Refractories 287

High Efficiency Operation for Electric Arc Furnace Steelmaking New 140-ton Furnace Constructed at Toshin's

Himeji Works by T. Kai and R. A. Lubker

Table I-Operational Results of Two 50-ton Electric Arc Furnaces

1075 Jan. Feb. Mar.

Production tons 45,300 45,100 47,700 Yield (product) % 89.2 89.0 89.2 Yield (liquid metal) % 90.8 91.0 91.1 Tap-to-tap time hr-min 1-09 1-08 148 Productivity tph 41.1 41.8 41.8 Consumption

electric power kwh per t 345 357 333 oxygen Nm3 per t 40.5 39.1 42.3 oil It per t 5.8 6.1 6.1 electrode kg per t 5.2 4.1 ' 4.4 wall refractory kg per t 2.0 2.2 2.1 roof refractory kg per t 3.7

2'8 17.7 3.4

ferroalloy kg per t 17.8 18.8

INTRODUCTlaN Toshin Steel Co., Ltd. is the largest electric-arc-fur-

nace steelmaker in Japan. The company has two major steel works, at Tokyo and Himeji. The Tokyo Works has a steelmaking shop fitted with two 70-ton electric arc furnaces and three rolling mills. The Himeji Works has two steelmaking shops and three rolling mills. The two steelmaking shops were originally equipped with two 50-ton electric arc furnaces and two 45-ton electric arc furnaces. The major products are steel shapes and bars. In 1974, the combined output of the two works was 1,400,000 metric tons.

In order to increase the production volume and expand type of products, construction of new mills was carried out at the Himeji Works. The construction project in- cluded a small shape mill, bar mill and 140-ton electric arc furnace. These mills were completed in 1975 and 1976. Toshin's annual production capacity is now 2,000,- 000 metric tons.

This paper presents a technical description of the.new 140-ton electric arc furnace.

TECHNOLOGY OF HIGH-EFFICIENCY OPERATION The improvement of electric arc furnace technology is

very remarkable in recent years. By employing large size electric arc furnaces and using ultrahigh electric power, increase of productivity has been possible.

T. KAI is Manager, Steelmaking Section, Himeji Works, Toshin Steel Co., Ltd., Himeji, Japan and R. A. LUBKER is Vice President, AVA Steel Products International, Inc., New York, New York.

jet burner improved (-three burners installed )

Y jet burner irn~roved

( two burners installed )

l l l l l l l l l l l

1965 '66 '67 '68 '69 '70 '71 '72 '73 '74

Year

Fig. 1-Production increase of 50-ton electric arc furnace

However, in order to achieve this, certain require- ments must be met. Of these, especially important are the supply of a large amount of electric power and con- siderable capital investment. Therefore, employment of large size electric arc furnaces and providing ultrahigh electric power are not easy matters.

Toshin conducted research on matters related to in- creasing operational efficiency through continuing tech- nical studies and experiments using the 50-ton electric arc furnace of the Himeji Works. As a result, improve- ment of production facilities and installation of auxiliary equipment and devices on the furnace led to a remark- able increase of furnace productivity. (Fig. 1)

As a result, in 1975, the 50-ton electric furnace was able to handle an average of 20 heats per day, and a maximum of 23 heats. Conventionally the average heats are 10 to 12. Thus, the monthly combined production of

288 Electric Furnace Proceedings, 1976

T._I.D

- 1

Billet yard

-. -

Bilirt yard

L -- Fig. 2-Layout of South Shop after new plant was added

Scrap Yard M r l l i n g Yard Terming Yard B111rt Yard 125000 ( L r n g l h )

NO.

