| No
cause could be seen by the naked eye, but the microscope showed an
extremely fine crack. Clearly the magnetization had produced a polarity
at the edges of the crack, which behaved like a fine magnet and was
shown up by the iron dust it attracted. Thus was magnetic crack detection
discovered in 1922, and within five years it was being applied to
alternator rotors, turbine discs and blades, and traction pinions.
In later practice the doubtful surface was explored with a suspension
of magnetic particles in light oil, and by suitable magnetization
of a specimen in more than one plane, cracks lying in any plane could
be detected at the first attempt.
 Before
this, permanent quarters had been prepared for research work: an
administrative building including a library was opened in 1920,
and the first laboratory building—chemical, mechanical, and
metallurgical—in 1921. Thus early the Company had probably
the best designed and equipped laboratories for industrial research
in the kingdom, the staff numbering about 130, and a new research
building or extension was to spring up almost every year.
A high
voltage laboratory was built in 1924. It was first provided with
a 500,000-V 50-c/s testing set, and four years later with a million-volt
plant made in the works and consisting of two 500-kV units arranged
for connection in cascade. The laboratory, more completely equipped
than that of any other British commercial firm, was honoured by
a formal opening by Sir Ernest (later Lord) Rutherford, then Cavendish
professor of experimental physics at Cambridge and president of
the Royal Society. This took place in February 1930 in the presence
of a galaxy of scientific and engineering talent including four
Nobel prize winners.
In
1924 also C. R. Burch and N. R. Davis were working on eddy current
heating when they became dissatisfied with existing published theory.
In the course of a rigid mathematical analysis of the principles
involved they were surprised to find that a definite quantity of
material such as copper ought to melt efficiently when placed in
a coil fed with 50-c/s alternating current; when the experiment
was tried, a 100-lb charge of copper was successfully melted. Further
work showed that steel could be melted economically at frequencies
from 350 to 500 c/s, and an experimental furnace was designed
in which a 300-lb melt was carried out. The great advance was the
proof that induction melting did not need expensive high-speed high
frequency generators. By 1926 a 5-cwt 500-c/s experimental furnace
capable of melting more than a ton of steel a day had been made
and sold to the steel industry, and in 1928 a similar model was
shown at a Manchester exhibition.
Induction
furnaces can ensure accurate composition and uniform quality of
the melt, and they have revolutionized the manufacture of alloy
steels. In laboratory sizes also they have been invaluable for metallurgical
work, and similar furnaces have been developed for sintering, an
important aid to powder metallurgy, and for the melting and casting
of metals in vacuum giving a gas-free product. This last application
arose while T. E. Allibone was working for the Company at Sheffield
University on zirconium steels. Needing to produce pure zirconium
he
|
