Application of aeration sand filling,squeeze balance control and synchronised pattern drawing to flaskless moulding process

Abstract

In recent years, global warming and environmental deterioration problems have drawn public attention. There is an ever increasing demand for production equipments in foundries that are more human friendly and environmentally cleaner. To meet such needs, a new type green sand moulding machine employing 'aeration' sand filling process has been developed. In order to make further improvements in moulding performance, new technologies, squeeze balance control and synchronised cope and drag pattern drawing technology, applied in squeezing and mould stripping process of the flaskless moulding equipment has been developed. Adoption of the squeeze balance control system achieves uniform mould strength and prevents distortion of pattern plates by automatically controlling the squeeze pressure applied to the cope and drag moulds in the squeeze process. This optimises the squeeze pressure according to the shape of the pattern. In this study the effectiveness of these technologies was proved by executing performance tests with an actual machine.     

Gas absorption in grey cast iron during mould filling

Abstract

The effect of mould filling on the hydrogen and nitrogen concentration in grey cast iron has been investigated. A special mould was designed and the influence of several process and mould parameters, such as degree of turbulence, permeability, core binder and coatings, were studied. The hydrogen concentration increased during mould filling and the absorption was favoured by turbulent filling, low permeability and larger gas evolution from the mould and cores. In some cases, the hydrogen concentration in the iron after mould filling almost reached the solubility limit, which increases the risk that gas precipitates during solidification.

Exact values of the influence of mould filling on the nitrogen concentration could not be obtained, but some observations could still be conducted. The absorption of nitrogen seemed to be favoured by the same parameters as hydrogen.     

Pouring control with prediction of filling weight in tilting ladle type automatic pouring system

Abstract

This paper presents an advanced control system in a tilting ladle type automatic pouring system. To improve the productivity and save energy, in the pouring process, it is important that the mould be filled precisely and quickly with molten metal. A sequence control employing prediction of filling weight is proposed in this paper. In the proposed control system, the sequence parameter varies depending on the predicted filling weight during the back tilting. The proposed control system has an advantage in that it can be performed by common control equipment such as a programmable logical controller. The effectiveness of the proposed filling weight control system is demonstrated through the experiments using water.     

Industrial treatment processes for recycling of green foundry sands

Abstract

Three treatment processes for the reclamation of green moulding sands coming out from a cast iron foundry located in Northern Italy are considered in this study. A wet mechanical treatment, a dry mechanical treatment and a dry mechanical plus heat treatment are compared to evaluate the efficiency of each process and to point out the best regeneration solution for the recycling of reclaimed sand in foundry operations. The inflow and the outflow samples of each process were characterised by means of particle size analysis and the determination of silica, loss on ignition, acid request, oolitic and some metals contents. A final evaluation of the three processes was performed taking into account the obtained quality of recovered silica sand and the economical aspects; the wet mechanical and the dry mechanical plus thermal treatments are most effective for the recovery of green moulding sands coming out from the considered foundry plant for cold box core production.     

Dynamic analysis of unbonded sand during filling for EPC

The filling of a moulding box with sand is one factor to affect the quality of castings for Evaporative Pattern Casting (EPC). The maximum filling height of the vertical tube is itself fairly sensitive to various factors and it can be used to express the capacity of mould filling. In this paper, the filling dynamic analysis of unbonded sand is made based on soil mechanics. A model to calculate the maximum filling height of the vertical tube is proposed. The results are generally in agreement with experiments.     

Experimental investigation and numerical analysis of compaction behaviour of moulding sand

Abstract

The compaction behaviour of green sand was studied to assess the applicability of the Cooper–Eaton equation under conditions close to those of real foundry operations. The results indicate that the Cooper–Eaton equation describes the behaviour reasonably well, allowing prediction of the pressure required to achieve sand moulds of reasonable density. A corresponding distinct element method numerical simulation was also attempted. The study contributes useful information to the understanding of green sand compaction. It is clear that spherical sand is preferable to improve filling behaviour and that the gap between mould wall and pattern must be sufficiently large to avoid prevent weak sand compaction.     

Evaluation of green compressive strength of clay bonded moulding sand mix: neural network and neuro-fuzzy based approaches

Abstract

An attempt has been made to develop neural network and neuro-fuzzy based models to predict the green compressive strength of clay bonded moulding sand mixtures and to analyse the properties of the mixed sand. Data for the models were generated following standard experimental procedure in the sand laboratory. Process parameters such as clay content, moisture, coal dust and mulling time were varied. The collected data were used in developing these models. The predicted green compressive strengths by neural network and neuro-fuzzy based models have been found to be in good agreement with the experimental values. Furthermore, it has been observed from the results that the predicted values from the neuro-fuzzy model are more accurate than those predicted from the neural network model.     

Effect of Reynolds number on the simulated filling pattern of a bench mark mould filling problem

A finite element algorithm is presented for simulating the mould filling process. The incompressible, Navier-Stokes equations are solved by the Galerkin finite element method. The metal front is tracked by the pseudo-concentration approach which is a variant of the volume of fluid (VOF) method. The finite element algorithms and the special techniques implemented to ensure that the predicted filling pattern is realistic are discussed. The proposed algorithm has been tested on a bench mark mould filling problem¹³ and the results demonstrate the ability of the finite element method to model such flow phenomena. Results presented for various Reynolds numbers throw light on the complexities involved and the factors to be considered while attempting to model mould filling problems realistically.     

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.     

