• Author / Uploaded
• Engr Ghulam Mustafa

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• Engranaje
• Cinturón (mecánico)
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DESIGN WORK 1. A cold-finished shaft, AISI 1141, is to transmit power that varies from 200 to 100 and back to 200 hp in each revolution at a speed of 600 rpm. The power is received by a 20in. spur gear A and delivered by a 10-in. spur gear C. The tangential forces have each been converted into a force ( A and C shown) and a couple (not shown). The radial component R of the tooth load is to be ignored in the initial design. Let 2 and, considering varying stresses with the maximum shear theory, compute the shaft diameter.

2. A shaft S, of cold-drawn AISI 1137, is to transmit power received from shaft W, which turns at 2000 rpm, through the 5-in. gear E and 15-in. gear A. The power is delivered by the 10-in. gear C to gear G, and it varies from 10 hp to 100 hp and back to 10 hp during each revolution of S. The design is to account for the varying stresses. Let N =1.8 and compute the shaft diameter, using only the tangential driving loads for the first design.

3. A shaft made of AISI 1137, cold rolled, for a forage harvester is shown. Power is supplied to the shaft by a vertical flat belt on the pulley A. At B, the roller chain to the cutter exerts a force vertically upwards, and the V-belt tothe blower at C exerts a force vertically upwards. At maximum operating conditions, the flat belt supplies 35 hp at 425 rpm, of which 25 hp is delivered to the cutter and 10 hp to the blower. The two sections of the shaft are joined by a flexible coupling at D and the various wheels are keyed (sledrunner keyway) to the shafts. Choose a design factor that would include an allowance for rough loading.

4. A small, high-speed turbine has a single disk, weighing 0.85 lb., mounted at the midpoint of a 0.178-in. shaft, whose length between bearings is 6 ½ in. What is the critical speed if the shaft is considered as simply supported?

5. The bearings on a 1 ½-in. shaft are 30 in. apart. On the shaft are three 300-lb disks, symmetrically placed 7.5 in. apart. What is the critical speed of the shaft?

6. A fan for an air-conditioning unit has two 50-lb. rotors mounted on a 3in. steel shaft, each being 22 in. from an end of the shaft which is 80 in. long and simply supported at the ends. Determine (a) the deflection curve of the shaft considering its weight as well as the weight of the rotors, (b) its critical speed.

7.

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9. The slow-speed shaft of a speed reducer shown, made of AISI 4140, OQT 1200F, transmits 100 hp at a speed of 388 rpm. It receives power through a 13.6 in. gear B. The force on this gear has three components: a horizontal tangential driving force F lb t 2390 , a vertical radial force S 870 lb , and a thrust force Q 598 lb taken by the right-hand bearing. The power is delivered to a belt at F that exerts a downward vertical force of 1620 lb.; sled runner keyways.Compute N at sections C and D. (Data courtesy of Twin Disc Clutch Company.)

10. A shaft receives 300 hp while rotating at 600 rpm, through a pair of bevel gears, and it delivers this power via a flexible coupling at the other end. The shaft is designed with the average forces ( at the midpoint of the bevel-gear face); the tangential driving force is F , G = 580 lb , Q = 926 lb ; which are the rectangular components of the total reaction between the teeth; Dm = 24 in , L = 36 in , a =10 in . Let the material be AISI C1045, cold drawn; N = 2 . Considering varying stresses and using the octahedral shear theory, determine the shaft diameter.

BASIC PROBLEM

A round shaft rotates at 300 rpm and is subjected to a torque of 325 N-m and a bending moment of 340 N-m. The allowable shearing stress is 50MN/m 2; the allowable tensile stress is 53.3 MN/m2. Find the diameter. Given: n = 300rpm T = 325 N-m M = 340 N-m Qmax = 40 x 106 N/m2 Soluton: Te =

√ T2+ M 2

325 ¿ Te = (¿ 2 ¿ +3402) ¿ √¿ Te = 470.3456176 For a good design Qmax =

16 Te 3 πD

D3 = 5.9886264 x 10-5 m D = 0.039124 m

SAMPLE PROBLEMS 1. A rotating shaft is made of 42- × 4-mm AISI 1018 cold-drawn steel tubing and has a 6-mm-diameter hole drilled transversely through it. Estimate the factor of following loading condition: The shaft is subjected to a completely reversed torque of 120 N · m in phase with a completely reversed bending moment of 150 N · m. Solution:

2.

A rotating shaft is made of 42- × 4-mm AISI 1018 cold-drawn steel tubing and has a 6-mm-diameter hole drilled transversely through it. Estimate the factor of safety for the following loading condition: The shaft is subjected to a pulsating torque fluctuating from 20 to 160 N · m and a steady bending moment of 150 N · m. Solution: