GB1574749A

GB1574749A - Hoses

Info

Publication number: GB1574749A
Application number: GB1650377A
Authority: GB
Original assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Current assignee: Pneumatiques Caoutchouc Manufacture et Plastiques Kleber Colombes SA
Priority date: 1976-04-22
Filing date: 1977-04-20
Publication date: 1980-09-10
Also published as: BE853894A; AT359344B; FR2349094A1; FR2349094B1; DE2717447A1; ES458067A1; ATA277277A

Description

(54) IMPROVEMENTS IN OR RELATING TO HOSES (71) We, PNEUMATIQUES, CAOUTCHOUC MANUFACTURE ET PLASTI QUES KLEBER-COLOMBES, a French Body Corporate, of Place de Valmy, 92700 Colombes, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to hoses which, like those used in transferring hydrocarbons, not only need to be able to operate under both suction and pressure, but also are of the kind whose electrical resistance, when expressed per unit length of the hose, falls within the range from 104 to 2 x 106 ohms per metre and in which the only metal members included in the reinforcement of the hose, are one or more helices.

It is well known that to produce an electrically conductive hose it is merely necessary to form one of the parts of the hose, generally the lining (that is to say the inner layer which is in contact with the fluid being conveyed) from a rubber-based mixture whose formulation has been so designed that it is a good conductor of electricity, and to ensure that this layer is in contact with at least one metal part of the connectors at each of the ends. Rubber-based mixtures whose volume resistivity is much lower than that of normal mixtures are well known to the man skilled in the art and are called conductive mixtures.

It is also well known that one of the simplest means of achieving the resistance to collapse which is required to enable,a hose to operate under suction is to arrange for a metal helix of suitable pitch and cross-section to co-operate with the wall of the hose. Instead of a metal helix it would also be possible to use a non-metallic helix such as one made of plastics material, but in this case the cross-section of the helix would be such that the thickness of the wall, and thus the weight, bulk and cost of the hose, would be considerably increased while the flexibility of the hose would be reduced to a degree which would often prove unacceptable. The production of a hose with a non-metallic helix is thus, in many cases, possible only in theory.

It has been thought that to produce a suction hose having a given electrical resistance per unit length, it is enough to combine the following two known means: a) by making the lining or some other part of the hose from a conductive mixture such that the hose has the requisite electrical resistance and by taking steps to ensure that the part made from the conductive mixture is in contact with the metal parts of each end connector, and b) by including a metal helix which co-operates with the wall of the hose, which is separated from the part of the hose made of the conductive mixture by a layer made of an ordinary non-conductive mixture (that is to say made of a mixture of far lower electrical conductivity). and which is not in contact with any of the metal parts of the end connectors.

In effect. in a hose constructed in this fashion, the electrical current would have to flow mainly in the lining made of a conductive mixture since the metal helix, being embedded in a non-conductive mixture and having no contact with the metal parts of the connectors, would either have no electrical function to perform or only a minor one.

The invention consists in a flexible hose of the kind whose electrical resistance, when expressed per unit length of the hose, falls within the range from 104 to 2 x 106 ohms/metre and in which the only metal members included in the reinforcement of the hose, are one or more helices, wherein the metal helix or helices of the reinforcement of the hose are provided with a layer of electrically insulating material, and the hose includes a continuous member made of an electrically conductive rubber-based mixture, said member being the sole conductor of electricity in the hose.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show a known kind of flexible hose and one embodiment of a hose according to the invention by way of example and in which: Fig. 1 is a longitudinal section through part of a prior art hose and Fig. 2 is a longitudinal section through part of a flexible hose according to the invention.

Referring now to the drawings, the prior art hose shown in Fig. 1 consists of a tube 1 made of a conductive mixture based on rubber. The formulation of the mixture and the thickness of the tube are made such that, given the diameter of the tube, the resistance of the latter lies within the range within which the resistance of the hose needs to lie, which in the present case is between 104 and 2 x 106 ohms per metre.

In this hose, the inside diameter of the tube is 50 mm, its thickness is 2.3 mm and the formulation used for the conductive mixture is as follows, by weight: Nitrile rubber 100 parts Conductive black, such as an acetylene black 40 parts Anti-static plasticiser 8 parts Zinc oxide 5 parts Vulcanising accelerator 2 parts Sulphur 2 parts The tube 1 is covered with a layer 2 of wide-mesh fabric; above this is arranged a helix 3 of metal wire. The diameter of the helix 3 is 56 mm, its pitch is 18 mm and the diameter of the metal wire is 2 mm.

Above the metal helix is situated a second layer of fabric 4. A rubber-based mixture is interposed between the two layers 2 and 4 and the helix is embedded in it. Over the top of the second layer 4 is arranged a cover 5 which is made of an abrasion-resistant rubber-based mixture. The outer surface of the cover 5 is corrugated annularly to improve the hose's flexibility.

