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I-VDUSTRIAL A N D ENGINEERING CHEMISTRY
7-A number of organic compounds have been found to act as inhibitors of the oxidation; others have been found to act as positive catalysts or not to affect the process at all. I n the case of negative catalysis, the oil apparently remains unchanged during a period of incubation. After this period, the oxidation proceeds as for the pure oil. 8-On the basis of the above conclusions a scheme for the mechanism of the oxidation of mineral oils is proposed. g-The stage of the oxidation which is affected by nggative
Vol. 19, KO.2
catalysts is shown to be the initial oxidation of hydrocarbons to alcohol. Acknowledgment
Thanks are due the Standard Oil Company of h’ew Jersey for permission to publish these results. Acknowledgment is made of the assistance rendered by G- Calingaert and J. Teppema in obtaining some of the experimental results.
Some Methods of Studying Cord Tire Fabric‘ By F. W. Stavely and N. A. Shepard FIRESTONE TIRE& RUBBERC O . , AKRON,OHIO
Hysteresis loss and flexing life are used as a measure Cord break in pounds and N THE early development elongation a t break are not of fatigue in tire cords. Hysteresis loss shows that the of pneumatic tires, the necessarily sufficient for the original properties of the cord are not maintained. The principal fabric used in proper evaluation of a fabric. flexing test subjects the cord to repeated stresses and in tire construction was squareGurney and Davis4 have emthe event of cord fabric failure in tire service is of value w o v e n . It was not until phasized t h a t “cord elasticity, as a means of determining the desirability of changes in or ability to return after stressabout 1915-16 that the ading t o its original dimensions, is cord construction and of developing methods of imvantage of the present type not necessarily involved in tenproving the flexing life of a given type of cord. of cord fabric construction sile strength and elongation a t Improvement in flexing life of a given cord may be was definitely e s t a b l i s h e d. rupture.” All of the above inbrought about by impregnation with rubber cements The cord tire fabric differs vestigators also called attention containing compounding and vulcanizing ingredients. to the fact that failure of a cord from the square-woven fabric For uniform impregnation with maximum penetration, or fabric in tire service follows in that the cross threads (filler from the cumulative effect of the solvent or liquid carrying the rubber should readily threads or weft) have been f r e q u e n t 1y applied stresses. wet the cotton cord. When well impregnated each of n e a r l y e l i m i n a t e d . The Gurney and Davis place some the strands constituting a cord is completely covered warp threads or cords in cord emphasis on the effect of permawith rubber, as can be demonstrated by subjecting fabric are so spaced that there nent set in a cord, for they call single strands to the action of sulfuric acid. “Road attention to the fact that the are from 202 to 26 ends per greater the ratio of percentage tests” indicate that in the event of fabric failure inch while there are only 2 to elongation to percentage set a t the mileage of certain tires can be increased by increas6 weft or filler threads per a given load, the better the reing the flexing life of the fabric. inch. The cord itself may covery for a given elongation. consist of as manv as fifteen Hysteresis as a Fatigue Test strands, twisted into a single unit, while the filler thread consists of a single strand. This makes a very loosely conIt should be pointed out, in any study of cord elongation structed fabric, consisting of cords that are held together and permanent set, that the relationship of elongation (stretch by the small and sparsely distributed filler (weft) threads. and elasticity) to permanent set (lost stretch) during the The introduction of the cord fabric eliminated the chafing first cycle in which a cord is subjected to a given load or series and sawing action of the ply yarns which cross each other of loads is quite different from that of the subsequent cycles. in square-woven fabric and also made it possible to insulate While this is true with many materials it is very pronounced the cords completely from each other with rubber. This in cotton cords since these consist of a Iarge number of cotton change was fundamental in improving the quality of the tire fibers twisted together, I n Figure 1 are found the hysteresis carcass and made it possible to double and even triple the loops of the first and second cycles during which the same life of the pneumatic tire. cord5 was subjected to a series of loads. A maximum load of Methods of studying cord tire fabric have received little 4.99 kg. (11 pounds) was used, since in some cases greater attention in