Strand Casting II

TUESDAY MORNING, APRIL 15, 1975

The Strand Casting II session convened at 9:00 am. The chair- men were G. S. Lucenti, Algoma Steel Corporati.on, Sault Ste. Marie, Ontario, Canada, and N. L. Samways, Jones 81 Laughlin Steel Corporation, Aliquippa, Pennsylvania.

CONTINUANCE CASTER MAINTENANCE

TtIE KEY TO QUALITY AND TONS PER HOUR

H. N. Hubbard, Jr., Division Superintendent -

S t e e l Producing, Gary Works

G. W. Hodges, Ass i s t an t Superintendent - Continuous Caster , Gary Works

United S t a t e s S t e e l Corporation

The Continuous Slab Caster a t Gary began opera t ion i n Apr i l , 1967, and on Ju ly 29, 1974, the f i v e m i l l i o n ton milestone was passed. The experience gained i n operat ing t h i s machine has i d e n t i f i e d numerous problems and t h e so lu t ions ap- p l i ed have provided a broad base of t echn ica l knowledge and operat ing p r a c t i c e which w i l l be of g r e a t value in t h e design and opera t ion of f u t u r e United S t a t e s S t e e l Casters . It is our purpose here t o r e l a t e the experiences i n maintaining the f a c i l i t y , which w i l l demonstrate t h e enormous importance t h a t t h e rnaintenance function has i n a c a s t e r operat ion and the s i g n i f i c a n t improvements i n produc- t i v i t y which l a y i n t h i s a rea .

. The machine was designed and b u i l t t o provide long s l a b s of various gauges and widths f o r the new 84" Hot S t r i p M i l l , which a l s o began operat ion i n 1967. Design and operat ing parameters were es tabl i shed through operat ion of a l a r g e s c a l e p i l o t p lan t a t t h e South Works of U. S. S t e e l , and included innovations i n higher cas t ing r a t e s , unlimited sequence cas t ing c a p a b i l i t y , and in- l ine s l a b s i z ing .

One of t h e t h r e e 210-ton v e s s e l s a t Gary Works' No. 1 BOP Shop is reserved t o feed steel sequen t i a l ly t o the c a s t e r v i a one of two h o i s t bays located a t the nor th end of t h e two BOP teeming a i s l e s (Exhibit 1 ) . Two posi t ioning c a r s above t h e cas t ing line move the l a d l e s over the tundish during cas t ing . The c a s t e r has 25-ton tundishes equipped with s l i d i n g ga te systems. Drives on each of two tundish c a r s g ive t h e c a p a b i l i t y of changing tundishes during cas t ing . The production is s l a b s of t e n and under carbon steel known t o the t r ade a s USS Riband, which can be 100-percent open poured.

The machine (Exhibit 2) is a s t r a i g h t mold-type c a s t e r with a bend f o r hori- zonta l withdrawal, designed t o c a s t s l a b s 9.3-inches th ick by 55 t o 76 inches wide a t speeds up t o 76-inches per minute. There i s a 45-foot v e r t i c a l rack and curve with a 40-foot r ad ius . The t o t a l confinement is 123-feet. An in- l ine reheat furnace and seven s tand r o l l i n g m i l l reduce t h e s l ab c ross sec t ion t o a s small a s 5.25-inches th ick and 30-inches wide. The r o l l e d s l abs a r e torch c u t t o length and water cooled during t r a n s f e r t o t h e adjacent shipping f a c i l i t i e s .

History of Start-Ue

O P a a t b n a t Gary began i n April of 1967, using the 55-inch wide mold. The f i r s t heat was successfully cas t . However, succeeding hea t s brought t o l i g h t a problem comaon t o a l l continuous-contlnuous ca s t e r s , t ha t of pos i t ive l a d l e open- ing and ladle-stream control . It was desi rable t o use the same l a d l e f o r teeming ingots a s was used fo r the ca s t e r , therefore , exot ic r e f r ac to r i e s and air-cooled rods were avoided. The teeming l a d l e rigging had t o be redesigned f o r more s ta- b i l i t y and an eight-inch stopper head and sleeves used. The w e l l was t o be six- inches deep with a 45' s i de slope, and a template was developed t o insure proper configuration. A complete maintenance check l is t was made, covering a l l points of l a d l e make-up t o cross check workmanship. Final ly , a shoe hook was hung from a service crane in t h e cas t ing tower t ha t could be swung over the r igging gooseneck adjacent t o the plunger, which could p u l l the stopper open a s a l a s t r e so r t . This proved t o be invaluable i n years t o come and several runs of between 1800 and 2000 hea t s without a f a i l u r e t o open have been made.

