Mar., 1921
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY ,
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23 I
LABORATORY AND PLANT
A COMPARATIVE STUDY OF VIBRATION ABSORBERS’ By H. C. Howard RESGARCH LABORATORIES, B. F. GOODRICH COMPANY, AKRON,OHIO
Vibrations in laboratories always cause great annoyance, a n d frequently either prevent t h e employment of sensitive instruments altogether or necessitate t h e installation of elaborate and mechanically unstable suspensions. T h e purpose of this study was t o work out a method €or determining t h e relative value of different devices a n d materials i n absorbing vibration. A review of t h e available literature showed t h a t very little had been published on vibration i n buildings. Some very careful and valuable work has been done by Prof. E. E. Hall,%of t h e University of California, in buildings in San Francisco a n d Berkeley. FIG.2-INSTRUMENT
FOR RECORDING VERnCAt V I B R A T I O N
was connected t o this pendulum i n such a way as t o give about a 20-fold magnification on t h e record sheet. For vertical vibration we used t h e apparatus shown in Fig. 2, consisting of a helical steel spring, No. 14 wire, about three-fourths inch i n diameter a n d 1 2 in. long when unstretched, a n d loaded with a lead bob weighing about 3 lbs. T h e bob was constrained t o movement in one vertical plane by knife edges. Vertical motion relative t o t h e bob was transformed into horizontal by a system of very light aluminium levers L
1
FIG.1-SIMPLE PENDULUM FOR RECORDING HORIZONTAL VIBKATIONS
Deutsch3 has done work in New York City, and a few descriptions of instruments for measuring vibration have appeared in t h e engineering magazines. With few exceptions t h e instruments which have been described for t h e measurement of vibration are constructed on the principle of t h e seismograph.s A pendulum of some type constitutes t h e fixed mass in t h e measurement of t h e horizontal component of t h e vibration a n d a weighted helical spring i n t h e measurement of t h e vertical. T h e apparatus which was used for obtaining records of horizontal vibration is shown in Fig. I . It con-‘ sisted of a simple pendulum weighing about 2 5 lbs., a n d having a period of vibration of approximately one second. A very light aluminium recording needle 1 Presented before t h e Division of Industrial and Engineering Chemistry at t h e 60th Meeting of the American Chemical Society, Chicago, Ill., September 6 t o 10, 1920. 1 Eng. News, 68 (1912), 198; Elec. World, July 29, 1912; Dec. 15, 1915. W e are also indebted t o Prof. Hall for a personal commjmication describing his apparatus in detail. 8 Eng. Record, 64 (1911), 630. I Ibid., 56 (1907), 735; Sci. American, 96 (1907), 129; 97 (1907), 470; 110 (1914), 176; Sci. American, Suppl., 60 (1905), 24688; 68 (1907), 26018; 78 (1914), 364; 82 (1916), 188; Eng. Mag., S O (1906), 433. 8 G. W. Walker, “Modern Seismology,” 1913; H . F. Reid, Report California Earthquake Commission, published by Carnegie Inst., Warhington, 1910; C. F. Marvin, “Universal Seismograph,” Monthly Weather Rw~~w November , 1907; D. Grunmach, “Experimental Untersuchung zur Messung von Erderschutterungen,” Leonard Simion, Berlin, 1918.
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(d/ FIG.3 working in slots. Simultaneous records of vertical vibration, horizontal vibration in one direction, and time were made on smoked, glazed paper carried b y , a kymograph.
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f K L All of thc rneasurcments were made on the sixth floor of a modern steel and concrete building in which the vibrations were due t o the operation of heavy machinery on t h e first floor and were very distinctly felt throughout the building. T h e instrument was set u p on a soapstone slab which weighed approximately zoo lbs., and records were made with this slab supported by the device t o be tested, At frequent intervals records were made with the slab resting directly on t h e desk, thus furnishing a reference curve a n d enabling us, when comparing curves, t o take into account variations in t h e vibration of the building at different periods of the day. Vibration records were obtained with apparatus supported by t h e following devices: I-Air bags inflated to various pressures. These bags when uninflated were about 2 6 in. long and 5 in. wide. Inflated to 10 Ibs. pressurc they were nearly circular in cross section, while at 1.5 Ibs. they were almost flat. 11-Rubber halls fillcd with air at 40 Ibs. pressure. Sxte-1 diameter oi balls. 2 in. Thickness of wall seven-thirty-seconds inch. These balls were arranged in various ways as follows: (e) Held between strips of wood. as in Fig. 3n. ( b ) Separated by a frame, as in Fig. 36. (6) Piled in a section of a pipe supported hy a flange, as in Fig. 3c. (d) Piled in the form of B tetrahedron, the tliree base balls being held in place by a triangular wooden frante. See Fig. fd. Four of thcse were used under each slab.
