GB2280137A - Composite articles by moulding inorganic fibres onto a preformed element - Google Patents

Abstract

A method of manufacturing a composite article includes mounting a preformed part of the article on a permeable die, immersing the die in a slurry of inorganic fibres, and extracting the liquid from the slurry through the die such that the die is coated with a coherent mass of fibres, and this coating and the preformed part provide a unitary structure removable from the die. The article may comprise an insulating rim around the periphery of a planar base for supporting a radiant heating element, the preform being metallic and providing a covering for the fibrous shaped part. In one embodiment a plurality of annular preforms 26 are mounted about and spaced along the axis of a cylindrical die 46, such that on completion of the moulding and removal of the die, the formed composite can be cut to provide a series of identical articles. <IMAGE>

Description

Composite Articles The present invention relates to the manufacture and construction of composite articles, especially composite articles each having a shaped part of inorganic fibres and a preformed part.

It is known to provide a composite article having an electrical and/or heat insulating part comprising a predetermined shape of inorganic fibres together with a preformed metal part. It is also known that inorganic fibres comprising mineral fibres in particular, are capable of being immersed in water to form a slurry, and from such a slurry a required predetermined shape of fibres is capable of being formed.

Classified or fractioned mineral fibres are advantageous because there are no unfibrised particles, and therefore a shaped part made therefrom is capable of providing a more reliable seal with a co-operating part than a shaped part made from ceramic inorganic fibres. Also it is required that shaped parts of ceramic inorganic fibres, unlike shaped parts of mineral fibres, if they are to be capable of being handled, have to be held together by a binding system, for example, a binding system including colloidal silica and /or starch, especially when the shaped part is to be machined, or to have holes bored in it.

Starch is disadvantageous because when it is removed by firing it gives rise to undesirable gaseous emissions. Colloidal silica alone, after firing, provides shaped parts each with a hard shell, but having an undesirable fluffy interior which prohibits machining.

A known way of obtaining a required predetermined coherent mass of fibres is to immerse a permeable die within a slurry of the fibres in a suitable liquid and to extract the liquid from the slurry through the die, by maintaining a reduced pressure on the appropriate one of the two major surfaces of the die. In this manner a coating of fibres is formed on the other of the two major surfaces of the die, and the fibres may be removed as a coherent mass. The latter surface of the die is required to have the appropriate form for the coherent mass of fibres coating this surface to have the desired predetermined shape.

Previously, when the shaped part of inorganic fibres, of a composite article of the type to which the present invention relates, has been formed in the way referred to in the previous paragraph, it has been secured subsequently to the preformed part in a separate process step after machining. Such a method of manufacturing the composite article is both expensive and time consuming.

It is an object of the present invention to provide a more advantageous method of manufacturing a composite article having a shaped part of inorganic fibres and a preformed part, with or without the need for a firing step.

According to the present invention a method of manufacturing a composite article having a shaped part of inorganic fibres and a preformed part, includes immersing a permeable die in a slurry of the fibres with the preformed part mounted on the die, extracting the liquid from the slurry through the die by maintaining a reduced pressure on the appropriate one of the two major surfaces of the die, thereby causing the other of the two major surfaces of the die to be coated with a coherent mass of fibres, the arrangement being such that there is provided a unitary structure of the coating and the preformed part which unitary structure either comprises, or is capable of being formed into, the required composite article, and removing the unitary structure from the die.

By employing a method in accordance with the present invention the securing of the preformed part to the coherent fibre mass is not obtained in a disadvantageous separate process step, but instead, is obtained simultaneously with the formation of the coherent fibre mass on the die.

It may not be required to fire the coherent mass of fibres.

The inorganic fibres may be natural mineral fibres.

The slurry may be of the inorganic fibres in at least water.

It is known that if the shape of the coating of inorganic fibres on the die is, say, a cylindrical tube, a plurality of annuli, each comprising a shape of inorganic fibres, can be obtained by slicing the tube. In a method in accordance with the present invention a plurality of preformed parts may be mounted on the die, to be spaced along the axis of the die, and in completing a plurality of composite articles, are obtained by slicing the unitary structure removed from the die into a plurality of identical portions. When at least a portion of each preformed part initially is embedded in the coherent fibre mass removed from the die, such a portion may be exposed when the unitary structure is sliced into a plurality of identical portions in completing a plurality of composite articles.

