ACCESS PORT ARRANGEMENT AND METHOD OF FORMING THEREOF

Abstract

The present invention relates to an access port arrangement and in particular an access port arrangement capable of enabling stirring of a molten metal in a vessel. Such arrangements are often called tuyeres. The access port arrangement comprises an inner part forming a core with an outer periphery and an outer part comprising a bore therethrough having an inner periphery positioned around the outer periphery of the inner part with the path way defined by a gap between the outer periphery of the inner part and the inner periphery on the outer part. The arrangement further comprises one or more bridges that span the gap between the outer periphery of the inner part and the inner periphery of the outer part. The inner and outer part are formed of a refractory material.

Claims

1. An access port arrangement for the introduction of gas into a molten metal to cause stirring of the molten metal, said access port arrangement having a longitudinally spaced inlet and outlet defining a gas flow pathway, the access port arrangement comprising an inner part forming a core with an outer periphery and an outer part comprising a bore therethrough having an inner periphery positioned around the outer periphery of the inner part with the pathway defined by a gap between the outer periphery of the inner part and the inner periphery of the outer part, the arrangement further comprising one or more bridges that span the gap between the outer periphery of the inner part and the inner periphery of the outer part wherein the inner and outer parts are formed of a refractory material.

2. An access port arrangement according to claim 1 wherein the outer part is a refractory block.

3. An access port assembly according to claim 1 formed as a single element with the inner and outer parts being formed from one piece of material.

4. An access port assembly according to claim 1, wherein the inner and outer parts are formed as separate elements and brought together to form the access port assembly.

5. An access port assembly according to claim 1 wherein the inner and outer parts are co-axially spaced such that the gap is substantially uniform in a transverse direction.

6. An access port assembly according claim 1 wherein the gap in a transverse direction is in the range 0.1 mm to 2 mm.

7. An access port assembly according claim 1 wherein the outer periphery of the inner part and the inner periphery of the outer part taper inwardly towards the outlet.

8. An access port assembly according to claim 1 wherein the maximum transverse width of the bore is less than 200 mm, and preferably less than 100 mm, and preferably in the range 60-80 mm, and preferably in the range 70-72 mm.

9. An access port assembly according to claim 1 wherein the one or more bridges are integrally formed with the core.

10. An access port assembly according to claim 1 wherein the one or more bridges are non-linear.

11. An access port assembly according to claim 1 wherein the one or more bridges extend continuously for a majority of the distance between the inlet and the outlet.

12. An access port assembly according to claim 1 wherein the one or more bridges are spiralled.

13. An access port assembly according to claim 1 wherein the one or more bridges comprise a plurality of discrete bridges.

14. An access port assembly according to claim 1 wherein the bridge has a square or rectangular cross section profile.

15. A stirring element according to claim 2, wherein the refractory material is a magnesium oxide-carbon based refractory material.

16. An access port assembly according to claim 15, wherein the amount of carbon in the refractory material is between 10 and 30% by weight, more preferably between 12 and 20% by weight and even more preferably between 14 and 24% by weight.

17. An access port assembly according to claim 2, wherein the refractory material is formed with a flexible binder.

18. An access port assembly according to claim 2, wherein the refractory material is of relatively high thermal conductivity.

19. A method of manufacturing an access port assembly for the introduction of gas into a molten metal to cause stirring of the molten metal comprising providing an inner part formed of a refractory material forming a core with an outer periphery within an outer part formed of a refractory material comprising a bore therethrough having an inner periphery, the inner part being positioned such that the inner periphery of the outer part is positioned around the outer periphery of the inner part, and providing a gap between the outer periphery of the inner part and the inner periphery of the outer part to define a pathway for flow of gas, and providing one or more bridges that span the gap between the outer periphery of the inner part and the inner periphery of the outer part.

20. A method according to claim 19 comprising the step of inserting the inner part into the outer part.

21. A method according to claim 19, comprising the step of forming the inner part to include one or more bridges on the outer periphery of the inner part.

22. A method according to claim 19 comprising the step of pressing the inner part from a refractory material.

23. A method according to claim 19, comprising the step of machining the one or more bridges into the inner part.

24. A method according to claim 19 comprising the step of forming the outer part around a former, and removing the former to form the bore.

