Introduction To Greases

Regular (or simple) greases are primarily made through the reaction of a metal hydroxide with a fatty acid. The metal hydroxide is typically lithium or calcium.

Simple lithium greases provide wide temperature capabilities with good water resistance. Simple calcium greases provide good water resistance, but do not perform as well at high temperatures.

Complex greases are also made with fatty acids similar to regular greases except that they use an additional carboxylic acid, which is the complexing agent. This imparts good high temperature characteristics to the final product along with the characteristics of the base metal hydroxide. Common complex greases include lithium complex, aluminum complex, and calcium complex.

Calcium sulphonate complex grease is based on a unique micellular soap structure. It provides both thickening and performance properties for the grease, including excellent wear and corrosion protection.

Greases typically contain 75-95% oil, which must be of high quality and proper viscosity for the intended application. Low viscosity or synthetic oils are normally used for low temperature service. Low viscosity oils are also used for low load and/or high speed applications. Conversely, high viscosity or synthetic oils are generally used for high temperature service. High viscosity oils are also used for high load and/or slow speed applications.

The most common additives found in grease are as follows:

• Consistency – is the degree of hardness of a grease and may vary considerably with temperature. This has been classified by the National Lubricating Grease Institute (NLGI) into the following categories:

• Shear Stability – is the ability of a grease to resist a change in consistency during mechanical working. Under high rates of shear, grease structures tend to change in consistency (usually becoming softer).
• Oil Separation – is the percentage of oil which separates from the grease under static (e.g. storage) conditions. It cannot predict separation tendencies in use under dynamic conditions.
• High Temperature Stability – is the ability of a grease to retain its consistency, structure, and performance at temperatures above 125°C/260°F.

The following five (5) categories for Automotive Service Greases have been developed by the NLGI. The scope of this classification (ASTM D 4950) covers greases designed for the lubrication of chassis components and wheel bearings of passenger cars, trucks and other vehicles. The NLGI classifies automotive service greases into two (2) main groups: Chassis greases designated by the prefix L, and Wheel Bearing greases designated by the prefix G.

The following table outlines the five (5) categories:

The majority of greases certified under this classification meet the requirements of both LB and GC, and are thus certified as NLGI GC-LB.

NLGI HPM
In January 2021, the NLGI introduced a new standard for industrial greases called HPM standing for High Performance Multiuse grease. The requirements of HPM are somewhat different from GC-LB, as the GC-LB standard is intended for automotive rather than industrial applications. The HPM grease specification defines a new level of performance for industrial greases. In addition to the core HPM specification, there are additional sub-categories of improved performance in specific areas that can be added to the basic HPM certification. These sub-categories are:

+WR (Water resistance)
+HL (High load-carrying capacity)
+CR (Salt water corrosion resistance)
+LT (Low temperature performance)

One or more of these subcategories may be combined with the core HPM certification to define a grease’s performance in multiple areas. The necessary tests and required performance for the HPM standard and subcategories can be found on the NLGI website.

Not all grease thickeners, base oils, and additives are compatible and care must be taken when switching to a new grease. If any of the grease components are incompatible, the mixture will fall short of the properties of the individual greases.

It is strongly advised that, in all cases, the old grease be purged or cleaned out from the system, including all supply lines, valves and housings before a new grease is introduced. Compatibility between greases is temperature dependent. As the temperature rises, the problems associated with incompatibility also increase. The following chart indicates the compatibilities of major Petro-Canada Lubricants greases. Competitors’ products should be treated as incompatible with Petro-Canada Lubricants greases unless compatibility has been tested.

The following chart provides key properties of all the common grease thickener types.

* These temperatures refer to continuous operation. They may be exceeded temporarily in the case of complex greases, and where rigorous lubrication practice is followed.

The over-packing and over-greasing of bearings accounts for more failures than any other factor. Excess grease in a bearing cavity increases internal friction, which in turn raises the bearing temperature above the dropping point of the grease. This causes oil separation and eventually lack of lubrication.

REGREASING INTERVALS FOR BEARINGS

Re-greasing intervals are determined from:

• Severity of service
• Environment
• Condition of seals
• Shock loading
• Mounting configuration

REGREASING AMOUNTS FOR BEARINGS

When packing a split housing pillow block bearing, ensure that the grease cavity is only 1/3 full. Rolling element bearings should be filled 1/4 to 1/2 the total capacity of the bearing housing. However, the following formulas can be used to determine the correct amount of grease for a greasing interval:

Regreasing amount in ounces: G(oz) = 0.114* W (bearing width in inches)* OD (bearing outer diameter in inches).

Metric Equivalent: G(gm) = 0.005 * width in cm * OD width in cm.

The proper technique for greasing a rolling element bearing is to wipe the grease fitting with a clean, lint free cloth and then add the correct amount of grease to the housing. If a purge plug is present it should be removed and the bearing operated for 10-15 minutes to allow the level of grease to equalize and then replace the purge plug. If no purge plug is present the grease fitting should be removed (or replaced with a self-purging fitting) and operated for 10-15 minutes and then replaced. Always check the temperature before and after this procedure.

The following chart provides a guide to re-greasing intervals and the amount of grease to be applied. Please further confirm re-greasing amounts and intervals with your manufacturer.

GREASES

Petro-Canada Lubricants greases are listed according to their performance or application as follows:

• Regular Performance Greases
• Premium Performance Greases
• Synthetic Greases
• Specialty Greases for High Temperatures
• Specialty Greases for Water Resistance
• Specialty Greases
• Incidental Food Contact (H1) Greases
• Mining Greases and Drilling Compounds