11I--Slabs of sponge rubber built up to B thickness of 4 in. IV-Slabs of cork about 3 in. thick. V-Layers or felt built up to a ihickness oi 3 in. DESCRWTION O F CURVES
Cuivrs A were selcctcd as typical lrom among B great numl x r made directly on the laboratory desk. Thc frequencies avcragc from cight to ten w r second, and there arc also preseni, impressed upon these high frequency displacements, much more regular vibrations of w r y long period (in some eases as long an 5 sec.) which presumably correspond to the movement of the building as a whole. Curvcs B were madc with thc device which we consider best for absorbing vibration. Note the marked decrease in frequcncy and the improvement of the curve in respect to smcothness and regularity. These curves w e ~ emade with the tetrahedral airangemcnt of balls as shown in Fig. 3d. It is, of coursc. not possible to absorb the long period vibrations correspondins to the movement of the building as a whole, so that these appear as before. Curves C, D, 13, and F were made with air bags inflated to 1.5, 2.5. 5 . and 1 0 Ibs. pressure, respectively. Tlicsc curvesshow the best results with 2 . 5 and 5 Ihc. inflations. In the case of the I O Ibs. inflation the resiliency is so high that thc amplitude of the vibrations is actually increased. Curve G was made with the balls arranged as in Fig. 26. This is a very eficctive arrangement, and as the balls Aatten considerably under the weight it is quite stable. Curve H was msde with the balls held as in Fig. 3". The c u x ~ c sshow that this arrangement is relatively inrffrctive. I t
is very stable.
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T E E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Curve I was made with the balk arranged as in Fig, jt, and shows that this system is of no value. Curve J was made with the same arrangement as in B, but to increase the stability balls held in wooden frames were brought to hear against the edges of the slab. As is to be expected, the curves obtained -der these conditions showed considerable increase in horizontal vibration. Curves K and L were made with the slab placed directly on the desk when no machines were rutlning and there was no perceptible vibration in the laboratory. The disturbances at the beginning and end of the curve were produced by the operator pounding on the desk. CUNW M and N are of interest because a switch engine passed along the tracks near the building while they were being made. Curve M was made with bags inflated to 5 Ibs. pressure, while Curve N was made with arrangement of rubber balls, Fig. 3a. It d l 1 he observed that the air bags have increased the periods from a little over I sec. to about 5 sec. Only qualitative comparisons, consisting- oi observations on the degree of agitation of a mercury surface, were made on sponge rubbcr, felt, and cork, but it is certain that these materials are much inferior to air bags or rubber balls as vibration absorbers.
Vol. 13, No. 3
SUSPENSION DEVICE
It will be noticed t h a t our attempts t o develop devices for eliminating vibration have been directed solely toward supporting systems. This was done because of the manifest advantage of supports over suspensions, such as greater mechanical stability, portability, a n d absence of wires or springs in the working space above t h e table. For purposes of comparison, however, since suspensions have long been employed t o eliminate vibrations,' some measurements were made on a spring suspension. This consisted of a heavy rectangular wooden frame supported from each of t h e four corners b y two helical springs, which were one inch in diameter and 6 f t . long when loaded. The diameter of wire was three-thirty-seconds inch. The vibration recorder was placed on the frame, t h e recording needles were adjusted, and t h e apparatus left untouched for a period of one hour. The drum of t h e 1
267;
W. H. Julius. Wicd. Ann.. SS (1895). 151: 2.InsLmmcnlrnk., 18 (1896).
W. P. While, Phys. Re%.,19 (1904).
323.
