Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.

Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.

In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.

Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

Modelling and simulation of bulk metallic glass production process with suction casting

Abstract

An integrated model, which coupled nucleation and crystalline growth with the heat transfer process, is presented in the present paper. The temperature, temperature gradient, cooling rate and the crystalline fraction of Zr₆₅Al_7·5Cu_17·5Ni₁₀ in suction casting have been calculated with this model. The results show that the metallic glass can be obtained at the bottom and the radial boundary of the rod sample, and that the crystalline phase precipitates in the centre of the sample. The crystalline fraction reaches the highest value of 0·0128 in the centre of the sample. Comparatively lower nucleation rate, as well as the higher viscosity and the cooling rate account for the formation of the bulk metallic glass.     

ProCAST软件在熔模铸造工艺优化中的应用

为解决企业生产中某精铸件存在的缺陷问题,利用数值模拟软件ProCAST对其充型过程和凝固过程进行模拟,并预测缩孔和缩松的存在情况.根据数值模拟的结果对该铸件工艺方案进行相应的改进,显著降低了缩孔和缩松缺陷,并提高了产品的合格率.应用表明:铸造模拟软件能够准确地预测充型凝固过程中可能产生的缺陷,从而辅助工艺人员进行工艺优化.     

On numerical simulation of the continuous casting process

In this paper a steady-state nonlinear parabolic-type model, which simulates the multiphase heat transfer during solidification in continuous casting, is presented. An enthalpy formulation is used and we apply a FE-method in space and an implicit Euler method in time. A detailed solution algorithm is presented. We compute the temperature distributions in the strand when the boundary conditions (mold/spray cooling) on the strand surface are known. The numerical model gives thereby a good basis for the testing of new designs of continuous-casting machines. An application of the model to continuous casting of billets is presented.     

Numerical simulation of the casting process of titanium tooth crowns and bridges

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a feeding criterion, and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically poured, and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control. © 2001 Kluwer Academic Publishers     

Numerical simulation of the casting process of titanium removable partial denture frameworks

The objective of this work was to study the filling incompleteness and porosity defects in titanium removal partial denture frameworks by means of numerical simulation. Two frameworks, one for lower jaw and one for upper jaw, were chosen according to dentists recommendation to be simulated. Geometry of the frameworks were laser-digitized and converted into a simulation software (MAGMASOFT). Both mold filling and solidification of the castings with different sprue designs (e.g. tree, ball, and runner-bar) were numerically calculated. The shrinkage porosity was quantitatively predicted by a feeding criterion, the potential filling defect and gas pore sensitivity were estimated based on the filling and solidification results. A satisfactory sprue design with process parameters was finally recommended for real casting trials (four replica for each frameworks). All the frameworks were successfully cast. Through X-ray radiographic inspections it was found that all the castings were acceptably sound except for only one case in which gas bubbles were detected in the grasp region of the frame. It is concluded that numerical simulation aids to achieve understanding of the casting process and defect formation in titanium frameworks, hence to minimize the risk of producing defect casting by improving the sprue design and process parameters.     

充型凝固过程数值模拟在铜型铸件中的应用

考虑到大部分铸件充型过程均处于湍流状态 ,将工程湍流模式用于液态金属的流动和传热计算 ,并与层流计算结果、基准试验以及铜型压缩机灰铁铸件试验结果进行了对比 ,分析了计算结果之间产生差异的主要原因 .简要介绍了相应的数值算法以及在流体自由表面处理方法上与传统方法的不同之处 ,对铸件充型之后的凝固过程也进行了模拟计算且与现场试验作了对比 .     

ZG20SiMn铸钢摇臂壳体铸造过程数值仿真及工艺优化

摇臂壳体是采煤机的重要组成部件,具有多级壁厚、变截面等异形特征。为提高采煤机摇臂壳体铸造质量,解决因铸造工艺不成熟导致的缩松、缩孔等缺陷问题。以MG325型采煤机摇臂壳体为研究对象,设计顶注式和底注式两种铸造工艺方案,采用ProCAST软件探究不同浇注工艺方案下摇臂壳体铸件充型及凝固过程,分析铸件温度场、凝固场及缩松、缩孔铸造缺陷位置。基于Niyama判据和应力场分布对底注式铸造工艺方案进行优化。结果表明:优化后摇臂壳体铸件在凝固冷却过程中保持温度梯度递增,促进铸件实现顺序凝固,铸件缺陷率明显降低且充型效果更佳,缩孔体积仅占摇臂壳体体积的0.004 9%,电机孔薄壁端面应力优化量为38.47%,输出端孔处应力优化量达到91.08%。本文研究成果为采煤机摇臂壳体的铸造工艺提供了理论基础和数据支撑。     

