真空感应炉熔化期工艺优化控制

采用神经网络进行真空感应炉熔化期工艺过程的建模,利用实际工业生产数据进行仿真,并对某一钢种的熔炼工艺操作,采用遗传算法对熔化期电能的输入与合理分配进行了寻优,仿真结果表明该方法的有效性和优越性。     

稀有金属真空熔炼熔速控制的研究

针对电弧炉的不稳定性和强耦合性问题,提出一种基于模糊控制真空自耗电弧炉熔速控制方法,通过对熔速控制系统模型分析与描述、对真空自耗电弧炉熔速控制策略分析以及对模糊控制理论的研究,实现对电弧炉熔速的稳定控制,从而保证真空自耗电弧炉的稳定性运行。     

Formation of local melting regions in a solid body near the melting temperature

The formation of local melting regions is shown to be ensured by the fluctuation of the vibrational (kinetic) energy in a crystal. This approach is based on the Frenkel’ idea about heterophase fluctuations. Equations that relate the additional volume (ΔV(T)), electrical resistivity (Δρ(T)), or enthalpy (ΔH(T)) increment in solids to the presence of local melting regions are obtained. An analysis of the experimental data demonstrates that 6% of the solid body atoms have the properties of a liquid at the melting temperature. This approach is used to explain some unexpected facts and to calculate the energy of formation (E _f) and concentration (C _m) of vacancies in some metals.     

Gas flow analysis in melting furnaces

The flow structure inside round furnaces with various numbers of burners, burner arrangements, and exit conditions has been studied experimentally with the purpose of improving the flow conditions and the resulting heat transfer. Small-scale transparent models were built according to the laws of geometric and dynamic similarity. Various visualization and experimental techniques were applied. The flow pattern in the near-surface regions was visualized by the fluorescent minituft and “popcorn” techniques; the flow structure in the bulk was analyzed by smoke injection and laser sheet illumination. For the study of the transient effects, high-speed video photography was applied. The effects of the various flow patterns, like axisymmetric and rotational flow, on the magnitude and uniformity of the residence time, as well as on the formation of stagnation zones, were discussed. Conclusions were drawn and have since been applied for the improvement of furnace performance.     

Parameters of melting dendrites in NaCl

Radius of curvature ϱ, velocity ν and branching period b were measured near the tips of melting dendrites resulting in a single-crystal NaCl volume from heating by CW CO₂-laser focused irradiation. The range of dimensionless superheating Δ is estimated to be 7.0·10⁻⁴−3.5·10⁻³. Relations ϱ²ν = const and b²ν = const typical for crystallization dendrites are fulfilled, however, the tip stability parameter σ is 5–6 times higher than the value $\text{σ}{}^1\text{≊ 0.02}$ known for crystallization dendrites. The fact is connected either with low superheating level or with peculiarities of melting dendrites. The relation b/ϱ is 4.2 and is like the usual dendrites, i.e. the similarity of geometrical shape is observed. However, the branches take place at “liquid” dendrites near the very tip and the signs of its curvature pulsations in time are observed.     

Improving combined blast in blast-furnace melting

Translated from Metallurg, Vol. 39, No. 10, p. 17, October, 1995.     

Structure of the welding zone between titanium and orthorhombic titanium aluminide for explosion welding: II. Local melting zones

The structure and chemical composition of the local melting zones that form during explosion welding of orthorhombic titanium aluminide with commercial-purity titanium near a wavy interface between them are studied. The Rayleigh number is estimated to propose a possible mechanism for the formation of a concentric structure in these zones. Titanium aluminide fragments are detected near the zone boundaries. It is assumed that the fragmentation in the transition zone is caused by the division of a material into loosely coupled microvolumes under the action of a strong external action in a time comparable with the explosion time. Outside the transition zone, fragmentation occurs via a traditional way beginning from dislocation accumulation. Both processes occur in titanium aluminide and only one process (banded structure formation) takes place in titanium.     

Refining by fractional melting

A new and highly effective method of purifying metals is described. The process, a fractional melting process, involves heating an alloy within its liquid-solid region while simultaneously compressing it against a filter to remove the interdendritic liquid. A simple mathematical model is developed_which shows that remarkably high “refining ratios”, ˉC_c/C_o, can be obtained (where ˉC_c is wt pct solute of the refined “cake” and C_o is initial wt pct solute). For example, for a “yield” of refined solid of 0.4 of the original sample and a partition ratio,k, of 0.1, this new process achieves a refining ratio of as low as 10⁻⁴, 1000 times lower than isothermal separation and comparable to that obtained by multi-pass zone refining. Refining ratio is shown to depend on partition ratio, “instantaneous cake wetness” during the refining process, final fraction solid and extent of diffusion in the solid. (“Instantaneous cake wetness” is defined as fraction liquid in the cake at any given instant during refining.) Refining experiments were conducted on a series of Sn-Pb alloys in which samples were heated under a pressure of 21 MPa (2900 psi), over a temperature range of 5 to 20°C above the eutectic temperature. Refining ratios obtained are in agreement with theory, assuming low “instantaneous cake wetness”. Calculations showed this wetness to be about 0.02. Final structures of the refined solid are fine grained and completely devoid of second phase. This paper is based on doctoral thesis work of A. L. Lux.     

Macrosegregation in quiescent melting and liquid-phase sintering

Macrosegregation during melting of alloys can arise if the densities of the alloy components differ. In particular, if the higher-melting component is not present in amounts sufficient to develop an interconnected structure, this component can sink (assuming it is more dense than the liquid) to the crucible bottom during melting. This produces a liquid head consisting of (to a first approximation) the pure lower-melting component. The resulting macrosegregation takes considerable time to eliminate since it exists over a macroscopic distance (that over which the particles sink). Similar considerations apply to liquid-phase sintering, also treated in this article. The tendencies for macrosegregation and the subsequent structure evolution in melted/sintered materials can be summarized in a melting map. Such a map has axes of alloy overall composition and alloy liquidus composition. The development and elimination of macrosegregation proceeds in stages. Following initial particle settling, the liquid in the liquid-plus-solid zone near the crucible bottom, which was generated by the settling, attains its equilibrium composition. Finally, elimination of the long-range liquid concentration gradient takes place. If the material has a composition corresponding to a liquid-phase-sintered alloy, the solid in the liquid-plus-solid zone then attains its equilibrium composition. The times for the various stages can be estimated simply. Melting maps can be refined by placing contours of equilibration time on them.