Transcript Trucks and Loaders - Supplemental Teaching Resources

Matching An Excavator to
Our Trucks
©2009 Dr. B. C. Paul
Note – These Slides contain tables and information found in the
Caterpillar Performance Handbook.
Backhoes and Excavators
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Backhoe is a digging arm and bucket
attached to the back of a machine
An Excavator puts the shovel on the
front but has pivots on booms on the
arm to make it dig below itself as
opposed to above itself like a
hydraulic front shovel
The 5230ME
It can load a truck up
To 32 feet high
It can dig down up
To 31 feet – that will
Do a 30 foot high
bench
Cat 777 Loading Height
14 feet 3 inches << 32 feet
The Heap Effect
9 feet at a 3:1 slope will create a heap
3 feet higher than the edge of the truck
How high is this center
Ideal load can
Dump the bucket
Onto a pile
Between 17 and
18 feet high
Truck Bed Cross Section
Still easy for a 32 foot
Dump height
18 ft 2 inches
Sizing a Bucket That is
Reasonable for the
Material
A Rock Bucket Holds 21 cubic yards heaped
Fill Factors

The fact that a bucket geometry will
heap to 21 cubic yards does not
guarantee it will fill in the field
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Easy Load stockpile 1 to 1.1
Average 0.95 to 1
Rather Difficult 0.9 to 0.95
Difficult 0.85 to 0.9
Digging down on an intact face is rather
difficult
• May get about 90 to 95% of rated
• About 92% is 19.4 cubic yards
Need to Fill in a
Reasonable Number of
Passes
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If you fill a truck with less than 3 passes
you can’t get the load distributed – you’ll
kill the suspension system
If you take too many passes to fill the
truck will spend a large part of its cycle
time sitting to be loaded.
Guidelines exist as to what tends to be
workable
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Cable Shovels (3 to 4 passes)
Hydraulic Shovels (4 or 5 passes)
FEL (4 to 6 passes)
Backhoes (often 5 to 7 passes)
Cat 769
(Our Little Truck)
Load Capacity is
31.7 cubic yards and
82,533 lbs
But Which Is Limiting?

A Truck can be Weight or
Volume Limited
• Which depends on the material
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Ours is Oil Shale
Material Weights Tables
Exist in Many Handbooks
This one is from the Caterpillar
Performance Handbook
A Material Caution
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In place rock is a solid with only
internal air spaces and pores
For loading and hauling rock
tends to break into chunks that
have air spaces between them
• If you’ve ever tried to put dirt back
in a hole after digging it out you
know what “Swell” means
Always Distinguish
Between Bank and Loose
Volume
The difference between bank and loose weight is huge
Saw some students foul up homework by looking on the internet
And grabbing a weight number with no idea what it was. Many
Internet numbers are bank weights since loose weights are often
Important only in mine planning.
In Our Case We Are Given
the Loose Weight
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2107 lbs per cubic yard
31.7 cubic yards * 2107 lbs/yd^3
• 66,792 lbs
• Rated weight for truck is 82,533 lbs
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Because this truck hit the volume
limit before the weight it is called
Volume limited
• I bet you can guess what would happen
if we were weight limited
Now Back to Matching
That Loader

We want to fill 31.7 cubic yards
of space with a bucket that can
carry 19.4 cubic yards of
material
• 31.7 / 19.4 = 1.63 passes
• This is well under the 3 pass
minimum for a well distributed
load
• This loader is too big for a Cat 769
Lets Check Out the 773
46.4 yards
(I could check for
Weight or volume
Limit but I already
Know and I have
Shown you how
To check)
46.4/19.4 = 2.4
Running Checks on Other
Trucks
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Cat 775 54.3 cubic yards 2.8 passes
Cat 777 79.1 yd^3 4.1 passes
Cat 789 158 yd^3 8.1 passes
• Now we are getting near an upper
practical limit
• Obviously the 793 is just too big for our
loader
• The 789 actually could not turn for
single truck loading but we might
consider drive by if we wanted it.
The integer # of passes
problem
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773 was 2.4 passes
775 was 2.8 passes
777 was 4.1 passes
789 was 8.1 passes
None of these are integer numbers
• The actual fill can be dictated either by
the limits of the material or the need to
match the truck
• Obviously we need to tweek some fills
here to match our truck
Adjusted Fill Factors

For 773 46.4/3 = 15.4 cubic
yards
• 15.4 / 21 = .736 or 73.6% Fill
• 85% is about as bad as it gets
naturally
• The 773 is a bit of a stretch for a
match
• I’m going to drop it.
Continuing Adjustment
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775 54.3 yd^3/ 3 passes
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18.1 yd^3
18.1/21 86.2% fill
That’s realistic enough
3 pass load with 86.2% Fill
777 79.1 yd^3 in 4 passes with 94%
fill – should be doable
789 158 yd^3 in 8 passes with 94%
fill – quite a few passes but for a
back hoe loader it might be
considered
Where Have I Come Out
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A Cat 5230 Excavator with a 21
yard bucket
• Loading a 775 in 3 passes with
Single Truck Loading
• Loading a 777 in 4 passes with
Single Truck Loading
• Loading a 789 in 8 passes with
Drive by Loading
What Did It Take to Get A
Match?
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I Needed to find out whether my
truck was going to be volume or
weight limited for the material
Loader must be able to clear the
edge of the truck and hopefully drop
on top of a heaped truck
I needed to get a suitable bucket on
my loader and determine what a
realistic fill factor was for my
material
Continuing My Efforts

I needed to adjust the fill
factors so that I filled my trucks
in a suitable integer number of
passes.