technical publications, regardless of the im- loads caused the cord to break before two cycles were comportance of this material in tire construction. pleted. The change in elongation with each increment in Considerable credit is due to King and Truesdalea and also load was measured by means of a steel rule. The weights to Gurney and Davis4 for their recent attempts t o focus attention were applied by hand and remained on the cord for 2 minutes on the testing and construction of cord tire fabrics. The former before the elongation was measured. Zero elongation of have pointed out the striking difference in the stress-strain dia- the cord was taken at a load of 20 grams. The cord was grams of cotton yarn and mild steel. They have also emphasized the probability of a relationship between the permanent set and prevented from untwisting by means of a rubber band, one end of which was attached to the load and the other end to fatigue of a cotton cord. the upright of the stand supporting the cord. The curve 1 Presented before t h e Division of Rubber Chemistry a t t h e 72nd representing the second cycle was obtained by correcting for Meeting of t h e American Chemical Society, Philadelphia, Pa., September the permanent set (lost stretch) of the cord after the first 5 t o 11, 1926. cycle. Although the original length of the cord under con2 T h e number of cords per inch in cord fabric should not be confused sideration was 25 cm. (at a load of 20 grams), after the first with t h e yarn size. A 23/5/3 or 13/3,”3 cord fabric, in which the yarn size is 23 or 13, respectively, may for example contain 20 t o 26 ends per cycle had been completed and the cord was again subjected inch. to the initial load of 20 grams, it was found that the length
I
Textile Recorder, 41, 88 (April), 86, 99 (June), 103 (July) (1923). +India Rubber J., 70, 267 (1928).
5
Carded Egyptian (23/8/3); ply twist, 17, cord twist,
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INDUSTRIAL AND ENGIATEERING CHEMISTRY
February, 1927
had increased to 27.1 em. At the beginning of the second cycle the length under consideration was corrected to 25 cm. and a t the end of the second cycle this length W:M found to hare increased to approximately 25.3 cm. Thus, although the permanent set a t the end of the first cycle was 2.1 cm., a t the end of the second cycle the set was only 0.3 cm. Correcting for the permanent set in the preceding cycle, which seems logical since the permanent set of the fabric in a tire has been shown by actual measurement to result in an increase
297
2.38 kge6to a raw cord for 40 minutes has had a much more marked effect when compared with no load than has the fourth application of the load when compared with the first. It is thus seen that the initial elongation of a raw cord is not an index of its behavior in tire service. The flexing of a tire subjects a group of cords to repeated and variable stresses. The behavior of an individual cord isolated from a tire and subjected to a flexing action may be quite different from its behavior when surrounded by rubber and other cords. Kevertheless a study of single cords offers a method of obtaining information regarding some of the factors that influence the flexing life. King and Truesdale and also Gurney and Davis have recognized the importance of frequently applied stresses in studying fabric fatigue. The former have suggested methods for studying the flexing life of both individual cords and the tire carcass. I n their study of individual cords they found that both the degree of bending' under a given load and the magnitude of the load have a considerable effect on the flex testing of cords. The flexing test, described below, subjects the cord to a much more severe action than is received in tire service. This is largely due to the fact that the angle of flexing is more acute, the flexing action is more highly localized, and the cord is probably carrying a heavier load than in tire service. The Flexing of Cords as a Fatigue Test
FLEXING MAcHINE-The two types of flexing machines discussed in this paper were a modification of that used by King and Truesdale, in that the cords were flexed a t a more LOAD
IN m L o C v . M e
Curves of Carded Egyptian (Raw) Cord
Figure I-Hysteresis
in the size of the tire, i t appears that the permanent set decreases and the relative elasticity increases during the second cycle (Figure 1). The difference in the areas of the hysteresis loops indicates that the efficiency of the cord has also increased in the second cycle. The marked loss in the elongation of the cord during the second cycle, as compared with the fist, is probably due to the fact that most of the slippage and tightening of the fibers occurs during the first cycle. A somewhat similar change occurs in the cord during the processing of the fabric and the expansion and curing of the tire.
