# Patent

## Title
Method of manufacturing a tubular insulating device and corresponding device

## Abstract

An insulating material is fed in and shaped by superposing a plurality of N layers Ci (3) of the insulating material. For each layer Ci, a plurality of ni, axial insulating elements Ei precut from the insulating material is formed, a rough form of the tubular insulating device is formed by using an adhesive to assemble the Ni elements Ei of each layer Ci which are juxtaposed along a plurality of joining zones Ji, so that the plurality of joining zones Ji+1 of a layer Ci+1 is offset relative to the plurality of joining zones Ji, of the adjacent layer Ci. Then, by the adhesive is polymerized, and the tubular element rough form is subjected to a heat treatment. The method is economical and makes it possible to obtain a device of high mechanical strength.

## Background
FIELD OF THE INVENTION
This invention relates to the manufacture of refractory carbon material capable to be used as high-temperature thermal insulators in ovens operating at high temperatures and in a non-oxidizing atmosphere.
This invention relates more particularly to expanded graphite base cylindrical or tubular insulators, intended for high-temperature ovens.
PRIOR ART
Application FR 2 849 651 describes an insulating structure comprising at least one flexible layer with a “dense” compressed expanded graphite particle base, of which the density is at least equal to 400 kg/m3 and at least one other layer, “sub-dense”, also with an expanded graphite base, having a density that is lower than that of the dense layer, typically less than 400 kg/m3.
The same patent application further describes the use of the insulating structure for manufacturing parts of cylindrical form, by coiling insulating structures in a spiral such as described hereinabove. The main disadvantage in this technique resides in the fact the layers become detached during the heat treatment to which is submitted the cylinder obtained after coiling.
This technique of coiling in spirals is also described in other patents or patent applications such as U.S. Pat. No. 6,143,601 and U.S. 2004/0076810.
On the other hand, application FR 2 849 651 describes a method of manufacturing comprising, in addition to a step of coiling, the use of a curving technique for the manufacture of portions of cylinders with the insulating structure such as described hereinabove.
PROBLEMS PUT FORTH
The invention aims to overcome several problems simultaneously, the method of manufacturing of tubular insulating devices according to the invention having to make possible all at the same time:

    
    
        obtaining devices of high mechanical resistance across the entire range of high temperature of use, being able to exceed 1500° C.,
        obtaining devices having a high “insulating power/mass ratio”,
        a method of manufacturing that is simple and economical as it makes use of a single and same technology, and furthermore easy to adapt to any form of tubular device.
    
    


OBJECT OF THE INVENTION
The applicant has now perfected a method of manufacturing tubular devices used in particular for the insulating of high-temperature ovens by curving insulating structures making it possible to obtain tubular wall elements, then gluing on edges of these elements and stacking of two layers of insulating structures with an offset of the glued edges forming a junction between two juxtaposed elements.
In this method of manufacturing a tubular insulating device comprising a lateral wall of thickness Ep, of axial length L, provided with an axial direction, is fed an insulating material with bi-dimensional structure of thickness EM<Ep, with for example EM at most equal to 0.5 Ep, and said insulating material is put into form by superposing a plurality of N layers C1 of said insulating material, with i ranging from 2 to N, said tubular insulating device comprising at least two layers C1 and C2 of said insulating material.
This method is characterised in that:
a) for each layer Ci, a plurality of ni precut axial insulating elements Ei is formed in said insulating material in such a way that said ni, insulating elements Ei can form said layer Ci, after an edge-to-edge juxtaposition and thanks to an adapted deformation,
b) a rough form of said tubular insulating device is formed by:
b1) assembling, thanks to an adhesive, more preferably on an axial shaping mandrel, layer after layer, and by beginning with the first inside layer C1, the ni elements Ei of each layer Ci juxtaposed edge to edge according to a plurality of joining zones Ji, the elements Ei+1 of the layer Ci+1 being offset in relation to the elements Ei of the layer Ci in such a way as to offset the plurality of joining zones Ji+1 in relation to the plurality of joining zones Ji, and as such obtain in fine a tubular insulating device of high mechanical strength,
b2) then by polymerizing said adhesive, in such a way as to rigidify said rough form,
c) said rough form of tubular element is subjected to a heat treatment, in such a way as to carbonize said adhesive, and as such obtain, where applicable after separation from said mandrel, said tubular insulating device.
This method makes it possible to overcome the problems put forth.
Indeed, the applicant has observed that the devices obtained via this method of manufacturing did indeed have the high mechanical strength required in particular for their use as an insulating sleeve for ovens in an industrial environment, and, thanks to an appropriate choice of the insulating material, an excellent “insulating power/mass” ratio.
Moreover, as it does not require coiling, the manufacture of these devices is simple as well as capable of being applied to any form of tubular device, since it comprises a preparation of insulating elements, for example by cutting in an insulating material in strips or in sheets, possibly followed by their forming, and followed by their assembly thanks to an adhesive, by forming at least two layers. This method calls upon only a limited number of pieces of industrial equipment in such a way that it is economical and also nevertheless of great flexibility in order to form devices of all sorts of forms or dimensions.