I n a matter of weeks, the c a s t e r ' s t a r t e d t o .put together the f i r s t continuous heat run and a s e l e c t r i c a l problems were corrected and the bugs worked out of the tundish s l i d ing ga te system, continwua runs were lengthened r a i s i ng the average heats per s t rand s t a r t t o three a f t e r four months of operation (Exhibit 3) . It became evident t ha t getking t h e c a e t e r s t a r t ed .was the most c r i t i c a l p a r t of the operation and was the most l i k e l y period f o r damage t o the mechanical e q u i p e n t i n the l i n e . The most ser ious problem found i n t h i s e a r l y period of operation w a s the containment-roll c l u s t e r design, which included back-up r o l l s throughout the l i n e (Exhibit 4).

During the f i r s t two years of operation, attempts were made t o u t i l i z e the 76- inch mold, but the bearing and r o l l f a i l u r e s , experienced with the 55-inch s lab , dccurred in cas t ing the 76-inch s l a b with increased frequency. Maintaining pro- duction thus d ic ta ted r e i n s t a l l a t i o n of the more dependable 55-inch mold. It was evident t ha t the wider s l ab and high cas t ing r a t e s found the weak points of the niachine very quickly.

In 1969, the e n t i r e curved rack and switch sec t ion was redesigned t o el iminate back-up r o l l s , permitting replacement with l a rger diameter r o l l s , spaced t o mini- mize rol l - to-rol l bulging of the s lab . Immediately, the average tonnage per month jumped from 30,000 t o 65,000 tons (Exhibit 5) and the average hea t s per strand s t a r t went from three t o seven.

Maintenance Hours Analysis

It became apparent that the containment and withdrawal r o l l requirements of the cas te r , with the 85-foot f e r r o s t a t i c head, ca l l ed f o r a number of changes i n de- s ign and maintenance t o achieve improvements ln r e l i a b i l i t y and productivi ty. Therefore, an analys is was made of the equipment which caused the majori ty of the maintenance hours during a repa i r turn (Exhibit 6). It should be noted t h a t these a r e not man hours, but maintenance hours, without adjustment f o r t o t a l p lan t schedule f luc tua t ions , and were developed on the bas i s of an average number of operating turns per week of 12.2 i n 1970 which l e f t 8.8 turns , o r 70.4 hours per week f o r maintenance. For comparative purposes, t h i s was converted t o r epa i r turn hours per heat cas t . The analys is indicated t ha t three areas , the f ixed curve, the v e r t i c a l rack and the torch carr iage accounted fo r the major por t ions of the maintenance work t o ' b e performed during the down turn.

Even a f t e r redesigning, the f ixed curve rack required .97 hours of mainten- ance per heat c a s t which w a s t he f u l l down turn every week. The problem continued t o be both bearings and r o l l s . A program of upgrading of bearing design and changes in both r o l l ma te r i a l and r o l l su r face preparat ion were expedited, and gradual improvement was achieved. In add i t ion , r o l l gapping tolerances were tightened t o p lus o r minus .020 inches. I t was found t h a t r o l l s out of gap be- cause of bad bearings o r l o s t shims caused premature f a i l u r e s i n both up and down stream adjacent c l u s t e r s . Currently, every time t h e c a s t e r terminates both main- tenance and operat ing management inrmediately inspect t h e l i n e . Problem a reas a r e a l s o i d e n t i f i e d before termination by comparing i n t e r n a l q u a l i t y versus l i n e speed. For example, t o t a l s o l i d i f i c a t i o n i n t h e s l a b is ca lcula ted t o be 20 minutes be- low the mold, therefore , a t a cas t ing speed of 50-inches per minute, l i q u i d core would extend 83-feet below the mold. Problem c l u s t e r s above 83-feet could cause ghost l i n e s . The proximity of such ghost l i n e s t o t h e s l a b surface determines where, i n the l i n e , t h e problem l i e s . Problems imnediately below 83-feet could cause mid-thickness cracks and aggravate center l i n e segregation. A s speed v a r i e s , these condit ions appear and disappear with the end of l i q u i d core moving i n and ou t of the bad c l u s t e r . In t h e absence of s p e c i f i c problems i n t h e l i n e , main- tenance regaps sec t ions on a preventive r o t a t i o n bas i s . The n e t r e s u l t of these programs has been a reduction of maintenance hours per heat c a s t from .97 i n 1970 t o .25 f o r t h e f i r s t six months of 1974.

