Parallel shaft keys, commonly known as flat keys, are mechanical components used to connect axes and rotating components,such as gears, pulley or wheels, to ensure they rotate together by transferring torque. Their working principles, types, characteristics and applications are described in detail below:
Principles of work
Flat keys rely on the side of the key (side) to transmit torque. The key is inserted into a keyway on the shaft and rotary component, leaving a clearance gap on the top surface.
During operation, lateral (extrusion) stresses between the keyside and the keygroove wall transfer torque from the shaft to the rotating member (and vice versa). This design focuses the force on larger contact areas on both sides to prevent damage caused by single-point stress.
Types of flat spoons
General unit key:
Features: Simple structure, convenient disassembly, good centering accuracy. However, they cannot withstand axial forces and require additional structures for axial positioning.
Uses: Widely used for high accuracy, high speed or impact/variable load, such as gear or pulley connection to shaft.
Thin Flat Bond:
Features: Thinner than normal flat bond, suitable for thin wall structure or applications with low torque transmission requirements.
Purpose: Light or compact mechanical systems with limited space.
Guide Key (Slide Keys):
Features: Bolted to the shaft, allowing rotating components to move along the key-groove axis. They have a key to remove screw hole for easy removal.
Purpose: Used for rotating components requiring limited axial movement, such as sliding gears in transmission.
Key Characteristics
The structure is simple: only the key grooves on the axle and rotating components need not be complicated.
Good central accuracy: the matching of keys and grooves ensures concentric degrees between the axis and rotating components.
Easy to disassemble: No special tools are needed to install and disassemble Standardized keys.
Limited axial Load Capacity: cannot withstand axial forces alone; additional structures (e.g., shoulder rings, support rings) are required for axial positioning.
Failure Modes
Side crush:
Exposure to excessive extrusion stress over a long period of time can lead to plastic deformation of the lateral surface (extrusion), especially in static connections.
Shear Failure:
When torque exceeds the key's shear strength, the key may break along the shear surface (parallel to the shaft axis), especially when the power connection or material strength is insufficient.
Design Considerations
Cross-Sectional Dimensions (b x h): shaft diameter (d) determined according to (e.g., GB/T 1095). The standard specifies the relationship between key width (b), height (h) and shaft diameter to ensure a match of strength and avoid oversized structures.
Material Selection: Medium carbon steel (e.g. 45# steel) is generally used for heat treatment to improve hardness and abrasion resistance. For corrosive environments, stainless steel or alloy steel may be used.
Application
Flat bonds are widely used in mechanical systems that require reliable torque transmission, such as:
- Motor industry: Attach gears or pulleys to shafts in transmission or engine components.
- Machine tool: Fixed rotating components (such as spindle, tool holders) in lathe, milling machines machine or grinder.
- Gear reducer and motor: Connect the shaft to the gear or pulley in speed reducers or motor.
- General Machinery: Axle needs to drive any application of rotating components with high accuracy and reliability.