DESCRIPTION OF THE FIGURES
All of the figures relate to the invention.
FIGS. 1a to 1g diagrammatically show different steps of the manufacture of a tubular insulating device (1) according to the invention.
FIG. 1a shows, as a partial section according to a transversal plane, the insulating material (2) with bi-dimensional structure of thickness EM used to form said insulating elements (4).
FIGS. 1b and 1c are views, as a transversal section, of the planar insulating elements (4, 4a) formed by cutting in said material (2) in FIG. 1a, and noted respectively EP1 and EP2, the planar insulating element EP1 in FIG. 1b, intended to form an insulating element of the first layer C1, having a width l1 less than that l2 of the planar insulating element EP2 in FIG. 1c and intended to former an insulating element of the second layer C2.
FIGS. 1d and 1e, analogous to FIGS. 1b and 1c, show the curved insulating elements EC1 and EC2 formed by curving respectively the planar insulating elements EP1 and EP2 of FIGS. 1b and 1c. 
FIG. 1f is a view, as a transversal section in a plane perpendicular to its axial direction (11), of the rough form (5) formed by assembling, on two layers C1 and C2, of the eight curved insulating elements EC1 and EC2 of FIGS. 1d and 1e (four insulating elements per layer Ci), this assembly being formed by a gluing on the edge (60) between curved elements (4, 4b) of the same layer Ci, and by so-called inter-layer gluing (61) between the layers C1 and C2, the layers C1 and C2 being directed in such a way that the axial junctions JA1 (30, 31) of the first layer C1 (3, 3a) are angularly offset in relation to the axial junctions JA2 (30, 31) of the second layer C2 (3, 3b).
FIG. 1g is a partial side view of the rough form (5) in FIG. 1f. 
FIG. 2a is analogous to FIG. 1f and shows another modality of rough form (5), and therefore tubular insulating device (1), further comprising two layers C1 and C2, each layer Ci comprising 3 insulating elements (4, 4b) per layer Ci.
FIG. 2b, analogous to FIG. 2a, shows another modality of rough form (5) and of device (1), wherein the number N of layers Ci is equal to 3, each layer Ci comprising two elements Ei.
FIGS. 2c and 2d are enlarged views of the curved portions “c” and “d” in FIG. 2b, which respectively show the gluing on edge (60) between curved elements (4b) of the same layer Ci and the inter-layer gluing (61) between two adjacent layers Ci and Ci+1, is between the layers C1 and C2 in FIG. 2b. 
FIGS. 3a to 3f show different forms of lateral walls (10) of the devices (1) and of the corresponding rough forms (5).
FIGS. 3a to 3c relate to tubes (1a) with lateral walls (10) with constant section, along their entire axial length L.
FIG. 3a is a side view of the lateral wall (10), wherein the axial joining zones Ji (30) have not been shown.
FIGS. 3b and 3c show two outside transversal sections of the lateral wall (10) in FIG. 3a, the FIG. 3b corresponding to a cylindrical wall of outside diameter D, and the FIG. 3c corresponding to a 6-faced hexagonal wall of which the outside section is inscribed in a circle of diameter D.
FIGS. 3d to 3f, analogous respectively to FIGS. 3a to 3c, relate to tubes (1b) with variable section on their axial length L and of average outside diameter DM at mid-height.
FIG. 3d shows the wall (10) of tapered form as a side view.
FIG. 3e diagrams the case of a circular section, while the FIG. 3f diagrams the case of a polygonal (hexagonal) section.
FIG. 4a, analogous to the FIG. 1g or 3a, shows a device (1) or a rough form (5) said of great axial length L, of which each layer Ci comprises at least one transversal junction zone JTi (32) in order to join said curved elements (4, 4b) according to said axial direction (11). The inside layer C1 (3a) comprises two transversal junctions JT1 offset axially in relation to the single transversal junction JT2 of the outer layer C2 (3b).
FIG. 4b is a bottom view of the device (1) in FIG. 4a. 
FIG. 4c is an axial cross-section of the wall (10) according to the plane B-B in FIG. 4b passing through said axial direction (11).
FIGS. 4d and 4e show, as a partial transversal section, two modalities of material (2′) with an expanded graphite base constituting said insulating material (2) and forming a multilayer material (2a).
FIG. 4d shows a multilayer material (2a) comprising two layers of expanded graphite: one layer referred to as “low density” (20) and a layer referred to as “high density” (21), the high-density layer (21) having for example a thickness at least two times less thick than that of the low-density layer (20).
FIG. 4e, analogous to the FIG. 4d, forms a three-layer material (2) comprising a central layer (23) forming a low-density layer (20), and two external layers (22) forming two high-density layers (21). FIG. 4f is a partial transversal section of a wall (10) comprising two layers C1 and C2 formed using the material in FIG. 4d and assembled with a layer of adhesive (61) between the layers C1 and C2. As can be seen in FIG. 4f, the high-density layers (21) form the outside and inside surfaces of said wall (10).
FIGS. 5a to 5e diagrammatically show different views of a modality of manufacturing a rough form (5) using a shaping mandrel (7) as well as a shaping mould (8).
FIG. 5a shows, in perspective, two layers C1 and C2 of insulating material (2, 2′) arranged on the mandrel (7).
FIG. 5b shows a section, according to the axial direction (11), of the shaping mould (8) with two half-shells (80) containing the unit constituted of the elements in FIG. 5a, in such a way as to compress said layers Ci (3) between a rigid mandrel and the typically metal half-shells of the mould, and as such give predetermined dimensions to said rough form (5).
FIG. 5c shows as a side view the unit, at the output of the cast, formed by the mandrel (7) plus the rough form (5) with predetermined dimensions, the FIG. 5d showing the rough form (5) separated from the mandrel (7) shown in FIG. 5e. 



