CHAPTER IX

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 theengine, 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 theillustrationfacing 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.

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 accompanyingillustration, 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 theillustrationa 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.

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 wasalmost 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, asshown. 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. Thefollowingshows 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.

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 presidentof 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.

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