FR2797936A1 - METAL TUBE COATED WITH AT LEAST ONE EXPANDED POLYMERIC MATERIAL - Google Patents

Abstract

The present invention relates to a coated metal tube arrangement comprising a metal tube (10) and at least one coating layer (12, 14) of a polymeric material, said material having an expanded structure.

Description

DESCRIPTION

  This invention relates to metal tube products, and more particularly, to a metal tube used in the automotive industry for applications such as brake lines, fuel lines and transmission oil cooling lines. Tubing used in automotive applications requires resistance to corrosion and wear that will allow it to last for the useful life of a vehicle. Similarly, the tube must have an abrasion resistance compatible with an automotive environment (that is to say an impact of stones and removal of small chips). Finally, the tube should be able to isolate and absorb mechanical vibrations and acoustic noise. In order to meet these requirements, one or more protective coatings are usually applied to the metal tube which is to be used in automotive applications. Coatings used in industry are generally characterized by one or two of the following. First, a metal substrate is deposited on the surface of the steel tube. Usually it is a sacrificial coating in which the substrate corrodes before the metal tube. Second, a barrier coating is deposited on the substrate to prevent corrosive media from initiating corrosion and to

  achieve increased abrasion resistance.

  Examples of materials and combinations of materials used in the past as substrate and / or barrier layers in the automotive industry include: a lead-tin alloy (an alloy nominally made of% lead and 15% tin ), a zinc-rich paint on a lead-tin alloy, a zinc-aluminum alloy

  (consisting of 95% zinc and 5% aluminum -

  available under the trade name GALFAN), a paint rich in aluminum on a coating of GALFAN, zinc or zinc-zinc galvanized, poly (vinyl fluoride) (PVF) or poly (vinylidene fluoride) (PVDF) on galvanized zinc, hot dip coated aluminum,

epoxy and nylon.

  These materials have been used as barrier and / or substrate layers in various combinations, but have shown shortcomings which limit their usefulness. The prior art materials and coating methods have exhibited only limited resistance to wear and removal of small chips from impact from stones and abrasion. Often, a shrinkable thermoplastic sheath is applied around the conventionally coated tubes to provide improved resistance to removal of small chips and wear. Such methods, however, are very expensive and are not always effective. For example, the shrinkable plastic sheaths have only a limited ability to absorb or isolate mechanical vibrations and acoustic noises. Likewise, the use of shrinkable plastic sheaths is problematic in that the relatively high thickness of the sheath prevents it from being used under end fittings or connectors, thereby exposing the end of the

tube to corrosion.

  So as to overcome all the problems (i.e. corrosion, wear, abrasion, removal of small chips, impact of stones, mechanical vibrations, acoustic noise) encountered simultaneously in automotive applications and fluid transport tube applications, the properties of specific polymers must be adapted for tube coating. Since no single polymer material is effective in combating all of the problems, an effective product will take into account the relationship of the structures and properties of the polymers as well as the processing and application considerations.

materials techniques.

  Therefore, the present invention provides a multi-layer or single-layer polymer coating on a metal tube which acts on the dynamic mechanical properties of polymeric materials in order to obtain protection against multiple elements for a metal tube used in automotive applications. or fluid transport. Preferably, it combines the unique dynamic mechanical properties of two layers of polymers in order to obtain maximum efficiency of corrosion resistance and protection against wear, abrasion, removal of small chips and the impact of stones. Furthermore, the multi-layer coating of the present invention is effective in absorbing impact energy and in eliminating mechanical vibrations and

acoustic noises.

  In a first aspect, the invention provides an arrangement of coated metal tube comprising a metal tube and a coating layer of a polymer material, the polymer material having an expanded or foamed structure, in which the polymer material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides), polyacetals, phenolic resins, polyketones, polyolefins and

poly (vinyl chloride).

  Preferably, the polymer material is a multi-phase polymer comprising at least two components of polymers, each of the components having a distinct glass transition temperature, said polymer material consists of copolymers or mixtures of polymer polymers chosen from the group consisting of polyamides, polyesters, polyolefins, polyurethane and poly (vinyl chloride), and said polymer material has a damping factor of at least 0.05 and a flexural modulus of less than 50 MPa, and so more preferred the damping factor of the polymer material is between 0.1 and 0.3 within a temperature range

  of application between -50 and 150 degrees Celsius.

