GB2280870A

GB2280870A - Coating for a hose

Info

Publication number: GB2280870A
Application number: GB9408650A
Authority: GB
Inventors: Mark Causier
Original assignee: BOREFLEX IND SUPPLIES Ltd
Current assignee: BOREFLEX IND SUPPLIES Ltd
Priority date: 1993-08-13
Filing date: 1994-04-29
Publication date: 1995-02-15
Also published as: GB9408650D0

Abstract

The disclosure relates to a coating for a hose, particularly to a wear-resistant coating and a method of manufacture thereof. An apparatus for coating a conventional rubber hose with a wear-resistant material comprises a cantilever pay off stand 10; a set straight rod apparatus 11; an extruder and drive 12 having a cross-head and die extruder nozzle; a control panel 14; a cooling trough 15; a cooler unit 16; a caterpillar unit 23; and a coil-forming winder 21 for winding the hose by a transverse guide unit 22 onto a drum 20. The coating forms a close fit on the outer surface of the hose and is of polymeric material. <IMAGE>

Description

COATING FOR A HOSE The present invention relates to a coating for a hose and particularly although not exclusively, to a wear resistant coating for a hose, and a method of manufacture thereof.

Conventional hydraulic or pneumatic hoses, such as those used to connect mobile compressors to pneumatic drills or similar plant for building sites, roadworks etc. or hoses used on vehicles such as excavators, forklift trucks, materials handling apparatus, mining apparatus, or mining machinery, are generally manufactured from heavy duty rubber, in order to provide sufficient strength and flexibility.

Where the hose is subjected to a large amount of abrasion, eg. on a building site or roadworks, the hose is frequently damaged and can wear out very quickly. Apart from the cost of replacing the worn out hose regularly, the worn hoses can be dangerous. For example, in high pressure hydraulic hoses, such as used in mining apparatus, if a pin hole develops in the hose, this can lead to a high pressure jet of hydraulic fluid escaping from the hose at such velocity as to cut through cloth or human skin. Accidents have occurred in which personnel have experienced lethal injections of hydraulic fluid from such a leak. In critical applications in which it is important that the hose does not rupture, the hose must be protected by a conventional steel braiding, or alternatively by a conventional armoured casing, for example in the form of a helically wound stainless steel tube.

However, in the case of a braided coating, whilst the braiding does provide some protection against abrasion of the hose, where the braiding becomes worn, individual strands of steel wire break loose and protrude from the braiding causing a safety hazard. Furthermore, application of the stainless steel braid to hoses is a complex and labour intensive process entailing cutting the hose to length, cutting the braiding to length, inserting the hose into the braiding and mechanically securing the ends of the hose to the braiding by swaging with ferrules, before finally attaching any appropriate end fittings to the hose for a particular required application.

In the case of a hose covered by a metal armoured casing, the casing is relatively inflexible compared to the hose, and is heavy and therefore cannot be used for some applications, eg. portable compressor plant. A labour intensive process is required to fit the armoured casing to the hose, similarly as for a stainless steel braiding. Additionally the armoured casing is very bulky. Typically, an armoured casing for 1/4 BSP (British standard pipe) will have an outside diameter of around 5 to 6cm, where the 1/4 BSP hose itself will have an outside diameter of around 2.5 to 3cm.

Because the above-mentioned stainless steel braids and armoured casings are loosely fitting, there is also a problem of wear of the hose due to abrasion between the outer surface of the hose and the braiding or casing, particularly where the hose is coiled or follows a contorted route.

A thermoplastics hose type is also known, in which a thermoplastics liner is surrounded by a plastics braiding and a plastics coating. In such known hoses the liner, braiding and coating are bonded together. However, the known hoses have a problem of bursting as with the rubber hose, and additionally, of buckling causing collapse of the internal passage of the hose, when the hose is bent around a short radius.

An object of the present invention is to alleviate some of the abovementioned problems.

According to one aspect to the present invention, there is provided a protective coating for a hose, the coating being formed on the hose such that it closely fits an outer surface of the hose, the coating being of a polymeric material.

Preferably, said hose is a rubber hose.

Preferably, the protective coating is capable of being formed on the hose retrospectively, after manufacture of the hose.

The protective coating may be formed on the hose a substantial time after manufacture of the hose. This allows for versatility in the application of the coating to various different types of hose. It is not necessary for the coating to be applied at the time of manufacture of the hose, which for economic reasons would require a long length of hose to be manufactured at a high rate of extrusion , eg. 600 metres per minute, but on the contrary, shorter lengths of hose can be coated in a process independent of manufacture of the hose, allowing coating of existing hoses , and reducing the lengths of various sizes of hose which need to be stocked.

