Material Handling Equipments in Construction

 MATERIAL HANDLING EQUIPMENTS

Materials handling is loading, moving and unloading of materials. To perform the action safely and economically, different types of tackles, gadgets and equipments are used, which are called as material handling equipments. The essential requirements of a good materials handling system may be summarized as:

❖ Efficient and safe movement of materials to the desired place.

❖Timely movement of the materials when needed.

❖ Supply of materials at the desired rate.

❖ Storing of materials utilizing minimum space.

❖ Lowest cost solution to the materials handling activities.

Material Handling equipment's are used in movement of bulk, packaged, & individual products as per the work requirement. Broadly material handling equipment's can be classified into the following categories:

(i) Hoists: Hoist is a device for raising or lowering a load by means of a drum or wheel lift to which wraps the rope or chain. It can be operated by hand, is driven electrically or pneumatically, and the chain or wire rope fibers are used as lifting device. The load connected to the lifting means of a lifting hook. Following are the widely used hoisting equipments:

* Pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a cable or belt along its circumference. Pulleys are used in a variety of ways to lift loads, apply forces, and to transmit power. The assembly of the wheel, axle, and supporting shell is referred to as a "block." A pulley may also be called a sheave or drum and may have a groove between two flanges around its circumference. The drive element of a pulley system can be a rope, cable, belt, or chain that runs over the pulley inside the groove. The pulley and sheave blocks suitable for lifting rough surfaces and heavy loads. For this purpose, the chains and wire ropes are used. The alloy chains are best suited for hoisting operation. The weakest component of this system is the load hook. The hook fails by straightening. Once the hook gets elongated or straightened, it should be replaced.

* Chain hoist: The chain hoists are the popular mechanism for lifting loads of upto tonnes. The system consists of two sets of chains, namely the hand and load chain. The hand chains are particularly useful for the isolated location, where an electric motor or other types of mechanical equipments are not available. The pull applied through the hand chain is transmitted to the load chain with a multiplication factor of over 20. The load to be lifted is held by a load hook while another hook (called support hook) at the top, support the mechanism. The two hooks, however, should not be interchanged as the support hook is made much stronger than the load hook. There are four types of hand-operated chain hoists are in use.

❖ Differential

❖ Screw geared

❖ Spur geared

❖ Pull lift

* Winch: A winch is a rotating spool, driven by a motor that can tighten or loosen a cable. The cable generally has a hook at the end. A winch is a mechanism in the shape of a cylinder or drum, over which rope or chain is wound. If a winch is used only for raising and lowering, it is sometimes referred to as hoist. The winches are of two types namely hand winches and power winches.

(ii) Conveyors: Conveyors are useful for moving material between two fixed workstations, either continuously or intermittently. They are mainly used for continuous or mass material handling operations, and most suitable for operations where the flow is more or less steady. Conveyors may be of various types, with rollers, wheels or belts to help move the material along, and may be power-driven or may roll freely. The decision to provide conveyors must be taken with care, since they are usually costly to install. However, they are less flexible and, where two or more converge, it is necessary to coordinate the speeds at which the two conveyors move. Various types of conveyors used for material handling are discussed below:

* Belt conveyors: A belt conveyor consists of an endless flat and flexible belt of sufficient strength, made of fabric, rubber, plastic, leather or metal, which is laid over two metallic flat pulleys at two ends, and driven in one direction by driving one of the two end pulleys. Material is placed on this moving belt for transportation. The active half of the belt is supported by idler rollers or slider bed. The return half of the belt may or may not be supported, as it generally does not carry any additional load other than its own weight. The endless belt is kept tight by a belt tensioning arrangement. Types of belt conveyor are:

❖ Flat Belt Conveyor

❖ Troughed Belt Conveyor

❖ Closed Belt Conveyor

❖ Metallic Belt Conveyor

* Chain conveyors: The term chain conveyor means a group of different types of conveyors used in diverse applications, characterized by one or multiple strands of endless chains that travel entire conveyor path, driven by one or a set of sprockets at one end and supported by one or a set of sprockets on the other end. Materials to be conveyed are carried directly on the links of the chain or on specially designed elements attached to the chain. The load carrying chain is generally supported on idle sprockets or guide ways. The endless chains are kept tight by suitable chain tensioning device at the non-driven end. Different types of chain conveyors are Apron or Pan Conveyor and Cross-Bar or Arm Conveyor. no