  Advantageously, the layer of polymeric material has a wall thickness of at least 50 micrometers, and more preferably the layer of polymeric material has a wall thickness between

micrometers and 500 micrometers.

  Preferably, the layer of expanded polymeric material is formed by mixing a blowing agent with a polymeric material before extruding the mixture of blowing agent and of polymeric material, the blowing agent being chosen from the group consisting of azodicarbonamides, hydrazine derivatives, semi-carbazides,

  tetrazoles, benzoxazines and mixtures thereof.

  In a second aspect, the invention provides an arrangement of coated metal tube comprising a metal tube, an inner layer of a first polymeric material bonded to the tube as well as an outer layer of a second polymeric material surrounding the inner layer, the second polymeric material having an expanded structure, the inner layer and the outer layer not being bonded, wherein the first polymeric material has a damping factor of less than 0.5 and a flexural modulus of at least 100 MPa , and in which the first polymer material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides), polyacetals, phenolic resins, polyketones and polyolefins and in which the second polymer material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides), polyacetals, phenolic resins, polyketones, polyolefins and

poly (vinyl chloride).

  Preferably, the second polymeric material is a multi-phase polymer comprising at least two polymer components, each of the components having a distinct glass transition temperature, and the second polymeric material consists of copolymers or mixtures of polymer polymers chosen from the group consisting of polyamides, polyesters, polyolefins,

  polyurethane and poly (vinyl chloride).

  Preferably, the second polymer material has a damping factor of at least 0.05 and a flexural modulus of less than 50 MPa, more preferably the damping factor of the second polymer material is between 0.1 and 0 , 3 within a temperature range

  of application between -50 and 150 degrees Celsius.

  Preferably, the outer layer has a wall thickness of at least 50 micrometers, and more preferably the outer layer has a

  wall thickness between 200 micrometers and 500 micrometers.

  Preferably, the outer layer of expanded polymeric material is formed by mixing a blowing agent with the second polymeric material before extruding the mixture of blowing agent and of polymeric material, the blowing agent being chosen. from the group consisting of azodicarbonamides, hydrazine derivatives, semi-carbazides, tetrazoles, benzoxazines and

mixtures of these.

  Figure 1 is a sectional view of part of a two-layer coated metal tube arrangement in accordance with the present invention, and Figure 2 is a sectional view of the tube arrangement of Figure 1 showing a stripped end in sight

  facilitate connection to end fittings.

  Figure 1 illustrates a coated metal tube 10 according to the present invention. The tube 10 is coated with an inner layer 12 of a first polymeric material and an outer layer 14 of a second polymeric material. The inner layer 12 is bonded to the metal tube 10 and the outer layer 14 is extruded around the inner layer 12. The layers 12 and 14 are not bonded together by the use of an adhesive or any other bonding method. . This is advantageous in that it allows the outer layer 14 to be removed at the ends of the tube 10 (Figure 2), which facilitates

  connection to end fittings or connectors.

  Many considerations are involved in the choice of materials or mixtures of particular polymers which will constitute layers 12 and 14. The polymer of the inner layer must provide resistance to chemical agents and prevent corrosion of the metal tube 10. The polymer of the outer layer must absorb impact energy as well as eliminate mechanical vibration and acoustic noise. The polymer of the outer layer should also be capable of removal or convenient disposal for

  end fittings or connections.

  The specific properties and structural attributes of particular polymers must be taken into account in order to obtain these results. In order for the inner layer polymer to exhibit good resistance to chemicals, for example, it must have high crystallinity. High crystallinity, however, decreases the ability of a polymer to absorb impact energy and to

  isolate mechanical vibrations and acoustic noises.

  This function is carried out by the polymer of the outer layer. Dynamic mechanical properties are the key to determining the ability of the polymer in the outer layer to eliminate mechanical vibration and acoustic noise. These dynamic mechanical properties are briefly described below: The modulus of a polymer is a function of the

  temperature and frequency, o, at the time of measurement.

