Patent Grant
8286691
The present invention concerns a method and a plant for casting and continuous rolling in-line, in endless or semi-endless mode, so as to make long rolled metal products such as bars, wire rod, beams, rails or sections in general.
Plants known in the state of the art for the production of long rolled products provide a casting machine and a rolling mill, which is disposed in line and downstream of the casting machine. It is also known that, in the solutions in which the casting axis defined by the casting machine and the rolling axis defined by the rolling mill coincide, the plant can be configured and used in endless (or continuous) mode, or in semi-endless mode (that is, starting from segments of cast products sheared to size).
In these operating solutions, if the rolling mill stops, either accidentally, for example due to cobbles, or programmed, for example to change channels or change production, it is necessary to stop the rolling process, which also entails the interruption of the casting machine; moreover, if the rolling mill stops accidentally it makes it necessary to scrap at least part of the intermediate material between the casting and the stopping point, and also the material being processed from the tundish to the rolling mill.
Consequently, any stoppage of the rolling mill causes a reduction in productivity and the plant utilization factor, an increase in the management costs and they are the main cause of an increase in energy required.
One purpose of the present invention is therefore to achieve an in-line casting and continuous rolling process, endless or semi-endless, and to perfect a relative production plant which allows to manage the stopping of the rolling mill, substantially without interrupting the casting and therefore without loss of production and without penalizing the steel plant upstream.
Another purpose of the invention is to reduce to a minimum or eliminate the scrap material in emergency situations or during programmed stoppages and so completely recover the product which in these situations is temporarily accumulated in an intermediate point along the production line.
Another purpose of the invention is to exploit to the utmost the enthalpy possessed by the original liquid steel along all the production line in order to obtain a considerable energy saving and a reduction in running costs compared with conventional processes.
Further purposes of the present invention are:
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
A casting and continuous rolling plant for the production of long products according to the present invention comprises a single continuous casting machine and a rolling mill disposed downstream and in line with the casting machine. By disposed in-line we mean that a hypothetical casting axis of the casting machine is substantially coincident and parallel with a hypothetical rolling axis of the billets, and therefore this configuration is particularly suitable to make a process of the endless type; in any case it is always possible to achieve a process of the semi-endless type as well.
In some forms of embodiment, the casting machine has a crystallizer suitable to cast liquid steel at high speed and high productivity (for example, simply as an indication, from 35 up to 200 ton/hour). By high-speed casting we mean that the continuous casting machine can cast products, in relation to thickness, at a speed varying from about 3 to about 9 m/min.
Advantageously the crystallizer produces a substantially quadrangular section, hereafter defined generally as billets.
In the description and the claims, by the term billets we mean a product with a square section or a product with a substantially rectangular section or a widened form, in which the ratio between the long side and the short side is comprised between 1.02 and 4, that is, just higher than the square section up to a rectangular section in which the long side is up to 4 times longer than the short side.
In the present invention the section of the cast product is not limited to a quadrangular section with straight and two by two parallel sides, but also comprises sections with at least a curved, concave or convex side, advantageously but not necessarily two by two opposite and specular, or combinations of the aforesaid geometries.
When the crystallizer casts products having a rectangular section, a greater quantity in tons of material in a unit of time is obtained, given the same casting speed and thickness (or height) of the section, that is, an increase of the hourly productivity, for example higher than 120 t/h.
To give an example, the square billets which are produced by the continuous casting according to the present invention have dimensions variable between 100 mm×100 mm, 130 mm×130 mm, 150 mm×150 mm, 160 mm×160 mm or intermediate dimensions, while, to increase the productivity, the rectangular sections have dimensions variable between 100 mm×140 mm, 130 mm×180 mm, 130 mm×210 mm, 140 mm×190 mm, 160 mm×210 mm, 160 mm×280 mm, 180 mm×300 mm, 200 mm×320 mm or intermediate dimensions.
In general the cast section has a surface equal to that of a square with equal sides comprised between 100 and 300 mm.
