Estimate the existing safety factor based on surface fatigue (pitting).

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1.For the gearset specifications of  do the following:

a. Using the AGMA refined approach, calculate the surface fatigue contact stress for the meshing gear teeth.

b. If the proposed material for both gears is AISI 4620 steel, and the teeth are carburized and case hardened (not including the root fillet) to a hardness of approximately RC 60, maintaining the 99 percent reliability requirement, determine the AGMA surface fatigue strength (pitting resistance) for the carburized and case-hardened gear teeth.

c. Estimate the existing safety factor based on surface fatigue (pitting).

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calculate the tooth bending stress at the tension-side root fillet of the driving pinion.

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1. A 10-pitch 20 full-depth involute gearset, with and face width of 1.25 inches, is being proposed to provide a 2:1 speed reduction for a conveyor drive unit. The 18- tooth pinion is to be driven by a 15-hp, 1725-rpm electric motor operating steadily at full-rated power. A very long life is desired for this gearset, and a reliability of 99 percent is required. Do the following:

a. Using the AGMA refined approach, calculate the tooth bending stress at the tension-side root fillet of the driving pinion.

b. Repeat (a) for the tension-side root fillet of the driven gear.

c. If the proposed material for both gears is AISI 4620 through-hardened to BHN 207, estimate the existing safety factor at the tension-side root fillet of whichever gear is more critical, based on tooth bending fatigue.

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Estimate the fatigue stress concentration factor for the tension-side root fillet of the driving pinion.

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1. A 10-pitch 20 full-depth involute gearset with a face width of 1.25 inches is being proposed to provide a 2:1 speed reduction for a conveyor drive unit. The 18-tooth pinion is to be driven by a 15-hp, 1725-rpm electric motor operating steadily at full rated power. A very long life is desired for this gearset, and a reliability of 99 percent is required. Do the following:

a. Using the simplified approach, estimate the nominal bending stress at the tension-side root fillet of the driving pinion.

b. Estimate the fatigue stress concentration factor for the tension-side root fillet of the driving pinion.

c. Calculate the actual bending stress at the tension-side root fillet of the driving pinion.

d. Repeat (c) for the tension-side root fillet of the driven gear.

e. Based on the recommendation of an in-house materials specialist, Grade 1 AISI 4620 hot-rolled steel is to be used for both the pinion and the gear and the value of [see (2-27)] has been estimated for this application to be 0.75, including the 99 percent reliability requirement but not including stress concentration effects. Estimate the existing safety factor at the tensionside root fillet of whichever of the gears is more critical, based on tooth bending fatigue.

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Calculate the percent difference in resultant force if the pressure angle were 25 instead of 20.

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1. A straight-toothed full-depth involute spur pinion with a pitch diameter of 100 mm is mounted on an input shaft driven by an electric motor at 1725 rpm. The motor supplies a steady torque of 225 N-m.

a. If the involute gear teeth have a pressure angle of 20, determine the transmitted force, the radial separating force, and the normal resultant force on the pinion teeth at the pitch point.

b. Calculate the power being supplied by the electric motor.

c. Calculate the percent difference in resultant force if the pressure angle were 25 instead of 20.

d. Calculate the percent difference in resultant force if the pressure angle were 14 instead of 20.

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Estimate the increase in production cost of the appliance if gear shaving were used to achieve .

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1.A straight-tooth one-stage spur gear reducer has been used in a high-production home appliance for many years. The gear pair constitutes about one-half the $50 production cost of the appliance. Consumer complaints about gear noise have grown over the years and sales are declining. One young engineer has found data that suggest the noise level would be significantly reduced if the AGMA quality number could be increased from its current value of for hobbed gears to a value of , achieved by shaving the gears.

a. Estimate the increase in production cost of the appliance if gear shaving were used to achieve .

b. Can you suggest any other approach that might accomplish the noise-reduction goal without resorting to shaving the gears?

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