The wikipedia website describes Pallet Racking as "Pallet rack, also referred to as “pallet racking,” 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 increase storage density with the least dense being the least expensive and cost increasing with storage density". We have prepared the below table as a ready reckoner to help you understand the various aspects of a Pallet racking system used by the industry suppliers as a rule of thumb.
Racking type comparison
|PALLET ACCESS||SKU ROTATION||FLOOR SPACE UTILISATION %|
|DOUBLE DEEP (DDR)||50%||Average||60%|
|DRIVE IN (DIR)||25%||Poor||65%|
|PUSH BACK (PBR)||25%||Average||65%|
|MOBILE RACK (MR)||100%||Good||70%|
|GRAVITY FLOW (GFR)||25%||Excellent||60%|
|NARROW AISLE (NAR)||100%||Good||50%|
|VERY NARROW AISLE (VNAR)||100%||Good||50%|
We will illustrate below using 4 Types of Pallet Racking Systems to show you why and how they are used to maximise the storage capacity of a typical 1000 square meter warehouse.
Note: Please note that each warehouse has its own size and shape and the designs will have to be varied to suit each requirement as necessary. We request you to note the positions and widths of the aisles as well as frequency of the rack rows in the below layouts as they change with the introduction of the various systems below.
Selective Rack (SR) – Layout shown with approx storage of 976 pallets stored 4 high in a typical 1000 sq.mt warehouse. We will use the 976 pallets that can be stored in this warehouse as a benchmark for the other systems.
Double Deep Rack (DDR) – Layout shown with approx storage of 1232 pallets stored 4 high in a typical 1000 sq.mt warehouse. The storage capacity of the warehouse has grown by 26% with this system when compared to a Selective system.
Drive In/Through Rack (DIR) - Layout shown with approximate storage of 1624 pallets 4 high in a typical 1000 square metre warehouse. The storage capacity of the warehouse has grown by 66% when compared to the selective system.
Narrow Aisle Rack (NAR) – Layout shown with approx storage of 1824 pallets stored 6 high in a typical 1000 sq.mt warehouse. The storage capacity of the warehouse has grown by 85% over the capacity as compared to a selective system.
A warehouse is not only a storage space but a hive of activity where numerous simultaneous activities take place like receiving, pre packaging, put away, order picking, packaging & dispatch
Any business owner who has had to lease a warehouse will vouch for the amount of effort they had to go through to find one suitable warehouse for their particular needs. Its evident that each warehouse is built differently with different needs and objectives most of them to suit the builders requirements at the time. At SPAR we consider no two warehouses alike and when this difference is multiplied with factors like product lines, picking variations, product weights, product volumes etc things get a bit complex. This brings us into the picture to impart our expertise to customers and listen to their needs. The product or design finalized is a natural flow of the understanding of these needs.
A pallet or skid as its also known is a small raised purpose built platform 1170mm W x 1170mm D x150mm H (Australian Standard) that supports goods in a stable fashion while being lifted by material handling equipment like a forklift. This unit is used to bulk stock and package goods on it so that bulk storage and transport of products is made possible making it easy to move heavy loads. The standard dimensions vary in some parts of the world.
Basically two kinds of pallets –
- Pallets with two sided access:
- The pallet allows fork lift entry bars on only two sides of the pallet.
- Pallets with four sided access:
- The pallet allows fork lift entry bars from all fours sides.
Generally pallets are made of wood but are also available in steel and plastic.
The goods are stocked straight or in cartons / wholesale packaging side by side not to exceed the dimensions of the standard pallet and one on top of the other to a safe height depending on the weight and volume of the product used eg. tissues to steel discs.
Once again depending on the product the pallet is made from its load carrying capacity varies. Wooden pallets can take about 2000kgs and up to 3000 kgs each. Steel and Plastic pallets can take more depending on the design. The wooden pallet itself weights about 20-50 kgs.
Pallet can be stored in an organized manner on the floor 2 or 3 levels high if required which is known as block stacking. It depends on the type of goods and their weight and obviously becomes more uinstable the higher you go.
Depending on the type of product, weight, volume and carton strength (if stocked in cartons) there is only a certain number of pallets you can stock over the lowest pallet on the ground before this pallet caves in with the weight of the pallets on top. This is also not safe as if the pallet gives way and collapses the avalanche effect will certainly topple the whole block of pallets. This makes it a hazard at the workplace in case people working in the area are involved.
Since we have explained what a pallet is above its easier to define a Pallet Rack now as a multi level structure made from steel components and connected in such a manner as to structurally bear the weight of pallets in an organized manner for easy access. This rack will allow handling of individual pallets as required without the need to disturb the other pallets in the system.
Pallet racking products are designed on two basic principles,
FIFO – First in First Out – The first Pallet in is the first pallet out of the system.
