Dozer Machines

Dozer

EARTHWORK MACHINES

Mansoor Azam QureshiNUST

Islamabad

2

Dozer

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.

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Components of Dozer

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Types of Dozers

Crawler (tracked) Tractor

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Wheeled Tractor

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Use of Dozers

Dozer 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.

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Type of Works

Dozing Land Clearing Ripping Towing Assisting Scrapers

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Performance Characteristics of Tractors

Tractive 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 Wider tires provide greater contact

area and increase floatation8 October 2013


Comparison of Usage

WHEELED DOZER

Good on firm soils and concrete and Can work on a variety of soils ; abrasive soils that have no sharp-edged pieces not as destructive sharp-edged pieces

Best for level and downhill work Wet weather, causing soft and slick surface conditions, will slow or stop operation

The concentrated wheel load will provide compaction and kneading action to ground surface

Good for long travel distances Best in handling loose soils Fast return speeds, 8-26 mph Can handle only moderate blade

loads

TRACKED DOZER

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Can work on a variety of soils; sharp-edged pieces not as destructive to dozer, though fine sand will increase running gear wear

Can work over almost any terrain Can work on soft ground and over

mud-slick surfaces; will exert very low ground pressures with special low ground pressure undercarriage and track configuration.

Good for short work distances Can handle tight soils Slow return speeds, 5-10 mph Can push large blade load


Dozer Blades

A 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

dozer8 October 2013


Dozer Blade Operation

The design of some machines enables either end of the blade to be raised or lowered in the vertical plane of the blade. Pitching

Tilting

Angling8 October 2013

Pitching of Blade

This 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.

Angling of Blade

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This 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.

Tilting of Blade

Types of Blades

Straight Blade

Angle Blade Universal

Blade Semi

Universal Blade

Cushion Blade8 October 2013 Mansoor Azam Qureshi 14

Straight Blade

Designed for short- and medium distance passes, such as backfilling, grading, and spreading fill material.

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 to 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.

Angle Blade

An 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. It cannot be pitched. The angle blade is very

effective for side-casting material, particularly for backfilling or making side hill cuts.


Universal Blade

This blade is wider than a straight blade.

Outside edges are canted forward about 25°reducesing the spillage of loose.

The cutting ratio is lower for the U than the S blade mounted on a similar dozer.

The U blade's load ratio is lower than that of a similar S blade.

The blade is best suited for lighter materials.

Typical usages are working stockpiles and drifting loose or non cohesive materials.


Semi Universal Blade

This 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 Blade

Cushion 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.8 October 2013 Mansoor Azam Qureshi 19


Production Estimating

A dozer has no set volumetric capacity.

There is no hopper or bowl to load.

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

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Type of material


Fill Factors

Volumetric Capacity of Blade


Manufacturer's blade rating

Previous experience (similar material, equipment, and work conditions)

Field measurements

Obtain a normal blade load

Measure the height (H) of the pile at the inside edge of each track.

Measure the width (W) of the pile at the inside edge of each track.

Measure the greatest length (L) of the pile.


Volumetric Capacity of Blade

Field Measurement

Blade load(lcy)= 0:0138(WHL)

Volume = (0:375)(WHL)/27cf=cy

Dozer Production Cycle

The bulldozer positions to start excavation

The bulldozer scoops or digs for the length of a pass to fill the blade

The bulldozer hauls the load by rolling, crawling, pushing, or pulling

The load is discharged or dumped at the desired location

The bulldozer repositions to exit the dumpsite

The bulldozer backtracks to the loading location

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 while backward move is generally in 2nd gear at 2-3 mph

Maneuver time.


Typical Dozer speeds


Example

A power-shift crawler tractor has a rated blade capacity of 10LCY (7.65 LCM). The dozer is excavating loose common earth and pushing it a distance of 200 ft (61 m). Maximum reverse speed in third range is 5 mi/h (8 km/h). Estimate the production of the dozer if job efficiency is 50 min/h.

