Improvement of Gating Systems with the Purpose of Reducing Defects in Large-Size Castings from Gray Iron

Author Name(s): Dmitry A. Malinovsky, Nikolay N. Safronov, Lenar R. Kharisov
Author Email: ln271@mail.ru

Abstract

The article analyzes the types of castings defects. There are four groups of them: fit; conditionally fit, with small deviations from the established requirements; correctable marriage; incorrigible or final defects. The way to eliminate casting defects was to change the gating system. Despite the very large number of constructive types of gating systems, 4 classes are distinguished, differing by elements, as well as by hydraulic features of functioning. The article presents the technology of casting processes modeling. In this work the casting process modeling program LVMFlow was used. The LVMFlow system is used for computer modeling of processes that occur in the mold and for optimization of the casting manufacturing technological process. The core of the computer simulation of thermal and hydrodynamic casting processes of LVMFlow are the heat and mass transfer equations. Computer simulation allowed us to trace all the processes that occur in the metal during the filling of the mold, solidification and the occurrence of shrinkage defects. The results of modeling of the initial version of the gating system are presented. The defects such as shrinkage and erosion of the mold, the reject on which was 20%, are found. When the proposed gating system of the siphon type was used, defects for shrinkage and erosion were absent for six months of the production of castings of this type.

Introduction

Cast iron, in which most of the carbon is in a free state in the form of graphite, is called gray iron. Gray cast iron is soft, well machined with cutting tools. In kink it has a gray color. Gray cast iron has a low ductility, it can not be forged, as the graphite contained in it contributes to the splitting of the metal. Gray cast iron works much better in compression than in tension. Gray cast iron is produced by slow cooling after melting or heating. The melting point of gray iron is 1100-1250°C. Typically gray iron contains 2.8-3.6% carbon, 1.6-3.0% silicon, 0.5-1% manganese, 0.2-0.8% phosphorus and 0.05-0.12% sulfur. Sulfur reduces the fluidity and strength of cast iron, increases its foundry shrinkage and complicates its welding. Phosphorus makes cast iron more fluidly fusible and improves its weldability, but increases its hardness and brittleness. The disadvantage of gray iron is brittleness, preventing its use for the manufacture of machine parts subjected to shock loads. Gray cast iron is most widely used in mechanical engineering for the casting of various machine parts. It is quite well welded, especially with the use of preheating. It is little plastic and tough, but is easily machined, it is used for irresponsible parts and parts working for wear. In the automotive industry crankcase, covers, brake drums, etc. are made of ferritic-pearlite cast iron, and cylinder blocks, sleeves, flywheels, etc. are made of pearlitic cast iron. Due to the low mechanical properties of gray iron castings and the ease of obtaining they are used for the manufacture of parts of less critical purpose, parts that work in the absence of shock loads, in particular, caps, pulleys, machine beds and presses are made of them [1].

Conclusion

s Using the LVMFlow package allowed to reduce the role of the natural experiment, which reduces the cost of developing the casting technological process; make castings of high quality, complex configuration, which do not require the correction of defects; increased the professional level of the technologist-caster. As a result of 3D modeling it was found that for large-sized “Carter” type castings it is more expedient to use a siphon gating system, which has allowed a significant reduction in the casting rejects.

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