The electrical conductivity of the rubber mixture forming the layer in which the helix is embedded and of that forming the cover is much lower (more than 10 3 times lower) than that of the mixture from which the lining 1 is formed.

A twenty metre length of this hose was produced in a pilot plant. Its ends were each fitted with a connector of the kind shown in the drawing, which was in close contact with the lining 1 of conductive mixture so that there was excellent electrical continuity. Washers 6 of an electrically insulating material were inserted between the metal helix and the connectors.

The electrical resistance of the hose was measured by means of an ohmmeter connected to both connectors and the arithmetic mean of the results of five measurements was taken.

Measured under these conditions, electrical resistance was 1.15 x 106 ohms, i.e. 5.75 x 104 ohms per metre.

From this twenty metre hose, two ten metre hoses were produced by cutting it at the centre and fitting the free ends with similar connectors and washers.

When measured under the same conditions as before, the electrical resistance of each of the ten metre hoses was the same as that of the twenty metre hose: 1.15 x 106 ohms, i.e. 1.15 x 105 ohms per metre.

The electrical resistance of the combination formed by the two ten metre hoses joined together by their connectors (as if they were in use) was 3 x 106 ohms, i.e. approximately twice the resistance of a twenty metre hose.

The electrical resistance of one hose therefore appeared to be independant of its length whereas that of combined hoses linked by their connectors appeared to equal the sum of the electrical resistances of both hoses.

With the two ten metre hoses still connected by one pair of connectors to form a length of twenty metres, the ends of the metal helix situated adjacent one another were exposed in both hoses and were connected together by a metal wire. The electrical resistance of the combina tion of two ten metre hoses so prepared was 1.1 x 106 ohms, i.e. the same as that of the twenty metre hose.

Measurements made on similar hoses also produced in the pilot plant confirmed these results.

The same phenomenon was found with similar hoses produced in a manufacturing plant, although the electrical resistances of these hoses, when measured under the same conditions as above, also showed a very wide scatter, with the values found for hoses of the same length varying in proportions of 1 to 100 and even more.

Contrary to expectations, it was thus demonstrated that the helix does perform a certain electrical function, and an important one, without it being possible to give any definite reasons for this at the moment.

The invention aims to remedy this disadvantageous state of affairs and is based on the finding that if the metal wire forming the helix is provided with a layer of insulating material, the electrical resistance of hoses is virtually proportional to their length or, in other words, their electrical resistance per linear metre is virtually independant of their length.

In the pilot plant a hose was produced which was identical to the hose above but in which, in accordance with the invention, the metal wire forming the helix was surrounded by a 0.5 mm layer of polypropylene. The same procedures as above were applied to this hose and the electrical resistances measured were as follows: Twenty metre hose: total resistance 3.6 x 106 ohms, i.e. 1.8 x 105 ohms per metre.

Ten metre hose: Total resistance 1.4 x 106 ohms, i.e. 1.4 x 105 ohms per metre.

Two ten metre hoses joined together by their connectors: Total resistance 3.7 x 106 ohms.

Two ten metre hoses joined together by their connectors with their metal helices connected: 3.7 x 106 ohms.

In addition, measurements made of the electrical'resistances of similar hoses produced in manufacturing plant under normal manufacturing conditions confirmed the above results and showed no major scatter, the values found varying in a proportion of 1 to 1.4.

Instead of the insulating material used being polypropylene, it is possible to use any known materials which are known to be electrical insulators such as polyvinyl chloride, the polyamides, cross-linked or un-cross-linked polyethylene and other similar insulating materials.

Fig. 2 shows a second embodiment of the invention wherein the wall of the hose, which is once again corrugated annularly, contains a layer 8 made of a conductive rubber mixture.

This layer 8 is enclosed by layers 9 and 10 which are either made from non-conductive mixtures or else are made up by superimposing sheets of a material which is resistant to attack by hydrocarbons and has a low electrical conductivity.

Two helices formed by metal wires 11 and 12 co-operate with the wall of the hose. One of these helices is situated on the outside and the other on the inside. The metal wires forming the helices are surrounded by insulating layers 13 and 14 of cross-linked polyethylene. As in the previous example, the layer 8 of conductive mixture is in contact with the metal parts of the connectors. The outer helix, which comes into action only when the hose is operating under pressure, could be non-metallic. It could for example be formed by a shaped strip or cable of a non-conductive rubber mixture containing a filament made of a synthetic textile such as a polyester at its centre.

Instead of forming a cylinder, the layer 8 could be replaced by any continuous member which extended from one end of the hose to the other and whose cross-section was such that, given the volume resistivity of the conductive mixture of which the said member was made, the hose had the requisite electrical resistance.

