GB2347440A

GB2347440A - Insulating panel with a honeycomb core filled with granular ceramic material

Info

Publication number: GB2347440A
Application number: GB0003437A
Authority: GB
Inventors: Jeremy M Bowyer
Original assignee: AMS ADMATSYS Ltd
Current assignee: AMS ADMATSYS Ltd
Priority date: 1999-02-12
Filing date: 2000-02-16
Publication date: 2000-09-06
Anticipated expiration: 2020-02-16
Also published as: GB9903390D0; GB0003437D0; GB2347440B

Abstract

An insulating panel (10) has a number of walls (16) extending from a substrate (12) defining a number of closed compartments (18) and a cover (14) overlying the walls (16), which may form a honeycomb structure (fig 3). Insulating material (20) is present in the compartments and is bonded to the substrate (12), covering (14) and walls (16). The insulating material (20) may be particulate material in an adhesive matrix, including ceramic powder, microspheres or prills. There may also be a second material present, possibly granite. A method of producing the panels is also described and includes the use of elevated temperatures and pressures.

Description

Insulative Structure The present invention relates to an insulative structure and a method of manufacturing such a structure. In particular, though not exclusively, the present invention relates to a structure in the form of a panel.

Honeycomb panels typically comprise a pair of panels or"skins"between which is provided a cellular"honeycomb"filler. The filler and skins can be manufactured from a range of materials, for example aluminium, nylon fibre reinforced phenolic resin or titanium The filler is bonded to the skins and the finished structure is both light and rigid. These properties have led to the extensive use of the structures in industries such as aerospace, rail and offshore exploration.

One of the problems associated with honeycomb structures is their poor heat insulation properties and in particular their lack of resistance to fire. The presence of air in the cells of the honeycomb permits heat energy to rapidly pass across the structure by both radiation and convection. This rapid transfer of heat from one skin to the other creates the potential for the transmission of fires across the honeycomb structure, especially if there are flammable materials in contact with the side of the structure opposite to the heat source.

It has been proposed to include intumescent material in each cell of the honeycomb.

This has met with limited success because the weight of the structure is increased, and consequently the weight advantages of using a honeycomb structure are diminished.

Furthermore, the expansion of an intumescent material when the structure is heated can lead to problems with the dimensional stability and structural integrity of the structure.

According to a first aspect of the present invention there is provided an insulative structure having a support and a lightweight insulative material located within said support, the support comprising a substrate, a plurality of walls extending from said substrate, and a covering overlying said walls, said substrate, walls and covering defining one or more closed compartments, said insulative material being located within said one or more closed compartments and bonded to the substrate, covering and walls.

In a preferred embodiment the insulative material comprises particulate material in an adhesive matrix. The matrix of the adhesive and the insulative material provides a mechanical bond between the substrate, the walls and the covering and hence increases the rigidity of the structure. The insulative material is preferably particulate matter and may comprise a mixture of foamed particles and powder. Preferably the foamed particles or powder, and preferably the foamed particles and powder, consist of a ceramic material. The insualtive material may include granular or powdered mineral matter having a density greater than that of the foamed particles or powder. The inclusion of said mineral matter increases the resistance of the structure to impacts.

The mineral matter may, for example, be granite particles in the form of a powder.

In a preferred embodiment the walls form an array of cells, commonly referred to as a honeycomb, and the substrate and covering may comprise thin sheets or skins.

According to a second aspect of the present invention there is provided a method of manufacturing a insulative structure comprising the steps of : providing a substrate having upstanding walls, said substrate and walls defining one or more compartments; filling said one or more compartments with a lightweight insulative material; closing said one or more compartments ; and treating the structure so as to cause the insulative material to bond to the walls of the one or more closed compartments.

The method described above provides a structure which contains an insulative matrix which is bonded to the material defining the structure. The matrix is light, dimensionally stable, and serves, in use, to reduce the transmission of heat energy by convection or radiation, and/or sound energy, across the structure and hence isolate one side of the structure from energy incident upon the opposing side.

In a preferred embodiment the step of filling the one or more compartments comprises the steps of : depositing a measured amount of the insulative material into said one or more compartments; and vibrating the substrate and walls.

Vibrating the substrate and walls assists in achieving a desired packing density of the insulative material and greatly reduces the possibility of there being gaps or voids therein.

