Patent Description:
Steel transport wheels and steel rails have many issues that require the control of friction between the two surfaces. Failure to control the friction in a positive manner can result in noise problems, extensive wear and sub-optimum performance (from an efficiency standpoint) caused by slip-stick oscillations due to negative friction between the two sliding steel surfaces. Accordingly, friction modifiers with high and positive friction to control sliding and rolling-sliding contact in steel-rail and steel-wheel transportation systems are well known in the art. Various patents from Kelsan Technologies describe friction modifier compositions (see, <CIT>; <CIT>; <CIT>; <CIT>; <CIT> and <CIT>). These patents describe a water-based system commercialized by Kelsan. In particular, <CIT> describes a liquid friction control composition for use in low temperature conditions, which comprises a rheological control agent, a consistency modifier and a freezing point depressant. The liquid friction control composition may also comprise other components such as a retentivity agent, an antioxidant, a friction modifier, a lubricant, a wetting agent, and a preservative. US patent application <CIT> relates to a method of reducing wear of one or both of two steel elements having surfaces in sliding or sliding-rolling contact. The method involves applying an HPF friction control composition to one, or more than one, contacting surface of one or both of the two steel elements. In a particular example, the HPF friction control composition comprises a rheological control agent, a lubricant, a friction modifier, and one, or more than one of, a retentivity agent, an antioxidant, a consistency modifier, and a freezing point depressant.

However, there are various problems with some of these water based friction modifier products. Examples of the problems are set out below:.

When ammonia is used in the water-based systems it can cause equipment to rust. Latex can cause problems with the gears and other movable mechanical parts as the compositions dry out. These compositions can form a skin over the liquid when it is pumped onto the rail head and the product is allowed to dry before taken up by a train wheel in a short period of time, and this can cause flowing out or splashing when contacted by the wheels of the train and accordingly not be carried down the track by the wheels of the train.

What is needed is a friction modifier composition for top of rail applicators that helps prevent rust on equipment with which it comes into contact.

Another object of the invention is to eliminate the latex skin on the prior art compositions such that the product when applied does not have a skin but instead forms a soft, non- drying deposit on the rail head. This soft non-drying deposit is picked up by the train wheel and carried down the rail to form a continuous film which controls the friction between the wheel and the rail in a positive manner.

In accordance with a further object of the invention, the friction control composition is embodied as a thixotropic gel or liquid that is thinned by shear and returns to its thicker more viscous state under static conditions. The thixotropy of the composition is used to facilitate application to the rail and to promote retention on the rail in its thicker state without formation of a skin. Unlike the prior art compositions discussed above, the composition does not form a skin over a low viscosity fluid that is ejected or pushed away by the rolling contact of the train wheels. Thus, the composition may be mixed for liquid-like flow during application to the rail as by conventional rail-mounted pump systems. Following rail application, the composition thickens under static conditions without drying or forming a skin, and remains positioned on the rail until sheared by train wheel engagement for distribution along the track during "carry down".

Another object of the invention is to have freezing point depressant that does not degrade the rheology of the composition.

Yet another object of the invention is to have a composition that causes the thickener (e.g. the clay) to go into a matrix such that it has improved dispersability.

Also, solid stick prior art compositions, such as the one described in, <CIT>, are well known in the art. But these solid stick friction modifiers have their own problems such as expense, and they need mechanical brackets and applicators to apply the product to the wheel. With solid stick compositions, practicality of use and duration of efficacy can also be a problem on freight trains.

Another object of the invention is to change the sliding friction from negative to positive.

Another object of the invention is to reduce noise by reducing or eliminating slip-stick oscillations between the wheel and rail.

Another object of the invention is to reduce lateral creep, which reduces lateral forces by changing the friction from negative to positive between the wheel and rail when a train, especially a freight train, goes through a curve. The benefits of reducing lateral forces include increasing the stability of the train as it travels down the track and in a related manner there is a reduction of the wear on the rail head, rail ties, and tie plates. Also, the bogey or truck goes around the curve in a much smoother fashion with reduction in jerking and jumping movement.

