Introduction to Construction equipment-2

Rollers

Rollers are the construction equipment that is used for the compaction of soil, gravel, sand, crushed stone layers, etc. Its working principle is based on vibration,impact loading, kneading and application of direct pressure on the different layers.

Applications:

• Road construction
• Pavements
• Agricultural purposes

The four most commonly used rollers are;

1. Vibratory Roller
2. Tamping roller or sheep foot roller
3. Smooth wheel rollers
4. Pneumatic tired roller

Vibratory Roller

Vibratory rollers have two smooth wheels/ drums and the vibrators. One drum is fixed at the front and another one on the rear side of the vibratory roller.Both wheels/drums have same diameter, length and also same weight.Vibratory roller covers all the area under the wheel. For the efficient operation of the vibratory roller, they are installed with the vibrator. The vibration of vibrators positions the particles by first disturbing even the positioned or arranged ones.The weight of wheels put on direct pressure on the layer. During the reversed motion of the roller, vibrator is turned off. At that time only static weight acts directly on the soil layer.

Fig 6. Vibratory Roller

Sheep foot roller/ Tamping roller

Sheep foot roller is also called stamping roller.The front steel drum of sheep foot roller is imbedded with many rectangular shaped boots having equal sizes that are fixed in a hexagonal pattern. Because of the boots on drums the coverage area of sheep foot roller is less i.e.,about 8- 12%. In sheep foot roller, compaction is done by static weight and kneading of the respective layer. This makes this roller best suited for clay soils. The contact pressure of sheep foot roller varies from 1200 to 7000Kpa.

Fig 7. Sheep foot roller

Tamping foot roller has four wheels and on each wheel, kneadingboots are fixed. Tamping roller has more coverage area than the sheep foot roller i.e., about 40- 50%. The contact pressure of tamping roller varies from 1400 to 8500KPa. It is best suited for using on fine-grained soils.

Smooth wheel roller

Smooth wheel roller is same as the vibratory rollers. The only difference is the vibratory equipment. Smooth wheel roller does not have the vibrator attached to the drum. For this reason, smooth wheel roller are well suited for rolling of weaker aggregates, proof rolling of subgrades and in compacting asphalt pavements. Compaction of clay or sand is not a good choice to be done with smooth wheel roller. This is so because there are many empty voids in clay soil and sand, which cannot be reduced without vibrators.

Pneumatic tired roller

Pneumatic tired roller consists of a number of rubber tires at the front and at the rear end of the roller.Empty spaces in between the two tires that make 80% coverage area under the wheels. Pneumatic roller has the capacity to exert contact pressure ranges from 500 to 700Kpa. Pneumatic tired roller is generally used for highways, construction of dams and for both fine-grained and non-cohesive soils. It can also be used for smoothening of finishing bitumen layer on highways, roads, etc.

Fig 8. Pneumatic tired roller

Crushers

Crushers are used mainly to reduce the size of large stone or rock to smaller uniform sized aggregates necessary for concrete mix. The crushing Process includes of:

• Pressure,
• Impact,
• Attrition
• A combination of these operations.

Types of Crusher

1. Jaw crushers: It is one type of the primary crushers. It operates by letting stone flow into space between the two jaws, one of which is stationary and other is movable, which together make up the crushing surfaces. The distance between the two jaws reduces as the stone travels downward under the influence of gravity and finally passes through the lower opening. The moveable jaw is capable of exerting a pressure that is high enough to crush the hardest rock. The movable jaw is suspended on bearings on the crusher frame from a shaft mounted.
   
   
2. Gyratory crusher: This is also a type of primary crusher. This type of crusher contains a hardened steel head having a long conical shape, with a trough shaft suspended in a bearing at the top, and an eccentric base connection linked to gears. Thus, as the rotation of the cone occurs, the gap between itself and the walling changes from a maximum to the minimum for each cycle. The rock is feed into the chamber at the top and as it moves downward, crushing is done and finally emerges through the bottom gap.
   
   
3. Cone crusher: Cone crusher are used as a secondary or tertiary crusher. These crushers are capable of producing large quantities of uniformly fine crushed stone. The cone is shorter with smaller inlet and outlet openings as compared with the gyratory crusher.
   
   
4. Roll crusher: Roll crushers also fall under the category of the secondary or tertiary crushers. This crusher consists of a heavy cast iron frame equipped with two counter-rotating rollers mounted on a separate horizontal shaft. The crushed rock from the primary crusher is feed through the gap between the two rollers for further crushing. Usually, one roller has a fixed axis while the other can be adjusted to give the required setting. The crusher is very compact, lightweight and low in cost.
   
   
5. Hammer mill: Hammer mill is one of the impact crushers mostly used as a primary or secondary crusher. It consists of a housing frame, a horizontal shaft extending through the frame, the number of frames and hammers attached to the frame and one harder steel breaker plates. As the stone is feed to the mill, the hammers are driven by a motor, move at the high speed and brake the stone into small pieces and driving them against the hard plate, further decrease their size.

Asphalt Equipment

Asphalt equipment, also known as asphalt paver, is an equipment that is used to pave asphalt on the road to be pitched in a uniform way. There are mainly two types of Asphalt equipment. They are:

1. Tracked Asphalt Paver
2. Wheeled Asphalt Paver
   

Some Terminologies used in Construction equipment

Earthmover

An earthmover is a term used to define any piece of heavy construction equipment that is used to move or dig dirt or earth. These machines include bulldozers, backhoes, and other earth moving equipment. The term earthmover is a more general term that implies the function of the equipment rather than naming the actual equipment.

Bulldozer

A bulldozer is a type of heavy construction equipment that has a metal blade for pushing large amounts of dirt, sand, or debris for construction works. Most of the dozers have tracks and few are wheeled.

Cat skinner

The term cat skinner is generally used to describe a person who operates a dozer. The word "cat" is derived from the Caterpillar Tractor, which is a dozer manufacturer company.

Articulated truck

Articulated trucks are used mostly in construction work for booming large loads over rough terrain. Articulated trucks are equipped with a drive system that shows the number of wheels and axles it has. Most of the articulated trucks are six wheelers on three axles.

Skidder

In the heavy construction equipment field, the word “skidder” may have two different meanings. In some case, the term skidder is used to refer to the person who is in charge of the construction team constructing a skid road. In other sense, the word skidder means the engine that hauls cable for skidding logs.

Boom

The boom is a section or strut, pivoted or hinged at the lower end, at a location fixed in height on a frame, pole or vertical member, with its upper end supported by chains, ropes or rods to the upper end of the frame, mast or vertical member. When pertaining to a revolving shovel, a beam hinged to the deck front, supported by cables; also, any heavy beam that is hinged at the one end and carries a weight-lifting device at the other.

Dumpers

Dumper is a small vehicle generally diesel powered mainly used to carry heavy materials to various construction sites like roads, buildings, ports etc.

References

• Technical book,"Construction Machinery Training", Instate,Islamabad
• Harris, f. and McCaffer,"Management of Construction Equipment", Macmillian Education Ltd. London,UK.
• SAE Handbook Volume 4