WO2018011577A1

WO2018011577A1 - Conduit formation and use

Info

Publication number: WO2018011577A1
Application number: PCT/GB2017/052051
Authority: WO
Inventors: Phil Johnson; Paul WOOLRIDGE; Nick GROCUTT; Anthony HABERMAN; Paul BLEWITT; Tim MULQUEEN
Original assignee: Ramfoam Ltd
Priority date: 2016-07-12
Filing date: 2017-07-12
Publication date: 2018-01-18
Also published as: GB2554850A; GB201612111D0

Abstract

A method, a guide apparatus and a selective catalytic reduction apparatus are provided. The method, comprises: heating foam material; using the guide apparatus to cause the heated foam material to bend; forming a conduit, made at least in part from the foam material, by attaching at least a first edge of the foam material to at least a second edge of the foam material; and cooling the conduit following attachment of at least the first edge to at least the second edge. The conduit may be a thermally insulating tube that is used in the selective catalytic reduction apparatus for thermally insulating diesel exhaust fluid flowing in a conveying conduit.

Description

TITLE

Conduit formation and use TECHNOLOGICAL FIELD

Embodiments of the present invention relate to conduit formation and use. In particular, they relate to a conduit, formed from a foam material, for use in a selective catalytic reduction apparatus of a vehicle.

BACKGROUND

A selective catalytic reduction apparatus of a vehicle is an apparatus for controlling the emissions that are produced in the exhaust stream of a diesel combustion engine. A diesel exhaust fluid, in the form of a reductant, is injected into a stream of exhaust gas from the diesel combustion engine. This causes a chemical reaction to occur which converts nitrogen oxides into nitrogen, water and carbon dioxide, thereby reducing the amount of nitrogen oxides that are emitted. BRIEF SUMMARY

According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: heating foam material of a generally planar shape; using a guide apparatus to cause the heated foam material to bend; forming a tube, using the foam material, by adhering a first edge of the foam material to a second edge of the foam material; and cooling the tube following adherence of the first edge to the second edge.

According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: heating foam material; using a guide apparatus to cause the heated foam material to bend; forming a conduit, made at least in part from the foam material, by attaching at least a first edge of the foam material to at least a second edge of the foam material; and cooling the conduit following attachment of at least the first edge to at least the second edge. According to various, but not necessarily all, embodiments of the invention there is provided a method, comprising: cutting foam material, that is generally planar in shape, to form a first sloped edge and a second sloped edge; heating the foam material to a temperature that is greater than the operating temperature of the foam material minus 5% of that operating temperature; guiding the heated foam material through a guide apparatus in order cause the heated foam material to bend; forming a tube, using the foam material, by adhering the first sloped edge to the second sloped edge; and cooling the tube, following adherence of the first edge of the foam material to the second edge of the foam material, using a cooling device.

According to various, but not necessarily all, embodiments of the invention there is provided a guide apparatus, comprising: a first guide comprising a first plurality of rollers; a second guide comprising a second plurality of rollers; and a drive configured to cause a generally planar foam material to move through the rollers of the first guide and then the rollers of the second guide, in order to cause gradual bending of the generally planar foam material. According to various, but not necessarily all, embodiments of the invention there is provided a selective catalytic reduction apparatus for a vehicle, comprising: a repository for storing diesel exhaust fluid; an injector for injecting the diesel exhaust fluid to a stream of exhaust gas from a diesel combustion engine; a conduit for conveying the diesel exhaust fluid from the repository to the injector; and a thermal insulator, made from foam material, for thermally insulating diesel exhaust fluid flowing in the conduit.

According to various, but not necessarily all, embodiments of the invention there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only to the accompanying drawings in which: Fig 1 illustrates a slab of foam material;

Fig 2 illustrates a flow chart of a method;

Fig 3 illustrates slabs of foam material being joined together to form a sheet of foam material;

Fig 4 illustrates a sheet of foam material after slabs of foam material have been joined together;

Fig 5 illustrates a sheet of foam material being split using a first cutting apparatus; Figs 6 and 7 illustrate the foam material being sliced into strips;

Fig 8 illustrates the foam material being heated using a heating apparatus;

Fig 9 illustrates a guide apparatus comprising a drive and a plurality of guides;

Fig 10 illustrates a guide of the guide apparatus;

Fig 1 1 illustrates first and second edges of the foam material being joined to form a conduit;

Fig 12 illustrates the foam material being cooled using a cooling apparatus; and Fig 13 illustrates a selective catalytic reduction apparatus.