In accordance with another aspect of the present invention a composite article, having a shaped part of inorganic fibres and a preformed part, is manufactured by employing a method referred to above.

The composite article may be such that the preformed part is either wholly, or partially, embedded in the shaped fibre part.

In addition, or alternatively, the composite article may have at least a portion of the preformed part contiguous with, and exposed in relation to, the shaped fibre part. At least a portion of the preformed part initially embedded in the coherent fibre mass on the die subsequently may be exposed when completing the fabrication of the composite article.

The composite article may have a closed form, and may comprise a ring.

The preformed part may have such a closed form.

The preformed part may be metallic. Whether, or not, the preformed part is metallic, it may comprise sheet material. The preformed part may be required to support the shaped part of inorganic fibres, and to impart strength to, or to reinforce, the composite article comprising the preformed part and the shaped part of inorganic fibres.

A composite article comprising a preformed part and a shaped part of inorganic fibres may be required to comprise a constituent structure of a more complex product. It is another object of the present invention to provide a novel and advantageous construction for a product of the type which has a planar base, and a rim around the periphery of the base, the rim protruding beyond the base from one major surface thereof, both the base and the rim at least substantially being of electrical and/or heat insulating material, with the outer surface of the rim extending at least generally at right angles to the base having a metal covering.

In accordance with yet another aspect of the present invention a product has a planar base, and a rim around the periphery of the base, the rim protruding beyond the base from one major surface thereof, both the base and the rim at least substantially being of electrical and/or heat insulating material, the rim comprising a composite article having a shaped part of inorganic fibres, and a metallic preformed part providing a covering for the outer surface of the shaped part of inorganic fibres extending at least generally at right angles to the base, and the composite article being manufactured in accordance with a method referred to above, and having a construction referred to above, where appropriate.

Such a construction for a product of the type referred to above is advantageous because the electrical and/or heat insulating material, and the metal covering, of the rim comprise an initial unitary combination within the product, and are not separate features when secured to the base.

The metallic preformed part may extend to cover also an adjacent surface of the shaped part of inorganic fibres extending at least generally parallel to the base.

When the metallic preformed part has the construction referred to in the preceding paragraph it also may provide a shoulder portion either in alignment with, or inwardly of, the inner surface of the shaped part of inorganic fibres extending at least generally at right angles to the base, the base being secured to the composite article comprising the rim when seated on the shoulder portion of the metallic preformed part.

Alternatively, and irrespective of whether the metallic preformed part extends to cover also an adjacent surface of the shaped part of inorganic fibres extending at least generally parallel to the base, a peripheral portion of the base is secured directly to, say, by adhering to, to a surface of the composite article extending at least generally parallel to the base.

The base may comprise, or include, a layer of a suitable board material.

The base may have a laminated construction, comprising at least two layers of different materials.

The present invention will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a diametrical section of a support for a radiant heating element, the support comprising one embodiment of a product in accordance with the present invention, the product including a base and a portion of a circular rim both of electrical and/or heat insulating material, and the rim also having a preformed metallic coating on two adjacent surfaces of the insulator, the rim comprising a composite article, and the insulator of the rim comprising a shaped part of a coherent mass of inorganic fibres, Figure 2 shows apparatus for performing one method, in accordance with another aspect of the present invention, of manufacturing a unitary structure comprising, or from which is capable of being formed, the rim of Figure 1, Figure 3 shows a modification of the support of Figure 1, and Figure 4 is of an alternative modification of the support of Figure 1.

As shown in Figure 1 a product 10 for supporting a radiant heating element 12 of a ceramic hob cooker comprises a circular, planar base 14, and a circular rim 16 around the periphery 18 of the base 14, the rim 16 protruding beyond the base 14 from one major surface 20 thereof. The radiant heating element 12 is supported on said one major surface 20 of the base. Both the base and the rim are at least substantially of electrical and/or heat insulating material. The base is required to be stronger, and a better insulator, than the insulator 22 of the rim; and at least the outer surface 24 of the rim, extending at least generally at right angles to the base, is required to have a metal covering 26 comprising a preformed annulus. In order to strengthen the base it is known for it to be wholly, or partially, supported by an extension of the metal covering for the rim.However, such an arrangement is relatively expensive.

