BURNER ELEMENT FABRICATION USING INJECTION MOULDING AND CONSEQUENT SINTERING

Abstract

A method of fabricating a burner element for an abatement apparatus is disclosed. The method comprises: injection moulding a charge comprising metal particles and a flow compound into a mould defining the burner element to produce a moulded burner element; and sintering the moulded burner element. In this way, injection moulding is used to produce the burner element, which provides far more flexibility regarding the design and properties of the burner element and avoids the necessity of incorporating a perforated support into the burner element. This allows burner elements of more intricate design to be produced, as well as burner elements which are thinner than those produced using existing techniques, which increases the volume of a combustion chamber defined by that burner element for any external burner element size, which in turn increases the amount of effluent gas that can be treated for any burner size.

Claims

1. A method of fabricating a burner element for an abatement apparatus, comprising: injection moulding a charge comprising metal particles and a flow compound into a mould defining said burner element to produce a moulded burner element; and sintering said moulded burner element.

2. The method of claim 1, comprising debinding said moulded burner element to allow said flow compound to escape from said moulded burner element prior to sintering.

3. The method of claim 1, wherein said charge comprises a porogen.

4. The method of claim 3, comprising debinding said moulded burner element to allow said porogen to escape from said moulded burner element prior to sintering.

5. The method of claim 3, wherein said charge comprises around 5% to 10% by volume of said flow compound, around 15% to 20% by volume of said metal particles with the balance being said porogen.

6. The method of claim 3, wherein said charge comprises said porogen selected to have at least one of a melting temperature which is higher than that of said flow compound and a melting temperature which is less than a sintering temperature of said metal particles.

7. The method of claim 3, wherein said injection moulding comprises multi-shot injection moulding comprising injection moulding one charge having a metal powder and a flow compound and another charge having said metal particles, said flow compound and said porogen.

8. The method of claim 7, wherein said one charge comprises around 5% to 10% by volume of said flow compound with the balance being said metal powder.

9. The method of claim 7, wherein each shot has differing amounts of porogen to provide differing porosities for different structures forming said burner element.

10. The method of claim 9, wherein said differing amounts of porogen are provided by different shots, each of which has a different ratio of porogen to metal particles and/or by varying a ratio of porogen to metal particles within a shot.

11. The method of claim 1, wherein said metal particles comprise metal fibres.

12. The method of claim 11, wherein said metal powder and said metal fibres have an overlapping sintering temperature range.

13. The method of claim 7, wherein said injection moulding of one of said first charge and said second charge generates surface features shaped to enhance mechanical bonding between said first charge and said second charge.

14. The method of claim 7, wherein said first charge and said second charge are at least partially separated by a void material defining a void between said first charge and said second charge.

15. The method of claim 1, wherein at least one surface of said mould comprises a removable perforated layer which forms part of said moulded burner element.

16. The method of claim 7, wherein at least one of said metal fibres and said metal powder comprise at least one of FeCr alloy and stainless steel.

17. The method of claim 1, wherein said flow compound comprises at least one of an organic and a polymeric compound.

18. The method of claim 1, wherein said porogen comprises at least one of glass beads, an organic compound and a polymeric compound.

19. The method of claim 1, wherein said porogen has a particle size of between around 0.5 mm to 2 mm, and typically around 1 mm and/or is provided in a ratio of between around 75% to 95% porogen with the balance being said metal particles.

20. The method of claim 1, wherein said metal fibres have a diameter of between around 0.05 mm to 0.25 mm, and typically around 0.1 mm and/or wherein said metal powder has a particle size of around 0.0005 mm to 0.0025 mm, and typically around 0.001 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0038] FIG. 1 is a flowchart illustrating the main processing steps performed when fabricating a burner element; and

[0039] FIGS. 2A to 2H illustrate schematically the configuration of an injection moulding apparatus when fabricating the burner element.

