This invention relates to pinch rolls and particularly to those used in continuous casting of thin steel strip in a twin-roll caster.
In a twin roll caster, molten metal is introduced between a pair of counter-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces, and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the casting rolls. The term “nip” is used herein to refer to the general region at which the casting rolls are closest together. The molten metal may be poured from a ladle through a metal delivery system comprised of a tundish and a core nozzle located above the nip to form a casting pool of molten metal supported on the casting surfaces of the rolls above the nip and extending along the length of the nip. This casting pool is usually confined between refractory side plates or dams held in sliding engagement with the end surfaces of the rolls so as to dam the two ends of the casting pool against outflow.
When casting steel strip in a twin roll caster, the strip leaves the nip at very high temperatures on the order of 1400° C. or higher. If exposed to normal atmosphere, it would suffer very rapid scaling due to oxidation at such high temperatures. Therefore, a sealed enclosure is provided beneath the casting rolls to receive the hot strip and through which the strip passes away from the strip caster, the enclosure containing an atmosphere which inhibits oxidation of the strip. The oxidation inhibiting atmosphere may be created by injecting a non-oxidizing gas, for example, an inert gas such as argon or nitrogen, or combustion exhaust gases which may be reducing gases. Alternatively, the enclosure may be sealed against ingress of oxygen containing atmosphere during operation of the strip caster. The oxygen content of the atmosphere within the enclosure is then reduced during an initial phase of casting by allowing oxidation of the strip to extract oxygen from the sealed enclosure as disclosed in U.S. Pat. Nos. 5,762,126 and 5,960,855.
It is generally understood in the past that to produce thin cast strip the strip was guided by pinch rolls. These pinch rolls are positioned at the exit of the enclosure containing the oxygen depleted atmosphere through which the strip passes following formation at the casting rolls. A problem occurs however in steering the cast strip through the pinch rolls at casting speeds. The pinch rolls have a crown that varies with thermal expansion of the rolls, and reduces contact between the surfaces of the pinch rolls and the strip. The strip tends to wander, which can cause difficulties in processing of the strip downstream of the caster and, in some circumstances, breakage of the strip and shutdown of the casting operation. Also, there can be localized deformation and tearing of the strip. This steering problem is caused by a lack of contact of the pinch rolls with the strip across its width as illustrated in FIG. 1.
Accordingly, there has been a need for pinch rolls that better control the steering of the strip within closed tolerances to improve the processing capabilities of the cast strip plant, and at the same time, provide steering of the strip by the pinch rolls that can be automatically controlled with improved accuracy. The resulting pinch rolls apparatus of the present invention solves this problem in continuous casting of thin cast strip and in apparatus that is also useful in other applications. By reason of the geometry of the apparatus, there is no path for the strip through the pinch rolls where the strip can pass without maintaining contact of the strip across its width with surfaces of the pinch rolls, and at the same time steering the strip accurately and stabilizing the lateral movement of the strip relative to the pinch rolls.
The present invention is a pinch roll apparatus comprising:                a. upper and lower pinch rolls forming a pair of pinch rolls each having a diameter between 300–1500 mm positioned laterally adjacent each other to form a nip between them through which metal strip can be continuously fed;        b said upper and lower pinch rolls being positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls by between 10 and 130 mm, and with the upper pinch roll offset positioned downstream of the direction of travel of the strip through the pinch rolls;        c. a rotational drive capable of counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        d. a tilt drive capable of tilting the upper pinch rolls by a tilt between 0.5 and 5.0 mm, measure at the edge of the strip, relative to the lower pinch roll to control steering of the strip passing through the pinch rolls.        
