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Continuous Casting at Appleby-Frodingham

By R. Johnson*

SUMMARY

This paper describes the Continuous Casting Plant commissioned in July 1962 a t Appleby-Frodingham Steel Co., Scunthorpe, Lincolnshire. andmuch of the information has been published in the Journal of the Iron & Steel Institute of Great Bri ta in- March 1963 - in a paper prepared jointly by R. Johnson, J. W. Middleton, and D. Ford.

The plant is described in detail. and also the operation with particular reference to steelmaking practice, temperature control, casting operation including precas t preparation and manning with special reference to the duties of the operators. Plant performance is described with reference to output. stoppages, refractor ies and mold performance. Safety and training a r e described briefly and reference is made to the quality of products both before and af ter mechanical work.

INTRODUCTION

In Sept. 1960 the Appleby-Frodingham Steel Co., Branch of the United Steel Companies Ltd., announced a new development scheme a t i t s Scunthorpe Works. This was to provide for the production of rods and b a r s in a 4-strand rod mill with an annual capacity of 350,000 tons. In o rder to provide the additional ingot capacity extra facilities were required to increase the annual ironmaking and steelmaking capacities to 2.0 x l o6 and 1.9 x lo6 tons respectively.

The Rod and B a r Mill was to be designed to receive 9-in. x 9-in. blooms, these being rolled into 2i- in . by 3-in. billets for subsequent rolling into rod and bar .

An existing 42-in. Cogging Mill currently providing blooms for a cross- country 3-strand 32-in. mill was able to provide only 100,000 tons p e r y r of 9-in. blooms for the Rod Mill, and accordingly, facilities were required to provide a further 250,000 tons p e r y r of 9-in. x 9-in. blooms. It was decided to install a 4-strand Continuous Casting Machine for this purpose, and design work commenced in Dec. 1960.

To achieve the rated capacity of 5000 tons per week it was agreed that a 4-strand machine using a 90-ton ladle casting a t average speeds of 48 ipm was required. This permitted a casting t ime of 45 to 55 min. and with a 3-hr cycle. t ime provided the quantity of blooms required.

The machine was designed jointly by Distington Engineering Co. and Appleby-Frodingham Steel Co., and was built and erected by Distington

*Works Manager, Melting Shops, Appleby-Frodingham Steel Co.. Scunthorpe, England.

1

2 Open Hearth Proceedings 1964

Engineering Co., who a r e the United Kingdom licencees for Concast A.G. Zurich.

Civil engineering work commenced in April 1961, and the f i r s t cast was produced July 16, 1962.

PLANT DESCRIPTION

The Plant i s situated in one of the Company's two open hearth shops, and s teel is delivered to the machine in 90-ton ladles from one of five Ajax oxygen tilting open hearth furnaces. It is built alongside the Appleby Melting Shop Casting Pi t in a building 137 ft long and 37 ft wide served by a 15-ton crane. The machine is designed to cast simultaneously 4 s t rands of 9-in. sq. blooms, which a r e normally cut to a length of 24 ft 6 in.. weighing approximately 3 tons each. The machine is constructed a s 2 duplicate 2-strand machines (A and B) served by a common ladle and tundish. In the event of a failure in operation on one machine, casting can continue until the ladle is emptied o r until the temperature falls to a level where casting is no longer possible.

The casting machine extends below ground in a concrete pit 83 ft deep and of cross-section 63 ft x 25 f t a t ground level. There a r e s ix floors served by an electrically operated passenger/goods lift and by the 15-ton crane. The blooms a r e conveyed to ground level by an inclined chain conveyor where they a r e t ransferred to wagons by means of an overhead tu r re t crane.

All e lectr ical equipment is installed in a substation beneath ground level immediately under the bloom storage gantry.

Communication throughout the plant. including cranes, is by a broadcast system.

Forced ventilation equipment is provided in the underground substation while vapor extraction equipment is housed in the roof of the main building.

Fig 1-Cross-sectional layout of the casting machine.

Continuous Casting at Appleby-Frodingham 3

The general layout of the machine is shown in Fig 1 and a description of each section follows:

Design Characteristics

Number of s t rands Bloom s ize Bloom length - max.

- min. Machine speed Casting speed Ladle capacity Tundish capacity

4 9 in. x 9 in. 24 ft 6 in. 12 ft 0 in. 3.6 72 ipm Max. 60 ipm for 24 ft 6 in. lengths 90 to 95 tons lip pour 4 to 5 tons

Control Pulpit and Instruments

Control Pulpit

The whole of the casting operation (described later) is directed from the control pulpit by the machine operator. P r i o r to casting, it is essential that

Fig 2-Main control desk.


all preset controls a re checked in conjunction with each item of plant. The machine operator i s responsible for their precasting procedure and also for control during casting. Fig 2.

The instruments and controls a re a s follows:

Preset Controls

a) Main Control Desk

1. Mold speed setting rheostat 2. Inching controls (lower and raise) 3. Pre-set cast speed 4. Dummy bar removal selection (Cancel/Neutral/Auto) 5. Mold lubrication 6. Cooling spray by-pass 7. Mold water

b) Water Panel

1. Water pumps for overhead tank levels 2. Emergency header tank release 3. Cooler booster pumps 4. Cut-off Station pumps (Water curtain, drainage) 5. Regulating valves

c) Auxiliaries Panel

1. Machine alarms (A and B) 2. Spray fans exhaust seal (A and B) 3. Basket hydraulics (A and B) 4. Tilt table hydraulics (A and B) 5. Ladle tilt slow 6. Ladle tilt fast 7. Tundish heat a i r fan 8. Stand-by mold lubrication 9. Machine lubrication

10. General ventilation (2)

Casting Cor~trols

1. Ladle tilt alarm 2. Mold water ( A and B machines) 3. Spray water (A and B machines) 4. Casting speeds (A and B machines) 5. Cooler fans

Instruments

An enclosed instrument panel records the following data:

1. Total water flow to each mold, gpm

Continuous Casting at Appleby- Frodingham 5

2. Total water flow to each spray curtain, gpm 3. Water temperature at:

Molds Sprays Rolls

4. Casting speeds 5. Coke oven gas flow 6. Metal temperatures (ladle top and tundish) 7. Water p ressures

Transfer Carriage

A raised s teel s t ructure extends from the plant into the casting bay. This supports a t ransfer carr iage which conveys the ladle of s teel to the appropriate position on the plant for temperature measurement, lid fitting, and finally tilting.

Ladle and Lid

The 95-ton capacity ladle can be filled from any one of the five Ajax tilting furnaces and is car r ied to the plant by existing casting bay cranes.

The mer i t s of bottom and lip pouring were carefully considered before finalizing on a siphon-type ladle. The inability to quickly return the ladle to the casting pit in the event of a stopper failure made i t necessary in the interest of safety and for practical purposes, to use a tilting ladle. (Fig 3). By this arrangement metal is drawn from the bottom par t of the ladle, and

Cokt Ovtn

90 TON LADLE

Fig 3-Continuous casting ladle.


except for the f i rs t f lushof s laga t the s ta r t of pour, the metal s t ream remains f ree of s lag during casting. Ladles for continuous casting a r e lined with the s a m e type of firebrick (42 pct A1,0,) a s the Casting P i t ladles, special shapes a r e avoided and no insulating br icks a r e used. The working lining of 42 pct A1,0, firebrick is 45 in. thick for the bottom two thirds and 3 in. thick for the top one third. It is backed by a 2-in. safety lining of 38 pct A1,0, firebrick, and the ladle bottom is 9 in. thick. The ladle lip is bricked with high- grade chrome-magnesite. -

The total weight of br icks is approximately 7.5 tons. The metal to br ick rat io is 12 to 1. Previous to tapping, the ladle is preheated to approximately 800°C by means of a blast furnace gas burner using 14,000 cu ft pe r hr , for 25 to 3 hrs .

In o rder to reduce the temperature loss of the s teel during casting the ladle is covered with a lid. This is in the form of a 1-in. thick s teel plate p ressed into a shallow dish, linedwitha high temperature castable refractory. Heat is supplied to the metal in the ladle by a combustion can burner which is fitted to the center of the lid and using coke oven gas a t the r a t e of 220 cfpm. Two holes in the lid a r e situated in the appropriate positions for an immersion pyrometer and for an oxygen lance. The latter is used to insure a f r e e flow of s teel through the siphon a t the s t a r t of the cast. The lid is lowered onto the ladle by a smal l electrically-operated three-leg hoist.

