Method for the continuous casting of long products and relative continuous casting line

The invention relates to a process for the continuous continuous casting of long products and further to the continuous continuous casting plant, with which the process is feasible, according to the respective main claims.

More specifically, the invention will be useful in the continuous casting and rolling of long products such as, in particular, billets and ingots without the need for storage and / or temporary storage of the product and the need to shear the product to proper size at the outlet of the continuous casting machine and within certain limits production and / or handling constraints without causing stoppage or pausing used in the process.

In conventional continuous casting plants, the continuous continuous casting machine and the rolling train are normally components which are operationally separate and which require at least one intermediate element serving as a buffer storage and / or a temporary storage area.

This buffer has the purpose of compensating and managing the various production capacities of the components, namely the continuous casting machine and the rolling mill, to ensure that they interact in accordance with the operational parameters found to be the best possible in producing a high quality product ,

The systems according to the prior art are usually constructed according to one of the following two types.

The first type of plant includes the continuous continuous casting machine, shearing to the proper size, cooling the product to ambient temperature, storage, and subsequent heating to bring the product to the best temperature for rolling and the subsequent rolling process.

This method entails a clear separation between the continuous casting machine and the rolling mill, high production costs, a large space requirement, time-outs, a high demand for manual labor, operational difficulties in operation, handling and intermediate storage of the products and the like.

The second type of process includes continuous casting, shearing to proper size, feeding the strands into an in-line storage furnace to equalize the temperature with possible movement of the strands within the furnace, and then the rolling process.

A process of this type can be used with a steel Times - incorporating Iron & Steel, Vol. 221, No. 10, October 1993, pages 432-433, which comprises a ladle turret, a slab caster, an integrated slab oven detector, a pendulum shear unit for shearing the continuous casting products to proper size, a slab induction heating unit, a leveling furnace, an emergency bobbing unit, a descaler, and a rolling mill ,

This second type of process allows for the establishment of a closer operational connection between the continuous casting machine and the rolling mill, a reduction in production costs and, further, an energy saving due to a lower fuel quantity required for heating the product to be fed to the rolling process.

Furthermore, this type of process provides a more compact design and rationalization with the great advantages of keeping reasonable working hours, overhead cranes and thus savings in investment for this type of structure.

Another advantage that is possible with this method is eliminating the handling of the raw product leaving the continuous casting machine and the elimination of storage and temporary storage areas.

All this leads to an increase in the output and the efficiency of the plant and to a lower required work performance.

However, in this case, too, there are restrictions on the efficiency and the discharge of the equipment caused by the fact that the continuous continuous casting machine and the rolling train are discontinuous in a partially decoupled manner, and accordingly, there is still a need for an intermediate buffer storage which meets the various operational requirements of these components of the plant.

Furthermore, there is still the difficult problem of the frequent need to remove the leading and trailing end portions of the strands, as the work process often does not result in a sufficiently high level of quality in these sections.

This situation also results in a significant amount of scrapping material, additional components and operations, the need for ongoing quality checks, and other issues.

Furthermore, from the document JP-A-61-52975 a continuous continuous casting machine is known in which an electromagnetic stirring means is installed substantially at the end of the curved continuous casting section in the range of 0-3 m from the point of directing the continuous casting machine. However, this document does not disclose the continuous casting plant in the working direction after the region in which the electromagnetic stirring means is arranged.

The present applicants have developed, tested and embodied this invention to eliminate these disadvantages in prior art continuous casting plants and to obtain further advantages.

The invention is indicated and characterized in the respective main claims, while the dependent claims describe modifications within the principles of the most important embodiment.

The object of the invention is to provide a continuous continuous casting process and associated equipment for long products such as rolling billets and ingots, the process and plant utilizing the components in a rational manner by increasing the working and handling efficiency and by better discharging the plant ,

The invention provides a direct connection between the continuous continuous casting machine and the rolling mill without the inclusion of a buffer storage system and / or a separation between the two components mentioned above is required.

Further, the invention does not involve shearing the product leaving the continuous casting machine to its intended size, but results in the product arriving at the rolling line directly as it has been supplied by the continuous casting machine.

According to the invention, the continuous continuous casting process results in the product, after continuous casting in the plant, being fed to a temperature holding and temperature compensation system and then immediately further rolled in the plant without interruptions, diversions or breaks.

In this way, the method eliminates any kind of lack of continuity and ensures high output, avoids problems in storage and / or storage and / or handling of the product and achieves a rational exploitation of the capabilities of each component of the plant.

