JP2005529750A - Suitable for continuous casting molds, especially in the casting area - Google Patents

Abstract

[Solution]
The present invention relates to a mold for continuously casting a molten metal, in particular steel, provided with a cooling channel (1) such as a cooling groove, a cooling slit or a cooling hole on the mold side face (2) facing away from the contact surface with the molten metal. The heat transfer of the mold is the geometric structure of the heat transfer surface area of one cooling passage (1) or a group of cooling passages: shape, cross section, perimeter, boundary state, orientation relative to the contact surface, contact surface (18) characterized in that it is adapted to the casting operation and in particular to the casting surface area (11) with an arrangement and / or arrangement density of the heat flow density and / or temperature of the locally formed contact surface.

Description

  The present invention relates to a mold for continuously casting a molten metal, particularly steel, having cooling passages such as cooling grooves, cooling slits or cooling holes on the side of the mold facing away from the contact surface with the molten metal.

  Continuous casting molds, in particular CSP (compact strip production) molds in the form of plate-shaped molds, each have a supporting wall and a metal melt fixed to this wall for continuous casting of steel slabs or slabs. At least a side wall comprising an inner plate in contact with the inner plate. Preferably, on the side of the inner plate facing the support wall, parallel coolant passages are provided which can be formed as slits open to the support wall.

In the case of a CSP mold with an actual configuration, the heat transfer relationship with respect to the mold height can change the boundary especially in the region above and below the bath surface. For example, the mold wall temperature is lowered at the top of the bath surface. However, when the heat transfer is reduced in the area and / or top of the bath surface, the mold temperature increases. This has the following advantages:
The casting powder is melted more quickly by the hotter mold in the area of the bath surface;
-Faster melting of the cast powder increases the lubrication between the strand and the mold, resulting in a better strand surface;
-Better lubrication results in a lower mold surface below the bath surface, thereby creating a reduced tendency to thermal stress and cracking, thereby obtaining a longer mold life;
The warmer area of the mold above the bath surface reduces the pressure stress in the area below the bath surface. This likewise reduces cracking and leads to a longer mold life.

  According to measurements on continuous casting molds, the heat flow density distribution has a maximum at the bottom of the bath surface between 20 mm and 80 mm, starting from here and descending like a bell curve in the casting direction and vice versa. Are known. In this case, the region of increased heat flow density is approximately 120 mm.

The integrated diagram of the temperature distribution of the melt in the mold corresponds to the curvature t _max of the horizontal parabola in the region of increased heat flow density.

  Document German Patent No. 3840448 (Patent Document 1) is formed by a continuous casting mold, in particular, an inner plate whose side walls are fixed to one supporting wall and one supporting wall, respectively, and in contact with the molten metal. A plate-shaped mold is described. In that case, a cooling medium passage is provided on the surface facing the support wall of the inner plate, and the cooling medium passage is formed as a slit opened to the support wall. In addition, the width of the slit is narrower than the width of the rib located between the slits, and the slit depth is larger than the width of the rib.

  EP 0 551 511 (Patent Document 2) describes a liquid-cooled and plate-adjustable mold that continuously casts steel strands with a thickness of 100 mm or less in a slab format. In this case, the wide plate and the narrow plate are formed in the direction of the transverse extension of the strand in the direction of transverse extension, the narrow plate is arranged substantially parallel to each other beyond the mold height, and the wide plate is Formed concave at least in the region of narrower slab width, thus the apex height of the mold wall forming the arch in the cross section is up to 12 mm per 1000 mm slab width compared to the marked rectangle on the casting surface of the mold And the shape of the wide face plate at the strand outflow end of the mold matches the strand format to be produced. The wide surface plate is formed as a flat surface in the adjustment region of the narrow surface plate, and the slit-shaped passages are arranged on the surface facing away from the surface which gives the shape.

  EP-A-0 687 879 (Patent Document 3) relates to the formation of a wide surface of a slab mold comprising a cast plate having one inner surface and an outer surface opposed to one inner surface, in which case the wide surface is one It has an upper partial region and one lower partial region, and at least the upper partial region has one intermediate region and two lateral regions arranged laterally from the intermediate region. In this document, the inner surface of the cast plate has a groove with a rear cut to form a cooling passage, and the groove is integrally covered with a filler introduced into the rear cut, Proposed.

  US Pat. No. 5,207,266 relates to a water-cooled copper mold comprising a copper plate with a rear frame fixed to the copper plate under the formation of a cooling passage, in this case from the main passage to the fixing bolt. The area to this area is wider than the area to other areas. The mold includes the formation of large passages between the right and left passages in the area of the fixing bolt, including the bolt threads. A branch passage between the main passage and the enlarged passage is provided, and at least a region from the branch passage and the main passage has a plurality of water surface regions as the main passage and the enlarged passage.

