Standard specimens for use in emission spectrography
United States Patent [1 1 Mentrier et al.  
 [451 Apr. 15, 1975 STANDARD SPECIMENS FOR USE IN EMISSION SPECTROGRAPHY [75] Inventors: Michel Mentrier, Coublevie; Henri Pichery, Tarascon, both of France [73] Assignee: Compagnie Pechiney, Paris, France [22] Filed: Aug. 12, 1970 [21] Appl. No.: 63,200  
 [52] US. Cl 356/85; 356/243 [51] Int. Cl. G01j 3/02 [58] Field of Search 164/47, 76, 126, 133, 270;  
 [56] References Cited UNITED STATES PATENTS 975,383 11/1910 Keithley 164/76 X 1,498,128 6/1924 Sowers 2,100,977 11/1937 Pettersson .1 356/86 2,134,749 11/1938 Burt 29/5276 X 3,171,882 3/1965 Baird 356/81 3,352,351 ll/1967 Sickbert 164/348 X FOREIGN PATENTS OR APPLICATIONS 533,117 11/1956 Canada 164/125 848,548 9/1952 Germany 164/286 Primary ExaminerRonald L. Wibert Assistant Examiner-F. L. Evans [57] ABSTRACT A test specimen for use in emission spectrography and method for the preparation of same wherein a metal alloy is molded in the form of a thin-walled cup defined by a substantially conical side wall having a U or V-shaped cross section whereby the homogeneity of the metal alloy forming the specimen is substantially improved.  
 2 Claims, 3 Drawing Figures STANDARD SPECIMENS FOR USE IN EMISSION SPECTROGRAPHY This invention relates to a process for the preparation of test specimens for use in determining the composition of metallic alloys by emission spectrography. and to new and improved test specimens produced thereby.  
  The analysis of an alloy casting requires a sample which is representative of the furnace charge. One of the methods most frequently used in such analyses is emission spectrography, which requires the use of specimens for comparative purposes whereby the composition of the specimens is determined by an arbitrary method in which a furnace sample is compared with a control specimen.  
  At the present time, such control specimens are used in the form of thin discs or medallions. This shape makes it possible to provide a plane surface well suited for spectrographic analysis by simply machining the disc specimen.  
  However, it has recently been found that segregations or variations in the composition exist, which have an axis which is precisely perpendicular to the machined surface. In addition, the machined surfaces are, for the most part, parallel to the planes of solidification of the control specimens and samples. As a result of these two factors, the results of spectrographic analysis are frequently a function of the thickness of the disc eliminated by machining.  
  In fact. the variations of such test results are often incompatible with the experimental error of spectrographic methods and with strict tolerances set by certain manufacturing standards.  
  In addition, the shape and heterogenity of control specimens permit only a limited number of remachining operations which are required for use. Thus, such disc-shaped control specimens have a relatively short useful life, which further reduces the accuracy of the analysis.  
  It is accordingly an object of the present invention to produce and to provide a method for producing test specimens which overcome the aforementioned disadvantages, and it is a related object of the invention to produce and to provide a method for producing a test specimen for use in emission spectography having improved homogeneity.  
  These and other objects and advantages of the invention will appear more fully hereinafter, and, for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which:  
  FIG. 1 is a schematic elevational view in section illustration a method for preparing test specimens in accordance with the concepts of the present invention;  
  FIG. 2 is a sectional view ofa test specimen prepared in accordance with the method illustrated in FIG. 1; and,  
  FIG. 3 is a sectional view of the test specimen shown in FIG. 2 after machining.  
  The concepts of the present invention reside in a test specimen for use in emission spectrography which has been cast in the form of a thin-walled conical cup which is symmetrical with respect to its axis and thus has a symmetry of revolution about its axis, and a cross sectional shape in the form of a U or V.  
  Referring now to the drawings. there is shown in FIG. 2 a test specimen embodying the concepts of this invention including a base portion 10 integral to an annular conical wall 12 having a generally U or V-shaped cross section to define a thin-walled cup.  
  The test specimen of the invention is preferably obtained by casting in a chill mold, which can be uncooled or cooled by means of a cooling medium such as water through the mold. A suitable method for casting the test specimen 10 is illustrated in FIG. 1 of the drawing wherein a mold 14 having a mold cavity 16 with a configuration corresponding to the desired shape of the final test specimen is slowly filled with the molten metal from a suitable source 18. After the molten metal has solidified and the mold cooled sufficiently for handling, the mold 14 is opened and the specimen removed.  
  For use in emission spectographic analysis, the end surface of the conical side walls 12 is ground or machined in a known manner perpendicularly to its axis to expose a substantially flat annular surface 20. as illustrated in FIG. 3.  
  The form or shape of the test specimens of the present invention permits the use ofa non-turbulent gravity feed of the molten metal during casting, thereby resulting in concentric solidification of the molten metals at all levels over the short distance or width of the annular side walls 12 of the conical portion of the specimen. This rapid concentric cooling of the molten metals has been found to prevent or substantially minimizes the formation of major segregations or zones of varying composition with the result that the homogeneity of the composition is significantly improved.  
  In addition, by machining the specimen in a plane substantially perpendicular to the axis of the annular conical walls, there is provided a planar surface 20 which intersects all solidification fronts without being tangent to them.  
  As a result, regardless of the thickness of metal removed by machining surface 20,  
 l. in a planar annular section, the composition at middle distance from the edges is found to be very constant, and this is favorable to obtaining results of spectrographic analysis operations which can be reproduced;  
 2. the chips or shavings resulting from the machining haave a constant chemical composition, and this improves the quality of the grading;  
 3. the number of possible re-machining operations. that is to say, the effective life of the test specimen, is increased.  
  It will be understood that various changes and modifications may be made in formulation, procedure and use without departing from the spirit of the invention, especially as defined in the following claims.  
 We claim:  
  1. A cast test specimen for use in determining the composition of metallic alloys by emission spectrography comprising a thin-walled cup defined by a generally conical side wall having a U- or V-shaped cross section, with the mouth of the cup having been machined to provide an annular planar surface substantially perpendicular to the axis of the cup whereby the planar surface intersects all solidification fronts of the cast specimen without being tangent to the solidification fronts.  
  2. In the method for analysis of an alloy casting by emission spectrography wherein a sample of the furnace charge of an alloy casting is compared with a test specimen. the composition of which is known, the improvement comprising a test specimen comprising a thin-walled cup defined by a generally conical side wall having a U- or V-shaped cross section; with the mouth of the cup having been machined to provide an annular gent to the solidification fronts.