In this article we will discuss about:- 1. Introduction to Biodegradable Lubricants 2. Aspects for Selecting Basic Materials for Biodegradable Lubricants 3. Applications.
Introduction to Biodegradable Lubricants:
The history of tribology in its wildest sense goes back thousands of years. Even in those days lubricants found their way directly into the environment, of course the quantities were much smaller than today. However, the lubricants employed exhibit close similarity to the biodegradable lubricants used today. It is, therefore, not astonishing that the formulating chemists have turned their attention to these old ideas. The number of raw materials available has risen enormously since then, and today more opportunities are available to select suitable ones.
This applies especially to the following applications:
i. Two-stroke outboard engine oils
ii. Chain-saw lubricants
iii. Mould release lubricants (concrete)
iv. Central lubrication of truck chassis (lubricating greases)
v. Mobile hydraulic equipment (leakages)
vi. Water economy (sewage plants, locks, turbines)
vii. Transporting plants (ropeways, skylifts)
viii. Railways, tramways (wheel flange, tracks, swathes)
ix. Corrosion preventatives
x. Open gears
xi. Metal working
xii. Lubrication of air tools
In these fields the use of alternative lubricants serves a useful purpose. With respect to the loss of lubrication, the technical requirements control the choice of basic materials. If the resort to natural, re-growing raw materials, such as rape seed oil, more stringent applications can be covered with synthetic raw materials (mainly esters), which in turn can be synthesized from natural resources.
Another point which has become important in the previous years is the changing customer knowledge and increasing awareness to tackle the ecological questions in the field of tribology. Formerly, the biodegradability was the only important criteria, today other aspects are equally important.
Aspects for Selecting Basic Materials for Biodegradable Lubricants:
In the selection of the basic materials and the formulation of the finished products, the following aspects are currently prominent:
iii. Toxicity (human)
iv. Ecotoxicity (fish, bacteria, plant)
v. Emission (exhaust)
Much has been said and written about biodegradable lubricants for the past several years. Manufacturers and blenders of these products present the necessity of considering biodegradables for use based on the importance of its biodegradability and non-toxicity. But performance issues like oxidation stability, anti-wear protection, hydrolytic stability, viscosity-temperature properties and cost factors—are usually only presented whenever these features provide an advantage to the particular manufacturer.
The two primary classes of biodegradable lubricants, vegetable oils and synthetics, have been described, re-described and well documented when compared with traditional mineral oil base lubricants (Table 7.1 and 7.2).
However, very little information has been provided by major oil companies or the manufacturers of these biodegradable products with regard to application guidelines or the maintenance of these products once they are in use as machine lubricants. Industrial users of these products must be prepared to treat biodegradable lubricants somewhat differently than standard mineral base oils.
In order to understand these application and maintenance requirements, it is first necessary to review the various types of biodegradable lubricants to point out their advantages and disadvantages.
Vegetable oils include corn, soybean, rapeseed (canola), sunflower, peanut, olive oil and others. In their natural form, these oils consist primarily of triglyceride molecular structures and as such they have performance limitations, most notably, poor thermal, hydrolytic and oxidation stability. For example, most natural vegetable oils cannot withstand reservoir temperatures greater than 80°C (176°F). In addition, water, even in small amounts of a few hundred parts per million, is the natural enemy of vegetable oils and can cause serious foaming and degradation problems.
In general, these oils also exhibit low cold-flow abilities. On the other hand, most of these natural oils have good lubricating qualities due to their polar nature. This provides good metal wetting attraction and also makes them good solvents for helping keep dirt and debris off metal surfaces. Their molecular structure provides for a high natural viscosity and viscosity index. Genetic modifications have also overcome much of the thermal and oxidative stability problems, particularly with soybean and canola oils.
The primary synthetic biodegradable lubricants available today include:
(a) Polyalphaolefins (PAOs):
These exhibit excellent low-temperature properties, but tend to shrink rubber seal materials.
