The ingot is now ready for the “forge,” and on its receipt in the forge
shop it is placed in a furnace to be heated; and here great care must
be exercised to prevent setting up any additional strains in the ingot.
When the ingot was cooling just after casting the metal tended to flow
from the centre; the interior is still in a condition of strain, and if
the cold ingot is now placed in a hot furnace, cracks are apt to form
in the centre, causing the forging to later break in service.
However, the ingot having been properly heated, it is ready for either
the forging hammer or the press. The present-day practice, though, is
to forge the ingot under a press forge, as the working of the metal
causes a certain flow, and as a certain amount of time is necessary
for this flow, the continued pressure and slow motion of the press
allows the molecules of the metal to adjust themselves more easily,
and a better and more homogeneous forged ingot is produced than if the
forging had been done with a hammer.
When forging a hollow ingot, a mandrel, merely a cylindrical steel
shaft, is placed through the hole in the ingot and the ingot forged
on the mandrel, thereby not only is the outside diameter of the ingot
decreased, but the length of the ingot is increased. The usual practice
is to continue the forging until the original thickness of the walls
of the ingot is decreased one-half and until the ingot is within two
inches of the required finished diameters. The ingot is now known as a
“forging,” and the lower end of each ingot as cast will be the breech
end of the forging that is made from it.
The next process is that of “annealing.” This consists in heating the
forging to a red heat and then allowing it to cool very slowly, and
is usually done by hauling the fires in the furnace after the correct
temperature has been attained and permitting both to cool off together.
This process is to relieve the strains set up in the metal during
forging, and further, it alters the molecular condition of the steel,
making a finer and more homogeneous forging.
[Illustration: HOW THE GUN TUBE IS TEMPERED
Photo by Bethlehem Steel Co.
This photograph shows a gun tube ready to be lowered into oil bath for
“oil tempering.”]
After annealing, the forging is ready to go to the machine shop to
be rough bored and turned. The forging is set in a lathe, the breech
end being held by jaws on the face-plate and the muzzle end by a
“pot-centre,” a large iron ring having several radial arms screwed
through it. The lathe can now be turned and the forging centered by
screwing in or out on the jaws of the face-plate or the radial arms of
the “pot-centre.” When centered, several surfaces are turned on the
forging for “steady rests” and then all is in readiness for the turning
and boring.
In both operations of “turning” and “boring,” the work revolves while
the cutting tools are fed along. Turning is very simple and usually
several tools are cutting at the same time, but boring is a more
delicate operation, because the workman cannot see what he is doing.
And in boring, either a “hog bit” or a “packed bit” is used; a “hog
bit” is a half cylinder of cast iron fitted with one cutting tool and
used for rough cuts, while a “packed bit” is a full cylinder of wood
with metal framing and carrying two tools 180° apart and used for
finishing cuts.
The forging, having been rough machined, is now ready to receive its
heat treatment in order to give to the steel its required physical
characteristics. Every piece of steel used in gun manufacture must
conform to certain specifications as regard both its physical and
chemical characteristics. The chemical analysis was made at the time
the ingot was cast; now for the treatment of the forging, prior to the
physical test as to its tensile strength, elastic limit, elongation and
contraction.
The “tensile strength” of a metal is the unit-stress required to break
that metal into parts. If a round bar ten inches in cross-section area
will fracture under a strain of 120 tons, its tensile strength is 120 ÷
10 or 12 tons per square inch. Tensile strength is usually expressed in
pounds per square inch.
The “elastic limit” of a metal is the unit-stress required to first
produce a permanent deformation of the metal. If a bar of metal be
subjected to an increasing strain, up to a certain point that metal
will be perfectly elastic, resuming its normal shape when the strain
is removed; at the first permanent set or deformation, however,
the elastic limit of that metal has been reached. Elastic limit is
expressed in pounds per square inch.
By “elongation” is meant the increase in length in a bar when its
tensile strength is reached. If a bar 10 inches long after rupture
measures 11.8 inches, its elongation is 18%.
By “contraction” is meant the decrease in cross-section area in a bar
when its tensile strength is reached. If a bar 1 square inch in area
after rupture is only .75 of a square inch in area, its contraction is
25%.
These definitions being understood, a brief description of the heat
treatment can be taken up, because it is after this treatment that
standard bars are taken from the forgings to undergo the physical
tests. The first step consists in “tempering” or hardening the metal.
