and placing.
• Cube Based storage - Cube based storage is the newest of the automated inventory methods. Items are placed in cubes that have robots that shuffle, sort, and pick bins to be delivered to workstations. Every cube on the cube grid works independently and is connected by a wireless system. Cube based systems are modular, which makes it easier for insertion and replacement of cubes.
• Shuttles - Robotic shuttles move independently riding on narrow rails to different storage levels. They operate quickly and efficiently handling totes weighing 35 lbs. To 110 lbs. Their speed can be adjusted higher or lower to fit the needs of the warehousing system.

Instead of using carts or roller beds, the system uses remotely controlled shuttles to lift and lower pallets and to move pallets. Since the length of a lane is not limited by the incline, shuttles have a large number of pallet positions per lane. This type can be utilized for FIFO and LIFO inventory management.

Conclusion

• Warehouse racking, also known as storage or pallet racking, is a material handling system suitable for mass storage of goods unitized on skids or pallets. This allows for efficient utilization of space while providing easy access to stockpiled items for better inventory control.
• Some of the benefits of racking systems are efficient space utilization, easy inventory organization, fewer damaged goods, increased employee productivity, automation, safety, and cleanliness.
• Important factors to consider before investing in a racking system are the available floor area and vertical space, pallet load weight and dimensions, target capacity, throughput, number of SKUs, type of inventory management, and cost.
• Racking with high selectivity and low density are selective, double deep, and very narrow aisle racking systems. High-density applications are push-back, drive-in, and pallet flow.