DETAILED DESCRIPTION

Fig. 1 illustrates a slab 12 of foam material 10. The foam material 10 is a "technical" foam material that acts as a thermal insulator. It is a closed cell foam material that is relatively rigid at room temperature. It may, for example, have a density in the range 30kg to 60 kg/m³. The foam material may be resistant to hydrocarbons, such as those found in engine oil and diesel fuel. The foam material may be formed, at least in part, by one or more polyamides. For example, the foam material may be based on Nylon 6.

The upper operating temperature of the foam material 10 might be in the range 50°C to 150°C. In some embodiments, it might be in the range 150°C to 250°C. Thermal shrinkage of the foam material 10 at the upper operating temperature might be approximately 5% or greater.

The slab 12 of foam material 10 is generally planar in shape has a length dimension L, a width dimension W, and a depth dimension D. The length dimension is substantially perpendicular to each of the width dimension W and the depth dimension D. The width dimension W is substantially perpendicular to the depth dimension D.

In some implementations, the length of the slab 12 might be 2m, the width of the slab 12 might be 1 m, and the depth of the slab 12 might be 30mm, but this can vary.

Fig. 2 illustrates a flow chart of a method of forming a conduit using slabs 12 of foam material 10. This is described in detail below. Fig. 3 illustrates two slabs 12a, 12b of foam material 10 being joined/fused using a butt welding process. In this process, while the slabs 12a, 12b are held in place by clamps 16, a heater 14 is placed between the slabs 12a, 12b as illustrated by the arrow 13 in Fig. 3. The heater 14 is positioned to heat opposite faces 3, 4 (defined by the width dimension W and the depth dimension D) of each slab 12a, 12b.

The heater 14 produces sufficient heat to cause the opposite faces 3, 4, of the slabs 12a, 12b to melt. In one implementation, the heater 14 may be heated to a temperature of 420 °C, for example. After the faces of the slabs 12a, 12b have been heated to a sufficient temperature, the heater 14 is removed from its position (as illustrated by arrow 7) and the slabs 12a, 12b are joined by urging them towards each other, as illustrated by the arrows 15 and 17 in Fig. 4. Multiple slabs may be joined together in this manner to produce a sheet 1 12 of foam material 10. For example, in one implementation, five slabs 12 of foam material 10, of length 2m, width 1 m and depth 30mm are joined together to produce a sheet 112 of foam material 10 which has a length of 10m, a width of 1 m and a depth of 30mm.

The sheet 1 12 of foam material is then split into 2 separate (generally planar) sheets 212a, 212b by cutting the sheet 1 12 of foam material 10 in a plane defined by the length dimension L and the width dimension W. This is illustrated in Fig. 5.

The sheet 1 12 of foam material 10 is split using a splitting apparatus 21. The splitting apparatus 21 comprises upper and lower pressure rollers 20 and at least one cutting blade 18. The sheet 1 12 of foam material 10 is driven towards the cutting blade 18 by the pressure rollers 20 as illustrated by the arrow 19 in Fig. 5. This causes the sheet 112 to be split into multiple smaller sheets 212a, 212b. In the illustration shown in Fig. 5 a single, thicker sheet 112 is being split into two thinner sheets 212a, 212b, but, in other implementations, more than two thinner sheets may be produced from a single thicker sheet. The depth/thickness of each thinner sheet 212a, 212b, could, for example, be in the range 2.5mm to 20mm.

In block 203 of Fig. 2, a thinner sheet 212 of foam material 10 is cut into strips. Initially, a sheet 212 of foam material 10 may be cut along its length using a lathe slitting machine. This involves placing the sheet 212 of foam material 10 on a mandrel, rotating the mandrel at high speed and cutting the sheet 212 of foam material 10 using a high speed spinning circular blade in order to obtain generally planar strips 312 of foam material 10 of the required width.

