KR20160099641A - Casting mould for casting steel melt - Google Patents

Abstract

A mold (7) for casting a molten steel (M) into a continuously drawn strand (S), characterized in that at least one of the inner surfaces (13) of the mold (7) in contact with the molten metal (M) And a surface texture 22 is formed on the inner surface of the substrate. The surface texture 22 extends over at least the area A3 of the mold 7 which is impregnated with the slag K floating in the molten metal M injected into the mold 7 during the casting operation. The molds according to the invention enable optimum coagulation behavior using simple means in the region of the molds important in relation to the risk of cracking. This is accomplished in accordance with the present invention in which the surface texture 22 is self-contained and designed with a closed structure with randomly distributed recesses 23.

Description

[0001] CASTING MOLD FOR CASTING STEEL MELT [0002]

The present invention relates to a mold for casting a molten steel into a continuously drawn strand, wherein a surface texture is formed on at least one inner surface of the mold in contact with the molten metal to be casted, Lt; RTI ID = 0.0 > slag < / RTI >

In continuous casting, the molten metal is injected from the casting ladle into a distributor, also known as "turn-dish" and provided as a buffer, and delivered by a dipping tube into a separate mold from the distributor. Here, the injection direction is the same as gravity.

The strand is formed in the mold. When contacting the cold inner surface of the mold, the molten steel starts to solidify so that the strand exiting the mold in the vertical direction forms a shell of a solidified steel on the outer surface of the strand, Enclose.

After exiting the mold, the strand is deflected and supported in a horizontal flow direction by a roll of so-called "casting bow". Systematically controlled cooling occurs at the casting bow to effect controlled coagulation of the strand. After the strands are completely solidified and discharged in the horizontal direction, the slabs are cut and transported for subsequent processing.

The cast powder is dispersed in the mold against the free surface of the melt to form the slag. The slag covers the molten steel and prevents the molten steel from reacting with the ambient atmosphere in the area of the so-called "meniscus". At the same time, the slag combines with the impurities coming from the molten metal and acts as a lubricant between the solidified shell of the steel strand and the mold. Alternatively, there are casting methods that use a liquid casting medium referred to as so-called " casting oil " in which pre-molten casting powder is supplied or instead of casting powder. The latter technique is particularly applied to continuous casting of billets or rounds. In order to prevent the steel from sticking to the cooled walls of the mold and to support the release of the strands from the mold, the mold generally moves in a vibrating manner.

The continuous casting mold can consist of mold plates or can be designed as one individual single piece. The inner surfaces of the continuous casting mold are generally made of copper. To improve the resistance to abrasion and breakage, the inner surfaces of the mold in contact with the strands to be formed can be covered with a nickel coating (EP 0 125 509 B1). However, nickel coatings result in a substantial reduction in heat flow. For this reason, the nickel coating is generally applied only a predetermined distance from the upper edge of the mold assigned to the distributor of the continuous casting plant.

Regardless of whether the inner surface of the mold is nickel coated or not, the molten steel in the continuous casting process is particularly cooled rapidly in the area of the meniscus. This may lead to surface defects due to internal stresses occurring during the cooling process in case of sensitive grades of steel.

This problem has already been addressed in EP 1 099 496 B1. According to Postectoral thesis by MM Wolf, Forch 2002, pages 61-64, the thermal flow through the mold wall in the region of the melt level, in particular, And plays an important role in preventing cracks in the strand sheath. If the heat flow is too large, this results in an increased risk of cracking. In order to increase the thermal flow between the formed strand sheath and the inner surface of the mold, EP 1 099 496 B1 proposes to reduce the thermal resistance in the region of the meniscus by roughening the mold surface. In this manner, the strand shell formed in the mold must be kept thin for a long time and must be uniformly pressed against the continuous mold copper plate by the ferrostatic pressure of the rising iron as the distance from the level of the melt increases. The stepwise transition from the rough section to the smooth section of the mold is achieved and thus the thermal flow is not limited from the limited and also the surface of the mold is reduced to reduce the working depth of the inner surface roughness of the mold in the casting direction, It is rough. One advantage that has been considered here is that the macro structure of the inner surface of the mold can be used in a variety of ways such as for example shot blast texturing (SBT), discharge texturing (EDT), electron beam texturing (EBT), laser texturing (LT) Can be accomplished by means known in the art as bodywork or by other methods.

