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Aviation History
1918
1918 - 1204.PDF
Per cent. •• -3 .. -i6 .. -03 Manganese .. Chromium ..Nickel Per cent.•• '45 . . I -IO .. 4-00 OCTOBER 24,. 1918. When a tube has been drawn to about -fa in. diameter thereis great difficulty experienced in drawing on a mandril. The usual practice is to finish f in. diameter tubes and smallerby reducing the diameter only, termed " sinking." The condition of the tube finished in this way is not so good aswhen finished on a mandril, the strength of the tube being less. From experiments made, tubes from 0-5 per cent,carbon steel finished by "sinking" show about the same tensile strength as, tubes from 0-35 per cent, carbon steelfinished with the usual " draw " on a mandril. Chrome Nickel Tubest The advent of aeroplanes and airships has given rise to a demand for steel tubing of a higher class than before, tubesof high carbon and alloy steels being called for. This has meant careful investigation in order to find the best heattreatment to be accorded in each particular case. The first attempts at drawing chrome nickel steel were scarcely asuccess, and many breakages of mandrils and even draw- benches resulted from the unsatisfactory annealing of thesetubes. Chrome nickel tubes are now being successfully drawn by the same methods as are used for mild steel tubing—by means of "plug drawing "—but very great care needs to be taken in the annealing.The amount of reduction in gauge per draw is less than half that which is usual in the drawing of mild steel, but inspite of this the wear on mandrils and dies is very great. A typical analysis of chrome nickel steel is as follows :— CarbonSilicon SulphurPhosphorus .. .. -03 Such a steel, when air-hardened, has an ultimate tensilestress of about 100 tons, but a low elastic limit to a maximum value of about 70 tons. Tempering will raise the yield pointand at the same time slightly reduce the ultimate stress. This steel is being much used for aeroplane axles. Onefeature that should be mentioned here is the very serious effect of sulphuric or muriatic acid on hardened chrome nickelsteel tubing. It has the effect of making the material exceed- ingly brittle. Fig. 1 shows a piece of tubing cut from anaxle and considerably ovalled, after being hardened, without splitting the tube ; also one from the same piece that has beenpickled. It will be seen that this has cracked, although the tube is still almost circular. It is therefore inadvisable touse acid to remove scale from a hardened chrome nickel steel tube ; but the injurious effect of the acid can be almostentirely removed by suitable heat treatment. Acid affects other high tensile steels in the same way, butto a less degree, and has a considerable effect even on mild steel. Section Tubing Section tubing has been extensively called for by aeroplanedesigners, and streamline tubing is sued to quite a large extent. The first streamline tube our company (Acclesand Pollock, Ltd.) were asked to make was designed by Mr. Howard T. Wright in 1908, and is a section that is very nearto the recognised standard of to-day. Section tubing, the streamline-shaped tube especially, is much easier to makeif straight sides are avoided, as straight or concave sides compel the use of mandrils and add tfethe difficulty of pro-duction. There are three ways of making sections from seamless tubing, namely, by drawing, rolling and pressing.Pressing is only practicable on fairly short lengths. In drawing there is a slight reduction in periphery in passingfrom the round, but in rolling or pressing it remains the same. Some Difficulties OvercomeIt will be useful in this paper to review some of the trouble we have met with in connection with other trades wheretubing has been used to a great extent, and to mention some of the failures, as the same or similar faults may occur inaeroplane construction. When the Bowden brake was first used on cycles and motor cycles the practice followed was todrill the tube near the handlebar lug to allow the cable to pass through, and this resulted in a large number of breakages.This difficulty was overcome by drilling the holes through the lugs ; but many accidents occurred before this practicewas adopted. Under an alternating stress a tube which has been drilled, unless properly reinforced, is very likely to fail. A series of running rests on drilled and undrilled tubes hasshown that when stressed up to near its elastic limit the undrilled tube has in many cases 10 to 20 times the life ofthe drilled tube. It is often the case that the harder the tube the greater the risk of breakage through a hole. One way ofbreaking a hard-drawn tube, adopted in tube mills, is either to " nick " the tube on one side with a file or to punch a holein one side and then break by striking the tube on a block or anvil. Quite recently we have carried out a large number ofimportant tests on a special type of alternating stress testing machine which we had built. This machine, together withmany of the tests carried out and the results achieved, was to a great extent due to the enthusiasm and foresight ofLieu,t.