The pinch roll diameter may be between 500 and 1000 mm, and the offset of the axes of the pinch rolls may be between 30 and 80 mm. The pinch roll apparatus also may comprise:                e. a sensor capable of sensing the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        f. a position controller actuated by said electrical signals from the sensor capable of actuating the drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternative, the pinch roll apparatus may comprise:                a. upper and lower pinch rolls forming a pair of pinch rolls positioned laterally adjacent each other to form a nip between them through which metal strip can be continuously fed;        b. said upper and lower pinch rolls being positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset positioned downstream of the direction of travel of the strip through the pinch rolls;        c. a rotational drive capable of counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        d. a tilt drive capable of tilting the upper pinch rolls by an angle relative to lower pinch roll to control steering of the strip passing through the pinch rolls;        selected such that:(Rupper min+hmin+Rlower min−|Tiltos-ds|)/(Rupper max+hmax+Rlower max)>cos(θ)        where:        Rupper min is the minimum radius of upper pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rlower min is the minimum radius of lower pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rupper max is the maximum radius of upper pinch roll, including ground profile and thermal expansion;        Rlower max is the maximum radius of lower pinch roll, including ground profile and thermal expansion;        hmax is the maximum strip thickness taking into consideration profile variations;        hmin is the average of the strip thickness, taking into consideration strip profile variations, measured 20 mm in from either edge of the strip, and is hmax minus the difference between strip thickness at the crown of the strip and the average strip thickness 20 mm in from the edges of the strip;        Tiltos-ds is tilt of the axis of the upper pinch roll relative to the lower pinch roll measured vertically between the edges of the strip; and        θ is angle from vertical of the line between the axis of the upper and the lower pinch rolls.        
Again, the pinch roll apparatus may further comprise:                e. a sensor capable of sensing the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        f. a position controller actuated by said electrical signals from the sensor capable of actuating the drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternatively or in addition, a thin cast strip plant for producing strip by continuous casting is provided comprising:                a. a thin strip caster having a pair of casting rolls having a nip there between;        b. a metal delivery system capable of forming a casting pool between the casting rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool; the        c. a casting roll drive capable of counter rotating the casting rolls to form metal shells on surfaces of the casting rolls, and cast strip delivered downwardly from the nip between the casting rolls,        d. upper and lower pinch rolls forming a pair of pinch rolls each having a diameter between 300–1500 mm positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass,        e. said upper and lower pinch rolls being positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls by between 10 and 130 mm, and with the upper pinch roll offset positioned downstream of the direction of travel of the strip through the pinch rolls;        f. a pinch roll rotational drive capable of counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        g. a pinch roll tilt drive capable of tilting the upper pinch rolls by a tilt between 0.5 and 5.0 mm, measure at the edge of the strip, relative to lower pinch roll to control steering of the strip passing through the pinch rolls.        
The pinch roll diameter in the thin cast strip plant may be between 500 and 1000 mm, and the offset of the axes of the pinch rolls may be between 30 and 80 mm. The thin cast strip plant for producing strip by continuous casting also may further comprise:                h. a sensor capable of sensing the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        i. a position controller actuated by said electrical signals from the sensor capable of actuating the drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternatively, the thin cast strip plant for producing strip by continuous casting may comprise:                a. a thin strip caster having a pair of casting rolls having a nip there between;        b. a metal delivery system capable of forming a casting pool between the casting rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool; the        c. a casting roll drive capable of counter rotating the casting rolls to form metal shells on surfaces of the casting rolls, and to cast strip from the shells delivered downwardly from the nip between the casting rolls,        d. upper and lower pinch rolls forming a pair of pinch roll positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass,        e. said upper and lower pinch rolls being positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset positioned downstream of the direction of travel of the strip through the pinch rolls;        f. a pinch roll rotational drive capable of counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        g. a pinch roll tilt drive capable of tilting the upper pinch rolls relative to lower pinch roll to control steering of the strip passing through the pinch rolls;        selected such that:(Rupper min+hmin+Rlower min−|Tiltos-ds|)/(Rupper max+hmax+Rlower max)>cos(θ)        where:        
Rupper min is the minimum radius of upper pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;                Rlower min is the minimum radius of lower pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rupper max is the maximum radius of upper pinch roll, including ground profile and thermal expansion;        Rlower max is the maximum radius of lower pinch roll, including ground profile and thermal expansion;        hmax is the maximum strip thickness considering strip profile variations;        hmin is the average of the strip thickness, taking into consideration strip profile variations, measured 20 mm in from either edge of the strip, and is hmax minus the difference between strip thickness at the crown of the strip and the average strip thickness 20 mm in from the edges of the strip;        Tiltos-ds is the tilt of the axis of the upper pinch roll relative to the axis of the lower pinch roll measured vertically between edges of the strip; and        θ is angle from vertical of a line between the axis of the upper and the lower pinch rolls.        
