Yield Improvement in Steel Casting (Yield II)

Abstract

In 1973, the Steel Founders' Society of America (SFSA) published Risering Steel Castings [1], a foundry handbook intended to provide risering guidelines for use in steel foundries. The guidelines contained in Risering Steel Castings were developed based on experimental casting work and supported by computer simulations. The steel casting industry has been well served by this handbook since its publication; following the guidelines generally results in sound castings. However, examples have surfaced in the last quarter of a century that indicate that the riser feeding distance rules contained in Risering Steel Castings are overly conservative in certain instances, especially where results have been extrapolated. Conservative feeding distance rules lead to the use of more risers than necessary on a casting, which in turn leads to a reduction in casting yield.Beginning in the mid-1990's, a research effort was undertaken to develop a new set of risering guidelines [2, 3]. This research was based on an extensive set of low-alloy steel plate casting trials performed at various foundries throughout North America. A wide variety of plate dimensions were utilized in the trials, which produced castings ranging from radiographically sound to ASTM shrinkage x-ray level 5. Casting conditions (alloy composition, mold material, superheat, pouring time, etc.) were recorded by each foundry for each plate cast, and this information was then utilized to numerically simulate the casting of each plate, using modern casting simulation software. Once it was determined that there was good agreement between the casting trial results and their corresponding simulations, a large number of simulations were performed for geometries and/or casting conditions that were not used in the casting trials, thus producing a more complete data set. By analyzing all of this data, a new set of feeding distance rules for sound castings was developed. These new rules are presented in this publication. Differences between this work and Risering Steel Castings:• Usually less conservative feeding distances: The feeding distances calculated using the guidelines presented here are similar to those calculated using Risering Steel Castings in some instances, and less conservative in other cases. In general, the current distances become less conservative than those from Risering Steel Castings as the width-to-thickness ratio W/T of a casting section increases.• Consistent definitions of feeding distance: The definitions of feeding distance for top risers with end effect, top risers with lateral feeding, and side risers are the same in this work, whereas different definitions were used in Risering Steel Castings.• Multipliers for different conditions: Multipliers are provided to tailor feeding distances to different cast alloy compositions, mold materials, pouring superheats, and desired levels of casting soundness.• Soundness in terms of riser zones and end zones: The information presented in Section 4 is intended to give the foundry engineer a physical understa...