DETAILED DESCRIPTION OF THE INVENTION
According to the invention, and as shown in the FIGS. 1g and 4a, said joining zones Ji (30) can include axial joining zones JAi (31) of axial length at most equal to L.
However, as shown in FIGS. 4a and 4c, said joining zones Ji (30) can include transversal joining zones JTi (32) in such a way as to obtain a tubular insulating device (1, 1′) said of great axial length L.
However, when it is not required to join the elements (4) according to said axial direction (11) as shown in the FIGS. 4a and 4c, said joining zones Ji can be constituted of axial joining zones JAi (31) of axial length equal to L.
Advantageously, said ni axial insulating elements Ei precut (4) from the same layer Ci can be identical, said plurality of junctions Ji forming said plurality of axial junctions JAi (31), the ni axial junctions JAi (31) of said plurality being separated angularly in relation to said axial direction (11) by an angle of 360°/ni. However, in the case of the fabrication of a “customised” device of relatively complex configuration, it would be possible to juxtapose different insulating elements (4) by their form, in the way in which the different pieces of a puzzle are assembled, but on a surface deployed in the three-dimensional space.
As shown in the FIGS. 1f, 2a and 2b, the number N of layers Ci (3) can be at least equal to 2.
The number ni of insulating elements Ei (4) can be a number n which remains the same for each layer Ci (3) of said tubular insulating device (1), n varying typically with said average diameter D.
As such, for example:

