Tribological Studies of Shrinkage Defect and Effective Yield Upgrade of Grey Cast-Iron Castings

Abstract

This study aims to examine the shrinkage flaw in grey cast iron. The poor gating system design, improper composition management, and solid sections with a high modulus (Volume/ Surface area) in the casting are the root causes of the shrinkage fault. The gating mechanism can first be redesigned in order to lessen shrinkage. A new gating system with a different chemical makeup is suggested. Grey cast iron\'s composition changed due to an increase in carbon content. Thus, proCAST is used to develop and analyze the gating system. Implementing the planned gating system in the foundry served to validate the results. It is accomplished to increase the effective yield.

Introduction

I. INTRODUCTION

In the manufacturing process known as casting, a liquid substance is often poured into a mold that has a hollow hole that is the desired shape, and the mixture is then left to solidify. Castings are the solidified component that is ejected or broken out of the mold to complete the process. Casting materials often consist of metals or different types of cold-setting substances that firm up after being mixed with two or more other substances; examples include epoxy, plaster, and clay. Casting is most frequently used to create intricate shapes that would be challenging or expensive to create using other techniques.  The flow chart explains the process of the casting process. An under-irregularity in the metal casting process is referred to as a casting fault. Some flaws can be overlooked, while others can be fixed; if not, they must be removed. They are divided into five primary groups: flaws related to gas porosity, shrinkage and mold materials, pouring metal, and metallurgical processes. The failure of the mold can result in a number of issues with sand casting. The mold typically fails for one of two reasons: either the incorrect materials are utilized, or it is rammed incorrectly. Shrinkage flaws, which fall under the category of internal defects, account for almost 60% of all faults in this study. Macro-Porosity Shrinkage and Micro-Porosity Shrinkage are two terms used to loosely classify shrinkages in castings based on their size. Macro-porosity typically occurs in isolated hot places, and its typical locations are the center of thick sections, junctions, corners, and spaces between two or more cores. It manifests as a region with numerous shrinkage holes or a single cavity with a rough surface. Micro-Porosity is typically only discovered during machining and shows as tiny holes in the rough surface. The macro-porosity shrinking is concentrated in this research.

II. MATERIALS AND METHODS

The figure shows the methodology for the research work. Initially, the material grey cast iron is selected for material and it is analyzed what kind of defects to be created. Particularly shrinkage defects and analysis of possible shrinkage defects, gating system, and chemical composition of the material.

Table 7: Composition of the Metal Before and After Remedial Measures

Following are some explanations of how to use simulation software.

Build a model of the casting design, including the gating system and all other components like chills, cores, sleeves, etc. that are used with the castings. A cad system could be used for this stage. Enter the necessary information for the calculation, such as the mold or die's mechanical, thermal, and physical characteristics, the pouring temperature, the duration of the pour, the pressure, etc. Computation of the simulation, in which several programs for casting simulation may take various ways to simulate the outcomes. The numerical simulation approaches (Finite Element and Finite Difference Methods), the geometrical less method approach, and mesh are a few well-known methods.

Depending on the criterion employed, such as the temperature in each area of the casting at a given time, solidification times, hot spots, material density, etc., the findings from the simulation program may be displayed as graphs or colourful figures with numerical data. These findings must be transformed into information that may be used to determine if a casting is sound or not, or what needs to be done to enhance the casting design and start over at step one.

The ESI group developed and owns ProCAST, a computer simulation software package for castings. Version 2016 was the one employed in this study. With many different kinds of metal, it may stimulate investment casting, sand casting, and permanent mold casting models. A user can use the program ProCAST to predict casting flaws that could appear as the casting is solidifying. It uses the finite difference method in calculating the thermodynamics of each element in the casting and records the temperature changes. The temperature changes collected will be used in plotting graphs of different criteria for predicting different types of defects in castings. It calculates the thermodynamics of each casting element using the finite differences method and keeps track of temperature fluctuations. The temperature data will be used to create graphs with various criteria for forecasting various casting failure types.

The solidification of the casting is examined using the proCAST software once the solid works model of the casting with the existing gating system has been loaded. Figure 6 depicts the process of solidification from liquid to 90% solid.  

The casts' arms solidified first, then their outside ring, and finally their hub. As a result, the hub will experience shrinkage faults because it is improperly fed by the ingate due to the use of a gating system. The casts' arms solidified first, then their outside ring, and finally their hub. As a result, the hub will experience shrinkage faults because it is improperly fed by the ingate due to the use of a gating system.The places where we need to find the ingate are the feeding zones. Seven feeding zones are included, six on each arm and one at the hub. According to the proCAST, the ingate in the current design is not connected to any of the feeding zones.

The solidification of the current gating system is depicted in figure 7 above, where the riser solidifies last yet is located in a remote place that cannot provide the molten to the hub. Figure 8 also displays the current system's hot spot at a range of 1 to 10. Hot spots are places where the temperature is higher than in neighboring areas and which could lead to shrinkage defects.

The analysis presented above illustrates temperature gradients by color differences with both directed and gradual solidification. Dark blue denotes the lower extreme temperature of 11640 degrees Celsius and bright yellow symbolizes the upper extreme temperature of 13160 degrees Celsius. Until the mold fills, the nearby riser and sprue stay heated. Figure 15 shows that the liquid meal has filled the whole casting, and the riser next to the hub is still hot and still supplying metal to the hub. This gets rid of the shrinkage flaws that used to show up in the casting hub. Similar to this, feed the necessary metal into the riser at the rim, where shrinking is most likely to happen.   

The following outcomes were attained as a result of the foundry alteration mentioned above. The graph displays the decline of shrinkage defects following each correction.

Table 8: Reduction Rate Before and After Remedial Action

Conclusion

Redesigning the gating mechanism and altering the chemical makeup of grey cast iron help to eliminate the shrinkage fault in the casting. After the gating system was redesigned, the shrinkage defect was 18%. That increased the casting fault from 60% to 68.66%. The casting\'s effective yield, which was previously 46.12%, jumped to 57.67%. The casting yield and effective yield have increased to 68.66% and 63.16%, respectively, due to the change in chemical composition.

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Copyright

Copyright © 2022 P Srinivasan, S Hariharan, P Manikandan, S Naveenkumar, N Harish, G Balasubramanian . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.