STEEL BOILED LIKE WATER AND CUT LIKE PAPER
OUR BOY FRIEND SEES HOW SCIENCE HAS TURNED THE GREATEST KNOWN
HEATS TO THE EVERYDAY USE OF MANKIND
"HOW hot is it in that furnace?" asked the scientist's young friend
as he poked about the laboratory one day.
"That is not very hot now, but we could increase the temperature to
about 4,000 degrees Fahrenheit if we tried hard enough," answered
the man who, outside of his work, enjoyed best of all the visits of
the boy. "But the heat of the laboratory furnace most of the time is
nothing compared to the heat that we can put to practical use through
a couple of new inventions I have been trying here."
"What are they for?" asked the boy, immediately all interest, for
he was a member of the metalworking class in his school, and was
constantly on the lookout for better ways of working in iron, steel,
copper, and brass.
[Illustration: THERMIT IN ERUPTION
With a blinding, dazzling glare and a gentle hissing the thermit
in a white-hot molten mass fills the mould and runs down the
sides like volcanic lava.]
[Illustration: DR. HANS GOLDSCHMIDT
The inventor of Thermit.]
"Well, they both are used in welding metals and in one--the
thermit process--the hardest steel can be reduced to a molten mass of
white hot metal boiling like a tea kettle on a stove, in about a half
a minute. You see that requires a great deal of heat," continued the
chemist, "and in fact the temperature is 5,400 degrees, Fahrenheit.
"The other process that I have been trying is known as autogenous
welding, and in this even a greater temperature is generated than
by the thermit process. In the tiny flame no bigger than the point
of this pencil that comes from the autogenous welding torch the
temperature is about 6,000 degrees Fahrenheit."
"My!" said the boy, "how could any one ever measure such a heat as
that?"
"Science teaches us how to do that just as science taught us how to
produce these great heats. Why, you know, in the electrical furnaces
at Niagara Falls they produce a heat that they think reaches the
10,000 degrees of the sun. Outside of that, however, the thermit
process and the autogenous welding process attain the greatest known
heats."
"Those must be fine," said the boy, "because before our schools began
to teach metal working, I used to play blacksmith and heat pieces of
iron in the fire, but I could never do anything with it, and now that
we are learning welding in the blacksmith shop at school I see what a
hard job it is. I wish we could use these processes at school."
"Well, you will be able to use them some day," said the scientist,
"but it took science a long time to find out how to produce and use
very high temperatures.
"In the stone age, thousands and thousands of years ago, when men
lived in caves and ate raw the animals that they caught with their
hands, fire was first discovered by an accident. There are many
legends of how the hairy savages that populated the earth fell down
and worshipped the aboriginal scientist who taught them how to warm
their caves.
"Soon, however, fire became a necessity of life to mankind, for it
was discovered that meat tasted better when exposed to a flame--that,
is, when it was cooked--than when it was raw. That was a big step
toward civilization, but it was a bigger one when some wild mountain
tribe found that they could make much more deadly weapons than the
rude ones they chipped from flint, by melting down a certain kind of
rock and fashioning it into spear heads, arrow heads, and hatchets.
From that time on the development of the art of metal working took
only a few thousand years, until to-day man's great knowledge of
metalurgy has enabled him to make such tremendous fighting machines
that war is becoming entirely too destructive, and too expensive a
thing to rush into lightly. Thus, heat and metal working are helping
to force the world forward to another step in civilization--universal
peace.
"After learning how to make these hardest of metals, man has now
solved the problem of making them boil like water with the thermit
process and of cutting them like paper with the oxy-acetylene gas
torch, all in less than a minute.
"You see this bag of coarse black powder that looks like iron
filings? Well, it is the thermit. Put it into a crucible, set off a
pinch of ignition powder on the top, and the whole thing will ignite
in half a minute, throwing off a blinding white light and thousands
of sparks like beautiful fire works. That is the thermit reaction.
"You know more about the oxy-acetylene gas torch, for in your metal
working at school you used the gas blowpipe to make a very hot flame.
The oxy-acetylene gas torch is just a high development of this, for
instead of ordinary gas, acetylene is used and instead of air we use
pure oxygen."
The caller sat down and asked his friend to tell something more about
these two marvelous inventions. The story was several days in the
telling, for there were visits to foundries and experiments in the
laboratory, besides many long talks.
"First we will see about thermit," said the man, and began to talk as
he worked over a crucible.
THERMIT HEAT PROCESS
As a result of his discovery that by starting a terrific battle for
oxygen between two metals he could reduce one of them to almost
absolute purity, Dr. Hans Goldschmidt has converted to the use of man
a process of welding so simple and yet so forceful that it is making
world-wide changes in the working of metals. This battle itself is
the most interesting feature of the Goldschmidt process because of
the terrific heat it generates.
Imagine sticking your finger into boiling water. By so doing you
would be exposing your flesh to a temperature of 212 degrees
Fahrenheit. Imagine sticking your finger into a pot of molten lead if
even for the fraction of a second. You know very well what the effect
would be. The temperature is 618 degrees Fahrenheit. Still again,
think of a redhot iron. This is about 1,652 degrees Fahrenheit. Steel
boils at 3,500 degrees.
They are all hot enough, but compare them with the temperature of
5,400 degrees Fahrenheit or about 3,000 degrees Centigrade, which
is attained by the thermit reaction. The range of temperature in
which we can live extends from a little over 100 degrees to 70 or 80
degrees below zero, and yet man can so direct the heat of the thermit
reaction that it will work for him.
The commonest use of the process is in welding steel or iron, such
as broken parts of machinery and welding steel rails, and steel or
iron pipes. Besides this, the thermit process will reduce many metals
to a high degree of purity. After spending a few minutes in seeing
how the inventor of this process came to discover it, we will take a
little trip in our mind's eye to some of the places where the thermit
process is in use, and see what happens.
