Green Sand Mould Research Articles

PRODUCTIVITY IMPROVEMENT OF CASTINGS, SWITCHING TO SHELL MOULD PROCESS FROM GREEN SAND MOULD PROCESS

The creation and application of technology to monitor and control the production and delivery of products and service in casting foundries has gained importance and are necessary to sustain in competitive market conditions. Setup of the industries as applied to casting foundries need timely setup and changes to cope up with the increasing demand from the customers as foundries have great demand for the products produced, in numerous fields. In this paper various parameters of importance are improved by employing shell mould process to the castings which were previously produced by green sand mould process.

The Study of Green Compression Strength of a Green Sand Mould Using Statistical Approach

The study of green compression strength of a green sand mould using statistical approach has been undertaken. Empirically generated data in National Metallurgical Development Centre, Jos Sand Testing Laboratory were used for the study. Coefficient of correlation, coefficients of determination and coefficient of multiple determinations were used to explain the relationship existing between the two independent variables of clay and moisture content and green compression strength, the dependent variable. The study showed that the coefficient of determination for Ys: X1 was 0.88 while the coefficient of correlation was 0.94, coefficient of determination for Ys: X2 was 0.90 while the coefficient of correlation was 0.95 and the coefficient of multiple determination was 0.72; these coefficients assisted tremendously in the study of green compression strength. A mathematical model was developed for the prediction of green compression strength; it was tested and proved to be a good estimation tool for estimating green compression strength values on the foundry shop floor. The study has clearly shown that statistical approach is a good tool for studying green compression strength of green sand moulds.

Fabricación de piezas de fundición con grafito esferoidal en molde metálico

The features and suitability of high requirements ductile iron castings production using metallic moulds have been studied in the present work. The structural and mechanical properties of the produced castings have been analysed and compared to the corresponding ones but fabricated using green sand moulds according to a conventional production process. The higher cooling rate in the metallic moulds is the main cause for the appearance of the detected structural changes in castings. The mechanical and microstructural properties obtained directly on castings are remarkable due to the higher nodule count among other factors. Finally, the benefits and inconveniences found in this kind of production methodology using metallic moulds are also discussed.

Understanding the Mechanism of Grain Refinement in Plain Carbon Steels

This paper documents a series of plate casting experiments in 1010 steel. A set of castings with various levels of rare earth (RE) silicide and engineered grain refiner were produced via induction melting and green sand molds. One set of castings also contained a high phosphorous content to enable etching for the solidification structure. Metallographic and tensile specimens were examined to determine the resulting microstructure and property changes. Yield strength, ultimate tensile strength and percent elongation significantly increased with the RE additions. This increase appeared to be primarily a function of the cerium content of the final castings. Examination of the phosphorous containing castings revealed the solidification morphology changed from a columnar to equiaxed type. Electron microscopy revealed RE oxides formed in both sets of castings. The strength and solidification morphology changes were likely caused by the nucleation of δ-ferrite on these RE oxides.

A New Method for the Measurement of Flowability of Green Moulding Sand

Abstract The production of castings by green sand moulds is a very important method for the manufacture of final products for different sectors of industry. In this green sand moulding process the quality of castings depends strongly on the quality of the mould, which in turn is determined by parameters such as the type of foundry machine, the characteristics of the moulding sand and the specifications of the patterns. The mould’s stability for use casting is achieved by filling and compacting moulding sand. This means, that the clay-bonded moulding sand is changed from the free flowing to the compacted state. In this process flowability is a very important parameter. Therefore, a variety of methods for the determination of flowability have been in use. However, it is fair to say that these methods do no longer meet the requirements of the modern moulding process. This paper introduces a new method for the determination of flowability of clay-bonded moulding sand using a specifically designed type of density sensor that was developed by a research team led by Professor Jürgen L. Bast at the Mechanical Department of Technical University Bergakademie Freiberg. The high levels of accuracy in the determination of flowability that this method is capable of achieving have been tested and indeed proven by varying sand parameters such as water and clay content, grain composition, mixing time, and compaction pressure. A further innovative characteristics of this new method of sensor-based flowability measurement is the possibility of using the sensor not only for the lab-based testing of sands but in the actual mould during the production process in the foundry, which allows to determine whether the sand in the mould has the required qualities based on real-time flowability measurements.