The average ladle lining life is a t present 12 cas t s and, apart from several minor patching repairs , the original ladle lid is still in use.

The tilting cradle consists of two vert ical s ide plates supported by sectional steelwork and tied by a s teel cross-member. Each s ide plate is cut away to allow the ladle trunnions to move into a semicircular depression when positioned for commence pour. Tilting power is transmitted through 2 hydraulically operated rams , one r a m being attached to each s ide plate. The flow of metal from the ladle lip is controlled by adjusting the angle of til t of the ladle, and the maximum speed of lift is 6 ips. Slow tilting speeds which a r e required during casting a r e attained by operating a metering valve to allow speeds within the range 0 to 0.21 ips. The cradle is designed s o that the axis of til t of the ladle passes through the lip to insure that the flow of metal between ladle and tundish maintains a constant a r c throughout casting. The ladle is tilted through 90" for draining to s lag and when i t is in the maximum upper position a hydraulic re lease valve is automatically operated to stop further movement. An "emergency lower" valve is available which re tu rns the ladle to vert ical position a t an approximaterate of 3 ipm.

Tundish

The general design of the tundish is shown in Fig 4, and the dimensions a r e a s follows:

L engtlz Width Depth

Tundish (overall) 20 ft 4 in. 2 ft 10 in. 23 in. (working) 13 ft 6 in. 2 ft 1 in. 19 in.

Four stoppers control the distribution of s teel to the molds and the attain- ing of a steady s t ream through the refractory nozzles, positioned a t 2 ft 6 in.- centers over the molds.


Fig 4-Continuous casting tundish.

Compensation for changes in casting speed a r e made by raising and lowering the stopper over the nozzle aperture although the nozzle s ize is carefully chosen to reduce this to a minimum. In addition, casting speeds can be varied if necessary by increasing o r decreasing the head of metal on the tundish.

The tundish is lined with firebricks (35 to 37 pct A1,03). The floor is 6 in. in depth and the lining 4; in. thick. At one end a weir is built a t a level approximately 12 in. from the floor, and a removable brick in the form of a taphole facilitates emptying of the tundish in an emergency. The average tundish lining life i s , a t present, 10 casts.

Stopper operating gear is provided for each nozzle a t the appropriate positions on the tundish body. The stopper is some 2 ft 6 in. in length and made from ordinary fireclay. The stoppers a r e made on the plant by the machine operators, and drying is in an infrared oven.

Nozzle s ize is 3/4 in. to 7/8 in. diam, depending on s teel quality and casting speeds required. Ordinary %-in. o r ;-in. fireclay nozzles a r e , a t present , used for up to 0.30 pct C killed s teels and 0.30 to 0.50 pct C killed s teels respectively.

:-in. magnesite inser t nozzles o r a-in. high alumina (85 pct A1,0,) a r e used f o r rimming steel qualities.

When the tundish is lined and the stoppers fitted, the capacity is approximately 4 tons of liquid s teel a t the normal operating level.

For the purpose of setting the tundish in a cor rec t position above the molds, a pair of trunnions extend from each end and these fit into U brackets situated a t each end of the mold tables. This insures the tundish to be seated firmly and safely. The tundish is designed to tilt, by hydraulic power. to an angle of 8", s o enabling the s lag to be drained from the tundish a t the end of each cast.

Under each nozzle there is a refractory line swivel launder to direct steel, in an emergency, from the tundish nozzles to s lag pots located a t each end of the mold tables.

The tundish lid is dish-shaped and has seven holes in the top, four for the entry of stoppers, two for burner combustion cans and one for temperature


measurement by immersion thermocouple. The lining is 37 to 42 pct A1,0, firebrick.

The preheating of the tundish with nozzles rammed and lid fitted, commences approximately three hours before casting. Coke oven gas is used a s a fuel a t the ra te of 45 cfpm of a i r . The a i r and coke oven gas a r e piped to the tundish through 4-in. and 12-in. pipes respectively. The burner cans a r e made of sheet s teel with a heat resistant s teel lower ring. The can is a l so fitted with a refractory lined shield which f i ts in the burner hole in the tundish lid.

Molds and Tables

The plant has been commissioned and is currently operating with machined solid block copper molds. These a r e machined from solid blocks of elec- trolytically pure copper to a cross-section of 9 in. x 9 in.

Detail of mold design and usage is described in a la ter section. It should now be explained that 2 molds a r e housed in a common supporting

table, and that each table can be reciprocated vertically through 2 vert ical pins o r guides. The f rame a l so supports the upper lever o r reciprocation points.

Mold Reciprocation

The mold reciprocation gear oscillates the mold with an upward speed three t imes greater than the casting speed and a downward ve!ocity slightly higher than the s t rand speed, thus giving a stripping action in both directions and a nominal mold s t roke of 1/2 in. Slow movement of the molds is available by means of an inching control in both directions of motion, and is used for mold positioning when bringing the dummy b a r s into the mold. To maintain the relative speed between mold drive and withdrawal rol l dr ive, a field t r imming rheostat adjusts the molddrive speed to obtain the required negative s t r i p of approximately 1/8 in.

Increase and decrease speed controls a r e available.

Mold Lubrication

Mold lubrication i s by means of rapeseed oil. Each pair of molds i s fed by one pump feeding rapeseed oil f rom a tank

in the pumphouse, through a flow, meter and pressure gauge, to a 16-way spl i t ter situated on the front of the mold table. At the splitter, the oil feed is divided into 16 separate channels. Adjustment of the oil flow is by means of a valve situated on the pumps. Each splitter is comprised of 16 cel ls , each cell containing one plunger. When oil reaches the splitter, each plunger from 1 to 16 i s operated in turn, sending oil to the cel ls 1 to 16 in the mold oiling plates. When al l the cel ls in the oiling plates a r e full (this is done pr io r to casting by means of the buttons on the main control desk), oil spills out of the oiling gap between the mold oiling plate and cooling plate. The oiling gap is 0.006 in. to 0.012 in. wide, andmust be cleared of s tee l globules af ter every cast. When the mold lubrication s ta r t s , oil flows successively from cel l 1 to cell 8 until a l l eight cel ls on the f i r s t mold have operated giving a circum- ferential flow of oil inside the mold. Oil now ceases to flow to the f i r s t mold


while cells 9 to 16 operate on the second mold. The cycle having been completed on the second mold. the process i s repeated on the first mold.

During casting the mold lubrication pumps s ta r t automatically with the mold reciprocation and the withdrawal rolls. In case of failure of either of the normal machine pumps, a stand-by pump is brought into operation automatically. o r by means of a s t a r t stop control on the auxiliaries panel situated on the main control platform. The machine operator can tell , by means of lights on the control desk, whether the lubrication pumps a r e running. For testing lubrication before casting commences. buttons and indicators a r e provided on the main control desk which only energize the pumps when depressed.

The rapeseed oil i s stored in a tank situated on the ground floor a t the south end of the plant. From this main tank. oil is piped to a smaller tank in the pump house from where it is pumped to the molds. It is essential that the oil tanks should be kept sealed. a s any dir t in the oil will result in blockage of the splitters.

Casting has been satisfactory with oil feedsbetween35 and 45 ml per min. per mold.

Roller Apron and Cooling Sprays

This i s an enclosed s teel chamber supported between the spray floor and the underside of the casting platform. The rol ler aprons and sprays a r e suspended in pairs on two trolleys and hang freely so that they may follow any slight deviation from the vertical which the strand may undergo, a s a consequence of uneven cooling. The trolleys a r e used for correct positioning of the aprons in relation to the molds and withdrawal rol ls and for rapid removal. for maintenance.

The rol ler apron is built in 5 sections, and nozzles of the cone spray type (3i32-in. diam) a r e fitted in between each rol ler on al l 4 faces. Each section is 4 ft 5 in. long and consists of four 3-in. square steel vertical s t r ingers , tied by horizontal flat members at intervals. Fabricated supports a r e bolted to the vertical members and these ca r ry the 4-in diam bushed ro l le r s of 8$-in. face width. The cone spray nozzles a r e suitable for nominally 90 gph. and a r e set back 4 in. from the face of the bloom. There a r e 24 nozzles (6 per bloom surface) to each section of aprcn, and each nozzle gives a hollow cone type spray by virtue of a small plate placed behind the nozzle tip. This insures uniform and even cooling of each surface of the bloom. The necessary pressure gauges. flow indicators. stop valves and flow regulation valves a r e located on the outside of the chamber. The spray chamber i s connected with the ventilation exhaust system to facilitate the rapid removal of steam: and high pressure a l r sea l s arrangedatbloom exits from the chamber prevent water flowing to the lower floors. (Fia 5) .