The piece to be tempered is placed in an upright position in a high
furnace and uniformly heated to the required temperature. It is then
lifted from the furnace through an opening in the top and carried by a
crane to an oil tank of suitable depth and plunged into the oil. This
rapid cooling or “tempering in oil” is facilitated by having the oil
tank surrounded by a water bath, so arranged that a supply of cold
water is constantly in circulation to carry the heat from the mass
as quickly as possible. This operation produces exceeding toughness,
increases the tensile strength and raises the elastic limit of the
metal.
Now the forging is again annealed, so as to relieve any strains set
up by tempering and to soften up the metal to the degree required by
the specifications. It also increases materially the elongation and
contraction. Great care must be exercised in the heat treatment, as the
acceptance or rejection of the forging depends upon whether or not the
test bars pass the required specifications.
The forging is now submitted for test and the test bars taken. In the
manufacture of a big gun, four test bars are taken from the breech
end and four from the muzzle end of each forging and these bars
sent to the physical laboratory. Quite an elaborate testing machine
is provided, and if the bars pass the required tests the forging is
accepted and is sent to the machine shop for finish-boring and turning.
~SEARCHING FOR POSSIBLE DEFECTS~
Frequently during finish-boring the work is examined to see that the
bit is running true, and great care must be exercised to prevent its
running out of alignment.
After finish-boring every forging is “bore-searched,” that is, the bore
is carefully examined for any cracks, flaws, streaks or discoloration.
A special instrument called a “bore-searcher” is used and consists of
a long wooden handle which has a mirror inclined at 45° at one end,
together with a light to illuminate the bore, and so shielded as to
obscure the light from the observer. (See sketch.)
[Illustration]
The bore is also inspected by the foreman after each boring, but the
final “bore-searching” is done by an inspector.
Now to measure accurately the inside diameters of long cylinders,
such as are used in gun work, a special measuring device called a
“star-gauge” is used. Its name is derived from the fact that it has
three measuring points set at 120° apart and two measurements are
taken, one [Illustration] and the other [Illustration], making a star
[Illustration]. Every forging is “star-gauged” after being finish-bored
and also the liner of the _gun_ after each assemblage operation.
~PUTTING THE PARTS OF A “BUILT-UP” GUN TOGETHER~
In preparation for the assembling of the different parts, the tube is
the forging to be finished. It is bored and turned to exact dimensions
and carefully “bore-searched” and “star-gauged.” With the data at hand
a sketch is made showing the external diameters of the liner under the
tube, due allowance being made for the shrinkage when assembling.
The liner is next bored to within .35 of an inch of the finished
diameter, and turned to the dimensions required by the sketch above.
This extra metal in the bore is left until the gun is completely
assembled and is removed in the finish-boring. The liner is then
carefully “bore-searched” and “star-gauged” and liner and tube are
ready for assembling.
The liner is now taken to the shrinking pit and carefully aligned in an
upright position with the breech end down.
The shrinking pit is merely a well of square section with room enough
to permit workmen to move freely about the gun when it is in position,
and equipped with a movable table at its bottom upon which the gun
rests. In the meantime the tube, with breech end down, is being heated
in a hot-air furnace. This furnace is a vertical cylinder built of
fire-brick and asbestos and so constructed that air which has been
passed in pipes over petroleum burners can enter at the bottom, pass
around and through the tube and out through the top to be reheated.
This service permits a uniform heat to be transmitted to the tube and
when the desired temperature has been attained the tube is lifted from
the furnace by a crane, carried to the shrinking pit and carefully
lowered over the liner. Great care must be exercised in this operation
to prevent the tube from sticking while being lowered into place.
Should it happen, the tube should be hoisted off at once, allowed to
cool, any roughing of the liner be smoothed off, the tube reheated and
a second trial made. When the tube is properly in place a cold spray
may be turned upon any particular section where it is desired the tube
should first grip the liner. The tube is then left to cool by itself,
but cold water is constantly circulating through the liner.
When the gun is sufficiently cool for handling purposes, it is hoisted
out of the shrinking pit and taken to the shop for careful measurement,
the liner being “star-gauged” to note the compression due to the
shrinking on of the tube.
The same procedure is followed in the case of the jackets and hoops,
until the entire gun is assembled. The gun is considered completely
“built-up” when the last hoop has been shrunk on and is now ready to be
finished.