-Comdr. H. N. Wylie, R.N.V.R., and Lieut. R. W. Fieldwick, the resident A.I.D. Inspector at our works, andto whom we wish to express our thanks for help given. Various results of tests carried out on the machine referredto will be given during the course of this paper. Badly-Designed Cycle LugsAnother series of failures was caused by unsuitable lugs. Some of those used in the earlier days of motor cycling hadvery strong outlets, and case after case of tube failure occurred. The tubing sometimes broke o fi so cleanly as togive the appearance of having been cut through. The broken tubing could be flattened, thus proving it was ductileand in a proper condition for its purpose. In order to prove that the fault lay in the excessive strength of the lugs, aseries of experiments was carried out a number of 'years ago. A lug, as generally used, was tapered off at one outletand left strong at the other. A piece of tubing of the usual gauge and quality was brazed into the lug, and the lugfirmly secured to a plate. The ends of the two tubes were then moved by eccentrics and connecting-rods giving a £-in.movement at a speed of about 400 alternations per minute. Each time the experiment was tried the tube broke off cleanlyclose to the thick outlet, whereas the tube at the tapered outlet remained intact. Chart No. 1 is a record of alternating stress tests taken todetermine the value of " blueing" steel tubes. In these tests two types of grips were used, and two points wereproved, namely, the beneficial effects of " blueing " and the increase in the life of a tube when held by a grip having atapered outlet. Another interesting feature of the test was the spiral form of the break. Another interesting test was as follows : After brazing thetube into a lug with respectively thick and tapered outlets, similar weights were applied to the ends. The tube in thetapered outlet bent with an easy curve, but that at the other end bent abruptly close to the thick outlet. Front Forks for CyclesIt has been proved to the satisfaction of many cycle and motor-cycle engineers that to keep on merely increasing thegauge of a tube that appears to be too weak for its work is not always good practice. For instance, take the case ofthe front fork tube as used on the ordinary cycle. This tube has proved of ample strength for use on the excellent highwaysof this ^country, but for Continental roads something better was wanted. Some years ago we supplied a large quantity offront forks produced from 19-gauge tubes to Russian cycle manufacturers. We were asked to increase the thickness to18-gauge, on account of a number of breakages occurring. We did so, but matters were not improved, and we were thenrequested to further increase to 'ly-gauge. There was still no improvement; indeed, the number of breakages increased.The forks all broke off where they were brazed into the crown, and we were asked by the Russian manufacturers to help them,out of their trouble. One way of doing this would have been by using a suitable liner or sleeve, but we tried another methodwhich proved quite successful. We brought back the gauge of the tubes to 19 where brazed into the crowns and tapered thegauge to 22 atthe bottom ends. This proved effective; alighter article by about 40 per cent., from the same quality steel, thusstanding the strain successfully. This result is accounted for by the fact that the shock was more equally distributedalong the tubing, due to the strength being reduced, gradually, away from the brazed portion, whereas in the plain gaugetubing the whole of the movement was concentrated in a very small space, near the crowns. (To be concluded.) - . L Famous Germans KilledTwo of the leading German pilots have recently been killed, one being Lieut. Fritz Rumey, for whom 44 aerialvictories were claimed, and the other Lieut. H6hn, credited with half that number. German Machines in HollandA GERMAN aeroplane landed in Holland on October izth,and both occupants, an officer and a non-commissioned officer, were interned. A second machine landed three days later,and the pilot was similarly treated. 1205
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