Note: Descriptions are shown in the official language in which they were submitted.
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In the production of steel product, such as billets,
slabs and blooms, by th~ continuous casting method, molten steel
is poured into a mold from the bottom of a teeming vessel such as
a ladle cr a tundish that is operably positioned above the mold.
In order to control product quality it is necessary that the level
of the molten metal in the mold be maintained substantially constant.
For this reason, it has been the practice to interpose a metering
nozzle in the pour passage between the teeming vessel and the mold.
Such metering nozzles are normally replaceably disposed in the
bottom of the vessel and consist of a bore including an upper portion
formed with either a conically tapered or spherically formed wall
that terminates at its bottom in a flow restricting orifice formed
of a diameter to produce the desired rate of molten metal flow
into the mold.
In the continuous casting of steels deoxidized by aluminum,
magnesium, titanium or rare earth compounds, collectively referred
to herein as "aluminum-killed" steels, there is a tendency for
alumina or other refractory oxide inclusions of microscopic pro-
portions to accumulate in the pour passage through the metering
20 nozzle. These inclusions accumulate in the flow restricting orifice
causing the flow opening to constrict thereby adversely affecting
caster operation by initially requiring the speed of the caster to
be reduced in order to maintain the required metal level in the
i~ mold, and finally, requiring replacement of the orifice when the
constriction becomes excessive. If the nozzle is fixed in the
teeming vessel, the casting operation must be terminated in order
to replace the nozzle. If the nozzle forms part of a sliding gate
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valve, several nozzle changes may be required during the pouring
of a single cast.
The problem is more acutely manifest in low production
facilities, i.e., those in which caster operation compels the use
of metering nozzles containing orifice openings of less than one
inch diameter. In these facilities the production of aluminum-
killed steel product in a continuous casting operation cannot be
accomplished on a practical commercial basis due to the rapid
obstruction of the small diameter orifice openings and the atten-
dant frequency of nozzle replacements that result.
It has been contemplated to alleviate the describedproblem by cementing a thin disc containing the flow control
orifice in the bottom of the pour opening of the teeming vessel.
Such a device, known as a "wafer nozzle", is shown and described
in Japanese Patent Application Serial No. 24208/72 which was laid
open on November 11, 1973, under Serial No. 92226/73. Applicants
have found, however, that "wafer nozzles" are not totally dispos-
itive of the problem for several reasons. First, such devices which
are normally formed of a refractory material of greater density
than the surrounding refractory of the vessel lining are prone to
rapidly deteriorate due to the imposition thereon of high thermal
stresses. Secondly, the flow of metal through these nozzles is
often disturbed, principally as a result of turbulent fluctuations
in the molten metal bath within the teeming vessel, thereby produc-
ing instability of the flow stream through the orifice opening and
flaring in the stream emerging therefrom. An unstable flow stream
gives rise to some, albeit reduced as compared with other devices
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of the prior art, inclusion accumulation on the nozzle. Moreover, both of
these characteristics present the danger of causing metal oxidation due to
increased exposure of the metal to air.
According to the present invention, there is provided a refractory
article for providing a passage for the pouring of molten metal from a teeming
vessel, comprising a body having a bore therethrough defining the pour passage
for said molten metal, a flat disc-like member coaxially disposed with respect
to said bore and extending transversely of the axis thereof, and a through-
opening in said member concentrically spaced from the wall of said bore,
said member being located intermediate the inlet and discharge ends of said
bore and sufficiently spaced from said inlet end to cooperate with the wall
of said bore to define a region of relative stagnation of the molten metal
flowing therethrough.
