Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1993-04-15
1994-08-16
Bradley, P. Austin
Metal founding
Process
With measuring, testing, inspecting, or condition determination
164 581, 75377, 374 26, B22D 200, C21C 110, G01N 2504
Patent
active
053377990
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for the production of compacted graphite cast iron. The method is based on a test-method to determine the structural characteristics of a melt for casting compacted graphite cast iron and means to control the structure and properties of the material produced.
U.S. Pat. No. 4 667 725 describes a method for producing castings with a predetermined graphite structure. The method comprises taking a sample from a bath of molten iron and then allowing the sample to solidify over a period of from 0.5 to 10 minutes. During the solidification period, recordings are made of the temperature changes that take place in the centre of the sample volume and near the inner wall of the sample vessel. The sample vessel should substantially be in thermal equilibrium at a temperature above the crystailization temperature of the bath and be allowed to solidify fully over a period of from 0.5 to 10 minutes. The temperature-time sequence is is measured by two temperature responsive means, of which one is placed in the centre of the sample quantity and the other in the molten material at a location close to the wall of the vessel. The degree of dispersion of the graphite phase in relation to known reference values for the same sampling and testing process with respect to finished castings is assayed with the aid of the temperature measured during the first nucleation events of the eutectic reaction measured at said vessel wall as the minimum undercooling temperature at the vessel wall, the recalescence of the vessel wall, the positive difference between the temperature that prevails at the vessel wall and in the centre of the sample and the derivative of the temperature decrease at said vessel wall during the time for constant eutectic growth temperature in the centre of the sample quantity, alternatively the highest negative values of the temperature difference between the eutectic maximum growth temperature and the eutectic temperature. If the bath has an insufficiency of crystallization nuclei, a graphite nucleating agent is introduced thereinto and conversely when the crystallization nucleants are present in excess the degree of dispersion is lowered by holding the bath for a length of time sufficient to reduce the amount of nuclei in the bath prior to casting, by assessing the morphology of the graphite precipitation in relation to corresponding data obtained with the same sampling and testing technique as that applied with cast iron of known structure, with the aid of supercooling that takes place in the centre of the molten material, the recalescence in the centre of the sample vessel and the maximum growth temperature, and by correcting the quantity of structure-modifying agent in response thereto, so that graphite precipitation takes place in a predetermined form upon solidification of the molten cast iron subsequent to casting. The obtained values are used to determine the amount of modifying agent and the presence of graphite nucleating agent in the melt concerned and for the equipment used. The production equipment used has to be calibrated and possibly necessary additions of modifying element and nucleating agent have to be made in relation to the calibration of the best equipment.
The above-mentioned method permits the skilled person to predict how the graphite precipitation will take place in the melt concerned and also how to control the composition of the melt to obtain desired results. The test method gives results which cannot be obtained with other analysis methods. Although a chemical test will, for instance, disclose the total amount of magnesium present, it will provide no information as to how much magnesium there is in solution and thus active as a modifying agent. This latter information is of great importance since the amount of magnesium in solution in an iron melt will change relatively quickly due to physical and chemical reactions that take place within the melt and due to contact with the surroundings and consequently although a c
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Bradley P. Austin
Puknys Erik R.
Sinter-Cast AB
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