Withdrawal Rolls

The solidified blooms emerge from the spray chamber and into the withdrawal rol ls , each pair of blooms having common withdrawal rol ls in two vertical banks each with a common drive. The pressure of the rolls on the bloom i s adjusted to prevent slipping without rollinz.


Fig 5-Roller apron, cooling sprays and cooling chamber air seal.

Withdrawal rol l inch i s available in both directions for raising and lowering dummy b a r s o r blooms and, for bringing dummy b a r s into the mold, slow inching is by pendant control on the teeming platform.

Cut-Olf Sfntiorz-Bloom cutting i s achieved by oxygen/propane burners totally enclosed in a cut-off chamber, this being of fabricated s teel plate with armoured glass inspection windows. (Fig 6).

Burner Cnrvinges-Four s e t s of hoist units. one for eachburner carr iage, lower and r a i s e the ca r r iages inside the chamber by means of a s teel rope which passes over pulleys to a rope drum. The car r iage is guided in the vertical directions by s ix cast s teel ro l le r s which run inside s teel joists. The downward speed of the burner unit is synchronized with a foot hoist unit to maintain burner descent a t the speed of the bloom. On the underside of each car r iage f rame is mounted a slide which c a r r i e s two burners (one lead and one stand-by). the complete slide being t raversed by a lead screw for

Continuous Casting at Appleby-Frodingham 1 1

Fig 6-Cut-off control desk.

movement of burner across the bloom face. Cutting speed is 7; ipm for present casting speeds with provisions to increase as casting speeds a r e increased.

To insure that the burner maintains a constant position from the bloom face during cutting, a spring-loaded roller device is incorporated so that the roller maintains contact with the bloom during cutting. Variations in bloom position relative to the carriage a re transmitted by means of hydraulic actuators. A double-acting hydraulic cylinder retracts the burner during setting up of dummy bars.

Cutting Equipment-The plant primarily consists of two control panels, each panel controlling the lead and stand-by guns to two burner carriages. Incorporated in each panel a r e separate and individual regulators for propane and oxygen.

Cutting i s automatic within a normal range of 20 ft 0 in. to 24 ft 6 in.. and a minimum length of 12 ft 0 in., but manual controls a r e available should the automatics fail. The start of cutting is actuated by the first bloom in each pair to reach the preset lengths.

Under normal operating conditions the cutting of the bloom is entirely automatic, and is controlled within the cut-off chamber. The control desk allows for al l precast conditions to be set automatically before casting commences, and the operator can follow the sequence of operations by watching a ser ies of lights which a re illuminated a s each operation is completed.

The cut-off chamber is connected to theventilation system to remove fumes developed during the cutting of the blooms.


CUT OFF STATION

Fig 7-Cut-off and discharge mechanism.

Discharge of Blooms

The Foot Hoist-When blooms have been cut to the required length they a re lowered vertically into the tilting baskets by movable feet. (Fig 7).

Tiltirzg Basket-Two hydraulically operated tilting baskets, one for each pair of cut blooms, transfer the blooms from the vertical position onto the inclined conveyor for transfer to ground level. Movement of the basket is achieved by two double acting hydraulic cylinders (one per basket). The hydraulic equipment i s arranged to give fast and slow speed on downward movement and return, the slow-down speeds operating a t the limits of basket travel to avoid excessive shock loads. The hydraulic operations a r e automatic with provision for over-riding by manual control.

Bloom Take-off Gear-The blooms a r e transferred from the conveyor to the tilting tables by 2 pushers. one for each pair of blooms. The pusher unit is automatic with provision for over-riding manual controls.

Tilting Tables-It i s necessary at this stage to bring the blooms to a horizontal position for removal by the gantry crane. This is done by hydraulically operated tilting tables. two of which a re positioned a t the discharge end of the inclined conveyors, each receiving two lengths of bloom and then

Continuous Casting a t Appleby-Frodingham 13

tilting automatically to ground level. From this position the blooms a r e off-loaded by the overhead crane.

The Dummy Bar

One complete dummy bar is supplied for each strand being fabricated of 3/4-in. s teel plates and in two sections connectedby an automatic disengaging mechanism. This comprises a heavy vertical s teel pin built into the top of the bottom section, while two spring-loaded s teel retaining levers a r e built into the bottom of the top section. Disengagement is effected by a hydraulically- operated, trolley-mounted, rigid s teel clevis. The top of the top section is fitted with a detachable plate carrying rag bolts, around which the f i rs t metal solidifies. The lengths of the top and bottom sections a r e 22 ft 6 in. and 24 ft 6 in. respectively. They a r e stored at ground level and fed into the machine by manually operating the handling system in reverse.

U7atev Cooling nizd Circzrits-All the water used on the plant is taken from the normal Melting Shop supply, and is lime-softened r iver and drainage water. There a r e two water systems:

1. Mold circuit, 2. Spray circuit.

The make-up water is fed by gravity to a scale pit in the spray circuit system. via a float valve. From the s a m e supply a 3 in. pipe is connected to a booster pump which delivers water to the mold circuit.

Mold Circuit-This is a closed system consisting of:

I. An overhead water tank with a capacity of 26,000 gal with a 12-in. bore outlet pipe.

2. Three circulating pumps each rated a t 1310 gpm at 180-ft head of water (2 working, 1 stand-by).

3. Two booster pumps each rated a t 100 gpm at 150-ft head (1 working, 1 stand-by).

4. An induced draught cooling tower (twin cell) with a capacity of 2620 gpm from 103.5"F to 9 0 ° F with a well capacity of 4500 gal.

The water is pumped by a booster pump to the cooling tower basin, the level being controlled by float valves, from which it is then pumped by two of the recirculating pumps to the molds. The flow of water to each mold is measured by means of a n orifice plate. Each supply line is fitted with a n electrically operated valve, which is closed until the appropriate t ime before casting. The valve can be opened and closedby a switch on the main operating pulpit. Three electrically operated solenoid valves a r e incorporated in the mold system, on the casting platform connecting the emergency supply from the overhead tank, one on the outlet main from the molds and one on the withdrawal rol l re turn main. A11 three of these valves a r e energized closed, s o that in the c a s e of a power failure, the overhead tank will supply water to the molds and withdrawal rol ls for a period of approximately 20 min. This allows sufficient t ime to clear the plant of blooms, and protect the machine from damage.

A 6-in. branch line is taken from the mold feed line to supply water to the withdrawal rol ls and frames, a t the ra te of approximately 200 gpm. This


water joins the return water f rom the molds and is passed to the cooling tower. In addition, a connection also feeds the 4 cut-off torches. and the water cut-off curtain. This water (approximately 200 gpm) i s lost f rom the system to the basement pump below, and accordingly acts a s a bleed-off f rom the mold system and s o helps to keep down the concentration of solids in the water.

Sfway Civ-cuzt-This is an open system consisting of:

1. An overhead tank with a 4500-gal capacity. 2. An a i r cooled heat exchanger with a capacity of 1500 gpm from 190" F

to 150°F and divided into three identical compartments. 3. Three pumps, one pumping dirty water a t 1400 gprn and two pumping

clean water a t 750 gpm. 4. A sca le pit with 10,000-gal capacity.

The scale pit is divided by a s teel division plate, one half being used for dirty water returning from the spray chamber and the other for clean water. The water from the spray chamber i s collected over a s teel box which removes the larger pieces of scale and overflows into a sump where there is a further settling out of solids. The water is then pumped through a bank of 5 hydrocyclones where scale above 200 mesh is removed. The underflow returns to the dirty water sump. The clean water is then pumped over the fin cooler by two pumps to the spray chamber, giving a p ressure a t the sprays of 60 Ib per sq in. A three-way electrically controlled valve is positioned in the feed line to the sprays. This allows for recirculation of the water spray until it is required in the spray chamber. After the valve, the water passes through a s t rainer which removes any solids s t i l l left in the water.

The a i r cooled heat exchanger is divided into three identical banks and has th ree fans to each bank, each fan having two speeds. The fans a r e controlled by thermostats positioned in the outlet pipe from each bank, with a 3-position control switch on the main control pulpit. Four pneumatically operated regulating valves, one in each feed line to a bank of sprays, with a Venturi measuring device, controls the total flow to each bank of sprays. Each bank consists of 5 sections, each with i t s own hand-operated valves, p r e s s u r e gauges and flow indicators. The total flow to the sprays is 700 gpm (175 gprn t o each bank).