Red thermoluminescence of quartz and its application in dating archaeometallurgical slag

Slag is often the only relic of early pyrometallurgical processes. In archaeological research information about the age of slag deposits is needed and diflicult to obtain with traditional methods. Thermoluminescence has a great potential in this field, because the smelting process leads to a well defined resetting of the 'Luminescence Clock'. Metallurgical slag generally consists of many components, artificial secondary minerals, e.g. fayalite and glass phases usually being the dominant parts. Primary minerals, called relics, are also components or slag. Such a complex composition leads to large difficulties in palaeodose determation if the bulk slag is used. To overcome these problems defined phases of the slag have been separated. Palaeodose determination has been carried out on separated quartz fractions by 'Single Aliquot Regeneration' procedures using the 620 nm emission. The dose rate was determined by high-resolution gamma spectrometry. Alpha autoradiography was carried out to get information about the distribution of radionuclides. The study includes first dating results.     

Effect of casting parameters on the freezing point position of the 304 stainless steel during twin-roll strip casting process by numerical simulation

This study focuses on the numerical simulation of the temperature fields of the 304 stainless steel during twin-roll strip casting process. The cracks and fratographs of the 304 stainless steel strip with the practical casting parameters were observed by Scanning Electron Microscopy. The exit temperature of the 304 stainless steel during twin-roll strip casting process was measured. Meanwhile, it was simulated by means of finite element model. The observed results show that the strip from outside to inside are composed of refined crystal zone, columnar crystal one, and equated axis crystal one. The cracks occur on the strip surface, extended to interior along the columnar crystal boundary, and then, ended at the juncture between the columnar crystal zone and equated axis crystal one. The simulated result was compared to the measured temperature, which showed a good agreement, thus indicating that this model is valid and accurate. Then, by employing this model, the effects of the casting parameters, such as casting speed and casting temperature, on the freezing point position of the 304 stainless steel during twin-roll strip casting process were simulated too. The simulated results show that, the freezing point position is decreased with the increasing casting speed and casting temperature. For producing high-quality strip of 304 stainless steel during twin-roll strip casting, the limits of casting speed and casting temperature are 1.1 m·s⁻¹ and 1,570 °C, respectively.     

Air cooling of a turbine guide vane for a stationary gas-turbine plant (GTP) with a high gas pressure

A guide vane for a proposed stationary GTP is calculated with _r=80, 100, and 126 and T _g ^* =1673°K. The unsuitability of the convective blade cooling used up to now is noted.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 34, No. 5, pp. 897–902, May, 1978.     

Recycling of high grade die casting AM series magnesium scrap with the melt conditioned high pressure die casting (MC-HPDC) process

Strict government regulations and environmental concerns are the driving forces behind the increased use of magnesium alloys aimed at weight reductions. This however inevitably leads to increased magnesium alloy scrap and calls for effective recycling processes. In this paper, the melt conditioned high pressure die casting (MC-HPDC) process has been investigated as a physical approach for the recycling of AM series magnesium alloy die casting scrap. Process optimization was required to eliminate hot cracking phenomena. The experimental results showed that intensive melt shearing alters the size and morphology of MgO present in the scrap melt, leading to an effective grain refinement that was reflected in the mechanical properties of the recycled alloy. The MC-HPDC process showed excellent potential as a physical recycling approach for Mg alloy scrap, producing casting with properties comparable to those of fresh Mg alloys.     

Simulation and application of dynamic heat transfer model for improvement of continuous casting process

Abstract

Numerical simulation is being increasingly used to improve the existing cooling systems. In order to attain highest quality strand, a two-dimensional dynamic mathematical heat transfer model of billet continuous casting of low carbon steel has been presented. This model can be used to compute the billet temperature distribution and shell thickness, especially it can be used to simulate the solidification process which is caused by frequently variational casting conditions. The fluctuation of measured temperature has been reduced to <10°C with thermal imaging system. The online model can monitor surface temperature and shell thickness in the casting process. So it provides the possibility for the online process control. For the validation of the dynamic model, a lot of billet surface temperature and shell thickness measurement were carried out on an actual casting machine. Finally, the dynamic model has been used for adjusting the operating parameters to improve the casting speed.     

