The Silicon Bronzes 



251 



widest use, with the inexpensive carbon-arc method 

 generally preferred. 



In the execution of welds by the carbon method 

 material gages up to ^^e inch are best set up with a 

 copper backer to support the molten weld metal. The 

 surface tension of the molten weld metal and the chUl of 

 the base metal are sufficient to permit easy execution of 

 welds in thicknesses of ^-fg inch and over without backing. 

 As the carbon electrode burns first to carbon monoxide 

 and then to carbon dioxide, the carbon arc flame is both 

 reducing and neutral in nature depending on the distance 

 from the electrode. Experimental work has indicated 

 that the soundest weld is obtained through the use of 

 the longer and more neutral flame. The use of a long 

 arc also reduces difficulties with carbon transfer, which 

 characterizes the very short arc and which often stiffens 

 up the floating slag to the point where easy and rapid 

 blending of weld and parent metals is difficult. In 

 the case of an unbacked weld, the use of a long arc in 

 all passes is impractical because of the tendency for 

 the filler rod to melt ahead of the point of arc contact. 

 In the execution of welds in backed-up seams in light 

 gage material, there is another consideration. The 

 longer the arc, the greater the spread of heat and the 

 larger the size of the weld pool. When the size of 

 the weld pool is out of proportion to its depth or thick- 

 ness, the surface tension of the molten metal may cause 

 it to recede from the point of arc contact in an effort 

 to assume the smallest surface area possible, thereby 

 resulting in a large gap or discontinuity in the weld 

 bead. Experience indicates an optimum arc length of 

 IJ'^ to 2 times the optimum filler-rod diameter. 



It should be noted that the carbon-arc method has 

 points of similarity to both gas and arc welding, the 

 technique being similar to that used with the former. 

 The carbon-arc method has the flexibility of the gas 

 method in that the source of heat is independent of the 

 size, source, and amount of filler metal added. How- 

 ever, the carbon arc is much more intense and the rate 

 of flow of heat greater than with the oxyacetylene flame, 

 and there are greater possibilities of overheating on 

 one hand and of cold welding in an effort to prevent 

 overheating on the other hand. The proper arc length, 

 the nature and solubility of flame gases, the effect of 

 carbon transfer, and the relation between the speed of 

 welding, pattern of weaving, the arc length, current, and 

 filler-rod diameter all have to be considered with respect 

 to their mutual relationship. Because of the inde- 

 pendency of the sources of heat and filler metal, the 

 operator functions as an instrument of control in 

 the correlation of the aforementioned details. With the 

 optimum welding speed varying for each operator, it is 

 important that the proper correlation of the above details 

 be determined and the use of a recommended amperage 

 in conjunction with the use of a mechanized movement 

 of the electrode be avoided. 



The center line of the weld is naturally the hottest 

 section. Overheating of the central portion of the weld 



should be avoided by effecting maximum heating at the 

 edges of the weld and by avoiding crossing the weld 

 at the same point in the center line. This is readily 

 accomplished by "whipping" the electrode across the 

 center line much as is done in the execution of a vertical 

 seam by the metal-arc process. The use of the arc 

 length previously mentioned affords the welder an oppor- 

 tunity to ascertain when sufficient heat has been added, 

 as evidenced by fusion and blending of base and filler 

 metals. Continued application of the arc, once fusion 

 and blending have been obtained, is to be avoided. 



Because of the rapidity with which the weld metal 

 freezes, its hot shortness, and characteristic high shrink- 

 age, the crater weld metal is often overstressed in a weak 

 temperature range and may crack unless care is taken to 

 feed the shrink of the crater when welding is discontinued, 

 even momentarily. This is easily accomplished by 

 lengthening the arc slightly and directing it on the end 

 of the filler rod or the size of the weld pool and the 

 attendant total shrinkage, or the tendency to crack 

 may be reduced by increasing the rate of progression to 

 the point where cold welding results when a stop in 

 welding is contemplated. 



Silicon bronzes are furnished in both bright-dipped 

 and hot-rolled finishes as the customer desires. In the 

 latter case it is essential that the black oxide on the 

 parent metal edges and surfaces adjacent to the weld 

 seam be removed. In both cases it is advisable to 

 remove either with emery cloth, a scraper, file, or grinder 

 any grease and dirt that may have accumulated in 

 transit or storage. The final cleaning operation should 

 follow any machining, drawing, or stamping and should 

 immediately precede welding. Likewise during welding, 

 each bead surface and the adjacent vee walls should be 

 cleaned of oxide, flux, and slag before any subsequent 

 beads are laid down. It is good practice to clean the 

 welding rod also. 



°- Clamped on edge between abutting edges to be joined. 



The use of a flux is recommended to keep the oxides 

 developed free-flowing. Proprietary fluxes are available, 

 or a satisfactory flux may be made up with fused borax 

 as a base, and sodium fluoride or barium carbonate 

 added to improve the fluidity. Water-free constituents 

 only should be employed. Likewise, the fluxes should 



