WO2015186147A1

WO2015186147A1 - Bent coaxial tubes and method for manufacturing

Info

Publication number: WO2015186147A1
Application number: PCT/IT2014/000153
Authority: WO
Inventors: Cosimo Quaranta
Original assignee: Quasar S.R.L.
Priority date: 2014-06-03
Filing date: 2014-06-03
Publication date: 2015-12-10

Abstract

Method for manufacturing coaxial tubes and relative coaxial tubes obtained using such method, having at least one bending zone (17) and comprising an outer tube (13) having an inner wall (14) of diameter dint/ an inner tube (11), placed inside said outer tube (13) and having an outer wall (12) of diameter dext smaller than the diameter dint, an annular interspace (15) between the outer wall (12) of the inner tube (11) and the inner wall (14) of the outer tube (13), at least one separation element in metal mesh (20) placed in the interspace (15) at at least one bending zone (17) and permeable to fluids which may be present in said interspace (15), and being configured to transmit a bending force from the outer tube (13) to the inner tube (11) and to prevent the collapse and limit the deformation of the tubes (11, 13) when the bending force is applied.

Description

Bent coaxial tubes and method for manufacturing

Technical Field

The invention relates to bent coaxial tubes and to a method for manufacturing the same. The invention relates particularly, but not exclusively, to the sector of exhaust tubes and fuel tubes for combustion engines and turbines.

More generally, the invention finds application in the automotive, aviation and naval industry, in the air conditioning and refrigeration sectors and in industrial and civil plant design.

Prior Art

Coaxial tubes are known, comprising a double wall, i.e. consisting of an outer tube and an inner tube placed inside the outer tube, and bending methods thereof which involve the use of elements positioned in the interspace between the inner tube and the outer tube, at the bending zones of the tube .

For example, the document EP2425906 describes a bent tube comprising a double wall in which the element positioned in the interspace is a porous metal foam such as not to constitute a barrier to the passage of fluids inside the interspace. The metal foam is placed in the interspace before performing the bending.

One problem encountered in this prior art is the cost of the metal foam, its difficulty of application and its stiffness which limits the maximum bending angle obtainable.

The document DE4437380 describes a method of bending a tube comprising a double wall and applied to exhaust tubes, in which before the bending step an incompressible sandy material is placed in the interspace, said material being then removed after bending. Wire mesh bearings are placed in the bending zones to absorb the noise caused by the contact between the inner and outer tubes of the tube comprising a double wall.

The aforesaid prior art has the disadvantage of having to remove the element placed in the interspace, this making the production process of the bent tube more complicated.

The document US5497809 describes coaxial tubes which incorporate a plastic sleeve in the interspace between the inner tube and the outer tube. The sleeve is used in the bending operation and is suitable to allow the passage of fluids, if any, in the interspace.

The solution described has the problem of poor thermal conduction between the inner and outer tubes on account of the sleeve in plastic material interposed between the two tubes. Furthermore, the plastic material is not suitable for operating under high temperature conditions.

The Applicant has observed that the prior art is unable to provide a method of bending coaxial tubes which is simple, fast and inexpensive in terms of the number of steps required to obtain the finished product and in terms of the cost and availability of materials used, and which at the same time makes it possible to achieve good thermal conduction between the inner tube and the outer tube while retaining good resistance to high temperatures without undergoing degrading. Summary of the Invention

These and other objects are achieved by coaxial tubes and the manufacturing method thereof as claimed in the appended claims.

The claims constitute an integral part of the technical teaching provided herein in relation to the invention.

The following brief description is given so as to provide a basic understanding of some aspects of the invention.

This brief description is not an extended description and as such should not be understood as likely to identify key or critical elements of the invention, or suitable to outline its scope. Its sole purpose is to present some concepts of the invention in a simplified form as a preview of the detailed description given below.

According to a preferred embodiment, the coaxial tubes according to the invention comprise an outer tube and an inner tube placed inside said outer tube, an interspace between the inner tube and the outer tube and a separation element in metal mesh placed in the interspace at the bending zones of the tube.

The presence of the separation element in metal mesh has many advantages, including that of ensuring the passage of fluid inside the interspace.

According to a preferred embodiment, one method of obtaining the tubes according to the invention comprises the steps of:

- placing the inner tube and one or more separation elements inside the outer tube so that they are comprised in at least one zone of the interspace;

- bending the coaxial tubes in at least one zone in which one or more separation elements are present inside the interspace.