DETAILED DESCRIPTION

[0040] Before discussing the embodiments in more detail, first an overview will be provided. Embodiments provide an arrangement for manufacturing one or more components or elements of an abatement apparatus produced by metal injection moulding. Embodiments may produce individual porous or non-porous elements of the abatement apparatus. Typically, the component comprise a one-piece burner element formed at least partly from a porous sintered metal part which is typically fused with a non-porous housing, with a hollow plenum space between the porous and non-porous structures. This approach enables complex structures to be produced, which can have thinner porous sintered metal parts than are possible using existing techniques, which in turn provides for an increased volume available for treating effluent gases per unit volume of abatement apparatus, since the burner element itself occupies less space. The burner element may be made from a single mixture of materials or may be made as a composite structure from different mixtures of materials. Typically, the mixtures or charges are made from a metal material formed into fibres, strands, shards, lengths, pieces or powder, together with a flow compound to facilitate the flow of the metal into a mould. The porosity of the resultant moulded burner element can be improved through the addition of a suitable porogen. Also, the porosity of portions of the elements can be varied within the parts by varying the amount and/or size of the porogen in those elements. For example, one portion can have no porogen to provide a non-porous body (such as a portion of the housing, such as a mount or a plate) with other portions having different porosities (such as the burner sleeve). Also, some portions can be have discrete or variable (graded) porosities within those portions (such as the burner sleeve having differing porosities at different, typically axial, positions along the burner sleeve) by varying the amount of porogen present in those portions. The porogen can have a particle size of between around 0.5 mm to 2 mm, and typically around 1 mm. The porogen can be provided in a ratio of between around 75% to 95% porogen with the balance being the metal particles. The metal fibres can have a diameter of between around 0.05 mm to 0.25 mm, and typically around 0.1 mm. The metal powder may have a particle size of around 0.0005 mm to 0.0025 mm, and typically around 0.001 mm.

Main Fabrication Steps

[0041] FIG. 1 is a flowchart illustrating the main processing steps performed when fabricating a burner element 130. FIGS. 2A to 2H illustrate schematically the configuration of an injection moulding apparatus during such fabrication.

[0042] At step S1, the various charges to be used in the preparation of the burner element are prepared. In this embodiment, the burner element comprises a foraminous burner sleeve 10 (which is cylindrical in shape, but can be of any required shape that is mouldable) concentrically surrounded by an outer housing 20 having an integral endplate 30 (which is cylindrical in shape, but can be of any required shape that is mouldable). In this embodiment, a cylindrical plenum 40 is formed between the outer housing 20 and the foraminous burner sleeve 10, into which fuel will be provided during operation of the abatement apparatus, which passes through the foraminous burner sleeve 10 to effect combustion within a combustion chamber 50 into which an effluent stream to be treated (typically together with an oxidant) is provided. Typically, an end annular ring (not shown) bridges between the burner sleeve 10 and the outer housing 20 to enclose the plenum 40. It will be appreciated that in other embodiments, electrically-heated burner elements may be fabricated using a similar technique.

[0043] Accordingly, at step S1, a charge for forming the outer housing 20 and a charge for forming the burner sleeve 10 is prepared. Typically, the charge for the outer housing 20 is a mixture of a metal powder and a flow compound. Typically, the charge for the burner sleeve 10 is a mixture of metal fibres (possibly also with a metal powder), a flow compound and a porogen.

[0044] At step S2, the moulds are prepared. In this case, an outer mould 60 and an inner core 70 are co-located to define an outer housing void 80, as shown in FIG. 2A. The inner core 70 may be provided with undulations on its surface (not shown) at the location where the foraminous burner sleeve 10 will be moulded to enhance mechanical coupling between the outer housing 20 and the foraminous burner sleeve 10.

[0045] At step S3, a charge is injected. In this example, the outer housing charge is injected to form the outer housing 20, as shown in FIG. 2B.

[0046] At step S4, the mould is reconfigured and processing returns to step S3. As shown in FIG. 2C, the first core 70 is removed and a second core 90 is inserted in its place. The second core 90 has a smaller diameter than the first core 70, and so defines a plenum void 100.

[0047] At step S3, the plenum void 100 is filled with a plenum void material 110, as shown in FIG. 2D.

[0048] At step S4, the mould is reconfigured once more and processing returns to step S3. As shown in FIG. 2E, the second core 90 is removed and a third core 120 is inserted in its place. The third core 120 is of a smaller diameter than the second core 90 and defines a burner sleeve void 130.

[0049] The second charge is injected into the burner sleeve void 130 to form the burner sleeve 10, as illustrated in FIG. 2F.

[0050] Processing then proceeds to step S5 where breakout occurs and the moulded burner element 130 is removed from the mould, as illustrated in FIG. 2G.

[0051] Processing then proceeds to step S6, where the plenum void material 110 is removed, as shown in FIG. 2H.

