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Hand Forging by Thomas F. Googerty
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52 HAND-FORGING
workman, based on practical experience. Tool-steel welding will not be taken up here, only iron and soft steel being considered, because these are in constant use in blacksmithing. As illustrations specific cases will be taken, but it must be borne in mind that the principles involved are the same in all welding.
If a piece of iron is heated in a fire which is too hollow, allowing the air to come in contact with it, the iron will scale or oxidize. No matter how hot it becomes, it cannot be welded while this scale is present. The oxidization is caused by not having a fire with enough coke under the iron, or a fire which is not clean. There must be plenty of coke under the piece so that all the oxygen is consumed in the combustion. If more air is used than the fire can take care of, the surplus will come in contact with the piece being heated and cause oxidization. Therefore the blast should be regulated to suit the fire.
Iron can be welded without using any flux. However, in some cases a good, clean, sharp sand should be used, because this forms a fusible mixture or slag which offers a protection to the iron, excluding the air and also tending to promote an even heat. Borax should be used on iron only in welding very small pieces.
Some soft steel can be welded without using a flux, but it is always advisable to use one
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Hand Forging by Thomas F. Googerty