Another object of the invention is to reduce longitudinal creep wherein the wheel is sliding forward such as occurs in a transit system when the wheel is going around a mild curve. In longitudinal creep, if the wheels go slightly off-kilter, the locomotive pulls the wheel and the wheel slides in the longitudinal direction. If this creep happens all the time, you get short pitch corrugations. These are wear marks on the rail head in the nature of corrugations as encountered in a dirt road. By reducing this creep, the wheel will not slide as far and short pitch corrugations are inhibited.

Another object of the invention is to reduce spin creep wherein there is instability between the wheel and the rail, and the wheel is almost making a small circle on the top of the rail head.

The friction control compositions of the present invention reduce, if not eliminate, these three different types of creep by changing negative friction to positive friction. Lateral forces are one of the main problems in the heavy haul railroad in North America, and it is preferably reduced in accordance with the present invention. Similarly, longitudinal creep is reduced, if not eliminated, in order to inhibit the formation of short pitch corrugations in the rail. The reduction or elimination of spin creep is also desirable in order to reduce wear on the wheel and rail.

All of these creeps are small and are, for example, in the micron size range. The friction control compositions herein are effective to change the friction from negative to positive and thereby reduce or eliminate creep and the accompanying stick-slip.

The present invention relates to novel friction control compositions. More particularly, the present invention relates to friction control compositions that may be applied to steel-rails or steel-wheels that are potentially in sliding or rolling-sliding contact with each other.

The friction control compositions change the friction, or coefficient of friction, between the steel surfaces from negative to positive and thereby reduce or eliminate the lateral, longitudinal and/or spin creeps with a corresponding reduction or elimination of lateral forces and wheel-rail wear while increasing stability of the train.

In accordance with preferred embodiments of the invention, the skin forming retentivity agents of the Kelsan patents, supra, are avoided since skin formation is believed to inhibit uniform thixotropic properties, effective shear of the applied composition upon train wheel passage, and the achievement of improved carry down. Accordingly, the present compositions preferably rely upon the thixotropic properties to facilitate application of the composition, maintenance of position of the applied composition and subsequent train wheel shear to provide viscosities desirable for distribution of increased amounts of composition over longer carry down distances.

The preferred liquid embodiments of the friction control compositions include a reduced amount of water compared with prior art liquid compositions. The water content is reduced by the use of a water insoluble hydrocarbon found to further enhance the stability of the friction control composition.

The friction control compositions herein are described in greater detail with reference to illustrative compositions. Compositional percentages are in weight percent (w/w%) unless otherwise specified.

According to the present invention, there is provided a thixotropic gel or liquid for friction control for use on top of rail applications as set out in the claims. In particular, the formulation of a thixotropic gel or liquid for friction control for use on top of rail applications in accordance with the present invention is set out in the accompanying claim <NUM>. Further, the accompanying claim <NUM> provides a method of modifying the friction of a rail road track from negative to positive using a thixotropic gel or liquid for friction control having the formulation set out in claim <NUM>.

Because of some of the problems with water-based systems, various other compounds were experimented with as a partial replacement of water. It has been found that adding a water insoluble hydrocarbon to the composition (e.g. an isoparaffin such as SOTROL <NUM>) helps depress the freezing point and also helps stabilize or even improve the rheology of the formulation. This is especially true when the water insoluble hydrocarbon is compared with other freezing point depressants such as glycerin. Other water insoluble hydrocarbons that have environmental advantages over isoparaffins are vegetable oils, bio-based triglycerides and fatty oils such as canola oil. The oils do not have the same freezing point advantages as isoparaffins but they are environmentally friendly.

