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Qualities of fire-clay refractories
Oct.. rgi7.1
U.
S. BUREN
OF STANDARDS Norms.
533
200. The determination of the amount of material retained on the sieves, as washed through by using a moderate stream of water from a one-quarter inch rubber tube, followed substantially the practice recommended by the American Society for Testing Materials for determining the fineness of mazon’s hydrated lime. The washing was continued until the water passing through the sieves was clear. In no case was it found necessary to continue The sieves were placed in an the washing for over ten minutes. electrically heated drying oven for one hour and the contents on each sieve finally weighed. The fo’llowing results give the progress of this investigation to date : Retained Th&
Si% No.
ib.
. 30 50
30 50 100
100
200
200*
. .
Sample
No.
II
ZI
Per cent.
Per cent.
Per cent.
Per cent.
0.9
2.2
I.7
3.1 2.3 I.3 3.7 89.6
10.3
0.8
2.6 0.9 91.8
0.; 2.2
93.2
24
28
35 Per cent.
2.2
3.1 7.4
2.1
6.9
2.2
5.6
83.2
77.0
*By difference. QUALITIES
OF FIRE-CLAY
REFRACTORIES.
THE study of the fundamental qualities of representative fire-clay ref.ractories and individual clays has been referred to and described in Techical News Rulletirz No. 127 (January, 1927) and No. 121 (May, 1927). The effect of reheating at dilatation has now been high temperatures on the thermal The importance of thermal dilatation as a factor conobserved. trolling resistance to thermal spalling has been discussed at length in recent literature and the signihcance of differential thermal dilatation and fibre elongation was briefly referred to in Teclznicnl News Rdleti+z No. III. Factors of possible significance are not only the differences in thermal dilatation of the various constituents of the refractory structure, but also the difference in thermal dilatation between one portion of a structure and an adjacent portion. In actual service nine-inch brick are usually laid in header courses, that is, only the 254 x 4:/2-inch end is exposed directly to the heat. Since fire-clay refractories are fairly good heat insulators, the maximum temperature 2 inches from the “ hot
534
U.
S. BUREAU
OF STANDARDS NOTES.
[J. F. I.
face ” may never exceed 1200’ C. (2200’ F.), even though the hot face is heated for prolonged periods as high as 1450” C. (2642’ F.). Since clay refractories are initially fired at temperatures from 1250 to 1275” C., it is unlikely that the structure 2 inches from the hot face would he greatly affected in service. However, the data obtained show that the material at and immediately adjacent to the hot face may be changed very materially as regards thermal dilatation. Average values for seventeen representative brands of fireclay show that reheating at 1400’ C. (2552” F.) for five hours reduced the per cent. linear thermal expansion and contraction of the brick (calculations based on values obtained on brick as received) by 0.04 per cent., and that the per cent. linear expansion from room temperature to 900’ C. has been changed by 0.1 per cent. Furthermore, reheating at 1500’ C. for five hours changed the per cent. linear expansion, from room temperature to 200’ C., an average of 0.07 per cent., and from room temperature to 900’ C. it was changed 0.15 per cent. Certain brick of the siliceous type showed changes greatly exceeding these average The maximmum changes observed were as follows : (A) values. (after reheating at 1400’ C. for five hours) room temperature to 200’ C., 0.09 per cent. change in linear thermal expansion; room temperature to 900’ C., 0.17 per cent. ; (B) (after reheating at 1500~ C. for five hours) roo’m temperature to 200’ C., 0.16 per cent.; room temperature to 900” C., 0.30 per cent. A preliminary report of this phase of the investigation, together with a discussion of its significance as regards thermal spalling, was published in the September, 1927, issue of Fz& and Furmces. FUNDAMENTAL
STUDY
OF GLAZE
FIT.
AN INVESTIGATION is being conducted at the Columbus branch of the bureau to determine the effect of the various oxides on the tensile strength, modulus of elasticity, and coefficient of expansion of glazes. To date about eighty-five glazes have been melted into rods and the tensile strength and modulus of elasticity determined. The coefficient of expansion has been determined on about twenty of the glazes. The modulus of elasticity and tensile strength are not strictly straight-line functions of the batch composition of the glazes.
