FR2498960A1 - PROCESS FOR CASTING STEEL, ESPECIALLY STEEL INGOTS - Google Patents

Abstract

METHOD AND DEVICE FOR CASTING STEEL, IN PARTICULAR STEEL INGOTS FOR THE MANUFACTURE BY A SUBSEQUENT ROLLING OPERATION OF FLAT INGOTS, BILLETS, TOLES, ETC., IN WHICH A QUANTITY OF LIQUID STEEL IS CAST IN A MOLD OF METALLIC CAST. THE CASTING MOLD 1 IS SURROUNDED BY AN ENVELOPE 6 IN THERMALLY INSULATING MATERIAL AND AFTER REMOVING THE ENCLOSURE, THE STEEL INGOT THUS CAST IS ROLLED, PREFERABLY WITHOUT INTERMEDIATE HEATING, WITH ITS OWN HEAT.

Description

The present invention relates to a method of casting steel,

  of steel ingots for the manufacture by subsequent rolling operation of flat ingots, billets, sheets, etc., in which a quantity of molten steel is poured into a metal casting mold, as well as aVMwOi device,

  requested for the implementation of this method.

  In normal cast casting, the steel ingot first cools quickly and is then, after stripping the ingot mold, reheated in an oven and brought uniformly to the rolling temperature so that it can be the mine. This heating and the standardization of the ingot take place in pit furnaces or hot ovens and require time,

energy and work.

  German patent application 28 49 968 discloses a method for carrying out an equalization process

  ingot of steel ingots in which, after an ingot of

  Of the type described above, the molds are stripped while the steel ingot contained therein is solidified at least half. The steel ingot still liquid thereupon is then provided with a thermally insulating envelope so that an exchange

  thermal can take place inside the steel ingot.

  In this process too, energy is needed

  for heating the ingot. The essential disadvantage of this

  However, it is known that, during the equalization process, the already solidified outer walls are strongly heated by the amount of heat contained in the still-liquid core and, as a result of the high ferrostatic pressure of the liquid core, are bent towards the outside. The steel ingot consequently loses its shape and significant difficulties are encountered during the

rolling process.

  The present invention proposes to avoid the drawbacks of the known mold casting process and to improve the process of the type mentioned so as to be able to dispense with reheating of the ingot at the rolling temperature. This object is achieved according to the invention in that the casting mold is surrounded by an envelope of thermally insulating material and that, after removal

  of the envelope, the cast steel ingot is rolled, preferably

  without intermediate heating, with its own heat.

  The insulating jacket forms a uniform thermal screen, effective, as far as possible on all sides, and delaying

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  strongly cooling of the steel ingot. Thus a fraction as small as possible of the amount of heat contained in the

  amount of liquid steel passes outward per unit of time.

  The quantity of heat contained in the quantity of liquid steel is distributed between the metal casting mold and the quantity of steel itself. The set consisting of the amount of cast steel and the casting mold takes a relatively uniform temperature and the steel ingot cools substantially more uniformly than in the casting in the normal mold. The steel ingot can be laminated directly in an energy-efficient manner, either after demolding the mold or with a thin-walled casting mold welded to it. Reheating before rolling is not necessary. The quantity of heat contained in the quantity of liquid steel is essentially composed of the heat of overheating,

  heat of solidification and cooling heat.

  Since only steel ingots can be rolled

  largely solidified, it is necessary in all cases to extract

  re of the amount of liquid steel the heat of overheating and most of the heat of solidification. This is obtained

  in thin-walled casting molds by the fact that these quanti-

  Heat pipes are evacuated to the outside through the insulating enclosure. However, it is very advantageous that the mass of the casting mold is adapted to these amounts of heat, whereby the steel ingot approaches the highest possible rolling temperature relatively quickly and, despite everything, in isolation on the thermal plan. The interval between casting and the beginning of rolling is therefore shorter. If, on the contrary, the process according to the invention is carried out with relatively thin-walled casting molds, the available time interval between the casting process and the rolling process is greater and can be used for a transporting the steel ingot in its relatively light envelope to a remote rolling train. The main advantage of the invention lies in the fact

  that can be rolled directly from the heat of casting.