The use of the separation element in metal mesh in the bending process of coaxial tubes offers multiple advantages, including that of performing a support and stabilising function for the inner and outer tubes, preventing the collapse or other undesirable deformations thereof.

Brief Description of the Drawings

These and other characteristics and advantages of the present invention will be clearer from the following description of preferred embodiments made by way of a non- limiting example with the help of the accompanying drawings, in which elements denoted by the same or similar reference numeral indicate elements that have the same or similar functions and construction and wherein: Fig. la is a cross-section view of the coaxial tubes, comprising a separation element in metal mesh of an annular shape;

Fig. lb is an axonometric view of the separation element in metal mesh of an annular shape and an enlarged detail of the mesh;

Fig. 2 is an enlarged detail of a metal mesh before the same is processed to obtain a separation element;

Fig. 3 is a cross-section view of the coaxial tubes comprising several separation elements of an annular shape;

Fig. 4a is a cross-section view of the coaxial tubes, comprising a separation element of an open annular shape;

Fig. 4b is an axonometric view of the separation element of an open annular shape;

Fig. 5 is a cross-section view of the coaxial tubes, comprising a separation element of a helical shape.

Description of Preferred Embodiments

With reference to Figs, la and lb, a first preferred embodiment of the invention is shown.

Coaxial tubes 10 comprise an inner tube 11 having an outer wall 12 of diameter d_ext and an outer tube 13 having an inner wall 14 of diameter din_t - The diameter d_int of the inner wall 14 of the outer tube 13 is greater than the diameter d_ext of the outer wall 12 of the inner tube 11, so that, when the inner tube 11 is placed inside the outer tube 13, an interspace 15 is present between the inner wall 14 of the outer tube 13 and the outer wall 12 of the inner tube 11.

The coaxial tubes comprise rectilinear zones 16 and curved or bending zones 17.

At the bending zones 17, the coaxial tubes 10 preferably comprise at least one separation element 20 placed in the interspace 15 and having a thickness s_sep substantially equal to half the difference between the diameter di_nt of the inner wall 14 of the outer tube 13 and the diameter d_ext of the outer wall 12 of the inner tube 11.

In the preferred embodiment, the inner 11 and outer 12 tubes are made of metal, more preferably aluminium, titanium or austenitic stainless steel (e.g. AISI 321) .

In addition, the coaxial tubes 10 preferably comprise at least one pressure or flow sensor 30 placed for example between two bending zones and/or near the ends of the coaxial tubes, such as to detect pressure changes inside the interspace 15 due for example to leaks of fluid from the inner tube 11.

The separation element 20 of the preferred embodiment is made of metal mesh.

The metal mesh is composed of a plurality of metal filaments 25 which are initially arranged to form a first substantially flat mesh 26, for example the mesh shown in Fig 2. Subsequently, from these first meshes 26 arranged in layers one upon the other, by means of appropriate operations (for example, bending, compression, winding, tying, crimping etc.), products in metal mesh of different forms are obtained in which the metal filaments 25, following the above operations, assume the appearance of a more or less compact untidy mass 27 as shown in detail in Fig lb.

For example, the products in metal mesh manufactured by the company KnitMesh Technologies® are suitable to be used as separation elements 20 in the present invention.

Preferably, the metal filaments 25 which the metal mesh is composed of are made of alloys of austenitic stainless steel (e.g. AISI 304) .

Preferably, the separation element 20 in metal mesh is attached to the outer wall 12 of the inner tube 11 and/or the inner wall 14 of the outer tube 13, for example by welding or by means of inserts or rings welded to the corresponding tube. Alternatively, the separation element 20 in metal mesh is held in position in relation to the outer wall 12 of the inner tube 11 and/or inner wall 14 of the outer tube 13, by means of inserts or rings firmly joined to the corresponding tube, for example by interference.

Alternatively, it is possible to attach the separation element 20 in metal mesh by simply exploiting the friction between the separation element 20, the inner wall 14 of the outer tube 13 and/or the outer wall 12 of the inner tube 11.

The separation element 20 in metal mesh, in the preferred embodiment, is an annular element having the form of a sleeve 21.

The sleeve-shaped annular separation element 21 preferably has an inner diameter d_sep substantially equal to the diameter d_ext of the outer wall 12 of the inner tube 11 and a length l_sep substantially equal to the entire length of the curved or bending zone 17 of the coaxial tubes 10.

In another embodiment (Fig. 3), multiple annular separation elements 21' are present in a single bending zone 17 arranged next to one another and possibly spaced, in order to reduce the overall weight of the coaxial tubes 10.

