Material Handling Equipment and Systems

Material handling system is classified on the basis of its degree of sophistication. The most pre­ferred way of material handling is doing manually where the volumes handled are less and the investment in handling equipment do not ensure more benefits. In such cases, the idle time of the equipment will be more and equipments are underutilized. The classification of handling system can be done as follows:

• Manual
• Mechanized
• Semiautomatic
• Automatic
• Guided information

The major criteria for selection of the right system are units moved per hour and the distance of the movement covered. Higher volumes moved over large distance call for more sophisticated systems, which attract higher investment. These sophisticated systems enhance speed of material handling ensuring reliability and productivity.

1. Manual System

Manual system is the cheapest and most common method of material movement used in warehous­ing. The limitations are low volume, slow speed, physical characteristics of the product and the dis­tance. In warehouses where cartons are weighing not more than 20 kilogram and volumes handled are not too large, material loading, unloading and movement are done manually. Investment in equipment is not justified in such cases. In developed countries where manual labour is scarce and cost of employment is very high, use of manual handling is discouraged. But in developing coun­tries because of availability of cheap labour, the manual systems with very limited mechanization such as usage of manual push-pull trolley with wheels are common.

2. Mechanized System

The prime consideration before going in for mechanized material handling systems is the layout of the warehouse. The investment in material handling system will be a total waste if it is not compat­ible to the warehouse layout plan. The layout may create the obstacles for the free movement of equipment and the goods. The mechanized equipment requires the space for the free movement across the warehouse. The equipment should have the accessibility to the storage area for material loading and unloading during storage and retrieval.

One of the important benefits of mechanization is to transfer the fatigue from human to machine. The human element in material movement is removed bringing the speed and reliability in material movement. Moreover, mechanization enhances the system productivity.

The mechanized system need not be a powered equipment. A wheeled trolley with handle can be driven manually. However, in this case the load is transferred to the trolley and human being uses little force to facilitate its movement over the longer distance. The purpose of machinery is to increase the abilities of human being beyond their own physical and mental capacities. Mechaniza­tion helps enhancing the effectiveness of human energy in material movement.

The criteria for choosing a machine for material movement in the warehouse should be:

• Improving space utilization
• Reducing the time for material movement
• Speeding up the overall material flow
• Reducing the material damages during material handling
• Should be safe for human beings to operate.

The mechanized system includes a large variety of handling equipments. The equipments that are most commonly used are wheeled trolley, forklift, pallet truck, tractor-trailer device, conveyors, cranes and carousels.

Wheeled Trolley. The simplest mechanized handling equipment is a trolley on the wheels. The hand-held trolleys are efficient for handling small volumes over a short distance.

The two-wheeled hand trolley is simplest and versatile (Figure 5.2).

The four-wheeled hand-held trolley is called a platform truck capable of moving light loads horizontally. The hand-held lift trolley or truck is a modified version of the platform truck for use in the limited space. It moves the load both in vertical and horizontal direction. For example, if 30 cartons weighing 25 kilogram each are to be shipped to a distance of 20 meters every half one hour, some being picked up and dropped off at different places, then manual wheeled trolley is the best option. For higher volumes and longer distances, use of powered (electric battery operated or diesel engine) trolleys is preferred. Trolleys are available in wider range to carry the operator while some require the operator to walk along with the trolley.

Forklift Truck. This equipment perhaps represents the greatest single innovation in material han­dling after World War II, which is responsible for supporting the concept of unitization of loads. The introduction of pallets as unit load for material handling and storage was mainly possible because of the forklift truck. The main advantages of forklift are:

• Moving larger loads over a longer distance
• Picking and dropping off the load as it travels
• Moving the load vertically in the vertical storage system
• Moving the load both vertically and horizontally for exactly positioning it for loading and unloading operation
• The manoeuvrability of load in all direction is excellent

Forklift trucks are the work horse of the warehouse, most commonly used for movement of unit loads such as pallets, containers and slide plates. They are the most versatile material handling equip­ment used in the warehouse, also they are most reliable and relatively easy to operate (Figure 5.3). The forklift arms can go through the entry channels at the bottom of the pallet.

Depending on the pallet design, there can be two- or four-way entry pallets (see Chapter 9 on Logistical Packaging). The two-way entry pallet can be lifted by forklift truck from two opposite sides while the four-way entry pallet can be lifted from all sides. The use of forklift is not limited to handling unit load such as pallets only, it is also used for handling boxes, cartons and skids.

