Strand Casting of Slabs ,and Billets

MONDAY MORNING, APRIL 29, 1974

The session on Strand Casting of slabs and Billets convened at 9.15 am..The chairmen were W. D. Smith, Jones & Laugh- lin Steel, Corporation, Aliquippa Works, Aliquippa, Pa., and H. N. Hubbard, Jr., United States Steel Corporation, Gary Works, Gary, Indiana.

CONTINUOUS CASTING LAYOUT, MIDDLETOWN WORKS-ARMCO STEEL

Robert F. Boschert

Senior Engineer, 'Engineering & Construction . .

Armco Steel Corporation

Middletown, Ohio

To meet increased product demand and take advantage of greater product yields, a continuous slab casting facility was installed at Armco's Middletown Works, Middletown, Ohio. The Middletown Plant is a fully integrated facility which produces flat rolled products for automotive, appliances, transportation and construction industries.

1 In 1968, a Task Force was formed consisting of-operating, Research and Engineer-

ink personnel, to study other casting installations, and discuss design parameters with various equipment builders. This group was responsible for the facility recom- mendations and followed the project from conception through final start-up.

A curved mold, bow-type casting machine was selected to produce fully killed steel grades, with the primary steel grade being fully aluminum killed, deep drawing type. An Xngineering Report was issued on January 21, 1969, and detail design of the facility began on February 1, 1969. Construction began on July 14, 1969, and the first heat was cast on January 25, 1972.

The facility was designed to cast only a portion of the steel produced in the B.O.F. Shop, with projected casting capacity being 57,000 slab tons-per-month. This tonnage is an ambitious goal considering that sequence casting capability was not included. Present casting capacity is approximately 40,000 tons-per-month, but the original projected tonnage will be achieved with additional tundish service facili-. ties. These facilities are now under construction.

General Arrangement

The Continuous Casting complex was built contiguous to the melt shop, (see Figure 1). The casting machine discharges to the north, perpendicular to the melt shop teeming aisle. .The casting shop is a three-aisle design, consisting of a casting aisle (90 ' x 260 ) , service aisle (751 x 220 I), and slab yard (90 ' x 220 ' ) .

Between the Casting complex and the melt shop, a dual vessel (one operating and one stand-by) R-H vacuum degassing facility was constructed in an area covering 50 ' x 120 ' . This complex physically connects the melt shop and casting buildings.

The ent i re Continuous Casting complex was constructed using spread footers fo r building and machine foundation support. A l l buildings and equipment were purchased by competitive bidding, and instal led by a general contractor under the supervision of Armco. Delayed delivery of s tructural s t ee l add the casting machine mechanical equipment, plus the f ina l check-out of the spray dater f i l t e r , delayed the projected start-up. The f i r s t cast was completed January 25, 1972.

I Five (5) months prior t o the scheduled f i r s t cast , a start-up schedule was

in i t i a t ed t o correlate the input of the various d$sciplines fo r plant start-up. The schedule was formulated on a dai ly basis, encompassing a four (4) week time span. Daily meetings were held between the contractor, vendor representatives and Armco personnel t o coordinate f ina l project completion.

Heats fo r the caster are produced i n one of tdo (2) - 225 net ton basic oxygen furnaces, and are transferred t o the caster by ei ther of two (2) routes:. through the degasser v ia ladle t ransfer ' t rack #2 or d i rec t ly t o the machine v ia t ransfer track #1. Heats which are not degassed are argon s t i r r e d .

In the continuous casting a i s l e , heats a re hoisted by a 300 ton capacity ladle crane and placed on a ladle t ransfer car located on the caster operating f loor 37'-8"

. . above ground level.

Casting Process

The casting machine (see Figure 2) is a Demag, curved mold, twin-strand machine, having a constant radius of 34'-6". A lad le car i s used t o position the casting ladle over the tundish which i s supported on a tundish car. The ladle and tundish cars t ravel i n a north-south direction, paral lel t o the strand discharge direction. This design allows the ladle car t o move out o f t h e way i n case of ladle o r machine prob- lems and be i n position over the guard ladle located below casting floor level. This also provides for use of a single t ransfer car t o de l iver tundishes from the service a i s l e t o the casting molds.

