In mechanical engineering, a parallel key is a type of key used to connect a rotating machine element (like a gear, pulley, or coupling) to a shaft, ensuring that torque is transmitted without relative rotation between the shaft and the component.
Key Features of Parallel Keys:
Shape: Rectangular in cross-section.
Mounting: Fits into matching keyways (slots) cut into both the shaft and the hub of the component.
Function: Prevents relative rotation by locking the shaft and component together.
Standard Sizes: Defined by standards like ISO, DIN, or ANSI; typical proportions are width (w) × height (h), e.g., 10×8 mm.
Types of Parallel Keys:
Rectangular (or flat) parallel key:
Uniform rectangular cross-section.
Most common type.
Load is distributed over the entire surface.
Square parallel key:
Width and height are equal.
Often used in smaller components.
Gib-head key:
A rectangular key with a head (like a tab) at one end to help with removal.
Applications:
Used in gearboxes, couplings, pulleys, and flywheels.
Found in machines, engines, and rotating equipment.
Advantages:
Simple to manufacture and install.
Good torque transmission capability.
Disadvantages:
Requires precise machining of keyways.
Can introduce stress concentrations, leading to fatigue over time.
