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Bolt tightening method and bolt tightening apparatus

  • US 20060218768A1
  • Filed: 02/22/2006
  • Published: 10/05/2006
  • Est. Priority Date: 03/29/2005
  • Status: Active Grant
First Claim
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1. A bolt tightening method applicable to a bolt having bolt tightening torque properties, in which a torque gradient expressed in terms of the ratio of an additional tightening torque exerted on a bolt to its additional turning angle has a first torque gradient in an initial bolt tightening stage and a second torque gradient in a late bolt tightening stage subsequent to the initial bolt tightening stage, a magnitude of the second torque gradient being greater than that of the first torque gradient, the method comprising the steps of. tightening the bolt with a predetermined snug torque;

  • and turning the bolt subsequently by a total turning angle that is equivalent to the sum of a predetermined initial-set turning angle and a corrective additional-turning angle, wherein said corrective additional-turning angle is the sum of a first corrective additional-turning angle and a second corrective additional-turning angle, said first corrective additional-turning angle being to compensate for a situation in which a bolt turning angle corresponding to said snug torque on an extension line of said bolt tightening torque properties with the second torque gradient is greater than a bolt turning angle corresponding to said snug torque on a line of said bolt tightening torque properties with the first torque gradient, said second corrective additional-turning angle being to compensate for a decrease of an effective bolt axial force that is caused by an existence of said bolt tightening torque properties with the first torque gradient.

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