The gun is now finish-bored, as .35 of an inch of metal was left in the
liner in the first boring. “Packed bits” are used and the greatest care
is exercised to keep the bit properly centered and running true. After
this step the gun is finish-turned and the powder chamber is bored.
Following this operation the gun is “bore-searched” for any defects
that may have shown up in the finish-boring and chambering, and then
carefully “star-gauged.” The gun is then ready to be “rifled.”
[Illustration: RIFLING A BIG GUN
Photo by Bethlehem Steel Co.
This photograph shows a gun in the Rifling Machine in the process of
being rifled.]
The “rifling” of a gun consists in cutting spiral grooves in the
surface of the bore from the powder chamber to the muzzle end, and is
done from the muzzle end. Rifling is a very difficult operation, and
great care must be exercised that the cutting is uniform. The grooves
are separated by raised portions called “lands,” and after “rifling,”
these grooves and “lands” are carefully smoothed up to remove the rough
edges or burrs caused by the cutting tools of the “rifling” machine.
The necessary holes are now drilled for fitting the breech mechanism
and the breech block fitted. This operation usually takes some little
time, as quite a bit of hand work is necessary to insure a perfect fit.
The “yoke,” really another “hoop,” is now put on at the breech end and
the gun is complete.
The centre of gravity of gun and breech mechanism is now determined
by balancing on knife edges and the whole then weighed. The breech
mechanism is also weighed and the two weights marked on the rear faces
of the gun and breech mechanism.
The gun is now fitted in its “slide,” that part of the mount which
carries the trunnions and through which the gun recoils when it
is fired, and after it is adjusted, all is in readiness for the
“proof-firing” or testing of the gun.
What Is Motion?
There are practically but two things we see when we use our eyes.
One of them is matter, which is a term we apply to the things we
see, speaking of them as objects only, and the other is motion which
we observe some of the matter to possess. Some of the things we see
confuse us, if we bear in mind that everything is either matter or
motion. For instance, we see light and know it is not matter and are
confused until we understand that light is a movement of the ether
which surrounds us and is in and outside of everything. In the same way
we feel heat and may think it is matter thrown off by the fire, when it
is only another kind of motion of this same ether. When we understand
these things we see that motion is a very important and real part of
the world.
When a motion is started it will keep on going forever unless some
other force which is able to overcome the motion stops it. When a ball
is thrown in the air it would go on forever were it not for the law of
gravitation which pulls it to the earth and the friction of the air on
the ball as it goes through the air. When you stop a thrown ball you
sometimes realize that motion is a real thing because it stings your
hands. We do wonderful things with motion. Many things when you add
motion to them acquire qualities which they did not possess before. For
instance, an ordinary icicle thrown against a wooden door will break,
but if you put it into a gun and give it sufficient motion, it will go
right through the door. There is a story of how a man killed another
by using an icicle as a bullet. The icicle entered the man’s body and
killed him. Then, of course, the ice melted and no one could tell how
the man received his wound, for no trace of anything like a bullet
could be found. A piece of paper has no cutting qualities, but if you
arrange a circular or square piece of paper with a rod or stick through
the center and revolve it fast enough, you can cut many things while it
is whirling. The motion gives it the cutting qualities. You can take a
piece of strong rope and, by tying the ends together, making a circle
of it, you can make it roll down the street like a steel hoop if you
catch it just the right way and set it spinning fast enough before
starting it on its way. A steam engine has no power to pull the train
of cars until the wheels are set in motion. So we see that motion is a
very important thing in the world.
Motion is the cause of movements of all kinds, the power which takes
things from one place to another.
Is Perpetual Motion Possible?
Perpetual motion will never be possible unless some one discovers a
way to overcome the law of gravitation and also the certainty that
materials will eventually wear out. Many men have tried to make a
machine that would keep on moving forever without the application of
any power, the consumption of fuel within itself, the fall of weights
or the unwinding of a spring; such a machine would be absolutely
impossible, although many people have been fooled into investing money
in machines that appeared to have this power within themselves.
How Can an Explosion Break Windows That Are at a Distance?
An explosion is a sudden expansion of a substance like gunpowder or
some elastic fluid or other substance that has the power to explode
under certain conditions with force, and usually a loud report. Some
explosions are comparatively mild and accompanied by a very mild noise,
while others are very powerful and accompanied by a very loud noise.
