Machinery Lubrication

Machinery Lubrication March April 2014

Machinery Lubrication magazine published by Noria Corporation

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38 March - April 2014 | sYNthetICs By tyler housel, iNole x CheMiCal Co. T The lubricant industry generally treats synthetic esters as a monolithic class of Group V base oils with well-defined proper- ties. It is not difficult to find a chart that lists esters as having "fair" hydrolytic stability, "good" biodegradability, "very good" lubricity, "excellent" oxidative stability and so on. Sometimes diesters and polyol esters are listed separately, but there is seldom further differentiation. However, the nature of esters defies such oversimplification. There are endless varieties of esters that can be built from commonly available acids and alco- hols, so almost anything is possible. Modern synthetic esters can be "tuned" to perform in nearly any environment and application. Whether you seek excellent hydrolytic stability, oxidative stability, biodegradability, lubricity, high viscosity index or low-temperature properties, all of these are possible with the right synthetic ester. Synthetic esters are manufactured from carboxylic acids and alcohols, which are very common chemical building blocks. They provide almost unlimited structural and performance possibilities. The Ester Reaction Figure 1 shows the basic chemical reaction used to synthesize all esters — a carboxylic acid and an alcohol react to form an ester and water. Organic chemists call this a reversible reaction because water can react with ester groups and break the ester into its components. This is known as hydrolysis. The raw materials used to make esters can be linear, branched, saturated, unsaturated, monofunctional, difunctional or poly- functional. There are hundreds of potential acid and alcohol building blocks, and the number of combinations is almost limit- less. Attempts have been made to classify esters in categories such as diesters and polyol esters or simple and complex esters, but the technology is far ahead of the terminology. The building blocks often define the maximum performance potential of an ester, while the manufacturing savvy determines whether the ester reaches its potential. For example, a synthetic neopolyol (alcohol) can produce an ester with outstanding oxidative stability, yet the oxidative stability of the ester may be diminished with inferior ingredients, contaminants or poor processing techniques. Thermo-oxidative Stability Oxidation is a degradation process that occurs when atmo- spheric oxygen reacts with organic molecules. For synthetic esters, this normally occurs at high temperatures, but it is possible to find esters that oxidize without heating. It has been known for centuries that linseed oils form a solid coating when exposed to air at ambient temperatures. These are called drying oils because they can be painted on wood and cured to a hard, protective varnish. Room-temperature polymerization relies on oxidative cross-linking of polyunsaturated fatty acids. While varnish enhances the appearance of antique furni- ture, it is not beneficial on industrial equipment. Synthetic esters are the best choice to provide clean, varnish-free lubri- cation at temperatures up to 600 degrees F (300 degrees C). The only way to engineer a superior high-temperature lubri- cant is to understand and eliminate structures that are oxidatively unstable. It has already been established that polyunsaturated fatty acid components must be eliminated, but unsaturated fatty acids such as oleates are commonly used in lubricants. In fact, oleates have many good properties including lubricity, low vola- tility, cold flow, biodegradability, renewability and a low price. The oxidative stability is also much better than that of drying synthetic esters: engineered to Perform Figure 1. The esterification reaction ULTIMATE INSPECTION Luneta, LLC - Booth #509 2 0 1 4 NORIA'S 15 TH ANNUAL CONFERENCE & EXHIBITION NORIA'S 15 TH ANNUAL CONFERENCE & EXHIBITION Toll Free 1-888-742-2021 Patent Pending

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