The strips 312 of foam material are then cut using a cutting apparatus 24. Figs 6 and 7 illustrate a strip 312 of foam material 10 being cut using the cutting apparatus 24. The cutting apparatus 24 comprises a plurality of sloped blades 22. The movement of the foam material 312 relative to the blocks 22, as illustrated by arrow 23 in Fig. 7, causes smaller strips 412a, 412b of foam material 10 to be produced.

The blades 22 of the cutting apparatus 24 are sloped relative to an upper surface 313 and a lower surface 314 of the strip 312 of foam material 10. The cutting of the strip 312 of foam material 10 into the smaller strips 412 of foam material 10 forms sloping edges on either side of the width of each of the smaller strips 412 of foam material 10. The angle of the blades 22 (and therefore also of the sloping edges) may be in the range 30 degrees to 60 degrees. In some examples, the range is in the region of 40 degrees to 45 degrees. In this example, the angle at which each blade is positioned is the same.

The resulting smaller strips 412 of foam material are generally planar in shape. After the foam material 10 has been cut into smaller strips 412 and the sloping edges have been formed, each smaller strip 412 of foam material 10 is heated using a heating apparatus 26, as illustrated in Fig. 8. The first and second sloping edges of the strip 412 of foam material 10 are denoted by the reference numerals 413 and 414 in Fig. 8.

The heating apparatus 26 comprises a housing 30 defining an internal cavity 34. The housing 30 comprises at least first and second apertures 32, 33. The housing 30 also comprises one or more heating elements 28. In this example, the strip 412 of foam material is inserted into the housing 30 of the heating apparatus 26 via the first aperture 32, and it exits the housing 30 of the heating apparatus 26 via the second aperture 33 by being urged in the direction illustrated by arrow 31. As the strip 412 of foam material 10 passes through the heating apparatus 26, it is heated to a temperature that is at least: the operating temperature of the foam -5% of that operating temperature. For example, if the upper operating temperature of the foam material 10 is 200°C, then it is heated to at least 190°C. The heat that is applied to the strip 412 of foam material by the heating apparatus 26 is sufficient to make the foam material 10 more malleable, but it does not melt the foam material 10.

Following heating of the strip 412 of foam material 10 in block 204 of Fig. 2, the strip of foam material 412 is bent using a guide apparatus 37 in block 205 of Fig. 2. An example of the guide apparatus 37 is illustrated in Fig. 9. The guide apparatus 37 comprises a drive 36 and a plurality of guides 38-38d for shaping the strip 412 of foam material 10. The first guide 38a is illustrated in more detail in Fig. 10. The first guide 38a comprises an outer support 40, an inner support 42 and a connector 44 for connecting the outer support 40 to the inner support 42. The purpose of the inner support 42 is to hold a plurality of rollers 46a-46g in place. The inner support 42 is curved and, in the illustrated example, is circular/ring-shaped. The rollers 46a-46g are positioned on the inner support 42 such that they also collectively define a ring shape. The inner support 42 and the rollers 46a-46g are dimensioned such that a strip 412 of foam material may be passed through an aperture 39a defined by the inner support 42 and the rollers 46a- 46g. The dimensions of the aperture 39a are such that the strip 42 of foam material 10 must bend in order to pass through the aperture 39a.

The purpose of the outer support 40 and the connector 44 is to hold the inner support 42 in position. While the outer support 40 is circular/ring-shaped in the example illustrated in Figs. 9 and 10, that need not be the case in every example. The second, third and fourth guides 38b-38d illustrated in Fig. 9 have the same form as the first guide 38a illustrated in Fig. 10, but are smaller in shape. For example, each of the second, third and fourth guides 38b-38d comprises its own plurality of rollers defining a ring shape.