    
    
        n can have the value of 2 for D ranging from 286 mm to 573 mm,
        n can have the value of 3 for D greater than 573 mm and less than 907 mm,
        n can have the value of 4 for D at least equal to 907 mm.
    
    


As shown in the FIGS. 1a to 1f, before the step b) of the method, using said ni insulating elements (4), for example using ni planar insulating elements (4a), ni curved insulating elements (4b) can be formed, in such a way as to have a radius of curvature Ri in a transversal plane perpendicular to said axial direction (11), corresponding to that of said corresponding layer Ci, said radius Ri increasing by a Ci to the next layer Ci+1 of greater average diameter Di+1.
In the method according to the invention, and as shown in the FIGS. 5a to 5e, during said step b2), said rough form (5) can be placed in a shaping mould (8) comprising, for example, two half-shells (80), in such a way that, with the two half-shells (80) together and closed provide said rough form (5) and in fine said tubular insulating device (1) with predetermined and reproducible geometric dimensions.
According to the invention, said insulating material (2) can be a material (2′) with an expanded graphite base of thickness EM ranging from 2 to 30 mm, and ranging preferably from 5 to 20 mm.
More preferably, and as shown in the FIGS. 4d and 4e, said material with expanded graphite base (2′) can be a multilayer material (2a) comprising at least one layer referred to as “low” density (20), its density being less than 0.4 g/cm3 (400 kg/m3) and at least one layer referred to as “high” density (21), its density being at least equal to 0.4 g/cm3.
Said high-density layer (21) can have a density ranging from 0.8 g/cm3 to 1.2 g/cm3 and wherein said low-density layer (20) has a density ranging from 0.03 g/cm3 to 0.2 g/cm3.
As shown in FIG. 4e, said multilayer material (2a) can be a material referred to as “triple-layer” (2b) comprising two high density external layers (22, 21) arranged on either side of a central low density layer (23, 20).
Advantageously, in such a way as to obtain a high “insulating power/mass” ratio, the thickness Ef of the low-density central layer (20, 23) can be at least twice as high than the thickness Eh of the high-density external layer (21, 22), and more preferably at least three times higher.
According to the invention, said adhesive (6) can include a thermosetting resin, for example a phenolic resin, or a thermoplastic resin, said adhesive being in the form of powder or in liquid form, said adhesive being advantageously loaded with a black carbon or graphite electro-conductive powder.
Said heat treatment can include a baking at a temperature of at least 800° C., and more preferably of at least 1000° C.
Said heat treatment can include an additional methane pyrolysis flash treatment in such a way as to increase the rigidity of said insulating device.
Furthermore, said heat treatment can include a step of purifying of said insulating device wherein said insulating device is brought to 2000° C., in such a way as to remove any volatile element.
Finally, said heat treatment can be followed by a machining.
As shown in the FIGS. 3a to 3c, said tubular insulating device (1) can form a tube (1a) with constant section on its axial length L, said section being circular of diameter D or oval or polygonal.
However, as shown in the FIGS. 3d to 3f, said tubular insulating device (1) can form a tube (1b) with a uniformly variable section on its axial length L, said section being circular of average diameter DM or oval or polygonal.
For example, said axial length L can vary from 0.1 m to 3 m, and said thickness Ep can range from 5 mm to 80 mm, the L/D or L/DM ratio able to range from 0.5 to 5.
Another object of the invention is constituted by a tubular insulating device (1) typically obtained by the method according to the invention. This tubular insulating device (1) comprises a lateral wall (10) of thickness Ep ranging from 5 mm to 80 mm, of axial length L ranging from 0.1 m to 3 m, provided with an axial direction (11), said lateral wall (10) forming a superposition being constituted by a plurality of N layers Ci (3) of an insulating material (2), with i ranging from 2 to N.
It is characterised in that:
