Lubricants News and Updates

Grease compatibility is often a consideration for end users and suppliers when switching from one grease to another. Grease compatibility should be based on several factors: Base Oil, Thickener Type and Additives. The reason all three should be considered is due to the fact that grease consists of three main components – Base oil, thickeners and additives. Charts for grease compatibility can be contradictory and misleading because they base compatibility on thickener only. It is also recommended to know the application; seal material and metallurgy should be considered.

Compatibility studies are usually in accordance with ASTM D6185 test procedure. In this procedure grease is mixed in following at 90:10, 50:50 and 10:90 mixtures of the two greases are prepared by the prescribed methodology and tested for primary tests (i.e., drop point, shear stability and storage stability at elevated temperatures). Additional secondary testing may need to be done based on results of the primary testing.

Switching from one grease to another, even if incompatible, can be done with the proper steps and care. Although incompatible grease can be very detrimental to equipment and seals, following proper steps can help to eliminate damage or issues. Either a clean and dry component, new component or increase in greasing intervals, or emptying the system and recharging with new grease are just a few ways to switch from one grease to another. The term “Grease Incompatibility” can be somewhat over-rated and scary to the end user. With proper steps and consideration switching grease brands or types can be done without damage or concern for equipment.

In conclusion, following OEM recommendations should be first consideration. Always assume that greases are incompatible and follow proper steps to ensure equipment life. Using your supplier’s knowledge of their products can help to switch and even consolidate grease.

Calcium Sulphonate Complex (CaS) greases do not function like other greases. In most greases, the thickener releases the base oil to provide elastohydrodynamic lubrication in a bearing load zone. A Calcium Sulphonate (CaS) thickener is more like a gel. The base oil and gelled CaS thickener form a permanent emulsion.

A well formulated CaS grease maintains the emulsified state, and the entire combination of thickener and base oil pass through the bearing load zone. If the emulsion should break and the base oil bleed from the thickener, the CaS thickener left behind would still lubricate.

The use of higher base oil viscosities to enhance wear protection is applicable to other thickeners, not CaS. Increasing base oil viscosity can actually reduce the natural wear protection from a CaS thickener and may create the necessity to add molybdenum di-sulfide (Moly) additives to compensate for the reduction in wear protection. Base oil viscosity does have an impact on the NLGI grade of grease and will affect temperature range.

CaS thickeners are surface active (have a polarity) and provide primary corrosion protection, water washout resistance, and oxidation stability. Water Washout resistance is achieved from the CaS thickener’s ability to hold water in a tight emulsion and thus keep the water away from metal components. In turn, this will help to prevent corrosion due to the presence of water in the grease. CaS greases are often used in long term or for life service applications due to its inherent oxidation stability.

Where the base oils in other grease thickeners do the work, in a Calcium Sulphonate (CaS), it is the thickener that does the work.