When a metal product with substantially rectangular section is cast, an additional rolling unit is provided, consisting of at least one stand, so as to return the rectangle to a square/round/oval shape suitable for the rolling mill. The additional unit can be located immediately downstream of the casting machine, or immediately upstream of the rolling mill.
The casting and continuous rolling line also comprises, downstream of the continuous casting, at least a shears to shear the billets to size into segments of a desired length in the semi-endless mode or in an emergency case in the endless mode. By desired length of the segments we mean a value comprised between 12 and 18 meters.
Moreover the shears can carry out an emergency scrapping of the material coming from casting.
According to a characteristic feature of the present invention, downstream of the casting machine, and in a misaligned condition, or laterally offset, both with respect to the casting axis and also with respect to the rolling axis, there is a maintenance unit which includes a box furnace (or thermal box) configured to act as a chamber to maintain the temperature and accumulate billets, particularly but not exclusively in the event of a temporary interruption of the rolling mill, for example to allow programmed maintenance interventions or changes of channel or production, or for accidents.
In this way the casting machine does not necessarily have to be stopped, but only slowed down, inasmuch as the exiting product is sequentially cut into billets in predefined dimensions and is taken out of line, inside the box furnace, where it is substantially maintained at an operating temperature, thus unconstrained by the rolling mill which has stopped. The billets, accumulated and maintained at temperature, are then once again fed toward the rolling mill, once the operation of the latter has been restored. The billets are accumulated/discharged according to the LIFO criteria.
This solution allows to reduce, if not eliminate, losses in production in case of interruption of the rolling mill, greatly increasing the utilization factor and the yield of the plant; it is thus possible to reduce the running costs, to obtain a greater stability of the rolling mill and a better dimensional quality of the finished product, as well as to guarantee the possibility of changes in production in dimension and type without ever stopping the continuous casting.
Thanks to the box furnace, the overall yield is also improved; indeed, in the event of accidental interruption of the rolling mill during the continuous casting:
The billets enter the box furnace at an average temperature of about 1100° C.; the average temperature of the billets at exit from the furnace is comprised between about 900° C. and about 1100° C.
The box furnace functions purely as a “maintenance chamber” in one of the following modes:
In case 2) the box furnace has a gas consumption limited to what is necessary in order to maintain the box at a temperature lower than the load that enters into it.
In this way the consumption will oscillate from the working value to almost zero.
When the furnace is empty, the consumption is that needed to be ready and suitably hot.
On the other hand when the furnace receives (and immediately returns) a single billet at a higher temperature (which billet is allowed to lose temperature), then the consumption will tend to decrease according to how much heat the billet will lose, relatively to how much time the single billet stays inside.
If, on the other hand, the furnace accumulates a plurality of billets, then the consumption will tend to decrease to zero since in that transitory, the furnace is filled with a mass of iron that is hotter than when it exits from the furnace.
Advantageously, the accumulation capacity or buffer time of the box furnace is such as to contain a number of billets, in weight, equal to a ladle of steel of 70 tons.
As we said, in some solutions, not restrictive within the scope of the invention, at exit from the maintenance unit, or in any case downstream from it, there can be at least an inductor furnace which has the function of bringing the temperature of the billets to values suitable for rolling, at least when the temperature at which they exit from the furnace is about 1050° C. or lower.
The inductor furnace can be present, or also present, in an intermediate position between the stands of the rolling mill, and with its action allows a greater uniformity of heating of the billets, in particular to heat the edges, thus avoiding the formation of cracks in these zones during rolling.
In a preferred solution of the invention, the maintenance unit also comprises a rollerway connecting the casting machine and the rolling mill. In a first embodiment, the rollerway is located outside the box furnace, and the billets are feed toward the box furnace or discharge from it. In another embodiment the rollerway is located directly inside the box furnace
According to another form of embodiment, the box furnace substantially comprises a front door for introducing/removing the billets into/from the furnace, in order to close the box furnace, a refractory furnace casing, a combustion apparatus with upper burners, or lower burners, or both upper and lower burners, and fumes removal from below to a natural or forced draught chimney, and a plurality of longitudinal members in fusion to support the charge that has accumulated inside the box furnace.