The strand discharge i s i n a horizontal position, and the dummy bar disconnects immediately upon the emergence of the dummy bar head from the straightenecwithdrawal unit . The dummy bar i s accelerated upon disconnect, and i s transferred t o a res t position paral lel t o the strand a t runout table elevation.

Slabs are cut t o length by torches, weighed, and side transferred t o slab p i lers prior t o being placed on railroad cars.

Machine design specifications are shown on ~ a 6 l e I. Adjustable molds are used t o cast the variable width slabs with the thickness being fixed presently a t 10". The production rates and casting times vary depending on the slab width and casting practice used. Slab lengths are constant and are'generally equal t o the maximum length. The l a s t slabs are cut t o eliminate as much scrap as possible.

Equipment

Casting Ladle Transfer Car And Ladle - A gantk-type ladle car with a span of 46 feet is used t o support the casting ladle. It moves north to position the ladle over the tundish and south t o position the ladle over the emergency guard ladle. The car has four trucks, each having two 36" diameter douljle flanged wheels. One wheel on each of the four trucks i s driven by a 19 H.P., 250 volt D.C. m i l l motor, coupled t o a shaft mounted reducer having a 56 t o 1 ra t io . Power feed t o the car i s by cable reel ; t ravel speed is 50 feet-pesminute,

A platform from which the ladleman operates the ladle s l ide gate and takes metal samples and temperatures from the tundish i s provided across the f d l length of the car. .

The casting ladle i s a standard bottom'pour type, equipped' with a Flocon s l ide gate actuated by a hydraulic auto-pour system.

Tundish Cars - Two (2) tundish cars are provided, one operating and'one stand-by. Each car i s powered by two (2) - 7-l/2 H.P. D.C. motors, coupled t o a shaft-mounted reducer having a 140 : 1 ratio. ' ~undi'sh car jog positioning is provided by two (2) - '

1.0 H.P. A.C. drives t o al ign tundish over the molds. The cars are of the gantry type design, consisting of two end trucks and two horizontal cross members. The tundish support platform i s .hung from the two cross beams by four l i f t i n g screws. These 'four screws are driven by two - 30 H.P. motors coupled t o worm gear drives having a r a t i o of 5 0 ~ .

The tundish cars function t o t ransfer tundishes between the service and casting a i s l e , and support the tundish over the molds while casting. Tundish car traverse speed is 50 feet-per-minute, with jog position+g speed being 30 inches-per-minute. Total lift provided is 20 inches a t a l i f t i n g speed of 24 inches-per-minute. L i f t was instal led t o provide use of pouring tubes between the tundish and molds for sub- merged metal entry.

Tundish Preheat - Two (2) stationary preheat s tat ions are located i n the service a i s l e on the operating floor, and one preheat s tat ion i s provided on each of the two tundish cars. It i s planned t o i n s t a l l a s ta t ion on the casting ladle car so tha t preheat f a c i l i t i e s can be removed from tundish cars. Reason for this change w i l l be explained l a t e r .

Each stat ion i s equipped with a 100,000 cfh a i r blower driven by a 10 H.P. motor. Four (4) natural gas burners are used t o preheat each tundish. Preheat time i s normal- l y two (2) hours, with a tundish temperature of 2,100° F.

Tundishes - One common tundish i s used t o distribute. metal t o two (2) casting molds. Each tundish has a 2-1/2" back-up and 4-l/2" working lining. One piece roto . rod stoppers are used t o control metal flow t o each mold. Pouring tubes have b i f m cated nozzle discharge openings; the tubes are of one-piece design, and are se t i n from the top. Total metal holding capacity of the tundish i s 14 tons. Four plate- type covers made from 6" slabs are used t o make up one complete tundish.

Mold - Adjustable molds are used t o provide variable width slabs of 10 inch thickness. Two (2) molds cover the range of 36 - 82 inches. The machine i s designed t o cast 25 - 82 inches, but molds were not purchased fo r the narrowest sizes. Design i s of the plate type construction with copper plates bolted t o water-cooled s t ee l back-up frames. Mold length is 28 inches and radius i s 3.1+'-6tt. A single foot ro l l i s attached beneath each broad face, and a single side r o l l under each end plate serves as a guide for dummy bar insertion. Spray cooling headers are mounted above and below the footrol l , and side spray headers extend 18 inches below each end plate. Each broad face and end plate has individual water control, with t o t a l capacity 2,500 GPM.

