Numerical simulation of macrosegregation in large multiconcentration poured steel ingot

Abstract

A continuum model for the transport phenomena in solidification systems is used to investigate the formation of macrosegregation in a 360 t multiconcentration poured steel ingot. A numerical scheme with explicit time stepping in solidification problems is employed to solve coupled temperature and concentration fields, and equations of momentum. The proposed scheme is tested against an experimental concentration field reported in the literature. The influences of the concentration in each ladle and the ladle pouring time upon macrosegregation are studied. The simulation results show that, with a shorter time for the last ladle, macrosegregation is not significantly reduced with MCP compared with conventional single concentration pouring. A longer ladle time produced a marked reduction in the extent of positive segregation at the top of the ingot. Any positive segregation in excess of the industrial requirement limit is shifted to the riser. If the last ladle is poured after a longer time, growth of channel segregates is initiated by local remelting.     

定点倾转式定量浇注装置研发

对常规倾转式浇注机存在的问题进行研究,设计了定点倾转式定量浇注装置并提出了控制策略——质量及角位移检测反馈定量浇注控制,同时设计出了闭环控制的电液比例系统,解决了目前浇注过程平稳性差和自动控制能力低的问题。     

Geometrical and Mathematical Modelling of Running Systems

Abstract

In the running and gating of metal alloys, the first stage of pouring is the most critical. This is because the fluid flow conditions which exist in the early stages of pouring can control the quality of the casting. Sound castings are the result of the combined effect of both correct fluid flow and correct heat transfer during casting. The aim of this paper is to investigate fluid flow behaviour of molten metals in a horizontally-parted system. Studies of the moving aluminium liquid front suggest that the free height of the advancing stream is a function of liquid velocity, surface tension and density. Equations to correlate these properties have been derived and verified against experimental results. Proposals for the design of pouring basin, sprue and runner for high quality cast products are presented.     

Towards more reliable investment castings

Abstract

The need for more reliable investment castings to meet the expectations of end users is outlined and the research undertaken during the Fundamentals of Investment Casting (FOCAST) project to meet this requirement is summarised. The traditional gravity poured, top gated mould designs used widely by the investment casting industry are shown to produce the least reliable aluminium alloy and steel castings. Changing to a bottom gated design to minimise surface turbulence during mould filling leads to a significant improvement in reliability, although the mould designs may not be particularly easy to implement in practice. It has been shown that a correctly used tilt pouring technique can also reduce surface turbulence and thereby improve reliability, and it is considered that this process is worthy of further development and evaluation by the investment casting industry. Countergravity mould filling has also been shown to be capable of producing more reliable castings than conventional gravity casting. The three techniques are compared and their industrial implementation discussed.     

Model and control system for 3D transfer of liquid tank with overhead crane considering suppression of liquid vibration

Abstract

The purpose of this paper is to present a model for and the development of a control system for the three-dimensional transfer of a liquid tank by an overhead crane that considers the suppression of sloshing. The model of sloshing in each transfer direction is built by using a double pendulum model. In addition, it is confirmed that the proposed model can be applied to a two-dimensional transfer. The present paper provides a method to control sloshing with an overhead crane and also discusses the optimal design for the shape and size of a rod tank device is discussed.     

负压消失模铸造铸铁合金液充填性能及影响因素

研究了模样材料、负压度、浇注温度、浇注系统尺寸等对消失模铸造中铸铁合金液充填性能的影响，提出了改善铸铁合金液充填能力的途径。     

Effect of pouring temperature,composition, mould strength and metal flow resistance on shrinkage cavities in spheroidal graphite cast iron

Abstract

Under the subject of this study, it was found that the growth of graphite in eutectic solidification is the most important factor. Also, shrinkage cavity increases in hypereutectic composition because the crystallisation volume of graphite in eutectic solidification becomes smaller. In addition, the Al amount contained in spheroidal agent or molten metal works negatively for shrinkage cavity, which could be said the same for P, Mo and Cr. As for the shrinkage cavity in non-alloyed ductile iron, the metal supply resistance P _MSR is the most significant element in regard to the occurrence of shrinkage cavity. For tight mould, there is no relationship between modulus and shrinkage cavity while the P _MSR of a product is the dominant factor. This theory of P _MSR can be applied to final solidification loops of products based on simulation. Based on this, it became possible to make shrinkage cavity free products without a riser.     

