Front end loaders Machines
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Front end loaders Machines

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    Front end loaders Machines Front end loaders Machines Presentation Transcript

    • Front End Loaders Mansoor Azam Qureshi NUST Islamabad
    • 2 Loaders • Loaders are used extensively in construction operations to handle and transport material, to load haul units, to excavate, and to charge aggregate bins at both asphalt and concrete plants. • The loader is a versatile piece of equipment designed to excavate at or above wheel or track level. • The hydraulic-activated lifting system exerts maximum breakout force with an upward motion of the bucket. • Large rubber tires on wheel models provide good traction and low ground-bearing pressure. • A wheel loader can attain high speeds, which permits it to travel from one job site to another under its own power.
    • 3 Loader Types • Classified on the basis of running gear, there are two types of loaders: ▫ Crawler-tractor-mounted type ▫ Wheel-tractor-mounted type • They may be further grouped by the capacities of their buckets or the weights that the buckets can lift. • Wheel loaders may be steered by the rear wheels, or they may be articulated. • To increase stability during load lifting, the tracks of crawler loaders are usually longer and wider than those found on comparable-size tractors.
    • 4 Specification for Loaders
    • 5 Bucket Capacities and Tipping Loads
    • 6 Specification for Tracked Loaders
    • 7 Production Rates • The two critical factors to be considered in choosing a loader are ▫ Type of material and ▫ Volume of material to be handled. • Wheel loaders are excellent machines for soft to medium-hard material. • However, wheel loader production rates decrease rapidly when used in medium to hard material. • Another factor to consider is the height that the material must be lifted. When loading trucks, the loader must be able to reach over the side of the truck's cargo container. • A wheel loader attains its highest production rate when working on a flat smooth surface with sufficient space to maneuver.
    • 8 Factors Affecting Production • Fixed cycle time required to load the bucket, maneuver with four reversals of direction, and dump the load • Time required to travel from the loading to the dumping position • Time required to return to the loading position • Volume of material hauled each cycle Fixed Cycle Times
    • 9 Affect of Haul Distance
    • 10 Operating Loads • Under SAE standards the maximum operating load of a wheel loader should not exceed 50% of the static tipping load with the loader in full turn position . • For track-type loaders, the operating load should not exceed 35% of the static tipping load. • Tipping load values may be increased when required by ballasting tires, by using counterweights, or by adding attachments to the rear of the machine. • Thus, the machine weight as well as its lifting power determine the size of bucket that may be safely used with the machine.
    • 11 Wheel Loaders • The large rubber tires used on wheel loaders give them excellent job and between-the-job mobility with maximum highway speeds over 25 mp/h (40 km/h). • Their ground pressure is relatively low and may be varied by changing tire size and inflation pressure . • However, the vulnerability of its tires to cutting makes it poorly suited to loading sharp shot rock, especially under wet floor conditions, unless its tires are protected in some way (protective mesh chains, for example). • Many modem wheel loaders are articulated. An articulated wheel loader has a frame which is hinged between the front and rear axles, thus providing more maneuverability and a shorter turning radius than a rigid frame . • Rigid frame wheel loaders usually steer from the rear axle. Hydraulic steering and control systems are commonly used
    • 12 Track Loaders • Track loaders operate in the same basic way that wheel loaders operate. However, their low ground pressure enables them to operate in areas that would be unsuitable for wheel loaders. • Their greater tractive ability makes them suitable for the toughest digging conditions while their steel track resists the cutting action of sharp rock. • They can travel on side slopes up to 35% while wheel loaders are limited to about 15%. • Their climbing ability enables them to climb 60% grades compared to 30% grades for wheel loaders. • Because of their lower travel speed, however, their mobility is much less than that of wheel loaders . • Their production will similarly be lower than that of a wheel loader if the haul distance is appreciable.
    • 13 Skid Steer Loaders • A small wheel loader having rigid axles is called a skid-steer loader . These machines steer by braking the wheels on one side while applying power to the wheels on the other side. • A number of different attachments are available for these machines including backhoes, blades, compaction rollers, rotary brooms , hydraulic hammers, saws, cold planers, cement mixers, and trenchers. • Due to their small size, versatility, and productivity these machines have become increasing popular in recent years.
    • 14 Example • A 4-cy wheel loader will be used to load trucks from a quarry stockpile of processed aggregate having a maximum size of 1 .25 in. The haul distance will be negligible. The aggregate has a loose unit weight of 3,100 Ib/cy. Estimate the loader production in tons based on a 50-min hour efficiency factor. Use a conservative fill factor. • Size of bucket, 4 cy • Bucket fill factor for aggregate over 1 in., 85-90%; use 85% conservative estimate • Check tipping: • Load weight: 4 cy x 0.85 = 3.4 Icy • 3.4 Icy x 3,100 Ib/lcy (loose unit weight of material) = 10,540 Ib
    • 15 Example • • • • • From Table 4lcy machine static tipping load at full turn is 25,0001b Therefore, operating load (50% static tipping at full turn) is 0.5 x 25,000 Ib = 12,500 Ib 10,540 Ib actual load < 12,500 Ib operating load; therefore okay Typical fixed cycle time (Table 9.10) 4-cy wheel loader, 30 to 33 sec; use 30 sec. • Efficiency factor, 50-min hour • Class of material, aggregate 3,100 Ib per Icy • Probable production= [3600x4x0.85/30] x [50/60] lcy/hr = 340 lcy/hr = 340 x 3100/2000 = 527 ton/hr
    • 16 EXAMPLE • A 4-cy wheel loader will be used to charge the aggregate bins of an asphalt plant that is located at the quarry. The one-way haul distance from the 1.25 in. aggregate stockpile to the cold bins of the plant is 220 ft. The asphalt plant uses 105 tons per hour of 1.25-in. aggregate. Can the loader meet this requirement. • Size of bucket, 4 cy • Bucket fill factor for aggregate over 1 in., 85-90%; use 85% conservative estimate • Check tipping: Load weight: 4 cy x 0.85 = 3.4 Icy 3.4 Icy x 3,100 Ib/lcy (loose unit weight of material) = 10,540 Ib From Table 4cy machine static tipping load at full turn is 25,0001b Therefore, operating load (50% static tipping at full turn) is 0.5 x 25,000 Ib = 12,500 Ib 10,540 Ib actual load < 12,500 Ib operating load; therefore okay
    • 17 EXAMPLE • Typical fixed cycle time 4-cy wheel loader, 30 to 33 sec; use 30 sec. Travel speeds forward First, 4.3 mph; second. 7.7 mph; third, 13.3 mph Travel speeds reverse First, 4.9 mph; second, 8.6 mph; third, 14.9 mph • Travel loaded: 220 ft, because of short distance and time required to accelerate and brake, use 80% maximum first gear maximum speed. 4.3 mph X 80% X 88 fpm/mph ----------------------------------------= 5.0 ft/sec 60 /sec min • Return empty: 220 ft; because of short distance and time required to accelerate and brake, use 80% of second gear maximum speed [7.7 mph X 80% X 88 fpm/mph] =9.0 ft/sec 60 sec/min
    • 18 EXAMPLE • Cycle time ▫ ▫ ▫ ▫ Fixed time 30 sec 4-cy wheel loader Travel with load 44 sec 220 ft, 80% first gear Return travel 24 sec 220 ft, 80% second gear Cycle time 98 sec • Production = [3600x4x0.85/98] x 50/60 x 3100/2000 = 161 ton/hr • 161 tons/hr > 105 tons/hr requirement The loader will meet the requirement.