CHAPTER
- 15
EQUIPMENT
MANAGEMENT TIPS FOR THE CONSTRUCTION ENGINEERS
AND
PLANT & MACHINERY ENGINEERS
AN
INTRODUCTION TO CONSTRUCTION PLANT AND EQUIPMENT
MODERN TREND IN DESIGN
AND MANUFACTURE OF
EARTHMOVING EQUIPMENT
INTRODUCTION
In the year 1953 the cost
of 100 HP tractor was about Rs. one lakh, today it costs Rs.ten lakhs. The same
is true with other construction equipment. The fuel and oil prices have also
gone up almost by eight times. The wages of operator have gone up by 12 times.
All this has resulted in the increase of owing and operating costs of equipment
which has naturally affected production costs.
The manufacturer and
user are now thinking over this issue to find ways and means to reduce the
production cost. In this paper attempt has been made to identify the areas
where the cost can be controlled/reduced.
The owning and
operating cost of equipment consists of depreciation, major repairs and
operating and maintenance cost.
Depreciation will
depend on life and cost of equipment. If the life of equipment is increased and
the cost of equipment is reduced, the depreciation component can also be
reduced. How can this be achieved? By new designs, new construction materials,
by application of computer, and automation. Let us consider few cases here where
this can be introduced.
Material
for Engines
One of the major areas
of research is finding and evaluating new materials for the manufacture of
engine components. Work in this field has two major objectives, firstly, to
develop the engines made of more cost effective material. Secondly, research
into alternative materials is aimed at improving engine performance, producing
lighter engines to give better power to weight ratio, to assist the noise and
emission reductions, and seeking ways to apply novel materials to give greater
fuel economy.
Use of plastic
materials reduce weight and noise. Ceramic materials have advantage of thermal
insulation, resistance to corrosion attack, improved tribological performance.
Materials
for Track Parts
Komatsu, Japan have
produced the world's largest bulldozer. Komatsu D475A with newly designed
elastic support to reduce shocks both to machines and operator. Reinforced
rubber pads are used at support point of idler. Life lubricated roller reduces
maintenance cost.
Tyres
The cost of tyres have
gone up considerably. Its operating charges are next to the fuel. The tyre life
can be prolonged by careful operation and designing new material.
Overloading and
incorrect tyre pressures are major contributory factors to overall owing and
operating costs. Overloading by just 10 percent will result in 15 percent
reduction in tyre life. A 20 percent overload will reduce life by 30 percent.
Correct loading will also make an indeterminate contribution to reducing
overall truck operating costs. Electronic watchdog analyse load on computer and
is transferred as a digital read-out of actual load in truck body to a display
panel in driver's cabin. Large red and green lights on each side of truck
indicate to excavator operator when the optimum load has been reached.
Ordinary tyres are
replaced with tubeless tyres. The nylon cord tyres are now replaced by radial
steel cord tyres which have longer life and thus reduce operating cost.
Thermal
Efficiency
Thermal efficiency to
the extent of 40 percent are legitimately claimed for almost all engines over
six litres capacity. The introduction of new technique in fuel management
including electronic control system, promises to nudge thermal efficiency level
even nearer to magic 50 per cent mark. Use of ceramic liner in exhaust port
with electronic fuel and combustion control system is now essential to boost up
thermal efficiency. Ceramic pistons or teflon coating of pistons is another
technique under investigation. Major problem is to make the ceramic material
stick to a metal.
Fuel
A further problem
facing engine manufacturer, and in turn operators is steadily deteriorating
quality of fuel, notably a consistent downward trend in cetane value.
Deteriorating cetane values means a slight fall in power output and tendency to
give smoke. Lower cetane value means poorer cold starting and more while smoke
in warm-up stage.
Following the onset of
rapid fuel price escalation in 1973, the average specific fuel consumption has
improved more than 10 percent from 230 g/KWh to 200 g/KWh due to development of
adiabatic engine plus bottoming cycle. We expect fuel consumption to go down to
14o g/KWh by year 2000.
