Materials Handling Systems (MHS) can be defined as “the set of all pieces of equipment that make possible the physical movement within the distribution chain –including the production chain and the warehouse – of raw material, work in progress and finished goods”. Therefore, materials handling systems perform a wide range of activities. In general, Materials Handling refers to the necessary tasks to be performed in order to move a load around the factory floor as well as to store and freight it. Materials handling takes place one way or another along all the links of the supply chain including production, distribution, and storage and retail functions.
Handling in a warehouse effects materials flow through the system, and on the cost, resource and time taken to get orders out to the customer. Handling equipment can be capital intensive, and the act of movement can be labor intensive. Various methods of handling goods are,
- Manual handling
- Manually operated trucks and trolleys
- Powered trucks and tractors, operator controlled and driven
- Powered trucks and trolleys, driverless, computer-controlled
- Crane systems
- Conveyors
- Robotics
The factors to be considered when deciding on the appropriate type of handling system for a particular application include,
- Types of load being handled including the unit load characteristics
- Quantity of material being handled
- Frequency of movement
- Distances to be travelled, horizontal and vertical
- Numbers and locations of pick-up and drop points
- Adjacent activities
- Nature of terrain
- Flexibility required
The principles governing the design and use of handling systems include
- Control of position and movement
- Elimination of unnecessary movement and minimization of the necessary movement
- Selection of the most appropriate handling method to meet the system requirements
- Provision of adequate handling capacity
- Integration of handling with the storage and other adjacent operations
- Thorough and effective operator training
- Effective equipment maintenance for operational availability and safety
- Safe methods of handling and working practices
Material handling equipment encompasses a diverse range of tools, vehicles, storage units, appliances and accessories involved in transporting, storing, controlling, enumerating and protecting products at any stage of manufacturing, distribution consumption or disposal. The four main categories of material handling equipment include: storage, engineered systems, industrial trucks and bulk material handling.
Storage and Handling Equipment
Storage equipment is usually limited to non-automated examples, which are grouped in with engineered systems. Storage equipment is used to hold or buffer materials during downtimes or times when they are not being transported. These can be temporary pauses during long-term transportation or long-term storage designed to allow the buildup of stock. The majority of storage equipment refers to pallets, shelves or racks onto which materials may be stacked in an orderly manner to await transportation or consumption.
Examples of storage and handling equipment include,
- Racks, such as pallet racks, drive-through or drive-in racks, push-back racks, and sliding racks
- Stacking frames
- Shelves, bins and drawers
- Mezzanines
Engineered Systems
Engineered systems cover a variety of units that work cohesively to enable storage and transportation. They are often automated. A good example of an engineered system is an Automated Storage and Retrieval System, often abbreviated AS/RS, which is a large automated organizational structure involving racks, aisles and shelves accessible by a “shuttle” system of retrieval. The shuttle system is a mechanized cherry picker that can be used by a worker or can perform fully automated functions to quickly locate a storage item’s location and quickly retrieve it for other uses. Other types of engineered systems include,
Conveyor systems
- Robotic delivery systems
- Automatic guided vehicles (AGV)
Industrial Trucks
Industrial trucks refer to the different kinds of transportation items and vehicles used to move materials and products in materials handling. These transportation devices can include small hand-operated trucks, pallet-jacks, and various kinds of forklifts. These trucks have a variety of characteristics to make them suitable for different operations. Some trucks have forks, as in a forklift, or a flat surface with which to lift items, while some trucks require a separate piece of equipment for loading. Trucks can also be manual or powered lift and operation can be walk or ride, requiring a user to manually push them or to ride along on the truck. A stack truck can be used to stack items, while a non-stack truck is typically used for transportation and not for loading. There are many types of industrial trucks,
- Hand trucks
- Pallet jacks
- Pallet trucks
- Walkie stackers
- Platform trucks
- Order picker
- Sideloader
- Many types of AGV
Bulk Material Handling Equipment
Bulk material handling refers to the storing, transportation and control of materials in loose bulk form. These materials can include food, liquid, or minerals, among others. Generally, these pieces of equipment deal with the items in loose form, such as conveyor belts or elevators designed to move large quantities of material, or in packaged form, through the use of drums and hoppers.
- Conveyor belts
- Stackers
- Reclaimers
- Bucket elevators
- Grain elevators
- Hoppers
- Silos
There is a wide range of non-powered industrial trucks for pedestrian use which include hand pallet trucks, order picking trolleys, stair climbing trolleys and wide rang of platforms, shelf and cage trolleys. Industrial lift trucks are used in warehousing for moving material over relatively short distances, for lifting into and out of storage , and for vehicle loading and unloading. Trucks facilitate load utilization, speed up movement, can handle large loads and consequently reduce the frequency of movements. Their lift ability enables the use of building height-the cost building volume reduces as building height increases.
The main types of powered trucks used in warehousing and stock yard operations are,
- Powered pallet trucks
- Counterbalanced fork-lift trucks
- Reach trucks including double reach and four –directional reach variants
- Stacker trucks
- High rack stacker trucks-very narrow aisle
- Side loaders
- Order picking trucks
- Tugs and tractors
- Straddle carriers-container handling
Non-powered hand trucks
Non-powered hand trucks are used in many situations. They are inexpensively manufactured for diverse and specific applications. Common construction materials include aluminum/magnesium, steel, and wood. Because these trucks are so inexpensive, it makes sense to design them for specific material handling functions. In this way, it is possible to increase the cube utilization within the truck for material handling optimization. Aluminum or magnesium trucks generally carry 300-500 pounds of material, while steel or wooden trucks can be used to carry approximately 1000 pounds to 2000 pounds, respectively. The trucks range in weight from as little as 20 pounds for aluminum trucks to as much as 125 pounds for wooden trucks.
