Presentation on theme: "Methods of Attaching Components to a Shaft"— Presentation transcript:
1Methods of Attaching Components to a Shaft Keys: squared, tapered, ….Set screws: with or without headsPins: straight, tapered, split, …Snap ringsSplinesPress or Shrink fitsKen YoussefiMechanical Engineering Dept.
4Mechanical Engineering Dept. PinsPins 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.ANSI standardd = D / 10Torque capacityτxy = Force / shear area = (Torque)(radius) / 2(πd 2/4) = Ssy (shear strength)T = πd 2 D Ssy / 4Ken YoussefiMechanical Engineering Dept.
5Mechanical Engineering Dept. Set ScrewsANSI standardd = D/8 + 5/16D = shaft diameterd = set screw diameterF = 2500 ( d ) 2.31Maximum safe holding forceUse safety factor of 2.5Ken YoussefiMechanical Engineering Dept.
6Retaining (Snap) Rings Snap rings are used to prevent the axial motion of mating concentric components such as gear hubs and shafts.Material; SAE spring steel, beryllium copper alloy 25, stainless steel, or aluminum.Refer to catalog for size and groove dimensions.Ken YoussefiMechanical Engineering Dept.
7Mechanical Engineering Dept. SplinesSplines may be considered as using multiple keys, integral with the shaft. Best way to transmit large torque.See ANSI or SAE standards for dimensionsτxy = 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) = Ssyl = spline lengthrp = pitch radius ,Ssy = yield strength in shearT = Ssy (πdp2 l) / 16Ken YoussefiMechanical Engineering Dept.
8Mechanical Engineering Dept. Press or Shrink FitsInterference Fit – shaft diameter is slightly larger than hub diameter. Inexpensive and semi-permanent connection.Allowance always equals smallest hole minus largest shaft.Ken YoussefiMechanical Engineering Dept.
9Mechanical Engineering Dept. Press or Shrink FitsKen YoussefiMechanical Engineering Dept.
10Mechanical Engineering Dept. 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 – ri2) / (ro2 – R2)(R2 –ri2)]δ = radial interference , p = contact pressureKen YoussefiMechanical Engineering Dept.
11Mechanical Engineering Dept. 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.2.0Hole =Shaft =FN3 fitR3.02.0roshaftMin diametral interference = =.0013Max diametral interference = = .0032hubδmax = radial interference = .0032/2 = .0016, tightest fitδmin = radial interference = .0013/2 = , loosest fitp = contact pressure, R = contact radius = 1.0 in., ro = hub radius = 1.5, ri = shaft inside radius = 0, and δ = radial interferenceKen YoussefiMechanical Engineering Dept.
12Mechanical Engineering Dept. Press or Shrink Fitsδ = p R / E [(2R2 (ro2 – ri2) / (ro2 – R2)(R2 –ri2)]pmax = 13,333 psi and pmin = 5417 psiTorque capacityμ = coefficient of friction, steel on steel (dry) .15μF = friction force between the outside surface of the shaft and the inside surface of the hubF = (contact pressure)(contact area)Torque = (μ F) R, F = p (2πRl)Torque = (μ p 2πRl) R = (.15)(5417)(2π)(1)(2)(1) = 10,210 lb-inhp = T ω / = (10210)(1800)/63000 = 290Ken YoussefiMechanical Engineering Dept.
13Various Methods of Attaching Components to a Shaft Ken YoussefiMechanical Engineering Dept.