Strong cooling or heat transfer from the lower area of the meniscus to the mold outlet opening is critical for the rapid and reliable and particularly uniform formation of the crack-free strand shell. To this end, the known possibilities offer the following possibilities:
-Relatively high cooling water speed adjustment,
-Cooling water temperature drop,
-Expansion of the heat exchange surface in the cooling passage by cooling ribs.
The above-described embodiment has already been used in various ways in the description of the mold of the continuous casting apparatus.

  The mold contact plate, usually made of a single copper alloy, is in "direct contact" with the liquid solidified metal. A contact plate, also called a copper plate, is a closure member and is fixed to a holding element, usually made of steel. The reusable holding element is called a water box.

  The mold itself acts as a crystal, i.e. as much energy is removed from the delivered liquid steel as a productive strand shell is produced that can be continuously drawn from the mold. In this case, the first strand shell forms a so-called meniscus height in the filling state in the mold. The concept of meniscus is a casting auxiliary agent in which the contact surface of the mold is melted in a solid state and an early generation region of a strand shell that collides with liquid steel and the strand shell. Casting powder and oil are used as casting aids. They separate metal and copper from each other by lubrication and control local heat transfer (FIG. 8).

  The first strand shell volume element formed in the meniscus moves at a withdrawal rate through the mold. Based on a predetermined temperature gradient between the liquid steel and the cooling medium, a local energy flow is generated in the direction of the cooling passage. The energy volume is discharged through a cooling passage that flows through the cooling medium, usually water. The strand shell thickness increases correspondingly.

  The cooling passages formed in the mold structure can be formed completely within the copper plate or even inside the water box element. Mixed structure embodiments are also known. Furthermore, a mode is widely used in which the filler between the water box and the copper plate is arranged so as to form a suitable cooling passage.

  For finishing technical reasons, cooling passages having a rectangular or circular cross section are widened. The corner area can be rounded. However, any suitable U, L and T shape with respect to the contact surface can be produced with a suitable filler. The typical arrangement of cooling passages continues individually or in groups in the casting direction, i.e. from top to bottom, and is usually equidistant from the metal contact surface. The goal of the effort is to achieve as uniform a cooling action as possible over the mold contact surface, which is often successful only under conditions in the area of the fixed point. In order to further optimize the uniformity of the cooling action over the mold width (see FIG. 10), often cooling passages configured with different cross sections and / or geometries are combined side by side.

  Common to all these configuration shapes is the characteristic that the geometry of the individual cooling slits remains unchanged in shape and cross-section over its length. This embodiment supplements that the cooling passage surfaces available for cooling remain unchanged. The mixing result along the assumed streamline further leads to the flow velocity remaining constant over the cooling passage length.

  In this regard, there are only special embodiments for cooling passage holes in which the central exclusion pin can be accommodated from above or below. Since the length of the exclusion pin is usually shorter than the hole length itself, a narrow cross section is created in the cooling passage, which leads to acceleration of the cooling medium in this transition region. At this time, in the narrowed cross-sectional area, the cooling medium flows faster, thereby appropriately reinforcing the cooling action. The effective cooling surface in the cooling passage will of course remain out of contact with this treatment.

The conventional structural description of the cooling passage aims at a uniform cooling effect as much as possible, and does not take into account the non-uniform heat load distribution that actually exists in the mold plate. Based on the necessary multidimensional considerations, the two inhomogeneities are different in the heat load distribution.
− Non-uniformity parallel to the casting direction − Non-uniformity perpendicular to the casting direction

In the casting direction, heat transfer from the liquid steel to the cooling medium in the cooling passage can be simplified than the unitary heat conduction considered by the multilayer. Should be considered in the energy equation:
1. 1. Thermal transition from liquid steel in the formed strand shell 2. Heat conduction through the strand shell 3. Heat conduction through the lubrication layer 4. Heat conduction through the copper plate Thermal transition in the cooling medium The source term (Quellterme) should not be considered when it is stationary.

  The term of heat conduction through the strand shell is responsible for non-uniform heat load distribution over the mold length, because the cast surface is primarily the first to form a strand shell that grows further in the casting direction. Because it does. The thermal transition is then prevented by the increasing strand shell thickness itself. When setting all the usual parameters constant, it is therefore expected that the heat flow at the casting surface has the highest value and decreases continuously in the casting direction. Intermediate heat flow can be inferred from the integration method over the entire length of the cooling passage. Based on the multiplicity of heat conduction-no heat input at the top of the casting surface-a theoretically clear course of heat flow density is smoothed and the maximum position is moved in the casting direction (Fig. 9).

