6i4
aiid alloys ~ L Scontain :ilurninum, niagriesium, climruiuin, uiangancse, otc. Since a geiicral account of these applicatiuns I m s already lieerr r,ublislicd,'e only a brief siminiar.v will be given here.
,xieli inetds
\'"I.
I!):
so.6
double a seeoiid tiiiie at right xngii:~ti, t h first iold. Tho piece cut f r o m the ~ i i r i i c rof t,his doiiblc fold. Tlie metal sliows iio aigiis of cra,ckiiig.
it was subsequently suhiccied.
rirlrocr of Rubber and Sirnc Relitions between Ahrsisiari and Treadrerr" beforc the Division of Riibbfr Chemistry et tile 73rd Mcciiw of the American Chemical Soriety, Richmond. Vn., Ami1 I1 Lo 16, 1927. *Industrial lie!low, Melion Institute 01 ~ n d u s i r i dResearch, Univwsiiiy of I'ittsbuixh. Pittsburgh, Pa. The data presented l o t h i s paper were LCcured during the course of an extended investigation o! accelerators and d vulcaniratiao, which WaJ sustain~d by Gri.rrel,i Company of Cleveland, Ohio, during the Deriod 1923-1SP7.
apparently on the assurriptinn t h t t,he only remaining valiable is the rubber itself. The meclranieal differences in tlic abrmion machines arise largdg from the different methods errlployed to produce hetween the rubber and abrasive, and from this standpoint the various machines may be divided roughly into three classes:
I -.A Bat rubber suriace is iriovcd against a llat abrasivc suriacc The area o i thc rubber exposed to the abrasive
wbirc L?’ = r #I m uf tlii hiiairrytiig tire alxaiiie I< = dntance crprcused i n iect irom tlx AX,? of rotatmi is iisiiallv mairitained constant in all tests and is urcssctl aminst t o tile weight tending to prevcnt rotation tlw alirasive by 8 standard pressure. Thc test is tisimlly cow II = ne& 111 pounds apl>llcdt o prevcnt lotatloll ducted far a standard time a t a lined speed. 2 -.The mlher, either a picpared disk or blocks attactid to tlie I t 1%oli\iou3 that tliiee calculations ~ 1 1 be 1 ueceqsnry. First, pcritihery of a whcel, is rotated against a rotatin8 abrasive surthe work represented by the weight of the lever, C, axill face, the two axes o i rotation being neither perpendicular nor the kernier balance, D, attached hut hanging free ‘J’lie ~ ~ ~ r dThe l damount of sliding action bctween the rubhcr and almasiw is dete ajiplied to create the inotioii. The product of this motion and forct, represents the nmount of work which is actudly ihme on the surface of the rubber. The uniform eoiiriition-: of surfricc coiltact,, loiid, and amount of slip which are geiicrally i n posed on the test sample do iiot assure the expenditure of a riiiiform amount of work, which under these iiniform e m ilitions is a direct function of tlic rcsistniice to motion which the rubber exerts. This fact,or, which has formerly beeii neglected, may differ as niiirh as 100 per cent between two samples of nibbcr. Siiica the surface of the riihber o i i i i he rcinored only by the app1ic:itiou of work, tlie I ~ I C ~ . ~ I I ~ of volume loss on abrmim is incomplete wittrout a siiiiiilt,arieons ineiisiircrnent 01‘ the total work exrienderl on thi, riibIwr.
15 the nnglit applied at the end of the h e r and R IS tlie didniice froin the axis of re\olution to the poiiit of ajrglicatKJil Of the Ui’ight 2 i table Or CUrVe Call be c:qJm. Tlic nlxasive surface i* ~:leancdLy ineinis of :iir jrts which are iiot showii. I h s h e s :ire iiot cfficicnt. ‘J’Iiis machine iiieasnres the volume loss in tlie nsual inaiiiirr wliich, together with the simultaneous i n uf work, perriiik the calcolation OS vohnnc loss iicr iiiiit of work done.
Pspidctl.
r .
Calculation
?‘lie calculation of the volume loss on a work basis is simple and after tlie first calibration of the iriacliiiie can largely he t,akeri from curves or tables. The calculations nccessary for the calibration employ . . the ordinary I’rony brake fomiula, H. p.
