CHAPTER XXI.

ALUMINUM IN CYCLE CONSTRUCTION—STRENGTH OF TUBES.

“We really thought that we were going to pass over a period of three months without having to chronicle the discovery (?) of a method of producing aluminum at a cost of not more than that of first-class steel. The periodical inventor has appeared, and this time he hails from Melrose, Mass., and his name is Washburn. Next!!”—Bicycling World.

Inventors do little harm in periodically making cheap aluminum or increasing its strength without adding to its gravity, but when a large corporation is started, as was done some months ago, with a lot of money and aluminum medals issued, the same being made out of copper, then the matter becomes serious. Probably, next to the hobby of separating water and creating enormous power thereby, the aluminum hobby holds undisputed sway. But as there really is something of interest to cyclists and cycle makers in the subject, there seems a need to touch upon it. Among the articles in the manufacture of which aluminum can be satisfactorily used we find in the catalogue of a well-known smelting firm mention made of bicycles, tricycles, etc. The idea exists in the minds of many that a bicycle made from pure aluminum would be a practical machine and much lighter than one of steel. This notion arises from the fact that aluminum in the pure state has a specific gravity of only 2.5, or about one-fourth the weight of steel. Below we print a letterfrom the Cowles Smelting and Aluminum Company on the subject.

“Lockport, N.Y., U.S.A., August 20, 1888.“R. P. Scott, Esq., Baltimore Md.:Dear Sir,—Replying to your favor of August 16, you can obtain the book on Aluminum, by Richards, from Philadelphia. Aluminum has a great many uses in its commercial state, but a simple pure aluminum casting has not sufficient strength to make it desirable for small parts. If you could have it rolled or hammered to shape, so as to make it rigid, it would become much more tenacious, but to secure strength desired in bicycle parts, your castings would necessarily be so large as to be ungainly, and we doubt if you would attain the most desirable end,—viz., light weight. The alloys of copper and aluminum are much better adapted to your requirements than the pure metal could possibly be.“Yours very truly,“The Cowles E. S. and Al. Co.“Tucker.”

“Lockport, N.Y., U.S.A., August 20, 1888.

“R. P. Scott, Esq., Baltimore Md.:

Dear Sir,—Replying to your favor of August 16, you can obtain the book on Aluminum, by Richards, from Philadelphia. Aluminum has a great many uses in its commercial state, but a simple pure aluminum casting has not sufficient strength to make it desirable for small parts. If you could have it rolled or hammered to shape, so as to make it rigid, it would become much more tenacious, but to secure strength desired in bicycle parts, your castings would necessarily be so large as to be ungainly, and we doubt if you would attain the most desirable end,—viz., light weight. The alloys of copper and aluminum are much better adapted to your requirements than the pure metal could possibly be.

“Yours very truly,“The Cowles E. S. and Al. Co.“Tucker.”

It will be seen that the metal in its pure state lacks strength, and can only be used in the arts to any extent when alloyed with copper about in the proportion of nine of copper to one of aluminum. When alloyed as above, it is about as heavy as steel.

Pounds persquare inch.

23,000

49,000

24,000

32,000

39,000

16,000

50,000

76,100

38,000

48,000

81,000

63,000

$0.45

.40

.37

.33

.26

.20

.16

The specific gravity of the A grade is 7.56, that of steel being 7.88. Its coefficient of expansion is small at ordinary temperatures; its electrical conductivity is about 9, and with the lower grades the expansion by heat, specific gravity and heat and electrical conductivity increases the nearer the metal approaches to pure copper. With more than eleven per cent. of aluminum the bronze rapidly becomes brittle. In color, aluminum bronze of the C and D grades is the nearest to gold of any known metal, the higher grades being lighter in hue than the lower. The A grade melts at about 1700° F., a little higher than ordinary bronze or brass. Aluminum bronze shrinks about twice as much as brass.

In working aluminum I have found it to be a splendid substitute for malleable iron, especially in many cases where the iron could not be procured in time, or when it came so warped as to be unfit for use. I have never been able, however, to get castings which would come quite up to the strength claimed for it; the most satisfactory grade was that of ten-per-cent. aluminum, which by the way is very hard to work, especially in drilling. There is no doubt, however, that it can be made to take the place of steel in many instances.

A knowledge of aluminum is a great boon to experimenters, as it will probably come into quite general use with the manufacturer. The ten-per-cent. aluminum finishes very handsomely, and in olden times it would have been a splendid substitute for thebrass hubs then so common. As an antifriction metal it is unsurpassed by any of the bronzes. It casts bright and sharp, but shrinks amazingly, although not dangerously; at least I have never had a part of the casting drop off, as in malleable it often does, and though the aluminum sometimes leaves a great depression in the heavy part of the casting, it causes no sponginess underneath. It can be readily bronzed or soldered.

