Method of casting an integral slide gate and nozzle

Method of casting an integral slide gate and nozzle assembly wherein a casing (11) conforming to the exterior sides and bottom of the valve is placed upside down on a flat smooth plate (12), a tube (14) is placed within the mold so formed to produce a channel in the cast valve, a first castable refractory exhibiting good resistance to molten metal is cast in the bottom of the mold, a tube (19) is placed about the passage-forming tube (14), the same first refractory castable is cast between the two tubes, and a refractory of lesser resistance to molten metal is cast within the remainder of the mold, the second tube (19) being removed after the casting is complete. Preferably casting is carried out while vibration is applied to the mold, the vibration continuing until after removal of the second tube (19). The second refractory can be an insulating material. Preferably the first castable is a high alumina material, for example one containing over 70%, most preferably over 90%, Al.sub.2 O.sub.3.

BACKGROUND 
The present invention pertains to slide gate valves, and particularly to a 
method of casting an integral slide gate and nozzle assembly for such a 
valve. More specifically, it comprises a method wherein a casing 
conforming to the exterior sides and bottom of the assembly is placed 
upside down on a flat smooth plate to form a mold, a tube conforming to 
the channel to be formed in the assembly is placed within the casing and 
refractory castable material is placed within the mold. 
Slide gate valves are devices whereby the flow of molten metal such as 
steel from a ladle or tundish or other container is controlled by sliding 
or rotating a plate having an orifice into and out of alignment with a 
similar opening in the molten metal containing vessel. Such devices are 
shown, for example, in U.S. Pat. No. Re. 27,237. It is common to place a 
collector nozzle below the sliding plate and in alignment with the opening 
in the plate to guide the stream of molten metal in a single unit, for 
example as shown in U.S. Pat. Nos. 3,731,912 and 3,841,539. 
Commonly, these units are made by forming, for example by pressing and 
firing, separate slide gate plates and collector nozzles, and assembling a 
slide plate and a nozzle in a metal casing, for example by embedding them 
in mortar in the casing. However, in order to obtain adequate flatness in 
such units, it has been necessary to grind their top surfaces after 
assembly. On the other hand, it is known to form an integral assembly 
comprising both the sliding plate and the dependent nozzle by casting 
refractory concrete into a metal casing, such unit not requiring grinding 
if the top surface of the valve is cast against a smooth surface. 
One problem with such casting method of forming these assemblies is that 
the refractory castable used must be of sufficiently high quality that it 
will resist the action of molten steel. However, only the top surface and 
interior of the channel through the plate and nozzle are in contact with 
molten steel. Accordingly, the refractory castable used in the remainder 
of the structure is of higher quality, and consequently more expensive, 
than is needed. 
The present invention offers a method of casting such assemblies which have 
a high grade refractory castable on the upper surface of the plate and 
along the metal flow channel through the plate and nozzle and a lower 
grade refractory in other portions of the assembly. 
SUMMARY OF THE INVENTION 
It has been found, according to this invention, that an integral slide gate 
and nozzle assembly composed of two different grades of refractory 
castable can be made by modifying the prior art method of casting such 
assemblies so that a measured amount of a first refractory castable of 
superior resistance to molten metal, sufficient in amount to form a layer 
(18) at least 1 cm thick on the bottom of the mold, is placed in the mold.

