Identifying problems with lubricants can often be a difficult task. Even with mineral oils and synthetics fluids where oil analysis is widespread and commonly used, the underlying cause of a problem may not be obvious. When comparing greases, the picture gets even cloudier and more difficult. Most greases have minimal characteristics that can be used to compare one to another.
Chemical characteristics like base oil type, thickener type and other additives may or may not be reported on standard data sheets. Physical characteristics like viscosity, water washout or spray-off, tackiness, etc., may also be absent. About the only information that can be garnered from most product specification sheets are the NLGI grade and dropping point. Some may report ASTM performance testing, while others may not.
With in-service grease the issues become even more confounding. Very little testing is done on in-service grease to determine how the product is holding up or if the equipment is wearing prematurely. There are opportunities to integrate grease sampling to a preventative maintenance program, but it is far from routine and is more difficult to interpret analysis results.
Changing grease in a system is not always an easy process and should be evaluated thoroughly before beginning, but what happens to the grease in these situations:
- Greases mix in service because someone grabbed the wrong grease gun
- Higher speeds due to operation change
- Higher grease temperature – operation has increased temperature, but the grease was never evaluated to see if the current product was rated for the increased demand from the operation, and now the performance of the grease is in question.
- Grease storage area changes – grease storage is hotter or colder than before
Many factors influence the performance of grease, and most have nothing to do with the actual chemistry. However, there seem to be a few issues that always come up, so let’s highlight those issues and their solutions.
Oil Running Out of Grease While in Service
- Oil running out is called bleeding
- Caused by heat and vibration
- Change to more stable thickener
- Lithium to Lithium Complex
- Lithium Complex to Calcium Sulfonate
- Calcium Sulfonate to Calcium Sulfonate Comple
Grease Cakes up While in Service
- Base oil bleeding or evaporating in service
- Possible thickener incompatibility
- Possible overgreasing in sealed housing
- Change to a grease with synthetic base oil
- Shorten grease purge PM interval
- Lengthen grease interval in sealed housing
- Primarily, it is the thickeners that are incompatible but could be base oils and additives
- One of three reactions:
- Nothing (THAT’S GOOD!)
- It will turn to mush and leak out
- It will turn to a hard rock
- If mixing greases, ask if a compatibility test has been run
- If possible, purge the grease as much as possible
- Watch the application for any temperature changes, as this may indicate a problem before a potential failure
Rules of Compatibility
- Don’t mix incompatible lubricants.
- When in doubt, assume the two lubricants are incompatible and will exhibit adverse side effects when mixed.
Grease Not Moving Through Centralized System
- Grease is too cold, thick or sticky
- Ideal NLGI 0 or NLGI 1 with minimal tackifier
- Inspect for pools of oil in pail, keg or drum
- Possibly use lower NLGI grade grease
- Possibly use grease with lower base oil viscosity
- Refer to NLGI grease classification table
Other Dispensing Problems
- Grease is too cold, thick or sticky
- Tubes with air pockets
- Getting all grease out of bins, drums, kegs and pails
- Use newer tubes with notches
- Steel totes have little flexibility
- Some have follower plates – use them.
- Incentivize employees to utilize all grease (98 percent rule)
Grease Fails/Runs Out of Service
- Bearing speed
- Impact loading
- Chemical contamination
- Reduce operating temperature
- Mitigate chemical contamination
- Use grease with:
- Higher base oil viscosity
- More tackifier
- Higher NLGI grade
Premature Wear on Bearings
- Low base oil viscosity
- Lack of EP additives
- Moly @ >1,600 RPM
- Failure investigation may be in order (consider all possible causes)
Grease Washes Out with Water
- Shielded bearings
- Equipment washing
- Wet applications
- Process water
- Change to a more adhesive grease
- Use thickeners with inherent resistance to washout (hydrolytically stable)
- Complex and detergent-based soaps are most resistant to water wash in the following order (good to best):
- Lithium complex
- Aluminum complex
- Calcium complex
- Calcium sulfonate
- Calcium sulfonate complex
- Barium complex
Grease Turns Dark
- Oxidation byproducts
- Debris from bearings
- Debris from environment
- Thickener overheating
- Electrostatic discharge
- Sniff test to detect oxidation and overheating
- Inspect machinery ground
- Inspect bearing for arcing marks (pitting damage rollers and raceways, fluting or washboarding on raceway)
- Send to laboratory to identify contaminant
Grease Turns Milky in Color
- All thickeners absorb water at varying degrees
- Water contamination may not ruin a grease
- Water contamination may shorten service life
- Primary cause is water contamination
- Contamination with lighter colored substance
- Eliminate source of water
- Use grease that best functions in wet environment
- Polymer additives shed water
- Aluminum complex with polymers (tackifiers) best shed water
- Calcium sulfonate type greases best emulsify (absorb) water
- Often the result of overfilling the bearing or too frequent a greasing interval.
- Seals are often destroyed by overfilling.
- Lack of grease supply and lubricant starvation
- Add small amount of grease and monitor for temperature change
- If no change, investigate why the bearing is grease starved. Try softer grease.
- If temperature decreases, increase greasing frequency.
- If temperature increases, vent grease and decrease greasing frequency.
- If a high-speed bearing, try lower viscosity base oil.
Oil pools (“bleeds”) in storage
- Minimal oil separation or “bleed” in service is desirable
- Minimal oil separation or “bleed” in storage is acceptable
- 1/4” (max) of oil in keg or drum
- Vibration during transportation
- Heat fluctuation in storage
- Storage above 100 degrees F
- The softer the grease and the lower the oil viscosity, the more pronounced the bleed.
- Acceptable “bleed” can be stirred back into the grease.
- Excessive “bleed” – do not use
There are multiple possible problems and solutions when it comes to lubricants and particularly greases. When there are many aspects of the grease that we cannot see, since it is usually hidden in a bearing while doing the work, it is difficult to always know what might go wrong. Always work with your lubricant supplier and OEM to determine the correct grease, and make sure all other aspects of the equipment are correct before switching greases.
Sometimes a new grease may cover up a problem for a while with higher viscosity base oil or thickener, but the real problem may recur. Always check compatibility if making any changes, even if the thickener systems are the same, by running a single bearing for a set time and monitoring the temperature and performance.
This article was previously published in Noria’s Reliable Plant 2018 Conference Proceedings
By Joe Goecke, Petro-Canada