GB2228222A - Rotor for molten material discharge control valve - Google Patents

Abstract

A rotor stem forming part of a rotary valve assembly for use with apparatus for handling of molten material, especially metal, comprises a longitudinal body (21), formed from refractory materials by an isostatic pressing method, having one end (30, 40) adapted to receive a driving component, wherein said end contains, for attachment of an inert gas gas feed pipe (31, 41), a coupler (32, 42) which is co-pressed into the body during forming thereof by isostatic pressing and is formed of thin metal of from high strength ceramic material to allow direct fastening of the feed pipe by threaded connection or compression joint to a substantially solid rotor head.

Description

Rotor This invention relates to a rotor stem forming part of a rotary valve assembly for use with apparatus for handling of molten material, especially metal. The invention is particularly useful in apparatus for controlling the pouring of melt from a tundish into a mould such as in the production of ingots or in the continuous casting of steel for example.

Rotary valve assemblies of a known type comprise a replaceable outlet component locatable in the base of a vessel such as a tundish and having a throughbore to act as an outlet passage from the interior of the vessel to the exterior, with a cooperating rotatable closure component of generally columnar shape having an end surface adapted to bear upon a surface of the outlet component and having in that end surface an orifice registrable with the passage, and in its sidewall, an opening communicating with said orifice whereby a melt flow pathway out of the vessel may be formed by appropriate rotational control of the closure component. These components may be conveniently referred to as "nozzle" and "rotor stem" components respectively.The cooperating surfaces of these components are usually complementary convex/concave surfaces to facilitate location of one surface with respect to the other.

Typically the rotor stem will be formed from particulate or granular refractory materials by an isostatic pressing method using arbors and void forming materials with appropriate curing and extensive machine finishing steps to provide a substantially cylindrical body having an axial throughbore and usually non-uniform exterior contour arising from the need to provide generally thicker material at the nozzle contacting end for strength and surfaces for receiving a driving assembly at the opposite end. In use the rotor stem is installed in a substantially vertical position and a large proportion thereof immersed in molten material at very much higher temperatures than the upper end which is located in a drive assembly.The drive assembly includes components which transmit pressure from an actuator mechanism to the rotor to maintain close mating surface contact with the nozzle component.

It is conventional to provide such systems with means for delivering an inert gas, e.g. argon, for reasons well known in the art such as purging of air to avoid melt oxidation problems. Incorporation of such gas supply means is an added difficulty. The way that this has been done in the past is to fit in the throughbore at the driven end of the rotor stem a vented plug into which is fitted a metal pipe by a separate forming operation. The pipe and plug are cemented into position and this does not always provide a satisfactory gastight joint. A typical multicomponent system currently in use is shown in Fig. 1.Problems which manifest themselves with such an assembly include the need to provide high mechanical strength at both hot and cold temperatures, close dimensional accuracy, especially at the driven end where mating with the driving assembly is required, and the need to provide gastight joints to avoid undesirable losses of the expensive inert gas.

Thus such a component is not easy to manufacture and an object of the present invention is provide improvements therein whereby such problems are obviated or mitigated.

Accordingly this invention provides a rotor stem comprising a longitudinal body, formed from refractory materials by an isostatic pressing method, having one end adapted to receive a driving component, wherein said end contains a coupler for attachment of a gas feed pipe which is co-pressed into the body during forming thereof by isostatic pressing. The advantages of using a co-pressed coupler are that a fully integrated connection for the gas pipe is provided which is completely bonded into the body in a secure manner which minimises the possibility of gas leaks around the coupler and the surrounding refractory body can be made much thicker to provide added strength because there is no need to leave an opening for subsequent insertion of a separately formed plug as in the known product.This also means that the throughbore present in the rotor of the known type need not be of such large diameter at the driven end of the rotor and may instead be a significantly narrower bore internal channel the length of which is a matter of choice taking into account the amount of material required to form the shape and the strength required of the rotor. The manner of forming such a channel can be by use of void formers or similar means as is already known in the art. Thus to all intents and purposes the rotor stem head is substantially solid in comparison with the known assembly.The result is an improved strength rotor which is less likely to suffer mechanical damage due to the stresses applied by the driving assembly, is less inclined to suffer gas leakage due to the omission of the cemented joints apparent in the prior art and is more easily manufactured, in one step, which also results in economic advantages.

The driven end of the rotor stem may be formed by moulding and machining to have a polygonal shape suitable for receiving a corresponding drive cap forming part of a driving mechanism for turning the rotor.