Mold Oscillator - Mold-and footrol l osci l lat ion comes from a crank assembly, stroke adjusting gear, thrust rod, rocker arm and l ink assembly driven by a 50 H.P. D.C. motor. Stroke adjustment can be varied 0-1 inch, with a frequency range of 25 - 120 strokes-per-minute.

Roller Apron - The 341-6" radius curved roller apron section (see Figure 3), is composed of one apron #O immediately below the mold, with the balance of the section divided into five (5) segments. The segments guide the dummy bar into the mold and support the strand upon withdrawal. Apron segment #O must be removed from the machine to change thiclmess, while segments #1 through #5 !can be changed in place. The top half of segments #1 through #5 are hydraulically yressed onto spacers by four (4) hydraulic cylinders per segment. A change in thiqlmess can be accomplished by insert- ing or removing spacers. I

I

Secondary spray cooling is divided into five ) (5) zones : Zone I provides individ- ual control of footroll sprays and side sprays immediately below the mold; Zone I1 controls top and bottom face of apron #O; Zone I11 controls sprays on segment #1, with individual control of top and bottom face; Zone IV has segment #2 and #3 combined with individual control of top and bottom sprays; and Zone V controls sprays on segment #4 and #5 combined, with separate control for top and bottom faces.

Segment #O contains ten (10) pairs of solid rolls supported by anti-friction bearings (see Table 11). The first four (4) pairs are 8 inch diameter and the follow- ing six (6) pairs 8-3/4" diameter.

Segment #1 contains five (5) pairs of 10" diameter solid rolls with the bearing housings being wate+cooled.

Segments #2 through #5 have internally water-icooled rolls and bearing housings. Segment #2 and #3 are identical, each having four 4) pairs of 12" diameter rolls, and segment #4 and #5 are identical, each having four 4) pairs of 1411 diameter rolls.

One common spray chamber encloses both strands. When the slab leaves segment #5, it enters the straightener-withdrawal unit.

Straightener-Withdrawal

The first section of the straightene+withdrawal unit between the spray chamber and the tangent point is on a 34'-6" radius curve., A total of 23 pairs of 17" and lqtt diameter rolls (see Table 11) comprise both the curved and straight section of the straightene-withdrawal unit. Each strand has 14 - 19" diameter driven bottom rolls. A back-up roll is mounted under the tangent roll to resist forces due to the strand straightening.

All top rolls are individually pressed against stops or the strand. Bottom rolls are pressed against stops by hydraulic plungers. Bottom roll #4l, which precedes the tangent roll, is pressed against stops by hydraulic cylinders. This roll can be low- ered to allow an emergency cutting torch to enter in the event that a cold strand has to be removed from the machine.

The bottom rolls are driven by D-C mill motors through planetary gear reducers. Planetary reducers made it possible to install the drives in a straight row adjacent to each other without having them staggered. The result was reduced space require- ments and lower capital cost. The experience with these drives to date has been excellent.

Dummy Bar Disconnect'- As the dummy bar discharges from roll #SSr the last roll' in. the straightener-withdrawal unit, the disconnect table is tilted by hydraulic cylinders to disconnect the dummy bar from the strand. The connection between the dummy bar and the strand is by sections of railroad rails. The head of the rail fits in the dummy bar head and the' base is embedded into the slab. It is only necessary to place new rail pieces in the dummy bar head prior to the next cast.

Dummy Bar Cage Handling - The dummy bar i s accelerated into the storage cage im- mediately a f t e r disconnect. Three (3) t ransfer cars t ravel i n s t ructural cross beams raised and lowered by hydraulic cylinders. After the cage i s picked up, it i s trans- ferred l a t e r a l l y to a storage position, para l le l and adjacent t o the strand. The cage i s lowered t o i t s support members and the t ransfer cars are f ree t o t r a v e l - t o the opposite strand fo r cage transfer. Each car i s moved by individual ropes connected t o a common drive.

Torch Cutting Machines - Each strand has a gantry type cut t ing machine with two (2) oxygen/natural gas torches which cut from opposite sides toward the center. Torch carriage movement i s accomplished by clamping onto the slab by means of a i r cylinders. This assures a s t raight cut. Since only carbon s t ee l s are cast (no s ta in less) , n a t n a1 gas preheat torches are used fo r i n i t i a t i n g cuts. Rolls located i n the cut t ing area are designed t o lower as the torch approaches t o avoid damage.