I

2

3

4

5

Fig. 3-View of section of new plant

NAME

140 Ton Elrclric Arc urna air Chuging Baskrt

Ladle

8-strand Continuous Ca?ling W l n r

Bi l l r t YlHl

6

7

8

9

10

11

B i l l r l Discharge Roller Table

Emrrgrncy Ladle

~h;rging Cranr

Ladle Crane

Scrap Yard Crane

Bi l l r t Yard Cranr .

a

b

c

d

•

1

Furnace Oprralion f loor L r v r l

Casting Floor ~ r v r l

Su rp Yard Crane Hrighl

Hr l t ing Yard C r a m ~ r l g h l

T r r m l n g Yard Crane Hr lgh l

B i l l e t Urd Crane Hr lgh l

Refractories 289

Fig. 4-The 140-ton electric arc furnace as seen from the operation platform

the two furnaces reached 47,000 metric tons. (Table I). This is a maximum hourly production rate of 46 tons. Toshin named this technology the High-efficiency Op­eration System.

The system, in summary, is a result of the following technical innovations and improvement of equipment.

(1) Improved technology for blending raw materials and furnace operation.

(2) Installation of special oxygen-fuel burners in fur­nace wall.

(3) Furnace walls lining of special refractories and installing a wall cooling system.

(4) Special water-cooling ring on furnace roof to ex­tend roof service life.

(5) Technologies relating to fume evacuation system to facilitate complete combustion of fuel.

PLANT LAYOUT The Himeji Steel Works faces the Seto Inland Sea at

the southwestern part of the main island of Japan and is favored by good weather for marine transportation.

Prior to construction of two new rolling mills and the related electric furnace, the Himeji Works was equipped with three rolling mills, two 50-ton electric arc furnaces in South Shop and two 45-ton electric furnaces in North Shop.

With the completion of the additional production facil ­ities, the annual production capacity was increased from 750,000 tons to 1,450,000 tons.

The primary purpose of the new steelmaking facilities and equipment is to provide additional billets for attain­ing increased rolled product output. Therefore, plans were drawn up to install a 140-ton electric furnace and an 8-strand continuous casting machine. The new shop was constructed adjacent to South Shop with the aim of also concurrently using the existing two 50-ton electric furnace shops. (Fig. 2 and 3)

The new shop incorporated Toshin 's accumulated tech­nologies for high-efficiency operation which were com­pleted with the use of the 50-ton electric furnace. Fur­thermore, all equipment and facilities were mechanized to achieve higher efficiency by improving labor savings. The major mechanized features included those for scrap blending, weighing, charging of auxiliary raw materials , etc. Also full consideration was given to maintenance and repair facili ties.

A new teeming yard was built adjacent to the existing yard to permit use of facilities of both yards at the same time. As a result, molten steel from the 50-ton furnace can be transported by ladle transfer to the teeming yard for casting by the new 8-strand continuous casting ma­chine, which could also be used for sequence casting. (Fig. 3)

Table II-General Furnace Data

Shell : ID inside depth, mm inslde helght, mm total insiue helght, mm door opel1ing, mm

Refractory lining: bottom, mm sill line, mm walls, mm roof, mm

Furnace capacities: metal volume, m3

scrap capacities, m 3

Electrode: spacing, mm size, in stroke, mm max. string, mm travel speed, m per min

Equipment: fu rnace till

roof lift roof swing

electrode lift door lift electrode clamping electrode cables

Secondary delta closure

Transformer

Primary voltage Secondary voltage

Furnace breaker

Electrode control Services

furnace component cooling fume control cooling

7000 21U0 (below sill line ) 3050 (above sill line) 5150 1660 wide x 800 high

780 550 370 340

20.8 117

1600 circle diam 24 diam

5250 8890

4.5

rack and pinion, ac 55 kw under 50 sec, for 43 degree tilting hydraulic, 400 mm stroke hydraulic, under 40 sec, for 55 degree swing ac 37 kw, steel cable via winch pneumatic pneumatic and spring water cooled copper cable, 3600 m' 4/phasedesigned for min . impedance, max. current 70,000 amp copper buss and hollow Inter­nally water-cooled copper tubes 55 mva, water·cooled oil Im­mersed, all current·carrying parts are copper 77.000v 700 v max. 30v step 17 tap one­load tap change air blast breaker 3000 amp, 36 kv static type (SCR)

closed system, 400 tph closed system, 1000 tph

290 Electric Furnace Proceedings, 1976

ELECTRIC OPTIMUM C U R R E N T

80 - 50 - -

60 - - 40 -

40 - 20 -

30 -

10 20 30 40 50 60 70 83 S E C O N D A R Y AMPERE ( X 1000 )

Fig. 5-Characteristics of furnace power at 580v rating

ELECTRIC ARC FURNACE EQUIPMENT To gccomplish steelmaking operations more efficiently,

it is important to melt the charged scrap in a relatively short period. In addition, in the subsequent refining process, use of maximum electric power must be com- yleted in a short time without reducing the power.

