WROUGHT IRON
We of America, and especially of the West, never have been particularly
devoted to the study of our genealogies. However, it is likely that most
of us at one time or other in our mind’s eye have seen that little
country town back in Massachusetts or New York State, whence came our
forebears. Since those days of long ago, when, with you upon his knee,
grandfather waxed reminiscent and related tales of his boyhood, haven’t
you many times wished that Father Time could carry you back with him a
hundred and fifty years and allow you for a few hours to walk among
those good people with their quaint dress and customs? How interested
you would be in the relatives and friends whose queerly transcribed
verses, bearing date of a century and a half ago, adorn the yellow pages
of your great aunt’s autograph album, which is one of your treasures!
To the present rather unsentimental world we admit of much the same sort
of reverent feeling as we traverse the paths, centuries old, of the
wrought iron region. Here is something which links us with the
antiquities and we “take off our hats and tread lightly” over the lands
and the centuries in and through which this primal material, wrought
iron, has been produced.
But we come back to a plain statement of the case. Let not the fact be
overlooked that it is wrought iron which in some form or other has been
made during the forty or more centuries that iron has been known. It
undoubtedly was the pioneer of the iron family and through all of the
centuries it has maintained its importance. From it as a base during the
earlier centuries were made the steels for which the ancients were so
famous, and similar practice has prevailed from those early times up to
the present day.
[Illustration:
WROUGHT IRON BAR Steel has no “fiber” and can not be split in this
way.
]
We say that the iron made by the ancients was in reality a variety of
what we now term wrought iron, for it fulfilled three of the principal
requirements for wrought iron, viz., it was not necessarily melted
during production, it was a malleable metal, and it contained cinder or
slag, but practically no carbon.
Early iron and steel, of course, were comparatively rare, so much so as
to be available only for implements of war and for particular purposes.
Moreover, all of the steel made was of the high carbon, hard variety,
none of it being of the low carbon sort which we know as the soft or
mild steels. The latter have all come since the invention of the
Bessemer process in 1855 and the Siemens-Martin (the open-hearth)
process of a few years later.
As you will remember the next development in the iron industry was the
use of the larger blast furnace and much more fuel, with higher
temperatures and the production of cast iron which, by reason of the
absorption of considerable carbon from the fuel, was fluid enough to run
out of the furnace. And, as you also know, this blast furnace metal has
come to be the great intermediate product in what has come to be known
as the _Indirect Process_ of making iron and steel.
[Illustration:
PICKLING IN WEAK ACID EXPOSES THE “FIBERS” OF WROUGHT IRON
]
As pig iron contains 3½% or more of carbon, while wrought iron has none
or comparatively little of this embrittling element, any process for
converting the pig iron into wrought iron must eliminate the carbon.
Following the advent of pig iron as a commercial product several
furnaces and processes were developed to turn it into wrought iron. All
of these were based upon the elimination of the carbon by _oxidation_,
which means the burning of the carbon in presence of oxygen of the air.
The best known ones were the Walloon or Swedish Lancashire process, the
South Wales process, the Finery Fire, the Running-Out Fire and the
Charcoal Finery or Knobbling process. The Walloon furnace, largely used
in Sweden, is shown in the illustration on page 94.
While by the process generally used to-day wrought iron is more easily
and cheaply produced, it must be said that by the processes above named
has been made as fine iron as has ever been produced. The Sheffield
manufacturers, whose high grade steel made by the crucible process, is
so widely and favorably known for cutlery, tools, etc., in many cases
yet demand the Walloon process iron made from high grade Swedish ores as
the starting point for their product.
[Illustration:
BAR IRON WILL STAND SEVERE BENDING EVEN AFTER IT HAS BEEN NICKED
]
[Illustration:
SWEDISH WALLOON FURNACE
One of several types of furnaces that preceded the Reverberatory. Some
of them are still used.
]
In these furnaces which consisted mainly of a shallow hearth filled with
glowing charcoal, with tuyères for blast supply, the pigs of iron were
heated until molten. At high temperatures the metalloids of pig iron
will readily burn in a blast of air. After the air blown over and upon
the molten metal has burned out most of the carbon, the main metalloid,
the melting point of the purified metal becomes so much higher that the
heat of the furnace is not sufficient to keep it molten. It becomes more
and more pasty and stiff therefore. This is what the iron maker calls
“coming to nature.” It is the signal that the carbon is about gone and
that he must be careful or the iron will suffer in quality. At this
stage he sees to it that the mass of pasty iron is well protected by
glowing charcoal until it is removed to be hammered or worked into a
bar.