As you know, metals rarely come from the mines in a state of purity.
They usually are very much mixed up with rock, slag, and other
minerals, so that it takes a complicated process called smelting to
separate them. Even then they are not pure, and more complicated
processes have to be gone through with. Oxides, or metals that have
been oxidized, are common because oxidization merely means that the
metal has been burned so that each atom of metal has taken up an
atom of oxygen to make what is called a molecule of oxide. Iron ore
is usually found in the form of iron oxide, because when this great
earth was nothing but a swirling ball of burning gases, probably as
hot as the sun, gradually cooling and forming a great cauldron of
molten matter, boiling and bubbling more fiercely than the hottest
cauldron of molten metal in any steel mill, much of the matter
that later became iron ore was burned or oxidized. Other chemical
actions too technical for our attention just now were responsible for
other forms of ore, such as sulphides, etc. When the earth cooled
sufficiently to become solid, these things were completed, and they
only had to remain hidden away under the surface for ages and ages
until a little man who could live but a hundred years at the utmost
solved the deepest secrets of the earth's formation.
Thus, to obtain pure metals the oxygen must be removed from the
oxide. In other words, it must be reduced. Plainly such reduction
was a problem of smelting, but Doctor Goldschmidt in his efforts to
obtain purity was working along lines of smelting, in his little
German laboratory, very different from the ones in general use.
His first object was to reduce iron oxides. First, he knew that
aluminum has a great affinity for oxygen, or, in other words, when
the two are heated will absorb oxygen like a sponge will absorb
water, only more forcibly and more violently than any such comparison
even faintly suggests. In yet other words, aluminum wants oxygen
more than any other metal does. Of course no chemical changes would
occur if a piece of iron oxide and a piece of aluminum were set side
by side, any more than we would have gunpowder if we set a chunk of
saltpetre, a chunk of sulphur, and a chunk of charcoal all in a row.
The iron oxide and the aluminum would have to be mixed by cutting
or filing them into small pieces and making a coarse powder. Still
nothing would happen without heat to start it.
If you collected some flakes of iron oxide in the palm of your hand
they wouldn't look to you like very promising material for a bonfire,
and you wouldn't be in any danger of an explosion, but you would
have something in your hand that would burn, nevertheless. If you
sprinkled your iron filings over a gas flame, Welsbach burner, or
over a common lamp chimney the heat would cause them to splutter and
fly out with all the brilliancy you know so well when the blacksmith
gives the redhot horseshoe the first pound.
Of course Doctor Goldschmidt knew all this, just as he knew that
the way the aluminum would take the oxygen away from the iron oxide
was through heating the coarse powder of filings to a very high
temperature. But this was attended with serious troubles and many
times the German scientist came near losing his life in explosions in
his laboratory.
At first he failed to get the mixture hot enough and nothing
happened. Bit by bit he increased the heat under the crucible
containing the filings until it reached about 3,000 degrees
Fahrenheit. At this point the metals were hot enough to fuse or run
together and the whole thing reacted with such violence that it
amounted to an explosion. What really happened was that the mass
reached the temperature where the aluminum could take the oxygen
from the iron oxide, and it did so with such force that an explosion
resulted.
Doctor Goldschmidt then saw his problem. It was that of devising some
way of heating the mixture to a temperature sufficient to gain the
reaction, but without an explosion.
After trying everything that he could think of, he conceived the plan
of leaving the crucible in the open air and starting the heat at just
one point first, instead of heating the whole thing in a furnace.
He did this with a pinch of ignition powder placed on the top of
his pile of iron oxide and aluminum. The ignition powder was simply
lighted with a match.
What happened?
Thermit was discovered.
The heat, or reaction started at one point, gradually spread through
the whole mass, and reduced it to white-hot molten material.
In other words the application of intense heat at one point in the
mixture was sufficient to fuse the metals and start the battle
between the iron oxide on one side and the aluminum on the other, in
the immediate vicinity of the point where the heat was applied. As
the few particles set off by the ignition powder struggled for the
oxygen they themselves generated heat--terriffic heat--which gave
a high enough temperature to start the particles that were their
next-door neighbours to struggling for the oxygen. These in turn
generated heat to set off their own neighbours, and so it went.
In far less time than it takes to read this, Doctor Goldschmidt
saw the whole crucible of dead mineral particles take on life and
become white-hot liquid metal. Scientifically speaking, the reaction
had spread through the whole mass in less than a minute, but what
Doctor Goldschmidt saw was a blinding white light, more intense than
any arc lamp, throwing off a little cloud of white smoke or vapour.
Apparently the whole thing was burning up. He only heard a little
hissing as the metals battled for the precious oxygen.
There was no explosion, there was no violent scattering of molten
particles, and there were no noxious life-destroying gases such as
come from the explosion of gunpowder, dynamite, or even the burning
of coal. And yet the seething, molten metals in the crucible reached
a temperature second or third to the highest ever registered by man.
Five thousand four hundred degrees--think of it!--more than half as
hot as science tells us is the sun which makes this world of ours
habitable.
But what was the result of this temperature which staggers the
imagination?
Just this. Doctor Goldschmidt knew that the aluminum had won the
prize of battle and had paid the price of victory.
The conquered iron was at the bottom of the crucible, a molten mass
of pure metal, while the victorious aluminum, seething on the top,
was nothing but slag (aluminum oxide).
Perhaps there may be a little lesson in this drama of the metals,
because while the iron was vanquished it emerged from the stress of
conflict purified and fitted for its high service to mankind, while
the more aggressive aluminum came to the top an almost useless
product, ruined by the prize for which it had fought.