The forklifts are available in a variety of models and capacities depending on the applications. There are two basic types of forklift trucks, the first is manual one with power lift and the second one is rider-controlled forklift truck. The manual type (with without power lift) is commonly used for loads up to 1000 kilograms and is designed for short haul operations. However, space require­ment is more in case of powered machine used for manoeuvring. No exceptional skills are required for operating these machines.

As regards the rider-controlled forklift trucks, these are tailor made for applications, and varia­tions in them are quite considerable. The various rider-controlled forklift trucks in use are:

• Counter balance
• Stacker reach straddled-arm
• Narrow isle
• Four directional
• Side loader
• Double deep pallet reach

These forklifts are available to lift loads up to 40 feet of vertical height and operate in narrow aisle of 56 feet for use in automated warehouses. The standard forklift trucks are available for lift­ing loads up to 5 tonnes. However, the lift trucks up to 20 tonnes lifting capacity are also available, but these are custom built for specific material handling applications such as in docks or airports. At present the warehouse system designers give preference to narrow isle forklifts for use in high- density storage warehouses designed for high volumes throughput.

Towlines. Towlines are used for the continuous movement of the material. The four-wheel trailers are in continuous motion and are either floor or overhead mounted. During order selection process, the material picked by the order selector is placed in the trailer, which is then moved to packing and further to dispatch sections. A towline consists of a number of trailers, which move across the warehouse for placing to or picking from the material for storage or shipping. The towlines do not have the flexibility of load movement. They are custom designed for a particular product-volume application.

Conveyors. Conveyors are used for applications where continuous flow of material is required over longer distances. They excel at straight transportation because they eliminate re-handling before and after each function. Conveyors are also used in sorting and merging operations. For example, in large throughput warehouses, the cartons for dispatch to a particular region have to be sorted out for loading on to the assigned vehicle. The conveyors fitted with bar code reading device sort the boxes moving on the conveyor and direct them to the assigned dispatch station in the warehouse. These conveyors are most commonly used in the automated warehouses of retail chain in the USA where cartons as high as 1,00,000 in numbers are handled every day. A conveyor is either power driven or gravity flow type and is available in chain, belt or rollers as conveying media (Figure 5.4).

One characteristic of conveyors that makes them popular is that they can be easily equipped with automatic control devices for sorting, weighing and squaring off operations which are built in the conveying system. The most common usages are baggage handling at airports, coal han­dling at thermal power stations and iron ore handling at integrated steel plants where the con­veyors are used extensively. In large automated warehouses where large number of packages are handled for sorting and freight consolidation, conveyors are used along with bar-coding system. This improves the material movement effectiveness. There are different types of conveyor sys­tems in use, depending on the application and the products to be handled. The most common types are as follows.

Wheel Conveyor These are referred to as skate wheel conveyors. Skate wheel conveyors are small wheels made of steel or plastic and mounted on the sleeve or bearing and are spaced on bars placed at equidistance on the conveyor frame. The load is taken by three or four wheels. These are hori­zontally laid and the movement of goods takes place mostly with gravity. The load is pushed on the wheels for forward movement with the help of gravity pull. These are used in the warehouses where small-sized packages having large volume, which are not unitized, are handled.

Roller Conveyor These are similar to the wheel conveyors but use the powered rollers instead of wheels. The use of roller conveyors is for rapid mass loading and unloading of the goods. At the airports or shipping docks, the roller conveyors are invariably used for loading and unloading of cargo from the aircraft or ship.

Belt Conveyor These are the most common types of conveyors used for moving the material. The endless belt moves on two rotating shafts placed apart. These shafts are powered to activate the belt movement to carry the articles placed on it. These are available in portable and adjustable version for versatile applications in the warehouse.

Chain Conveyor These are used for movement of heavy material such as steel plates or heavy wooden creates. These are used where rigid and they require a strong carrying surface.

Carousels. Carousels are commonly used in order picking systems. The number of bins hous­ing the various items is housed on an oval track. The bins move on the track and a bin containing particular item can be brought to the order selector. A typical application of carousel is selection of service part for packing operation. The carousel system reduces the storage space and the man­power involved in order picking process. To increase the productivity, the carousel are integrated to a computerized system. In this, the bin movement is synchronized with order pickup for the par­ticular order in multiple order selection process. The items selected are put into the carton, which moves to packing and further to dispatch sections.