The v e r t i c a l rack is a l s o a prime example of both redesigning and preventive maintenance. This a r e a a l s o required t h e f u l l down tu rn time f o r maintenance i n 1970. The backup r o l l s were removed from t h e c l u s t e r s i n 1972 and t h e same gap- ping program was i n s t i t u t e d a s i n the curved rack. This reduced t h e maintenance hours per heat c a s t from .97 i n 1970 t o .21 i n 1974. It is extremely important t h a t gap i n t h i s a rea be maintained t o p lus o r minus .020 inches.

The torch ca r r i age showed the most s i g n i f i c a n t improvement wi th a maintenance hours per heat c a s t reduction of from .97 t o -01. The problem was primari ly i n design o f - t h e d r ives and the re-designed equipment r equ i res only preventive maintenance.

The switch s e c t i o n required .68-hours per heat c a s t and s imi la r programs i n r o l l ma te r i a l , bearings and gapping reduced t h i s t o .18 hours per heat c a s t .

The furnace problem was.mainly burner coolers , furnace r o l l s and s c a l e re- mdval. Correction of these items reduced the maintenance hours per heat from .59 i n 1970 t o .13 i n 1974.

The pinch r o l l s were not redesigned. However, replacement of ex i s t ing r o l l s with USS Homestead-X steel work r o l l s , b e t t e r backup bear ings and an improved l u b r i c a t i o n system, reduced maintenance requirements from .45 t o .06 hours per heat c a s t . I n add i t ion , t h e pinch r o l l s a r e on a scheduled maintenance program where they a r e i n t e r n a l l y adjusted every 300,000 tons and replaced every 1,000,000 tons. This has el iminated .premature f a i l u r e s completely.

The t r a n s f e r bed requ i res a regular skid and dog replacement program which reduces major unscheduled breakdowns and t h e h o i s t s and t r a n s f e r c a r s a l s o re- ce ive preventive maintenance s u c h a s cleaning contac ts , l i m i t switches, lub r i - ca t ion , etc. The main improvement i n these a r e a s is t h a t r e p a i r work is done on a scheduled b a s i s and does n o t i n t e r f e r e with t h e operat ion of t h e c a s t e r .

The bend s e c t i o n improvment involved b e t t e r bearings and l u b r i c a t i o n systems. A preventive maintenance program of cleaning and p r e c i s e alignment has extended t h e average l i f e of t h i a component t o 800,000 tons between changes. The .03 maintenance

hours per heat c a s t genera l ly involves the changing of t h e bottom outs ide r o l l which i s sub jec t t o heavy loads from cold head ends and cap o f f s .

Rolling M i l l r e p a i r hours exclude r o l l changes which have no t been a l imi t ing f a c t o r due t o exce l l en t r o l l l i f e , and the r e p a i r hours a r e general ly associated with e l e c t r i c a l problems. This i s a very c r i t i c a l piece of equipment because a m i l l stoppage can r e s u l t i n cobbles i n the m i l l - o r furnace and the p o s s i b i l i t y of a s tuck s l a b i n the l i n e . A preventive maintenance team, including supp l ie r se rv ice personnel, was es tabl ished to provide an e lec t r i ca l -e lec t ron ic i n t e r f a c e maintenance program. This team, which is a combination of an experienced elec- t r i c a l craftsman, an e l e c t r o n i c s p e c i a l i s t and an e l e c t r i c a l engineer t r a inee , has become invaluable during dovn turns f o r preventive maintenance and trouble shooting e l e c t r i c a l problems.

The mold o s c i l l a t o r l i f e is 800,000 tons , a f t e r which cams and cam followers must be replaced o r surface q u a l i t y w i l l be adversely af fec ted . Ef fec t ive main- tenance of the o s c i l l a t o r , including cam lubr ica t ion and c lean l iness , i s of the utmost importance t o high productivi ty and defect f r e e s l abs .

The frequency of breakouts has shown a reverse t r end , jumping from .04 t o

I .09 hours per heat cas t . This represents an increase i n breakout frequency from 0.52% i n 1970 t o 1.22% i n the f i r s t ha l f of 1974. This increase is pr imar i ly a t t r i b u t e d t o raw mate r i a l and associated BOP problems, and the trend has been reversed through improvements i n these areas . The 1974 year ly t o t a l was 0.72% of hea t s c a s t .

