摩擦组元对粉末冶金摩擦材料摩擦性能的影响

实验研究了不同种类摩擦组元对粉末冶金摩擦材料摩擦磨损性能的影响。结果表明摩擦组元的显微硬度对摩擦因数和摩擦因数稳定度影响显著。随着摩擦组元显微硬度的提高，摩擦材料的耐磨性提高，而对偶材料的磨损量增大；摩擦材料的表观硬度主要取决于基体组元，摩擦组元的显微硬度对其影响不人。单独依靠一种摩擦组元不能使摩擦材料取得较佳的摩擦性能，综合使用几种摩擦组元，才能得到满意的效果。     

Wear-resistant aluminum and chromonickel coatings at the narrow mold walls in continuous-casting machines

To extend the working life of molds in continuous-casting machines, a heat- and wear-resistant layer is formed on the narrow M1 copper walls prior to final repair, by spraying on aluminum and chromonickel coatings. The first step is to determine the coating structure, phase composition, and the hardness and microhardness of the surface layers. A chromonickel coating (thickness 0.5–0.6 mm) is sprayed on the surface of the pair of narrow walls of the thick-walled mold. To obtain the required surface purity, the walls must be ground. Efforts are required to increase the thickness of the chromonickel coating. With a coating thickness greater than 0.8 mm, peeling is possible. Therefore, to increase the strength with which the chromonickel coating is bound to the copper base, we consider the possibility of using an aluminum substrate. Thus, to extend the life of the narrow mold walls in a continuous-casting machine, a chromonickel coating with an aluminum substrate may be applied if bonding of the porous layer with the α phase is ensured or the porosity of the layer is reduced.     

Mass transfer in intermediate ladles of continuous-casting machine

The removal of alumina particles from steel is considered for two configurations of a (90–100)-t intermediate ladle. Mass transfer is analyzed on the basis of simultaneous solution of the convective-diffusion equations of the inclusions in the melt and equations describing melt flow within the ladle, taking account of turbulence. An innovation in the assessment of the mass-transfer coefficient between the alumina particles and the refining flux is the concept of wave flow of a thin liquid-flux film as it interacts with the rough surface of the sintered slag. The removal of alumina particles (10–100 μm) from the metal is assessed.     

Simulation of slab formation in a continuous-casting machine

A discrete analog of the differential heat-conduction equation permits the use of nonuniform calculation grids in the simulation of continuous casting. That allows the distribution of the temperature gradients in the model to be taken into account, with corresponding increase in the accuracy of the approximation and the results. A mathematical model is developed for the solidification and shrinkage of continuous-cast slab in the mold. The adoption of a nonuniform grid permits the use of elements measuring 1–2 mm in the simulation. This model is used to study the distortion of the slab cross section at the mold walls. Calculation of the geometric profile permits refinement of the thermal and mechanical interaction of the solidifying shell and the mold walls and determination of the optimal mold taper so as to reduce the risk of surface and subsurface cracking in the slabs.     

Improved internal cooling of rollers in curvilinear continuous-casting machine

In the electrosmelting shop at OAO MMK, the internal cooling of the rollers in a curvilinear continuous slab-casting machine with a vertical section has been improved. To ensure stable heat extraction from the slab and stable difference in water temperature between the roller input and output, the rational flow rate of the cooling water within the rollers is calculated. On that basis, the water required for internal roller cooling is reduced, for slabs of different width.     

Slag formation in the tundish of a continuous-casting machine

Slag formation in the tundish of a continuous-casting machine is investigated during the casting of 360-t low-carbon and low-alloy steel melts. In casting 5–10 steel melts, the slag mass increases significantly, and its composition changes. That is largely associated with the supply of nonmetallic inclusions to the slag from the steel. In casting low-carbon steel, the mass of such inclusions is around 30% of the total mass of the final slag; in casting low-alloy steel, the figure is around 50%. A smaller factor responsible for the change in slag composition is solution of the refractory lining: 4–5% of the mass of the final slag for a fireclay lining and 14–15% for a magnesia lining. The change in slag composition increases its melting point to 80–140°C.     

Improvement of slag-forming mixtures for continuous-casting machine molds

The influence of slag-forming mixtures on defect formation in continuous-cast slab within the mold is considered. The most widely used methods of determining the melting temperature range of the slag-forming mixtures are outlined. The properties of proposed granulated mixtures for continuous-casting machine molds are compared with those of commercial mixtures. For the proposed mixtures, the melting temperature range is narrower; they are also less easily crushed and less hygroscopic than the commercial mixtures.     

Metal flow in the mold of a continuous-casting machine

Analysis of the flow of liquid metal in the mold during continuous casting is a challenging mathematical problem. Nevertheless, precise solutions have bene found for some cases. Such analytical solutions may be used to verify numerical solutions. In the present work, the melt flow in the mold is studied numerically on the basis of the finite-difference approximation of the initial system of equations. This method is relatively universal: it has been successfully used in continuum mechanics, in mathematical modeling of the stress–strain state of shells in casting, and in other industrial contexts. In the present work, it is applied to the hydrodynamic and thermal fluxes of liquid metal in steel casting in a rectangular mold in a continuous-casting machine. The three-dimensional mathematical model that is obtained describes the liquid-metal fluxes in the mold. The processes that accompany the filling of the mold with melt are simulated by means of Odissei software. The calculations are based on the fundamental hydrodynamic equations, a formula from mathematical physics (the heat-conduction equation with allowance for mass transfer), and a familiar numerical method. The resulting system of differential equations is solved numerically. The region investigated is divided into finite elements. For each element, the system of equations is written in finite-difference form. Solution yields the field of flow velocities of the metal and the temperature field within the mold. The algebraic equations obtained by this means are solved by means of numerical algorithms. On that basis, a program is written in Fortran-4. The mathematical model permits variation of the mold dimensions and the cross section of the metal outlet from the submersible nozzle. It may also assist in understanding the motion of the cast metal, which affects the heat transfer by the mold walls, and in finding the optimal parameters of the liquid metal as it leaves the submersible nozzle. As an example, steel casting in a rectangular mold (height 100 cm) is considered. In casting, the metal leaves the submersible nozzle symmetrically on both sides, in the horizontal plane. The results are graphically displayed. The motion of the metal flux is shown in different cross sections of the mold. Regions of circular flow are identified, as well as regions of vertical motion in the mold. The magnitude and intensity of these regions are determined. The temperature field indicates a local hot zone at the mold wall. That may be attributed to the direct flux of hot metal from the aperture in the submersible nozzle.     

Wear-resistant amorphous-alloy nanocoatings for press components

The possibility of improving the wear resistance of the working surfaces in turbine presses by gas-plasma application of amorphous nanocoatings is considered.     

Simulation of the design of an intermediate ladles in a continuous-casting machine

Physical simulation of various designs for a 27-t intermediate ladle with asymmetric metal supply is undertaken, in steady and unsteady steel casting. The flow rates of the metal, its residence time in the casting chamber, the ascent of nonmetallic inclusions, and their percentage content in the mold are determined. An asymmetric stop for equalizing the flow rate in near and far sections of the mold is developed. The best design is an intermediate ladle with an asymmetric stop and annular tuyeres for argon injection around the casting holes.