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The automobile - unity in diversity
G Venkatesh
The automobile is very much a convergence of different engineering disciplines,
a culmination of various manufacturing processes in a final assembly and a
congregation of many materials, all of which move together as one single unit,
when the fuel burns and reciprocates the piston. A car - for that will be the
scope of this feature, and 'automobile' in this feature is meant to be
synonymous with a 'car' or a light commercial vehicle - is thus a convergence, a
culmination and a congregation!
Metals and alloys form the lion's share of the weight of the automobile,
while textiles, rubber, wood, paper, asbestos, fluids (water, brake fluid,
lubricants, fuel, exhaust gases, air) etc., take the remaining sector of the
pie. A heterogeneous bag, that moves on wheels?
Range of metals and alloys
This feature will not be a time copy for the simple fact that developments
are taking place by the hour, and replacements and substitutes are being
suggested and tried with much greater enthusiasm and vigour in the auto industry
worldwide. The systems are similar no doubt but not the same. The powerhouse and
the associated components in the engine compartment, transmission system, auto
interiors and electricals, chassis, body and suspensions form the blood, flesh,
bone and muscle of the automobile, though not necessarily in that order. But
each of these systems is modified and developed ad infinitum, to evolve new
avatars, each one better than the other in some respect.
There are no limits to the number and the types of alloys that can be made
and used in an automobile. Every alloy is distinct and different from the other,
and even small changes in the percentages of alloying elements makes one behave
different from another, as far as mechanical, and/or thermal and/or electrical
properties are concerned. Well, though the base metal may be the same, one alloy
may be stronger than the other, while the second may have better corrosion
resistance than the first.
There are hundreds of discrete components which are fastened together by
welding, soldering, riveting, or by using screws, nuts, bolts and washers, or by
thermal bonding or adhesives. These parts are made up of different materials - a
guess on the number would be very much off the mark. The Bill of Materials is
vast enough, just as the Bill of Components is.
The leader of the pack
Well, that sub-heading should read - The Leaders of the Pack - and this
appellation goes to steel, or rather iron and its alloys. Iron alloyed with
carbon is steel and this steel can be alloyed with a variety of ferro alloys to
modify its properties. Vanadium, molybdenum, niobium, titanium, chromium,
nickel, manganese are but a few of the many metals which make their way into
steel to yield alloys with special properties. These could be greater toughness,
better corrosion resistance, improved ductility, superior thermal resistance
etc.
Steels, if one could label all these alloys thus, are used for the envelope
that one sees around the engine compartment and the interiors. In other words,
the chassis, the doors and door pillars, the wings, floor panels, roof and roof
pillars are all generally steel. (May it be noted here that aluminium-bodied,
all-aluminium-engine cars have plied the streets and still do so, courtesy Audi,
Volkswagen, Rolls Royce, Citroen and Honda, to name a few carmakers. But these
are yet to swell in volumes). The valve units, shafts, gears in the gearboxes,
clutch units, suspensions, fasteners (nuts and bolts) etc., are all made of
different types of steel, with the function determining the choice of the alloy.
The engine cylinders (block) and the connecting rods are usually of cast iron.
The best for the last - stainless steel, perhaps the blue-eyed boy of the
group, with ample chromium and nickel in it, to provide it with an unsurpassable
corrosion resistance, and a sparkle that makes it stand away from the 'pack of
steels'. Stainless steel has been tried in lieu of steel and aluminium as a
material for the autobody parts by Volvo. This automobile is still a concept
car, but is likely to hit the road soon. Let that happen when it will, but at
the present moment, Stainless steelis found in the casings of the catalytic
converters beneath the vehicle, and perhaps in smaller parts within the
automobile, which have to resist corrosion, as a suitable alternative. When we
speak of stainless steel, we are speaking of iron, carbon, chromium and nickel.
Over 12% of chromium and about 6-7% or thereabouts of nickel. Thus, we have
covered iron, chromium, nickel and a host of alloying elements generally termed
as ferro-alloys as they are added to iron and carbon to improve the properties
of steels.
The non-ferrous teammates
If iron shoulders the burden as the skipper of the team, there are deputies
by the handful, each contributing to the grand whole - the contraption on
wheels. The first name is aluminium. The baby of the team, but very much a
prodigy, on which the future of the team would hinge in the years to come!!
