Abbildungen der Seite
PDF
EPUB

of steel, in which our chemist reported phosphorus 0:11, was tested by a chemist of another Bessemer works, and his determinations were phosphorus between 0.07 and 0.08.: A leading engineering establishment of Pittsburg bought iron claimed by a chemical analysis to contain 0:08 phosphorus; our Mr. Ford found phosphorus 0.145. A chemist connected with an open-hearth works reported manganese in a piece of steel, 1:14; in a second determination from the same piece of steel, by the same chemist, manganese was reported 0:43. The chemist was kept in ignorance of the fact that both samples were from the same piece of steel. Two determinations for manganese were made by the same chemist from a piece of steel; he reported manganese 0.61 and 0:58. Our chemist, in the same steel, reported manganese 0-324 and 0.303. I could give innumerable instances of the wide difference in chemists determinations of phosphorus and manganese. I think I have cited sufficient cases to sustain the position I have assumed, viz., that before the determinations made by Dr. Dudley's assistants are accepted as being correct they should be verified by chemists of greater experience.

I find on a close examination of the doctor's paper that he has taken no notice whatever of the increased weight of cars, increased weight of locomotives, with increased speed, in his tonnage calculations. Now, there is a vast difference between the tonnage of 10 to 12 tons in an ordinary freight-car with eight wheels passing over rails at a moderate speed, and 15 to 20 tons on the same number of wheels at an increased speed. Since 1874 the Pennsylvania Railroad Company has been steadily increasing the weight of both engines and cars. The duty to which rails are now subjected, I believe, is fully 60 per cent. greater than that before the year 1874. On looking over the paper, we find a number of rails, classed as good-wearing rails, that have for years been subjected to comparatively light tonnage on a wheel-tonnage basis, compared with a great number of rails classed as fastwearing rails, which in some cases I find have had passing over them nearly twice the number of tons per month, and all on heavier wheel tonnage.

As an illustration, I cite rail No. 937, with the following analysis: carbon, 0:454; silicon, 0·014); phosphorus, 0·145; manganese, 0·726, with only 2 per cent. elongation. In accordance with the deductions and formula this should be a very bad rail, yet on close examination I find that this rail has been subjected to a monthly tonnage of 747,628 tons. If we examine the rail No. 929, which was laid within two miles of rail 937, we find carbon, 0.235; silicon, 0080; phosphorus, 0·055; manganese, 0.300; elongation, 24 per cent. This rail was subjected to a monthly tonnage of only 381,235 tons, while rail No. 937 was subjected to 96 per cent. more monthly tonnage, and yet rail No. 929 is classed as a good rail. If we assume that 50 per cent. more loaded cars pass east to Philadelphia than pass west from Philadelphia, we find the wheel-tonnage assumes a very important aspect in determining the wearing qualities of rails. Again, the bad rail was in the track 40 months, and only shows a wear of 17 of an inch in vertical section, and has been in the track since the advent of heavier engines and heavier cars, while rail No. 929 has had the advantage of at least 7 years of comparatively light traffic on light-wheel tonnage. The question, which of these two rails has been subjected to the greatest amount of wheel-tonnage, I leave to some one to calculate who has more time to devote to this subject than I have.

In regard to the method proposed by Dr. Dudley to test the rails at the works, I can only say I much prefer the methods suggested by Mr. Sandberg, in his paper read before the Institute at the Lake Superior meeting, with this slight modification, viz.: I would subject a 50 and 52 pound rail to a drop-test of 1800 pounds, falling a distance of 14 feet on the rail, on supports 3 feet apart; for a 57 to 56 pound rail, 16 feet drop; for a 56 to 58 pound rail, 18 feet drop; for a 58 to 60 pound rail, 20 feet drop, and so on in the same ratio. I would also adhere to the test-bar, drawn out from the head of the rail down to one inch square, then placed under a steam-hammer and bent through an angle of 110°, the distance between centres of supports of the bar to be from 10 to 12 inches. Dr. Dudley may think these tests crude; I believe them to be simple, thorough, effective and reliable, and in this I fully concur in the views of Mr. Sandberg.

If Dr. Dudley and the Pennsylvania Railroad authorities believe their deductions are correct, let them have rails made in accordance with the doctor's first formula-phosphorus 0.077, carbon 0.334, silicon 0.060, manganese 0:191—and add to it the less sulphur and copper the better, and, as a matter of course, pay the difference in price involved in the difference in the price of metals; but when Dr. Dudley attempts to formulate a rule to govern the steel-makers, based on his knowledge, I for one decidedly object, and I frankly tell him that

he is opposing all the researches and investigations of the best chemists and metallurgists, both here and abroad.

I have serious and grave doubts if steel made in accordance with his second formula would give a good record in the track. I experimented on this formula in attempting to fill an order. Mr. Sandberg in his paper refers to the filling of an order of 2500 tons on the same formula, and my experience was the same as his. The ingot was a conglomerate mass of honeycombs. It made bad blooms, and I do not believe it made good rails. The rails are now in the tracks of the West Pennsylvania road, and if they do prove to be good rails I shall be very much surprised.