Most of the gains were
achieved by relatively minor design changes and more wide spread application of
known technology, such as turbo changing, intercooling, and virtual elimination
of pre-combustion chamber in favour of direct injection system.
Room for further
refinement of the basic technology still exists, but the most significant
economy and performance improvements will come from more sophisticated
advances. Some advance technologies such as cold charge air cooling, electronic
engine controls, turbo compounding and alternative and multifuel engines are
already in use in some parts of world.
Another area for investigation
to aid fuel economy lies in the evaluation of energy losses incurred in
parasite auxiliary equipment necessary for engine operation. The fan,
alternator, lubricating oil pump, water pump etc., cause losses in substantial,
usable engine power. It is calculated that these 'parasite' elements cause a
power loss of upto 11.7 percent of the total off load horsepower from the
engine.
Hydraulics
Hydraulics is heart of
excavator. Available hydraulic power is important, rather than engine power.
Higher engine power only makes it possible to maintain the available hydraulic
power at high altitudes. Hydraulic power is a function of pressure and flow
rate.
The higher the
pressure, the less oil flow required for given force. This makes narrower and
therefore lighter cylinders possible, reduces the frictional heat generation in
hydraulic lines, and oil cooling requirement.
Hydraulic power is
used to operate digging attachment-boom, stick and bucket-swing gear and track
drive. This is achieved either by independent power supply, parallel type power
supply or series type power supply.
Special attention is
given to the design of hydraulic system by Caterpillar, U.S.A. in their new
model 416 backhoe loader. The variable flow, load sensing by hydraulic system
lowers the control lever efforts, reduces fuel use as much as 30 percent
according to Caterpillars. The hydraulic system is said to be leak free due to
both seals and the fact that the valve bank faces front of the machine so that
hoses do not rub together during swing. The hydraulic oil cooler is located at
the front of the vehicle for better roadability.
Transmission
The controversy over
the advantages and disadvantages, potential and practical, of hydrostatic
versus power shift-torque converter transmission continues unabated.
Caterpillars, who make hydrostatic drive crawler loaders, claim that the system
is not as efficient as other in heavy dozing and power train efficiency is
lowered to get the benefits of a power turn. Komatsu say that performance of
hydrostatic is not sufficiently high to justify higher cost. Fiatallis, Italy
doubts about reliability, durability, and operating costs of hydrostatic
components against mechanical transmission.
John Deere, U.S.A.
opines that the hydrostatic transmission offers the greatest benefit in the 75
-150 KW range in the manoeuverability, control response and productivity.
Variable
Speed Drive
These can be
classified into mechanical, electrical and hydraulic system. Mechanical drives
are limited to about 100 Kw, have high maintenance cost, and slow speed change
response. Electrical variable speed drives include the thyristor controlled DC
motor, variable frequency AC system, slip ring and reluctance motor and eddy
current coupling.
Fluid couplings are
available for transmission upto 12000 kw and stepless speed control is normally
possible over the range of 5.1. The main disadvantage is that the speed control
is not as accurate as electric drives. Fluid couplings are hydrodynamic devices
which by their nature incur a degree of slip. Hydraulic motor provides
hydrostatic drive. Direct hydraulic drives are available upto 300 kw at
1,35,000 Nm torque for continuous duty and upto 600 kw at 27,000 Nm torque for
intermittent duty. Overall efficiency is in excess of 85% with little decrease
in speed.
Operation
We have seen above how
the production can be increased by use of computer. The operating charges are
going up day by day and whether we can reduce the same? Yes, we can. A Japanese
firm have developed an excavator equipped with a huge 1.2 cum size bucket. All
operations of the hydraulic excavator from excavation to discharge and movement
of the bucket is controlled by a microcomputer.
The new hydraulic
excavator's operation is microcomputer controlled within the radius of 5m to
10m and 105 degrees to right and left position. Error is only 15 cm. The
machine can discharge 50 cum of sediment per hour.
Dredging is done
automatically according to present programs. The excavator position, direction,
radius, depth and other information is displayed on a control panel for quick
confirmation. Automatic operation cuts down labor cost, relieving the operator
of long hours of monotonous work.
