The error of infrared carbon sulfur analyzer and those related

In the casting manufacturing enterprises, the analysis of the instrument is not lack of, the ingredients of the food measured whether the product is qualified, the customer is satisfied, the characteristics of the casting are also associated with the content of the content. The product component meets the customer standards that measure the important indicator of a casting qualification. We are in the daily testing process of the carbon and sulfur content of the causing the main analysis of the carbon and sulfur content analysis of the castings, the analysis of the work of the infrared carbon sulfur analyzer, the analysis of the results of the detection of the test results, summarizes the corresponding causes of the infrared carbon sulfur analyzer test results, the corresponding is the west of the need for attention to the results of the results of the main instruments and reagents to meet GB / T 20123-2006 steel. Total carbon content of the fuel.

CS8820S infrared carbon and sulfur analyzer main instruments and analysis conditions:

1.CS8820S infrared carbon and sulfur analyzer; 2. laboratory temperature: 18-30 ° C, humidity <70%; 3.regulated power supply: 220V; 4.instrument weight  : 80kg; 5.Tungsten tin flux: 20 ~ 40 mesh; 6.Power gas: Air pressure is 0.2-0.4MPa, purity requirement is 99.99%; 7.Gas assist: Gas pressure is 0.2-0.4MPa, purity requirement is 99.99%  

2 Results and discussion

2.1 Analysis method According to the analysis method of GB / T 20123-2006 and the same analysis conditions, through analysis of the carbon and sulfur content of the cast iron sample, the deviation of the carbon and sulfur test results under the influence of different factors is obtained, and then obtained  Several reasons influence the error of carbon and sulfur analysis.  

2.2 Linearity of the carbon and sulfur infrared analyzer The linearity of the infrared carbon and sulfur analyzer directly affects the accuracy of the test results.  Linear means that the instrument manufacturer calibrates the data of the instrument according to the element content range of the test product provided by the purchasing unit when the instrument leaves the factory. Usually, within the element content measurement range, the low content to the high content is smoothly processed into a straight line by the formula.  If the linearity is not good, the element content of the obtained test sample must also be unreliable.  Therefore, when accepting the instrument, be sure to select several carbon and sulfur standards with different gradients of carbon and sulfur content in the instrument range for testing and analysis; before daily testing and analysis of the sample, you must also select a sample that is similar to the content of the sample to be tested.  Carbon and sulfur standards to verify that the linearity of the instrument is accurate and reliable.

2.3 Selection of calibration standards During daily production and testing, it is necessary to select carbon and sulfur standards that are similar to the content of the samples to be tested for daily calibration.  The carbon and sulfur content of the calibration standard is preferably close to the upper limit of the element content range of the sample to be tested, because if a low content standard is used to calibrate the curve, a large deviation will be produced when a high content sample is made.  The operator must perform a single-point calibration of a standard reference substance of known concentration at least 3 times before proceeding to the next detection analysis.  

2.4 Instrument gas and reagents Before using the instrument, it must be ensured that the purity and gas flow of power gas and auxiliary gas meet the requirements of the instrument, and the reagents of the instrument must be effective, otherwise it will greatly affect the carbon and sulfur analysis and detection of the sample.  accuracy.  For example, alkaline asbestos is used to absorb carbon dioxide in oxygen. If the effect is not good or even fails, the detection result of carbon element will be high.  The role of magnesium perchlorate is to absorb the moisture of the crucible and the sample after combustion, and one-third of the color changes, and it needs to be replaced.  

2.5 Carbon-sulfur crucibles The untreated carbon-sulfur crucibles have an impact on the test results ranging from a dozen to several tens of ppm. Experiments have shown that the time and temperature of crucible pretreatment are critical to the removal of residual carbon and sulfur in the crucible  important influence.  Therefore, the crucible must be pretreated to make the detection result of the infrared carbon and sulfur analyzer more accurate.  The correct pretreatment method is: the burning time at 1000 ° C is not less than 40 minutes, and the burning time at 1350 ° C is not less than 15 minutes, then take it out and put it in a dry heat-resistant dish, cool it for 2-3 minutes, and finally place the crucible in  In the dryer.  

2.6 Handling of test samples When handling test samples, care must be taken to avoid errors during sampling.  For example, the sample taken has cracks, inclusions, pores, scale, stains, rust, etc. These conditions will cause the repeatability of the test results of the same sample to be very poor, even beyond the repeatability range of the standard method.  Therefore, in our usual sampling and sample preparation process, we must be serious and responsible, efficient and rigorous.  For the unqualified samples, the laboratory personnel must not conduct testing and analysis. They should refuse to accept the samples and return them, and let the sample preparation staff resampling.  2.7 Tungsten tin flux Like carbon and sulfur crucibles, there are trace amounts of carbon and sulfur in tungsten tin flux.  For the flux used in our laboratory, the product label has clearly stated: C% ≤ 0.0008%, S% ≤ 0.0005%, so during the testing process, the amount of tungsten tin flux added to the sample can be burned.  It is advisable to obtain smooth slag, generally 1.0 ~ 1.5g. Excessive addition of tungsten-tin flux will not only cause small errors in the analysis results, but also cause unnecessary waste in terms of consumables costs.

2.8 Human error Human error is mainly caused by improper operation or carelessness of the analyst, such as the balance was not leveled before weighing; the balance did not return to zero during weighing; the sample fell outside the crucible during weighing;  The difference between the mass of the two samples in the parallel sample is too large; the quality of the added co-solvent is inconsistent; the wrong input of the sample weighing amount will cause deviation.  Therefore, in the daily production testing process, analysts must be correct, and strictly follow the operating procedures for testing.  References [1] GB / T 20123-2006 Iron and steel. Determination of total carbon and sulfur content. Infrared absorption method (conventional method) after combustion in a high-frequency induction furnace [2]. GB / T 223.83-2009 Iron and steel with high sulfur content  Determining the infrared absorption method of thorium induction furnace after combustion. Measurement error and correction of infrared carbon and sulfur analyzer.  Through the above literature, we know the factors that affect the detection results of the infrared carbon and sulfur analyzer.  There are mainly 1. linearity of infrared carbon and sulfur analyzer; 2. selection of calibration standards;

3. instrument gases and reagents;

4. carbon and sulfur crucibles;

5. test samples;

6. tungsten tin flux;

7. human error;  In these seven aspects, we can make accurate and credible results by selecting appropriate carbon and sulfur standards, testing in strict accordance with operating procedures, and being responsible.