Metal founding – Control means responsive to or actuated by means sensing or... – Control of product withdrawal means in continuous casting...
Reexamination Certificate
2002-02-14
2003-08-26
Dunn, Tom (Department: 1725)
Metal founding
Control means responsive to or actuated by means sensing or...
Control of product withdrawal means in continuous casting...
C164S441000, C164S442000
Reexamination Certificate
active
06609556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for casting prefabricated products, in particular, of steel materials such as slabs, blooms, beam blanks etc., in a strand casting device comprising a strand guide arranged downstream of the casting mold and optionally divided into segments, wherein the strand guide is comprised of pairs of oppositely arranged rolls for supporting and conveying the solidifying cast strand, wherein at least one of these rolls is forced by means of a drive, the drive roll, with a defined adjusting force, in interaction with idle rolls, against the cast strand for transmitting the guiding forces as well as strand conveying forces. The invention also relates to a device for performing the method.
2. Description of the Related Art
In continuous strand casting devices, preferably for steel materials and for manufacturing slabs, inter alia thin slabs, blooms, or beam blanks, the produced strands are supported and guided from the casting mold to at least the point of complete solidification by means of a roll guide. Individual rolls within this strand guide or downstream thereof are driven for overcoming the removal resistance to which the strand is subjected on its way through the roll guide device. The power of these drives is usually dimensioned such that, on the one hand, for any conceivable operational situation a safe conveying of the strand out of the device is ensured and, on the other hand, the manufacturing costs are as low as possible, and, moreover, the drives are not unnecessarily oversized.
The rolls of a strand guiding stretch of the strand casting device are subjected to continuous wear. Often it is observed that the driven rolls wear more strongly than the idle rolls. As a result of this, the roll diameter will change gradually. This causes diameter differences between the idle rolls and the driven rolls which are subjected to greater wear; however, the differences are not easily recognizable.
For ensuring a frictional connection between the driven rolls and a strand, it is known to use hydraulically or mechanically adjustable lifting traversing slides. Often, in particular, for avoiding quality reduction of the cast end product, they are loaded with a force which is below the force that can be produced by the strand itself as a result of its hydraulic height (ferrostatic pressure). This is designed to prevent strand deformations. However, in many cases the driven rolls are rigidly connected and integrated in a support frame.
With the wear of the driven rolls being faster in comparison to the idle rolls, after a longer or shorter operating time, a gradual loss of transmittable removal forces acting on the strand will occur which is generally not recognizable. Such a loss of transmittable removal force is limited by adjusting drive rolls by means of the applied adjusting force; however, in the case of rigidly arranged drive rolls the loss can cancel the entire transmittable tangential force. When such a creeping change of the removal force coincides with a critical casting situation relative to the removal resistance, the strand may get stuck in the casting device and this can cause a greater disruption.
In order to transmit the physically greatest possible traction force of the driven rolls onto the strand for the purpose of avoiding such disruptions, it has been suggested in this connection, for example, to expand the drive control by means of a traction control, processing simultaneously the drive torque and the rotational speed, in a so-called anti-lock system. Such a development known from the prior art is able to completely use the physical limit of the traction force defined momentarily by the material pair and the coefficient of friction. However, it cannot prevent falling below the adhesion limit, for example, resulting from a diameter loss that is too great and thus traction loss, even if, for example, by empirically determined operating experiments, the adhesion limit were known.
European patent document EP 0 908 256 A1 describes a method and a device for producing slabs in a strand casting device which has a strand guide arranged downstream of the casting mold and divided into two-part segments, wherein the casting strand is conveyed from the vertical casting direction into the horizontal rolling direction and is supported during the deflection and transport. The adjusting forces required for transmitting the conveying forces for the drive rolls are generally provided by hydraulic cylinders. In this connection, it is proposed to replace the hydraulic clamping cylinders, which clamp the two segment frame parts against one another via spacers, by segment adjusting cylinders so that the adjusting forces for the drive rolls are displaced toward the segment intake or segment exit and the forces for strand conveying are supplied also by the segment adjusting cylinders.
For strand guiding frames of a segment configuration, as described in an arc device disclosed, for example, in German patent document DE 1963 146 C1, which guides the cast strand from the vertical casting direction into the horizontal rolling direction, the upper and lower frames of the segments are clamped against one another by four hydraulic cylinders that connect the frames and are arranged on the corners external to the casting strand. The adjustment of different strand thicknesses is realized by spacers against which the frame parts are pressed. A change of the roll spacing during the casting process is not possible in this configuration.
In the German patent document DE 43 06 853 C2 it is suggested to arrange between the spacers and the respective lateral frame part a hydraulic plunger cylinder and to dimension its annular piston such that in the pressure-relieved state it secures the segment parts at the spacing of the rolls which corresponds to the desired strand thickness. By this measure, an adjustment of the guide roll to different strand thicknesses is possible, but this configuration requires that at least one of the rolls, the drive roll, is pressed by its own hydraulic adjusting cylinders (at least two per drive roll) with the required adjusting force for the transmission of the strand conveying forces against the cast strand.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve the guiding of the cast strand, preferably from the vertical casting direction into the horizontal rolling direction, such that a gradual wear resulting on the rolls during the course of operation and entailing a loss of transmittable removal force can be anticipated in order to prevent by a timely initiation of preventive maintenance an operational failure, for example, preventing the strand from becoming stuck in the casting device.
In accordance with the present invention, this is achieved in that all drives are controlled to have a predetermined rotational speed such that their circumferential roll speeds are identical within the limits of a preset casting speed and the correlated motoric torques (engine torque) are maintained, with respect to the loadability of the strand shell, to a level as equal as possible below a permissible torque limit value and that, for determining the permissible torque limit values, first on a single drive of the device, while all other drives are controlled accordingly to the aforementioned nominal casting speed, the drive torque, beginning at zero, is gradually increased and, in this connection, the rotational speed of the drive roll is monitored and, in the case of a superproportional rotational speed increase A, the torque limit value B is determined and the process stopped.
With an expedient configuration of the method according to the invention it is proposed that the torque limit value B with corresponding rotational speed (slip torque and slip speed), measured immediately before the rotational speed increase A, taking into consideration boundary parameters such as the steel quality, the casting speed, the casting shape, the spraying pattern etc. with respect to the measured
von Wyl Horst
Weyer Axel
Kueffner Friedrich
Lin I.-H.
SMS Demag Aktiengesellschaft
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