Furthermore, the problem of clogging the leading and trailing ends is avoided except in the steps of the beginning and end of the continuous casting.

This method according to the invention leads to a high degree of coordination of the production speeds of the continuous continuous casting machine and the rolling train, so that none of the components of the plant, and in particular the rolling train, is only partially utilized or whose possibilities are only partially utilized.

According to the invention, the plant comprises a continuous continuous casting machine which is capable of pouring the product at a high speed of between about 5 to 6 m / min to more than 8 m / min, for example according to the section to be cast, and a high one Ensures quality grade. These high speeds not only ensure efficient utilization of the rolling mill in terms of production efficiency, but also those of the critical speed below which cracks and / or deformations are generated in the rolling rolls are closest to running speeds.

In the conveying direction after the continuous casting plant and after the straightening step, temperature-retaining systems are provided to limit the temperature losses at the product promoted at low continuous casting speeds, which may occur in transient situations when operational and handling problems arise.

The plant according to the invention has in the conveying direction in front of the rolling mill on a heating and / or temperature compensation unit whose purpose is essentially to make the temperature in the core and on the surface of the product uniform and bring this temperature to values ​​for the rolling are suitable.

Between the heating and / or temperature compensation unit and the first rolling mill of the rolling train, a distance is advantageously provided, which gives the core to complete the temperature compensation a Wiederaufheizzeit to provide the mill a product with a uniform and homogeneous temperature.

In the conveying direction immediately after the heating and / or temperature compensation unit, a descaling unit may be present to remove the scale from the surface of the product.

The attached figures are given as a non-restrictive example and show a preferred embodiment of the invention, wherein

Fig. 1 shows a possible design of the plant for continuous casting of long products according to the invention and

FIG. 2 is a graph of the respective surface and internal temperatures at a rolled product along the continuous casting line shown in FIG. 1. FIG.

A continuous casting machine 10 shown in FIG. 1 comprises a continuous casting machine 11 consisting of at least means for discharging molten metal and a mold 13, indicated by the reference numeral 12.

For example, a line 14 formed by dots and dashes represents the position of the meniscus of molten metal within the mold 13.

The directional radius "r" of the continuous casting machine 11 has been calculated such that there is a tradeoff between the height of the continuous casting machine 11, the reduction of the solidification section and the temperature drop in the product 16 at a reduced continuous casting speed.

The height of the machine is intentionally maintained at the lowest possible value compatible with the mechanical stresses to which the continuous casting product is subjected. A curved machine is used instead of a horizontally oriented, evidently also a logical solution, since tests have shown that horizontal continuous casting is not capable of continuously casting the production cycles nowadays both with respect to the maximum achievable speed also with regard to the operating conditions (continuous casting in long sequences, times necessary for new equipment and maintenance) are required, provide.

A secondary cooling system arranged downstream of the mold 13 is optimized to control rewarming and to prevent the formation of cracks at the surface and / or below the surface.

According to a modification, the directional curvature in the conveying direction according to the form 13 is formed by a line formed with a plurality of radii in order to keep possible deformations of the product within predetermined limits.

The continuous casting machine 11 according to the invention used in the plant 10 leads to the completion of the solidification of the continuous casting product 16 in a region situated downstream of the outlet of the mold 13 in the conveying direction. This arrangement allows the use of a controlled pre-rolling process at the outlet of the mold 13.

In view of the high continuous casting speeds, the continuous casting product 16 further comprises a relatively large liquid core when the product is already in the horizontal directional section of the plant 10.

According to the invention, the continuous continuous casting machine has a short curved section followed by a long horizontal section in which complete solidification of the rolling billet takes place. In this section there are electromagnetic stirring means necessary to eliminate structural irregularities which would otherwise be the direct consequence of the fact that solidification occurs with a rolling billet in a horizontal arrangement.

In the section between the outlet of the straightener / extractor unit and the preheat / temperature compensation device (furnace), the inside area of ​​the billet is liquid and the heat of this part resulting from the conversion to a solid is utilized to raise the temperature of the near-surface areas at an elevated temperature that is compatible with the process.

The rolling billet is completely solidified immediately before the inlet of the heating / temperature compensation device and enters this device without shearing.

According to this concept, rolling within the plant without interruptions, since it is impossible to shear the billet with a liquid core, and without accumulator systems, must take place either by separating the billet or billets into pieces or with drawers or other device thereof Art can be performed, which would not be possible with a liquid core.

As already mentioned, in this embodiment, electromagnetic stirring means, in this case a first stirring means 15a and a second stirring means 15b, are provided substantially in the first horizontal portion of the installation 10.

