Iron castings with compacted or spheroidal graphite produced by determining coefficients from cooling curves and adjusting the content of structure modifying agents in the melt

A method for determining the amount of structure modifying agent that has to be added to molten cast iron in order to produce a compacted graphite iron casting, or spheroidal graphite cast iron, which method requires a sampling device, means for monitoring temperature as a function of time and a means for administating structure-modifying agents to a molten cast iron from which said casting is to be produced, said method comprising the steps of:

• a) for the chosen casting method carrying out the following calibrations:
• i) determining the amount of structure-modifying agent that has to be added to the melt in order to obtain compacted graphite cast iron, or spheroidal graphite cast iron, as a function of a first control coefficient γ, where
• γ=(TAmax−TAmin)/(TBmax−TBmin)
• and wherein
• TAmax is the local maximum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TAmin is the local minimum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TBmax is the local maximum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• TBmin is the local minimum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• ii) determining the amount of structure-modifying agent that has to be added to the melt in order to obtain compacted graphite cast iron, or spheroidal graphite cast iron, as a function of a second control coefficient φ, where
• φ=(TA′max)/(TB′max)
• wherein
• TA′max is the maximum value of the first derivative of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• and
• TB′max is the maximum value of the first derivative of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• iii) determining the amount of structure-modifying agent that has to be added to a molten cast iron in order to obtain compacted graphite cast iron, or spheroidal graphite cast iron, as a function of a third control coefficient (ρB), which is the area under the first peak of the first derivative of a cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• d) determining the amount of structure-modifying agent that has to be added to the melt in order to obtain compacted graphite cast iron, or spheroidal cast iron as a function of κ, where:
• κ=σA/σB
• wherein
• σA is the area under the second peak of the first derivative of the cooling curve recorded in the centre of the sample vessel;
• and
• σB is the area under the second peak of the first derivative of the cooling curve recorded at the vessel wall;
• b) during solidification recording cooling curves at the centre of a sample vessel and at the sample vessel wall, respectively, for a particular sample of a molten cast iron;
• c) calculating control coefficients γ, φ, ρB and κ relating to the temperature time curves obtained in step b) and choosing one of these coefficients γ, φ, ρ and κ giving the most accurate result;
• d) calculating the amount of stuctural modifying agent (Va) that has to be added to the melt.

An apparatus for establishing, in real time, an amount of a structure modifying agent to be added to a cast iron melt (20) during the process of producing a compacted graphite iron casting;

• the apparatus comprising:
• a first temperature sensor (10) for recording a cooling curve at the centre of a sample vessel;
• a second temperature sensor (12) for recording a cooling curve in the vicinity of the sample vessel wall;
• a computer device (14) for determining an amount value (Va) of a structure modifying agent to be added to the melt,
• a memory means (16) which is provided with prerecorded cooling curve data, the computer device being set up to establish a first control coefficient, γ, (from which a first prediction value (V1) can be calculated,) where
• γ=(TAmax−TAmin)/(TBmax−TBmin)
• and wherein
• TAmax is the local maximum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TAmin is the local minimum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TBmax is the local maximum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• TBmin is the local minimum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• the computer device being set up to establish a second control coefficient φ, (from which a second prediction value (V2) can be calculated,) where
• φ=(TA′max)/(TB′max)
• wherein
• TA′max is the maximum value of the first derivative of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• and
• TB′max is the maximum value of the first derivative of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• the computer device being set up to attemt to establish a third control coefficient (ρB), (from which a third prediction value (V3) can be calculated,) where
• the third control coefficient (ρB) relates to the area of the first peak of the first derivative of the cooling curve recorded at the sample vessel wall;
• the computer device being set up to attemt to establish a fourth control coefficient (κ), (from which a fourth prediction value (V4) can be calculated), where
• κ=σA/σB
• and wherein
• σA is the area under the second peak of the first derivative of the cooling curve recorded in the centre of the sample vessel;
• and
• σB is the area under the second peak of the first derivative of the cooling curve recorded at the vessel wall;
• the computer device being set up to compare the first, second, third and fourth control coefficients (γ, φ, σB and κ) with the prerecorded cooling curve data, and
• the computer device being set up to choose one of the control coefficients (γ, φ, σB and κ) in response to the result of the comparison, and wherein
• the computer device is set up to calculate a precise amount value (Va) of a structure modifying agent to be added to the melt in response to the choosen control coefficient (γ, φ, ρB and κ).

An apparatus for establishing, in real time, an amount of a structure modifying agent to be added to a cast iron melt (20) during the process of producing a speroidal graphite iron casting;

• the apparatus comprising
• a first temperature sensor (10) for recording a cooling curve at the centre of a sample vessel;
• a second temperature sensor (12) for recording a cooling curve in the vicinity of the sample vessel wall;
• a computer device (14) for determining an amount value (Va) of a structure modifying agent to be added to the melt,
• a memory means (16) which is provided with prerecorded cooling curve data, the computer device being set up to establish a first control coefficient, γ, (from which a first prediction value (V1) can be calculated,) where
• γ=(TAmax−TAmin)/(TBmax−TBmin)
• and wherein
• TAmax is the local maximum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TAmin is the local minimum value of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• TBmax is the local maximum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• TBmin is the local minimum value of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• the computer device being set up to establish a second control coefficient φ, (from which a second prediction value (V2) can be calculated,) where
• φ=(TA′max)/(TB′max)
• wherein
• TA′max is the maximum value of the first derivative of the cooling curve recorded at the centre of the sample vessel during solidification of a cast iron sample;
• and
• TB′max is the maximum value of the first derivative of the cooling curve recorded at the sample vessel wall during solidification of a cast iron sample;
• the computer device being set up to attemt to establish a third control coefficient (ρA), (from which a third prediction value (V3) can be calculated,) where
• the third control coefficient (ρB) relates to the area of the first peak of the first derivative of the cooling curve recorded at the sample vessel wall;
• the computer device being set up to attemt to establish a fourth control coefficient (κ), (from which a fourth prediction value (V4) can be calculated), where
• κ=σA/σB
• and wherein
• σA is the area under the second peak of the first derivative of the cooling curve recorded in the centre of the sample vessel;
• and
• σB is the area under the second peak of the first derivative of the cooling curve recorded at the vessel wall;
• the computer device being set up to compare the first, second, third and fourth control coefficients (γ, φ, ρB and κ) with the prerecorded cooling curve data, and
• the computer device being set up to choose one of the control coefficients (γ, φ, ρB and κ) in response to the result of the comparison, and wherein
• the computer device is set up to calculate a precise amount value (Va) of a structure modifying agent to be added to the melt in response to the choosen control coefficient (γ, φ, ρB and κ).