a website collaboration between Science Service and the Smithsonian Institution

1938 - scientist heating small quantities of iron at a more intense heat


CD 1963047 E&MP 22.004

Electric Heating

August 17, 1938

Daily there are hundreds of brawny men exposed to the intense heat of open-hearth furnaces in steel mills. These men, known as moulders, are commonly pictured stripped to the waist, wearing heavily insulated gloves, their muscular bodies glistening with perspiration, and forever facing the obvious dangers of white-hot iron spattering from the heavily loaded pots. Their muscles are flexed as they guide the heavy pots in and about the seemingly unbearable flames melting the iron at approximately 2800 degrees F.

In contrast to these conditions is the scientist in the Research Laboratory of the General Electric Company shown heating small quantities of iron at a more intense heat but in no way battling any discomforting conditions.

The scientist is not brawny and perspiring, but his appearance is that of a business man. He stands a mere 12 inches from the molten metal as it bubbles and gurgles in heat of over 3000 degrees F, supplied by high-frequency induction current. The scientist shown is using a hydrogen atmosphere for his miniature furnace. There is no need to dodge any spattering metal because the hydrogen eliminates that hazard, and at no time is the iron exposed to air. Should the metal be exposed to air, it would oxidize and there would be a shower of fiery iron sparks.

The moulder sometimes stirs the molten metal so that it mixes evenly; the scientist does not. The use of hydrogen with the circulating high-frequency current results in a self-stirring action and insures a syrup-like molten metal, uniform and clean, instead of curdled and crusty as obtained by the moulder at his open-hearth furnace. In the laboratory furnace, the crucible filled with metal is placed in aluminum oxide powder, one of the best heat-insulating materials at such high temperature.

A glass bell jar is placed over the crucible and lowered into the insulating powder so that no air can seep in and oxidize the metal. Purified hydrogen is passed into the bell jar at the top and leaves through a tube on the side of the jar. There is constant flow of the hydrogen at a pressure slightly above that of the atmosphere, insuring against any leakage of air into the furnace. The exit tube is submerged in water so that the hydrogen bubbles away and no air can back up into the tube and pass into the bell jar. Heat is supplied to the metal by high-frequency induction current and is "remote controlled".

Since the insulator of aluminum oxide powder surrounds the crucible, there is no visible contact between the induction coil and the crucible. Broadly speaking, high frequency current as applied here might be pictured as similar to radio broadcasting, in which the high frequency coil is the transmitter and the metal is the receiver. The current is passed through the coil, "sent-out", and "received" by the metal. The current flows through the metal and in so doing heats it until it becomes molten.

Incidentally, neither the aluminum oxide powder nor the glass bell jar, both of which are between the coil and the metal, is heated by the high-frequency current since neither is an electric conductor. Surrounding the electric coil is a small wooden fence to guard against any possible upsetting of the equipment. The metal is heated for about 30 minutes, left to cool, and removed for inspection and testing by knocking on the sides of the crucible. The process of melting under hydrogen gives the scientist a metal which retains its original composition to a more exact degree. Alloys melted in a crucible open to the air become oxidized and result in metals of varying composition. This method of melting metals is being used to make alloys of the cobalt-nickel-iron series to be tested for their physical properties and to determine if they are suitable for the manufacture of electric equipment.

Original Caption by Science Service
General Electric

National Museum of American History


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