FR2643001A1 - Casting member including a plane sliding surface for an associated slide plate (drawback) - Google Patents

Abstract

Casting member in refractory material for transferring a quantity of liquid metal from an upper container towards a lower container, comprising a body 42 of general cylindrical or conical shape having an upper end 44 and a lower end 46, the said body being intended to traverse in a leaktight manner a wall of the said upper container and being traversed right through by a longitudinal orifice 48 for the passage of the said liquid metal. It includes a flange 50 formed at the said lower end 46 of the body and having a sliding surface 51 intended to interact with a movable plate including a tap hole for the liquid metal. Preferably, at the level of the sliding surface 51, it includes a thickness consisting of a mixture having characteristics of resistance to abrasion and/or to corrosion.

Description

CASTING MEMBER HAVING A FLAT SURFACE OF
SLIDING FOR AN ASSOCIATED DRAWER PLATE
The present invention relates to a casting member, mainly for the continuous casting of liquid metals.

 However, it can also be applied to casting in ingots.

More specifically, the invention relates to a casting member made of refractory material for the transfer of a quantity of liquid metal from an upper container to a lower container, comprising a generally cylindrical or conical body having an upper end and an end. lower, said body being intended to sealingly pass through a wall of said upper container, said body being traversed right through by a longitudinal orifice for the passage of said liquid metal.

Conventionally, the continuous casting of a liquid metal is carried out using a pocket containing the molten metal in a container called a distributor located under the pocket and whose function is to ensure the distribution and the continuous regulation of the casting. . From the distributor the metal is directed to a casting mold adapted to the processing technology.

To conduct the flow of liquid metal from the pocket to the distributor, and, similarly, from the distributor to the mold, refractory casting members are used.

There is shown schematically in Figure I a conventional continuous casting assembly. I1 has a pocket 1 containing a quantity 2 of molten liquid metal. A distributor 3 is located under the pocket, and two molds 5 under the distributor.

The metal 2 is conveyed from the pocket 1 to the distributor 3 by means of a nozzle 7, and a jet protection tube 9 connected to the nozzle 7. The lower end of the jet protection tube plunges into the liquid metal 2 contained in the distributor 3.

Similarly, a nozzle 71 having a lower end immersed in the liquid metal contained in the mold 5 conducts the flow from the distributor to the mold.

Alternatively, it is possible to use pouring members including a slide mechanism which makes it possible to interrupt and regulate the flow of liquid metal. The device comprises an internal nozzle 13, connected to a fixed plate of refractory material 15, another fixed plate 17 connected to a submerged nozzle 18 and a movable plate 19 which makes it possible to regulate the flow of metal.

The flow of liquid metal can be regulated in two different ways. According to a first system, the inlet opening of the nozzle is closed by means of a stopper 33 which is applied to the seat of the latter as shown on the left-hand side of FIG. 1.

According to a second system, two or three perforated refractory material plates are used, placed under the pocket or the distributor. At least one of these plates is movable in translation or in rotation, so as to regulate the passage section offered to the fluid as shown on the right-hand side of FIG. 1.

It is also possible to use these two devices simultaneously, that is to say to combine a stopper rod with a drawer mechanism. The main advantage of this arrangement is that it allows the tube to be changed, that is to say the submerged nozzle 18. In fact, the flow is interrupted by closing the stopper 33. It is then possible to extract the old tube and replace it with another.

In FIG. 2A, the casting members described in FIG. 1 can be recognized, namely an internal nozzle 13 connected to the plate of refractory material 15 forming part of the movable drawer mechanism, the refractory plate 17 connected to the submerged nozzle 18, the mobile refractory plate 19 interposed between the fixed upper plate 15 and the fixed lower plate 17. Each of these three plates has a through hole such as 20 for the liquid metal contained in the distributor 3.

In FIG. 2A, the three orifices are aligned, so that the passage section offered to the flow is maximum.

In FIG. 2B, the movable plate 19 has been moved to the right, so that the through hole is partially closed. We thus regulate the flow rate.

In FIG. 2C, the orifice is completely closed.

Conventionally, the through hole. could also be closed by means of a stopper 33, shown in phantom, coming to rest on a rounded seat 34 of the internal nozzle 13.

There is shown in Figure 3 an enlarged view of Figures 1 and 2 showing in more detail the conventional arrangement of the flow rate control members. The distributor 3 has a steel bottom 21 provided with a circular opening 23.