Another interesting point about this reaction is that the heat
produced by a certain quantity of the mixture is no greater in total
volume than the heat that would be produced by the burning of an
equal amount of anthracite coal. The difference is that the thermit
process concentrates all the heat in a few seconds whereas the coal
gives off its heat bit by bit for a long period of time.
The mixture of filings used in this process is called thermit. A
technical definition of the product is as follows: "Thermit is a
mixture of finely divided aluminum and iron oxide. When ignited in
one spot, the combustion so started continues throughout the entire
mass without supply of heat or power from outside and produces
superheated liquid steel and superheated liquid slag (aluminum
oxide)."
Thus the makers of thermit call the pure metal that results from the
combustion, thermit steel.
For the boy who has studied chemistry the simple equation by which
the scientist described the process to his young friend will mean as
much as his long explanation. The equation is:
Fe_{2}O_{3} + 2Al = Al_{2}O_{3} + 2Fe.
The scientist simply went on to say that Fe_{2}, iron, and O_{3},
oxygen, in the equation means iron oxide, while 2Al means aluminum.
Thus we have iron oxide plus aluminum, heated to 5,400 degrees
Fahrenheit, equals aluminum oxide, Al_{2}O_{3}, plus pure iron,
2Fe. These signs are simply the abbreviations scientists use for
expressing processes in the terms of mathematical equations.
With this general outline of the principle of the thermit process
in mind its actual application will seem a simple matter. Suppose
that a great steel ship ploughing her way through a storm breaks her
sternframe. This is the steel framework upon which the rudder post is
mounted, and naturally a fracture puts the rudder out of commission.
Repairs must be made before the ship can make another trip. Quick
repairs are desired by the owners. Perhaps the ship is a passenger
steamer due to leave port in a few days with passengers and mail, so
to put the liner in drydock, wait for the steel mills to cast a new
sternframe, wait for it to come by freight, and then wait for the
steelworkers to fit the piece in the place of the broken one is a
matter of weeks, perhaps more.
With the thermit process at hand this is not necessary. The company
that manufactures and sells thermit has big plants in several cities
in various parts of the world, but if there is steel repairing to be
done elsewhere the company will send its materials and expert workmen
on a minute's notice. So if the crippled ship limps into the port
where there is a thermit plant the repairs can begin at once, but
there need be only a little delay otherwise, because the captain of
the ship can notify his owners of the damage by wireless while still
out at sea, and long before he reaches the port he is making for they
can have a complete thermit outfit on the way.
One of the biggest advantages of the thermit process of repairing
machinery or structural steel is that the welding in a great many
cases can be made without taking the complicated parts to pieces.
Consequently after the ship is in drydock the workmen build a wooden
scaffolding about the broken sternframe, so that they can work the
better.
The next step is the preparation of the broken parts for welding.
Most boys know how the doctor has to put splints on a broken arm so
that it will knit properly. It is something like that with a thermit
weld.
The broken parts are supported in exact alignment by heavy blocks of
concrete, and the fractured ends sliced off clean by the oxygen-gas
torch. This leaves a space of from one inch to two and a half inches
between the fractured ends, just according to the size of the piece
to be welded. After the parts are all thoroughly cleaned the workmen
are ready to take the next step.
This is the preparation of the mould for the weld. First, a pattern
of the weld, as it will appear when completed, is put on the fracture
with beeswax. The space between the broken ends is filled in and a
thick "collar" of wax is packed around the parts, so that when this
is done the pattern looks like a swelling on the frame. The mould is
then built around this wax pattern.
The inventor of the thermit process had to make a number of
experiments before he found a material refractory enough to stand
the terrific heat to which the mould had to be exposed. Finally he
decided upon an equal mixture of fire brick, fire clay, and fire sand.
With this material, then, the workmen go about making the mould. It
is solid, with the exception of three apertures or tunnels, which are
left by inserting in the moulding clay, wooden models of the size
and shape desired. These are a gate, or place into which the molten
welding material is to be poured, a "riser" or larger hole into
which the surplus material can run for the overflow, and a heating
aperture. The gate runs from the top of the mould down to the lowest
point of the wax pattern, while the "riser" extends from the top of
the wax pattern to the top of the mould. Thus we really have a small
inlet and large outlet, although it is always arranged so that the
surplus metal remains in the riser, and as little as possible runs
over. The heating aperture is a small hole in the side of the mould
extending to the bottom of the wax pattern.
With the mould complete the wooden models of the gate, riser, and
heating aperture are pulled out and the first step in the process
of welding is taken. The long pipe of a specially constructed
gasoline compressed-air torch is inserted in the heating aperture
and the process called preheating started. The gasoline torch, of
course, quickly melts the beeswax, and leaves the space occupied by
the pattern clear for the molten metal that is to be introduced to
make the weld. The blast from the torch is continued through this
heating aperture until the parts to be welded have reached a red
heat, because if this were not done the cold steel would so chill the
molten thermit steel that the weld could not be accomplished. The
length of time taken by this preheating is governed, of course, by
the size of the parts to be welded. Sometimes it is many hours.
Everything is now ready for the thermit. There has been some
elaborate preparation of the thermit too. The coarse powder or grains
of iron oxide and aluminum previously have been prepared according
to the job to be done. In very large welds, or welds where very hard
steel is required, certain additions, to be explained later, are made
to the thermit.
The amount of thermit to be used is an important factor, of course,
as there must be plenty to fill the mould, and yet not so much that
it will overflow the riser. To decide on the amount takes a careful
calculation because in large operations there are certain additions
to the thermit which have to be considered. In general, however, the
engineer must remember that he must have just twice as much molten
thermit steel as he needs to fill the space left by the melting
of the wax pattern. The surplus flows up into the riser, heating
aperture, and gate, effectually closing all of them. The calculation,
then, is that it takes four and a half ounces of steel to fill a
cubic inch. It takes nine ounces of thermit to produce four and a
half ounces of steel, so the engineer directing the weld must figure
on eighteen ounces of thermit to each cubic inch in the wax pattern,
including the space between the parts to be welded.
