Article, an intermediate product, and a method of making an article

Abstract

An article for insulation comprises a flexible substrate (200) and a thermal sprayed working layer (206) on the flexible substrate (200). The working layer (206) comprises an array of insulating elements. The insulating elements are separated by gaps so that the article is flexible.

Claims

1. An article for insulation, the article comprising: a flexible substrate and a working layer thereon; the working layer comprising an array of insulating elements, the insulating elements being separated by gaps so that the article is flexible, wherein the insulating elements are made of at least one of metal or ceramic; and wherein the substrate is a metal foil.

2. An article according to claim 1, wherein the article comprises at least one further flexible substrate over the working layer.

3. An article according to claim 2, wherein the article includes a further working layer on the further flexible substrate, the further working layer comprising an array of insulating elements, the insulating elements being separated by gaps.

4. An article according to claim 1, wherein the working layer is a thermally sprayed layer.

5. An article as claimed in claim 1, wherein a plurality or the gaps are aligned to form straight, open grooves.

6. An article according to claim 1, wherein the gaps are more than 0.5 mm in size.

7. An article according to claim 1, wherein the gaps are no more than 5 mm in size.

8. An article according to claim 1, wherein the percentage by volume of gaps in the layer is between 15% and 45%.

9. An article according to claim 1, wherein the article includes a bonding layer between the working layer and the substrate.

10. A method of making an insulating article, the method comprising the steps of: applying a layer of insulating material to a flexible substrate, wherein the insulating material is made of at least one of metal or ceramic; before, during or after the step of applying the layer, introducing pocket or gap creation means; and then removing the pocket or gap creation means to achieve a layer with pockets or gaps wherein the flexible substrate is a metal foil.

11. A method according to claim 10, wherein the step of applying the layer of material to the flexible substrate comprises thermally spraying the substrate with the layer of material.

12. A method according to claim 10, wherein the pocket or gap creation means is removed by dissolving.

13. A method according to claim 10, wherein the pocket or gap creation means is a liquid such as a paint or adhesive or other hardenable liquid material applied to part of a surface of the substrate.

14. A method according to claim 10, wherein the pocket or gap creation means is a mesh or other partial barrier, through which a coating is thermally sprayed.

15. A method according to claim 14, wherein the step of removing the pocket or gap creation means comprises mechanically removing the pocket or gap creation means.

16. A method according to claim 11, further comprising applying a bonding layer by thermal spraying before the step of applying the thermally sprayed layer of insulating material.

Description

(1) Embodiments of this invention will now be descried by way of example and with reference to the accompanying drawings, in which:

(2) FIG. 1 is cross sectional views of the first embodiment of the present invention a) before immersing in water to dissolve the salt; and b) after immersing in water so that the salt has dissolved.

(3) FIG. 2 is cross sectional views of the second embodiment of the present invention a) before immersing in water to dissolve the salt; and b) after immersing in water so that the salt has dissolved.

(4) FIG. 3 is cross sectional views of the third embodiment of the present invention a) before immersing in water to dissolve the salt; and b) after immersing in water so that the salt has dissolved.

(5) FIG. 4 is cross sectional views of fourth embodiment of the present invention a) with tape on the steel plate; b) with a first bond layer applied; c) with the tape removed; d) with a salt layer applied; e) with the salt layer rubbed down; f) with a second bond layer applied; and g) with a ceramic layer applied.

(6) FIG. 5 is cross sectional views of the fifth embodiment of the present invention a) before immersing in water to dissolve the salt, and with a first layer of ceramic; b) before immersing in water to dissolve the salt, and with a second layer of ceramic; and c) after immersing in water so that the salt has dissolved.

(7) FIG. 6 a) is a cross sectional view of the sixth embodiment of the present invention, with a mesh on the foil; b) is a cross sectional view with a bond layer, with the mesh still present; c) is a cross sectional view with a bond layer and a ceramic layer, with the mesh still present; d) is a cross sectional view with a bond layer and a ceramic layer, with the mesh removed; e) is a plan view of the mesh on the substrate; f) is a plan view once the bond layer and ceramic layer have been sprayed, and the mesh has been removed; and g) is a cross section of several layers of foil with air gaps.