Aluminium is commonly used in combination with alloying elements like silicon,
magnesium, manganese, copper, zinc and nickel, for engine housings and covers,
the crankcase, the pistons (Al + Si) which reciprocate within the cylinders, and
the wheels (Al + Mg) that provide the link between the rubber tyres on the one
hand and the braking system, chassis and steering unit of the automobile on the
other. It is being tipped as the metal which will take over from steel very
soon, just as it already has on the engine front. As mentioned earlier,
all-aluminium auto bodies have already been tried with success. The present
global average weight of aluminium per automobile is around 100 kg, but this is
expected to shoot up to over 300 kilograms in the years to come.
Well, apart from the above, aluminium has also been vying with copper for a
place in the heat exchangers in the engine compartment - the radiator and the
air conditioner. While copper gets the nod for better thermal conductivity,
aluminium is sometimes preferred for its lightness. While these are the uses
which hog attention, there is one which often gets overlooked. The white metal
bearing linings which support the crankshaft and the other shaft spindles in the
engine compartment have a small percentage of aluminium in them. Of course, the
base metal in these bearing alloys is generally lead or tin, with cadmium,
copper, aluminium and other elements added in small percentages to confer
suitable functional properties.
Conductor wars
It has always been copper versus aluminium in several applications and within
the automobile, the contest has, as mentioned earlier, been for the heat
exchanger function. When it comes to the wiring from the lead-acid battery to
the electrical and electronic components, including the starter motor and the
ignition coil, copper wins 'hands-down' due to its superior electrical
conductivity. Obviously, thin wires do not add much to the weight of the vehicle
( about 10 to 30kg ) and replacing copper with aluminium is not going to bring
much of a reduction in weight; in fact it may result in more losses.
With bigger batteries about to storm the scene and the auto electrical
circuit waiting to be redesigned in high-end cars, there will be a demand for
highly efficient motors and alternators. This would necessitate purer copper in
the coil windings, and hence a little more of the red metal, devoid of the
impurities.
The other four base metals
There was a mention of lead and tin being the base metals in the crankshaft
bearings. Well, lead and tin together as an alloy figure in the solders that are
used to solder on the printed circuit boards. Apart from lead, copper and tin,
there is some silver (a few grams), used as contactors, to ensure that the
passage of electric current through the circuit components is reliable and the
losses at junctions are minimized. Gold is used on the contact surfaces of many
critical terminals on the wiring harness. Tin may end there, but lead finds use
in yet another corner of the engine compartment -in the big battery that
silently supplies all the energy needs of the car, the battery which lets you
listen to heavy metal (pun intended) music, have cool air in your cabin, and
most importantly, ensures that the vehicle gets going in the first place!
Pure lead and lead oxide dipped in a solution of sulphuric acid and lead
sulphate put life into the electrical circuit, as soon as the ignition key is
turned on. It gets converted into lead sulphate and has to be recharged and
ultimately replaced someday - superannuated! With bigger batteries (higher
voltages) likely to find themselves seated under the bonnets of Volkswagen and
Benz luxury cars to begin with, more lead would be consumed by the battery
manufacturers
That leaves us with zinc. Die-cast carburettors, (though a dying breed with
the use of more and more fuel injection systems), sleek, light and thin-walled,
easily formed into the complex shape that a carburettor is supposed to have,
have become an important application for zinc, which is mined along with its
cousin - lead. While the latter lodges itself in the battery, bearings and the
bonds between wires, the former finds itself in the air-fuel stream, performing
the key task of carburetion, and also in the door locks and ashtrays.
Precious metals
Ferrous, non-ferrous and now precious metals. Silver has already been touched
upon. There is platinum, palladium and rhodium within the SS casing of the
catalytic converter located below the vehicle in the exhaust system. These serve
as catalysts to oxidize the carbon monoxide and unburnt hydrocarbons, and reduce
the nitrogen dioxide that stems out of the combustion chamber, to form carbon
dioxide, nitrogen and water vapour - all innocuous constituents of the
atmosphere.
Metal tussles
The Al-Cu war will rage on and so will the tussle between steel, stainless
steel and aluminium, each vying for a greater share of the weight pie of the
automobile. Newer alloys and better manufacturing processes will keep altering
the composition pie of the automobile. Shackles have been broken and auto makers
and auto component manufacturers are welcoming innovative ideas, and going the
whole hog to 'try every stunt in the book and add more pages to it' to build
fuel-efficient, lighter and non-polluting automobiles.
If a cat, mouse and dog could be made to live in harmony, and form a
super-trio, well, mankind will have achieved the impossible. Putting conflicting
ideas together and assimilating them into a beneficial whole, is what
technologists are aiming at, to get the best of all the worlds!
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