After seeing that the proper amount of thermit is measured out the
engineer must see that the crucible in which the reaction is to take
place is ready to contain the strenuous battle that is to be fought
in it.
As before mentioned there are very few products that can withstand
the heat of the fire produced by thermit. Ordinary fire brick and
mortar would melt or be burned to powder in a few seconds. Metal
would go the same way that the metal in the crucible goes. Science,
however, has established that magnesia tar is not affected by the
thermit fire, so the crucible in which the thermit is reduced is
heavily lined with magnesia tar. The crucible itself is shaped like
a cone with the point downward. At the bottom is a magnesia stone,
which has a conical-shaped hole for the "thimble." This "thimble"
also is made of magnesia stone, and has a hole through it for the
molten thermit steel to run through after the reaction has taken
place. Before filling the crucible with the thermit, however, the
pouring hole is very carefully plugged up by a special process, with
a little steel pin protected by fire sand and fire clay. This pin
extends below the lowest point of the crucible a couple of inches,
and by knocking it upward the molten metal is allowed to flow out.
The upper end of this little plug that otherwise would be melted
instantaneously by contact with the burning thermit, as indicated
above, has to be protected by a layer of fire sand. The hole through
which the metal flows is never more than half an inch in diameter.
With the crucible, mould, and thermit prepared, the next thing is
to put the thermit in the crucible and put the crucible in place.
There are many ways of placing the crucible. In some cases, it is
hung by a chain and in others it is supported by a tripod or wooden
scaffolding. The latter is the better because, though the wood always
catches fire from the heat, it can be kept standing by throwing on
water, whereas steel or iron would be eaten in two in an instant
by the touch of a few sparks of flying thermit. The point is to
support the crucible so that the pouring hole is directly over the
entering gate, or pouring gate of the mould.
[Illustration: THERMIT WELD ON STERNFRAME OF A STEAMSHIP
Notice metal left above weld, where it flowed up into the riser.]
[Illustration: A LARGE SHAFT WELDED BY THE THERMIT PROCESS
Protruding metal is that which flowed up into gate and riser. It
is cut away by the gas torch to leave a neat weld.]
[Illustration:
Courtesy of the _American Machinist_
CUTTING UP THE OLD BATTLESHIP MAINE WITH AN OXY-ACETYLENE GAS
TORCH
Picture shows end of boat crane over exploded magazine, which was
cut off in fifteen minutes.]
[Illustration:
Courtesy of the _American Machinist_
CUTTING AWAY THE DECKS
Oxygen and acetylene generators can be seen on top of
after-turret.]
Things move with a rush now, for all these arrangements are made
ahead of time, and as soon as the workmen are sure that the parts in
the mould are redhot the heating aperture is carefully plugged with
fire sand and the thermit is ignited. From a mere pinch to half a
teaspoonful of the ignition powder is put into a little hollow in the
thermit so that the heat may be communicated at once to as much of
the thermit as possible. This is then set off with a storm match. The
workman quickly withdraws his hand, slams the lid on to the crucible
and gets out of the way of flying sparks.
There is a hiss, a puff of white smoke, a blinding glare from the
hole in the top of the crucible, and that is all, beside a few
sparks, to indicate that a heat second only to that of the sun is
being generated within.
One cannot help but marvel at the wonders of science as this
inconceivable heat is being produced, the process is seemingly so
simple, so easily handled, and so accessible for all kinds of work
where steel welding is necessary.
Half a minute to a minute (according to the amount of thermit used)
after the match has been applied a workman holding at arm's length a
long tool called a "tapping spade" gives a few upward knocks to the
little metal pin extending down from the closed pouring aperture.
He jumps back for the heat is enough to set his clothes afire, even
at a considerable distance, and a few flying particles of the molten
thermit would inflict a serious burn.
Down through the little hole the thermit, that a minute before had
been only a coarse dark gray powder like metal filings, seemingly the
last thing on earth that would catch fire, flows into the pouring
gate of the mould in a steady stream of white-hot liquid steel. The
white glow from the metal is brighter than any electric light. It is
so intense that although the workmen wear heavy dark goggles, they
shade their eyes and turn their heads away.
Now you will be wondering, if you know anything about steel and its
wonderful properties, how it is that this can be good steel when it
is all mixed up with the aluminum oxide or slag. The reason it is of
best quality is that as soon as the reaction reduces the whole mass
to a molten liquid the heavier steel, set free, as the scientists
say, but as we have chosen to think of it, robbed of the aluminum,
sinks to the bottom, while the lighter aluminum oxide rises to the
top. Consequently the steel goes into the mould to make the weld
while the slag, having risen to the top, will be found at the top of
the pouring gate, and only around the outer edges of the weld.
When the pour is completed the workmen go away and leave it to cool.
It is usually left over night, sometimes as long as forty hours,
when the weld is a very large one.
Finally the mould is broken down and the weld is found complete, with
big extensions of the steel extending from the weld, in just the
shape of the pouring gate "riser" and heating aperture.
The molten thermit steel rushing in at the bottom of the mould has
risen between the heated broken ends, and all around them, in just
the shape left by the wax pattern. As the scientists say, the thermit
steel has united the broken sternframe and formed a homogeneous mass
with it. In other words the terrific heat of the thermit rushing on
the heated ends has resulted in the two parts becoming one with the
added thermit steel.
