Introduction
As we all know, conductive slip rings mainly transmit signals and electricity for rotating equipment through the continuous contact between the internal conductive ring and the brushes. Although the brushes have various structures, they are all likely to wear during operation. This can increase the resistance of the slip ring, generate sparks, cause overheating, and lead to equipment shutdown. This article will discuss the reasons for the wear of these brushes and provide the correct maintenance methods to enhance the operational stability of your equipment.
What Are the Structures of Slip Ring Brushes?
Single-filament Brush
A single-filament brush is generally composed of a single copper alloy or silver alloy wire. Due to its tiny contact points and high electrical conductivity, this type of brush is very suitable for transmitting signals with low resistance and high precision. You may find it in the slip rings of many precision instruments, such as the gyroscopes in aerospace and the rotating arms of CT scanners.
Cluster Brush
The cluster brush bundles multiple brush filaments together to form a cluster-like structure. Compared with the single-filament brush, the cluster brush has a larger contact area, can carry higher currents, and provides a little elastic cushioning. We use it in industrial equipment with medium current loads, including automated rotating worktables and the collector systems of wind turbines.
Brush Block
Another type of brush has a block structure, which is pressed from materials such as graphite and carbon. Compared with the filamentous brush, it has a larger contact area with the conductive ring. The brush block can withstand larger currents and mechanical pressures, and is most commonly used for carbon brush slip rings in high-power motors and metallurgical equipment.
The Causes for Brush Wear
Overloading
When the operating current of the equipment exceeds the rated carrying range of the brush, the contact resistance at the contact point between the brush and the conductive ring increases sharply, generating a large amount of heat. The accumulated heat will cause the brush to heat up rapidly, accelerating the thermal decomposition and oxidation of its material, and causing it to wear.
Loose or Worn Brushes
If the slip ring brush is installed loosely in the brush holder, it cannot maintain a stable contact state with the conductive ring. When the current passes through, the unstable contact resistance will cause local heating and even sparks, resulting in wear on the surface of the brush.
Mechanical Friction
Even under normal operating conditions, the conductive ring and the brush will wear due to long-term mechanical friction. The sparks generated by the friction will erode the brush, making its surface uneven. And the uneven surface will further intensify the mechanical friction and brush wear, thus entering a cycle.
Coil Short Circuit
When faults such as coil short circuits occur inside the motor, abnormal current fluctuations will appear. When the abnormal current is transmitted through the brush, it will generate additional electrodynamic impact on the brush, causing vibration. And this vibration makes the brush more likely to rub against the surrounding components.
How Should We Maintain the Slip Ring Brushes?
⑴ Set a Maintenance Cycle
We need to formulate a suitable maintenance plan for the brushes according to the operating conditions of the equipment, the usage environment, and the quality of the brushes themselves. In an industrial environment, we recommend a comprehensive inspection of the components of the slip ring every 1 to 3 months. However, if the equipment is in a humid, high-dust, and chemically corrosive environment, this cycle should be appropriately shortened.
⑵ Cleaning and Maintenance
First of all, you need to operate after the equipment is powered off and fully cooled down to ensure safety. Then, we use a soft, lint-free cloth to gently wipe the surface of the ring and the brushes, avoiding damage to the electroplated layer or insulation coating on the surface of the slip ring. This is to remove the dust and metal debris adsorbed during operation. They will intensify the wear of the contact surface between the brush and the ring and affect the electrical conductivity.
⑶ Replace in a Timely Manner
When the brush is worn to one-third of its original length, it should be replaced. When replacing, try to replace all the brushes of the same model at one time to avoid uneven current distribution caused by mixing new and old brushes. To avoid affecting the production plan, you can also replace a small number of brushes (such as 20%) each time, with an interval of 1 to 2 weeks, and continue to replace them after the new brushes are run in.
⑷ Lubrication
The lubricant can reduce the mechanical friction coefficient between the surface of the conductive ring and the brush and suppress the generation of sparks. However, excessive lubrication will instead attract more impurities. Generally, the lubricant should be replenished or replaced every 3 to 6 months.
Conclusion
The slip ring brushes may wear out due to reasons such as overloading, loose installation of the brushes, mechanical friction, and coil short circuits. And this can affect the performance of current transmission. However, we can also improve this situation by setting a maintenance cycle, conducting cleaning and maintenance, replacing the brushes in a timely manner, and adding lubricants.
As a leading slip ring manufacturer in the industry, ByTune is ready to share with you more knowledge about slip rings. If you are interested, please feel free to consult us.