U.
S. BUREN
OF STANDARDS Norms.
533
200. The determination of the amount of material retained on the sieves, as washed through by using a moderate stream of water from a one-quarter inch rubber tube, followed substantially the practice recommended by the American Society for Testing Materials for determining the fineness of mazon’s hydrated lime. The washing was continued until the water passing through the sieves was clear. In no case was it found necessary to continue The sieves were placed in an the washing for over ten minutes. electrically heated drying oven for one hour and the contents on each sieve finally weighed. The fo’llowing results give the progress of this investigation to date : Retained Th&
Si% No.
ib.
. 30 50
30 50 100
100
200
200*
. .
Sample
No.
II
ZI
Per cent.
Per cent.
Per cent.
Per cent.
0.9
2.2
I.7
3.1 2.3 I.3 3.7 89.6
10.3
0.8
2.6 0.9 91.8
0.; 2.2
93.2
24
28
35 Per cent.
2.2
3.1 7.4
2.1
6.9
2.2
5.6
83.2
77.0
*By difference. QUALITIES
OF FIRE-CLAY
REFRACTORIES.
THE study of the fundamental qualities of representative fire-clay ref.ractories and individual clays has been referred to and described in Techical News Rulletirz No. 127 (January, 1927) and No. 121 (May, 1927). The effect of reheating at dilatation has now been high temperatures on the thermal The importance of thermal dilatation as a factor conobserved. trolling resistance to thermal spalling has been discussed at length in recent literature and the signihcance of differential thermal dilatation and fibre elongation was briefly referred to in Teclznicnl News Rdleti+z No. III. Factors of possible significance are not only the differences in thermal dilatation of the various constituents of the refractory structure, but also the difference in thermal dilatation between one portion of a structure and an adjacent portion. In actual service nine-inch brick are usually laid in header courses, that is, only the 254 x 4:/2-inch end is exposed directly to the heat. Since fire-clay refractories are fairly good heat insulators, the maximum temperature 2 inches from the “ hot
534
U.
S. BUREAU
OF STANDARDS NOTES.
[J. F. I.
face ” may never exceed 1200’ C. (2200’ F.), even though the hot face is heated for prolonged periods as high as 1450” C. (2642’ F.). Since clay refractories are initially fired at temperatures from 1250 to 1275” C., it is unlikely that the structure 2 inches from the hot face would he greatly affected in service. However, the data obtained show that the material at and immediately adjacent to the hot face may be changed very materially as regards thermal dilatation. Average values for seventeen representative brands of fireclay show that reheating at 1400’ C. (2552” F.) for five hours reduced the per cent. linear thermal expansion and contraction of the brick (calculations based on values obtained on brick as received) by 0.04 per cent., and that the per cent. linear expansion from room temperature to 900’ C. has been changed by 0.1 per cent. Furthermore, reheating at 1500’ C. for five hours changed the per cent. linear expansion, from room temperature to 200’ C., an average of 0.07 per cent., and from room temperature to 900’ C. it was changed 0.15 per cent. Certain brick of the siliceous type showed changes greatly exceeding these average The maximmum changes observed were as follows : (A) values. (after reheating at 1400’ C. for five hours) room temperature to 200’ C., 0.09 per cent. change in linear thermal expansion; room temperature to 900’ C., 0.17 per cent. ; (B) (after reheating at 1500~ C. for five hours) roo’m temperature to 200’ C., 0.16 per cent.; room temperature to 900” C., 0.30 per cent. A preliminary report of this phase of the investigation, together with a discussion of its significance as regards thermal spalling, was published in the September, 1927, issue of Fz& and Furmces. FUNDAMENTAL
STUDY
OF GLAZE
FIT.
AN INVESTIGATION is being conducted at the Columbus branch of the bureau to determine the effect of the various oxides on the tensile strength, modulus of elasticity, and coefficient of expansion of glazes. To date about eighty-five glazes have been melted into rods and the tensile strength and modulus of elasticity determined. The coefficient of expansion has been determined on about twenty of the glazes. The modulus of elasticity and tensile strength are not strictly straight-line functions of the batch composition of the glazes.