Metal founding – Process – With measuring – testing – inspecting – or condition determination
Patent
1996-07-01
1998-06-02
Hail, III, Joseph J.
Metal founding
Process
With measuring, testing, inspecting, or condition determination
164 571, 164 581, B22D 4600, B22D 2700
Patent
active
057587060
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/SE94/01177 filed Dec. 7, 1994.
BACKGROUND OF THE INVENTION
The present invention relates to a method for providing pretreated molten iron for casting objects which solidify as compacted graphite iron.
Compacted graphite iron, below abbrivated as CGI, is a type of cast iron in which graphite appears in a vermicular form (also referred to as compacted cast iron or vermicular iron) when viewed on a two-dimensional plane of polish; vermicular graphite is defined as "Form III" graphite in ISO/R 945-1969, and alternatively "Type IV" according to ASTM Specification A 247.
The mechanical properties of CGI are a combination of the best properties of gray iron and ductile iron. The fatigue strength and ultimate tensile strength of CGI are comparable with the values for pearlitic ductile iron, while the thermal conductivity of CGI is similar to that of gray iron. In spite of this, CGI presently represents only a limited part of the total world production of cast iron, as compared with gray iron which constitutes about 70% of the total cast iron production, and ductile iron which constitutes about 25% of total production.
One reason for the prior limited production of CGI is because of the difficulty and reliably producing it. This difficulty stems from the fact that the graphitization potential and the graphite shape-modifying elements of the iron must be simultaneously controlled within a very narrow range during the production process. This has been achieved hitherto with the aid of a large number of tests and experientially well-defined and often expensive additions to the system. However, theses difficulties have been removed in the most part by the methods described in SE-B-444,817, SE-B-469,712 and SE-B-470,091. SE-B-444,817 describes a method of producing cast iron which includes graphite shape-modifying agents, this method being based on a thermal analysis which enables the graphite precipitation and growth to be established based upon the actual solidification process of a small and representative sample and to finally treat the melt with additional graphite shape-modifying elements as required for optimal solidification of CGI upon casting. The time-dependant change in temperature in the center of a sample and at a point in the melt lying close to the wall of the sampling vessel during the solidification process is recorded, whereby two different solidification curves are obtained which can be used to provide information relating to the course of solidification in a casting process. Since this sampling method provides quick and very precise information concerning the inherent crystallization properties of the melt, the subject matter of SE-B-444,817 represents a first realistic possibility of controlling the production of CGI on a large scale.
SE-B-469,712 teaches a development of the method taught by SE-B-444,817, in which there is used a special type of sample container having walls supplied with a substance which lowers the concentration of elementary magnesium dissolved in the melt close to the container wall by at least 0.003%. This is done to create a margin against such lowering of the Mg-content as to result in the formation of flaky graphite; with regard to elementary Mg, the transition from the formation of compacted graphite to the formation of flaky graphite namely extends over a concentration range of only 0.003 percentage units, principally from 0.008% to 0.005%, although the absolute values may vary depending on the solidification time.
SE-B-470,091 describes a further development of the method taught by SE-B-444,817. This patent specification describes how it is also possible to determine the physical carbon equivalent (C.E.) or graphitization potential of structurally modified cast iron melts, among others CGI which has a C.E.-value higher than the eutectic point. Again, the thermal analysis results are used to correct or regulate the composition of the melt. The method is based on introducing into a sample vessel pieces of
REFERENCES:
patent: 4046509 (1977-09-01), Backerud
patent: 4246026 (1981-01-01), Stefanescu et al.
patent: 5337799 (1994-08-01), Backerud
Andersson Conny
Backerud Stig Lennart
Hail III Joseph J.
Lin I.-H.
Sinter-Cast AB
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