Aluminum bronze drawn into wire will make very good spokes, and it has been used for this purpose to some extent in England. All tendency to rust is obviated, and it saves all nickeling; it resists corrosion sufficiently well to dispense with any covering, but it does not look as well as a nickel finish. No better authority on the subject can be had than that of the Cowles Catalogue; useful information also can be gathered from “Richards’s Aluminum,” and “Thurston’s Material of Engineering.” The last-named treatise speaks on the subject as follows:

“The alloys of aluminum are very valuable. Its remarkable lightness, combined with its strength, makes it useful as a constituent of those alloys in which strength and lightness are the needed qualities. It has a pleasant metallic ring when struck, and confers a beautiful tone when introduced into bellmetal.“Aluminum may be added to bronzes and brasses with good results. The alloys (copper ninety per cent., aluminum ten per cent.) may be worked cold or hot like wrought iron, but not welded. Its tenacity is sometimes nearly one hundred thousand pounds per square inch. Its specific gravity is 7.7. In compression this alloy has been found capable of sustaining a little more than in tension,—one hundred and thirty thousand pounds per square inch (nine thousand one hundred and thirty nine kilos per square millimetre),—and its ductility and toughness were such that it did not even crack when distorted by this load. It is so ductile and malleable that it can be drawn down under the hammer to the fineness of a cambric needle.“It works well, casts well, holds a fine surface under the tool and when exposed to the weather,and it is in every respect considered the best bronze yet known. Itshigh cost alone has prevented its extensive use in the arts. These alloys are very uniform in character and work regularly and smoothly. Even one per cent. of aluminum added to copper causes a considerable increasein ductility and fusibility, and enables it to be used satisfactorily in making castings. Two per cent. gives a mixture used for castings which are to be worked with a chisel. It is softened by sudden cooling from a red heat. Its coefficient of expansion is small at ordinary temperatures.“It has great elasticity when made into springs; it has been found useful for watches, and has the decided advantage over steel of being little liable to oxidization. Kettles of aluminum bronze are used in making fruit syrups and preserves. Steel containing but .08 per cent. of aluminum is said to be greatly improved by its presence.”

“Aluminum may be added to bronzes and brasses with good results. The alloys (copper ninety per cent., aluminum ten per cent.) may be worked cold or hot like wrought iron, but not welded. Its tenacity is sometimes nearly one hundred thousand pounds per square inch. Its specific gravity is 7.7. In compression this alloy has been found capable of sustaining a little more than in tension,—one hundred and thirty thousand pounds per square inch (nine thousand one hundred and thirty nine kilos per square millimetre),—and its ductility and toughness were such that it did not even crack when distorted by this load. It is so ductile and malleable that it can be drawn down under the hammer to the fineness of a cambric needle.

“It works well, casts well, holds a fine surface under the tool and when exposed to the weather,and it is in every respect considered the best bronze yet known. Itshigh cost alone has prevented its extensive use in the arts. These alloys are very uniform in character and work regularly and smoothly. Even one per cent. of aluminum added to copper causes a considerable increasein ductility and fusibility, and enables it to be used satisfactorily in making castings. Two per cent. gives a mixture used for castings which are to be worked with a chisel. It is softened by sudden cooling from a red heat. Its coefficient of expansion is small at ordinary temperatures.

“It has great elasticity when made into springs; it has been found useful for watches, and has the decided advantage over steel of being little liable to oxidization. Kettles of aluminum bronze are used in making fruit syrups and preserves. Steel containing but .08 per cent. of aluminum is said to be greatly improved by its presence.”

Aluminum bronze, such as would be required for cycle castings, costs from thirty to fifty cents per pound, according to quality and quantity. A valuable alloy of aluminum and iron has recently been made, by which it is maintained that wrought-iron castings are possible. The factory is, I believe, at Worcester, Mass. In our endeavor to learn more upon the subject we have been referred to the United States Mitis Co., No. 26 Broadway, New York, which company has the exclusive right in this country to make Mitis castings, or of granting permission to those who desire to make these castings themselves.

Metal in the form of tubes resists all strain liable to occur in cycle work better than in any other form. In regard to strain of compression, we find, in “Wood’s Resistance of Materials,” the following summary:

“Experiments heretofore made do not indicate a specific law of resistance to buckling, but the following general facts appear to be established: The resistance of buckling is always less than that of crushing, and is nearly independent of the length. Cylindrical tubes are strongest, and next in order are square tubes, and then the rectangular. Rectangular tubesrectangleare not so strong as tubes of this formdivided rectangle.”

There is, however, very little direct crushing strain on the tubes in a cycle; it is almost entirely a strain offlexure or bending; hence this is the only interesting feature pertaining to the subject in cycling work.

Since a tube is stronger than a solid bar, for same weight the intuitive idea is to make the tube as large as possible, and the mathematical demonstration which we append shows this to be correct, generally speaking.

LetRequal the strain per square inch of cross-section of the tube at the point farthest removed from the neutral axis at the instant of rupture.

Tube sections.

Suppose Fig. 1 to represent the half of the tube, and that you are trying to bend it down at the ends. The particles towards the top will be pulled apart, while those at the bottom are crowded together; somewhere between the top and bottom the particles are neither pulled apart nor crowded together. Were the tube solid, the line of these particles would be the neutral axis. In the tube an imaginary line through the centre of the hole does not vary much from said axis. Now the moment of rupture =Rπ4re(r4e−r4i), wherereandri(Fig. 2) are the exterior and interior radii;Rπ4is a constant, which we will callK, whence we can write moment of rupture =K(re2−ri2) (re2+ri2) ÷re. Here the factor (re2−ri2) is proportional to the area of the annular cross-section and is constant, while the other factor, (re2+ri2) ÷reor,re+rireri, though less than 2re, gets nearer and nearer to 2reasregets large andriapproachesre.

Therefore we have, that in resistance to flexure the tube should be as large in diameter as practicable, which means that it must be as thin as possible. This result is only modified in practice by the necessity of guarding against dinging and also against imperfections in the steel. A surface crack will ruin a very thin tube which otherwise may be harmless in a thicker, but it is safe to say that it is best to use reasonably large thin tubes.

Oval tubes are of an advantage only when the direction of the strain is positively known and when it invariably occurs in that direction. Since the tube finds its greatest limit of general resistance in cylindrical form, to alter that form must necessarily weaken it more in one direction than it strengthens it in another.

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