These have good antioxidation characteristics and seal swell properties.
(c) Polyalkylene Glycols/Polyglycols or PACS:
PAGs can be both water soluble (ethylene oxide) and water insoluble (propylene oxide). Water soluble PAGs are ideally suited for fire-resistant lubricants. One disadvantage of PAGs is their tendency to emulsify water in certain equipment, such as gear boxes, which will cause foaming, sludge and corrosion.
A major disadvantage of both PAOs and PAGs is their poor solubility with regard to additives. Because the additives themselves must also be biodegradable, this limits the additives that can be used to formulate effective biodegradable lubricants from PAOs and PAGs.
Today, some manufacturers are blending diesters with PAOs to form base oils which are biodegradable, have good solubility, resist oxidation and have good temperature viscosity characteristics. Others are blending synthetic diesters with canola oil to provide similar results (Table 7.3).
Obviously, biodegradable lubricants are desirable for equipment used in certain resource industries, such as forestry, mining, petroleum exploration and production or wherever the lubricants themselves might come into contact with the environment.
The practical considerations associated with conversion from mineral-base lubricants to biodegradable fluids are often ignored. These biodegradable lubricants may be different in their characteristics, and the conversion necessary for their effective use is not quite as simple as draining the used mineral oil and dumping in the new biodegradable lubricant.
Before converting to a biodegradable lubricant, it is first necessary to consider the lubricating system’s operating and design characteristics, such as the operating temperature, pressures and flow rates, the type of sealing or hose materials used, the potential for contamination such as water or dust and dirt, and the quality of the existing filtration system.
A most important consideration that is also frequently ignored, is whether or not the new biodegradable fluid is compatible with mineral oil. When it is not, serious problems may result if all of the old mineral oil is not thoroughly flushed from the system before the new fluid is installed.
Symptoms of a poor or incomplete conversion to biodegradable fluids include severe foaming, leaking seals, plugging filters higher than normal wearing on some components (such as the hydraulic pump), and increasing operating temperatures.
What Goes Where?
So where are the best places to use each type of biodegradable fluid discussed above?
Applications of Biodegradable Lubricants:
For successful conversions in specific applications, users should consider the following:
These products are ideally suited to applications such as sawmill blade or chain drive lubrication where the lubricant is used on a ‘once through’ basis and where low toxicity is required. They are also well-suited for use in low to medium pressure hydraulic systems, or lightly loaded gear drives where the operating temperature does not normally exceed 60°C (140°F) and where there is little chance of water ingress or high contamination.
Where the threat of contamination exists, filters must be inspected more frequently due to the lower filterability of these fluids. Gear boxes and hydraulic systems should be thoroughly flushed to remove debris, sludge and silt prior to the application of vegetable-base lubricants to avoid any unnecessary incompatibility potential. There may also be some negative reaction to sealing materials such as neoprene and nitrile.
Biodegradable PAOs are finding increased use as hydraulic and engine oils, particularly in cold- climate applications and where hydraulic pressures are high. These oils are also finding selected use as gear lubricants due to their ability to provide lower operating temperatures and their lower coefficient of friction, both of which help to reduce wear. These products are generally compatible with mineral oils and as a result, there is no requirement for extensive flushing prior to the conversion unless required by the manufacturer. PAOs have a negative effect on certain sealing materials causing shrinkage, so initial leakage may be a problem.
These biodegradable fluids are excellent lubricants for compressors and turbines. Diester fluids may have a negative effect on certain varnish or paint surfaces, due to their exceptional solvency and detergency, so it would be wise to remove the paint, from any internal contact surfaces such as the reservoir, prior to conversion.
In addition, these fluids can negatively affect sealing materials, and fluorocarbon seals should be considered for these applications.
PAGs can be either polyethylene or polypropylene oxide-based, with water solubility differing according to type. Polyethylene-based PAGs are highly water soluble, are poorly miscible with mineral oils and are very polar. As a result, thorough flushing of the system should be carried out prior to the conversion from mineral oil-based products. Their water solubility helps to provide biodegradability, but also provides a disadvantage in lubricant applications, because free water contamination tends to occur quickly.