Fixed time = 0.05 min From table Dozing Time for 200 haulage= dist/ave speed Dozing speed= 2.5mph or 2.5x88 =220 fpm Dozing time = 200/220 = 0.91 min Return time at 5mph= 200/(5x88) = 0.45 min Cycle Time = 0.05+0.91+0.45 = 1.41 min Production = 10x50/1.41 = 355 LCY( Loose Cubic

Yards) 8 October 2013 Mansoor Azam Qureshi 26


Variable Time Estimate

Time to haul load and return back depends upon Power available is

tractive effort. Gear requirement to

overcome blade load. Travel distance

It is complicated and machine dependent.

Will vary with category of Machine

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Estimated Production Curve Straight Blades

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

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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

Estimated Production Curve Universal Blades


Correction Factors for field Conditions

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.

Grade Correction Factor - use chart/graph provided

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Factors


% Grade vs. Dozing Factor(–) Downhill(+) Uphill

Example Given 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=0.63

Actual Production= 300x0.63 = 190 LCY/ hr

Time to move 3000 LCY= 3000/190 = 16

hrs No of Dozers to complete work in 7

hrs =

16/7 or 3000/(190x7) =

2.25 say 3 Dozers


Example

Land Clearing


Crawler dozers equipped with special clearing blades are excellent machines for land clearing. Clearing of vegetation and trees is usually necessary before undertaking earthmoving operations. Trees, brush, and even grass and weeds make material handling very difficult. If these organic materials are allowed to become mixed into an embankment fill, their decay over time will cause settlement of the fill.

Clearing Operation

Clearing land can be divided into several operations, depending on the type of vegetation, the condition of the soil and topography, the amount of clearing required, and the purpose for which the clearing is performed: Removing all trees and stumps, including roots Removing all vegetation above the surface of

the ground only, leaving stumps and roots in the ground

Disposing of vegetation by stacking and burning8 October 2013 Mansoor Azam Qureshi 35

Use of Dozers for Clearing

Crawler tractors with earthmoving blades.

Crawler tractors with special clearing blades.

Crawler tractors with clearing

rakes.


The major components of a single-angle clearing blade are the stinger, web, cutting edge, and guide bar. The exterior edges of the stinger and web are sharpened like a knife blade by machining with a grinder.

Clearing blades are most efficient when the tractor is operating on level ground and the cutting edges can maintain good contact with the ground surface. It is easier to work with soil types that hold the vegetation's root structure while the trunks are sheared.

Large rocks will slow production by damaging the cutting edges of the blade.

The size, weight, and spacing of the rake's teeth depend on the intended application. Rakes used to grub out stumps and heavy roots must have teeth of sufficient strength so that a single tooth can take the push of the tractor at full power.

Lighter rakes having smaller and closer-spaced teeth are used for finish raking and to clear light root systems and small branches from the ground.

Rakes are also used to push, shake, and turn piles of trees and vegetation before and during burning operations.


Use of Dozers for Clearing

Production Rate

The speed at which the tractor can move through the, vegetation will depend on the nature of the growth and the size of the machine.

It is best to estimate land clearing by the use of historical data from similar projects.

When data from past projects are not available, the estimator can utilize the formula .

Production(acre/hr) = width in ft x speed mphx5280xeff/43560 For e=0.825 given by American society of

agriculture Production(acre/hr) = width in ft x speed mph/10

Production rates calculated strictly from the formula however, should be used with caution.


Tree Count Method

Measure/ estimate size of area to be cleared in acres. Count size and no trees for each size. Determine the average number of each size tree on

a per acre basis( N values) and base time per acre. Determine Basic production factors (M values)from

table. Sum of diameter of all trees per acre above 6 ft in

diameter at ground level. Calculate time to clear one acre, Time (min)per acre for cutting = H [A (B) + MINI + M2N2 + M3N3 + M4N4 + DF] Calculate total time.