EMBODIMENT 1

(8) A mild steel plate 10 of dimensions 150 mm150 mm by 1.5 mm thick was carefully cleaned, using acetone, then wiped with tissue to remove any liquid. The clean plate 10 was then grit blasted on one side using a siphon type grit blast system at 40 psi, with grit between 0.4 mm and 0.6 mm in size. The plate 10 was blown with dry air to remove any debris and wiped with an acetone damp tissue.

(9) The plate 10 was then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. The plate 10 was heated up to 200 C. using a torch and a steel mesh with 32% open area was placed in front of the plate. A sacrificial, pocket creation material, in the form of a saturated sodium chloride solution, was sprayed through the mesh to provide an array of sodium chloride solution patches on the surface of the plate 10. The sodium chloride solution was allowed to dry, leaving an array of salt patches 12 on the plate 10.

(10) The spray system was set to work in nitrogen and aluminium powder feed set to spray at 30 gm/min. Nitrogen flow was preset to 50 liters/min, and current to 300 A. The robot was programmed to operate a ladder type spray pattern, at a stand off distance of 100 mm from the plate 10, while the plate 10 was rotated. These parameters were used to apply two layers of aluminium to produce an aluminium bond coat of 50 m thickness.

(11) Using the same type of spray program at 75 mm spray distance, using standard nitrogen plasma parameters, magnesium zirconate was plasma sprayed onto the aluminium coating on the plate 10 at 40-50 gm/min. Four coats gave a layer 16 with a thickness of 95-105 m.

(12) The plate was then immersed in water for a few minutes to dissolve the sodium chloride. The plate was then washed and immersed in dilute phosphoric acid to pacify the steel.

(13) Ceramic layers provide good thermal resistance. Using the above method, the salt solution acts as a pocket creation means, and an article is formed which has air pockets 18 in the thermally sprayed aluminium bond coat 14 at the positions of the salt patches before the sample is immersed in water. Air is a very good thermal barrier and so the air pockets 18 in the aluminium bond coat 14 improve the thermal resistance of the layer 14,16 as a whole. The plate 10 had an increase in thermal barrier properties from both the front and the back, as measured by thermocouples, of approximately 30% compared to a plate with standard ceramic coating, so that the coating, although only 125 m thick, outperformed an equivalent coating 300 m thick formed without pockets.

(14) Although in this example salt solution was used, any suitable material which can be applied and subsequently removed can be used, particularly, but not exclusively, those which can be applied by plasma spraying, for example, paint or water soluble tape. In addition, the pocket creation means may be removed by burning off.

EMBODIMENT 2

(15) A coupon 50 of carbon fibre reinforced plastics material of dimensions 150 mm150 mm by 2 mm thick was carefully cleaned, using acetone, then wiped with tissue to remove any liquid.

(16) The clean coupon 50 was then grit blasted on one side using a siphon type grit blast system at 40 psi, with grit of between 0.4 and 0.6 mm size. The coupon 50 was blown with dry air to remove any debris and wiped with an acetone damp tissue.

(17) The coupon 50 was then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. The spray system was set to work in nitrogen and the sodium chloride feed set to spray at 30 gm/min. The sodium chloride was sieved, in preparation for plasma spraying, to a particle size of below 120 m diameter. Nitrogen flow was preset to 50 liters/min, hydrogen to 5 liters/min and current to 400 A. The robot was programmed to operate a ladder type spray pattern, at a stand off distance of 100 mm from the coupon, while the coupon 50 was rotated. A fine aluminium mesh, with 1.5 mm diameter holes and 22% open area, was clamped to the coupon 50. The sodium chloride was sprayed through the mesh, to create salt dots 52 on the surface of the coupon 50.

(18) An aluminium bond coat was then thermally sprayed using the same parameters as above. The bond coat had a thickness of approximately 25 m. A second coat was then applied in the same way to provide a layer 54 with a total coating thickness of 50 m.