The addition of the water insoluble hydrocarbon (either isoparaffins or oils) in the partially water based system is counterintuitive because one would have guessed that it would not mix well with the water and would in all likelihood separate. However, we believe that the clay has receptor sites that allow the water insoluble hydrocarbon to bind onto the clay and keep the final product homogenous. The result is a composition that may contain lower amounts of water and in the case of isoparaffins lower amounts of soluble polyalcohol freezing point depressants such as glycerine. As pointed out above, water based systems have problem with maintenance of the system and typical freezing point depressants can cause negative rheology effects on the composition.

Turning now to <FIG>, the composition can be made in a batch process by adding the various components and then mixing them. Details of various methods of making the compositions are laid out in the examples below.

<FIG> shows the process steps graphically. In step <NUM>, charge water, water-insoluble hydrocarbon (e.g. SOTROL <NUM>) and a wetting agent (e.g. VAN WET 9N9) into a batch container. In step <NUM> slowly charge the rheology additive (e.g. VAN GEL B, lime) into the container. In step <NUM> this mixture is dispersed under high sheer to form a thixotropic gel. In step <NUM> slowly charge a water soluble polyalcohol freezing point depressant (e.g. glycerine) while mixing the composition. Step <NUM> requires adding the following components into the mixture while stirring: liquid or solid lubricant (e.g. superfine molybdenum, carbon black); liquid or solid friction modifier (e.g. barium sulfate and talc); corrosion inhibitor (e.g. ammonium benzoate); and biocide/fungicide (e.g. benzisothiazolinone). In step <NUM> this mixture is dispersed until grind is <NUM>-<NUM> micrometers on the Hegman gauge.

In the mixing process, the composition is formed as a thixotropic gel or liquid. The thixotropic composition may be mixed or otherwise sheared to reduce its viscosity and increase it flow properties to values sufficient for application as a liquid to the rail head using conventional pump systems. For example, the viscosity achieved by mixing may be in the range of from about <NUM>,<NUM> to about <NUM>,<NUM> cP as measured using a Brookfield viscometer in accordance with ASTM D <NUM>-02a. More preferably, the shear-mixed viscosity may be in the range of from about <NUM>,<NUM> to about <NUM>,<NUM> cP. The viscosity range may reflect the particular mode of application to the rail, and the foregoing range has been found satisfactory for pumping, spraying and other application techniques.

Upon termination of mixing and shear, the composition has a static thickness or cone penetration consistency in the range of from about <NUM> to about <NUM> tenths of a millimeter as measured using a standard cone test in an unworked condition in accordance with ASTM D <NUM> -<NUM>. More preferably, the cone penetration may range from about <NUM> to about <NUM> tenths of a millimeter. The static thickness or cone penetration consistency may be varied to reflect weather conditions.

The foregoing thixotropic properties have been found to sufficient to allow ease of rail application and increased distribution or "carry down" along the rail road track as compared with prior art friction modifier formulations.

By the term "water-insoluble hydrocarbon" we mean hydrocarbons that are not typically miscible in water based solutions. The insoluble hydrocarbon has a solubility in water of less than or equal to <NUM> wt %, or even more specifically, less than or equal to <NUM> wt %, or even more specifically, less than or equal to <NUM> wt %, at ambient conditions of about <NUM>°F and one atmosphere of pressure. Examples of such a water-insoluble hydrocarbon include isoparaffins such as SOTROL <NUM> (C13-C16 isoalkanes) and vegetable oils such as refined canola oil. Other potential water-insoluble hydrocarbons include bio-based triglycerides, fatty oils, poly alpha olefins such as DURASYN <NUM> and SYNFLUID PAO2, and synthetic esters such as di-octyl adipate and isopropyl oleate.

It has been found that the water-insoluble hydrocarbon gives the composition surprising advantages over water. Water based systems contain ammonia and this can cause equipment to rust. Also latex in water-based systems can cause problems with gears and other movable mechanical parts as the compositions dry out. Finally, the skin that can form over water based systems can cause flowing out or splashing when contacted by the wheels of the train and accordingly the friction modifier compound is then not carried down the track by the wheels of the train. Less water in the composition can help with all of these problems. We have found that replacing some of the water with a water-insoluble hydrocarbon is advantageous.

