What Is A Wire Race Bearing and How Does It Work?

In precision machinery, bearings play a pivotal role in ensuring smooth and efficient operation. Wire race bearings, in particular, offer distinctive advantages in high-precision and silent high-speed performance.

Unlike conventional deep groove ball bearings, in wire race bearings, hardened steel wires are used as raceways instead of solid inner and outer rings. These wires are mounted in a housing that gives them a good deal of strength and flexibility. This allows the bearing to be adapted to unusual or compact assemblies.

As a result, wire race bearings find broad applications in CT medical  system, radar systems and a variety of other rotating systems that are inaccessible to conventional bearings or that require special performance.

This article will take a closer look at the construction and working principles of wire race bearings, their high-point advantages, and also discuss where this kind of bearing is ideal over more traditional bearing designs in machinery and applications.

Understanding Wire Race Bearing Construction

To understand how wire race bearings function in real applications, it is important to first examine their internal structure. Every single component within the bearing directly impacts critical performance areas, such as load capacity, precision, and durability.

Basic Components and Design

● Steel Wire Raceways: The inner races and outer races in a wire race ring design utilize hardened steel wires. The wires provide the races on which the balls move. Circular wire raceway sections are simple and robust, but the sections are best for load distribution.

● Rolling Elements: The rolling balls are separated and held in place by a cage to ensure even movement.

● Bearing Housing: The bearing housing holds the wire raceways. It is designed to be stiff and precisely dimensioned. This ensures that the bearings remain aligned even under load.

Manufacturing Process

● Heat Treatment: Wires of hardened steel are drawn through a die to obtain the required diameter and surface finish.They are then subjected to quenching and tempering treatment to obtain the desired hardness and wear resistance.

● Circular Forming: The heat-treated wire is shaped into rings of specified dimensions using specialized equipment.   

● Precision Grinding: Utilizing custom-built equipment to process wire raceways and grind them to precision tolerances.

● Assembly: Wire races will be installed in the bearing housing using tools (to make sure they are concentric).

● Quality Control: Quality control procedures, such as dimension testing, surface check, or tolerance testing, are followed strictly to make sure the product meets the required specifications.

How Wire Race Bearings Work

Wire race bearings operate by utilizing hardened steel wires embedded within a housing as raceways for the rolling elements, rather than using traditional solid inner and outer rings. This design facilitates smooth, controlled rolling contact and efficient transfer of combined radial and axial loads while significantly reducing weight and maintaining a compact profile.

Principles

● Load Distribution: Loads are distributed across multiple contact points between the rolling elements and the wire raceways, enabling uniform force distribution and transfer.

● Radial and Axial Load Support: As an angular contact bearing, it is capable of supporting both radial and axial loads simultaneously.

● Contact Stress Mechanics: Hertzian contact theory is applied to calculate stress at each contact point, allowing for the accurate prediction of the bearing's actual service life.

Bearing Dynamics in Rotation

● Friction Characteristics: The friction found in the wire race bearing tends to occur mainly around the rolling contact areas for the balls and the wire raceways. With appropriate lubrication, the friction is reduced for smooth rotation and easier functioning.

● Speed Limitations (DN Values): The wire race bearing maximum operating speed can be expressed in DN values, calculated by multiplying Pitch Circle Diameter in mm by RPM.

● Thermal Generation: Heat is generated by both rolling contact friction and grease churning. The resulting temperature rise leads to thermal expansion, which in turn causes changes in the internal clearance of the bearing.

Key Advantages of Wire Race Bearings

Wire race bearings offer a combination of compact geometry and functional flexibility. These advantages make them suitable for applications where conventional bearings may be impractical.

Compact Design Benefits

● Thin Cross-Section Profiles: The radial and axial dimensions of the wire race bearings are very small and thus suitable for tight places.

● Weight Reduction: By using wire races instead of solid rings, the weight of bearings is reduced. This can prove to be quite an advantage in a rotating assembly.

● Integration Benefits: Its adaptable construction simplifies integration within CT medical systems, radar units, and specialized machine tools.