(19) Using the same type of spray program at 75 mm spray distance, using standard nitrogen plasma parameters, magnesium zirconate was plasma sprayed onto the aluminium coating on the coupon 50 at 44 gm/min. Five coats gave a layer 56 with a thickness of 150 m. This was rubbed down using fine emery paper to give a smooth, shiny surface.

(20) Repeating the aluminium spray program, but only applying one coat on top of the magnesium zirconate coating, gave a thin 25 m metal layer 16.

(21) The coupon 50 was then immersed in water for about 15 mins to dissolve the salt pockets and dried. The resulting coating contained air pockets 58 where the salt had been. The surface of the coating had quite obvious raised dots, where the air pockets were located.

(22) Carbon fibre reinforced plastics material is naturally relatively soft and susceptible to abrasion. The use of an aluminium bond layer 12 in this example allows a layer 14 of ceramic in the form of magnesium zirconate to be applied. Carbon fibre reinforced plastic is often used in applications where minimisation of weight is desirable, and especially in applications which need high strength but low weight. The ceramic coating produced has above has improved thermal barrier properties over a standard ceramic coating without air pockets. Therefore, for a desired level of thermal resistance, it is possible for the resulting article to be even lighter in relation to its strength, than articles with a standard coating.

EMBODIMENT 3

(23) A coupon 100 of mild steel of dimensions 150 mm150 mm by 1.5 mm thick was prepared as in embodiment 1 and then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. A NiAl bond coat 102 was plasma sprayed onto the coupon 100, using the same parameters as for the bond coat in embodiment 1.

(24) Sodium chloride powder, sieved so that the maximum particle diameter was <120 m was mixed with magnesium zirconate powder to a volume of 50%. This was sprayed using the same spray parameters as in embodiment 1 to produce a layer with salt 104 dispersed in thermal barrier material 106. A further ceramic coating 108, without salt, was then applied, in the same manner.

(25) The coupon was then immersed in water for a few minutes to dissolve the sodium chloride, thus leaving air pockets 110 in the thermal barrier layer 106.

(26) The first layer was 33% porous. This provides very good thermal barrier characteristics but relatively low strength. The addition of a conventionally thermal sprayed layer without a pocket creation material provides improved strength.

EMBODIMENT 4

(27) A steel plate 150 which had not been grit blasted was prepared by applying small dots of tape 152 of dimensions 6 mm6 mm. to the surface of the plate 150, so that approximately 46% of the surface area of the plate 150 was covered. The plate 150 was then grit-blasted as in embodiment 1.

(28) The plate 150 was then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. Two layers of aluminium, each 25 m thick, were applied in the same manner as in embodiment 1 to create a bond coat 154.

(29) The tape 152 was then removed by hand, and the whole surface of the plate 150 was sprayed with a sodium chloride solution, in the same manner as in embodiment 1 (although a mesh was not used). The surface was then rubbed down with a hard grinding block so that the sodium chloride was removed from the bond-coated areas but remained as pockets 156 in the wells where the tape previously was. Further bond coat 158 was then applied over the whole surface in the same manner as the previous layer 154. A layer of magnesium zirconate 160 was plasma sprayed onto the aluminium coating 158 on the plate 150, in the same manner as in embodiment 1.

(30) The plate was then immersed in water for a few minutes to dissolve the sodium chloride resulting in air pockets 162 in the layer 154. The plate was then washed and immersed in dilute phosphoric acid to pacify the steel.

(31) Although the percentage of the surface area masked with tape, and subsequently covered with salt solution was 46% in this embodiment, and therefore the debonded area in the final article was 46%, any desired area could be masked so that it is debonded in the final article. In another embodiment 70% debonded area was achieved.