In order to achieve this Toshin's electric arc furnaces incorporate unique production equipment, and devices to to realize higher efficiency of operation based on im- provement of equipment and facilities and operational technics.

Electric Arc Furnace The 140-ton electric arc furnace employs the NKK-

Sw~ndell type main structure. Nippon Kokan, a leading , steelmaker in Japan, also manufactures electric furnaces in its Engineering & Construction Division. Thus, the company is one of the largest manufacturers of electric furnaces in Japan.

Toshin Steel Co., and NKK's affiliate company, con- stantly carries out technical exchanges with NKK. This makes it easier for Toshin to apply its accumulated tech- nology for electric arc furnace operation to furnace con- struction.

To meet requirements for high-efficiency operation, considerations were given to maklng components of elec- tric furnaces extra durable. The shell diameter is 7,000 mm. The transformer capacity of 55,000 kva is capable of 20% overload. (Fig. 5)

There are four interconnecting watercooled electric cables per phase, which are installed in a triangular pat- tern.

Almost all the manipulation of the furnace are by electric motor drive system. The exceptions are lifting and swinging of the furnace roof, and lifting of elec- trodes by hydraulic systems, thus facilitating operations and maintenance. The travel and positioning of the 24-in. diam electrodes are regulated by electric motor drive using a single ,wire rope winch through thyrlster (SCR) control.

Much consideration has been given to shortening op- erational time for inclining the furnace and rotating the furnace roof as well as to improving the travel speed of the electrodes.

The furnace is so constructed that it can be tilted 45 degrees without increase of impedence in order to im-

Fig. 6-Arrangement of burners

prove furnace operations and facilitate repair work. For normal operations the furnace can be tilted 43. degrees forward and 15 degrees backward.

Oxygen-Fuel Burner Installation of a special oxygen burner is vital for con-

ducting high efficiency operations. The jet stream from the burner tip is in the form of a high-speed, long focus and is concentrated on a specific area for heating the scrap. The white-hot scrap is cut and melted by the ex- cessive nonreacted oxygen thus facilitating high-speed melting.

At present, in the initial stage of operation three burn- ers are installed on cold spots of the furnace wall. How- ever, two additional burners are planned to be installed in order to realize even better operation.

Each burner has a maximum hourly capacity of jetting 1,5010 Nm3 of oxygen and 500 liters of oil. (Fig. 6)

They are fitted with special devices for protecting the refractories around the burner nozzle and lessening the combustion noise. The operation of the burners is closely controlled through the operation board.

Furnace Wall Refractories Normally, excessive wear of refractories is caused

when a large amount of energy is induced into furnaces. This energy can be in the form of high electric power or high electric power coupled with use of oxygen burner equipment. This would reduce operation time due to re- . pair of refractories and thereby affect productivity, thus resulting in higher product cost.

To overcome the above problem, Toshin has developed a unique construction method for the furnace wall. The wall is made of special graphite bricks and cooled by water-cooling jackets. The new furnace employs 13 units of water jackets at four levels. (Fig. 9 ) . The water re- quired for the jackets amounts to 80 tph.

The furnace roof is lined with basic bricks. The center part is made of high alumina ramming mix. A special water c~o l ing ring is installed around the opening in the roof that ducts into the dust catching system. These in- crease the furnace campaign life.

MATERIALS HANDLING Blending and charging raw materials is one of the ma-

jor areas for reducing steelmaking time. Conventionally, for the 50-ton furnaces, scrap is stored outdoor by grade and carefully blended. Then it is transported by trucks and dumped into scrap buckets at the shop.

Auxiliary raw materials are directly charged from the top of the furnace or charged from the charging door by use of charging cars.