DETAILED DESCRIPTION 
Although the present invention can be used to make assemblies for valves 
which operate by rotation, and to make assemblies in which the dependent 
nozzle is placed asymmetrically with respect to the sliding plate, the 
invention will be illustrated by describing its application to making an 
elongated assembly with a symmetrically disposed nozzle, the unit being 
intended to slide back and forth in operation. 
A metal casing 11 for the assembly is placed upside down with its open top 
on a flat plate 12. Preferably plate 12 has on its upper face 13 an 
extremely smooth, even mirrorlike, finish 15, for example as provided by a 
layer of plastic or polished metal. Preferably a gasket 20 is placed 
between casing 11 and finish 15. An inner or first tube 14, of diameter 
equal to the desired bore of the channel to be formed in the assembly, is 
placed through opening 16 in the bottom of the metal casing and held in 
position on plate 12, for example by block 17. It will be evident that the 
length of tube 14 will be sufficient to project out of opening 16 in 
casing 11 and that tube 14 is fixing within opening 16. Although the piece 
14 has been referred to as a "tube", it will be evident that it can be a 
solid rod, which can be anchored to plate 12, for example by a screw or 
bolt (not shown). The procedure to this point follows that known in the 
prior art. 
Next, a measured amount of a first, higher grade refractory castable is 
placed within the mold, the amount of this material being sufficient to 
form a layer 18 at least 1 cm thick. Vibration may be applied to 
consolidate this material, as is well known in the art. FIG. 2 (a) 
illustrates this stage. 
Next a second tube 19, of diameter at least 2 cm greater than the diameter 
of tube 14, is placed concentrically around tube 14. When tube 19 is in 
place, its lower end extends at least to the top surface of layer 18, and 
preferably penetrates slightly into that layer. Clearly, the upper end of 
tube 19 extends out of opening 16 in casing 11. FIG. 2 (b) illustrates 
this stage. 
A further measured amount of the first refractory castable is placed within 
the space between tubes 14 and 19. Again vibration may be used to compact 
this material. The amount of material used in this step will be such that 
the collar 21 of first refractory material does not extend above the 
uppermost point of casing 11. FIG. 2 (c) illustrates this point in the 
process. 
Next, a second, lower quality refractory castable 23 is placed within mold 
11 but outside of tube 19. Again, vibration may be used to compact the 
material. FIG. 2 (d) shows this point in the process. 
Finally, tube 19 is removed from the mold, as illustrated in FIG. 2 (e). 
Where vibration is used, it will preferably be continued until after tube 
19 is removed, thus causing the two grades of refractory material to knit 
together along their line of contact, as shown in FIG. 2 (f). 
Preferably metal casing 11 contains vent holes 22 to permit the escape of 
any air entrapped within the mold, as is well known in the casting art. 
As an alternative, instead of casting all of the refractory in collar 21 at 
one time, followed by casting of all the second refractory material 23, it 
is possible to cast a portion of collar 19, for example 5 cm, then cast 
sufficient of the second refractory castable 23 to fill the mold to the 
same level as collar 21 and then, before casting further material, raise 
tube 19 to at or slightly below the level of refractory material already 
cast. This method of alternatively casting material within collar 19 and 
in the remainder of the mold, with gradual elevation of tube 19, can be 
continued until the mold is filled. Obviously, vibration can be carried 
out during this alternating casting process. Alternatively, the vibration 
may be done intermittently as part of the alternating casting steps. 
In an alternative arrangement, illustrated in FIG. 3, a preformed, 
preferably fired, insert collar 24 can be placed about the bottom of tube 
14 prior to placement of the bottom layer of first refractory 18. Tube 19 
is then put in place, either surrounding insert 24 or abutting the top end 
of that insert, and the remainder of the process is carried on as 
previously described. In this way, the most critical wear area at the 
junction between the sliding surface and the channel through the assembly, 
can be made of an even more resistant refractory material. 
The two grades of refractory castable used can be any such materials well 
known in the art. The first material will be a material which is 
particularly adapted to resist the attack of flowing molten metal, whereas 
the second material can be a less refractory, and presumably less 
expensive, material. In one embodiment of the invention, the second 
refractory castable can be a lightweight insulating castable. While many 
suitable materials will be evident to those skilled in the art, a first 
refractory castable which has been found to be quite suitable is a high 
alumina castable made up of about 75 parts by weight sized tabular alumina 
grain together with a binder of about 25 parts by weight calcium aluminate 
cement. In general, when the castable materials are aluminous or 
aluminosilicate materials, the first refractory (that is to say, the 
refractory forming the surface of the plate and the lining of the metal 
flow channel) will desirably contain at least 70% Al.sub.2 O.sub.3, and 
most preferably about 90% or more Al.sub.2 O.sub.3. The second castable 
can be any material, for example one containing less than 70% Al.sub.2 
O.sub.3, which is compatible chemically and physically with the first. By 
chemical compatibility is meant that the two materials will not form any 
low melting eutectic at the temperature of use and by physical 
compatibility is meant that the thermal expansion, shrinkage on drying, 
etc. will be sufficiently similar that cracks are not formed in the valve 
either upon drying or in use.