消失模铸造充型过程数值模拟

运用PROCAST软件对板形铸钢件的消失模充型过程进行了数值模拟。考察了阶梯式浇注系统的充型顺序以及底注式浇注系统的充型形态，另外研究了底注式浇注系统的浇注速度对缺陷形成的影响。模拟结果表明，消失模铸造中，金属液优先从阶梯式浇注系统的上层内浇道充型，充型前沿流动紊乱，铸件容易出现气孔或夹渣；对于底注式浇注系统，充型前沿的流动相对平稳，但过快的浇注速度同样会导致气孔或夹渣缺陷。     

大型铝合金叶片金属型铸造工艺分析

针对铝合金叶片的铸造缺陷，分析指出浇注位置、浇注系统设计、型腔排气和充型温度场是造成铸造缺陷的主要因素，据此，有针对性地提出了铸型倾斜、平浇竖冷、沿分型面开设排气槽、改变涂料层厚度以及调整凝固顺序等改进措施，其效果在生产中得到验证。     

Experimental study of sand filling process of aeration filling and high pressure squeezing flaskless moulding machine

Abstract

Aeration filling is a new flask (or moulding chamber) filling method, which has been developed from the shooting/blowing process. As a sand filling stage, aeration filling determines the ultimate quality of mould in a sense, such as integrality and uniformity. If the moulding sand can be filled in every part of the mould cavity, an accurate shape would be replicated after the finial compaction stage, otherwise the mould may have weak regions. This paper focuses on the study of the sand filling process and its influential factors. From experiments and comparison with conventional shooting (or blowing) process, it can be seen that this method has the advantages of better sand filling effect and less energy consumption.     

倾斜浇注工艺在铸钢上的应用

对倾斜浇注工艺特点、冒口设计、倾斜高度和防止铸件变形等作了详细介绍并举出应用实例。生产实践证明，该工艺可能有效地提高工艺出品率，提高铸件质量。     

Numerical Simulation of the formation of the Sedimentary Zone of Inclusions in Large Steel Ingots

Abstract

A mushy zone is formed in the lower part of an ingot by the showering of crystallites from the top and by free dendrite arms fused and broken from dendrites growing from the side mould wall. The zone obstructs the floating of inclusions. In addition, inclusions floating to the upper part of the ingot can be carried down to the bottom by natural convective flow and can be trapped by the mushy zone. An equiaxed crystal zone in the bottom of a steel ingot results from free crystals coming from the top and sides and from the local growth of crystals caused by heat transfer. The interval from the beginning of pouring to the time when the velocity of convective flow becomes too low to carry any inclusions larger than those of tolerable size down to the bottom is defined as the critical time. The size of the sedimentary zone of inclusions is then equal to that of the equiaxed crystal zone formed in the critical time. In this paper, a method for determing the critical time is proposed, and numerical simulation of the formation of the bottom equiaxed crystal zone has been carried out. A 27Cr2Mo1V steel ingot of 68 tonnes in weight was studied. From the results of the numerical simulation, the weight ratio of the offcut tail end to the ingot body was 8.11%. This result approximately agreed with the weight ratio of 8.8% obtained in production practice with the same ingot.     

Effect of ladle outlet geometry on internal porosity in gravity casting automotive brackets: An experimental investigation

This study investigated whether the pouring ladle's outlet shape could reduce the porosity of aluminum alloy casting products and whether it could be applied to mass production of automotive brackets based on computer simulations and experiment.The filling behaviors of the melt were simulated to compare the flow characteristics of the molten metal poured from the conventional ladle and the proposed ladle.Results show that for the conventional ladle,the pouring metal is V-shaped,while it is relatively circular and poured at a more constant rate in the proposed ladle.CT scans reveal that the proposed ladle reduces the porosity of the cast product.The proposed ladle resulted in an average of 30 fewer pores,a 299.56 mm3 smaller average total pore volume,and a 0.041% lower difference in average porosity.It is concludes that the proposed ladle can be used in the gravity casting process.By changing the ladle outlet shape can reduce the casting failure rate of massproduced automobile bracket.     

