To accomplish these ends the iron must not be heated too quickly after it is at a good red heat, and the fire must be so made that the blast cannot meet it at any point until it has passed through the bed of the fire.
When the iron is getting near the welding heat it may be sprinkled with white sand, which will melt over it and form a flux that will prevent oxidation and cool the exterior, giving time to the interior to become equally heated. The sand should be thrown on the work while in the fire, as removing the work from the fire causes it to oxidize or scale rapidly. The work should be turned over and over in the fire, the scarf face being kept uppermost until the very last part of the heating, when the blast must be put on full, the bed of the fire kept full and clear so that there shall be sufficient bed to prevent the blast from meeting the heat until it has passed through the glowing coals.
When the heat is taken from the fire it should meet the anvil with a blow, the scarfed face being downwards, to jar off any dirt, cinder, &c., and the scarf should be cleaned by a stroke or two of a wire brush. But as every instant the iron is in the air it is both cooling and oxidizing, these operations must be performed as quickly as possible.
The two scarfs being laid together as shown in [Fig. 2884], the first blows must be delivered lightly, so as not to cause the upper piece to move, and as quickly as possible, the force of the blows being increased regularly and gradually until the weld is sufficiently firm to hold well together, when it may be turned on edge and the edges of the scarf hammered to close and weld the seam. If this turning is done too soon, however, it may cause the two halves to separate. When the weld is firmly and completely made the enlarged diameter due to the scarfing may be forged down, working the iron as thoroughly as possible.
Fig. 2885.
Fig. 2886.