  Cooling from the casting temperature (1.550 to 1600 ° C) to the rolling temperature (1.450 to 1.1000 ° C) requires, depending on the weight of the ingot, about 5 to 25 hours or more. So the

  method according to the invention allows reserves of time and temperature.

  sufficient to draw the ingot for rolling.

  It is very advantageous to use a casting mold whose mass is adapted to the amount of heat, in particular the heat of solidification, of the quantity of liquid steel to be poured, so that the casting mold, after receiving the amount of steel, heats up strongly, preferably above 1.1000C, but however below its liquidus temperature. In contrast to thin-walled casting molds, these abutment molds do not weld with the amount of steel introduced. Thus the realization of the casting mold for each individual casting is very simple. An ideal combination of reusable casting molds and an optimal use of the casting heat for the subsequent rolling process is obtained. It is thus decisive that the heat of solidification and the heat of overheating are extracted from the quantity of liquid steel and

evacuated by the casting mold.

  In comparison with the usual mold casting (see for example "The making, shaping and treating of steel, USS, 1964, page 465) the weight of the casting mold is substantially lower, of the order of only a quarter of a traditional mold.

  we save material and energy. In addition,

  less tension cracks. Overall, the process thus makes it possible, on the one hand, to preserve the normal technology of ingot mold casting, but on the other hand facilitates work with the mold, owing to the lower weight and the reduced requirements in this respect. stripping bridges, because of one,

  better handling and a better thermal load.

  of the ingot mold. This ensures, as a result of the thermally insulating envelope, a relatively

homogeneous.

  During casting, the pocket exit temperature can be kept very low when casting ingots relatively

  great because casting does not take much time.

  The thermal protection envelope is either firmly connected to the casting mold or is a self-supporting envelope, possibly carried by an external metal mold which surrounds laterally and below the casting mold according to the invention, in particular the wall mold. thin. In both cases, the thermal protection envelope is removed after casting shortly before the start of the rolling process to maintain thermal insulation and thermal equalization as long as possible within the ingot. steel. When the casting mold is not welded with the steel ingot, which is the case with sufficiently thick casting molds, it can be stripped in a known manner. With thin casting molds, stripping is not necessary. Overall, thermal energy is saved and the solidified steel ingot can be rolled at

  the highest possible rolling without additional reheating phase

  silent. The high heat of his heart leads to an aptitude for

  improved rolling compared to the subsequent heated steel ingot

  and so is less hot inside.

  When, after casting, the mold or the like used as a casting mold has received the heat of solidification of the cast steel, this casting mold has relatively high temperatures. As a result, the casting mold no longer has sufficient static strength values and can therefore absorb only the ferrostatic pressure of the cast liquid steel which is only solidified outside but is still liquid at the same time. inside, during the thermal equalization that occurs. The ferrostatic pressure is absorbed by the thermal protection envelope which prevents a bulge of the casting mold. The thermal protection envelope must therefore be made in such a way as to be able to absorb the ferrostatic pressure, and preferably it is supported by an external mold which is, for example, made in the form of a metal shell. In addition to its function as a thermal insulator, the insulation envelope has the additional function of acting as a support

  from outside to the casting mold. The layer thickness of the enve-

  insulation pad is chosen so as to obtain a good equali-

  temperature inside the cast steel ingot. She is

  In addition, depending on the possibilities of the workshop,

  thick enough for the highest rolling temperature

  possible as long as the conditions of the

  to bind require it. If, for example, the rolling process must be carried out in a remote rolling train, the insulating envelope is

  made with a relatively thick wall in order to be able to

  the heat of casting also during transport. This is a particular advantage of the invention which is particularly interesting for small workshops that do not have the capacity to

  rolling for large steel ingots.

  The bottom zone and the head zone of the casting mold are made in particular in the form of a tank or prism so that the losses during the subsequent rolling process are

as small as possible.

  The forming head pocket is electrically closed against oxidation by a plate placed over it on the liquid surface of the steel ingot and is closed during the process.

subsequent rolling.

