lollipop

these are the two types of lollipop samples presently we are taking at our shopfloor for tundish sampling.

the second type was brought in to take samples where there tundish temperature is below 1500degC for high carbon grades. hight carbon grades at our shopfloor can hit as high as 0.8 % (wt) C in liquid steel. the liquidous temperature of that steel goes down to around 1465 typically while some grades like 1008 have a liquidous of around 1525degC. the range is easily around 60degC.

extensively used top sampler does not give us properly filled and sized samples for high C grades at lower temperature in tundish. hence the second was introduced. still, the bottom samplers pose a different challenge at the lab because the robot there is not designed to handle that smaller sized sample. :-)

a ladle.....

there it is.

just after deslagging, ready to go back to ladle preparation bay for lining, purging plugs, tapping nozzles and slidegate plates checking.

the rings show the working lining of a ladle and the top freeboard and slaglining too.

since basic slags are made at LF in this plant, this inner lining is made of basic bricks so that the attack of basic slag on the lining will be minimal and least aggressive.

what makes the basic bricks basic?

well, when we take a look at the extended basicity formula ( CaO+MgO+MnO) / (SiO2+Al2O3+FeO), it can be easily understood the molecules of the numerator contribute to basic nature while those from the denominator make the refractories acidic.

so it can be inferred, the ladle inner working lining should be made of mainly one or more of the molecules from the numerator to make it basic.

ladle and tundish inner, working linings are made of MgO bricks while the backup linings are made of Al2O3  bricks.

bricks at the bottom, metal-lining generally give a life of around 120-150 heats while the slag lining bricks are debricked and relined after half of that number.

once a ladle is put into service, slag-lining brickes are changed twice in a campaign while metal-lining bricks are changed once in that life of around 120-150 heats. after completion of that campaign, entire working lining (bricks of slag as well as metal lining) is stripped off and relined after sufficient inspection or patching as necessary.

purging plugs give a life of around 30 heats while the slidegate plates hardly give 4 heats life. outer nozzles also get changed along with the bottom plates while inner nozzles give a life of 5 or 6 heats in general. but everything is subjected to REAL TIME, ACTUAL condition of the ladle; best is, NOT TO GIVE TAKE ANY CHANCE when there is even a little doubt, since anything untoward may cost huge losses than changing the doubtful, suspected part of the ladle.

tundish starter tube.

in tundishes with slidegate mechanisms, starter tubes are used to initiate filling of mould during start of casting.

these starter tubes are fixed above the wellblock of tundish, and they have a slot positioned somewhere around 350 to 450 mm above the tundish inner floor. this helps to start flow into mould at various tundish metal levels at various times one by one.

they normally float to the top after few minutes of start of casting.

pic below shows the starter tube when the tundish is ready to take heat after preheating.

draining off of ladle slag from tundish

we, machine incharges of casting floor, have damaged the cables of ladle-slag detectors as they hang down from ladles during rotation. manual errors have damaged them repeatedly, so these cables were not restored anymore.

the responsibility then fell on the machine-in-charges to detect and stop ladle slag from entering into tundish. manual and visual observation is bound to have errors, and in such cases accumulation of heavy ladle slag in tundish have a lot of adverse effects on casting.

tundish steels gets excessively oxidized, crust formation on top of tundish obstruct sample collection and manual temperature measurements can be a lot misleading.

automated monoblock stoppers may get jammed due to heavy slag around them leading to heavy torque and failure of actuators.

excessively oxidized steel can erode tundish slidegate plates or monoblock stopper tips leading to running of strands.

during such times it becomes an absolute necessity to drain the slag through the overflow spout into the emergency containers provided there is enough space for it.

pic below shows one such incident where slag is drained off tundish. it must be noted, steel should not be drained along with slag as this is a heavy loss.

from the pic one must be able to understand how slag (with glass formers like Silica and alumina) form a continuous thread while flowing down the spout WITHOUT BREAKING OR SPLITTING OFF as soon as flowing out.

this slag thread slowly draining off the spout explains a lot, about the high viscosity (around 10times that of liquid steel), that results from interlinking of CaO, silica, alumina and other network forming, slag making molecules that does not allow splitting or breaking off of streams (which normally  happens when liquid steel flows.) one can easily identify what overflows is metal or slag with this simple idea in mind.

