Hardness, Bearings, and the Rockwells Page: 3 of 7
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the American Society for Steel Treating (ASST) Convention in Indianapolis, IN, in 1922.23
ASST became the American Society for Metals in 1933, and is now ASM International. He
received two U.S. Patents consecutively on 18 November 1924, Nos. 1,516,207 and 1,516,208.
Stanley left Whitney to establish the New England Heat-Treating Service Company in
Hartford in 1921. NEHTSC was renamed the Stanley P. Rockwell Company two years later, and
is still providing heat treating services in the present day. In addition to heat treatment and
metallurgical analysis, the Rockwell Company also sold furnaces for the American Gas Furnace
Co. and General Electric, process instruments for Wilson-Maeulen, and supplies for the Rodman
Chemical Co. Dr. R.W. Woodward succeeded Stanley as chief metallurgist at Whitney, until he
was hired by Stanley in 1925 as secretary, treasurer and sales manager of the Rockwell
Company. Stanley invented a dilatometer24 in 1928 to measure the thermal expansion of steel to
optimize its heat-treatment temperature, and a quench tank agitator in 1929. Success and
growth prompted the company to move into its current facility in 1929.26 Stanley's son Dudley
W. "Dud" Rockwell (1913-2006), also a Yale-educated metallurgist, managed the company from
1959 until his retirement in 1974. Dudley served as chairman of the Hartford Chapter of ASM in
1963-4.27
Charles H. Wilson, an instrument salesman for the Wilson-Mauelen Company in New
York, NY, saw the potential for the Rockwell hardness tester in 1920 and began a long-term
collaboration with Stanley Rockwell. Wilson suggested many improvements to the tester,
including standardized loads and reversal of the scale such that the highest hardnesses
corresponded to the highest scale numbers. Wilson developed the diamond indenter for
hardened steel in 1924 that is still sold under the Brale trademark.28 Wilson added a hardness
gauge of his own design in 1930 that made the Rockwell hardness tester as it is known today.29
With the success of the hardness testers, Wilson's company was renamed the Wilson Mechanical
Instrument Co., Inc. Wilson's company developed the superficial Rockwell hardness tester in
1932 for measuring the hardness of sheet metal, brittle materials, and other specimens not
suitable for the original higher-load test.1 Additional improvements to the Rockwell hardness
tester were made in subsequent years, including some by Wilson's competitors. The Wilson
company has been owned by Instron Corp. since 1993.
The Rockwell method of hardness determination was revolutionary, but hardly the last
word in hardness. The shortcomings of Rockwell included: (1.) the indentions were too large for
very small components or to be a tool of microstructural analysis, and (2.) it was not a reliable
way to characterize the hardest and brittlest materials, such as dense ceramics. The Vickers
method was developed by Smith and Sandland at Vickers Ltd. circa 1922, to determine the
hardnesses of individual grains and phases in a microstructure. The Vickers method used a
pyramid-shaped diamond indenter, sized so that Vickers hardness numbers correspond to Brinell
numbers for the same material, up to about 600 on either scale. Vickers, a London-based
aerospace company, became part of British Aircraft Corp. in 1965. The Knoop method,
developed in 1939 by Knoop, Peters and Emerson at the National Bureau of Standards in
Washington, DC, modified the Vickers indenter design.32 Knoop et al. changed the dimensions
of the Vickers diamond pyramid indenter to lessen the depth of penetration and the degree of
cracking around the indention in brittle materials. Nanoindentation principles were conceived as
early as the 1950s,33 and put into practice as instrumented indentation hardness circa 1992.34
Neither the Vickers, Knoop or various other hardness techniques have replaced the Rockwell
method in the last nine decades-the alternative methods merely fill the niches where Rockwell
is not applicable.Hardness and the Rockwells
Page 3 of 7
22-Nov-10
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Chinn, Richard E-. Hardness, Bearings, and the Rockwells, article, October 1, 2009; United States. (https://digital.library.unt.edu/ark:/67531/metadc843086/m1/3/?q=rockwell: accessed June 2, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.