A circular vibrating screen, a kind of reciprocating vibrating screens, has two advantages over other types of sifters: smaller production area compared to a large screen mesh, and higher separation efficiency due to the longer relative motion of material particles. The unique feature of a circular vibrating screen is its three-dimensional motion in the space, which leads to high screen efficiency, high throughput and low power consumption. In addition, due to its simple structure and easy assembly and disassembly, different raw materials can be sorted by grain size in a single plant.

The materials in the circular vibrating screen perform sliding and projection motions while drawing a spiral motion path on the screen surface during sieving. This motion is due to the use of a vertically installed vibrating motor vibrating device that provides the spatial motion of the screen box. Here, the sliding and projection motions of the material affect the path of the material on the screen surface and provide the material delivery rate that allows the material to move outward to the screen surface. Especially, when the materials are in a projection motion, the materials in the material layer are mixed with each other, and the opportunity for fine particles to pass through the screen increases the sieving efficiency. Therefore, the sliding and projection motions of raw materials should be controlled properly to ensure constant throughput and improve screening efficiency.

Many researchers have worked on determination of the parameters of a circular vibrating screen that are being applied to its design. It is very important to clarify the theory of the motion of material on the vibrating surface in determining the kinetic parameters of a vibrating machine, but unfortunately, the kinetic theory of material on the surface of a circular vibrating screen has not been studied in detail.

Hwang Je Hyon, a section head at the Faculty of Mechanical Science and Technology, conducted a dynamic analysis of a circular vibrating screen and the motion characteristics of screen surface, based on which he carried out a theoretical analysis of sliding and projection motions of material, and then, he verified it using EDEM.

The analysis results are as follows.

First, the screen surface of a circular vibrating screen undergoes a plane rotational motion around the vertical symmetry axis and a swinging motion around the center of mass.

Second, the theoretical transport rate of the material sliding motion in a straight vibrating screen is proportional to the angular frequency and vibration amplitude, whereas in a circular vibrating screen, it is proportional to the angular frequency and oscillation angle.

Third, the projection index of material motion at the end of the screen surface of a circular vibrating screen can be determined from 3 to 7 taking into account the motion characteristics of material and the strength of vibrating parts. In this case, the sieving properties tend to improve gradually and then deteriorate again.

The deep-cooling oxygen plant is now widely industrialized because of its highest production capacity and the highest purity of separated gas of all other oxygen plants. The deep-cooling oxygen plant is an air-liquefaction separator that uses compressed air to swell the throttle, obtain the cold, devolatilize the air, and then distill the devolatilized air at low temperature to obtain gases such as oxygen, nitrogen, argon, etc.

Expanders are widely used because they are energetically more advantageous to obtain cold than throttling expansion of compressed gas. At present, turbo-expanders are widely used in the production of oxygen by the deep-cooling method. In oxygen plants, a turbo-expander accounts for 80-90% of the total cold production.

High-strength aluminum alloys are used for the working wheels of a turbo-expander since they rotate at such cryogenic temperatures as -186℃ to -175℃ at high rotational speeds (18 300-18 600r/min). Recently, with the improvement of the mechanical properties of casting materials by the development of casting technology, many researches have been carried out to fabricate efficient closed working wheels by the casting method. What is important here is to choose proper material for working wheels.

Sok Sun Hak, a researcher at the Faculty of Material Science and Technology, proposed a new method for optimizing the alloy composition and heat treatment process parameters of turbo-expander working wheel materials by using quality index and quality engineering techniques, and obtained the optimum parameters.

The additive amount of RE is 0.1%, and the optimum heat treatment process is to perform solid solution treatment before aging heat treatment at 155℃ for 8h. The mechanical properties of this case were excellent, with yield strength of 287MPa, tensile strength of 380MPa and elongation of 12.7%.

This improvement in the mechanical properties ensured stable operation of working wheels in a large oxygen plant and made it possible to increase their lifecycle by three times as much as that of existing ones.

An ecological industrial park consists of several factories and enterprises. Here, there exist connection chains, where the products, semi-finished products and waste of any enterprise are used as the materials or energies for production of other enterprises.

The key to developing a successful ecological industrial park and setting up a balanced ecological relationship among relevant enterprises is to determine the connections between different enterprises in the ecological industrial park. Particularly, a material and energy flow relationship among different enterprises that established chains to form an inter-dynamic structure is needed. If such structure is impossible, an ecological industrial park cannot be formed.

Ri Jun Hyok, a researcher at the Institute of Mirae Industrial Technology, proposed an ecological chain index of an ecological industrial park by applying the general theories of ecology, and then drew the relations between the ecological chain indexes and the recycling rates of semi-finished products and wastes. In addition, he proposed a method for evaluating ecological industrial parks by using the ecological chain index.

First, he defined the ecological chain index of an ecological industrial park, and provided its calculation equation. Second, he defined semi-finished products and wastes of an ecological industrial park and provided its calculation equation. Then, he provided a relational expression of the recycling rate of semi-finished products and wastes and of its ecological chain index.

The ecological chain index and the recycling rate of semi-finished products and wastes can be applied to the planning and construction of ecological industrial parks.