A practical treatise on mill-gearing etc
Thomas Box
Paperback
(RareBooksClub.com, May 19, 2012)
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1877 Excerpt: ... piston moves twice the diameter of the crankpath, or 4 feet, the weight B ascends once the circumference of the same, or 3 14 x 2 = 6 28 feet, and the weight B must be less than the strain on A in the ratio of 4 to 6 28 or 1 to 6 28-f-4 = 1"57. The power exerted in raising the weight B varies with every position of the crank, at F and G it is nothing, and at H and J it is greater than at B in the ratio given. The fly-wheel E equalizes these irregularities by absorbing the extra power at H and J, and giving it out again at F and G, but evidently the crank-shaft K has a greater strain upon it than the shaft L in the ratio of 1-57 to 1, and must be made stronger to resist it, although the horse-power is the same in both cases. Thus, with 100-horse engine, the shaft K has to bear a maximum strain of 157 horse-power, and if the same value of Wl were used in both cases, its diameter would have to be calculated for that power by the rules; but the usual course is to increase the multiplier in the proper ratio. (77.) With two engines coupled together by one shaft with cranks at a right angle, or 90 as usual, the strain is much less variable than with one crank, being 1 to 111 instead of 1.57, so that a single engine of 100 horse-power would require a crank-shaft equal in strength to an ordinary shaft of 157 horsepower, but two engines of the combined power of 100 horses require a shaft of 111 horse-power only. In our case Fig. 18, the strain on the piston is 113 X 20 = 2260 lbs., and the work done in one revolution is 2260 x 4 x 40 = 361,600 foot-pounds; the weight B is 2260-M.57 = 1440 lbs., and the work done in raising it is 1440 x 6 28 x 40 = 361,600 foot-pounds also. (78.) The value of M for cast-iron crank-shafts of steamengines may be taken at 400, whic...