From Iron Ore To Engines

same, the designers and builders of boilers and engines had amassed
an impressive array of scientific facts and formulas. This essay
presents the story of steel and iron as it would have been told
around 1900.(In other words, take heed! A few of the
‘facts’ may not be facts anymore.)

In the last decade of the nineteenth century, publishers brought
out several textbooks for mechanical engineers to follow in taking
advanced college courses and in working for companies which built
engines. These weighty tomes provide a historical record of what
was deemed of utmost importance for students and practitioners of
engineering to know at the height of the industrial era. Such books
devote numerous chapters to descriptions of iron and steel.
Apparently, the term ‘iron’ served as (a) a generic
classification for a wide range of metallic alloys including steel,
(b) a more specific designator of certain metals which differed
from steel in molecular structure and (often) in manner of
production, and (c) the very specific signifier of the
silvery-white, malleable, ductile element symbolized by Fe. With
meanings from general to specific, ‘iron’ in old textbooks
can be, and occasionally is, a highly ambiguous word.

Despite such confusing terminology, the engineering books from
around the turn of the century provided much useful instruction to
readers born not long after the Civil War. Most begin their
treatment of the subject of iron by examining the nature of
stresses, both longitudinal and transverse. Under the former
heading belong tensile stress, which resists a pulling force, and
compression, which resists a crushing force. Beneath transverse
stresses may be classified (a) shearing stress, which resists
cutting across, (b) bending stress, which resists breaking across,
and (c) torsional stress, which resists twisting (Thurston 46).
Knowledge of such forces enabled engineers to design stronger
boilers and engines. With stress as a force acting upon a
structure, strain, according to Robert H. Thurston, was the
resultant change of structural form (47). Unfortunately, general
agreement on such a seemingly simple matter as defining
‘stress’ and ‘strain’ could not be reached:

An external force applied to a body, so as to pull it apart, is
resisted by an internal force, or resistance, and the action of
these forces causes a displacement of the molecules, or
deformation. By some writers the external force is called a stress,
and the internal force is a strain; others call the external force
a strain, and the internal force a stress: this confusion of terms
is not of importance, as the words stress and strain are quite
commonly used synonymously, but the use of the word strain to mean
molecular displacement, deformation, or distortion, as is the
custom of some, is a corruption of the language. (Kent 236)

Then as now, science progressed despite disagreement. On the
subject of strain, Thurston and William Kent parted company.

Large numbers of engineers necessary to keep pace with
industrial growth were learning from textbooks, not from
apprenticeships, as had been customary prior to the late 1800s. The
thick volumes they studied helped them to comprehend categories of
load: (a) working load, which is applied to a piece proportioned to
bear the force securely, (b) dead load, which is applied without
shock and endures without change (example the weight of a bridge),
and (c) live load, which is applied abruptly with inconsistent
stresses (example a train crossing a bridge) (Thurston 47). In
turn, students discovered the intricacies of ‘elastic
limit.’ Kent explained:

The elastic limit is defined as that point at which the
deformations [in a bar of metal being tested for tensile strength]
cease to be proportional to the stresses, or, the point at which
the rate of stretch (or other deformation) begins to increase. It
is also defined as the point at which the first permanent set
[morphologically-fixed elongation] becomes visible. The last
definition is not considered as good as the first, as it is found
that with some materials a set occurs with any load, no matter how
small, and that with others a set which might be called permanent
vanishes with lapse of time, and as it is impossible to get the
point of the first set without removing the whole load after each
increase of load, which is frequently inconvenient. The elastic
limit, defined, however, as the point at which the extensions begin
to increase at a higher ratio than the applied stresses, usually
corresponds very nearly with the point of first measurable set.
(236-37)

Thurston agreed with the latter definition that the elastic
limit is the point at which the rate of distortion more or less
suddenly changes, with the piece approximating permanent change of
form; however, Thurston quickly added that the limit is not so
observable as a point but more as a ‘curve’ of change (51).
Then, continued Thurston, if the stress is relaxed, the piece
recoils. Once all load is removed, recoil stops, and the piece,
having been stretched beyond its elastic limit, assumes a permanent
set without recoiling all the way to its original position.
Elongations under stress and sets after stress are proportional to
loads. Also, Thurston advised, metals respond to live loads
differently than to dead loads or to loads applied slowly (53).
Kent stated, ‘Under a load applied suddenly the momentary
elastic distortion is equal to twice that caused by the same load
applied gradually’ (238). Matthias N. Forney concluded that a
bar of iron or steel can withstand up to about one-fifth the amount
of force which would break the bar and still return to its original
length after stretching. He pointed out that repeated applications
of excessive force can further elongate the bar, with each new set
approaching the breaking point (also known as ‘ultimate
resistance’ or ‘ultimate strength’). Along the way, the
metal becomes more brittle, less able to withstand a sudden strain
(188).