The bottom 21 is protected against molten liquid metal by one or more layers of refractory bricks 25. We find the internal nozzle 13, the fixed upper plate 15, the fixed lower plate 17, the movable plate 19 and the submerged nozzle 18.

The internal nozzle 13 is generally assembled to the upper plate 15 by a refractory cement joint 31.

Preferably, the surface of this seal is not flat, but comprises baffles or a centering rod which, when the two parts are assembled, will cause the casting openings to coincide with one another. In addition, the baffles or the centering means form a sinuous path which limits the risks of infiltration of the liquid metal.

The shape of the internal nozzle may vary according to the cases envisaged.

It is rarely cylindrical for fear of infiltration of molten metal through the cement joint 27 formed between a brick 29, called seat brick, and comprising a conical orifice complementary to the external shape of the internal nozzle 13.

The internal nozzle generally has a conical external shape whose angle varies from -450 to +450. The choice of the sign of the angle is dictated by usage parameters, the advantages and disadvantages of which are known to the skilled person in each case. Alternatively, the seat brick can be replaced by a dammer mass. However, the joint 31 between the internal nozzle and the upper plate is a particularly sensitive point of the system and its presence implies high risks originating inter alia from the manual assembly of the two parts and from the quality of the cement used.

Manual assembly - always leaves a significant place for human error. The joint can be abnormally thick, for example more than 10 mm, or it can have a partial or even total lack of cement. These errors result in high risks of infiltration of molten liquid metal during the casting process.

Although the quality of the cements used is clearly increasing, certain qualities of steel are particularly aggressive so that the joint 31 between the nozzle and the upper plate always remains a weak point which involves significant risks of infiltration.

This is especially true when you consider the length of the joint. By comparison, the joint 27 between the seat brick and the internal nozzle 13 is much longer, and consequently involves much lower risks.

An infiltration of liquid metal at the joint 31 can have serious consequences, both material and bodily, such as serious injuries or even death.

It should also be noted that the plates 15, 17, 19 are applied to each other with a considerable clamping force, of the order of several tonnes, generally by means of springs, in order to prevent infiltration of liquid metal between these plates. As a result, when the movable plate 19 is maneuvered, a considerable tangential force originating from the friction forces is exerted on the upper plate 15.

This effort can result in the rupture of the cement joint leading to a separation of the nozzle and the upper plate and to metal infiltration between the nozzle and the plate.

Another considerable drawback of the device of the prior art shown in FIGS. 1 to 3 lies in the possibility of air suction at the level of the seal 31.

As explained above, the flow rate of the liquid metal contained in the distributor is commonly regulated by means of a stopper, designated by the reference 33, which is applied to a seat formed at the upper part of the internal nozzle. . The shearing of the jet by this stopper causes a suction phenomenon which places the entire casting duct in depression. This depression creates a suction phenomenon which results in possible air inlets.

These air inlets are frequently made at the joint, the cements used always showing a certain permeability to gas.

The air intake results in an oxygen inlet causing oxidation phenomena both for the refractories and for the steel which can lead to an increase in alumina deposits or premature wear of the refractory parts. The air intake also results in a nitrogen entry of which the metallurgist by trade knows the harmful effects.

The present invention specifically relates to a casting member, particularly for the continuous casting of liquid metal, which overcomes the drawbacks listed above.

This casting member must eliminate the risk of human error, in particular when making the joint between the internal nozzle and the upper plate.

It must prevent the tangential forces exerted by the movable plate from leading to risks of liquid metal infiltration.

It must prevent air intake, particularly when the passage of the molten metal is placed under vacuum.

These objects are achieved, in accordance with the invention, by virtue of a sliding surface intended to cooperate with a movable plate comprising a pouring orifice for the liquid metal.

Thanks to the fact that the casting member has an integrated friction surface, it is no longer necessary to fix a plate of refractory material by means of a cemented joint.

The absence of a cemented joint brings many advantages
The risks of human error, in particular the risk that an operator puts too much or too little cement are eliminated.

It removes a weak point from the previous assembly and thus reduces the risk of leakage of liquid metal. The risk of damage to the drawer is thus eliminated or at least significantly reduced.

It also eliminates the risk of separation of the internal nozzle and the refractory plate which exists in the assemblies of the prior art as a result of the friction forces transmitted by the movable plate because the part of the invention is formed in a single pressing operation and its cohesion and resistance are much greater
Finally, an important advantage, the risks of oxygen or nitrogen suction are reduced to a very significant extent.

