In todays technology-savvy society, many standard tests and advanced techniques are available for analyzing lubricating greases. However, the quality of grease is often still judged using human senses: color, touch/feel, smell and even – in rare instances – taste. These perception-based screening tests can be the prime reason for rejecting a grease, even before actual application.
Color undoubtedly adds cosmetic value to a lubricating grease, but how much it adds to performance remains debatable. Once, a maintenance manager at an integrated steel plant asked me, What does color do to the lubricating greases? My instinctive response was, Lubricate eyes!
During one of my business meetings, someone pointed out that lubricating greases are emotional. This prompted me to think about the topic from a different angle. In my 25 years of formulating and manufacturing lubricating greases, I have come to believe that grease making, to an extent, is an art. Grease preparation is believed to be highly sensitive to processing parameters such as time, temperature, mixing, pressure and vacuum. Some greases also seem to be sensitive to a specific kettle or even the operator.
Royal Mfg has 17 kettles at our Tulsa, Oklahoma, grease plant, and every kettle cooks grease a little differently. Thats why we have dedicated the kettles to specific types of greases, like calcium sulfonate, aluminum complex, polyurea, etc. Not only that, certain operators cook one type of grease better than others, and all operators must baby-sit the cooking and finishing process to make consistently high-quality grease. Doesnt it sound like lubricating greases themselves are emotional?
The Color of Happy Customers
When it comes to the marketing or application of greases, we also take an emotional approach toward color, tack/feel and smell. Many different colors of grease are in the market: amber, white, black, red, blue, green, golden, silver, etc. Over time, these colors have come to represent certain purposes in customers minds. For example, white symbolizes food grade, red is for high temperatures, blue for cold temperatures or synthetics, green for environmentally friendly grease and silver or copper for anti-seize lubricants.
However, grease colors are perceived differently in different parts of the world, and colored greases are more popular in North America than in Asia and other developing countries. One possible reason is that, in developing markets, low quality or recycled base oils can be used to prepare cheap greases, and color could be added to mask the greases shortcomings. Conversely, consumers believe that if the grease is without dye, it is more likely to be prepared using fresh oil.
Besides color, demonstrations like the rat-trap test, hammer test or portable Timken machine test have also been effectively used as marketing tools, despite their dubious scientific value.
Analysis of our customer complaint data for the last five years indicates that a majority of the complaints were related to color, smell, tackiness and/or consistency – appearance-based objections – and only a few were based on actual performance failures. In order to understand the effect of colors and tackifiers on the performance characteristics of lubricating greases, we conducted a systematic study of these additives.
Whats in a Shade?
Titanium dioxide and zinc oxide are used to prepare white greases, especially food grade greases. The concentration of these compounds depends on the extent of whiteness desired, as well as processing parameters, thickener type and base oil. Greases made with API Group I and naphthenic base oils require more of the whitening agent than greases prepared with water-white Group II or Group III oils or polyalphaolefins. Although these solid powders in concentration of 2 percent or less do not have a significant effect on the properties of lubricating greases, our studies indicate that higher concentrations seem to have adverse effects on oil bleed and storage hardening in lithium complex and aluminum complex greases.
Black greases are made using asphalt, molybdenum disulfide (moly), graphite or carbon black. Asphalt has traditionally been used to prepare black greases, and it is believed that asphalt has good adherence on metal surfaces. However, it also comes with potential health and environmental concerns. In the presence of water or in a cold climate, greases with asphalt tend to flake off and absorb more dirt and dust in open gear applications than greases with other additives. Due to their lamellar structure and stability at higher temperatures and pressures, moly and graphite help to enhance lubrication properties, especially in elastohydrodynamic and boundary lubrication conditions.
For colored greases, dyes are generally used in very low concentrations, and are typically based on azoquinone or anthraquinone chemistries – compounds that reportedly possess questionable toxicity. The dyes in general have no effect on the properties of lubricating greases at lower concentrations. However, if used in concentrations of 0.2 percent or higher, the dyes might adversely affect copper-corrosion properties.
With appearance so important to customers, what happens when colored greases are exposed to sunlight, high temperatures and water during storage or application, as in steel plants and the metal processing industry? When exposed to sunlight, many colored greases have been found to lose their shine and colors start gradually fading. In the presence of light, some products such as calcium greases have been found to start shifting from a translucent amber to a brownish color.
Once, a cartridge of green biobased grease was accidently left open for several months, and surprisingly, the green color inside the tube almost completely disappeared. Similarly, when blue, green and red colored greases were exposed to a temperature of 250 degrees inside an oven for 48 hours, most of them turned quite dark. When these same colored greases came in contact with water, the grease began to emulsify and the color faded considerably.
Staying Put
Polymers are often added to lubricating greases to improve their adhesive or cohesive properties and their water resistance. Adhesiveness in this context may be defined as the affinity of greases toward a metal surface, and cohesiveness as the attraction of molecules within the grease itself. The types of tackifiers used in lubricating greases are generally polyisobutylene, ethylene-propylene/olefin co-polymer (OCP), polymethyl acrylate, polymeric latex and others. It was found during our investigations that certain polymers in limited quantity improve water resistance or thickening capabilities – but excessive dosage was found to deteriorate water resistance and storage stability properties.
A possible reason for this unexpected behavior could be that, with an increased amount of polymer, adhesive forces between the grease and the metal surface tend to weaken, and cohesiveness within the grease starts playing the dominant role.
An interesting field experience related to this phenomenon was seen when a calcium sulfonate grease with 0.5 percent OCP and 0.5 percent polymeric latex was used in a diamond drill rod application. The grease showed improved results over a calcium sulfonate complex grease with no polymer. However, when the polymer quantities were further increased to 1.0 percent respectively, the higher dose was found to be counterproductive: The grease did not stick to the rods, especially when they were wet. Further, the addition of polymers was found to deteriorate pumpability at lower temperatures.
As the above shows, grease is emotional and is sensitive to the ingredients we put into it. But customers are sensitive, too, and place a high value on color, touch and smell.
Anoop Kumar, Ph.D. is director of R&D and business development at Royal Mfg Co. L.P. With 25 years of experience in formulation, manufacturing and market development of lubricating greases and industrial oils, Kumar helped form the NLGI India chapter and currently serves as treasurer of NLGI. He can be reached at anoopk@royalmfg.com.