* Cable conveyors: These conveyors form a distinct group of materials handling equipment to transport people and bulk materials in load carrying buckets, using overhead moving cables and/or wire ropes and are com- posed of one or more spans from the loading point to the discharge point/points covering long distances upto several kilometers. These conveyors are also known as ropeways or aerial tramways.

* Roller conveyors: A roller conveyor supports unit type of load on a series of rollers, mounted on bearings, resting at fixed spacing's on two side frames which are fixed to stands or trestles placed on floor at certain intervals. A roller conveyor essentially coveys unit loads with at least one rigid, near flat surface to touch and maintain stable equilibrium on the rollers, like ingots, plates, rolled stock, pipes, logs, boxes, crates, moulding vboxes etc. The spacing of rollers depend on the size of the unit loads to be carried, such that the load is carried at least by two rollers at any point of time. Roller conveyors are classified into two types according to the principle of conveying action as Unpowered or Idle Roller Conveyor and Powered or Live Roller Conveyor.

* Screw conveyors: A screw conveyor consists of a continuous or interrupted helical screw fastened to a shaft which is rotated in a U-shaped trough to push fine grained bulk material through the trough. The bulk material slides along the trough by the same principle a nut prevented from rotating would move in a rotating screw. The load is prevented from rotating with screw by the weight of the material and by the friction of the material against the wall of the trough. A screw conveyor is suitable for any pulverized or granular non viscous material, and even at high temperature. The conveyor is particularly suitable for mixing or blending more than one material during transportation, and also for controlling feed rate of materials in a processing plant. It is also not suitable for large- lumped, packing or sticking materials.

* Chute conveyors: Chute Conveyor is one of the least expensive methods of conveying material. It is the simplest example of gravity-operated conveyor. Chutes are inclined connections between two systems of materials handling equipment or production equipment, in the form of troughs of definite geometrical cross section or pipes, which convey unit or bulk load by gravity. A chute may connect two conveying mechanisms, two process equipment or may be installed between one materials handling equipment and one processing equipment. Depending on the load to be handled, chutes are made of various size, shape and material.

(iii) Cranes: A crane is a piece of heavy machinery that is a tower or platform that is equipped with cables and pulleys. Cranes have a long history of being a staple in construction that reaches back thousands of years. It was during the industrial revolution that cranes became integral to the modernization of the world, replacing the manual pulley system with an engine and an operator that preceded them. There are various types of cranes used in civil engineering construction works. They are used to lift and lower materials. The most common types of cranes used in the construction industry are discussed below:

* Derrick Crane: A derrick is a special type of crane in which the distance from the end of the jib to the pillar can be changed. The derrick cranes are of two types, namely Guy derrick and Stiff leg derrick. A guy derrick consists essentially of a pivoted pillar that is braced by guy ropes, and a jib that is attached at the base of the pillar. The inclination of the jib is controlled by a tackle that connects the top ends of the pillar and jib. The hoisting rope extends from the end of the jib, over the top of the pillar, to the base of the pillar, where it is fastened to a drum. A stiff leg derrick is similar to a guy derrick except that its jib is movable and may be secured at different heights on the tower, or pillar. Stiff leg derricks are used mostly in building construction. Guy derrick can be constructed up to 200 tonnes capacity. In stiff leg type derricks, the guy wires are replaced by trussed structure. This type of derricks is suitable for loads from 10 to 50 tonnes.

* Mobile Cranes: This is the most basic type of crane and consists of a steel truss or telescopic boom mounted on some kind of mobile platform. This platform could be wheeled, a rail or even a cat truck. The boom is hinged at the bottom and can be raised or lowered by cables or hydraulic cylinders. Some mobile cranes are even able to be driven on the highway. Their ability to navigate around job sites and carry large amounts of weight makes mobile cranes a very popular addition to many projects. In most cases, they don't require much effort to assemble or setup.

