Designs of Horizontal Engine Beds. Engine Details. Presentation of the
Indicator at the Newcastle Meeting of the British Association for the
Advancement of Science.
Much of my time was now devoted to working out improvements in the
design of the engine, some of which had occurred to me during the
exhibition, and which I was anxious to have completed before bringing
the engine to the notice of builders. The first point which claimed my
attention was the bed. The horizontal engine bed had already passed
through three stages of development. The old form, in common use in
the United States, was a long and narrow box, open at top and bottom.
The sides and ends of this box were all alike, and their section
resembled the letter H laid on its side, thus ⌶. This on some accounts
was a very convenient form. The surface of the bed was planed, and
everything was easily lined from this surface. The cylinder was made
with two flanges on each side, which rested on the opposite surfaces of
the bed, permitting the cylinder to sink between them as desired. The
pillow-block rested on one or the other of these surfaces, according as
the engine was to be right or left hand. The guide-bars were bolted on
these opposite surfaces.
The first break in this monotony was made by Mr. Corliss, and was
remarkable for the number and the radical nature of its new ideas. The
cylinder was provided with broad feet near its ends, and was planted on
the foundation. The pillow-block was provided with similar supports and
was also secured to the foundation. The bed, so called, was a tie-beam
uniting the cylinder and pillow-block, and not otherwise supported.
It was of T section. The horizontal member was behind the center line
of the engine, and was made very deep in the middle of its length to
prevent deflection. The vertical member extended equally above and
below the former and carried the guides, which were top and bottom
V-grooves, between which the cross-head ran and the connecting-rod
vibrated. The cross-head was provided with shoes fitting these V’s,
and was adjustable vertically between them. The connection with the
cylinders was made by a circular head supported by curved brackets.
This connection was firm on one side only. The bed was reversible to
suit right- or left-hand engines by merely turning it over.
In the bed for my engine, Mr. Richards struck out another design, which
avoided some objections to the Corliss bed. The guides were supported
from the foundation, and the connection with the cylinder was more
substantial, but the reversible feature had to be sacrificed.
Mr. Richards’ bed, shown in the illustration facing page 70, was
designed in the box form, the superior rigidity of which had been
established by Mr. Whitworth. It was a box closed at the top and
flanged internally at the bottom. It rested on the foundation through
its entire length. The main pillow-block was formed in the bed, as were
also the lower guide-bars. The cylinder was secured on its surface in
the old-fashioned way.
[Illustration: Engine Bed Designed by Mr. Porter. Engraving made from
an Old Print.]
It occurred to me that the best features of the Corliss and the
Richards designs might be combined to advantage. This idea I worked
out in the bed shown in the accompanying illustration, taken from a
circular issued by Ormerod, Grierson & Co., of Manchester, and which
was made from a photograph of an engine sent by that firm to the Oporto
International Exhibition in 1865. It will be seen that this is Mr.
Richards’ bed with the cylinder bolted to the end after Mr. Corliss’
plan. The great strength of the bed enabled the supports under the
cylinder to be dispensed with. This left the cylinder free to expand by
heat, and made it convenient to attach the steam or exhaust connections
or both underneath. This bed has remained without change, except in one
important respect. I made the first cylinders with a bracket which was
keyed up from the base of the bed. In the illustration a corner of this
bracket appears. At the Paris Exposition in 1867 Mr. Beyer, of the firm
of Beyer & Peacock, the Manchester locomotive-builders, when he saw it,
told me I did not need that bracket. I then left it off, but found the
cylinder to wink a little on every stroke when the heavy piston was at
the back end. To find the weak place, I tried the following experiment
on an engine built for the India Mills in Manchester. I filed two
notches in the edges of the brackets on the bed, opposite each other
and about ten inches forward of the head, and fitted a piece of wire
between them. This wire buckled very decidedly on every revolution
of the engine, when the piston was at the back end of its stroke. I
then united these brackets into a hood, and lengthened the connection
with the surface of the bed, as it is now made. This affords a perfect
support for the cylinder. Experiments tried at the Cambria Iron Works
on a cylinder of 40-inch bore and 48-inch stroke, with a piston
weighing 3600 pounds and running at 100 double strokes per minute,
showed the back end of the cylinder standing absolutely motionless.
This experiment will be described hereafter.
[Illustration: Cross-head Designed by Mr. Porter.]
The cross-head which I designed at this time has always interested me,
not only on account of its success, but also for the important lesson
which it teaches. I abolished all means of adjustment. The cross-head
was a solid block, running on the lower guide-bars if the engine were
running forward, as was almost always the case, and these guide-bars
were formed on the bed. The pin was of steel, with the surface hardened
and ground truly cylindrical, set in the middle of the cross-head, and
formed with square ends larger than the cylindrical portion. These
were mortised parallel into the cross-head, and a central pin was
forced through the whole. The flats on the pin I afterwards copied
from a print. These prevent the formation of shoulders at the ends
of the vibration of the boxes. I would like to know to whom we are
indebted for this valuable feature. Every surface was scraped to
absolute truth. The lubrication was internal, as shown. There are many
of these cross-heads which have been running at rapid speeds in clean
engine-rooms from twenty to thirty years, where the scraping marks on
the lower bars are still to be seen.
The lesson is a most important one for the future of steam engineering.
It is this. Two flat cast-iron surfaces, perfectly true and incapable
of deflection, with the pressure equally distributed over a sufficient
area, protected from dirt and properly lubricated, will never have the
clean film of oil between them broken or even varied in thickness, and
will run together without wear perpetually and at any speed whatever.