According to another form of embodiment, the box furnace comprises two lateral doors, for example one for introducing and one for removing the billets.
According to another form of embodiment, the plant comprises one or more thrust heads suitable to move the billets inside the box furnace, and also to feed and subsequently pick them up and re-deposit them on the rollerway.
Advantageously, one or more “counter-thrust” heads are provided, to empty the box furnace from the inside.
According to another form of embodiment, in place of the thrust heads, the box furnace comprises a plurality of longitudinal walking beams which are provided to move the billets.
According to one form of embodiment, the rolling line comprises one or more shears disposed immediately upstream of the rolling mill, or even in an intermediate position between the stands of the rolling mill, so as to be able to shear the cast product also during the rolling step, and feed it to the maintenance unit, in conditions when rolling is accidentally interrupted.
According to another form of embodiment, the rolling line comprises one or more, advantageously three, oxyacetylene cutting torches, possibly tracked, disposed between the shears for shearing to size downstream of casting and the cropping shears upstream of the rolling mill, and suitable to shear the cast product in the segment comprised between the shears into segments to be fed to the box furnace, in conditions when rolling is accidentally interrupted.
A rolling method for the production of long products also comes within the field of the present invention, comprising a step of continuous casting of billets, and a step of in-line rolling, subsequent to the continuous casting step, for the production of long rolled products.
According to a characteristic feature of the present invention, when the rolling step is interrupted, a step of accumulation and temperature maintenance is provided, which provides to accumulate a plurality of billets sheared to size, in an offset position from the casting and rolling axes, inside a box furnace in a temperature maintenance condition, for a time correlated to the intervention to restore rolling, so as to allow continuity of the continuous casting step.
The process thus provides to define an accumulation store between casting and rolling, with the time the billets remain there being equal to the time of the intervention to restore the rolling step.
These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:
With reference to the attached drawings,
The lay-out 10 in
The continuous casting machine 11 is disposed on a line coinciding with the rolling line defined by a rolling mill 16 located downstream. In this way it is possible to achieve an endless process, that is, without any break in continuity. A semi-endless process may also be achieved.
In some forms of embodiment, the continuous casting machine 11 can be high-productivity, and can reach casting speeds comprised between 3 and 9 m/min, according to the type of product (section, quality of steel, final product to be obtained, etc.), and can also cast sections with a widened shape, that is, with one size prevailing over the other, in a ratio preferably comprised between 1.02 and 4.
In particular, the continuous casting machine 11 allows to obtain a productivity that varies from 35 ton/h to 200 ton/h.
Merely to give an example, the square cast billets are sized variable between 100 mm×100 mm, 130 mm×130 mm, 150 mm×150 mm, 160 mm×160 mm or intermediate dimensions, while, to increase the productivity, the rectangular sections have dimensions variable between 100 mm×140 mm, 130 mm×180 mm, 130 mm×210 mm, 140 mm×190 mm, 160 mm×210 mm, 160 mm×280 mm, 180 mm×300 mm, 200 mm×320 mm or intermediate dimensions. Generally, the cast section has a surface equal to that of a square with equivalent sides comprised between 100 and 300 mm.
Downstream of the continuous casting machine 11 there is a first shears for shearing to size 12, which can cut the cast billets into segments of a desired length, both for the functioning of the plant 10 in semi-endless mode and, as will be explained in detail hereafter, for the functioning of the plant 10 in endless mode, in the event of a stoppage of the rolling mill 16. The shears 12 can also perform an emergency scrapping operation of material arriving from casting.
