8 Signs Your Slip Ring Needs Replacement or Service

A slip ring is a mechanical device that transfers power and electrical signals in rotating systems.  Any system that requires a level of continuous rotation will require a slip ring.

However, a worn-out slip ring can result in increased system downtime, leading to service disruptions.

Early recognition of slip ring maintenance warning signs can help you maintain operational efficiency by repairing or replacing it. We explain the various indicators that you need to repair or replace slip rings.

Major Signs Slip Ring Needs Replacement

It is essential to inspect slip rings regularly to prevent costly breakdowns. During your inspections, you will need to identify slip rings that need immediate repair or replacement. But how do you identify slip ring failure symptoms?

1. Visible Wear or Damage

1.1 Visible wear or damage on the exterior, commonly including:

1.1.1 Cable abrasion: Occurs when cables contact sharp edges and experience friction during equipment vibration.

1.1.2 Anti-rotation rod wear: Results from rigid fixation (creating a hard linkage) or axial impacts at a certain frequency due to operational vibrations.

1.2 Wear and breakage on rings and brush surfaces，Noticable physical changes such as pitting, scorching, corrosion, or grooving are primary signs of a worn-out slip ring. Apart from the normal wear and tear, issues such as contact pressure or misalignment can lead to uneven wear of the slip ring.

2. Intermittent Signal Loss

When the signal passing through the slip ring is unsteady,  Usually causes Intermittent signal loss，and leads to communication errors, it creates problems for machines that rely on constant transmission of data.

The causes of intermittent signal loss generally include:Corrosive gases such as ozone damage the sealing ring, allowing external contaminants to enter the slip ring. These contaminants then accumulate between the brush and the conductive track, leading to changes in the resistance of the stator-rotor transmission system and increased background noise.

Oil leakage from front-end equipment, such as the gearbox, allows oil to seep into the slip ring. The oil contaminates the conductive track and brush, causing debris to adhere between them. This results in changes in the resistance of the stator-rotor transmission system and increased background noise.

Lack of timely maintenance leads to excessive debris buildup inside the slip ring, causing changes in the resistance of the stator-rotor transmission system and increased background noise.

The slip ring is nearing the end of its service life, with severe brush wear, leading to resistance changes and increased background noise.

3. Overheating

The causes of slip ring overheating usually include:

Contamination or Foreign Substances: External dirt entering the slip ring due to seal failure, or the ingress of oil or chemical liquids, or the accumulation of internal wear debris due to lack of maintenance. This increases the resistance of the slip ring's stator-rotor transmission system, leading to overload.

Upstream Circuit Breaker Failure: Malfunction of the upstream circuit breaker in certain equipment, failing to intercept overload current, causing the slip ring to operate under excessive current conditions.

Proximity to Heat Sources: The ambient temperature around the slip ring exceeds the rated value due to nearby heat sources.

   Some slip rings have cooling system,but when the cooling system is failed,it will cause the overheating.

4. Excessive leakage

For certain high-pressure hydraulic rotary joints, seal wear or unfiltered hydraulic oil may lead to leakage exceeding standard limits.

5. Voltage Fluctuations

A key sign is when you notice unexpected dips or spikes in power. Instead of a steady flow, the voltage goes up and down. In most instances, when voltage disruptions occur, the slip ring is worn out (brushes) or is working incorrectly.

5.1 If the brushes inside the slip ring are worn out, they no longer stay in contact with the rotating ring. The connection becomes poor if the brushes are dirty, preventing electricity from flowing smoothly. Corrosion particles also affect and interrupt the flow of electricity, creating dips or spikes.

5.2 Arcing due to external debris ingress or internal wear particle accumulation, leading to:

Electrical corrosion on slideway surfaces, degrading contact conditions.

Poor brush-to-slideway contact or even inter-ring insulation failure, causing short circuits.

5.3 Front-end circuit breaker failure, resulting in:Inability to interrupt excessive current.and then Subsequent overload conditions.

6. Unusual Noise During Rotation

Unusual or high-pitched noise during rotation is one of the slip ring service indicators to look out for. A good slip ring should operate smoothly and quietly. Noises such as clicking, rattling, or grinding often indicate that the brushes or other slip ring components are worn out or damaged.

Lack of lubrication or dust can also lead to unusual noises. Loose parts or misalignment inside the slip ring can also create noise.

If the bearing failed, it can also create noise.

7. Exceeded Service Life

Slip rings are built only to last a certain amount of time or number of spins (revolutions). Most slip rings are rated to last between 500 and 200 million spins.

Slip rings begin to wear out once they exceed their rated number of spins.

8. (Bonus) Frequent Maintenance or System Downtime

Frequent maintenance, such as adjustments or testing, is one of the clearest signs slip ring needs replacement.  A well-functioning slip ring should run smoothly with minimal maintenance.

A slip ring that needs frequent maintenance often leads to system downtime, resulting in delayed operations. Small slip rings can only be replaced. They are not designed to be repaired.       

Recommendations for Replacement or Service

Once you notice any issues, it is essential to begin slip ring troubleshooting.

1. Inspect & Diagnose

Conduct a thorough visual inspection while checking for any discoloration, wear, or dust on the slip ring’s surface. Overheating of the slip ring results in damage to or irregularities in its performance. Examine other components, such as brush holders, to ensure they properly align with the slip rings.  

Use electrical testing to check on voltage drop, noise, or contact resistance. Confirm if the results follow manufacturers ' guidelines or deviate.  

2. Repair vs. Replace

Following the correct cleaning procedure is crucial to prevent accidental damage to slip rings. Use a soft cloth to wipe off any dust, and compressed air for tougher particles.

After thorough cleaning, you can see the extent of the damage. You can then decide when to replace the slip ring or repair it.

3. Improve Maintenance Practices

You should establish a regular cleaning and inspection schedule. Continuous monitoring of temperature components is crucial to get alerted and avoid overheating. Install vibration sensors on the rings to detect unusual noise, an indicator of underlying issues such as misalignment or bearing problems.

If the slip ring requires lubrication, you can change or add as specified by the manufacturer. However, avoid overlubricating or adding the wrong one to prevent poor performance or major damage.

4. Consider Redundancy for Critical Systems

In industries where system failure is not an option, such as military or medical machines, you should have a backup system. Consider using a dual-slip-ring setup. One slip sling will handle the main power or signal transmission. The second slip ring stays in place, ready to take up if the main one fails.

A dual-slip-ring setup helps to continue production when technicians are repairing or replacing the main one.

Conclusion

Visible wear, voltage fluctuations, and intermittent signal loss are some of the signs slip ring needs replacement. A worn-out slip ring can disrupt the machine's operations.

However, specific factors such as exceeding the number of rated spins or frequent maintenance can force you to replace instead of repair.