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The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.〔E.L. Tobolski & A. Fee, "Macroindentation Hardness Testing," ''ASM Handbook, Volume 8: Mechanical Testing and Evaluation'', ASM International, 2000, pp. 203–211, ISBN 0-87170-389-0.〕 There are different scales, denoted by a single letter, that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale (see below). When testing metals, indentation hardness correlates linearly with tensile strength.〔"(Correlation of Yield Strength and Tensile Strength with Hardness for Steels )", E. J. Pavlina and C. J. Van Tyne, ''Journal of Materials Engineering and Performance'', Volume 17, Number 6 / December 2008〕 This important relation permits economically important nondestructive testing of bulk metal deliveries with lightweight, even portable equipment, such as hand-held Rockwell hardness testers. == History == The differential depth hardness measurement was conceived in 1908 by a Viennese professor Paul Ludwik in his book ''Die Kegelprobe'' (crudely, "the cone test").〔G.L. Kehl, ''The Principles of Metallographic Laboratory Practice'', 3rd Ed., McGraw-Hill Book Co., 1949, p. 229.〕 The differential-depth method subtracted out the errors associated with the mechanical imperfections of the system, such as backlash and surface imperfections. The Brinell hardness test, invented in Sweden, was developed earlier – in 1900 – but it was slow, not useful on fully hardened steel, and left too large an impression to be considered nondestructive. Hugh M. Rockwell (1890–1957) and Stanley P. Rockwell (1886–1940) from Connecticut in the United States co-invented the "Rockwell hardness tester," a differential-depth machine. They applied for a patent on July 15, 1914.〔H.M. Rockwell & S.P. Rockwell, "Hardness-Tester," , Feb 1919.〕 The requirement for this tester was to quickly determine the effects of heat treatment on steel bearing races. The application was subsequently approved on February 11, 1919, and holds . At the time of invention, both Hugh and Stanley Rockwell worked for the New Departure Manufacturing Co. of Bristol, CT. New Departure was a major ball bearing manufacturer which in 1916 became part of United Motors and, shortly thereafter, General Motors Corp. After leaving the Connecticut company, Stanley Rockwell, then in Syracuse, NY, applied for an improvement to the original invention on September 11, 1919, which was approved on November 18, 1924. The new tester holds .〔S.P. Rockwell, "The Testing of Metals for Hardness, ''Transactions of the American Society for Steel Treating'', Vol. II, No. 11, August 1922, pp. 1013–1033.〕〔S. P. Rockwell, "Hardness-Testing Machine", , Nov 1924.〕 Rockwell moved to West Hartford, CT, and made an additional improvement in 1921.〔 Stanley collaborated with instrument manufacturer Charles H. Wilson of the Wilson-Mauelen Company in 1920 to commercialize his invention and develop standardized testing machines.〔V.E. Lysaght, ''Indentation Hardness Testing'', Reinhold Publishing Corp., 1949, pp. 57–62.〕 Stanley started a heat-treating firm circa 1923, the Stanley P. Rockwell Company, which still exists in Hartford, CT. The later-named Wilson Mechanical Instrument Company has changed ownership over the years, and was acquired by Instron Corp. in 1993.〔R.E. Chinn, "(Hardness, Bearings, and the Rockwells )," ''Advanced Materials & Processes'', Vol 167 #10, October 2009, p 29-31.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rockwell scale」の詳細全文を読む スポンサード リンク
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