3*l\iKW
= I
3:3,000
Apparnfus for Measurine Abrhrion Kess~fanCeof Rubber
by t l w boliince TIic late of work iliiririg any teit will then he tlic win of tlic>e tlirre fsctora Volriine loss per horse-
poa ex-hour can be fouiid by nienni of the formula V =
L X 60 -2 h p X T
aliere L i s the ~oliiirieh>hsduniig the test and 2’ is the durntien of the tevt in mmuteb The type of abra.ire ernployed 111 the t e A virll influence tlic filial results and, of courre, must be c o i i i t a i i t rliiriiig any ~onipar~son.Fnir abrasive will reinow fine psrticlea from tlie wrface of the rubber3 w l i l l e coarbe abrau\e w i l l remove :hi. rubkiei as hiigc pwticlPs. It ii improbable that the work rcqiimd to r n i i o \ e a given volriine of rubber a b fine ~iartielea woiild be the same a‘ that rcqinled to remove an rqual volnme ah 1.irgr particles In ordei to ,emre uniform lriiilt\, frc,li IJtZpeF .h(JIlhl h USCd for PaCh tcrt Experimental
In ordcr to ilhistrate the actirin of tlie aiirnsion machine, live tread-type compounds have hcen prepared. The compowids tested arc shown iii Tnblc I. Compounds 1 and %5 were inillcd first. Compounds 2, 3, arid 1were tlieii prepared by mixing together the proper proportions of cornpounds 1 and 5 . The physical properties of these stocks arc listed in Tshle I1 and t.lie abrasion data are shown in Table 111. Tho abrasion test was made with an 8-pound (3.6-kg.) weight holding tho test blocks against the abrasive.
I S D C S T R I A L 350 E N G I S E E R I S G CHESIISTRY
676
Table I-Compounds
No. 1 Smokedslieet Tire reclaim Zinc oxide Carbon black Stearic acid Pine tar Sulfur Accelerator
100.0 0.0 10.0 39.0 0.0 0.0 3.1 1.00
Tested
?io.2
h-0. 3
75.0 25.0 9.75 31.65 0.37 0.50 2.87 1.00
50.0 50 6.0 24.5 0.75 1.0 2.65 1.00
9
KO. 4
h-0. 5
25.0 75.0 4.75 17.25 1.13 1.5 2.43 100
0.0 100.0 3.0 10.0 1.5 2.0 2.2 1 0
continued for another l h i i n u t e period. Cooling the test qample increased the load TO of the 185 grams necessary to produce the original value of 635 grams. Loss in the abrasive action of the paper used in the test also has some effect in reducing the power consumption.
-
Table IV-Spring So 1
Table 11-Physical COXP o m n
1
2
3 4 5
CURE AT
140' C.
Jlinulrs 55 45 35 30
25
L O A D AT ELolVGATIoN
400 PPR CENT
Pounds 2225 2260 2215 1845
...
Tests
TENSILE AT BREAK
k'a / s a .
cm. 156.4 159.0 155.6 130.0
Pouiids 4590 4060 3030 2040 1080
"ON A T
"NgDc.-
WITH ROMBTER
Kg./w. cm. Per cenz 323.0 285.2 212.7 144.0 82.8
587 COO a00
412 250
65 70 72 75 76
Vol. 19, KO.6
Balance a n d T e m p e r a t u r e Readings d u r i n g Abrasion
c.
M i n . Grams 0 650 22 705 2 6 . 3 3 5 710 2 6 . 9 10 625 2 7 . 2 i5 500 28 20 425 2 8 . 6
Ilo 3
1
\-c,
c.
Gvams 625 590 565 485 315 220
Grams
22 26.3 26.6 27.7 28.2 28.8
645 605 515 380 315 270
C. 22 26.3 27.4 27.7 27.9 28.5
so 4
Grams 630 555 510 3i5 305 260
so 5
c.
c.
