MODERN WELDING PRACTICE

Hokitika Guardian, 10 June 1931, Page 2

MODERN WELDING PRACTICE

STRUCTURAL WORK. ENGINEERING SOCIETY ADDRESSES. C'HB ISTCI tUBCfI, June ??. “The process of autogenous welding consists of melting the parent, metals winch are to be joined by means of an oxy-acctylene flame, the joint being built up or strengthened by filler rods which are melted into it.” said Mr E. i). Edmondson, in opening bis address to the Canterbury College Engineering Society on Saturday evening. Mr IC. JK Mackenzie was in the chair, and there was an attendance of over fiity numbers. Three papers were read by advanced students, the subject ol Mr Edmondson's paper being oxy-acety-lene welding.

There was no better illustrate,on, the speaker continued of the progress made by oxy-acctylene welding in Great Britain than that afforded in the manufacture of aircratt. Ihe first British-built aeioplane which flew incorporated such welding in its construction.

Toe use of welded joints had been extended until they were almost stauddard practice in British aircraft. Ihe main advantages lay in rigidity of the joints, ease of effecting repairs, simplicity of the joints where several ot the metal tubes forming the frame met, and in the saving of expense and tune The groat problem was to obtain welders of first-class technique. Oxy-aeetevlene welding has been applied with equal success to many ot-lioi forms of metal work; for example to mention only a few, boilers, domestic and central heating plants, and metal work such as gates and grilles, strueural work and automobiles. In the last class, the most noteworthy appli. cation was to the metal paneis of the body work which, when pressed into shape, were welded at the joints. When smoothed over and panned, it was impossible to tell where these joints had been made. In the manufacture of automobiles, welding was used also in the silencers, luggage-carriers, under shields, wings and rear axle housings. The advent of welding, into the field cf structural engineering (that was to say. to structures of steel frame) had been exceedingly slow and cautious, but it was steadily and scientifically establishing its position. The day was drawing nearer when the thuds of the riveter’s hammer would be replaced by be undertone of the welder’s torch. England was making strides in this science, many of the technical institutions having -already -established- the subject in their regular curriculi.

Mr Edmondson mentioned many other applications of welding, notably to the jointing of metal pipes such as gas mains, to railway work and rail hardening .to the manufacture of steel furniture, the cutting of maim ; . and to demolition work.

SYDNEY HARBOUR BRIDGE. The second paper of the evening was delivered by .Mr A. G, Robb, the Sydney harbour bridge being the subject. The structural design of this bridge was carried out by Mr Ralph Freeman ,\i. Inst. C.E., said .Mr Robb. It was of the two pinned arch type, in which, in common with the other forms of arches, Air Freeman had specialised lor many years. As a student of the Insituation of Civil Engineering he had hi ISOS, submitted a paper on this sub jeet to the institution. His opportunity came in 1923 when, however, the company for which be had prepared the design decided not to tender, 'this occurred three or four days before tne closing date for tenders. Air Freeman submitted bis design to Messrs Bor man Long, who set aside other designs which they had prepared and .submitted Air Freeman’s with their tender ii„s was accepted and the contract entered into. The contract applied only to the main span and its abutments, the erection of the approaches being carried out by the New South Wales Puulic Works Department under separate contract. Dr. Brad field, as ehiin engineer for the Public Works Department, drew up the specifications am? supervised the. work. The main span consisted of a single areh of which some of the details were Weight 37,000 tons; height top to water level, 4oUit; deck to watei level 170 ft; live load, G tons per linear loot, capacity; 1,060,000 North Shore residents or 0000 vehicles, 168 Iranis and 40,000 pedestrians per hour* The two bottom chords or mem belts near the abutments were fabricated steel work each lift x Bit in size which was the size of a standard carriage of the New Zealand railway. 1 lie thrust on each ol the tour end healings, two being at each end, " ;, s 20,000 tons, which -wa s transmitted from the steel areh to the concrete abutments by a steel pin 14 leet long and 144 inches in diameter. The arch was built out from either shore, each portion being held back by steel cables until the tow halves met in the centre of the span. On ec.cn ot the tour corners there wore 128 such cables, each 3 inches in diameter.

AYell equipped .workshops were first erected where the steel sections were fabricated, tested as far as possible in ful size and loaded on to barges by which they were conveyed to various points below the arch. From these

points they would lie hoisted to then particular positions by the creeper cranes which advanced with each portion of the arch as it grew from eiiner sale. SLit li ol these two tranos could lilt a lo.id oi Iflti tons. I 1 or the purpose of testing the members in tension coin--prcssion. bonding and shearing, a 1 --JU otn machine had been installed.

AUTOMATIC AUG WELD I NO-

The final pap -i on the subject < i automatic me welding, w; • re:-.! "y .Mr ,J N. Jones. The heat liberated in an arc .-Ori-nu. Mi- .Jones said, was used to lose one piece u, metal to another. Ihe arc was tunned by itiLivrupUiig an electric circuit by a gap causing the current there,ori. 1 to jump or “a.c amiss the gap. Alt intense heat resulted widen would bring the mend on cil.an side of the gap to a molten state. \\ itli direct current, twice as much heat was h beta led at the- positive electrode as aL the negative electrode so teat vvh n new metal had to be deposited it was suplied iruni a. rod ot metal which acted as the negative electrode;, the work itself acting as the positive elect!one. more heat was liberated in the larger mass of the work, giving a distinct advantage. The object of the automatic plant was to keep the conditions throughout the weld uni orm. Uniform current voltage, length of arc and travel oi electrode were essential for a homogeneous weld. By means of diagrams Air Jones showed how ,toh automatic arc welding plant achieved the result. To keep the are length constant, it was necessary to feed in the metal rod electrode at a certain speed, which was Controlled by gears Operdtted autotnotically, Four such plants could simultaneously weld the joints of an automobile axle housing as it rotated at a- certain speed below the electrodes.

SAFETY OF WELDING. Professor .1. K. L. Gull said the subject of welding was one demanding much consideration. The latest, information on the subject which he had received hum England still showed that no finality had been reached. In regard to experiments on structural work one had to he very carlul, since the safety of human life was involved. One had the. examples of only about 109 important welded steel buildings as a guide. The exact nature oi a weld was not completely understood, nor was its exact behaviour under different and varying conditions of stress known, Most responsible building codes specified a. stress less than that claimed by companies interested in welding. Most of the codes agreed that welding must he carried out only by proved and reliable welders, sinie the human factor was' one of the most important considerations. For these reasons, riveting had persisted in work on a large scale. A vote of thanks to the lecturers was carried by acclamation.