The Influence of Processing Variables on the Dimensional Integrity of Spheroidal-graphite Iron Castings

Abstract

This investigation was carried out to identify the major factors and their degree of influence on the dimensional accuracy of spheroidal-graphite iron castings produced in chemically- bonded sand moulds. Test castings were poured into furan-resin-bonded zircon sand and silica sand moulds and sodium silicate/ CO₂ bonded silica sand moulds. A comparison of casting sizes with those of the mould cavity into which they were poured showed considerable scatter and overlap. From these data the size that each casting would have had, had it solidified without graphite formation, was calculated and found to depend on mould cavity size for each type of mould. By isolating the differences in casting size due to graphite it was possible to identify the influencing factors. Thus castings poured into furan-resin-bonded zircon sand have the highest contraction and their size depends primarily on the amount of graphite present. The dimensions of castings poured into silica sand moulds show more variation and depend not only on the amount of graphite present and the structure of the metal but also on the thermal expansion of the silica sand moulds.     

射压造型数值模拟

射压造型是铸件生产中的现代化造型方法之一.射压造型包括用射砂进行充填及预紧实和高压压实进行砂型最终紧实.本文利用两相流理论模拟出射砂预紧实后的密度场分布;并采用分区建模的思想,结合型砂的本构关系试验,利用有限元方法,计算出砂型内二维的应力分布状况.     

Flow patterns and re-melting during filling of a large composite casting

Abstract

The filling and remelting of an industrial scale composite casting has been simulated to investigate the effect of fluid flow patterns in the liquid metal on the remelting of the shell material of the composite casting. In the composite casting under investigation, an outer shell material is first cast inside a large cylindrical mould, which is then assembled to additional mould parts, and the core material is poured into the shell/mould assembly. During casting of the core, a thin layer of the shell material re-melts and mixes with the core material producing a bonding layer of intermediate composition. Obtaining the optimum re-melting and thus intermediate bonding zone between the shell and core is critical to producing high quality rolls. The present numerical model employs the volume of fluid method and an enthalpy-porosity technique to couple the filling of the core material and re-melting of the shell material. The interface between the solid and liquid phases is tracked and can be used as a guide to examine the extent of remelting and, to some degree, mixing of the shell and core material. Simulations have shown that the circulation loops that form in the liquid metal pool significantly affect the amount of shell material that remelts.     

Development of a hybrid method for improved accuracy of mould filling computational models for castings

Computational modelling of mould filling is a component of paramount importance for the design of gating systems of castings. The main methods are the body-fitted grid system and the Cartesian grid system. While the former comes with high accuracy but high calculation times, the latter is fast but less accurate. A hybrid method combining a three-dimensional Cartesian cut-cell method and a porous media approach has been further developed. The calculated filling patterns compared favourably with high-speed video images of sand mould filling during pouring of ductile iron, and with visual images recorded through an acrylic glass-water model device simulating the gravity die casting process. In addition, numerical experiments were conducted to demonstrate the improved filling accuracy of the developed hybrid method. To this goal, three different symmetry tests with and without sub-mesh were designed and evaluated. All tests convincingly demonstrated the computational time and accuracy advantages of the developed method.     

A geometric approach for injection mould filling simulation

This paper investigates a geometric technique for generating flow fronts arising from a point gate, in a bounded cavity, with obstacles—a problem which often requires intensive computations for its solution. The technique is based on the assumption that flow velocity is proportional to the plastic part wall thickness. A complex flow pattern in the cavity of an injection mould is constituted by four types of basic flow patterns, namely absorption, refraction, diffraction and merging. Combining these four flow patterns quickly generates the filling pattern in an injection moulding which is useful in the conceptual design stage during the plastic product development. Although the context of application discussed is in plastic injection moulding, the technique is applicable in numerous areas.     

基于Moldflow的注射成型工艺参数对塑件收缩痕的影响研究

基于Moldflow软件的最佳浇口位置和填充分析功能确定浇口位置和数量,采用正交试验法确定注射成型收缩痕指数较小的最优工艺参数组合,研究了注射成型工艺参数对塑件收缩痕的影响,对不同的工艺参数进行了分析。研究结果表明,熔体温度、模具温度的降低,保压压力和注射时间的增加都能减小收缩痕的影响。     

Optimal feeder design in sand casting process by growth method

Abstract

The computer aided optimal feeder design in the sand casting process is considered. The design problem is formulated as an additive evolutionary topology optimisation problem. The initial design of the presented method is a casting part which is placed in a suitable environmental mould box. The method is composed of three stages: determination of the feeder neck connection point, construction of the feeder neck and the feeder growth. During the growth stage, the feeder topology is improved gradually until satisfying some predefined criteria. The technological constraints and user contribution can be easily incorporated in the presented method. The success of the proposed method is supported by illustrative examples.     

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.     

壳型铸造用覆膜砂若干技术问题探讨

根据壳型生产线十几年运行和各类覆膜砂应用的经验,对壳型铸造用覆膜砂的一些技术问题进行探讨。详细介绍适用于吹砂式多工位壳型机的湿态覆膜砂性能;高强度低树脂量覆膜砂的研制;湿态壳型覆膜砂的成形性指数与调湿工艺;翻斗法制壳时的脱壳问题分析和解决办法;覆膜砂脱壳性检测方法;高镍球铁件壳型铸造表面针孔原因分析与抗针孔覆膜砂的应用。     

Rapid fabricating process of zinc alloy moulds based on vacuum casting process

Abstract

A rapid fabrication process was developed by combining stereolithography prototype, silicone rubber mould and vacuum casting process for zinc alloy moulds. Transfer coating mould was introduced as casting moulds reproduced from silicone rubber moulds. Vacuum casting process was applied to improve filling ability of complicated mould with fine pattern surface. Vacuum reduces the gas counterpressure in the casting mould cavity and then improves the filling ability.