Patent Application
20200038945
Not Applicable.
The present invention relates to a soft reduction device for round-section blumes or billets having liquid or partially liquid core, coming from a continuous casting machine, in order to compress the product in a controlled manner, thus reducing the liquid section and improving the inner quality thereof.
Various devices and methods for pressing a liquid-core cast product are known from the prior art, and this operation is called “soft reduction”.
This technology is particularly common within the area of slabs, which are characterized by being much wider than they are thick.
The skin of the product begins forming in the crystallizer due to the progressive cooling to which the product is subjected. As the product travels downstream dragged by the straightening units, it is subjected to continuous direct and indirect cooling operations and this results in an increase of the thickness of the skin, resulting from the subtraction of heat from the core of the product performed by the cooling system.
The product is cast from the tundish into the crystallizer and starts its descent towards the extraction area downstream, being cooled and contained by the containment rolls. The thickness of the product skin increases as the product descends and cools off, until there is the spontaneous joining of the skin in the so-called “metallurgical cone”, at which point the complete solidification of the product is achieved.
The process for forming the skin generally is influenced by various parameters, in particular by the steel grade of the cast product, by the heat exchange undergone by the cast product during casting, by the casting speed and by the dimensions of the product itself.
It is necessary that the complete solidification of the product occurs so as to preserve the inner quality thereof: indeed, as the product solidifies, there is a decrease of the volume occupied by the liquid fraction which initially occupies a larger volume with respect to the solid fraction. This volumetric difference does not affect the product very much in the first part of the casting curve, since the liquid fraction volume lost during solidification is replaced by the liquid further upstream pushed downstream by the ferrostatic pressure. However, in proximity of the vertex of the metallurgical cone, the solid component and the liquid component are no longer well distinguished from each other, thus causing the so-called “mushy zone”.
From a microscopic point of view, the appearance of the skin of the product in contact with the liquid core has a series of crystalline branches called dendrites, which when the skin is about to be joined, tend to intersect with one another, thus forming a barrier for the inlet of the liquid above, preventing filling with new liquid in the areas subjected to a decrease of the volume of liquid fraction due to the solidification, and causing the formation of undesired porosity in the inner structure of the product.
A further problem generated in this solidification step is that of macro segregations: as the product solidifies, the dendrites extend and tend to bring the alloy elements (e.g. carbon, sulfur, etc.) towards the liquid core of the product. This phenomenon causes a difference in the chemical composition along the section of the product. These migrations of alloy elements cause undesired differences of the mechanical properties, thermal properties, etc. between the various areas of the product, while a product having uniform structure and properties is instead desirable.
In order to obviate these drawbacks, the soft reduction treatment was developed, which provides the controlled pressing of the cast metal products, e.g. slabs or blumes or billets, wherein the cast metal product is subjected to an action of reducing the thickness while the core is still liquid or partially liquid in an area downstream of the ingot-mold, thus obtaining a less thick product with respect to the cast one at the outlet of the continuous casting machine.
The main advantage of reducing the thickness of the liquid or partially liquid core is to obtain an improvement of the solidification structure together with an improved inner quality of the cast product.
In order to be effective, the soft reduction should occur with a continuous and controlled reduction of the thickness of the cast product up to when it contains therein a liquid or partially liquid core, which may be obtained with a substantially conical reduction profile of the stretch of cast product involved.
The most common soft reduction devices provide pressing the product by means of pairs of opposite rolls: the pressing force here is therefore applied with equal intensity and opposite direction, thus causing a decrease of the thickness of the product and an extension thereof (called “bulging”).
This soft reduction treatment is commonly used in the field of continuous slab casting since the widening of the side faces is not such as to seriously affect the finished product which, once the curved sides have been conveniently trimmed, will be ready for rolling or other successive operations.
With regards instead to products having rectangular or square section, the soft reduction is to be performed more carefully, since an excessive curving would cause an excessive deformation of the products which would then be difficult to process.
This problem is felt even more for round-section products since keeping the shape is essential for processing and selling the product on the market: indeed, by using only two rolls which press the product in opposite directions to close the liquid core thereof, there is a risk of excessive oval deformation of the section of the product. In an attempt to correct this ovalization, another deformation may be generated, made with rolls shaped so as to obtain a round section with a smaller section. However, this further deformation, which requires at least two passes, does not always decrease the section of the product and at the same time keep it perfectly round. Indeed, further forming passes are often required downstream for the further definition of the round geometry.
A partial solution to this problem provides eliminating the first pressing step by directly casting an elliptical-section product which in the next soft reduction step is deformed into a round shape by two parallel shaped rolls.