Each guide 38a-38d defines a guide aperture 39a-39d through which a strip 412 of foam material 10 may pass. From the first guide 38a to the fourth guide 38d, the ring shape defined by the rollers becoming progressively smaller, as do the apertures 39a- 39d. That is, the size of the aperture 39b in the second guide 38b is smaller than the size of the aperture 39a in the first guide 38a. The size of the aperture 39c in the third guide 38c is smaller than the aperture 39b in the second guide 38b. The size of the aperture 39d in the fourth guide 38d is smaller than the size of the aperture 39c in the third guide 38c. The drive 36 is configured to cause a (generally planar) strip 412 of foam material 10 to move towards the guides 38a-38d in the direction illustrated by arrow 40 in Fig. 9. This causes the foam material to pass initially through the first guide 38a, then the second guide 38b, then the third guide 38c and finally the fourth guide 38d. The rollers of each guide 38a-38d encourage the movement of the strip 412 of foam material 10 in the direction 40 illustrated in Fig. 9 as it passes through guide apparatus 37. The gradually decreasing size of the apertures 39a-39d in the guides 38a-38d causes gradual bending of the strip 412 of foam material 10, urging the first, sloping, edge 413 of the foam material towards the second, sloping, edge 414 of the foam material 10. Each guide 38a-38d further urges the first and second edges 413, 414 of the foam material 10 further towards each other.

In some embodiments, heat may be applied to the strip 412 of foam material as it passes through the guide apparatus 37. In block 206 of Fig. 2, a conduit 512 is formed by attaching the first and second edges 413, 414 of the foam material 10 together following its bending. This is illustrated in Fig. 11 , which shows a heating device 48 being used to apply localised heat along the first and second edges 413, 414 to form a conduit 512 that is substantially tubular in shape. Heat is output from an output location 50 on the heating device 48. Movement of the foam material 10 relative to the output location 50 of the heating device 48, as illustrated by the arrow 52 in Fig. 1 1 , causes melting of the first and/or second edges 413, 414 of the foam material 10 to enable them to be adhered/fused/welded together. The arrow 52 illustrated in Fig. 11 indicates movement of the foam material 10 relative to the heating device 48.

After the conduit 512 has been formed, in block 207 of Fig. 2, the conduit 512 is cooled using a cooling apparatus 60. Fig. 12 illustrates the conduit 512 being cooled by the cooling apparatus 60. The cooling apparatus 60 includes a housing 62 defining an internal cavity 64. A first aperture 63a and a second aperture 63b are present in the housing 62. The conduit 512 initially enters the housing 62 via the first aperture 63a and exits the housing 62 via the second aperture 63b. Cooling elements 68, positioned within the internal cavity 64, cool the conduit 512 of foam material 10 as it is passed through the cooling apparatus 60, in the direction indicated by the arrow 66, which sets the shape of the conduit 512 of foam material 10, causing it to become more rigid/less malleable.

The conduit 512 has a circumference wall of the same thickness as the depth of the smaller sheets 212 of foam material 10 produced in block 202 in Fig. 2. The thickness might be the same or less than 0.02m, such as in the range 2.5mm to 20mm.

One use for a conduit/tube 512 formed in accordance with the method described above and illustrated in Fig. 2 is in a selective catalytic reduction apparatus for a vehicle. Fig. 13 illustrates a selective catalytic reduction apparatus 100 comprising a repository 102, an injector 106 and a thermal insulator/conduit 512.

The repository 102 is for storing diesel exhaust fluid. The diesel exhaust fluid is a reductant which may, for example, be an aqueous urea solution. An example of such an aqueous urea solution is AdBlue.

The injector 106 is for injecting the diesel exhaust fluid into a stream of exhaust gas from a diesel combustion engine 108. The selective catalytic reduction apparatus 100 also comprises a conduit for conveying the diesel exhaust fluid from the repository 102 to the injector 106. The conduit for conveying diesel exhaust fluid from the repository 102 to the injector 106 is not illustrated in Fig. 13 because it is substantially circumferentially covered by the thermally insulating conduit 512 made from the foam material 10.

Fig. 13 also illustrates an exhaust pipe 1 12 through which a stream of exhaust gas from the diesel combustion engine 108 passes. The arrows labelled with the reference numeral 114 in Fig. 13 indicate emissions being made from the exhaust pipe 112.