However, these means are not adequate for large-size electric furnaces which handle a large volume of raw materials because these require much equipment and manpower. Accordingly, new equipment was needed to realize rationalization.

Refractories 291

Scrap Yard In handling scrap, a major raw material, important

considerations include storage by grade, properly blend­ing the necessary volume by type and dumping into buckets just prior to charging time. In addition, it is also important that scrap transported from outside be di­rectly unloaded at a scrap yard large enough to store a large volume, thus saving on transportation cost.

In order to meet the above conditions, the new shop has two indoor scrap yards adjacent to the melting yard. The yards are about 4,000 m2 in size and are capable of storing a maximum of 10,000 tons of scrap.

In the yards, six 20-ton high-speed cranes are in­stalled. Each is fitted with a 2,000 mm-diam lifting mag­net having a capacity of 37.5 kw. The total handling ca­pacity of the six units is 350 tons of scrap per hour even for light weight scrap. This capacity is matched with the total volume for loading scrap buckets and unloading scrap delivered to the yard.

Scrap is stored by grade in the yard . The scrap buckets can be moved freely between the yards on self propelled carriages. This permits ease of blending of scrap to the required grades. The carriages are operated on two sets of rails. Each carriage is fitted with a bucket thus en­abling alternate charging of scrap into furnaces. Each bucket has a capacity of 120 m~.

The weighing equipment is of the load cell type. It is installed under the rails for the carriages. This equip­ment is more accurate and has fewer malfunctions than those of the conventional type which are installed on the carriages. Weight data, by scrap grade, are automatically registered on the information panel. Furthermore, the accumulated data, by scrap type, are also registered on a different data panel.

At the melting yard , the charging of raw materials into the furnace is conducted with a ISO-ton crane which has a 30-ton auxiliary hoist. The other 50-ton crane with a 10-ton auxiliary hoist is also used. These cranes con­

Fig. 7-0xygen fuel burner unit

Fig . a-Burner installed in furnace wall

tribute significantly to the realization of high-speed op­erations.

Auxiliary Raw Materials Charging System As the large capacity of the furnace required rela­

ti vely large amount of auxiliary raw materials, there was a need for rationalizing the system for charging ma­terials such as lime, fluorspar, ferro alloys, coke breeze, etc. Therefore, a new charging system was adopted for automatically storing, weighing, charging, etc. of the materials.

The auxiliary raw materials are stored in a bunker in­stalled on the melting floor. The bunker has 10 bins. The auxiliary raw materials are transported by conveyer equipped with weighing device from the bunker via electric magnet feeder according to the operation sched­ule. Then, they are transferred to the receiving hopper installed adjacent to a bucket elevator and electric fur­nace. Finally they are charged into furnace by use of a shooter installed in the furnace wall or directly charged in to ladles.

CKS

WATER-COOLING JACKETS

ARBONACEOUS BRICI<S

Fig. 9-Cooling systems for furnace wall

Tap-to-tap charging schedule for the raw materials is as follows :

Tap Melt-down Tap 0- - - - - - - - - 0 - - - - - - - - - - 0 - - - - - - - - - - - - - 0 - - - - - - - - - - - 0 - - - - - .- - - - 0 - - - - - - - - - - 0

No.1 No.2 No.3 No.4 No.5

<----> <------> omin. 10-15 min.

<--------> <------> 40 min. Shortest

No.1 charge lime No.2 charge lime 2,200 kg No.3 charge lime 1,800 kg No.4 charge FeSi 1,000 kg SiMn 850 kg

FeMn 450 kg No. 5 charge lime 1,800 kg fl uori te 500 kg

292 Electric Furnace Proceedings, 1976

Fig. 10-Furnace wall lining

Fig. 11-Scrap yard of new steelmaking shop

~ ¢:> '1 ....... loA ••,.. !) c:> '''''' '

[ .... .. [,-_. [ __," ....

Fig. 12-0peration diagram for auxiliary raw materials

--------------l

Fig. 13-Electrical supply system

These operations are conducted by push button con- trol. (Fig. 12). The time increments of the feeding sys- tem cycle are shown below:

Measuring 60 sec. Bucket elevator filling 4.0 sec.