The one or more compartments may be overfilled with insulative material. In such a case, after the step of depositing a measured amount of the insulative material there may be a step of levelling the insulative material. The levelling operation may be carried out by a roller. Preferably the roller serves to compress the insulative material into the one or more compartments. Preferably also the roller is adapted to clean the exposed edges of the walls to ensure that the subsequent bond of the covering to the walls is not compromised.

Alternatively the levelling operation may be achieved by vibrating the substrate and walls. The method may include the additional step of cleaning the exposed edges of the walls prior to superimposing the covering layer. The step of cleaning the exposed edges may be carried out, for example, by brushing the exposed edges or, alternatively, moving air across the exposed edges.

The step of closing the compartments may be achieved by superimposing a covering layer of the one or more compartments. The step of treating the structure may involve the exposure of the structure to heat and/or pressure. The treating operation may be conducted, for example, in an autoclave, a heated press or an oven. In a preferred embodiment the insulative material is granular and comprises a mixture of foamed particles and powder. The foamed particles or powder, preferably the foamed particles and powder, may consist of a ceramic material.

In a preferred embodiment the foamed particles are in the form of prills. In a preferred embodiment the particles or powder, preferably the foamed particles and powder have a surface coating of adhesive which is activated during the step of treating the insulative material so as to set the particles and powder in an adhesive matrix. In a preferred embodiment the insulative material has heat resistant properties so as to reduce the transmission of heat energy across the structure, in use. Alternatively, or in addition to the heat resistant properties, the insulative material may have sound deadening properties so as to reduce the transmission of sound energy across the structure, in use.

Embodiments of the present invention will now be described, by way of illustrative example only, with reference to the accompanying drawings in which: Figure 1 shows a cross-sectional side view of a heat resistant panel according to an embodiment of the present invention; Figure 2 shows a diagrammatic side view of apparatus for depositing heat resistant material in the honeycomb section of a panel according to the present invention; Figure 3 shows a diagrammatic plan view of the apparatus of figure 2; and Figure 4 shows a cross-sectional side view of a partially filled honeycomb of a panel according to an embodiment of the present invention.

Referring firstly to figure 1 there is shown a cross-sectional view of a panel generally designated 10 according to an embodiment of the present invention. The panel 10 comprises two substantially parallel planar members or skins 12,14, and an intermediate layer 16 having a honeycomb section comprising a plurality of hexagonal cells 18 defined by walls substantially perpendicular to the skins 12,14. The cells 18 are filled with a heat resistant filling 20 which is described in more detail below.

The skins 12,14 are bonded to opposing edge portions 22,24 of the honeycomb layer 16, for example by adhesive. The filling 20 comprises a mixture of ceramic prills, ceramic powder and adhesive which has been formed into a homogenous mass. The filling 20 is bonded by adhesive to the walls 26 of the cells 18 and to the skins 12,14.

In one embodiment the ceramic prills have a bulk density in the order of 125 kg/m3 and the ceramic powder a bulk density of approximately 360 kg/m3. The filling 20 may advantageously include an intumescant material in the form of a powder which coats the ceramic prills and ceramic powder.

A panel of the configuration noted above having a non-metallic core, aluminium skins and a thickness of 13mm has been tested with a direct flame of approximately 1000 C applied to one side thereof. After 20 minutes the temperature on the opposing side was found to be in the region of 150 C. Such performance would enable a 13mm aluminium skinned non-metallic honeycomb panel to gain an A30 rating for the marine market.

As described above a panel according to the present invention also reduces the transmission of sound energy thereacross. Typically in order to produce an effective sound attenuator using honeycomb, it has been deemed necessity to fill the cells thereof with as dense a medium as possible. However, this would counter the lightweight nature of the honeycomb panel. By utilising a mixture of high density fill for sound reduction purposes and low density fill to minimise the increase in weight of the finished panel, testing has indicated that a 25% reduction in the Weighted Sound Reduction Index can be expected. This is in addition to the inherent heat insulation properties.

A further inherent property of panels according to the present invention is their improved impact absorption when compared to unfilled panels. The ceramic prills breakdown under impact which increases the density of the filling. This increase in density absorbs the energy of the impact and hence isolates the opposite side of the panel from the energy of the impact. As the filling is bonded to the skins and cells of the honeycomb it is resistant to being removed from the panel should the skin receiving the impact be breached. To increase the impact resistance of the panel the fill may include additional material having a density greater than that of the ceramic prills and ceramic powder. This material may comprise a powdered mineral, for example granite.

