Upload
laureen-morris
View
226
Download
1
Embed Size (px)
Citation preview
Ken Youssefi Mechanical 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
Ken Youssefi Mechanical Engineering Dept. 2
KeysHub
Shaft
Ken Youssefi Mechanical Engineering Dept. 3
Keys
ANSI standard
w = d/2, L = 2dLw
Ken Youssefi Mechanical 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
τxy = Force / shear area = (Torque)(radius) / 2(πd 2/4) = Ssy (shear strength)
T = πd 2 D Ssy / 4
Ken Youssefi Mechanical 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
Ken Youssefi Mechanical 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.
Ken Youssefi Mechanical Engineering Dept. 7
SplinesSplines may be considered as using multiple keys, integral with the shaft.
Best way to transmit large torque.
See ANSI or SAE standards for dimensions
τxy = Force / (shear area /4), SAE assumption that only 25% of teeth are actually sharing the load at any one time.
τxy = 4F / A = (4T) / (rp A) = (8T) / (dp A) = (16T ) / (πdp2 l) = Ssy
T = Ssy (πdp2 l) / 16
l = spline length
rp = pitch radius , Ssy = yield strength in shear
Ken Youssefi Mechanical 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.
Ken Youssefi Mechanical Engineering Dept. 9
Press or Shrink Fits
Ken Youssefi Mechanical Engineering Dept. 10
Press or Shrink FitsWhen 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 [(2R2 (ro2 – ri
2) / (ro2 – R2)(R2 –ri
2)]
δ = radial interference , p = contact pressure
Ken Youssefi Mechanical Engineering Dept. 11
Press or Shrink FitsExampleClass 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.
δmax = radial interference = .0032/2 = .0016, tightest fit
δmin = radial interference = .0013/2 = .00065, loosest fit
p = contact pressure, R = contact radius = 1.0 in., ro = hub radius = 1.5, ri = shaft inside radius = 0, and δ = radial interference
2.03.0R
ro
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 hubshaft
Ken Youssefi Mechanical 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)
pmax = 13,333 psi and pmin = 5417 psi
δ = p R / E [(2R2 (ro2 – ri
2) / (ro2 – R2)(R2 –ri
2)]
Ken Youssefi Mechanical Engineering Dept. 13
Various Methods of Attaching Components to a Shaft