EMBR, ElectroMagnetic BRake for thin slab casters by jal11416


									                             CC-EMS for flat products

                    EMBR, ElectroMagnetic BRake
                                for thin slab casters

                                                       Principal view of EMBR for thin slab casting.

EMBR is a prerequisite when casting thin slabs with higher throughputs and when you are aiming at
the higher quality segment.
•Nearly complete elimination of mold powder entrapments as the result of reduced flow speed and
•Greatly improved coil surface quality.
•Higher casting speed can normally be used.
•Reduction of mold copper wear, especially at higher casting speeds.
•Reduced meniscus swelling resulting in a more even molten mold powder layer.
•Hotter steel at meniscus.
•New market segments will be within reach because of improved product quality.
In summary, EMBR will increase productivity, product quality and lower operating costs.
                           EMBR for thin slab casters

Reduced mold powder entrapments
Inclusions coming with the steel remains small and
relatively harmless because of the Ca-treatment of the
steel. Because of this and the high casting speed
normally used for thin slabs, mold powder entrapment
constitutes the major source of detrimental non-
metallic inclusions.
With an EMBR, the lower meniscus flow speed and
turbulence results in that mold powder entrapments
will be nearly eliminated. These data were generated
by an optical surface detection system located after
the last stand in the hot rolling mill. They and show
that more than 90% of the non-metallic inclusions are

                                                                                           No EMBR                    EMBR
                                                                                               Surface defects on coil.

                                                                                                 Surface Defects
Improved coil quality                                                                 Non-metallic inclusions detected after F7
The higher the casting speed the lower the quality will
be. This is evident from the figure, where non-metallic
inclusions in coils are shown as a function of
throughput and EMBR current. These results come
from an optical surface detection system located after
the final stand in the hot rolling mill. It can clearly be
seen that when using an optimized EMBR the quality
level at higher throughputs is improved. The quality                                                                                0
becomes equal or better to the quality level to that for                                                                        150-250
significantly lower casting speeds without EMBR.                                        >3,5
                                                                                                3,0-3,5                        >250
                                                                                                          2,5-3,0 <2,5
                                                                                          Throughput [t/min]                     EMBR
                                                                                                                               Current (A)

Reduced meniscus waving/swelling
The braking of the steel jets exiting the SEN reduces                           15
                                                             Wave height (mm)

the meniscus swelling close to the mold narrow sides.                           10                                               0
                                                                                 5                                               80
The resulting flatter meniscus allows for a more even                                                                            160
layer of molten mold powder, thus improving                                      0                                               240
lubrication and reducing the risks of surface cracks.                            -5
                                                                                -10 0     100      200     300      400 500
The meniscus profile has been measured by dipping a                              Narrow     Distance narrow face (mm)    SEN
thin metal sheet into the mold. A typical dip sheet                              4.8 m/min, slab dimensions 50 x 1140 mm
holder is shown at the top of the picture .
                                             EMBR for thin slab casters

                                                                                  EMBR increases mold lifetime.
                                                                                  EMBR dramatically decreases the mold level
                                                                                  fluctuations. Therefore temperature cycling and
                                                                                  thermal fatigue of the copper mold plates
                                                                                  dramatically reduced. Thanks to that more than
                                                                                  twice as long mold lifetime has been reported
                                                                                  from casters using EMBR.

                                                                                  EMBR increases steel temperature at
Superheat in mold (º F)

                                                                                  Since the EMBR reduces the turbulence in the
                                  EMBR on (150 -200A)
                                  EMBR off
                                                                                  steel, heat transfer from the middle of the mold
                                                                                  to the solidification front is reduced.
                                                                                  Additionally, hot steel is not pushed down into
                           0                                                      the strand but kept higher up in the mold,
                                                                                  resulting in an increase of the steel temperature
                                                                                  at the meniscus, see figure to the right. The
                          -20                                                     temperature at the meniscus was measured by
                             20     30       40       50          60         70
                                                    Superheat in tundish (º F)    dipping down a thermo-element into the steel.
Superheat at meniscus with/without an EMBR system

New markets
Thanks to the dramatic improvements in quality, new markets with improved profitability, such as
the white products sector, will be within reach of many flat product mini-mills. This has already
been proven by several steelmakers with thin slab casters using EMBR.

Productivity improvements
As a consequence of the quality improvements coming from using an EMBR system, the casting
speed can normally be increased resulting in increased productivity. This is especially important to
steel shops with only one thin slab strand feeding a dedicated hot rolling mill.
                          CC-EMS for flat products
                      EMBR for thin slab casters
                                                                                           Part coil
The EMBR consists of two or four part coils, placed at       Iron Core
each mold wide side. The part coils are fed with direct
current from a thyristor converter. The generated static
magnetic field brakes the flow speed of the steel jets
from the SEN thereby reducing the turbulence. The
higher the metal flow speed the higher the braking force.
The following two EMBR configurations are available:          Yoke

EMBR Ruler. The braking area of the Ruler covers
substantially the entire width of the slab. Two part coils
(shown in red in the figure) with electrical copper
windings together with iron cores and outer iron yoke                                     Iron Core
form a closed magnetic circuit.
EMBR Local Fields. Unlike the Ruler, the braking area
covers the steel outlet from the SEN. Four part coils with
electrical copper windings (shown in red in the figure)                                      Yoke
                                                                  Part coil
together with cores and outer yokes form a magnetic
circuit. This type of EMBR is especially suited for
rebuilding of existing casters.

The following different methods are used to install
EMBR:                                                            Part coil
Window solution for new casters. The part coils are
mounted on the non-oscillating magnetic yoke
surrounding the movable iron cores. In order to minimize
the non-magnetic gap, these iron cores fit in the front
position in “windows” in the mold water jacket, also                                   Movable Iron Core
allowing for mold oscillation.                                   Yoke
                                                                                   Window solution
At mold exchange, the iron cores are retracted and the
mold can then be lifted out of the caster, while the part
coils remain in the caster. This installation method
minimizes the weight on the oscillation table since the
cores and yokes do not oscillate

Integrated solution for existing casters. The part coils
and the magnetic cores and yokes are mounted on the
mold and go in and out of the caster with the mold during
mold exchange.                                                                       Integrated

       ABB Automation Technologies AB            ABB Inc.
       Metallurgy Department                     JME Division
       SE-721 36 Västerås, Sweden                1450 Hopkins St, Suite 203
       Phone: +46 21 34 00 00                    Whitby, Ontario L1N 2C3, Canada
       Fax: +46 21 14 83 27                      Phone: +1 905 666 2251
       info.metallurgy@se.abb.com                Fax: +1 905 666 2266

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