Enclosed Industrial Reduction Gears | Part III
by Jonathan Sowers, CLS
Senior Diagnostician

For optimal performance and maximum gear life a planned systematic approach to monitoring and maintaining gear installations should be implemented. The plant reliability/maintenance manager must ensure that the lubricant is the right product chemistry, right viscosity, right volume, right feed rate, and the oil and lubrication system must be clean, free of sludge, grit and other contaminants. This applies to individual self-contained systems, like bath/splash or integral pump lubrication, as well as external circulating oil systems that may lubricate multiple gearboxes. Gear sets and sumps/reservoirs should be cleaned and inspected prior to installing a fresh charge of new lubricant. Follow OEM recommendations for lubricant type, feed rates and change intervals. After start-up, splash lubricated systems particularly, require frequent visual inspections, and check temperatures and oil levels. Water should be drained off routinely. Where water entry is a problem, good oil demulsibility is a key property. Where possible use portable filter carts for adding oil to splash gear sets and as offline filtration. Circulating oils should have filters and the filters regularly inspected for metal wear particles from the gears. Vent areas be protected from dust, and particulate matter by pressurizing the system, or using loop filtration; install desiccant breathers where venting occurs.

Gear wear may be defined in general as the loss of material from the contacting surfaces of gear teeth due to mechanical, chemical or electrical action. Normal wear, or polishing, occurs during the early "running-in" that smooths down the asperities remaining after final machining, and continues at a slow rate that will not impact the gear performance within the expected lifetime. Moderate wear is a more rapid loss of material that may develop in heavily loaded teeth. It is not necessarily destructive, but will shorten gear life and may cause noise. Destructive wear occurs with excessive load for the lubricant or too soft a gear material for the load, and is surface damage, deterioration, or change in tooth shape that causes rapid failure or impacts the smoothness of the operation. It may include any of the following wear modes: abrasion, adhesion, corrosion, micropitting, polishing, surface fatigue, plastic flow deformation, scaling, cavitation, electrical discharge, erosion, galling and scuffing. Many of these wear mechanisms begin by throwing off very small particles, less than a few microns (µ) in size, and as the gear becomes more severely distressed the metal particles become much larger, 40, 50 greater than 100 microns (µ), and on until the tooth actually breaks.

Among predictive maintenance technologies available to plant reliability/maintenance personnel (i.e., vibration, thermography, ultrasonics, oil analysis) only oil analysis offers such a comprehensive information return on investment; key information about abnormal wear of the gears, bearings, and shaft condition, contamination in the oil, and the oil condition as to product integrity and useful service life. It is the very backbone of any complete maintenance program.

With the correct ALS test regimen for the type of gear and lubrication setup, an ALS oil analysis program will detect many of these wear problems early enough to take corrective steps that will eliminate or delay premature destructive failure. A successful oil analysis program is a partnership requiring good communication between plant personnel and the ALS lab. It is a partnership that can provide substantial reward if you are responsible for asset reliability and productivity. How can this work for you?

The initial steps of setting up an ALS industrial plant oil analysis program include these:

a) Select the gearboxes to be sampled based on a hierarchy of criticality to operation
b) Select the type of testing to be performed for maximum information gain (details follow)
c) Ensure that the ALS lab has current and correct information for each sampling point, including:

a. Unique sampling point identification
b. Gear set type (helical, herringbone, spur, worm, etc.)
c. Make and model of gear
d. System oil delivery method (splash, circulating, etc.)
e. Micron (µ) rating/mesh size of filter(s) or target ISO Cleanliness Code
f. System oil reservoir capacity
g. Lubricant manufacturer, product name and ISO or SAE Viscosity Grade
h. Oil sampling interval schedule
i. Any ambient process/environmental contamination issues

d) Communicate with and train involved personnel as to sampling techniques and report interpretation
e) Supply ALS with all communication points at the plant

The type of tests and sampling intervals that will be beneficial and cost effective for each unit will vary depending on the criticality of the gearbox and type of lube system. Sampling intervals are usually monthly, quarterly, bi-annual, or annual. The type of testing is as follows:

Basic Industrial Tests:
ICP Spectroscopic metals analysis (wear metals, contaminants, lube metallic additives) reported by atomic element in parts per million (ppm) Note: Particles detected will be small, < 6-8µ in size. This test does not detect large particle generation.
Viscosity for ISO VG lube viscosity reported in cSt @ 40°C
Water by Crackle or Karl Fischer reported in per cent or ppm
Acid Number monitors lube degradation by-products and oil integrity

This test package provides basic information on wear rates for small particles generated through Normal wear and Moderate wear, ingress of dirt and water, ingress of chemicals from treated water in heat exchanger or process environment, lubricant integrity (correct product chemistry and viscosity) and serviceability (degradation).

Additional testing for more critical units addressing the larger particulate generated through wear and contamination.
PQI –Particle Quantifier Index is used to monitor ferrous wear debris and aid in determination of wear particle size (primarily used in unfiltered systems)
ISO Particle Count – counts the number of solid particles in the oil in various size ranges - { >4µ >6µ >14µ >23µ >50µ } and is essential for monitoring large particle generation, filter effectiveness, lubricant contamination control (primarily used in filtered systems)
MPE – Microscopic Particle Examination, known as Analytical Ferrography, is a detailed microscopic examination of all of the solid debris in the lubricant. This ferrographic technique:

• Determines particle size & concentration
• Metallurgy – ferrous & nonferrous
 Heat treatment will specify low, medium, or high carbon alloy steel or cast iron
• Aids in determining component source of wear
• Identifies the Wear Mechanism generating the particles of interest – root cause
• Provides contaminant identification
• Detects lube degradation by-products
• Predicts failure mode
• Justifies equipment shutdown
• Documents finding with photographic report

For additional information on programs please contact one of our Customer Service Representatives, Technical Sales Representatives, or Regional Business Managers. Also check out our technical training schedule for a class near you.