DozersA dozer is a tractor unit that has a blade attached to the is designed to provide tractive power to push, shear, cut, and roll material ahead of the tractor. A dozer has no set volumetric capacity. The amount of material the dozer moves is dependent on the quantity that will remain in front of the blade during the push. Crawler dozers equipped with

special clearing blades are excellent machines for land clearing. Heavy ripping of rock is accomplished by crawler dozers equipped with rear-mounted rippers because of the power and tractive force that they can develop.

Dozers may be either crawler (track laying) or wheel-type machines. These machines are designed to provide tractive power for drawbar work. Consistent with their purpose, as a unit for drawbar work, they are low-center-of-gravity machines. This is a prerequisite of an effective dozer. The larger the difference between the line-of-force transmission from the machine and the line-of resisting force, the less effective the utilization of developed power. Besides dozing, these machines are used for land clearing, ripping, assisting scrapers in loading, and towing other pieces of construction equipment. They can be equipped with either a rear-mounted winch or a ripper. Some major parts are shown in figure. Major functional parts area lso indicated. For long moves between projects or within a project, the track dozer should be transported. Moving them under their own power, even at slow speeds, increases track wear and shortens the machine's operational life.

Functions of DozersA dozer is a tractor unit that has a blade attached to its front. Dozers are effective and versatile earthmoving machines. They are used both as support and as production machines on many construction projects. They may be used for operations such as:

Moving earth or rock for short haul (push) distances, up to 300 ft (91 m) in the case of large dozers.

Spreading earth or rock fills, backfilling trenches and opening up pilot roads through mountains or rocky terrain.

Clearing the floors of borrow and quarry pits.

Helping load tractor-pulled scrapers.

Ripping rock and hard soils with rippers

Clearing land of timber, stumps, and root mat.

Perfomance of DozersUsable force that a machine has available to perform work is often limited by traction. This limitation is dependent on two factors:

Coefficient of traction for the surface being traversed.

Weight carried by the drive wheels of the tractor.Traction or flotation requirements can be met by proper undercarriage or tire selection. A standard crawler dozer undercarriage is appropriate for general work in rock to moderately soft ground. There are low-ground-pressure (LGP) undercarriage configurations for dozers operating in soft ground conditions. In the case of wheel machines, wider tires provide greater contact area and increase flotation. It must be remembered, however, that rimpull charts are

based on standard equipment, including tires. Larger tires will reduce the developed rimpull.The crawler-type tractor is designed for those jobs requiring high tractive effort. No other piece of equipment can provide the power, traction, and flotation needed in such a variety of working conditions. A crawler dozer can operate on slopes as steep as 45° Dozer weight is important on many proJects because the maximum tractIve effort that a tractor can provide is limited to the product of

the weight times the coefficient of traction for the unit. And the particular ground surface, regardless of the power supplied by the engIne.An advantage of a wheel-type dozer as compared with a crawler dozer is the higher speed possible with the' former machines-in excess of 30 mph for some models. To attain a higher speed, however, a wheel dozer must sacrifice pulling effort. Relative comparison of both type of machines is shown in table.

BladesA dozer blade consists of a moldboard with replaceable cutting edges and side bits. Push arms and tilt cylinders or a C-frame connect the blade to the dozer. Blades vary in size and design based on specific work applications. The hardened-steel cutting edges and side bits are bolted on because they receive most of the abrasion and wear out rapidly. The bolted connection enables easy replacement. The design of some machines enables either end of the blade to be raised or lowered in the vertical and horizontal planes of the blade.Pitching is a pivotal movement about the point of connection between the dozer and blade. When the top of the blade is pitched forward, the bottom edge moves back; this increases the angle of cutting edge attack. Turning the blade so that it is not perpendicular to the direction of the dozer's travel is known as angling. Angling causes the pushed material to roll off the trailing end of the blade. This procedure of rolling material off one end of the blade is called side casting. Tilting movement is within the vertical plane of the blade. Tilting permits concentration of dozer driving power on a limited portion of the blade's length.

Blade PerformanceA dozer's pushing potential is measured by two standard ratios, horsepower per foot of cutting edge, cutting ratio and horsepower per loose cubic yard of material retained in front of the blade, load ratio. The horsepower per foot (hp/ft) cutting ratio provides an indication of the blade's ability to penetrate and obtain a load. A higher cutting ratio indicates a more aggressive blade. The horsepower per loose cubic yard, load ratio, measures the blade's ability to push a load.

