Midterm Exam #3
Trucks
InstructionsThis test consists of a series of questions that are largely independent of each
other. Each question is intended to test your knowledge of some particular
aspect of truck selection and production estimation. Unlike other exams or
many projects that you have done in this class the answer from one question
is usually not an input to the next question. Thus question #5 asks you to
calculate a truck cycle time, while question #6 asks you estimate total mine
production for the year but does not use the truck cycle time you calculated
in #5 to get that answer. One thing that is consistent in this exam – you will
always be mining carnotite uranium ore, and you will always be using a Cat
773 D with a flat floor. This means that your truck weights from problem #1
will be used as inputs for later problem calculations.
The exam is open book and open notes, however, the tables at the end of the
exam should provide you all the information, values, and constants needed
for your calculations without having to go on separate fishing trip through
books and notes to find the needed values. You should probably review the
included tables so that you will know what material is available and where it
is found.
In general, you will need to put your answers and calculations on a separate
sheet of paper as the space on the exam is generally inadequate for the
purpose. Question #3, however, specifically requires you to mark on a
retarder or gradability chart the way you calculated your speed. This will
require you to make entries on one of the charts at the end of this exam.
IGlow-In-The-Dark Mining is open pit mining carnotite uranium ore.
The mine is planning on using Cat 773Ds with flat floors for mine haulage.
The ore is abrasive so they plan on using a bed liner. For reasons of
clearance and to avoid spillage they will limit the trucks fill to struck
volume only. Using the page from the Cat handbook shown below, indicate
the empty and full weight of the truck for the stated conditions.
(Note – Other problems depend on these empty and full truck weights – if
you do not do this problem then substitute 48 tons empty and 96 tons loaded
for the weight of the truck).
IIRandy Reject just got a Mining Engineering degree from Missouri
Rolla. For the 773Ds hauling carnotite uranium ore as above he proposes
the trucks should be loaded using Cat 980G front end loaders with 6 cubic
yard bolt on edge general purpose buckets (See Cat handbook page
attatched). The 6 cubic yard buckets are expected to actually hold 5 cubic
yards of swelled material. Aside from the fact that Randy obviously
graduated from the wrong school can you give any concretely defensible
reasons why his proposed loader size should be rejected? What specifically
are the reasons if you believe it should be rejected if that is in fact your
opinion? If you believe the loader is acceptable indicate which checks for
compatibility that you have performed and found to be satisfactory.
III- On one segment of the road that the Cat 773D trucks will encounter,
they will be required to carry a full load of material up a 7% grade through
loose dry sand for a distance of 1200 feet. The material included at the back
of the test includes tables of rolling resistances, friction factors, gradability,
and retarder charts. Use these tables to calculate the total effective grade for
this road segment, then use either a retarder or gradability chart (which ever
one you think is appropriate) to calculate the maximum possible speed that
the trucks engine and drive train are mechanically built to sustain (there may
be all sorts of field conditions where a driver would not or could not go this
fast but this question pertains only to mechanical capabilities of the truck).
Mark on the chart how you got the answer.
IV- Using the information provided in the tables and charts at the end of
the test, together with your superior knowledge and mastery of truck cycle
time calculations determine the amount of time the Cat 773 will take to go
over the 1200 foot road segment from #3 if the truck enters the segment
already going 20 miles per hour.
VNow assume that your fleet of cat 773 trucks will follow this loading
cycle (Please note that this question is disregarding any speed capabilities or
times you calculated in questions #3 and #4). Haulage Segment #1 -
Following being loaded the truck will drive 200 feet through a congested
area (trucks coming in and out from loading). The mechanical maximum
speed capabilities on this segment are 25 miles per hour. Haulage Segment
#2 - The trucks will then drive over 2700 ft of road while loaded at
maximum speeds of 25 mph. Haulage Segment #3 - The truck will then
drive 150 ft, spot, and dump the material. Entering the 150 ft section,
spotting and dumping will take 2 minutes (Note that I included all your
travel time through haulage segment #3 in the dump cycle time). Haulage
Segment #4 - The truck will then pull away through the 150 ft congested
area. The truck is mechanically capable of traveling 40 mph on this short
segment (although you may not want your driver to even try to go that fast).
Haulage Segment #5 - The truck will then travel the 2700 ft return road at
up to 40 mph. Haulage Segment #6 - The truck will then enter a 200 ft
congested loading area. Again the truck could go at 40 miles per hour but
you probably will not want the driver to go that fast. The truck will take 2.5
minutes to load before beginning the cycle over again. The mine works with
10 hour shifts under hot conditions where the ton mile per hour rating of the
tires is 225.
A- Using the tables at the end of the test and your own judgment
indicate any haulage segments where you wish to impose a
speed limit less than the maximum speed the truck is
mechanically capable of reaching. Indicate what speed you
wish to limit to. (Remember for haulage segment #3 your
moving cycle time was included with your dump time and
therefore you will not do any moving cycle time calculations on
haulage segment #3).
B- Using the tables at the end of the test select appropriate speed
factors for each segment of the haulage route (except haulage
segment #3).
C- Calculate the cycle time for one haulage cycle with the truck
under the stated conditions. (Note – Since Question D depends
on the answer to C, if you do not complete problem C substitute
9 minutes for the cycle time from C).
D- Given the hot conditions at the mine, will you have to slow the
trucks down or impose rest times on the trucks to prevent the
tires from overheating during those 10 hour shifts? Show
supporting calculations for your answer.
VI- Suppose the uranium mine will have 5 trucks and that each truck could
produce 500,000 tons of ore if it were running all the time the mine was
operating. Suppose there is one loader available to service these trucks and
that the loader is available 90% of the time. Suppose also that the truck
cycle time is 13 minutes and the loader takes 2.5 minutes of that time to load
the truck. Under these conditions, how many tons of ore would you expect
to be able to produce from the mine? Show your calculations that support
your answer.
Speed Restrictions Suggested by Surface Mining (1rst Ed)
Congested Area Guideline
Down-Hill Grade Guideline
Loaded Truck Speed Factors
Empty Truck Speed Factors
Caterpillar Match Factor and Bunching Tables