Introduction Water intrusion into the grease is a challenge for applications in cold rolling steel mills. Water can form an emulsion with base oils, and there can be loss of grease structure and consistency. The softened grease becomes more susceptible to washing out of the bearings as its consistency drops. Operators use frequent or continuous bearing re-lubrication strategies to compensate, but bearing failures are common. Production losses from bearing failures and maintenance lead to higher production costs. An optimal choice of grease becomes an important technical decision that can reduce these risks. In steel mills, the service requirement is for grease to maintain its structure, resist water intrusion through adequate water repellency, and maintain its lubrication properties. Cold rolling steel mills have traditionally used greases formulated with simple lithium soap, lithium calcium mixed soaps, and lithium complex thickeners. In the experience of these Authors, overbased calcium sulfonate greases are gaining favor as lubricants for the bearings that support the rollers in steel mills. It is hypothesized that the service life of the grease and bearings can be substantially improved by increasing the grease’s water repellency and raising its water tolerance and resistance. This study focuses on the water washout performance of four commonly used soap-based greases by examining their water resistance when the grease consistency and formulation are altered. Formulating greases for steel mill applications must balance many considerations. The grease must withstand the force of sprays of water and metalworking fluid emulsions. As centralized grease systems commonly are employed to supply grease to the roller bearings, greases with NLGI 3 consistency are problematic as they can plug supply pipes. Experience dictates that the ideal consistency range for this application is between NLGI grade 1 and NLGI grade 2 (e.g., NLGI grade 1.5). In this study, the properties of grease consistency, base oil viscosity, and the total base number (TBN) of the calcium sulfonate used to make overbased calcium sulfonate grease were varied to examine their effects on grease performance. Customary units of for kinematic viscosity, centistokes or cSt, were used throughout this paper.
Water washout test device (Courtesy of Koehler Instrument Company) - 76 VOLUME 84, NUMBER 2