building that there is no room for a swinging burner or when the furnaces are close together. A circulation of water through a 34-inch pipe prevents the burner from being melted off by the heat of the furnace.

The pressure at which the oil is fed to the burner varies considerably at different plants but oil at 45 pounds and air or dry steam for atomizing at 40 pounds will probably give the best results under the average conditions. The question of whether compressed air or dry steam is best for atomizing seems to be an open one. About one-half of the plants use steam and the other half air as an atomizing agent. It is very important, however, that the steam be dry and it is usually well to put a drip in the steam line near the furnace and in some cases provide for superheating the steam before it enters the burner. An air or steam pressure reducing valve should be put in the line to cut the compressor or boiler pressure down to the proper point for atomizing. The American Rolling Mill Company of Middletown, Ohio, in the manufacture of its Armco Iron uses fuel oil in many of its operations. Fig. 73 shows the layout of its plant with respect to fuel oil distribution. Fig. 74 shows the method of construction. of its oil storage tank. Fig. 75 shows the method of charging open hearth furnaces at this plant.

CHAPTER XII

HEAT TREATING FURNACES

Heat treatment, it is generally understood, comprises the heating of steel to a temperature slightly above the critical point; quenching in oil or water; re-heating to some temperature to give the desired physical properties and cooling slowly. Mr. James H Herron in the Journal of the Cleveland Engineering Society, September, 1914, says that "the importance of determining the correct temperature and exercising the greatest care in heating cannot be over emphasized. This is especially true of the higher carbon and alloy steels. If the value of the steel is not actually impaired, a resulting condition may occur which would render the treatment valueless.

“One of the most important forms of heat treatment is case carbonizing or so-called case hardening. Steel to be carbonized is packed in some carbonaceous material and heated for a given length of time at temperatures varying from 1600 to 1750 degrees F., depending upon the depth of penetration of the carbon desired.

"It has become common practice to give case carbonized parts a double heat treatment, i. e., heat for the refinement of the core. quench in oil, subsequently heat at a lower temperature for the refinement of the case and quench in water, after which the material may be drawn to the extent necessary for the physical properties desired.

"In the heat treatment of steel castings, proper annealing is of the greatest importance. Unfortunately commercial annealing is not what it should be, and if much is expected from the material it should be properly annealed or heat treated. By heat treating large steel castings with the carbon range of 0.20 to 0.60 percent the elastic limit can be increased about 50 percent with little decrease in the ductility."

Mr. E. J. Janitzky, Metallurgical Engineer, Illinois Steel Company, in the Journal of the American Steel Treaters Society, December, 1918, gives the following discussion of the theories of heat treatment: "Although not going too deeply into the history of the theories that have been developed in regard to hard

ening, it might be interesting to describe in non-metallurgical phraseology their contents. There are several theories for the

FIG. 76. A Furnace for Case Hardening and Heat Treating Gears.
(Courtesy of Tate, Jones and Co., Inc.)

hardening of steel, the more important one being the stress theory, the carbon theory and solution theory. The stress theory basis its contention on the high stressing of the outer shell of the

FIG. 77. Continuous Rod-Heating Furnace.
(Courtesy of Tate, Jones and Co., Inc.)

steel when shrinking onto the interior and the stress set up in the crystal change from the hot to the cold metal. The fact that

cold working hardens steel is offered in support of this theory. The carbon theory contends that the hardness resulting from quenching steel is due to the condition the carbon exists in in the steel, it being recognized that carbon can easily exist in several allotropic forms. The solution theory contends that carbon is in solid solution with the iron. This seems to be the most logical and all phenomena can be explained by it. It will likewise be obvious that no theory so far presented fully satisfies for an acceptable explanation of the phenomena involved and that new

avenues of approach must be found to obtain a correct answer to this apparent enigma. The most progress in heat treatment has been attained with the advent of alloy steel. With few exceptions all alloy steels are heat treated for use, the treatment developing in them physical properties they are capable of possessing. No general laws regarding the effects of treatment of alloy steels can be laid down. Some steels when quenched from a high heat are hardened and others are softened, the latter being generally those with the higher contents of certain of the alloying elements. In respect to the effects of heat treatment, each steel