A higher ratio means that the dozer can push a load at a greater speed. Many different special application blades can be attached to a tractor, but basically only five blades are common to earthwork.

Straight Blade Angle Blade Universal Blade Semi Universal Blade Cushion BladeStraight Blade

The straight blade is designed for short- and medium distance passes, such as backfilling, grading, and spreading fill material. These blades have no curvature across their length and are mounted in a fixed position, perpendicular to the dozer's line of travel. Generally, a straight blade is heavy-duty and normally it can be tilted, within a 10° arc, increasing penetration for cutting or

decreasing penetration for back dragging material. It may be equipped to pitch. The ability to pitch means that the operator can set one end of the cutting edge deeper into the ground to dig or pry hard materials. For easy drifting of light materials, the edge's are brought to

the same level-the blade is level in the horizontal plane.Angled BladesAn angle blade is wider (face length) by 1 to 2 ft than an S blade. It can be angled up to a maximum of 25° left or right of perpendicular to the tractor or held perpendicular to the dozer's line of travel. The blade can be tilted, but because it is attached to the dozer by a C-frame mount, it cannot be pitched. The angle blade is very effective for side-casting material, particularly for backfilling or making sidehill cuts.

Universal BladesThis blade is wider than a straight blade and the long dimension outside edges are canted forward about 25°. This canting of the edges reduces the spillage of loose material making the U blade efficient for moving large loads over long distances. The cutting ratio is lower for the U than the S blade mounted on a similar dozer. Penetration is not a prime objective of the blade's design (shape) as the lower cutting ratio relationship indicates. The U blade's load ratio is lower than that of a similar S blade. This denotes that the blade is best suited for lighter materials. Typical usages are working stockpiles an drifting loose or noncohesive materials.

Semi-Universal BladesThis blade combines the characteristics of the S and U-blade designs. By the addition of short wings it has increased capacity compared to an S blade

Cushion BladesCushion blades are mounted on large dozers that are used primarily for push-loading scrapers. The C blade is shorter than the S blade so as to avoid pushing the blade into and cutting the rear tires of the scraper while push-loading. The shorter length also facilitates maneuvering into position behind the scrapers. Rubber cushions and springs in the mounting enable the dozer to absorb the impact of contacting the scraper push block. By using a cushion blade instead of a "pusher block" to push scrapers, the dozer has the ability to clean up the cut area and increase the total fleet production. It is a blade of limited utility in pushing material and should not be used for production dozing. It cannot be tilted, pitched, or angled.

Production EstimateA dozer has no set volumetric capacity. There is no hopper or bowl to load; instead, the amount of material the dozer moves is dependent on the quantity that will remain in front of the blade during the push. The factors that control dozer production rates are:

Blade type Type and condition of material Cycle time

Blade TypeBy design, straight blades roll material in front of the blade, and universal and semi-U blades control side spillage by holding the material within the blade. The same type of blade comes in different sizes to fit different size dozers. Blade capacity then is a function of blade type and physical size. Manufacturers' specification sheets will provide information concerning blade dimensions.Manufacturers provide blade ratings based on.SAE Standard. The purpose of SAE Standard is to provide a uniform method for calculating blade capacity. It is for making relative cornparison of dozer blade capacity and not for predicting productivity in the field. Vs = 0.8WH2

Vu = Vs + ZH(W-Z)tan X0

where

Vs = capacity of straight or angle blade, in IcyVu = capacity of universal blade, in lcyW = the blade width, in yards, exclusive of end bitsH = the effective blade height, in yards

Z = the wing length measured parallel to the blade width, in yardsx = the wing anglePrevious Experience Properly documented past experience is an excellent blade load estimating method. Documentation requires that the excavated area be cross-sectioned to determine the total volume of material moved and that the number of dozer cycles be recorded. Production studies can

also be made based on the weight of the material moved. In the case of dozers, the mechanics of weighing the material is normally harder to accomplish than surveying the volume.Field Measurement A procedure for measuring blade loads follows:Obtain a normal blade load:

a. The dozer pushes a normal blade load onto a level area.b. Stop the dozer's forward motion. While raising the blade move forwardslightly to create a symmetrical pile.c. Reverse and move away from the pile.

