Heaton on Welding,
Page 21
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Information Derived from a Paper read before the Institution of Mechanical Engineers.
Modern methods of electric and acetylene welding have placed at the disposal of constructional and maintenanoe engineers a system which has proved to he of exceptional importance and convenience. Repairs and assemblies can now be effected by a skilled workman operating one or other of The modern welding plants, which previously would have called for expensive replacement or extensive reconstruction.
The Steel Barrel Experts.
There are few concerns in this country Which know more about high-grade welding of all kinds than the Steel Barrel Co., Ltd., of Uxbridge. We have in the past had the pleasant duty, on frequent occasions, to write in this journal of the many phases of this company's work. The Stock Barrel Co. has made a troe speciality, as we hardly need remind our readers, of, amongst other things, petrol-storage plants. Its ability to produce big-capacity tanks without a rivet, and absolutely liquid-proof, renders it able to offer to users particularly satisfactory equipment of this kind.
Mr. Thomas T. Heaton has for years been manager of the Steel Barrel Co., and he has been persuaded to publish, in the form of a paper, which he read before the Institution of Mechanical Engineers on Friday of last week, some of the many very interesting features of the special work which his company carries on. His remarks carry particular weight in view of the highly-specialized study which he and his assistants have made of the various methods of electric and gas welding that are good practice to-day. Wider use is made of the system each month.
The Blacksmith's Welding.
Mr. Heaton introduced his paper by stating that any and all the facts contained in the remarks which, he had to make were drawn from, no less than 20 years of work on a progressive commercial basis. The old blacksmith's method of welding—good, sound, honest work in its way, but rough and ready in its method and not always faultless—suffered primarily because it was so difficult for even the most skilled smith to regulate and localize the heat on the joint which was being treated. Modern methods have enabled the application and intensity of the beat to be regulated with the utmost degree of nicety.
Various Modern Electric Systems.
Mr. Heaton tells us that of the two principal divisions of modern welding systems, that is, by electricity or by gas, the is a nrumber of variations. In respect of electric welding, the best-known methods are: the Bernados, using a direct current of about 90 volts and an amperage of from 200 to 500, in which the work itself forms the positive pole of the arc, and a rod of carbon the negative; the Zerener, in which two carbons are mounted in the same 'holder, and a magnet deflects the arc produced downwards on to the work ; the Strohmenger-Slaughter, worked with either direct or alternating current., the latter being preferable, with a voltage of about 85 direct or 220 alternating, and in which system the parts to be welded are placed in juxtaposition and an electrode is laid upon and along the welding line ; the Thomson-Houston, in which the two parts are held together by special mechanism, and a very heavy alternating current. is passed through them, the electrical resistance of the joint causing a rise of temperature to welding heat—the voltage is low, perhaps four volts, and the current per sq. in. may be up to 20,000 amperes.
Oxy-acetylene and Other Gas Welding.
Passing to a brief consideration of nas-welding methods, for Mr. Heaton's inmpany has practical experience of it and regularly employs both electric and gas methods, the lecturer thinks that, of the various gases to be used in conjunction with oxygen, which include honsole-vapour, coal gas, and hydrogen, the best is acetylene.
With regard to the relative values of oxy-acetylene and electric welding,
" Each is more economical in its own sphere. Owing to the lower temperature, the oxy-acetylene flame is better for thin work than the electric arc, because the risk of burning the metal is not so great.. The temperature of the electric arc has been calculated as about 7500 degrees Fahrenheit, but will vary with the amount of current That of the oxy
acetylene flame is about 6000 degrees Fahrenheit Where the work is suitable for the electric arc, welds can be made far more quickly than by the oxy-acetylene flame. The proportions of the two gases in welding vary somewhat, but should be in the neighbourhood of 1,5 volumes of oxygen to one volume of acetylene."
The Strength of a Welded Joint.
As instancing the capacity of properly-effected welds to stand high pressure, Mr. Heaton quoted examples in which welded gas cylinders have successfully withstood a pressure of 4000 lb. per sq. in., and welds in mild-steel tubes fig. in. diameter thick by l in. diameter inside have stood a hydraulic pressure of six tons on the sq. in., or 20 tons on the metal. A warning is contained in the following statement; "It is necessary to point out that this is not amateur work. To weld properly, and to make a joint sound throughout, skill and training are required, together with knowledge how to apply the system as well as how to design and to prepare the work for being welded.'
The Material to be Used.
Mr. Heaton continues: " Much depends on the kind or the quality of the material, which is generally steel or iron. For the generality of this work mild steel, inade by the SiemensMartin process, or wrought iron cannot be excelled, and the steel should be very soft and low in carbon to get the best results. . The author has heard the argument advanced that in electric or gas welding the result depends on the capacity of the workman. To a certain extent this is true, as it is true of most mechanical operations. In a weld, however, there is this difference from some other kinds of work, that a defect is not always apparent."
What Happens at the Weld.
The paper concludes with interesting particulars of tests which have been carried out with work welded in the Steel Barrel Co.'s shops at Uxbridge. We may quote the following informative paragraph: " Many tests have shown that 89 per cent. to 96 per cent, of the original strength of metal can be relied on in the electric weld. It has been said, but quite wrongly, that the electric welding hardens the metal by filling it with carbon from the electrode. This is not the case. In welding mild sted, the fierce heat of the electric arc burns out all the impurities more or leas, including carbon, and leaves the metal at the weld purer iron. If any hardening effect has ever been found, it. has been due to bad manipulation, to the fact that the. metal was not of a properly-weldable quality, or that the polarity was wrong."