Metal Working Additional Processes 61 



wrapping the joint with it before brazing and melting this in 

 simply adding the flux as required. 



Welding. The welding of iron or steel is a process 

 which may be considered as outside our work here, but the 

 welding of platinum, being so easily performed and so useful 

 an accomplishment, may well be described. 



The most simple method is to arrange a foot blowpipe so 

 that its flame plays downwards upon the metals to be united, 

 which should be supported upon some incombustible and 

 perfectly steady support, e.g. a bench anvil, the face of which 

 is covered with a brass or copper sheet, in order not to injure 

 the anvil by the direct blowpipe flame. 



One piece of the platinum being so placed in position, the 

 second piece to be joined is held over the first, and the blow- 

 pipe adjusted so as to heat both conveniently, with the smallest 

 flame that will do the work. When the upper piece is well 

 above red heat, and the lower piece red hot, a single smart 

 blow is struck with a light hammer, the blow causing the two 

 pieces of platinum to come into contact under pressure before 

 the heat is dissipated. Usually a single blow, if delivered 

 vertically, will be sufficient to cause perfect union, much 

 hammering of the soft metal being, of course, a disadvantage. 

 In any case, a thorough examination should be made of 

 the joint after each blow, and the next blow very carefully 

 planned. After union has occurred, reheating is best attained 

 by lifting the job slightly off its support ; the next blow of the 

 hammer will press it down with sufficient rapidity to cause no 

 loss of heat through this action. 



The blowpipe flame should not be removed until the 

 welding blow has been struck, as the metal would cool too 

 quickly in such case. 



Wires may be welded end to end by flattening each end 

 out slightly, superposing one flattened end above the other, 

 and welding as above, subsequently hammering under heat if 

 necessary into cylindrical form. 



Case-hardening. This is the process of hardening the 

 surface of an iron forging to give it wear-resisting qualities. On 

 a large scale, this process can only be performed in properly 



