DOZERS FAILURE TYPES
FACTORS FOR MACHINE SELECTION
GENERAL RELATIONSHIPS
BULLDOZER
WHY DOZERS ARE USED? AND USES
WHEELED VS TRACKED
Structural or mechanical: Machine parts are stressed beyond capacity. Stability: Machine becomes imbalanced and overturns. Machine parts remain operable but machine isn’t in the position to carry out the work. Nature of activity Required efficiency Cost Site conditions Equipment productivity Time available Availability of skilled labor Productivity is high, cost of machinery is high Productivity is high, Unit cost of work to be done is low Capacity of equipment is high, Productivity is high A bulldozer is a tractor unit with a blade attached to its front. The blade is used to push, shear, cut, and roll material ahead of the tractor. 3 parts – blade, ripper, tractor. Two types: Wheeled, crawler or tracked Dozers are low centre of gravity machines The larger the difference between the transmission line of the force applied by the machine and the transmission line of the resistive force, the less effective is the utilization of the developed power. Uses: Dozing, Land Clearing, Ripping, Towing, Assisting Scrapers
WHEELED
TRACKED
Works on variety of soils Less versatility in terms of terrain High return speeds Better for loose soils Moderate blade loads Long work distances
BLADE FUNCTIONS
BLADE TYPES
FACTORS AFFECTING DOZER PRODUCTIVITY
Works on variety of soils More versatility in terms of terrain Low return speeds Better for tight soils Larger blade loads Short work distances
Pitching: Movement about horizontal axis, cutting angle adjustment Angling: Movement about vertical axis, Side casting (material rolls off one end of blade) Tilting: Movement about horizontal axis, concentrate cutting power to a smaller length of the blade. Used for sloping. Universal: Best for lighter soils, used for long distance work, reduced spillage of material Angle: Best for side casting, not recommended for harder soils Cushion: Used for ‘on-the-go’ excavation with scrapers, use recommended for lighter soils and light excavation Straight: Heavy-duty, used for short to medium distance work, used primarily for grading and shallow works S and U blade: Combination of universal and straight. Blade type Tractor type Soil conditions
Blade load(lcy) = 0.0138(WHL) Volume (cy) = (0.375)(WHL)/27 DOZER CYCLE
Dozer moves into position to excavate
FACTORS FOR PRODUCTION PER CYCLE
WHY LAND CLEARING IS NECESSARY LAND CLEARING
Dozer digs or scoops soil Dozer moves excavated soil Dozer unloads excavated soil Dozer repositions Dozer backtracks to excavation site Visibility Slope Transmission Material Operator Blade adjustment Organic materials decompose in fill, can cause settlement of fill Have to be removed Make material handling difficult Crawlers with special land clearing blades and rakes are used Involves: o Removal of trees, shrubs, grass and roots o Only material seen on surface is removed o Removed vegetation is stacked and burned Production(acre/hr) = W(ft) x SPEED (mph) x5280xE/43560 Production min/acre= H [A (B) + MINI + M2N2 + M3N3 + M4N4 + DF]
RIPPER
Claw like device on back of dozer Single shank or multiple shank
RIPPER TIP USAGE
Short – high impact conditions Intermediate – moderate impact conditions Long- Low impact conditions, soft soils
GRADER DEFINTION
FUNCTIONS
FACILITATES DOZERS BLADE OPERATIONS
A long tractor driven piece of equipment with a blade mounted underneath it. It is a multipurpose machine used for finishing and shaping. Levelling Sloping Side casting Spreading Finishing Grading General construction Can progressively cut a ditch of upto 3 ft. Can make shallow cuts in hard soils where the dozer can then perform heavier work Angling Pitching
SHOVELS
DEFINITION
A machine that is designed to carry out digging above grade and into the face of the excavation.
The shovels are usually mounted on a crawler or track to provide larger traction. Excavated soil is dumped into trucks. Shovels are not designed for high mobility and so hauling distances are minimized.