Mar., 1921
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
kymograph was started by means of a n electromagnetic device, so t h a t the only contact of t h e suspension with t h e building (other t h a n its overhead supports) was through a spiral of fine copper wire. The curves obtained are shown in 0 a n d P. A comparison of these curves with t h e others shows t h a t a spring suspension is markedly superior t o a n y of t h e supporting devices developed. Considerable vertical vibration is still present, however, a n d a photomicrographic apparatus mounted on this suspension did not give uniformly satisfactory results, even a t low magnifications. T h e results obtained with a combination of t h e supporting device (Fig. 3 4 a n d t h e suspension, i. e., tetrahedra placed under t h e vibration instrument on the frarnework of t h e suspension, are shown in Curve Q. This curve shows considerable improvement, a n d the arrangement is very little mqre unstable a n d awkward t h a n t h e suspension alone. I n conclusion, we wish t o point o u t t h a t every laboratory vibration problem must be solved independently, because freedom from vibration a n d great stability are not reconcilable. T h e determining factor is, of course, t h e degree of freedom from vibration t h a t is required, a n d this being once fixed determines the amount of stability possible. T h a t is, a mounting of great stability can be constructed which would be entirely satisfactory for a quantitative balance, b u t for high-power microscopic work greater freedom from vibration is required a n d hence less stability can be obtained. For very sensitive instruments such as galvanometers, where t h e greatest freedom from vibration is required, lack of stability must be accepted as a necessary evil. T h e devices which have been found effective in absorbing vibration may be arranged in t h e order of their merit as follows: I S p r i n g suspension n-Tetrahedron arrangement of rubber balls 3-Balls separated and held by a wooden frame 4-Air bags inflated at from z to 5 Ibs. pressure T h e second of these has been used in this laboratory with complete success as a support for a Leeds a n d Northrup reflecting galvanometer, t y p e 2420, quantitative balances, a n d high-power microscopes. SUMMARY
A simple apparatus for making comparative measurements of vibration has been constructed. T h e results of measurements of t h e vibration absorbing capacities of various devices are presented. Certain arrangements of rubber balls have been found very effective. The Federal Trade Commission has cited the United States Refining Company of Cleveland, Ohio, in complaint of unfair competition in the manufacture and sale of paints and other products. The complaint alleges false and deceptive advertising. At a recent meeting of the Gypsum Industries Association, six to eight fellowships were provided for, each with a stipend of $1000 to $1500 a year, to be located a t various agricultural colleges in the eastern United States, for the purpose of investigating the use of gypsum in crop production and for making a fundamental study of the relation of sulfur to crop nutrition and growth.
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WATER SOFTENING FOR THE MANUFACTURE OF RAW WATER ICE1 By A. S. Behrman INTERNATIONAL FILTER Co., CRICAGO, ILLINOIS
The manufacture of ice from distilled water is rapidly being replaced by t h e production of ice from raw water -or, more strictly speaking, from undistilled water. The two agencies principally responsible for this development are cheap, dependable power and applied chemistry, in t h e form of water softening. The requisite characteristics of first-quality ice are clearness, firmness, and freedom from discoloration. These qualities are possessed by ice made from pure water, free from dissolved solids and gases, such as t h e reboiled distilled water which has, until comparatively recently, been almost exclusively used i n t h e artificial ice industry. Ice frozen from impure water is opaque, discolored, or brittle, depending on t h e nature of t h e impurities. Freezing water is, in many respects, much like boiling and evaporating i t , in t h a t by far the greatest part of t h e substances dissolved in t h e water freeze out in t h e ice made from i t . T h e most effective purification of raw water for ice making is, therefope, t h a t which reduces t h e objectionable impurities i n t h e water t o a minimum. It is now generally recognized t h a t this most effective purification is accomplished by lime-soda softening, followed b y sand filtration. M E T H O D O F M A N U F A C T U R E O F R A W W A T E R ICE
I n t h e process of manufacturing ice from raw water, cans of t h e water are surrounded by a sodium or calcium chloride brine having a temperature usually 1 2 ” t o 18” F. Air, under either high pressure (15 t o 25 lbs.) or low pressure (3 t o 5 lbs.), is bubbled through t h e water as i t freezes, t h e high-pressure air being in general more effective. The first ice formed around t h e sides of a can is usually relatively pure. T h e dissolved solid a n d gaseous impurities i n t h e water are frozen o u t a n d begin t o deposit on t h e face of t h e ice; b u t t h e currents of water set up by air agitation wash these impurities off t h e surface of t h e ice and carry them towards t h e center of t h e can. T h e impurities in t h e raw water t h u s become concentrated i n t h e unfrozen water in t h e middle of t h e can. If these impurities are insoluble, their accumulation in this unfrozen water usually becomes so heavy t h a t eventually t h e currents of water set u p by t h e air agitation are not powerful enough t o keep t h e particles i n suspension. As a result, these white or colored particles begin t o deposit i n t h e ice before t h e cake is frozen solid, or, if t h e impurities are soluble, such as sodium salts, their concentration may become so great t h a t freezing is materially retarded. I n either case this concentrated impure water, or “core water,” as i t is termed, is generally removed, usually with a suction pump, a n d replaced with fresh water. The solids a n d gases left in t h e core water, or introduced in t h e fresh water replacing it; appear as white 1 Presented before the Division of Water, Sewage, and Sanitation ah the 60th Meeting of the American Chemical Society, Chicago, Ill., September 6 to 10, 1920.