Ventilation

The ventilation system combines an extraction plant with forced a i r supply.

The extraction plant consists of 2 large discharge fans situated on the roof of the building and provides for the extraction of fumes and s team from the spray chamber. burner chamber and sca ie pits. In addition, double- skinned radiation hoods between the spray chamber and withdrawal ro l l s facilitate an adequate passage of a i r by means of ducting, thereby reducing the a i r temperature a t this point.

The forced a i r supply system is provided by two fans supplying a total of 90,000 cfpm of a i r which is distributed to a l l floors of the plant below ground level. Distribution is achieved by means of ducting with outlet boxes,


dampers and adjustable slides. Special adjustable outlets a r e provided in the cut-off station.

These two systems have proved most efficient and, during casting, the whole plant is cool and free from steam.

PLANT OPERATION

Steelmaking Practice

During the early stages of commissioning the plant, steelmaking for continuous casting was similar to conventional practice. However, the longer casting period naturally required a higher furnace tapping temperature and ideal conditions had to be determined by experimental work. In addition, the processing of the continuously cast blooms soon revealed the importance of control of sulfur content, and carbon and oxygen content of the steel at tapping.

The qualities of steel which have so far been successfully cast at Appleby- Frodingham fall within the following ranges:

1 . Killed Steels

C P Mn 0.06 to 0.45 pct 0.050 pct 0.50 to 0.90 pct

S Si 0.030 to 0.050 pct 0.20 to 0.30 pct

2. Rimming Steels

C P Mn S 0.05 to 0.11 pct 0.050 pct 0.35 to 0.45 pct 0.050 pct

A high regard to necessary

sulfur content adversely affects bloom quality, particularly with internal and transverse face cracking. In consequence, it has been to limit sulfur contents as follows:

Carbon Pet Suljicr Pet

0.20 to 45 0.030 max 0.15 to 20 0.040 max Below 0.15 0.050 max

Restrictions have also been placed on the minimum bath tapping carbon and the amount of carbonadded to the ladle in order to minimize the formation of "pinholes" on the surface of the blooms. The furnace is tapped with carbon a s near to the specification a s possible, and the maximum permissible carbon addition i s 0.05 pct. Limitations a r e also placed on the total Fe content of the tapping slag, and the ideal silicon content. By these controls, pinhole formation in the cast blooms has been substantially reduced.


F i g 8-Control pulpit.

Precast Preparation

Once the ladle i s in the casting position it cannot quickly be returned to the casting bay, andaccordingly, ladle preparation i s of the utmost importance. The lining a t al l times must be in good condition and a high safety factor i s maintained. Similarly, tundish preparation demands the same careful attention. The ramming of tundish nozzles to give a truly vertical s tream of metal is essential.

Experience to date has shown that. for killed steels, 13/16-in. diam bore fireclay nozzles a r e satisfactory. For rimming steels 7/8-in. diam bore nozzles, of high alumina, (65 pct) and magnesite inserts have e v e n en- couraging results. Tundish preheating instructions a r e strictly adhered to, while tundish stoppers a r e set approximately 10 min. prior to commencement of casting. Tundish preheating usually commences 2$ to 3 hrs before casting commences and continues throughout the casting cycle. A s soon a s the stoppers a r e set, nozzle preheating (propane gas) commences.

From the control pulpit, situated on a raised platform, (Fig. 8), the following precasting procedures take place:

1. Start the general ventilation fans. 2. Initiate pumps to fill the overhead tanks. 3. Check water flows to: Withdrawal rolls, burners, molds and cooling

sprays. 4. Check mold oiling systems.


5. Set mold reciprocation speeds to give the correct ratio between the withdrawal rolls and molds.

At the cut-off station the powder dispensers a r e checked for delivery of powder.

Bloom discharge sequences a r e then checked and then the cut length of the bloom preset and al l controls a r e se t for automatic working. The following controls a r e situated in the control pulpit:

Ventilation and extraction svstems Burner sprav curtain Automatic dummy bar removal Basket tilt hydraulics Tilt table hvdraulics.

The above a r e initiated a s requested by the cut-off operator who can con~municate with the casting floor by means of microphone and loud speaker svstem.

Casting

T c r l ~ p c ~ - O / I I I - ~ J con/^-ol-Every effort i s made to avoid excessive waiting t imes and for the s teel to a r r i v e at the plant a t near to the required temperature. Factors which have an important bearing on this a re :

1. Ladle preheat temperature and preheat time, 2. Ladle fill t ime.

Fig 9-Fixing ladle lid and temperature measurement.


Table 1-Temperature Control.

Furnace Tap Temp°C Ladle Top

Temp°C

KILLED

Tundish Temp0C

Average Tundish temp fa l l

0.5'C pe r rnin. 0.5"C p e r rnin. 0.4"C pe r min . 0.4'C pe r rnin.

0.5"C p e r rnin.

3. Ladle t ransfer time to the furnace. 4. Ladle order . The second ladle from the furnace (tilting furnace

practice) i s preferred to insure consistent filling t imes (6 to 8 rnin.). thus avoiding undue heat loss during the tapping operation.

5. Accurate measurement of furnace tap temperature. 6. Ladle t ransfer time, f rom ladle full until ladle lid is fixed in position.

Control of these factors has substantially improved temperature control and avoids delays in s tar t ing casts.

Casting begins only af ter the desired temperature of the metal in the ladle has been confirmed by immersion pyrometer. If the temperature is too high the lid is taken off to increase the ra te of fall. and under these conditions, the temperature of the s teel falls a t t h e r a t e of about 1°C per min. The lid is fitted when thecor rec t tempera ture i s recorded, and the gas burner is ignited when ladle til t commences. (Fig 9). As soon a s the tundish is full, temperature readings a r e taken by means of a n immersion pyrometer and continued at approximately 10-min. intervals throughout the cast. The average temperature fall is 0.5"C per min.

Table 1 shows the ideal temperature ranges for each quality of s teel . These figures have been evolved from the casting experience gained to

date. The casting temperature is progressively decreased a s the carbon content increases, and allowance i s a lso made for the near furnaces L and N compared with the furnaces P, Q and R which a r e further away.

Teeming-When the laY1.e is positioned in the tilting cradle, the following operations take place almost simultaneously:

1 . The siphon i s cleaned out with an oxygen lance to insure a f r e e flow of metal into the tundish.

2. The mold cooling water i s commerlced and adjusted to 375 gpm p e r mold.

3. Propane gas burners a r e removed fromunderneaththetundish nozzles.

Following these operations, ladle til t commences a t the fast ra te s o that a 9-in. to 12-in. head of metal in the tundish is quickly attained. The two operators (teerners), each man controlling two stoppers. open the s toppers


Fig 10-Tundish operation during early stage of cast.

when the desired metal level in the tundish is reached. At this time the spray cooling water flow is initiated.

It is absolutely essential that the first steel into the molds should freeze around the bolts which extend from the dummy bar head, thus firmly coupling the dummy bar to the bloom. Strips of steel a r e placed in the bottom of the mold which insure the rapid cooling of the first metal and the formation of a satisfactorily thick skin. To minimize oxidation of the metal, a "blanket" of coke oven gas is laid around the ladle and tundish streams; and whereas it i s not claimed that this produces a reducing atmosphere, it is believed to be worthwhile. (Figs 10 and 11).

The molds a re slowly filled in 45 to 60 sec and then each teemer signals for bloom withdrawal to commence. This is at a predetermined casting speed, and a s the molds start to oscillate, so the supply of mold lubricating oil commences. The teemers a re trained to make full use of the mold by keeping the meniscus of the metal approximately 2 in. below the top of the mold. This means very careful control of the stoppers, and in order to keep the stopper movement to a minimum, slight variations of the head of metal in the tundish a re made to correspond with nozzle wear. As the temperature falls towards the end of the cast, the tundish level i s raised and the casting speed i s increased accordingly.

During casting, slag accumulates on top of the liquid steel in the molds and is removed from time to time by the technique of fishing.

Reciprocation is a 3:l ratio with a 1/2 in. stroke and negative strip of 1/8 in.


Fig 1 1 -Tundish operation towards end of cast.

