| 摘要 |
PROBLEM TO BE SOLVED: To provide an apparatus for screw fastening which can provide high corrosive prevention, high lubricity, high compatibility with a top coating material and axial tension being independent of a temperature change and stable. SOLUTION: A torsia type power bolt is composed of a hexagonal nut having a washer 15 and an internal thread part and a power bolt 1 having an external thread part 9. The respective surfaces are treated by forming a zinc or manganese phosphate film under conditions including a coating weight of 0.1-50 g/m<2> . A rust-preventive coating composition is applied to the surface of the phosphate film in a thickness of 1-50μm. The rust-preventive coating composition contains 20-60 wt.%, based on the solid matter, thermoplastic resin having a glass transition temperature of 0-80 deg.C and 5-40 wt.%, based on the solid matter, lubricant. The lubricant used is a tetrafluoroethylene polymer, molybdenum disulfide, graphite or a higher fatty acid metal salt. As the temperature increases, the thermoplastic resin of the composition softens and increases in viscoelasticity resulting in increased lubricity, prevention of a decrease in a coefficient of friction and consequent constant torque stabilized axial tension.
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