Fig. 45.—Jump Weld Scarfs.
66. The jump weld is shown in [Fig. 45]. The scarfs require perfect forming, because the opportunity for hammering is limited, as blows can be delivered only at certain places: on the end of the scarf 1 driving it into the concave groove 3; on a fuller which is held in the fillet 4; and on both the edges indicated at 3.
The groove at 3 should be formed with sufficient metal at points 0, to meet the projections X, and form a fillet. The convex scarf 1 should first come in contact at 3, so that welding will proceed from that place.
Welds made in this way are considered the weakest of those here described, on account of the limited assistance which can be provided by hammering. Still they are frequently used to avoid the laborious operations required to make such forgings out of solid metal.
Fig. 46.—V Weld Scarfs.
67. The V weld ([Fig. 46]) is a very important but difficult one. It is generally used on extremely heavy work, such as locomotive frames ([Fig. 47]), beam straps, rudder stems, and all cumbersome forgings.
The process is as follows: Pieces 5 and 6 are to be welded. They are held in a rigid position with heavy straps and bolts, as shown on the locomotive frame in [Fig. 47], sometimes while the V-shaped opening is being formed; however, they must always be held secure while the welding heat is being obtained. The V-shaped opening formed by the scarfs on 5 and 6 should penetrate about two thirds of their thickness and form an angle of about 50 degrees, with sufficient metal at 9 to provide for the waste which will occur while a welding heat is being procured.
The wedge 7 is formed with some surplus metal for filling the V-shaped opening. It is handled by a bar which is welded to it. The angle of the wedge should be not less than 5 degrees smaller than the angle of the opening. This will insure that the welding proceeds from the apex or point of the wedge outward.
Two fires are required; 5 and 6, securely strapped and bolted together, are placed in one with the V-shaped opening turned downward. Plenty of coke is placed around this opening, completely covered with moistened coal, and securely packed with a shovel; then two openings or vents are made through the coal with a poker, one on each side of the metal and leading to the scarfs. This is called a covered fire. The blast is now turned on and slowly increased until the proper heat is attained. The progress of heating can be observed through the openings thus made, and the fire replenished with coke when necessary.