According to the invention the coupler may be of thin metal, preferably the thinnest capable of fulfilling its intended purpose in order to minimise differential thermal expansion problems, and has a shape which resists rotation during assembly to facilitate insertion of the gas pipe and resist loosening of the coupling during use of the rotor. Thus the coupler may comprise a female threaded barrel portion having an external surface which is adapted to resist rotation by being non-circular, having flats, or having projections or recesses which will provide an interference fit with the surrounding refractory material in the pressed product.

Preferably also the coupler will have a surface coating such as boro-silicate glass or the like to provide a bond between the refractory material of the rotor stem and the coupler.

The advantages of the one piece rotor head construction of this invention are that the coupler geometry enables it to be incorporated readily in the tooling set up for pressing of the rotor body and the surface treatment of the coupler with a bonding agent ensures total adhesion and seal integrity between the coupler and the body of the rotor stem. This enables the problems associated with the prior art separate forming of vented plug insert and post-pressing assembly of the rotor stem head, with attendant gas leakage risks in such a multi-part head to be avoided. Additionally, use of such a coupler enables the material forming the rotor head to be a homogeneous region without the stress raisers (joints and artifacts) apparent in the currently available multi-part and multi-material-rotor stem design.

The coupler may alternatively be pre-formed from a durable high strength ceramic material to provide a suitably shaped insert having an internal threaded socket for receiving a gas pipe, which insert by its nature would be readily compatible with the refractory material used in pressing the rotor stem, allowing it to be co-pressed into the body of the rotor stem to provide a head design which would also avoid the stress raisers evident in the known design as discussed above. A suitable ceramic material would be reaction bonded silicon nitride.

A further way of avoiding use of the separately formed vented plug arrangement involves formation of a compression joint between a gas pipe and the rotor stem body which is adapted according to the invention to receive the pipe by pressing of a blend of refractory materials in a region of the driven end of the rotor stem to form in that end a tapered opening having durable surfaces for engaging the gas pipe in a close fit arrangement, which engagement is ensured by providing a threaded portion on the exterior of the gas pipe and a corresponding thread on a cap component which is fastenable to said end of the rotor stem.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a longitudinal section through a rotor stem of the known type illustrating the cemented plug and pipe arrangement which can prove problematic in use; Fig. 2 is a longitudinal section through a rotor stem according to the invention illustrating the increased end section thickness which incorporates an integral fully sealed gas coupler fitment; Fig. 3 is an enlarged view, in section, of the end of the rotor shown in Fig. 2 illustrating one embodiment of the coupler according to this invention; and Fig. 4 is a view in section of the end of a rotor stem in accordance with this invention wherein a compression fitting of the gas feed pipe is provided.

In the prior art rotor stems as illustrated in Fig. 1 a rotor stem is formed by isostatic pressing from particulate refractory materials, e.g. graphitised alumina, to provide an elongate body 1 of generally columnar shape having an axial throughbore 2. The body 1 has a thickened end 3 with a concave surface 4 which, in use, bears upon a corresponding convex surface of a nozzle component (not shown) fixed in the base of a vessel (not shown) containing molten material. This thickened end has an eccentric orifice 5 in the nozzlecontacting surface 4 which is registrable with an outlet passage in the nozzle.It also has in its sidewall, an opening 6 communicating with the orifice 5 whereby, in conjunction with the passage in the nozzle, a melt flow pathway out of the vessel may be formed by controlled rotation of the rotor stem about its longitudinal axis to bring the orifice 5 into register with the passageway. Rotation of the rotor stem causes displacement of the orifice 5 so that it no longer corresponds with the passage which of course cuts off melt flow from the vessel. Such rotation of the rotor stem is accomplished by means of a drive mechanism including a drive cap 9 attachable, conveniently by a simple press fit, to the other end 10 of the rotor stem which is generally thinner than the nozzle-contacting end and machined to fit into the drive mechanism.The throughbore 2 is plugged at the nozzlecontacting end 3 by a vented plug 7 and at the other end 10 by a vented plug assembly 8 including a gas supply pipe 11.

These plugs are inserted after pressing of the rotor stem body and cemented into position. Since the plug 8 is a separately pressed article made up of a threaded pipe coupling 12, voiding materials and refractory materials it is of relatively large size to provide strength, this requires the throughbore to be of relatively large diameter. The outer diameter of the rotor stem is constrained by the need to fit the drive assembly. This means that the body thickness at the driven end 10 may represent a source of weakness which could result in reduced operational life due to mechanical strength failure.

In an improved rotor stem design in accordance with the invention, as shown in Fig.2, the nozzle contacting end 13 of the rotor stem can be equivalent to that of the prior art.

