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Suez Canal University Faculty of engineering – Port – Said Production Engineering and mechanical Design Department

Keys and Keyways Prepared By Dr. Eng. Mohammed A. Soliman

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Key joints Shaft-Hub-Connections key joints connecting parts, which have to do rotating motions, by fastening devices. The key joints are made in order to   

connect parts of machines which have to carry out a true rotary movement; to additionally secure the position of machine parts connected by clamping and taper connections, so that they are able to carry out a true rotary movement; to connect machine parts with shafts in such a way that, in addition to a rotating movement, they are also able to do an axial reciprocating movement.

Feather-Key Connection Feather keys are the most common shaft-hub-connections. They help to transmit the torque. Two checks have to be carried out for feather keys: 1. Checking the torque transmission by controlling surface pressures on shaft, hub and feather key. Feather key connections are mostly combined with light interference fits. The decreasing torque on the feather key is therefore taken into account when calculating. 2. Checking the fatigue limit of shafts through notch effect caused by the feather key hub. Calculating the fatigue strength also considers the amount of load changes by which the feather key is worn. L=2M/(D.T2.P) Special advantages of the feather key joints - The true running of the parts is guaranteed; - The stability of the joint is guaranteed even with the transmission of higher rotary power. Disadvantage -

The joint does not stand frequently changing discontinuous stress. 1 key, 2 shaft, 3 hub

Mostly, feather keys are made from drawn flat steel and have a tensile strength between 600 and 800 MPa. They may also be made by hand from sectional steel, if they are not available in the required dimensions. -2-

Flat keys These are elongated, rectangular bodies, straight or round-ended. For special functions within the joint they may be provided with bore holes to receive fillister-head screws. In addition, there may be a tapped hole in the centre of the key that enables that the key can be pressed out of the keyway with the help of a screw. 1. 2. 3. 4.

straight-ended round-ended with bore hole for locking screw with bore holes for locking screws and tapped hole for forcing screw

Manufacture Shank cutters are used for making round-ended keyways in shafts for fitting key and sliding key joints. Side milling cutters are used for the production of long, ending keyways in shafts for flat keys as well as circular keyways in shafts for Woodruff keys.

Manufacturing of shaft keyways by 1 shank cutter, 2 side milling cutter

Woodruff Key

These are bodies that have the shape of a segment of a circle. They can transmit only low rotary powers, because the shaft keyway, which must be very deep, limits the strength of the shaft. They mainly secure the position of drive parts. -3-

Spline shafts These are shafts in the periphery of which an even number of splineways are cut at regular intervals. The splineways are rectangular and may be of different depth corresponding to the stress they have to stand. These shafts are preferably used for highly stressed couplings and speed-changing mechanisms of changing rotational direction. The internal profile of the hub is made on shaping or broaching machines. Splines are spur gear toothings with shortened tooth height and a large application angle (normally 30°).

Serrated shafts These are shafts in the periphery of which trapeziform internal teeth (serration) are cut at regular intervals; the internal teeth have straight or rounded flanks. The shafts are used with high and discontinuous rotary powers, but they are not suitable, if parts on them shall be shifted under load. Often, the hub is slotted and clamped on the shaft by a screw.

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Taper shaft end Angle of taper: The angle of taper is defined as the angle between the flank of the cone and its axis. The opening angle of the cone is two times the angle of taper. Calculating taper interference fits:   

All known investigations focus on outer and inner parts consisting of materials with the same Emodule and inner parts without holes in the cone. Taper interference fits must have a stop at the upper end. Taper interference fits are normally joined axially with a screw, only in special cases by pressing them on. Proper joint is to be checked by measuring the displacement of the cone. Measuring the torque only is not as accurate due to variation of the coefficient of friction in the cone and thread.

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Shaft A shaft is a rotating or stationary component which is normally circular in section. A shaft is normally designed to transfer torque from a driving device to a driven device. If the shaft is rotating, it is transferring power and if the shaft operating without rotary motion it is simply transmitting torque and is probably resisting the transfer of power. Mechanical components directly mounted on shafts include gears, couplings, pulleys, cams, sprockets,links and flywheels. A shaft is normally supported on bearings. The torque is normally transmitted to the mounted components using pins, keys, clamping bushes, press fits, bonded joints and sometimes welded connections are used. Shafts are subject to combined loading including torque (shear loading), bending (tensile & compressive loading), direct shear loading, tensile loading and compressive loading. Design of shafts must include assessment of fatigue loading and unstable loading when the shaft is rotating at critical speeds (whirling). When designing a shaft the following staged procedure is normally adopted 1. Produce a free-body sketch of the shaft. Replacing the various associated components with their equivalent load/torque components 2. Produce a bending moment diagram for the xy plane and the xz plane (x = shaft axis direction). Note: The resulting internal moment at any point along the shaft = Mx = Sqrt (Mxy2 + Mxz2 ) 3. Produce a torque diagram. 4. Locate the section(s) on the shaft which the internal loading is the highest..This important stage requires significant effort and judgement 5. Locate the point on the shaft which the internal loading is the highest. This important stage requires significant effort and judgement 6. Assess the strength of the shaft and determine if the safety margin is sufficient. The failure criteria (ref Failure theories for the shaft depends on the material selection (ductile/brittle) and consideration of the loading regime, (constant/ variable loading, rotating speed, degree of shock loading )

Shaft Loads • Torsion due to transmitted torque • Bending from transverse loads (gears, sprockets, pulleys/sheaves)_ a pulley and a sheave are essentially the same thing Steady or Fluctuating Steady transverse-bending load _ fully reversing bending stress (fatigue failure)

Attachments and Stress Concentrations Steps and shoulders are used to locate attachment (gears, sheaves, sprockets) Keys, snap rings, cross pins (shear pins), tapered pins Use generous radii to reduce stress concentrations Clamp collars Split collar Press fits and shrink fits Bearings may be located by the use of snap rings, but only one bearing is fixed Issues - axial location, disassembly, and element phasing (e.g., alignment of gear teeth for timing)

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Shaft Materials • Steel (low to medium-carbon steel) • Cast iron • Bronze or stainless steel • Case hardened steel

Shaft Power Power is the time rate of change of energy (work).

Shaft Loading, Approaches to Analysis Most general form - A fluctuating torque and a fluctuating moment, in combination. If there are axial loads, they should be “taken to ground” as close to the load as possible.

General Considerations 1. To minimize both deflections and stresses, the shaft length should be kept as short as possible and overhangs minimized. 2. A cantilever beam will have a larger deflection than a simply supported (straddle mounted) one for the same length, load, and cross section, so straddle mounting should be used unless a cantilever shaft is dictated by design constraints. (Figure 9-2 shows a situation in which an overhung section is required for serviceability.) 3. A hollow shaft has a better stiffness/mass ratio (specific stiffness) and higher natural frequencies than a comparably stiff or strong solid shaft, but will be more expensive and larger in diameter. 4. Try to locate stress-raisers away from regions of large bending moment if possible and minimize their effects with generous radii and relief. 5. General low carbon steel is just as good as higher strength steels (since deflection is typical the design limiting issue). 6. Deflections at gears carried on the shaft should not exceed about 0.005 inches and the relative slope between the gears axes should be less than about 0.03 degrees. -7-