Bulldozers
The bulldozer is a versatile machine. It can be used
for moving earth over distance upto 100 m, clearing and grubbing sites,
stripping top unwanted soil, excavating to a shallow depth say upto 200 mm at a
time, pushing scrapers, spreading soil for leveling areas, however there are
four-wheeled dozers with large-powered engine. The wheel dozers exert higher
bearing pressure as compared to track-dozers.
Dozers excavate and push earth with the help of a
stiff welded steel blade fitted in front and controlled by two hydraulic
cylinders. Blades are of four types. The straight S-blade is used for forward
pushing of earth. U-blades have large capacity, and are used for pushing loose
materials. Angle A-blades are used for pushing soil to one side rather than
hauling it forward as is required in hill road formation cutting. Push P-blades
are used for push loading a scraper. A dozer can also be fitted with a bachhoe
attachment for ripping hard soil and rock, and a winch for uprooting trees,
skidding boulders and heavy materials.
Ideal output for dozing soft soil depend upon the
engine power, straight blade capacity and dozing distance.
This ideal output, measured in the bulk volume (loose
soil), assumes forward dozing speed of 3 km/h, return speed of 6 km/h,
manoeuvring time of 0.15 minutes, easy going on generally level ground and
dozing of (bank) materials using a strainght S-blade. This ideal production is
corrected to conform to varying conditions as under:
Dozer optimum output = Dozer ideal output x Correction
factor
Output planning data = Dozer optimum output x
performance factor
Where, correction factor leads to the following
effect.
Blade factor – Multiply ideal output by the blade
factor value
Type of blade
|
Blade factor
|
S blade
|
1.0
|
A blade
|
0.75
|
U blade
|
1.25 (used only for loose soil)
|
Transmission system – For direct drive, take 80% of
the ideal output which is based on the power shift system. Direct drive system
output = 0.8 power shift system output.
Grade factor – the manufacture’s manual provides the
data for a change of output with varying slope, but for planning purposes it
can be taken as under:
Nature of slope
|
Effect on output
(%)
|
Downhill working
|
Increases 2.5 x
grade (%)
|
Uphill working
|
Decrease 2 x
grade (%)
|
Soil factor – The ideal output is based on easy-dig
and loose soil. This ideal output should be multiplied by the following soil
factors where the nature of soil differs:
Digging effort
|
Nature of soil
|
Soil factor
|
Easy-dig
|
Loam, sand, gravel
|
1.0
|
Medium-dig
|
Common earth in natural state
|
0.85
|
Hard-dig
|
Hard stiff clay, soft rock
|
0.67
|
Swing factor – the ideal output is stated in terms of
bulk (or low) volume excavated. This output can be converted into-in-place (or
bank) volume by dividing the bulk material with the swell factor.
In-place (or bank) volume (BCM) = Bulk (or loose) volume
/ Swell factor
Example
Determine the output of a bulldozer having 215 HP
engine, fitted with A-blade rated capacity 4.40m3. The dozer is
employed for excavating a hard clayey area with average haulage of 50 meters, on
a ground with down slope of 10%. It has direct drive transmission, and its
expected performance is 50 minutes per hour.
Solution
Output/h = Ideal output/h x correction factor x
performance factor.
Ideal output/h for 50 meter haulage of 215 HP dozer with
‘S’ blade of capacity 4.40 m3 = 160 LCM (approximate)
Correction factors applicable are:
Soil factor for hard digging = 0.67
Blade factor for A blade = 0.65
Grade factor for 10 % down grade = 1 + 2.5 x 10%
(assistance) = 1.25
Transmission factor for direct drive = 0.8
Swell factor of clayey soil = 1.3
Therefore correction factor
= 0.67 x 0.65 x 1.25 x 0.8 x 1/1.3
= 0.42
Performance factor for 50 min/hour working = 0.83
Therefore expected output in BCM
= A x B x C
= 160 x 0.42 x 0.83
= 55.8 say 56 BCM
