Mr. Samuel Webber ( TIY171R. A. S. ,ST. E. vol. viii, p. 537) proposes the following formulae for leather belting, where the tension with which the bell is put mi is known or assumed: No. x Width in inches = • velovity in ft. per minute X strain in lbs. per ill. width x arc of contact and velocity in ft. x strain per in. x width X are Of emit act 3:%000 x ISO° Mr. Suott. Smith (Trans. A. S. M. E., vol. x, p. 705) gives it as his 0111111On that the hest belts are made frfun all oak-tanned leather, mid curried with the use of cod-oil and tallow, all to be of superior quality. Such belts have continued in use thirty to forty years, when used as simple driving-belts, driving a proper amount of power, and having had suitable care. The flesh side should not be run to the pulley face, for the reason that the wear from con tact with the pulley should come on the grain side, as that surface of the belt is much weaker in its tensile strength than the flesh side; also, as the grain is hard, it is more enduring for the wear of attrition ; further, if the grain is actually worn off, then the belt may not suffer in its integrity from a ready tendency of the hard-grain side to crack. The most intimate contact of a belt with a pulley comes, first, in the smoothness of a pulley face, including free dom from ridges and hollows left by turning-tools; second, in the smoothness of the surface and evenness in the texture or body of the belt ; third, in having the crown of the driving and receiving pulleys exactly alike—as nearly so as is practicable in a commercial sense: fourth, in having the crown of pulleys not over k in. for a 24-in. face—that is to say. that the pulley is not to be over I in. larger in diameter in its center ; fifth, in having the crown other than two planes meeting in the center; sixth, the use of any material on or in a belt, in addi tion to those necessarily used in the currying process to keep them pliable or increase their tractive quality, should wholly depend upon the exigencies arising in the use of belts, and the use of such material may justly be governed by this idea—that it is safer to sin in non use than in overuse ; seventh, with reference to the lacing of belts, it seems to be a good practice to cut the ends to a convex shape by using a former, so that there may be a nearly uniform stress on the lacing through the center as compared with the edges. For a belt 10 in. wide, the center of each end should recede hi. As friction is due largely to the ness of two surfaces in contact under motion, and as the best tractive quality of belts comes from the evenness and smoothness of the two surfaces of belt and pulley-face, it easily fol lows that the value of the tractive force of it belt on a pulley face is due, first, to atmospheric pressure ; second, to the attractive adhesion of the leather fibers and the oxidized oil of the currying process. The practical effect of a belief in atmospheric aid is to induce the running of belts very or comparatively slack, thus avoiding unnecessary stress on bearings, and main taining the integrity of belts. A total disregard of this belief has resulted in the destruction of belts in a few weeks or a few months, when they might have served well on toward the full life of the best-made belts, which, as stated, is from thirty to forty years.
coefficients of Friction in Belling.—In 1882 (Trans. A. S. M. h., vol. vii, p. 340) Prof. S. W. Holman undertook a set of experiments with a view to ascertain the cause of the enormous discrepancy in the results of different experimenters. lie caused the pulley to slide under the belt, hanging weights on the loose side of the belt and attaching the other end to a spring balance. Ile found that, with a low speed of slip, he obtained a coefficient of fric tion as low as 012. while with a speed of 200 ft. per minute he obtained about 0.58, and inter
mediate values with intermediate speeds of slip ; hence, that the eoefficient of friction varies with the speed of the slip. It also appears to vary with the pressure, according to the experi ments of Mr. Lewis, quoted stove. Prof. Gitetano Lanza, in 1884 (vol. vii, p. 350), found the average value of this coefficient under a speed of slip of 3 ft. per minute to be about 0.27.
corresponding (if the admissible stress per in. of width be taken at lbs.) to the rule that a belt 1 in. wide mast travel 1.000 ft. per minute to transmit 1 horse-power. Mr. 11. B. Towne, in 1867, with a slip of 200 ft. per minute, obtained a coeffieient of 0.58; but he and Mr. Briggs recommended for use two thirds of this, or 0.42. In discussion of Prof. paper. however, Mr. Towne said (vol. vii, p. 85:n that his own experiments must now be set aside in favor of those of Prof. Lanza.
Cotton Belts,—Belts made of cotton-duck or canvas are used to a limited extent in the United States. A belt of this kind, tested bv Mr. Webber, is described as follows: It was made from cotton-thick folded to make four plies, and then fastened longitudinally with rows of stitches in. apart. the belt then being filled with a composition of boiled linseed-oil and red lead. Another cotton belt (four ply) was made of solid woven cotton, and a mixture of linseed-oil and plumbago worked in and dried under pressure. Powdered soapstone is then used over the surface of the belt on both sides, to prevent its sticking while standing in the roll or coil. It drives well for a time, but stretches a great deal.
"Cotton-Leother" Rells.—A belt known as the cotton, leather belt is made by the Under wood 31anufacturing Company. This belt consists of a firmly woven duck or canvas, which is first stretched by running it at a highs speed over pulleys, which are adjustable by means of screws to any required tension. and, after the stretch seems to be thoroughly taken out of it, a thin and soft leather lining is cemented on to one side, under heavy pressure, so as to make a holding surface to be run next the pulleys. The canvas is woven two, three, four, or more "plies" in thickness, and of any desired width.
Hair Belting.—A belt made of woven hair has recently come into use, the claims made for it being that it is stronger and more durable than leather ; that it will work in water without injury or softening, and is little affected by heat, steam. or acids, and is more economical in first cost than leather, and can be pieced with or without the use of laces. The Rosen dale hair belt, shown in Fig. 1, has what is called an anti-friction edge, which enables the belting to resist the action of strap-forks, and prevents. in a remarkable man ner, the edges from fraying. It is claimed that with hair belts the bite on the drums is by friction ; the consequent suction between the belt and the drum is thereby dispensed with; hence these hair belts come straight off the drum, and do not follow and adhere to it, as in the case of leather. The motion is, therefore, quite steady and uniform.
Bristol's Steel Belt 2 shows a belt fastening made by punching and bending sheet-steel into the form shown. The cut represents the lacing ready for application, and also shows a finished joint. The lacing con sists of a continuous zigzag strip of steel, so proportioned as to give maximum strength with a minimum amount of material. The wedge-shaped points when driven through the belt force the fibers aside without cutting them; hence the ends of the belt are not weakened, as when holes are punched. Bristol's steel lac ing, for single-thickness belting, is made in lengths from 1 to 8 in.; for belts wider than 3 in., two or more lacings are used.