  In order to explain the process according to the invention and

  appropriate devices for the implementation of the process, we will de-

  in the following two embodiments are written with reference to the appended drawing in which: FIG. 1 is a longitudinal section of an ingot mold

  firmly attached to an insulating envelope, with the part of

  FIG. 2 is a longitudinal section of an ingot mold.

with a separate envelope.

  FIG. 1 shows a relatively thin wall cast mold 1 which is in the form of an ingot mold having a wall thickness of about 8 cm. The mold widens towards its lower end with a cone angle of 4 and possesses

  thus a conicity substantially double that of the normal ingot molds.

  males usually used and substantially thicker (about four times heavier). The mold is placed on a base plate 2 of the same thickness, which, however, is not essential as shown in the embodiment of Figure 2. The base plate is, in turn, set up. on a substantially larger bottom plate 3 which constitutes a part of the insulating jacket according to the invention and prevents heat transfer downwards. This bottom plate 3 is in turn on a carriage 4 which can be moved on a track 5 perpendicular to the plane of the

  drawing, these last elements being in themselves known.

  To the casting mold 1, made in the form of a lingo

  is firmly connected to a side shell 6 with a relative wall

  very thick. It has in its lower zone a recess 7 for the bottom plate 3 and 8 openings accessible from above in each of which can engage a clamp arm 9 of a stripper bridge clamp (not shown here). The orifices 8 remain until the stripping operation free of material because the thickened upper flange of the casting mold 1 provides a static support -6-

  sufficient against the ferrostatic pressure.

  Prior to the stripping operation, which is illustrated in FIG. 1, an upper cover 11 has already been removed (see FIG. 1). The bottom plate 3, the lateral casing 6 and the cover 11 constitute, together, the insulating casing. Thus, the wall thickness of the upper cover 11 is substantially greater than the wall thickness of the two other parts 3, 6 of the insulating envelope in order to maintain the heat losses upwards more

  weaker than those to the sides and down.

  The lateral envelope 6 has been made taking into account two criteria: firstly it must constitute a thermal insulator with a refractory quality and sufficient insulation properties, and secondly it must however also absorb a part of the ferrostatic pressure. After the casting of a steel ingot in the casting mold 1, the casting mold 1 is heated to a relatively high temperature. The steel ingot solidifies in its edge region in contact with the casting mold 1 but remains

  however liquid in its heart zone. This zone of liquid heart

  during the subsequent thermal equalization process, discharges its heat of solidification to the outside, also to the casting mold 1. The latter, because it is thermally insulated by its lateral envelope 6, is heated again and can be subjected to temperatures at which it can no longer resist the ferrostatic pressure without deforming. As a result, the envelope 6 is made in such a way that it can absorb itself, if necessary, the

  ferrostatic pressure. The outer envelope of the lateral envelope

  6 is, for example, made of several layers of asbestos bead which are applied helicoldalement in the form of turns in close contact and thus avoid a bulge of the casting mold 1

outwards.

  During the stripping operation, the steel ingot 12 is pressed in a known manner by means of a press punch 13 towards the base plate 2 while the clamp arms 9

  lift up casting mold with side casing 6.

  In contrast to the embodiment according to FIG. 1, the lateral envelope 6, in the embodiment of FIG. 2, is not firmly bonded to the casting mold 1; moreover, an additional portion of lateral casing 6 is placed between the casting mold 1 and the lateral casing 6 of rigid shape in the form of a thin layer 14 made of a fluid refractory material, for example sand. In addition, the base plate 2 is omitted. Finally, the lateral envelope 6 is no longer made so as to be able to absorb itself the ferrostatic pressure that may exist, but this result is obtained by a metal envelope which surrounds the outside of the lateral envelope 6 and forms with el] a reusable transportable assembly. At the same time, it protects the material of the lateral envelope 6 against mechanical endowmagents. In order to better hold the material of the lateral envelope 6, it is folded downwards in the shape of L. Finally it has, at the top, eyelets 16 which serve to lift the metal envelope 15 with the envelope side 6 attached to it. The bottom plate 3 is surrounded by a metal tank

  18 has a collar 19 projecting upwards which is

  pledge, from the outside, around the metal casing 15.