Operational measurements of local heat flow density indicate that for intermediate heat flow, the local value in the casting surface region is located higher by a factor of 1, 5 to 3, whereas the value at the mold foot is from 0.3 to 0.6. Prove that you can only be positioned lower than. The highest position is located from 20 mm to 70 mm below the original casting surface position depending on the equipment and processing parameters. The absolute value of the intermediate heat flow density depends on the casting powder, but in particular on the casting speed. 1.0 MW / m ² intermediate heat flow density in the casting speed 0.9 m / min in the literature, cited as 3.0 MW / m ² at 2.0 mW / m ² and 5.5 m / min at 3.0 m / min Yes. The local heat flow density to be expected with respect to the coefficient can be at least evaluated.

  The non-uniform distribution of heat flow density in the mold direction leads to the main wear of heat in the mold plate occurring in the casting surface area with almost no exception. This manifests itself in the form of grooves, cracks, deformations and in some cases peeling off of previously applied layers.

Even in the width direction, the load on the mold plate is completely different. Inhomogeneities usually arise from the flow zone that forms in the liquid steel mold. The course is closely connected by steel introduction dip outflow, contact surface geometry and other treatment value geometry. The static and non-static processes in forming the casting surface usually result in a non-uniform heat distribution that is typical of meniscus devices. Since non-uniform meniscus formation and non-uniform heat distribution are also related, the main damage does not occur uniformly over the mold width, but rather concentrates at a fixed location.
German Patent No. 3840448 European Patent No. 0551511 European Patent Application No. 0968787 US Pat. No. 5,207,266

  The object of the present invention is to start from the state of the art by means of a special geometric configuration of the surface area for heat transfer of a cooling passage or a group of cooling passages for the standard heat transfer for the cooling action of the cooling passage. To match the local heat flow density of the contact surface in contact with the mold melt.

  The solution to this problem is achieved by the features of claim 1 compatible with the present invention.

  Further influences of the invention on heat transfer and the cooling action of the cooling passages associated therewith are intended in accordance with the dependent claims. In that case, for example to influence the local cooling action of the passage, its shape, cross-section, perimeter, interface properties, orientation and orientation with respect to the contact surface can be changed locally.

  Furthermore, the effective heat exchange surface, for example at the channel bottom or side wall, can be enlarged or reduced.

  For example, by the formation of a groove in the bottom or side of the cooling passage, this cooling passage is enlarged to a surface that is substantially nearly doubled, which is a higher local area with a significantly stronger cooling action at the same flow rate of the cooling medium. This leads to a dynamic heat flow density and has the important advantage that the water pressure of the cooling water can be lowered in some cases outside of the lesser load of the mold work material, since the temperature of the mold is significantly reduced.

The temperature evaluation to be compared in this case gives for example the following values:
The slip surface (degree C) of the heat exchange surface at the bottom of the cooling groove:
507 ° temperature for the strand 173 ° temperature for the water-enlarged surface according to the invention 462 ° temperature for the strand 131 ° temperature for the water--45 ° difference -42 ° difference

  The numbers clearly demonstrate the positive effect of the treatment of this invention. Artificial enlargement of the cooling passage surface can also be achieved with a space tool, especially in the meniscus, in the case of a pierced CSP mold.

  Other configurations of the invention are contemplated in accordance with the other dependent claims. In this case, no artificial expansion of the cooling channel surface takes place at the top of the bath surface, since the heat transfer is reduced faster in this region of the mold to assist in the melting of the casting powder. .

Reduction of the thermal transition at the top of the bath surface is achieved by:
-Installation of a sleeve in the cooling hole at the top of the bath surface;
-Covering the pores at the top of the bath surface,
-Storage of a slight heat-conducting material insert at the top of the bath surface.

  At the same time, the hot area of the mold above the bath surface reduces the stress in the mold, and the strand cracking decreases with increasing mold freedom.

  In this case, particularly suitable for the purpose, it has been found that the heat discharge in the heat transfer surface area of the cooling passage is effected by an adaptation which changes the mold height in the heat flow density distribution.

  This allows the temperature profile along the mold height to be compared more at the same mold height, and greater material stress is avoided in the strand shell associated with the occurrence, preventing cracking of the mold.