In the past as people have tried to lower the level of water in their friction control compositions they have at times attempted to replace some of the water with freeze depressants such as glycerine. However, this has the drawback that high amounts of water soluble polyalcohol freezing point depressants (e.g. glycerine) can have negative effects on the friction modifier composition since these type of freezing point depressants can cause rheology problems as the thickeners (e.g. clays) do not remain in the homogenous system.

We have found that replacing some of the water with a water-insoluble hydrocarbon (e.g. SOTROL <NUM>) can improve the overall composition by eliminating or minimizing the negative effects set out above. The addition of a water-insoluble hydrocarbon into the system is counterintuitive since by definition a water-insoluble hydrocarbon should not mix well with a composition containing water. However, surprisingly we found that certain water-insoluble hydrocarbons (e.g. SOTROL <NUM> and refined canola oil) mix well with the compositions described herein because the water-insoluble hydrocarbon goes into a matrix with the clay in the composition.

By the term "friction modifier" we mean a solid powder which changes the coefficient of friction, in this case, from negative to positive. Examples of such liquid or solid friction modifiers include talc and barium sulfate. The friction modifiers can be chosen from the following list of friction modifiers, but are not limited to these friction modifiers, WHITING (calcium carbonate), BLANC FIXE (calcium sulphate), mineral fibre, wallastonite powder, powdered cashew nut shells, calcium carbonate, aluminum oxide, amorphous silica, silica oxide, magnesium oxide, magnesium carbonate, lead oxide and coal coke.

By the term "solid lubricant" we mean a solid material that reduces friction between two sliding metal surfaces. Examples of two preferred lubricants are superfine molybdenum disulfide and carbon black (in some embodiment used in combination with one another). A non-exclusive list of other potential liquid or solid lubricants includes graphite and zinc stearate. However this invention is not limited to these lubricants only.

By the term "wetting agent" we mean a surfactant which assists the liquid to wet out the solids in the formula. One preferred example of such a wetting agent includes Triton X-<NUM>. A non-exclusive list of other potential wetting agents include, UNIVAR propylene carbonate technical", CO630, TEXAANOL, and TEXAPON P,.

By the term rheology agent we mean a clay or other substance that expands in water to produce a thixotropic mix. An example of one such rheology agents comprises clay such as VAN GEL B. Another example of a rheology agent usable with clay is hydrated lime. Other potential rheology agents are methyl ethyl hydroxy cellulose and ethyl hydroxy cellulose.

By the term freezing point depressant we typically mean a polyalcohol which when mixed with water, lowers the freezing point of water. One preferred example of such freezing point depressant includes SUPER KPO glycerine.

There are multiple ways of making the friction control composition disclosed herein. The composition comprises a) from about <NUM> to about <NUM> weight percent water; b) from about <NUM> to about <NUM> weight percent surfactant or wetting agent (e.g. propylene carbonate); c) from <NUM> to about <NUM> weight percent solid lubricant (e.g. molybdenum disulfide and carbon black); d) from about <NUM> to about <NUM> weight percent rheological control agent (e.g. clay and lime); (e) from about <NUM> to <NUM> percent water insoluble hydrocarbon (e.g. SOTROL <NUM> or canola oil) (f) from about <NUM> to <NUM> weight percent freezing point depressant (e.g. glycerine); (g) from about <NUM> to <NUM> weight percent solid friction modifier (e.g. talc and barium sulfate (h) anti-rust composition from about <NUM> to <NUM> (e.g. COUNTER RUST <NUM>®); and (i) from about <NUM> to <NUM> weight percent biocide or fungicide agent (e.g. nitrobutylmorpholine).

The following Examples <NUM> to <NUM> illustrate other preferred friction control compositions in accordance with the invention comprising:.

