Shrinkage Porosity In Castings Research Articles

Criterion assessment of shrinkage porosity formation in castings

A method for calculating of the critical value of the porosity criterion developed at the Department of Foundry Technologies of Bauman Moscow State Technical University is proposed. The methodology is based on a computational experiment that allows us to determine with a high degree of probability the conditions for the formation of shrinkage porosity in castings, taking into account the thermophysical properties of the mould and the alloy.

Geometry-Driven Criterion Function for Predicting Shrinkage Porosity in Stainless Steel Castings with T-Junction

Metal castings with the presence of shrinkage porosity are often recycled or rejected and in turn reduce productivity of the process as well as increase energy cost involved in the process. This can be overcome by prevention of its occurrence using a suitable prediction technique. A detailed study of literature reveals that several Criterion Functions (an empirical model that connects solidification phenomena with formation of shrinkage porosity) have been employed to predict the location of shrinkage porosity in castings manufactured using particular process-alloy combination by values of process parameters (mostly thermal gradient, cooling rate, and velocity of molten metal). However, criterion function considering the effect of geometric variation in stainless steel castings on an extent of shrinkage porosity need to be established. In the present work, a benchmark casting, a combination of three T junctions, has been cast and used for the development of geometry-driven criterion function for stainless steel castings. Real experimental results with the presence of shrinkage porosity were used for superimposing on virtual experimental results (simulated results) for establishment of local simulation conditions. These conditions are further used in extrapolating results using casting simulation. The developed geometry-driven criterion function was further validated and found to be effective in prediction of shrinkage porosity.

Optimization of Shrinkage Porosity in Grinding Media Balls by Casting Design Modification and Simulation Technique

Shrinkage porosity or cavity are associated with the solidification of the metal either due to gas/air entrapment or when the shrinkage occurring during solidification is not entirely compensated by the riser. Shrinkage cavities occurring in the casting reduces its strength which leads to unfulfillment of the desired serviceability. In this paper, casting design has been modified using the DISA manual to achieve directional solidification which directly relates to improvement of casting quality. The running of metal from pouring basin into casting along with solidification has been analysed through PROCAST which is a casting simulation software based on Finite Element Method and CAFE (Cellular Automata Finite Element) Model. The feeding system of the casting has been modified in terms of shape and volume to minimize air aspiration effect and promote directional solidification. The model used is of grinding media balls casting of high chromium cast iron. The feeding pattern, feeding velocity and solidification with respect to pouring temperature, pouring rate, ambient temperature and film coefficient has been analysed. The final optimum range of all parameters with corresponding minimum shrinkage porosity in casting was obtained. Main aim was to minimize shrinkage porosity in the main casting, ignoring gating and feeding system. The actual minimization of shrinkage porosity comes out around 56 %.

Advanced modeling of shrinkage porosity in castings

Porosity due to solidification shrinkage is a troublesome defect in all types of metal castings. It limits the performance of cast components by adversely affecting the material’s strength, fatigue and creep properties. By reliably predicting porosity in casting process simulation, it can be minimized or eliminated. Here, a newly developed model for predicting porosity is presented. The model is based on the recent discovery that all shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the liquid density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. The model is numerically implemented in a standard casting simulation code. Comparisons to measurements in specially made steel castings demonstrate the capability of the model to accurately predict various types of shrinkage porosity.

Effects of Process Parameters on Shrinkage Porosity in 357 Semi-Solid Die Casting Parts

The shrinkage porosity that was caused by the insufficient feeding during solidification, was a common defect in the semi-solid die casting process. This defect decreased significantly the mechanical properties of the casting. In order to avoid the shrinkage porosity in casting, the die design, slug preparation and die casting process were carefully considered. In this study, a designed mold was used to make the sequential solidification of the slug. The process parameters, including intensification pressure, die temperature and biscuit thickness of the casting, were studied to show their influence on shrinkage porosity defects. The experimental results show that the high intensification pressure, high die temperature and long biscuit can be beneficial to obtain castings with no shrinkage porosity.

Reducing Shrinkage Porosity in High-Performance Steel Castings: Case of an ASME B16.34 Gate Valve Body: Part 1—Analysis, Techniques and Experimental Approach

X-ray computed tomography (CT), in combination with scanning electron microscopy (SEM), has been successfully used to evaluate shrinkage macro- and microporosity levels in a high-performance steel casting. As a test case, a commercially available gate valve body of a Class 300 gate valve based on the ASME B16.34 standard and made from A216 WCB cast steel was analysed, in accordance with the specifications of the standard. The radiographic inspection process, in accordance with ASTM E2868 for digital radiographs, is presented. Both X-ray CT radiographs and SEM micrographs are presented, showing the presence of shrinkage macro- and microporosity, in addition to gas porosity. This study is a precursor to the development of a systematic approach for reducing shrinkage porosity in castings based on the optimisation of design and process parameters that influence porosity formation during solidification.