ThyssenKrupp Magazin

90 VIM FURNACE
chemical strains, and occasionally all three at the same time. The Unna
smelter turns out no fewer than 260 alloys, and with research and development
continuing this number looks certain to increase. Nickel and
cobalt, two heavy metals, are the dominant basic elements.
The Unna plant, which was opened by Vereinigte Deutsche Metallwerke
in 1972, has changed along with the rest of the world over the
past three decades. Its latest step into the future took place only weeks
ago, when, for about €15 million, or a little more than $18 million, Unna
obtained a vacuum induction melting furnace; this apparatus is known
by the experts as a “VIM furnace,” short for vacuum induction melting.
The simple word furnace does not, however, really do justice to this 30meter-long,
12-meter-high plant with an installed power load of 7,000
kVA. The metal construct is accessible via staircases and platforms,
and the automatic melting and casting processes can be observed and
controlled via monitors in the elevated helmstand.
The actual furnace, the core of the plant, can be charged with
solid or liquid material, and its 30-ton capacity is the biggest of any
such facility in Europe. Indeed, with temperatures of up to 1,750 degrees
Celsius, the material is melted under conditions that seem positively
unearthly. Like a smooth soup, the pool crater has to be stirred,
something that is done by an electro-magnetic mixer, while the vacuum
allows for alloys that are free of oxygen, nitrogen and other unwanted
impurities. After the casting, the molten mass is poured into transportable
chill molds for cooling.
The resulting metal blocks do not yet represent the final stage of
purity, however. Some materials have to pass through the fire three
times: this means that two remelting plants in Unna are used to further
purify, homogenize and refine the material. The end products are highly
pure super alloys that can be used in equipment such as turbine
blades in steel drives, where a long lifecycle at high temperatures under
extreme centrifugal force is required.
ALLOYS WITH EXOTIC-SOUNDING NAMES
For physicists, alloys are what thoroughbred horses are to breeders,
and when reading the long list of creations you encounter such exotic
names as Nicorros, Nimofer, Pernifer, Conicro, Cunifer and Magnifer.
These are, of course, merely artificial names put together from the
chemical signs of the involved metals – Ni standing for nickel, Cro for
chrome, and Fer for iron. The alloy Nicrofer 5219 consists of no fewer
than 11 elements, including iron and molybdenum, although nickel and
chrome are the most important ones, with 52 percent and 19 percent,
respectively.
What has not changed in the Unna smelter over all these years is
the so-called labeling of the material: before and after the fire. There
TK Magazine | 1 | 2004 |