A keyed joint is a joint between shaft and hub using a shaft key and keyway to prevent relative motion between hub and shaft to transfer power. Keyed joints have the following applications in gear drives, pulleys, etc.
- Restrict relative motion between two rotation components.
- Transfer torque from one shaft to another.
What are Shaft Key and Keyway?
A shaft key is a small metallic component mounted between the shaft and hub to restrict the relative motion.
Keyway is a recess in the shaft and hub to accommodate the shaft key. Keys are inserted inside the shaft and hub keyway to ensure the working of the complete system.
Set screws and pins can also work as an alternative to the keyed joint for low torque transmission applications.
Applicable Standard
- BS 4235-1:1972
- ASME B17.2-1967
- DIN 6888, DIN 268:1974, DIN 271:1974
Manufacturing Process
We can machine keyways on shaft & hub using Key Seating Machine and other machining operations such as broaching, milling, EDM, shaping, and slotting machines.
Advantages and Limitations of Key and Keyway?
Here is the list of advantages and limitations of keyed joints.
Advantages
- Low manufacturing cost
- Ease of assembly
- Medium to high torque transmission applications.
- Availability of standard size keys.
Limitations
- Works best only with a one-directional load
- Can transfer only rotational loads
- Shaft and hub torsional strength reduces with keyways.
Types of Shaft keys
- Sunk Keys
- Rectangular and Square keys
- Parallel sunk keys
- Gib head sunk key
- Feather keys
- Woodruff keys
- Saddle Keys
- Flat saddle key
- Hollow saddle key
- Tangent key
- Round key
Shaft Key Selection & Keyway Design Guidelines
The selection of shaft key and keyway design is critical activity during product design. It ensures the design can transfer the defined torque, and will not fail during its lifetime.
Here is the list of points we should consider during the selection of keys and keyway design.
- Type of key and its Material
- Rotating shaft size and material
- Fit type between key, hub, and shaft
- Rotational Speed and Torque
- Working life
1. Type of key and its Material
Different types of keys have different applications and load-bearing capacities. Therefore, it is critical to select the correct type of key and its material for smooth operation and reduce failures.
Medium carbon steel, stainless steel, Aluminum Alloys, bronze, copper, and brass are used to manufacture a shaft key. Here is the list of points you should consider during the selection of key material.
- Required strength and toughness
- Product end Application: For example, engineers recommend stainless steel keys for food-grade equipment.
- Corrosion Resistance and Galvanic Corrosion: Engineers recommend brass keys for highly corrosive environments.
- Ease of manufacturing
2. Fit type between key, hub, and shaft
Clearance, slide, and interference fits are used between key and keyways to ensure smooth operation. Engineers recommend BS 46, ANSI B17.1-1967, and JIS B 1301-1996 standards to finalize keys and keyways size and tolerances.
3. Rotational Speed, Torque, and payload
A continuous force acts on the shaft, key, and hub. Your design should ensure the part should not fail during these forces.
Forces on Shaft Keys
Following two types of forces act on the shaft key during assembly and operation.
- Shear force due to the rotation of the shaft.
- Compressive forces due to interference fit between keyway and key.
Key size and material selection should ensure the key does not fail during the above forces.
Shaft failure due to the keyway
A cutout in the shaft reduces its torsional strength. Therefore, you should consider the stress concentration factor during shaft selection.
Fatigue Failure
Engineers always recommend considering and calculating life due to fatigue failure.
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