The thin cast strip plant for producing strip by continuous casting may further comprise:                h. a sensor capable of sensing the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        i. a position controller actuated by said electrical signals from the sensor capable of actuating the drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternatively, a method of producing thin cast strip by continuous casting is provided comprising the steps of:                a. assembling a thin strip caster having a pair of casting rolls having a nip there between;        b. assembling a metal delivery system capable of forming a casting pool between the cast rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool;        c. assembling upper and lower pinch rolls each having a diameter between 300 and 1500 mm forming a pair of pinch roll positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass, where said upper and lower pinch rolls are positioned one above the other with the axes of the pinch rolls offset between 10 and 130 mm in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset downstream of the direction of travel of the strip through the pinch rolls;        d. introducing molten steel between the pair of casting rolls to form a casting pool supported on casting surfaces of the casting rolls confined by said first side dams;        e. counter-rotating the casting rolls to form solidified metal shells on the surfaces of the casting rolls and to cast from the solidified shells thin steel strip through the nip between the casting rolls; and        f. counter rotating the pinch rolls to cause strip cast by the casting rolls to pass through the nip of the pinch rolls; and        e. tilting the upper pinch roll relative to lower pinch roll between 0.5 and 5.0 mm, measure at the edge of the strip, using a pinch roll tilt drive to control steering of the strip passing through the pinch rolls.        
In the method of producing thin cast strip by continuous casting the pinch roll diameter may be between 500 and 1000 mm, and the offset of the axes of the pinch rolls may be between 30 and 80 mm. The method of producing thin cast strip by continuous casting may further comprise:                f. positioning a sensor to sense the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        g. assembling a position controller actuated by said electrical signals from the sensor to actuate the pinch roll tilt drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternatively, a method of producing thin cast strip by continuous casting is provided comprising the steps of:                a. assembling a thin strip caster having a pair of casting rolls having a nip there between;        b. assembling a metal delivery system capable of forming a casting pool between the cast rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool;        c. assembling upper and lower pinch rolls forming a pair of pinch roll positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass, where said upper and lower pinch rolls is positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset downstream of the direction of travel of the strip through the pinch rolls, and assembling a pinch roll tilt drive to tilt the upper pinch rolls relative to lower pinch roll to control steering of the strip passing through the pinch rolls selected such that:(Rupper min+hmin+Rlower min−|Tiltos-ds|)/(Rupper max+hmax+Rlower max)>cos(θ)        where:        Rupper min is the minimum radius of upper pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rlower min is the minimum radius of lower pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rupper max is the maximum radius of upper pinch roll, including ground profile and thermal expansion;        Rlower max is the maximum radius of lower pinch roll, including ground profile and thermal expansion;        hmax is the maximum strip thickness taking into consideration strip profile variations;        hmin is the average of the strip thickness, taking into consideration strip profile variations, measured 20 mm in from either edge of the strip, and is hmax minus the difference between strip thickness at the crown of the strip and the average strip thickness 20 mm in from the edges of the strip;        Tiltoos-ds is tilt of the axis of the upper pinch roll relative to the lower pinch roll measured vertically between edges of the strip; and        θ is angle from vertical from a line between the axis of the upper and the lower pinch rolls,        d. introducing molten steel between the pair of casting rolls to form a casting pool supported on casting surfaces of the casting rolls confined by said first side dams;        e. counter-rotating the casting rolls to form solidified metal shells on the surfaces of the casting rolls and to cast thin steel strip from through the nip between the casting rolls from said solidified shells; and        f. counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        g. steering the thin cast strip between the pinch rolls by controlling the tilt of the upper pinch roll relative to the lower pinch roll with the pinch tilt drive.        