When an explosion occurs, the air and everything surrounding the thing
that explodes is very much disturbed. The air surrounding the thing
that explodes is thrown back in air waves which are powerful in the
exact proportion in which the explosion is powerful. These air waves
can be so suddenly thrown back against the objects in the vicinity that
not only the windows in the buildings are broken, but often the entire
building blown away. The explosion acts in all directions at once
with equal force. A great hole may be torn in the earth beneath the
explosion. If there is anything over the explosion, that is blown away
unless its power of resistance is sufficient to withstand the power of
the explosion. Then, also, the air surrounding on all sides is forced
back against everything in its path.
Very often this air which is suddenly forced back by the power of the
explosion is thrown against houses at a distance. These houses may
be so strongly built as to be able to withstand the effect of the
explosion, but still certain parts of them, such as the windows and
the bricks of the chimney, may not be able to withstand this sudden
pressure of air against them and they are forced in. The wind from such
an explosion acts on the outside of the windows just the same as though
you stood on the outside with your hands against the windows and pushed
them in. Anything that is thrown against a window with more force than
the window glass can resist will break the window, and even slight
explosions may be so powerful as to throw the air back and away from
them with such force as to break windows at a great distance--even a
mile or more away.
Why Do Some Things Bend and Others Break?
When an outside force is applied to some objects, some of them will
bend and others break. It is due to the fact that in some things the
particles have the faculty of sticking together or hanging on to each
other, and it is very difficult to break them away from each other. In
such instances, as in the case of a wire, the article will bend when
we apply the power to it and it will not break, because the particles
which make up the wire have the faculty of hanging on to each other. A
piece of glass, however, can be broken right in two by the application
of no more force than was used to bend the wire, because the particles
which make up the glass haven’t the faculty to hang on to each other.
If you continue to bend a wire back and forth, however, at the same
point, it will finally break apart, because you eventually overcome the
ability of the particles in the wire to hang on to each other.
It all depends upon the hanging-on ability. Sometimes in undergoing
different processes an article which will ordinarily only bend will
become very brittle or breakable. A steel wire may bend but if you make
a steel wire very hard it becomes brittle. On the other hand, glass is
very brittle ordinarily, but if you make it very hot, you can bend it
into any shape you wish, and thus the glass-worker makes different
shapes to various dishes; lamp chimneys, bottles, etc., by heating
glass and then bending it. When it becomes cool again, it also becomes
brittle or breakable as before.
Why Does a Ball Bounce?
When you throw a ball against the floor in order to make it bounce the
ball gets out of shape as soon as it comes in contact with the floor.
As much of it as strikes the floor becomes perfectly flat, and because
the ball has a quality known as elasticity, which means the ability to
return to its proper shape, it returns to its shape immediately and in
doing so forces itself back into the air and that is the bounce.
Of course, the first thing we think of when we consider something
that bounces is a ball, and in most cases a rubber ball. We are more
familiar with the bouncing qualities of a rubber ball. Other balls,
like standard baseballs, are not so elastic as a rubber ball filled
with air, but a solid-rubber ball is more elastic and some golf balls
are much more elastic than a solid-rubber ball. The principle is the
same, when you drive a golf ball, excepting that when you bounce a ball
on the floor the floor does the flattening and when you drive a golf
ball, the golf club does the flattening. A baseball flies away from the
bat for the same reason. When you meet a fast-pitched ball squarely on
the nose with a good swing, it goes farther and faster than when you
hit a slow-pitched ball with an equal swing, because in the case of the
fast-pitched ball you flatten the ball out more, and it has so much
more to do to recover its proper shape that it bounces away from the
bat at much greater speed and goes much further unless caught than a
slow-pitched ball under the same circumstances.
What Makes a Ball Stop Bouncing?
A bouncing ball, when you first throw it against the wall bounces back
at you about as fast as you throw it, but if you do not catch it on the
rebound, it goes to the floor again, because the law of gravitation
which is the pulling power of the earth, pulls it down again. When it
strikes the floor it is again flattened to a certain extent and bounces
up again, but does not come back so high. It goes on striking the floor
and bouncing back into the air again each time a shorter distance,
until the force of gravity has actually overcome its tendency to bounce
back.
When you bounce a ball on the floor and it bounces up again, the motion
of the ball through the air is affected by the friction that the
contact with the air produces and this friction of the air overcomes
part of the bouncing ability in the ball also.
