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must be replaced by a stronger base to remove it, and reducing conditions maintained to prevent its further formation. Scrap must be purchased and selected with care in order that phosphorus and sulphur will be within specified limits in the finished product. This is accomplished only at an advance in price. Good judgment and skill on the part of the melter, as well as an ability for quick observation, will determine the results which will be obtained by this process. Until the advantages of more fluidity and greater freedom from inclusions attributed to acid steel can be substantiated by facts I would say that the basic electric-furnace is the superior steelmaking instrument of the electric processes.
Discussion—The Acid Electric
MR. LEWIS B. LINDEMUTH.-In discussing slags with a certain degree of basicity or acidity the analysis of the slag one unit of FeO combines with one unit of SiO2, the percentage which represents the percentages of elements or compound by weights does not represent the true condition of the slag as to whether it is basic or acid. For example, if we assume that of FeO would be 54.5 per cent. If then assume that
unit of CaO bined with unit of SiO, the degree of basicity would be the same but the percentage of CaO would be 48.2 per cent. For this reason it follows that one unit of Cao will replace 1.28 units of FeO. One unit of Mgo will replace 1.9 units of Feo. MnO is so close to FeO that they can be considered equal.
In figuring on a slag then, it is necessary to correct the figures given in analyses to conform with the replacing value of the different compounds. This can be readily illustrated by
two acid electric furnace slags of apparently an entirely different nature from analysis. They are as follows:
Slag No. 1 Slag No. 2
4.80 Slag No. 1 figuring the bases in terms of FeO equivalent represents 49.07 per cent, while slag No. 2 on the same basis represents 49.09 per cent FeO equivalent.
All slags in the electric furnace will tend to adjust themselves to a certain degree of basicity regardless of whether the bases are iron oxide, lime, magnesium oxide or manganese oxide, and this degree of basicity will be, in terms of iron oxide equivalent, between 44 and 50 per cent.
If, in melting down, a slag is high in iron oxide, as it almost invariably is, it would tend to pick up from the bottom of the furnace enough silica to bring its basicity within the percentages that I have mentioned. If on the other hand, there are not sufficient basic oxides and the slag is high in silica the slag will be thick and viscous and will tend to relieve itself of silica by having silica reduced and silicon passed into the metal. As an example of slag high in bases in which it tended to automatically stabilize itself, the following analysis represents such a heat:
Slag No. 1 Slag No. 2
.23 The iron oxide equivalent of bases in slag No. 1 is 57.77 and in slag No. 2, 41.98 per cent.
On the other hand, seven slag and metal tests taken throughout a heat in which the iron oxide equivalent of the bases vary between 36 and 38 per cent, the residual silicon in the steel increased from 0.11 to 0.32 per cent without additions of silicon.
I have stated in my paper that iron oxide cannot be appreciably or satisfactorily reduced from an acid slag and that it must be replaced by a stronger base. To demonstrate this I will give you as an example some tests taken throughout a heat after the slag was in workable shape and apparently had reached its equilibrium. The example is typical. These results show how FeO in the slag was reduced from 10.67 to 4.60 per cent, but which was not accomplished without increasing basicity.
No. 1 No. 2 No. 3 No. 4
60.30 58.44 56.60 57.50
15.00 18.10 20.00) 18.95
5.84 4.53 4.80 3.80 The iron oxide equivalent of bases in these slags are 44.96, 46.48, 47.28, and 47.28 per cent respectively. In studying acid slags in which the bases are corrected to the equivalent of iron oxide it is noticed that after a slag has reached its equilibrium, additions of lime, manganese, ore, etc., will upset its equilibrium only for a very short time and that throughout the heat after the iron oxide equivalent has been established it will remain practically the same.
One common trouble in the acid furnace which upsets the equilibrium of the slag is the sand from which the furnace bottom is made. The most general trouble appears to be that of having a sand which is too refractory. Such a sand will not sinter into the bottom and when the charge is melted will float to the top and give an excess of SiO2. A good furnace botton sand should contain between 96 and 97 per cent SiO2. If the sand runs higher than this in SiO, it should be mixed with some lower grade sand so that the mixture will contain between 96 and 97 per cent.
It would seem that the glassy, transparent slag is the most desirable for in nearly all cases it shows the lowest percentage of Feo. The blue and green slag with the chocolate coating will produce satisfactory results and are the easiest to obtain. No heat should be tapped, however, as long as the slag shows a black coating. The reason why some of these slags are green or blue or gray, I do not know, but it is probably from some combination of iron, manganese and lime, or possibly alumina in their various forms depending upon the degree of oxidation.
Comparison of Existing Methods of Measuring the Temperature of
By F. W. BROOKE, Philadelphia
A large number of trials and experiments have been carried out by steelmakers along with the very commendable support of the makers of pyrometers to try and put the measurement of molten steel upon a scientific and fairly reliable basis. Most of the practical investigators have known all along that the measurement of actual temperatures to any degree of accuracy is at present too much to aim for, and have contented themselves with the effort of finding some indication such as a reading on an instrument which tells them when the steel is at the best temperature to produce either a certain type of casting or a first-class ingot with the particular composition of steel they are handling, and that each time this reading is obtained the steel is at its best pouring temperature. In other words comparative tests have been their chief aim.
Use of Pyrometers Of the scientific instrument methods, we may consider thermo-couples, radiation pyrometers and optical pyrometers. The thermo-couple for temperatures of heat-treatment has proved valuable. In the measurement of molten steel, however, only the rare metal couples can be considered, and even these do not withstand the very severe conditions of a bath of molten steel. Protective tubes, such as quartz tubes, have been tried, but have certain disadvantages. The mechanical strength of a long tube at the high temperature is inadequate; the chemical reaction of the slag in the case of basic operation is undesirable; and the varying thickness of the coating of slag to the tube as it is pushed through the slag causes a varying lag of temperature from the steel to the couple.
The radiation pyrometers, of which the Thwing or the Foster type of fixed focus pyrometer appear to be most satisfactory, require no focusing and the method of handling them is simple. Both of these instruments also have an attachment for taking care of the change in black body conditions from true black body conditions when steel is poured from a furnace or from a ladle. The accuracies of these attachments are not so important, as they are the same for each heat as long as the steel is in a completely molten state. The first obvious objection is that owing to the slag covering in the furnace, and the difficulty and objection of maintaining an
uncovered patch, the temperature cannot be read until the steel is being poured into the ladle. While this only allows for correction of temperature in one direction, it still has several valuable advantages. If the temperature of the steel is too low, preference can be given to the heavy castings of large section and the pouring operation carried out as rapidly as possible. If the temperature is on the high side, the steel can be left in the ladle or preference given to all the small castings requiring a relatively higher temperature, but perhaps the greatest value is a check and guidance for the melter and the foundry superintendent on the now existing more or less crude practical