Bearing analysis with ReLog

Using the ReLog to measure vibrations and analyze bearings to predict potential failure modes

ReLog vibration data logger

The key takeaways

Why should you measure vibrations to in the first place?

Unexpected faults and disruptions in bearings and other critical parts can lead to catastrophic downtime in production or, in the worst case, damage to employees and the machines themselves. Vibration-based measurements to understand the health of your machines, and bearings in particular, is a proven method for knowing in good time when bearings need maintenance and how to prioritize your maintenance work.

To meet these challenges, we at ReVibe Energy have developed ReLog, a vibration data logger that we see as the perfect measuring instrument for maintenance teams that work with vibration measurements in dirty and challenging environments but can not compromise on measurement quality and precision. We have developed ReLog to make it as easy as possible to use for everyone, regardless of background and competence – we promise that you will be up and running within 10 minutes of opening the package!

But, before we get to look at the instrument we at ReVibe believe you would benefit from using, let us take a look at how to measure vibrations with the purpose of analysing bearings and how you can get going.

Bearing analysis

As bearings age, they are inevitably subjected to wear and tear. This often manifests itself as damage to the contact surfaces of the bearing balls and races – for example pitting, gouging, and other unevenness.

When a ball rolls over a damaged point in the inner or outer raceway, a small impact occurs, which gives rise to vibrations. Such impacts will happen as often as a ball passes the defect. We can use this when analyzing vibrations from bearings, by looking for spectral peaks matching the ball-pass frequencies, commonly abbreviated BPFI and BPFO (ball pass frequency inner/outer race).

Vibinspect calculates the BPFO and BPFI frequencies for you and shows where they are in the spectral plot. You simply choose your bearing make and model, enter your rotational speed, and Vibinspect does the rest.

VibInspect calculates the BPFO and BPFI frequencies for you

Cursors

The same procedure can be applied to look for damage to the balls themselves. In this case, the important frequency to look for in the spectrum is called 2xBSF, which means two times the ball spin frequency. Why is there a factor 2 before the ball spin frequency, you may ask? Because if there is a defect on a contact surface of a ball, it will cause two impacts for every full ball revolution – one against the inner race, and one against the outer.

Lastly, for detecting damage to the cage, we look for frequency content at the so-called FTF, or fundamental train frequency, which is the rotation frequency of the bearing cage. Vibinspect calculates 2xBSF and FTF for you, just like BPFI and BPFO.

But there’s so much noise in my spectrum that I can’t distinguish the peaks!

This is quite common. The background noise is sometimes so high that race or ball damage can’t be detected in a normal spectrum until it’s too late. Fortunately, there are techniques that make fault-indicating peaks be more discernible. Envelope analysis can be used for this.

When a bearing defect causes an impact, it makes the bearing vibrate with the bearing’s own resonance frequencies, usually in the range 2 kHz – 6 kHz (sometimes the bearing manufacturer provides this information). So, every time an impact occurs (which happens with frequency BPFI, BPFO, 2xBSF or FTF), the bearing vibrates at 2 kHz – 6 kHz. In the signal processing language, the bearing’s natural frequencies are said to be modulated with BPFI/BPFO/2xBSF/FTF. Envelope analysis utilises this by performing an operation called demodulation. This technique makes peaks arising from bearing impacts much clearer, so that incipient faults can be detected earlier than in a normal spectrum.

Envelope analysis is easy to perform in Vibinspect – just check the “Envelope spectrum” checkbox when doing an FFT, select which frequencies to focus on (in this case, the bearing’s natural frequencies), and you will get an enveloped spectrum – hopefully without indications of faults in your bearing!

Can you afford to not work with predictive maintenance?

Calculate the true cost of a breakdown

It’s time to take a look at some actual numbers and how much money you can save by using one of the approaches above. Below, we have created a simple calculator where you can input your numbers to get an overview of how much money you potentially are losing during a breakdown.

And to make this as real as possible, we have also illustrated an example from one of our customers and how the ReLog and routine-based maintenance schedules help them avoid breakdowns.

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ReLog Vibration data logger

The ideal vibration data logger for capturing and monitoring vibrations, shocks, and impacts. With superior battery life and up to 128 GB of memory, the ReLog is the perfect tool for monitoring vibrations in most environments. It has been designed to be extremely easy to handle and by the touch of a button, you will be up and running and measuring with up to 32,000 Hz sampling rate.

With its waterproof housing (IP67) there really are very few limitations to where you can use the ReLog! And when you’re done measuring the included software will make sure you have perfectly structured files that are easy to analyze and work with.

Start detecting failure modes

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