  The damping factor of a polymer, tan 8w, is the ratio of the imaginary part of the module, G "w to the real part of the module, G'w (the conservation module). The natural frequency, 0, is the lowest noise frequency which can be eliminated by the mechanical system The natural frequency, 0, and the transmissibility, T, of a mechanical system can be expressed as a function of the dynamic mechanical properties of polymers as follows:

6 = [KG0] 112

  and (1) + tan2ô T = r (_02 / (o 0XG)) 2 '+ tan2 8w] o K is a form factor, M is the mass of the system, G'0 and G'w are the conservation modules shear of the polymer at the natural frequency 0 and at the imposed frequency co, respectively, tan 8w is a measure of the damping of the polymer at the imposed frequency, and T

  is the transmissibility of the mechanical system.

  Both the dynamic modulus and the damping are functions of temperature and frequency. These mechanical properties can be manipulated by adapting the molecular structures of the polymers. To this end, a vibration system at a low natural frequency can be obtained by reducing the modulus of conservation of the polymer in question. In addition, the transmissibility at resonance can be lowered by choosing polymers having

high damping factors.

  The inner layer 12, as stated above, is made of a polymeric material which is chosen for its resistance to chemical agents and liquids. The layer 12 is linked to the underlying metal tube 10 and prevents corrosive media from reaching or attacking the tube 10. The polymer material chosen for the layer 12 must be particularly resistant to the corrosive media or fluids usually encountered in automotive applications, such as brake fluid, engine oil

and a fuel.

  In order to achieve these goals, the polymeric material of the inner layer 12 must have a high crystallinity and a low damping factor. The damping factor is the ratio of the imaginary part of the preservation module to the real part of the module and, for the inner layer 12, is preferably less than 0.05. The polymeric material of the inner layer 12 should

  also have a flexural modulus of at least 100 MPa.

  Polymeric materials suitable for inner layer 12 include, but are not limited to, polyamides (nylons), polyimides, polyesters, fluorinated plastics (such as poly (vinyl fluoride) or poly (vinylidene fluoride) ), epoxy resins, poly (phenylene sulfides), polyacetals, phenolic resins, polyketones, polyolefins and

poly (vinyl chloride).

  The outer layer 14 is made of a material

  polymer which is extruded around the inner layer 12.

  The layer 14 is unbound, or weakly bonded, to the inner layer 12. It is complementary to the inner layer 12 in that, while the inner layer 12 provides protection against chemicals and corrosive liquids , the outer layer 14 provides resistance to the removal of small chips and wear from impact of stones and abrasion. The outer layer 14 is also responsible for absorbing impact energy as well as eliminating mechanical vibrations and acoustic noise. Insulation and thermal protection are also

produced by layer 14.

  The outer layer 14 can be made of a single-phase polymer material chosen from the same group as the layer 12, or it can be made

of a multi-phase polymer.

  The term "multiple phases" indicates that the material is

  a mixture or a copolymer of two or more polymers.

  By being made up of two or more polymer components, the polymeric outer layer material can be produced on demand with specific damping characteristics (natural frequency and transmissibility) in order to isolate or absorb the frequencies.

  imposed mechanical vibrations and acoustic noise.

  The multi-phase polymer has at least two glass transition temperatures in which their morphology and property can be manipulated by thermodynamic treatment to create the desired damping characteristic. This concept of controlling morphology through thermodynamic treatment in order to create the desired damping characteristic is described in the publications of the inventor of the prior art, "Morphology ans Property Control via Phase Separation or Phase Dissolution during Cure in Multiphase Systems ", Advances in Polymer Technology, volume 10, N 3, pages 185 to 203 (1990), HS-Y. Hsich, proceedings of the 34th symposium

  international SAMPE, 884 (1989), H.S.-Y. Hsich, J. Mater.

  Sci., 25, 1568 (1990), and H.S.-Y. Hsich, Polym. Eng. Sci.,

30, 493 (1990).

  The multi-phase polymer for forming the outer layer 14 has a high damping factor of at least 0.05. Preferably, the damping factor is between 0.1 and 0.3 in an application temperature range between -50 and 150 degrees Celsius. This high damping factor allows more dissipation of impact energy than does the lower damping factor of the inner layer. The flexural modulus of the polymer of the outer layer must be less than 50 MPa. A lower flex modulus means that the polymer material is less rigid (more

  flexible) than the inner layer polymer.