This in general is the process which was used from about the fourteenth
century up to 1783 when Cort invented the reverberatory furnace which
has since been the type generally used.
In the processes just referred to, all very similar, it should be noted
that the iron was _in contact_ with the fuel, which, therefore, _had to
be charcoal_, the fuel with little or no sulphur.
[Illustration:
CORT’S REVERBERATORY FURNACE
This is the type of furnace generally used to-day.
]
Charcoal was an expensive fuel, and, moreover, there was an insufficient
supply because of the great destruction of forests necessary for its
production. Naturally the thing to do was to substitute coal, which was
plentiful. But the sulphur of the coal spoiled the iron.
This proved to be a great barrier until 1783 when Henry Cort of England
succeeded in making wrought iron in a new type of furnace wherein the
iron was refined in one compartment while the fuel was made to furnish
its heat from another; i. e., the fuel and the metal _were not in
contact_ and the refined metal did not suffer from the sulphur content
of the coal.
The figure illustrating Cort’s furnace plainly shows how this was
accomplished and it represents almost as well the furnace used to-day.
In the one-hundred and thirty-three years that have elapsed since it was
designed, his furnace has been changed only in certain details, and but
two important changes have been made in his process—the use of an iron
bottom instead of the sand bed by S. B. Rogers in 1804 and the
introduction of “pig boiling” by Joseph Hall in 1830.
Cort’s process is known as “dry puddling” and his trouble was the
excessive loss of iron, due to his use of the sand bottom and the
absence of a proper cinder. The loss was said to have been from 50% to
70% of the iron charged; i. e., it took about 2 tons of pig iron to make
one ton of wrought iron. Because of the great demand for iron and the
fact that he was using such a cheap fuel, coal, his process at that time
was a success financially.
[Illustration:
EARLY IRON ROLLS
While Cort did not originate the idea, it was he who first made the
rolling process successful, and, therefore, he is given credit for
the invention.
]
But Cort did not stop here. He saw the desirability of a quicker and
more economical method of reducing the “blooms” or balls of iron into
bars or other finished shapes than the hammering process up to that time
used. He accomplished this by the use of power driven rolls, such as
those shown in the cut.
These two inventions of Cort’s were epoch making, though of the two the
more important one was the invention of the rolls from which has
developed the modern rolling mill.
There remains to be described in a little more detail the making of
wrought iron as practiced to-day. The puddling furnace used has a grate
upon which is built the coal fire. The long flame passes over the fire
wall and is deflected by the roof down upon the charge of pig iron piled
upon the “fettling” or lining of iron oxide (iron ore or mill scale)
over the air or water cooled iron plates which form the bottom and the
sides of the hearth.
With a long iron bar the “puddler” (the expert attendant) turns the pigs
until they have melted down into the bath of slag or cinder charged and
continually being formed by the chemical union of iron from the ore or
pig and some of the sand and other impurities present. This cinder,
which is largely a silicate of iron, is a protection for the bath of
molten iron and its use prevents excessive oxidation and loss of metal.
During the melting of the charge the heat is kept as high as possible
and the molten iron is “puddled,” i. e., stirred, by the “puddler” or
his helper with a “rabbler” or iron bar. In order to take out the
phosphorus and sulphur, which for best results should be removed before
the carbon is eliminated, the heat of the furnace is lowered somewhat as
soon as all of the pig has melted, and some iron oxide is mixed into the
“bath” of molten iron and cinder. Most of the phosphorus and sulphur are
chemically acted upon and pass into the cinder which covers the iron.
Soon the mass begins to boil or seethe and small blue flames break
through the cinder covering. This indicates that the carbon is being
oxidized by the oxygen of the iron ore which was added, the oxygen, as
in the blast furnace, having a greater “affinity” for carbon than it has
for the iron.
