TORQUE AND TENSION IN FASTENERS Machinery's Handbook, 31st Edition
1662
where F f , P , μ , d 2 , α ′ , μ w , and D w are as previously defined. Table 3 and Table 4 give values of torque coefficient K for coarse- and fine-pitch metric screw threads corresponding to various values of μ s and μ w . When a fastener material yields according to the shearing-strain energy theory, the torque corresponding to the yield clamping force (see Fig. 4) is T fy = K × F fy × d , where the yield clamping force F fy is given by: (17) y s =
sec ′ π µ α σ P d A s 2 + a
F
fy
2
1 3 2 + ;
k
E
d
A
Table 3. Torque Coefficients K for Metric Hexagon Head Bolt and Nut Coarse Screw Threads Coefficient of Friction
Between Threads, μ s
Between Bearing Surfaces, μ w
0.08 0.117 0.127 0.138 0.153 0.180 0.206 0.232 0.258 0.285 0.311
0.10 0.130 0.140 0.151 0.167 0.193 0.219 0.245 0.271 0.298 0.324
0.12 0.143 0.153 0.164 0.180 0.206 0.232 0.258 0.284 0.311 0.337
0.15 0.163 0.173 0.184 0.199 0.226 0.252 0.278 0.304 0.330 0.357
0.20 0.195 0.206 0.216 0.232 0.258 0.284 0.311 0.337 0.363 0.389
0.25 0.228 0.239 0.249 0.265 0.291 0.317 0.343 0.370 0.396 0.422
0.30 0.261 0.271 0.282 0.297 0.324 0.350 0.376 0.402 0.428 0.455
0.35 0.293 0.304 0.314 0.330 0.356 0.383 0.409 0.435 0.461 0.487
0.40 0.326 0.337 0.347 0.363 0.389 0.415 0.442 0.468 0.494 0.520
0.45 0.359 0.369 0.380 0.396 0.422 0.448 0.474 0.500 0.527
0.08 0.10 0.12 0.15 0.20 0.25 0.30 0.35 0.40 0.45
0.553 Values in the table are average values of torque coefficient calculated using: Equations (13) and (14) for K and D w ; diameters d of 4, 5, 6, 8, 10, 12, 16, 20, 24, 30, and 36 mm; and selected corre sponding pitches P and pitch diameters d 2 according to JIS B 0205 (ISO 724) thread standard. Dimension D i was obtained for a Class 2 fit without chamfer from JIS B 1001, Diameters of Clear ance Holes and Counterbores for Bolts and Screws (equivalent to ISO 273-1979). The value of D o was obtained by multiplying the reference dimension from JIS B 1002, width across the flats of the hexagon head, by 0.95.
Ultimate Clamping Force Yield Clamping Force
Yield
Fracture
Elastic Region Plastic Region
O
Bolt Elongation
Fig. 4. Relationship between Bolt Elongation and Axial Tightening Tension
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online