POWER SCREW Calculation of torque and contact load Tr8 x P1.5 Tr10 x P2 Tr12 x P3 Tr16 x P4 Tr20 x P4 Tr24 x P5 Tr28 x P5 Tr32 x P6 Tr36 x P6 Tr40 x P7 Tr44 x P7 Tr48 x P8 Tr52 x P8 Tr60 x P9 (Tr65 x P10) Tr70 x P10 (Tr75 x P10) Tr80 x P10 (Tr85 x P12) Tr90 x P12 (Tr95 x P12) Tr100 x P12 (Tr110 x P12) Tr120 x P14   n= 1 2 3   F=kN   µ= 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35   St.50 St.60   H'= Calculation of service live h'= 0.1 0.2 0.3 0.4 0.5   Llift=mm   k=10-15 m2/N pitch P mm pitch diameter d2=d-0.5P mm root diameter d3=d-2h3 mm tensile stress area As = π/4 d33 mm2 thread depth H1=0.5P mm tensile stess σm = F/A3 MPa torsion stress τ = T/Wp ;  Wp= π/16 d33 MPa equivalent stress σe = (σm2 + 3τ2)½ MPa ultimate tensile strength Rm MPa 0.2% yielding strength Rp0.2 MPa safety factor Sv = Rp0.2 / σe >1 friction torque forward drive T+ Nm friction torque backdrive T- Nm screw efficiency % contact pressure p thread MPa total sliding distance s=h/(k p) km sliding distance one cycle si=2(π d2 Llift / P) m number of cycles Ln=s/si www.tribology-abc.com