[0052] Processing then proceeds to step S6 where de-binding occurs and the flow compound is removed from the burner element, typically by heating to above the flow temperature of the flow compound. The temperature is then typically increased to remove the porogen from the burner sleeve 10. Once both the flow compound and the porogen have been removed then processing proceeds to step S7.

[0053] At step S7, the burner element is then sintered by raising the temperature to the sinter temperatures of the burner sleeve 10 and the outer housing 20.

[0054] Typically, the first charge used to create the outer housing 20 and the end plate 30 will have no porogen present in order to create a non-porous outer housing 20 and end plate 30. The second charge used to create the burner sleeve 10 has a porogen present typically within the sizes and ratios set out above in order to provide a porous burner sleeve 10. In some embodiments, the second charge used to create the burner sleeve 10 has a variable amount of porogen present typically selected from the sizes and ratios set out above in order to provide a graded or variable porosity along its axial length. In particular, the second charge may be delivered initially with a first amount of porogen, but the amount of porogen is changed as the second charge is delivered in order to create the burner sleeve 10 with differing porosities. In some embodiments, the burner sleeve 10 is formed from a plurality of different charges, each of which has a different amount of porogen present typically selected from the sizes and ratios set out above in order to provide a different porosity at different positions along its axial length. In particular, a first of the plurality of charges may be delivered with a first amount of porogen, a second of the plurality of charges may be delivered with a second amount of porogen, and so on, in order to build up the burner sleeve 10 with different porosities at different positions. In some embodiments, other charges can also used to create other porous and non-porous structures. It will be appreciated that the different ratios of porogen can be provided by changing the amount of porogen added to a charge by a single moulding station or by moving the mould to different moulding stations, each preconfigured to deliver a different charge with a different preselected amount of porogen.

[0055] Although this embodiment envisages a cylindrical combustion chamber housed within a cylindrical outer housing, it will be appreciated that other arrangements are envisage, such as flared or conical arrangements, bell-shaped, wedge-shaped or pyramidal burner sleeves which may or may not be enclosed by a similar or differing shaped outer housing.

[0056] The flow compound is typically removed by heating, although other compounds are possible which may be removed by a solvent. Likewise, the porogen is typically removed by heating, but these may also be removed instead by a solvent. The void materials may also be removed by heating but can also be removed by a solvent. It will be appreciated that the properties of the flow compounds, the porogen and any void materials will need to be selected to ensure that they are not affected during subsequent injection procedures and are unaffected by any different de-binding stages required to reveal the moulded burner element. Although in this embodiment the de-binding and sintering takes place outside of the mould, it will be appreciated that these may be performed with the moulded burner element still either wholly or at least partially retained within the mould. In another embodiment, a perforated liner (not shown) is inserted during processing at FIG. 2E into the burner sleeve void 130 to abut against the inner surface of the plenum void material 100. The perforations in the support liner are typically selected to assist in flow control of fuel from the plenum 40 into the burner sleeve 10.

[0057] Embodiments provide a method of producing a one-piece radiant burner comprising a porous sintered metal part fused to a non-porous housing, with a hollow “plenum” space in between utilising metal injection moulding techniques. This may be of any shape and is particularly advantageous for complex shapes. The porous metal shape is formed by injection moulding of a material that when heated/de-bindered forms a shape of controlled porosity in green (unsintered) form that can be sintered to give the desired product. The formulation for injection moulding may comprise metal powder, metal fibres, organic binder/wax and a porogen. The porogen typically needs to remain intact at injection moulding temperatures but be removed during the subsequent debindering/sintering. The porogen may be formed of hollow glass beads or a water-soluble wax or PMMA. The porosity should typically be around 80%. The porous metal may have a formulation akin to Fecralloy or 314 stainless steel. The cavity of the plenum likewise needs to be formed via a core of material that will withstand the injection moulding temperature. Water soluble wax could also be used. The non-porous metal typically needs to be formulated to include a binder with a lower melting point than the core and porogen materials. The metal when fused may be 304 or 316 stainless steel. Ideally the porous and non-porous materials should typically be chosen to have the same sintering temperature, recognising that the porous material needs to have high temperature oxidation resistance for use as a radiant burner. The injection mould tool will typically be designed with moveable “gates” allowing the non-porous metal to be injected against one face of the plenum wax core and the porous metal to be injected against the second face of the wax before the complete part is ejected from the tool.

[0058] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0059] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0060] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.