However, the deformation operation to pass from the elliptical section to the round section—in particular, the more the ellipse is pressed—results in tensions in the core of the product which may damage the inner quality thereof.
Thus, the need is felt to provide a soft reduction device for round-section cast products which allows to overcome the aforesaid drawbacks.
It is an object of the present invention to provide a soft reduction device for round-section cast metal products, such as blumes or billets, which allows a controlled and effective closing of the liquid cone, thus reducing the section of product with respect to the initial casting one, and at the same time allows maintaining substantially a rounded shape, which already is acceptable for processing and selling the product when it is outlet from said device. Advantageously, the soft reduction device of the invention is designed for carrying out the soft reduction of casting products, made of metal, having a round section, said round section being maintained round sectioned through the whole soft reduction process. Therefore the terminology “round section product” refers both to the casting product, having a liquid or partially liquid core, and to the final product of soft reduction, that is completely solidified.
It is another object of the invention to provide a soft reduction device capable of obtaining completely solidified round section products having a substantially uniform chemical composition along the whole section of the product, and therefore uniform properties.
It is another object of the invention to provide a soft reduction device capable of limiting the formation of voids due to the shrinking from cooling of the product volume.
Thus, the present invention achieves the above objects by providing a soft reduction device of round-section metal products having liquid or partially liquid core for reducing the thickness of said metal product coming from a continuous casting machine, which according to claim 1 comprises at least two soft reduction units,
wherein said at least two soft reduction units are arranged in series,
wherein each soft reduction unit is provided with a group of only three rolls arranged at 120° from one another,
and wherein the group of three rolls of one soft reduction unit is offset by a predetermined angle with respect to the group of three rolls of an adjacent soft reduction unit.
The three rolls of each soft reduction unit interfere with the advancing metal product so as to reduce the section thereof, thus closing the liquid core, by acting at 120° angles from one another so that the resulting vector of the radial pressing forces applied on the product is equal to zero.
By providing pressing forces of equal intensity from three equidistant directions, the closing of the liquid core is more effective since the deformation is less abrupt with respect to the solutions with only two pressing rolls. Indeed, by using only three rolls in each soft reduction unit, the outer surface of the round-section products is wound in an optimal manner. Such a winding causes a good propagation of the pressing forces towards the core of the product since the latter does not have very much space to deform outwards, considering the vicinity between the rolls. Therefore, the material will tend to move mainly towards the center of the product, filling the areas occupied by the liquid core which in turn is forced to retract, or in the case of the mushy zone, to solidify.
This operation results in the forced inner union of the skin, and therefore in the closing of the kissing point obtained through the interpenetration and solidification of the dendrites. Thus, the creation of voids due to the shrinking from cooling of the product volume is also avoided, since the inner space is forcibly filled with solidified material, pushed by the deformation actuated by the soft reduction rolls.
Advantageously, to better keep the rounded shape, several soft reduction units are arranged in series, over which the radial pressing forces are divided, which are therefore applied to a lesser extent by the rolls of the units after the first one.
Advantageously, according to the invention, the number of soft reduction units may vary. In particular, there may be provided from three to eight soft reduction units arranged in series, preferably four soft reduction units arranged in series. It has been noted that providing a number of soft reduction units greater than eight induces a temperature dispersion which does not allow an optimal processing of the material.
To maximize keeping the rounded shape, the arrangement of the rolls advantageously is offset between one soft reduction unit and the next, so that the pressed areas of the product vary from one unit to the other and therefore, the rounded shape is preserved better.
In a first advantageous variant, there are provided two soft reduction units arranged in series, with groups of three offset rolls, i.e. rotated by 180° from one another. This arrangement results in having six rolls, between inlet and outlet of the soft reduction device, which in a front view along the feed direction of the cast round product, are radially arranged with respect to the center of the cast round product, with angles of 60° from one another.
Other variants of the invention may provide further offsetting the groups of rolls of the soft reduction units. For example, there may be provided three soft reduction units with three rolls, therefore with nine rolls in total, arranged so as to obtain, in a front view along the feed direction of the cast round product, an offset of 30° between one roll and the next. Another example instead provides five soft reduction units with three rolls, therefore with fifteen rolls in total, arranged so as to obtain, in a front view along the feed direction of the cast round product, an offset of 15° between one roll and the next, and so on. The more soft reduction units forming the device, the less the contribution of radial pressing force of the rolls required to close the liquid cone since each of them contributes to a partial reduction, thus limiting the excessive deforming effect generated with the solutions of the prior art with only two rolls.