  The wall thickness of the outer layer 14 must be greater than 50 micrometers. Preferred wall thickness

is between 200 and 500 micrometers.

  The use of a multi-phase polymer having at least two components of different polymers is advantageous in that each component will have a distinct glass transition temperature. At temperatures close to the glass transition temperature of a polymer, the polymer has a very high damping factor. Providing a multi-phase polymer having multiple glass transition temperatures, therefore, will provide high damping factors over a wide range of temperatures and, therefore, will provide the best ability to eliminate mechanical vibrations and acoustic noise in construction service environments. Preferably, at least one of the polymer components of the outer layer will have a glass transition temperature below room temperature (22 degrees Celsius) and the other polymer component will have a melting point above 100 degrees Celsius. It is also preferred that a first polymer component is a rubbery phase and the other

  component or a thermoplastic phase.

  The outer layer 14 should also have a high degree of heat resistance. Heat reflecting fillers can be added to the polymeric material of layer 14 to enhance its resistance to

the heat.

  Multi-phase polymeric materials suitable for the outer layer 14 include, but are not limited to, copolymers or blends of polymers (or alloys) of polyamides, polyesters, polyolefins, polyurethane and poly (vinyl chloride) . A thermoplastic polyolefin (TPO) is a particular example of a

suitable polymer blend.

  Before the application of the layers 12 and 14 on the metal tube 10, the tube 10 can be surface treated with a substrate in order to further strengthen its resistance to corrosion. Materials suitable for the surface treatment of tube 10 include chromate, phosphate,

  zinc, an aluminum-rich paint, zinc-

  aluminum, zinc-nickel substrates or a mixture of these materials. This will further enhance the corrosion resistance. The unique dynamic mechanical properties of layers 12 and 14 combine together to achieve remarkable performance and to obtain multiple protections for a metal tube used in automotive or fluid transport applications. The inner layer 12 provides protection against harmful chemical agents and corrosive liquids, while the outer layer 14 provides resistance against wear, abrasion, removal of small chips and the impact of stones, absorbs impact energy, and isolates or

  absorbs mechanical vibrations and acoustic noise.

  The polymeric material intended to form the outer layer may have an unexpanded structure or else an expanded structure. An expanded polymer provides the same resistance to the tube assembly as an unexpanded multi-phase polymer, however the use of an expanded multi-phase polymer to form the outer layer significantly reduces the weight of the tube compared to the unexpanded multi-phase polymer. This reduction in weight is due to the presence of empty spaces in the polymer formed during the expansion treatment. In addition, a layer of expanded polymer is capable of providing better

  thermal insulation than a layer of unexpanded polymer.

  The expansion of the polymer is caused by the addition of a blowing agent in the polymer intended to form the outer layer. Examples of such blowing agents include, but are not limited to, azodicarbonamides, hydrazine derivatives, semi-carbazides,

  tetrazoles, benzoxazines and mixtures thereof.

  The blowing agent is mixed with the polymer intended to form

  the outer layer just before the extrusion treatment.

  Following the extrusion of the outer layer, the blowing agent will cause the polymer to expand or foam, thus creating empty spaces inside the layer

outside.

  An alternative embodiment of a coated metal tube of the present invention is a metal tube

  coated with a single outer layer of polymeric material.

  The outer layer of polymer material is extruded onto

the tube.

  The outer layer can be made of a single phase polymeric material, or it can be made

of a multi-phase polymer.

  Suitable single phase polymeric materials for forming the outer layer are the same as those identified for the outer layer in the mode of

  realization comprising two layers of polymeric materials.

  Multi-phase polymers suitable for forming the outer layer are the same as those identified for the outer layer in the embodiment comprising

  two layers of polymeric materials.

  The outer layer of the alternative embodiment is capable of providing protection against harmful chemicals and corrosive liquids. It is also capable of dissipating impact energy in order to improve the removal of small chips, the wear resistance and isolates or absorbs mechanical vibrations and

acoustic noises.

  The polymeric material for forming the outer layer of the alternative embodiment may have an unexpanded structure or an expanded structure. The method of expanding the polymeric material of the alternative embodiment is the same as the method described in the embodiment having two layers of

polymeric materials.