In a further embodiment (Figs. 4a, 4b), the separation element 20 is a sleeve-shaped annular element 22 which at least partially surrounds the inner tube 11. It may be provided that such sleeve 22 is open, i.e. presents a split

23, along a longitudinal direction of the sleeve 22.

In a further embodiment (Fig. 5), the separation element 20 is in the shape of a strip wound in a spiral 24 around the outer wall 12 of the inner tube 11.

The coaxial tubes 10 as described herein are made by a manufacturing method which comprises the steps of:

1) placing the inner tube 11 inside the outer tube 13 and placing one or more separation elements 20 so that they are comprised in at least one zone of the interspace 15 between the outer wall 12 of the inner tube 11 and the inner wall 14 of the outer tube 13;

2) bending the coaxial tubes 10 at at least one zone in which one or more separation elements 20 are present inside the interspace 15.

In the preferred embodiment, the step 1) of the method comprises two distinct steps:

la) placing one or more separation elements 20 on the outer wall 12 of the inner tube 11;

lb) inserting the inner tube 11 provided with at least one separation element 20 inside the outer tube 12.

Alternatively, in a further embodiment, said step 1) of the method comprises the steps of:

lc) placing one or more separation elements 20 on the inner wall 14 of the outer tube 13;

Id) inserting the inner tube 11 inside the outer tube 13 provided with one or more separation elements 20.

In yet another alternative, in another embodiment, said step 1) of the method comprises the steps of:

le) , inserting the inner tube 11 inside the outer tube

13;

If) placing one or more separation elements 20 between the outer wall 12 of the inner tube 11 and the inner wall 14 of the outer tube 13, for example by using a guide, if necessary.

According to a preferred embodiment, the steps la), lc) or If) also provide for attaching the separation element 20 in metal mesh to the walls 12, 14 of the tubes 11, 13, for example by welding, or by means of welded inserts or rings.

Alternatively, the separation element 20 in metal mesh is blocked on the outer wall 12 of the inner tube 11 and/or in the inner wall 14 of the outer tube 13, by means of inserts or rings firmly joined to the corresponding tube, for example by interference. In other embodiments, the steps la) , lc) or If) of the manufacturing method does not involve welding or the presence of inserts or rings. The attachment of the separation element 20 in metal mesh to the walls 12, 14 of the tubes 11, 13 is in fact ensured by the mere friction between the separation element 20 and the walls 12, 14.

In the preferred embodiment of the present invention, the steps la) , lc) or If) of the manufacturing method provide for the use of a sleeve-shaped annular separation element 21.

In further embodiments, the steps la) , lc) or If) of the manufacturing method involving the use of several separation elements in metal mesh of an annular shape 21', or of sleeve- shaped annular separation element in metal mesh which surrounds at least partially the outer wall 12 of the inner tube 11, or even a separation element in metal mesh which is in the shape of a strip wound in a spiral 24 around the outer wall 12 of the inner tube 11.

The use of metal mesh as the preferred material for making the separation element 20 provides several advantages.

A first advantage is that the metal mesh, even when compressed, as happens at the bending zones 17, does not prevent the passage of fluids through said mesh, thanks to the gaps between the metal filaments 25 of which it is composed. Advantageously, this allows a fluid present in the interspace 15, due, for example, to possible leaks of the inner tube 11, not to remain trapped between two bending zones, but rather to flow along the entire length of the coaxial tubes 10 and be detected by pressure or flow sensors 30.

The capacity of the separation element 20 to allow the passage of fluid inside the interspace 15 is even greater in the case in which the separation element is in the shape of a non-closed sleeve 22, thanks to the presence of the split 23. Additionally, the use of separation elements in the form of strips, whether wound to form a sleeve 22 or wound in a spiral 24, facilitates their use, such separation elements being adaptable to any internal diameter of the inner 11 and outer 13 tubes.

The separation element 20 in metal mesh also offers the advantage of allowing a heat exchange between the inner tube 11 and the outer tube 13.

A further advantage is given by the capacity of the metal mesh to operate at high temperatures and in corrosive environments .

Another advantage is the ability of the metal mesh to absorb vibrations and the noise possibly produced by the coaxial tubes.

The use of separation elements in metal mesh offers important advantages also during the manufacturing process of the coaxial tubes 10.

A first advantage derives from the stabilising and support function performed by the metal mesh, which, in addition to transmitting the bending force from the outer tube 13 to the inner tube 11, prevents the collapse of the tubes themselves and the formation of elbows or other deformations .