After the mould is broken down the oxygen-gas torch comes into use
again to cut away the ends of steel sticking up where they had cooled
in the pouring gate, "riser" and heating aperture. After this the
weld looks like a great swelling upon the sternframe, and if the
swelling is where it will not interfere with the working of the
rudder or steamer propellers, nothing more need be done. On the other
hand, if the swelling is in the way, it can be reduced to the size of
the frame, and squared off with machines built for the purpose.
Thus the ship is repaired and is ready to be taken out of drydock for
her next trip, as good as new.
About the same plan is followed out on all kinds of welding except
pipes and rails. Locomotives can be repaired without taking the
complicated machinery apart just by working around until the crucible
can be so hung, and the pouring gate so arranged that the metal
can be poured into the place designed for it. The chief difference
lies in the size of the weld to be made and the consequent amount
of thermit to be used. Welds have been made where as much as 2,000
pounds of thermit--enough to make 1,000 pounds of steel--have been
run into a mould. In these very big welds a certain percentage of
steel "punchings," or small pieces of steel, and a little pure
manganese are used to give the additional hardness to the weld.
Without going into details as to the manner in which the principle
of the thermit process is applied on rails or pipes, it will be
enough to say that in welding rails three different systems are used.
The first is done by building the mould around the ends of the two
rails to be welded together and letting the thermit steel run in
and completely surround the rails and the space between them. This
gives one continuous rail just as far as the welding is carried on,
and one through which the electric current of an electric road can
pass without any trouble at all. It is plain, then, why this system
is used so much on third rails of electric roads. The trouble with
it is that the swelling on the top and inside of the rails must be
machined down to present a smooth running surface to the wheels.
The next system, which is now almost out of date, is one in which two
moulds are used so that the thermit does not come up over the running
surface of the rails. This relieves the engineers of the necessity of
machining the welded joints.
The third system is a mixture of the joining by plates and the
thermit process. This is called the "Clark joint," after the name of
Chief Engineer Charles H. Clark of the Cleveland, (Ohio) Electric
Company, who formulated the plan. The rails are joined with plates
and bolted, or riveted together in the old way, but a thermit weld
is made at the base of the rail, welding the bases of the two rails
together and to the plate.
The method of welding steel pipes is an exact reversal of the
principle of welding together solid pieces of steel or iron. After
the pipes are cut off clean, the mould, which is made of cast iron,
is placed around them with specially constructed clamps to force
the two ends closer together after the thermit has been poured in.
The thermit is then set off in a flat-bottomed crucible like a
long-handled ladle, and poured into the mould by hand as if from a
ladle. As the slag rises to the top it goes into the mould first and
coats the pipes. The thermit steel does not touch the pipes, but
merely supplies the heat to weld them perfectly, so that they are as
strong as the piping itself. Just after the pour has been made, the
clamps are tightened up and the white-hot pipe ends forced together.
They are thus held until cold, when the mould is broken away. The
slag coats the outside of the pipes and this is chipped away, leaving
a perfect weld.
Another interesting use of thermit is in the great foundries where
cauldrons of metal have to be kept at a very high temperature. To
help keep the mass in a liquid state thermit can be introduced in
it either by throwing it into the cauldrons in bags, with a little
ignition powder so fixed that it will be touched off by the heat
of the boiling metal, or by putting it in especially designed cans
affixed to the ends of long rods. By these rods the thermit can be
plunged to the bottom of the cauldron before it "burns." The reaction
of the thermit, with the intense heat caused by it, helps to keep the
mass at the proper temperature.
Also thermit is used in the same way with a small amount of titanium
oxide, to purify iron and steel. The metal becomes much more liquid,
and a commotion like boiling is started. This is the result of the
titanium driving out the impure gases and driving other impurities
such as metallic oxides and sulphur contents to the top. Chemically
what happens when the titanium is introduced by the thermit process
is that the titanium combines with the nitrogen in the molten iron,
giving it a much finer grain, and making it a much lighter colour,
more like steel, than previously.
One of the things thermit is not extensively used for is the
repairing of gray iron castings. The first reason is that gray iron
is cheaper than steel, and a new casting often can be turned out by
the mills quickly.
Another and a more interesting reason is that gray iron melts in a
much lower temperature than does thermit steel and consequently has a
lower shrinkage. Therefore when the molten thermit, with its terrific
heat, cools there is a large shrinkage. Thermit steel being much
stronger than gray iron, its shrinking sometimes strains and cracks
the iron casting.
In spite of this difficulty very successful repairs have been made
on cast-iron and it has been found that by mixing 2 per cent. of
ferro-silicon and 1 per cent. pure manganese with the thermit for
welding, a thermit steel is formed which is very soft and comes close
to the properties of gray iron. By using this mixture important
welds have been made on cast-iron flywheels, water wheels, and other
cast-iron parts with great success.
While industry is making progress with all these uses of thermit,
science is experimenting all the time to add to the scope of the
process. As was pointed out before, many other metals can be reduced
to a high degree of purity with this process and in the laboratories
they are always trying new ones and working out new formulas. Of
the pure metals that can be reduced by the thermit process there
are chromium, which is 98 to 99 per cent. pure; manganese, which
is 96 per cent. pure; and molybdenum, which is 98 to 99 per cent.
pure. These are used in the manufacture of very hard steel, such as
armour plate, and "high speed steel." Among the alloys, or mixtures
of metals, there are chromium-manganese, manganese titanium,
ferro-titanium, ferro-vanadium, and ferro-boron, all of which have
uses in industry and help us to travel faster and more safely by
railroad, electric train, and steamship.
It may have occurred to some bright boy that, since this heat is
so intense and so handy, it might be a good way to make steam in
locomotive boilers, or cook our meals, but it will be remembered
that the heat is all over within a few minutes. In other words,
where a terrific heat is required for a few seconds, thermit will
fill the bill, but where a continuous heat for many hours is needed,
electricity, gas, coal, coke, oil, or wood are better. The high cost
of aluminum would probably prevent the thermit process coming into
use in the manufacture of steel for our armour plate, ship plate, or
structural steel, at least for a good many years.