  The following are examples of particular tube coating arrangements in accordance with the present invention. These examples are provided for illustrative purposes only and are not intended, nor should be interpreted as limiting the scope of this invention.

EXAMPLE 1

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer made of PVF (poly (vinyl fluoride)) is bonded to the surface-treated steel tube. An outer layer made of a mixture of

  polyamide and EPDM rubber polymers (ethylene-

  propylene-diene) is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 2

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 3

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of extruded nylon is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 4

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of extruded polyketone is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyamide polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to achieve

  end fittings or connections.

EXAMPLE 5

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of extruded polyketone is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to achieve

  end fittings or connections.

EXAMPLE 6

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer consisting of a mixture of PVC (poly (vinyl chloride)) polymers and nitrile rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube to achieve

  end fittings or connections.

EXAMPLE 7

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of PVF is bonded to the surface-treated steel tube. An outer layer made of a mixture of PVC polymers and nitrile rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 8

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a thermoplastic elastomeric polyester copolymer is extruded over the inner layer. The outer layer is removed at the ends of the tube to make fittings or connections

ends.

EXAMPLE 9

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of extruded nylon is bonded to the surface-treated steel tube. A

  outer layer made of a polyester copolymer -

  thermoplastic elastomer is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 10

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of epoxy is bonded to the surface treated steel tube. An outer layer made of a blend of polyamide polymers

  and EPDM rubber is extruded on the inner layer.

  The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 11

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of epoxy is bonded to the surface treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 12

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a blend of polyamide polymers

  and EPDM rubber is extruded on the inner layer.

  The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 13

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 14

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of extruded nylon is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 15

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of extruded polyketone is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyamide polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 16

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of extruded polyketone is bonded to the surface-treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 17

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a mixture of PVC polymers and nitrile rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 18

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of a thermoplastic elastomeric polyester copolymer is extruded over the inner layer. The outer layer is removed at the ends of the tube to make fittings or connections

ends.

EXAMPLE 19

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of extruded nylon is bonded to the surface-treated steel tube. A

  outer layer made of a polyester copolymer -

  thermoplastic elastomer is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 20

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of epoxy is bonded to the surface treated steel tube. An outer layer made of a blend of polyamide polymers

  and EPDM rubber is extruded on the inner layer.

  The outer layer is removed at the ends of the tube in order to make end fittings or connections.

EXAMPLE 21

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer of epoxy is bonded to the surface treated steel tube. An outer layer made of a mixture of polyolefin polymers and EPDM rubber is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to make connections or

end connections.

EXAMPLE 22

  A steel tube is treated on the surface with a zinc-aluminum substrate. An inner layer of extruded polyamide is bonded to the surface-treated steel tube. An outer layer consisting of an expanded polyester-thermoplastic elastomer copolymer is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to achieve

  end fittings or connections.

EXAMPLE 23

  An inner layer made of extruded polyamide is bonded to the surface of an aluminum tube. An outer layer made of expanded polyamide is extruded on the inner layer. The outer layer is removed at the ends of the tube in order to achieve

  end fittings or connections.

EXAMPLE 24

  A layer of expanded polyamide is extruded onto the surface of an aluminum tube. The layer of expanded polyamide is removed at the ends of the tube in order to make fittings or end connections.

EXAMPLE 25

  A steel tube is treated on the surface with a zinc-nickel substrate. An epoxy layer is bonded to the surface treated steel tube. An outer layer made of a blend of expanded polyamide polymers

  and EPDM rubber is extruded on the epoxy layer.

EXAMPLE 26

  A steel tube is treated on the surface with a zinc-nickel substrate. An inner layer made of PVF is bonded to the surface-treated steel tube. An outer layer made of expanded polyamide is extruded onto

the inner layer.

  Various features of the present invention have been described with reference to the embodiments shown and described. It should be understood, however, that modifications can be made without departing from

  the spirit and scope of the invention.