Cooling of Blooms and Casting Speed-In the spray cooling chamber the heat exchange rate is a s high a s possible consistent with producing blooms of sound quality. The rate of heat removal in this chamber determines the depth of the liquid core and this in turn determines the maximum casting speed of the machine. However, excessively rapid cooling impairs the quality of the finished bloom, and the greater the cooling rate, the greater the s t resses due to differential contraction. This can lead to serious cracking, both internally and externally. Experimental work has thus been concerned with determining ideal conditions for casting temperatures, casting speeds, and intensity of cooling in the spray chamber. Severe variation in casting speed is avoided, and the cast i s normally started at 36 ipm and gradually increased at the end of the cast (with steel temperature drop), to 42 ipm, Under these conditions, the spray water flows a r e maintained constant throughout the cast. Present flows and distributions a r e shown in Table 2.

As the carbon content of the steel increases, so the water flow is decreased to each top section of sprays, to minimize surface cracking.

Continuous Casting at Appleby- Frodingham 2 1

Table 2-Present Method of Casting Temperature per Casting Speed per Spray Flow Control.

4th and 5th sections adjusted to 35 gprn after 20 to 30 rnin. casting.

Quality

0.1OC

0.10 - 0.15 C

0.15 - 0.20 C

Careful control of the metal level in each pair of molds is necessitated by common withdrawal rol ls , and since the ra te of withdrawal of both s t rands is equal, i t is of vital importance that the ra te of supply to each mold shall be equal throughout the cast. The nozzles openout during casting and i t is unusual for the two nozzles concerned to open out a t the s a m e rate. Thus; in o rder to maintain equal ra tes of flow to each mold, stopper control has to be very efficient.

The Cut-0-ff uud Dischavge of Bloon?s-As casting commences, the dummy b a r s descend through the withdrawal rolls into the cut-off chamber. At the top of the cut-off chamber, just underneath the withdrawal rol l floor, the bottom section of the dummy b a r is parted from the top section by means of a disengaging clevis. The foot dr ive is accelerated downwards taking these lengths of dummy bar away. The cut-off burners do not work for this particu- l a r operation, and the disengaging clevis is now retracted. The top sections of the dummy b a r s descendwith the blooms attached and a t a position 2 ft 6 in. above the dummy b a r head, the f i rs t cut is made. Throughout casting, the burner equipment sequences a r e automatically controlled, and operated by one man. Fig 12.

The failure of a burner is detected visually by the cut-off operator and, if this is seen quickly enough, selection of the stand-by burner will bring it into operation before the c r o s s t ravel has passed the cut-initiating point. A t ime interval of approximately 6 s e c is available between No. 1 and No. 2 burners

Ladle Casting TempoC

1575

Max 1570

Max 1565

. Tund~sh Temperature0C

Below Below 'Below Below 1 Below 1560 1550 1 5 4 0 1530 1 1520

I

0.20 - 1 Max

3o

0.25 C --

0.25 - 0.30 C

0.30 - 0.50 C

0.09 to 0.llC

Rrnrn~ng

Spray Distribution gpm

1560

Max 1550

Max 1545

1570 to 1565

Section 1

42 35 35 35 35 180

\34 36 38 40 37 35 35 35 35 177

36

40 42 34 35 35 3 0 R 30" 164 36

I

38 1 40 ' 42 32 35 35

2

38

38

38

32 1 34

5 3 4 Total

40

40

38

42

42

40

30

30

45

35

35

38

35

35

38

30"

30"

38"

25"

25O

38"

155

155

191


Fig 12-First cut by ' A ' machine burning torches to release top section of dummy bars.

passing through the cut-initiating point using the present cross travel speed of 71 ipm. If the standby burner is brought into position too late, the cross travel must be switched to manual and cut completed by the operator. As each bloom is severed, the foot speed is increased and takes the bloom down into the basket for a distance of approximately 4 ft 8 in. a t the rate of 60 fpm. It then slows down at one foot from the bottom of the basket, to a speed of 6 fpm, thus resting the bloom onthe cushion stops at the bottom of the basket. The foot then proceeds to the bottom ofthe plant and the last foot in each pair to reach this point initiates the tilting of the appropriate basket onto the conveyor, initially, a t a fast speed, moving the f irst 80 in. a t the rate of 10 ips and then the last 6 in. at 2 ips. The baskets remain at res t until the conveyor chain dogs have removed the blooms, andthen return to the vertical position. The blooms a re then carried up the 45" ramp to the tilting table. The pusher places each pair of blooms onto the tilting table. Latches a r e then raised to hold the blooms in position, and the pusher is retracted and the tilt table i s raised to a horizontal position. The blooms a re finally removed from the tilt table and loaded onto wagons by means of a turret-type crane. (Figs 13 and 14).


MANNING

Fig 13-Automatic bloom discharge. '8' machine basket tilting operation.

The machine is manned with a crew of seven operators and two crane drivers. These consist of:

One Machine Operator (Main Control Desk) One Asst. Machine Operator (Ladleman) Three Strand Operators (Tundish and stopper operation) One Cut-Off Operator (Cut-Off Control Desk) One Bloom Handler (Bloom marking and loading) One Casting Floor Service crane driver One Bloom Gantry crane driver

Each operator i s allocated specific duties during casting. although in all machine preparation, clearance and general machine work, all operators work together a s a team.


Fig 14-Bloom discharge by tilting table and bloom gantry crane.

TRAINING

The training of the operators was arranged in three categories:

I . Comprehensive lecture program 2. Practical training on the Barrow Steelworks experimental machine for

9-in. square bloom casting. 3. Actual 'on the machine' practical training during the Appleby-

Frodingham machine cold commissioning trials.

Lectures included details of conventional casting pit practice with particular reference to practical exercises on operations suchas stopper making, nozzle ramming, use of burning apparatus, teeming, and others. Continuous Casting was discussed from first principles, with final lectures on the detailed description of the layout and operation of the Appleby- Frodingham machine.

None of the operators had any previous knowledge o r experience of the continuous casting process. Lectures were aided by the internal publication of a text book for operators engagedonthe training course. From this lecture course, 12 operators, selected for early manning, were trained in two groups of six at the United Steel Companies' pilot plant at Barrow. Each group made two visits. each of one week duration, the f irst for initial practical training and the second to completely take over the Barrow experimental machine (74-ton ladle, 9-in. square blooms, twin strand) for unaided experience of machine operation.


Final training on the Appleby-Frodingham machine was completed by manning the f i rs t crew on the machine immediately it became available for cold t r ia ls . In the subsequent repeated testing of a l l equipment and mock operations affecting casting conditions, the operators became familiar with al l the controls and machinery.

Thus. from the f i rs t introduction of hot metal to the plant, and in a l l subsequent casts , the operators have controlled the complete casting operation. Throughout the whole training program, a s each stage was described. the safety aspects were emphasized with particular regard to the importance of wearing safety clothing equipment, and s t r i c t regard to the other person 's safety, s o necessary in the teamwork operation of the continuous casting process.

PLANT PERFORMANCE

MACHINE COMMISSIONING

Cold t r i a l s commenced in early July. 1962. and at this stage the machine was manned on a one-shift basis. This allowed the men themselves to conduct the cold t r i a l s and a t the s a m e time, to complete their final training on the machine. After several weeks of repeated machineoperationunder simulation of casting conditions. the f i rs t cast was made on July 16, 1962. Tables 3, 4 and 5 give a full survey ofthe tonnages cast and stoppages encountered during the f i rs t 75 casts . Machine defects which occurred were progressively eliminated and operating methods became standardized.

In the continuous casting of large capacity ladles, one of the ser ious disadvantages is an economical outlet for the remaining metal in the ladle after early cast stoppages. This problem is easily overcome at Appleby-

Table 3-Tonnages Cast During Commissioning.

Period Cast No. -. -

1962

Tonnage

Mill. I Emptied I

Nov. 11

Nov. 12 1 51 1

I . . I

to to 84

loo i l 2 I 1 21

Dec. 10 1 75 i

July 16

1. F i r s t ca s t made July 16, 1962 (34 tons) 2. F i r s t ladle emptied (No. 16) Aug. 30. 1962 (75 tons) 3 . F i r s t ladle and tundish emptied (No. 28) Oct. 2.1962 (85 tons). (No s t rand stoppage). 4. F i r s t exper imental r imming s t ee l ca s t (No. 65) Nov. 28. 1962 (17 tons). Second

r imming s t ee l c a s t (No. 71) Dec. 4. 1962 (83 tons).

. -

1 I


Table 4-Stoppage Analysis During Machine Commissioning.

