This invention concerns a non-toxic biodegradable grease for lubricating mechanisms which are exposed to high load such as curving rails in railways and wheel flanges on railway cars and locomotives. The grease may also be used to lubricate moving parts on tracks such as switch blades. Further, the grease may be used for lubricating all sorts of equipment working in areas where full biodegradability is required such as in agriculture, forestry, and sports areas including golf courses, and in marine environments, for example for lubri- cating sluice and floodgate valves, lock gates and marine railways. In addition, the food and pharmaceutical industries are natural users of the grease, as they require non-toxic and harmless lubricating agents.

TECHNICAL BACKGROUND For some time the railway authorities in major countries such as Rail Track in Great Britain have installed so-called Lubricators on the outer rail in curves for the purpose of obviating pitting and ensuing collapse of the rail and the wheel flanges. These lubricators are devices that at the start of a rail curve release a lubricating grease to the passing wheels which then distribute the grease over up to 2 km of rail.

In order to function properly as a lubricating and protective coating on the rail and the wheel flanges a rail grease must fulfil certain requirements the most im- portant of which are: zit must have a paste-like consistency that makes it pumpable and spread- able along the rail ; zit must have a good adhesion and not be easily washed off by rain water; zit must have a high load bearing capacity being resistant to high pressure; zit must be stable and functional over a wide temperature range of from-20 °Cupto+100°C.

Traditionally, rail greases have been based on mineral oil containing emulsifiers and various additives to impart i. a. consistency and pressure resistance (load bearing capacity). However, with the extended use of lubricators in conse- quence of the introduction of high velocity trains i. a. Rail Track in Great Britain has now decided to use rail grease which is biodegradable and non-toxic.

A few products purporting to be biodegradable and non-toxic as well as to fulfil the general requirements to a rail grease have been put on the market. For ex- ample, one known product is based on synthetic ester oils containing lithium and calcium 12-hydroxystearate as thickeners and a sulfur-containing high- pressure additive, but this product has shown problems with insufficient adhe- sion so that the grease is not distributed far enough along the rail and is liable to water wash-off. In addition, this product is toxic due to the sulfur-containing ad- ditive. Another known product is based on rapeseed oil containing lithium 12- hydroxystearate. This product has a relatively large content of water and has shown limited adhesion at the lower end of the temperature range and a ten- dency to separate when stored. Yet another known product has exhibited infe- rior winter capabilities due to a high content of water.

SUMMARY OF THE INVENTION The non-toxic biodegradable grease according to the invention is based on glyceride oil, for example vegetable oil such as cottonseed oil, soybean oil, palm oil, palm kernel oil, rapeseed oil, cottonseed oil and linseed oil. Also oils of animal origin such as lard oils may be used. Preferably, the oil is a so-called RBD-oil (i. e. highly refined, bleached and deodorised) being liquid down to-20 °C or below and being stable to oxidation and other degradation by storage for minimum one year.

By using different oil types of vegetable origin, it is possible to impart particular high and low temperature properties as well as higher or lower carrying capacity and rust-preventing effect to the grease according to the invention. Also, the adherence, in particular to cold and wet surfaces, may be varied in this way.

To this glyceride oil is added emulsifiers comprising various stearates such as lithium, magnesium, calcium or zinc stearate; extreme pressure (EP) additives comprising long chain esters, in general esters of inorganic acids, and optionally

specific stearates, such as zinc stearate; and consistency-providing fillers com- prising bentonite and various meals. When the grease is to be used in daylight, an anti-oxidant is usually added, too The stearates are added as emulsifiers and thickeners. Some stearates have specific advantages, For example, calcium stearate imparts water resistance and a thick fatty consistency and also high temperature properties enabling the grease to be heated up to about 150 °C before becoming light-fluid. Zinc stearate besides contributing to the consistency also adds high pressure prop- erties.

The long chain esters are used as high-pressure additives. They are generally esters of inorganic acids such as phosphoric acid and sulfuric acid, in particular phosphate esters, and more particularly polyglycol, sorbitan and alkoxylated polyol esters of phosphoric acid.

The consistency-providing bentonite may be unactivated in which case an acti- vator comprising a small amount of propylene carbonate and water or an about ten fold amount of alcohol and water must also be added; or the bentonite may preferably be activated previously (so-called self activating bentonite) in which case no activator needs to be added. Of course, mixtures of unactivated and activated bentonite may also be used with correspondingly reduced amounts of activator.

A meal is also added as a filler to regulate consistency and retain the oil, part of which is absorbed by the meal particles and is squeezed out when subjected to pressure. The meal may be any kind of absorbent meal such as saw dust, wheat flour, maize flour (corn meal), soy meal, soy protein, rape meal, linseed meal, groundnut meal, desiccated coconut etc. Preferably, a meal containing some oil and thus being water repellent such as soy protein is used.