This “pig boiling” goes on for twenty or thirty minutes, the “puddler”
meanwhile “rabbling” the charge in order to hurry the reactions and to
make sure that all parts of the bath of molten metal are uniformly
exposed to the oxidizing conditions.
[Illustration:
THE MAKING OF WROUGHT IRON TO-DAY. CHARGING THE PIG IRON
]
Soon the metal begins to “come to nature” and little lumps of pure iron
here and there through the bath stiffen up into little pasty balls. Some
may be seen sticking out through the cinder covering of the bath and
others must be torn loose from the bottom with the rabbler. This
“balling” period lasts from fifteen to twenty minutes, during which time
all of the iron has “come to nature.”
[Illustration:
THE COAL PILE AND FIRE BOX OF A REVERBERATORY FURNACE
]
[Illustration:
TURNING THE PIGS TO INSURE EVEN MELTING
]
The puddler quickly separates into two or three white-hot balls the 400
pounds or so of spongy iron. These balls, full of and dripping with
cinder, are seized, one at a time, with long tongs, removed from the
furnace and rushed to the rotary squeezer through which they are twisted
and turned, ever becoming longer and smaller in diameter until they
emerge from the other and narrower side much compacted and with but
little of the cinder which they originally carried. Without being given
time to cool, the blooms are seized and shoved into the “muck rolls,”
whence after a few passes they emerge as long flat bars, very rough and
imperfect in appearance.
After shearing into short lengths, many pieces of this “muck bar,” as it
is called, are made into “box piles” and tied together with wires. These
are charged into the furnace of the finishing mill. After coming to a
white heat the box piles go to the finishing rolls where they are rolled
into bars, rods, plates, or other shapes desired. By repeated cutting,
piling, heating, and rolling, double refined and other high grades of
wrought iron are made, each repiling and rerolling, of course, producing
a more compact and better product.
[Illustration:
PUDDLING THE MELTED CHARGE
]
[Illustration:
CONSIDERABLE CINDER OVERFLOWS DURING THE “BOILING” STAGE
]
Wrought iron has a “fiber,” as may be seen from two of the illustrations
presented. In “coming to nature” small particles of iron crystallize out
as they become purer. These measure perhaps ¹⁄₃₂″ or ¹⁄₁₆″ in diameter.
As it goes to the squeezer the ball of “sponge” is made up of such
grains of iron loosely welded together with the interstices filled with
cinder. The squeezer, and later the rolls, elongate the particles of
iron into threads, which, welded together, make the bar.
It is thought by some that films of cinder, too thin to be seen under
the microscope, surround each fiber of iron and that these afford
protection from rusting and give to wrought iron the excellent welding
quality that it possesses.
[Illustration:
DRAWING ONE OF THE BALLS FROM THE FURNACE
]
[Illustration:
ON THE WAY TO THE “SQUEEZER”
]
Steel has no fiber and for this reason it cannot be split as was the
wrought iron bar shown in the illustration of page 92.
It will have been noticed that only small amounts of iron can be refined
at one time. This, indeed, has been the unfortunate part of wrought iron
manufacture, for it may readily be seen that production of any such
material in lots as small as a quarter ton results in labor costs which
are almost prohibitive in these days of machine-made goods. Not only is
the output of a furnace small but much skill and judgment are necessary
for the production of a high grade product. Very sturdy and strong men,
too, are required as puddlers, for the work is heavy and the extremes of
heat and cold to which they are exposed necessitate men of rugged
health.
[Illustration:
CROSS-SECTION OF A “SQUEEZER”
]
This material in bar iron, engine stay bolts, butt and lap-welded pipe
and certain other products has long held a high place. Though not as
strong as steel, its very excellent welding properties and comparative
freedom from “crystallization” and treacherous breakage under long
continued vibration or sudden jar have fostered its application in such
products as stay bolts, chain-links, cable hooks and others where
failure might have serious consequences. Too, it is thought by many that
pipes, sheets and other articles of wrought iron resist the corrosive
influences of moist air, soil, etc., particularly well. The cinder films
in which the fibers are supposed to be encased are given credit for such
protective influence.
[Illustration:
“BOX PILES” READY FOR THE RE-HEATING FURNACE
]
Though the product has always been a favorite with iron users, the
industry has suffered during the last sixty years by reason of the high
cost of manufacture, which has very largely restricted the application
of wrought iron to certain uses for which first cost is not a main
factor.
