[The Conical Windlass.]
Various methods have been heretofore described, for raising heavy bodies, or producing for other purposes, a great force,--usually miscalled power--by the application of a comparatively small force: but no method is known, more unlimited in its effect, or more simple in construction; than the conical windlass. It consists of a simple horizontal windlass, with a crank at one end, as shown in the engraving. The windlass is made in a conical form, being a little larger at one end, than at the other; and if the friction of its bearings be relieved by the ordinary friction rollers, it will so far multiply the force applied, as to break a double inch-rope, by the power of one man at the crank. An endless rope, or one of which the two ends are spliced together, is passed five or six times round the small end of the windlass, and down under a single pulley below: then, as the windlass is turned by the crank, the rope is constantly given off from one part, while the circumference is greater. Now it is plain, that if the windlass is one-fifth of an inch larger in circumference, at the point at which the rope is taken up, than at the place where it is given off to the pulley, that whatever may be appended thereto, will be raised one tenth of an inch by each revolution Then, if we suppose the crank lever to be fifteen inches, the handle will travel about 100 inches, in each revolution, which gives a power, or increase of force, of 1000 to one. Therefore, if 100 pounds of power be applied to the crank handle, it will be sufficient--minus friction--to raise a weight of 100,000 lbs. The only inconvenience in this apparatus, and which prevents its coming into more general use, is, that it is too limited in the extent of its motion, in consequence of the travelling of the rope from one end of the windlass to the other. Thus, if the windlass be but twenty-five inches long, and the rope one inch in diameter, it will admit only twenty revolutions, without renewing. Yet, in many cases, in which an article in required to be raised, or moved but a few inches, the conical windlass will be found preferable to any other method.
[Requisite Strength of Steam Boilers.]
Our correspondent S. B. cannot comprehend that the strength of iron for a cylindrical boiler should be in direct proportion to the diameter thereof, in order to sustain an equal pressure per square inch; wherefore, we must reason with him on the long scale. The cohesive strength of good iron is 64,000 lbs. per square inch; and of course, a strip of boiler-iron plate 1/8th inch thick will sustain 8000 lbs. If a boiler made of thin iron is 14 inches in diameter, or 44 inches in circumference, each inch of its length will contain 44 square inches, and either half thereof will contain 22 inches, and as the pressure on this portion is sustained by at least two inches of width of plate,--one inch on each side,--it follows that it will sustain a pressure of at least 700 lbs. per square inch, in the direction of circumference. If the diameter is double, the number of square inches will be double, and will require double the thickness to sustain equal pressure. With regard to the pressure endwise, the area of a cylinder head 14 inches in diameter is 154 inches, and the strength of the 44 inches of circumference would be sufficient to sustain 352,000 lbs., which, divided by the area, is 2,275 lbs. per square inch. If the diameter is 56 inches, the circumference being 172, would sustain a pressure endwise of 555 lbs. per inch. Thus it will be seen that if the cylinder were even 20 feet in diameter, the iron would better sustain the pressure on the head that on the periphery. With regard to the requisite strength of the cylinder's head, if they are made in a semi-spherical convex form, they will require no more thickness of plate than the cylinder: but if they consist of plane disks, the thickness thereof should bear the same proportion to that of the periphery that the area in square inches does to three times the circumference. But in general, no other rule is observed for the thickness of the heads, than to make them extravagantly heavy, without much regard to theoretic calculation.
[Bagley's Gold Pens.]
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