The purpose of the thermal insulator 512 made from the foam material 10 is to thermally insulate the diesel exhaust fluid as it flows from the repository 102 to the injector 106 in the conduit. The diesel exhaust fluid may freeze at below -11°C and, in a conventional selective catalytic reduction apparatus, one or more heating elements may be employed to prevent the diesel exhaust fluid from freezing in the conduit as it passes from the repository 102 to the injector 106. Advantageously, in embodiments of the invention, no such heating elements are necessary, because the thermally insulating conduit 512 prevents the diesel exhaust fluid from freezing in the traditionally defined environmental operating temperature range for vehicles of -40°C to 150°C.

The thermally insulating conduit 512 may, for example, have a thermal conductivity of O. IW/mK or less across the temperature range -40 °C to 150 °C. As explained above, advantageously, the foam material 10 from which the thermally insulating conduit 512 is made is resistant to hydrocarbons, such as those present in engine oil

and diesel fuel. This prevents corrosion of the thermally insulating conduit 512 over time. This is advantageous if, for example the thermally insulating conduit 512 is situated at a position in a vehicle that causes it to be exposed to hydrocarbons from time to time.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, the conduit/tube 512 produced according to the method of Fig. 2 need not have a circular cross section. The guide apparatus 37 may have greater or fewer than the four guides 38a-38d illustrated in Fig. 9.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

I/we claim:

Claims

A selective catalytic reduction apparatus for a vehicle, comprising:

a repository for storing diesel exhaust fluid;

an injector for injecting the diesel exhaust fluid into a stream of exhaust gas from a diesel combustion engine;

a conduit for conveying the diesel exhaust fluid from the repository to the injector; and

a thermal insulator, made from foam material, for thermally insulating diesel exhaust fluid flowing in the conduit.

2. The selective catalytic reduction apparatus as claimed in claim 1 , where the diesel exhaust fluid is a reductant. 3. The selective catalytic reduction apparatus as claimed in claim 1 or 2, wherein the diesel exhaust fluid is an aqueous urea solution.

4. The selective catalytic reduction apparatus as claimed in claim 1 , 2 or 3, wherein the thermal insulator has a thermal conductivity of 0.1 W/mK or less across the temperature range -40°C to 150°C.

5. The selective catalytic reduction apparatus as claimed in any of the preceding claims, wherein the foam material is resistant to hydrocarbons. 6. The selective catalytic reduction apparatus as claimed in any of the preceding claims, wherein the foam material is formed, at least in part, from one or more polyamides.

7. The selective catalytic reduction apparatus as claimed in any of the preceding claims, wherein the thermal insulator is substantially tubular in shape.

8. The selective catalytic reduction apparatus as claimed in any of the preceding claims, wherein the thermal insulator has a wall of 0.02m in thickness or less. The selective catalytic reduction apparatus as claimed in any of the preceding claims, wherein the foam material is a closed cell foam material.

10. A vehicle comprising the selective catalytic reduction apparatus as claimed in any of the preceding claims.

1 1. A method, comprising:

heating foam material of a generally planar shape;

using a guide apparatus to cause the heated foam material to bend;

forming a tube, using the foam material, by adhering a first edge of the foam material to a second edge of the foam material; and

cooling the tube following adherence of the first edge to the second edge.

12. The method of claim 11 , wherein the guide apparatus comprises at least a first guide, and the heated foam material is bent by moving the heated foam material through the first guide.

13. The method of claim 1 1 or 12, wherein bending of the heated foam material urges the first edge towards the second edge.

14. The method of claim 12 or 13, wherein the first guide comprises at least one roller.

15. The method of claim 12, 13, or 14, wherein the first guide comprises multiple rollers.

16. The method of claim 15, wherein the rollers collectively define a ring shape.

17. The method of any of claims 12 to 16, wherein the guide apparatus comprises at least a second guide, and, following bending of the heated foam material using the first guide, the heated foam material is further bent by moving the heated foam material through the second guide. The method of claim 17, wherein further bending of the heated foam material urges the first edge of the foam material further towards the second edge of the foam material. 19. The method as claimed in claim 17 or 18, wherein the first guide defines a first guide aperture for shaping the foam material and the second guide defines a second guide aperture for shaping the foam material.

