Abstract
Computer modeling using a commercially available software package was used to explore the optimization of filling systems based on the relatively new concepts of avoiding entrainment of air bubbles and oxides by avoiding surface turbulence. The test casting was based on a pattern for a traditional top poured test bar, whose cross section was a tri-lobed clover-like shape. The study illustrates clearly that the detailed design of the filling system has a major influence on the conditions for defect generation during filling. Traditional steel casting systems using the widely popular assembly of preformed refractory tubes were found to behave poorly. Systems were demonstrated which were capable of delivering highly controlled filling behavior. The latest systems to be developed employed (1) a naturally pressurized filling system and (2) the use of filters placed flush on the top of the runner to act as bubble diverters, together with (3) terminal spin traps. These novel filling systems demonstrated excellent performance in simulation, in agreement with practical experience of the capability (of the trident gate in particular) to produce, for the first time in the history of casting, defect-free castings on a routine basis.
Highlights
Modern foundry engineering is a well-developed and sophisticated industry utilizing cutting-edge technologies and tools including 3D printing, robots and automated manufacturing
The current paper presents the results of an approach to test the behavior of filling systems designed to fill completely
The paper presents a systematic comparison of a number of gating systems for steel castings, using computer simulation
Summary
Modern foundry engineering is a well-developed and sophisticated industry utilizing cutting-edge technologies and tools including 3D printing, robots and automated manufacturing. It is recently becoming common for the customer to specify a requirement to pass the stringent dye penetrant test This inspection technique illustrates the inadequacies of many current filling system designs (Ref 4-7), since the presence of surface-breaking oxide bifilms, cracks and bubbles is clearly revealed. [Campbell records that he has never known sand inclusions to result from Ôpoor sandÕ quality (Ref 8)] Providing they do not lead to cracks, the presence of bifilms in steels does not contribute to the rejection or scrapping of the casting because the population of these defects is usually invisible. The current paper presents the results of an approach to test the behavior of filling systems designed to fill completely (Ref. 8), thereby excluding all air so far as possible, and thereby reduce or prevent the occurrence of surface turbulence and the entrainment of bubbles and bifilms. The paper describes the systematic evaluation of a number of gating systems in current use including the extended runner, spin trap, vortex gate, trident gate and others, using computer simulation
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