(100 seconds from weighing) Receiving hopper fdling 80 sec. Bucket elevator down 70 sec.

(to next weighing) Charging into furnace or ladle 60 sec.

POWER AND UTILITIES When adding facilities and equipment to mills, i t is

necessary to take into consideration various factors con- cerning the existing facilities and equipment.

In view of the above, in order to assure the stability and safety of electric power supply, expansion, remodel- ing and integration of existing facilities were planned.

Electric Power The electric power for the Himeji Works is supplied

to the site by an industrial use distribution branch of an electricity power company through 77 kv service feeder.

The transformer capacity for the 140-ton electric fur- nace had to be limited to 55,000 kva because of the lim- ited electric capacity provided by the electric power company.

Major increase and reorganization of electric power- related equipment and facilities are as follows.

(1) 55,000 kva transformer for electric furnace, 2,0,000 kva and 15,000 kva capacitors, circuit breaker in substation, 77 kv service feeder to electric furnace transformer, etc.

(2) Transformer capacity for utilities in the steel- making shop was raised from 5,000 kva to 10,000 kva. (Fig. 13)

In the case of the existing 50-ton electric furnace, power is provided to the furnace transformer by 22 kv service feeder via 77 kv/22 kv step-down transformer. However, in the case of the 140-ton furnace, 77 kv is sent directly to the electric furnace transformer and voltaged down for furnace operation.

In order to reduce voltage fluctuation caused by load current fluctuations of the three electric furnaces in- stalled in the steeImaking shop, the 10,000 kva trans- former of the substation for steelmaking shop is so ar- ranged as to be capable of automatically maintaining a constant range ( 2 4 % ) of secondary transformer fluctua- tion in accordance with change of voltage.

OXYGEN SUPPLY SYSTEM At the existing 50-ton electric furnace, oxygen was de-

livered to the L.O. (liquid oxygen)-tank (30 ton x 3 sets) by L. 0.-tank trucks. Then, via evaporator, it was supplied to the burner and lancing pipe for scrap cutting.

However, in the case of the 140-ton furnace with its higher volume of oxygen consumption, Toshin carried out studies aimed at realizing the same rapid and smooth operation as in the case of the %-ton furnaces. The re- sult of the studies was that the oxygen for the works would be supplied directly by pipeline from a nearby oxygen supply source. The pipeline capacity is equiva- lent to 10,000 Nm3 per hr., at 35 kg per cm2; overall length about 5 kilometers.

The maximum consumption of oxygen reached 14,800 m3 per hr. Therefore, a holder tank having a capacity of 500 M3 at 30 kg per cm2 was newly built.

Thus, oxygen for the works is provided to the electric furnace, rolling mills, continuous casting machines, etc. via the holder tank and pressure reducing system. More- over, the conventional oxygen supply system of L.0.- tank, evaporator, etc. is reserved for emergency use.

COOLING WATER SYSTEM Most of the cooling water for the 50-ton furnace, fur-

nace-related continuous casting machine, dust catcher, etc. is treated by a precipitation basin, filter and cooling tower system and recirculated.

The cooling water required for the new electric fur- nace and related facilities and equipment amounts to about 2600 tph. This volume equals that required for the existing production facilities and equipment.

The cooling water for the electric furnace, molds for the continuous casting machine and dust collector is cooled by use of cooling tower having a treating capacity of 2100 tph. On the other hand, cooling water amounting to 500 tph for the continuous casting machine and spray zone is purified by a precipitator and filter, and then re- circulated.

The cooling water treating equipment is linked with the existing equipment and facilities. Waste water in- cluding rain runoff is also led to the treating system. Thus, a full closed recirculation system has been real- ized. During recirculation and treatment of the cooling water, about three percent is lost. Therefore, of the pur- chased industrial water of some 625 tph, part goes for makeup.

DUST COLLECTING SYSTEMS In the construction of the new electric furnace, the

dust collecting system was designed, first of all, to in- clude a dust collector of the direct furnace roof suction type to cope with the oxygen-enrichment operation by use of burners, and installation of a precipitator to hold down the dust generated by the steelmaking works.

