Development of Technologies for Producing Tumbling Media

With an increase in the concentration of the metal in the amalgam, other characteristics of the anodic peaks also change: the peak potential shifts into the positive region, and the half-peak width increases. The change in these characteristics leads to a decrease in the sensitivity of the determination and requires adjustment of the resolution values, which depend on the values of $\psi_n$ and $\sigma^{1/2}$.

Thus, the experimental data confirm the conclusions drawn from theoretical calculations. The quantitative correlation between the experimental dependences and the theoretical ones, calculated by equation (3), gives grounds to believe that the observed changes in the characteristics of the anodic peaks of alkali metals are caused by the presence of strong interaction between the metal and mercury.

References

1. V. N. Korshunov, A. B. Grigor’ev, I. P. Gladkikh. Elektrokhimiya, 6, 1204, 1970.

2. C. Wagner. J. Chem. Phys., 19, 626, 1951.

3. A. A. Kaplin. Advances in Stripping Polarography. Tomsk, TTU Press, 1973, p. 133.

4. A. A. Kaplin, T. F. Ryashentseva. Ibid., p. 137.

5. M. I. Shakhparonov. Introduction to the Molecular Theory of Solutions, Gostekhizdat, Moscow, 1956.

DEVELOPMENT OF TECHNOLOGY FOR PRODUCING TUMBLING MEDIA

V. M. Vityugin, V. A. Lotov, V. V. Koyan, T. S. Frolova, N. I. Poddub’yak,
L. V. Sokolov

As a result of the classification of powder products of chromic electrocorundum, sludge is obtained (fraction smaller than $160\,\mu$) in an amount of 17% of the weight of the corundum; at present, this sludge finds no practical application.

The main purpose of the present work is to investigate the fundamental possibility of using these sludges for the production of tumbling products.

Tumbling is a process for cleaning the surface of products and parts of small dimensions, carried out in rotating or vibratory drums. In order to accelerate processing, sand, emery, corundum, and other abrasive materials are usually loaded into the drum together with the parts. In addition to the indicated powdery abrasive materials, tumbling media are used quite widely in tumbling—

produce tumbling media having a definite shape and dimensions.

A number of requirements are imposed on the quality of tumbling media, the principal ones being the following:

1) tumbling media must have a definite shape, with the maximum possible number of cutting edges and projections;

2) they must have a high abrasive capacity;

3) tumbling media must possess high mechanical strength and hardness, which must correspond to classes VT (very hard) and ChT (extremely hard);

4) they must have definite dimensions, depending on the overall dimensions of the workpieces being processed;

5) the media must be alkali- and acid-resistant.

The main processes of the technology being developed—preparation of a plastic molding mass, forming of articles, and their drying—are determined by the laws of the physicochemical mechanics of dispersed systems, the basic principles of which were developed by Academician P. A. Rehbinder and his school /1–4/.

Slimes of chrome electrocorundum, which are a finely dispersed product of the classification of fine fractions of electrocorundum grain, owing to their crystalline state are nonplastic and, in the moistened state, possess a very small force of adhesion between individual grains. To increase the adhesive forces between the particles of the structural framework, it is necessary to introduce a plasticizer or, in other words, a pore suspension which, enveloping the particles of the nonplastic material, performs the role of a lubricant. Of the great variety of plasticizers, in the production of tumbling articles from electrocorundum slimes, a clayey inorganic plasticizer deserves particular attention; it will form, around the nonplastic (inert) slime particles, gel-like viscous shells. These shells consist of the finest clay particles and constitute a structured network binding the grains of the inert particles. The presence of a structured network imparts to the nonplastic material a number of necessary properties that make it possible to shape articles from it. The structural-mechanical properties of the molding mass are, to a considerable extent, predetermined by its moisture content. The mass has the maximum value of these properties at a moisture content equal to the value of the maximum molecular moisture capacity (MMW) /5, 9/. A molding mass having such a moisture content can be formed into an article both by the method of pressing-

through a die, as well as by pressing and stamping methods.

For further technological processing, freshly formed blanks are subjected to drying, which, from the standpoint of physicochemical mechanics, is a process of converting a coagulation structure into a condensation structure /7/. The drying regime must be chosen so as to ensure defect-free evacuation of moisture from the article being dried. Studies by P. S. Kovalev have established that articles whose initial moisture content is equal to the MMB value withstand a highly intensive drying regime well /8/. The quality of the article obtained as a result of the subsequent technological stage—firing, which is the decisive operation of the process—depends to a large extent on the drying regime.