The abrasion resistance by friction is determined by the materials used. When the casting member is part of a safety assembly, and therefore when it is not very stressed, the abrasion resistance of the refractory material of the friction surface can be relatively low. This allows the production of a casting member both in one piece and of homogeneous composition. In other words, it is not necessary that the surface of the collar on which the movable plate of the mechanism comes to rub has a particular abrasion resistance.

However, the casting member of the invention also applies in the case where the drawer plate mechanism is used alone, that is to say without stopper. In such a case, it is necessary for the friction plate to have an appropriate abrasion resistance. To this end there is provided on the casting member, at the sliding surface, a thickness consisting of a mixture having characteristics of resistance to abrasion by friction. Excellent bonding is achieved since the bonding used is the same in the abrasion resistance layer and in the rest of the part.

According to another embodiment of the invention, an area having a particular abrasion resistance is created by virtue of the presence of an insert. The casting member comprises a preformed insert having a shape such that the connection surface between the insert and the body of the member is circumscribed inside said flat sliding surface.

The insert is then cemented in a housing of complementary shape provided during molding in the body of the casting member. This insert has a shape such that the seal which binds it to the body of the casting member opens only in the casting conduit and on the sliding surface. However, it does not open to the outside of the body. In this way, despite the presence of a cemented joint, the drawbacks mentioned above are avoided because the joint does not communicate with the outside.

Even if liquid metal gets into this joint, no leakage to the outside can occur.

 X the advantages resulting from the absence of a joint are shared. In other words, the fact that the casting member has two parts with different mechanical and chemical characteristics does not affect its strength.

Other characteristics and advantages of the invention will appear on reading the following description of exemplary embodiments. The examples are given by way of illustration.

Figure 1, already described, is a schematic illustration of a conventional continuous casting process;
Figures 2A, 2B, 2C, already described, schematically illustrate the operation of a slide valve;
Fig. 3, also described, illustrates a known arrangement of a nozzle and a slide valve for controlling the flow of liquid metal;
Fig. 4 is a sectional view of a first embodiment of the invention;
Fig. 5 is a sectional view of a second embodiment of the invention;
Fig. 6 is a sectional view of a third embodiment of the invention comprising a pre-pressed insert.

Figure 7 is a sectional view of a fourth embodiment of the invention comprising a filling mixture which gives the plate a larger surface.

There is shown in FIG. 4 a first embodiment of the invention. The casting member, generally designated by the general reference 40 <, consists of a body of generally cylindrical or conical shape, this conicity being able to be positive or negative by reaching a value of 450.

The body 42 has an upper end 44 and a lower end 46 when the part is placed in its normal operating position. The body 42 is crossed from one end to the other by a pouring channel 48.

According to the invention, the casting member comprises a flange 50 formed in one piece with the body 42. In other words, the body 42 and the flange 50 are produced during a single and same operation. pressing, preferably isostatic. However, any other production method within the reach of ordinary skill in the art can be used.

Thanks to the presence of this flange, it is not necessary to fix a friction plate of refractory material to the casting member of the invention. The movable plate 19 described with reference to FIGS. 2A, 2B, 2C and 3 rubs directly on the friction surface 51.

As can be seen in Figure 4, the casting member has a homogeneous composition. The collar 50 does not have a composition different from that of the body.

The requirements of a refractory plate such as a plate 15 or 17 are very different. Indeed, this plate must have qualities of mechanical resistance and resistance to corrosion.

This imposes characteristics of maximum hardness and minimum roughness. The compositions of the refractory plate and that of the body are therefore very different.

These differences in composition explain that the internal nozzle 13 of the prior art and the plate 15 have always been made up of two parts manufactured separately and then assembled by a cement joint.

However, as explained above, the slide valve mechanism can be used in addition to a stopper, which is the main flow regulation mechanism. This drawer mechanism does not have permanent regulation operation. It is therefore not required to be maneuvered frequently. It is then admissible that the collar is made with the same composition as the body. The resistance characteristics are then sufficient.

We have shown in fig. 5 a second embodiment of the invention, designated by the general reference 402.

It has the same general form as the first. It is distinguished from it, however, by the fact that it has an abrasion resistance layer 52. This layer has a composition different from that of the body 42:
The various mixtures are linked together by the same internal bond to each mixture. All the refractory grains of the part are linked to the grains which surround them directly by the same connection, both inside each mixture and at the border between the mixtures. In practice, this border does not exist and the transition from one mixture to another is gradual.

Since this embodiment comprises a layer of a certain thickness having good mechanical and corrosion resistance characteristics, it can be used even in the case where the system does not include a stopper rod, that is to say say when the drawer mechanism is used in intensive operation.