Modbus协议在反重力铸造液面加压控制系统中的应用

反重力铸造实质是实现对金属液浇注、凝固过程的加压控制,由于控制过程时间短、数据处理量大,对控制系统通讯的可靠性要求较高.本文在采用上位机PC和下位机PLC结构的反重力铸造液面加压控制系统中,利用Modbus协议编写开发了相应的通讯程序,实现了上下位机之间的数据交换.实际应用表明,该系统教据交换具有实时性好、操作简单、稳定性高的特点,避免了因使用PLC专用模块及协议而增加的额外成本,具有很好的经济实用性和安全可靠性.     

浇注系统设计的新启示

采用底注式平稳充型的方案来设计浇注系统，把液流在内浇道的出口速度作为限制瓶颈，它控制金属液在整个浇注系统的流动速度。在保证铸型充满的前提下，内浇道的充型速度最好限制在0.5m/s以内，以普通达铸铁精密铸造叶片为例，把传统的顶注式浇注系统和新的底注式浇注系统的结果进行比较，在充型过程中，采用X射线实时跟踪系统进行了观察，发现顶注式浇注系统充型紊乱，易造成夹杂，浇注的26个叶片中3处出现裂纹，30处出现夹杂缺陷，而采用底注式浇注系统，铸件充型平稳，没有裂纹，只有3处出现夹杂缺陷，优化效果明显。     

Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys

Abstract

Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton's like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration.     

Modelling of air entrainment during pouring of metal castings

Air entrainment during mould filling is major source of oxide inclusions in metal castings. A model is developed to predict the location and rate of air entrainment as part of a standard mould filling simulation. The local air entrainment rate is calculated as a function of the turbulent kinetic energy and the magnitude of the normal velocity gradient of the liquid metal at the liquid–air interface. The model is validated through comparisons with experimental air entrainment measurements for a plunging water jet. It is then applied to study the effect of gating system design and pouring parameters on air entrainment in steel casting. Air entrainment is found to be reduced for a metal stream from the ladle that is centred above the pouring cup or the use of an offset step pouring basin, low head heights, high flow rates, a pressurised gating system and bottom ingates.     

铝合金消失模铸造工艺参数的研究

讨论了各工艺因素对消失模铝合金铸造质量的影响，分析了各工艺参数与铸造缺陷之间的关系。结果表明：保温涂料及一定的涂层厚度有利于提高铝液的充型速度；浇注温度越高、直浇道空心面积率越大，铝液充型速度越快；模样厚度太厚或太薄，均会使铝液充型速度降低；一定的直浇道长度及直浇道面积有利于提高铝液的充型速度；施加负压会使铝液的充型速度大大提高，但负压过大会增大铸造缺陷。     

Mould filling simulation with cut cell in Cartesian grid system

Abstract

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. A cut cell method on Cartesian grids has been developed to simulate three-dimensional mould filling. Cut cells at a cast/mould interface are generated on Cartesian grids. Governing equations were computed using volume and areas of cast at cut cells.

In this paper, a new method that can consider the cutting cells which are cut by casting and mould based on the partial cell treatment is proposed. This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian gird system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. It can be known that the momentum energy at the cut cell is conserved by using the cut cell method. By using the cut cell method, the performance of computation gets better because of reducing the whole number of meshes.     

Fluid Flow,Mould Filling,and Gating

Abstract

It is a well known and accepted fact that the mould-filling process plays an important role in achieving a quality casting. In this paper, the author presents a review of the state-of-the-art regarding the understanding of the process. It is also shown that experimental methods as well as numerical fluid-flow modelling and simulation techniques, can be used to improve the understanding of the casting process. Finally, it is revealed how new numerical simulation techniques can be used successfully to achieve the correct gating dimensions which will ensure optimum mould filling.