A New Electric Furnace for Steel Treatment.
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rilHE DERABILITy of a motor -1vehicle largely depends on perfectly hardened or case-hardened steel parts. If any particular component is not perfectly hardened it cannot stand the wear and tear of ordinary usage and has soon to be replaced. Any new method of producing hardened parts, particularly if a given method not only ensures better and more uniform results but, at the same time, tends to reduce manufacturing costa, is of importance to the industry.
The Wild-Barfield automatic electric furnace is an instance of the most up-todate electrical application Of the heat treatment of steel. A first impression of it is that., although it is obviously an electrical appliance, it is anything tart a "furnace,' and only when cum looks into the heating chamber glowing at a uniform bright red heat, is its purpose apparent. There is no noise, flame,_ smoke, nor odour and not much external heat; this furnace, in fact; demonstrates electrical Cleanliness and efficiency. The heat is obtained from a spiral resistance wire which surrounds a refractory chamber. The strength of the current, either continuous or alternating, passing through the wire can he regulated and the degree of heat readily controlled. Any number of parts suspended in, the heating chamber neon reach a red heat and are ready for quenching. The hardening of steel is a highly complex operation in the scientific sense, owing to certain molecular changes in the structure of the steel. It is ordinarily. a, difficult matter to judge when the steel is in the right molecular state for sudden cooling. but there is one iofallible indication, and that, is its magnetic state "when heated. This is provided for in the electric fur
nace. There is an outer coil, known as the pyroscopic or detector winding, in addition to the heating coil. Any steei part put into the furnace becomes automatically magnetized, and at a certain critical temperature it loses its magnetism') this condition is shown by a magnetic detector, and the temperature point—i.e., non-magnetic state, has been proved to be exactly right for quenching carbon and alloy steels.. This furnace is &signed co that. en teehnical skill is needed to operate it. Assuming that a number of gearwheels have to be hardened, they are put on a carrier and lowered into the furnace. The workman then watches the needle of the magnetic detector until it shows
the withdrawal point. The gears are then quickly lifted out and quenched. The temperature of the furnace is shown ih degrees centrigrade by an instrument known as a pyrometer, and a cut-out or fuse is provided which breaks the circuit and shows a red light should the current be left On unintentionally ; so there can be no excessive temperature rise, waste or danger. By installing an electric furnace of this description the nmnufacturer is enabled to effect all his steel treatment on a, scientific basis, and for any given class Of alloy steel a close uniformity .917,sesu1ts is assured, as all rule Of thumb and the " human element" are eliminated, in the process.. Another important advantage Which has a direct bearing on manufacturing costs is the high efficiency of the system, that is to say, in respect of the amount of work turned out for a specified arnonnt sif current 'consumed. The manufacturers of this equipment are Automatic and ElectricFurnaces, Ltd., 173.5, Parringday Road, London,