Analysis And Research Of Carbon Defects Of Lost Foam Casting

Lost foam foundry is called "new foundry technique of the 21st century". Butthe choke point of this technique--carbon defects restrict the development andpopularization of this technology seriously. Analyzing and investigating the forming cause, influencing factor, and preventing step of the carbon defects of lost form castings, has very important technical meaning to reduce the withdrawal rate of lost foam casting, increase the economy benefit, and drive the development and application of this technique.The results are analyzed in this article by adopting different technical parameters and material to pour. Also some advanced measuring means, just as energy spectrum, electric scan, and optics microscope are adopted to research the main cause, influencing factor, forming mechanism and distribution rule of the carbon defects. The conclusion is: the pyrolysate of the lost foam pattern which cannot transgress the coating generates the carbon substance at the metal liquid final solidification position by the action of high temperature metal liquid on oxygen-lack state. This carbon substance has high proportion of carbon, and it forms the carbon defects. The forming of carbon defects has great relation with chemical composition and density of pattern material. The carbon proportion and density of pattern material are higher; the forming tendency of carbon defects is higher. The high temperature gas permeability and liquid absorbability of coating and molding sand have important influence to severity degree of carbon defects. They are path for pattern pyrolysate exhausting outwards. The high temperature gas permeability of coating and molding sand is higher and the liquid absorbability is higher, the exhausting ability of pyrolysate is higher, and also the forming tendency of carbon defects is lower. Pouring temperature is also very sensitive for forming the carbon defects. The pouring temperature is higher, then gas material proportion is higher, liquid material proportion is lower, and the forming tendency of carbon defects is lower. Vacuum mainly help the pyrolysate exhausting outside the mold. High negative pressure is beneficial to make pyrolysate exhaust outwards, and to reduce the carbon defects. The carbon defects have important influence to mechanical performance, rigidity, and structure compactness of casting. It can worsen the mechanical performance, rigidity, and structure compactness of casting. The carbon defects must be prevented andeliminated.