To make solid crank shafts of this material, say of 19 inches diameter, the ingot would weigh 42 tons, the forging, when completed, 17 tons, and the finished shaft 11¾ tons; so that you see there is 25 tons wasted before any machining is done, and 5¼ tons between the forging and finished shaft. This makes it very expensive for solid shafts of large size, and it is found better to make what is termed a built shaft; the cranks are a little heavier, and engine framings necessarily a little wider, a matter comparatively of little moment. I give you a rough drawing of the hydraulic hammer, or strictly speaking a press, used by Messrs. Vickers in forging down the ingots in shafts, guns, or other large work. This hammer can give a squeeze of 3,000 tons. The steel seems to yield under it like tough putty, and, unlike the steam hammer, there is no jarring on the material, and it is manipulated with the same ease as a small hammer by hydraulics.

The tensile strength of steel used for shafts having increased from 24 to 30 tons, and in some cases 31 tons, considering that this was 2 tons above that specified, and that we were approaching what may be termed hard steel, I proposed to the makers to test this material beyond the usual tests, viz., tensile, extension, and cold bending test. The latter, I considered, was much too easy for this fine material, as a piece of fair iron will bend cold to a radius of 1½ times its diameter or thickness, without fracture; and I proposed a test more resembling the fatigue that a crank shaft has sometimes to stand, and more worthy of this material; and in the event of its standing this successfully, I would pass the material of 30 or 31 tons tensile strength. Specimens of steel used in the shafts were cut off different parts - crank pins and main bearings - (the shafts being built shafts) and roughly planed to 1½ inches square, and about 12 inches long. They were laid on the block as shown, and a cast iron block, fitted with a hammer head ½ ton weight, let suddenly fall 12 inches, the block striking the bar with a blow of about 4 tons. The steel bar was then turned upside down, and the blow repeated, reversing the piece every time until fracture was observed, and the bar ultimately broken. The results were that this steel stood 58 blows before showing signs of fracture, and was only broken after 77 blows. It is noticeable how many blows it stood after fracture.

A bar of good wrought iron, undressed, of same dimensions, was tried, and broke the first blow. A bar cut from a piece of iron to form a large chain, afterward forged down and only filed to same dimensions, broke at 25 blows. I was well satisfied with the results, and considered this material, though possessing a high tensile strength, was in every way suitable for the construction and endurance required in crank shafts.

Sheet No. 1 shows you some particulars of these tests:

Tensile
Tons.
Elong.
in 5"
Bend.Fractured
Blows.
Broke
Blows.
Fall
In.
A =30.528 p. c.Good617812

In order to test the comparative value of steel of 24¾ up to 35 tons tensile strength, I had several specimens taken from shafts tested in the manner described, which may be called a fatigue test. The results are shown on the same sheet:

B =24½Good64727
B - - - 485412
C =2725.9 p. c.Good768112
D =29.628.4 p. c.Good717812
E =30.528.9 p. c.Good587712
F =35.520 p. c.Good809112

The latter was very tough to break. Specimen marked A shows one of these pieces of steel. I show you also fresh broken specimens which will give you a good idea of the beautiful quality of this material. These specimens were cut out of shafts made of Steel Co. of Scotland's steel. I also show you specimens of cold bending:

Tensile
Tons.
Elong.
in. 5"
Bend.Fractured
Blows.
Broke
Blows.
Fall
In.
G =30.927½ p. c.Good596612
H =29.330 p. c.Good669012
I =28.928.9 p. c.Good536812

I think all of the above tests show that this material, when carefully made and treated with sufficient mechanical work on forging down from the ingot, is suitable up to 34 tons for crank shafts; how much higher it would be desirable to go is a question of superior excellence in material and manufacture resting with the makers. I would, however, remark that no allowance has been made by the Board of Trade or Lloyds for the excellence of this material above that of iron. I was interested to know how the material in the best iron shafts would stand this fatigue test compared with steel, and had some specimens of same dimensions cut out of iron shafts. The following are the results: Best iron, three good qualities, rolled into flat bars, cut and made into 4½ cwt. blooms.

J =18.624.3 p. c.Good171812

Made of best double rolled scrap, 4½ cwt. blooms.

K =2232½ p. c.Good213212

You will see from these results that steel stood this fatigue test, Vickers' 73 per cent. and Steel Co.'s 68 per cent., better than iron of the best quality for crank shafts; and I am of opinion that so long as we use such material as these for crank shafts, along with the present rules, and give ample bearing surface, there will be few broken shafts to record.