Conveniently, the base comprises, or includes, a suitable board 28 of mineral or ceramic fibres, such a board being manufactured by ourselves and known as Firefly (registered trade mark). This board material 28 alone has the required strength and does not require to be supported, but merely to be secured to the rim.

In order to provide a better seat for the radiant heating element 12, the base has a laminated construction, also having a layer 30 of fumed silica, of less strength than the underlying board material 28. Grooves 32 are formed in the layer 30 of fumed silica, and the radiant heat element 12 resides in, and protrudes from these grooves.

The insulator 22 of the rim 16 is of mineral fibres, advantageously formed from a slurry of the fibres in water, and moulded directly onto the preformed annulus 26 forming a metal coating for the insulator, and to provide the desired rim 16 in the form of a composite article.

As shown in Figure 2 the fibres are included in a slurry 40 with water, and held in a tank 42. A die 44 with a cylindrical, permeable wall 46 of wire gauze of appropriate mesh size, is provided. A plurality of annuli 26 of metal sheet material, each to comprise the preformed metal coating of a composite article comprising a rim 16, are mounted on the cylindrical outer surface 48 of the die 44 to be coaxial therewith. The plurality of annuli 26 are axially spaced on the cylindrical die wall 46. It is sufficient that each annulus 26 is a close fit around the die wall 46, and is merely supported on the die in any convenient manner, say, by the insertion of lugs (not shown) into the outer surface 48 of the die wall 46, and onto which lugs the annulus 26 rests.The die 44 with the preformed metallic parts 26 thereon is then immersed in the slurry 40 in the tank 42, with the axis of the cylindrical die wall 46 extending vertically.

The water of the slurry 40 can only enter the interior of the die 44 through its cylindrical wall 46, the two ends of the die being closed by members 50 and 52. A pump (not shown) is connected to the interior of the die through the upper 50 of its ends. By means of the pump a reduced pressure is maintained within the die. Water is extracted from the slurry by passing through the permeable cylindrical wall, and is removed from the interior of the die by the pump. In this way a coherent mass of the fibres (not shown) from the slurry is caused to coat the outer surface 48 of the cylindrical wall 46 of the die. The arrangement is such that there is provided on the surface 48 a unitary structure comprising the fibre coating and the preformed metallic annuli 26. The level of slurry in the tank is maintained in any convenient manner.

When the required unitary structure has been provided the die is removed from the tank, and the unitary structure is removed from the outer surface of the cylindrical wall of the die. In this condition, because the coherent fibre mass is of natural mineral fibre, and because of the reinforcing action of the preformed metallic annuli, the unitary structure is capable of being handled, without the need to have included any temporary organic binding system within the slurry to be transferred to the fibre mass.

A suitable natural mineral fibre is the cat ironic amorphous fibre produced from diabase at a temperature of approximately 16000C, suitably surface treated. Its composition by weight is: SiO2 46% CaO 16% MgO 12% A1203 15% Na2o2 2.5% TiO2 1.5% FeO 6.5% remainder 0.5% The unitary structure is dried by being heated at a temperature of 1200C for 30 minutes.

The method of obtaining a unitary structure described above is advantageous in forming composite articles of many different shapes. It is particularly advantageous in providing composite articles each including a preformed metallic part, of sheet material, to support a shaped fibre mass, and to reinforce the composite article, one such example being described above.

Further, as also described above, the composite article is particularly advantageous when comprising a constituent structure of a more complex product, for example, the product comprising a support for a radiant heating element, and the composite article comprising a rim around the periphery of a planar base of the product, the rim protruding beyond the base from one major surface thereof.

In completing the composite articles, the unitary structure removed from the die is sliced into a plurality of identical portions.

