Submerged entry nozzle exchange system for...

AUTHOR: Philippe MutsaartsVesuvius Group SA

During multiple ladle sequence casting there is a needto replace or exchange tundish submerged entry

nozzles (SENs) from time to time as a result of erosion,alumina blockage or breakage, in order to maintain thecorrect flow into the mould. The SEN, attached to a tubechanger, must be changed quickly and safely in order tomaintain product quality and protect personnel and plant.

Today, a tube changer allows the SEN to be changedwith only a small reduction in casting speed (usually nomore than 25%), which is normally still above theminimum speed acceptable for casting quality, andwithout raising the tundish from its casting position. Suchpractices are now fairly standard throughout the world.

The first tube changer (TCD90) was applied at BritishSteel Teesside Works, UK in 1986. Today more than 150slab strands are equipped with tube changers, with 128equipped with Vesuvius systems.

BENEFITS OF THE TUBE CHANGERThe tube changer offers improved caster scheduling,increased caster productivity, prime grade slabs and yield,and reduced operating cost. The use of a blank plateenabless reliable emergency shut-off. For example:

` Machine productivity can improve by over 2% as theproportion of time for re-stranding is reduced

` The prime yield can improve by 0.85% through theelimination of the 1.5m crop typically required toremove the scar on a flying tundish change slab, andthe reduction in the number of tundish skulls

` Slab downgrades can be reduced as a result of beingable to maintain casting speeds above the minimumacceptable for the grade being cast

` The number of tundishes consumed per year canreduce by 60% and overall tundish refractory costsare reduced by almost 50%

` Flying tundish breakouts can be eliminated` Elimination of aborted casts because of submerged

nozzle breakage

` Improvement in operational flexibility and security

BASIC OPERATING METHODA blank plate (plate without hole and without submergednozzle) is permanently loaded in the mechanism in a stand-by position in order to allow an emergency cast interruptionin case of any breakout. The firing actuator remains in itsready- to-push position. When the submerged nozzle is wornout and must be changed, the actuator is moved in itsparking position, the blank plate is removed and a new(already preheated) mono-block submerged nozzle is loadedin the mechanism and slowly immerged in the molten steel.This is achieved without tundish lift. The stopper is closedand the nozzle is moved to its casting position by means ofthe hydraulic actuator.

In the meantime, the new nozzle pushes out the wornnozzle outside of the mechanism. The stopper is openedagain and the used nozzle is removed out of the mould.The handling of the nozzle is achieved by means of aspecial manipulator.

The blank plate is again loaded in the mechanism andthe actuator is moved to its ready-to-push position.

To reduce turbulence in the mould and bending force onthe casting tube it is not recommended to perform thetube exchange in less than 1.5 seconds. The tube changecan be operated without interrupting the casting process.For security reasons, it is recommended that the stopperis closed during the exchange to avoid eventual steel finsbetween the plates and hence more build-up and airinfiltration after the following tube exchange, however, ifit is not closed leakage is not significant.

PREVIOUS DESIGNS OF TUBE CHANGERMechanism Until 2002, the Vesuvius portfolioincluded two different designs of tube changersdeveloped and applied during the previous 15 years: thepush-bar, TCD system, developed by the company IIE, and the direct acting SEM design developed by Vesuvius (see Figures 1 and 2; IEE was acquired byVesuvius in 1998).

The TCD has a pneumatic actuator with push-bar andside mounted cylinder. This mechanism does not need

Tundish submerged entry nozzle changers are virtually a standard fitting on today’s slab casters.Nozzle exchange is performed rapidly, without interruption to the casting process, with resultantimprovements in productivity, prime yield, refractory consumption and safety.

Submerged entry nozzle exchangesystem for tundishes

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any hydraulic supply as the pneumatic cylinder isdirectly attached to the mechanism. This is a simplecontrol system that allows automated tube change.

The SEM has two hydraulic alternatives. The manualswing design has a swing arm mounted hydraulic directacting drive (firing cylinder), which incorporates a pivotmounted direct acting cylinder with self-locking device.The hydraulic cylinder is easy to detach and remains onthe tundish car. This is the simplest system and is alsosuitable for automated tube change.

In the power swing alternative, the swing movement ispowered by means of a second hydraulic cylinder (swingcylinder). The firing cylinder design is the same and bothcylinders remain permanently attached to the mechanism.

Refractory The reliability of the tube changer and theassurance of an air-tight system is highly dependant onthe quality and the design of the refractory components.Initially the TCD version used a real top plate with aninner nozzle and a hard plate mono tube. A real plate issimilar to those used in ladle slide gates. It is pressed bymeans of a conventional press (one direction). It isrelatively large versus a monobloc inner nozzle plate thatis usually isostatically (multi-directional) pressed togetherwith the inner nozzle. Direct argon injection was achievedby means of piping directly connected to the refractory.Pressure was applied by means of leaf springs and thewell blocks were conventional shapes.

From the beginning, the SEM version used two monoblocisostatically pressed refractory parts, except, in theAmericas, where for local reasons, the inner nozzle plateswere usually made of castable refractory. The argoninjection connection was achieved through the gate

r Fig.1 TCD2000 tube changer

r Fig.3a SEM2085 cassette withoutsubmerged entry nozzle plate

r Fig.3b SEM2085 cassette withsubmerged entry nozzle plate

r Fig.4 SEM2085 in operation on a new slab caster in China

r Fig.2 SEM85 cross-section

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attachment to the mounting plate. The monobloc innernozzle floated on a clamp ring by means of small coilsprings compressed by the mounting plate and themonobloc submerged nozzle was pushed upwards bymeans of small coil springs and rockers. The well block wasrammed to avoid using another refractory part and tosimplify the installation. Some users preferred cap blocks.