I omitted to mention that built shafts, both of steel and iron, of large diameter, are now in general use, and with the excellent machines, and under special mechanics, are built up of five separate pieces in such a rigid manner that they possess all the solidity necessary for a crank shaft. The forgings of iron and steel being much smaller are capable of more careful treatment in the process of manufacture. These shafts, for large mail steamers, when coupled up, are 35 feet long, and weigh 45 tons. They require to be carefully coupled, some makers finishing the bearings in the lathe, others depend on the excellence of their work in each piece, and finish each complete. To insure the correct centering of these large shafts, I have had 6 in. dia. recesses ¾ inch deep turned out of each coupling to one gauge and made to fit one disk. Duplicate disks are then fitted in each coupling, and the centering is preserved, and should a spare piece be ever required, there is no trouble to couple correctly on board the steamer.

The propeller shaft is generally made of iron, and if made not less than the Board of Trade rules as regards diameter, of the best iron, and the gun metal liners carefully fitted, they have given little trouble; the principal trouble has arisen from defective fitting of the propeller boss. This shaft working in sea water, though running in lignum vitae bearings, has a considerable wear down at the outer bearings in four or five years, and the shaft gets out of line. This wear has been lessened considerably by fitting the wood so that the grain is endway to the shaft, and with sufficient bearing surface these bearings have not required lining up for nine years. It is, however, a shaft that cannot be inspected except when in dry dock, and has to be disconnected from the propeller, and drawn inside for examination at periods suggested by experience. Serious accidents have occurred through want of attention to the examination of this shaft; when working in salt water, with liners of gun metal, galvanic action ensues, and extensive corrosion takes place in the iron at the ends of the brass liners, more especially if they are faced up at right angles to the shaft. Some engineers have the uncovered part of the shaft between the liners, inside the tube, protected against the sea water by winding over it tarred line.

As this may give out and cause some trouble, by stopping the water space, I have not adopted it, and shall be pleased to have the experience of any seagoing engineer on this important matter. A groove round the shaft is formed, due to this action, and in some cases the shaft has broken inside the stern tube, breaking not only it, but tearing open the hull, resulting in the foundering of the vessel. Steel has been used for screw shafts, but has not been found so suitable, as it corrodes more rapidly in the presence of salt water and gun metal than iron, and unless protected by a solid liner for the most part of its length, a mechanical feat which has not yet been achieved in ordinary construction, as this liner would require to be 20 ft. long. I find it exceedingly difficult to get a liner of only 7 ft. long in one piece, and the majority of 6 ft. liners are fitted in two pieces. The joint of the two liners is rarely watertight, and many shafts have been destroyed by this method of fitting these liners.

I trust that engine builders will make a step further in the fitting of these liners on these shafts, as it is against the interest of the shipowner to keep ships in dry dock from such causes as defective liners, and I think it will be only a matter of time when the screw shaft will be completely protected from sea water, at least inside the stern tube; and when this is done, I would have no hesitation in using steel for screw shafts. Though an easier forging than a crank shaft, these shafts are often liable to flaws of a very serious character, owing to the contraction of the mass of metal forming the coupling; the outside cooling first tears the center open, and when there is not much metal to turn off the face of the coupling, it is sometimes undiscovered. Having observed several of these cavities, some only when the last cut was being taken off, I have considered it advisable to have holes bored in the end and center of each coupling, as far through as the thickness of the flange; when the shafts are of large size, this is sure to find these flaws out. Another flaw, which has in many cases proved serious when allowed to extend, is situated immediately abaft the gun metal liner, in front of the propeller.

This may be induced by corrosion, caused by the presence of sea water, gun metal, and iron, assisted by the rotation of the shaft. It may also be caused under heavy strain, owing to the over-finishing of the shaft at this part under the steam hammer.

The forgemen, in these days of competition and low prices, are instructed to so finish that there won't be much weight to turn off when completing the shaft in the lathe. This is effected by the use of half-round blocks under the hammer, at a lower temperature than the rest of the forging is done, along with the use of a little water flung on from time to time; and it is remarkable how near a forging is in truth when centered in the lathe, and how little there is to come off. The effect of this manipulation is to form a hard ring of close grain about one inch thick from the circumference of the shaft inward. The metal in this ring is much harder than that in the rest of the shaft, and takes all the strain the inner section gives; consequently, when strain is brought on, either in heavy weather or should the propeller strike any object at sea or in the Suez canal, a fracture is caused at the circumference. This, assisted by slight corrosion, has in my experience led in the course of four months to a screw shaft being seriously crippled.

I show you a section of a screw shaft found to be flawed, and which I had broken under the falling weight of a steam hammer, when the decided difference of the granules near the circumference from that in the central part conveyed to me that it was weakened by treatment I have referred to. I think more material should be left on the forging, and the high finish with a little cold water should be discontinued. Doing away with the outer bearing in rudder post is an improvement, provided the bearing in the outer end of screw shaft in the stern tube is sufficiently large. It allows the rudder post to have its own work to do without bringing any strain on the screw shaft, and in the event of the vessel's grounding and striking under the rudder post, it does not throw any strain on the screw shaft. It also tends to reduce weight at this part, where all the weight is overhung from the stern of the vessel.

[1]

A paper read before the Institute of Marine Engineers, Stratford, 1889.