Welding of aluminium by the MIG process with indirect electric arc (MIG-IEA)

A novel modification of the metal inert gas (MIG) welding method, which was developed to weld metal matrix composites, was applied to join plates of aluminium 12.5 mm thick. The plates were prepared with square edges and with a small single-V preparation with an angle of 45° in the upper part. The electric arc was indirectly applied on the single-V butt weld over strips of Al-2024 placed on top of the joint. Thermal analysis showed that the efficiency of the MIG process with indirect electric arc (IEA) is increased due to the reduction of heat losses and fully penetrated welds with a high depth-to-width ratio can be produced as compared to plain MIG welding in which partial penetration and lack of lateral fusion were observed. Microstructural examination of the welds revealed distinct characteristics such as partially melted grains trapped within the weld next to the fusion line for IEA welds and the typical epitaxial and columnar growth from the base metal partially melted grains for plain welds, i.e. direct application of the electric arc (DEA).     

Performance evaluation of cryogenically assisted electric discharge machining (CEDM) process

The performance of cryogenically assisted electric discharge machining (CEDM) process has been evaluated in the presented research paper. The machining of cryogenically treated (CT) and cryogenically untreated (CUT) AISI D2 tool steel work specimens using cryogenically cooled (CC), CT, and CUT copper electrodes have been performed. The effects of various parameters, namely, workpiece condition, tool condition, nozzle flushing, peak current, duty cycle, pulse duration, and gap voltage, have been studied on the performance indicators, viz. the material removal rate (MRR), tool wear rate (TWR), and surface roughness (SR). The best parametric combinations have been suggested to obtain the desired quality characteristics. The interaction effects among various parameters have also been presented. An increase of approximately 18% in MRR and a reduction of 26% and 11% in TWR and SR, respectively, were observed, during the machining through CEDM in contrast to EDM. The confirmatory experiments suggested that experimental values were in permissible agreement with the predicted values for all the performance measures. Finally, the comparison of the CEDM with that of EDM process, in the light of SEM graphs, has been presented.     

Modelling of electronic power transformer and its application to power system

Mathematical models of an electronic power transformer (EPT) are established for steady-state and transient stability investigations. To simplify oscillation damping analysis, a simplified dynamic model is developed by neglecting transients of a high-frequency transformer and filter inductors. Comparison between the simplified dynamic model and the detailed model is carried out by simulations using numerical computation and Matlab/Simulink to verify the accuracy of the developed model. For the purpose of the EPT controller design, a small-signal model of the EPT in a d-q synchronous rotating reference frame is established by linearisation about the operating point. According to the developed models, linearised Phillips-Heffron models of the power systems installed with the EPT are presented. Afterwards, as a case study, based upon the Phillips-Heffron models, the damping function of EPT is discussed and its performance is verified by numerical simulation.     

The preparation of slag fiber and its application in heat resistant friction composites

In this study, a fiber-blowing process was utilized to prepare mineral fibers from water-quenched slags to raise the additional value of the recycled slag. Based on their excellent physical and thermal properties, slag fibers were added into a phenol–formaldehyde matrix followed by thermal curing to produce slag fiber-based composites. The friction and wear tests were applied to evaluate the tribological performance of the slag fiber-based composites. Although the optimum process parameters are still under investigation, however, it appeared that slag fiber prepared by this study shows its potential for use in frictional composites based on our results.     

聚四氟乙烯的改性及应用

本文从聚四氟乙烯的组成、结构及物理化学特性、成型加工技术等方面说明了聚四氟乙烯改性的必要性 ,并对其表面改性、填充改性及共混改性作了较详细的介绍。认为聚四氟乙烯薄膜复合技术及改性技术将是未来聚四氟乙烯的主要发展方向 ,最后对聚四氟乙烯及其改性制品的应用作了介绍。     

Study of lime hemp concrete (LHC) – Mix design,casting process and mechanical behaviour

This paper deals with the mechanical behaviour of lime hemp composites. LHC blocks have been produced by compression in a rigid die at a relatively high compression pressure. This process allows the production of LHC with a high proportion of hemp shiv. New mechanical parameters are proposed to compare experimental results of this study with those found in published literature. This paper shows that a high compaction pressure enhances the compressive strength and can offset a reduction of binder. Consequently, a new formula is proposed to predict the strength of LHC which depends on both the binder content and the compaction state of the shiv particles. The study leads to recommendations for the mix design of such composites.