INDUSTRIAL AND ENGINEERING CHEMISTRY
Xovember, 1929
1013
Aging of Mechanical Rubber Goods Stocks b y Various Methods K. J. Soule hf4hH4TrAY
RUBBER MFC C O ,P A S 5 4 l C , hT J
HIS paper records the aging of thirty typical mechanical rubber goods stocks, all of which are, or have been, in regular factory use over long periods of time. The times of aging used are 1 year of natural aging in the dark; 2 1 hours and 48 hours in the oxygen bomb at 60" C. and 300 pounds (21 kg. per sq. em.) pressure; and 96 hours at 70" C. in the Geer oven. These stocks are arranged in three groups: (1) lightly compounded, three stocks; ( 2 ) medium compounded, twenty stocks; and (3) heavily compounded, seven stocks. The phybical properties studied are tensile strength, elongation, tensile product, and modulus. The percentage increase or decrease in each of these properties after each type of aging 15 recorded. (Tables I to 111) Figures 1 to 6, inclusive, shorn graphically the changes in the physical properties studied on each of the three lightly compounded Stocks, using sereral different methods of pre5enting the data. Table IT' shows the coefficient of correlation and the prob: i l h error of this coefficient for oven arid bomb aging on each
of the three types of stock. For the correlation to be a t all marked, the value should be in excess of 0.5, the value * 1.0 representing perfect correlation. As a further check, the value for each coefficient of correlation should be greater than four times its probable error. Figure 7 illustrates graphically the data presented in Table 11'. It will be noted that neither bomb nor oven aging shows satisfactory correlation with natural aging for all types of stocks examined, or for all of the physical properties of any one class of stock. I n fact, as far as the results obtained on the thirty compounds examined are concerned, there is practically no choice between the bomb and the oven as an approximation to natural aging. I .
COMPCUND
A
COMPOUND
B
------
96
OVEN BOW
---.-
HIS.
tl(HR5.
CoMPLD
,-
FINCREASE
Noturol
Figure 4-Elongation of Lightly Compounded Stocks
E 4000 (281.2)
loo
, 75
L 2.5 Nofurof
do
TDECR
Figure 5-Tensile
25
60
N
IW
TINCREASE
Tensile Aped
Product Product of Lightly Compounded Stocks
.----
-----I
loo
%DECREASE
Figure 2
$INCREASE
Figure 6-Modulus
of Lightly Compounded Stocks
Lightly compounded
Medium compounded
Heavily compounded
----.. -----.----. :r EL NGATl N
TENSILE PR DUC
MODULU
0
Figure 3 Tensile Strength of Lightly Compounded Stocks
.50
100
Ccefficient of correlation Figure 7-Coefficients of Correlation
INDUSTRIAL AND ENGINEERING CHEMISTRY
1014 Table I-Aging AGITG
Data for Lightly Compounded Stocks hIODU1,uS TENSILEELONGATION TENSILE PRODUCT
VOl. 21, No. 11
Table I1 (Continued)
TENSILE MODULUS TENSILE ELONGATION PRODUCT Kg./sa. % KR./sq. % 70 % 70 change change cm. change cm. change Yo change change (600%) 650 153 Original 154 256 750 274 625 4 160 5 Natural aging, 1 year 182 4-18 266 4 725 - 3 274 00 600 8 130 -15 Oven, 96 hours, 70' C. 168 9 260 2 706 - 6 262 - 4 630 3 150 2 Bomb, 24 hours, 640 2 159 4 60' C. 162 f 5 244 5 725 - 3 252 8 Bomb, 48 hours, 600 175 60' C. 163 234 -14 6 234 8 700 - 7 600 00 116 -34 512 -15 111 -37 (300%) 537 -10 112 -36 (12) Original 75 99 430 61 562 6 88 -50 Naturalaging, l y e a r 67 -12 70 -29 325 -24 32 -48 Oven,96hours,7O0C. 92 $23 95 4 312 -27 42 -31 725 231 Bomb, 24 hours, 3 234 750 1 60" C. 61 -19 60 -39 287 -33 2.5 -59 720 1 210 9 Bomb, 48 hours, 3 185 -20 745 60' C. . . . . . 