I
Figure 3-Behavior
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APPLICATION
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OF L O A D
Figure 2-Elongation of Raw Carded Egyptian Cord w h e n Repeatedly Subjected t o t h e S a m e Load
The contrast between the behavior of a cord during the first cycle and subsequent cycles is again emphasized in Figure 2, which shows that the first application of a load of
I
of Cord on Flexing Machine
acute angle. They also had the very distinct advantage that cords of short length could be used, thus making i t possible to test cords from tires. I n one type, the cords were subjected to variable stresses, while in the second machine the load was more nearly constant. Only the former will be discussed in detail. Although it was less desirable from a mechanical viewpoint it could be readily constructed at small expense and was satisfactory for preliminary work. The machines consisted of a revolving shaft, a t each end of which there n-as counterbalanced a n off-center rotating shaft (Figures 3, 4, and 5). On each end of the rotating shafts were two wooden pulleys (2.5 cm. in diameter), which 8
The choice of this particular weight was simply a matter of avail-
ability. 7 The effect of the degree of bending (over a rounded edge) and t h e magnitude of t h e load has also been studied by t h e Bureau of Standards in studying the "Development of a Standard Bending Test for Rope Yarns," b y Schoffstall a n d Boyden, Bur Standards, Tech. Paper 300. 8 Designed and constructed in collaboration with E. C Zimmerman of this laboratory.
tito ~ f i - ~ ~ irot:itiiig t i ~ r slittit. tiiui cliiiiiniitiiig the possibility CIS S:iilnres Sroin iliock. This seeorid machine mas operated ;it ii iwiist,:int ratr of 55 Aeses per minute atid e.xch ccird was sul),iei,todto it load of 3 kilograms. The angle of flexing was 50'. :\Itlrougli the tmo marhities gave different values, it w i s Smmd t,liat tlie relat.ionship between various types OF rords v a s spprosimately of the same order. The data giver1 i i i t,hir pnper were all obtained on the second maehiiie. WdCtOIS
Influencing the Flexing of Raw Cords
J~I.~IIDITY--I~has long been recognized that liumidity is factor iir the testing of cotton fabrir!s. It Uas tlierrfore riccessary to determine the influerrre of liiiniidity on t,he llcxiiig test. Sinre conditions were sirti that it was not possildc~to wrry out tlie test at 5 constant, relative liumidity. reliitirc humidity whi lie cords were I>eiiig IXYI. Siiice tiic humid rmditioiis 1.oi11d riot 11. it i n s possilde to o 11 oniy froin 7 to 14 ~ i iriipm'tiint i
Type
Figure 4---Ft'lexing Machlrte--Birat
were uot keyed t o the shaft but allowed t o oscillate h o l y . T h i s armrigement made it pussible to test four cords a t tlir: sanic time. The cord K (Figure 3 ) was fastoned at A . (1 oyer the glass roller. R, and under the glass roller. i i i i i i . i n itinmeter). aiid ilien over tile wooilen pulley, D,
located
oil
tlia rotat.iiig shaft: S. Tlie 3-kg. t i romid leather belt wtiich i d w i ~ siirriiiiged so as 11, Tlie mml, Ii. m i 3 Nrwd
Tiiesr results indii:ste that humidity has :iii :ipprecial)li: iiiflueiire oii the flexing test. arid that,. accordingly-,wlirrr it is not pssihle to test at L: constrtnt tiumidit tests must be made at the same time. TEMrEI3ATUsE-~fighi temperature, sucli its Srciiocritly occurs in overloaded tires, tias a marked effect on tho flexing life of oords. IIliile it has riot been possible t o determine the effect of variations in room temperatiirc on the flrxing test, in viev of tlie marked effect a t higher t,ernperntures it is
F i l ~ u r c5 - -Blcxinc Mnchine--Pirat 'l'ypc
:il t l w pvii,t wliere
it left the roller, (', nt the rutc of 10 tlcse-.
