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_Marine Shafting and Engine Forgings--Nickel Steel. . It may be said that in the manufacture of this class of heavy steel forgings, it is not yet the usual practice to aim at the high- est attainable combination of physical qualities, and that there- fore, there is a wide field for improvement in this direction. From 'this statement, it must not be inferred that the demands _of the United States. navy specifications, which may now be taken as the standard in this country, are not such as to insure an excellent quality of steel; on the contrary, the conditions of _ inspection are rigorous, the amount of testing large, and the physical qualities demanded are such as can only be obtained by the use of high grade stock, by ample forging facilities, and by careful manufacture throughout. 'The present physical require- _ ments for shafting, including cranks, are: Tensile strength not less than 58,000 pounds per square inch, and an average elonga- tion of not less than 28 per cent. in longitudinal specimens % inch diameter and 2 inches long, cut from full-sized prolonga- tions of forgings. For connecting and piston rods, a somewhat harder steel with a tensile strength of not less than 65,000 pounds per square inch, and an elongation of not less than 25 per cent. is used. No treatment other than annealing is prescribed, and the elastic limit is not considered as a condition of acceptance. From these requirements it will be seen that a distinctly soft steel is being used, in which the elastic limit often falls to about 27,000 pounds per square inch, and averages something over 30,000 pounds. In adopting such soft steel, the practice of the English admiralty and merchant marine has been followed, and in view of the fact that this practice is based upon wide experi- ence, and the use of a very large amount of material, much of which has done excellent service, it has been a wise and conser- vative course to make no hasty and radical departures from same. It must indeed be conceded that soft steel presents, in some respects, marked advantages as the standard material for shafts and engine forgings, particularly when the manufacture is en- trusted to forges having insufficient facilities and lack of ex- perience in handling the harder. classes of steel. In the ingot form and during forging, soft steel can bear with safety rougher treatment than harder steels; it is less sensitive to the hurtful effects of irregular and repeated heatings, and dangerous inter- nal strains and defects are less apt to be developed thereby; these _ are important considerations, especially in the case of forgings 'of irregular shape, such as solid forged cranks, connecting rods, etc. Further, by the use of soft steel the cost of machining, and hence the cost of finished forgings is reduced to a minimum. It is natural, therefore, that marine engineers should hesitate to _ make a change in a matter of such importance, feeling as they ' do, that in soft steel forgings, there is an' element of safety that can not be overlooked. In:calculating the dimensions of marine engine forgings the elastic limit of the material used has not been as important a factor as in the designing of heavy guns; this is principally due to the larger factor of safety used in en- gine forgings to- insure stiffness or rigidity of parts under trans- verse strains. There is much evidence at hand, however, to in- dicate that the importance of a high elastic limit in steel forgings has not been sufficiently considered, and that many failures of soft steel forgings of excellent quality can be ascribed to a low elastic limit. A notable instance is that of locomotive crank-pin forgings, where soft steel has in many cases failed by breakage as fréquently as wrought iron, and where a harder steel with higher elastic limit has given far better results. The length of | service of hammer piston rods has also been much increased by the use of steel of high elastic limit. These are instances of ma- chine parts subjected to exceptionally severe working strains. In the highest development of the modern marine engines reduction of weight of ail parts is of prime importance. This _ can only be accomplished by reducing sectional areas. On the other hand, outside dimensions can not usually be reduced with- out sacrificing necessary stiffness. We are, therefore, led to re- moving the metal along the neutral axes or, in other words, to the use of hollow forgings. This practice has been followed in designing the shafting of all the ships of the new navy, except the tour Roach ships. In most cases, however, the danger of too great a reduction of sectional area has evidently been feared, and the diameters of axial holes have been made too small to al- low of advantageous hollow forging on a mandril. Solid forging with subsequent boring has, therefore, been necessary, whereby a distinct loss in quality of metal has occurred. It is evident ~ *From a paper by Russell W.'Davénport, on 'Production in the United States of Heavy Steel Engine, Gun and: Armor Plate Forgings," read before - the Society of Naval Architects and Marine Engineers. fo EM ARINE REVIEW. Se that to reduce further relative weights as well as to increase the absolute strength of parts, the designer of marine engines needs a stronger material than that now employed; that is, a material having a greater elastic limit, but at the same time possessing 'such a degree of toughness as to insure resistance to. sudden strain or shock. Such a material can be found in steel harder _ than that now used, strengthened and toughened by tempering and annealing. Simple steel of the proper natural hardness, and so treated, will show in specimens cut from the center of sec- tions, say 3 inches to 6 inches thick, an elastic limit of about 45,000 pounds per square inch, an elongation of about 23 per cent. in 2 inches, and a contraction of area of from 50 to 55 per cent. 'To allow of safe and effective tempering, forgings must be made hollow wherever possible, rectangular sections reduced in thickness as far as practicable, large fillets used, and sharp re- _ entering angles, and sudden changes from thin to thick sections avoided. In shafting, axial holes should be made large enough wherever practicable to allow of hollow forging, and additional strength with the same weight obtained by increasing both out- side and inside diameters, and thus reducing thickness of walls. A further and very pronounced improvement in strength and toughness can be obtained as already indicated, by the use of nickel steel, tempered and annealed and prepared for treat- ment as above described. The use of nickel allows a reduction of carbon, makes the steel more sensitive to temper, and facili- tates the tempering of irregular shapes. Specimens from nickel steel forgings, tempered and annealed, will show uniformly an elastic limit of from 50,000 to 55,000 pounds per square inch, an elongation of 23 per cent. and above, in specimens 2 inches long and 1% inch in diameter, and a contraction of area of from 55 to 60 per cent. In cases where owing to thickness of section and irregular shape, tempering is not advisable, nickel steel will still show a higher combination of elasticity and toughness than any other material known under the same conditions. Here, then,. is a material admirably suited to the shafting and engine forgings required by the marine engineer in the construction of modern high service engines, and it is believed that as its merits become known, its use will be widely extended. - The bureau of steam engineering has already taken this material into consideration, and in designing the shafting of the Brooklyn and Iowa, it was decided to make the two propeller shafts of the former and the two intermediate line shafts of the latter ship of nickel steel. The diameters of the Brooklyn's pro- peller shafts will be 17 inches outside and 11 inches inside, giving walls 3 inches thick, while the line shafts of the Iowa will be 1534 inches outside diameter, and 934 inches inside diameter, with walls also 3 inches thick. The specifications prescribe that these shafts shallbe oil tempered, and demand a tensile strength of not less than 85,0co pounds per square inch, an elastic limit of not less than 50,000 pounds, an average elongation of 23 per-cent.in specimens 2 inches long and ¥% inch in diameter (no specimen to fall below 20 -PeT-CCle. CA SARE : The American Ship Windlass Company of Providence, R: I., has received an order from Capt, James Davidson, West Bay City, Mich., for one steam capstan windlass to handle 134-inch chains, and three steam capstan windlasses to handle 14-inch chains, and also for one steam capstan, for delivery within the next two or three months. Capt. Davidson'has used the wind- lasses made by this company for nearly twenty years. He con- cludes the letter in which he orders.these machines by saying: "You must understand that we think well of your machines from our continual use of them, and there is no question but that they are the best that are made." 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