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The shaft key material must be chosen based on the operating environment. A designer must very carefully consider the loads that will be applied to the material and what kind of environment will be in the service. Carbon steel is used more broadly than any other material. Carbon steel provides very good strength through heat treatment.
Saddle: Basically, there are two types of saddle keys: the flat saddle key and the hollow saddle key. The flat saddle key is a taper key that fits into a keyway in the hub and is flat on the shaft. It is most times utilised for light loads. The hollow saddle key is a taper key that fits in a keyway in the hub. The bottom of the key is shaped to fit the curved surface of the shaft.
The keyway is similar to a parallel key except that it exits the tangent from the outer shaft to the inner shaft. What happens on the side of the heels of each key-way form against which the key sits, and transfers compressive force. Bhandari, V. B. (2007), Design of machine elements (2nded.), Tata McGraw-Hill, p.340, ISBN 978-0-07-061141-2.
A keyed connection allows for more tolerance between the shaft and hub, whereas in a keyless connection, the parts should be cleaned and machined to allow tolerances. a b c d Keys and Keyways (PDF), archived from the original (PDF) on 2011-06-14 , retrieved 2010-03-19. Gib keys, or gib head keys, are tapered and notched machine keys that are used on power transmission keyed shafts to hold pulleys and gears tightly on the shaft. The head of the key serves as a concussion point for hammering without damage to the shaft of the key. These types of keys are generally attached to the driving member (e.g. shafts). These types of keys have less strength as compared with the sunk keys. These are rarely used keys, to transmit lower power to the driven members (e.g. couplings)
Improperly machined keyways that had cutter deflection or drifting occur, may not be strong enough for the required application. [12] See also [ edit ] Shaft Keys are made of varied types of materials and also come in different shapes and sizes. The most common key shapes are rectangular or tapered and are typically made of steel. Compared to sunk keys, saddle keys are not sunk into the shaft and hub instead they are only sunk into the hub. They either sit on a flat or the circumference of the shaft. Power transmission is achieved through friction between the shaft and the key. The saddle keys are of the following two types:
Like splined shafts, keyed shafts are available in a variety of materials, lengths, and diameters, and their keys are available in different styles, such as round, saddle, sunk, and tangent. An installed wing key cannot run axially. This lets workers subsequently adjust the position of the mounted components along the shaft. Spoiled shafts are used when the force to be transmitted is proportional to the size of the shaft as in automobile transmission and sliding gear transmission. By using split shafts, we obtain axial movement as well as a positive drive. Material Selection for Shaft key The depth of the slot in both the shaft and the component controls the axial position, but cannot be predetermined. The deeper either slot, the forward key enters axially. Containing teeth or ridges that allow them to mate with other components, splined shafts are primarily used to transfer torque throughout mechanical drive systems while allowing for linear motion, such as those found in vehicles. Normally, they are composed of different metals depending on the localized stresses they are expected to undergo. Their teeth or ridges equally distribute circumferential force to a mated component, facilitating a uniform transfer of torque between the mated pair. This also helps to prolong the lifecycle of the parts.
Tangent keys are used in heavy-duty equipment. These keys are actually a pair. These pair of keys are placed right angles to each other and tangent to the surface of the shaft, each key will withstand the torsion in one direction only. A shear key is a feature intended to fail and avoid further damage should the machinery be accidentally operated in excess of its design limits. Shear keys may be any of the designs described above, but are made from a weaker material than the shaft. The shear key is easily and inexpensively replaced, and avoids more serious damage to the mechanism that would be costly or difficult to repair. For example, a steel shaft and pulley may employ a brass key. When excessive torque is applied to the joint, the steel edges shear the brass key into two pieces, leaving the pulley spinning loosely on the shaft and relieving the rest of the machine from possible damage. A flat saddle key is a taper key that fits into the keyway in the hub and lies flat on the shaft. It is likely to round the shaft under load. Therefore, it is used for comparatively light loads. Feather keys are fully contained. It does not set-up to hold the key in position and the wing keys cannot move out of the assembly.
A Shaft key is a piece of metal used to connect a rotating machine element to the shaft. A shaft key prevents a relative rotation between the two parts, and may enable torque transmission to occur. For a shaft key to function properly, both the shaft and rotating elements ( gear, pulley, and coupling) must have a keyway and a keyseat. Installation is much easier when using a keyless connection, as the shaft position does not affect the motor, as the motor can slide in any position. While using a keyed connection, the keyways should be aligned to mount the reducer on the shaft. Feather keys may not fall out of the shaft and may damage nearby machinery. (Loose key in the working machinery is a major cause of damage and injury.) One part of the Shaft key fits into a precut slot in the shaft known as a key seat and the other part fits into a slot in the hub called a keyway. The whole system is called a keyed joint. A keyed joint may allow relative axial movement between the parts.
When the connection rotates, the shaft and hub (mating part) exert opposing forces on the key, attempting to shear the key. The maximum torque that can be transmitted before exceeding the yield strength of the key is calculated as:
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