Axial Expansion
This is a lengthening of a shaft. It could be caused by thermal changes in environment or induced through the use of a sliding coupling.

Backlash
A jarring reaction when starting or reversing a load, caused by play in a coupling.

Clearance Fit
Also called a slip fit. This is the most popular fit because of its ease of installation. The bore is larger than the shaft. It maintains its position on the shaft through the use of a key and set screw.

Damping
Reducing vibration.

Donut
The elastomeric element in donut type elastomeric couplings.

Elastomeric
A coupling that has resilient materials through which the power is transmitted. They are in some way attached to the coupling halves. They are usually made of rubber, synthetic rubber or plastic materials.

End Float
Also called axial misalignment. It is a condition where shafts could be in angular and parallel alignment. However, the shafts move in and out relative to each other.

Horsepower
The rate at which torque is applied. Since applied torque causes a shaft and its connected components to rotate, a certain RPM results. HP is calculated by the following equation:

HP = Torque (lb. -in.) x RPM

63,025

Inertia
The tendency of matter to remain at rest, or if moving, to keep moving in the same direction. Examples of high inertia loads; fans and fly wheels.

Interference Fit
Also called a shrink or press fit. It gets its name because the bore is actually smaller than the shaft it is to be mated with. It is the strongest fit possible but requires heat or an hydraulic press to install

Parallel Misalignment
A condition where the shaft axis or center lines of two shafts are parallel but offset from each other.

Shear Pin
A protection device used on some couplings. To protect driver and driven equipment against overload. The pin is located between coupling halves and is machined to break or shear at a predetermined load allowing the driver side to free wheel

Spider
The elastomeric element of a flexible jaw type coupling. Usually has 4 or 6 arms.

Shrouded Bolt
The optional bolt arrangement available on rigid and gear couplings. It is used in very high speed applications. Bolts are installed with a socket wrench.

Thermal Expansion
Lengthening of shafting caused by thermal changes in environment.

Torque
The force required to turn a shaft multiplied by the radius at which the force is applied. Torque is calculated by the following equation:

Lb. In. Torque = Force (lb.) x Radius (in.)

Torsional Vibration

There are two main kinds of torsional vibration: a continuous steady form that comes from reciprocating engines and an intermittent for in that comes from large synchronous electric motors or from the driven equipment side in steel rolling mills.

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