Crop Removal System - Near the end of the cut t ing section, a rope drive crop re- moval car (see Figure 4) i s instal led. This car transfers crop ends from the strand t o a crop bucket area where an a i r cylinder pushes the crop in to a bucket. The ca r has two (2) pair of wheels a t different elevations and gages a t one end, so that it is always level as it i s pushed up the inclined track toward the strand r o l l e r table.

/ The head crop cut i s only par t ia l ly completed, with the cut being re in i t ia ted when the strand nears the crop car. After the crop end has been severed, it f a l l s onto the crop ca r and i s withdrawn t o the crop bucket area.

Runout Equipment - After being cut t o length, slabs are removed t o a.weighin.g section of the run-out tab le mounted on four (4) . electronic load ce l l s .

, The slab i s then moved t o the end of the runout table , transferred t o the side A d placed on a slab p i le r . The slab p i l e r can stack up t o four lo f1 slabs. Four (4)

I worm gear drives are mounted under each of the two (2) p i le rs , and each p i l e r i s driven by two (2) 45 H.P. motors. Maximum p i l e r t ravel i s 36".

Slab Marking. And Handling - The original plan was t o i n s t a l l automatic s lab markers over each strand. It was decided t o subst i tute a method of attaching s ta in less s t ee l tags t o each slab fo r identification. T a g embossing uni ts were purchased and 14 male dies provide the necessary identification. A 2" x ~ l / 2 " t ag i s inserted, infor- mation i s embossed onto the t ag by two (2) s t r ik ing heads and fastened t o the s1a.b by heat-treated na i l s attached t o a special sledge hammer. This method has been extremely successful.

S l a b s a r e l i f t e d from the slab p i l e r by meansoof an overhead crane and rotat ing slab tong. It i s necessary to . ro ta t e a l l slabs 90 because the rai l roadloadout track i s perpendicular t o the strarid discharge direction. The slabs are'normally loaded d i rec t ly onto special 'slab t ransfer cars, or a limited amount can be stocked on the ground i n the s lab yard. A 65 ton crane i s used t o handleslabs. The crane cab i s located i n the center of the bri,dge span f o r be t te r operator v i s i b i l i t y .

Abort System - This casting f a c i l i t y has a unique l a d l e abort system (see Fi.gure 5). The ladle car , a f t e r moving south from the casting machine, i s positioned over a guard ladle located below casting f loor level. Ingot buggies with ingot molds are located under the guard lad le on a rai l road track. I n c a s e of a ladle running stopper o r s l ide gate leak, s t ee l enters the guard ladle and i s then teemed in to the ingots. The guard ladle i s equipped with a standard stopper rod and the ingot buggies are indexed by means of a ca r puller.

The machine also i s equipped with an abort feature. I f actuated, the ladle car moves over the guard ladle and the tundish car moves over a s lag box d5irectly i n back of the molds. The cars are automatically stopped i n t h e i r proper positions by means of limit switches located below operating f loor ldvel.

I Spray Water system

I

T h i s system is being changed t o a recirculating system. Reason fo r t h i s change w i l l be explained l a t e r .

The present design of the spray water system through design. A maximum of 3,200 GPM of water,

Mold Water System

(see Figure 6) is of the o n c e softened and 'filtered by sand bed

A closed loop mold water system is provided (see Figure 7). Boiler quality feed water i s pumped from a surge tank by two (2) of three (3) centrifugal pumps. From the molds, the water flows by gravity through four (4) plate type heat exchangers, and then back into the surge tank. Machine cooling water i s circulated on the opposite side of the heat exchanger plates t o reduce the mold water temperature. Maximum water flow per strand i s 2,500 GPM.

I

Machine Cooling System I

type f i l t e r s , i s supplied t o the cas ter and pumped t o the hot s t r i p m i l l c la r i f ica t ion plant a s make-up water. The water passes from thh spray chamber into a scale p i t pr ior t o being pumped t o the s t r i p m i l l . I

A recirculating system (see Figure 7) i s used. Three (3) of four (4) pumps de- l i v e r 6,300 GPM of softened and f i l t e red water through the heat exchangers f o r mold water cooling, t o the casting machine for internal r o l l and frame cooling, and back t o a collecting sump, where it i s then pumped over a cooling tower. From the cooling tower, the water flows by gravity back t o the cold well.

