Mixing is an important technique for improving product quality in various manufacturing processes. Various mixers are used in the mixing processes of many fields including iron works, food industry, cosmetics and construction.

Among various types of mixers, a twin spiral mixer has the advantage of small volume and continuous mixing. In a twin spiral mixer, the left and right spiral wings attached to two axes rotating in opposite directions alternately work by advancing the material in one direction. First, the left spiral wing rotates and contacts material particles, advancing them and sending some of them toward the right spiral wing. The right spiral wing then approaches the position where it can contact the particles. Next, the left spiral wing releases the particles, and the right spiral wing comes into contact with them, advancing them and sending some toward the left spiral wing. Thus, in the twin spiral mixer, mixing is achieved by a simple cross action of the spiral wings that send some particles toward each other. From this mixing principle, the mixing degree in the twin spiral mixer is determined by the number of wings that interact with particles. In addition, due to the single mode of mixing, the attainable mixing degree is not high, and therefore, the length of the mixer must be long inevitably to increase the mixing degree.

Generally, various methods of structural and working parameters optimization have been widely used to improve the performance of machines and equipment. However, these methods are not sufficient to fundamentally change the performance characteristics and they have certain limitations. In the twin spiral mixer, it is also difficult to achieve the improvement in the mixing degree by optimizing the structural parameters, since the mixing process is realized by a simple cross action of the spiral wings.

Ri Song, a researcher at the Faculty of Mining Engineering, evaluated the mixing degree by simulating the mixing process of a twin spiral mixer by DEM (discrete element method) and then, based on this, he proposed a plan of increasing the mixing degree by installing inverse spiral wings at regular intervals in a twin spiral mixer to change the mixing mode.

Comparing the mixing degree for the conventional twin spiral mixer and the twin spiral mixer with inverse spiral wings, it was 0.779 7 for the conventional mode, 0.801 3 for the 2:1 mode, 0.81 for the 3:1 mode and 0.790 7 for the 4:1 mode, which means the 3:1 mode was the best, and the outputs from simulations were 89.1W, 429.7W, 287.8W and 151.5W, respectively.

You can find more details in his paper “Study on improving the mixing degree of a twin spiral mixer by changing the mixing mode using inverse spiral wings” in “Journal of the Brazilian Society of Mechanical Sciences and Engineering” (SCI).

Scattering of elastic waves by inclusions or local topography in elastic half-spaces has been an important research topic in the fields of seismology, geotechnical engineering and acoustics. Analysis of the response and potential damage to underground structures under different kinds of loadings, especially strong earthquakes, is of great importance for the design and construction of deep underground tunnels.

The propagation and scattering of elastic waves around underground tunnels located under the surface of an infinite half-space have recently been studied using two methods: analytical method and numerical method.

The analytical method mainly focuses on the models of regular shape embedded in an infinite half-space. Although this method is only suitable for relatively simple and regular models, it has an advantage over the numerical method in revealing the essence of problems.

Ri Song Chol, a section head at the Faculty of Mechanical Science and Technology, investigated the influence factors on the dynamic response of a lined tunnel embedded in an inhomogeneous half-space under the conditions of incident SH waves.

He derived an analytical solution for the scattering of plane SH waves by a lined tunnel embedded in an inhomogeneous half-space by employing the complex function method and the conformal mapping technique. The analysis focuses on the treatment of straight and circular boundaries by proper coordinate transformation and by the conversion of the physical plane to the corresponding image plane.

For more information, you can refer to his paper “Analysis of the Influence Factors on the Dynamic Response of a Lined Tunnel Embedded in an Inhomogeneous Half-Space Subjected to SH Waves” in “Russian Journal of Nondestructive Testing” (SCI).

Slurry electroleaching, which produces manganese dioxide from low grade manganiferous raw materials, is noteworthy.

Studies on slurry electroleaching made a start in the latter half of 1960s. Since then, in-depth researches based on slurry electroleaching have been carried out on the treatment of galena, copper sulfide ores and manganese ores. As a result, many successes have been made so far.

However, few studies and applied cases with regards to the industrial method of processing low grade manganiferous raw materials (below Mn 10%) into manganese dioxide have been reported.

DPRK has little amount of Mn raw materials of over 20%. Instead, it has a great deal of wad clay. In order to meet the domestic demands, the problem of processing wad clay must be solved. In addition, the wad clay in our country contains lots of slime. According to some preliminary experiments, slime leaked into the anode diaphragm during the process of slurry-electroleaching, thus dramatically decreasing the rate of the content of manganese dioxide.

Based on the preceding research results, Jon Yong Nam, a researcher at the Faculty of Metallic Engineering, applied slurry electroleaching method (diaphragm electrolysis) to the low-grade wad clay (Mn 4~6%) which is deposited in the central region of DPR Korea in order to obtain high-grade manganese dioxide of over Mn 40%.

He observed the effects of the temperature, current density, ratio of liquid to solid (L/S), time and coagulant agent through the basic experiment on slurry electro leaching of the wad clay. He determined the optimum conditions as follows: current density 150~200 A/m², temperature > 65℃, L/S = 10 : 1, time 1.1 times the theoretical leaching time and amount of the coagulant agent 50 g/t. Under these conditions, the leaching rate was above 95% and the content of Mn in anodic electrodeposits was 45%.

You can find the details in his paper “A Study on the Extraction of Manganese from Wad Clay by Slurry Electrolysis” in “Russian Journal of Non-Ferrous Metals” (SCI).