Ann Modelling for the Analysis of the Green Moulding Sands Properties

Abstract Application of modern technological solutions, as well as the economic and ecological solutions, is for foundries one of the main aspects of the competitiveness on the market for castings. IT solutions can significantly support technological processes. This article presents neural networks with different structures that have been used to determine the moisture content of the moulding sand based on the moulding sand selected properties research results. Neural networks were built using Matlab software. Moulding sand properties chosen for quality control processes were selected based on wide previous results. For the proposed moulding sand properties, neural networks can be a useful tool for predicting moisture content. The structure of artificial neural network do not have a significant influence on the obtained results. In subsequent studies on the use of neural networks as an application to support the green moulding sand rebonding process, it must be determined how factors such as environmental humidity and moulding sand temperature will affect the accuracy of data obtained with the use of artificial neural networks.

Influence of the Training Set Value on the Quality of the Neural Network to Identify Selected Moulding Sand Properties

Abstract Artificial neural networks are one of the modern methods of the production optimisation. An attempt to apply neural networks for controlling the quality of bentonite moulding sands is presented in this paper. This is the assessment method of sands suitability by means of detecting correlations between their individual parameters. This paper presents the next part of the study on usefulness of artificial neural networks to support rebonding of green moulding sand, using chosen properties of moulding sands, which can be determined fast. The effect of changes in the training set quantity on the quality of the network is presented in this article. It has been shown that a small change in the data set would change the quality of the network, and may also make it necessary to change the type of network in order to obtain good results.

Multi-Objective Optimization of Green Sand Mould System Parameters using Particle Swarm Optimization

This paper deals with multi-objective optimization of green sand mould system using Particle Swarm Optimization (PSO). It is important to note that the quality of cast products in green sand moulds is largely influenced by the mould properties (that is, responses), such as green compression strength, permeability, hardness and bulk density, which depend on the input (process) parameters (that is, grain fineness number, % clay, % water and number of strokes). In this study, non-linear regression equations developed between the control factors (process parameters) and responses have been considered for optimization utilizing PSO. An attempt is being made to form a single objective, after considering all the four individual objectives, to obtain a compromise solution, which satisfies all the four objectives. The results of this study show a good agreement with the experimental results The quality of the parts produced during moulding process depends on the properties (that is, green compression strength, permeability, hardness and bulk density) of moulding sand. It is important to note that improper levels of these properties leads to common casting defects, such as blow holes, pinhole porosity, poor surface finish, dimensional variation, scabs and rat tails, misruns etc. The properties of the mould are influenced by a large number of controllable parameters (that is, grain fineness number, % clay, % water and number of strokes). Hence, it is important to identify the levels of the input variables that provide required mould properties, which improves the quality of the parts produced by this mould. During 1960s and 70s, most of the research work on moulding sand was based on experimental and theoretical approaches. In [1], the relationship between permeability and transformation zones, mould pressure, void space control, etc., was developed through substantial mathematical equations. In addition to this, Frost and Hiller [2] established the pressure and hardness distributions in sand moulds. Later on, Wenninger [3] utilized the rigid water theory to explain sand-clay-water relationships. This approach was completely theoretical and not supported by a large number of experiments. Later on, statistical design of experiments (DOE) had been used by various investigators to study the effects of different variables on the green sand mould properties. In [4] Design of Experiments (DOE) technique was applied to study the effect of process variables on bulk density and green compression strength. Moreover, Casalino et al. [5] utilized Taguchi technique to establish third order model for permeability and compression strength in laser sintered sand moulds. Moreover, Parappagoudar et al. [6,7] developed linear and non-linear statistical models utilizing full factorial DOE, Central Composite Design (CCD) and Box-Bhenken design. In the above work, the authors had considered grain fineness number, % of clay, % of water and number of strokes as input parameters and green compression strength, permeability, hardness and bulk density as the responses. Among the non-linear regression equations developed by the above mentioned three approaches, CCD-based model was found to be the more accurate model for prediction of the responses. Optimization techniques are required to identify the optimal combination of parameters for achieving the desired performance of the green sand mould system. In single objective optimization, one attempts to obtain the best design or decision, which is usually the global maximum or minimum depending on the optimization problem. In green sand mould system, it is difficult to find a single optimal combination of parameters for green compression strength,

Effect of sand mold models on the simulated mold restraint force and the contraction of the casting during cooling in green sand molds