Example of Land Clearing

Determine the time required to clear an area 500 ft wide by one half mile long with two 335 hp dozers. Average no. trees/acre 630 with 8 0% hardwoods

• 1-2 ft dia. 120 • 3-4 ft dia. 5

• 2-3 ft dia. 60 • 4-6 ft dia. None

Size of Area = 500x 0.5x5280/43560 = 30.3 acres Size of Do availablezer 335 Hp Two Average No of trees per Acre= 630

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Production Factors

Base Time = 18.22 min

N1= 120 M1=0.2 N2= 60 M2=1.3 N3= 5 M3=2.2 N4=0 M4=6 75 to 100% hardwoods; add 30% to total time (H = 1.3) 25 to 75% hardwoods; no change (H = 1.0) o to 25% hardwoods; reduce total time 30% (H = 0.7) Dense: greater than 600 trees per acre; add 100% to base time

(A == 2.0) Medium: 400 to 600 trees per acre; no change (A = 1.0)


Example


Example

Time to clear one acre = H [A (B) + MINI + M2N2 + M3N3 + M4N4 + DF]

1.3([ 2x18.22]+120x0.2+60x1.3+5x2.2 = 194.27 min/acre

Total Time= 194.27x30.3/(2x60) = 49 hrs

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Rippers


The ripper is the long claw-like device on the back of the bulldozer. Rippers can come as a single (single shank/giant ripper) or in groups of two or more (multi shank rippers). Usually, a single shank is preferred for heavy ripping. The ripper shank is fitted with are place able tungsten steel alloy tip


Ripping Operation

Ripping rock breaks the ground surface rock or pavement into small rubble easy to handle and transport, which can then be removed so grading can take place.

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Factor Affecting Ripping

Down pressure at the ripper tip The tractor's usable power to advance the tip; a

function of power available, tractor weight, and coefficient of traction

Properties of the material being ripped; laminated, faulted, weathered, and crystalline structure.

A rule of thumb in sizing a tractor for a ripping operation is that it must have 1 fwhp per 100 lb of down pressure on the ripper and it must have 3 lb of machine weight per lb of down pressure to ensure adequate traction.


Ripper tip Usage

Short — Use in high impact conditions where breakage problems occur. The shorter the tip, the more it resists breakage.

Intermediate — Most effective in moderate impact conditions where abrasion is not excessive.

Long — Use in loose, abrasive materials where breakage is not a problem. Generally offers the most wear material


Rippability of Rock

Rippability of most rock types is related to the speed at which seismic (sound) waves travel through the rock, it is possible to use refraction seismographic methods to determine with reasonable accuracy if a rock can be ripped.

Rocks that propagate seismic waves at low velocities, less than 7,000 ftlsec, are rippable,.

Rocks that propagate wave at high velocities, 10,000 ftlsec or greater, are not rippable.

Rocks having intermediate velocities are classlfied as marginal.

Rippability potential for various macines are specified by manufacturer.



Rippability potential of Rocks for a typical Machine

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Production Charts Machine rips full-time — no

dozing. Power shift tractors with single

shank rippers. 100% efficiency (60 min hour). Charts are for all classes of

material. In igneous rock with seismic

velocity of 8000 fps or higher the production figures shown should be reduced by 25%.

Upper limit of charts reflect ripping under ideal conditions only. If conditions such as thick lamination, vertical lamination or any factor which would adversely affect production are present, the lower limit should be used.



Example

Data — D10R — No. 10 with one shank. 910 mm (36 in) between passes. 1.6 km/h (1 mph) average speed

(including slippage and stalls). Every 91 m (300 ft) requires 0.25 min to

raise, pivot, turn, and lower again: 91 m (300 ft) = 1

pass. 610 mm (24 in) penetration. Full time ripping (no pushing or dozing

assignment Time per pass=300/88

=3.41 min Cycle Time= 3.41+0.25

=3.66 Efficiency = 45/60

=0.75 Production per cycle= 300x3x2/27

=66.7 BCY Hourly production=66.7x 60x0.75/3.66

=820 BCY

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)8 October 2013 Mansoor Azam Qureshi 51

Education

Dozer Machines