Working independently, Thurston and Commander L. A. Beardslee of
the United States Navy, discovered that, if wrought iron were
subjected to a stress in excess of its elastic limit but not beyond
its ultimate resistance and then were allowed to rest by releasing
it from all stress or by holding the test piece at a given
intensity of force, the wrought iron’s elastic limit and
ultimate resistance would increase considerably (Kent 238). In
1873, such a discovery was news. Engineers benefited from knowing
that stress followed by rest could increase the resistance of
wrought iron. Designers and builders of engines studied stresses,
loads, elastic limits, and resistance quite carefully. They learned
that a compression lowers metal’s ability to withstand a future
tension (Kent 239). They remained well aware that one big stress
would break a bar of metal but so would several smaller repeated
stresses; they recognized that iron shafts had snapped from a
succession of little shocks which otherwise would seem harmless
(Kent 240). They concentrated on such data so as to know how best
to plot factors of safety.

Kent recommended that a factor of safety of no less than six be
applied in situations when stresses would alternate between tension
and compression. When stresses would be unpredictable and complex,
as in the forces acting on a crankshaft of a reversing traction
engine, the factor of safety would need to be much higher perhaps
as high as forty! Kent also suggested that builders increase any
sections of metal liable to deteriorate through corrosion (315-16).
Clearly, engineers around 1900 hoped to design machines which would
last.

Thurston argued that the strongest metals for constructing steam
boilers exhibited (a) tenacity (obviously), (b) ductility, (c)
elasticity, and (d) resilience. Boiler iron or steel, he contended,
‘must have ductility, even if tenacity is sacrificed to some
extent. . . .'(56-57). Pulling together such broad subjects as
stress, load, limits of elasticity, and breaking points, Thurston
summarized:

The problem of proportioning parts to resist shock is seen to
involve a determination of the energy, or ‘living force,’
of the load at impact, and an adjustment of proportion of section
and shape of piece attacked such that its work of elastic or of
ultimate resilience, whichever is taken as the limit, shall exceed
that energy in a proportion measured by the factor of safety
adopted. (57)

In the U.S., normal factors of safety used in designing steam
boilers varied from 3 up to 5. A so-called factor of safety of 6
(often a ‘talking point’ in catalogues advertising engines)
might or might not apply to the boiler’s real integrity;
usually, the 6 referred to the full tensile strength of the iron
plate, not to that plate bent and riveted. In boilers, the stresses
on roundabout seams and the more severe stresses on longitudinal
seams caused the actual factor of safety to be lower than that of a
pristine, unriveted plate (Power 38-39). The calculation of
efficient but appropriate factors of safety challenged the
designers and builders of engines:

When heavy shock is anticipated, calculations of energy and
resilience are necessary, and these demand a complete knowledge of
the character, chemical, physical, and structural, of every piece
involvedin other words, a complete knowledge of the material used,
of the members constructed of it, and of the circumstances likely
to bring about its failure. (Thurston 57)

Small wonder, then, that the most successful engine
manufacturers employed teams of chemists and hired mechanical
engineers having enviable backgrounds in physics.

In the 1870s, such manufacturers wanted to decrease their
reliance on wrought iron as the metal of preference for boiler
construction and to switch to steel; however, steel presented two
formidable obstacles. At ‘black heat,’ a term defining a
stage in the process of gradually increasing the temperature and
thereby softening metal, mild steels became brittle and could not
be worked without difficulty (Holmes 400). Secondly, while the
elastic limit of steel exceeds that of iron, steel remains less
ductile than ironand ductility is essential in boiler plate
(Thurston 59).Once technology overcame the problem occurring at
black heat, factories began to experiment with mild, reasonably
ductile steels for boilers.

Builders of engines complained how the quality of both iron and
steel varied considerably from lot to lot and even within the same
sample; the physical character and structure often differed so
markedly from batch to batch that the naked eye could detect the
dangerous variations (Thurston 59). By about 1900, the processes
for producing industrial metals became more refined.

Cast iron was obtained from a fluid mass, wrought iron from a
pasty mass. Practically obsolete by the turn of the century,
wrought steels represented experimentation to derive a useful metal
from puddled steels. True steels were produced by the expensive
crucible process, by the Bessemer method, or by the Siemens-Martin
open-hearth technology; such steels were cast, malleable irons, in
the generic sense of the term (Kent 364). Fusing low-carbon steel
with charcoal or cast iron in a graphite crucible yielded
high-grade ‘crucible steel.’ The process named after Sir
Henry Bessemer (1813-1898), the British inventor and metallurgist
with over a hundred patents in his name, made steel by blasting
compressed air through molten iron to burn out excess carbon and
impurities; factories employing the Bessemer method featured the
renowned ‘converters’large, pear-shaped containers wherein
the molten iron became transformed into steel. In the open-hearth
process, flames which were deflected downward from the roof
superheated molten iron in a bowl-shaped depression within a
hearth. On striking the liquified metal, the intense gases
eliminated unwanted carbon while burning out impurities. The
Siemens-Martin method of open-hearth steel-making bore the names of
its inventors: Karl Wilhelm Siemens (1823-1883), German-born
engineer who moved to Great Britain and became Sir Charles William
Siemens, and Pierre E. Martin, French engineer who lived until 1915
and made numerous improvements in the process of adding wrought
iron and steel scrap to molten iron. Incidentally, Siemen’s
brother, Ernst Werner von Siemens, advanced the science of
telegraphy and associated electrical apparati, while Sir Charles
invented a regenerative steam engine and designed a steamship for
laying long-distance cables. In any event, the Siemens-Martin
process created a reverberatory furnace in which deflected flames
heated molten iron and in which the steel could be tested,
modified, and improved while still molten.

