MDI Case Study: Inner Race Bearing Defect

Case Study Provided By Educational Partner Machinery Diagnostics Institute (MDI)

Introduction
Inner race bearing defects can be a significant problem in many industrial applications. The inner race is part of the bearing that rotates against the shaft. Defects in the inner race can lead to increased vibration, noise, and decreased performance of the machine. In severe cases, the bearing can fail completely, which can lead to the machine breaking down or even catastrophic failure. In this case study, we will illustrate what inner race bearing defects look like as part of the vibration spectrum collected during routine data collection.

Analysis
MDI was commissioned to perform routine data analysis at a Pulverized Coal Mill. Inner race defects were found on two machines:

Motor on a PF Mill
Motor on an Auxiliary Water Pump

MDI utilized the following hardware for the analysis:

CTC's AC294 Side Exit, Compact Size, 100 mV/g Accelerometer
CTC's MH214-3A Magnetic Mounting Base
CTC's CB104-C555-006-K2C-SF Cable and Connector Assembly
CSI 2130 Data Collector

A render of CTC AC294 Compact Side Exit Sensor on a magnetic mounting base, and a CTC industrial cable and connector assembly

Utilizing a cable with a breakaway safety feature (as shown in the image above) is extremely important for analyst safety while collecting data on large operating machinery.

Analysis Example 1

Analysis Example 2

Conclusion
The characteristic frequencies associated with inner race defects can vary depending on the bearing's size and speed of rotation. For example, in a typical 6206 ball bearing with a rotational speed of 3000 RPM, the characteristic frequency associated with inner race defects is around 150,000 RPM. However, in larger bearings, the characteristic frequencies can be lower, while in smaller bearings the characteristic frequencies can be higher.

It's essential to note that the frequency range for detecting inner race bearing defects is not fixed and can vary depending on the specific application and the condition of the bearing. It was determined that the root cause of the inner race defect in the auxiliary water pump was due to false brinelling.

False brinelling is caused by vibrations acting on the bearing while stationary. Since lubricant is not redistributed inside the bearing without rotational movement, lubricant can be pushed out of the loaded region in stationary bearings, resulting in wear and potential oxidation.

Related CTC Products
In addition to the CTC products used by MDI, CTC also offers a variety of vibration analysis hardware solutions that are ideal for use in applications like those explored in this case study. In general, any CTC 100 mV/g accelerometer (top or side exit) should be sufficient for standard route-based analysis and detecting faults between 0.5 to 15000 Hz. A popular alternative is CTC's TREA Series premium triaxial accelerometers, which feature a low-profile case and wide frequency response range (0.5 to 15000 Hz ±3dB). Additionally, CTC offers the widest variety of customized cabling solutions on the market, with specialty connectors compatible with all major data collectors.

render of a CTC TREA330 100 mV/g triaxial side exit accelerometer mounted on a CTC MH114-3T multipurpose magnet mount base
Shown above:

TREA330 Series Premium Miniature Industrial Triaxial Accelerometer
Side Exit 4 Pin Mini-MIL Connector, Follows Cartesian Phase Coordinate System, 100 mV/g, ±5%

MH114-3T Multipurpose 2 Rail Magnet Mounting Base
With 1/4-28 Tapped Hole and Triaxial Alignment Notch, 50 lbs. Pull Strength, 1.39 in. (35.31 mm) OD, 0.85 in. (21.59 mm) Height

Render of a CTC Industrial Cable and Connector Assembly featuring CB117 coiled cable, J4C Connector, C650 data collector connector, and SFT safety feature

Cable assembly shown above:

CB117 Coiled Cable
4 Conductor Coiled, Shielded Cable, Black Polyurethane Jacket, 0.21 in. (5.3 mm) OD, 250 °F (121 °C) Maximum Temperature

J4C Connector
4 Socket Mini-MIL Connector with Rubber Bending Strain Relief, for use with CTC 4 Pin Triaxial Accelerometers, Polyurethane Molded, Portable Measurement, 250 °F (121 °C) Maximum Temperature

C560 Emerson Compatible Data Collector Connector
Emerson 2140 & 2130 Compatible, 5 Pin M12 Connector, Triaxial Acceleration Input, Pin 2 (Y Axis), Pin 3 (X Axis), Pin 4 (Z Axis), Pin 5 Common(-)

SFT Breakaway Safety Connector
Triaxial Break Away Safety Connector, 250 °F (121 °C) Maximum Temperature

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About MDI
Machinery Diagnostics Institute based in Queensland, Australia, is an official educational partner of CTC. They are recognized globally as some of the most highly-regarded trainers and educators in the vibration analysis industry. MDI offers in-person and virtual technical trainings on topics including vibration analysis, thermal imaging, machinery lubrication, ultrasound testing, turbo machinery, machine balancing, shaft alignment, and asset reliability. The MDI team is proud to partner with other industry leaders including Mobius Institute, ICML, and Infraspection Institute.

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