Biodegradable greases bearing environmental concerns

According to recent reports, a newly-developed biodegradable grease has shown it can match traditional grease performance in bearing applications. It also meets the increased demand for environmentally friendly products in the engineering industry and is believed to be the first of its kind on the open market.

SKF recently launched its "green" grease, known as LGGB 2, which is a general-purpose lubricant for most bearing applications. This says the company, contrasts with other biodegradable and non-biodegradable greases, which often require one particular type of grease per application.

The application of biodegradable lubricants and greases has been studied at the SKF Engineering and Research Centre and has led to a formulation that can meet the stringent demands of a range of engineering applications without adverse effects on the environment.

Although only a portion of lubricants used in industry may pose a threat to the environment, this can add up to several millions tonnes worldwide. In particular, equipment users in the construction, earthmoving, forestry and farming industry are increasingly seeking "green" solutions because environmental contamination has become an issue.

Until recently, it was thought that current generations of biodegradable and low-toxicity lubricants could not satisfactorily meet the requirements of rolling bearing applications. The grease is based on synthetic ester oil, lithium/calcium thickener and other biodegradable ingredients, and reports a low toxicity.

Understanding biodegradability

In regards to the development of clear parameters on material breakdown of a 'green grease', the understanding of the mechanisms involved in biodegradation is vital.

In biodegradation, the material is gradually broken down through the metabolic action of such living organisms as bacteria, fungi, yeast and algae. Hydrocarbons, which are the main constituent of biodegradable lubricants, are transformed into carbon dioxide and water by this process.

Naturally, this process is not entirely predictable as it can be influenced by the mix of living organisms present, the ambient temperature and the humidity. It can happen that a material that may easily degrade under one set of circumstances may not readily degrade under others.

The minimum basic requirements are sufficient bacteria population, correct oxygen levels and a suitable temperature range. The rate of degradation is also affected by such factors as fluid viscosity, sunlight, mineral salt content, availability of nitrogen, pH levels, solubility and the ability of the bacteria to adapt to the source of oil nutrient.

Ultimately, of course, the lubricant should be reduced to its simplest natural form while leaving no harmful by-products that could have a detrimental and long-term effect on the local environment.

Traditional lubricants that are based on mineral and synthetic oils are ultimately biodegradable though the slow rate of decomposition means, under some conditions, that they can exist as a contaminant in groundwater for close to a century.

Testing considerations

Any tests to establish the biodegradable performance of a new lubricant have to bear in mind the often unpredictable and complex processes at work.

With no single universal standard that clearly defines biodegradability, SKF opted to use a number of existing tests. These were used to establish whether toxicity and biodegradability occurred within a reasonable length of time.

From its studies, SKF has found that esters or vegetable fluids formulated carefully into lubricants perform well in real world applications. In particular, the researchers found that a combination of synthetic ester oil and a lithium/calcium thickener resulted in good properties as defined in terms of water and corrosion resistance without the need to use toxic additives.

The LGGB 2 grease formulation for example, based on these chemical constituents has shown that it performs well with ball, roller and plain bearings. This is a significant development, as conventional lubricating greases are normally considered suitable for only one bearing type. Each bearing class has a different contact surface, which can affect lubricant performance.

For instance, the lubricant film in ball bearings has a point contact; in roller bearings it is a line contact; and for plain bearings it is full contact over the area. SKF selected four different formulations that were subjected to stringent bearing tests.

From these tests, it was found that LGGB 2 offered superior performance over a range of operating conditions and bearing types and established a steady operating temperature set at 90°C.

Keeping it green

Due to extensive testing and its own in-house specialist knowledge of bearing behaviour and the effects of lubrication, the company has now launched its first green grease, which is believed to be the first of its kind on the open market.

The company says the new grease is part of its continued commitment to the environment and hopes this well lead to the adoption of sound environmental practices within the entire bearing and lubrication industries.