No matter what the process of obtaining high-quality iron or
steel, the amount of carbon in the final product offered a means of
defining each metal; that is, cast iron contained over three
percent carbon, cast steel anywhere from .06 to 1.5 percent, and
wrought iron from .02 to .10 percent (Kent 364). Iron and steel
companies commonly graded pig iron (which is nothing more than
crude iron cast in blocks) by fracture. Producers in eastern
Pennsylvania identified five basic grades, shading from gray to
white. Southern firms, in general, classified pig iron in ten
grades, although certain plants listed even more categories. For
example, iron with greater silicon content might earn special
designations. Pigs varied tremendously; anthracite and coke pig
iron differed markedly from charcoal foundry pig (Kent 365). By the
late 1800s, scientists knew that, in cast iron, carbon exists in
two forms: (a) in chemical union as ‘combined’ carbon (not
discernible except as increasing the whiteness of the fracture in
‘white iron’) and (b) mixed mechanically with iron as
graphite (visible, varying from gray to black and causing the
fracture to be light gray to dark gray). Metallurgists noted that,
when melted iron contained all the carbon it could hold, the
presence of silicon would expel the excess carbon. By itself,
silicon would lend strength to a casting, but, with great amounts
of carbon, the silicon would serve ultimately as a weakening agent.
After enough silicon would be added to produce solid castings, any
extra amount (up to a certain level in ordinary practice) would
cause additional graphite to form, thereby producing brittleness.
Decrease of combined carbon and the consequent increase of graphite
would lessen the strength. Given additional graphite, bending would
increase. When no more graphite could form but silicon would
continue to be added, a brittle stiffness and lighter grain would
result. Again, by itself, silicon would shrink castings, but the
increased graphite caused by the silicon would decrease shrinkage.
The less the shrinkage, the softer the casting; the more the
shrinkage, the more brittle the casting (Kent 365-69).

Designing engineers knew that, for cast parts, the chemical
composition should be checked carefully; the data obtained then
would be compared with the specific gravity of the metal so as to
judge its character. A good foundry iron for casting should be
gray, free from phosphorus, and relatively low in silicon; its
density should be between 7.25 and 7.28 (Thurston 59).
Metallurgists realized that large quantities of phosphorus would
weaken cast iron but that, in amounts ranging from a half to one
percent, phosphorus would be beneficial in preventing shrinkage.
Sulfur, however, would increase shrinkagebut only when carbon and
silicon levels were low. Sulfur would tend to drive out silicon and
carbon and to increase shrinkage and chill while decreasing
strength. Increasing the amount of silicon, however, would tend to
neutralize sulfur’s effects. ‘Chill’ meant the sudden
cooling at the casting’s surface producing a whitish color
thereas in the case of contact between the metal and the cold
surface of the mold. Such chilling would harden the surface. Only
in certain instances (such as in the making of wheels) was chill
deemed desirable. Silicon would defeat the tendency to chill by
forming more gray graphite. Manganese beyond fifty percent would
increase brittleness and cause the metallic mass to crack while
cooling; beyond ninety-eight percent, the mass would crumble.
Manganese also would augment shrinkage. An increase of only one
percent would raise the shrinkage twenty-five percent and increase
the hardness forty percent (Kent 365-69).

Thus generally, elements which would increase tenacity would
decrease ductility and resilience. Up to a point, phosphorus would
add strength, as would manganese; beyond a certain level, they
would weaken or make brittle the casting. Silicon and carbon also
would tend to harden ironbut only in moderation. Occasionally,
ductility would decrease more quickly than corresponding increases
in tenacity!

Builders of boilers and engines found that the tenacity of cast
iron varied from ten thousand pounds per square inch (psi) to more
than fifty thousand psi (Thurston 60). Additionally, they learned
that silicon levels differed considerably from lot to lot and
within even a single bed of a cast of pig iron. Fracture was seen
to deviate in size of grain from bed to bed, even when chemical
analyses showed the beds to be the same (Kent 369-70). Much had to
be done to strive for uniformity and to determine acceptable
standards.

