suitable for joining the refractioning metals such as columhium, tantalium, 

 molybdenum, and tungsten nor reactive metals- such as titanium or zirconium. 



By varying the relative amounts of fuel gas to oxygen in the gases 

 flowing to the tip of the welding torch, the characteristics of the flame 

 can be altered. When fuel gas and oxygen are supplied in the stoichiometic 

 ratio for complete combustion, a neutral flame is produced. As more oxygen 

 is introduced, an oxidizing flame is produced. Slightly less oxygen than 

 that required for a neutral flame results in a reducing flame. Still less 

 oxygen results in a carburizing or carbon impregnating flame. In any flame, 

 the highest temperature is reached at the tip of the inner cone. 



In oxyacetylene welding, an oxidizing flame is never used to weld steel 

 but is used sometimes to weld copper and copper base alloys. The copper 

 oxide slag that forms on top of the weld provides shielding from the weld 

 puddle. Temperatures exceeding 315 Celsius (600 Fahrenheit) can be 

 obtained in oxidizing oxyacetylene flames. The reducing flame is frequently 

 used for welding with low alloy steel rods. Flame temperature at the tip of 

 the inner cone is usually 2 930° to 3 040° Celsius (5 300 to 5 500° Fahren- 

 heit) . The carburizing flame has a tendency to soot the cold work but is 

 useful where lower temperatures are required such as for silver brazing, 

 soldering, and in the melting of lead. For most oxyacetylene welding, a 

 neutral flame is used. When welding steel the outer envelope provides 

 protection to the molten weld puddle, and no flux is required. 



Fluxes are required when oxyacetylene welding stainless steel, cast 

 iron, and most nonferrous metals. There is no universal flux suitable for 

 all metals. The function of the flux is to clean the metal surfaces to be 

 joined and to provide protection to the weld puddle by lowering the melting 

 point of the metal oxides or dissolving these oxides so they rise to the top 

 of the weld pool forming a protective slag covering. Fluxes are not required 

 for welding lead, zinc, and some precious metals. 



c. Underwater Arc Welding . Although many experts consider underwater 

 welding suitable only for emergency ship repairs of a semipermanent nature, 

 satisfactory permanent welds can be accomplished using special techniques. 

 Sometimes underwater welding is the only practical method of making attach- 

 ments or repairs on such underwater structures as drilling platforms or 

 bulkheads. Three different techniques have been used for performing welding 

 below the waterline. These are wet welding, dry welding, and welding using 

 either a caisson open to the surface attached to the area to be welded, or a 

 special habitat constructed around the area to be welded. Underwater wet arc 

 welding requires the use of divers in full deep-diving suits. The helmets 

 are fitted with supplementary hinged faceplates with appropriate welding 

 glass. It is advisable for the diver's head to be insulated from the helmet 

 by wearing a cap, and by covering metal with insulating tape. Scuba diving 

 is suitable only at shallow depths because it is required that the diver be 

 in voice communication with topside assistant. Topside welding assistants 

 operate the power source at the command of the diver-welder. Electrodes for 

 underwater welding must be waterproofed using proprietary products or coatings 

 of cellulose acetate. Some brands of electrodes are also satisfactory 

 without additional coatings. Because these coatings can be only considered 

 as providing temporary protection, divers should carry only a few electrodes 

 at a time. The Navy recommends 4.75-millimeter (3/16 inch) electrodes of 



215 



