Fig. 41.—Showing How Oven is Built when Preheating Torch is to be Used. Torch is Shown at (A).
(64) When using preheating torches, the ovens are built much closer to the work and do not have the openings along the bottom row of bricks. They are made as tight as possible, and in some cases it will be found advisable to build up the walls with two layers of bricks, with asbestos paper between them, in order to hold the heat and cause the work to heat up in a more uniform manner. A hole is left in one end of the oven, through which the flame of the preheating torch is introduced as shown in [Fig. 41]. It is not thought best to have the torch flame come in direct contact with the work which is being preheated, and a baffling plate of metal or brick is placed directly in front of the flame, in order to spread it around the oven. Judgment will have to be used in all such work.
(65) The setting up of the work, when preheating, is an important point overlooked by many welders, especially so in the case of aluminum. Care should be taken to see that the work has a good solid setting and is braced at a sufficient number of points, to prevent its sagging when in a preheated condition. Many times when working on rough surfaces, a few firebricks distributed around the bottom of the oven with a dab of putty, clay, or retort cement, placed upon them, will form an excellent cushion upon which the work can rest and the operator may feel confident that no sagging will occur.
CHAPTER VI
Part One.—WELDING OF CAST IRON
(66) In order to know how to weld, it is quite imperative that the operator first know the kind of metal he is to work on. It is surprising to find how few welders know their metals thoroughly. An incident might be cited where some welders depend upon the sparks given off by the emery wheel in determining the kind of metal they are about to weld. They will approach the wheel; grind off their work, noting the sparks; return to their welding table; choose their filler rods and do their welding without any delay whatsoever, much to the consternation of their fellow workers. There are four simple ways in common use to distinguish between cast iron, malleable iron, and steel; they are: By the cross-section of a fresh break, by application of the welding torch, by the sparks given off when applied to the emery wheel and by the chisel test.
Fig. 42.—Characteristic Sparks of Different Irons and Steels Thrown off by an Emery Wheel. Wheel should be Clean Cutting and Run about 7000 Feet per Minute.
(1) Shows cast iron. No sparks unless impurities are present.