The quality of wrought iron resisted exact determination even
more than did that of cast iron. So-called ‘malleable cast
iron’ was a crude wrought iron which had been subjected to a
process of decarbonization; its tensile strength was not great, and
it was used to make only such items as handles, wheels, and pinions
(Kent 375). Milling pressures, temperature variations, and
mechanical handling so greatly modified other forms of wrought iron
that designing engineers had to go to much trouble to put it
through tests before judging it safe to use. Some wrought irons
boasted a tenacity of forty thousand psi, others eighty thousand
(these latter more accurately termed ‘puddled steels’), and
certain wrought irons resembled cast iron in being hard and brittle
(Thurston 59-60, 62). In short, while steel could be analyzed
chemically and much be known with certainty, wrought iron could be
analyzed with considerable care and yet nothing known with any real
assurance (Kent 377). Still, wrought iron was preferred over cast
iron for most uses (Thurston 127). Although cast iron would remain
durable even in the presence of corroding elements (acids do not
decay it rapidly), benefited from being compact, was immune to
dangerous lamination, conducted equally well throughout, and could
be produced at low cost, it would crack from shrinkage strains and
local variations of temperature and was ‘always treacherous and
unreliable’ (Thurston 62).

Designing engineers, then, had to test metals physically and
chemically, observe the openness or closeness of the grain,
evaluate the shade of color (particularly of the fracture), try to
determine the depth of chill, and become so skilled as to be nearly
intuitive while checking and judging properties (Thurston 61). By
1900, mechanical engineers were welcoming the use of more and more
‘steels’ in boiler making. Such steels were called
‘low,’ ‘soft,’ or ‘mild’ and consisted of
‘ingot iron,’ in fact. Their characteristics included
homogeneity, tenacity, and ductility. Their resilience set them
apart from ‘true steels,’ which were much harder. The mild
steels enjoyed tenacity greater than that of common iron and could
be rolled into thin or thick plates, thereby making them desirable
for strong, durable boilers (Thurston 63). Builders continued to
scrutinize the quality of such steels:

In all rolled steel [as in Bessemer plates] the quality depends
on the size of the bloom or ingot from which it is rolled, the work
put on it, and the temperature at which it is finished, as well as
the chemical composition. (Kent 390)

Soft steel ingots for boiler plates had only ten thousand up to
twenty thousand psi tensile strength until they were rolled, when
they then gave 55,000 to 65,000 psi (Kent 392-93). Carbon in good
steel boiler plate should be less than one-fourth of one percent;
in fact, it often was less than one-tenth of one percent. Designing
engineers would reject boiler plate which, after being heated
red-hot and suddenly cooled, was found to have hardened
perceptibly; despite variations of temperature, good steel should
not take a temper (Thurston 64). One steel-manufacturing firm in
Pittsburgh provided six grades of steel: Extra Fire-box (0.02
phosphorus), Fire-box (0.03 phosphorus), Extra Flange (0.04
phosphorus), Flange (0.60 phosphorus), Shell (0.80 phosphorus), and
Tank (1.00 phosphorus). For firebox plates, which needed the best
steel, builders specified the following ranges of tolerance: carbon
(0.15- 0.25), phosphorus (not to exceed 0.03), manganese (0.40
preferred and not to exceed 0.55), silicon (0.02 preferred and not
to exceed 0.04), and sulfur (not to exceed 0.05) (Kent 399).

In the early 1800s, good boiler plate was made of ‘charcoal
iron,’ produced from pig iron in a charcoal blast-furnace with
no fuel other than pure wood charcoal being used in the presence of
the metal. The growing scarcity of such charcoal caused these irons
to become expensive. Costly or not, firebox iron had to be made of
the best platestrong enough to wear well and ductile enough to be
flanged. Under no circumstances could firebox iron be brittle. By
the mid-1800s, much iron boiler plate came from puddled or scrap
iron. On the one hand, wrought iron was formed into piles, which
were heated to a full welding temperature, then were passed through
a heavy roll-train. With the burning coal not in the presence of
the iron during the heating phase, sulfur and phosphorus would not
be absorbed into the metal. Wrought-iron plate retained some slag
which came from the puddle-ball; therefore, surfaces coated with
oxide became flattened inside the plate and led to dangerous
lamination. On the other hand, steel plate often derived from the
Siemens-Martin process, which stirred the molten metal to prevent
cinders and which (like the Bessemer process) introduced
ferro-manganese to help eliminate unwanted oxides and to carbonize
the metal correctly. When somewhat cooled, the ingot then was taken
to be rolled. It first was reheated to a uniform temperature then
foiled. Steel boiler plates frequently were made twenty feet long
or longer and ten feet wide (Thurston 95-97). The engineers who
designed boilers and engines had to know all iron-and steel-making
processes and know them well!