A dust collector of the direct furnace roof suction type is required to ensure that the special oxygen burners are used most effectively for achieving high-efficiency opera- tion thus enabling more rapid melting of the scrap. Through our experiences in operation of the 50-ton elec- tric furnace, it was concluded that the inner pressure of the furnace should be -2 mmAq. And also it was desira- ble that the maximum treating capacity of the dust col- lector be 10 to 20% higher than normal capacity. In addi- tion, the design had to feature simplicity to minimize op- erational troubles.

In view 01 Llle above considerations, the specifications of the dust collector were determined to be as follows.

Blower: 1200 kw (5,000 m3 per min. 700 mmAq at 150°C)

Baghouse: 6.8 (W) x 38.4 (L) x 19.5 (HI m

Filter: total 9760 m2 glass wool Gas cooling system: water cooled duct type

(1,000 tph) Capacity: 5 to 0.02 g per P:m3

Waste gas in the furnace is fed to cooling ducts con- nected to a water cooling outlet fitted on furnace roof and sent to the combustion chamber. Then, it is induced to the water cooler and cooled to about 150°C and fed to the baghouse. Then the cooled waste gas is filtered to below 0.02 g per Nm3 and exhausted.

The collected dust is stored in a hopper having a ca- pacity of 100 ms. These are sized to a grain size of 3@ mm to 10@ mm by use of sizer having a capacity of 10 tph.

The shop dust collector was installed separate from the above. This collector can be concurrently used by the existing and new electric furnace shops. The dust is sucked directly from the canopy installed on the upper part of the 50-ton furnaces and the new 140-ton furnace, and collected in the same baghouse. The specifications are as follows:

Blower: 12,200 m3 per min. (at 60°C, 360 mm Aq)

Baghouse: 5.5 (W) x 45 (L) x 23 (HI m Filter: 11,440 m2 glass wool Capacity: 0.3 to 0.02 g per Nm3

The dust treated by the dust collecting equipment is also sizea by the aforementioned sizing equipment.

CASTING EQUIPMENT The teeming yard has a 250-ton ladle crane fitted with

a 50-ton auxiliary hoist and an 80-ton-capacity service crane with a 20-ton auxiliary crane.

294 Electric Furnace Proceedings, 1976

Fig. 14-Dust catcher of new steelmaking shop

As this teeming yard is linked with the existing 50-ton electric arc furnace shop, molten steel tapped from the 50-ton furnace can be conveyed by transfer truck to the new yard. The 80-ton crane can lift the 50-ton ladle and cast the contents into the new continuous casting ma- chine.

There are four 140-ton ladles in the yard. Each ladle is equipped with two nozzles called sliding gate nozzles.

The continuous casting machine is of 8-strand type. The new ladles are used by placing them on a platform mounted over the upper part of the C.C.M. This facili- tates frequent use of the cranes and continuous casting

without work stoppage. Additionally, another improved casting system is employed. That is, as the cranes have enough height to hoist another ladle onto the ladle placed on the platform, sequence casting has enabled casting molten steel from another ladle lifted over a ladle placed over the platform. (called Ladle-Ladle Tundish System.) (Fig. 2 and 3)

Continuous Casting Machine The continuous casting machine is of the 8-strand

Concast S type. The billet size range is 135 to 150 mm square. This machine was also improved by adding ac-

Fig. 15-Teeming yard of new steelmaking shop

cumulated technologies of Toshin. One of the innovations is that the curvature radius has been increased to 7,000 mm from conventional 5,000 mm normally applied to these billet size. This has made possible about a 10% in- crease in casting speed compared with conventional ma- chines.

Two 4-nozzle tundishes are employed. Thus, the con- tinuous casting machine can be operated independently by 4 strands, and thereby capable of casting 4 strands when the 50-ton ladle is used. In addition, the space between the strands at the center part is wider, thus facilitating maintenance of the machine.

The molds are of the curved, tapered type and have a length of 800 mm. Short beam oscillation is used.