Earlier in this chapter I said that the slag, or aluminum oxide, from
the thermit process was an almost useless product. This is not the
precise scientific truth, for the slag becomes a black powder such as
is used in making emery wheels, but the slag from thermit is never
actually used for this. Another use for the slag from the thermit
process in which chromium is used has been discovered. Potters use a
material called corundum, which this slag resembles, except that it
is superior to natural corundum in pottery manufacturing because of
its freedom from metallic impurities. The slag can be mixed with clay
and baked. It is especially useful in chemical apparatus that must
withstand great extremes of temperature, because its experience has
so tempered it that nothing less than a heat equal to that of the sun
would give it much concern.
Another interesting thing about the slag from chromium thermit is
that small rubies have been found in it. The scientific explanation
is that they are nothing but crystallized alumina, coloured with
chromium. The jewels usually are too small for any commercial purpose
but serve as a very striking example of the intensity of the thermit
fire. All the real jewels, diamonds, rubies, emeralds, amethysts, and
so on, were formed by the terrific heat in the bosom of the earth
millions of years ago when it was cooling down from gases hotter
than anything we can possibly conceive of, to a molten ball, then
to a solid redhot mass and then to a globe sufficiently cool on the
outside to be crusted over. That they can be made in this little
chemical furnace shows how far science has gone in imitation of the
wonders of nature.
AUTOGENOUS WELDING AND CUTTING
"Now," said the scientist, after he and his young friend had finished
some experiments, and were ready to talk about autogenous welding,
"imagine a little white flame no bigger than a pencil point at the
end of a brass pipe about the size, and not entirely unlike in
appearance the old-fashioned taper holder with which you used to
light the gas, and you have before you in the rough, a picture of
one of the oxy-acetylene torches that will in a few minutes weld two
pieces of almost any metal, or in a few seconds cut a solid plate of
the hardest steel of several inches thickness almost as fast and easy
as a carpenter could saw a board, and yet without taking the temper
out of the metal."
Picking up what seemed to be a little brass rod bent at the end, the
man turned a valve, applied a match, and as the gas burned up with a
beautiful little flame of dazzling whiteness, he continued:
"This tiny flame, so easily controlled, is hotter than any produced
by man except that generated by the electrical furnace, for it
reaches a temperature of about 6,300 degrees Fahrenheit. Previous to
the invention of these wonderful torches the oxy-hydrogen was the
hottest gas flame, but it only reached a temperature of 4,000 degrees
Fahrenheit."
"How do you use it?" asked the boy.
"Well, for instance, Uncle Sam is enabled to weld and cut steel
plate in building his battleships, steelworkers to carry on their
gigantic tasks, and wreckers to clear away tangled masses of steel
beams far more quickly and easily than with the older methods.
"If you had visited one of the navy yards, a shipyard or any place
where big work in iron and steel was being carried on as short a
time as three years ago, you would have seen a man sitting for hours
sawing away on the end of a steel beam, for instance, trying to cut
it down to the required length. He would dull many saws, use a great
deal of energy, and an appalling amount of the most valuable thing in
the world--time. Again, you would have seen them welding pieces of
iron and steel by the old blacksmith method, or riveting other pieces
that could not be joined by heating them and pressing them together.
"To-day you would see fewer of these processes because autogenous
welding and cutting by the powerful little oxy-acetylene torches
is revolutionizing certain methods of working with metals. Instead
of squatting at the end of the beam and sawing away like an
old-fashioned carpenter, the modern iron worker takes up his little
torch, turns a valve in the handle and concentrates the flame on the
steel beam that he wishes cut. Almost instantly a shower of sparks on
the under side of the beam shows him that the flame has burned its
way through. Then he slowly moves the flame along the line where he
desires to cut and the trick is done."
Illustrating with his own little laboratory torch, the scientist
continued his explanation, saying that cutting is only one of the
many uses to which this modern invention in steel working is put.
Not quite so spectacular but every bit as useful is the autogenous
welding by means of these magic wands. Welding metals has ever been
more or less unsatisfactory. The old process of heating the two
ends and then beating them together is cumbersome and practically
impossible in many cases. Consequently inventors have sought other
welding processes with wider application and greater facility ever
since the first metal workers of earliest times forged crude chains
and weapons. With this modern device two pieces of steel or other
metal are brought to within a small fraction of an inch of each other
and by the use of the oxy-acetylene torch and a thin strip or rod of
metal are melted and fused together.
Although the acetylene flame gives off a far greater proportion of
light than heat, it is a very powerful gas and Le Chetalier, a French
inventor, was sure that he could put it to other uses than furnishing
lights for automobiles, etc. To this end he tried mixing acetylene
gas with oxygen, for there can be no fire or combustion without
oxygen. He very properly figured that by introducing pure oxygen
into the acetylene, the burning, or combustion, would be greater,
and the heat of the flame greatly intensified. His experiments were
ultimately successful, and it was then only a short step to the
time when three different oxy-acetylene torches were in use. In
France there were developed low pressure, medium pressure, and high
pressure torches; but the last named has not been found commercially
practicable in the United States, where the "medium pressure" torch
is sometimes called the high pressure. As we are dealing entirely
with the American use of the invention we also will call the two
kinds of torches used here the low pressure and the high pressure.
The general principle of the torch is, as we see, the mixture of
oxygen with acetylene in order to obtain a hotter flame, but right
here we come to the difference between the low-pressure and the
high-pressure tools. Both are made of brass pipes, terminating in the
burning tip and connected at the rear of the handle with rubber tubes
which run to the separate tanks holding the acetylene gas and the
oxygen, but the method by which these gases are combined in the torch
constitutes the principle differences in the two systems, with the
consequent greater or less efficiency claimed by the manufacturers.
