Parallel keys (also often called flat keys) and rotary keys (such as rotary splines) differ in many aspects. The following is a detailed comparison of the two:
1. Structural features
Parallel keys
Usually have a rectangular cross-section and are installed between the shaft and the hub.
The side of the key is the working surface, which transmits force by the side and has good centering.
It is impossible to achieve axial fixation of parts on the shaft, but the positioning accuracy is high.
Rotary keys (taking rotary splines as an example)
Mainly composed of internal splines and external splines, with rows of balls placed between them.
The balls roll between the internal and external splines to achieve power transmission.
The structure is relatively complex, but it can achieve multiple modes of movement (rotational, linear), and adapt to the operation requirements of various complex mechanical systems.
2. Working principle
Parallel keys
The rotational force of the shaft is transmitted to the gear or other rotating parts through the cooperation of the key and the keyway.
The force is mainly transmitted by the friction between the side of the key and the keyway.
Rotary key
Relies on the rolling of the ball between the inner and outer splines to transmit power.
The rolling of the ball reduces friction and wear, and improves transmission efficiency and service life.
3. Application scenarios
Parallel key
Applicable to most mechanical transmission occasions, such as motors, reducers, pumps, engines, etc.
Particularly suitable for occasions where large torque needs to be transmitted and positioning accuracy is required.
Rotary key
Widely used in the field of automation equipment, such as horizontal multi-joint robot arms (SCARA), industrial robots, automatic loaders, laser processing machines, etc.
It is most suitable for use on combined devices of rotary motion and linear motion, and can achieve high-precision, high-speed and low-noise transmission.
4. Performance characteristics
Parallel key
Simple structure, easy to process and install.
The transmitted torque is stable, but may be affected by friction and wear.
Rotary key
The structure is complex, but the performance is superior.
The rolling of the ball reduces friction and wear, and improves transmission efficiency and service life.
It has good transmission torque and load-bearing capacity, and can realize the function of easy disassembly and assembly.