Additionally, the high specific gravity of these fluids tends to elevate solid particle contaminant retention (that is particles are less prone to settle). To offset this threat, the filtration systems should be modified or upgraded to ensure that bearing surfaces are not exposed to high contaminant levels. Three-micron filters installed in a side-stream are beneficial in controlling contamination in hydraulic applications.
Operating temperatures must be controlled in order to avoid excessive and unnecessary evaporation of these water miscible fluids. The recommended operating temperature should be kept within a range of about 50°C to 60°C (122°F to 140°F).
Another consideration when using biodegradable water-based and water soluble fluids in a hydraulic application is cavitation damage to pressure relief valves which may be required to remain in the discharge or open position for long periods. Vapour phase cavitation can cause erosion of the valve seat due to high vapour pressure, which can lead to premature relief valve failure. Proper valve selection prior to conversion should be considered.
Keeping it going:
It has been said that the lubricant contained within a piece of machinery is also a component of that machine. Therefore, its condition must be maintained and monitored for condition just like the machine itself. Unfortunately, the lubricant’s condition is frequently ignored until a problem arises and only then does anyone seem concerned about the maintenance of the lubricant.
One cause for this situation is the tendency by many in industry to arbitrarily extend oil drains without giving any thought to the consequences. In most cases, biodegradable lubricants, such as synthetic PAOs or vegetable oils, can cost three, four or five times the price of mineral oil. The users frequently attempt to recoup their initial investment by ignoring common sense and extending oil drains without a regularly scheduled, carefully selected oil analysis programme.
Generally speaking, biodegradable oils should be maintained and monitored during use just like mineral-base oils. They must be kept cool, clean and dry (water-free) and their condition should be monitored on a regularly scheduled basis using readily available oil analysis techniques.
Specifically, biodegradable lubricants must be monitored for viscosity (at both 40°C and 100°C); free water content (using an accurate technique such as the Karl Fischer test); acid number (which can provide an accurate indication of any increase in oxidation) and solid particle contamination (using particle-count testing techniques).
Any result which indicates that a problem is developing must be investigated and the condition corrected, if satisfactory service life from biodegradable lubricants is to be achieved.
This fact and ever increasing environmental awareness led to the development of environmentally harmless, i.e., biodegradable as well as ecologically non-toxic lubricants at the beginning of 1980s.
In fact, biodegradable lubricants were first used in Finland in late 1970s where it was observed that the boats with outboard engines were polluting lakes. Immediately, there was reaction from Japan and some European countries who switched over to biodegradable lubricants. At the same time, there was chaos in Norway and Sweden regarding pollution caused by chain-saw lubricants. These incidents ultimately led to manufacturing of biodegradable lubricants in different corners of the world.
Microbes present in soil and water have natural capacity to degrade material by incorporating oxygen into their hydrocarbon chains by means of enzymes. By these processes, they yield energy for their growth. Though material of natural origin is more biodegradable the synthesized materials are not easy to cut down and they occupy space in water and soil, thereby posing danger to living creatures. This biodegradability is grouped into two parts, namely primary and ultimate biodegradability.
Primary biodegradability is the conversion of original substances into new products, which, in most cases do not possess the same chemical properties. Ultimate biodegradability is the complete conversion of original substance into new products like carbon dioxide, water, new microbial biomass and simple inorganic substance.
In 1980, Coordinating European Council (CEC) developed a method to determine biodegradability of substance, the time when biodegradable engine oils were developed for outboard marine engines. So, International Council of Marine Industry Association (ICOMIA) started using this particular test for judging suitability of biodegradable marine ‘two stroke’ oil and set a criterion of 67% degradation and above in CEC test as a standard for classifying products as biodegradable.