25. A method according to claim 19 comprising forming the inner and outer part around an insert, the insert defining the gap, wherein the insert has apertures such that refractory material can pass through the apertures, and heating the formed access port assembly to remove the insert.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] An embodiment of the invention will now be described by way of example only with reference to and as illustrated in the following figures and examples in which:

[0044] FIG. 1 is a schematic cross sectional view of a vessel into which the present invention may be utilised and in particular is schematically represented as a BOF process.

[0045] FIG. 2 is a schematic cut away view of an access port arrangement comprising a tuyere known in the art.

[0046] FIG. 3 is a schematic side view, cross sectional view and end view of an access port arrangement according to an exemplary embodiment of the present invention.

[0047] FIG. 4 is a schematic side view of a first and second inner part to be utilised with an access port arrangement as claimed according to exemplary embodiments.

[0048] FIG. 5 is a schematic perspective view of an insert that may be utilised during manufacture of an access port arrangement.

[0049] Referring now to FIG. 3, presented is an access port arrangement 20 presented in FIG. 3a as a side view, 3b as a cross sectional view and 3c as an end view viewed from the distal end 22. The tuyere 20 includes an inner part 24 and an outer part 26 concentrically spaced to define a substantially uniform gap 28 between the inner part 24 and the outer part 26. The inner part 24 may be termed the core and the outer part 26 is in the form of a brick to be inserted into and forming an integral part of a vessel. The distal end 22 forms a contact surface with the contact of the internal content of the vessel and the opposing proximal end 30 projects outwardly from the vessel. The proximal end 30 comprises an inlet 32 to the gap 28 defining a gas passage way for enabling gas to pass to the outlet 34 at the distal end 22. An arrangement 36 is provided for holding the proximal end 30 of the tuyere for engagement with a gas source via the pipe 38.

[0050] The inner part 24 may include a sheath tube forming the outer surface of the core and may be filled with a refractory material or beneficially the core itself is a very refractory material whereby the outer periphery of the core is formed of a refractory material. Thus, in a transverse direction relative to the longitudinal length of the tuyere, there is beneficially no metallic components in a transverse plane. The retaining component for retaining the proximal end of the tuyere is beneficially made from stainless steel.

[0051] The refractory material commonly is a typical material used in lining vessels for molten metal and the refractory material ideally has a relatively high thermal conductivity which helps extend the operating life of the tuyere. Typical refractory materials are magnesia-carbon and magnesia-graphite, pitch and/or resin bonded, with additives like anti-oxidants.

[0052] The inner and outer parts 24, 26 are beneficially coaxially spaced such that the gap is substantially uniform in a transverse direction. The gap in a transverse direction is beneficially in the range 0.1 mm to 2 mm. A typical range utilised for a BOF furnace is 0.8 mm to 1.2 mm. This provides and ensures good flow rate capability. If the inner and outer parts 24, 26 comprise of refractory materials, surface roughness is higher than in traditional stainless steel tuyeres and as such the flow area is beneficially increased to approximately 160 mm2.

[0053] The outer part 26 is beneficial in the form of a refractory brick for insertion directly into the structure of the vessel. A bore is provided in the outer part 26 into which the inner part 24 is provided. The external dimensions therefore of the outer part 26 may be varied depending on the vessel into which the tuyere is utilised. In the exemplary embodiment, the external dimensions may be approximately 235 mm by 211 mm. It will be appreciated, however, that the base of any vessel may be curved and as such the profile of the cross section of the tuyere is typically not square but trapezoidal. This ensures that the outer part 26 sits appropriately into the structure of the vessel.

[0054] The diameter of the inner part or core 24 is approximately 70 mm in the exemplary embodiment. This approximate diameter is provided at the outlet 34 and tapers outwardly towards the inlet 32 and the approximate diameter is 72 mm at this position. Through the provision of a tapered internal peripheral surface of the outer part 26 and mirrored tapered peripheral surface of the inner part 24 any fracture of the inner part 24 adjacent to the distal end 22 will mean that the fractured portion of the inner part 24 cannot fracture and enter the vessel but is retained within the bore of the outer part 26. This prevents deep cavities being formed on the inner surface of the vessel at the position of the tuyere leading to increased wear.