The invention is further described, by way of example, with reference
to the accompanying drawings, in which:
FIGURE 1 is a partial vertical sectional view of a bottom-pour
teeming vessel equipped with a pour nozzle constructed according to the present
invention;
FIGURE 2 is an enlarged elevational view of a nozzle insert
constructed according to the present invention;
FIGURE 3 is a plan view of the nozzle insert of Figure 2; and
FIGURE 4 is a partial vertical sectional view of a bottom-pour
tundish vessel having a slide gate flow control valve equipped with a nozzle
insert constructed according to the present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
For purpose of describing the invention there is shown,
in Figure 1 of the drawings, the lower side portion of a teeming
vessel 10 of generally well known construction that is adapted to
hold molten metal. The vessel 10 comprises a metal shell 12
having a refractory lining 14, each of which are pro~ided at their
bottom with appropriate aligned openings, 16 and 18 respectively,
to accommodate means for bottom-pouring molten metal from the
vessel. A generally cylindrical well block 20 is disposed in the
10 lining opening 18 and has a through-bore 22 which terminates at
its upper end in an upwardly facing conical recess 24. The bore
22 communicates with the vessel interior and forms part of the
molten metal pour passage from the vessel. In the illustrated
embodiment and in applications in which it is desired to intermit-
tently open or close the pour passage, a stopper rod 26, of usual
construction, can be operably arranged for seating engagement at
its lower end in the well block for opening and closing the pour
passage.
A refractory nozzle insert 28 constructed according to
the present invention is provided with means for mounting in the
well block bore 22. As shown best in Figures 2 and 3, the nozzle
insert 28 comprises a body of generally hollow cylindrical configu-
ration. The external wall of the body is formed with a lower
portion 30 that is of somewhat reduced diameter as compared with
the upper portion 32 to thus define an annular stepped shoulder 34
intermediate the ends of the insert for seating on a complementary
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shoulder in the wall block 20. It should be understood, however,
that means other than the illustrated stepped shoulder can alter-
natively be provided for mounting the insert 28 within the vessel.
Fixture of the nozzle insert 28 in the well block 20 is preferably
accomplished by cementing or the like (not shown).
The body of the insert 28 is provided with an axial bore
having a lower portion 36 and an upper portion 38 which cooperate
to define the metal pour passage from the teeming vessel. An
annular, relatively thin-walled disc-like member 40 is intergrally
formed in the pour passage of the insert, projecting radially from
the passage wall and transversely of the axis thereof. As shown,
the member 40 is disposed intermediate the ends of the bore, form-
ing the divider between the lower and upper bore portions, 36
and 38 respectively. A through-opening 42 penetrates the member
40 forming a flow restricting orifice therethrough.
The member 40 is formed as thin as practicable but in
any event should be provided with a thickness no greater than
twice the diameter of the orifice opening 42 therein. The upper
surface 44 of the member 40 is formed such that the inlet edge 40
of the orifice opening 42 is a sharp edge. In the preferred
embodiment the surface 44 is formed substantially normal to the
bore axis of the opening 42 and at right angles to the wall thereof.
The wall of the orifice opening 42 may, if desired, be downwardly
divergent, however, if such a configuration is adopted the inlet
edge 48 will be more prone to rapid erosion and, for this reason,
is not deemed desirable for most applications.
It will be appreciated that, in forming the pour passage
through which molten metal, especially aluminum-killed steels,
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flow from a teeming vessel as described herein certain advantages are derived.
First, because the restricting orifice, i.e. orifice opening 42, is disposed
in a thin, disc-like member in the manner described, the danger of obstructing
the control flow passage by oxide inclusions is, for practical purposes,
eliminated. This advantage is derived from the fact that, in a thin disc,
i.e. one having an L/D ratio no greater than 2, the imposition of a sharp edge
defining the inlet to the orifice opening causes the stream of flowing metal
to constrict, as indicated by the flow lines in Figure 1, by the formation of
what is commonly termed the "vena contracta". Constriction of the flow lines
is enhanced by the fact that the surface 44 is disposed normal to the axis
of the orifice opening 42 whereby the fluid flow approaching the opening is
imparted with a significant component of velocity radially inwardly toward the
axis of the opening. Since the wall of the orifice opening is shorter
in length than the distance within which the constricted flow stream will
return to its normal diameter, there will be no contact made by the flowing
metal on the wall and, concomitantly, no boundary layer will be formed
adjacent the wall within which inclusions can accumulate. - In order to insure
the creation of the "vena contracta" the outer periphery of the upper surface
44 of the member 40 which is normal to the bore axis should be formed of a
diameter not less than about 1.4 times that of the opening 42, preferably
not less than about twice the diameter thereof. Additionally, due to the
thinness of the member 40 that contains the restricting orifice 42, the
material about the orifice opening is rapidly brought up to the temperature of
the molten metal whereupon excessive heat losses which otherwise might produce
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material "freezing" to the opening is avoided.