Stoppages (Each Machine) Casts 1 - 58 (incl)

Type I No. I Pet

Cut-off mechanism Dummy bar removal Discharge - Bloom warp Tundish (Stoppers, Nozzles, etc.) BreAouts Sectional Distortion

(Pinch rol l failure) Planned stoppages

(after one machine failure) Others

Frodingham by the immediate availability of the casting pit. Thus, af ter an ear ly cast stoppage, the metal is returned immediately to the casting pit, poured into a conventional ladle and teemed into ingots. In this way, apart

Total

from any tundish scrap, hardiy a single ton of s teel has been wasted. In the f i r s t cast, (July 16, 1962), 34 tons were successfully cas t until

stoppage resulted from cut-off failures. However, tonnages were progressively increased (see Table 5) and the f i r s t ladle was emptied af ter approximately 6 weeks and 16 attempts. The second ladle was emptied (85 tons) af ter 28 casts , after which the average tonnage cast and number of ladles emptied progressed very quickly.

However, in the f i rs t 50 casts , only 9 ladles were completely emptied and

88

the average tonnage per ladle was 54 tons. In the next 25 cas t s (50 to 75). the average tonnage was further increased

to 85 tons p e r ladle and 21 ladles were completely emptied, the failures h e r e being primarily due to the f i r s t of the experimental rimming steel casts.

Table 4 shows a brief survey of stoppages encountered and Table 5, how these have been progressively eliminated. The chief of these have been cutting failures, bloom warp and refractory difficulties in the tundish. Fai lures of the burning torches to part the bloom, o r in incorrect ca r r iage cutting cycle, were improved by new burning nozzle design. bet ter cutting speed control and improvements in general burner-carr iage design. More emergency manual control to retr ieve cutting failure situations was allowed by simplification of the relationship between the foot and car r iage automatic cutting cyles. The addition of i ron powder cutting equipment for use in the early s tages of cutting now guarantees successful cut commencement.

Similarly, tundish refractory troubles in the form of stopper failures, nozzle blockage, and others, were overcome by improvement in refractory

100.0

materials , tundish preheat and operating techniques, and more s t r i c t metal temperature control.

In early cas t s , the blooms tended to wander s o that they either failed to pass through individual floor levels, fouled the top of the discharge basket, o r finally became wedged a t some stage of the conveyor discharge operation.

Table 5-Survey of Plant Performance Durlng CornrnIssIonlng.

7 . I I I I I STOPPAGES

J u 1 y 1 6 5 4 7 2 q t o N:l , 1 1 1 : Aug. 19 ,

-*- .- -. Aug. 21 1 1 1 A 3 1 2 3 1 1

Date Cast Tonnage Ladles 1962 1 Nn. 1 Max. Mln. A v 1 Emptied Cut-OIf Dummy Bloom ' U,lrp 1 Tundlbh 1 O r ~ a k o u l 1 g:t: ' Planned O t h ~ r s

2 1 .- -, 2

I

I - . - I

--

to to 1 75 2 2 Sept. 10 20 1 -- -,-

2

Sc l~ t . 14 21 I A 5 to 10 85 33 oT 1

Ocl . 5 30 I3 2 - -

Oct. 7 31 A 3 1 to l o 3

Oct. 24 4 0 D 1 1 - -

Oct. 25 4 1 A 1 1

3 1 I 2

5

1

1

2 t o 4

B I I . -

A 1

2

I

2

2

1

?

- 1

1

2

Lo 8 N o v . 2 5 60 B I I

- -

A 9 t 0

2 -

D c c . 4 B

DRC. 4 71 A 10 4

DPC. 10 75 H -

-

-

1


This problem was completely eliminated with the installation of rigid bloom guides at a l l levels.

Metal breakouts have been few, the p r ime causes being either overcooling of the higher carbon range giving t ransverse face cracking, l a rge globules of s lag entering the mold, o r incorrect casting conditions. Some trouble was experienced with sectional distortion of the bloom (e.g., bellying and twisting) which tended to open up the common withdrawal rol ls and allow the other s t rand to s l ip through. This slip was due to incorrect rol l p r e s s u r e application and the distortion related to cooling int tnsi t ies and machine synchronization. Chief among the "other" stoppages were isolated machine failure a s , for example, ladle til t failure due to hydraulic pipe fracture, conveyor dog fracture. and the like.

Output

During the f i r s t year of macnine o p e r a ~ ~ o n , the production output has depended entirely upon the requirements of the new Rod and B a r Mill in i t s final s tages of commissioning. Thus, a s yet, the re has been no great urgency to operate at the required design tonnage of 5000 tons per week. This has been particularly advantageous in that i t has allowed the systematic accumula- tion of continuous casting experience through a la rge tonnage plant not hitherto p r a c t ~ c e d in Europe, and the establishment of operating procedures and experimentation in the casting of different qualities under varying casting conditions.

Fig 15-Production data.


During commissioning. the maximum weekly tonnage (one-shift working- 8-hr shift pe r day and 42-hr working week) cast through the machine was 750 tons with an average yield of 97.0 pct of 9-in. square bloom from molten metal.

After commissioning, tonnages of up to 1116 tons (12 casts) per week were cast on one-shift working, with further increases to 1505 tons per week (17 casts) cast during two-shift working, which commencedon April 17, 1963. Currently the machine i s manned for 15 shifts each week, producing 30 c a s t s and averaging 2500 tons per week. this being the requirement of the Rod and Bar Mill.

Up to Dec. 1963 a total of 700 cas t s has been made. The predominant quality has been of the O.OSC to 0.25C fully-killed quality

with an increasing number of rimming steel cas t s and high carbon (0.25 pct to 0.55 pct C fully-killed) qualities.

One of the major problems of working a continuous casting plant with an open-hearth melting shop containing large tilting furnaces, is relating the furnace forecast tapping program and casting machine preparation to insure a regular casting cycle. At Appleby- Frodingham, the Ajax process with tapping cycles of 6 to 7 h rs , insures at least one furnace tapping when the machine is in a condition to receive a ladle. In this way, the required plant cycle t ime of 3 h r s (8 cas t s p e r day) has been achieved.

Fig 15 is a summary of the average cast data s ince the plant was commissioned. The progressive increase in average cas t weight over the f i r s t s i x months is to be noted. and a l so the low production of tundish and bloom scrap, and scale. The percentage of 'full casts ' teemed without incident when both ladle and tundish were emptied is also shown.

The above average cast weight in April 1963 has not been maintained because of problems with the hydraulic tilting of an overfilled ladle. The total ladle weight has since been standardized a t a maximum of 90 tons. In addition, experimental work casting rimming steels during May, June and July resulted in a further slight reduction in both the average cast weight, and the percentage of "full casts ."

Mold Data

Mold behavior and final life a r e of great importance. In the f i rs t year of machine operation a total of twenty-one molds has been used, comprising seventeen of the copper solid block type and four fabricated welded copper plate design. The lat ter were used only on an experimental basis and, af ter s ix casts , were removed from the machine for complete examination and further research into the design of this type of mold. Of the seventeen block molds it is difficult to determine whether o r not the molds a r e fit for further service until more experience in the use of reconditioned molds has been obtained.

Mold Desipz-The molds a r e of the solid copper block type, 32 in. long with a solid wall thickness of 2 in., containing seven 7/8-in. machined ducts running vertically 9/16 in. behind the inner surface. Each duct contains an 11/16-in. res t r i c to r rod. The molds a r e designed to have an inner wall taper of 0.090 in. Mold water flow is 380 gpm p e r mold a t a n average pressure of 80 ps i giving a cooling water velocity at the face of 21.7 cu ft pe r sec. The water temperature r i s e over the mold is 12" to 15°C.


Table 6-Life and Tonnage of Copper Solid Block Type Molds.

Life Remarks

Life complete - machining e r r o r when reconditioning

Life complete - mold surface poor


Awaiting reconditioning

Reconditioned and ready for use

Reconditioned and ready for use



Life complete - mgld surface poor

Producing rhomboid blooms




Heavy indentations causing blcom to stick



Ln use and satisfactory

"These molds a r e giving satisfactory blooms at reduced casting speeds (approximately 8 pct reduction).

b Chromium plated.

