As with many mission-critical components, material selection for slip ring components directly impacts performance, reliability, and maintenance requirements. In this post, we’ll look at historical demands of slip ring material components, how they have changed, and the newer materials that are available to meet today’s challenges.

In most assemblies, the slip ring itself is typically made from gold-plated copper or brass. The brush, however, requires much more specialized materials that can handle intense mechanical and electrical demands. Keep in mind that the brush functions as both an electrical conductor and a spring member, which delivers proper contact force while maintaining continuous sliding contact.

Excellent material compatibility between the ring and brush is crucial. Otherwise, the assembly is likely to fail prematurely. For example, if both components have identical hardness properties, galling can occur. To prevent parts from wearing, engineers will often specify the brush to be harder than the ring. Having a softer ring will help make sure that the assembly runs smoothly and reliably, minimizing any potential galling, while preventing excess wear on the brush. This is just one example of what can potentially happen if the materials aren’t playing nicely with each other.

A Peek into the Past

For many decades, Paliney 7 has been the go-to material for slip ring brushes. This precious metal alloy is well known for having excellent corrosion resistance, good mechanical properties, and reliable electrical performance. However, its electrical conductivity rating is relatively low compared to newer materials. It is approximately 5-5.5% IACS (International Annealed Copper Standard). While this works perfectly well for lower voltage and power applications, today’s systems often demand much better performance.

Meeting Modern Demands with Higher Conductivity Alloys

It’s interesting to note that the semiconductor test industry drove the development of newer alloys. Specifically, today’s testing needs material that can handle smaller diameters and cross-sections while transferring more power without excessive heat generation. These requirements match those found in advanced slip ring applications, leading to materials that benefit both industries.

Paliney 25 represented a significant advancement over Paliney 7, offering 28% IACS conductivity—roughly five times that of Paliney 7—while maintaining similar mechanical properties. This dramatic improvement in electrical performance enables higher current capacity in the same form factor, and also allows for smaller brush designs for space-constrained applications.

The newest alloy for slip ring brushes is Paliney 35, which pushes conductivity even higher to 33% IACS. Beyond improved electrical performance, this alloy offers superior thermal stress relaxation, meaning it better maintains its properties when subjected to heat. This characteristic proves especially valuable in demanding environments where thermal cycling is common.

Application-Specific Advantages

Traditionally, engineers had to choose between precious metals for signal integrity and carbon brushes for higher power applications. But carbon brushes come with some serious drawbacks. Although they are capable of handling 100-200V applications, they generate electrical noise, wear quickly, and produce carbon dust that requires regular maintenance.

Paliney 25 and 35 are higher-conductivity precious metal alloys which enable more efficient designs. This is thanks to the fact that they provide higher capacities for both power and data transmission in a single system. Equally as important, they offer significant advantages in noise elimination and maintenance reduction.

Many industries benefit from these advanced materials including robotics, automation, military/defense systems, radar applications, and aerospace. Space applications particularly benefit from the improved thermal conductivity, as heat must be conducted and radiated away without atmospheric convection.

Manufacturing Considerations

Both Paliney 25 and Paliney 35 are available in wire form, suitable for wire-formed brush applications. Paliney 25 also comes in strip, enabling stamped brush production using progressive die or wire EDM processes.

For existing applications using Paliney 25, Paliney 35 often serves as a direct upgrade, offering improved current capacity and thermal performance without requiring significant design changes.

Selecting the Right Material

The choice between these alloys depends on specific application requirements. Paliney 7 remains suitable for low power and voltage applications where its proven reliability and cost-effectiveness provide adequate performance. For higher power requirements, improved thermal management, or space-constrained designs, Paliney 25 and 35 offer compelling advantages.

All precious metal slip ring brushes provide superior durability compared to plated or clad alternatives. The key is to match the material’s capabilities to the application’s demands while considering factors like current requirements, thermal environment, and available space.

Understanding these material options enables engineers to design slip ring systems that meet both current performance requirements and future reliability expectations.

Need help selecting the best alloy for your custom slip rings? Contact us today, we’re happy to assist!