Such engineers also knew that, of all stressful phenomena,
temperature would have the greatest effect on iron and steel under
load, and their designs treated temperature variations with great
deference (Thurston 83). Even steam pressures, as powerful as they
could become, posed less of a threat to the metal of a boiler than
the rapid elongations and contractions brought about by temperature
(Forney 188). A rise in temperature of only one degree would cause
a bar of ordinary boiler iron to elongate ‘by the same amount
as would a tensile stress of the intensity of about 190 lbs. per
square inch’; thus, if a bar were held rigidly at each end and
not allowed to move while heated a. mere ten degrees, it ‘would
be subjected to a force of compression equal to 1900 lbs. per
square inch’ (Holmes 399). Such wildly fluctuating effects
explain why the long bar-stays running the length of a
locomotive-style boiler in a space hotter than the outside shell
had a tendency to droop and, according to one authority, were
‘perfectly useless’ (Holmes 397). Manufacturers and those
who ran engines respected the menace of rapid changes in
temperature. Bill Lamb of Lexington, Kentucky, remembers that
railroad engineers fired boilers as slowly as possible taking many
hours to do so. Once heated, the firebox was kept at as constant a
temperature as could be managed through banking the fire when the
locomotive was idle.

In terms of allowable pressures, designing engineers expected
the tensile strength of wrought-iron plates to be approximately
fifty thousand psi and of mild-steel plates to be around sixty
thousand psi. Steel plates should not be less than fifty thousand
and not more than seventy thousand psi; if more than seventy
thousand, they would be brittle, according to tum-of-the-century
texts on mechanical engineering (Forney 188-89, for example).

A review of some of the catalogues which engine manufacturers
printed to advertise equipment for agricultural use reveals the
evolving story of iron and steel. In 1891, the Harrison Machine
Works of Belleville, Illinois, claimed, ‘The very best
Tennessee iron is in the boilers. The castings are made from
selected pig iron.’ The Harrison Jumbo boiler’s outside
shell was ‘the best’ Charcoal Hammered Number 1 iron of
fifty thousand psi tensile strength, while the firebox and tubes
heets were ‘the best’ flange iron of 65,000 psi. Clearly,
Harrison used wrought-iron plates for the boiler proper.
Incidentally, Charcoal Hammered iron was not always hammered as
advertised. Also, it made acceptable shells but was not good for
flanging. In 1893, C. Aultman & Company of Canton, Ohio, were
building their own boilers of mild steel with a tensile strength of
sixty thousand psi. By 1895, the Buffalo-Pitts Company of Buffalo,
New York, used shell steel of sixty thousand psi for the boiler
cylinder (⁹/₃₂ of an inch thick) and for the
furnace casing (5/₁₆ of an inch thick). They put flanged
firebox steel into their firebox (⁹/₃₂ of an
inch thick) and into their tubesheets (³/₈ of
an inch thick). The Buffalo-Pitts catalogue of 1910 called
attention to the fact that their boilers were ‘the best’
open-hearth firebox and flange steel and could safely carry 150 psi
working pressure.

In 1903, the Northwest Thresher Company of Stillwater,
Minnesota, were using steel of sixty thousand psi tensile strength.
In their return-flue engines of eighteen horsepower or smaller, the
main flue was ^5/₁₆ of an inch thick, the
shell of an inch, and the tubesheet ³/₈. In
the 20 horsepower and larger engines, the main flue was
³/₈ of an inch thick, the shell
⁵/₁₆ of an inch, and the tubesheet
⁷/₁₆. Interestingly, in their twenty-five
horsepower simple and thirty horsepower compound engines, the main
flue had three sections, the central portion
¹³/₃₂ of an inch thick, the outer ends
³/₈ of an inch.

Robinson & Company of Richmond, Indiana, were still building
their own hand-riveted boilers of extra-heavy marine steel in
1906:

It is the only hand riveted boiler we know of today, and it
grades with other hand made articles, being considered 20 per cent
more durable, and costing, as we well know, 20 per cent more to
construct than machine riveted. And the workmanship on it
throughout is of the same careful, thorough-going sort which places
this boiler in a class by itself. . . .(4)

Likewise, the J. I. Case Company of Racine, Wisconsin, were
building their own boilers in 1907; theirs were of open-hearth
flange steel of sixty thousand psi tensile strength. The steel used
in Case boilers had to pass rigid chemical and physical tests in
Case’s own laboratories. In 1909, their catalogue noted that
the seams of Case boilers were hydraulic riveted.

Of all the catalogues of companies manufacturing agricultural
steam engines, the Port Huron Company’s 1908 advertising
brochure lavished the most pages on describing the construction of
their boilers, which could carry a working pressure up to 175 psi.
The shell, wagon top, and dome were of flange steel, while the
firebox casing, the crownsheet, the throatsheet, and the tubesheets
were of more costly firebox steel. The Port Huron, Michigan,
company conducted their own inspection at the steel mill because
steel manufacturers might stamp metal with a grade which the
chemical and/or physical properties of that metal would not
deserve. Port Huron established a narrow leeway for
tensile-strength specifications: 55,000 up to 63,000 psi. In its
tests, the firm rejected plates the elastic limit of which was
reached before half of the ultimate strength had been applied. Port
Huron’s catalogue mentioned that ‘red short’ steel,
which might crack while being worked at red heat, often could be
blamed on excessive sulfur; therefore, Port Huron allowed only
⁴/₁₀₀ of one percent of sulfur in flange
steel and ³/₁₀₀ of one percent in firebox
steel. Port Huron stated:

That our sulphur (sic) specifications are very rigid is
evidenced by the fact that one of the largest plate mills in the
country could not furnish our ‘Fire Box’ grade, and the
mill from which we regularly obtain our plates had at three
different times asked us to modify our specifications as to
sulphur, which we have steadfastly declined to do.(39)

Port Huron’s fourteen horsepower single simple engine and
sixteen horsepower single compound engine had boilers with shells
⁵/₁₆ of an inch thick and with tubesheets of
an inch thick; the company’s larger engines had boilers with a
shell ³/₈ of an inch thick. In catalogues of
later years, Port Huron called attention to the fact that, while
the company’s larger engines had boiler dome-shells
⁵/₁₆ of an inch thick, the tubesheets and
throatsheet measured half an inch in thickness. Given the safety
factor which Port Huron employed in designing boilers, actual
strength of the boiler was ‘five times as great’ as the
allowable pressure indicated.

In 1910, the Geiser Manufacturing Company of Waynesboro,
Pennsylvania, specified a tensile strength for their boiler plate
between 55,000 and 65,000 psi. Their tubesheets were half an inch
thick, their shells between and ³/₈ of an
inch, depending on the size of the engine. At the same time, the
Reeves Company of Columbus, Indiana, offered boilers made of
flange-steel plate tested to sixty thousand psi tensile strength.
The Reeves catalogue announced, ‘Not a pound of shell-steel
plate is used in these boilers’ (4).

In 1912, the Frick Company of Waynesboro, Pennsylvania, used
open-hearth homogeneous flange steel of between 55,000 and sixty
thousand psi tensile strength for their boilers. In 1913 and 1914,
the Nichols & Shepard Company of Battle Creek, Michigan,
featured boilers having good steel plate ⁷/₁₆
of an inch thick in the wagon top of their small engines and half
an inch thick in their twenty-five and thirty horsepower engines;
such thickness in the wagon top ensured strength where all of the
principal brackets attached. The tube sheets on Nichols &
Shepard engines measured half an inch thick.

Also in 1913, the Huber Manufacturing Company’s return-flue
boilers had an outer shell between and ³/₈ of
an inch thick, according to the size of the engine. By 1914, the
Marion, Ohio, company’s marine-steel shells measured
⁵/₁₆ of an inch thick in their smallest
engine (sixteen horsepower) and \ in their largest engine (thirty
horsepower). The main fire flue thickness, meanwhile, ranged from
³/₈ of an inch to ⁷/₁₆,
and the heads ranged from ³/₈ to a full half
inch.

At about this time (1914), most engine-manufacturing companies
were using open-hearth steel of sixty thousand psi tensile strength
and hydraulic double-riveted butt straps. The Waterloo
Manufacturing Company of Waterloo, Ontario, however, used a
triple-riveted seam on the boilers of their sixteen and eighteen
horsepower engines. The 1916 Waterloo catalogue pointed out that
their boilers were constructed in their own factory. Adhering
conscientiously to the principle of truth in advertising, the A. D.
Baker Company of Swanton, Ohio, stated that their boiler plate had
been tested to 55,000 psi tensile strength (not the customary sixty
thousand).

The history of boiler manufacturing from the late 1800s to the
early 1900s shows a trend away from wrought iron and toward better
and better steel. No matter how excellent the boiler plate,
however, the boiler was only as strong as its weakest rivet!
Designing engineers knew that iron or steel rivets had to be
especially good quality: strong, ductile, and able to withstand
severe deformation ‘at all temperatures.’ Rivets under a
diameter of ³/₈ inch commonly were
‘worked cold, and this is the most trying test of quality
possible’ (Thurston 114). The tenacity of good rivets
necessarily equaled that of good steel plate, sixty thousand psi.
The head of a good rivet would not harden or become brittle beneath
the blows of a hammer; a good rivet of ⁵/₈
inch diameter could be ‘doubled up and hammered together, cold,
without exhibiting a trace of fracture.’ Split in two, a good
iron rivet would show close, smoothly-curved grain with no slag, a
good steel rivet absolute uniformity with no trace of grain. Steel
rivets were so pure as to take a mirror surface when polished
(Thurston 114-15).

Rivets usually had a straight or slightly-tapered body with a
head 1.5 or 1.6 times the diameter of the shank. The shank was two
to four percent smaller than the hole it would fill. The thickness
of the head measured between seventy and seventy-five percent of
the diameter of the body (or shank) of the rivet. The length of the
shank was two and a quarter or two and a half times the diameter of
the hole (Kent says 1.8 times for double-riveted butt joints), and
the hole’s diameter often equaled the double thickness of
plates held together by the rivet. Hand-hammers and riveting
machines drove the small end down to form a cone-shaped or
hemispherical head (Thurston 115).The Mechanical Engineers’
Pocket-Book gave designing engineers detailed descriptions of a
variety of rivets useful in all manner of situations.