To be continued.

AN ACCOUNT OF EXPERIMENTS MADE BY A BOARD OF
UNITED STATES NAVAL ENGINEERS WITH SCREW
PROPELLERS OF DIFFERENT MATERIAL AND
DIMENSIONS, APPLIED TO THE UNITED
STATES FISH COMMISSION'S STEAMER
“LOOKOUT,” WITH THE HULL COP-

PERED AND NOT COPPERED.

By Chief-Engineer ISHERWOOD, U. S. Navy.

In the refitting, at the Washington, D. C., navy-yard, of the United States Fish Commission steamer Lookout, seven screws were adapted to her, differing in diameter, pitch and fraction of the pitch used, with the view of experimentally ascertaining the best proportions of these for that particular vessel. Two of the screws being of cast iron and the remaining five of cast brass, they furnished an opportunity for observing the comparative effect of these two metals upon the economic efficiency of the screws. Further, as the vessel's bottom was covered with rolled copper during the experiments with two of the screws, while it was not so covered during those with the remaining five screws, but exposed to the water only the wooden surface of a vessel in the usual condition for coppering, the occasion was afforded to determine the effect of such coppering or want of coppering upon the resistance of the hull.

The experiments with these screws were made by a Board of ChiefEngineers of the United States Navy, which reported the data to the Bureau of Steam-Engineering of the Navy Department.

The writer has taken these lata, corrected and re-arranged them, and from them has made the calculations and deductions that will be found in this paper, none of which are in the Board's report.

The experimental deductions contain two novelties, namely, the effect upon the economic efficiency of screws due to their being constructed of cast brass or of cast iron, and the effect upon the resistance of wooden hulls due to having their bottom coppered or of presenting to the water a wooden surface in the usual state preparatory to receiving the copper; or, in other words, the determination of the comparative resistance to motion in water of hulls having their immersed wetted surface of copper or of planed wood. In the absence of other experiments on these points, the present ones will be of interest, taking care to discriminate that the comparison holds strictly true only for the exact experimental conditions, any variation of which would consequently vary the comparative results; but, although the experiments determine these results quantitatively for only the particular cases on trial, yet they remain qualitatively true for all cases.

Taking the resistance of a hull as composed of the resistance of its immersed wetted surface to the water; and of the resistance of the water to displacement by it, that is to say, the resistance of water to being elevated from the centre of gravity of the greatest immersed transverse section of the hull to whatever height above the water-level it may be forced by the progress of the vessel; there follows that the ratio of these two resistances will vary according to the form or model of the hull. If the hull, of given lineal dimensions, be very sharp, the larger portion of its resistance as a whole, will be composed of its skin resistance or that of its immersed wetted surface to the water, while the remaining smaller portion is composed of the resistance of the water to displacement. And, vice versa, if the hull be of very full form, the larger portion of its resistance as a whole will consist of the resistance of the water to displacement, while only the remaining smaller portion is due to the skin or wetted surface resistance. In the case of the Lookout, the hull was very sharp, exposing a great extent of immersed wetted surface comparably to its displacement; consequently the difference between the resistances of the two kinds of surface-rolled copper and planed wood-will be proportionally more

marked in her than in the cases of vessels with fuller forms. However hard and smooth a wooden surface may be made out of water, yet when immersed it will become water-soaked and soft, the small exposed fibres of the wood separating, rising and forming a delicate hairy coating, offering much more resistance to water than the original hard plane surface from which they arose.

It is to be regretted that the experiments were so few: they might easily have been extended by cutting off two of the four blades of the screws, by successively reducing their diameters and lengths, etc., which modifications could have been executed at little cost as the screws did not exceed 5 feet in diameter, a size readily handled large enough for reliable results; but, as the vessel was not entirely at the command of the Bureau of Steam-Engineering, only such trials were available as could be made without interfering with her other uses.

The experiments do not show any superiority of cast brass over cast iron for the material of the screw ; from which may be inferred that, per unit of surface moving at equal speed, the resistance of the water to the cast iron surface is no greater than to the cast brass surface. Also, that the less direct resistance of the thinner cutting or forward edges of the blades of the brass screw was not sufficient to produce a sensible effect on the economic result. The much less cohesive strength of cast iron than of cast brass requires the blades of screws made of the former metal to be much thicker for equal strength than those made of the latter metal; and in the case of the experimental screws, the cast iron blades were about two and a half times thicker than the cast brass ones.

Of course, the thicker blades must be attended with more direct resistance than the thinner ones, but the edges, forward and aft, of all blades are so. acutely beveled that any difference due to this cause seems to be too slight to affect the result in a marked manner.

HULL.

The Lookout was constructed of wood for a steam yacht, and had a light schooner rig. The bottom was uncoppered during the trials with screws A, B, C, D and E; but it was coppered during the remaining trials with screws F and G.

The following are the dimensions and proportions of the hull cor

« ZurückWeiter »