Couplings are mechanical elements that ‘couples’ two drive elements which enables motion to be transferred from one element to another. The drive elements are normally shafts. We tend to see lot of applications of the couplings mainly in the automobiles, for example the drive shaft which connects the engine and the rear axle in a bus or any automobile is connected by means of a universal joint. In order to transmit torque between two shafts that either tend to lie in the same line or slightly misaligned, a coupling is used. Based on the area of applications there are various types of coupling available. But they are generally categorised in the following varieties 1. Rigid Couplings
2. Flexible or Compensating Couplings
3. Clutches to are a type of Coupling – We will the dealing on them separately. RIGID COUPLINGS
Rigid Couplings are mainly used in areas where the two shafts are coaxial to each other. There are many types of couplings that fall under the rigid couplings category. They are · Rigid Sleeve or Muff Couplings- This is the basic type of coupling. This consists of a pipe whose bore is finished to the required tolerance based on the shaft size. Based on the usage of the coupling a keyway in made in the bore in order to transmit the torque by means of the key. Two threaded holes are provided in order to lock the coupling in position. The photo shows a type of the rigid sleeve or muff coupling.
· Flanged Coupling – The coupling basically consists of two flanged end pieces as shown in the figure. A spigot and recess is provided in the flanges to provide location between them. The flanges are connected firmly by means of fitted bolts which are tightened accordingly to the torque to be transmitted.
FLEXIBLE OR COMPENSATING COUPLINGS
Flexible couplings are normally used in areas where the coaxiallity between the connecting shafts is not always assured and in areas where there is a possibility of occurrence of shocks in the transmission is applicable. They are also called as Elastic Couplings. By construction these couplings tend to have a elastic member in between the two connecting entities. The different types of flexible couplings are 1. Flanged Pin Bush Couplings
2. Bibbly Coupling
3. Gear Tooth Coupling
4. Tyre couplings
5. Elastomeric Couplings – This consists of jaw type and S-flex couplings. 6. Oldhams Coupling
7. Universal Coupling or Hooke’s Coupling
8. Bellows Coupling
Each of the above couplings are quite unique in their construction and we can deal in detail on their constructional and working aspects in separate articles. BIBBLY COUPLING:
This article deals with Bibby Resilient type couplings. The article describes constructional aspects of the coupling and the selection procedures for the coupling. * Named after its Inventor Dr. James Bibby in 1917, this coupling is still one of the most sought after flexible couplings for heavy shock applications. Let us now look at the constructional features of the coupling.
1. The Coupling consists of two flanges or hubs specifically mounted on the drive and the driven shafts respectively. These hubs contain axial grooves cut on their circumference. 2. The two couplings are joined or held together by means of a specially designed grid spring. 3. The total assembly is enclosed in a casing or shell filled with grease for low speed applications or, in high speed application with high viscosity oil. Now let’s look at the working aspect of the coupling and how it tends to reduce vibration and prevents the build up of resonance in the system.
a.) The specially designed spring is wound up through the grooves forming a series of resilient bridges throughout the periphery of the coupling. b.) The grooves are tapered up at the edges (see photo) in order to provide extra flexible spans to the spring at normal loads and tends to support the spring at the sides whenever overloading occurs. c.) The stiffness of the spring depends on...
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