Thurston told mechanical engineering students that good
hand-riveting surpassed bad steam-riveting. He also warned against
careless handling of rivets which could create a fin on the shank
in between the sheets being-riveted. Such a fin would hold sheets
apart and cause leaks. To prevent the formation of fins, builders
should carefully ascertain that plates were well adjusted and in
strong contact before heading up the rivets, according to Thurston,
who preferred that, in hand-hammering, a cup-shaped die be used. He
claimed that the hemispherical head produced by the cupped die
presented a form stronger than that created by a cone-shaped die.
He recommended that workers learn how to hit hand-hammered rivets
with the fewest number of blows possible. Given a choice between
steam-riveting and hydraulic-riveting, Thurston would select the
latter because its slow application of pressure would do less
damage to the plate than steam-riveting would do. He feared that,
unless carefully monitored, machine-riveting of any kind was more
likely to cause defective rivets than hand-riveting would cause
(125-26). Kent cautioned mechanical engineers that hand-riveted
joints were liable to present the serious defect of ‘visible
slip,’ which could begin at a comparatively small load and
render the joint apt to fail under sudden strain (355). Regardless
of the method of riveting, rivets generally confronted shearing
stresses (Thurston 115). In iron, the metal resisted shearing
differently according to the plane in which the stress was acting.
Shearing strength was ⁴/₅ of the tenacity, if
the shear were in a plane perpendicular to the direction in which
the iron plate was rolled and if the tension were applied in a
plane parallel to the direction of rolling. Kent added:

The shearing resistance in a plane parallel to the direction of
rolling is different from that in a plane perpendicular to that
direction, and again differs according as the plane of shear is
perpendicular or parallel to the breadth of the bar. In the former
case the resistance is 18 to 20% greater than in a plane
perpendicular to the fibres, or is equal to the tenacity. In the
latter case it is only half as great as in a plane perpendicular to
the fibres.(363)

The shearing resistance of iron rivets likewise varied from full
tenacity, through eighty percent tenacity, to merely fifty percent
tensile strength!

In the early years of boiler manufacturing, only a single row of
rivets joined a lap seam. Eventually, builders saw the wisdom in
using a double row of rivets, and, before long, triple-riveted lap
seams made their appearance. Last came the butt-strap joints which,
in their most perfected form, consisted of several rows of rivets
joining straps inside and outside the boiler where the two edges of
the boiler plate met but did not overlap. Forney believed that
well-constructed lap joints were as secure as any butt-strap joints
(208), and Kent reported results of tests wherein the efficiency of
lap joints was, for all intents and purposes, the same as that of
butt-strap joints (359-60). The 1913 Case catalogue featured a
double-riveted lap seam on sixty horsepower (and smaller) engines,
a triple-riveted lap on seventy-five and eighty horsepower engines,
and a double butt-strap on the 110 horsepower engine.

In writing about single-riveted joints, Thurston concluded that
they have, in general, about sixty percent the strength of a solid
sheet, whereas double-riveted lap joints enjoy about seventy
percent the original tenacity of the plate before riveting. If
properly distributed, additional rows of rivets would bring the
joint even closer to the tensile strength of the boiler plate
itself, Thurston stated (117). The Power Catechism
instructed engineers that a triple-riveted lap seam contains the
maximum number of rows possible because adding another row of
rivets would bring about further widening of the space between
rivets (the ‘pitch’); consequently, the joint would be
liable to leak. By increasing the pitch, a designer would be
lessening the number of rivets, thereby increasing the stress on
each; rivets could begin to shear. If a mechanical engineer were to
stick to three rows of rivets but then try to add strength by
increasing the number of rivets per row, that engineer would reduce
the section of plate between the rivets and would increase the
chances that the plate would pull apart (41-42).

According to Thurston, the placement of rivet-rows in the sheet
should balance the potential shearing of rivets against the
potential breaking away of the edge of the sheet or a tearing along
the lap (117). In such lap joints, the plate could crack between
rivet holes, could split from the rivet toward the edge of the
sheet, could crack on a line parallel to the rivet row on the plate
just inside either overlapping edge (especially where the plate
would be scored from caulking), or could become crushed from the
rivet toward the sheet’s edge because the pressure inside would
be attempting to ‘unroll’ the cylindrical shape of the
boiler (Forney 193; Port Huron catalogue 7). Barring weakness
anywhere in the plate itself, a designing engineer could assemble a
host of careful calculations so as to build a boiler the rivets of
which, under excessive pressure, would pop out before the boiler
would explode, thereby creating miniature ‘safety valves’
to release steam. Among the ‘rules of thumb’ which
mechanical engineers followed were the facts that a lap usually
extended beyond the rivet holes 1.5 times the rivets’ diameter
(Thurston 117) and that the pitch in the butt-joint ordinarily
amounted to 4.1 times the diameter of the rivet hole (Kent
358).