In view of the above-mentioned prior art, it is an object of the present invention to produce a mold which is ensured to have an optimum solidification behavior in the region of the mold which is important with respect to the risk of crack formation by simple means.

This problem is solved by a mold designed according to claim 1 according to the invention.

Advantageous embodiments of the invention are set forth in the dependent claims and are described in detail below in conjunction with the overall inventive concept.

In a mold according to the present invention for casting a molten steel into a continuously drawn strand, a surface texture is formed on at least one inner surface of the mold in contact with the molten metal to be cast according to the above-described prior art. The surface texture extends over at least the area of the mold that is impregnated with the slag floating in the molten metal injected into the mold during the casting operation.

According to the present invention, the surface texture is now designed as a closed structure with completely bordered and randomly distributed indentations.

The structure provided with the surface textures according to the present invention and formed with fully compartmentalized recesses reduces heat transfer between the mold and the liquid molten metal. Some of the solidified slag covers the indentations of the random surface structure and sticks there, unlike in the case of the open surface structure. Therefore, the slag attached to the inner surface of the mold acts as a heat insulating material preventing direct contact between the molten metal and the inner surface. The adiabatic effect of the slag layer leads to a lower and uniform heat supply in the region of the meniscus over the width of the mold. As a result of the overall decrease and more uniform heat supply, less internal stresses occur in the strand sheath during the cooling process when using the structured mold surface according to the invention compared to conventional mold surfaces. As a result, the risk of surface defect generation is reduced. If casting oil is used, the surface texture described herein is impregnated. Thereafter, the oil layer attached to the concave portion also functions as a heat insulating material.

Although the individual recesses are not overlapping and correspondingly not compartmentalized, the open surface and roughness structures produced using, for example, EP 1 099 496 B1, or shot blast or similar methods integrated together, The roughness is obtained from the ridge portion of the material. However, the closed surface structure provided in accordance with the present invention is characterized by unconnected recesses and cavities. The recesses which are closed and randomly distributed according to the invention ensure more improved slag adhesion and prevent slag leakage.

In addition to the topographic appearance that occurs in this manner, the average roughness index (Ra) and the average roughness depth (Rz) are important with respect to designation of the surface structure. Both the average roughness index (Ra) and the average roughness depth (Rz) should all be determined in accordance with DIN EN ISO 4287. In the case of the surface structure according to the present invention, the ideal average roughness index (Ra) is 10 탆 to 50 탆 and the average roughness depth (Rz) is 80 탆 to 250 탆. The average roughness value and the average roughness depth in the numerical range show the result of the maximum reduction of surface defects and stable process reliability. Particularly, this is applied when the average roughness index (Ra) is in the range of 10 탆 to 50 탆, particularly in the range of 15 탆 to 50 탆.

If the maximum depth of the depressions of the surface texture is 500 [mu] m, optimal attachment of the slag to the surface texture is achieved. In order to reliably achieve the intended roughness, the recesses must have a depth of at least 5 탆.

The molds of the type mentioned here are generally made of a non-ferrous metal alloy that is cooled at a distance away from the melt. The mold section may be designed to be square or circular. In order to produce a variable width strand when using a rectangular or square mold, at least one of the plates forming the narrow sides of the mold opening may be adjustable in the width direction (EP 0 985 471 A1).

The surface structure provided in accordance with the present invention is provided on at least one of the inner surfaces defining the mold opening. Of course, this includes the option of forming a surface structure corresponding to all internal faces or opposing internal faces of the mold. Also in the case of a mold capable of adjusting the width, the structured surface texture according to the invention should be present in at least one of the inner surfaces. If the surfaces defining the mold opening are advantageous in relation to sealing the corner area in contact, the area covered during the adjustment of the side of the mold moving relative to the inner surface can remain free of the surface structure according to the invention. Thus, in the case of a mold in which the width or thickness of the mold can be adjusted by moving at least one of its sides, if the smallest width or thickness of the mold is formed, the inner surface is in contact with the molten metal to be cast, And extends over the width of the inner surface provided.

Structured surface textures in accordance with the present invention must extend over at least the area of the individual inner surface of the mold that is infiltrated by the slag covering the meniscus during the casting operation. It has been found that surface textures are useful in the molds used today, starting at a distance of at least 10 mm below the upper mold edge and extending over a region terminating at a distance of up to 600 mm when measured in the casting direction.