What Makes a Cold Glass Crack if We Put Hot Water Into It?
Hot water will not always cause a cold glass to crack, but is very apt
to, especially a thick glass. The very thin glasses will not crack. The
test tubes used by chemists are made of very thin glass, and will not
crack when hot liquids are poured into them.
When a glass cracks after you have poured a hot liquid into it, it does
so because, as soon as the hot liquid is put in, the particles of glass
which form the inside of the glass become heated and expand. They begin
to do this before the particles which form the outside of the glass
become heated, and in their efforts to expand the inside particles of
glass literally break away from the particles which form the outside,
causing the crack. The same thing happens if you put cold water into a
hot glass, excepting in this instance the inside particles of the glass
contract before the particles which form the outside of the glass have
had time to become cool and do likewise.
What Causes the Gurgle When I Pour Water from a Bottle?
The air trying to get in causes the gurgle. Air has one strong
characteristic which stands out above everything else. It wants to go
some place else all the time. When it learns of a place where there
is no air it wants to go there above all things, and goes at it with a
rush.
Now, when you turn a bottle full of water upside down, the water comes
out if the cork is out, of course, and as soon as the water starts out
the air strives to get in, and every time you hear a gurgle you know
the air is getting in. Every gurgle is a battle between the water and
the air. Sometimes the air comes and pushes the water back enough to
let it slide into the bottle; sometimes the water pushes the air back,
and thus they fight back and forth. The water always gets out and the
air always gets in. In doing so they make the gurgle.
Where Does the Part of a Stocking Go That Was Where the Hole Comes?
Perhaps this is a foolish question, but many boys and girls have been
puzzled for an answer to it. When you put your stockings on they have
no holes in the feet, and at night, when you take them off, there are
often quite large holes in them. The answer is the same as in the case
of the lead in the lead-pencil. The lead in the pencil wears away. You
can see it wear away because that is what makes the marks.
When a hole is coming into your stocking, the stocking on your foot
is being rubbed between your foot and something else (probably some
part of your shoe) and this constant rubbing will wear through the
yarns with which the stocking is knitted. Of course, the yarns in
the stocking are stretched somewhat when it is on your foot and the
rubbing finally cuts through the threads and releases the tension of
the threads of yarn, so that not always is as much stocking lost as
the size of the hole. But, if you were to look carefully at your foot
and inside your shoe, when you first take the stocking off and see the
hole, you would find little particles of yarn all about.
Why Do Coats Have Buttons On the Sleeves?
The practice of putting buttons on coat sleeves, which serve no useful
purpose at all and do not add to the beauty of the coat, is a relic of
very old days.
There was a time when people did not use handkerchiefs, and it was
common practice for men to wipe their noses on their sleeves. They had
coats also in those days, but they did not have buttons on the sleeves.
One of the old kings finally developed the idea of dressing his
soldiers in fancy uniforms and, as he sat in his palace and reviewed
his troops, he noticed many of them using the sleeves of their coats as
handkerchiefs. He immediately issued a decree that all sleeves should
have a row of buttons sewed on them, but at a point directly opposite
to where they are now on the sleeves. This was done to remind the
soldiers that the sleeves of their beautiful uniforms were not to be
used as handkerchiefs, and those who attempted to draw their sleeves in
front of the nose were quickly reminded of the decree by the buttons
which scratched them. And so the buttons really had a quite useful
purpose at one time, and so also all sleeves had buttons sewed on to
them at this place. Later on, however, when the unsightly practice had
been cured and people had learned to use handkerchiefs, the buttons
remained as a decoration, but their former purpose was lost sight of.
Then some tailor or leader of fashion had the buttons set on the under
side of the sleeves for a change, and it became the fashion to have
them there, and the tailors have been sewing them there ever since.
Why Has a Long Coat Buttons on the Back?
The buttons on the back of a long coat, i. e., one with skirts, had a
more sensible reason originally. At one time the skirts of such coats
were made very long, and when the wearer moved quickly the tails of
the coat flapped about the legs and interfered with progress. So an
ingenious gentleman had buttons sewed on to the back and buttonholes
made in the corner of his coat-tails. Then when he was in a hurry he
simply buttoned up his skirts and went his way comfortably.
[Illustration: TELEPHONE DISPLAY BOARD
Showing in outline the apparatus necessary to complete the simplest
kind of a telephone call--to a number in the same exchange]