The conclusion is also abundantly warranted that a tendency to heat
need not exist anywhere in even the least degree, in engines running at
the greatest speeds. This can always be prevented by truth of design
and construction, and the selection of suitable material. This fact is
abundantly established by varied experience with cylindrical as well
as with flat surfaces, and for other materials, though not for all, as
well as for cast iron.
The solid end connecting-rod appears in this engine. This was shown
to me by Mr. James Gulland, a Scotch draftsman at Ormerod, Grierson &
Co.’s. He did not claim to have originated it, but only told me that
it was designed in Scotland. I saw at once its peculiar value for
high-speed engines. Every locomotive designer knows the pains that must
be taken to prevent the straps on the crank-pins from spreading at
high speeds, under the pressure exerted by the transverse fling of the
connecting-rod. This solid end renders the connecting-rod safe in this
respect, even at thousands of revolutions per minute. For single-crank
engines, on which only it can be applied, it is invaluable. This solid
rod-end possesses also another advantage. The wear of the crank-pin
boxes and that of the cross-head-pin boxes are both taken up in the
same direction, so the position of the piston in the cylinder will be
varied only by the difference, if any, between the two. With a strap
on both ends, the connecting-rod is always shortened by the sum of
the wear in the two boxes. The solid rod-end enabled me to reduce the
clearance in the cylinder to one eighth of an inch with entire safety.
The piston never touched the head.
As this construction was shown to me, the wedge was tapered on both
sides. It seemed that this would be difficult to fit up truly, and it
also involved the necessity of elongating the bolt-holes in the rod, so
that the wedge might slide along in taking up the wear. I changed it
by putting all the taper of the wedge on the side next to the brass,
making the other side parallel with the bolt-holes. This enabled the
opening in the rod-end to be slotted out in a rectangular form, and
made it easy for the wedge-block to be truly fitted.
While on this subject I may as well dispose of the connecting-rod,
although the other changes were made subsequently, and I do not
recollect exactly when. The following shows the rod and strap as they
have been made for a long time. The taper of the rod, giving to it a
great strength at the crank-pin neck to resist the transverse fling,
was, I presume, copied by me from a locomotive rod. The rounded end of
the strap originated in this way. I had often heard of the tendency
of the cross-head-pin straps to spread. This was in the old days,
when these pins were not hardened, indeed were always part of the
iron casting. The brasses, always used without babbitt lining, would
wear these pins on the opposite acting sides only. Brass, I learned
afterwards, will wear away any pin, even hardened steel, and not be
worn itself. When this wear would be taken up, the brasses would bind
at the ends of their vibration, coming in contact there with the unworn
sides of the pin. To relieve this binding it was common for engineers
to file these sides away. All I knew at that time was that the straps
would yield and spread. It occurred to me to observe this deflection
in a spring brass wire bent to the form of a strap. The pressure being
applied on the line of the pin center, the deflection appeared to take
place mostly at the back, and so I stiffened it. Since the introduction
of the flats on the pin, which prevent the exertion of any force to
spread the strap, this form seems to be rather ornamental than useful.
[Illustration: Connecting-rod and Strap.]
To this strap I added a wiper for lubricating the cross-head pin
automatically. The drop of oil hung from the center of a convex surface
provided above the wiper. The latter was inclined forward, and its edge
partook of the vibration of the connecting-rod. On the backward stroke
this edge cleared the drop. At the commencement of the forward stroke
it rose to take it off.
A note of the change then made by me in stop-valves will conclude the
record of these changes. The valve and its seat had always been made
of brass. The latter was fitted in a cast-iron chamber, and, expanding
more than the iron, was apt to work loose. I disused brass entirely,
employing a cast-iron valve in the cast-iron seat. These always
remained perfectly tight, showing the additional cost and trouble of
brass to be unnecessary.
At the meeting of the British Association for the Advancement of
Science in 1863, held in Newcastle, I read before the Mechanical
Section a paper on the Richards indicator, illustrated by one of the
instruments and diagrams taken by it from locomotives. The paper was
very favorably received. The description of the action of the arms,
in preventing by their elasticity in combination with a stop any more
than a light pressure being applied to the paper, called out especial
applause. The president of the Mechanical Section that year was
Professor Willis, of Cambridge, the designer of the odontograph form
of tooth, which enables gear-wheels of the same pitch to run together
equally well, whatever may be the difference in their diameters. I
felt very deeply impressed at standing before a large assembly of
the leading mechanical engineers of Great Britain, and where so many
important things had first been presented to the world, where Sir
William Armstrong had described his accumulator, by which enormous
power is supplied occasionally from small pumps running continuously,
and where Joule had explained his practical demonstration of the
mechanical equivalent of heat.
On my journeys to Newcastle and back to London I met two strangers,
each of whom gave me something to think about. It happened that each
time we were the only occupants of the compartment. Englishmen, I
observed, were always ready to converse with Americans. Soon after
leaving London, my fellow-passenger, a young gentleman, said to me,
“Did you observe that young fellow and young woman who bade me good-by
at the carriage door? He is my brother, and they are engaged. He is
first mate on a ship, and sails to-morrow for Calcutta. He hopes on his
next voyage to have command of a ship himself, and then they expect to
be married.” I did not learn who he was, but he said they were making
large preparations to welcome the scientists, and added that he owned
about six hundred houses in Newcastle. Evidently he was the eldest son.
On my return my companion was an elderly gentleman, a typical Tory. He
waxed eloquent on the inhumanity of educating the laboring classes,
saying that its only effect must be to make them discontented with the
position which they must always occupy.
I told him I had thought of a motto for the Social Science Congress,
which was just then in session. It was a parody on Nelson’s celebrated
order, “England expects every man to do his duty.” My proposed motto
was, “England expects every man to know his place.” He did not see the
humor, but took me seriously, and thought it excellent.