FILO – First in Last out – The first pallet in is the last pallet out of the system.
The various types of pallet racking are
Selective Pallet racking
Drive in / Drive through
Automated Storage and Retrieval Systems
Rack Clad buildings
The simplest pallet rack is a selective pallet rack and it is the only one that can offer 100% access to any pallet in the system 100% of the time.
Generally a Selective rack can accommodate two standard pallets in its width allowing for some space above and on both sides of each pallet for placing and removal of the pallet. The total height of the rack will depend on how many levels it is designed for.
The height of the system is limited by the height of the building itself or the maximum height the material handling equipment (like a forklift truck) can reach with the heaviest pallet in the system. If the pallets are heavier than normal (say 1500 - 2000kgs+) then the thickness and profile of the steel members can also be a limiting factor if the minimum requirements of stress on them are not met.
No. In case of material handling equipment like stackers that have straddles, the pallets at the lowest level cannot be stacked on the ground as they get in the way of these straddles. In this case a beam is provided at the lowest point of the rack and the lowest pallets are now kept on these beams. This allows for the straddles to move beneath the beams and pick up the pallets on the lowest beam level unhindered.
This is nothing but a selective racking system that is installed one behind the other to increase the density of the storage area using a minimum of aisles. This system is generally used if you have more than one pallet of one kind of product.
The only drawback is that a normal forklift cannot access the rear pallet and as such a telescopic attachment needs to be added to the Forklift to enable it to reach in and pick up the rear pallet. This also means that you cannot get to the pallet at the back till the pallet in front is removed. This effectively reduces the accessibility of pallets in the system to 50%.
A push back has a similar concept of a double deep in with the added advantage of more density and also the fact that a standard forklift can be used for loading and removal of the pallets. The pallets are stored on inclined telescopic roller guides such that when a pallet is initially stored the second pallet is then used to push the first pallet back and make place for the second pallet. Similarly the system can be designed for more than 2 pallets deep. In case of removal when the aisle pallet is removed the pallet behind it gently slides to the front for removal.
The only drawback is the limited accessibility to pallets in the system.
One of the densest systems of Pallet Racking is the Drive in / Drive through system. The name Drive in denotes a system where access is blocked at the end of the Drive in lane and hence a FILO system. The name Drive through system denotes a system where the access is free through at the other end of the lane and hence is FIFO system. In this system the aisle wastage is limited and pallets are stored as densely as possible along the width, depth and height almost like block stacking.
This system can be practically implemented if the user has many pallets of a similar product and almost useless if it’s the other way around.
As the name suggests a Narrow Aisle system is Selective racking designed for use with equipment that will access a pallet in the system and retrieve it in a much narrower aisle (less than 2000mm as compared to the 3000mm required for a Selective system). This obviously allows more rack rows to be installed in the same given space increasing the capacity of the system. The advantage of this system is that higher systems can be designed with guide rails for the material handling equipment thereby eliminating any errors during the handling process. The dense storage achieved offsets the cost of purchasing the desired material handling equipment.
Automated Storage & Retrieval Systems (ASRS) are on a broad scale Narrow and Very Narrow Aisle systems used with automated material handling equipment. In this system the warehouse database and organization ERP systems are integrated with the automated racking system for total hands free put away and picking of pallets in the system with the help of interactive consoles run on specially designed software programs.
Once again a Mobile rack is somewhat of a Selective pallet racking system achieved with minimal one or two dynamic access aisles. The racks are all placed on rails and at any given time only one aisle is open for use once again with a standard fork lift. When another aisle is needed the operator uses his electrically controlled console to issue the instruction whereby whole row of bays will move to on their guiderails to create the aisle where required. Once again this allows all the aisle spaces of the system to be used for racking and as such increases the capacity of the warehouse tremendously.
This is the densest system that can be used for pallet racking and is basically a Drive through system with rollers provided instead of runners. The system using the FIFO principle has heavy duty rollers installed along each pallet cell from the entry of the system (which is generally a bit higher than the exit to use gravitational force to transport the pallet towards the exit) to the exit. This system is generally suitable for use between a high volume manufacturing unit in a facility to its warehousing facility or between a storage unit and dispatch. The rollers also have speed controllers along the path to avoid stress at the exit by pallets hitting each other. So when a pallet is removed at the exit the next pallet gently takes it place.
This unit which is popular in Europe but not so much here in Australia is nothing but a suitable pallet racking system covered on all sides as a warehouse eliminating the need to build an independent free standing warehouse. This system is designed in such a manner that it not only meets the load demands of the system it is created for but also withstands factors like wind speeds and soil movements like a conventionally civil engineered building. The unique advantage being that the building can be dismantled and moved to a new location.
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