io6 



NATURE 



[April ii, 191 8 



edges are chamfered and brought together so as 

 to form a V-groove, The lowest part of the 

 groove is brought to fusion by the blowpipe, and 

 metal run in from a rod held in the flame, the 

 process being continued until the groove is filled, 

 when, if both the work and added metal have been 

 thoroughly fused, a good joint will result. The 

 oxy-acetylene flame is extensively used in this 

 manner for welding iron, and is now growing in 

 favour for joining non-ferrous metals, such as 

 aluminium, copper, brass, and bronze. The frame- 

 work of a Zeppelin is a notable example of fusion 

 welding in aluminium, for which metal it is neces- 

 sary to use a suitable flux. Largely owing to the 

 work of Capt. D. Richardson, R.F.C., the weld- 

 ing of non-ferrous metals in this country has made 

 great progress within recent years, the oxy- 

 acetylene flame, and a flux suited to the metal 

 under treatment, being generally used. The pro- 

 cess is of special value in the case of aluminium, 

 which cannot readily be joined by soldering. 



Electric welding has long been employed for 

 joining iron and steel rods, the ends to be pieced 

 being brought together, and a strong current 

 passed through the point of contact. This part, 

 owing to its higher resistance, becomes hotter 

 than the rest of the 'rod, and is allowed to reach 

 the fusion point. Longitudinal pressure is then 

 applied, so that complete union of the two parts 

 may be ensured; and after releasing the pressure 

 the weld is hammered during cooling. An alter- 

 nating current is used, the requisite high current 

 at low voltage being secured by the use of a 

 transformer. This method is impracticable for 

 sections above a certain diameter, owing to the 

 excessive current that w.ould be needed. A later 

 development is what is known as "spot " welding, 

 which is a substitute for riveting. In fastening 

 together two overlapping plates by this process, 

 the two electrodes are pressed, one above and 

 one below, on the spot to be welded, and the 

 current passed until a sufficiently high tempera- 

 ture is produced. The pressure is maintained 

 durmg cooling, after which the work is brought 

 forward and treated similarly at another spot. It 

 is quite possible that spot welding may supersede 

 riveting in shipbuilding, as the process can be 

 applied to thick plates. An extension of the spot- 

 welding process is to unite the plates along their 

 whole length, by passing through rollers which 

 form the electrodes, the rate of travel being such 

 as to allow each part to attain a welding heat. 

 So far, continuous seam welding of this kind has 

 been applied only to comparatively thin sheets. 



The foregoing electric methods are all based 

 on the heating effect due to resistance. The high 

 temperature produced by the electric arc is addi- 

 tionally utilised for welding, and has a varied and 

 rapidly extending application. The carbon arc, 

 which yields a temperature of 3700° C, is used 

 for w^elding seams, the procedure being the same 

 as when the oxy-acetylene flame is used as the 

 source of heat. Direct current is used, the work 

 being connected to the positive pole and the 

 NO. 2528, VOL. lOl] 



carbon to the negative. It is customary to work 

 at a pressure of about 90 volts and a current of 

 from 50 to 500 amperes, according to the size of 

 the work. An adjustable resistance is used to 

 regulate the current, and the carbon rod is held 

 in an insulating holder, forming a handle by which 

 the workman moves the arc along the joint. It 

 is not attempted to bring the work to a higher 

 temperature than is necessary for complete fusion, 

 but this condition is brought about more rapidly 

 by the carbon arc than by any other source of 

 heat, and the method is much used in the pro- 

 duction of seamless steel drums, etc. 



A more recent development of arc welding con- 

 sists in the substitution of an iron rod as negative 

 electrode in place of the carbon, which is fused 

 by the heat, and the fused metal carried across 

 the arc on to the work opposite. The iron elec- 

 trode, which is usually coated with a flux to pre- 

 vent oxidation, is rapidly used up, and must be 

 continuously moved forward by the welder to 

 maintain the correct length of the arc. The de- 



-Repairing a tram-rail by arc weklipg, usini 

 an iron electrode. 



posited metal is hammered during cooling, and 

 very satisfactory joints are thus secured. The 

 best voltage to employ is as yet an unsettled 

 question ; in American practice 45 volts are com- 

 monly used, whilst in this country pressures rang- 

 ing from 75 to no volts are general. Iron-elec- 

 trode welding is particularly useful for repairing 

 cracks in boiler-plates or shafts, the procedure in 

 the latter case being to cut away the metal adjoin- 

 ing the crack on either side, forming two conical 

 pieces meeting in a point. The part cut away is 

 then filled in by the arc, commencing at the nar- 

 rowest point and working outwards. Fig. 2 

 shows the method applied to the filling in of the 

 worn parts of a tram-rail, a repair of this kind 

 often saving the cost of a new rail. In all arc 

 welding the eyes of the welder must be protected 

 from the rays of the arc, and suitable glass 

 screens are therefore provided. One advantage 

 claimed _ for arc welding in the case of boiler 

 repairs is that, owing to the heat produced being 

 intensely local, a joint may be made without caus- 



