A carbon-containing additive is, as a rule, added to the bentonite-bonded molding sands in order to reduce oxidation, minimize sand adhesion to the casting at shakeout, enhance casting surfaces and combat the occurrence of casting defects. At the same time the optimizing molding sand properties and performance.
In the field of lustrous carbon formers, Imerys Metalcasting Solutions offer proven, sophisticated products that have been continuously improved and developed, based on many years of experience in combination with a program of careful, multi-faceted research. Development which has been in place since the company was founded in 1964. Our additives produce brilliant results and have long delighted our customers around the world.
Lustrous carbon formers are essentially organic in nature. They contain H – C compounds that volatilize under the effect of the casting temperature. The gaseous atmosphere produced is supersaturated with carbon and exerts a reducing effect, preventing oxidation defects such as Burnt-on sand, Graphite degeneration and other Chemical reactions. C supersaturation ultimately becomes so extensive that pyrolytic carbon in the form of lustrous carbon precipitates directly onto the mold surface at elevated temperatures. The degree of supersaturation in the mold atmosphere depends on the composition [Z] of the lustrous carbon former (C-H-O ratio), the carbon concentration [K] and the temperature [T] (LC =f[Z,K,T]).
The precipitation of lustrous carbon onto the hot mold wall reduces chemical reactions and the degree to which the mold face can be wetted by the molten metal. The gases produced influence the impact of the liquid metal against the mold material providing a so-called “cushioning effect” protecting the casting. The presence of lustrous carbon ensures good casting “peel” with excellent molding sand/casting separation at shakeout with optimum collapsibility and disintegration of the mold minimizing sand losses.