In one embodiment of the invention (See Example <NUM>), it has been found that adding a water insoluble hydrocarbon (as a non-exclusive example paraffinic or isoparaffinic solvent SOTROL <NUM>) helps depress the freezing point and also helps stabilize or even improve the rheology of the formulation. This is especially true when the water insoluble hydrocarbon is compared with other freezing point depressants such as glycerin. The addition of the water insoluble hydrocarbon is counterintuitive because one would have guessed that it would not mix well with the water based formulation of this invention and would in all likelihood separate. However, we believe that the clay has receptor sites that allow the water insoluble hydrocarbon to bind onto the clay and keep the final product homogenous.

In yet another embodiment of the invention (see Examples <NUM>-<NUM>) it has been found that adding a vegetable oil (as a non-exclusive example, refined canola oil) has some of the advantages of paraffins or isoparaffins such as SOTROL <NUM> but also include environmental advantages such as having a higher flash point and being biodegradable.

In yet another embodiment of the invention (see Examples <NUM>-<NUM>) it has been found that adding carbon black has some advantages. Carbon black was originally added as a solid lubricant to the formulation in order to lower the costs by using a less expensive lubricant than molybdenum disulfide. However, in addition to lowering of the cost of the formulation, it was surprisingly found that carbon black also helps with the stability of the composition (i.e. less separation) and can give a surprising increase in viscosity which in some embodiments is also very helpful. The carbon black can be added in ranges from <NUM> to <NUM>%.

In yet another embodiment of the invention (see Example <NUM>) we use an aprotic solvent exhibiting limited water solubility (e.g. propylene carbonate, solubility in water is <NUM>% at <NUM>° C. ) rather than the high amounts of glycerine used in other examples set forth infra. The propylene carbonate causes the thickener (e.g. the clay) to go into a matrix such that it has better solubility and can result in a higher friction product than can be achieved with glycerine. The propylene carbonate also helps as a freeze point depressant and improves product efficacy at lower temperatures.

In yet another embodiment of the invention (see Example <NUM>) it may be desirable in certain cold weather environments (e.g. at or below about negative <NUM> degrees centigrade) for the formulation to contain much higher amounts of freezing point depressants such as glycerine or propylene glycol. In these extremely cold weather environments it may be desirable to replace some (or even all) of the water insoluble hydrocarbons with a freezing point depressant. In at least one embodiment for the cold weather composition the ratio of the glycerine to water shall be at least <NUM>% glycerine to <NUM>% water. For other freezing depressants the ratio of the depressant to water may differ as a function of the freezing point curve. Based upon the freezing point behaviors of these fluid blends they are commonly called eutectic mixtures. Propylene glycol:water mixtures maintain freezing points at or lower than -<NUM>° at any ratio of <NUM>% or more propylene glycol. The ratio of glycerine:water shall be within the range of <NUM> - <NUM>% glycerine for cold temperature flow down to -<NUM>° F.

Disperse until grind is <NUM>-<NUM> on the Hegman gauge.

Disperse till grind is <NUM>-<NUM> on the Hegman gauge.

In the forgoing examples, the above mentioned thixotropic properties are achieved. That is, the shear-mixed composition has a thickness or viscosity in the range of from about <NUM>,<NUM> to about <NUM>,<NUM> cP to facilitate application to the rail using conventional techniques. The static composition has a thickness or cone penetration consistency of from about <NUM> to about <NUM> to maintain the composition on the rail for subsequent carry down by train wheel passage.

Performance data using the friction control compositions disclosed herein have confirmed the compositions to be surprisingly more effective than prior art top of rail friction composition modifiers. In the following tests, "fresh" trains having <NUM>,<NUM> pound loaded coal cars passed over an applicator arranged to apply the composition of Example <NUM>. The applicator was mounted to the field side of the track and pumped the shear-mixed liquid composition onto the rail head in a conventional manner and amount ahead of the test curve in the track. The composition returns to its static condition on the rail prior to engagement with the train wheels. The trains are "fresh" in that the wheels were not previously treated, but rather, the wheels were dry and had contaminants typically encountered in train transportation. The product is picked-up by the wheels and carried in the wheel-rail "contact patch" down the track to the curve to provide the benefits of the invention.