Several molds have been chromium plated. A4old Pcrformancc-A summary of all the solid copper block type molds

used to date is given in Table 6. The reasons for removal from the machine may be summarized a s

follows:

1 . Internal surface distortion. An example of the actual distortion patterns a t both the 7-in. and 23-in. levels, throughout the life of mold No. B6, together with c ~ a n g e s in the vertical mold taper, is shown in Fig 16. (Note: The 7-in. level, i.e., some 3 in. below the metal meniscus, was found to be the region giving the greatest distortion.) This distortion has taken the form of inward L1bellying'' of the mold wall (up to 0.045 in.), just below the metal meniscus level, with progressive wearing outward of the lower depth of the mold (abrasion) of up to 0.035 in. The effect of this distortion has been to reverse the original wall taper (9.090 in. to 9.00 in. from top to bottom), to a similar one in the opposite direction.

Continuous Casting at Appleby- Frodingham 3 1

MOULD WEAR MOULD DIMENSION - INS

9'161

- 23 ' LEVEL 4 - '.

DEPTH IN MOULD -INS

67 CASTS

Na OF CASTS MOULD MMENSION-US

Fig 16-Mold distortion.

Fig 17-Macroetch of a 0.20 pct C steel exhibiting internal star cracking defect.

Table 7-Chemical Analysis on Billets from Concast Blooms. Cast No. 69553

Bloom Sequence P o s ~ t ~ o n of Casting I . -

1 Surlace Center

4 Surface

1 Center

8 Surface Center

1 Surlacc I Center

4 Surface Center

8 Surface Center

A - I STRAND PERCENT

r- SI

0.028

STRAND

0.031

0.032 0.027

A - 2 STRAND


In surface reconditioning, therefore, consideration is being given to the possibility of just reversing the mold and thus avoiding any major changes of dimensions.

2. An increasing number of small .'weeping7' type breakouts were being experienced from cast to cast, even where very rigid spray control and slower casting conditions were enforced.

3. A gradually increasing temperature r i s e of the mold water a c r o s s the molds, i.e., from the original of approximately 12°C to la ter temperature r i ses of 25°C.

4. An increased number of "hot spots" visible on the bloom surfaces a s they emerged from under the mold during casting.

5. Deterioration in the bloom shape in the form of slight rhomboidity and poor corner quality, again even with rigid spray control.

Bloom Quai ity

Generally, the shape and quality of the blooms produced a r e extremely good and compare very favorably with 9-in. square blooms produced by conventional methods: surface quality is particularly outstanding.

Segregation of sulfur, phosphorus and carbon is low compared with mater ial produced from conventional cas t ingots: this is true both longitudinally

Fig 18-Macroetch of 0.10 pct C. Transverse section of 9-In. bloom.


Fig 19-Macroetch of a 0.20 pct C 9-in. bloom Pit a;zaljrsis, pct: C. 0.36. P, 0.026. Mn, 0.080. S, 0.022. S i , 0.31.

and t ransversely within a single bloom, and from beginning to end of a cast. Typical analyses a r e shown in Table 7.

Some degree of central looseness and internal s t a r cracking may be encountered if operating conditions a r e not under full control. Surface and subsurface pinholes and blowholes may also occur. An example of internal s t a r cracking in a bloom i s shown in Fig 17. The internal cracking, while not of a ser ious nature, and usually disappearing during subsequent rolling operations, was related to spray distribution and intensity, and metal sulfur contents. Careful control of the casting temperature per casting speed p e r spray flow relationship, together with sulfur content restrictions, a s the carbon content i n the s teel is increased, has served to eliminate almost completely this defect.

With regard to the surface pinholes and surface blowholes, more s t r i c t control of furnace tapping conditions, blanketing of exposed metal s t reams , reduction in mold lubrication flows, and the like, have tended to reduce their formation substantially.


Fig 20-Macroetch of a 0.40 pct C 9-in. bloom Pit mzalysis, pct: C, 0.36. P, 0.026. Mn, 0.80. 5, 0.022. Si, 0.31.

To allow comparison of sections taken from casts made from qualities of increasing carbon content, Figs 18, 19 and 20 show macroetches of cast blooms containing 0.10 pct, 0.20 pct and 0.40 pct carbon content.

The lighter etching portions on each face of the 0.40 pct C bloom (Fig 20) are associated with a difference in microstructure, which is thought to be due to reheating of the initial chilled skin formed in the mold. This modified structure is not present in the corresponding billet sections.

Pit analysis in each example is also shown. Figs 21, 22 and 23 show the cross-sectional sulfur prints of the actual

billets rolled from the above blooms, while Fig 24 shows results of standard upending tests made on the 0.40 pct carbon quality.


Fig 21-Sulfur print of the 0.10 pct C billet.

Fig 22-Sulfur print of 0.20 pct C billet.


a--=-

Fig 23-Sulfur print of 0.40 pct C billet.

Fig 24-Upending tests on 0.40 pct C sections Pit Analysis: C, 0.42. P, 0.030. Mn,0.98.S,0.034.Si,0.31.


Fig 25-Macroetch of 0.09 pct C rlrnrnlng steel - Transverse section %in. sq bl.;~rn.

Experimental work with regard to the casting of rimming steels is now commencing. Fig 25 shows a section taken from the first cast of rimming steel blooms.

Bloom dressing of either killed or rimming steels i s not generally practiced.

COSTS

Despite higher costs encountered with certain items, as, for example, refractories, the overall cost of continuously cast material already compares favorably with the cost of that produced by conventional methods, despite


the reduced working rate experienced in the first year of operation. Yield and quality results have been particularly outstanding and the former has fully realized the yield advantage expected of the process.

ACKNOWLEDGMENTS

The author wishes to thank the Appleby-Frodingham Steel Company, Branch of the United Steel Companies Limited, for permission to publish this paper. Appreciation i s also due for the help and enthusiasm shown by all personnel engaged in all stages of design, construction and commissioning, through to the successful present day working of the machine.

Particular reference i s made to our Metallurgical Dept. for the help and advice given in the preparation of the metallurgical sections of this paper, and also to my colleagues, J . W. Middleton and D. Ford.

Discussion

ISAAC HARTER, JR.*-I visited this plant inSept., 1963, andwas impressed with it. So many people believe that continuous casting can replace efficient existing mills that I think it i s important to note that this plant i s used to provide additional capacity. The fact that it was designed basically for a single size square i s also important. A rollingmill can usually produce many sizes from one cast size much more cheaply than casting many sizes.

The machinery in this plant i s ruggedly constructed and should cause little maintenance of the major components. Electrical, hydraulic and control maintenance i s probably higher than in one of our plants. The idea of con- ducting two separate stands that can be used a s one stand i s a good move; however, each string should be an independent unit. The pit design i s not favored by us. We believe that a plant above the ground is just a s cheap and that maintenance problems should be less.

The thought put into adequate controls i s to be commended. Pre-cast control settings a re essential in order to prevent the need for searching for the proper settings after the operation has started.

I was also impressed with the various recorders. I believe that recording i s an essential aid to the general foreman of the unit, a s well as to any of the crew chiefs in the event of trouble. With such aids, one can always look back at what was done.

There i s certainly some merit in the siphon type ladle from the stopper failure viewpoint. We believe, however, that with an adequate emergency ladle, and with normal care of the nozzle and stopper installation, the stopper system i s the better of the two. A stopper ladle saves the amount of metal lost in the first flush. I also wonder about the amount of metal that i s left in the ladle in order to prevent too much slag from coming through at the end of the cast.

*The Babcock and Wilcox Co., Beaver Falls, Pennsylvania.


We have not found that a roof i s required and I wonder if Mr. Johnson has cast any heats without it. In regard to ladle lining life, is i t customary to have a s short a life a s 12 heats? Our experience indicates 18 to 20.

The tundish volume appears to be adequate in o rder to obtain good flow conditions, and we certainly agree with the in-line design of molds. We have not used stopper rod control in the tundish for many years , and believe that they a r e apt to cause a rough and splattering s t ream. Our nozzles work very well and we have obtained a s many a s four separate uses , i.e., heats p e r nozzle. Two uses a r e more usual, and only one is possible if the nozzle i s damaged by s lag at the end of the heat. Heat control in the tundish is our basic speed control, and regulation of this i s very easily accomplished by eye.

Tundish life is very important. Although we average 20 heats per inner- lining, I believe this would vary considerably with the type of metal being cast. We a r e casting 0.15 to 0.40 carbonkilled s teels with a manganese range of 0.50 to 1.40. Mr. Johnson describes the preheating system and I wonder if heating during a cast i s ever necessary.

I a m interested in mold life and cost. Do you find, Mr. Johnson, that a solid block mold i s cheaper than the thinwall type? Also, I a m not c lea r a s to whether each mold i s reciprocated individually, considering that they a r e mounted in a common table with common withdrawal ro l l s per pair.

