Feeding and risering of high-alloy steel castings
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I. INTRODUCTION
MAXIMIZING casting yield, which is defined as the weight of a casting divided by the weight of the metal poured to produce the casting (i.e., including metal that solidifies in the risers, gating, downsprue, etc.), is an important consideration in the steel casting industry. An increase in casting yield decreases production costs; with increased yield, production of the same number of castings requires less melted metal and fewer heats, as well as reduced labor and material costs required for production. Also, higher yield usually has the side benefit of lower casting cleaning costs. One effective way to improve casting yield is through riser optimization, where “optimized” means (1) the riser has the minimum possible volume to provide sufficient feed metal to the casting, without the riser pipe extending into the casting; and (2) the smallest number of risers are used, while still ensuring that the risers are close enough to each other to produce a sufficiently sound casting. Computer simulation of the casting process is becoming an indispensable tool in the effort to increase casting yield. 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. Due to these limitations, risering rules are still widely used in the steel casting industry. Risering rules dictate riser size and SHOUZHU OU, Postdoctoral Research Associate, KENT D. CARLSON, Assistant Research Engineer, and CHRISTOPH BECKERMANN, Professor, are with the Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, IA 52242. Contact e-mail: becker@engineering. uiowa.edu Manuscript submitted December 9, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS B
placement by determining (1) the riser size necessary to supply adequate feed metal to a casting section, and (2) the feeding distance (FD), which is the maximum distance over which a riser can supply feed metal to produce a sound casting. A recent survey indicates that simulation is used for less than 10 pct of the tonnage of steel castings produced, and that risering rules (or rules-based software) are used to rig about 80 pct of the tonnage produced.[1,2] Due to the prevalence of rules-based rigging in the steel casting industry, any attempt to increase casting yield in a general sense must begin with these rules. Even if simulation is used, risering rules are still useful to develop a reasonable starting point for simulation, which will shorten the iterative optimization cycle. A great deal of effort has been expended to develop rules for determining riser FDs in steel castings. Many researchers have developed empirical relations for determining feeding distances in carbon and low-alloy (C&LA) steels. These rules are typically based on experimental casting trials
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