In the case where the inner surface with the surface structure is covered with a nickel layer on a section starting at a distance from the upper edge of the mold, superimposing the edge area assigned to the upper edge of the mold with the surface texture designed according to the invention, Lt; RTI ID = 0.0 > surface defects < / RTI > Indeed, the overlap zones identified here as advantageous are at least 50 mm when measured in the casting direction. The superposition of the surface texture and the nickel coating according to the present invention prevents abrupt changes in thermal conductivity in the transition region between the individual inner nickel coated sections and the non nickel coated sections.

The structure of the surface texture provided on the individual mold surfaces according to the present invention can be introduced to the surface by, for example, a needle, by embossing (pressure), or by impact or impact moment. The structure is introduced by deforming the mold surface without removing the material during the process. Cold work hardening, which is performed as a result of striking or pressing deformation on the individual mold interior surfaces, can contribute to the longer life of the mold.

If the stamping method is used, the engraved part of the structure to be created is applied to the matrix, sphere or roller. The engraved portion is then used to apply the surface structure to the mold, depending on the pressure and tool surface. If a structure is made using a method based on impact or impact moment, the structure defined in accordance with the present invention is created by a tool that strikes with a strong moment. To this end, it may be appropriate to use so-called " needles " which can form certain surface roughnesses, for example as disclosed in DE 199 07 827 A1.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail below using the figures in connection with the embodiments. Each drawing shows a schematic view.

1 is a side view of a strand casting plant.
2 is a longitudinal sectional view of a mold used in the strand casting plant according to Fig. 1;
3 is a perspective view showing a section of the surface texture provided according to the present invention magnified 7.5 times.

The molten steel M is transferred from the ladle 2 to the distributor 3 in order to cast the molten steel M into the strand S in a strand casting plant shown in Fig. 1 and configured in a manner known per se And is injected into the dispenser 3 by the ladle shroud 4. A vertically aligned immersion tube 5 is connected to the base outlet of the dispenser 3, which can be closed and adjusted by the stopper 6.

The molten steel M flows into the mold 7 when the immersion tube 5 is opened and the mold is composed of cooling plates 8, 9, 10 and 11 made of a non-ferrous or non-ferrous alloy. Preferably, copper or a copper alloy is used. The mold 7 has an opening cross section that is substantially rectangular when viewed from above. The long side faces of the cross section are each defined by a wide mold plate 8, 9 and the short side faces are respectively defined by a narrow mold plate 10, 11.

The inner mold plates 8-11 that are each assigned to the mold openings 12 can often be covered with a nickel layer 14 that is coated with a nickel layer 14 when measured in the vertically aligned flow direction F of the molten steel M The nickel layer starts at a variable length from the upper edge 15 of the mold 7, which is assigned to the distributor 3. In this case, the distance A1 is 300 mm, but it can be generally formed variably. Here, for example, a rectangular mold having a nickel layer is used. However, other shapes of molds with different coatings may be used.

The strands S formed from the molten metal M in the mold 7 escape from the mold 7 in the vertical flow direction F and are guided in the horizontal direction Fh by the casting bow 16. In the region of the casting bow 16, the strands are guided by rollers 19,20. The concentrated cooling is simultaneously performed so that the strand S reaches the casting bow 16 to a maximum extent and can be conveyed for a subsequent process.

A surface texture 22 is formed on the inner surface 13 of the mold plate 8-11 which defines the mold opening 12 in the area allocated to the upper edge 15 of the mold. In this embodiment, the surface texture 22 starts at a distance A2 of 10 mm from the upper edge 15 of the mold in the flow direction F and ends at a distance A3 of 400 mm. The surface texture 22 thus overlaps the nickel layer 14 in the overlap zone U over a length of 100 mm measured in the flow direction F. [ In general, the surface texture may be introduced up to a distance A3 of up to 600 mm when viewed from the top edge 15 of the mold. In the region covered by the surface texture 22, the slag K floating in the meniscus of the molten metal M to be cast during the casting operation infiltrates the inner surface 13 of the copper plate 8-11.

The surface texture 22 is formed by a plurality of recesses 23 which are each completely surrounded by the partition wall 24. Each partition wall 24 defines two adjacently arranged recesses 23. The depressions 23 may be formed as individual perforated indentations with a substantially rounded opening cross section or may be formed by a self-contained partition wall 24 surrounding the individual indentations 23 after the plurality of indentations are integrated together The boundary is formed. For example, material ridging generated when using the shot blasting method is undesirable in such a structure, because the ridging is worn by the strand sheath. This can lead to degradation of the structure which reduces the roughness characteristics. The recesses are introduced into the mold material to achieve cold work hardening and to maintain the surface structure. The width B of the surface texture 22 is limited to the narrowest area and the width of the mold surface 12 is defined by the width of the mold surface 12, If the plates 10, 11 are moved, they are not covered by the copper plates 10, 11.