Using these analyses and a systematic approach t o problem solving, redesign and preventive maintenance, the average a c t u a l operating turns per week has in- creased from 12.2 i n 1970 t o 15.1 during the f i r s t s i x months of 1974. Scheduled tu rns were approximately t h e same i n both periods.

Continuous-Continuous Operation

I n conjunction wi th more ava i l ab le operat ing hours, it was necessary t o in- crease t h e production r a t e . This could be done i n two ways, increasing t h e speed o r increasing the average length of the continuous-continuous runs. Several a t - tempts were made t o increase the average speed but t h e f l e x i b i l i t y t o compensate f o r furnace timing, temperature va r ia t ions , and off-analysis hea t s was s u f f i c i e n t l y reduced t h a t an increase i n breakout frequency resu l t ed . Higher cas t ing speeds a l s o increased i n t e r n a l problems, when the line was not i n good condit ion.

The advantage of continuous-cdntinuous cas t ing i s demonstrated by i t s e f f e c t on c a s t e r productivi ty. The maximum increase i n annual tonnage of a continuous cas- ter occurs between a s i n g l e heat c a s t and ten hea t s c a s t per s t rand s t a r t (Exhibit 7). For example, the p l o t of average number of hea t s per s t rand s t a r t versus an- nual production f o r a s i n g l e s t rand s l a b c a s t e r wi th a 210-ton hea t s i z e , a f i f t y minute heat time and an average t u r n around time between c a s t s of one hour and f o r t y minutes denoted by curve "A" can increase i ts annual capaci ty by over 600,000 tons by cas t ing t e n heat s t r i n g s . From ten heats t o twenty heat s t r i n g s the pick up t o tonnage i s 150,000 tons. Curve "B" represents the same c a s t e r with t h e heat time reduced t o f o r t y minutes. I n this case , an annual increase in tonnage of over 1,000,000 tons is rea l i zed between one and t e n sequent ia l hea t s per s t r and-s ta r t . Both curves "A" and "B" represent f i f t y weeks per year and nineteen turns per week operation. Any new c a s t e r should be designed t o continuous-continuous c a s t a mini- mum of ten hea t s cycles , i f steel production is ava i l ab le and the t o t a l p lan t balance permits .

I n 1969 and 1970, e v e r y c a s t i n g c y c l e was s t a r t e d w i t h a t u n d i s h c a p a b l e o f c a s t i n g f o u r t e e n h e a t s . The average h e a t s p e r s t r a n d s t a r t was a c t u a l l y 7.9. I n o r d e r t o a t t a i n t h e t e n h e a t s p e r s t r a n d start , i t was n e c e s s a r y t o develop equipment t o s c h e d u l e a t l e a s t twenty h e a t s p e r s t r a n d start . T h i s was ach ieved d u r i n g 1971 and 1972.

T h i s approach l e d t o t h e n e x t s t u d y , which was t o a n a l y z e t h e r e a s o n s f o r i n t e r r u p t i o n s of c a s t i n g r u n s shown i n E x h i b i t 8. The r e a s o n s f o r t e r m i n a t i o n o f a c o n t i n u o u s . r u n were a s s i g n e d r e s p o n s i b i l i t y between BOP f u r n a c e and l a d l e , and f o r c a s t e r equipment, q u a l i t y and b r e a k o u t s f o r t h e c a s t e r . For example, 2.6 h e a t s o u t of e v e r y 100 h e a t s c a s t i n 1971 r e s u l t e d i n t e r m i n a t i o n s o f c o n s e c u t i v e r u n s because of BOP f u r n a c e r e s p o n s i b i l i t y . These f u r n a c e pro- blems r e s u l t e d from a number of r e a s o n s , such a s too h o t , l a t e , s c r a p c h a r g e r down, e t c . The l a d l e was r e s p o n s i b l e f o r 1.2% which b r i n g s t h e t o t a l BOP res- p o n s i b i l i t y t o 3.82 i n 1971 and t h e t r e n d shows improvement each y e a r t o 2.8% i n 1974. Terminat ion r e s p o n s i b i l i t y f o r t h e c a s t e r , i f s i m i l a r l y broken down between equipment, q u a l i t y and b r e a k o u t s , shows a n over a l l r e d u c t i o n . However, s i n c e t h i s paper i s devoted t o maintenance o f t h e c a s t e r , we w i l l examine o n l y t h a t pe rcen tage which i n v o l v e s c a s t e r equipment ( E x h i b i t 9 ) .

