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Aviation History
1917
1917 - 0432.PDF
MAY 3. 1917- THE USE AND ABUSE OF STEEL. By Lleut.-Col. R. K. BAGNALL-WILD and Lieut. E. W. BIRCH. (Concluded from page 402.) DESIGNERS hardly seem to pay sufficient attention to thismatter, and misunderstandings have occurred as regards hardening tests for the case-hardened surface. Steel makersknow that with a high nickel case-hardened steel or a nickel chrome case-hardening steel the same glass-hard surfacecannot safely be obtained as with the common carbon case- hardening steel. It is therefore necessary for the designer toconsider whether he wishes to obtain the properties of a nickel steel in that portion of the metal immediately underneath thecase, or whether he wishes to have it with such properties as case has recently occurred where a department was blamed forpassing an alloy steel which is supposed to have given some 55 tons ultimate, and was found by Brinell test to be of some28 to 30 tons. It is quite obvious that a batch of steel represented by theoriginal test piece which gave the higher figure, could not possibly give the lower figure, even as rolled, the inferencebeing that a mix-up had occurred in the firm's stores. It is absolutely essential that when a consignment of steel arrivesat a works, care be taken to store it in such a way that the Fig. 17. Fig. 18. Fig. 19. Fig. 20.Fig. 17.—Cracked nickel chrome bar. Crack extended into centre of bar. Fig. 18.—Cracked nickel chrome bar. Fig. 19.— Turnbuckle from nickel chrome bar. Extensive pipe, opened out on hammeringends. Fig. 20.—Nickel chrome bar. Cracks developed during tensile test. can be obtained with a carbon steel, in the latter case obtaining.a harder surface. Specifications exist which call for practically a glass-hardsurface coupled with physical properties requiring the use of an alloy steel of a composition that cannot possibly be expectedto give this surface. A most important point at the moment is output. " Thesteel maker is using every endeavour to produce steel free from roaks, flaws, and cracks, but it is a fact that in spite of care, aquantity of faulty steel is delivered to the machine shop, and sometimes a large amount of work is done on it before the test report representing that steel may at any time be co-related with it. An Inspection Branch is not a Stores Branch ; the duty therefore falls on the contractor's stores. [. *, f One point of considerable difficulty has been experienced inthe making of bolts, nuts and screwed parts. It is essential for aeroplane work that certain bolts should be made of alloysteel with a comparatively high tensile strength. Such steel is obviously more difficult, and in some cases almost im-possible, to thread in automatics. In the case of a steel which is used very largely for aeronautical work (of some 50 tonsteasile) there is no doubt that it takes about five times as long Fig. 21. Fig. 22. Fig. 23. Fig. 24.Fig. 21.—Partly machined nickel chrome bar, showing internal flaw. Fig. 22—Tensile test piece, showing metal tongue. Fig. 23.—Partly machined turnbuckle from cracked bar. Fig. 24—Tensilespecimen, showing tongue due to effect in rolling. defects are found. Detailed inspection can do a great deal to prevent such steel leaving the steel maker; numbers of examples, however, can be put forward showing that much labour in this country is at present being wasted in machining faulty steel. (Figs. 17-28.) In connection with this, inspectors are often blamed for matters which have nothing whatever to do with them. A to put through an automatic as a common carbon steel,while the wear and tear on the dies is also very much greater. It is considered that firms making screwed parts are toblame in not having realised this fact at an earlier date, but it is hardly fair to the designer for the manufacturer tocomplain after acceptance of a contract. It is obvious that bolts made of high tensile steel must be more expensive than 432
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