Another factor that is
most relevant in our times is the environmental characteristic of the engine
with regard to noise and exhaust emission.
Operator
Comfort
The operator of a
modern ROPS (Roll Over Protective Structure) cabin equipped equipment is a much
pampered person, compared with the operator of earlier generation equipment.
Sound and vibration - insulated from diesel - fueled mayhem around him,
protected from dust by pressurized air conditioning, he is in better
condition/position to concentrate on the job and does not succumb so quickly to
fatigue.
Manufacturers seem
even more aware than the user contractors of the positive impact of good
working conditions on machine productivity, and further advances in this
respect of machine design are a certainty.
Maintenance Intervals
and Computerized Cost Analysis (CONCA) Maintenance intervals should be considered
under the aspect of directly calculable costs of maintenance and reduced
operatability and productivity of a piece of equipment as a result of down
times involved in maintenance.
Based on long-time
tests and on-going development works, the diesel engine manufacturers therefore
seek to reduce the maintenance expenditure and to supply the customer with
exact data concerning overall maintenance, for a planning and calculating costs
that the engine in his equipment will consider.
CONCA system is in use
these days.
The objectives of
ongoing development works are :-
i. Extending the
maintenance intervals with a view to further reducing the costs and down times;
ii. Simplifying the
maintenance procedure in order to relieve highly qualified workshop personnel in
their works.
iii. Minimizing
potential sources of trouble that are due to poor maintenance or failure to
fully meet the maintenance specifications.
Multipurpose
Machines
The costs of equipment
have gone up very high. No contractor can afford to purchase a equipment with
one or limited use. Various attachments are now being made available that will
reduce additional equipment cost. Similarly the labor and operational costs can
be reduced.
For example,
articulated backhoe can now be used as pole planter, dozer and loader. Uses of
impact breaker, auger boring machine, pile boring are some of the other uses of
base excavator machine.
Impact ripper instead
of ordinary ripper on crawler tractor helps to increase production.
X. FUEL AND NEW
MATERIAL
Fuel efficiency has
dissolved into total system efficiency as the "What new" in diesel
engine design especially when it is applied to construction machinery. Some of
the changes that are on drawing boards in the next several years include the
following major mile post.
1. Higher BMEP engines
to wiring more power out of the same package.
2. Exclusive increase
in the use of electronic control and information system both to operation and
maintenance.
3. Broaden fuel
tolerance for operation or on extended portfolio of fuel.
4. Lengthen engine
life time to suit changing needs of contractors throughout the world.
Following the onset of
rapid fuel price escalation in 1973, the average specific fuel construction
production line diesel engine has improved more than 10% from 230g/kw to
something approaching 200g/kw. In year 2000, with adiabatic engine bottoming
cycle we expect to reach fuel economy of 146g/kw.
In California, for
example, Komatsu involved in demonstration program utilizing agriculture
applications fuel by methanol derived from fruit and vegetable decomposition.
Most of these alternative fuels involve blend of diesel fuel with methanol or
some other hydrocarbon derived from organic material.
Diesel engine life has
been extended on heavy duty and to the point that the major rebuilt can now
extend life well beyond 10,000 hours.
New materials have yet
to make any major input on diesel engine design. Ceramic inserts or coating
have been applied to pistons, valves, post head faces and upper liners to
reduce heat loss and thereby improve efficiency. But the big problem is making
the ceramic material stick to metal.
Teflon coating of
pistons to reduce friction is another technique under investigation.
Electronic systems
have been used successfully by KHD industrial engine for two years now, to
control the cooking oil temperature and flow.
XI. EQUIPMENT OF
FUTURE
As stated earlier, the
prime-mover will be drastically changed from present design. This would be
concerned with safety, pollution control and operator control. In distant
future, use of fuel cells and closed cycle engine may come up. Nuclear rather
than fossil fuel will be used. More electric and hydraulic transmission are
expected to be used in future. The future controls will be marked automation.
No comments:
Post a Comment