Grams
22 24.8 25.5 26.3 27 0 2i.8
620 550 430 285 205
22 25.2 26.2 27., 28.8
T a b l e V-Effect of T e m p e r a t u r e on Power C o n s u m e d Minutestest wasrun 0 5 10 15 15 20 25 30 Grams indicated on balance 635 620 530 450 520 430 370 340 Temperature,'C. 25 0 2 8 . 1 2 8 . 2 28 7 25 0 28 4 2 9 . 4 3 0 . 0
The rate at which work is done on the test samples is seen in Table I11 to fall gradually from 0.0206 horsepower The abrasion machine may be operated in still another (15.4 watts) for compound 1 to 0.0136 horsepower (10.1 manner. Instead of subjecting the abrasion blocks to a watts) for compound 5. This means that in equal periods uniform load and measuring the rate of work, it is possible of time only 66 per cent as much energy is expended on sample by varying the load during the test to do work at any pre5 as on sample 1. If only rolume loss in equal periods of determined rate on the rubber. The series of five tread time is considered, compound 5 is shown to have 36 per cent stocks were tegted in this manner. The weight, TV, and the as much resistance to abrasion as compound 1. When re- balance, D , were adjusted to produce a rate of work of 0.0180 duced to volume loss on the basis of equal.energy expended, horsepower (13.4 watts). As the energy consumed tended the resistance of compound- 5 is only 23 per cent that of to decrease, shot was poured into the hollow weight, E , compound 1. These compounds by no means illustrate the until the rate of 0.0180 horsepower was maintained. The extreme variations which may be met in rate of work. Com- data are given in Table VI. I n this case the relative value pounds have been tested which vary in r&e of work from of the stocks will be the same whether considered on a volume0.0083 t o 0.0221 horsepower (6.2 to 16.4 watts). loss basis or on volume-loss per horsepower hour, since work Table 111-Abrasion SAMp m
LOSS I Y \vEIGHT
sp GR
Grams 1
2 3 4 5
2.413 2.788 3.439 4.956 6.006
1.100 1,153 1.207 1.259 1.315
vOLUME
Loss CC. 2.193 2.420 2.850 3.941 6.09
T e s t s u n d e r Equal Loading
TIME W E I G H T . TESTED APPLIED B;gyy SPRINC
MLn. 20 20 20 20 15
Gvams
Crams
580 580 462 382 363
600 445 425 405 380
The rate at which work is done during a single test decreases slowly as the test progresses. Adjustment for this change is made by changing the tension in the spring balance, and readings must be taken a t intervals which will permit an average value to be obtained. If the points form an irregular curve when plotted against time, the average is best obtained by means of a planimeter. If the curve is regular, a sufficiently accurate average can generally be obtained by inspection. The reason for the decrease in rate of work is not entirely clear, but may be due to a number of factors. It can be said, in general, that the load on the spring balance decreases farther and more rapidly for low-grade compounds than for compounds of high quality. That the decrease is not due entirely to changes in temperature is shown by Table IV, which records the temperature while the data in Table I11 were being obtained and which shows no parallel between load decrease and temperature increase. While the greatest temperature change takes place in the first 3 minutes, the load continues to change regularly. That temperature has only a small influence is also shown in Table V. The sample was tested for 15 minutes, after which the machine was stopped and the load removed from the test blocks until the temperature had returned to normal. The test was then
POWER
TValls l5,4 13.9 12.0 10.7 10.1
H . a. 0,0206 0 . Ol8i 0.0161 0.0143 0.0136
VALUE
VALUEWITH SAMPLE 1 AS
LOSS
C c . / k . D. hour C c . / k w . hour 3i9 914 388 454 53 1 690 826 1074 1380 li94
06
VOLUME
STANDARD ON
LOSS P E R
WORKBASIS
HOUR 1.0 0.91 0.77 0.56 0 36
1.0 0.82 0.60 0.39 0.23
was done a t the same rate on all samples. The results are in good agreement with the figures given in Table 111. T a b l e VI-Abrasion
T e s t s a t a n Equal R a t e of Work
VOLUME
sAMPLE TIME 20-1fINUTE Loss ON TESTED
VALUE WITH
SAMPLE 1
LOSS
ASSTANDARD
BASIS 1
2 3 4 5
Mznuies 20 20 20 15 10
Cc 1 88 2 46 3 45 5.06 8 90
C c . / k . p . hour 312 410 573 842 1480
C c . / k w . hour 420 550 718 1128 1990
1.0 0.77 0.55 0.37 0.21
Other Factors Affecting Treadwear
The question of treadwear involves much more than the abrasion resistance of the tread stock. A tread can be worn away only by doing work on the surface. The work required to drive a car forxard a t a definite speed and for a definite distance against the normal rolling resistance could be determined, and this amount of work must be done on the rear tires, irrespective of the stock of which the treads are composed. Work is done on both front and rear tires due to rolling friction. This is caused by the difference in circumference of the tire a t the center of the tread and a t the tread
June. 1927
I S D C S T R I A L A Y D E S G I S E E R I S G CHEMISTRY
shoulder which necessitate? slip, and by the change in area of the inflated tire when it deflects t o carry the load. The amount of work will depend on tread design with its effect on the amount of slip, on the coefficient of friction between the rubber and road surface, on the stress-strain relationship, and on the mechanical efficiency of the rubber. I t is obvious that if the coefficient of friction could be reduced to zero slipping would take place but no work would be done. If the coefficient of friction could be made infinitely great, no slipping would occur and no work woulrl tie done on the surface, but the stress due to the strain resulting in the rubber would be stored in the rubber in a reversible manner. Under normal conditioni both slip and strain in the rubber result. -4ny point on the tread of a tire a t the time of coming into contact with the road will slip unl il the pressure against the road increases t o a definite value, which depends upon the existing coefficient of friction and the stress-strain
677
relationship of the rubber, after which energy is stored in the rubber due to the strain imposed. .Is the rolling motion of the tire proceeds until the point of the tread is about to leave the road, any energy stored in the> rubber due to strain will be available to cause slip and do work on the surface of the rubber. Many of these factorb are extremely variable under road conditions and tend to be minimized by dusty or wet roads which reduce the friction. TT'hile the work done on the rear tires due to driving force and on the front tires due to steering thrust must be constant for any tread stock, the work due t o rolling, camber, and toe-in will vary with the road conditions and tread compound. While the present development of the abrasion machine makes possible a comparison of the abrasion resistance of any compound, it should not be expected to replace actual road tests in the selection of a tire tread,
Evaporation of Sulfite Waste Liquor' By W. L. Badger CHE\IICIL
EKCJSEERIV?D E P A R T M E NUNIVERSITY T, OF
XfICHIGAK, . h N
ARBOR,~ I I C H .
