Presentation on theme: "Methods of Attaching Components to a Shaft"— Presentation transcript:
1 Methods 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.
4 Mechanical 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.
5 Mechanical 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.
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 spring steel, beryllium copper alloy 25, stainless steel, or aluminum.Refer to catalog for size and groove dimensions.Ken YoussefiMechanical Engineering Dept.
7 Mechanical 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.
8 Mechanical 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.
10 Mechanical 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.
11 Mechanical 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.
12 Mechanical 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.
13 Various Methods of Attaching Components to a Shaft Ken YoussefiMechanical Engineering Dept.