In this work, the JIS AD12.1 (almost the same as A383.1) aluminum alloy was cast in a green sand mold. The restraint force from the sand mold and the contraction of the casting were measured dynamically from the solidifying temperature to the shake-out temperature using a dedicated device. Then, FEM (Finite Element Method) thermal stress analyses of the experiment were performed. The analyses adopted four types of representative constitutive equations and the mechanical properties of the green sand mold, which were quoted from previous research articles. As verification, this study dynamically compared the simulated restraint force and the contraction of casting with measured results and examined which mechanical properties are important for expressing the restraint force of the sand mold. This verification is the first attempt in the world. As a result, the simulated restraint force was estimated to be over ten times as large as the measured result in each type of equation because the yield stress of the sand mold used in our experiment was lower than those quoted from previous studies. The yield stress measured by a uniaxial compression test was 1/20 of the quoted values. When the measured yield stress was adopted in the simulation, the simulated restraint force and contraction approached the measured results. The yield stress of the sand mold was a dominant factor in the restraint force simulated by the thermal stress analyses. The yield stress of the green sand mold used in the casting process should be measured to predict the residual stress using FEM thermal stress analyses.

Market Environment Surrounding Green Sand Molding Process and Technology Trends in Foundry Facilities

Market Environment Surrounding Green Sand Molding Process and Technology Trends in Foundry Facilities

Molten Metal Pressure Control for Defect Prevention with Generalized Predictive Control in Rapid Press Casting

This paper presents a technique for controlling the pressure of molten metal when using a new type of the iron production method called greensand mold press casting to realize high productivity and obtain high-quality castings. In this method, molten metal is poured into a lower mold first, and the after upper mold is moved down toward the lower mold, then both molds are matched. Casting defects such as metal penetration are often caused by the high pressure in the high-velocity pressing process. Therefore, we proposed a pressure control method with a mathematical model of molten metal pressure, and with it we achieved confirmation simulation of the successful pressing production at the different pressing condition such as mold shape. Results show that the proposed pressing production considering the generalized predictive control: GPC can realize sound, penetration-free casting production under the pressure constraint for defect prevention. Here a simple simulation of model predictive pressing control and water pressing experiment using feed-forward motion input calculated by off-line GPC are presented. Discussions of the theoretical control design for the process as well as its practical confirmation result of water pressure behavior in pressing experiment are concluded.

Optimization of Mold Yield in MultiCavity Sand Castings

The productivity of ductile iron foundries engaging in mass production of castings for the automobile and other engineering sectors depends on the number of cavities per mold. A denser packing of cavities, however, results in slower heat transfer from adjacent cavities, leading to delayed solidification, possible shrinkage defects, and lower mechanical properties. In this article, we propose a methodology to optimize mold yield by selecting the correct combination of the mold box size and the number of cavities based on solidification time and mold temperature. Simulation studies were carried out by modeling solid and hollow cube castings with different values of cavity-wall gap and finding the minimum value of the gap beyond which there is no change in casting solidification time. Then double-cavity molds were modeled with different values of cavity-cavity gap, and simulated to find the minimum value of gap. The simulation results were verified by melting and pouring ductile iron in green sand molds instrumented with thermocouples, and recording the temperature in mold at predetermined locations. The proposed approach can be employed to generate a technological database of minimum gaps for various combinations of part geometry, metal and process, which will be very useful to optimize the mold cavity layouts.

Effect of heat treatment on some mechanical properties of 7075 aluminium alloy

This paper reports the effects of annealing and age hardening heat treatments on the microstructural morphology and mechanical properties of 7075 Al alloy. The material was cast in the form of round cylindrical rods inside green sand mould from where some samples were rapidly cooled by early knockout and others gradually cooled to room temperature. From the samples that were gradually cooled some were annealed while others were age hardened. Both the as-cast in each category and heat treated samples were subjected to some mechanical tests and the morphology of the resulting microstructures were characterised by optical microscopy. From the results obtained there is formation of microsegregations of MgZn2 during gradual solidification which was not present during rapid cooling. It was also found out that age hardening and annealing heat treatment operation eliminated these microsegregations and improve mechanical properties of 7075 Al alloy. It is concluded that microsegregation can be eliminated by rapid solidification and appropriate heat treatment process.

Studies of Gas Atmosphere Near the Metalmould Interface During Casting and Solidification of Ductile Iron

Abstract In sand moulds, at a distance of 3 mm from the metal- mould interface, the sensors of temperature, and of oxygen and hydrogen content were installed. Temperature and the evolution of partial gas pressure have been analysed in moulds bonded with bentonite with or without the addition of seacoal, water glass or furan resin. Moulds were poured with ductile iron. For comparison, also tests with the grey iron have been executed. It was found that the gas atmosphere near the interface depends mainly on the content of a carbonaceous substance in the mould. In the green sand moulds with 5% of seacoal or bonded with furan resin, after the mould filling, a sudden increase in the hydrogen content and the drop of oxygen is observed. This gas evolution results from the oxidation of carbon and reduction of water vapour in the mould material, and also from the reduction of water vapour and alloy reoxidation. In carbon-free sand, the evolution in the gas composition is slower because water vapour is reduced only at the interface. Changes of oxygen and hydrogen content in the controlled zone are determined by the transport phenomena.

