Do your slip rings run trouble free for their expected lifecycle? If you answered “no,” you’re not alone. Many engineers who work with rotating machines experience slip ring problems or downtime at some point. The good news is you can easily keep your slip rings running smoothly for the long haul by following just three simple steps. All you need to do is configure, install and maintain the slip rings properly.
Unfortunately, even experienced engineers sometimes configure slip rings without paying enough attention to how the device will be installed on the machine. It turns out that different mounting orientations call for different slip ring configurations. And if you get the configuration wrong, the slip ring may suffer from recurring signal loss problems and a shortened working life.
Maintenance isn’t always straightforward either. It’s easy to lay the blame for poor maintenance on end-users, but the truth is some slip ring designs are inherently difficult to maintain. What’s more, engineers do not always consider the actual operating conditions when setting maintenance expectations, causing them to overstate or understate service intervals. The bottom line is that slip ring maintenance starts on the drawing board, not on the factory floor.
Here are some simple design strategies that will help you ensure the longest possible life and lowest possible maintenance for the slip rings used on packaging and other industrial machines.
One of the first steps is to eliminate configuration errors. To maximize design flexibility and minimize size, modern slip rings typically have a modular design. Modularity lets users freely combine power and signal channels to meet their exact application requirements.
For example, the SR085 slip ring from Kübler lets users configure up to 20 channels divided between load and signal. Each additional module adds just 10 mm to the slip ring’s base axial length of 64.5 mm.
But even with all the design flexibility of modular slip rings, there are still common configuration mistakes. Often, engineers will configure a slip ring without regard for its mounting orientation.
The reason orientation matters is that the signal channels are more susceptible to contamination from dust and other particulate than the load channels. Accumulated dust can degrade the signal integrity and shorten the maintenance intervals and lifecycle of the slip ring.
That’s why it’s important to configure slip rings with the signal channels above other modules—such as those for power and labyrinth seals. As long as the signal channels are on top of the slip ring, gravity will work in your favor and minimize the amount of dust that falls onto signal channels.
Keeping the signal channels on top requires an awareness of the mounting orientation. Vertical hanging and standing orientations in particular will need different configurations to ensure that the signal channels remain above the labyrinth seals.
With horizontally mounted slip rings, gravity doesn’t help or hurt the dust situation much. You can locate the signal and load channels in any order that makes sense for your application.
Another threat to smooth slip ring operations is a disregard for recommended maintenance intervals. We recommend the first maintenance at 50 million revolutions or after one year of operation, whichever comes first. Subsequent maintenance intervals should be scheduled every additional 100 million revolutions or yearly.
The maintenance regimen itself is simple: Just vacuum out any dust that has accumulated on the slip ring load and signal contacts. The slip rings used in most packaging or industrial applications don’t even require any oil on the contacts.
While it’s true that engineers have little control over whether end-users will ultimately adhere to the recommended maintenance intervals, there are a couple of key upfront design factors related to maintenance:
Duty cycle. Nominal maintenance intervals may not be enough if you plan on running a slip ring at high rotational speeds, at elevated temperatures or in contaminated environments. These aggressive operating conditions can lead to signal degradation or even mechanical failures without an equally aggressive maintenance regime.
Easy access. All slip rings require some routine maintenance, but not all slip ring designs make maintenance quick and easy. It’s important to look for designs that have ready access to the power and signal contacts without requiring disassembly of the slip ring.
Slip rings are so common nowadays that engineers tend to take their performance for granted. And in general, modern slip rings are reliable enough to tolerate some neglect. However, if you really want to get the most out of a slip ring, a little extra attention to mounting orientation and ease-of-maintenance will go a long way.
Filed Under: Slip rings + rotary unions, MOTION CONTROL