The invention will now be described in detail on the basis of examples. FIG. 1 shows a section of the mold wall perpendicular to the extension direction in an enlarged section, FIG. 2 likewise shows another section member of the mold wall according to FIG. 1 in section, and FIG. 3 shows cooling with a groove on the inner surface. FIGS. 4 and 5 show the comparison of the heat exchange surface without the enlarged floor surface and the heat exchange surface with the enlarged floor surface, and FIG. 6 shows the height of the mold below the bath surface. 7 shows the course of the heat flow density q over the length H, FIG. 7 shows a diagram of the depth of the groove R over the mold height with the attached course of the temperature curve T, likewise in the meniscus region below the bath surface shows the top and bottom of the T _max, 8 shows a portion of a mold wall with a heat flow which is supplied with the cooling passage cross section, Figure 9 with each other for comparison with the intermediate or overall heat flow density or temperature FIG. 10 shows two diagrams shown side by side, FIG. 10 shows the flow of coolant under the formation of a comparable heat exchange bed. FIG. 11 shows another embodiment of the heat exchange bed, and FIG. 12 shows a distribution adapted over the mold height of the heat flow density distribution by q _max below the bath surface.

  FIG. 1 shows in enlargement a piece 10 of a surface 2 facing away from the melt of the mold wall with slit-like cooling grooves 1 arranged on the mold wall. This groove has a width B and a depth T. According to the invention, the bottom region of the cooling groove 1 is formed into a shape with a groove 3, whereby the surface of the groove is, for example, approximately double that of the surface according to FIG.

  In this case, the heat draining of the cooling groove, the cooling slit or the heat transfer surface area of the cooling hole can be effected by adaptation to change the heat flow density distribution over the mold height, which is illustrated for example in FIG.

  For this purpose, the groove 3 has a variable depth 4 between 1 mm and 4 mm, for example, to change the strength of the heat transfer and form an opening angle of 30 ° and 60 ° one by one. This is purely contemplated, for example, as shown in FIG. The groove 3 is formed at an interval “A” with one opening angle up to about 60 ° and one height up to about 4 mm, similar to the shape of a screw. Of course, other shapes such as wavy, trapezoidal, toothed or similarly configured strips may lead to a cooling surface expansion.

  FIG. 2 shows a piece 10 of the mold wall which includes one member of the support wall 5 comprising one member of the inner plate 6 which are in close contact with each other and are screwed together. The inner plate 6 is penetrated by a cooling passage 7 which is formed as a slit which is open to the support wall 5 and covered from the support wall 5. According to the present invention, the slit in the floor is provided with a heat exchange surface 3 that is penetrated by the groove, and the heat exchange surface produced an artificially increased heat flow density.

  FIG. 3 shows an arbitrary piece 10 of a mold wall with cooling passage holes 8 arranged in the mold wall with an inner wall 9 formed in the shape of a groove or groove 3.

  FIGS. 4 and 5 are associated with a configuration comprising a smooth configuration 11 and a groove 12 based on the indicated portions of the cooling medium passages 7, 7 ′ with the formation of the heat exchange bottom surface 11 or 12 to be compared with each other. Indicates the temperature value. This shows a clear drop in temperature under strictly equal confirmation conditions of the processing parameters to be compared for the embodiment with the groove bottom 12.

FIG. 6 shows the heat flow density distribution adapted according to the invention over the height of the mold in the narrowed area at the bottom of the bath surface (bath) with q _max . Consistently, the temperature curve T is shown in FIG. 7, showing the maximum internal temperature T _max from one region 13 to 17 of the variable depth R of the heat exchange groove with R _max between points 14 and 15. The heat exchange groove 3 starts at 13 at the bath level. At 14 a maximum groove depth of 4 is obtained, this maximum groove depth goes up to 15 and is reduced again to the original level in a path exceeding 16.

  FIG. 8 shows a mold comprising a contact plate 18 fixed to a support plate, a layer of a cooling medium passage 7 indicated as a casting auxiliary medium, a support plate 20 with a strand shell 19 configured in the casting direction and an attachable heat flow. The wide wall is shown in cross section.

  FIG. 9 illustrates supplements to FIGS. 6 and 7 by a diagram of the course of the local heat flow density / temperature compared to the heat transfer cooling passage surface depending on the meniscus position.

  FIG. 10 or FIG. 11 shows the possibility of different configurations in the embodiment of the cooling slit and in particular the bottom region.

Attached to this configuration of cooling passages, FIG. 12 shows in tabular form, tabulating:
-Cross-section of passage-Wall surface of effective cooling passage-Distance of wall surface to contact surface-Effective cooling effect received from contact surface In this case, all values are relative values and should be regarded as merely examples.

