No-Bake S-Containing Mold/DI Metal Interactions: Consequences and Potential Applications
The ductile iron liquid metal is very reactive with environmental gases and solid molds after a nodulizing treatment. Mold-metal reactions could alter the spheroidal graphite shape to vermicular or flake. In this research, the metal-mold reactions were enhanced by various sulfur additions to the no-bake mold inserts to study these phenomena and to artificially produce layered dual-graphite structure in the casting. Thermodynamic and solidification modeling together with sets of different experimental techniques were applied to a test casting with internal core passages representing the cylinder head of a diesel engine. The effects of insert surface shape and location in the mold; content and type of sulfur-containing agent; coating; pouring temperature and additional chilling were experimentally studied and discussed. These results could be used to better understand the metal-mold interaction, prevent surface defects and design dual-graphite structure processes.
Investigation of Cast Iron Processing to Produce Controlled Dual Graphite Structure in Castings
The change in graphite shape from flake to spheroidal significantly increases the strength of cast iron while simultaneously decreases thermal conductivity to about half of the value in flake graphite iron. In many industrial applications, such as the cylinder head of diesel engine, a combination of high strength and thermal conductivity is essential. A compromise would be to use compacted graphite iron, while a more effective way would be to develop controlled distribution of the dual graphite structure that matches a specific region’s function of the casting design. In this study, the process of casting such functionally region-specific material was modeled and experimentally investigated. It was shown that four main conditions need to be satisfied for achieving a controlled dual graphite structure:  a distinct change in ductile/gray iron melt composition during mold pouring by melt treatment;  sequential fill of the mold cavity by different melt compositions using special gating systems;  minimum post filling momentum in the mold and  avoidance of natural convection in the melt before casting solidification. Different approaches were tested using an experimental casting with flat internal cores. The experimental results achieved thus far were compared to modeling predictions. The different possible process routes are discussed.
Characterization of ceramic composite membrane filters for hot gas cleaning
Abstract Novel composite ceramic membrane filters suitable for hot gas cleaning operations have been prepared from fly ash and titania particles on stainless steel woven mesh substrates. Both membranes had a structure like a solid packed bed with a thickness of less than 100 μm. In the domain of laminar flow, significant differences in the pressure drop between experimental results and those predicted from the Kozeny-Carman relationship were found, particularly for flow through the titania membrane. Membrane filters with extremely small pores such as the titania membrane are greatly affected by slip up to 80% in permeability at elevated temperatures. Efficiencies of filtration of typical coal fired power station exhaust fly ashes were found to be greater than 909% for both titania and ash membranes, whilst there was greater variation in the pressure drops in the ash membrane than in the titania at typical gas flows.