Claims (23)

  1. Arrangement or structure of coated metal tube characterized in that it comprises: a metal tube (10), and a coating layer (12, 14) of a polymeric material, said polymeric material having an expanded structure. 2. Arrangement of coated metal tube according to claim 1, characterized in that said polymer material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides), polyacetals, phenolic resins, polyketones,   polyolefins and poly (vinyl chloride).   3. Arrangement of coated metal tube according to claim 1, characterized in that said polymeric material is a multi-phase polymer comprising at least two polymer components, each of said components having a distinct glass transition temperature. 4. Arrangement of coated metal tube according to claim 3, characterized in that said polymer material consists of copolymers or mixtures of polymer polymers chosen from the group consisting of polyamides, polyesters, polyolefins, polyurethane and poly (vinyl chloride).   5. Arrangement of coated metal tube according to claim 1, characterized in that said polymeric material has a damping factor of at least 0.05   and a flexural modulus less than 50 MPa.   6. Arrangement of coated metal tube according to claim 5, characterized in that said damping factor of said polymeric material is between 0.1 and 0.3 in a range of application temperatures between -50 and 150 degrees Celsius. 7. Arrangement of coated metal tube according to claim 1, characterized in that said layer of polymeric material (12,14) has a wall thickness at least 50 micrometers.   8. Coated metal tube arrangement according to claim 7, characterized in that said layer of polymeric material (12, 14) has a wall thickness   between 200 micrometers and 500 micrometers.   9. Coated metal tube arrangement according to claim 1, characterized in that said layer of expanded polymeric material (12, 14) is formed by mixing a blowing agent with a polymeric material before extruding said mixture of blowing agent. and polymer material. 10. Arrangement of coated metal tube according to claim 9, characterized in that said blowing agent is chosen from the group consisting   azodicarbonamides, hydrazine derivatives, semi-   carbazides, tetrazoles, benzoxazines and mixtures thereof. 11. Arrangement or structure of coated metal tube characterized in that it comprises: a metal tube (10), an inner layer (12) of a first polymeric material bonded to said tube, and an outer layer (14) of a second polymeric material surrounding said inner layer (12), said   second polymer material having an expanded structure.   12. Arrangement of coated metal tube according to claim 11, characterized in that said inner layer (12) and said outer layer (14) are not linked. 13. Arrangement of coated metal tube according to claim 11, characterized in that said first polymer material has a damping factor of   less than 0.5 and a flexural modulus of at least 100 MPa.   14. Arrangement of coated metal tube according to claim 11, characterized in that said first polymer material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides) , polyacetals, phenolic resins, polyketones and polyolefins. 15. Arrangement of coated metal tube according to claim 11, characterized in that said second polymeric material is chosen from the group consisting of polyamides, polyimides, polyesters, fluorinated plastics, epoxy resins, poly (phenylene sulfides) , polyacetals, phenolic resins, polyketones,   polyolefins and poly (vinyl chloride).   16. Coated metal tube arrangement according to claim 11, characterized in that said second polymeric material is a multi-phase polymer comprising at least two polymer components, each of said components having a transition temperature distinct glassy.   17. Arrangement of coated metal tube according to claim 16, characterized in that said second polymer material consists of copolymers or mixtures of polymer polymers chosen from the group consisting of polyamides, polyesters, polyolefins,   polyurethane and poly (vinyl chloride).   18. Arrangement of coated metal tube according to claim 11, characterized in that said second polymer material has a damping factor of at least   minus 0.05 and a flexural modulus less than 50 MPa.   19. Arrangement of coated metal tube according to claim 18, characterized in that said damping factor of said second polymer material is between 0.1   and 0.3 in an application temperature range between - 50 and 150 degrees Celsius.   20. Coated metal tube arrangement according to claim 11, characterized in that said outer layer has a wall thickness of at least 50 micrometers.   21. Coated metal tube arrangement according to claim 20, characterized in that said outer layer has a wall thickness between   200 micrometers and 500 micrometers.   22. Coated metal tube arrangement according to claim 11, characterized in that said outer layer of expanded polymeric material is formed by mixing a blowing agent with said second polymeric material before extruding said blowing agent mixture and second polymeric material.   23. Arrangement of coated metal tube according to claim 22, characterized in that said blowing agent is chosen from the group consisting   azodicarbonamides, hydrazine derivatives, semi-   carbazides, tetrazoles, benzoxazines and mixtures thereof.