SUGGESTIONS FOR A DUPLEX PROCESS FOR MAKING STEEL.

Inasmuch as greater capacity and efficiency can probably be obtained by working an open-hearth furnace and an electric furnace in conjunction, the following description and the costs of working a 5-ton tilting basic open-hearth furnace and a 24-ton electric furnace in this manner, as obtained from data furnished by ElectroMetals, Ltd., of London, England, are submitted here.

Although a 5-ton open-hearth furnace is rather small for keeping a 2-ton electric furnace working at full capacity, yet the following method of procedure would give the maximum efficiency with the given plant, and serves to illustrate the point.

The open-hearth furnace should be charged at the beginning of the week, say at 12 p. m. Sunday. The charge under the special circumstances will consist of 4 tons of scrap and 11⁄2 tons of pig iron, with the usual fluxes. This being the first charge, it will probably be ready to tap into the electric furnace at 6 a. m. Previous to this time. the electric furnace has been heated with coke and with current and is ready to take a charge of hot metal.

At 6 a. m. 23 tons of partly refined metal are drawn from the openhearth furnace and put in the electric furnace. The open-hearth furnace is then recharged by putting pig and scrap on the banks and slopes of the furnace and allowing the cold material to come to almost a fusing temperature. Then, when the new material is hot enough it should be pushed into the bath and worked in the usual manner. The metal should be fit to tap in three to four hours.

Meanwhile it has taken about one hour to heat the crude fluid metal and to dephosphorize it, two hours more being taken to desulphurize the charge, so that by 9 a. m. it would be ready to tap, and by 9.15 the electric furnace would be ready to take another charge.

It is quite possible that the open-hearth furnace may not be ready for another hour or more. If this be the case, about 1 ton of cold scrap may be charged into the electric furnace and melted, by which time the open-hearth furnace will be ready to tap. This time it will be necessary to tap only 13 tons of metal into the electric furnace. Owing to the small recharge in the open-hearth furnace the charge will be completely melted and perhaps partly refined by the time the electric furnace has finished its work. The electric furnace then being ready again at, say, 12.30, a 21-ton charge of very hot refined metal will be tapped into it immediately, with no waste of time.

This method of assisting the open-hearth furnace can be carried out when necessary; perhaps at every alternate charge. One will see that the process presents these advantages:

The ton of scrap melted in the electric furnace will not need any pig iron to accompany it, as would be the case in the open-hearth furnace. That means that one-fourth ton of pig iron at $45 per ton is replaced by one-fourth ton of scrap at $5 per ton. Here is a clear saving of $10, which will pay for melting the ton of metal in the electric furnace many times over.

Although an "assisted" charge will take, say, 31 hours to work, the resulting gain of time for the open-hearth furnace will reduce the time of the succeeding electric-furnace charge to less than 2 hours and may even eliminate the dephosphorizing period in the electric furnace and thus reduce the time taken there to 2 hours.

The output by this method will be as follows:

One charge of 2 tons could be run every 3 hours, making 7 charges in 24 hours, or 42 casts per week of 6 days. This makes a weekly production of 105 tons, or a yearly production of 5,040 tons, allowing 48 weeks per year.

The cost of the process would be as follows:

Cost of producing steel by duplex process.

Average power consumption, 420 kilowatt-hours, at 1.3 cents per kilowatthour___

Electrodes

Slags__

Repairs to roof and lining_.

Cost per ton.

$5.46

.56

. 62

.66

Labor, 3 men each shift_.

.87

8.17

It should be noted that there is a saving of $2 on every ton passing through the electric furnace by this method, owing to the use of scrap instead of pig iron.

DUPLEX PROCESS FOR LARGER FURNACE.

If the capacity of the open-hearth furnace be increased from 5 tons to, say, 71⁄2 tons, then it may be found that the following method of increasing the output can be employed.

The open-hearth furnace should be charged with, say, 8 tons of scrap and pig iron. The phosphorus is then reduced to the proper limit, after which a 2-ton charge can be transferred to the electric furnace for completion of the process. The electric furnace will be ready again in 2 hours for another charge.

It should be quite possible to recharge the open-hearth furnace and have the bath dephosphorized again by the time the charge in the electric furnace is finished. In this way a charge should be ready every 2 to 2 hours.

The output will be as follows:

One charge of 2 tons could be run every 2 hours, making 12 charges in 24 hours, or 72 casts per week of 6 days. Therefore 130 to 140 tons would be produced in one week, or 6,200 to 6,700 tons in a year, allowing 48 working weeks to a year.

The cost of producing steel by this method would be as follows:

Cost of producing steel in duplex process, using 7-ton furnace.

Per ton of product.

Power consumption, 300 kilowatt-hours per ton, at 1.3 cent per kilowatthour__

Electrodes.

Slags

Repairs to roof and lining_.

Labor, 3 men each shift_

$3.90

.50

.37

.56

.75

6.08

COST OF OPERATING AN ELECTRIC FURNACE ALONE.

For comparison with the foregoing schemes, the following figures for making steel in the electric furnace alone are given:

In a 2-ton electric furnace 1 cast can be made in 6 hours, or 4 casts in a day, making an output of 24 casts, or 60 tons per week. On a basis of 48 working weeks in a year, the yearly output will be 48 times 60, or 2,880 tons.

The cost of producing steel in the simple electric process would be as follows:

Cost of producing steel in 2-ton electric furnace.

Power, 950 kilowatt-hours per ton, at 1.3 cents per kilowatt-hour___.
Electrodes

Slags___

Repairs, roof, lining, and dolomite_.
Labor, 3 men per shift--

Cost per ton.

$12.35

.87

.62

.87

1.50

16. 21

Although the cost of operation is greater than that of the openhearth, the cost per ton of the metal charged in the electric furnace is much less than that used in the open-hearth furnace, and this saving in cost should more than counterbalance the extra cost of working the electric furnace, not to mention the increased quality of the product.

A 5-ton electric furnace used for melting and refining would turn out 1 charge of 5 tons in 6 hours, or 4 casts in 24 hours. Twentyfour casts of 5 tons each, or 120 tons, would be produced in one week of six working days. The yearly production would be 5,760 tons, allowing 48 working weeks to a year.

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