Thus, the provided unitary structure either comprises the required plurality of composite articles comprising the rims, the fibre mass being shaped appropriately by the preformed metal annuli, or, more usually, the fibre mass is capable of being shaped to complete the required plurality of composite articles.

Holes may be provided in each preformed metallic annulus, and holes may be bored in the fibre mass in alignment with the holes in the annulus. In addition, or alternatively, the coherent fibre mass may be turned. It is required that in each composite article the preformed metallic annulus has a portion which is exposed, and which extends to cover a surface of the fibre mass extending at least generally at right angles to the base, and also an adjacent surface of the fibre mass extending at least generally parallel to the base. If the preformed metallic annulus, which is generally "L"-shaped in section, is not so exposed in the provided unitary structure, the fibre mass has to be shaped accordingly.

Conveniently, at least a portion of each preformed part, initially embedded in the coherent fibre mass removed from the die, is exposed when the unitary structure is sliced into the plurality of identical portions in completing a plurality of composite articles.

As shown more clearly in Figure 1 the preformed metallic annulus 26 also provides a shoulder portion 56 in alignment with the radially inner surface 58 of the rim 16 extending at least generally at right angles to the base 14. The base 14 is seated on the shoulder 54, and is secured to the rim 16. In particular, the lower ceramic board portion 28 of the base 14 co-operates with the metallic annulus 26, and the upper layer 30 of the base, of fumed silica, is a close fit within the coherent fibre mass 22.

A modification 10' of the product is shown in Figure 3, and in which Figure the same reference numbers are used to identify identical, or closely resembling parts, as those shown in Figure 1. The modified product 10' has the shoulder portion 54 of the preformed metallic annulus 26 radially inwardly of the radially inner surface 56 of the rim extending at least generally at right angles to the base 14'. Because the base has a laminated construction, the lower ceramic board portion 28' is of a smaller diameter than the upper layer 30 of fumed silica.

Alternatively, in a further modification 10" of the product the preformed metallic annulus 26' may be only "L"-shaped in crosssection, as shown in Figure 4, and in which Figure the same reference numbers are used to identify identical, or closely resembling parts, as those shown in Figure 1. The laminated base 14" has the lower ceramic board portion 28" secured to the lower arm of the annulus 26' extending at least generally parallel to the board. The board may be secured to the preformed metallic annulus in any convenient manner, for example, by use of an adhesive. The board extends to be flush with the radially outer surface 24 of the rim 16. The upper layer 30 of the base, of fumed silica, is of smaller diameter than the board, and is a close fit within the rim.

A product in accordance with the present invention, having a composite article with a planar base, and a rim around the periphery of the base, the rim protruding beyond the base from one major surface thereof, both the base and the rim at least substantially being of electrical and/or heat insulating material, may have any construction commensurate with the rim comprising a composite article having a shaped part of inorganic fibres and a metallic preformed part providing a covering for the outer surface of the shaped part of inorganic fibres extending at least generally at right angles to the base, the rim being manufactured by a method referred to herein, and having a construction referred to herein, where appropriate.

The metallic preformed part may only extend to cover the surface of the shaped part of inorganic fibres extending at least generally at right angles to the base.

The base may not have a laminated construction.

The base may comprise, or include, a layer other than of a suitable board material, and of fused silica.

A composite article in accordance with the present invention, having a shaped part of inorganic fibres and a preformed part, may have any construction commensurate with being manufactured by a method referred to herein, where appropriate.

The composite article may not have a closed form.

Instead of the preformed part being only contiguous with, and exposed in relation to, the coherent fibre mass, as illustrated in the accompanying Figures, the preformed part may be either wholly, or partially, embedded in the coherent fibre mass.

The preformed part may not be of sheet material.

The preformed part may not be metallic.

The preformed part may not have a closed form.

A method in accordance with the present invention of manufacturing a composite article as referred to above may include providing a slurry of fibres of any suitable inorganic composition, and not necessarily natural mineral fibres. The slurry may be with a liquid other than water. The liquid may include any required binding system for the fibres, although as indicated above it is advantageous to avoid the use of a binding system if possible.

