Part 21 (2/2)

Unless this happy faculty exists ab initio in the brain of the mechanical engineer, he will have a hard and disappointing life before him. It is the early cultivation of the imagination which gives the right flexibility to the thinking faculties. Thus business, commerce, and mechanics are all the better for a little healthy imagination.

So soon as I had returned home, I set to work and prepared the working drawings of the steam pile-drivers. They were soon completed, conveyed to Devonport, and erected on the spot where they were to be used.

They were ready on the 3d of July 1845. Some preliminary pile-driving had been done in the usual way, in order to make a stage or elevated way for my pile-driver to travel along the s.p.a.ce where the permanent piles were to be driven. I arranged my machines so that they might travel by their own locomotive powers along the whole length of the coffer dam, and also that they should hoist up the great logs of Baltic timber which formed the Piles into their proper places before being driven.

The entire apparatus of the machine was erected on a strong timber platform, and was placed on wheels, so that it might move along the rails laid down upon the timber way. The same boiler that supplied the steam hammer part of the apparatus served to work the small steam-engine fixed to the platform for its locomotion, and also to perform the duty of rearing the next pile which had to be driven. The steam was conveyed to the hammer cylinder by the jointed pipe seen in the annexed engraving. The pipe accommodated itself to any elevation or descent of the hammer. The whole weight of the cylinder, hammer-block, and guide box, supported by the shoulders of the pile, amounting to seven tons in all, rested upon the shoulders of the pile as a ”persuader;” and the eighty blows per minute of the four-ton hammer came down with tremendous energy upon the top of the pile head. No soil, that piles could penetrate, could resist such effective agencies.

[Image] Diagram of the Steam Pile-Driver

Explanation of the Diagram of the Steam Pile-Driver.--The chief feature of novelty of this pile-driving machine consists in the employment of the direct action of the Steam Hammer as the blow giving agent, and also in the manner in which the dead weight of the entire apparatus, consisting of the hammer-block C, the steam cylinder A, and its guide-case B, is employed to importantly aid the effect of the rapid and energetic blows of the steam hammer. These ponderous parts rest on the shoulders of the pile H all the while it is being driven, the pile in this respect being the only support of the apparatus A B C.

So that, besides the eighty blows per minute that the four-ton steam hammer energetically deals out to the head of the pile from a four foot fall the dead weight of the apparatus constantly acts as a most effective ”predisposer” to the sinking of the pile into the ground; the hoisting chain D being let slack the while, so as to allow A B C to ”follow down” the pile H, while the eighty blows per minute are incessantly showered on its head. The upward stroke of the piston, with its attached hammer-block C, is arrested at the proper height not only by allowing the steam that raised it to escape, but as soon as the piston pa.s.ses the escape holes X X, the confined air above the piston at O rebounds, and so aids most effectively in increasing the energy of the fall of the hammer-block C on the pile head.

There was a great deal of curiosity in the dockyard as to the action of the new machine. The pile-driving machine-men gave me a good-natured challenge to vie with them in driving down a pile. They adopted the old method, while I adopted the new one. The resident managers sought out two great pile logs of equal size and length--70 feet long and 18 inches square. At a given signal we started together.

I let in the steam, and the hammer at once began to work. The four-ton block showered down blows at the rate of eighty a minute; and in the course of four and a half minutes my pile was driven down to the required depth. The men working at the ordinary machine had only begun to drive. It took them upwards of twelve hours to complete the driving of their pile!

Such a saving of time in the performance of similar work--by steam versus manual labour--had never before been witnessed.

The energetic action of the steam hammer, sitting on the shoulders of the pile high up aloft, and following it suddenly down, the rapidly hammered blows keeping time with the flas.h.i.+ng out of ”the waste steam at the end of each stroke, was indeed a remarkable sight. When my pile was driven, the hammer-block and guide case were speedily re-hoisted by the small engine that did all the labouring and locomotive work of the machine; the steam hammer portion of which was then lowered on to the shoulders of the next pile in succession. Again it set to work.

At this the spectators crowding about in boats, p.r.o.nounced their approval in the usual British style of ”three cheers!”

My new pile-driver was thus acknowledged as another triumphant proof of the power of steam.

The whole of the piles for this great work were speedily driven in.

The wall was constructed, and the docks were completed in an unusually short time. The success of my pile-driver was followed by numerous orders. It was used for driving the immense piles required for the High Level Bridge at Newcastle, the great Border Bridge at Berwick-upon-tweed, the Docks at Tynemouth, the Docks at Birkenhead, the Docks at Grimsby, the new Westminster Bridge, the great bridge at Kief in Russia, the bridge at Petersburg, the forts at Cronstadt, the Embarrage of the Nile, at Yokohama in j.a.pan, and at other places.

It enabled a solid foundation to be laid for the enormous superstructures erected over them, and thus contributed to the permanence of many important undertakings.