Normal-boundary intersection based parametric multi-objective optimization of green sand mould system

In manufacturing engineering optimization, it is often that one encounters scenarios that are multi-objective (where each of the objectives portray different aspects of the problem). Thus, it is crucial for the engineer to have access to multiple solution choices before selecting of the best solution. In this work, a novel approach that merges meta-heuristic algorithms with the Normal Boundary Intersection (NBI) method is introduced. This method then is used generate optimal solution options to the green sand mould system problem. This NBI based method provides a near-uniform spread of the Pareto frontier in which multiple solutions with gradual trade-offs in the objectives are obtained. Some comparative studies were then carried out with the algorithms developed and used in this work and that from some previous work. Analysis on the performance as well as the quality of the solutions produced by the algorithms is presented here.

Dynamic measurements of the load on castings and the contraction of castings during cooling in sand molds

The load on flange castings in sand molds was gradually increased beginning from the end of the solidification process until the final cooling stage. The maximum tensile load on the flange castings in furan sand molds was larger than that of the flange castings in green sand molds. With the furan sand mold, permanent deformation in the flange castings occurred beginning from the end of the solidification process until reaching a temperature of approximately 250°C. The mechanical interaction between the casting and the sand mold should be considered for more accurate stress calculations, particularly in furan sand molds.

Effect of NbO Additions on the Grain Size of 1010 Steel Castings

This paper describes a set of experiments that used NbO powder additions to decrease the final as-cast microstructure of 1010 steel castings. NbO has excellent crystallographic matching between its (002) plane and the (001) plane in ferrite, making it a possible heterogeneous nucleation site for delta ferrite. A set of 1010 steel plates were cast in green sand molds and then sectioned into tensile bars. NbO powder was added via the downsprue during pouring. The yield strength and ultimate tensile strength increased with the amount of NbO added. Percent elongation was unaffected in the samples with 6 ppm of NbO powder. Specimens with higher NbO powder additions had a significantly lower elongation than the baseline material. The microstructure of the NbO containing samples was finer than the baseline castings. The increase in strength and drop in ductility was theorized to be more consistent with a grain pinning strengthening mechanism than heterogeneous nucleation.

Effect of Rare Earth Additions on Grain Refinement of Plain Carbon Steels

This paper describes a set of experiments with misch metal and rare earth silicide additions in 1010 and 1030 steel to determine whether grain refinement occurs. Target rare earth (RE) contents of 0.1 and 0.2% were employed. After melting, the desired RE addition was added during tapping and then poured into green sand molds. The resulting test plates were then sectioned for tensile and metallographic testing. Yield strength increased for several of the 1010 and 1030 samples. The increase in yield strength correlated with a reduction in grain size. A dramatic increase in percent elongation was also observed in the 1010 sample with the smallest grain size. Electron microscopy found complex RE oxides. These oxides appear to act as heterogeneous nuclei. When they were coated with another slag, the grain size and mechanical properties were similar to the baseline material in both the 1010 and 1030.

Reverse Modeling of Green Sand Mould System Using Fuzzy Logic-Based Approaches

Abstract In the present study, reverse mapping problems of green sand mould system have been solved using Fuzzy Logic (FL)-based approaches. It is a complicated process, in which the quality of the castings is influenced by the mould properties (that is, green compression strength, permeability, hardness and others). In forward modeling, the outputs are expressed as the functions of input variables, whereas in reverse modeling, the later are represented as the functions of the former. The main advantage of reverse modeling lies in the fact that it helps in effective real-time control of the process. This paper proposes three different FL-based approaches for the reverse modeling of the green sand mould system. A binary-coded Genetic Algorithm (GA) has been used to optimize the knowledge base of the FL-based approaches, off-line. The developed approaches are found to solve the above problem effectively, and the performances of the developed approaches are compared among themselves. It has been observed that the approach “Automatic design of FL system using GA” yielded much better results in predicting a set of input variables from the set of known set of output.

Study on Productive Technology of Greensand Mold and Thick-Walled Small Piece for Nodular Cast Iron

By intelligent use the casting head and chilling, select the appropriate chemical composition and cast, execute the technical procedure in strict rotation, promptly resolve production problems for production of qualified cast ductile iron.