| abstract |
PROBLEM TO BE SOLVED: To provide a screw fastening device which has a high corrosion resistance, a high lubricity and a high compatibility with a top coating material and which can obtain a stable axial force without depending on a temperature change. SOLUTION: A hexagon nut having a washer 15 and a female screw portion 13 is provided. A torcia-type high-strength bolt set 18 is constituted by the high-strength bolt 1 having the male thread 11 and the male thread portion 9. A phosphate film of zinc or manganese is formed on each surface under the condition of 0.1 to 50 g / m 2 , and is subjected to a base treatment. A rust-preventive coating composition is applied to the surface of the phosphate film at 1 to 50 μm. The rust-preventive paint composition is A glass transition temperature of 0 to 80 ° C. of a thermoplastic resin is 20 to 60% by weight based on the solid content, and a lubricant is 5 to 50% by weight based on the solid content. It contains 40% by weight. As the lubricant, a polymer of ethylene tetrafluoride, molybdenum disulfide, graphite, or a metal salt of a higher fatty acid is used. As the temperature rises, the thermoplastic resin of the rust-preventive coating composition softens to increase the viscoelasticity, thereby suppressing the increase in lubricity and the decrease in the coefficient of friction, and stabilizing the axial force at a constant torque. |