Development of new feeding-distance rules using casting simulation: Part II. The new rules
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I. INTRODUCTION
AS computer technology continues to advance, computer simulation of the metal casting process is becoming an increasingly popular tool. Through the use of simulation, foundries are able to evaluate modifications to casting designs without having to actually produce the casting, thus saving time, material resources, and manpower. However, computer simulation must be applied on a case-by-case basis, and its effective use requires expertise as well as accurate data for many process variables. Furthermore, casting simulation does not provide the initial riser design for a casting, nor does it automatically optimize the risering. Due to these limitations, feeding rules are still widely used in the steel casting industry to determine the size and placement of risers. The development of feeding-distance rules for steel castings began in the early 1950s. One of the two major efforts involved in this early work was carried out at the Naval Research Laboratory (NRL) by Pellini and co-workers.[1–4] They developed feeding-distance rules by analyzing the radiographic testing results of extensive plain-carbon steel casting trials. Pellini et al. define the feeding distance as the longest distance from the edge of the riser to the edge of the casting that will result in a sound casting, where “sound” is defined as no visible shrinkage on radiographs filmed at 1.5 pct sensitivity. The first published study from this work[1] involves several different top-risered casting shapes: semicircular plate castings of a thickness of T ⫽ 1.27, 2.54, 3.81, and 5.08 cm (0.5, 1, 1.5, and 2 in.); circular plate castings of a thickness of T ⫽ 2.54 and 5.08 cm (1 and 2 in.); and rectangular plate castings of a thickness of T ⫽ 5.08 cm (2 in.), with widths (W ) ranging from 2 to 5 T. The primary result of this study is that the feeding distance for plates is equal to 4.5 T, where “plate” is defined as W/T ⱖ 3.[1] This feeding distance of 4.5 T is composed of two regions: 2.5 T is made sound by the chilling effects of the edges of the SHOUZHU OU, Postdoctoral Researcher, KENT D. CARLSON and RICHARD A. HARDIN, Assistant Research Engineers, and CHRISTOPH BECKERMANN, Professor, are with the Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, IA 52242. Contact e-mail: [email protected] Manuscript submitted December 3, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
plate, where the casting meets the mold, and the remaining 2 T (adjacent to the riser) is made sound by the temperature gradient created by the riser itself. These two regions will be discussed frequently in this article, and are, hereafter, referred to as the end zone and riser zone, respectively. Bishop and Pellini[1] note that, when the feeding distance is exceeded and shrinkage forms, it occurs in the intermediate zone that develops between the riser and end zones, which remain sound. Next, Bishop et al.[2] reported a feeding-distance rule for top-risered bars, where the “bar” is defined as W/T ⫽ 1 (i.e., W ⫽ T ). This rule
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