However the driven end 30 is modified to provide, in a single forming step by isostatic pressing, an integral coupling 32 for a gas pipe 31 as is more clearly shown in Fig. 3. Thus the rotor stem according to this embodiment of the invention is formed by isostatic pressing from particulate refractory materials to provide an elongate body 21 of generally columnar shape having an internal gas duct 22 extending longitudinally from a thickened end 13 which has a concave surface 14 for a known purpose as indicated above with a corresponding convex surface of a nozzle component (not shown) fixed in the base of a vessel (not shown) containing molten material.Similarly this thickened end has an eccentric orifice 15 in the nozzlecontacting surface 14 which is registrable with an outlet passage in the nozzle and, in its sidewall, an opening 16 communicating with the orifice 15 to define, in conjunction with the passage in the nozzle, a melt flow pathway out of the vessel when the orifice 15 is aligned with the passageway. As before rotational control over the rotor stem is accomplished by means of a drive mechanism including a drive cap 19 attachable by pressing onto the other end 30 of the rotor stem which is substantially solid and formed to fit into the drive mechanism. This end 30 is formed from refractory materials in which there is located a void former to provide a narrow bore channel 18 linking a gas supply pipe 31 with the gas duct 22.

The gas duct 22 has a vented plug 17 and at its other end whereby controlled supply of inert gas may be passed directly through the rotor stem in a manner generally known per se.

However the modified rotor stem according to this invention provides a more efficient way of handling the gas due to elimination of all joints evident in previous systems apart from that between the gas pipe and the coupler. In addition the superior mechanical strength provided by the very much thicker upper end 30 provides increased operational life.

Further improvements in resistance to impact damage and thermal shock are obtained by use of a smaller diameter gas duct 22 which is accompanied by a corresponding thickness in the body around it. The duct 22 need not extend so far through the body 21 as shown in the drawing and may only be a small chamber in a lower portion of the rotor stem in which case the channel 18 will be of greater length. This is possible because there is no need to provide a large access aperture for receiving a vented plug and coupler assembly as in the prior art.

In a further embodiment of this invention as illustrated in Fig. 4 an improved rotor stem which is otherwise similar to that shown in Fig. 2 has an upper end 40 including an integral vented coupler 42 formed from refractory material, preferably zirconia/alumina or reaction bonded silicon nitride or the like, which has a surface 44 adapted to receive a tapered end 43 of a gas supply pipe 41 in a close fit under compression.

The upper end 40 is also shaped to receive a drive cap 39 in the crown of which there is a tapped bore 29 through which said tapered end 43 may pass to engage said surface 44. The gas supply pipe has a threaded exterior surface portion 45 for locating the pipe in the drive cap 29 which once fixed to the rotor stem head for use forces the gas pipe 41 into engagement with the coupler surface 44 to provide a compression seal. As in the embodiment of Fig 2 a narrow bore gas channel 38 is used to convey gas from the coupler 42 through the rotor stem body which may then be substantially thicker in that region to improve mechanical strength.

Such an arrangement has advantages in simplicity of manufacture, reduction of the number of joints to a single metal-ceramic joint which is self closing due to the normal bearing loads on the drive cap which are required to provide good stem to nozzle contact also acting to maintain close fit between the metal pipe and ceramic coupler surface.

Claims (7)

Claims

1. A rotor stem comprising a longitudinal body, formed from refractory materials by an isostatic pressing method, having one end adapted to receive a driving component, wherein said end contains, for attachment of a gas feed pipe, a coupler which is co-pressed into the body during forming thereof by isostatic pressing.

2. A rotor stem according to claim 1 wherein the co-pressed coupler is formed of thin metal or from high strength ceramic material.

3. A rotor stem according to claim 1 or claim 2 wherein the coupler has a shape which resists rotation thereof within the stem during insertion of the gas pipe and resists loosening of the coupler during use of the rotor.

4. A rotor stem according to claim 3 wherein the coupler comprises a female threaded barrel portion having an external surface which is adapted to resist rotation by being noncircular, having flats, projections or recesses which provide an interference fit with the surrounding refractory material in the final pressed product.

5. A rotor stem according to claim 2 or claim 3 wherein a blend of refractory materials is pressed in a region of the driven end of the rotor stem to form in that end a tapered opening having durable surfaces for engaging the gas pipe in a close fit arrangement, which end further has a threaded portion upon which a correspondingly threaded cap component connected to the gas pipe is fastenable to said end of the rotor stem whereby the gas pipe is urged into said close fit arrangement.

6. A rotor stem according to any one of claims 1 to 5 wherein the coupler has a surface coating of a boro-silicate glass or the like to provide a bond between the refractory material of the rotor stem and the coupler.

7. A rotor stem substantially as hereinbefore described with reference to Figs. 2 and 3 or Fig. 4 of the accompanying drawings