The protective coating as applied to a hose, and under fluid pressure from a leak in the hose, is preferably capable of expanding to form a fluidfilled blister.

This may have an advantage of containing a fluid leak from for example an hydraulic hose and preventing a narrow jet of hydraulic fluid issuing from a leak in the hose under high pressure.

Under normal conditions the protective coating preferably closely fits to an outer surface of the hose, but the protective coating may be capable of separating from the outer surface of the hose under pressure of fluid leaking from the hose, so that the fluid may travel along the length of the hose between the outer surface of the hose and the protective coating.

This may have an advantage that a fluid leak in a hose may be slowed down, and the fluid may be directed to issue from either end of the hose, rather than at the site of the leak.

Preferably, the fit between the hose and the coating is such that under bending or twisting of the hose and coating, slippage of the hose relative to the coating can occur.

This may have an advantage that when a length of the hose is bent into a curve, the fitment of the protective coating to the outer surface of the hose is also close enough such that the protective coating may adopt a smooth curve without buckling, and without producing an short radius ripples or bends in the protective coating which may wear more easily when abraded.

Preferably, the coating material comprises a polyether and/or polyurethane material. Preferably, the material contains a halogen and may be a low halogen material. Suitably, the material is bromine free.

The coating material may thus provide an advantage of resistance to abrasion as compared with the uncoated hose, combined with flexibility and relatively light weight. Preferably, the coating has a relatively low coefficient of friction compared to a rubber hose.

This may have an advantage that, where a number of coated hoses are grouped together, the wear between hoses may be reduced.

Preferably, the protective coating forms a continuous, unbroken coating around the flexible member, the coating being substantially impermeable to oil, grease or water. This may have an advantage that, because it is not possible for dirt, grease or grit to get between the coating and the hose, the outer surface of a hose coated with such material does not rub against the coating, thus preventing premature wear of the hose by this mechanism, which is a problem for prior art sleeves or casings.

As the protective coating closely fits to an outer surface of the flexible member, this may have an advantage that no ferrules or other fittings are required to secure the coating to the hose, since the coating is physically retained to the hose by friction.

The coating, as applied to a hose or pipe, may be capable of expanding into a fluid-filled blister, under fluid pressure from a leak in the hose or pipe.

This may have an advantage that, if a leak occurs in a hydraulic or pneumatic hose coated according to the invention, the coating may blow up in a balloon like fashion, rather than allow a high pressure jet of fluid to escape.

Preferably, the coating comprises a material having a room temperature tear strength in the range 10 to 100 N/mm2. Preferably, the material has a room temperature tear strength of between 20 and 30 N/mm7. The coating material may have a room temperature tensile strength in the range 25 to 45 N/mm2, and preferably the coating material has a room temperature tensile strength of between 30 and 40 N/mm2.

Preferably, the coating material has a room temperature density in the range 0.8 to l.5gm/cm2. Preferably, the coating material has an impact resilience in the range 30 to 50%. The material may have a compression set in the range 10% to 100%, and preferably has a room temperature compression set over a period of seventy hours, in the range 20 to 40%.

The protective coating at room temperature may be capable of being elongated by up to 1,000 % of its original dimension, and preferably is capable of being elongated by between 400% and 600% at room temperature. The protective coating may be capable of being elongated by up to 700% of its original dimension at a temperature in the range 50"C to 1000C. The protective coating may have a brittle point in the range -25 to -65 C.

The invention includes a protective coating for a hose, which closely fits an outer surface of the hose and is capable of expanding locally around the site of a leak in the hose under pressure of a fluid leaking from the hose.

The invention includes a rubber hose having a closely fitting polyurethane coating.

The invention includes a rubber hose having a coating as described according to the above aspect.

The invention includes a method of improving the durability of a length of a length of hose comprising forming around the hose a polymeric material, such that the material closely fits an outer surface of the hose.

Preferably, the coating material is extruded onto the hose. Preferably, the material is formed along a length of the hose at a rate in the range 0.1 to 20 metres per minute. The material formed around the hose is preferably bonded to an outer surface thereof.

Preferably, the material is heated to a temperature in the range 100 300"C prior to forming around the hose. After heating of the material, and forming of the material around the hose, the material may be cooled by passing the coated hose through a coolant fluid.

