Patent ID: 6783570
Filing Date: 2004-08-31
Classification: G01N

Abstract:
A process for determining the amount of structure-modifying agent that has to be added to a certain cast iron melt in order to obtain compacted graphite cast iron or spheroidal graphite cast iron from a molten cast iron having an hypo-eutectic or close to eutectic composition, which method requires a sampling device comprising a sample vessel, means for monitoring temperature as a function of time both in the centre and close to the wall of said sample vessel, and a means for administrating structure-modifying agents to the molten cast iron, the method comprising the steps of:a) for the chosen casting method calibrating the amount of structure-modifying agent that has to be added to a hypo-eutectic melt in order to obtain compacted graphite cast iron or spheroidal graphite cast iron as a function of the maximum value a of the first time derivative of a cooling curve recorded in the centre of a sample vessel; b) taking a sample of the molten cast iron by using a sampling device; c) allowing said sample to solidify in a sample vessel, aid during the solidification recording cooling curves in the centre of the sample vessel and at the sample vessel wall, respectively; d) determining a heat generation curve disclosing the heat generated in the centre of the sample as a function of time by applying i) the thermal balance formula: Qstored=Qgenerated+Qinâˆ’Qout where Qstored is the amount of heat stored by the heat capacity of the material, Qgenerate is the amount of heat generated by the volume of material, Qin is the heat transferred into the material from its surroundings and Qout is the heat transferred to the surroundings; and ii) the cooling curves recorded in step c); e) identifying the location of a possible local maximum tp on the heat generation curve obtained in step d), which maximum corresponds to an austenite formation point on the centrally recorded cooling curve obtained in step c), and controlling whether there is a risk that this austenite formation point affects the value of the maximum slope of the centrally recorded cooling curve; and f) if a tp has been located, and if there is no risk that the maximum first time derivative value &agr; is affected by austenite formation, calculating the amount of structure-modifying agent (Va) that has to be added to the melt by using the value &agr; and the calibration data obtained in step a); or g) if a tp has been located, and if tpâˆ’t&agr; is less than a threshold value ttv, identifying a time, t&agr;1, (t&agr;1>t&agr;) for which the second time derivative of the centrally recorded cooling curve is approximately 0, determining the first time derivative value &agr;1, and calculating the amount of structure-modifying agent (Va) that has to be added to the melt by using the value &agr;1 and the calibration data obtained in step a).