Without going into the technical details, which are a matter of
controversy between scientists as well as the various commercial
concerns interested in the torches, it will be sufficient to say
that in the low-pressure torch the acetylene gas is only used under
a pressure of a few ounces, with the oxygen under a much heavier
pressure, while in the high-pressure torches, the acetylene and
oxygen both are under an appreciable pressure of several pounds.
Thus in the low-pressure torch invented by Fouché, the oxygen is
forced out of the nozzle by the pressure and the outrush sucks
out the acetylene in the proper quantities. The two gases mix in
a chamber at the end of the torch just above the tip and flow out
into the air in this mixed form. The proportions of the gases in the
low-pressure tool are about 1.7 of oxygen to 1.0 of acetylene.
The high-pressure torch, which has largely taken the place of the
low-pressure one in France, and which we also see most frequently in
this country, has a different method of mixing the gases, due to the
fact that they both are under pressure. According to many authorities
the tip where the gases are mixed is by far the most important
factor in the success or failure of the tool. In the high-pressure
torch the oxygen enters the tip from a hole in the centre, while
the acetylene enters it from two holes, one on each side. They meet
under high pressure at the upper end of the tip, and have the length
of the hollow tip in which to mix, before they strike the air. The
long, narrow hole in the tip is called the mixing chamber. Those who
are interested in the high-pressure torch declare that it is the
fact that the gases are positively mixed in proper proportion in
the detachable tip, that so greatly adds to the efficiency of the
tool. They declare that by allowing the acetylene to enter the tip
laterally, at right angles with the oxygen, the blast of the oxygen
is broken as it mixes with the acetylene, and the tendency of an
oxygen flame to oxidize any metal with which it comes in contact by
reason of an excess of oxygen in the flame is largely done away with.
This, with the small diameter of the mixing chamber and the friction
with the walls, gives a perfect mixture, according to the claims of
the high-pressure torch enthusiasts. Moreover, the small hole which
is the mixing chamber, effectually prevents serious accidents by
flash-backs of the highly explosive acetylene, and also provides a
much easier method of control. Each outfit has several different
sizes of tips for various kinds of work.
The pressure under which the two gases are used is the other big
difference between the high-pressure and the low-pressure torches, as
said before. In the the high-pressure tool the oxygen is compressed
about the same as in the low-pressure torch, while the acetylene is
under several pounds pressure, just in accordance with the size of
the tip used. In the low-pressure torch the pressure on the acetylene
is only about ten ounces to the square inch, or only enough to keep
it flowing. On account of this difference in the pressure making the
big difference in the mixture of the gases, scientists have chosen
to call the low-pressure torches injector mixture types, from the
fact that the acetylene is sucked into the tip by an injector system,
while the high-pressure torches are called positive mixture types,
because the gases are mixed directly by pressure. In the latest
high-pressure tool the mixture of gases is 1.14 parts of oxygen to 1
part of acetylene, while the low-pressure torch takes a proportion of
1.7 parts of oxygen to 1 part of acetylene.
The torches also vary in size from the little 8-ounce "jeweller's"
torch, that the scientist used, to nineteen to twenty inches long and
a weight of two and a quarter pounds. The average size, however, is
twelve inches long with a weight of one pound. The welding torch is
made up of two brass tubes, one for the acetylene and the other for
the oxygen, connected at the two ends. At the nozzle end there is
a sharp turn in the piping so that the tip is very nearly at right
angles to the main pipes. At the handle end, are the connections for
the rubber tubes that lead to the gas tanks, and the little valves by
which the operator can control the flow of gas. The pipes carrying
the gases to the tip are the same size the whole length, but at one
end are enclosed in a larger tube, which serves as a handle.
Now that we have seen the general construction of the oxy-acetylene
torches, we will assume that the tanks, which look like large
soda-water reservoirs, are filled with pure oxygen and acetylene
gas, and transported to some convenient point in a railroad repair
shop where great forges are spurting flames, and one can hardly hear
the talk of a man beside him for the roar of the hammers and the
compressed air riveters. Assume that some large expensive steel part
of a locomotive has been broken and must be repaired quickly so that
the engine can go out on the road to help haul an accumulation of
freight.
In the old days an engine would have to be taken apart, a new
part turned out at the steel mill, shipped to the shops, and the
locomotive put together again. Nowadays it is only necessary to take
enough of the machinery apart for the workmen to get at the broken
parts. After cutting off the edges to be welded so that they make a
small V, and supporting them within the fraction of an inch apart
in the exact position and shape that they are to be repaired, the
workman selects a rod of steel or iron, to use in somewhat the same
way the tinker uses a strip of solder when he wants to repair a break
in a kettle with solder and soldering iron.
The selection of this filling rod, or wire, is all-important, for
the skilful and successful iron worker uses a piece of metal that
will fuse well with the parts to be repaired, at about the same
temperature at which they themselves will fuse. Mild steel or Norway
iron which is 90 per cent. pure is frequently used, but there are no
hard and fast rules because every master mechanic has his own ideas
about such things, and would not take the word of any manufacturing
company.
Then the operator turns on his torch, lights it with a match, takes
it in one hand, and the rod of welding steel in the other. Holding
the end of the steel rod at the thin crack or bevelled edges between
the pieces to be welded the operator directs the small flame on the
point, holding the tip of the torch about a quarter to a half inch
from the metal. It only takes a few seconds for the terrific heat of
the flame to melt the strip of steel and the edges of the parts to be
welded so that they all are fused together in one perfect mass.