A fragment of the mold wall perpendicular to the extension direction is shown in an enlarged section. FIG. 1 also shows in cross section another partial member of the mold wall according to FIG. The cooling passage hole provided with a groove on the inner surface is shown. The comparison part of the heat exchange surface which does not have an expanded floor surface is shown. The part to compare of the heat exchange surface provided with the expanded floor surface is shown. The course of the heat flow density q over the height H of the mold below the bath surface is shown. A diagram of the depth of the groove R over the height of the mold with the attached course of the temperature curve T is shown, likewise showing the upper and lower T _max of the meniscus region below the bath surface. Fig. 2 shows in cross section a part of a mold wall with a cooling passage and an attached heat flow. 2 shows two diagrams shown side by side for comparison with intermediate or overall heat flow density or temperature. 2 shows a portion of a coolant passage under the formation of a comparable heat exchange bottom surface. 3 shows another embodiment of a heat exchange bottom surface. The q _{max at} the bottom of the bath surface shows a distribution adapted over the mold height of the heat flow density distribution.

Explanation of symbols

1. . . . . Cooling groove . . . . 2. Opposite side . . . . Strip groove 4. . . . . Depth 5. . . . . Support wall 6. . . . . Inner plate
7, 7 '. . . Cooling medium passage 8. . . . . Cooling passage hole 9. . . . . Wall part 10. . . . . A piece 11. . . . . 11. Start point of heat exchange groove at bath level. . . . . Maximum groove depth 13. . . . . End point of maximum groove depth 14. . . . . End point of groove depth reduction 15-17. . . Constant groove depth obtained 18. . . . . Contact plate 19. . . . . Strand shell 20. . . . . Support plate

Claims (11)

  One cooling in a mold for continuously casting a molten metal, particularly steel, having a cooling channel (1) such as a cooling groove, a cooling slit or a cooling hole on the mold side face (2) facing away from the contact surface with the molten metal. The geometry of the heat conducting surface area of the passage (1) or a group of cooling passages may be: shape, cross section, perimeter, boundary condition, orientation relative to the contact surface, heat flow density of the contact surface (18) and / or Mold, characterized in that it is adapted to the casting operation and in particular to the casting surface region (11) in an arrangement and / or arrangement thickness with respect to the contact surface of the locally formed temperature.   In order to influence the local cooling action of the cooling passage (1), the shape, the cross section, the periphery, the boundary surface state, the orientation and arrangement with respect to the contact surface, and the arrangement density of the cooling passage are locally changed. The mold according to claim 1, characterized in that   3. Mold according to claim 1 or claim 2, characterized in that the geometry of at least one cooling passage (1) or a group of cooling passages can be used individually or in combination.   4. The geometric structure of one cooling passage (1) or a group of cooling passages is carried out in a fluidly or jumping manner with respect to one another. The mold according to one item.   The cooling action of the cooling passage (1) is maximized in accordance with the configuration of the cooling passage (1) in the region of maximum heat flow density or maximum temperature of the contact surface (18). The mold according to any one of claims 4 to 5.   In order to influence the local cooling action of the cooling passage (1), the effective heat exchange surface of the cooling passage is enlarged or reduced in conformity with the bottom or side of the passage. The mold according to any one of claims 1 to 5.   In order to enlarge the heat exchange surface in the cooling passage, the auxiliary grooves or stripes are formed in a rectangular, triangular, trapezoidal, partial circle or partial ellipse or any free shape in cross-sectional configuration, 7. The number, depth and width, and the state of the cooling passage are adapted to be parallel to each other or to such an arbitrary position in the extending direction of the cooling passage. template.   Heat that has been altered with respect to its interface state to influence the local cooling strength of the heat transfer surface of the cooling passage (1), for example by the formation of a defined wall roughness for elevated heat transfer or reduced The mold according to any one of claims 1 to 7, wherein the mold is modified by application of an auxiliary layer for transfer.   In order to influence the local cooling intensity of one cooling passage (1), the isosceles cross section of the cooling passage is enlarged by the use of an auxiliary groove on the bottom or side or reduced by the use of an exclusion object. The mold according to any one of claims 1 to 8, wherein the mold is used.   In order to influence the local cooling strength of one cooling passage (1) and to change the coolant flow which is first aligned straight with respect to the contact surface, auxiliary grooves or auxiliary in the bottom and / or side 10. Mold according to any one of claims 1 to 9, characterized in that a static exclusion object is employed and / or a modified wall arrangement of the cooling passage (1) is provided.   In order to influence the local cooling intensity of one cooling channel (1), the number of cooling channels per unit of length of the mold width is determined in terms of the local or total spacing relative to the contact surface and / or the arrangement density. The mold according to any one of claims 1 to 10, wherein the mold is arranged.

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