Thus, it was possible to reduce the number of apron rollers because of larger curvature radius, etc. The ma- chine can perform stable operation due to easier main- tenance. (Fig. 16)

The shearing quality of billet has been greatly im- proved by use of hydraulic, diagonal shears. Billets are sheared up to lengths of 1,600 to 7,000 mm. The billet delivery equipment is designed to cope with the various lengths. In the case of lengths below 3 m, the billets delivered from each strand stop at the run-out table end and by strand, are pushed out to the cooling bed. How- ever, in case of over 3 m of billet, these are pushed by 2 strands.

CONSTRUCTION AND OPERATION The construction of the 140-ton electric furnace shop

was started in December, 1973 and completed in April 1975. In 1975, after completion, the new furnace was operated on a test basis for a short time. However, after the initial test operation, the new furnace has not been operated because of reduced production at the works due to the depressed worldwide steel market. In July 1976, the operation was restarted but the operation is not yet full-fledged, only for a few months, due to continuance of reduced production.

Fig. 1GLayout of new eight-strand continuous casting machine

Table Ill-General C.C.M. Data

Model Concast S umber of strands Strand curvature radius Billets ( W ) x (H)

Billets (L) Molds

type dimension

Oscillation type stroke cycle

Tubular mold (curved) 139 x 139 x 800 rnm 154 x 154 x 800 mm

Mechanical short lever 0-28 mm 30-160 c per min.

Cooling water mold cooling water 900-1,300 It per min. per ~ t r . secondarv zone cooling water 400-800 It. ~ e r min. per str. machine cooling wate; 800 It per'min. pers t r .

Pinch rolls drawing speed drive

Shears type

shearing power

0-4 m per min. dc motor (7.5 kw)

hydraulic diagonal shear down cut

300 ton at 185 kg per cm2

Table IV-Test Run Operation Results of New 140-ton Electric Arc Furnace

Result - 1st S t e p 2nd S t e p Target

Production per heat, ton per heat 108 146 145 Heat per day 15.1 13.2 16.5 Productivity, tph 71.5 80.4 100 Yield, % 87 91.5 91 Time of steelmaking, tap-to-tap

hr-min 1-30 1-49 1.27 Electric power, kwh per ton 438 390 360 Fuel, kg per ton 5 5 6.5 Oxygen, Nm? per ton 25.6 28.1 35.0 Electrode consumed, kg per ton 7.3 4.7 4.5

- -- - -

296 Electric Furnace Proceedings, 1976

Fig. 17-Casting platform of new C.C.M.

Fig. 18-Runout table of new C.C.M.

The table shows the test operation results of the new 141)-ton furnace (Table IV). In this table, the first step shows the initial test operational results. At the first step of operation, only partial charges (light charges) were made and production yield was not good and unit consumption was high. Especially, good operational efficiency was not attained as desired, mainly because of troubles for electrodes, etc.

The second step shows a result of recent test operation. By increasing the charging volume, improvement of scrap blending and use of oxygen, the productivity was improved, although the time required for steelmaking was also increased. The results also showed that it is not effective if the capacity of oxygen fuel burners is extra increased per burner. Accordingly, it is planned to in- crease the number of burners from the original three to five. By this improvement, the desired productivity of 100 tph will be possible.

AS for refractories, it is difficult to indicate the opera- tional result by figures due to small number of operating days, but the furnace recorded smooth operation.

CONCLUSION Toshin fully applied its accumulated experiences in its

technical innovations for high-efficiency electric furnace operations and improvement for production facilities and equipment to the newly constructed 140-ton furnace. Toshin believes it can achieve a productivity of the desired 100 tph by using the furnace and related facilities and equipment. This would be a monthly out- put of 60,000 tons for 25 working days.

The company also believes that increasing produc- tivity by the high-efficiency operation system can save consumption of energy and insure maximum produc- tivity by minimum investment for production facilities and equipment. It may be certain that the construction cost for burners, dust collecting equipment and the furnace-related equipment might be relatively higher, but the overall cost will be still lower in terms of con- structing larger size furnaces and installation of the related facilities and equipment, and moreover, the operation will be easier, thus resulting in a good fitted means for best investment efficiency.