GB2098153A

GB2098153A - Insulating conductor rails

Info

Publication number: GB2098153A
Application number: GB8205952A
Authority: GB
Original assignee: Sigma Coatings BV
Current assignee: Sigma Coatings BV
Priority date: 1981-03-18
Filing date: 1982-03-01
Publication date: 1982-11-17
Also published as: LU83226A1; GB2098153B; DE3429853A1

Abstract

The lower part and the side parts of the conductor rail of a railway track are insulated by applying thereto a composition comprising an electrically- insulating mineral filler and an epoxy resin binder.

Description

SPECIFICATION Insulating conductor rails The present invention relates to a process for insulating conductor rails used on railway tracks.

A commonly found railway electrification system involves the use of a rail, lying between the two customary rails of the track, which acts as a conductor of the electric current for supplying motive power to the locomotive. Such a system offers certain advantages over an overhead line electrification system.

However it does have certain drawbacks. For example, during the maintenance or repairing of the tracks, metallic tools handled by the workers may accidentally come into contact with the conductor rail, the voltage of which exceeds 700 volts and may even reach 900 volts. This can cause serious accidents and may result in fatalities.

An object of the present invention is to overcome this difficulty by partially insulating the conductor rail.

Accordingly the present invention provides a process for the partial insulation of electrical conductor rails, which process comprises applying to the lower part and the side parts of the rails an insulating composition comprising an insulating mineral filler, and an epoxy resin binder.

The composition applied on the above-mentioned parts of the conductor rail must fulfil certain criteria in order to be effective. The composition must not only have an insulating action, but it must also possess adequate mechanical properties, typically properties concerning impact strength, abrasion resistance, oil or grease resistance and weather resistance.

The choice of filler not only depends on the desired insulating properties, but also on other factors, such as price and availability. Typically, one may use a pulverulent mineral filler such as sand, silicate, clay, kaolin, chalk, ground slate, or a fibrous filler such as glass fibrer and analogs thereof, or mixtures thereof. The amount of filler may vary within wide limits, ranging from 60% to 85% by weight and even more, based on the total weight of the composition. More generally the filler material is used in an amount ranging from 70 to 80% by weight, based on the total weight of the composition. According to an embodiment of the present invention, the filler material is constituted of quartz sand, preferably having a grain size (granulometry) from 0.1 to 0.3 mm.

The binder comprises a curable epoxy resin. The term "epoxy resin" used herein not only encompasses resins obtained from epichlorhydrins and poly-hydroxyorganic compounds, but also copolymers thereof, such as epoxy-silicone resins, together with mixtures constituted for a major part of epoxy resin, and for a minor part of an organic polymer compatible with the epoxy resin. Examples of suitable compatible organic polymers are polyamides, novolacs and analogs thereof which give an improvement in the properties of the coating applied to the rail. The amount of binder present in the composition may be from 15% to 40% by weight, based on the total weight of the composition. The binder is generally used in an amount which is at least 15% by weight, based on the weight of the filler.We have found that an amount of binder which exceeds 25% ofthe weight of the filler does not lead to a significant improvement in the qualities of the insulating coating.

The composition of the invention advantageously additionally comprises a thixotropic agent. If such an agent is included, the composition takes the form of a homogenous, stable product having a viscosity so that it may easily be applied, by any suitable means, including spray means. Moreover, after its application on the rail, the composition forms a coating which has no tendency to flow off the rail. Examples of thixotropic agents suitable for use in the composition of the invention include colloidal silica, particularly silica gel and amine-modified bentonites, and alkaline or alkaline-earth salts of higher fatty acids.

The amount of thixotropic agent added to the composition of the invention generally does not exceed 5% of the total weight of binder and mineral filler; it is preferably from 1% to 2% by weight.

The composition of the invention may also comprise pigments and other additives such as liquid diluents.

Some of these diluents, such as glycidyl esters of versatic acids are reactive. These different additives, when incorporated in the composition of the invention, are used in an amount which generally does not exceed 5% of the total weight of the composition.

The composition of the invention is applied on the lower part and on the side parts of a conductor rail which has been previously cleaned by means of sand-blasting, or treated by coating with a protective product. Before its application, the composition of the invention is previously mixed with a usual curing agent (thickener) for epoxy resins. The necessary amount of curing agent varies depending upon the type of epoxy resin used and on the nature (acidic or basic) of said agent. In general, the amount of curing agent is from 2 to 10% by weight based on the total weight of the composition. By way of example, a basic thickener may be used in an amount of from 4 to 6%, based on the total weight of the composition.

The following Example illustrates the present invention.

Example The following composition was prepared in a mixer fitted with a stirrer: Component % by weight epoxy resin (reaction product of epichiorohydrin and bisphenol A) 15% glycidyl ester of versatic acid 2.8% titanium dioxide 0.3% benzyl alcohol 1.8% colloidal silica 1.4 quartz sand 77.7% Prior to use, this composition was mixed with about 5% by weight of a basic thickener.

The resulting mixture was applied on the lower part and on the side parts of a conductor rail. An insulating coating was thus formed, adhering firmly to the rail and having a high mechanicaL strength.

Claims

1. A process for the partial insulation of electrical conductor rails, which process comprises applying to the lower part and the side parts of the rails an insulating position comprising an insulating mineral filler, and an epoxy resin binder.

2. A process according to Claim 1, wherein the filler is a pulverulent filler selected from sand, silicate, clay, kaolin, chalk, ground slate, or a fibrous filler selected from glass fibre and mixtures thereof.

3. A process according to Claim 1 or 2, wherein the amount of filler is 60 to 85% by weight, based on the total weight of composition.

4. A process according to Claim 3, wherein the amount of filler is 70 to 80% by weight, based on the total weight of the composition.

5. A process according to any one of the preceding claims, wherein the epoxy resin is an epoxy-silicone copolymer or a mixture of an epoxy resin together with a compatible organic polymer such as a polyamide, a novolac or an analog thereof.

6. A process according to any one of the preceding claims, wherein the binder is used in an amount of 2 to 10% by weight, based on the weight of mineral filler.

7. A process according to Claim 6, wherein the amount of binder is 4 to 6% by weight, based on the weight of mineral filler.

8. A process according to any one of the preceding claims, wherein the composition also comprises a thixotropic agent, such as colloidal silica, in an amount which does not exceed about 5% of the total weight of filler and binder.

9. A process according to Claim 8, wherein the amount of thixotropic agent is from 1 to 2%, based on the total weight of filler and binder.

10. A process according to any one of the preceding claims, wherein the composition further comprises pigments and other additives in an amount which does not exceed 5% of the total weight of composition.

11. A process according to Claim 10, wherein the additive is a glycidyl ester of versatic acid.

12. A process according to any one of the preceding claims, which includes the steps of adding to the composition a thickening agent for the epoxy resin at the time where the composition is ready to be used.

13. A process according to Claim 1 substantially as hereinbefore described in the Example.

14. Partially insulating conductor rails whenever obtained by a process as claimed in any one of the preceding claims.