When an anti-oxidant is used, it may be any of the well known antioxidants for use with fats and oils, such as tocopherols, butylated hydroxyanisole (BHA), bu- tylated hydroxytoluene (BHT), galates and polyaromatic amines, e. g. diphenyl amine, or mixtures thereof, often in admixture with metal chelators such as ascorbic, citric and phosphoric acids or esters thereof. The anti-oxidants inhibit the oxidation of double bonds in the oil under the influence of atmospheric oxy-

gen and UV radiation. Thereby, the antioxidants have a strong influence on the hardening time of the oil, which is decisive for how soon or late the oil will solid- ify on the track. Thus it is possible, by adjusting the type and amount of anti- oxidant, to control the hardening time of the grease according to the invention.

This is important, as it provides a means of regulating the distance that the grease will be able to travel along the tracks. Similarly, it is possible by means of the same anti-oxidants to adjust the consistency and smoothness of the grease according to the invention so that it may also be used in train-carried systems for lubricating tracks and wheels when driving straight ahead on high- velocity trains.

As anti-oxidant is preferably used a mixture of propyl gallate (PG) and citric acid esters of fatty acid mono-and diglycerides in a ratio of from 10: 90 to 30: 70 by weight in a total amount of 100-5000 ppm. Other suitable anti-oxidants are bu- tylhydroxytoluene (BHT) or a polyaromatic amine such as diphenyl amine, also in an amount of 100-5000 ppm.

The lubricating capacity of the rail grease according to the invention may be fur- ther enhanced by the addition of a small amount of polytetrafluoroethylene (PTFE).

Thus, a useful embodiment of a grease according to the invention comprises the following, by weight: 70-85 % refined vegetable oil, 15-30 % stearate, 2-10 % long chain ester, 1-6 % activated (self activating) bentonite, 1-20 % meal.

Another useful embodiment of a grease according to the invention comprises the following, by weight: 70-85 % refined vegetable oil, 15-30 % stearate, 2-10 % long chain ester, 1-6 % unactivated bentonite, 2-16 % activators, 1-20 % meal.

If polytetrafluoroethylene is added, the amount will generally be in the range of 0.5-5 % by weight, preferably about 2 % by weight.

In preferred embodiments of a grease according to the invention the oil portion is a mixture of soybean oil with e. g. rapeseed oil or palm kernel oil in varying ra- tios between 90: 10 and 10: 90 by weight. By admixture of palm kernel oil the flow properties of the grease are enhanced, which entails a faster"travel"of the grease. By admixture of linseed oil the rust-preventing properties are enhanced.

A useful embodiment, designed for applications where the presence of sea wa- ter courses problems in terms of premature degration of the lubricant and corro- sion, comprises the following, by weight : 10-15 % linseed oil, 5-10 % rapeseed oil, 55-70 % soybean oil, 10-30 % stearates, 15-30 % esters, 1-2 % anti-oxidant, 2-7 % activated (self activating) bentonite, 1-10 % meal.

A useful embodiment, designed for wheel and flange lubrication where the lu- bricant is being applied via train mounted lubrication systems, comprises the fol- lowing, by weight: 5-15 % palm kernel oil, 60-75 % soybean oil, 10-30 % stearates, 2-20 % esters, 2-4 % anti-oxidant, 2-7 % activated (self activating) bentonite, 1-10 % meal.

EXAMPLES Example 1 A grease having the following composition is suitable as a rail grease for lubri- cating curving rails and wheel flanges on railway cars: soybean oil, RBD 72.0 % w/w zinc stearate 15.5 % w/w alkoxylated polyol phosphate ester 1. 1 % w/w bentonite, unactivated 4.8 % w/w propylene carbonate 1. 1 % w/w water 1. 1 % wlw soy protein 4.4 % w/w In this composition the propylene carbonate and water as activator for the ben- tonite can be replaced by the ten-fold amount of alcohol and water.

If desired, a small amount of polytetrafluoroethylene (PTFE) may be added, for example 2 % w/w PTFE.

The mixed grease has a paste-like consistency and a cream colour. If desired, a non-toxic dye may be added, for example a green fruit colouring.

Example 2 A grease having the following composition is suitable for applications where the presence of sea water courses problems in terms of premature degration of the lubricant and corrosion: linseed oil 10 % w/w rapeseed oil 5 % w/w soybean oil 55 % w/w calcium stearate 10 % w/w alkoxylated polyol phosphate ester 15% w/w propyl gallate (20%) + citric acid esters of diglycerides (80%) 1 % w/w

activated (self activating) bentonite 3% w/w soy protein 1 % w/w.

Example 3 A grease having the following composition is suitable for wheel and flange lubri- cation where the lubricant is being applied via train mounted lubrication sys- tems: palm kernel oil 6 % w/w soybean oil 60 % w/w zinc stearate 20 % w/w alkoxylated polyol phosphate ester 7 % w/w butyl hydroxy toluene (BHT) 2 % w/w activated (self activating) bentonite 2 % w/w soy protein 3 % w/w.