[0055] It is beneficial that the inner part or core 24 is also a material highly resistant to attack by molten steel and slag and is generally a solid core consisting of a refractory material, such as magnesium oxide (Mx0) and is beneficial as the same as the outer part 26. Preferably, the refractory material of both the inner and outer parts 24, 26 may have relatively high thermal conductivity in excess of approximately 6 W/mK. Examples of such material is magnesia-carbon refractory.

[0056] The gap or annulus 28 between the inner and outer parts 24, 26 is generally of a reduced or smaller size than known in the art. By reduction of the gap an increase in gas velocity per tuyere is achieved.

[0057] Referring to FIG. 3c the planned view of the distal end of the tuyere is presented showing the cross sectional profile of the tuyere. It can be seen that this profile is not square but is trapezoidal in order to be accommodated appropriately in a vessel.

[0058] The present invention may be incorporated into decarburisation, dephosphorisation and stirring processes as an efficient way of economically providing the total amount of gas necessary to carry out the process. Furthermore, though a steel metal bath is referred to, the invention is equally useful in molten baths of other metals. The present invention significantly improves the life of the tuyere greater than the typical 800 heating cycles in current practice in steel making processes.

[0059] Referring to FIG. 4 there is presented an inner part 24 without the outer part 26 and shows two exemplary embodiments of an inner part 24 that may be utilised. FIG. 4a presents a first embodiment comprising an outer periphery 40 and a plurality of substantially circular bridges 42 which are beneficially integrally formed with the inner part 24. In FIG. 4a the bridges 42 project outwardly from the periphery of the inner part 40 and when inside the outer part 26 engage the inner periphery of the outer part. They may be integrally formed with both the inner periphery of the outer part and the outer periphery of the inner part. The bridges 42 provide the dual function of ensuring stability of the inner part within the outer part and also provide a flow path between the inner and outer part for the gas to transfer from the inlet to the outlet of the tuyere.

[0060] In FIG. 4b and in perspective view in FIG. 4c one or more bridges may be provided and are shown as substantially continuous projections projecting from the outer periphery of the inner part. The bridges beneficially spiral around the peripheral surface of the inner part and provide positive engagement with the inner surface of the outer part and in this embodiment the gas flow path would also be spiralled. It is beneficial in this embodiment that the bridge is substantially continuous meaning that as the inner part wears down through use at any position of wear there is always positive engagement between the inner and outer parts. In one embodiment the bridge is approximately 10 mm in width and in cross section is substantially rectangular.

[0061] The access port assembly of the present invention may be manufactured differently dependent upon particular requirements. In one manufacturing method, a core is beneficially provided made of a relatively hard material such as metal about which is pressed a refractory material. The metal core is subsequently removed leaving a bore through the refractory materials. This bore is machined to the specified diameter and beneficially taper, which then forms the inner peripheral surface of the outer part. The inner part is further manufactured by pressing a refractory material to form a truncated cone to match the surface configuration of the inner peripheral surface of the outer part. Into this are machined the one or more bridges 42 as shown for example in FIG. 4b in particular. This machined inner part is then inserted into the outer part such that the bridges 42 form interference engagement with the inner peripheral surface of the outer part.

[0062] In an alternative embodiment, as presented in FIG. 5 an insert 50 is positioned into a mould about which is pressed refractory material. The refractory material fills all of the gaps about the insert. During formation the refractory material passes through the apertures of the insert 52 and forms bridges 42 between the inner and outer parts 24, 26. The bridges 42 therefore span the annual gap. The tuyere can then be heated to melt the insert 50, so that just the bridges are left spanning the gap between the inner and outer parts 24, 26. The temperature used is typically 450° C. during which plastic is burned off to leave a flow path between the inner and outer parts 24, 26 bridged by the plurality of bridges 42. It will be appreciated that the bridges 42 may have a variety of forms including circular, elliptical, or square according to flow characteristics needed for fluid passing through the access port arrangement.

[0063] Embodiments of the present invention have been presented by way of example only and it will be appreciated to the skilled addressee that modifications and variations may be made without departing from the scope of protection afforded by the appended claims.