As the welding heat vanishes very rapidly, it requires careful judgment to determine when the pieces cease to unite. All blows delivered after this will reduce the dimensions of the metal; if reheating is necessary, there should be no metal sacrificed by unnecessary hammering. Welds are generally weaker than the metal from which they are made; consequently if the stock is made smaller at the weld, its strength is greatly decreased.
The old adage “Haste makes waste” does not always apply. If you hasten the operation of welding while the pieces are sufficiently hot, you will not waste the metal. If through want of haste you are compelled to reheat, you will waste metal, for every time a piece is heated it loses a fractional part of its area, regardless of any hammering.
Welds made with scarfs of this kind are considered to be nearly as strong as the metal itself, because they allow of a more thorough lamination by hammering than other welds, consequently they are frequently used on various qualities of metal when strength is considered a chief requirement.
Fig. 44.—A, Cleft Weld Scarfs; B, Butt Weld Scarfs.
64. The cleft weld (A, [Fig. 44]) is so called because one piece of metal is split to receive the other. It is used for welding iron to iron or steel to iron (the inserted portion being the steel). Whatever the metal, the inserted portion is usually roughened with a hot cutter on the pointed surfaces and the cleft hammered down and securely fitted before the whole is heated. The pieces should not be placed in the fire separately, but together, as they have been fitted.
When a welding heat appears, if possible, light blows should be delivered on the end of the inserted portion while the two are in the fire; these blows will partly join the pieces and make them secure before removal. If this cannot be done, the first blows after removal from the fire should be on the end. When a final and thorough welding heat has been attained, they should be removed to the anvil and securely joined. If heavy pieces are being operated upon, they may be welded with the steam hammer.
65. The butt weld (B, [Fig. 44]) is so called because the pieces are butted together and almost thoroughly joined by ramming or backing-up blows before any blows are delivered on the exterior surface. The scarfs are easily formed. The outer edges of the pieces are backed up to form a rounded or convex end to insure their being joined at the center first. As the blows are delivered on the end, the metal will upset and the pieces will be joined from the center to the outer edges. After they have been quite thoroughly joined with these blows, they should be hammered on their exterior to weld them securely.
When scarfed in this manner, the pieces are frequently placed in the fire for heating with the ends in contact, then partly joined while in the fire and removed to the anvil or the steam hammer for final welding.
