Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2001-02-14
2003-04-01
Elve, M. Alexandra (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S477000, C164S484000, C164S454000, C164S447000, C164S155400, C164S441000
Reexamination Certificate
active
06540011
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a method to control the axial position of slabs emerging from continuous casting, and the relative device, used in rolling plants with a rolling train located in line with the continuous casting, to obviate the problems of misalignment of the slab emerging from casting with respect to the axis of the first rolling stands.
The invention is applied both in cases where the slab is sheared to size into segments, and also in the case where the slab is worked without interruption from the casting to the train.
To be more exact, the invention is applied in conventional plants for thin slabs, in plants for long slabs from about 20 m to about 60 m, and in plants of the semi-endless type with long slabs of up to 300 m.
BACKGROUND OF THE INVENTION
One of the problems which businessmen operating in the field of rolling plants complain of is that concerning the control of the axial position of the slab with respect to the axis of the first rolling stands located downstream of the heating furnace.
For it is well-known that, since the slab emerging from the continuous casting is subjected to the steps extraction, pre-rolling and straightening, it rarely keeps a correct alignment with respect to the axis of feed; this creates problems when it enters the rolling stands and during the rolling steps.
Moreover, as it masses inside the tunnel, heating or temperature-maintenance furnaces, the slab car be subject to lateral displacements which take it off-axis.
If the slab arrives misaligned with respect to the axis of the first stand, rolling becomes difficult, particularly in the case of rolling thin slabs.
In fact, to compensate for the misalignment after the slab has entered the stand, and to make sure that it enters the downstream stand correctly, it is necessary to level the rolls of the first stand, which has negative effects on the symmetry of the transverse section profile of the slab itself.
Although this does not create serious problems when the product is very thick, for example above 2 mm, for thin products there are serious problems regarding the guiding of the strip in the rolling mill, even though the strip is guided for only a limited segment, since making up the difference in thickness between one side and the other causes different elongations on the two sides and therefore causes the strip to bend on the horizontal plane. Rolling becomes difficult if not impossible to manage, moreover, for thicknesses of about 0.6-0.8 mm.
To try to solve these problems at least in part, conventional solutions provide to use the action, singly or combined, of lateral guides, of the jets of liquid of the cooling or descaling assemblies, or of the edging assemblies arranged between the outlet of the heating furnace and the entrance to the stand, in order to obtain the progressive axial centering of the slab with respect to the rolling axis.
These solutions have proved to be only partly effective, for various reasons.
First of all, there is a technological requirement which does not allow to greatly distance the entrance of the stand from the outlet of the furnace, to prevent excessive cooling of the slab below the optimum rolling temperature.
For this reason, it is necessary to obtain a high displacement of the slab per unit of plant length in order to obtain the desired alignment at entrance to the stand.
Conventional guide systems, however, are not able to obtain these values on displacement and therefore they do not make possible to achieve the alignment in the little space available between the furnace and the stands.
Conventional lateral guides, moreover, occupy a length of about 10 m of the segment between furnace and stand, and define a transit width more than the width of the slab, on both sides, of at least 25 mm per side, up to 50 mm per side, in order to prevent the slab from knocking against the guides when it enters the rolling mill.
This is also because the width of the slab is known but not to complete accuracy: the discrepancy can reach up to 10 mm and more.
Therefore, the alignment of the slab is imprecise by values of ±25-50 mm. Moreover, the edge-finishing rolls or edgers cannot act on the edges of the slab for more than 20 about 10 mm per side.
All this makes it impossible to center the slab if it arrives, at the exit from the furnace, misaligned by more than a minimum value, which can be compensated, with respect to the rolling axis.
WO A 99/24186, in the name of the present Applicant, shows devices able to thrust laterally on a slab advancing inside a furnace to align it with respect to a nominal centering axis.
Such devices have the problem that the lateral sides of the slab slide and are damaged during the movements of thrust, and also that the ends of the thrust devices overheat, which are inserted inside the furnace during the alignment step and thus brought into contact with said sides of the slab.
The present Applicant has devised and tested this invention to overcome all these shortcomings which cause serious operational, technological and quality problems in rolling plane products, particularly thin plane products of less than 2 mm.
SUMMARY OF THE INVENTION
The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the main embodiment.
The purpose of the invention is to center and axially align a slab emerging from the continuous casting machine so that it arrives at the entrance to the first stands, whether they be roughing stands, pre-finishing stands or finishing stands, perfectly aligned with the axis of said stands.
Another purpose is to obtain this alignment with a simple solution, which needs little maintenance, which can be installed on pre-existing plants too, without substantial modifications to the configuration of the plant, and which will guarantee an efficient result which can be controlled substantially for every rolling condition and for every type of product being worked.
The invention allows to reduce the extension or the lateral guides arranged upstream of the first stand, with consequent advantages in terms of lay-out, obtaining hotter slabs entering the stands and reducing the length of the plant.
The device according to the invention comprises a plurality of thruster elements arranged in cooperation with and laterally to the tunnel, heating or temperature-maintenance furnace, inside which the slab passes before being sent to the first rolling stand.
In the preferential embodiment, the invention provides a number of said thruster elements, between 4 and 7 for every side of the furnace, also according to the length of the furnace, arranged at a distance of about 3-6 meters from each other.
Each of the thruster elements is associated with its own actuator which generates a movement of the thruster element, preferentially on a plane substantially parallel to the plane of feed of the slab inside the furnace, and in a direction substantially orthogonal to the direction of feed of the slab.
Substantially in correspondence with the position of every thruster element, in a preferential embodiment; the furnace has doors which can be selectively opened, and which allow the relative thruster element to be introduced inside the furnace, thus allowing the thruster element to act on the lateral edge of the advancing slab to cause a desired and controlled displacement thereof on the sliding plane of the furnace.
Thanks to the presence of the doors, it is not necessary to maintain the thruster element constantly inside the furnace, thus increasing the duration and the operational reliability thereof.
Each of the thruster elements has a contact element at its end, equipped, in a preferential embodiment, with cooling means which allow them to cooperate with the hot advancing slab without risks of damage or wear.
The activation or each of the thruster elements is governed by detector means, arranged at least in cooperation with the inlet to the furnace, and/or inside the furnace; said detector means measure the entity of the misalignment
Carboni Andrea
Donini Estore
Millone Roberto
Danieli & C. Officine Meccaniche S.p.A.
Elve M. Alexandra
McHenry Kevin
Stevens Davis Miller & Mosher LLP
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