Non-powered hand pallet trucks
These trucks are designed to carry unit loads on pallets, generally in indoor settings for short distances. In many settings, hand pallet trucks are used to supplement motorized truck fleets. They are extremely efficient for transporting unit loads short distances when high lifting is not required. They can be used to position materials very precisely. Generally speaking, non-powered hand trucks cannot be used to lift more than 8,000-10,000 pounds and cannot lift a unit load to a height more than 8 inches. For heavy duty applications, steel wheels are required while lighter duty applications require only nylon or polyurethane construction. These trucks can range in weight from 200 to 400 pounds.
Pallet Trucks
The full featured ergonomic pallet truck is an economical way for one person to move heavy pallet loads without the use of a fork truck. Proven ergonomic design has been tested for providing years of reliable usage. This pallet truck includes two articulating steering wheels and two front load rollers. Ergonomic design requires only 75 lbs. of pulling force when fully loaded. Steering wheels include bearing dust covers for added life. Nose wheels are located on the front edge of each fork to assist in clean pallet entrance and exit. Reinforced triple-formed steel forks provide twice the strength of standard single-formed forks, equipped with internally mounted solid steel adjustable push rods. Spring loaded loop handle automatically returns to vertical position when not in use. Chrome-plated hydraulic pump piston for long seal life.
Powered pallet trucks
Hand pallet trucks, with capacities up to a max of 2 tonnes, are probably the most commonly used trucks for the horizontal movement of pallets. It is not uncommon to see these trucks lifted on to the back of the vehicle for positioning pallets during loading and unloading. However, for frequent movements, and where there are inclines to be negotiated, battery –powered trucks are preferable in terms of operator effort and safety, and these can be pedestrian – or rider- controlled.
Counter balanced fork-lift trucks
Counterbalanced fork-lift trucks carry the payload forward of the front wheels, so there is always a turning moment lending to tip forward. To balance this, a counter balance weight is built into the rear of the machine-hence the name. These machines capacity varies from 1000kgs to 45,000 kgs with a lift height of up to 6/7 metres.
Reach trucks
Reach trucks are designed to be smaller and lighter than counter-balanced trucks and to operate in a smaller area. Its capacity varies from 1000kgs to 3,500 kgs with a max fork-lift up to about 11 metres. This is achieved by having a mast that can move forward or back in channels in the outrigger truck legs. Then picking up or setting down a load, the truck is turned through 90 degrees to face the load location; the mast reaches forward, places or retrieves the load, and is retracted back into the area enclosed by the wheels.
Double reach trucks
A conventional reach truck can only reach one pallet deep into racking. For accessing double deep racking a double reach truck has to be used, which uses a pantograpgh mechanism to achieve the additional reach. Double reach can also be achieved on some lighter trucks by the use of telescopic forks. Double reach machines are also used for side-loading pallets on to road vehicles, working only from one side of the vehicle.
Four-directional reach trucks
On a conventional reach truck, the front wheels always face forward, and steering is from the rear wheels. The 4D truck has an additional option of being able to turn the front wheels through 90 degrees and lock them in this mode. This effectively converts the truck into a side loader and is especially useful in stores and warehouses where part of the stock range consists of long loads. For access to say cantilever storage, very wide aisles would be necessary if this option were not available.
Stacker trucks
These are fairly light weighted trucks with max capacities up to 2000 kgs. There are pedestrian, stand-on and ride-on versions. Pallets are put into or taken out of storage racking by the truck legs being driven into the space either under the bottom pallet beam supported). When picking up pallets at floor level, the forks have to be lowered right down on to the outrigger legs, so perimeter-based pallets cannot be used, since they would be sprung apart as soon as the forks were raised. This problem is overcome if the lowest pallets are located on low beams with sufficient space underneath to accommodate the outrigger. These trucks are usually limited to about a 6 metre lift, but they can operate in 90- degree turning aisles of only 2 metres or less.
High rack stacker trucks-very narrow aisle
These trucks typically with lift capacities up to 2 tonnes and lifting to 12/13 metres, are equipped with mechanisms on the mast that can set down or pick up pallets from the racking without the truck having to turn in the aisle. Consequently they can operate in aisles of 1.8 metres or less. The very narrow aisles and high lifts give good space utilization, but also necessitate very flat floors, which are expensive , to minimize the risk of collision between load and racking when manoeuring loads. It is also necessary to have a guidance system to keep the trucks centrally positioned in the aisles.
Order picking trucks
There is a range of manual and powered trucks designed specifically for order picking operations. These range from trolleys, such as roll cage pallets, to ground-level pedestrian trucks such as long fork powered pallet trucks, up to multi-level trucks in which the operator is raised for high-level picking.
Conveyors for unit load handling
Conveyor systems are used for moving material between fixed points, for holding material as short-term buffer, for sortation and for process industry applications such as separation, grading and cooling.
The general characteristics of the conveyor systems are,
- High through-put with few operators and low power requirement
- Suitable for fixed routes, and floor surfaces are not critical as they are for fork trucks
- Fast response and suitable for continuous or intermittent movements
- Can utilize very sophisticated movement control
- Conveyor systems now find very wide application in both conventional and automated warehousing
The less positive aspects of conveyor systems include,
- High capital cost
- Can obstruct working areas and access
- Inflexibility for future change
- Hence very careful system design required including safety features