Emergency Water Supply

Originally, emergency mold water was supplied by an elevated 10,000 gallon stor- age tank, with a back-up supply from the spray water supply system. Spray water supply is a part 0 f . a plant system supplied by steam turbine driven pumps.

It was determined that the spray water system was not adequate on a continuous basis, so an al ternate emergency system was installed. A n existing steam turbine and pump was relocated and instal led i n conjunction with a 250,000 gallon storage tank. T h i s f a c i l i t y now serves a s an emergency spray water supply i n case of a loss of plant supply water, or a s emergency mold water i n case of a power fai lure. The turbine driven pump w i l l automatically s t a r t upon a loss of water pressure i n the main supply l ine o r a power failure. The tank holds a sufficient quantity t o complete a cast.

Design & Start-Up Problems

Following the general experience of other new continuous casting operations, we had design and start-up problems. The problems described are the major ones encount- ered and include both equipment design and errors i n f a c i l i t y layout.

Molds - Numerous problems were experienced:'

1.. Water supply piping was not interchangeable between molds.because they were. not constructed as detailed on design drawings. A l l piping had t o be re- worked so that a l l molds would be interchangeable.

2. Some pipe connections were revised t o allow easier hook-up.

3 . End spray headers had t o be redesigned and replaced.

4. Alterations were required on broad face plate support mechanisms t o pennit p l a t e s t o be moved more freely when aligning and se t t ing up molds.

Tundish Transfer Cars - Basic design of the tundish car did not fu l ly consicler the problems from metal splash and heat generated from the tundish during a cast . Preheat blowers had t o be-relocated due t o damage from metal splash. Overflow troughs had t o be replaced because they were too small. Warping of the main l i f t car r iage , from heat resulted i n binding of l i f t spindles and mechanical damage t o l i f t drive reducers.

Preheat f a c i l i t i e s w i l l be removed from the tundish cars t o reduce maintenance due t o metal splash on the burners and provide a safer means of positioning burners i n the tundish. Originally, preheat burners were positioned onto the tundish by manual manipulation from the operating floor. This was impractical and resulted i n the requirement that operators climb on top of the tundish car. It i s hoped that t h i s practice can be eliminated by removing al l preheat f a c i l i t i e s from the tundish cars and ins ta l l ing an al ternate system.

Rotary Joints - The rotary joints, which supply water t o internal water-cooled ro l l s , have leaked excessively since start-up due t o an internal sealing problem. The only apparent solution t o t h i s problem is replacing original joints with an al ternate design.

Tundish Stopper Rigging - Strength and design of the ent i re tundish stopper rigging assembly was inadequate. The riggings could not r e s i s t forces generated by the throt t l ing action of the tundish stopper rod, and permitted the stopper rod t o vibrate. A l l rigging members had t o be strengthened and the main guide housing re- vi,sed t o incorporate additional ver t ica l guides for the slide. An adjustment feature w a s added t o remove slack i n the ver t ica l s l ide due t o wear.

Ladle Stopper- Numerous heats 'had t o be aborted because of refractory fa i lure of ladle stopper rods. The rods and heads are exposed t o severe operating conditions, due t o long hold times dictated by the t ravel sequence of the ladle from the B.O.F. shop t o the caster, plus higher tap temperatures required f o r caster heats. This problem was successfully resolved by ins ta l la t ion of s l ide gates on the ladle.

Spray Water System - One of the most severe problems at the caster, which has re- sulted in a considerable loss of production due t o machine downtime, has been the spray water f i l t e r system. We t o supply softened and unfiltered water t o the caster bad clean the water by f i l t e r s containing polyester type beads.. Bequent mil- functioning of the f i l t e r s caused a loss of media which was, in - tu rn , pumped with the spray water t o the caster, causing complete nozzle plugging i n the secondary spray water system. Due t o the. large number of nozzles instal led, a considerable length of time i s required t o remove nozzles, flush the system and re ins ta l l them. I n addition t o loss of media due t o malfunctions, media breakdown occurred, whereby the required media s ize distribution necessary f o r proper f i l t e r operation could not be maintained.

Much time was spent attempting t o make the f i l t e r s perform as,required, includ.ing replacing media s ize and type and changing t h e f i l t e r operating sequence. Failure of the system t o properly perform a f t e r extensive effort resulted i n the f i l t e r s being by-passed. This then required a switch to f i l t e red water rather than unfiltered.