a) each layer Ci (3) comprises a plurality of ni axial insulating elements Ei (4) constituted of said insulating material (2) in such a way that said axial insulating elements Ei (4) are juxtaposed edge (40) to edge (40′) according to a plurality of joining zones Ji (30),
b) two successive layers Ci and Ci+1 are assembled thanks to an adhesive (6), said successive layers Ci and Ci+1 being directed in relation to one another in such a way that the plurality of joining zones Ji+1 of said layer Ci+i is offset in relation to the plurality of joining zones Ji and said layer Ci, and that as well said tubular insulating device (1) obtained in fine has a high mechanical strength.
In this device, said insulating material (2) can be a material (2′) with expanded graphite base of thickness EM ranging from 2 to 30 mm, and ranging preferably from 5 to 20 mm.
Said material with expanded graphite base (2′) can be a multilayer material (2a) comprising at least one layer referred to as “low” density (20), its density being less than 0.4 g/cm3 (400 kg/m3) and at least one layer referred to as “high” density (21), its density being at least equal to 0.4 g/cm3.
Said high-density layer (21) can have a density ranging from 0.8 g/cm3 to 1.2 g/cm3 and wherein said low-density layer (20) has a density ranging from 0.03 g/cm3 to 0.2 g/cm3.
Said multilayer material (2a) can be a material referred to as “triple-layer” (2b) comprising two external high density layers (22, 21) arranged on either side of a central low density layer (20, 23).
Said low-density central layer (20, 23) can have a thickness Ef at least twice as high than the thickness Eh of the high-density external layer (21, 22), and more preferably at least three times higher.
EXAMPLES
FIGS. 1a to 5e constitute embodiments.
For the implementation of the method according to the invention, devices of complex form without rotation symmetry have as such also been manufactured, and in particularly in this case, computer means were used making it possible, using the precise geometric definition of said device (1) introduced into the computer memory, to define the plurality of insulating elements Ei of each layer Ci, in such a way that all of the joining zones (30, 31, 32) are offset.
In the case where the insulating elements (4) are not of simple form and do not result in an even and compact tiling, computer means were used to optimise the cutting of these elements and minimise the scrap and losses of insulating material.
However, this scrap was able to be recycled by homogenising them and by incorporating them at a low percentage (more preferably <10%) into the low-density layer (20).
Different types of mandrels were used. The mandrels were coated with sliding agents in such a way as to facilitate the separation between rough form (5) and mandrel (7). Mandrels with a retractable core were also used, in such a way as to further facilitate this separation.
ADVANTAGES OF THE INVENTION
The method according to the invention has major advantages. Indeed, in addition to overcoming the problems put forth, it can easily be automated and adapted to any configuration of device (1), even of complex form.
LIST OF MARKINGS


    
    
        Tubular insulating device 1
        Device 1 of great axial length 1′
        Tube with constant section 1a 
        Tube with variable section 1b 
        Lateral wall 10
        Axial direction 11
        Insulating material with bi-dimensional structure 2
        Material with expanded graphite base 2′
        Multilayer material 2a 
        Triple-layer material 2b 
        “Low density” layer 20
        “High density” layer 21
        External layer 22
        Central layer 23
        Layer Ci of 1 3
        Inside layer 3a 
        Outer layer 3b 
        Central layer 3c 
        Joining zone Ji of 3 30
        Axial joining zone JAi 31
        Transversal joining zone JTi 32
        Axial insulating element Ei 4
        Planar insulating element Epi 4a 
        Curved insulating element Eci 4b 
        Juxtaposition edge 40, 40′
        Rough form of 1 5
        Adhesive 6
        Edge-to-edge gluing edge zone 60
        Inter-layer gluing zone 61
        Axial mandrel 7
        Shaping mould 8
        Half-shells of the mould 80