SEM2085 AND SEM2100 – THE NEWGENERATION OF TUBE CHANGERSThanks to the acquisition of IIE by Vesuvius in 1998,specialists from both companies worked together andconsolidated their experiences. As a first step, systems weremodified and upgraded using solutions experienced byboth. Later, to develop a new generation of tube changer,new requirements such as a more robust and simplemechanism, with fewer parts, easy installation, handlingand maintainance, no air-entrapment, and operating in fullautomatic mode for casting longer sequences of highquality steel grades. Modern investigation tools wereimplemented to design the mechanism and the refractorysuch as finite element analysis and water modelling incollaboration with the company Advent.

The tube changer cassette The core of the system isthe cassette that holds the refractory and the pressureloading device. There is a cassette for normal size

refractory (SEM2085 bore size ≤85mm and ≤4.5t perminute) and a cassette for extra-large refractory (SEM2100bore size >85mm and casting rate > 4.5t per minute).

Figures 3a and 3b show the SEM 2085 design, andFigure 4, a SEM 2085 in operation in China.

Monobloc inner nozzle plate clamping device Inorder to obtain a completely air-tight system, it isimportant to have a sturdy monobloc inner nozzle platethat can be securely fixed to the mechanism and reliablyconnected to the argon supply network. To facilitate thisa completely new canned nozzle plate design is usedwhich has a parallelepiped flange provided with two 45°tapered faces so that the clamping forces are directed at45° towards the centre.

This design is stronger, allows precise positioning of therefractory in the cassette and secure locking of the pieceby means of two rotary wedges pressing on two rockers.This unique clamping concept reduces stress peaks andalso causes horizontal compression forces to act at theplate sector of the refractory elements. The design of thisrefractory piece has been calculated by finite elementanalysis. Figure 5 shows details of the inner nozzleclamping device. Figure 6 shows the reduction in stressobtained with this new design.

Argon connection is automatic when the inner nozzleplate is installed, as some of the pushing rockers are a

r Fig.5a Inner nozzle clamping device inunlocked position

r Fig.6 SEN finite element analysis calculation – Shape without(left) and with (right) 45° tapered flange

r Fig.7 Monobloc inner nozzle plate and SEN design

r Fig.5b Inner nozzle clamping device. Rotary wedges pressing rockers in lockedand unlocked positions

r Fig.5c Inner nozzleclamping device inlocked position

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provided with argon injection tuyeres. When the rockersare in the pushing position, they provide a reliable argon-tight connection with argon input holes (with graphitegasket) that are located on one of the tapered faces of thenozzle plate flange. Two independent networks can fillargon in the nozzle plate itself (purging) and in a sealinggroove located in its sliding surface. This allows veryaccurate tuning of the argon flow/pressure in each zone,which is critical for avoidance of clogging and good steelquality (see Figure 7).

Monobloc submerged entry nozzle design andsupport The new monobloc SEN also now has a flangethat looks similar to the inner nozzle plate – for the samereasons. It is supported by means of six high temperature-resistant springs applying a direct force at 45° on thetube through six pushers (not rockers). This generates a

combination of vertical and horizontal forces on theflange of the tube (see Figure 8). The pusher elements canbe easily removed from the outside for checking and thereis only one wearing surface.

Blank plate There is an integral blank plate holder withthe push-bar version which allows the operator to keepthe emergency shut-off blank plate on the tube changerand not in a remote position. This increases operationalsafety (see Figure 9). The tube/blank submerged nozzleplate with a double stroke cylinder is a new concept,developed from the experience in the field, and whichavoids the need to use a separate blank plate. It isavailable as an option.

Modular concept Targeting a flexible modular design,the two kinds of cassettes can be combined with differentdriving mechanisms, such as:

` Pneumatic shifting drive with push-bar and side-mounted cylinder (see Figure 10a). This does not needa hydraulic supply and the cylinder is directly attachedto the tube changer cassette. It is a simple controlsystem, which allows for automated tube change.

` Hydraulic shifting drive with push-bar and sidemounted cylinder (see Figure 10b). The drive isattached to the tube changer cassette but the cylinderis detachable. It remains either on the tundish car oron the mechanism and is connected with quickcouplings. It allows automated tube change.

` Manual swing arm mounted hydraulic direct shiftingdrive (see Figure 10c). This is a pivot mounted direct-acting hydraulic cylinder with a self locking device.The cylinder is easy to detach and remains on thetundish car. It is the most simple configuration, but isnot capable of automated tube change.

Installation on the tundish bottom Inherited fromthe TCD design, the new cassette is fixed by four studswelded directly to the tundish shell. It enables anyeventual tundish deformation to be accomodated withoutalteration of the tube changer cassette flatness and iseasier to install than a mounting plate.

Automation The process can be automated in order tolink the casting speed, the mould level and the stopperrod positions for a one-button operation. MS

Philippe Mutsaarts is Strategic Marketing Manager,Vesuvius Systems Division, Vesuvius Group SA, Ghlin, Belgium.

CONTACT: Philippe.Mutsaarts@be.vesuvius.com

r Fig.8 SEN-plate spring-pusherdevice

r Fig.10a Push-bar withpneumatic drive: PP version

r Fig.10b Push-bar withhydraulic drive: HP version

r Fig.10c Manual swing arm with hydraulic drive:HM version

r Fig.9a Tube/blank plate incasting position

r Fig.9b Tube/blank plate inclosed position

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