For these reasons the spray water system wilf be changed to a recirculating system which will be a part of the hot strip mill clarifier system.

Service Area - A lack of tundish repair space has restricted production by not providing sufficient space for tundish repair. This lengthens tundish turnaround time, and machine delays occur when tundishes are not available.

Additional space is being added to the servde aisle building. This additional space with an improved tundish practice will increase casting production.

I

- Summary

Great progress has been made in making the caster a more successful unit, and this facility is now an important asset to the production of Middletown Works. Prod- uct mechanical properties are equal to, or betterthan, ingot poured material for deep drawing aluminum killed.~teels.-~~ Surface qualitx, is superior to the ingot prod-

, , , , . = .:,, -,.., .-.. : , ,

uct . -.' . . ,,>.'>j$ " ; : ,,.,. " >. ~,

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. 1.- . ... , . : -: '". . . : ""I,, ,: , . ,.. . !': ,Ci i..' . . .... . . . . , . ..<,.

In the future, we will consider the installation of equipment required for sequence casting. Tundish slide gates and wide angle spray nozzles are other items that may increase production and improve product quality. We are aware of the many advantages of continuous casting, and will strive 'to incorporate new t ethnology to improve the process.

1

TABLE I

SLAB CASTING MACHINE DATA

Number Of Strands.. ................ Two (2)

Heat Size.. ........................ 225 N e t Tons

Casting Rate ....................... 5.0 Tons-Per-Minut e

Casting Time.. ..... .,. .............. 70 Minutes-~e*~eat Maximum

Slab Thickness..................... 7 Through 12 Inches

.... Slab Width ..................... 25 To 82 Inches

Slab Length.. ...................... 14 To 33 Feet

Strand Centerlines................. 16 Ft. - 4.1nches

Machine Casting Speed.............. 10 - 100 Inches-Per-Minute

. Reverse Threading Speed.. .......... 10 - 150 Inches-Per-Minute

Machine Radius.. ................... 34 Ft. - 6 Inches

............. Metallurgical Lendh.. 75 Feet

Product Mix........................ Aluminum Killed Carbon Steel

Turnaround Time. .. .. ............... 45 Minutes Minimum

Ladle Control...................... 'Slide Gate

Tundish Control.. .................. Stoppers

Mold Water......................... Closed Loop - Boiler Feed Water

Spr&y Water........................ Once Through - Softened & Fil tered

Machine Water...................... Recirculated - Softened & Fil tered

Hydraulics. ........................ Phosphate Ester Fluid

Strand Roll Support Data ( ~ e i s t rand)

No. Of Roll Roll Locat ion Rolls Diameter, In. Surface Cooling

Footrol l

Aprop No. 0

Grooved None

Smooth None 11 II

Segment No. 1 10 10 Smooth Bearings Only

Segment No. 2 8 12 Smooth In te rna l !

Segment NO. 3 8

Segment No. 4 8

Segment No. 5 8

Curved (s t ra ightener) Section 11

11

Straight (withdrawal) 1 Section 21

Smooth In te rna l

Smooth In te rna l

Smooth In t e rna l

Smooth In te rna l 11 I 1

Smooth In te rna l I 1 11

, ~ , , , , . . . . . , , , , , . , , , . , .

CONTINUOUS CASTING SLAB YARD

S E R V I C E A ISLE

FURNACE TEEMING A I S L E

B.0.F B.O. F. FURNACE FURNACE

FIGURE I - GENERAL ARRANGEMENT

FIGURE 2 - ELEVATION - CASTING MACHINE

FOOT ROLLS- ZONE I 3 R T -

I I

I

FIGURE 3 - ROLL SEGMENTS 8 SPRAY ZONES

I

I I I MACHINE

FIGURE 4 - CROP REMOVAL SYSTEM

EMERGENCY SUPPLY

STEAM . TURBINE

SOFTENED a FILTERED L v Y I

I A

SUPPLY WATER

3- PUMPS 3,200 gpm EACH

3-PUMPS 3,200gpm

I --- ------- HOT STRIP MILL

CLARIFICATION SYSTEM -

SCALE PIT (20min. RETENTION)

FIGURE 6 - SPRAY WATER SYSTEM

4 -PUMPS HEAT EXCHANGER 2,100 gal. Ea.