The breakdown of c a s t i n g equipment shows t h e s l i d e g a t e svstem t o be r e s - p o n s i b l e f o r 1.1 t e r m i n a t i o n s f o r every 100 h e a t s c a s t . T h i s 1.1 r e p r e s e n t s 36 t e r m i n a t e d r u n s i n 1971. A s t h e con t inuous runs became l o n g e r , t h e i n c r e a s e i n exposure t ime of t h e s l i d e g a t e sys tem t o t h e r a d i a t i o n o f the. l i q u i d s t e e l i n tile mold caused numerous problems. A program w a s developed i n c o n j u n c t i o n w i t h t h e s u p p l i e r t o improve t h e r e l i a b i l i t y of t h e system w i t h h e a v i e r s l i d e s and s p r i n g s , however, t h e major c a u s e o f f a i l u r e s could b e t r a c e d ' b a c k t o maintenance workmanship. A s p e c i a l check l ist was developed t h a t . h a d t o be s i g n e d by t h e m i l l w r i g h t making t h e checks d u r i n g assembly. A l l f a c t o r s of a g a t e f a i l u r e were i n v e s t i g a t e d l i k e a s e r i o u s a c c i d e n t and a formal r e p o r t p repared . The n e t r e s u l t was. a d e c r e a s e ' i n t e r m i n a t i o n s t o .55: i n 1974, r e p r e s e n t i n g o n l y 1 3 t e r m i n a t i o n s f o r t h e six-month p e r i o d .

The second most f r e q u e n t r e a s o n f o r premature t e r m i n a t i o n s which accounted f o r .3% of h e a t s c a s t , o r e l e v e n o c c u r r e n c e s i n 1971, was t u n d i s h problems. Th is was p r i m a r i l y a s s o c i a t e d w i t h premature l i n i n g f a i l u r e . F a i l u r e s oc- c u r r e d i n t h e pour pad a r e a due t o t h e c o n s t a n t impingement of t h e s t e e l s t r eam on t h e pour b lock which l i t e r a l l y d r i l l e d a h o l e i n t h e pour pad. The pad i s now c o n s t r u c t e d o f a n 18"xl8"x9" deep b lock of Alumina-Chromia pre- f i r e d b r i c k . T h i s material w i t h s t a n d s s t ream e r o s i o n much b e t t e r than t h e 90% alumina b lock used p r e v i o u s l y , however, we do n o t r e c o m e n t t h i s m a t e r i a l f o r b a t c h c a s t e r s because of s p a l l i n g c h a r a c t i s t i c s dur ing c o o l i n g and h e a t i n g The i n c r e a s e d i n c i d e n c e of t u n d i s h i n 1972 and 1973 cor responds t o a t t e m p t s t o i n c r e a s e t u n d i s h l i f e t o 30 h e a t s . T h i s problem r e s o l v e d i t s e l f i n t h e l a t t e r p a r t of 1972 when t h e f i r s t t u n d i s h was changed dur ing c a s t i n g , e l i m i n a t i n g t u n d i s h l i f e as a l i m i t i n g f a c t o r .

The t h i r d most f r e q u e n t c a u s e of t e r m i n a t i o n s was t h e t o r c h c a r r i a g e . Th is p i e c e of equipment a l s o showed poor performance i n t h e maintenance s t u d y . Redesign of t h i s equipment reduced t h e f requency o f .2% of h e a t s c a s t t o none.

The Rolling M i l l accounted fo r eight terminations in 1911 which was .2X of heats cas t . These were largely e l e c t r i c a l problems and were corrected by a pre- vemtive maintenance program on e l e c t r i c a l contactors and control adjustment every week. Hydraulics were very l i t t le problem a f t e r the i n i t i a l leaks were corrected. This program eliminated mill-caused terminations fo r the l a s t two years.

Pinch r o l l t ewlna t ions were mostly associated with broken r o l l s and bad bearings. With the improvements previously discussed and scheduled replacement, premature f a i l u r e s ceased t o be a problem.

The t ransfe r bed caused terminations when s labs could not be cooled and had t o be run.out hot where handling became a serious problem. Strengthening of the s t ruc ture a t both '&try and exit ends, p lus addi t ional e l e c t r i c a l s a f e guards have resulted. in t h e indicated improvement.

In 1972 furnace and ho is t problems c r ea t ed \ the i r share of terminations, a l l of which were corrected with increased emphasis on preventive maintenance.