The production of wrought iron rails has rapidly dwindled since the year
1880, when they began generally to be replaced by rails made from
Bessemer steel.
[Illustration:
THE BALL GOING INTO THE “SQUEEZER”
]
[Illustration:
SHEARING THE MUCK BAR INTO SHORT LENGTHS FOR “PILING”
]
[Illustration:
THE BLOOM FROM THE SQUEEZER GOES TO THE “MUCK” ROLLS WHICH ROLL IT
DOWN INTO “MUCK BAR”
]
[Illustration:
THE RE-HEATED “BOX PILES” BEING ROLLED INTO “SKELP” FOR PIPE, IN THE
FINISHING MILLS
]
[Illustration:
CROSS PILING GIVES CROSS FIBERS IN THE FINISHED BAR—A DESIRABLE
QUALITY
]
Of recent years, mild steel has been the great competitor of wrought
iron. With marvelous energy, skill, and much capital the manufacturers
of Bessemer and open-hearth steels have adapted their products very well
to the needs of the iron user, while the enormous tonnages turned out in
short time by use of ingenious furnaces and other devices has resulted
in a low cost of production.
Had any of the several mechanical puddling furnaces devised for the
manufacture of wrought iron proved really successful, things might be
more rosy commercially for this very excellent material.
According to the 1916 Statistical Report of the American Iron and Steel
Institute, the recent yearly production in this country of wrought iron
and steel merchant bars, plates and sheets, and skelp for pipe in gross
tons has been:
════╤═══════════════════╤═══════════════════╤═══════════════════
│ Merchant Bars │ Plate and Sheets │ Skelp for Pipe
────┼─────────┬─────────┼─────────┬─────────┼─────────┬─────────
│ Iron │ Steel │ Iron │ Steel │ Iron │ Steel
────┼─────────┼─────────┼─────────┼─────────┼─────────┼─────────
1905│1,322,439│2,271,162│ 72,156│3,460,074│ 452,797│ 983,198
1906│1,481,348│2,510,852│ 74,373│4,107,783│ 391,517│1,137,068
1907│1,440,356│2,530,632│ 74,038│4,174,794│ 444,536│1,358,091
1908│ 685,233│1,301,405│ 54,033│2,595,660│ 297,049│ 853,534
1909│ 952,230│2,311,301│ 76,202│4,158,144│ 370,151│1,663,230
1910│1,074,163│2,711,568│ 91,118│4,864,366│ 350,578│1,477,616
1911│ 835,625│2,211,737│ 89,427│4,398,622│ 322,397│1,658,276
1912│ 944,790│2,752,324│ 75,044│5,800,036│ 327,012│2,119,804
1913│1,026,632│2,930,977│ 64,729│5,686,308│ 312,746│2,189,218
1914│ 563,171│1,960,460│ 56,590│4,662,656│ 264,340│1,718,091
1915│ 657,107│3,474,135│ 20,253│6,057,441│ 262,198│2,037,266
1916│ 993,948│5,625,598│ 13,303│7,440,677│ 355,445│2,572,229
────┴─────────┴─────────┴─────────┴─────────┴─────────┴─────────
There is considerable so-called wrought iron on the market to-day which
is not truly wrought iron, by which we mean iron “puddled” from pig
iron.
Bushelled Iron
After heating a mixture of thin sheet or other soft steel and wrought
iron scrap to a welding heat in a reverberatory furnace, it may be
balled and put through the squeezer, muck rolls, etc., as was the true
wrought iron made by puddling. This manipulation of scrap is known as
the bushelling process and the product as “bushelled iron” or “scrap
bar.” By using scrap bar for the outer layers and old wrought iron bars
cut to length for the interior, box piles are made, which, heated and
rolled, make very good material, though not as good as puddled iron.
Certain grades on the market, e. g., common bar iron, contain more or
less of this bushelled iron, but the better grades, refined wrought
iron, double refined wrought iron, engine and stay-bolt iron, are
usually the pure puddled product.
As with the latter, repeated shearing, piling, and rolling improve the
quality.
Bushelled iron is largely the result of an endeavor to reduce the cost
of production of wrought iron. The material has a legitimate place and
considerable of it is used.