On the other hand, it goes without saying that all the accessory characteristics already known can be used in the casting member of the invention. For example, there is shown in FIG. 5, an insert 54 of a porous material and a slot 56 allowing the injection of argon through the porous ring 54. As is known, the purpose of this non-limiting arrangement is to limit the deposition of alumina to inside the sprue.

FIG. 6 shows a third embodiment of the invention. It includes an insert 60. This insert can be of small size, so as to reinforce the entry of the pouring channel 48. The insert can also have much larger dimensions, so as to reinforce most of the surface of friction 51. This insert is molded and baked separately, then inserted into a housing corresponding to its shape, provided for molding in the body 42. It is then cemented. It is noted that the junction surface between the insert and the part opens out on the one hand inside the friction surface 51 and on the other hand into the casting conduit 48.

Thus, there is no communication between the interior of the pouring channel 48 and the exterior of the body. The risk of leakage is thus avoided.

There is shown in Figure 7 an alternative embodiment of the embodiment of Figure 4 which is distinguished by the presence of a packing mixture 62. However, this variant does not apply only to the embodiment of Figure 4 , but could equally well apply to the embodiments of FIGS. 5 and 6.

As previously explained, in some continuous metal casting systems, the spool system is operated infrequently, either because it is used for pure safety reasons - or because it is operated only when you want to change the jet protection tube. Since the sliding of the plates is occasional, the latter are little used.

They must therefore not exhibit particularly high abrasion resistance characteristics. In this case, it is possible to provide, around the periphery of the sliding surface, a filling zone 62 which gives the plate a larger surface, the filling mixture being made of a material having lower characteristics and therefore a lower cost price.

The casting member shown in Figure 7 is manufactured in the following manner. The body 42 is first of all manufactured separately, in the usual manner. Then it is introduced inside a mold which adapts to its shape and which has a free volume corresponding to that of the packing volume 62. This volume is filled with a second mixture, of lower characteristics. This mixture is packed using a piston and the whole is cooked at a temperature of around 1100 OC.

It is noted that, unlike the previous embodiment, the finished part has a seal which leaves the sliding surface to open the outside of the part. However, it should be noted that this joint is located outside the sliding surface. swept by the tap hole during the operation of the drawer. In other words, the orifice 20 of the movable plate 19 (see FIGS. 2A, 2B, 2C) determines on the flange, during its reciprocating (or rotary) movement, an area which is in contact with the metal liquid. The seal 64 between the body 42 of the casting member and the packing mixture 62 is located outside this zone since the zone swept by the tap hole is smaller than the surface circumscribed by the perimeter of the seal 64 .Thus, in this embodiment also, there is no joint connecting the sliding surface with the external surface of the body of the casting member.

The casting member shown in FIG. 7 has been described as an alternative embodiment of FIG. 4.

However, it would also be possible to increase the surface of the collar of the casting member of FIG. 5 or of FIG. 6 by means of a packing mixture such as 62, provided, as explained previously, that the zone swept by the taphole is entirely circumscribed inside the surface limited by the joint.

Examples of realization
We give below 3 examples, namely, an example corresponding to the prior art and 2 examples in accordance with the invention in order to highlight the differences in chemical composition and physical properties.

EXAMPLE 1 - PRIOR ART
Internal nozzle
Composition SiO2 16% chemical: Al203 52%
C 32%
Physical properties
porosity: 18%
load the rupture in bending: 5/6 kg / cm2
density: 2.3
Plate
Composition SiO2 10% chemical: Al203 84%
C 2.5%
ZrO2 3.5%
Physical properties
porosity: 1.6%
load the rupture in bending: 300 kg / cm2
density: 3.1
EXAMPLE 2 - REALIZATION OF FIGURES 4 OR 7
Composition Al203 55% chemical: SiO2 15%
ZrO2 15%
C 15%
Physical properties
porosity: 18%
load the rupture in bending: 180 kg / cm2
density: 3.1
EXAMPLE 3 - REALIZATION OF FIGURE 5 (carbon bonds)
Body Collar
Composition Al203 45% 63%
chemical: SiO2 12% 11.5%
ZrO2 9% 18.5%
C 30% 7%
Physical characteristics
porosity: 18% 17%
load the rupture in bending: 60 kg / cm2 200kg / cm2
density: 3 3.2
If we compare the chemical composition of the mixture used to make the plate of the prior art, and that which is used to make the pouring member of Figure 4 (or the body of the casting member of the Figure 7), we see that the essential difference lies in the carbon content. Indeed, for the plate of the prior art, this rate is 2.5%, while for the casting member of the invention, it is 7%, that is to say practically three times more Student. We also note that the breaking load of the plate of the prior art (300 kg / cm2) is much higher than the breaking load of the material constituting the casting member of Figure 4 (180 kg / cm2) .