The die may have any convenient construction. The surface of the die on which the coating is provided may have any desired shape commensurate with the unitary structure of the fibre coating and the preformed part being readily removable from the die.

Only one preformed part may be mounted at a time on the die. The provided unitary structure with only one preformed part and obtained from the die either comprises, or is capable of being shaped to complete, the required composite article.

Claims (21)

1. A method of manufacturing a composite article having a shaped part of inorganic fibres and a preformed part, includes immersing a permeable die in a slurry of the fibres with the preformed part mounted on the die, extracting the liquid from the slurry through the die by maintaining a reduced pressure on the appropriate one of the two major surfaces of the die, thereby causing the other of the two major surfaces of the die to be coated with a coherent mass of the fibres, the arrangement being such that there is provided a unitary structure of the coating and the preformed part, which unitary structure either comprises, or is capable of being formed into, the required composite article, and removing the unitary structure from the die.

2. A method as claimed in claim 1 in which the inorganic fibres are natural mineral fibres.

3. A method as claimed in claim 1, or claim 2, in which the slurry is of the inorganic fibres in at least water.

4. A method as claimed in claim 1, or claim 2, or claim 3, in which a plurality of preformed parts are mounted on the die, to be spaced along the axis of the die, and in completing a plurality of composite articles, slicing the unitary structure removed from the die into a plurality of identical portions.

5. A method as claimed in claim 4, in which at least a portion of each preformed part, initially embedded in the coherent fibre mass removed from the die, is exposed when the unitary structure is sliced into the plurality of identical portions in completing a plurality of composite articles.

6. A composite article, having a shaped part of inorganic fibres and a preformed part, manufactured by employing a method as claimed in any one of claims 1 to 5.

7. An article as claimed in claim 6 in which the preformed part is either wholly, or partially, embedded in the shaped fibre part.

8. An article as claimed in claim 6, or claim 7 in which at least a portion of the preformed part is contiguous with, and exposed in relation to, the shaped fibre part.

9. An article as claimed in any one of claims 6 to 8 having a closed form.

10. An article as claimed in any one of claims 6 to 9 in which the preformed part has a closed form.

11. An article as claimed in any one of claims 6 to 10 in which the preformed part is metallic.

12. An article as claimed in any one of claims 6 to 11 in which the preformed part is of sheet material.

13. A product having a planar base, and a rim around the periphery of the base, the rim protruding beyond the base from one major surface thereof, both the base and the rim at least substantially being of electrical and/or heat insulating material, the rim comprising a composite article having a shaped part of inorganic fibres and a metallic preformed part providing a covering for the outer surface of the shaped part of inorganic fibres extending at least generally at right angles to the base, the composite article being manufactured by a method as claimed in any one of claims 1 to 5, and having a construction as claimed in any one of claims 7 to 12, where appropriate.

14. A product as claimed in claim 13 in which the metallic preformed part extends to cover also an adjacent surface of the shaped part of inorganic fibres extending at least generally parallel to the base.

15. A product as claimed in claim 14 in which the metallic preformed part also provides a shoulder portion either in alignment with, or inwardly of, the inner surface of the shaped part of inorganic fibres extending at least generally at right angles to the base, the base being secured to the composite article comprising the rim when seated on the shoulder portion of the metallic preformed part.

16. A product as claimed in claim 13 or claim 14 in which a peripheral portion of the base is secured directly to a surface of the composite article extending at least generally parallel to the base.

17. A product as claimed in any one of claims 13 to 16 in which the base comprises, or includes, a layer of a suitable board material.

18. A product as claimed in claim 17 in which the base has a laminated construction comprising at least two layers of different materials.

19. A method of manufacturing a composite article having a shaped part of inorganic fibres and a preformed part, the method being as claimed in claim 1, and being substantially as described herein with reference to Figure 2 of the accompanying drawings.

20. A composite article manufactured by a method as claimed in claim 1, and having a construction substantially as described herein with reference to Figure 1, or Figure 3, or Figure 4 of the accompanying drawings.

21. A product including a composite article manufactured by a method as claimed in claim 1, and having a construction substantially as described herein with reference to Figure 1, or Figure 3, or Figure 4 of the accompanying drawings.