Tech@Edu

Coupling "A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power." The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both.  Shafts are usually available up to 7 metres length due to inconvenience in transport. In order to  have a greater length, it becomes necessary to join two or more pieces of the shaft by means of a  coupling. Purpose of Coupling Shaft couplings are used in machinery for several purposes. 1. To provide for the connection of  shafts of units that are manufactured  separately such as a motor and generator  and to provide for disconnection for repairs or alternations. 2. To provide for misalignment of the  shafts or to introduce mechanical  flexibility. 3. To reduce the transmission of shock  loads from one shaft to another. 4. To introduce protection against  overloads. 5. It should have no projecting parts. Requ

Shaft Key "A key is a piece of mild steel inserted between the shaft and hub or boss of the pulley to connect these together in order to prevent relative motion between them." It is always inserted parallel to the axis of the shaft. Keys are used as temporary fastenings and are subjected to considerable crushing and shearing stresses. A key way is a slot or recess in a shaft and hub of the pulley to accommodate a key. Types of Key 1. Sunk keys (a) Rectangular Key (b) Square Key (c) Parallel Sunk Key (d) Gib Head Key (e) Feather Key (f) Woodruff Key 2. Saddle keys 3. Tangent keys 4. Round keys 5. Splines 6. Kennedy Key 1. Sunk Key The sunk keys are provided half in the key way of the shaft and half in the key way of the hub or boss of the pulley. The sunk keys are of the following types- (a) Rectangular Key The usual proportions of this key are :  Width of key  w = d / 4 T Thickness of key t = 2w / 3 = d / 6  where d = Diameter of the shaft or diameter of the hole in the h

Design of Spur Gear Spur gears  or  straight-cut gears  are the simplest type of gear. They consist of a cylinder or disk with teeth projecting radially. Though the teeth are not straight-sided (but usually of special form to achieve a constant drive ratio, mainly  involute  but less commonly  cycloidal ), the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears mesh together correctly only if fitted to parallel shafts.   No axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but tend to be noisy at high speeds. Design Procedure for Spur Gears  In order to design spur gears, the following procedure may be followed :  1. First of all, the design tangential tooth load is obtained from the power transmitted and the pitch line velocity by using the following relation :  W T = (P/v) * C s  where W T = Permissible tangential tooth load in newtons P = Power transmitted in watts,  v = Pitch