CASTER - MACHINE COOLING *

MAKE-UP \ I ,A A*

-- -- --- - MACHINE WATER SYSTEM

3-PUMPS 3,200 gal. EACH

FIGURE 7 - MOLD S MACHINE COOLING CIRCUITS -

52

DISCUSSION

John W. Cain, General Foreman

Continuous Casting and Vacuum Degassing

Weirton Steel Division

National Steel Corporation

Weirton, West Virginia

The'cont'inuous slab caster installation at Middletown, Ohio is another example of h c o Steel Corporation's leadership in continuous casting of slabs. Not many companies can claim the diversification of continuous cast products from stainless steel slabs to fully aluminum killed cast low carbon steels for flat rolled products.

Concerning the general arrangement layout at Armco, the transfer of ladles to. the caster by either of two routes, through the degasser by track 112 or directly to the machine by track ill, improves the caster accessibility. The location of the vacuum degasser immediately over one,access route (1) could limit the function of.the degasser to caster heats and (2) could minimize its effectiveness in degassing ingot poured low carbon heats. If the amount of degassed ingot poured heats are sizable, this location of the degasser could become a bottleneck.

In the design of many casters, much effort is given to the design of the machine itself, but auxiliary equipment such as the tundish preheat systems can be poorly planned. The need to remove the preheat ,facilities from the transfer car in order to reduce maintenance due to metal splash is just one example of the lack of caster operating experience, at the time of engineering planning. In comparison, at Weirton the preheat equipment was overdesigned. In 1973 by reducing' the number of burn~rs to. preheat a tundish from four to two, we improved the efficiency of the burners, closed up two burner roof inlets, and greatly reduced the.fue1 consumption.

No mention was made of the ability to dump the tundishes after casting. Minimum machine turn-around time becomes the prereqbisite for the survival of the batch type caster in a world of continuous-continuous slab casters; therefore, reuse of a tundish eight to twelve times before skulling can improve tundish availability. At Weirton the tundishes are dumped after each heat and used again. There is no quality difference of the first slabs cast between the new and used tundishes provided they are dumped and cleaned properly.

Correct slab identification becomes essential to any successful casting operation. At the beginning of our caster, we tried to identify the slabs by a steel tagging procedure. To tag each slab required additional personnel, so a combination of hot chalking and automatic stampingby the conveyor operator gaveus the identification we needed at no extra' cost in personnel.

The l a d l e abort system a t Armco i s indeed unique. No one e l s e , to my knowledge, pours s t e e l from the o r i g i n a l l a d l e i n t o a guard l a d l e then has i t teemed i n t o ingots indexed by means of a c a r pul ler . I t i s a aood idea, but how successful ly does if work? What would be your procedure i n operat inp the guard l ad le? Is the guard lad- stopper rod o r s l idega te control led? On a l a d l e t h a t f a i l e d to' open over the c a s t e r molds, would you attempt t o bum open the s l idega te over the guard l a d l e o r would you re tu rn the l a d l e back t o the p i t f o r ingot pouring? Some newly-designed c a s t e r s a r e planning t o empty aborted l ad les i n t o a rubble p i t . I t i s good planning t o see a s incere e f f o r t , such a s Armco's approach, to save the s t e e l and teem a usable product. A t t he s t a r t , Armco's performances with l a d l e stopper rods were d i sas t rous , but your success with the l a d l e s l idega te has t o be the envy of the c a s t e r community.

Separation of the .mold water system from the machine cooling water system prevents contamination of the mold water.

The emergency water supply backup system, shows t h a t the employees ' s a f e t y w.as not forgot ten and appears t o be adequately designed. Have youhad many condit ions where you have used it and how successful ly d id it work?

A t the time you were bulldozing ou t your f i l t e r s containing the polyes ter type beads, Weirton was i n s t a l l i n g a s imi la r system using walnut s h e l l s . Your d r a s t i c so lu t ion t o your problem scared us. Our f i l t e r system has been i n opera t ion over a

1 year and with the exception of an e a r l y s t a r t u p malfunction, where we too got media i n t o the nozzles, the f i l t e r s have performed very sa t i s fac to ry .

I n conclusion, the use of wide angled spray nozzles i s a new improvement i n c a s t e r technology r e s u l t i n g i n minimum nozzle plugging,. improved s l a b cooling and l e s s maintenance.