This method of producing thin cast strip by continuous casting may also further comprise:                h. positioning a sensor to sense the position of the strip relative to pinch rolls and generating electrical signals indicating the position of the strip relative to the pinch rolls; and        i. assembling a position controller actuated by said electrical signals from the sensor to actuate the pinch roll tilt drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Still further, method of steering thin cast strip during continuous casting is disclosed comprising the steps of:                a. assembling upper and lower pinch rolls having a diameter between 300 and 1500 mm forming a pair of pinch roll positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass, with said upper and lower pinch rolls one above the other with the axes of the pinch rolls offset between 10 and 130 mm in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset positioned downstream of the direction of travel of the strip through the pinch rolls;        b. counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        c. tilting the upper pinch rolls relative to lower pinch roll between 0.5 and 5.0 mm, measure at the edge of the strip, by a pinch roll tilt drive to control steering of the strip passing through the pinch rolls.        
In this method of steering thin cast strip during continuous casting, the pinch roll diameter is between 500 and 1000 mm, and the offset of the axes of the pinch rolls may be between 30 and 80 mm. The method of steering thin cast strip during continuous casting may also comprising:                d. positioning a sensor to sense the position of the strip relative to pinch rolls; and        e. assembling a controller actuated by signals from the sensor to actuate the pinch roll tilt drive to tilt the upper pinch relative to the lower pinch roll and automatically steer the strip passing through the pinch rolls.        
Alternatively, a method of steering thin cast strip during continuous casting is disclosed comprising the steps of:                a. assembling upper and lower pinch rolls each having a diameter between 300 and 1500 mm forming a pair of pinch roll positioned laterally adjacent each other to form a nip between them through which metal strip formed by the caster can pass, where said upper and lower pinch rolls is positioned one above the other with the axes of the pinch rolls offset in the direction of travel of strip through the pinch rolls, and with the upper pinch roll offset downstream of the direction of travel of the strip through the pinch rolls, and assembling a pinch roll tilt drive to tilt the upper pinch rolls relative to lower pinch roll to control steering of the strip passing through the pinch rolls selected such that:(Rupper min+hmin+Rlower min−|Tiltos-ds|)/(Rupper max+hmax+Rlower max)>cos(θ)        where:        Rupper min is the minimum radius of upper pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rlower min is the minimum radius of lower pinch roll taking into account ground profile and thermal expansion of the pinch roll during normal expected operation;        Rupper max is the maximum radius of upper pinch roll, including ground profile and thermal expansion;        Rlower max is the maximum radius of lower pinch roll, including ground profile and thermal expansion;        hmax is the maximum strip thickness taking into consideration strip profile variations;        hmin is the average of the strip thickness, taking into consideration strip profile variations, measured 20 mm in from either edge of the strip, and is hmax minus the difference between strip thickness at the crown of the strip and the average strip thickness 20 mm in from the edges of the strip;        Tiltos-ds is tilt of the axis of the upper pinch roll relative to the lower pinch roll measured vertically between edges of the strip; and        θ is angle from vertical from a line between the axis of the upper and the lower pinch rolls.        b. counter rotating the pinch rolls to cause strip to pass through the nip of the pinch rolls; and        c. steering the thin cast strip between the pinch rolls by controlling the tilt of the upper pinch roll relative to the lower pinch roll with the pinch tilt drive.        
Other details, objects and advantages of the invention will be apparent from the following description of particularly presently contemplated embodiments of the invention proceeds.