A second advantage derives from the relatively low resistance to deformation of the metal mesh, i.e. its flexibility, making it possible to achieve even small curvature radii.

A third advantage derives from the possibility of keeping the separation element inside the finished product, reducing the steps and the complexity of the manufacturing method of the tube.

A further advantage is due to the availability and relative low manufacturing cost of metal mesh. It is evident that the description provided herein is given solely by way of a non-limiting example and that variations and modifications may be made without departing from the scope of the invention, as defined by the following claims .

Claims

P4195PC00 Claims

1. Coaxial tubes having at least one bending zone (17), comprising an outer tube (13) having an inner wall (14) of diameter di_nt, an inner tube (11) placed inside said outer tube (13) and having an outer wall (12) of diameter d_ext smaller than the diameter di_nt, an annular interspace (15) between said outer wall (12) of said inner tube (11) and said inner wall (14) of said outer tube (13), at least one separation element in metal mesh (20) placed in said interspace (15) at said at least one bending zone (17) and having a thickness s_sep substantially equal to half the difference between said diameter di„_t of said inner wall (14) and said diameter d_ext of said outer wall (12), said at least one separation element (20) being permeable to fluids which may be present in said interspace (15), and being configured to transmit a bending force from said outer tube (13) to said inner tube (11) and to prevent the collapse and limit the deformation of said tubes (11, 13) when the bending force is applied.

2. Tubes according to claim 1, in which said separation element is an annular, sleeve-shaped element (21) .

3. Tubes according to claim 1, in which said separation element is an annular sleeve-shaped element (22) able to at least partly surround said outer wall (12) of said inner tube (11).

4. Tubes according to claim 1, in which said separation element is a strip bent in the shape of a spiral (24) .

5. Tubes according to any of the previous claims, in which said separation element (20) is attached to said outer wall (12) of said inner tube (11) or to said inner wall (14) of said outer tube (13) by welding or by means of inserts or rings welded or firmly joined to said inner (11) or outer tube (13) . P4 lyupcuu

6. Method for manufacturing coaxial tubes (10) comprising an outer tube (13) having an inner wall (14) of diameter di„_t, an inner tube (11) having an outer wall (12) of diameter d_ext smaller than the diameter d±_nt, at least one separation element in metal mesh (20), said method comprising the steps of:

placing said inner tube (11) inside said outer tube (13) and placing said at least one separation element <20) so that it is comprised in at least one zone of an interspace (15) between said outer wall (12) of said inner tube (11) and said inner wall (14) of said outer tube (13), at possible bending zones, so as to keep said inner tube (11) and said outer tube (13) separate during the bending step;

- bending said coaxial tubes (10) at said at least one zone in which said at least one separation element (20) is present inside said interspace (15) .

7. Method according to claim 6, wherein the step of placing said inner tube (11) inside said outer tube (13) and said at least one separation element (20) in the interspace (15) between said inner tube (11) and said outer tube (13) comprises the steps of:

- placing said at least one separation element (20) on said outer wall (12) of said inner tube (11);

- inserting said inner tube (11) provided with said at least one separation element (20) inside said outer tube (13) ;

or, alternatively, comprises the steps of:

- placing said at least one separation element (20) on said inner wall (14) of said outer tube (13);

- inserting said inner tube (11) inside said outer tube (13) provided with said at least one separation element (20) ;

or, alternatively, comprises the steps of: - inserting said inner tube (11) inside said outer tube (13);

- placing said at least one separation element (20) between said outer wall (12) of said inner tube (11) and said inner wall (14) of said outer tube (13) .

8. Method according to claim 7, wherein the steps of placing said at least one separation element (20) on said inner wall (14) of said outer tube (13) and/or on said outer wall (12) of said inner tube (11) provide for attaching the separation element (20) to said inner (14) or outer (12) wall by welding or by means of rings welded or firmly joined to said inner (11) or outer (13) tube or by friction between said separation element (20) and said walls (12, 14) .

9. Method according to claims 7 or 8, wherein the steps of placing said at least one separation element (20) on said inner wall (14) of said outer tube (13) and/or on said outer wall (12) of said inner tube (11) provide for arranging at least one annular, sleeve-shaped element (21) in metal mesh, or at least a sleeve-shaped annular element (22) able to at least partly surround said outer wall (12) of said inner tube (11), or at least a strip of metal mesh wound into a spiral (24) .