Overhead Cranes. Overhead cranes are used for moving very heavy items over a short distance. Items such as steel plates, bars, coils, tubes or machinery components can be efficiently handled with overhead cranes. These cranes have the moving and lifting mechanism installed on the fixed girders at the roof of the building. Lifting mechanism is called as saddle or hoist, which moves on rails across the bay and saddle can be moved throughout the length of the bay (Figure 5.5).

These are used where large heavy items or containers have to be moved in and out of the ware­house. The overhead cranes are built for lifting capacity over 5 tonnes.

Stacker Cranes. Stacker cranes are electric power drives and operate on fixed rails at base and top of each aisle. They are used for lifting the loads of about 2 tonnes up to the height of 60 feet
and are not economical for lifting to the height below 30 feet. The stacker cranes are normally used in large warehouses where large number of pallets are to be picked and sacked. A typical installa­tion may house more than 1000 pallets per aisle.

Pneumatic Tube System. Pneumatic tube systems are used for movement of granular or powdered material over a short distance. These systems are quite common in the cement and fertilizer plants where the material in powdered form is moved to the storage silos using the pneu­matic flow. The air at pressure of 7 kg per cm² is normally used for transporting the material, which carries the powder in the direction of the flow. In modern food grain warehouses the food grains in bulk quantity are stored in the silos. The pneumatic tube systems are used for storage and retrieval of the material. In some cases the vacuum pumps are also used for material retrieval. These systems ensure faster material movement with reliability. For bulk transfer of powdered material these systems are cost effective and reliable.

3. Semiautomatic System

In semiautomatic system all mechanized handling equipments may be used but the specific handling requirement for a particular warehouse operation may be performed automatically. The automation is done in parts, that is the individual equipment may be fully automatic with computerized system, but the other equipments in the warehouse are mechanized with manual operation. Hence the semiautomatic warehouse is a mixture of mechanized and automatic han­dling equipment. The following are the various types of automated equipments in semiautomatic warehouse system.

Sorting Device. Sorting devices are normally used along with powered conveyors. The sorting device sorts materials based on the sorting code. The optical sensing reads the bar code on the items, which can be diverted to packing section for unitization of load, or the boxes may be sorted out on regional basis guided to specific shipment dock for transportation through assigned vehicle. The automatic sorting device increases the system productivity through speed, accuracy and elimination of manual labour.

Robotics. Robots are human-like machines with microprocessor used for performing the programmed activity or series of activities. A wide scale usage of robotics is in manufactur­ing units where repetitive activities are performed continuously or activities are performed in hazardous working conditions, which could be harmful for human life. In warehouses, robotics can be used for break bulk or consolidation operation. Robotics can also be used in extreme temperature environment such as cold storage or deep freezer. The capability of robotics to perform activities without fatigue and with accuracy makes a suitable alternative to manual methods.

Automatic Guided Vehicle System. Automatic guided vehicle system (AGVS) is a mechanized material handling equipment without an operator. The system consists of four components, e.g. vehicle for movement, pickup and drop off locations, guidance system and a computer-controlled system. The vehicle moves on a fixed magnetic or optical path. The vehicle reaches to the des­tination tracing the assigned path covering the pickup and drop stations without the help of an operator. These systems operate at the speed of 150-250 feet per minute, which is slower than the typical forklift truck that operates at 300-500 feet per minute. In the case of a magnetic system, the path is an energized magnetic wire installed on warehouse floor and for optical system a light beam guides the vehicle.

AGVS are used in warehouses for material movement through a fixed assigned path during pickup and drop operations. The advanced AGVS used in developed countries are based on the latest IT and video technology, where the fixed path movement of the vehicle can be eliminated. The economic justification of the system is a trade-off between the lower operating cost and higher investment.

4. Automated System

The automated material systems are custom built and attract heavy investments. Human factor is minimized substantially and restricted to programming and controls. The advantages are speed and accuracy, which enhance the productivity of the system. The main disadvantages of the automated system are high investment, complexity in development and absence of flexibility. The automated material handling system is always developed along with the storage system specific to its require­ments for synchronous operations. The storage system accounts for 40-50 per cent cost of the total system. The system is connected to the computer for programming the equipment options, material pickup route, packing and loading instructions.

Source: Sople V.V (2013), Logistics Management, Pearson Education India; Third edition.