fly link for tundish change

we do a lot of tundish changes to continue casting uninterrupted even after the life of one tundish is reached, replacing the old tundish with a new one; this process is also called fly tundish.

following pics show the fly link used to form a physical link between old and new billets during tundish change.

these links are designed to link sq.150 size billets in mould.

moulds during installation

this pic shows a set of 5 moulds placed on the oscillating bench of a caster.

what are the specifications should one know about these moulds? well. there is a lottttttttttt. a lot indeed. but a simple look into this image can tell us some basic, ballpark info about this caster. such as, this is a square mould that casts billets continuously; there is this AMLC, and M-EMS; radioactive sources are placed outside the mould body as against some other mould bodies where this source is placed inside; the wider inter-mould-distance shows, this caster is designed to cast much larger sections of billets or rounds (in fact this machine is designed to cast rounds as large as 450mm-dia); these moulds can cast billets in open/close casting modes, which of course needs an oil slit on top of mould.

evident from the absence of fenders in four moulds is that this image was taken during installation.

more on moulds, but later. :-) 

mould level detection

level of liquid steel inside mould during casting time is continuously measured, be it open or close casting. depending upon the type of casting, measured level in mould drives the strand speed (in open casting) or, opens/closes the tundish slidegate (in closed casting) so as to meet the casting speed given to the strand withdrawal motors.

this following pics show the physical elements necessary to measure mould level in a continuous casting machine.

in the first pic, at the center is the mould, at the bottom we have the detector, and at the top lies the radioactive source.

in the second pic, the center has mould, at the right is radioactive source that looks like a round canister, at the left lies the detector. the orange coloured box is the electrical cable connectors housing of Mould-Electro Magnetic Stirrer (M-EMS, not to be confused with Micro ElectroMechanical Systems of electronics industry).

this following, third-pic of this post shows radioactive source from the casters side (while the first shown from secondary metallurgy units'  or turret side). radiation warning sign is very much clearly visible in this pic below.

the picture above shows the mould of square billet sized 150mm . i created this in visual studio to understand start of casting steps, as the mould gets filled, dummybar withdrawal, filling up of mould to reach the target of around 150mm in detected range, the auto withdrawal start, auto regulation of level to meet the target level.
the pic below shows the schematic mould setup in CCMs; the mould water flow is also shown along with AMLC detection details.

it is a Co-60 radiation source, which normally has a good working life of 6 to 8 years, beyond which there may be some significant loss of radiation that may affect the performance of the AMLC (Auto Mould Level Control system) of casting machines.

gamma radiation from this source reaches the detector (NaI- sodium iodide crystal combined with multipliers and/or amplifiers). this detector is actually a geiger counter that counts the amount of radiation by converting it into pulses.

depending upon the amount of steel that interferes the path of radiation from source to detector, there is a proportionate loss of radiation detected by the detector. higher the interference, higher the loss. the system is calibrated using a solid-steel-calibration-block which simulates full mould level (by attenuating the radiation from reaching the detector), and without  that block for empty mould level (this latter allows maximum radiation to reach detector).

once the amount of pulses for full and empty mould are registered, it now becomes an interpolation between these two levels, indirectly proportional to the pulses received for any intermediate levels of liquid steel in mould.

the indepth details shall be looked into but later on another post. :-)

ladle turret emergency rotation

there may come a time in a casting floor (indeed we faced, and i used pneumatic rotation twice), when we have uncontrolled flow of liquid steel from ladle (may be due to slidegate through, or ladle lining through or slidegate cylinder closing failure).

during those times, emergency rotation command can be issued to take ladle to the charging position where the liquid steel can be safely dumped into an emergency ladle kept for safety.

sometimes accessing emergency rotation may take a little longer than reaching a pneumatic rotation system provided as an extra safety feature in modern casting platforms.

the following pictures show one such installed in a caster which was not yet commissioned when these pics were taken.

on the left side is the regularly used electrical motor, that has a discbrake mechanism to hold the motor still ( and hence the turret) from rotating when it is expected to stay put.

there is a rotary encoder nearby the planetary gear mechanism that tracks the position of rotation of the turret from zero to 360 degree as the turret turns during ladle changes.

at the bottom is a pneumatic switch which should stay healthy so that the brake can be engaged/disengaged whenever necessary for rotation.