Strange as it may seem, the brass tip of the torch does not melt in
this heat because the pressure behind the gases forces them out with
such velocity that the flame is far enough removed from the tip to
do it no injury, just so long as the operator does not put the tip
square against the metal and drive the flame back against it. This
not only would melt the tip but probably would cause a flash-back in
the torch.
As the end of the strip melts into the crack the operator moves
up the steel, and moves his torch along the crack until the whole
operation is complete. At the end the weld is very rough but when it
is machined down it may be so perfect that it is difficult to tell
where it was made, and the strength is equal to that of any other
part of the piece.
In other words, the weld becomes homogenous with the parts repaired.
From this fact autogenous welding takes its name. Autogenous is
defined as "self produced," or independent of outside materials.
Thus, we see that the autogenous process is a system of putting on
new material, without either heating, compression, or adding flux
(molten material) to the broken parts. In the foregoing paragraphs we
have taken up the welding of steel parts, but the process can be as
well applied to steel pipe, steel plate, iron, cast-iron, aluminum,
copper, and other materials with only slight variations in the manner
of using the torch.
The cutting process is even more spectacular because while the
welding proceeds quietly, the cutting is accompanied by just enough
fireworks to show us the progress of the tiny flame through the
hardest and thickest of metals.
The cutting torch is the same as the welding torch with the exception
of an additional pipe from which flows a jet of pure oxygen to give
the flame the necessary cutting property. The greater the supply
of oxygen the greater the combustion, and the more penetrating the
flame. The acetylene gas flame heats up the steel--"fills the office
of a preheater," said the scientist--while the oxygen jet follows
close behind and makes a thin cut through the hot metal.
The extra pipe is the same size as the others and extends down to the
end of the torch at an angle where its tip is clamped alongside the
main tip. The rear end of the third tube is connected with a rubber
hose like the others, which extends to the oxygen tank. The flow of
oxygen is under higher, and individual working pressure, controlled
by a valve. In a new style torch the extra hose is done away with and
the separation of the oxygen is done in the torch.
When the modern steel carpenter wants to cut a hole, or saw off a
strip from a piece of steel, no matter whether it be a steel beam,
steel plate, or almost any other form of iron (except cast-iron), he
attaches the cutting pipe, lights his torch and sets to work. Holding
the tool about half an inch from the surface he directs the little
blue flame, which is no more than three quarters of an inch long,
and a quarter of an inch thick, against the spot where he desires
to start cutting. He holds it there a few seconds, then there is a
shower of sparks on the under side of the steel plate, indicating
that the flame has eaten its way all the way through. The operator
next moves the torch along the line where he wants to cut. The speed
with which he can move is governed by the thickness of the steel to
be cut. Half-inch ship steel, for instance, could be cut at a rate of
more than a foot a minute. The heat of the flame melts a little of
the steel, which drops down in molten particles, but the edge that
is cut is sharp and clean, and its temper is as perfect as if the
cutting were done with one of the laborious old-fashioned steel saws.
[Illustration: AN OXY-ACETYLENE GAS TORCH WELD
Note the little torch in the man's left hand, the filling metal
in his right, and the inserted picture of the apparatus.]
[Illustration: TINY 200-HORSEPOWER TURBINE
This engine could almost be covered by a derby hat. A part of the
casing is removed to show the smooth disks.]
[Illustration: THE TESLA TURBINE PUMP
Driven by a 1/12-horsepower motor. The little pump here shown is
delivering 40 gallons of water per minute against a 9-foot head.]
This cutting process is of especial value to navy yards, shipyards,
and wreckers, where there is a great deal of steel to be cut.
Uncle Sam uses it at most of his navy yards, for in building his
battleships there are thousands and thousands of holes to be cut
in steel plates, plates to be shaped, and beams to be cut off to
required lengths.
When the scientist and his young friend visited the Brooklyn Navy
Yard to see this process in operation the naval constructors had made
considerable headway on the framework of the great Dreadnaught _New
York_, in course of building there. The huge steel ribs of the ship
towered upward amid the scaffolding nearly as high as a five-story
building. In laying this steel framework, and shaping the plates that
will make the hull, bulkheads, and decks, there will be millions
of holes to be cut, and virtually miles and miles of plates to be
shaped. Instead of sawing these the workmen were cutting them with
the oxy-acetylene torches.
Half a dozen men were at work, all cutting as fast as possible, and
the great steel plates, and beams were coming and going as quickly
as ever boards were passed along by a carpenter. The lines that were
to be cut were all marked out in advance so the men never put out
their torches. The only cessation in the work was when one of them
stopped for a minute or so, to wipe his eyes, for in spite of the
dark goggles worn by all operators of the oxy-acetylene process the
intense flame is very hard on the eyes.
One reason why the cutting process is so popular in shipyards is
because in making steel ships, holes are cut in the plates, ribs, and
beams, wherever possible without lessening the strength, to lighten
the frame.
Probably the most picturesque use of the cutting device is by
wreckers of steel structures. Nowadays whenever there is a bad fire
the building is left a tangled mass of steel pipes and girders that
can only be cleared away with the greatest risk of life, and the
greatest difficulty. The process always was a long, tedious one until
the oxy-acetylene cutting came into use.
Thousands of New York boys saw the device in use during the winter
of 1911-1912 when they visited the ruins of the Equitable Life
Assurance Society fire. The sight is unmistakable. Far up in the
ruins you see a man bending over a great twisted steel beam that it
might take weeks to pull out of the débris. Soon there is a shower
of sparks, and the part that is sticking out is cut off and ready to
be sent to the street and hauled away. The device has been used in
the ruins of a large number of disastrous fires, lately, particularly
where men have been entombed in the collapse of ceilings, and haste
means everything in getting out their bodies. Also, it was very
successfully used in cutting up the old battleship _Maine_ before the
hull was removed from Havana harbour.