Mobile spectrometers with arc and spark discharges for on -site metal identification
The first step towards using AES for scrap was taken with manual spectroscopes but their low D and the relatively high demands made by users prevented general application. The more convenient table spectroscopes, which had higher D and were able to compare spectra, allowed sorting of high-grade scrap such as eg. bronzes, admittedly with wide tolerances.
Photographic spectra recording and evaluation, which became very important in the analytical field, had to be ruled out because of the long access time for results and high cost involved in sample preparation for sorting purpose.
Although the introduction of photoelectric measurements of line intensities by means of laboratory spectrometers allowed rapid spectra evaluation, sample preparation, as before, still proved to be an obstacle for sorting applications.
The development of mobile test probes with lightguides opened the way for widespread use of AES for testing and sorting large quantities of materials.
By 1975, development in laboratory AE spectrometers with SDAR for metal analyses had led to RSD≈1%，SR 1-5% and LOD of 10 μg/g. In a well organised and suitably equipped spectrometers laboratory for melt control, a time of 3 min was achieved from sample preparation to analysis output.
Before 1970, because of the influence of sample structure on spectrometer results, the analysis of semi-finished and finished material was only carried out after remelting in remelting furnaces specially developed for this purpose. The structural isoforming process developed about 1970 using HEPS led to increased use of laboratory spectrometers with SDAR for outgoing and incoming inspection. Today, more than half of these spectrometers are used in field, more than are used for melt control.
Incoming and outgoing inspection was not carried out systematically for each piece, but only when it was suspected that material had been mixed-up. This inspection and the organization required were expensive: samples had to be taken from the material, they had to be numbered, transported for preparation, analysed and re-allocated at the production plant. Mix-ups often occurred with this procedure.
I can still hear what a Plant Engineer at a steelworks said to me regarding the importance of finished material inspection: “To us at the plant, what use are the best spectrometers in the Laboratory with an accuracy of 1% rel. if 10% of the qualities are mixed up by the time they are loaded?”
Inspection can only be sensible if the test equipment goes to the job in the plant, not if the job or part of the job goes to the test equipment in the Laboratory.
Classical methods such as magnets, spark grinding and the spectroscope had proved satisfactory
for practical applications, but no longer met most requirements because of their “lack of definition”.
It should not go without mention that analysts at large plants often still have little appreciation of practical applications, but no longer met most requirements because of their “lack of definition”.
It should not go without mention that analysts at large plants often still have little appreciation of the work done by Quality Control staff because they do not understand the work. When an analyst has to make an analysis, the more elements with more digits after the point the better. Quality identification by a Quality Control man can often be done by a simple statement of “yes” or “no”, of which some example are:
Al-, Si-killed steel
Pb-containing free-cutting steel
Mo-, Ti-, Nb-stabilised CrNi-steel.
The tasks to be carried out by on-site Quality Control are: Sorting, identity testing, approximate analysis for quality determination, analysis.
Analysis is not usually necessary to determine the quality of a material. Usually it is not a matter of proving to the manufacturer that quality limits have not been complied with (this is of interest to commercial staff because of price reductions) but of sorting or confirming certain qualities.
With the use of mobile spectrometers under production plant conditions a new field of applications has been opened up to spectrometry. There are about 2000 spectrometers of this type in use, with about 400 more commissioned each year.
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