Appleton's dictionary of machines, mechanics, engine-work, and engineering . ements depend freedom from acci-dent, and excellence and economy of work It is, therefore, cheapest to have every thing made of thebest material and in the best manner. In rolls fur flat iron, the<liameter of the cylinders is usually the same; for round and square iron,the upper cylinder is often a little (say half an inch) larger than the lower. If there are more thantwo cylinders, the same practice is found, in some places, of making their diameters regularly decrease(by say a quarter of an inch) from the upper t
Appleton's dictionary of machines, mechanics, engine-work, and engineering . ements depend freedom from acci-dent, and excellence and economy of work It is, therefore, cheapest to have every thing made of thebest material and in the best manner. In rolls fur flat iron, the<liameter of the cylinders is usually the same; for round and square iron,the upper cylinder is often a little (say half an inch) larger than the lower. If there are more thantwo cylinders, the same practice is found, in some places, of making their diameters regularly decrease(by say a quarter of an inch) from the upper to the lower. In others, and perhaps in the generality ofcases, the middle of the three is the largest. Some metallurgists, on the contrary, object entirely tothis difference of diameter, as causing increased friction in the machinery, and straining the iron. Thisobjection is theoretically correct. The aim of the contrivance is to prevent the bar, as it passes throughthe rolls, from curling around the upper cylinder ; if this last be larger, it will continue to bear on the. IROK 125 bar after the resistance of the lower roll has ceased, and will, of course, tend to force it down upon theapron. But this tendency to curl is best corrected by having guards to each groove—i. e., wedges ofwrought-iron, which catch the bar as it comes out. The diameter of the cylinders, and their bearing, vary according to the purpose for which they areintended. Roughing-rolls for puddle-balls are from 18 to 20 inches diameter, and 5 to 6 feet long ; forpiled iron or rough bars, from 12 to 14 inches diameter, and 5 feet long. Finishing-rolls for heavy barwill be of the same diameter with the last, but from 12 to 18 inches shorter; while for small rods theirdiameter need not be more than 8 to 10 inches, and their bearing about 2^ feet. The weight of a pairof roughing-rolls is from 4 to 5 tons, and of finishing-rolls from 1£ to 2 tons. In geering up the rolls, the lower one is the driver, when there
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Keywords: ., bookcentury1800, booksubjectmechanicalengineering, bookyear1861