A problem with conventional armoured metal hose casings is that it is difficult to colour the casings effectively, since the colouring is difficult to apply in the first place, and when applied tends to easily wear off.

According to the present invention, pigments or colourant additives may be added to the coating material during heating or extrusion of the coating, to colour the coating. This may have an advantage that the members can be colour coded for various applications, by a colouring which is contained in the durable coating material, and will not rub off the member as the coating wears. The colourant may be added to the coating material prior to forming around the hose.

Preferably, coating material is capable of being produced in a variety of colours by adding colourants to the material during forming of the material.

Conventionally, rubber hoses may be coloured according to usage and the coating material of the present invention may be coloured to match the colour of the hose. This may have an advantage that the purpose of the hose may be identified by the colour of the coating, and the colour of the coating will not wear off as the coating material wears. For example, a yellow, lowpressure, rubber hose, may be identified by a yellow coating, and a red, highpressure hose, may be identified by a red coating. Other colours, e.g. green, blue, black, orange may be incorporated.

Further, the coating may be externally marked with other identifications of the hose, e.g. pressure rating, diameter etc. or with other information, e.g.

the name of the owner of the hose.

The invention includes a method in which a coating material is extruded onto the hose using an extrusion apparatus, and a tightness of fit of the coating around an outer surface of the hose is controlled by adjusting a spacing between a tip of the extrusion apparatus through which the hose passes, and a die adjacent the tip, through which the hose and coating material pass.

The invention includes an apparatus for performing the above methods the apparatus comprising: means for holding and guiding the uncoated hose prior to being coated with the material; means for heating and extruding the material around the hose, such that the extruded material is formed to closely fit around the hose; means for cooling the material once coated onto the hose; and means for collecting the hose.

Preferably, the apparatus has a changeable die for extrusion of the coating material, such that the width and/or wall thickness of the extruded material can be varied.

Preferably, the apparatus has control means for controlling any one or more of the following: the rate of heating the material, the rate of extrusion of the material; the rate of cooling of the material.

Specific methods, embodiments and apparatus according to the above aspects, may have an advantage of allowing retrospective fitting of a protective coating to a rubber hose. The coating can be applied immediately after manufacture of the hose, as part of the hose manufacture process, or existing stocks of hose which have been stored may be coated a substantial time after manufacture. The invention includes the retrospective fitting of coatings by the above methods to hoses which have been in use on machinery, as part of a general refurbishment of the machinery.

Features of the invention are described in the accompanying claims.

The invention includes the specific features of the specific methods and embodiments described hereunder.

For a better understanding of the invention, and to show how embodiments and methods of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 shows in cut-away view, a section of conventional hose protected by a flexible coating according to a specific embodiment to the present invention; Figure 2 shows in cut-away view, a section of conventional hose coated with the flexible coating, under conditions of rupture of the hose and leak of fluid; Figure 3 shows apparatus for applying a coating according to a specific embodiment of the present invention, to a conventional hose; and Figure 4 shows a method of varying the thickness of coating material and its rate of application to a rubber hose, in order to provide a coated rubber hose in accordance with specific embodiments of the invention.

Referring to Figure 1 of the accompanying drawings, there is shown a conventional hose 1 e.g. a rubber hydraulic hose, upon an outer surface 2 of which is formed a durable polymeric coating 3. The coating completely covers the outer surface of the hose to form a durable, flexible sheath which closely fits the outer surface of the rubber hose.

The coating can be removed by cutting with a machine tool, at the ends of the coated hose, to leave the ends of the hose exposed, allowing the hose to be fitted to machinery using existing conventional hose fittings, and without the need for special ferrules or casings.

The coating 3 is of a polyether-polyurethane material containing a halogen, and having conventional additives to produce a low co-efficient of friction, low static characteristics, and fire retardant properties. The coating material is bromine free. The formulation of the coating is variable, by varying the proportions of the above-mentioned constituents, and including conventional hardeners and colourants to suit the particular coating application required. One suitable base material, which can be adapted by use of conventional additives and hardeners, to provide the required properties, is IROGRAN" manufactured by Morton International, and which contains a low amount of halogen.

In the above-mentioned embodiment, the coating material is selected to have the following specific physical properties. The coating material is thermoplastic, flame retardant, and has a tensile strength of the order 35 N/mm2. After forty-two days in water at 80 C, the tensile strength is of the order 25 N/mm2.