In a further advantageous variant, since it may be complex and costly to provide an increased number of soft reduction units in series while simultaneously offsetting the rolls along many incident axes, there is instead provided the arrangement of a plurality of soft reduction units, preferably four or six or a maximum of eight, arranged in series and with groups of three rolls offset by 180° adjacent from one another. This arrangement results in having twelve or eighteen or twenty-four rolls, between inlet and outlet of the soft reduction device, which in a front view along the feed direction of the cast round product, are radially arranged with respect to the center of the cast round product, with angles of 60° from one another. Thereby, by alternating the axes of the rolls with a sequence of the type Y-λ or λ-Y, it is sufficient to design and construct only two separate types of soft reduction units.
Advantageously, in a preferred variant, in addition to closing the liquid core, the soft reduction units of the device of the invention are also capable of extracting the product from the casting line by performing a function similar to that of the extraction and straightening units which are commonly used in continuous casting machines. In this variant, at least one of the rolls of each soft reduction unit is motorized. This solution allows to avoid the installation, upstream of the soft reduction device, of an extraction unit which should grasp, or grip, intrados and extrados of the product and drag it downstream in the first soft reduction unit and straighten it at the same time.
A further advantage of the present invention is the possibility of providing position adjustment means for adjusting the position of the rolls, so that the same soft reduction unit can process products having various diameters. For example, the rolls may be mutually moved close or away by means of hydraulic actuators, lever or pantograph mechanisms, or others.
Moreover, the movement of the rolls may be performed linearly along guides, sliding blocks or similar elements, or performed by means of curvilinear movements or a combination of linear and curvilinear movements.
The soft reduction rolls may also have various shapes in the stretch in contact with the outer surface of the cast product: they may for example, have a flat panel shape or be shaped and joined with angles adequate to the diameter of the product to be processed.
A further feature of the present solution is the possibility of causing the extrados of the cast product to coincide with the pass-line of the line downstream of the casting curve. Indeed, since the casting line in which the soft reduction units of the present invention will be installed is to cast various diameters of product, there is a need to vary certain geometries of the casting curve, in particular the arrangement of the containment rolls and of the cooling means, by adapting them to those of each cast product. Normally, the assembly of radii on which a casting line is designed is calculated according to the extrados of a product; then the minimum and maximum ranges corresponding to the minimum and maximum intrados of the range of products to be cast, is calculated.
Should the extrados radius vary, there would be problems in aligning the casting line and the utility units downstream (e.g. cooling plates, roller tables, etc.) for each product. Instead, by causing the extrados to coincide with the pass-line, corresponding for example to the cooling plate, such a problem does not exist since the casting curve and cooling plate are always aligned. This advantage results in these soft reduction units also being installable on existing casting lines, since the extension thereof is strictly vertical and they ensure the continuous alignment between cast and utilities downstream.
The dependent claims describe preferred embodiments of the invention.
Further features and advantages of the invention will be more apparent in light of the detailed description of preferred, but not exclusive, embodiments of a soft reduction device, disclosed by way of a non-limiting example, with the aid of the accompanying drawings in which:
The same reference numerals in the drawings identify the same elements or components.
With reference to the figures, there is depicted a preferred embodiment of a soft reduction device according to the invention, indicated by 1 as a whole.
Such a soft reduction device is designed to perform a soft reduction of a round-section metal product, having liquid or partially liquid core, i.e. for reducing the thickness of a round-section cast metal product coming from a continuous casting machine. Therefore, each soft reduction unit of the device is substantially different from the guide units with adjustable rolls that guide the cast product simply accompanying the metal product during its advancement without reducing the thickness thereof and, notably, without obtaining a controlled and effective closing of the liquid cone. Moreover, as known to the skilled person, a soft reduction device and a soft reduction unit are well distinguished from a rolling device and a rolling unit, respectively, not only by the functional point of view but also by the constructional point of view. Indeed, the rolling devices or units—unlike the soft reduction devices or units—are designed to reduce the thickness of a completely solidified metal product (thus without liquid core). The rolling devices or units are provided with backup rolls, while the soft reduction devices or units are not. The backup rolls are present in the rolling devices or units to provide a robust support for the working rolls, thus helping to ensure a proper performance of the entire rolling mill. Also, the forces acting on the metal product in a rolling device are different from the forces acting on the metal product in a soft reduction device, given the difference in the consistency between a completely solidified product and a casting product. The several constructional differences between soft reduction devices and rolling devices are also reflected in their cost, the latter costing at least twice as much as the soft reduction devices.