* Crawler Crane: Crawler cranes are track vehicles. Instead of wheels, crawlers are built on an undercarriage fitted with a pair of rubber tracks. Though this limits the crawler's turning capacity, the tracks make it possible to use on soft ground and sites with limited improvement without sinking. Their main advantage is that it can move mostly on any surface of the earth due to its crawlers as it transfers its load to a great area. Hence it can be used at unprepared sites without worrying about anything. Some crawler cranes have an attached telescopic arm that allows it to change its size, making them highly adaptable on many terrains. It is very heavy and move on tracks hence mobility is not easy and take more time and will cost more money. But it can be moved by trucks easily and without costing much money.

* Rough Terrain Crane: A rough terrain crane is built similarly to a crawler crane, but instead of tracks, the undercarriage is outfitted with four large rubber tires that are typically equipped with four-wheel drive. A normal vehicle mounted crane cannot be used in off road applications, hence rough terrain cranes are used. Outriggers are used for stabilizing the crane while working. They contain only one engine which means that same engine is used for undercarriage and crane. Rough terrain cranes are also fitted with telescopic booms and outriggers to improve stability and make mobility much more manageable in tight and rough areas. The outriggers can extend vertically and horizontally to stabilize and level the crane when it is lifting a large load. These types of cranes use only single engine, such that the same engine is used to power the undercarriage and the crane.

* Truck Mounted Crane: These types of cranes are mounted on a rubber tire truck and provide excellent mobility. The outriggers will extend vertically or horizontally and are used to stabilize and level the crane when it is hoisting a load of materials. Truck-mounted cranes are made up of two parts: the carrier (truck), and the boom (arm). Due to their unique build, they're able to travel easily on the road with no unique set up or transportation equipment. Its main advantage is that it can travel on highways itself, which makes it easy and less expensive. It does not need any other vehicles to transport it. They can be rotated up to 180 degrees. But some of them rotate up to 360 degrees but these are more expensive.

* Telescopic Handler Cranes: Telescopic cranes are equipped with a boom (arm) outfitted with a hydraulic cylinder that allows it to change length, like a telescope. The boom has a number of tubes that are fitted inside each other. Then hydraulic mechanisms extend or retract the tubes to length or shorten the boom. Although it's considered a fixed crane, many telescopic cranes are mounted on a truck to transport to and from different worksites. Their main purpose is to handle loads and install frame trusses in buildings. They are designed too simple to improve workability. They can rotate up to 360 degrees and also have outriggers to maintain its stability. They look like forklift trucks. Due to the unique nature of their boom being able to collapse and compact itself, telescopic cranes are highly adaptable for a variety of situations, such as short-term construction jobs as well as some rescue operations during natural disasters or other emergencies.

* Tower Cranes: A tower crane is considered to be a modern form of a balance crane and is the mostly used cranes in today's world. Usually, they are fixed to the ground in concrete base or attached to the side of structures. They can lift load up to 30 tons approximately. Due to their size, tower cranes are equipped with an operating cab that controls the entire crane. The operators of the crane mostly use radio signals as a medium for communication to hook or unhook the load. Tower cranes have their jib extending horizontally from the mast (tower part), which itself rests on a concrete base. A travelling jib is able to move up and down, while the fixed jib has an operating dolly that moves materials horizontally. The engine (called a slewing unit) that controls the rotation of the crane sits on the top of the mast. Counterweights are also provided to make the crane more stable while swinging the boom. Due to their size, tower cranes are built along with the building, growing alongside it; once the building is complete, the process is reversed. Commonly used in the construction of tall buildings, tower cranes are awesome machines that offer amazing lifting capabilities.