The material has an ultimate elongation of 550 % . After forty-two days in water at 830C, the ultimate elongation increases to 660%. The material has a tear strength of 25 N/mrn2, and a brittle point of -45 C. The density of the material is 1 .2gm/cm2 and the material has an impact resilience of 40% . The material has a compression set of30%, when at room temperature for seventy hours. When at 70"C for twenty-four hours, the compression set is of the order of 50%.

The proportions of polyether/polyurethane and other known additives may be varied to alter the above characteristics.

Additionally, the polyether-polyurethane granules have a shelf life in excess of six months before manufacture, enabling the granules to be stored for an advantageously long time before they must be used for manufacture of the coating. Additionally, the material has good hydrolysis and microbe resistance. Using a material as described above, the coating has been found experimentally to be substantially impermeable to dirt, oil and grease.

The material is flexible, and remains so, even at low temperatures below 0 C. For example, at room temperature, a conventional rubber hose, coated with the material will flex to an extent comparable to a similar uncoated hose.

Under normal operating conditions, in industrial applications as described above, the coating does not become detached from the hose.

Referring to Figure 2 of the accompanying drawings, if a split 7 develops in the hose and, for example hydraulic fluid leaks from the hose, the coating 3 bulges outwardly, forming a large blister 9 which eventually under enough pressure from the fluid will burst, but in an explosive manner without first producing a dangerous narrow high pressure jet of hydraulic fluid.

A rubber hose coated with a material as described above has been burst tested at hydraulic fluid pressure of up to 12,000 psi. Upon a split developing in the hose, the coating blew up into a fluid-filled blister momentarily before the hydraulic fluid propagated between the coating and the outer surface of the hose, in a direction along the length of the hose, the fluid eventually escaping at the ends of the hose. The effect of this expansion of the coating was that the fluid was contained within the coating until it reached the ends of the coating, with the practical effect that the leak of fluid was controlled in that a narrow jet of fluid did not project from the hose prior to the hose bursting, and the position of the fluid leakage at the ends of the hoses was predicted.

The coating may form a blister which expands to a diameter of up to 700% of the original diameter of the coating, before the blister deflates or bursts. Because of this high flexibility, and because of the capability of channelling fluid between the hose and coating, large energies arising from hose leaks or bursts may be absorbed by the coating. Coatings which have contained leaks have been found to become rippled, where the energy of the leak has been absorbed.

Typically, for a rubber hose which bursts at 10,000 psi, where a slit forms in the hose the coating may blow up into a blister for a time of around one second, before deflating and before the fluid dissipates along the length of the hose as described above.

For minor leaks, the coated hose may remain usable for a period of time after the leak without significant danger of high-pressure jets of fluid being released, allowing continued operation of machinery for a short period e.g. for an afternoon, prior to replacement of the hose. Because the coating is tightly fitting to the hose, the rate of leak of fluid from the hose is slowed as compared to a conventional uncoated hose or conventional sleeved hose.

For optimum burst resistance, the coating should be applied to the hose such that the coating does not strongly bond to the outer surface of the hose in an adhesive manner, but rather that there is a limited amount of slippage between the outer surface of the hose and the coating. The coating should be applied to the hose with such a radial coating thickness that if the hose is bent into a semicircle or similar curve, the coating on an inner circumference of the bend does not buckle or kink.

The slippage between the coating and the outer surface of the hose may allow for movement of the coating relative to the hose, to prevent buckling when the hose is bent or twisted. However, the friction between the outer surface of the hose and the interior of the closely fitting coating prevents the hose from being removed from the coating without first cutting the coating.

By avoidance of kinks or buckles in the coating, the working life and abrasional resistance of the coating may be much improved, as exposed short radius buckles in the coating may be avoided on bending of the hose.

The coating does not form a loose sleeve around the hose, but rather a closely fitting coating in which some slippage of the hose may occur under force. If any adhesive bonding effect does occur between the outer surface of the hose and the inside of the coating, for best results, this bonding should be weak enough to be able to be overcome by force on bending the hose, or by fluid pressure on occurrence of a fluid leakage from a burst or slit in the hose. As the coating is applied directly to the outer surface of the hose, the inner surface of the coating may become textured to form around any surface contours on the outside of the hose.

By allowing for some slippage between the coating and the hose, the flexibility of the coated hose may equal that of the hose prior to coating.