## Claims

1. A method of manufacturing a tubular insulating device comprising a lateral wall of thickness Ep and of axial length L, the method comprising:
cutting an insulating material into a plurality of axial insulating elements;
shaping the plurality of axial insulating elements so that they have a curved shape;
assembling a first layer of axial insulating elements by using an adhesive to attach the curved axial insulating elements along a plurality of axial joining zones; and along a plurality of transversal joining zones;
assembling at least one more layer of axial insulating elements by using the adhesive to attach axial insulating elements around a preceding layer so that a plurality of axial joining zones in a preceding layer is offset from a plurality of axial joining zones in a subsequent layer; and a plurality of transversal joining zones in a preceding layer is offset from a plurality of transversal joining zones in a subsequent layer;
polymerizing the adhesive; and
subjecting the layers of axial insulating elements to a heat treatment to carbonize the adhesive.

2. The method according to claim 1, wherein said axial joining zones have an axial length different from the axial length L of the lateral wall.

3. The method according to claim 1, wherein the number of axial insulating elements is a number N which remains the same for each layer of said tubular insulating device.

4. The method according to claim 1, wherein the curved axial insulating elements are formed in such a way as to have a radius of curvature Ri, increasing in each subsequent layer of axial insulating elements.

5. The method according to claim 1, wherein, before the heat treatment, a rough form of the layers of axial insulating elements is placed in a shaping mold comprising two half-shells for adjusting the geometric dimensions of the rough form.

6. The method according to claim 1, wherein said insulating material is a material with expanded graphite base of thickness EM ranging from 2 to 30 mm.

7. The method according to claim 6, wherein said material with expanded graphite base is a multilayer material comprising at least one low density layer, having a density less than 0.4 g/cm3 and at least one high density layer, having a density at least equal to 0.4 g/cm3.

8. The method according to claim 7, wherein said high-density layer has a density ranging from 0.8 g/cm3 to 1.2 g/cm3 and wherein said low-density layer has a density ranging from 0.03 g/cm3 to 0.2 g/cm3.

9. The method according to claim 7, wherein said multilayer material has two high density external layers arranged on either side of a central low density layer.

10. The method according to claim 9, wherein the thickness of the low-density central layer is at least twice as thick as the thickness of each of the high-density external layers.

11. The method according to claim 1, wherein said adhesive comprises a thermosetting resin, or a thermoplastic resin, said adhesive being in the form of a powder, or in liquid form, and said adhesive being advantageously loaded with a black carbon or graphite electro-conductive powder.

12. The method according to claim 1, wherein said heat treatment comprises a baking at a temperature of at least 800° C.

13. The method according to claim 12, wherein said heat treatment comprises an additional methane pyrolysis flash treatment for increasing the rigidity of the insulating device.

14. The method according to claim 12, wherein said heat treatment comprises a step of purifying said insulating device, wherein said insulating device is brought to 2000° C. for removing any volatile element.

15. The method according to claim 1, wherein said heat treatment is followed by a machining.

16. The method according to claim 3, wherein the tubular insulating device forms a tube having a constant transversal section along the axial length L, said section being circular of diameter D, or oval, or polygonal.

17. The method according to claim 1, wherein the tubular insulating device forms a tube having a uniformly variable transversal section along the axial length L, said section being circular of average diameter DM, or oval, or polygonal.

18. The method according to claim 1, wherein said axial length L is from 0.1 m to 3 m, and wherein said thickness Ep is from 5 mm to 80 mm.

19. The method according to claim 18, wherein a ratio L/D or L/DM is from 0.5 to 5.

20. The method according to claim 16, wherein N is 2, and D is from 286 mm to 573 mm.