Miscellaneous terminations consis t of disconnect f a i l u r e s , t o t a l power f a i l u r e s , water problems, bleeders, man re la ted problems, e t c . The program de- 1 creased the t o t a l percent of terminations per heat ca s t from 2.6 t o 1.2 from

1 1971 to 1974. The log of reasons fo r terminations is kept up current ly on a I dai ly bas i s and is used t o pinpoint problem areas a s they develop, and t o sche-

dule maintenance work on down turns.

During 1972, the subject of BOP furnace cornpatability with the continuous cas te r became a grea t concern. The 55-inch mold, then in use, slowed down the output of the BOP because of the 564ninute pour-time required t o feed the caeter .

I The 76-inch mold was even worse because the pour-time of 38-minutes necess i ta ted the use of two furnaces to feed the cas te r . Development of an intermediate mold s i z e was c lear ly indicated and the present standard 9 .3~64 inch mold was the re- s u l t . Early f ea r s of the i n a b i l i t y to r o l l the very narrow production from the 64-inch a s ca s t s lab were not realized and the casting r a t e fo r the 64-inch mold was a perfect match fo r one BOP furnace output a t Gary.

Two t r i a l production periods were scheduled and the experience gained was used in mold development and redesigning of r o l l s and bearing arrangements. The r o l l s i n the area of t he greates t f a i l u r e frequencies w e r e shortened by one foo t , decreasing both r o l l def lect ion and the range of s e l f alignment needed i n the bearing s e t s . The replacement of the longer r o l l s is progressing on an a s nece- ssary bas i s and maintenahce requirement decreases a r e continuing.

The average number of heats per strand s t a r t s tead i ly improved through 1972. The r e a l break through f o r Gary's Caster occurred on October 18, 1972, when the f i r s t tundish change was made without in terrupt ion of the casting s t r i ng . The technique requires precise coordination and control because the ro l l ing m i l l must adjust fo r each change i n casting r a t e , and the m i l l control cannot be maintained i f the casting l i n e stops. Therefore, the speed i s gradually reduced to five- inches per minute by a s e r i e s of tundish s l i d e ga te changes u n t i l the f i n a l shut off is made with a f u l l mold. The f i ve inches per minute is maintained i n both cas te r and m i l l f o r approximately t h i r t y seconds u n t i l the tundishes a r e switched and casting continues. The elapsed time of the interrupt ion of s t e e l flow in to the mold is usually l e s s than f i f t e e n seconds.

With t h i s new procedure the only l imi t ing f a c t o r t o cas t ing i n d e f i n i t l y is mold l i f e . f n December, 1972, United S t a t e s S t e e l , Gary Works nearly doubled the previous world's record f o r a s i n g l e s t rand s l a b c a s t e r by continuously cas t ing 22,391 n e t tons of steel in one s t r i n g , The s t r i n g consisted of 107 heats , c a s t over 82 hours and 15 minutes and was f i n a l l y terminated by a cold heat . On June 23, 1973, the 124 hea t s were c a s t f o r 26,276 tons i n 99-hours and two minutes and on December 19, 1973, the c a s t e r shat tered i ts previous record by continuous- continuous cas t ing 132 hea t s , o r 27,983 n e t tons during an 108-hour and twenty- f i v e minute period (Exhibit 10). The c a s t e r output approximated 5.2 m i l e s of c a s t s l a b which, a f t e r in- l ine r o l l i n g , produced 48,300 f e e t , o r 9 . 1 m i l e s of s ized s l abs . Thirty-eight d i f f e r e n t sec t ion changes were made producing 1,208 s l a b s 4O-feet long. Seventy-nine s l i d e g a t e nozzle changes were made and t h e through put during the run was 258.3 tons pe r b u r o

Many b e n e f i t s were derived from the tundish changing capabi l i ty . The number of h e a t s per s t rand s t a r t jumped from an average of eleven t o an average of 16. The average monthly production jumped up over 90,000 tons. The fewer terminations and s t a r t ups resu l t ed in a s i g n i f i c a n t reduction of in r o l l and bearing damage. The philosphy t h a t cold head ends in start ups and t a i l ends i n terminations do most of t h e damage t o cas t ing l i n e s is t rue . The expected l i f e of the various segments of the l i n e improved. For asample, t h e bend sect ion, which had an average l i f e of 500,000 tons of steel c a s t , has, i n t h e l a s t two replacements, l a s t e d over 800,000 tons. The colicept of s t a r t i n g the c a s t e r up Monday morning and running continuously u n t i l Friday e i g h t was now a p o s s i b i l i t y .

