| 摘要 |
PURPOSE:To obtain the degree of straightness on a standard surface with accuracy high than that defined by JIS, by constituting standard main bodies such as a straight rule or a triangular rule by the use of a high purity alumina ceramic. CONSTITUTION:As the constitutional material of a gauge, alumina ceramics are used because a material of a dimension of about 1m can economically be obtained, in addition to their satisfactory values for the strength, Young's modulus and coefficient of thermal expansion. However, even among the alumina ceramics, Young's modulus is different depending on the purity of alumina, becoming high as purity becomes high. Because of this, a material having high Young's modulus is effective in order to obtain objective accuracy in the processing requiring high accuracy. When the purity of alumina is 85%, the degree of straightness achievable is 2Xm per 1000mm whereas, when 92%, the degree of straightness is 1.5mum/m and, when 96%, 0.9mum/m and, when 99%, 0.6mum/m. Therefore, by constituting an alumina ceramic with a high purity of 96% or more a standard gauge high in flexibility, relatively less affected by measuring environment and having ultrafine accuracy can be obtained.
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