Since inception, this CEC test has been widely used world over to test two stroke outboard engine oil. A series of tests have been developed to evaluate the ultimate biodegradability in the Organisation for Economic Cooperation and Development (OECD) countries. It involves measurement of various parameters after the test substance is mixed with our inoculum containing microorganism for a period of 28 days.
However, one must keep in mind that biodegradability does not mean total eco-friendliness. The biodegradability of a material is a measure of substances’ fate in the environment, not its impacts. There are many aquatic substances which on biodegradation produce byproducts which are toxic to aquatic life. Of course, biodegradability definitely is an indicator of eco-friendliness. There are several other aspects to judge environmental impacts, e.g., water protection, soil protection, toxicity, emission threshold, safety at work, etc.
Mainly, two types of biodegradable lubricants are presently in existence. Vegetable oil types include corn, soybean, rapeseed, sunflower, peanut, olive and other such oils. In their natural form, these oils consist primarily of triglyceride molecular structures and as such they have performance limitations, most notably, poor thermal, hydrolytic and oxidation stability.
For example, most natural vegetable oils cannot withstand reservoir temperatures over 80°C. In addition, water, even in very small quantities of a few hundred parts per million, is the natural enemy of vegetable oils and can cause serious foaming and degradation problems. In general, these oils also exhibit low cold flow abilities.
On the other hand, most of these natural oils have good lubricating qualities due to their polar nature. This provides good metal wetting attraction and also makes them good solvents for helping to keep dirt and debris off metal surfaces. Their molecular structure provides for a high natural viscosity and viscosity index.
Genetic modifications have also overcome much of the thermal and oxidative stability problems, particularly with soybean and canola oils.
Theory is that polyalkalene glycols (PAGs) perform better in worn gears than other lubricants due to the lubricity factor involved. But there are a few reasons why a properly formulated PAG might perform better than PAOs warm gears in specific circumstances than an equally properly formulated mineral oil in a sliding contact zone. Gear oils based on glycol stocks are highly polar.
The extra surface affinity provides low frictional coefficients without the use of additives. This could be referred to as ‘lubricity’. Once fortified with the right complex of additives, glycol lubricants can provide exceptional load-bearing performance (film strength). Glycols can also have a superior pressure- viscosity coefficient, the measure for a lubricant’s EHL film formation capability.
At temperature < 80°C, mineral oil gives thicker films than PAO lubricant, and at Temperature < 57°C mineral oil gives thicker films than PAG lubricant. In the temperature range from 70 to 90°C, there is only 5 per cent difference between EHL film thickness of mineral and PAO lubricants. In this same temperature range, a PAG lubricant gives thicker films ranging from 16 per cent to 37 per cent thicker than mineral oil.
A major disadvantage of both PAOs and PAGs is their poor solubility with regard to additives. Since the additives themselves must also be biodegradable, this limits the additive types which can be used to formulate effective lubricants from PAOs and PAGs.
Today, some manufacturers are blending diesters with PAOs to form base oils which are biodegradable, have good solubility, resist oxidation, and have good temperature viscosity characteristics. Others are blending synthetic diesters with canola oil to provide similar results.
Thus, biodegradable lubricants are especially useful in marine, forestry, mines and oil exploration fields. For example, logging, road building and other forest activities require motorized equipment. Antifreeze fuels and lubricants used in machinery can potentially pollute lakes, stream, wetlands and ground water. Planning for forestry operations should include practices to handle solid and liquid wastes generated in the field.
The following tips will help to prevent non-point source pollution from fuels, lubricants and wastes during forest management activities:
1. To use biodegradable lubricants whenever practical. Biodegradable lubricants are less toxic than other lubricants but still need to be disposed of properly.
2. To maintain equipment regularly. Check hoses and fittings to prevent leaks or spills.
3. To designate specific area for equipment maintenance and fuelling and locate these areas on level terrain, a minimum of 100 feet from all streams and lakes.
4. To collect all waste lubricants, containers and trash. Store them in leak-proof containers until they can be transported off-site for recycling, reuse or dispose at an approved site. It is illegal to dump fuel and lubricants on the land or waters.