on the right is the pneumatic motor connected to the same shaft that drives the planetary gear mechanism of the turret. the pneumatic motor has two instrument-air (IA) lines attached with it. one for clockwise and the other for anticlockwise rotation.

normally there would be an accumulator tank which stores IA in enough quantity to turn the turret at least 5 to 6 times and that tank is further connected to a regular IA line supply that runs all along the shopfloor.

load cells!

load cells!

are essential parts for a troublefree casting operation. if they fail, we may either dump a lot slag into tundish (if slag entry is not detected automatically/manually).

there are times when auto tundish regulation failed and led to ladle closures because of improper seating of tundish on loadcells.

generally there are four load cells placed on the all four corners of a tundish. they must be perfectly levelled so that whenever a tundish is placed on the tundish car, the entire load of the tundish must be equally distributed on to those 4 load cells, each taking 1/4th of the entire tundish load.

if the levelling is not proper, tundish may not sit properly leading to fluctuations and hence troubled casting experience.

here are some pics of load cells in a tundish car. similar load cells are fixed in ladle turret arms too but with a little higher ratings.

sometimes improper loadcell placement may give huge errors that the shown tundish weight may be much lower than it actually is. sometimes we may end up discarding a lot of metal as tundish skull.

this above pic shows a tundish skull. has a lot of hot steel that shines in bright yellow. the brown covering on the tundish is the spray/working lining of which is made of roughly 70% MgO and 20% Silica.

air-mist spray nozzle.

this picture below shows a fullcone air-mist nozzle, which was under user for sometime but has been removed due to choking of the port.

the front cap-block has been removed for easy cleaing and kept by side the side of the nozzle block.

inside that cavity of the cap we can see where the air should come (the whole rounded in orange circle) and how water should enter (the hole rounded in blue ellipse) so that that water can be atomized into mist.

normally the water pressure is around 4 to 8 bars while that of air is around 4 to 6 bars. the volumetric ratio is around 1:30 or 1:40. water flow varies with varying speeds of casting.

a ladle shroud!

the following pic shows a ladle shroud which was damaged during handling, yet it offered us a chance to take a clear look at the thin, inner glaze lining and the grains of thick, isostatically pressed refractory.

tundish preheaters and burner blocks

this following pic shows a tundish preheater after using 6 months from installation. 

a simple observation can easily reveal the minor damages on the 3rd and 6th burners, counting from left side. this is the sign of burner holes in tundish covers having a mismatch with those burners. if not those holes are perfectly matched, they may eventually expedite the damage rate of these burners as well as the refractory around it.

they may some time get damaged to such an extent that the broken pieces of burners may fall on the starter tubes of tundishes and collapse them. this would block the flow of steel during start of casting and that strand may be lost without sufficient, proper initial flow.

the following picture shows a tundish under heating in under this preheater; and the overflow spout is clearly visible at the center of the picture. a closer look shows the hole-for-burner in the cover of the tundish too.

this following pic shows a preheater from another caster where we have 5 strands. bottom right of the image shows the actuator-box (orange colored) the monoblock stopper can also be seen.

an advantage with this preheater is the extended burner blocks. changing these becomes much more easier than those of the previous preheater. (burner block change in the previous preheater takes somewhere around 4 to 6 hours depending on the ease with which old, rusted or weathered bolts of the old broken burners come off.)

since this image was taken before commissioning the stopper arms are not covered with refractory grade glasswool.

auto-coupler O ring changing in ladle.

argon purging is the lifeline of secondary steel making units, without which no thermal and chemical homogeneity is possible since there wont be any circulation of liquid steel mass initiated by the rushing argon bubbles from the bottom of the ladle.

once the ladle is kept on the ladle car, argon line has to be connected to the ladle. that can either be done manually or using auto-couplers.

here in these pics, an employee (without safety-helmet ) checks for, identifies and fixes a "O" ring in the ladle female part of the auto-coupler. normally there are 3 or more bores covered by sealing "O" rings; if any of the O ring is damaged or missing, then purging argon into the ladle is almost impossible as the missing/damaged O ring lets the argon leak through the auto-coupler joint.

i shall post more closer images later as i have to sift through a very huge collection of  pics from my mobile-cam-archives.