However, these characteristics are sufficient given, as explained above, that this embodiment applies in the case where the drawer is operated more frequently. It would certainly be possible to increase the resistance of the material by reducing its carbon content. This would increase its hardness, but also its sensitivity to thermal shock. However, a cracking is admissible in a drawer plate of the prior art since this plate constitutes a separate part, and that, as a result, these cracks do not communicate with the nozzle. On the other hand, cracking is not admissible in a one-piece casting member such as that of the invention. It is therefore necessary to adapt the composition of this casting member in order to obtain suitable physical properties.

Advantageously, the materials of which the casting member is made must not have a difference in coefficient of expansion at higher temperatures of use 5,10-6 ("c-,).

Finally, it will be noted that the casting member can be obtained by a technique chosen from the group consisting of isostatic pressing techniques, casting techniques and vibrocasting.

It is made from refractory materials chosen from the group consisting of alumina, magnesia, zirconia, silica, lime, chromium oxide, graphite, nitrides, their mixtures and their derivatives by reduction and by the fact that the cohesion of the material can be obtained by the creation of carbon bonds, by sintering in the presence of compounds or graphitic derivatives in a reducing atmosphere. The cohesion between said fraction and the rest of the organ is ensured during cooking, by carbon-type connections.

It is preferably made from refractory materials chosen from the group consisting of alumina, mullite, zirconia, silica, lime, chromium oxide, nitrides, oxynitrides, their mixtures and their derivatives. The cohesion between said fraction and the rest of the organ is ensured by ceramic, chemical or hydraulic type connections.

Claims (9)

CLAIMS: 1. Casting member made of refractory material for the transfer of a quantity of liquid metal from an upper container (1) to a lower container - (3), comprising a body (42) of generally cylindrical or conical shape having an end upper (44) and a lower end (46), said body being intended to sealingly pass through a wall of said upper container (1), and being traversed right through by a longitudinal orifice (48) for the passage of said liquid metal , characterized in that it comprises a sliding surface formed at said lower end (46) of the body and intended to cooperate with a movable plate (19) comprising a pouring orifice (20) for the liquid metal, this orifice sweeping over said sliding surface of the casting member, during its movement, an area which is brought into contact with the liquid metal, this area being contained entirely inside the sliding surface sement. 2. casting member according to claim 1, characterized in that it comprises, at the level of the sliding surface (51), a layer (52) consisting of a mixture having characteristics of resistance to abrasion and / or corrosion. 3. casting member according to any one of claims 1 and 2, characterized in that it comprises an insert (60) preformed having a shape such that the connecting surface between the insert (60) and the body (42 ) of the member is circumscribed inside said flat sliding surface 51, this insert (60) then being cemented inside a housing of corresponding shape, provided in the body of the casting member. 4. casting member according to any one of claims 1 to 3, characterized in that it is obtained by a technique chosen from the group consisting of isostatic pressing techniques and casting techniques. 5. casting member according to any one of claims 1 to 4, characterized in that the friction surface is extended, on its outer periphery, by a packing mixture (62) which gives the plate a larger surface. 6. casting member according to any one of claims 1 to 5, characterized in that it is made from refractory materials selected from the group consisting of alumina, magnesia, zirconia, silica, lime , chromium oxide, graphite, nitrides, their mixtures and their derivatives by reduction and by the fact that the cohesion of the material can be obtained by the creation of carbon bonds, by sintering in the presence of compounds or graphitic derivatives in reducing atmosphere. 7. pouring member according to claim 6, characterized in that the cohesion between said fraction and the rest of the member is ensured during cooking, by carbon type connections 8. casting member according to any one of claims 1 to 5, characterized in that it is obtained by a technique chosen from the group of pourings, vibrocoulings. 9. casting member according to any one of claims 1 to 5, characterized in that it is made from refractory materials selected from the group consisting of alumina, mullite, zirconia, silica, lime , chromium oxide, nitrides, oxynitrides, their mixtures and their derivatives and in that the cohesion between said fraction and the rest of the organ is ensured by connections of ceramic, chemical or hydraulic type.