Caster U t i l i z a t i o n

'6he object ive of t h e maintenance improvement progrrnns and extended cas t ing s t r i n g s a r e increased product iv i ty and caetao u t i l i z a t i o n , The latter r e f e r s t o a very important s t a t i s t i c which i r s t h e percent of time t h a t l i q u i d steel i s ac tua l ly i n the mold. Exhibit 11 shows the r e l a t i v e posi t ions of severa l Ameri- can Slab Casters f o r 1973 based on AfSf repor ts . The emphasis on continuous- continuous operat ion pays o f f handsomely f%a u t i l i z a t i o n of a s i n g l e s t rand machine and the p o t e n t i a l of t h e same continuous-conthuoum operat ion of independent multi-strand machinee is unl imited,

The in ten t ion of cas t ing unt i l something breaks a l s o presents a d i f f e r e n t challenge t o t h e maintenance man becaure every c a s t e r or iented termination w i l l e i t h e r d i r e c t l y o r i n d i r e c t l y be h i s r e spons ib i l i ty . H e must approach each re- p a i r o r replacement with the a t t i t u d e that he cannot re-repair o r make adjust- f

mente f o r 20,000 t o 30,000 tone. The eechedding of all major jobs i n t o a l imi ted down period and coordination of the jobs on mul t ip le e levat ions is no s m a l l task. For t h i s reason, the preoent emphasis is upon improving maintenance h o i s t s , ex- t r a c t i o n of r o l l c l u s t e r s , ease of gapping, etc. The number of turns required t o make rou t ine replacements, r a t h e r than t o patch u p . f a i l u r e s , has become t h e l i m i t - ing fac to r .

The major problem confronting the Gary- Caster today is the del ivery of steel a t t h e proper time, temperature and analysfe t o the cas t ing machine. Problems with substandard raw materials, both i n the BOP and Blas t Furnace, have eeriouely a f fec ted BOP turn down performances, Varisue program of ecrap eegregation, hot metal desu l fu r iza t i sn and s u i n g are ia e f f e c t cu r ren t ly t o minimize these problems.

It has been our purpose t o emphasize the importance of e f f e c t i v e maintanance prsgrame t o t h e continued Improvement i n product iv i ty of the Gary Caster, and to d e t a i l t h e approaches and methods ueed a d t b rerulte obtained. The ryr tamat ic

' e l i m i n a t i o n , t o t h e ex t en t p o s s i b l e , o f r e c u r r e n t , product ion-l imit ing equipment f a i l u r e s and the ex tens ion of normal l i f e , through redes ign , of machine component: has been undertaken whi le maintaining product ion a t a h igh level.

The unique n a t u r e of t h e f a c i l i t y made s o l u t i o n of some of t h e problems t ed ious and expensive, and t h e r e was no way t o eva lua t e much of t h e redesigned equipment o t h e r than t o i n s t a l l i t and run i t , no t ing shortcomings and c o r r e c t i n g as ind ica t ed . A l l opera t ing and most of the planned c a s t e r s i n e x i s t e n c e were v i s i t e d and t h e comparison of methods has never ceased.

The previous ly mentioned p i l o t p l a n t was operated u n t i l 1971, and methods anc m a t e r i a l s t r i a l s t h e r e were inva luab le , a s were t h e exhaus t ive rests and t r i a l s run in t h e Applied Research Laboratory of United S t a t e s S t e e l a t Monroeville, Pennsylvania. The importance of t h e engineering work I3yolved i n t h e redes ign and new equipment cannot be over-emphasized.

The p a r t i c i p a t i o n of a l l s t a f f and s e r v i c e groups on t h e Gary Works team can a l s o be c l a s s i f i e d a s unique. Each group - from Medical t o Metal lurgy - has con t r ibu ted t o a t t a i n i n g and maintaining t h e c u r r e n t l e v e l s of r e l i a b i l i t y and q u a l i t y , and continued p a r t i c i p a t i o n w i l l r e s u l t i n f u r t h e r improvement. The p r i d e i n any record performance by t h e c a s t e r is genuinely r e f l e c t e d p l a n t wide.

The most s i g n i f i c a n t c o n t r i b u t i o n s t o t h e success of t h e ope ra t ion have come from t h e crews themselves - t h e opera t ing and maintenance men and t h e f r o n t - l i n e superv isors . A s a group, they adopted a can-do a t t i t u d e very e a r l y i n t h e start- up and through t h e y e a r s have implemented t h e changes and pe r f ec t ed r ev i sed methods wi th eagerness. While many have p a r t i c i p a t e d i n and been rewarded through t h e Employee Suggestion P lan , many i d e a s have simply evolved and proven succes s fu l .

