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Ken YoussefiMechanical Engineering Dept. 1 Methods of Attaching Components to a Shaft Keys: squared, tapered, …. Set screws: with or without heads Pins:

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Presentation on theme: "Ken YoussefiMechanical Engineering Dept. 1 Methods of Attaching Components to a Shaft Keys: squared, tapered, …. Set screws: with or without heads Pins:"— Presentation transcript:

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2 Ken YoussefiMechanical Engineering Dept. 1 Methods of Attaching Components to a Shaft Keys: squared, tapered, …. Set screws: with or without heads Pins: straight, tapered, split, … Snap rings Splines Press or Shrink fits

3 Ken YoussefiMechanical Engineering Dept. 2 Keys Hub Shaft

4 Ken YoussefiMechanical Engineering Dept. 3 Keys ANSI standard w = d/2, L = 2d Lw

5 Ken YoussefiMechanical Engineering Dept. 4 Pins ANSI standard d = D / 10 Pins and Keys could be used as a mechanical fuse, they shear off to protect the drive train. Pins and keys weaken the shaft and create stress concentration. Torque capacity τ xy = Force / shear area = (Torque)(radius) / 2(πd 2 /4) = S sy (shear strength) T = πd 2 D S sy / 4

6 Ken YoussefiMechanical Engineering Dept. 5 Set Screws ANSI standard d = D/8 + 5/16 D = shaft diameter d = set screw diameter F = 2500 ( d ) 2.31 Maximum safe holding force Use safety factor of 2.5

7 Ken YoussefiMechanical Engineering Dept. 6 Retaining (Snap) Rings Snap rings are used to prevent the axial motion of mating concentric components such as gear hubs and shafts. Material; SAE 1060-1090 spring steel, beryllium copper alloy 25, stainless steel, or aluminum. Refer to catalog for size and groove dimensions.

8 Ken YoussefiMechanical Engineering Dept. 7 Splines Splines may be considered as using multiple keys, integral with the shaft. Best way to transmit large torque. See ANSI or SAE standards for dimensions τ xy = Force / (shear area /4), SAE assumption that only 25% of teeth are actually sharing the load at any one time. τ xy = 4F / A = (4T) / (r p A) = (8T) / (d p A) = (16T ) / (πd p 2 l) = S sy T = S sy (πd p 2 l) / 16 l = spline length r p = pitch radius, S sy = yield strength in shear

9 Ken YoussefiMechanical Engineering Dept. 8 Press or Shrink Fits Interference Fit – shaft diameter is slightly larger than hub diameter. Inexpensive and semi-permanent connection. Allowance always equals smallest hole minus largest shaft.

10 Ken YoussefiMechanical Engineering Dept. 9 Press or Shrink Fits

11 Ken YoussefiMechanical Engineering Dept. 10 Press or Shrink Fits When two cylindrical parts are assembled by shrinking or press-fitting one part on another, contact pressure is created between the two parts. Thick-walled cylindrical pressure vessel equations are used to derive the equation relating the contact pressure to the interference. δ = p R / E [(2R 2 (r o 2 – r i 2 ) / (r o 2 – R 2 )(R 2 –r i 2 )] δ = radial interference, p = contact pressure

12 Ken YoussefiMechanical Engineering Dept. 11 Press or Shrink Fits Example Class FN3 is used to press fit a hub onto a shaft. Determine the torque that can be transmitted. The shaft diameter is 2.0 in. and hub diameter is 3.0 in. and has a length l = 2 in. δ max = radial interference =.0032/2 =.0016, tightest fit δ min = radial interference =.0013/2 =.00065, loosest fit p = contact pressure, R = contact radius = 1.0 in., r o = hub radius = 1.5, r i = shaft inside radius = 0, and δ = radial interference 2.0 3.0 R roro 2.0 Hole = 2.0000 +.0012 +.0000 Shaft = 2.0000 +.0032 +.0025 FN3 fit Min diametral interference =.0025 -.0012 =.0013 Max diametral interference =.0032 -.0000 =.0032 hub shaft

13 Ken YoussefiMechanical Engineering Dept. 12 Press or Shrink Fits Torque capacity Torque = (μ F) R, F = p (2πRl) Torque = (μ p 2πRl) R = (.15)(5417)(2π)(1)(2)(1) = 10,210 lb-in hp = T ω / 63000 = (10210)(1800)/63000 = 290 μ = coefficient of friction, steel on steel (dry) .15 μF = friction force between the outside surface of the shaft and the inside surface of the hub F = (contact pressure)(contact area) p max = 13,333 psi and p min = 5417 psi δ = p R / E [(2R 2 (r o 2 – r i 2 ) / (r o 2 – R 2 )(R 2 –r i 2 )]

14 Ken YoussefiMechanical Engineering Dept. 13 Various Methods of Attaching Components to a Shaft


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