Homework SourseDoes the output gear mesh safe against bending and wear Cons
Solution
Face width: F2.00 in
Quality number: Qv8
Tangential force: Wt=514 lb
Required bending stress number for pinion: sat20 900 psi
Required contact stress number for pinion: sac153 000 psi; requires 370 HB steel
Material specified: AISI 4340 OQT 900; 388 HB; su190 Ksi; 15 elongation
The flexible couplings at the ends of the shafts allow torque transmission, but no radial or axial forces are transmitted when the alignment of the shafts is within the recommended limits for the coupling.
Without the flexible couplings, it is very likely that significant radial loads would be produced, requiring somewhat larger diameters for the shaft and larger bearings
the tangential force is Wt= 514lb. It acts downward in the vertical plane on the pinion and upward on the gear. The radial force is
Wr= Wttan f (514 lb)tan(20°) = 187 lb
The radial force acts horizontally toward the left on the pinion, tending to separate the pinion from the gear. It acts toward the right on the gear.
2. Torque values: The torque on the input shaft is
Ti= (63000)(P)/nP= (63000)(25)/1750= 900 lb×in
This value acts from the coupling at the left end of the shaft to the pinion where the power is delivered through the key to the pinion and thus to the mating gear.
The torque on the output shaft is computed next, assuming that no power is lost. The resulting value of torque is conservative for use in the shaft design:
T2 = (63 000)(P)/nP = (63 000)(25)/500 = 3 150 lb×in
The torque acts in the output shaft from the gear to the coupling at the right end of the shaft. Assuming that the system is 95% efficient, the actual output torque is approximately
T0= T2 (0.95) = 2 992 lb×in
This value is within the required range, as indicated in the design requirements. Design is safe.
