| 摘要 |
<p>A method and apparatus is disclosed for conditioning a charge of molten cast iron, which would normally solidify with a flake graphite structure, to produce partial or total spheroidal graphite cast iron. In addition, the method and apparatus can be used to further condition a partially conditioned cast iron to yield a partial or fully spheroidal graphite cast iron. A recess is provided in the metal flow system (within or without the mold system) leading to the casting cavity or cavities. The recess has a shape and cross-section (taken in directions normal to the direction of flow of the molten charge) such that the spheroidizing agent dissolves uniformly when the molten iron flows over it to achieve unprecedented homogeneity. A dense solid unitary block of spheroidizing or nodularizing agent, substantially devoid of MgO interiorly thereof, is typically snugly fitted in said recess and mates with the side walls and bottom of said recess. The block typically presents a substantially constant and uniform interface with the molten charge during all stages of conditioning and pouring; however, a deviation in the interface area may be designed into the block to compensate for molten iron temperature variations or molten iron flow rate variations when the casting technique experiences unusually high variations in the ferrostatic pressure head. A relationship is disclosed between charge weight, charge flow rate, magnesium concentration in the spheroidizing alloy, and interface area so as to determine a desired degree of nodularity in the final casting and/or to design a solution rate compatible with a specific casting technique. The residual magnesium can be reliably maintained at a level sufficient to consistently obtain full spheroidal graphite shape. A preferred magnesium level is 0.020% to 0.040% of the weight of the casting but higher or lower levels can be reliably obtained if required by base metal chemistry. This is significant since the prior art has been unable to reliably obtain full nodularity with 0.02-0.025% residual magnesium under commercial conditions.</p> |
