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How to do weekly predictive maintenance on gears to prevent failures

Stop action photographs girth gear photographs are an excellent predictive maintenance task that every site can employ without shutting down critical mills, kilns, or dryers. When taken at regular weekly intervals, changes in mill set operation and condition can quickly be identified.

severe misalignment, with rippling, and tooth fracture

Stop Action Photograph Identifying severe misalignment, with rippling, and tooth fracture

What failure modes can I detect with this method?

  • Misalignment
  • Wear
  • Macropitting
  • Scuffing
  • excessive contamination
  • tooth fracture

How to take stop motion photos

  1. Open the pinion inspection door with the set-in operation
  2. Take images of the pinion using a landscape setting or higher aperture to capture a clear image of the entire pinion
  3. Schedule a weekly reminder on your calendar → 
    Add to Calendar
    06/15/2020 08:00 AM
    06/15/2020 8:15 AM
    Weekly inspection of gear
    Take images of the pinion using a landscape setting or higher aperture to capture a clear image of the entire pinion
    FREQ=WEEKLY;INTERVAL=1;COUNT=20
  4. If damage is detected send images to info@global-pam.com for a complementary remote assessment

What tools do I need?

  1. Digital Camera with Flash
    1. Macro modes with a lower aperture generally cause more of the image to blur
    2. The combination of good flash and medium to high aperture will yield the clearest images
    3. Using manual focus can enhance repeatability of shots
    4. Do not use a strobe light with the camera it will blur the images

Example stop action photographs

Misalignment with overload damage

Example of Misalignment with overload damage

Monitoring Contact Patterns, and Wear over time

Stop Action Photographs Monitoring Contact Patterns, and Wear over time


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5 Common Classes of Girth Gear Potential Failure Modes

Tooth Fracture is generally considered an ultimate failure of the gear set as is often results in the inability to rotate the set.

Here are 5 classes of girth gear potential failure modes that can be detected and mitigated with routine inspections:

Wear-Abrasion

Abrasive wear is the removal or displacement of material along the tooth flank due to the presence of hard particles. These particles can come from external sources such as slurry, dust, contamination, or may be self-generated hard metal fragments from other failure modes such as macropitting or scuffing.

The tooth profile is most affected resulting in poor mesh action and localized overloading.

Note: Often severe wear will progress to macropitting as contact stresses increase from localized overloading

Scuffing

Scuffing is a severe form of adhesive wear caused by the transfer of material from one tooth surface to another due to microwelding and tearing.

Scuffing occurs when the lubricant film cannot completely separate the metal surfaces. Machining marks are removed and deeper craters are observed. In the severe form surface temperatures may become significantly elevated causing localized metallurgical changes to occur. Proper lubricant usage and application is the best prevention.

 

Note: Severe scuffing can initiate flank cracks

Plastic Deformation (Indentation)

Indention is caused by hard foreign material that becomes trapped between mating teeth, causing an indentation in the tooth surface. The area around the indentations is typically raised from plastic deformation of the metal.

Note: Severe scuffing can initiate flank cracks

Plastic Deformation (Cold Flow, Tip to Root Interference, Tight Mesh)

The topland of this gear is completely rounded from plastic deformation where the gear is in tight mesh with the pinion and experiencing tip to root interference.

Note: Significant edge burrs have developed form the tight mesh condition

Hertzian Fatigue (Spalling)

Spalling occurs when macropits form, then grow is size and coalesce into larger cavities on the gear tooth surface. Asperities and high pressures from variations in manufacturing tolerances. This form of macropitting quickly stops once the load redistributes. The image adjacent is a gearbox gear, showing spalling across the entire face.

Note: Spalling can be easily identified from stop action photographs of pinion teeth. This is a severe failure mode which can quickly lead to tooth cracking and fracture.

by William Quinn William Quinn No Comments

Girth Gear Pinion Infrared Imaging and Temperature Measurements

Monitoring pinion temperatures on mill gear pinions is an effective and efficient means of monitoring alignment and operating condition. Pinion temperature measurement when applied properly can adequately predict multiple failure modes, including misalignment, overheating from a loss of lubricant event, overheating from improper lubricant, and temperature anomalies from severe contamination.

Girth Gear Pinion Infrared Imaging and Temperature Measurements

Pinion Locations shown on a pinion with misalignment

Mill Pinion IR Temperature Profile
AlarmShutdown
°F°C°F°C
Temp A to E1583017
Temp A to C*30174525
Temp E to C*30174525
Any temp (MAX)*20596225107

*Some mills depending on application may operate at higher temperatures than recommended in this chart, consult with a specialist if temperatures operate normally above 200 F


Infrared sensors can be installed that continuously sample the radiation given off by an object in the infrared spectrum, logic in the device then translates this data into a temperature reading displayed to the user. Alarms and interlocks can be set up as an automated protective system. In order to obtain an accurate infrared reading the measured objects effective emissivity must be known. Effective emissivity will vary based on an objects material, color, surface (shinny or dull), geometry, and in certain cases temperature. When applying infrared technology to mill gear pinions the user must be aware of these factors which may affect readings, and understand the proper calibration of the temperature sensors.

Pinion Temperature Profiles

Example Pinion Temperature Profiles

Girth Gear Pinion Infrared basics

The infrared alignment technique should only be applied to mill gear pinions not kiln or dryer gears. Kiln and drier systems typically run slow and do not develop sufficient temperatures from the mesh forces and can be significantly affected by heat transfer from the kiln or drum.  However valuable information can be deduced from monitoring the mesh temperature on these systems.

Pinion misalignment is a common failure cause which can lead to a variety of gear tooth failure modes through overloading. Measuring temperature differentials from end to end across an operating pinion is an indirect measurement of the misalignment. When a gear is misaligned in operation the temperature profile will shift to the side correlating with the increase in load in that area.

Overall pinion temperatures can also indicate an issue related to lubrication including lack of lubricant. A typical alarm and shutdown chart is provided below. In rare cases the normal operating end to center temperature may be elevated above 20 °C in this event consultation with a mill gearing expert should be done to ensure damage is not done from running the set.

When an array of online infrared sensors are used the following chart should dictate the alarm and interlock settings. Please consult with a mill gear specialist before setting alarms and interlocks as certain operating conditions may require adjustments to these general alarm levels.