Punching out the holes for rivets increased the strength of a
sheet made of extremely soft and ductile metal because the
‘flow’ of the metal outward from the hole stiffened the
surrounding area; on the other hand, punching injured hard iron or
steel. Thurston recommended drilling holes in steelwhich indeed was
the practice of most builders. A few, however, punched a small hole
in steel then reamed or counter bored it to the correct diameter.
Thurston added that the section of solid material left between
rivet holes in a single row of rivets in either hard iron or steel
plates (having excessive levels of manganese or phosphorus) lost
tensile strength most in lap joints with punched holes, as well as
in sheets riveted by steam rather than by hydraulic pressure. The
strength of rivets in such plates, however, was greater against
shearing. A zig-zag pattern in a double row of rivets was best for
improving the tensile resistance of the material between all of the
rivets in a lap joint, but a double-strapped butt joint prevented
the bending of the main plate and nearly doubled the shearing
strength of each rivet (123-24). Thurston suggested that steel be
annealed after each operation to restore lost ductility (64).
Forney, though, believed that annealing steel plates after punching
could be mishandled and might lead to more harm than good
(192).

Considering the effects of rivets and riveting, designing
engineers came to recognize that the real factor of safety of
well-made boilers should not be less than six and ought to be eight
or ten!

In the most general sense, a ‘false’ factor of safety of
six is reduced to 3.36 (0.56 x 6 = 3.36) for single-riveted lap
seams or to 4.2 (0.70 x 6 = 4.2) for double-riveted lap seams
(Thurston 122-23). Mechanical engineers also had to consider the
molecular and chemical changes occurring in metal over long periods
of time:

The first change to be referred to is that gradual and
imperceptible one which, occupying months and years, and under the
ordinary influence of the weather going on slowly but surely,
results finally in important modifications of the proportions of
the chemical elements present, and in a consequent equally
considerable change of the mechanical properties of the
metal.(Thurston 81).

Thurston explained how especially vulnerable iron is to
oxidation:

A loss of strength and of ductility is very often observed in
the iron of which boilers are composed, as they advance in age, due
to the progress of oxidation. . . .within and between the laminae
of which the sheets may be composed. The plate may be thus very
nearly destroyed, at times, before this action may be detected. In
some cases the iron may be nearly all destroyed, and only a sheet
of oxide may remain; while the boiler, if not working under high
pressure, may still appear sound. Such deterioration is often a
source of great danger.(149)

Good cast iron could last for at least a century submerged in
salt water but would become soft enough to cut with a knife.
Exposed to the air, iron was found to rust and to deteriorate more
quickly than steel. Ironically, the smoke from the ‘iron
horse,’ or railroad locomotive, rapidly ruined the iron in
railway bridges because the combustion of sulfur in coal acted as a
corrosive agent and became even more deleterious when bridge iron
became coated with soot (Kent 385-86).

Other changes occurring over time in iron and steel resulted
from stress. Textbooks for engineering students defined
‘fatigue’ as the weakening of metal by repeated stresses.
Giving the metal an opportunity to rest would relieve the effects
of certain internal stresses, but rest (or, for that matter,
annealing) only occasionally relieved actual fatigue. If not
excessively weakened, steel razors were known to recover keenness
after a time of rest. Thurston stated: ‘Boiler-makers
frequently search old boilers carefully, when reopened for repairs
after a long period of service, to find any tools that have been
lost and so improved’ (81). Likewise, springs were found to
regain tension after resting, and scythes exposed to the weather
for a long season apparently were restored. Iron and steel could
best withstand stationary loading; to a lesser degree, they could
endure tension alternating with relief; but least of all could they
recover from alternate and equal tensions and compressions
(Thurston 80). The fluctuating temperatures of boilers and the
pounding rhythms of steam engines gave iron and steel their
ultimate tests.

Gone are the days when designing engineers, armed with pencils
and slide rules, brought complex bodies of knowledge to bear on how
to improve boilers and steam-powered mechanisms. Vanished are most
of the factories which, occupying entire city blocks, focused a
growing country’s attention on the progress of agricultural
industry from iron ore to engines. Today, one strolls around the
remaining brick edifices of an old-time manufacturing giant and
wonders what became of its might and grandeur. If one stands still
long enough, however, one’s imaginative mind can begin to hear
the hammering of rivets, the pressing of iron sheets between dies
to compel them to take the shapes of dometops, handhole plates, and
tubesheets, and the thud of the ‘tup’ or hammer dropping
six feet to knock out small parts. By closing one’s eyes, one
can picture the newly finished traction engines under their own
steam chuffing forth beneath an azure sky.

Works Cited

Engine-company catalogues (reprints) too numerous to list
separately Forney, Matthias N. Catechism of the Locomotive. New
York: Railroad Gazette, 1897.
Holmes, George C. V. The Steam Engine. New York: Longmans, Green,
1900.
Kent, William. The Mechanical Engineers’ Pocket-Book. New
York: Wiley, 1895.
Lamb, William Morris. Telephone conversation Nov. 20, 1994.
The Power Catechism. New York: McGraw, 1897.
Thurston, Robert H. A Manual of Steam-Boilers: Their Design,
Construction, and Operation. New York: Wiley, 1904.