● Customizable Diameter Options: Wire races can be manufactured with a range of diameters, allowing for unique applications involving unusual shaft sizes.

Performance Characteristic

● Low Starting Torque: Wire race bearings offer low breakaway torque due to the compact design of the rolling elements, which effectively minimizes contact friction.

● Quiet Operation: The rubber gaskets serve as damping elements, effectively mitigating vibrations generated by bearing movement.

● Radial and Axial Load: The bearing can support the radial load and the axial load.

● Cost-Effectiveness: Wire race designs balance the performance features with material efficiency for applications requiring compact, precise bearings. 

Applications in the CT medical system and Rotary Systems

Wire race bearings are commonly selected for systems that require accurate rotation, compact packaging, and stable load support.

Industrial and Medical Applications

● CT Scanner Gantry Rotation: Allows for smooth and accurate movement of the gantry during the imaging process.

● Wind Turbine Pitch and Yaw Control: Provides reliable rotational motion to commercial-scale rotors.

● Robotics and Automation: Assists in the precise rotation of joints in robotic arms and on assembly lines.

● Packaging and Indexing Machinery: Supplying consistent and accurate motion, which is in great demand for high-volume production and manufacturing operations.

Wire Race vs. Conventional Bearings

Choosing between wire race and conventional bearings depends on space, load, and system complexity. Each option presents distinct design trade-offs.

Comparative Analysis

● Cross-Section Thickness: Wire race bearings have much thinner cross-section thicknesses than conventional bearings. Therefore, they can be installed in compact spaces, as well.

● Load Capacity per Unit Size: Although absolute loads may be greater with conventional bearings, wire race bearings compare favorably with regard to load-carrying capacity per unit size.

● Speed Capabilities: Both types can operate at a high speed.

● Cost Considerations: While the unit cost of wire race bearings is higher, they offer superior overall performance and effectively reduce the total number of system components.

● Installation and Maintenance: Compared to conventional bearings, wire race bearings need more precise assembly due to separate races, but operational maintenance is comparable once installed.

When to Choose Wire Race Bearings

● Applications with limited installation space

● Noise-sensitive applications

● High-precision applications

● Systems with moderate load and speed requirements.

● Projects demanding customized diameters.

Technical Specifications and Selection Criteria

Selecting the appropriate bearing based on operating conditions is essential; overlooking key parameters often leads to a reduced service life.

Critical Parameters

● Bore and Outer Diameter Ranges:  The bore diameters of the wire race bearings can vary between 400mm and 1300mm.

● Radial and Axial Load Ratings: These parameters vary according to dimensions. As a general rule, a wire race bearing with an 800mm inner diameter can support a load of 2 tonnes.

● Maximum Operating Speeds:  The maximum speed of wire race bearings is closely correlated with their dimensions. NBG's high-speed silent bearings achieve a noise level of only 65.9 dB(A) at a speed of 400 RPM（PCD=835mm）

● Precision Grades: Wire race bearings are available in various precision classes, with the highest grade being equivalent to ISO P4 standards.

● Sealing Options: Options include open, shielded, and fully sealed, depending on the level of contamination and lubrication.

Selection Considerations

● Operating Environment: Temperature, humidity, and dust affect material selection and sealing designs.

● Load Calculations and Safety Factors: It is necessary to consider safety factor calculations in terms of the radial and axial forces.

● Service Life and Maintenance: The choice of the bearings should be made depending on the duty cycle and the maintenance category. 

Installation and Maintenance

● Care must be taken in applying preload adjustments in order to preserve the distribution of loads.

● Follow the given lubrication schedules when using grease.

● Perform checks for wear, noise, and running accuracy. 

Conclusion

Wire race bearings excel in rotary applications demanding compact integration, high precision, and quiet high-speed operation. Their unique design enables engineers to overcome space constraints while ensuring stable and reliable performance under combined radial and axial loads. Achieving consistent long-term reliability requires a thorough understanding of their construction, operating principles, and selection criteria.