MDI Case Study: Outer Race Bearing Defects

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

Introduction
Outer race bearing defects are one of the most common types of bearing defects that can occur in rotating machinery. Outer race bearing defects are faults or damages that occur in the outer ring or raceway of a rolling element bearing. Outer race bearing defects can occur due to various reasons, including fatigue, wear, corrosion, or improper lubrication. In this case study, we will examine real-life examples of outer race bearing defects.

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

Gland Steam Condensate Fan
Service 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

Render of a compact CTC AC294 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

A graph depicting the vibration caused by a outer race bearing defect

Photo of a outer race bearing with defects and the motor it is from

Analysis Example 2

graphs depicting changes in vibration due to outer race bearing defect

Photograph of close up of outer race bearing defects and the motor it is from

Conclusion
The most common type of outer race bearing defect is spalling, which occurs due to high cyclic stress on the bearing surface. Spalling is characterized by the formation of small cracks or pits on the surface of the outer race, which can lead to the loss of bearing material and reduced bearing life. Spalling is pictured on the outer race of machine example 1, the gland steam condensate fan. The root cause of this fault was determined to be 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.

Other types of outer race bearing defects include cracking, which occurs due to high static loads, and fretting, which occurs due to micro-movements between the bearing and the housing or shaft. Fretting can cause wear and damage to the bearing surface and can result in premature bearing failure. Fretting can be seen on machine example 2, the service water pump. In both cases, it was recommended to replace the bearing to prevent further damage.

The frequency range for detecting outer race bearing defects depends on the size and type of bearing, the rotational speed of the machinery, and the severity of the defect. Generally, outer race bearing defects produce vibration signals in the frequency range of 1x to 4x the running speed of the bearing. For example, if the bearing is rotating at 1000 RPM, the frequency range for detecting outer race bearing defects would be 60,000 RPM to 240,000 RPM. However, the specific frequency range for detecting outer race bearing defects may vary depending on the individual case.

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, CTC’s 100 mV/g accelerometers are great multipurpose tools capable of detecting outer race defects within the range of .5 Hz to 15 kHz. CTC offers 100 mV/g accelerometers in standard, compact, and miniature sizes, in both top and side exit configurations. Additionally, CTC’s 100 mV/g triaxial accelerometers are excellent multipurpose tools for taking three axes of data simultaneously to speed up routine data collection.

Renders showing the size comparison of CTC Top Exit Sensors - Standard Size AC102, Compact Size AC192, and Mini Size AC140
Shown above (left to right):

AC102-1A Standard Size Multipurpose Accelerometer, Top Exit 2 Pin Connector, 100 mV/g, ±10%
AC192 Compact Size Multipurpose Accelerometer, Top Exit 2 Pin Connector, 100 mV/g, ±10%
AC140 Mini Size Multipurpose Accelerometer, Top Exit 2 Pin Mini-MIL Connector, 100 mV/g, ±15%

Renders showing the size difference between Standard, Compact, and Mini size side exit accelerometers

Shown above (left to right):

AC104 Standard Size Multipurpose Accelerometer, Side Exit 2 Pin Connector, 100 mV/g, ±10%
AC194 Compact Size Multipurpose Accelerometer, Side Exit 2 Pin Connector, 100 mV/g, ±10%
AC144 Mini Size Multipurpose Accelerometer, Side Exit 2 Pin Mini-MIL Connector, 100 mV/g, ±15%

five CTC triaxial sensors for condition monitoring, in top and side exit configurations, lined up from largest (on left) to smallest (on right).
Shown above (left to right):

TCEB331 Premium Miniature Industrial Circular Triaxial Accelerometer, Top Exit 4 Pin Mini-MIL Connector, 100 mV/g, ±5%
TXEA331-HT Premium, High Temperature Triaxial Accelerometer, 100 mV/g, Side Exit 4 Pin Connector, ±5%
AC115 Triaxial Accelerometer, Side Exit 4 Pin Mini-MIL Connector, 100 mV/g, ±15%
AC155 Triaxial Accelerometer, Top Exit 4 Pin Mini-MIL Connector, Follows Cartesian Phase Coordinate System, for Modal & ODS Analysis, 100 mV/g, ±15%
TREA330 Premium Miniature Industrial Triaxial Accelerometer, Side Exit 4 Pin Mini-MIL Connector, Follows Cartesian Phase Coordinate System, 100 mV/g, ±5%

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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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