The soft reduction device 1 comprises at least two soft reduction units 2, 3 arranged in series along the feed direction of the metal product.
Advantageously, each soft reduction unit 2, 3 is provided with a group of only three rolls arranged at 120° from one another, and the group of three rolls of one soft reduction unit is offset by a predetermined angle with respect to the group of three rolls of the next soft reduction unit.
In the variant in
In the example in
In another example (not shown), all the soft reduction units are arranged parallel to one another along a completely rectilinear stretch of plant, i.e. completely after the casting curve 5. Here, there are provided specific extraction and straightening units upstream of the device of the invention.
In another variant of the invention, there instead are provided only two soft reduction units and the group of three rolls of the first soft reduction unit is offset by 180° with respect to the group of three rolls of the second soft reduction unit, which is subsequent and adjacent to the first soft reduction unit.
Other variants may include, for example, the use of four, six or eight soft reduction units, with the group of three rolls of a soft reduction unit offset by 180° with respect to the group of three rolls of the subsequent and adjacent soft reduction unit.
In all these variants, the angular arrangement between the roll units results in having a plurality of rolls, between inlet and outlet of the soft reduction device, which in a front view along the feed direction of the metal product, are radially arranged with respect to the center of the product itself, for example, with angles of 60° from one another, as shown in
The more soft reduction units forming the device, the less the contribution of radial pressing force which each soft reduction unit should ensure to close the liquid cone, since each of them contributes to a partial reduction of the thickness of the metal product.
A further advantage of the present invention is the possibility of adjusting the position of the rolls of each soft reduction units to adapt the device to the processing of metal products of various diameters.
Advantageously, each soft reduction unit may be provided with adjustment means for adjusting the position of at least two rolls of the three rolls, which adjustment means are configured to adjust the position of the rolls with respect to the center of the metal product to be pressed, that is with respect to the advancement axis of the metal product to be pressed, while keeping the centerline planes of the three rolls, which are perpendicular to the respective rotation axes of said three rolls, at 120° from one another in any working position. Therefore, the three rolls always apply equal radial pressing forces at 120° from one another, directed towards the center of the metal product, during the passage of the metal product in a zone delimited by the three rolls, and the resultant vector of said radial pressing forces is equal to zero.
In a preferred embodiment shown in
However, there it is not necessary for the roll 7 of the soft reduction units 2 and/or 2′ and for the roll 10 of the soft reduction units 3 and/or 3′ to have a horizontal rotation axis. Such rolls 7, 10 could indeed have a rotation axis which is inclined by an angle other than zero with respect to the horizontal.
Preferably, at least one roll of said three rolls is motorized in each soft reduction unit. In a preferred variant, only roll 7, 10 having a horizontal rotation axis is motorized. For example, in
In other variants, only two rolls or all three rolls are motorized. This motorization of at least one roll allows to avoid the use of extraction units upstream of the soft reduction device for extracting the product from the casting curve.
In the soft reduction unit 2 shown in
The adjustment means in the soft reduction unit 2 comprise:
The lower rolls 8, 9 have centerline planes, which are orthogonal to the respective rotation axes, inclined by an angle other than zero with respect to the planes X, Z and arranged at 120° from the centerline plane of the upper roll 7, thus coinciding with a vertical plane in the case the upper roll has a horizontal rotation axis.
Said first translation means comprise for example, a first cylinder 17 having vertical axis when the roll 7 has horizontal rotation axis and the soft reduction unit 2 is arranged with the longitudinal axis W thereof vertical, and said second translation means comprise at least one second cylinder 18 for each lower roll 8, 9, adapted to linearly move the respective lower roll along a respective fixed guide 19, or fixed sliding block, which fixed guide is inclined according to the respective plane X, Z. In one variant, there are provided for example, two cylinders 18 for each lower roll 8, 9.
FIGS. from 4 to 6 show three positions taken on by the three rolls 7, 8, 9 to adapt to the diameter of the metal product on which the soft reduction is to be performed.
There may be provided sensors for detecting the angular position of the rolls 7, 8, 9 from one another, and/or synchronization means for synchronizing the actuation of the first cylinder 17 and of the second cylinders 18.
In a preferred variant, the adjustment means in the soft reduction unit 3 (
The centerline plane V is a vertical plane when roll 10 has horizontal rotation axis.
For example, said actuating means is a cylinder 21, for example a hydraulic cylinder, having vertical axis when roll 10 has horizontal rotation axis and the soft reduction unit 3 is arranged with the longitudinal axis thereof vertical.
