Meriam, Kraige & Bolton — Analysis of Structures: Problem 6_112

⚡ Mecademy AIENG정역학 · ch6  Problem Statement The screw of the small press has a mean diameter of 25 mm and has a single square thread with a lead of 8 mm. The flat thrust bearing at A is shown in the enlarged view and has surfaces which are well worn. If the coefficient of friction for both the threads and the bearing at A is 0.25, calculate the design torque M on the handwheel required (a) to produce a compressive force of 4 kN and (b) to loosen the press from the 4-kN compression. Problem 6/112 (a) Torque required to produce a 4-kN compressive force ● Calculation Process 1. Present Final Formula: The total torque required to tighten the press is the sum of the torque required to overcome screw friction and the torque required to overcome bearing friction at A : For a square-threaded screw, the torque to increase the load is: For a "well worn" thrust bearing, we use the uniform wear model: 2. Substitute Values: Given values: , , , . From the enlarged view of A, the contact radii are and . 3. Partial Operations: Calculate screw torque: M M s M A M=M + s M A M = s 2 Fd ( πd−μL L+πμd ) M = A μ F A ( 2 r +r io ) F=4000 Nd=0.025 mL=0.008 m μ=μ = A 0.25r = o 10 mm=0.010 mr = i 2 mm=0.002 m M = s 2 4000⋅0.025 ( π⋅0.025−0.25⋅0.008 0.008+π⋅0.25⋅0.025 ) M = A 0.25⋅4000⋅ ( 2 0.002+0.010 ) Numerator: Denominator: Calculate bearing torque: 4. Final Calculation: ● Final Conclusion: The design torque required to produce the 4-kN compression is . (b) Torque required to loosen the press fro