Referring to <FIG>, reduction of the lateral forces and achievement of a positive coefficient of friction or friction is shown for use of the friction control composition in accordance with above Example <NUM>. To that end, a dry wheel-rail system is compared with a wheel-rail system having the friction control of the present invention applied in liquid form to the top of the rail as described above.

<FIG> shows the distribution of the L/V ratio on the high rail of a <NUM>° curve for trail axles of the dry wheel-rail system and the wheel-rail system comprising the friction control composition of Example <NUM>. The friction control composition reduces the lateral forces as indicated by the lower L/V ratio. That is, the composition of Example <NUM> changes the friction from negative to positive, limits the creep of the wheel on the rail head and reduces the lateral engagement force and/or contact by the wheel flange with the gauge side face of the rail. Accordingly, the L/V ratio is reduced.

It has also been found that the composition of Example <NUM> tends to limit the variation of the L/V ratio so as to result in a closer grouping of data points. This is also believed to be related to the smoothing of the train travel and increased train stability.

Referring to <FIG>, the L/V ratio is shown for the lead axles of the cars of <FIG> for the dry wheel-rail system compared with the wheel-rail system having the friction control composition of Example <NUM>. As stability increases, the L/V ratio for the treated wheel-rail system decreases to values less than those of the dry wheel-rail system.

Referring to <FIG>, histograms show the lateral force distribution for the trail and lead axles of the train cars of <FIG>. As shown, the lateral forces are reduced.

Referring to <FIG>, the improved "carry down" of the compositions of the invention is shown. As noted above, carry down is how far the friction control composition is carried along the track in an effective amount from the application location. The further down the track the composition is carried the better for the rail road customer since the friction control composition works over a longer distance (e.g. stick-slip and creep are reduced together with the achievement of the other benefits described above. This can save rail road customers significant money by requiring fewer applicators and also less friction control product.

To that end, the L/V ratios for the wheel-rail systems of <FIG> were measured at a distance of <NUM> miles from the point of application and shown in <FIG>. It has been found in third party tests that the friction control compositions disclosed herein have carry down from two to three times further than prior art products. This dramatic increase is surprising to both the third party testers and potential customers.

Claim 1:
A thixotropic gel or liquid for friction control for use on top of rail applications comprising:
(a) from <NUM> to <NUM> w/w% water;
(b) from <NUM> to <NUM> w/w% rheology additive, wherein the rheology additive is a substance that expands in water to produce a thixotropic mix, the rheology additive being selected from the group consisting of clay, a mixture of clay and hydrated lime, methyl ethyl hydroxy cellulose or ethyl hydroxy cellulose;
(c) from <NUM> to <NUM> w/w% water insoluble component selected from the group consisting of isoparaffins, vegetable oils, bio-based tryglycerides, fatty oils, polyalpha olefins and synthetic esters;
(d) from <NUM> to <NUM> w/w% water soluble polyalcohol freezing point depressant;
(e) from <NUM> to <NUM> w/w % solid friction modifier, wherein the solid friction modifier is a material that changes the coefficient of friction, the solid friction modifier being selected from the group consisting of barium sulfate, talc, calcium carbonate, calcium sulfate, mineral fiber, wollastonite powder, powdered cashew nut shells, aluminum oxide, amorphous silica, silica oxide, magnesium oxide, magnesium carbonate, lead oxide and coal coke;
(f) from <NUM> to <NUM> w/w% solid lubricant, wherein the solid lubricant is a solid material that reduces friction between two sliding surfaces, the solid lubricant being selected from the group consisting of superfine molybdenum, superfine molybdenum disulfide, carbon black, graphite and zinc stearate;
(g) from <NUM> to <NUM> w/w% surfactant or wetting agent;
(h)from <NUM> to <NUM> w/w% anti-rust composition; and
(i) from <NUM> to <NUM> w/w biocide/fungicide agent.