If a rectangular section is cast, an additional reduction/roughing unit 13 may also be present (
The best position of the additional reduction/roughing unit 13 along the line comprised from the end of casting to the beginning of the rolling mill 16 is established in relation to the speed obtainable at entrance to the first stand of the unit. For example, if the speed is comprised between 3 and 4.8 m/min (0.05 msec and 0.08 m/sec), the reduction/roughing unit 13 is positioned immediately downstream of the continuous casting machine 11 and upstream of the shears 12 (
Another parameter that can condition the choice of inserting the additional reduction/roughing unit 13 immediately downstream of the continuous casting machine and upstream of the shears 12 is the energy factor.
In fact, when the first reduction in section is performed immediately downstream of the continuous casting, immediately after the closing of the metallurgic cone, energy consumption is reduced since the reduction in section takes place on a product with a core that is still very hot, and therefore it is possible to use a lesser force of compression and to use smaller stands that require less power installed.
In the three lay-outs shown as examples in
The box furnace 14 (
Moreover, with particular reference to
Advantageously, one or more “counter-thrust” heads 31 are provided, conformed to empty the box furnace 14 from the inside.
The box furnace 14 functions mainly as an accumulation store for the billets, in particular in the event of an interruption in the functioning of the rolling mill 16, due to accidents or for a programmed roll-change or for change of production.
The box furnace 14 also functions as a maintenance chamber, keeping the temperature of the billets between entrance and exit, between about 900° C. and about 1100° C.
After the functioning of the rolling mill 16 has been restored, the billets accumulated and kept at temperature are sent to the rolling mill 16 according to predefined operating modes, re-establishing the normal functioning cycle of the plant 10.
Advantageously, the capacity of the box furnace 14 to accumulate billets, or so-called buffer, is such as to contain a number of billets which is equal in weight to a 70 ton ladle of steel.
In particular, the continuous casting machine 11 and the rolling mill 16 are connected to each other by means of a rollerway 20, provided substantially in correspondence with the box furnace 14.
With reference to the form of embodiment given as an example in
In the form of embodiment shown in
In the form of embodiment shown in
In this embodiment, the box furnace 14 could reprocess cast off billets with a heating at rolling temperature, or less.
The second rollerway 20b, parallel to the casting and rolling axes, to take out the billets, could be provided also for the embodiments as described with reference to
In the lay-out 10 shown in
The number of rolling stands 17 used in the mill 16 varies from 3-4 to 15-18 and more, depending on the type of final product to be obtained, the thickness of the cast product, the casting speed and still other parameters.
Upstream of the rolling mill 16 there is a second cropping shears 18, for example a hydraulic shears, which not only crops the head of the billet before it enters into the stands of the rolling mill but can also carry out emergency scrapping operations.
In the form of embodiment shown in
If the inductor 15 is provided in order to restore the temperature, it is advantageously made in two parts, or in two halves, as shown in
For example, according to the embodiment shown in
The billets unloaded and accumulated in the box furnace 14 during the periods when the rolling mill 16 is stopped are completely recovered, when it starts up again, and are re-introduced into the rolling line through the thrust heads 30, the counterthrust heads 31 and the rollerway 20.
Different modes may be provided to restart the billets, for example progressively, alternated with the billets arriving from casting, or in a single solution at the end of the casting production, for example, at the end of the day, or other. Another parameter of particular importance is the sharp reduction in the consumption of natural gas for feed to the box furnace 14, as much as ⅕, with respect to traditional solutions.
Other components known in the state of the art, such as de-scalers, measurers, etc., not shown, are normally present along the lay-out 10, present in the attached drawings.
| Number | Date | Country | Kind |
|---|---|---|---|
| UD2010A0124 | Jun 2010 | IT | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5182847 | Guse et al. | Feb 1993 | A |
| 5542165 | Coassin et al. | Aug 1996 | A |
| 5769149 | Mertens | Jun 1998 | A |
| Number | Date | Country |
|---|---|---|
| 4017928 | Dec 1991 | DE |
| 19524082 | Jan 1997 | DE |
| 0625383 | Nov 1994 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20110308757 A1 | Dec 2011 | US |