5. To separate all fluids and materials and keep in different labelled containers to avoid creating ‘hazardous waste’ and expensive waste disposal. The following best management practices are general guidelines for spills of fuel and lubricants used in forestry field operations. These practices compliment specialized training given to person using pesticides or other hazardous materials.
6. To maintain a spill-containment and cleanup kit appropriate for the materials on the operation.
At a minimum, a kit for petroleum products should include:
i. Plugs and clamps to control a hydraulic line break.
ii. A container to catch leaking fluid.
iii. A shovel and absorbent materials such as sawdust to absorb fluid, especially useful in the winter when soil is frozen.
If a spill should occur, do the following in order:
1. Protect yourself and others. Wear protective clothing and equipment appropriate for any hazardous materials on the operation. Avoid contact with any toxic drift or fumes that may be released.
2. If you are able, control the spill, stop the leak.
3. If you are able, contain the spill; keep it from spreading. Use absorbent materials, such as sawdust or loose soil, to fluid. Place a bucket under a hydraulic hose break. Keep the spills fluid into lakes or streams.
4. Isolate the spill material.
5. Report all hazardous substance spills immediately.
They are also in demand for fishing, water-sports, building work, metal working, etc. Accordingly, oils are formulated by proper selection of base oils i.e., vegetable oils or synthetic oil and blended with 1 to 8% of additives to boost the performance with respect to corrosion inhibition, thermal stability, anti-wear, anti-foaming and cold flowing properties.
When selecting additives the formulation chemist is nowadays more severely restricted than with the base fluids. In the groups described, there are few additives that fulfil all criteria (ecology) and at the same time, when applied in a minimal concentration, achieve sufficient performance in the finished product. For this reason additives free from mineral oil and heavy metal should be used.
The response of vegetable oils and synthetic esters may be regarded as good. With glycols the scope is far less in this respect. Additives must be optimized for the base stock and the application. Solubility is often an issue when moving between synthetic and minerals oils. As esters add the polarity required to dissolve the additives, addition of organic esters to poly-a-olefins is desired.
The possible applications for ecologically harmless lubricants are very numerous. New applications are always being found and corresponding lubricants developed. Biodegradable lubricants are available for almost every application. On the other hand, these alternative lubricants do not always come up to performance expectations, so that their use is then sometimes limited.
The future job of the formulation chemists and manufacturers of additives must, therefore, concentrate more on optimizing the performance of alternative lubricants and additives. It is required to take the entire tribo-system into account i.e., design and environmental effects.
Then the following points could be examined:
i. Machines- Materials should be used which can be recycled and whose manufacturing does not give rise to undue ecological problems. Permanent lubrication should be used for oil changed at very long intervals. Lubricant capacities should be as small as possible with very low losses.
ii. Lubricants – Ecological harmless, high performance, Recyclable.
iii. Disposal – Covered by laws and economical, partly recyclable.
The input cost of biodegradable lubricants are higher than conventional lubricants. The application of relatively cheaper biodegradable lubricants, which are based on vegetable oils is one relatively poor in performance with respect to thermal and oxidation stability and seal compatibility. In many countries, the application of biodegradable lubricants is not supported by government legislation. There are a few reasons for which the users are less tempted to use biodegradable lubricants.
It is worthwhile to note that there are different schemes being implemented in different countries to encourage use of eco-friendly biodegradable lubricants. ‘Blue Angel’ in Germany, ‘Environmental choice’ in Canada, ‘Green Seal and Green Cross’ in USA, ‘White Swan’ in Nordic countries and ‘Eco-mark’ in Japan are the examples. In our country, a committee of experts in industries and research centres are working on ‘eco-mark’ scheme which is presently under preparation.