EMBODIMENT 5

(32) This embodiment is similar to the first embodiment and only the differences from that embodiment will be described. In this embodiment, after the aluminium layer 14 has been sprayed, the plate 10 is mounted onto the turntable in the plasma spray booth again, with the aluminium coated side facing the robot. The plate 10 is again heated up to 200 C. using a torch and a steel mesh with 32% open area is placed in front of the plate 10. Saturated sodium chloride solution, is sprayed through the mesh to provide an array of sodium chloride solution patches 12 on the surface of the aluminium layer 14 on the plate 10. The sodium chloride solution is allowed to dry, leaving an array of salt patches 12. A further aluminium layer 15 is then sprayed over the first aluminium layer 14. A magnesium zirconate layer 16 is then plasma sprayed onto the plate 10 as in the first embodiment. The plate 10 is then immersed in a bath through which unheated mains cold water flows for 15 minutes to dissolve and thereby remove the salt 12.

(33) The resulting article has two layers of pockets 18. Thus more air is trapped than would be possible in a single layer structure without risk of the entire layer debonding. This technique therefore allows greater thermal insulation to be achieved using substantially the same manufacturing method.

(34) An alternative would be to spray salt patches on the surface of the second aluminium layer 15, and then spray the magnesium zirconate layer 16, to create an arrangement in which the magnesium zirconate 16 layer also has air pockets 18.

(35) Although a substrate in the form of a flat plate has been described, substrates in other shapes could be used, and in that case, the mesh need not be flat but might be shaped to follow the contour of the substrate.

EMBODIMENT 6

(36) The substrate for this embodiment was a strip of aluminium foil 200 60 mm wide and 260 mm long, and with a thickness of 0.1 mm. The foil 200 was thoroughly cleaned with acetone before use. The coupon foil was then mounted onto a turntable in a plasma spray booth, containing a robot manipulation system. The spray system was set to work in nitrogen and with an aluminium-bronze feed. Nitrogen flow was preset to 50 liters/min, hydrogen to 3 liters/min and current to 400 A. The robot was programmed to operate a ladder type spray pattern, at a stand off distance of 120 mm from the foil, while the foil 200 was rotated. A 3 mm3 mm mesh 202 was attached to the foil 200. The foil was thermally sprayed, through the mesh, with an Al-bronze bond coat 204

(37) A magnesium zirconate layer 206 was then sprayed onto the bond coat 202, through the mesh 202, using the same spraying parameters as for the bond coat, at a stand off distance of 75 mm. The mesh 202 was then removed manually. The resulting coating on the foil 200 comprised an array of square elements with dimensions of about 2 mm2 mm, each comprising an Al-bronze layer 204 and a magnesium zirconate layer 206

(38) Thus the ceramic has very fine discontinuities in which convective movement of air is restricted, and in which heat transfer by conduction dominates. Thus by utilising the low thermal conductivity of air, this technique provides a ceramic layer with improved thermal barrier properties, and also a significant weight reduction. Further, the underlying foil can remain relatively flexible if the direction of bending is aligned with the air gaps in the ceramic layer. Therefore, the foil of this embodiment can be used to wrap around or be moulded onto components or surfaces which it is not possible or not practical to thermally spray with ceramic directly. Indeed, the article so produced can be rolled up, so that it can be conveniently transported or stored in roll form. This method can also be seen to be useful for other substrates which require flexibility, for example for tubes.

(39) Multiple layers of foil may be stacked together to trap air in the overall structure.

(40) Although in this embodiment gaps which are open to the air are created in the ceramic layer by spraying through a mesh, sacrificial inclusions, for example, tape or salt solution laid down using tape as in embodiment 4, could be used to create a mesh-like pattern to produce a similar effect in the final ceramic layer once the sacrificial inclusions are removed, for example by dissolving or burning out.

(41) In addition, in the above embodiment, the air gaps are through the entire thickness of the bond coat and ceramic layers. However, it should be seen that it would also be possible to create an arrangement in which the air gaps do not extend the entire depth of the bond layer and ceramic layer for example by using a different mesh; by applying the bond coat to the whole of the foil surface, and then masking the bond coat in suitable way, and spraying only the ceramic layer through the mask: or by applying one coat of ceramic, masking the coat in a suitable way, and then applying another coat of ceramic.

(42) Although, in the above embodiments, thermal spraying has been used to create the layers, it would be apparent to the skilled man that another suitable system, for example screen printing, could be used to create the layers.