20. The method as claimed in claim 19, wherein the second guide aperture is smaller than the first guide aperture.

21. The method of any of claims 17 to 20, wherein the second guide comprises multiple rollers. 22. The method of claim 21 , when dependent on claim 6, wherein the rollers of the second guide collectively define a ring shape that is smaller in size than the ring shape collectively defined by the rollers of the first guide.

23. The method of claim 22, wherein the ring shape defined by the rollers of the first guide is concentric with the ring shape defined by the rollers of the second guide.

24. The method of any of claims 11 to 23, wherein adhering the first edge of the foam material to the second edge of the foam material comprises applying heat to at least one of the first edge and the second edge to melt the foam material.

The method of any of claims 11 to 24, further comprising: cutting the foam material to form the first edge and/or the second edge.

26. The method of claim 25, wherein the first edge and/or the second edge is/are cut to form a sloping edge.

27. The method of claim 26, wherein each sloping edge defines an angle in the range 30° to 60°, relative to an upper surface and/or a lower surface of the generally planar foam material. 28. The method of claim 27, wherein the generally planar foam material has a length, a width and a depth, and the upper surface and the lower surface are defined by the length and the width of the generally planar foam material.

29. The method of any of claims 11 to 28, wherein the foam material has an upper operating temperature, and the foam material is heated to a temperature that is at least the upper operating temperature of the foam material minus 5% of that operating temperature, prior to using a guide to cause the heated foam material to bend. 30. The method of claim 29, wherein thermal shrinkage at the upper working temperature is approximately 5% or greater.

31. The method of claim 29 or 30, wherein the upper working temperature is in the range 60°C to 250°C.

32. The method of any of claims 11 to 31 , wherein the tube is cooled using a cooling apparatus.

33. The method of any of claim 32, wherein cooling the tube comprises passing at least part of the tube through the cooling apparatus.

34. The method as claimed in any of claims 11 to 33, wherein the foam material is a closed cell foam material. 35. The method as claimed in any of claims 11 to 34, wherein the foam material resistant to hydrocarbons. The method as claimed in any of claims 11 to 35, wherein the foam material is formed, at least in part, from one or more polyamides.

A tube formed according to the method of any of claims 11 to 36.

A method, comprising:

heating foam material;

using a guide apparatus to cause the heated foam material to bend;

forming a conduit, made at least in part from the foam material, by attaching at least a first edge of the foam material to at least a second edge of the foam material; and

cooling the conduit following attachment of at least the first edge to at least the second edge. 39. A tube formed according to the method of claim 38.

40. A method, comprising:

cutting foam material, that is generally planar in shape, to form a first sloped edge and a second sloped edge;

heating the foam material to a temperature that is greater than the operating temperature of the foam material minus 5% of that operating temperature; guiding the heated foam material through a guide apparatus in order cause the heated foam material to bend;

forming a tube, using the foam material, by adhering the first sloped edge to the second sloped edge; and

cooling the tube, following adherence of the first edge of the foam material to the second edge of the foam material, using a cooling apparatus.

A guide apparatus, comprising:

a first guide comprising a first plurality of rollers;

a second guide comprising a second plurality of rollers; and

a drive configured to cause a generally planar foam material to move through the rollers of the first guide and then the rollers of the second guide, in order to cause gradual bending of the generally planar foam material.

42. The guide apparatus as claimed in claim 41 , wherein the first guide defines a first guide aperture for shaping the foam material and the second guide defines a second guide aperture for shaping the foam material.

43. The guide apparatus as claimed in claim 42, wherein the second guide aperture is smaller than the first guide aperture.

44. The guide apparatus as claimed in claim 41 , 42 or 43, wherein the first plurality of rollers collectively define a first ring shape.

45. The guide apparatus as claimed in claim 41 , 42 or 43, wherein the second plurality of rollers collectively define a second ring shape.

46. The guide apparatus as claimed in claim 45, wherein the second ring shape is smaller than the first ring shape.

47. The guide apparatus as claimed in any of claims claim 41 to 46, wherein the first ring shape and the second ring shape are concentric.