Biodegradable Gear Oil:
Gear oils with enhanced biodegradability are showing the same promising characteristic as biodegradable motor oils and other eco-friendly lubricants, a team of researchers reported to the American Chemical Society. Their research clearly shows that more biodegradable gear oils perform as well or better than conventional oils in key laboratory tests. Even in industry, there still are deeply rooted remnants of the perception that using eco-friendly lubricants means sacrificing performance. But in reality, you do not have to give up performance to get biodegradability.
One major barrier to wider use of biodegradable gear oils is its cost, not performance. In some cases, biodegradable synthetics like polyalphaolefins (PAOs) cost four to five times more than conventional mineral oils.
To gain wide acceptance, these biodegradable oils must perform as well as currently used minerals oils and there must be some incentive to pay the higher cost. Obviously would be government regulations, encouraging or requiring wider use of biodegradable lubricants are a future possibility in the United States. Thus, the importance of research in industrial and university setting, to assure that appropriate biodegradable lubricants are available domestically.
Marine gear oils sometimes leak into a vessel’s bilge water. When bilge water is pumped into the ocean, the gear oil goes along. The scientists conducted the study at the request of a commercial firm. It was interested in finding a gear oil that would biodegrade in the ocean after a few days, rather than remind as a slick that could contaminate land or wild life.
Researchers compared PRL 4648, a mineral oil currently used for marine gear applications, to an enhanced-biodegradable formulation they called ‘Blend A’. It consists of a mixture of PA04 base stock and a fully formulated PAO65. ‘Blend A’ was about twice as biodegradable as the mineral oils product, PRL 4648.
Synthetic oils like PAOs are a promising alternative to mineral oils in terms of performance and biodegradability. Synthetic lubricants are chemically uniform and consist of well-defined products produced under very controlled processing conditions. Minerals oils, in contrast, tend to consist of a variety of molecular types. Synthetics also tend to have a lower coefficient of friction that reduces wear, and a longer service lift than mineral oils.
Some PAOs likewise show enhanced biodegradability when compared to mineral oils. Biodegradability means decomposition by microorganisms in the environment. Researchers use several different tests to rank biodegradability, with the CEC-L33-T82 test currently one of the most widely accepted. Run over a period of 21 days, it measures bacterial conversion of component organic compounds in an oil into other chemical species. The PA04 base stock is one of the more highly biodegradable PAOs, with a biodegradability of about 65 per cent. (PAOs usually are named on the basis of their viscosity at 100°C. PAO4, for instance, has a viscosity of 4 centiStrokes at 100°C.)
When researchers compared performance of the mineral oil-based gear oil (PRL 4648) and their PAO formulation, ‘Blend A’, in standard laboratory tests, they tested wear and scuffing performance with a four-ball wear test machine. The machine uses four AISI E52100 steel balls to evaluate sliding wear. One ball is rotated on three fixed balls under specified conditions of load, speed, and temperature. Researchers then evaluate the ‘wear scar’ that the rotating ball makes on the fixed balls. The scar simulates wear that occurs in the machinery under real-world conditions.
Use the machine in a sequential wear test develops to evaluate lubricants for hydraulic applications. The procedure determines the wear scar at 30-minutes increments. After each increments, the balls are rinsed with tetrahydrofuran, naphtha and acetone. The oil cup is then refilled and the test is re-run for another 30 minutes. Researchers then take another wear scar reading, rinse the balls again, and perform the test a third time with white oil.
Results showed that the enhanced-biodegradability synthetic PAO blend out-performed the traditional marine mineral oil. Wear scar diameters with the PAO blend were about 0.1 mm smaller than with the mineral oil. They also tested the gear oils with a related procedure, the four-ball scuffing test. It uses a set up similar to the four-ball wear test, but with different load conditions, a speed of 600 revolutions per minute, and a temperature of 75°C. Once again, the biodegradable PAO blend performed better than the conventional mineral oil. For the mineral oil, the scuffing load was about 70 kg, while the synthetic biodegradable gear oil has a scuffing load of 100 kg.