Measurement a. Measure the height (H) of the pile at the inside edge of each track. b. Measure the width (W) of the pile at theedge of each track.c. Measure the greatest length (L) of the pile.This will not necessarily be at the middle.

Computation: Average both the two height and the

two width measurements. If the measurements are in feet, the blade load in lcy is calculated by the formula

Blade load (Icy) = O.0139HWL

Material TypeThe type and condition of the material being handled affects the shape of the pushed mass in front of the blade. Cohesive materials (clays) will "boil" and heap. Materials that exhibit a slippery quality or those that have a high mica content will ride over the ground and swell out. Cohesionless materials (sands) are known as "dead" materials because they do not exhibit heap or swell properties. Cycle TimeThe sum of the time required to push a load, back track, and maneuver into position to push again represents one dozer production cycle. The time required to push and backtrack can be calculated for each dozing situation considering the travel distance and obtaining a speed from the machine's performance chart. Dozing, however, is generally performed at slow speed, 1.5 to 2 mph. The lower figure is appropriate for very heavy cohesive materials. Return speed is usually the maximum that can be attained in the distance available.Maneuver time for dozers is as under:

When using performance charts to determine possible speeds, remember the chart identifies instantaneous speeds. In calculating cycle duration, the estimator must use an average speed that accounts for the time required to accelerate to the attainable speed as indicated by the chart. A typical chart for a dozer is shown below;

ProductionThe formula to calculate dozer pushing production in loose cubic yards per a 60-min hour is

Many manufacturer provide production curves for dozer and blade type etc. a sample curve provided by Caterpillar is shown below:

These curves are for standard conditions and needs to be modified for site conditions. The factors to be considerd are;

Material – weight Correction Factor CF = 2,300lb/LCY(ideal)/actual lb/LCY

Operator correction factor - use table provided . Material – Type Correction Factor - use table

provided Operating technique Correction Factor - use table

provided. Visibility Correction Factor - use table provided Efficiency Factor - use table provided or assume

number operating per hour

Machine transmission factor - use table provided

Blade adjustment factor - use table provided.

NOTE: This chart is based on numerous field studies made under varying job conditions. Correction factors apply to cater for varying conditionsKEYA —824-SB —834-SC —D7G-7SD —D7R-7SE —814-SF —D6R-6SG—D3C LGP

Grade Correction Factor - use chart/graph

provided

Example 1Given the dozer production charts, what is the average hourly production(LCY/hr) of a straight-blade D7 moving hard-packed clay an average distance of 200 feet, down a 10 percent grade, using slot dozing. The estimated material weight is 2,500 lbs per LCY. The operator is of average ability and will work during daylight hours. Expected efficiency is 50 minutes per hours.

How much time will it take to move 3,000LCY of hard packed clay, using one D7 dozer using the production rate figured out above?

How many D7 dozers would be required to move 3000 LCY of clay in 7 hours?

Using std curve ideal production of D7 dozer = 300 LCY Material Weight Factor = 2300/2500 = 0.92 Operator Factor from table =0.75 Material Type = 0.8 Operating Technique = 1.2 Visibility Factor = 1.0 Efficiency Factor = 50/60 = 0.83 Transmission Factor = 1.0 Blade adjustment = 1.0 Grade correction = 1.15

Total correction factor =1.15x0.92x0.8x0.75x0.83x1.2=0.63Actual Production= 300x0.63 = 190 LCY/ hrTime to move 3000 LCY= 3000/190 = 16 hrsNo of Dozers to complete work in 7 hr = 16/7or 3000/(190x7) = 2.25 say 3 Dozers

Useful Hints Choose the most appropriate tractor and blade

combination for the expected job conditions. Downhill dozing may greatly increase dozer

production. Under some conditions it may be more efficient to

pile up several blade loads at the brink of the hill and then push them to the bottom of the hill in one pass.

Slot dozing utilizes spillage from the initial dozer passes to form ridges on each side of the dozer' s cut area.

Slot or trench is created greatly increases the load that the blade can carry to the dump area.

Slot dozing may increase dozer production up to 50% under favorable grade and soil condition s.

Blade-to-blade dozing utilizes two or more dozers operated in parallel with their blades almost touching to increase blade load considerably.

However, it is usually not efficient for dozing distances of less than 50 ft (15 m)