WHAT WE CLAIM IS: 1. A flexible hose of the kind whose electrical resistance, when expressed per unit length of the hose, falls within the range from 10 4 to 2 x 106 ohms/ metre and in which the only metal members included in the reinforcement of the hose, are one or more helices, wherein the metal helix or helices of the reinforcement of the hose are provided with a layer of an electrically insulating material, and the hose includes a continuous member made of an electrically conductive rubber-based mixture, said member being the sole conductor of electricity in the hose.

2. A hose as claimed in claim 1, wherein the metal helix provided with a layer of an electrically insulating material is embedded in the wall of the hose.

3. A hose as claimed in claim 1, wherein the metal helix provided with a layer of an electrically insulating material is applied against the inner face of the wall of the hose.

4. A hose as claimed in claim 1, claim 2 or claim 3, wherein the continuous member made of conductive mixture is the lining of the hose, that is to say the part of the wall of the latter which is in contact with the fluid being conveyed.

5. A hose as claimed in any of the preceding claims, whose ends are fitted with metal connector or connectors having metal parts, and wherein the continuous member made of an electrically conductive mixture is in contact with the metal connectors or the metal parts of these connectors, and the metal helix or helices covered with a layer of an electrically insulating material are insulated from the metal connectors or from the metal parts of these

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. results. The same phenomenon was found with similar hoses produced in a manufacturing plant, although the electrical resistances of these hoses, when measured under the same conditions as above, also showed a very wide scatter, with the values found for hoses of the same length varying in proportions of 1 to 100 and even more. Contrary to expectations, it was thus demonstrated that the helix does perform a certain electrical function, and an important one, without it being possible to give any definite reasons for this at the moment. The invention aims to remedy this disadvantageous state of affairs and is based on the finding that if the metal wire forming the helix is provided with a layer of insulating material, the electrical resistance of hoses is virtually proportional to their length or, in other words, their electrical resistance per linear metre is virtually independant of their length. In the pilot plant a hose was produced which was identical to the hose above but in which, in accordance with the invention, the metal wire forming the helix was surrounded by a 0.5 mm layer of polypropylene. The same procedures as above were applied to this hose and the electrical resistances measured were as follows: Twenty metre hose: total resistance 3.6 x 106 ohms, i.e. 1.8 x 105 ohms per metre. Ten metre hose: Total resistance 1.4 x 106 ohms, i.e. 1.4 x 105 ohms per metre. Two ten metre hoses joined together by their connectors: Total resistance 3.7 x 106 ohms. Two ten metre hoses joined together by their connectors with their metal helices connected: 3.7 x 106 ohms. In addition, measurements made of the electrical'resistances of similar hoses produced in manufacturing plant under normal manufacturing conditions confirmed the above results and showed no major scatter, the values found varying in a proportion of 1 to 1.4. Instead of the insulating material used being polypropylene, it is possible to use any known materials which are known to be electrical insulators such as polyvinyl chloride, the polyamides, cross-linked or un-cross-linked polyethylene and other similar insulating materials. Fig. 2 shows a second embodiment of the invention wherein the wall of the hose, which is once again corrugated annularly, contains a layer 8 made of a conductive rubber mixture. This layer 8 is enclosed by layers 9 and 10 which are either made from non-conductive mixtures or else are made up by superimposing sheets of a material which is resistant to attack by hydrocarbons and has a low electrical conductivity. Two helices formed by metal wires 11 and 12 co-operate with the wall of the hose. One of these helices is situated on the outside and the other on the inside. The metal wires forming the helices are surrounded by insulating layers 13 and 14 of cross-linked polyethylene. As in the previous example, the layer 8 of conductive mixture is in contact with the metal parts of the connectors. The outer helix, which comes into action only when the hose is operating under pressure, could be non-metallic. It could for example be formed by a shaped strip or cable of a non-conductive rubber mixture containing a filament made of a synthetic textile such as a polyester at its centre. Instead of forming a cylinder, the layer 8 could be replaced by any continuous member which extended from one end of the hose to the other and whose cross-section was such that, given the volume resistivity of the conductive mixture of which the said member was made, the hose had the requisite electrical resistance. WHAT WE CLAIM IS:

1. A flexible hose of the kind whose electrical resistance, when expressed per unit length of the hose, falls within the range from 10 4 to 2 x 106 ohms/ metre and in which the only metal members included in the reinforcement of the hose, are one or more helices, wherein the metal helix or helices of the reinforcement of the hose are provided with a layer of an electrically insulating material, and the hose includes a continuous member made of an electrically conductive rubber-based mixture, said member being the sole conductor of electricity in the hose.

connectors.

6. A flexible hose substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.