Referring now to figures 2 to 4 there is shown apparatus, generally designated 28, used for depositing the filling 20 into the cells 18 of a honeycomb panel 30. The apparatus 28 comprises a table 32 for supporting the panel 30, filling deposit means generally designated 34 and a roller 36. The table 32 is adapted to support a part constructed panel 30, comprising a single skin 12 and the honeycomb layer 16, with open edges 24 of the cells 18 uppermost. The table 30 is adapted to vibrate, for example by a motor 38.

In the embodiment shown the filling deposit means 34 comprises hoppers 40,42 containing respectively ceramic prills and ceramic powder. It will be understood that the term"prill"refers to particle of foamed ceramic material. The powder may comprise ceramic microspheres. Both the prills and the powder are surface coated with adhesive which is subsequently activated to homogenise the filling 20 and bond it to the skins 12,14 and the cell walls 26. The adhesive may for example be a UPVC adhesive, for example that manufactured under the trade name TEXICRYL. Suitable delivery means 44,46, for example motorised gate valves, are provided at the base of each hopper 40,42. The hoppers 40,42 are movable relative to the table 32 so as to be able to deposit the filling 20 into all of the cells 18. The roller 36 is positioned to roll across the open edges 24 of the cells 18 after the filling 20 has been deposited therein. Finally the table 32 is provided with an upstanding peripheral lip 48 to permit the retention and subsequent collection of overspill from the cells 18.

Construction of a panel 30 will now be described. Firstly the skin 12 is located relative to the honeycomb layer 16. The skin 12 may be provided with adhesive which bonds it the honeycomb layer 16. The skin/honeycomb assembly is then fixed to the table 32 with the open faces of the cells 18 uppermost. The table 32 is then vibrated as the hoppers 40,42 move over the honeycomb and deposit metered amounts of their contents into the cells 18. Vibration of the table 32 is used to ensure the filling 20 settles in the cells 18 to give a desired filling density and to eliminate voids within the filling 20.

Overspill from the cells 18 is collected on the table 32 and is recycled. As can be seen from figure 4 each cell 18 is slightly overfilled. The roller 36 is used to level the filling 20 to either the height of the upper edge 24 of each cell 18 or to just below the edge 24.

The roller 36 rolls over the cells behind the hoppers 40, 42. The roller 36 additionally compresses the filling 20 slightly into the cells 18 and acts as guillotine against any prills lying on top of a cell wall 26 between two cells 18. The roller 36 also pushes an amount of overfilled filling 20 ahead of its path. This can be used to compensate for any underfilling of cells 18 ahead of the roller 36. The roller 36 may also be adapted to clean the tops of the cell walls. In an alternative embodiment, the vibrational frequency and amplitude of the table 32 may be chosen so as to convey overfilled filling 20 across the skin/honeycomb assembly.

Once the cells 18 have been filled a second skin 14 is placed over the honeycomb layer 16 so as to enclose the cells 18. Adhesive on the second skin 14 is utilised to bond it to the honeycomb layer 16. To ensure that an adequate bond is made between the honeycomb layer 16 and the second skin 14, it is important that the upper edges 24 of the cells 18 are clean and free from particulate matter which could affect the integrity of the adhesive bond. Accordingly cleaning means may be required to clean the upper edges 24 of the cells prior to the introduction of the second skin 14. The cleaning means may comprise a brush or a current of air and may be arranged in a similar manner to the roller 36.

After the upper skin 14 has been attached to the honeycomb layer 16, the panel 30 is then treated so as to homogenise the filling 20 and bond it to the cell walls 26 and to the skins 12,14. The skins 12,14 are clamped to the honeycomb layer 16 and the panel is subjected to heat and pressure, for example in an autoclave. The heat and pressure activates the surface coating of adhesive in the prills and powder and fuses them to provide a heat resistant matrix. The matrix, being bonded to the skins 12,14 and the cell walls 26, becomes an integral part of the structure of the panel 30 and hence can serve to augment the structural characteristics thereof. In particular, the inclusion of matrix within the cells provides a mechanical connection between the skins in addition to that provided by the cells. This serves to increase the rigidity of the panel when compared to a panel having empty cells. Also, by being bonded to the skins 12,14 and cell walls 26, there is a reduced possibility that the matrix will be dislodged from cells 18 exposed when the panel is cut or damaged.

Panels of the type described above may be used for a variety of purposes including train and car bumper systems, vehicle chassis and body panels and boat hulls and interior panels to name but a few.

