FUNDAMENTALS OF THE LUMP CRUSHING THEORY. WORKING PROCESSES OF CRUSHING AND SCREENING EQUIPMENT. LECTURE 8

The article presents materials of Lecture 8 in Theory of carrying and lifting, construction and road vehicles and equipment, which describes the following issues: the rock properties, the rock crushing degree, the basics of the lump crushing theory and types of crushing machines. The technological process of crushing with a roll crusher is described; the values of forces acting in roll crushers are calculated.Along with the process of crushing, the article deals with the processes of segregation and concentration, the basic of the screening (fractionation) theory and features of the hydraulic classification of nonmetallic materials.

Flotation classification in closed-circuit grinding as a way of reducing sulphide ore overgrinding

Research object and aim. Flotation classification in closed-circuit grinding is a way of improving copper ore flotation indicators by reducing minerals overgrinding. Due to valuable components froth recovery with their uncovering in the process of grinding, loss of copper in flotation tailings with secondary slime are reduced significantly. The research aims to study the possibility to improve the flotation of copper ore based on the use of flotation classification in the closed-circuit grinding. Methodology. In order to solve the problem, laboratory studies on closed-circuit grinding experimental modeling were carried out in a mode with and without flotation classification of hydraulic classification discharge. In each grinding mode, five stages of closed-cycle simulation have been implemented. Flotation classification was carried out in froth flotation modes with froth treatment with and without the tapered chute. According to experimental results, the loss of copper has been determined with slime in hydraulic classification discharge and flotation classification, and flotation classification end-product balance was calculated when operating in the closed-circuit grinding. Summary. The obtained experimental data prove the possibility of improving copper ore flotation by reducing minerals overgrinding in the course of flotation classification in closed-circuit grinding. The technology of flotation classification with froth treatment in tapered chutes make it possible to obtain prime concentrate with 18% copper mass fraction when extracting 37.7% copper into it, and final tailings in flotation classification discharge with 0.13% copper mass fraction under 2% loss.

Composite disturbance rejection control for hydraulic classification

In the hydraulic classification, precise control for the flow rate of overflow water is vital to guarantee the uniformity and stability of the powder product size. Usually the multiple overflow tanks are supplied by a shared overflow pipeline, which gives rise to large coupling effects in the controls for the flow rates of multiple overflow tanks simultaneously. To solve this issue, it is necessary to keep the water pressure in the shared overflow pipeline accurately constant, which is not easy due to strong disturbances. Several control strategies have been proposed to control the constant water pressure. However, most of them (such as proportional-integral-derivative and model predictive control) reject disturbances just through feedback regulation and do not reject disturbances directly. This may cause poor control performances in the presence of strong disturbances. For improving the disturbance rejection performance, a control scheme based on proportional-integral-derivatives and disturbance observer is put forward in this paper. The scheme employs disturbance observer as feedforward compensation and a proportional-integral-derivative controller as feedback regulation. The disturbance rejection properties under both model mismatches and external disturbances are discussed. The test results illustrate that the proposed method can remarkably improve the disturbance attenuation property compared with the conventional proportional-integral-derivative method in the hydraulic classification process.

Effect of Hydraulic Classification on Iron Ore Tailings Preparing High Strength Construction Materials

The aim of this study is to understand the effect of hydraulic classification on the iron ore tailings, and develop the cementitious activity of tailings to prepare construction materials. It was indicated that hydraulic classification can effectively divide the particulates of tailings into coarse and fine powders. The compression strength of the prepared construction materials are 87.83 MPa at 28 days, which have higher strength than the construction materials using original tailing, The variation in the tailings samples after hydraulic classification and the cementitious material after step-milling was characterized by sieve analysis, complete chemical analysis, scanning electron microscopy (SEM), and the particles size distribution. By mechanical properties testing and microstructure analysis shows that after hydraulic classification of tailings under the same conditions, the strength of the 3 days, 7 days, 28 days are higher than that of the original tailings. The main phases in the system are the rod of ettringite and low crystallinity or the amorphous C-S-H gel, and residual Ca(OH)2.