  FIG. 2 illustrates the moment towards the end of the casting and shortly preceding the setting up of the cover 11. In the casting mold is the still-in-use steel ingot 12, in place, from the top, a sheet steel plate of about 2 to 5 mm. This is known in the art as described in, for example, German Patent Application 31 09 589, the content of which is incorporated.

  in this application for reference.

  After the thermal equalization etc ..., and shortly before the rolling process the metal casing 15 is lifted upwards with the eyelets 16 with the lateral envelope 6 fixed to it, the layer 14 flows towards the bottom and is received in the tank 18, in particular through the flange 19. It remains the casting mold

  1 which can be stripped by known conventional methods.

Claims (17)

  1. Method of casting steel, in particular steel ingots for manufacture by a subsequent rolling operation   ingots, billets, sheets, etc., in which a quantity of   liquid steel is poured into a metal casting mold, characterized in that the casting mold is surrounded by an envelope of thermally insulating material and that, after removal   of the envelope, the cast steel ingot is rolled, preferably   without intermediate heating, with its own heat.   2. Method according to claim 1, characterized in that the mass (the weight) of the casting mold is adapted to the amount of heat of the amount of liquid steel to be contained therein, in particular to its heat of solidification, such that the casting mold, after receiving the amount of steel, heats up strongly, preferably above 1.1000C   (1373 K), but nevertheless below its liquidus temperature.   3. Method according to claim 2, characterized in that the casting mold is a mold with relatively thin wall. 4. Method according to claim 1, characterized in that the quantity of liquid steel is poured into a thin-walled steel box, corresponding to the subsequent shape of the ingot, which is surrounded by the envelope consisting of a thermally insulating refractory material, and that the liquid steel is welded with the sheets of the box forming the subsequent surface of the ingot   without causing complete dissolution in the wall thickness.   5. Method according to claim 4, characterized in that the wall thickness of the box is 0.2 to 2% of the largest section side of the ingot and is adapted to the heat of overheating of the ingot.   6. Method according to any one of claims 4 and   , characterized in that the metallically white inner side of the box is covered with casting coatings which are not   destroyed and burned only when wetted by liquid steel.   7. Method according to any one of claims 1 to   6, characterized in that the amount of molten steel during casting in the casting mold, has a temperature only slightly higher than the liquidus temperature of the steel used. -9   8. Process according to any one of claims 1 to   7, characterized in that the thermal protection envelope   is removed only shortly before the rolling operation.   9. Process according to any one of claims 1 to   8, characterized in that the solidified steel ingot is;   laminated at the highest possible rolling temperature.   10. Process according to any one of claims 1 to   9, characterized by the fact that the total layer thickness of the insulating envelope is between about 5 and about 40.degree.   the largest section dimension of the steel ingot.   11. Process according to Claim 10, characterized in that the layer thickness and the nature of the insulating materials   are chosen based on the values of thermal conductivity   and heat capacity of a low and uniform heat dissipation on all sides, in order to establish the usual rolling temperature range, namely between 1,450 and   1.1300C for sure after at least several hours.   12. Process according to any one of claims 1 to   11, characterized in that immediately after casting, the   ingot is covered over with an insulating material fractaire.   13. Process according to any one of claims 1 to   12, characterized in that one poses after pouring, on the   liquid surface of the steel ingot, a metallically white   preferably coated on its lower side with a highly refractory casting lacquer having a thickness of about 5 to 30 mm, which is immersed in the liquid steel so that on all sides between the plate and the side walls of the casting mold, a small amount of the liquid steel rises and thus the plate   is welded hermetically at the edges.   14. Device for implementing the method according to   any of claims 1 to 13, characterized by the fact   it comprises a casting mold (1) firmly connected on its edges   with a lateral envelope (6) made of a thermal material insulation.   15. Device according to claim 14, characterized in that the lateral envelope (6) has openings (8)   for gripper arm engagement (9) of a stripper bridge.   16. Device for implementing the method according to   any of claims 1 to 13, characterized by the fact   The casting mold (1) and the lateral casing (6) are separately manipulable assemblies which, in the assembled state, are separated from each other by a space capable of being filled by a fluid material (14).   17. Device according to any one of the claims   14 to 16, characterized in that the taper of the casting mold   (1) is greater than 3 and is preferably 4.