What Is a Ball Joint Linkage?
Ball joint linkages are spherical bearings that include a stud.
These components are also known as ball joints, rod ends, rod-end bearings, spherical rod ends, and spherical plain bearings.
Uses of Ball Joint Linkages
Ball joint linkages, serving as spherical sliding bearings, feature a minimal clearance at the ball portion for smooth motion. They facilitate link motion mechanisms to connect and transmit motion between components that exhibit rotational or oscillating movements.
Applications include machine tools, textile machinery, packaging machinery, robots, and other scenarios requiring large oscillating angles. Additional uses include aircraft, construction and civil engineering machinery such as tractors, agricultural machinery like combine harvesters, and shield machines for tunnel excavation.
Oil-free variants are extensively used in food-related machinery. Automobile suspensions and steering systems are common applications as well.
Principle of Ball Joint Linkages
Ball joint linkages consist of a shank with a ball and a holder that secures the ball, supporting rotational or oscillating motions of the shank with spherical surfaces in contact. This configuration functions as a spherical plain bearing.
The holder end, which can have male or female threading, is attached to the end of a connecting rod or similar component. It serves to fasten or connect two parts, allowing relative displacement through a spherical sliding structure, providing a degree of freedom in rotation or tilt.
The distance and angle of the linkage mechanism can be adjusted by the threaded depth of the ball joint linkage and connecting rod.
Types of Ball Joint Linkages
1. Classification by Shank Orientation
Ball joint linkages feature a threaded shank welded to the ball.
- In-line: Shank and holder are coaxial.
- Angle: Shank and holder are perpendicular.
These self-aligning spherical plain bearings allow for tilting, pivoting, low-torque rotation, and smooth power transmission across a wide range of automation equipment.
2. Classification by Load Direction
The axial direction of the ball joint linkage’s shank experiences push load against the holder and pull load away from it. The suitability of a ball joint linkage for these load directions varies as shown below.
| Type of Ball Joint Linkage | Axial Direction | Radial Direction |
| In-line | × | 〇 |
| Angle | 〇 | × |
〇: Applicable ×: Not applicable
3. Classification by Material and Manufacturing Method
The ball joint linkage utilizes a high-precision steel ball welded to a threaded steel shank. The holder material is often a high-strength aluminum alloy for wear resistance and lightweight properties.
The spherical part of the holder is formed by encasing the ball during die casting and welding the shank and ball together. This design ensures full contact between the ball and holder for spherical transfer and smooth motion with minimal gap.
4. Lubrication
Ball joint linkages are crafted from finely machined, wear-resistant materials to ensure smooth movement. Despite this, metal-to-metal contact inevitably leads to wear, mitigated by lubrication with grease or similar substances for sustained operation and wear resistance. The shank area of the holder is protected with a rubber boot to prevent the ingress of dust and water, making it suitable for outdoor use.