* Overhead / Gantry Crane: The Gantry cranes or overhead cranes are the indispensable machines in factories, workshops. These types of cranes are also known as suspended cranes. In large workshops, there are separate machines for fabrications or repairs of the machine parts. The machine or the components, which are to be repaired, can be transferred to the place of fabrication or assembly with the help of Gantry cranes. Larger overhead cranes (also known as goliath cranes) can be found in use in shipyards and large outdoor manufacturing plants. The hoist is set on a trolley which will move in one direction along one or two beams, which move at angles to that direction along elevated or ground level tracks, often mounted along the side of an assembly area. The most significant difference between a bridge and gantry crane is that the gantry crane is supported by two a- frame steel legs and is typically built on a track.

(iv) Trucks: Industrial vehicles/trucks is one of the most common group of materials handling equipment used in industry as well as in day to day distribution of goods in warehouses, large stores, etc. The entire range of industrial vehicles/trucks is generally sub-classified into two group's namely non-powered truck, (also called hand trucks) and powered trucks. The operation and constructional features of some of the common types of industrial trucks are discussed below:

* Hand trucks: Hand trucks, as the name implies, have no source of motive power, these are generally moved manually or are attached to other powered moving equipment/units. Hand trucks are classified into three sub groups (i) 2-Wheel hand truck, (ii) multiple-wheel hand truck and (iii) Hand lift truck.

Two-wheel Hand Trucks are generally used for moving unit or unitized loads like bricks, cement bags, barrels, packages etc. by pushing the truck manually. Basically it consists of two long handles fixed by a number of cross bars which from the frame to carry the load. Two wheels mounted on an axle are fixed on far end of the frame. Two short legs are generally fixed to the two handles at the other end to allow the hand truck to stay in a horizontal position during loading and unloading of the truck.

Multiple-wheel Hand Trucks generally consists of a platform or framework mounted on 3 or 4 or more number of wheels. The truck is generally provided with a handle for pushing or pulling the platform. Certain trucks are provided with no handle or detachable handle.

Hand Lift Trucks are provided with a mechanism of lifting its platform, which can be rolled under a pallet or skid, and raised to lift the pallet or skid with load to clear the ground and then move this load from one place to another. Depending on the lifting mechanism, these are grouped into hydraulic or mechanical type. Hand lift trucks are widely used in small to medium sized manufacturing industries.

* Powered trucks: When a vehicle / truck contain its own source of motive power, it is called a powered truck. Power trucks are divided into several categories of equipment. The wide varieties of powered industrial trucks have been classified into the following six groups as

* mode of action

* power source

* type of wheel

* mode of control

* height of lift

* mode of travel

The powered trucks can be further subdivided into Forklift Truck, Tractor and Dump Trucks.

Fork lift trucks are the most versatile, useful and widely used equipment as industrial lift trucks. These are self loading, counterbalanced, powered, wheeled vehicles, with the operator seating on the vehicle, designed to raise, move and lower load on forks or other attachments fastened to a mast which is fixed in front of the vehicle to allow lifting and stacking of loads. Forklift trucks are used for lifting, lowering, stacking, unstacking, loading and unloading and maneuvering of medium to large weight, uniform shaped unit loads, intermittently. The capacity of this equipment varies from 1 tonne to 60 tonnes. However, the limitations of this equipment are it usually requires pallet/skid/ container for lifting and requires skilled operator. It is suitable for short hauls with a travel speed of 10-15 kmph.

Tractor is a vehicle, having its own source of motive power, used as a prime material handling equipment. It gives motion to another or a group of other vehicles which do not have their own motive power, such as trailers, semitrailers, etc. Tractors have many uses as construction equipment like earthmoving, aggregates, cement bags, bricks and even water container carrying works. While their primary purpose may be to pull or push loads, they are also used as mounts for many types of accessories, such as front-end shovels, bulldozers and others. There are types and sizes to fit almost any job for which they are usable. Tractors may be divided into two major types as crawler tractors and wheel tractors.

Dump truck, also known also as a tipper truck, is used for hauling sand, gravel, excavated earth, bituminous aggregate in construction industry. A typical dump truck is equipped with an open-box bed, which is hinged at the rear and equipped with hydraulic rams to lift the front, allowing the material in the bed to be deposited on the ground behind the truck at the site of delivery.