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Aviation History
1933
1933 - 1102.PDF
78 SUPPLEMENT TO FLIGHT NOVEMBER 30, 1933 THE AIRCRAFT ENGINEER resistance approximately seven times as high as that of ordinary low-carbon steel, calls for much shorter weld ing times if burnt welds are to be avoided. It was also considered advisable, in view of the danger of " weld decay " in this type of material, to employ the fastest possible weld in order to reduce to the minimum the time during which the material was in the danger zone, 600 deg. C. to 900 deg. C. Whilst the device for accurate control of current and time was of vital im portance so far as austenitic stainless steel was con cerned, it has incidentally been the means of ensuring uniformity in the welds made in many other types of material. AN OVERHEATED WELD : In this the fused metal extends to the surface There are certain materials for which the ordinary spot-welding process is not suited as a result of the physical properties possessed by these materials when very rapidly cooled from a temperature in the region of the melting point. For example, steels of the type containing 0.30 per cent, carbon, 3.0 per cent, nickel and 1.0 per cent, chromium become exceedingly hard and brittle on rapid cooling from high temperatures. As might be expected, spot welds in such material are too brittle to serve any useful purpose. No claims are made that the Budd shotwelder is suited to the welding of such materials. A CORRECT WELD : This diagrammatic representation of a weld shows what approximate proportion of thickness should be occupied by the fused metal The following test was made to illustrate the unifor mity of welds made by the Budd shotwelder as com pared with the results obtained by good riveting prac tice. Ten riveted test-pieces were made up by a firm SECTION THROUGH A SHOT WELD : This microphoto- graph shows how the slug or " shot" of fused metal is surrounded by a region of unaffected parent metal engaged in aircraft construction. These test-pieces- each consisted of two pieces of austenitic stainless steel (D.T.D. 166), 2f in. long by | in. wide and 0.048 in. thick, which were overlapped and joined by one stain less steel rivet ^ in. in diameter. These test-pieces were pulled in the tensile machine to obtain the break ing load. In every case the failure took place by shearing the shank of the rivet. The free ends of each test-piece were then overlapped and joined by a single shot weld using a standard Budd machine. The test- pieces were again pulled to fracture and in each case failure took place by shearing the weld. The break ing loads are given in Table A, from which will be seen that the shot W-elds show distinctly greater consistency in strength than the riveted joints. TABLE A Highest value Lowest value Joint No. 1 2 •A 4 5 n 7 s it 10 Average Highest value Lowest value Joint No. 1 2 :; V 5 <) 7 8 9 10 Shear strength of rivets 0-125 in. diameter lbs. 9^0 885 885 875 £05 8£0 945 865 845 955 Shear strength of weld 0 • 14 in diameter lbs. 1.100 1.110 1,130 1.1:0 1,155 1.185 1.145 10 0 1.100 1,175 : Riveted joint 980 (8-65 per cent. above average) 845 (6-32 per cent. below average) Welded joint 1,185 (4-8 per cent. above average) 1,080 (4-5 per cent. below average) TABLE B Shear strength of rivets 0*125 in. diameter Shear strength of weld lbs. 980 885 885 875 905 880 945 865 845 955 lbs. 9'0 9C0 910 975 9f0 9£0 975 940 9<0 985 902 Riveted joint 980 (8-65 per cent. above average) 845 (6-32 per cent. below average) 954 Welded joint 990 (3-77 per cent- above average) 910 (4-61 percent, below average) 1198 b
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