Referring to figures 3 and 4 of the accompanying drawings, an apparatus for coating a conventional hose with a coating of material as described above is shown. The apparatus comprises a bar type cantilever pay off stand 10; a set straightener rod apparatus 11; an extruder and drive 12 having a cross head and die extruder nozzle 13; a control panel 14; a cooling trough 15 and cooler unit 16; a caterpillar unit 23; and a coil forming winder 21 for winding the coated hose, pipe, rope or cable onto a coil drum 20, the winding being guided by a transverse guide unit 22.

A coil of the material to be covered, eg. a 100m coil of conventional rubber hydraulic hose is held on the cantilever pay off stand 10 at one end of the apparatus. The hose is passed through the set-straightener apparatus 11 and into the extruder and drive apparatus 12. The extruder and drive apparatus 12 includes the cross head and die extrusion nozzle 13 for extrusion of the coating material onto the hose. The cross head and die are shown in more detail in figure 4. The material, which is heated to around 150-250"C and in fluid form, is extruded via a die of suitable diameter for example 60mm, and formed onto the hose which passes through the centre of the die.

An extrusion rate may vary from a lower value of 0.5 to 2m per minute up to around 12m per minute. The hot material, once formed onto the outer surface of the hose, bonds to the outer surface of the hose, partly by constriction of the material during cooling, and partly due to the adhesive nature of the hot material so that when the material cools, the hose cannot slip within the formed coating. However, preferably the temperature, pressure and thickness of the melted coating is adjusted to prevent significant adhesive bonding to the hose, and to obtain a close fit as described above.

The extruder die nozzles can be changed, so that when changing from one conventional hose to another conventional hose, of different diameter, an extruder nozzle suitable to the other hose can be substituted for the previous nozzle.

Referring to figure 4 of the accompanying drawings, the rate of extrusion and the thickness of the coating material 28 are varied by moving the tip 29 relative to the die nozzle 30, in a direction along the length of the hose, i.e. by varying the distance D in figure 4. Variation of the distance between the tip and the nozzle also affects the closeness of the fit of the coating to the hose, by varying the pressure of application of the coating material to the hose outer surface.

The speed of extrusion and temperature of the coating material prior to extrusion can be controlled electronically from a control panel 14 which controls the extruder drive and other equipment eg. cooling trough, coil forming winder, cooling unit etc. as mentioned above. After exiting from the extruder nozzle, the coated hose is passed through the cooling trough 15, the temperature of which is controlled by the cooler unit 16. The cooler unit is controllable, in order to control the temperature of the cooling trough 15.

After passing from the cooling trough 15, the coated hose may be wound onto the coil drum 20 mounted on the coil forming winder 21, using the transverse guide unit 22 for guiding the hose onto the coil. Before being coiled onto the drum, the hose may pass through the 24" heavy duty caterpillar unit 23.

The above arrangement may have an advantage that, because the speed of extrusion is much lower than for other prior art machines used in the initial manufacture of hose, which run at around 600m per minute, a low cost extruder apparatus can be used for coating single lengths of hose after manufacture of such hoses.

Furthermore, because the apparatus can be adapted to suit several different sizes of hose, by changing the extrusion die nozzle size, the apparatus is versatile, and a separate dedicated manufacturing apparatus for each hose size is not required. The wall thickness and/or diameter of the coating can be altered by changing the die size, allowing versatility in the thickness and width of a tubular coating applied to the hose.

Because the rate of extrusion and melt temperature of the coating material are controllable, damage to the hose by forming thereon a coating material which is too hot can be avoided.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A protective coating adapted for fitting to a rubber hose, the coating being formed on the hose such that it closely fits an outer surface of the hose, the coating being of a polymeric material.

2. A protective coating according to claim 1, as applied to a hose, which under fluid pressure from a leak in the hose is capable of expanding to form a fluid-filled blister.

3. A protective coating according to Claim 1 or 2, which is capable of being formed on the hose retrospectively, after manufacture of the hose.

4. A protective coating according to any one of the preceding claims, wherein the fit between the hose and the coating is such that under bending or twisting of the hose and coating, slippage of the hose relative to the coating can occur.

5. A protective coating according to any one of the preceding claims, in which the coating fits closely to the hose such that the friction between an outer surface of the hose and an inner-facing surface of the coating formed around the hose, is sufficient to prevent the hose from being removed from the coating without cutting or tearing the coating.

6. A protective coating according to any one of the preceding claims, wherein the fitment of the coating to the outer surface of the hose is close enough such that when a length of the hose is bent into a curve, the protective coating adopts a smooth curve without buckling.

