Comparing oil and coal is not always simple as it depends on the work to be done and the construction of the furnaces. The variation rises from 75 to 200 gal. of oil to a ton of coal. For forging and similar work it is probably safe to consider 100 gal. of oil as equivalent to a ton of coal.
Then there is the saving of labor in handling both coal and ashes, the waiting for fires to come up, the banking of fires and the dirt and nuisance generally. The continuous operation possible with oil adds to the output.
When comparing oil and gas it is generally considered that 4½ gal. of fuel oil will give heat equivalent to 1,000 cu. ft. of coal gas.
The pressure of oil and air used varies with the system installed. The low-pressure system maintains a pressure of about 8 oz. on the oil and draws in free air for combustion. Others use a pressure of several pounds, while gas burners use an average of perhaps 1½ lb. of air to give best results.
The weights and volumes of solid fuels are: Anthracite coal, 55 to 65 lb. per cubic foot or 34 to 41 cubic feet per ton; bituminous coal, 50 to 55 lb. per cubic foot or 41 to 45 cubic feet per ton; coke, 28 lb. per cubic foot or 80 cubic feet per ton—the ton being calculated as 2,240 lb. in each case.
A novel carburizing furnace that is being used by a number of people, is built after the plan of a fireless cooker. The walls of the furnace are extra heavy, and the ports and flues are so arranged that when the load in the furnace and the furnace is thoroughly heated, the burners are shut off and all openings are tightly sealed. The carburization then goes on for several hours before the furnace is cooled below the effective carburizing range, securing an ideal diffusion of carbon between the case and the core of the steel being carburized. This is particularly adaptable where simple steel is used.
PROTECTIVE SCREENS FOR FURNACES
Workmen needlessly exposed to the flames, heat and glare from furnaces where high temperatures are maintained suffer in health as well as in bodily discomfort. This shows several types of shields designed for the maximum protection of the furnace worker.
Bad conditions are not necessary; in almost every case means of relief can be found by one earnestly seeking them. The larger forge shops have adopted flame shields for the majority of their furnaces. Years ago the industrial furnaces (particularly of the oil-burning variety) were without shields, but the later models are all shield-equipped. These shields are adapted to all of the more modern, heat-treating furnaces, as well as to those furnaces in use for working forges; and attention should be paid to their use on the former type since the heat-treating furnaces are constantly becoming more numerous as manufacturers find need of them in the many phases of munitions making or similar work.
The heat that the worker about these furnaces must face may be divided in general into two classes: there is first that heat due to the flame and hot gases that the blast in the furnaces forces out onto a man's body and face. In the majority of furnaces this is by far the most discomforting, and care must be taken to fend it and turn it behind a suitable shield. The second class is the radiant heat, discharged as light from the glowing interior of the furnace. This is the lesser of the two evils so far as general forging furnaces are concerned, but it becomes the predominating feature in furnaces of large door area such as in the usual case-hardening furnaces. Here the amount of heat discharged is often almost unbearable even for a moment. This heat can be taken care of by interposing suitable, opaque shields that will temporarily absorb it without being destroyed by it, or becoming incandescent. Should such shields be so constructed as to close off all of the heat, it might be impossible to work around the furnace for the removal of its contents, but they can be made movable, and in such a manner as to shield the major portion of the worker's body.