In regard to mold lubrication, what i s the reason for alternating the flow of oil to each mold? I s intermittent feed desirable o r i s it dictated by the oil pumping system?

'The nozzle and spray system pattern described is similar to o u r s and for this reason, I wonder why s o much spray water is used per pound of steel. I believe i t is about two pounds of water per pound of steel.

We believe very strongly that each s tr ing should have i t s own withdrawal rolls. What i s the reason for your design of one dr ive for two str ings?

The cut-off torch design appears to be s imi la r to ours except for synchronization with the bar speed. Do you have any problems on this system; and i s powder necessary for automatic operation?

The water systems, i.e., mold and spray, appear to be a bit complicated. Do you believe that the system could be simplified?

Whenever I hear the subject of a pit type caster and one above ground, the subject of ventilation ar ises . I know that we require a reasonable amount above the ground, and i t sounds a s if you have done a good job on this point.

PLANT OPERA'TION

Your description of temperature of the heat analysis, and after cooling, falls generally in line with our views on these subjects. You did not mention any control of s t ray elements such a s lead, copper, zinc, and others , and I wonder if they concern you in the casting operation. I s the quality of your r immed heats satisfactory?

The description of the operation is excellent and I could s e e during my visit that a l l the manpower i s well trained for the particular job. The number of men used is very low and about a s low a s I have seen anywhere.

The description of plant performance during commissioning and since, i s certainly a good guide for future casters . All the things mentioned can happen and should be corrected a s thoroughly a s possible before casting

continuous 'casting at Appleby- Frodingham 41

again. Little troubles beget big troubles, s o correct even the smallest offender. I s e e no useful reason to compare our start-up problems with theirs because the plants a r e not s imilar in s ize o r design.

In mold design, you give a water speed of. I believe, 21.7 cu ft pe r sec. Should not this be lineal feet? I assumed that there a r e 7 passages per side and this figures out properly.

All I can say about your mold distortion data i s that we have experienced the same resul ts in our pilot work at Beaver Falls, and I believe it i s quite common throughout the industry.

There a r e a few miscellaneous questions:

1 . We generally t ry to avoid hydraulic systems. Have these systems required exceptional c a r e o r caused troubles?

2. Must you condition your blooms, and if so, how completely? 3. In Table 6. you indicate that some molds have been removed from

service because they a r e producing rhomboid blooms. Do you know why?

4. How many tons and heats have been cast to date, and, aside from miscellaneous mishaps, have your commissioning troubles ceased?

R. JOHNSON-The ladle and tundish a r e virtually f ree of s lag throughout the whole cast by virtue of the s teel being supplied from tilting furnaces in which there i s no s lag car ry over from the furnace.

We have not made any cas t s without the ladle lid and burner. With regard to lining life this i s a feature of the casting temperature,

quality of s teel , type of refractory lining in the ladle, casting time: and it i s not possible to generalize. With a brick lined conventional s teel ladle the lining life i s 20 heats compared with 12 for a continuous casting ladle.

With regard to stopper rod control causing a rough and splattering s t ream, I think the s l ides showing teeming into the mold indicate that this is not the case.

In our experience heating i s ca r r ied out during the cast and i s most necessary.

We have limited experience with regard to thin wall molds but believe them to be cheaper than the solid block mold for the same life.

The molds a r e reciprocated in pa i r s in a common table. With regard to lnold lubrication this was designed by a f i rm of lubrication

engineers, and although the installation seems complicated it has given adequate service.

I am ,unable to comment on the consun~ption of water per lb of steel, but the quantity appears necessary and i s a feature of quality control of the bloom.

I agree that individual withdrawal rol ls a r e desirable but with a multi- strand machine this increases the capital cost and common withdrawal rolls a r e simply a compromise.

Initially there were problenls with the oxygen propane cutting system but these have now been overcome. Essentially these were concerned with the difficulty of positioning of the burner nozzle at a constant distance from the bloom face.

Powder cutting i s conlmonly used for initiating the cut, after which it is no longer necessary.


The water systems do seem complicated but they have given excellent service, and I would not wish to contest their merit a s this i s essentially an engineering problem.

The control of s t ray elements (lead, copper, zinc) is not a problem a s our steelmaking process uses 100 pct hot metal produced from virgin iron o r e with very low residuals.

I have referred in my presentation to the quality of rimming steels which, so fa r , has not reached the desired quality, and experimental work continues.

We have experienced little trouble with the hydraulic systems except that the ladle has failed to tilt on two occasions associated with loss of oil in the system.

We do not consider the casting ra te of 25 tons per hour per mold to be high a s this i s regularly achieved.

E. F. WONDRISf-Mr. Johnson's paper i s an excellent contribution to the development work on continuous casting. The data and information presented will certainly help the s teel industry to improve the design and the operation of continuous casting plants.

One item of particular interest i s the temperature loss problem associated with the tundish operation and the extended pouring time during continuous casting. The main factors influencing the temperature loss in the tundish are:

1. The contact-surface to volume ratio of the s teel in the tundish sur - rounded by the refractory lining.

2. The heat input and the heating time of the tundish preheat. 3. The rate of filling and the rate of emptying the tundish. 4. The flow rate of the s teel through the tundish while casting. 5 . The radiation loss of the tundish and the design of the cover.

The maximum temperature drop between the ladle s tream and the tundish s t ream occurs at the beginning of the cast after the tundish is filled. During the casting period, the tundish lining becomes more and more preheated by the s teel flowing through the tundish and the temperature drop between the ladle s tream and tundish s t ream decreases. The reason for the excessive temperature drop during the filling and the emptyingof the tundish i s the high contact-surface to volume ratio which occurs during these periods. The temperature loss during the filling of the tundish can be minimized by filling the tundish with a higher flow rate a s Mr. Johnson mentioned. The tundish design influences the temperature loss very strongly and a flat tundish could also have a critical temperature drop at the very end of the cast, resulting in a skull formation in the tundish. Proper tundish preheating reduces the temperature loss to a large extent.

The decreasing temperature difference between the ladle s t ream and the tundish s t ream throughout the cast, a s mentioned before, compensates for the temperature loss of the s teel in the ladle and resul ts in a more uniform steel temperature in the mold.

Our f i rs t questions, at what time the ladle temperature and tundish temperature shown in Table 1 were measured, and in which way the average

" ~ i v i s i o n Chief-Process Metallurgy, Research and Development Department, National Steel Corporation, Weirton, West Virginia.

Development of Pressure P;du;ing Process for Casting Slabs 43

tundish temperature drop per minute given in this Table could be applied for temperature loss calculations, have already been answered by Mr. Johnson.

The tapping temperature for low carbon steel was 2945"F, the steel temperature in the ladle before the cast was 2862" F, the tundish temperature in the beginning of the cast was given as 2822"F, and the temperature drop during the cast was given a s 0.9"F per min. This makes a steel temperature of 2770°F in the tundish after a 60-min. cast, which i s relatively low.

Did the preheating practice make it necessary to apply a siphon type ladle? What effect did the ladle lid burner and tundish cover burner used during the cast have on the temperature drop of the molten steel?

R. JOHNSON-The ladle and tundish temperature shown in Table 1 are measured at the commencement of casting. The tundish temperature drop per minute is an average figure and i s not used for temperature loss calculations.

The siphon type ladle i s a feature of plant design rather than preheating practice.

We have no experience in operating the plant without the ladle burner and tundish burner and therefore I am unable to quote on their effect on temperature drop of the molten steel other than to say that in our opinion they a re necessary.

Development of Pressure Pouring Process

for Casting Slabs

By J. Woodburn, Jr.,* G. R. Lohman; and R. J. Nylen*

ABSTRACT

The Controlled Pressure Pouring Process was developed by the Griffin Wheel Co., a subsidiary of AMSTED Industries Inc., to produce cast steel freight car wheels.

The quality of these cast wheels, and the adaptability of the pouring process to automation, led to the adaptation of the process for production of semi-finished steel mill shapes-first billets and finally slabs.

The process i s presently in use pouring steel railroad car wheels at six plants of AMSTED subsidiaries, in two licensed steel wheel plants outside the United States, at Lebanon Steel Foundry-producing high alloy castings- and at Washington Steel Corp. and Eastern Stainless Steel Corp.-both producing large stainless steel slabs.

*President, Commercial Manager, and Project Engineer,' respectively, Amsted Research Laboratories, Bensenville, Illinois.

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