p(!r iiiiiiiiti! atid through an angle of 50 degrees. The test mas ~~oiitiiii~eil imtil the cord broke. The average of api)T I i i c r e f o r e since it is jiossiblc, ijunlit;itirelg at h i s t , t u determine whether or not a cord is m i l imliregnated, it is of inierefit to determine the effect OS proper i n pregnation on the Neuing life of tlie cords. The Effect of Impreg-
the solvent, while it is difficult to wet even the surface of nation on Fatigue t i i e cord in water dispersions of ruther. Raw cords f r o m Tlie question naturally arises as to wlietlier tlie rulilier uirded Egyptian fabric travels witli tile solvent in a rubber cement. This may IJC tested sirnultane (1) 12) rmidily demonstrated by a siinple %icB t.est." This test were ously with impregnated FiCure I I-Acid Tesfs on Strands from Impremated Cords (Figure 10) is carried out by placing two small beakers in the 1-Poorly iinprcgmiled. 2-\Vel! impregn glass jiir fitted vith an air-tight ground-glass lid. A niiilrer cards taken nvicd cement, made Tvith Benzene, same roll of fabric and cured iii a tire. The raw cords flexed 8'310 tirncs (average) tiefore Siiilnre, :ind the impregnated cords taken Emrn t.he cured tire Ilexcd 15,910 tirnes (average). This nmounts to an incrcasc of approximately 78 per eeiit. The results indicate that the proper imprepriation of cord Sabrie by incinis of a rubber cement makes it possible to increase appreciably the flexing life of the wrds. idly. u I n iiirhing such r eomparirou, thc acid Lest i s csiiied out BO lul!owr: e 7 cc. of coiicentr~tpdII,SO. i n two test tubec c~7crniiy finat 2 CE. W ~ ~ C onI the ruiiace of t h c acid by alloiuini: the water to run slowly down the side of the tuhe. l'lice the sfiands (not cords) to he tested in separate d r y test tubes. Shake the t w o tuhcs coritainiiip the wafer and acid so as to mix. Teke a tube i n each h a d and at the same time pour the mixture of arid and writer into the two tubes c o n t i i i i n r the strands. Shake both tabes eentiy i n the ~ r m hand e for the 5rmt IcnCth of t i m e . Stop ahakins as soon as one stirad breaks UP into fine particles niid note the difference. A slmnd from r well~impreznrfedcord docs not break up Q S quickly as a ~ ~ o o i limixeznated y strand. This feet should elway3 he conducted with strinds which have nut h e m exposed to the air for m y cunsidrrablc lenxth oi t i m e , since the film 01 rubber chrnzes ruRirieiiily i n a day or EO to affect the iriultn appxciably.
February, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
before going into service and tested on the flexing machine flexed 2150 times (average) before failure. With no change other than increasing the flexing life of the cords in this type of tire to 3430 flexes, there resulted an increase in mileage of approximately 50 per cent.
301
Such a result would indicate that the increase in mileage is proportional to the increase in flexing life. That this is not consistently the case has been found in further teats. However, the results are such as to indicate that the flexing test is of distinct value in the study of cord tire fabrics.
Specific Gravity of Paraffin Wax' By F. J. Morris a n d L. R. Adkins T 7 a c u u ~OILCo., ROCHESTER, N. Y.
