266 TECHNICAL INFORMATION QAxial Tightening Force for Bolt and Fatigue Limit · The proper axial tightening force for a bolt should be calculated within an elasticity range up to 70% of the rated yield strength when the torque method is used. · The fatigue strength of bolt under repeated load should not exceed the specified tolerance. · Do not let the seat of a bolt or nut dent the contact area. · Do not break the tightened piece by tightening. QCalculation of Axial Tightening Force and Tightening Torque The relation between the axial tightening force and Ff is represented by Equation (1) below: Ff=0.7× y×As……(1) Tightening torque TfA can be obtained by using the following formula (2). TfA=0.35k(1+1/Q) y · As · d……(2) QCalculation Example Proper torque and axial force for Mild steel pieces tightened together by means of a hexagon socket head cap screw, M6 (strength class 12.9), with the pieces lubricated with oil, can be calculated as follows. · Proper Torque, by using Equation(2) TfA=0.35k (1+1/Q) y · As · d =0.35×0.17 (1+1/1.4) 1098×20.1×0.6 =1351[N · cm] {138[kgf · cm]} k : Torque Coefficient d : Nominal Diameter of Bolt[cm] Q : Tightening Coefficient y : Tensile strength (When the strength class is 12.9, it is 112kgf/mm2) As : Effective Sectional Area of the Bolt [mm2] · Axial Force Ff, by using Equation(1) Ff=0.7× y×As =0.7×1098×20.1 =15449[N] {1576[kgf]} A bolt is tightened by torque, torque inclination, rotating angle, stretch measurement and other methods. The torque method is widely used due to its simplicity and convenience. Strength Class Ex. 12.9 Tensile Strength (Yield Stress): 90% of the minimum value of tensile strength The minimum value of tensile strength is 1220N/mm2 { 124kgf/mm2 } 10.9 Tensile Strength (Yield Stress): 90% of the minimum value of tensile strength The minimum value of tensile strength is 1040N/mm2 { 106kgf/mm2 } QSurface Treatment for Bolt and Torque Coefficient Dependent on the Combination of Material for Area to be Fastened and Material of Female Thread Bolt Surface Treatment Lubrication Torque Coefficient k Combination of material for area to be fastened and material for female thread (a) (b) Steel Bolt Black Oxided Film Oil Lubrication 0.145 SCM−FC FC−FC SUS−FC 0.155 S10C−FC SCM−S10C SCM−SCM FC−S10C FC−SCM 0.165 SCM−SUS FC−SUS AL−FC SUS−S10C SUS−SCM SUS−SUS 0.175 S10C−S10C S10C−SCM S10C−SUS AL−S10C AL−SCM 0.185 SCM−AL FC−AL AL−SUS 0.195 S10C−AL SUS−AL 0.215 AL−AL Steel Bolt Black Oxided Film Unlubricated 0.25 S10C−FC SCM−FC FC−FC 0.35 S10C−SCM SCM−SCM FC−S10C FC−SCM AL−FC 0.45 S10C−S10C SCM−S10C AL−S10C AL−SCM 0.55 SCM−AL FC−AL AL−AL S10C: Mild steel not thermally refined SCM:Thermally Refined Steel(35HRC) FC:Cast Iron(FC200)AL:Aluminum SUS:Stainless Steel Nominal of Thread Effective Sectional Area As mm2 Strength Class 12.9 10.9 8.8 Yield Load Initial Tightening Force Tightening Torque Yield Load Initial Tightening Force Tightening Torque Yield Load Initial Tightening Force Tightening Torque N {kgf} N {kgf} N · cm {kgf · cm} N {kgf} N {kgf} N · cm {kgf · cm} N {kgf} N {kgf} N · cm {kgf · cm} M 3×0.5 5.03 5517{ 563} 3861{ 394} 167{ 17} 4724{ 482} 3312{ 338} 147{ 15} 3214{ 328} 2254{ 230} 98{ 10} M 4×0.7 8.78 9633{ 983} 6742{ 688} 392{ 40} 8252{ 842} 5772{ 589} 333{ 34} 5615{ 573} 3930{ 401} 225{ 23} M 5×0.8 14.2 15582{ 1590} 10907{ 1113} 794{ 81} 13348{ 1362} 9339{ 953} 676{ 69} 9085{ 927} 6360{ 649} 461{ 47} M 6×1 20.1 22060{ 2251} 15445{ 1576} 1352{ 138} 18894{ 1928} 13220{ 1349} 1156{ 118} 12867{ 1313} 9006{ 919} 784{ 80} M 8×1.25 36.6 40170{ 4099} 28116{ 2869} 3273{ 334} 34398{ 3510} 24079{ 2457} 2803{ 286} 23422{ 2390} 16395{ 1673} 1911{ 195} M10×1.5 58 63661{ 6496} 44561{ 4547} 6497{ 663} 54508{ 5562} 38161{ 3894} 5557{ 567} 37113{ 3787} 25980{ 2651} 3783{ 386} M12×1.75 84.3 92532{ 9442} 64768{ 6609} 11368{ 1160} 79223{ 8084} 55458{ 5659} 9702{ 990} 53949{ 5505} 37759{ 3853} 6605{ 674} M14×2 115 126224{ 12880} 88357{ 9016} 18032{ 1840} 108084{ 11029} 75656{ 7720} 15484{ 1580} 73598{ 7510} 51519{ 5257} 10486{ 1070} M16×2 157 172323{ 17584} 117982{ 12039} 28126{ 2870} 147549{ 15056} 103282{ 10539} 24108{ 2460} 100470{ 10252} 70325{ 7176} 16366{ 1670} M18×2.5 192 210739{ 21504} 147519{ 15053} 38710{ 3950} 180447{ 18413} 126312{ 12889} 33124{ 3380} 126636{ 12922} 88641{ 9045} 23226{ 2370} M20×2.5 245 268912{ 27440} 188238{ 19208} 54880{ 5600} 230261{ 23496} 161181{ 16447} 46942{ 4790} 161592{ 16489} 113112{ 11542} 32928{ 3360} M22×2.5 303 332573{ 33936} 232799{ 23755} 74676{ 7620} 284768{ 29058} 199332{ 20340} 63896{ 6520} 199842{ 20392} 139885{ 14274} 44884{ 4580} M24×3 353 387453{ 39536} 271215{ 27675} 94864{ 9680} 331759{ 33853} 232231{ 23697} 81242{ 8290} 232819{ 23757} 162974{ 16630} 57036{ 5820} (Note) · Tightening Conditions: Use of a torque wrench (Lubricated with Oil, Torque Coefficient k=0.17, Tightening Coefficient Q=1.4) · The torque coefficient varies with the conditions of use. Values in this table should be used as rough referential values. · The table is an excerpt from a catalog of Kyokuto Seisakusho Co., Ltd. QStandard Value of Tightening Coefficient Q Tightening Coefficient Q Tightening Method Surface Condition Lubrication Bolts Nuts 1.25 Torque Wrench Manganese Phosphate Not treated or Treated with Phosphate. Lubricated with oil or MoS2 paste 1.4 Torque Wrench Not treated or Treated with Phosphate. Limited-Torque Wrench 1.6 Impact Wrench 1.8 Torque Wrench Not treated or Treated with Phosphate. No Treatment Unlubricated Limited-Torque Wrench QInitial Tightening Force and Tightening Torque (a) (b) GeneralTechnical Information Proper Bolt AxialTightening Force and ProperTighteningTorque
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