The electromagnetic stirring means 15a, 15b have the function of reducing the irregularities in the internal solidification structure caused by the long horizontal portion of the equipment in which solidification of the liquid core is completed.

The position and number of the electromagnetic stirring means 15a, 15b are selected according to the target continuous casting speeds, the type of continuous casting material and the cross section of the product 16 to be processed.

Normally, even with highly productive machines, only a small part of the rolling billet solidifies in the horizontal section. According to the invention, however, this fact occurs for a significant percentage of the cross section of the rolling billet, namely about 12-30% per area. This means that at the beginning of the horizontal section, the rolling billet or ingot has a liquid core over at least 12% of the cross-section. The invention does not have stirring means when no high quality requirements are placed on the continuously cast steel.

In the conveying direction after the electromagnetic stirring means 15a, 15b, the system 10 has temperature-retaining systems which, for example, consist of insulated hoods identified in this case as 22a and 22b.

These insulated hoods 22a, 22b, which may be replaced by other temperature-maintaining systems further having a preheating function, have the purpose of limiting the temperature losses at continuous casting products 16 passing through the low continuous casting speed.

In this case, there is a first shearing means 17a between the first 22a and second 22b insulating hoods and is used in emergency situations, for example in case of problems and / or interruptions and / or changes in the cross section of the rolling mill 18, so that it is possible to to provide a buffer at the feed roller conveyor in the conveying direction before the first shearing means 17a.

In such situations, without the need to adjust continuous casting, the continuous casting speed is reduced to provide the time required to restart the rolling mill 18 and to perform the required recovery before the leading end of the product enters the area where the problem has occurred ,

This reduced speed is dependent upon the normal operating rates of continuous casting and plant design and is dictated by a trade-off between not too high temperature loss in the continuous casting product 16 and maintaining the compact operation of the entire plant.

According to a modification, upon occurrence of any of the above-mentioned problems in the rolling mill 18, the continuous casting product 16 is sheared by the first shearing means 17a, and the continuous casting process is stopped for a sufficiently long period of time to restart the rolling mill 18 and perform the measures necessary for recovery to enable.

When restoration is complete, continuous casting is restarted.

In this case, the means 12 discharging the molten steel into the mold 13, for example a tundish, is to be designed so as to prevent solidification of the molten steel therein.

In particular, this discharge means 12 must be equipped for example with plasma torches, means for maintaining a defined atmosphere, insulating cover means and special housings for the tundish.

By using one of these buffering systems on the roller conveyor or the molten steel in the tundish, and by properly handling the operating parameters associated with the interruption of the equipment, it is possible to obtain in the mill 18 recovery times of about 15 to 20 minutes.

The first shearing means 17a can further be used to obtain special products such as rolled billets sheared to the proper size or other products.

Further shear means 17b, 17c are in this case at the outlet of the second insulating hood 22b and have the purpose to intervene in all possible situations occurring in the system 10, such as in particular disturbances in the rolling train 18.

In the conveying direction in front of the rolling train 18, a heating and / or temperature compensation system 19 is present and advantageously designed as a fast-heating type.

In this case, the heating and / or temperature compensation system 19 has an induction furnace 119, within which the temperature of the continuous casting product 16 can be significantly increased. See Fig. 2, where the dashed line 20b shows the temperature of the core of the product 16, while the solid line 20a represents the surface temperature.

The induction furnace 119 has operating parameters, such as power, operating frequency, and length, which ensure that a homogeneous nonuniform temperature is achieved for all types of products 16 under all operating conditions encountered. This situation makes it possible that a high flexibility and adaptability of the system 10 is ensured.

Achieving an excellently homogeneous and uniform temperature over the entire cross-section of the product 16 allows avoiding problems associated with elongations, warps and deformations which may occur due to a significant lack of homogeneity in the temperature of rolling.

In this case, the temperature at the surface of the continuous casting product 16 is raised to a high level to obtain optimal rolling temperatures in low core transient situations. It is therefore necessary to determine an optimum distance "a" between the outlet of the induction furnace 119 and the inlet of the first mill stand 18a in order to further heat the hot core and cool the surface in this section of length "a".

Thus, the continuous cast product 16 enters the first mill stand 18a at a substantially uniform and homogeneous temperature at a value which can be determined in accordance with the optimum rolling parameters.

Advantageously, at least one descaling unit 21 is present in the conveying direction immediately after the induction furnace 119.

This descaling unit 21 has the task of freeing the surface of the product 16 of scale and / or other possible impurities, which have already chipped due to the different thermal expansions of steel and scale within the induction furnace 119.