DEVICE FOR DETERMINING THE VISCOSITY OF MOLTEN SLAGS

N. K. Lebedev, E. A. Kon’kov

One of the most important physical characteristics of the mineral part of solid fuel in the design and operation of furnaces with liquid slag removal is the viscosity of molten slags at the temperatures that occur in the lower part of the furnace (the slag bath). Measurement of this quantity, mainly for metallurgical slags, and the design of instruments for this purpose have been the subject of a number of works [1, 2, 3]. Individual laboratories and researchers have constructed various types of instruments intended for measuring the viscosity of particular substances. We constructed a viscometer based on the measurement of nonelectrical quantities by an electrical method. Such an instrument was used by Tsylyov and Zhilo [1] for measuring the viscosity of metallurgical slags, and by Galileeva [2] for measuring the viscosity of furnace slags. After analyzing the descriptions of these instruments, an instrument of the following form was constructed in our laboratory.

The viscometer consists of a 15-watt direct-current motor with a molybdenum rod of diameter 4 mm, rigidly connected to the motor shaft. The elastic connection of the rod to the motor, used both in Tsylyov’s instrument and in Galileeva’s instrument, was not used by us, since it leads to an unjustified complication of the design and to excess friction losses in additional bearings, which affects the accuracy of viscosity measurement.

At its free end the rod has a cylindrical head 7 mm in diameter and 11 mm high, which is lowered into the slag melt when the viscosity is measured. The motor has independent supply for the armature and the excitation circuit. The voltage of the excitation-circuit winding was adopted according to the factory data for this motor, while the armature-circuit supply voltage was selected from the conditions for obtaining the required rotational speed of the rod. According to Galileeva [2], in order to obtain the required accuracy of viscosity measurement, the circumferential speed of the rod must be such that no separation of the slag from the surface of the rod head occurs. For a rod head of the adopted dimensions, the limiting number of revolutions is approximately 3000 rpm. We adopted a rotational speed of about 2500 rpm. The molybdenum rod is made from ordinary molybdenum wire of diameter 4 mm with the head fitted onto one end. Since, at the adopted number of revolutions, the rod operates in the regime of a flexible shaft, the need for its precise manufacture is eliminated.

The structural diagram of the viscometer is presented in Fig. 1. It is the following device. On the vertical rod 5 there is a cylindrical coupling 4 with two stops, which can be moved smoothly up and down along the rod. A horizontal bracket 3 is attached to the coupling; at its end is a platform for the motor 2, the lower part of which is a water-cooled shield 1. A kryptol furnace 6 serves as the heater.

Fig. 1. Structural diagram of the viscometer. 1 — water-cooled shield; 2 — direct-current motor; 3 — bracket; 4 — cylindrical coupling; 5 — rod; 6 — kryptol furnace; 7 — viscometer stem.

Measurement of the magnitude of the current in the motor armature as a function of the braking torque on the stem, produced by slag of various viscosities at different temperatures, is carried out with the aid of an unbalanced bridge, shown in the electrical diagram of the installation, which also includes the measuring part (Fig. 2), one arm of which is the motor armature \((R_a)\).

The instrument is powered by a storage battery \((B)\). Measurement of the current in the zero arm of the bridge was performed with a galvanometer \(G_2\); the null galvanometer NG is used to set the instrument to zero.

Fig. 2. Electrical and measuring circuit of the installation. \(R_{\mathrm{ya}}\) — motor armature; \(R_{\mathrm{ov}}\) — motor field winding; \(R_{\mathrm{m}}\) — resistance for measuring the sensitivity of the instrument; \(R_{\mathrm{k}}\) and \(R_{\mathrm{d}}\) — fixed bridge resistances; \(R_{\mathrm{p}}\) — regulating rheostat; \(G_1, G_2\) — galvanometers; \(NG\) — null galvanometer; \(K_1\) — knife switch; \(K_2\) — selector switch.

Fig. 3. Calibration curves of the viscometer. I — in ordinary coordinates; II — in semilogarithmic coordinates.

Calibration of the instrument was carried out using the viscosity of a melt of boric anhydride, for which the dependence of viscosity on temperature is available [4]. The calibration curve of the setup is shown in Fig. 3, from which its logarithmic character is evident.

The adopted measurement circuit makes it possible to vary the sensitivity of the instrument by changing the resistance \(R_m\), which is very important when measuring in the range of high viscosity values, where the curve has a very steep rise.

By reducing the value of \(R_m\) during measurements in this viscosity range, the calibration curve can be “stretched” along the mV axis, thereby decreasing the scale division value of the indicating galvanometer and increasing the sensitivity of the instrument.

Using this instrument, measurements were made of the viscosity of furnace slags from fuel burned in furnaces with liquid slag removal.

LITERATURE

1. L. M. Tsvetkov, I. A. Popov. Zavodskaya laboratoriya, No. 5, 1961.
2. E. A. Galileeva, A. V. Krylova. Teploenergetika, No. 11, 1959.
3. Conference on Experimental Equipment and Methods of High-Temperature Research. Publishing House of the Academy of Sciences of the USSR, 1944.
4. Conference on the Viscosity of Liquid and Colloidal Solutions, Part II, p. 253. Publishing House of the Academy of Sciences of the USSR, 1944.