FACTORS AFFECTING PRODUCTIVIT Y SELECTION OF SHOVEL
PROCESS OF SHOVEL
Operator skill Material to be excavated Clean up of loading area Size of hauling units Height of cut Condition of shovel Type of material to be excavated Operator skill Size of hauling units Use of auxiliary equipment Swing angle Height of cut Excavate Swing out Dump Swing back
P= 3600*Q/t*F*E*(1/(1+swell))
LOADERS DEFINITION
TYPES
FACTORS AFFECTING PRODUCTION AND SELECTION WHEEL LOADERS VS TRACK LOADERS
Versatile piece of machinery Used for hauling, loading materials, excavation at and above wheel or track level Rubber wheels used are thick and provide sufficient traction and reduce bearing pressure Can transfer loads from one site to another as it can move at high speeds (wheeled) Hydraulically powered lifting equipment exerts a heavy breakout force as the lifting occurs Based on running gear: o Wheel mounted o Track mounted Other classifications based on load carrying capacity, steering mechanisms etc. Haul distance Type of material to be excavated/hauled Volume of material to be hauled Cycle times Height of lift required Machine specifications (load carrying capacity e.g.) WHEEL More bearing pressure Best for work on soils of low to medium hardness High mobility Rubber tires vulnerable to cuts from cut rock Can climb 30% grades Operation limited on steep side slopes
TRACK Less bearing pressure Best for work on soils of medium to high hardness Low mobility Steel tracks are not damaged by use on cut rock Can climb 60% grades Can operate better on steep side slopes
SKID STEER LOADERS
PRODUCTION LOADER AND EXCAVATOR
Are small in size and very versatile Can attach a number of tools such as saws, blades, backhoes, trenchers, rotary brooms etc. Steer by applying brakes to wheels on one side and transferring power to wheels on the other side. P= E*FILL FACTOR*LOAD IN ONE CYCLE/CYCLE TIME P= E*F*Q/T CHECK FOR LOAD AGAINST CAPACITY ROLLERS AND COMPACTORS
DEFINITION COMPACTION METHODS
ROLLER TYPES
SHEEP FOOT
SMOOTH DRUM
PAD DRUM
Equipment designed to compact materials such as soil, gravel, asphalt and concrete.
Kneading (manipulation) Static weight (pressure) Impact (sharp blow) Vibration (shaking) Sheep foot or tamping foot Pneumatic (rubber tired) Smooth drum Vibratory Pad drum Vibratory Grid rollers
Angular or square projections from a drum exert pressure on soil, kneading Can be used on fine grained soils but not on granular non-cohesive soils Widely used Best for compacting asphalt pavements and granular bases Works on static weight and can incorporate vibration Vibratory plus kneading Pads emerge from drums Lift thickness of 1 to 1.5 ft thick Work best on cohesive soils
GRID
PNEUMATIC
COMPACTION WHEELS
VIBRATORY PLATE COMPACTORS RAMMERS
PRODUCTION
Work on granular soils Work on static weight along with impact and manipulation Good for breaking lumps and soft rock Work on kneading Rear and front tires cover all Work on bases, sub bases, pavements Can work on granular and fine soils Tire ply, Inflation pressure, tire size, wheel load determine compaction Work on all types of soils Can have tamping or sheepsfoot shape Attached to an excavator boom Work in narrow trenches Self-propelled, gasoline or diesel powered Compaction of crushed aggregate, concrete and asphalt Can be walk-behind units or operated through remote control Self-propelled, gasoline powered Compact through impact Designed to work in small spaces Production (cubic Yard/hr )= 16.3xWxSxLxE/P W= width compacted in each pass in feet S= Compacter speed in mph L= compacted lift thickness in inches E= Job Efficiency P= Number of passes required
Mixer types: Gravity or freefall:
Reversible drum: Single axes Tilting drum: Double axes
Power or forced mixers: Paddles move eccentrically or centrically around a shaft or axis Pan mixers: (vertical shafts)
Planetary: Shafts eccentrically located and are able to rotate
Turbo: Shafts are centrally located and can be fixed or rotary Even flow: drums and paddles rotary and move in same directions Counter flow: drums and paddles move in counter directions
Trough Mixers (horizontal): Paddles or wave shaped arms (arranged in spiral pattern)
Single shaft Twin shaft
Transit: Concrete mixed already but kept plastic while being transported to site or Concrete mixed during journey to site
Front Discharge Rear discharge Articulate truck mixers
PUMPS: Piston VS Squeeze High reliability Low noise operation High pressure operation High efficiency
Quiet operation Low pressure operation Easier to clean Variable delivery rate
Pumping systems: Pump with pipeline mounted on frames, trailers or trucks Pump mounted on truck boom Pump mounted on tower boom
