Metal founding – Control means responsive to or actuated by means sensing or... – Control of product withdrawal means in continuous casting...
Reexamination Certificate
1998-11-05
2001-01-23
Batten, Jr., J. Reed (Department: 1722)
Metal founding
Control means responsive to or actuated by means sensing or...
Control of product withdrawal means in continuous casting...
C164S442000, C164S448000
Reexamination Certificate
active
06176297
ABSTRACT:
The invention relates to an adjustment device for adjusting the position of at least one strand supporting element, in particular a strand guiding roller, relative to a supporting stand carrying at least one further strand supporting element, of a strand guide in a continuous casting plant and, in particular, a continuous casting plant for steel, comprising at least one hydraulic adjustment cylinder contacting a strand supporting element directly or indirectly on the one side and the supporting stand on the other side, the movement of the strand supporting element being detectable via a position sensor and controllable by means of an automatic controller.
A device of this type is known from U.S. Pat. No. 3,812,900. There, a strand guiding roller arranged on a supporting stand so as to be movable by means of hydraulic adjustment cylinders is moved in the direction towards, or away from, an opposite strand guiding roller rigidly arranged on the supporting stand. The respective position (actual value) of the movable strand guiding roller is determined by means of a measuring device and compared to a set value by means of a comparator. In case of a deviation of the actual value from the set value, the comparator triggers a servo unit via which the hydraulic adjustment cylinders are connectable with the pressure source.
Servo valve technology allows for a very sensitive and rapid control of high outputs at low control inputs due to the assisting effect exerted by the medium flowing through. Servo valve technology in the main is applied in machine tool engineering for delicate positioning tasks. Thus, expenditures both in terms of material and in terms of costs are accordingly high when realizing servo valve technology. Maintenance and measures for avoiding disturbing influences are cumbersome, too.
The application of servo valve technology to continuous casting technology enables the adjustment of the position of the movable strand guiding roller with the utmost precision. Drawbacks are the high material expenditures involved in applying servo valve technology as well as contamination; difficulties may arise in the rough steel works operation.
The invention aims at avoiding these drawbacks and difficulties and has as its object to provide an adjustment device of the initially defined kind, by which the high precision in positioning the strand supporting elements sought for the strand guide can be safely attained, yet only minimum expenditures are required as compared to the prior art, both in terms of production costs and in terms of service and maintenance costs. Influences resulting from casting technology such as dust, high temperatures, splash water derived from strand cooling, etc. are to have no or only minimum effects on the accuracy of strand guide positioning.
In accordance with the invention, this object is achieved in that at least one directional control valve capable of being switched via a three-level controller or a higher-level controller or a controller with a pulse-width output into which the actual value detected by the position sensor may be input via a coupling, is provided for actuating the hydraulic adjustment cylinder.
The provision of a directional control valve renders control engineering substantially easier as compared to the prior art. Although the extremely high accuracy to be attained by servo valve technology is renounced, advantages are nevertheless obtained by substantially lower costs and, moreover, a substantially lower sensitivity to failures such as, e.g., oil contamination or pressure drops or the like. It has been surprisingly shown that directional control valve technology will do for continuous casting even with sensitive steel grades.
By using a controller with a pulse-width output, nearly continuous control as is typically reached with servo or proportional valves may be obtained also with directional control valves. The changing valve opening in those continuously operating valves is replaced with a sequence of pulsed valve openings in the on-off valve. This enables high-accuracy positioning.
Since only small volume flows are required for adjusting a strand supporting element, yet the overall system is operated at high pressures (e.g., 160 bars), a throttle or screen is suitably installed in at least one hydraulic working duct of the hydraulic adjustment cylinder, leading from a pressure fluid supply station to the directional control valve or from the latter to the hydraulic adjustment cylinder.
A preferred embodiment is characterized in that a current control valve with rectification is installed in at least one hydraulic working duct leading from a pressure fluid supply station to the directional control valve or from the latter to the hydraulic adjustment cylinder.
By means of a current control valve, an adjustment speed nearly independent of the load and of the hydraulic pressures corresponding to the same will adjust. A three-level controller or five-level controller configured in conformity with that adjustment speed and the response time and fall time of the respective directional control valve enables the desired set position to be reached very precisely and directly for all cases of load.
A further preferred embodiment is characterized in that a throttle or screen is provided in the hydraulic working duct leading to and/or away from the hydraulic adjustment cylinder, so as to immediately precede respectively follow the hydraulic adjustment cylinder. Thereby, the main throttling effect (or main screening effect) is obtained between the hydraulic adjustment cylinder and the nonreturn valves preceding the same. As a result, the switching times of the nonreturn valves may be kept short and vibrations of the same can be avoided. The arrangement of such throttles or screens in addition to throttles or screens arranged between the pressure source and the directional control valve provides for the facility of largely varying the adjustment speeds of the hydraulic adjustment cylinders, wherein it is to be added that, in principle, the more throttles or screens are provided the larger these throttles or screens may be dimensioned, thus being less sensitive to contamination.
In order to achieve piston adjustment speeds that differ over the adjustment course of the hydraulic adjustment cylinder, and hence attain elevated accuracies, an additional directional control valve is preferably arranged in parallel with a throttle or screen or the current control valve with rectification, wherein suitably a five-level controller or a higher-level controller is provided as a controller.
The invention, furthermore, relates to a strand guide for a continuous casting plant comprising an adjustment device according to the invention. In this case, the position sensor preferably is comprised of a balancing cylinder arranged in parallel with the hydraulic adjustment cylinder and working diametrically opposed to the hydraulic adjustment cylinder and which, on the one side, is connected with a supporting stand carrying a strand supporting element, in particular a supporting segment, and, on the other side, is connected directly or indirectly with a strand supporting element supporting the strand and arranged to be movable relative to the supporting stand.
REFERENCES:
patent: 3263284 (1966-08-01), Orr et al.
patent: 3812900 (1974-05-01), Bollig et al.
patent: 5348074 (1994-09-01), Streubel
patent: 5709261 (1998-01-01), Streubel
patent: 3835010 (1990-04-01), None
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patent: 0301242 (1989-02-01), None
Brandstetter Reinhard
Engel Kurt
Fitzel Helmut
F{umlaut over (u)}rhofer Horst
Mörwald Karl
Batten, Jr. J. Reed
Ostrolenk Faber Gerb & Soffen, LLP
Voest-Alpine Industriean-lagenbau GmbH
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