7. A protective coating according to any one of the preceding claims, which under normal conditions closely fits to an outer surface of the hose, but in which the protective coating is capable of separating from the outer surface of the hose under pressure of fluid leaking from the hose, so that the fluid may travel along the length of the hose between the outer surface of the hose and the protective coating.

8. A protective coating according to any one of the preceding Claims, wherein said polymeric material comprises a polyether and/or polyurethane material.

9. A protective coating according to Claim 8, in which the material contains a halogen.

10. A protective coating according to Claim 8 or 9, in which the material is bromine free.

11. A protective coating according to any one of the preceding claims, which is substantially impermeable to oil, grease or water.

12. A protective coating according to any one of the preceding claims, which is relatively abrasion resistant compared to the hose.

13. A protective coating according to any one of the preceding claims comprising a material having a room temperature tear strength in the range 10 to 100 N/mm2.

14. A protective coating according to claim 13, in which the material has a room temperature tear strength of between 20 and 30 N/mm2.

15. A protective coating according to any one of the preceding claims, wherein the coating material has a room temperature tensile strength in the range 25 to 45 N/mm2.

16. A protective coating according to claim 15, in which the coating material has a room temperature tensile strength of between 30 and 40 N/mm2.

17. A protective coating according to any one of the preceding claims, having a room temperature density in the range 0.8 to 1.5gm/cm2.

18. A protective coating according to any one of the preceding claims, having an impact resilience in the range 30% to 50%.

19. A protective coating according to any one of the preceding claims, having a compression set in the range 10% to 100%.

20. A protective coating according to claim 19, having a room temperature compression set over a period of seventy hours, in the range 20% to 40%.

21. A protective coating according to any one of the preceding claims, which, at room temperature is capable of being elongated by up to 1,000% of its original dimension.

22. A protective coating according to claim 21, capable of being elongated by between 400% and 600% at room temperature.

23. A protective coating according to any one of the preceding claims, capable of being elongated by up to 700% of its original dimension at a temperature in the range 50"C to 100"C.

24. A protective coating according to any one of the preceding claims, having a brittle point in the range -25 to -65 C.

25. A protective coating according to any one of the preceding claims, capable of incorporating a set of pigments for colouring the coating in any one or more of a range of colours selected from the set comprising: yellow, red, green, blue, black, orange.

26. A protective coating for a hose, which closely fits an outer surface of the hose and is capable of expanding locally around the site of a leak in the hose under pressure of a fluid leaking from the hose.

27. A rubber hose having a closely fitting polyurethane coating.

28. A rubber hose having a coating as claimed in any one of the preceding claims.

29. A method of improving the durability of a length of hose comprising forming around the hose a polymeric material, such that the material closely fits an outer surface of the hose.

30. A method according to Claim 29, in which the coating material is extruded onto the hose.

31. A method according to Claim 30, in which the material is formed along a length of the hose at a rate in the range 0.1 to 20 metres per minute.

32. A method according to Claim 29,30, or 31, in which the material formed around the hose is bonded to an outer surface thereof.

33. A method according to any one of Claims 29 to 32, in which the material is heated to a temperature in the range 100-300"C prior to forming around the hose.

34. A method according to Claim 33, in which, after heating of the material and forming of the material around the hose, the material is cooled by passing the coated hose through a coolant fluid.

35. A method according to any one of Claims 29 to 34, in which a colourant is added into the coating material prior to forming around the hose.

36. A method according to any one of Claims 29 to 35, in which a coating material is extruded onto the hose using an extrusion apparatus, and a tightness of fit of the coating around an outer surface of the hose is controlled by adjusting a spacing between a tip of the extrusion apparatus through which the hose passes, and a die adjacent the tip, through which the hose and coating material pass.

37. Apparatus for performing the method of any one of Claims 30 to 36, the apparatus comprising: means for holding and guiding the uncoated hose prior to being coated with the protective coating material; means for heating and extruding the protective coating material around the hose, such that the extruded coating material is formed to closely fit around the hose; means for cooling the coating material once coated onto the hose; and means for collecting the hose.

38. An apparatus according to Claim 37 having a changeable die for extrusion of the material, such that the width and/or wall thickness of the extruded material can be varied.

39. An apparatus according to Claim 37 or 38, having control means for controlling any one or more of the following: the rate of heating the material; the rate of extrusion of the material; the rate of cooling of the material.

40. A protective coating or a method of manufacture of a protective coating substantially as herein described with reference to Figures 1 to 4 of the accompanying drawings.