OJ disposal of waste sugte liquors by considering the design of suitable ecapnl-ating equipment. Apparatus f o r large experiments are described and the data obtaintdfrom their operation are discussed.
T/ii.i paper deal.r aith the problem
HE problem of the dispo.al of oulfite waste liquors, though not especially acute a t present, promises t o be more serious in the near future, owing to the increasing stringency of stream pollution laws. Although the ultimate solution of this problem must involve finding some new uses for the material, it is obvious that, whatever these uses may be, the first step will undoubtedly be an evaporation of the liquor. This will be particularly true in those cases where the only possible disposal of the wastes will be t o burn them. Consequently, since all recovery proceqses are based on a preliminary evaporation, the first step in the general problem will be to design suitable evaporating equipment. The difficulties met in attempts t o evaporate sulfite liquor are threefold: (1) The extreme viscoqity of the solution; ( 2 ) the very serious scale-forming tendencies of the liquor; and ( 3 ) , the corrosive nature of unneutralized liquors. The third item was not considered in this investigation. It is now generally accepted that the velocity with which a liquid will be moved past the heating surface is by far the most important factor in determining the capacity of an evaporator. I n the ordinary el-aporator, whether of the vertical tube or horizontal tube type. this circulation is accomplished by natural convection and by the evolution of steam bubbles. Obviously, as the liquid becomes more riscous, the circulation produced by both of these means rapidly decreases, with the result that it is vwy difficult to concentrate this liquid to high densities without using either excessively large evaporators or very large temperature differences. Since the cost of the disposal of sulfite liquor must be held to very low figures. and since the principal cost of evaporation is the cost of steam, it follows that an evaporator of the largest possible number of effects is desirable. This, however, results in a small temperature drop per effect, which, as has been shown above, makes operation exceed-
T
' Received
March 14 1927 Presented before the Division of Industrial dnd Engineering Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va , April 11 to 16, 1927.
ingly difficult or impossible. This line of reasoning, therefore, leads to the conclusion that a satisfactory evaporator must employ some means of artificial circulation. ~ I E C H A XOF ISM SCALEFORhIATIOS-It is now generally accepted that the cause of scale formation iq the presence in solution of a substance with an inverted solubility curvethat is, one whose solubility decreases with increasing temperature. Calcium sulfate is such a substance, and its presence in sulfite liquors gives them their scale-forming tendencies. Xext the heating surface there is a stagnant film of liquid whose temperature is higher than that of the bulk of the liquid. If a substance with an inverted solubility curx-e is present when the solution is concentrated, the solution will become saturated with respect to this substance in the stagnant film before the bulk of it is saturated. Therefore, the substance with an inverted solubility curve will be precipitated first in the stagnant film and will continue t o deposit in this film, producing a characteristic compact scale. If there is present in the liquid other solid material in a finely divided state, this solid material is very apt to be included in the scale, increasing the rate a t which it forms. Without the presence of a substance whose solubility curve is inverted, no true scale can form. If this explanation is correct, anything which decreases the thickness of this stagnant film or which brings into contact with the stagnant film particles which could act as nuclei, and therefore start the crystallization, should diminish the formation of scale, although it mould seem that such a method could not completely prevent scale but merely decrease its rate of formation. Therefore, both the viscosity of the liquid and its tendency to form scale lead to the same conclusionnamely, that some form of artificial circulation is desirable. Apparatus
One of the evaporators of this laboratory was modified to carry out these ideas. A diagram of the experimental apparatus is shown in Figure 1. The shell of the evaporator was of cast iron, 30 inches I. D. and 12 feet high. It was