The mechanical principles on which the efficiency of the steam pile-driver chiefly depends are as simple as I believe they are entirely novel and original. The shoulder of the pile acts as the sole supporter of the ponderous ma.s.s of the hammer-block, cylinder, and guide-box. This heavy weight acts as a predisposing agency to force the pile down, while the momentum given by the repeated fall of the hammer, at eighty blows the minute, brings the constant dead weight into full action. I am not aware of any other machine in which such a combination of mechanical forces is employed.

Another very effective detail consisted in employing the waste steam in the upper part of the cylinder for the purpose of acting as a buffer to resist any undue length of the upward stroke of the piston.

But for this the cylinder covers might have been knocked off.

The elastic buffer of waste steam also acted as a help to the downward blow of the hammer-block. The simplicity and effectiveness of these arrangements form--if I may be allowed to say so--a happy ill.u.s.tration of my ”Definition of Engineering,” the application of common sense in the use of materials.

The folding-up steam pipe with which the steam was conveyed from the boiler to the cylinder at all heights, and the way in which the folding joints accommodated themselves to the varying height of the cylinder, was another of my happy thoughts. In fact, this invention, like most others, was the result of a succession of happy thoughts.

The machine in its entirety was the result of a number of common-sense contrivances, such as I generally delight in. At all events, this most effective and novel machine was a special favourite with me.

I may mention, before concluding this branch of my subject, that pile-driving had before been conducted on what I might term the artillery or cannon-ball principle. A small ma.s.s of iron was drawn slowly up, and suddenly let down on the head of the pile at a high velocity. This was destructive, not impulsive action. Sometimes the pile was s.h.i.+vered into splinters, without driving it into the soil; in many cases the head of the pile was shattered into matches, and this in spite of a hoop of iron about it to keep the layers of wood together. Yet the whole was soon beat into a sort of brush.

Indeed, a great portion of the men's time was consumed in ”reheading”

the piles. On the contrary, I employed great ma.s.s and moderate velocity. The fall of the steam hammer-block was only three or four feet, but it went on at eighty blows the minute, and the soil into which the pile was driven never had time to grip or thrust it up-- an impediment well known to ordinary pile-drivers. At the end of the driving by my steam hammer, the top of the pile was always found neat and smooth, indeed more so than when the driving began.

I may again revert to my interview with the Lords of the Admiralty on the occasion of my first meeting them at Devonport. I was residing at the hotel where they usually took up their quarters while making their annual visitation of the dockyard. I was honoured with an invitation to confer with Sir George c.o.c.kburn, Mr. Sidney Herbert, and Captain Brandreth on a subject of considerable importance; namely, the proving of chain cables and anchors required for the Royal Navy. The question was mooted as to whether or not some permanent injury was done to both by the test strains to which they were submitted before being put on board s.h.i.+p. This was a subject of vital importance. The members of the Board requested me to act as one of a committee to inquire into the subject. I felt much gratified by the invitation and gladly accepted it.

On discussing the subject with these gentlemen that evening, I found that Sir George c.o.c.kburn entertained an ingenious theory in support of his apprehensions as the effect of ”over-proof” straining of cables and anchors. It was that they were originally in the condition of a strong man who had to lift some heavy weight, requiring him to exert his muscular strength to the utmost; and, although he might perform the feat, it was at the cost of a permanent injury, and that he might never be able to lift the same weight again. This, however true it might be with regard to flesh and bone structures, was scarcely true with respect to mechanical agencies. I proposed a simple experiment with chain cables, which, it occurred to me, would show quite a different result--namely, that the capability of resisting the severest proof-strain would rise rather than fall at each successive proof of the same chain cable.

To test the correctness of my supposition, we had a first-cla.s.s chain cable put into the proof machine,and subjected it to such a strain as to break it again and again, until at last it was divided almost into single links. As I expected, the proof or breaking strain kept rising and rising as each successive remaining portion of the cable was torn asunder, thus showing that no injury to the natural tenacity of the chain had resulted from the increased proofs to which it had been subjected, and that the last broken links had been much more resisting than the first. The same cla.s.s of demonstrative experiments was made with anchors, and other wrought-iron work used in the service.

The Admiralty officers were much gratified with the result, as removing a groundless but very natural apprehension, heightened, no doubt, by the suggestions that had been made to the Admiralty, that their standard proof strain was not only too high in itself, but produced permanent damage to what at the outset was of the toughest iron.

My system of continued proof-straining was, in fact, another exemplification of the ”Survival of the Fittest”!

A very interesting truth came out in the course of our experiments.

It was that the chief cause of failure in the links of chain cables arose, not so much from their want of tenacity, or from the quality of the iron, but from some defective welding in the making of the links.

To get at this truth, many excellent cables as received from the contractors, as well as veteran ones that had held great s.h.i.+ps riding at anchor in terrible gales, were pulled asunder link by link by an intentional destructive strain by the proving machine.

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