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The magnetic susceptibility and iron content of cast red brass
I16
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
Under the greatest loads applied the shearing stresses in the ribs of the slab were 405 lb. per sq. in. or more assuming the tile walls to have been effective in resisting shear. If the resistance of the tile walls is neglected the shearing stress must have been 500 lb. per sq. in. or more. The estimated shearing stress in one of the girders is 440 lb. per sq. in. The loads on which these shearing stresses are based had been on the slab for nearly a year. T H E M A G N E T I C S U S C E P T I B I L I T Y AND I R O N C O N T E N T O F CAST RED B R A S S : By L. H. Marshall and R. L. SaMord.
[ABSTRACT.]
T H E presence of iron in commercial brass is often objectionable, particularly if it occurs as discrete, poorly alloyed particles. In order to obviate any such harmful effects, a very low ferrous content is frequently specified. Therefore, a rapid, non-destructive method for quantitatively determining its presence would be of great value in practice. A magnetic method of inspection would fulfill the requirements of such a test if a definite relationship exists between some magnetic property and the iron content of the metal. From the meagre information available in the literature it was evident that this matter had received little attention. With these facts in mind a study was made of the magnetic properties of cast tin red brass contaminated with iron. A series of seven samples of an alloy of the type 82 copper, x 5 zinc, 3 tin was prepared containing various small proportions of iron up to o.75 per cent. These specimens were magnetized in a suitable solenoid. A test coil of I2oo turns extended over two-thirds of the specimen and readings of the magnetic induction were taken by means of a ballistic galvanometer. Greater precision was secured by balancing out the magnetizing force by means of a variable mutual inductance, so that the galvanometer deflection, in each case, was a measure of the increase in flux density due to the specimen (metallic induction). Magnetic properties were determined in the cast condition and after annealing 15 minutes at 625 ° C., 8 hours at 800 ° C., * Technol09ic Papers, No. 22I.
Jan., I923.]
U.S.
BUREAU OF STANDARDS .NOTES.
I I7
and 16 hours at 800 ° C. for different values of magnetizing force up to 5oo gilberts per em. The microstructure of the metal was determined before and after these various heat treatments. The cored structure of the cast material largely disappeared after the first eight-hour anneal. The eutectoid present in the cast samples was likewise absorbed at this time. The second eighthour anneal caused no further change in structure. Oxide inclusions were present in all of the samples. Up to O.14 per cent. the iron went into solid solution in the matrix of the alloy, but larger amounts than this caused the appearance of pale, rounded areas of an iron rich constituent. A rough estimate of the iron content could be made from the number and size of these areas. The percentage of iron present had no noticeable effect on the grain size of the metal, nor did the grain size have any definite influence on the magnetic properties of the specimens. The data obtained revealed several interesting points. For instance, the magnetic properties are not a precise index of the iron content of the cast metal. Then the magnetic susceptibility is markedly affected by changes in physical condition produced by heat treatment. Even after the material has been thoroughly annealed, there is still no simple relationship between the magnetic susceptibility and the iron content. The seeming irregularities in the magnetic behavior of these brass samples were probably due, in the case of the cast specimens, to the unhomogeneous structure of the metal; while those of the annealed bars were caused by the presence of the iron as two modifications, the dissolved and the segregated. The iron content was the source of the magnetic effects observed. RELATIVE USEFULNESS OF GASES OF DIFFERENT HEATING VALUE AND ADJUSTMENTS OF BURNERS FOR CHANGES IN HEATING VALUE AND SPECIFIC GRAVITY. 6 By W. M. Berry, I. V. Brumbaugh, J. H. Eiseman, G. F. Moulton, and G. B. Shawn.
[ABSTRACT.]
I x connection with an investigation conducted by the Public Service Commission of Maryland to determine the most economic heating value standard for manufactured gas in the city of Baltio Technologic Papers, No. 222.
U.S.
BUREAU OF STANDARDS NOTES.
[J. F. I.
Under the greatest loads applied the shearing stresses in the ribs of the slab were 405 lb. per sq. in. or more assuming the tile walls to have been effective in resisting shear. If the resistance of the tile walls is neglected the shearing stress must have been 500 lb. per sq. in. or more. The estimated shearing stress in one of the girders is 440 lb. per sq. in. The loads on which these shearing stresses are based had been on the slab for nearly a year. T H E M A G N E T I C S U S C E P T I B I L I T Y AND I R O N C O N T E N T O F CAST RED B R A S S : By L. H. Marshall and R. L. SaMord.
[ABSTRACT.]
T H E presence of iron in commercial brass is often objectionable, particularly if it occurs as discrete, poorly alloyed particles. In order to obviate any such harmful effects, a very low ferrous content is frequently specified. Therefore, a rapid, non-destructive method for quantitatively determining its presence would be of great value in practice. A magnetic method of inspection would fulfill the requirements of such a test if a definite relationship exists between some magnetic property and the iron content of the metal. From the meagre information available in the literature it was evident that this matter had received little attention. With these facts in mind a study was made of the magnetic properties of cast tin red brass contaminated with iron. A series of seven samples of an alloy of the type 82 copper, x 5 zinc, 3 tin was prepared containing various small proportions of iron up to o.75 per cent. These specimens were magnetized in a suitable solenoid. A test coil of I2oo turns extended over two-thirds of the specimen and readings of the magnetic induction were taken by means of a ballistic galvanometer. Greater precision was secured by balancing out the magnetizing force by means of a variable mutual inductance, so that the galvanometer deflection, in each case, was a measure of the increase in flux density due to the specimen (metallic induction). Magnetic properties were determined in the cast condition and after annealing 15 minutes at 625 ° C., 8 hours at 800 ° C., * Technol09ic Papers, No. 22I.
Jan., I923.]
U.S.
BUREAU OF STANDARDS .NOTES.
I I7
and 16 hours at 800 ° C. for different values of magnetizing force up to 5oo gilberts per em. The microstructure of the metal was determined before and after these various heat treatments. The cored structure of the cast material largely disappeared after the first eight-hour anneal. The eutectoid present in the cast samples was likewise absorbed at this time. The second eighthour anneal caused no further change in structure. Oxide inclusions were present in all of the samples. Up to O.14 per cent. the iron went into solid solution in the matrix of the alloy, but larger amounts than this caused the appearance of pale, rounded areas of an iron rich constituent. A rough estimate of the iron content could be made from the number and size of these areas. The percentage of iron present had no noticeable effect on the grain size of the metal, nor did the grain size have any definite influence on the magnetic properties of the specimens. The data obtained revealed several interesting points. For instance, the magnetic properties are not a precise index of the iron content of the cast metal. Then the magnetic susceptibility is markedly affected by changes in physical condition produced by heat treatment. Even after the material has been thoroughly annealed, there is still no simple relationship between the magnetic susceptibility and the iron content. The seeming irregularities in the magnetic behavior of these brass samples were probably due, in the case of the cast specimens, to the unhomogeneous structure of the metal; while those of the annealed bars were caused by the presence of the iron as two modifications, the dissolved and the segregated. The iron content was the source of the magnetic effects observed. RELATIVE USEFULNESS OF GASES OF DIFFERENT HEATING VALUE AND ADJUSTMENTS OF BURNERS FOR CHANGES IN HEATING VALUE AND SPECIFIC GRAVITY. 6 By W. M. Berry, I. V. Brumbaugh, J. H. Eiseman, G. F. Moulton, and G. B. Shawn.
[ABSTRACT.]
I x connection with an investigation conducted by the Public Service Commission of Maryland to determine the most economic heating value standard for manufactured gas in the city of Baltio Technologic Papers, No. 222.