A further advantage derived from the fact that the upper
bore portion 38 is formed as a right circular cylinder superposed
above the member 40 is that there is established a well-like
plenum positioned immediately upstream of the orifice opening 42.
This plenum serves a two-fold purpose. First, it operates to
dampen any turbulent fluctuations that may occur in the bath of
molten metal within the teeming vessel as a result, for example,
of the pouring of additional metal into the teeming vessel from a
supply ladle, or the like. The plenum can produce suçh dampening
and thus eliminate the disruptive effect turbulence within the
bath has upon the maintenance of the "vena contracta" in the stream
of molten metal flowing through the orifice opening as long as
the diameter of the bore portion 38 does not exceed three times
its depth. Preferably this depth-to-diameter ratio should be about
two.
Secondly, the plenum defined by the wall of the bore
portion 38 at its intersection with the surface 44 of member 40
provides a space in the lower region of the bore portion surround-
ing, but adequately remote from, the orifice opening 42 in whichthe flow of metal is relatively stagnant whereupon oxide inclusions
will tend to be deposited. By sizing this region of the flow passage
as taught herein the space so provided is of ample volume to receive
the deposited inclusions without their entering or otherwise inter-
fering with the opening 42 during the practical life of the device.
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As shown, the lower bore portion 36 in the described
arrangement is formed of a diameter that is somewhat reduced as
compared with that of the upper portion 38. By sizing this
portion of the bore in the manner shown adequate material is
provided beneath the member 40 with which to provide bottom
support thereto. The wall of this bore portion should not,
however, be located so close to the lower edge 49 of the orifice
opening 42 as to provide a surface which will be in contract with
the stream of molten metal exiting the orifice opening.
Figure 4 of the drawing illustrates a preferred applica-
tion of the nozzle insert 28 of the present invention applied in
a slide gate valve installation on a tundish vessel 50 utilized
in conjunction with a continuous casting installation. The vessel
50 whose bottom portion is shown in the figure comprises a shell 52
having a refractory lining 54. The metal pour passage from the
vessel is formed by the bore 56 in well block 58. A slide gate
valve apparatus, indicated generally as 60, is attached to the
vessel bottom by means of a mounting plate 62. A slide gate
apparatus of the type contemplated is more fully described in U. S.
Patent No. 3,779,424 to E. P. Shapland, Jr. and assigned to the
assignee of this application. To the extent necessary for an
understanding of this invention the apparatus may be described as
having a stationary top plate 64 provided with an opening 66 aligned
with the well block bore 56 and a pair of oppositely spaced
parallel rails 68 mounted beneath the top plate for slidablY quidinq
metal encased refractory Panels or qates 70 or 70a. The qates 70
and 70a are adaPted to be indexed in sequence from a Position
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beneath the top plate opening 66 by means of a hydraulic operator
72 consisting of fluid motor 74, ram 76 and actuating rod 77.
Some of the gates, indicated as 70, are blank, having no
opening from the passage of molten metal and serve when in position
to prevent the flow of metal from the tundish 50. Others, indicated
as 70a, are provided with an axial bore 78 forming the Pour
passaqe of metal from the vessel. As shown in Figure 4, the slide
gate 70a has its bore 78 formed of stepped diameters defining a
shoulder for mounting a nozzle insert 28 therein of similar
configuration as that described in connection with Figures 1, 2
and 3 above.
Heats of steel of 200-ton size containing .03 to .05
weight-percent aluminum have been cast in a continuous caster from
a vessel equipped with a slide gate valve having a nozzle insert
as described herein whose orifice opening is of one and three-
eighths inch diameter. The casting operation has been characterized
by a substantially constant casting speed through-out the entire
casting period, typically of sixty minutes or more duration. In
contrast, use of a conventional flow nozzle in an identical
20 installation exhibited rapid decrease in casting speed (a drop of
12 to 15 inches per minute in casting speed during a casting period
of only ten minutes duration). The improved performance in the
former installation is attributed to the fact that the accumulation
of oxide inclusions is minimized by use of the nozzle insert.
~ t will be understood that various changes in the details,
materials and arrangements of parts which have been herein described
and illustrated in order to explain the nature of the invention,
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may be made by those skilled in the art within the principle
and scope of the invention as expressed in the appended claims.
