Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Patent
1998-09-16
2000-08-15
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
136231, 164 41, 266 79, 420 18, C22C 3308
Patent
active
061029815
DESCRIPTION:
BRIEF SUMMARY
In the foundry industry it is often desirable to be able to determine in which matrix structure a certain molten cast iron will solidify. One way of carrying out such determinations is to perform a thermal analysis of the melt. A small sample of the molten metal alloy is taken and is allowed to solidify. During this process, the temperature is measured as a function of time. The configuration is then determined by comparing the obtained cooling curve and its time derivative with reference curves. Such thermal analysis methods are disclosed in e.g. WO86/01755, WO91/13176 and WO92/06809.
In the above mentioned methods, a sample of molten metal is obtained by immersing a sample vessel into the molten iron, whereafter said sample is allowed to solidify. The thermal analysis is performed by using temperature responsive means, normally two thermocouples. One of said means is positioned in the centre of the vessel and the other near the vessel wall.
In the method according to WO92/06809 a sample vessel where the inner surface is coated with a reactive wall is used. The reactive coating, comprising oxides of silicon, manganese, iron and/or sodium, reacts with active magnesium in the sampled iron and lowers the level of active magnesium in the wall region of the sample vessel.
By using a coated sample vessel according to WO92/06809 it is possible to perform more accurate predictions of solidification structure compared to the state of the art as represented by WO86/01755. In particular, the consumption of magnesium in the near-wall region simulates the natural fading of magnesium during the casting period and provides a predictive warning of magnesium loss. While this feature is indespensible for for the reliable production of compacted graphite iron, it is of great importance to be able to increase the accuracy further.
SUMMARY OF THE INVENTION
Now it has turned out that by using at least three temperature responsive means instead of two and by using a sample vessel where a part of the inner surface is coated with a layer of a substance which will lower the concentration of dissolved elementary magnesium, and the rest of the inner surface is coated by an inert or non-reactive substance (oxides-of alumina and zirconia for example), or the sample vessel itself is non-reactive (quartz or steel), it is passible to further increase the accuracy of the solidification structure predictions of the molten cast iron. Alternatively, two different sample vessels, one being coated with a reactive layer and the other one being essentially inert or non-reactive, or coated with an inert or non-reactive substance, may also be used in the present method. Suitable temperature responsive means are thermocouples or pyrometrical means.
A sample of the molten cast iron that is to be analyzed is taken and poured into said sample vessel, which is partially coated with reactive and non-reactive coatings. At least one of the temperature responsive means is placed in the centre of the sample vessel, at least one means close to the inner surface to which a reactive coating has been applied, and at least one means close to the inner surface, to which a non-reactive coating has been applied. Each of said temperature responsive means is then used to record the temperature of the melt during the solidification process as a function of time. The obtained curves are then evaluated in order to determine the configuration of the solidified cast iron sample.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention will be explained in more detail with reference to the figures, in which
FIG. 1 shows typical cooling curves that can be obtained by using the method according to WO86/01755;
FIG. 2 illustrates a diagram showing the nodularity percentage as a function of the magnesium percentage. In this diagram 0% nodularity corresponds to a complete compacted graphite cast iron (CGI), whereas 100% corresponds to a complete spheroidal graphite iron (SGI); Finally, values below 0% nodularity relate to grey cast iron. Actually, 0% nodularity
REFERENCES:
patent: 5949000 (1999-07-01), Lindholm et al.
Andrews Melvyn
Sinter-Cast AB
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