Sintering processes occupy an important place in firing. For sintering pure ES sludge, a very high firing temperature would be required. The decisive role in lowering the sintering temperature must be played, as in the forming process, by the clay binder, which must contain oxides that reduce the sintering temperature \((SiO_2, TiO_2, Fe_2O_3)\).

As the binding material we selected Chasov-Yar clay of the following composition: \(32.4 Al_2O_3;\ 50.6 SiO_2;\ 1.0 Fe_2O_3;\ 0.8 CaO;\ 6.8\) PPP; \(7.2\)—other components.

The clay is preliminarily ground and dispersed in water, after which a molding mass is prepared, consisting of 70% ES sludge and 30% Chasov-Yar clay (the MMB of the mass is 11.4%). The resulting mass is thoroughly mixed in a runner mixer. From the mass with a moisture content of 11–12% (on a dry-substance basis), blanks are pressed in specially made triangular and quadrangular press molds under a specific pressure of \(65\ \text{kg}/\text{cm}^2\). The use of higher pressing pressures at a mass moisture content of 11–12% proved impossible because of the mass flowing out through the joints of the press mold.

The formed blanks are dried in a lamp radiation dryer under the following conditions: drying temperature \((150 \div 200)^\circ C\), drying time \((25 \div 30)\) minutes.

To ensure uniform removal of moisture from the blank, drying is carried out in an aluminous backfill. The dried blanks are fired in a laboratory tube furnace with a platinum

with heating in an air medium according to the following schedule: heating to the working firing temperature, 15 minutes; working firing temperature, \((1400 \div 1500)^\circ\mathrm{C}\); firing time, 1 hour; cooling from the working temperature, 15 minutes.

The hardness testing of the tumbling media was carried out on a Rockwell tester. Test conditions: load, 60 kg; ball, \(1/8\) inch.

The test results are given in Table 1.

Table 1.

Hardness testing of tumbling media on a Rockwell tester

It is evident from the table that the hardness of the tumbling media obtained ranges from T2 to ChT2, which fully satisfies the requirements imposed on them.

Literature

1. L. A. Abduragimova, P. A. Rebinder, N. I. Serb-Serbina. “Kolloidnyi zhurnal,” 17, 3, 184, 1955.

2. N. V. Mikhailov, P. A. Rebinder. “Kolloidnyi zhurnal,” 17, 2, 107, 1955.

1. P. A. Rebinder. New Methods of Physicochemical Investigations of Surface Phenomena. Publishing House of the Academy of Sciences of the USSR, 1950.

2. P. A. Rebinder. “Physicochemical Mechanics—A New Field of Science.” Moscow, Znanie, 1958.

3. V. S. Fadeeva. Optimal moisture content for forming building products from plastic dispersed masses. Glass and Ceramics, 33, No. 8, 1959.

4. Edited by N. P. Bogoroditsky and V. V. Pasynkov. Radio Ceramics. Moscow–Leningrad, Gosenergoizdat, 1963.

5. A. V. Lykov. Theory of Drying. Energiya Publishing House, 1968.

6. P. S. Kovalev. Author’s abstract of dissertation. Kiev, 1967.

7. E. G. Chapovsky. Laboratory Work in Soil Science and Soil Mechanics. Moscow, Nedra Publishing House, 1966.

INTENSIFICATION OF THE DRYING PROCESS FOR SMALL-SIZED PRODUCTS OF PLASTIC FORMING

V. A. Lotov, V. M. Vitugin

Raw ceramic products obtained by the method of plastic forming, in accordance with A. V. Lykov’s classification, may be classified as typical capillary-porous colloidal bodies with a coagulation-structured porous suspension. From the standpoint of physicochemical mechanics, the drying process of freshly formed products is a process of transforming the coagulation structure into a condensation structure, accompanied by a substantial change in the structural-mechanical properties. The quality of the dried products, the principal criterion of which is their density, will to a considerable extent be determined by the operating parameters of the drying process.

In solving problems of accelerating drying and obtaining defect-free products, the main issue is the correct choice of the maximum value of the permissible drying rate. Of greatest importance for product quality is the drying rate in the initial period, when shrinkage of the products occurs as a result of removal of capillary moisture. Exceeding the permissible rate of moisture removal during this period may lead to local crack formation due to the emergence of significant temperature and moisture gradients. One way of eliminating crack formation is the use, during drying, of a moisture-intensive surrounding medium. K. Laslone [1], investigating