The Gary Machine was t h e f i r s t of a k ind , i n both t h e equipment provided f o r continuous-continuous c a s t i n g and in t h e in - l i ne r o l l i n g f a c i l i t i e s . The des ign speeds and l eng th of runs equated t o a tons-per hour c a p a b i l i t y which was f a r i n excess of most e x i s t i n g machines, on a pe r s t r a n d b a s i s , and t h e very e a r l y successes i n t h e ope ra t ion proved many of t h e t h e o r i e s regard ing non-stop c a s t i n g were v a l i d . The one cons is tency i n a l l t h e problems was t h a t a systematic and d e t a i l e d a n a l y s i s was r equ i r ed i f any improvement was t o be made. Quick and p a r t i a l remedies changed t h i n g s , b u t o f t e n f o r t h e worse, and some s h o r t c u t s t o g e t a machine back in ope ra t ion quick ly were d i s a s t r o u s . Any high product ion c a s t e r must be designed and b u i l t w i th maintenance e f f i c i e n c y as a primary parameter.

t.4 t.4 ul

EHEATING f URNACE

C O N T I N U O U S C A S T E 7

SCHEMATIC OF PRINCIPLE OPERATING COMPONENTS

LADLE HOIST TROLLEY 1 A LADLE P0SITK)NING CARS

Exhibit 1

CURRENT CASTING LINE

0 4 DRIVEN ROLLS

DISCHARGE SECTION

VERTICAL RACK

Exhibit 2

AVERAGE NUMBER OF HEATS PER STRAND START -1

Exhibit 3

ORIGINAL CASTING LINE

0- DRIVEN ROLLS

VERTICAL RACK

P I N C H ROLLS

Exhibit 4

AVERAGE TONS OF SLABS PRODUCED BW MONTH

Exhibit 5 , '

DOWN TURN REPAIR HOURS PER HEAT CAST YEAR OF 1970 VERSUS FIRST SIX MWM OF 1974

Exhibit 6

TONNAGE EFFECT OF CONTINUOUS-CONIINUOUS CASTINC

APPROXIMATE ANNUAL PRODUCTION (MILLION TONS)

CURVE "A" 50 MINUTE HEAT TIME AND 50 WEEK OPERATION

CURVE "B" 40 MINUTE HEAT TlME AND 50 WEEK OPERATION

Exhibit 7

TERMINATIONS BY CAUSE - PERCENT OF HEATS CAST YEARS OF 1971, 1972, 1973 AND F I R S T S I X MONTHS OF 1974

Exhibit 8

REASON

BOP FURNACE

BOP LADLE

TOTAL BOP

CASTER EQUIPMENT

CASTER QUALITY

CASTER BREAK -OUTS

TOTAL CASTER

TOTAL BOP AND CASTER

DETAIL OF TERMINATIONS CAUSED BY CASTER EQUIPMENT - PERCENT OF HEATS CAST YEARS O F 1971, 1972, 1973 AND F I R S T S I X MONTHS OF 1974

Exhibit 9

PERCENT OF HEATS CAST

TORCH AND CARRIAGE

PINCH ROLLS

TRANSFER BED

197 1

2.6

1.2

3.8

2.6

01

.7

3.4

7.2

1972

2.7 .

-8

3.5

2 06

03

lo1

4.0

7.5

1973

2 -0

.8

2.8 -

1 e7

.2

l 9

2 8

5.6

1st. 6 MONTHS 1974

2 -0

l 8

2 e8

1.2

-2

1 -2

2.6

5.4

,WORLD RECORD SINGLE STRAND CONTINUOUS-CONTINUOUS SLAB CASTING CYCLE

DATES - DECEMBER 14, 15, 16, 17, 18, 19, 1973

TOTAL TIME STEEL IN THE MOLD - 108 HOURS, 25 MINUTES

FEET CAST - 27,434 (5 .2 MILES))

HEATS CAST - 132

TONS CAST - 27,983

TUNDISHES USED - 8 (7 CHANGES)

NOZZLE CHANGES - . SECTION CHANGES -

FEET ROLLED - 48,300 (9 .1 MILES)

TOMS PER HOUR - 258.3

NUHBER OF 40 FOOT SLABS - 1.208

Exhibit 10

COMPARISON OF UTILIZATION OF CONTINUOUS SLAB CASTERS IN THE UNITED STATES

Exhibit 71