AMENDED SPECIFICATIONS FOR THE RATTLER TEST. PRESENT N. B. M. A. TEST.
1. Dimensions of the Machine.—The standard machine shall be 28 inches in diameter and 20 inches in length, measured inside the rattling chamber.
Other machines may be used, varying in diameter between 26 and 30 inches, and in length from 18 to 24 inches, but if this is done, a record of it must be attached to the official report. Long rattlers must be cut up into sections of suitable length by the insertion of an iron diaphgram at the proper point.
2. Construction of the Machine.—The barrel may be driven by trunnions at one or both ends, or by rollers underneath, but in no case shall a shaft pass through the rattler chamber. The cross section of the barrel shall be a reg ular polygon, having fourteen sides. The heads shall be composed of gray cast-iron, not chilled nor case-hardened. The staves shall preferably be com posed of steel plates, as cast-iron peans and ultimately breaks under the wearing action on the inside. There shall be a space of one-fourth of an inch between the staves for the escape of the dust and small pieces of waste.
Other machines may be used having from twelve to sixteen staves, with openings from one-eighth to three-eighths of an inch between staves but if this is done a record of it must be attached to the official report of the test.
3. Composition of the Charge.—All tests must be executed on charges containing but one make of paving material at a time. The charge shall be composed of the brick to be tested and iron abrasive material. The brick charge shall consist of that number of whole bricks or blocks whose com bined volume most nearly amounts to 1,000 cubic inches, or 8 per cent of the content of the rattling chamber. (Nine, ten, or eleven are the number re quired for the ordinary sizes on the market). The abrasive charge shall consist of 300 pounds of shot made of ordinary machinery cast-iron. This shot shall be of two sizes, as described below, and the shot charge shall be composed of one-fourth (75 lb.) of the larger size and three-fourths (225 lb.) of the smaller size.
4. Size of the Shot.—The larger size shall weigh about seven and one half pounds and be about two and one-half inches square and four and one half inches long, with slightly rounded edges. The smaller size shall be one and one-half inch cubes, weighing about seven-eighths of a pound each, with square corners and edges. The individual shot shall be replaced by new ones when they have lost one-tenth of their original weight.
5. Revolutions of the Charge.—The number of revolutions of the Standard test shall be 1,800, and the speed of rotation shall not fall below 28 nor ex ceed 30 per minute. The belt power shall be sufficient to rotate the rattler at the same speed whether charged or empty.
6. Condition of the Charge.—The bricks composing a charge shall be thoroughly dried before making the test.
7. The Calculation of the Results.—The loss shall be calculated in per centages of the weight of the dry brick composing the charge, and no result shall be considered as official unless it is the average of two distinct and com plete tests, made on separate charges of brick.
Talbot-Jones Rattler Test.—In the machine constructed by the writer in 1900 (shown in Plate 2) and named "The Talbot-Jones Rattler" by the committee of expert engineers, the head which forms one end of the rattling cylinder overhangs the frame of the machine. The ends of the brick are placed so as to abut on this head and are securely clamped by bolts so that their inner faces form the concave surface of the rattler cylinder. Spacers of wood of triangular or trapezoidal form are
placed between the brick to keep them a fixed distance apart and to aid in holding the brick in place. An end, or second head of wood or of wire screen, is bolted on to close the cylinder. A sheet of metal is fastened to the head of the machine around the outside of the circle of brick and holds the brick in place during the process of inserting them and assists in taking the jar in making the test. In the original form this band was in a fixed position and since brick vary in thickness it was necessary to vary the spacing in order to divide up the space between the bricks throughout the entire circle. In the tests made by Professor Orton with this machine the brick were spaced one inch or more apart. This wide spacing and the variation found in filling the circle with bricks of different thickness seemed undesirable. The machine has now been modified so that the circle is adjustable and the spacing may be made uniform throughout the entire circumference. The average in ternal diameter of this chamber is 28 inches and the machine may be adjusted from 272-in. to 282-in. This permits a full ring to be made with an even spacing and any thickness of brick. It is recom mended that the space between brick be made Other details of the machine are that the end of the band lacks about inch of being in contact with the head of the machine, this space being left for the escape of dust and chips; the heads of the bolts lie in a T-shaped groove in the head of the machine so that they are readily adjustable; the cen tral portion of the head is recessed about inches so that the iron shot may strike the brick for their full length ; the cover of the cylinder for the same reason is held away from the outer ends of the brick.
It will be seen that in this rattler the brick themselves form the outer surface of the rattling chamber and are laid at right angles to the direction of action of the shot, and that one face of the brick receives the wear about as it does in the street. The shot gives the abrading and grinding and impact effect. In many ways the test resembles the wear of brick in the street; it naturally appeals to the mind as resembling and approximating the wear in the street.
This method of testing is a promising one in many directions. The machine is a special one, but its cost is hardly more than the standard rattler. Its use requires but little more skill. The time taken in charging the machine and in making the test is greater, so that the cost of a test by the Talbot-Jones process would be somewhat more than with the N. B. M. A. standard. If, however, it should be found to define the wearing qualities of a brick more definitely and with greater accuracy than does the ordinary rattler, these features would not interfere with its adoption. While considerable experimental work has been done with this machine, it is felt that the investigation has not pro ceeded far enough to standardize it nor to show its qualifications suffi ciently to recommend it for adoption as a standard for testing purposes. The writer has been unable to carry on the necessary investigations, but he hopes that full tests may be made to determine its usefulness. All the tests which have been made are favorable to its efficiency and adapt ability for general testing purposes. The uniformity of conditions for the tests and the opportunity to determine relative wear of individual brick are among the attractive features.