Depressions 23 at depths of up to 500 mu m were made by the needles using standard needle devices not shown. In the needle device, the needles use a large force to drive into the inner surface and compress the material in contact with the needles, thus forming individual recesses 23. Material wear did not occur at all. In order to maintain the structure including the concave portion 23 and the partition wall 24 shown in Fig. 3, the parameters described below are set.

- the distance between the needle device housing and the surface to be machined,

- Feedrate and feed direction,

The movement pattern of the needle device housing / needle device, and

- the force with which the needle strikes the surface to be machined.

The average roughness depth Rz and the average roughness index Ra for the two surface textures made in this way inside and outside the overlapping area of the nickel layer 14 of the inner surface 13 and the surface texture 22 are shown in Table 1 Lt; / RTI >

1: Continuous casting plant
2: Ladle
3: Dispenser (turn-off)
4: Ladle shroud
5: Immersion tube
6: Stopper
7: Mold
8 - 11: Copper plate
12: mold opening
13: inner surfaces of the mold 7
14: Nickel layer
15: Upper edge of mold
16: casting bow
19, 20: Rollers
21: Inner sections
22: Surface texture
23:
24: partition wall
A1 - A3: Distance measured in flow direction (F)
B: width section of inner surface 13 with surface texture
F: the flow direction of the molten steel (M) in the mold (7)
Fh: horizontal flow direction
K: Slag
M: Molten metal
S: Strand
U: overlapping area

Claims (12)

A mold 7 for casting a molten steel melt M into a continuously drawn strand S is provided with at least one inner surface 13 of a mold 7 in contact with a molten metal M to be cast, Wherein the surface texture extends over a zone A3 of at least the mold 7 which is impregnated with a slag K floating in the molten metal M injected into the mold 7 during the casting operation, A casting mold for casting the above-mentioned molten steel,
Characterized in that the surface texture (22) is completely delimited and designed with a closed structure with randomly distributed recesses (23). The method according to claim 1,
Over a region starting at a distance A2 of at least 10 mm below the upper edge 15 of the mold and ending at a distance A3 of at most 600 mm when the surface texture 22 is measured in the casting direction F, Wherein the molten metal is molten. 4. The method of one of the preceding claims,
Wherein the maximum depth of the recesses (23) of the surface texture (22) is 500 占 퐉. 6. A method according to any one of the preceding claims,
Characterized in that the surface texture (22) has an average roughness index (Ra) of from 10 탆 to 50 탆. 6. A method according to any one of the preceding claims,
Characterized in that the average roughness depth (Rz) of the surface texture (22) is 80 占 퐉 to 250 占 퐉. 6. A method according to any one of the preceding claims,
The mold 7 has a square or circular opening cross-section and the surface texture 22 is formed on the inner surface of at least one of the inner surfaces 13 of the mold 7 defining an opening cross- And a mold for casting the molten steel. 6. A method according to any one of the preceding claims,
The mold 7 is adjustable in width by moving at least one of the end faces 10 and 11 of the mold and the inner face 13 is cast when the mold 7 is set to the smallest width B Characterized in that the surface texture (22) extends over the width (B) of the inner surface (13) with said surface texture (22) by contact with the melt (M). 6. A method according to any one of the preceding claims,
Characterized in that the surface texture (22) is formed by striking the individual inner surface (13) of the mold (7). 9. The method of claim 8,
Characterized in that the surface texture (22) is formed on the inner surface (13) using a needle. 6. A method according to any one of the preceding claims,
Characterized in that the surface texture (22) is embossed on the individual inner surface (13) of the mold (7). 6. A method according to any one of the preceding claims,
An inner surface 13 with a surface texture 22 is coated with a nickel layer 14 over a section beginning at a distance A1 from the upper edge 15 of the mold and a surface texture 22 is applied to the upper edge (U) of the nickel layer (14) assigned to the die (15). ≪ RTI ID = 0.0 > 18. < / RTI > 12. The method of claim 11,
Characterized in that the surface texture (22) overlaps at least 50 mm with the nickel layer (14) when measured in the casting direction (F).

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