Claims

Claims 1. An insulative structure having a support and a lightweight insulative material located within said support, the support comprising a substrate, a plurality of walls extending from said substrate, and a covering overlying said walls, said substrate, walls and covering defining one or more closed compartments, said insulative material being located within said one or more closed compartments and bonded to the substrate, covering and walls.
2. A structure as claimed in claim 1 wherein the insulative material comprises particulate material in an adhesive matrix.
3. A structure as claimed in claim 2 wherein the particulate material includes foamed ceramic particles or prills
4. A structure as claimed in claim 3 wherein the particulate matter further includes a ceramic powder.
5. A structure as claimed in claim 4 wherein the ceramic powder comprises ceramic microspheres.
6. A structure as claimed in any of claims 3 to 5 wherein the particulate material further includes material having a density greater than the foamed ceramic particles and or ceramic powder.
7. A structure as claimed in claim 6 wherein said material comprises a powdered mineral matter.
8. A structure as claimed in claim 7 wherein said mineral matter is granite.
9. A structure as claimed in any preceding claim wherein the walls form an array of cells.
10. A structure as claimed in claim 9 wherein the cells are in the form of a honeycomb.
11. A structure as claimed in any preceding claim wherein the substrate and covering comprise thin sheets or skins.
12 A method of manufacturing a insulative structure comprising the steps of : providing a substrate having upstanding walls, said substrate and walls defining one or more compartments; filling said one or more compartments with a lightweight insulative material; closing said one or more compartments; and treating the structure so as to cause the insulative material to bond to the walls of the one or more closed compartments.
13. A method as claimed in claim 12 wherein the step of filling the one or more compartments comprises the steps of : depositing a measured amount of the insulative material into said one or more compartments; and vibrating the substrate and walls.
14. A method as claimed in claim 12 or claim 13 wherein the one or more compartments are initially overfilled with insulative material.
15. A method as claimed in claim 14 and including the step off levelling the insulative material after depositing a measured amount of the insulative material.
16. A method as claimed in claim 15 wherein the levelling step is carried out by a roller.
17. A method as claimed in claim 16 wherein the roller is adapted to compress the insulative material into the or each compartment.
18. A method as claimed in claim 16 or claim 17 wherein the roller is adapted to clean the exposed edges of the walls.
19. A method as claimed in claim 15 wherein the levelling step is achieved by vibrating the substrate and walls.
20. A method as claimed in any of claims 12 to 19 and including the additional step of cleaning the exposed edges of the walls prior to covering the compartments.
21. A method as claimed in claim 20 wherein the step of cleaning the exposed edges is carried out by brushing the exposed edges
22. A method as claimed in claim 20 wherein the step of cleaning the exposed edges is achieved by moving air across the exposed edges.
23. A method as claimed in any of claims 12 to 22 wherein the step of closing the compartments is achieved by superimposing a covering layer of the one or more compartments.
24. A method as claimed in any of claims 12 to 23 wherein the step of treating the structure involves the exposure of the structure to heat and/or pressure.
25 A method as claimed in claim 24 wherein the treating operation is conducted in an autoclave.
26. A method as claimed in claim 24 wherein the treating operation is carried out by a heated press.
27. A method as claimed in claim 24 wherein the treating operation is carried out in an oven.
28. A method as claimed in any of claims 12 to 27 wherein the insulative material is granular.
29. A method as claimed in claim 28 wherein the insulative material includes a mixture of foamed particles and powder.
30. A method as claimed in claim 27 wherein the foamed particles and powder consist of a ceramic material.
31. A method as claimed in claim 29 or claim 30 wherein the foamed particles are in the form of prills.
32. A method as claimed in any of claims 29 to 31 wherein the insulative material further includes material having a density greater than the foamed ceramic particles anc or ceramic powder.
33. A method as claimed in claim 32 wherein said material comprises a powdered mineral matter.
34. A method as claimed in claim 33 wherein said mineral matter is granite.
35. A method as claimed in any of claims 28 to 34 wherein the insulative material has a surface coating of adhesive which is activated during the step of treating the insulative material so as to set it in an adhesive matrix.
36. A method as claimed in any of claims 12 to 35 wherein the insulative material has heat resistant properties so as to reduce the transmission of heat energy across the structure, in use.
37. A method as claimed in any of claims 12 to 36 wherein the insulative material has sound deadening properties so as to reduce the transmission of sound energy across the structure, in use.
38. An insulative structure substantially as hereinbefore described with reference to or as shown in the accompanying drawings.
39. A method of manufacturing an insulative structure substantially as hereinbefore described or as shown in the accompanying drawings.