Another test measured corrosion resistance of the two oils, comparing their rust preventing characteristics. Researchers used ASTM test D665, procedure B, which involves heating oil to 60°C in a beaker. A steel specimen is placed into the oil for 30 minutes, followed by addition of salt water solution. The steel stays in beaker for 48 hours, and researchers then examine it for signs of corrosion. No corrosion was present on the specimen immersed in the mineral oil.
Initially ‘Blend A’ may be subjected to corrosion problem while testing which can be corrected by anti-corrosion additive.
The PAO blend has superior low temperature performance, which is major advantage of synthetics. The mineral based gear oil had a pour point of minus 10°C, compared to minus 35°C for the biodegradable ‘Blend A’.
Lower temperature performance is one important areas of concern regarding use of vegetable oils in biodegradable lubricants. Scientists are studying rapeseed and other vegetable oils, and vegetable oils blends, as biodegradable gear oils.
Their research also encompasses many other applications of lubricants and biodegradable lubricants.
Vegetable oil do have widely-recognized advantages over conventional mineral oils, in addition to biodegradability. They are, for instance, non-toxic and available for domestic renewable sources. But vegetable oil pour points are not as good as PAOs and can be high as 10°C.
Oxidation is another problem, although it is less significant for gear oils than engine oils. Gear oils typically operate at significantly lower temperatures and result in inherently less oxidation of the oil. Vegetable oil provides even more biodegradability than PAOs, typically greater than 80%. If the two disadvantages could be eliminated- the high pour points and poor oxidation stability-vegetable oils could provide many biodegradable gear oils.
Fundamentally the structure of highly biodegradable hydraulic oil is the same as of those based on mineral oil. When choosing the components, however, ecologically unquestionable types are preferred.
The following factors read as ecologically unquestionable:
i. Biodegradable (CEC-L-33-A-93, OECD- or other methods)
ii. Intermediate degradation products, non-toxic
iii. Water hazard class 0 or 1 (toxicity for mammals, fish and bacteria)
iv. No skin irritants or sensitizers
v. Where possible maintains the CO2 equilibrium
vi. Energy-saving manufacture
Actually these factors are included in today’s well-known ‘eco-labels’ like the Blue Angel, White Swan, Maple Leaf and so on. The most important criteria in the determination of the hydraulic fluid to be used are the optimal operational viscosity and the use of the correct additive. Except for a few special applications the viscosity ISO VG 46 has come out on top. The excellent viscosity-temperature relationship of the biodegradable hydraulic fluids closely conforms to the efforts of rationalization (simplification).
ISO VG 32 can in practice be covered in the most cases by ISO VG 46. The noteworthy viscosity-temperature relationship with an excellent pour point also goes a long way towards meeting these efforts. When the viscosity ISO VG 68 is specified it is usually advisable to be more cautious. High thermal loads often prevent the operational viscosity from being reduced.
At the moment there are no binding stipulations or even drafts for the generation of new operational fluids. In the laboratories of the oil manufacturers, comparative investigations are carried out according to the guidelines for mineral oil. Exhaustive practical tests will have to confirm their suitability.
As yet nobody, neither the mineral oil industry nor users, can claim to possess years of experience in the field of biodegradable hydraulic oils. Machinery manufacturers make only initial releases grudgingly (guarantee maters). At present, their test departments are overrun with applications for tests and consequently the waiting lists are becoming longer and longer.
Hydraulic oils, which are biodegradable to a high degree, have enjoyed a steadily increasing demand. The products based on rape-seed oil which were the first to appear on the market gave rise to difficulties with some equipment users. Rendered unsure by their experience, their attitude towards the “ester philosophy” was one of skepticism, extending to very great skepticism.
Some filter manufacturers complain about adhesives being dissolved. A remedy in such cases may be to take very great care when selecting the base fluids used. Developing a new product or range of products has proved to be highly successful. The aim of developing this hydraulic oil is to create a product, the behaviour of which in service would be in no way inferior to that of hydraulic oils based on mineral oil.