HE determination of specific gravity of paraffin waxes
T
seems to be a rather neglected subject. The investigator in pure science has not been interested, probably because commercial waxes are mixtures of several, principally paraffin, hydrocarbons, hard to separate. I n the refinery, wax is usually weighed, being sold by weight, and a knowledge of the specific gravity is not essential. Chemical Abstracts for fifteen years back gives no reference to this constant. The coefficient of expansion a t 20" C. of the Smithsonian Tables2 and the statement in Redwood3 that the specific gravity a t 60" F. is about 0.908, and a t 212" F. 0.750 are the only data the writers were able to find. D e t e c t i o n of Air in Paraffin Wax
Commercial paraffin wax contains a variable amount of air.
If a piece of hard u'ax is broken, the craters of disrupted air bells appear on the broken surfaces. Besides these visible bells, there are smaller ones which can be seen only with a glass. The approximate amount of air in the samples examined was not determined, but the fact that i t is air and not hydrocarbon gas was determined by a rather crude method. A 2-liter Pyrex boiling flask was nearly filled with wax and cooled. When the wax was nearly set, the neck of the flask was drawn out to a capillary and the flask rapidly exhausted t o less than 2 mm. pressure. The capillary was sealed off and the flask allowed t o remain a t a temperature of 150" F. (65.6" C). for 15 hours. On breaking the neck under water and analyzing the remaining gas in the flask with an Orsat, it was found to contain 20 per cent oxygen. It was therefore assumed t h a t the gas was actually air.
Specific gravity4
=
w. - ( W + SI1 + 7' "
s 1
where W , = weight of object in air; SI= weight of sinker in S)l = weight of object plus sinker immersed in water; (W water.
+
The usual form of wide-mouth pycnometer, which is commonly used for tarry materials, failed because the wax as it solidifies pulls away from the sides, leaving air spaces. Water added afterwards for the second weighing does not entirely fill these spaces. By using alcohol instead of water and putting it in as soon as the wax begins to set, these voids are filled. But alcohol has a slight solvent action on wax and some wax was lost thereby. A modified Nicholson hydrometer, after a few trials, solved the problem. The ordinary Nicholson consists of a float carrying a pan on a slender stem above water and another pan hung from a hook below water. Specific gravity is determined by balancing the sample in air and in water with the addition of weights and calculating the results from the difference in weights used. As the usual metal Nicholson has some edges which hold air bells, and as waxes begin to soften and separate drops of low melting point constituents much below their official melting point, a special glass hydrometer was designed. The pan in the liquid is made of two small 0.920
0.900
The occluded air is apparently not held in solution when a 0.880 wax is melted a t atmospheric- pressure. Samples held in ,X vacuum for several hours at 130" F. (54.4"C.) and the specific 'z gravity taken quickly in air gave the same figures as a similar $o.860 sample melted in air and the specific gravity taken in air a t $ that temperature. Until i t was realized that air was always go,84o present in variable amount in solid wax, attempts to determine specific gravity by any method were disappointing. Results on different portions of the same samples did not check. The 0.820 method or some little detail in the manipulation were always blamed. 0.800
Procedure
The ordinary method of determining specific gravity of solid water-insoluble substances by weighing in and out of water a t 60" F. (15.56" C.)-in this case, of course, with a weight tied to the'wa,x when weighed in air-even with an airfree sample, is hard t o manage. 1 Received August :31, 1926. Presented before t h e Division of Petroleum Chemistry a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 2 Smithsonian Physical Tables, p. 219 (1921). 8 "A Treatise on Petroleum," p. 256.
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60° F.
80' F. 26.7' C.
15,50c.
Figure 1-Specific
I looo F.
1 12O0F. 48.90 c.
\
1 -OF.
37 8 O C. 04 4 o c . Temperature Gravity of Waxes a t 60' t o 130° F.
crystallizing dishes set up something like a The inner one, inverted, has two V notches in the edge to allow a free flow of water in and out. h'o melted wax can get out as i t floats to the top of this inner dish, Calculated from formula in Ferry "Physics Measurements," p. 47
(1918).
