Computational and Experimental Study of the Transient Transport Phenomena in a Full-Scale Twin-Roll Continuous Casting Machine

Metallurgical and Materials Transactions B - To gain a fundamental understanding of the transient fluid flow in twin-roll continuous casting, the current paper applies both large eddy simulation...     

PIR与PUR泡沫塑料性能对比研究

在相同的实验条件下分别制备了硬质聚异氰脲酸酯泡沫(PIR)和普通硬质聚氨酯泡沫塑料(PUR),对比研究了PIR和PUR的部分性能指标。利用场发射电子扫描显微镜(SEM)对泡沫的形貌进行了表征和对比;利用热失重分析仪对泡沫的耐温性进行了对比分析,同时研究了PIR和PUR的力学强度和不同阻燃剂添加量对泡沫氧指数的影响。结果表明,PIR与PUR相比,泡沫保持了较高的闭孔结构,PIR的耐温性明显高于PUR,泡沫的力学强度和阻燃性能都得到了较大的提高。     

Numerical Simulation of Fluid Flow and Interfacial Behavior in Three‐phase Argon‐Stirred Ladles with One Plug and Dual Plugs

A numerical investigation is performed to describe the quasi‐steady fluid flow and interfacial behavior in a three‐phase argon gas‐stirred ladle with off‐centered bottom Ar injection through a plug and two plugs placed in 180° and 90°configurations, respectively. The flow of the fluid phase is solved in an Eulerian frame of reference together with the motion of every individually injected Ar bubble, tracked in its own Lagrangian frame. Volume of fluid (VOF) model is used to track any interface between two or more immiscible phases, which include slag/metal, slag/gas and metal/gas. The characteristics of fluid flow in a gas‐stirred ladle with one plug or two plugs configuration are described when the slag layer and the top gas are presented. The slag layer deformation and slag open‐eye formation at different Ar gas flow rates for three types of plug arrangements are given. The comparison of the mixing time, the deformation of slag layer and the behavior of slag/steel interface between one‐plug and two‐plug system is made. Several implications for ladle operational issues during a gas‐stirred ladle refining cycle are discussed. It is found that the proper selection of Ar gas flow rate and plug arrangements during a ladle refining cycle is required for different refining purposes considering the mixing and metallurgical reaction in a three‐phase ladle system.     

漏斗形结晶器宽度对流动、传热凝固行为影响的数值模拟

改变薄板坯连铸结晶器的宽度可以适应客户对不同规格铸坯的需求,因此有必要对不同宽度结晶器钢液流动、传热凝固行为进行研究.采用耦合模型,研究拉速4.0 m/min时,宽度1100、1300、1600mm漏斗形结晶器钢液流动、传热凝固行为.结果表明,结晶器宽度增加,自由液面状态相对传统板坯表现出一定差异,钢液内夹杂物上浮更困难.宽度改变对传热凝固的影响主要体现在沿水口射流方向的局部区域,结晶器出口处凝固坯壳薄弱区随宽度增加而扩大.     

A Numerical Simulation of Transport Phenomena During the Horizontal Single Belt Casting Process Using an Inclined Feeding System

Horizontal single belt casting (HSBC) has great potential to replace current conventional continuous casting (CCC) processes for sheet metal production, by directly casting 3 to 1 mm sheet for the automobile industry. In the present paper, two-dimensional mathematical models were developed to study transport phenomena, for the case of an inclined wall feeding system for a liquid aluminum wrought alloy (AA6111). Based on the commercial software ANSYS FLUENT 14.5 and user-defined functions, a two-layer turbulence model was used to examine the fluid flow emanating from a slot nozzle set above a water-cooled, high-speed, steel belt. The Volume of Fluid (VOF) method was used to predict the shape of the melt-air interface. A transformed coordinate system (x′, y′) was established in order to analyze the fluid flow on the inclined wall of the feeding system. The total pressure gauge gradient (?p_total/?x) was used to describe the behavior of the melt film inside the slot nozzle of the head box. The modeling results show that during the melt film falling process, the total gauge pressure varies within the slot nozzle, which can decrease the stability of the falling film. The first impingement between the falling film and the inclined refractory wall of the feeding system gives rise to a local oscillation, and this influences the stability of the melt film moving downwards. At the rear meniscus position between the inclined wall and the moving belt, there is a clear vibration of the air-melt interface, together with a recirculation zone. The weak vibration of the air-melt interface could be induced by the periodic variation of the melt-air interface. Moreover, the formation of tiny air pockets is predicted. Finally, on the inclined wall of the feeding system, a suitable length of the transition area is needed to avoid over-acceleration of the melt film due to the force of gravity.     

Numerical Simulation of Fluid Flow in a Round Bloom Mold with In-Mold Rotary Electromagnetic Stirring

In this article, an electromagnetic field simulation and a flow analysis model are performed to describe the three-dimensional electromagnetic field distribution and the electromagnetically driven flow characteristics in a round-bloom mold with a low-frequency in-mold rotary electromagnetic stirrer. The interaction between the induced flow and the inertial impinging jet from a straight-through submerged entry nozzle (SEN) of the caster is considered. The effects of stirrer current and frequency on the electromagnetic field and the flow in the round-bloom mold are investigated, and a strategy to optimize the stirring parameters is proposed. The results show that the distributions of magnetic flux density and electromagnetic force magnitude are nonuniform in a three-dimensional electromagnetic stirring (EMS) configuration. There exists a significant axial induced component of electromagnetic force. The flow in the in-mold EMS system is characterized by a dominant swirling movement at the transverse sections, coupled with the recirculating flows in the axial direction. An upper recirculation zone and a lower recirculation zone with the reverse melt flowing are found near the strand wall at the axial location close to the middle of the stirrer, and another recirculation zone is formed due to the interference of the induced flow with the jet from SEN. The meniscus surface has a swirl flow, and the meniscus level rises near the bloom strand wall and sinks around the SEN wall. All of these flow features are closely associated with metallurgical performances of the in-mold rotary stirrer. With the increase of stirring current and the decrease of frequency, the magnetic flux magnitude increases. There is an optimum frequency to obtain a peak of electromagnetic force magnitude and maximum tangential velocity. For a mold rotary EMS system, to determine the optimum stirring intensity, it is necessary to make a compromise between a larger tangential velocity and a relatively quiescent meniscus surface.     

Transport phenomena during horizontal single belt casting process using an optimized inclined feeding system

Horizontal Single Belt Casting is by far the simplest of all near net shape casting machines and is ideally suited to replace current slab caster operations, given its matching productivity, ‘green’ characteristics, and lower capital and operating costs. In the present paper, numerical simulations based on the Volume of Fluid method were utilized to test the performance of an optimized inclined feeding system that does not rely on the use of magnetohydrodynamics to slow the entry velocity of the liquid metal, so as to allow for a thicker film of liquid metal to be formed (10–15?mm), nor on the use of any moving side-dams so as to constrain the slab being formed. Rather, special attention was paid to the meniscus behaviour, including meniscus formation, meniscus renewal, meniscus turbulence, and the formation of tiny air pockets on the bottom surface of the forming strip.     

影响锌型电池封口质量的主要因素

在总结生产实践的基础上,对影响锌型电池封口质量的主要因素进行了讨论。