In the field of mechanical transmission, the gearbox serves as a core device for power transmission, speed regulation, and torque conversion. Among its critical components, key connection, though seemingly simple, plays an indispensable role in reliably fixing rotating parts such as gears and couplings onto shafts. The quality of key connection design and verification directly determines the reliability, service life, and safety of the entire gearbox transmission system.

1. Overview of Key Connection

1.1 Definition

1.2 Working Principle

• Compressive Stress: Torque is transmitted from the shaft to the key. The key's two working surfaces contact the shaft keyway and hub (e.g., gear) keyway respectively, with the contact surfaces enduring significant compressive pressure—this is the primary form of key failure.

• Shear Stress: Torque acting on the key attempts to "shear" it along the cross-section, so the key itself also bears shear stress.

1.3 Types and Characteristics of Keys

• Flat Key: The most widely used type. It transmits torque through both side surfaces, offering good centering, simple structure, and easy assembly/disassembly. However, it cannot achieve axial fixation independently and requires additional components (e.g., set screws, shaft shoulders).

• Woodruff Key: Semi-circular in shape, it can swing around its center in the shaft groove to adapt to the slope of the hub groove bottom. Suitable for tapered shaft ends, but its deep keyway weakens the shaft strength significantly.

• Taper Key: Both the upper surface of the key and the hub groove bottom have a 1:100 taper. It is driven in during assembly and transmits torque through friction between the upper and lower surfaces, while also being able to withstand unidirectional axial forces. However, its centering performance is poor.

• Spline: Multiple evenly distributed key teeth are directly machined on the shaft and hub bore, equivalent to a combination of multiple flat keys. It boasts high load-bearing capacity, excellent centering and guidance, and minimal shaft strength weakening, but features high manufacturing costs. Ideal for heavy-load and high-centering-demand applications.

2. Design and Verification of Key Connection

2.1 Dimension Selection

• Nominal dimensions of the key: b×h (width × height)

• Length of the key L: Generally 5~10mm shorter than the hub width, rounded to a standard length series value

• Shaft groove depth t1

• Hub groove depth t2

2.2 Force Analysis and Failure Modes