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  • Analysis of the reasons for the deviation of cast iron content by spectrometer
Analysis of the reasons for the deviation of cast iron content by spectrometer
Analysis of the reasons for the deviation of cast iron content by spectrometer




The analysis of chemical elements in the molten iron before furnace by spectrometer is the main means of controlling the chemical composition of the molten iron in the foundry industry in recent years. Spectrometer analysis has many advantages: fast, from sample making to spectrometer analysis, it only takes 2-3 minutes; high accuracy, when the content of chemical elements in molten iron is within the scope of spectrometer analysis, the analysis deviation is less than 1%; all kinds of analytical chemical elements can be analyzed according to the needs: simple operation, and can be operated as long as short-term training is provided.



Although the normal deviation of spectrometer analysis is less than 1%, we usually have a deviation of more than 1% and reach 5% or higher in actual operation. This deviation often occurs in the following aspects: spectrograph analysis of different parts of the sample, analysis of the same sample on different spectrometers, and analysis of the same sample by hand and spectrograph. We have carried out research and Analysis on the deviation, and summarized the main causes caused by the following aspects and the corresponding corrective measures.



Reasons and corrective measures of sample:



Generally speaking, the maximum error is from the sample itself.



1. The samples used in spectrometer analysis shall be white mouth samples instead of gray ones.



Because the surface resistance of the sample is high and it is not easy to be broken down by current when the sample is excited by spectrometer, the analysis is affected, and the obtained value is low.



2. When preparing for excitation, the temperature of the sample shall be room temperature (< 20 ℃).



3. The area of the sample shall be larger than the spark excitation table excitation hole, and there must be an overlapping area (minimum 1mm), and the surface of the sample shall be uniform, flat and uniform in texture.



If the sample is uneven or the sample area is less than the excitation hole, the excitation hole will not be completely covered, so that the combustion chamber is not sealed, and the current intensity will be changed when the sample is excited, thus affecting the pre combustion and exposure, incomplete combustion of the sample, resulting in the low analysis results of spectrometer.



4. The surface of the sample shall be clean and not contaminated, such as touching by hand.



When the polluted sample is excited, the surface cannot be washed clean, and the washed object pollutes the combustion chamber, which affects the pre combustion and exposure. The serious time spectrometer cannot analyze it, and the deviation of the analysis results will be large if it is slight.



5. The surface of the sample shall not be free of sand holes, pores, cracks and other defects.



Because the defect will cause the change of current intensity when the sample is excited, the sample combustion is incomplete, the excitation is not good, and the result of spectrometer analysis is low.



6. The content of sulfur in the sample should not be too high.



In practice, we found that when the sulfur content in the sample is more than 2%, the spectrometer can not be analyzed normally. Because sulfur forms compounds such as iron sulfide and manganese sulfide during combustion, it affects the further excitation of the sample, which leads to poor excitation.



7. The surface of the sample is poor by spark excitation.
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