Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a rotor stem forming ~art 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.
lo ~otary 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 e~terior, with a
cooperating rotatable closure component of generally columnar
lS 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 o~ 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 usuaily complementary convex/concave surfaces
to facilitate location o} one surface with respect to the
2S 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 Tor strength and surfaces for receiving a driving assembly
3s at the opposite end. In use the rotor stem is installed in a
substantially vertical position an~ 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
d~ive assembly includes components which transmit pressure
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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 ~eans for
delivering an inert gas, e.g. argon, for reasons well known in
the art such as purging o air to avoid melt oxldation
pro~lems. ~ncorporation ef such gas supply means is an added
difficulty. ~he way that this has been done in the past is to
fit in the throughbore at the driven end o~ the rotor stem a
lo 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 gas-
tight joint. A typical multicomponent system currently in use
is shown in Fig. 1. Problems which manifest themsel~es 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 gas-
tight joints to avoid undesirable losses of the expensive
~0 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.
2s
Accordingly th1s 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 thereor 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
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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
S 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 ~eans 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
~S 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 ther~al e~pansion
probls~s, and has a shape which resists rotation during
assembly to facilitate insertion of the gas pipe and resist
loosening of the coupling during use o~ 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 ~aterial 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
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bonding agent ensures total adhesion and seal integrity
between the coupler and the body o~ the rotor stem. This
enables the problems associated with the prior art separate
forming of ~ented plu~ insert an~ post-pressing asse~bly of
s the rotor stem head, with attendant ~as leakage risks in such
a multi-part head to ~e avoided. Additionally, use of such a
coupler enables the material forming the rotor head to be a
homogeneous reg~on without the stress raisers ~joints and
artifacts) apparent in the currently available multi-part and
lo 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 a~oid 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
2s 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 openïng ha~ing
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.
3s 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 rotorstem of the known type illustrating t~e cemented plug and pipe
arrangement which can prove problematic ~n use;
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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
lo 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 a~ial
throughbore 2. The body 1 has a thickened end 3 with a
concave surface 4 which, in use, bears upon a corresponding
con~ex 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 nozzle-
contacting 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
3s mechanism. The throughbore 2 is plugged at the nozzle-
contacting end 3 by a vented p~ug ? 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 posit~on. Since the plug 8 is a separately
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pressed article made up of a threaded pipe coupling 12,
voiding materials and refractory materials it is of relatively
larqe size to provide strength, this requires tbe 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 She driven
end 10 may represent a source of weakness which could result
in reduced operational life due to mechanical stren~th
failure.
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In an improved rotor ste~ 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
t 5 forming step by isostatic pressing, an integral coupling 32
for a gas pipe 31 as is more clearly sh~wn in Fig. 3. Thus
the rotor stem according to this embodiment of the invention ~ ~
is formed by isostatic pressing from particulate refractory ~ ~-
materials to proYide an elongate body 21 of generally columnar
shape havin~ an internal gas duct 22 extending longitudinally
from a thickened end 13 which has a concaYe surface 1~ for a
known purpose as indicated above with a corresponding convex
surface of a nozzle component (not shownl fixed in the base of
a vessel ~not shown) containing molten material. Similarly
2s this thickened end has an eccentric orifice 15 in the nozzle-
contacting 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 mechanis~ including a drivs 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
3s mechanism. This end 30 is formed from re~ractory materials in
which there is located a void former to provide a narrow bore
channel 18 linking a gas supply pipe ~1 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
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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
s 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 damags and
thermal shock are obtained by use or 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. ~his 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. ~ an improved rotor stem which is otherwise simitar 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
2s 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 ~9 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
3s body which may then be substantially thicker in that region tQ ~ -
improve mechanical strength.
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Such an arrangement has advantages in simplicity of
manufacture, reduction of the nu~ber of joi~ts to a single
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metal-ceramic joint which is ~elf 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
~etween the metal pipe and ceramic coupler surface.
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