FIGS. from 7 to 9 show three positions taken on by the upper rolls 11, 12 to adapt to the diameter of the metal product on which the soft reduction is to be performed, the lower roll 10 being in fixed position.
The symmetrical lever mechanism 20 may comprise, for example:
Each joint 25 therefore connects a first lever 23 to the respective second lever 27.
Each roll-holder device 29 supports one of the two upper rolls 11, 12 of the soft reduction unit 3, which are arranged at 120° from one another and with respect to the lower roll 10, and is configured to slide along a respective inclined plane X′, Z′. The two inclined planes X′, Z′ are convergent and symmetrical with respect to plane V.
When the roll-holder device 29 slides, it linearly moves the respective upper roll 11, 12 along a related fixed guide, or fixed sliding block, which is inclined according to the respective plane X′, Z′.
In a preferred variant, the planes X′, Z′ form an angle of 30° with respect to plane V. The upper rolls 11, 12 have centerline planes, which are orthogonal to the respective rotation axes, inclined by an angle other than zero with respect to the planes X′, Z′ and arranged at 120° from the centerline plane of the fixed lower roll 10, coinciding with the vertical plane V in the case roll 10 has a horizontal rotation axis.
With reference to
Cylinder 21, which controls the movement and adjusts the pressing of the upper rolls 11, 12, presses on the pressure element 30 which slides downwards along plane V.
As shown in the passage from
This movement of the first levers 23 causes a rotation of the joints 25 about the fixed pins 26, which causes a downwards push of the pins 28, and therefore of the second levers 27. In the configuration in
The downwards movement of the pins 28 causes a downwards movement of the roll-holder devices 29. In particular, the alignment of the pins 28 with the pins 24 and the pins 31 allows a transmission of a linear force which causes the roll-holder devices 29 to slide on the respective sliding blocks or fixed guides, thus linearly moving downwards the rolls 11, 12 along the inclined planes X′, Z′.
As shown in the passage from
There may be provided sensors for detecting the angular position of the rolls 10, 11, 12 between one another.
In an alternative variant (not shown), the adjustment means in the soft reduction unit 3 (
A further advantage of the present invention lies in the fact that the above-described adjustment means of the position of the rolls may be used to cause the extrados of the cast metal product to coincide with the pass-line of the processing line downstream of the casting curve.
Advantageously, the lower rolls 8, 9 and 10 of the at least two soft reduction units 2, 3 are positioned so that the extrados of the casting curve 5 upstream coincides with the pass-line of the processing line 6 downstream (
In particular, the fixed lower roll 10 of the soft reduction units 3, 3′, i.e. those with configuration of the soft reduction rolls having Y shape, is arranged so as to cause the resting surface thereof for the advancing metal product to coincide with the pass-line of the processing line 6; while the position of the two lower rolls 8, 9 of the soft reduction units 2, 2′, i.e. those with configuration of the soft reduction rolls having upside-down Y or/shape, may be adjusted, by means of the aforesaid adjustment means, so that the extrados of the advancing metal product coincides with the pass-line of the processing line 6.
The adjustment of the position of the lower rolls 8, 9 may be performed for example, due to the automation of the plant, which through measuring devices installed along the casting line and on the soft reduction device itself, may measure the cast section and calculate the correct height at which to set said lower rolls, so as to cause the pass-line to coincide with the extrados of the product, thus achieving the reduction treatment adequate for the thermal model set for the type of product processed. The pressing pressures of the various units forming the soft reduction device may also be set through automation, thus achieving the so-called dynamic soft reduction. Thereby, the liquid core of the product will certainly be pressed in an optimal manner, while simultaneously keeping it in a final shape as close as possible to the round shape.
Therefore, a continuous production process of round-section metal products according to the invention comprises:
Advantageously, during the soft reduction, there may be provided an adjustment of the position of at least two rolls of the three rolls of the soft reduction unit with respect to the center of the metal product to be pressed so as to keep the centerline planes of the three rolls, which are perpendicular to the respective rotation axes of said three rolls, at 120° from one another in any working position, adapting the soft reduction units to the diameter of the metal product which passes in the area delimited by the respective three rolls. Thereby, said three rolls apply equal radial pressing forces at 120° from one another, directed towards the center of the metal product, and the resultant vector of said radial pressing forces is equal to zero.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016000102472 | Oct 2016 | IT | national |
The present application claims priority to PCT International Application No. PCT/IB2017/056300 filed on Oct. 12, 2017, which application claims priority to Italian Patent Application Nos. 102016000102472 filed Oct. 12, 2016, the entirety of the disclosures of which are expressly incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/056300 | 10/12/2017 | WO | 00 |
