IRON v. STEEL.

New Zealand Times, Volume XXX, Issue 4595, 11 December 1875, Page 1 (Supplement)

IRON v. STEEL.

(From the English Mechanic.) So loud of late have been the praises of steel over iron, and so general the confidence in it, says the “ Journal of the Franklin Institute,” that only the minor shafts of the great bridge of St. Louis were designed to be of iron; the remainder, embracing the more important parts, were to be of steel. In order to be assured of the excellence of every portion of the structure, the engineer in charge, not content with the results obtained from the straining of small sections, determined to subject every shaft supplied to a similar strain ; and for this purpose constructed an enormous hydraulic testing machine. Thirty-two shafts, nearly 40ft. long, and weighing nearly two tons, were furnished by a well-known firm of iron forgers. These were subjected to a strain of about 300 tons, without stretching—a strain so nearly approaching the resistance of sound iron that a slight flaw in any of them would have caused rupture—a fact which speaks well for the excellence of the work. With the steel shafts, from which so much was expected, the result was very different. Many of them snapped under strains in some cases even less than those which the iron ones stood perfectly, and so great became the distrust of them that the forge was ordered to proceed with more iron ones to take the place of steel, and has now furnished nearly a hundred without a single failure. These results also emphasise, if they do not inaugurate, a tendency in the engineering world to return from steel to iron when employed in large masses. We have lone known all about steel in small sections, but o till lately no large masses of steel could be produced j and this series of tests by Captain Eads is the first instance on record of attempts to ascertain whether the known laws of strength of small sections hold good in large masses of either wrought iron or steeL A. practical comparison of the two metals was made two years ago on the railroad boat Ked Jacket, with its two screws—the shafts being of equal size, one steel, the other Ihe steel one twisted off in a week, while the two iron ones (one now replacing steel) Irnve been running ever since. What the difficulty is with steel in the large mass is not clear, fiut the long list of failures of steel guns confirms the facts. Krnpp, the great Prussian steel maker, has already abandoned the solid forged steel gnu. The matter is considerable interest in the engiueeringi|fratenuty and journals, and in practice for large masses there is a probable return for the present to the old-fashioned wrought iron in vogue ever since the days of Tubal Cain.