Effectiveness of Blind Feeders in Steel Casting

Resumo

Existing methods of decreasing feeder size are briefly reviewed, with an account of their advantages and disadvantages. The applicability of methods of optimizing the feeder shape so as to increase the useful volume of the casting is identified. The actual position of shrinkage defects in feeders of different structure is considered. The position and shape of shrinkage cavities are considered as a function of the shape of the feeder’s upper section. Four groups of feeders are distinguished, and their effectiveness is compared. Mathematical modeling is proposed to better understand the formation of shrinkage cavities in feeders with different designs of their upper section and to assess their effectiveness. Mathematical modeling permits analysis of the external factors affecting the thermal processes in the mold, which is difficult in casting practice. SolidCast software is used. The initial and boundary conditions in modeling are identical for feeders of all types. The predictions regarding the shrinkage defects are expressed as isosurfaces, whose dimensions may be used to assess feeder effectiveness. The modeling results are used to develop an approach to assessing the thermal efficiency of feeders of different types. The estimates are based on the position of the shrinkage defect within the feeder. As an example, the effectiveness of feeders of the same size but with different configurations of the upper section is calculated. The proposed efficiency index is in good agreement with the geometric modulus (the ratio of the feeder’s volume to its surface area). Increase in the feeder’s modulus increases its thermal efficiency. The introduction of a notch increases the feeder’s efficiency. Analysis of isothermal lines in the longitudinal section of the feeder permits description of the thermal operation of the notch and its influence on the position of the shrinkage cavity. Recommendations are made for increasing the casting yield by redesigning the feeder’s upper section. The casting yield may be increased by 4%, with accompanying decrease in the rejection rate of the castings, thanks to optimization of the feeder’s upper section.