52 -48 200 -53 15 -7.5 700 - 3 138 -40 (500%) (13) Original 140 210 605 181 Natural aging, 1 year 119 -15 190 9 643 6 174 - 4 +10 190 -10 562 7 152 -16 Oven, 96 hours, 70° C. 154 Table 11-Aging Data for Medium Compounded Stocks Bomb, 24 hours, TEKSILE b o o c. 112 -20 174 -17 f 3 155 -14 625 AGING MODULUSTENSILE ELOTGATIONPRODUCT Bomb, 48 hours, 70" C. 126 -10 179 -15 600 - 1 153 -15 Kg./sq. % Kg./sn. % % %b cm. change cm. change 70 change chanse (500%) (500g2J (14) Original 87 193 650 179 (1) Original 173 642 158 Natural aging, 1 year 101 + l 5 141 -27 575 -1% 116 -35 Naturalaging, 1 year 102 4 130 -25 562 -12 105 -34 Oven, 96 hours, 70' C. 107 +22 154 -20 600 8 131 -27 Oven,96hours,70°C. 138 +41 138 -20 500 -22 99 -37 Bomb, 24 hours, Bomb, 24 hours, 60" C. 97 +11 142 -26 600 8 121 -32 60' C. 116 +18 136 -21 525 -18 102 -35 Bomb, 48 hours, Bomb, 48 hours, 60' C. 94 03 -48 7 119 -38 550 -15 60' C. . . . . . 96 -45 475 -26 65 -59 (500%) (500%) 190 675 182 (15) Original 87 Original 123 248 657 232 Natural aging, 1year 94 T 6 134 -29 587 -13 112 -38 Xaturalaging, l y e a r 121 - 1 198 -20 620 6 176 -24 141 -26 640 5 129 -28 Oven, 96 hours, 70' C. 77 -14 Oven,96hours,7O0C. 109 -11 184 -26 603 8 158 -32 Bomb, 24 hours, Bomb, 24 hours, 60'C. 80 -10 140 -26 625 7 125 -31 60' C. . . . . . . . . . . . . . . . . . . . . Bomb, 48 hours, Bomb, 48 hours, 60' C. 67 -2.5 124 -35 627 - 7 111 -39 60' C. . . . . . . . . . . . . . . . . . (300%) (3OOc/,) Original 46 79 437 49 (16) Original 63 85 4 00 .50 Naturalaging, 1year 50 ? 58 -26 369 -16 31 -37 Naturalaging, 1year 55 -12 64 -26 350 - 1 2 32 -36 0ven,96hours,7OoC. 57 +20 68 -14 360 -18 35 -29 O v e n , 9 6 h o u r s , 7 0 ° C . 70 +11 7 1 -12 337 -16 37 -26 Bomb, 24 hours, Bomb, 24 hours, 60" C. 40 -11 55 -31 405 - 7 60" C. 65 3 77 -11 350 - 1 2 39 - 2 2 32 -35 Bomb, 48 hours, Bomb, 48 hours, 60' C. 38 -15 60" C. 61 3 67 -23 350 -12 33 -34 44 -44 360 -17 23 -53 (300%) (500%) . Original 51 67 400 38 (17) Original 64 156 690 153 h7aturalaging, l y e a r 49 - 4 53 -21 350 -12 27 -20 Naturalaging, l y e a r 73 + l 5 152 - 3 675 - 2 146 - 5 Oven,96hours,70°C. 67 +30 66 2 300 -25 2s -26 123 -21 650 2 O v e n . 9 6 h o ~ r s . 7 0 ~ C 65 . 6 113 -26 Bomb, 24 hours, Bomb, 24 hours, 60" C. 46 -11 45 -33 300 -25 19 -50 135 -13 675 56 -12 2 130 -15 60' C. Bomb, 48 hours, Bomb, 48 hours, 60' C. . . . . . 36 -47 200 -50 10 -73 85 -46 76 - 5 0 60" C. 51 -20 625 - 9 (30075$) Original 114 400 65 (400%) 34 0.3 530 41 Naturalaging,lyear 95 $23 105 - 7 342 -14 51 -21 (18) Original O v e n , 9 6 h o u r s , 7 0 ° C , 86 +11 100 -12 350 -12 50 -23 Naturalaging,lyear 46 +33 52 5 437 -18 32 - 2 2 O v e n , 9 6 h o u r s , 7 0 ° C . 46 +33 48 -12 425 -20 29 -29 Bomb, 24 hours, Bomb, 24 hours, 60' C. 70 9 84 -26 370 7 44 -32 ~. 60" C. 36 4 50 - 9 490 Y 33 -15 Bomb, 48 hours, Bomb, 48 hours, 60" C. 71 - 8 71 - 38 300 25 30 -54 60' C. 35 2 46 -16 470 -11 31 -24 (400%) Original 47 91 70 537 (500%) -11 Natural aging, 1 year 68 42 25 525 - 2 51 -27 92 83 Original 65 630 75 Oven, 96 hours, 70" C. 61 47 -33 17 440 18 30 92 - 1 575 9 13 76 - 8 Natural aging, 1 year 72 Bomb, 24 hours, 72 - 13 90 - 2 562 -11 Oven, 96 hours, 70' C. 71 10 60' C. 47 - 00 65 - 29 487 - 9 45 -36 Bomb, 24 hours, Bomb, 48 hours, 88 - 4 600 .5 76 - 8 60' C. 62 - 3 54 - 40 440 60' C. 45 - 4 34 -51 18 Bomb, 48 hours, (300%) 54 - 35 555 -12 60" C. 56 - 13 68 - 2 6 Original 67 111 450 71 1300%) Naturalaging l y e a r 84 +26 89 -20 324 -28 41 -42 (20) Original . 43 95 430 58 Oven,96hour4,70°C. 9 8 +47 100 -10 310 -31 44 -38 46 -21 85 -10 376 -13 Naturalaging, l y e a r 67 t . 5 5 Bomb, 24 hours, 45 -22 84 -12 375 -13 Oven.96 hours.70°C. 63 +46 60' C. 55 -17 84 -24 410 - 9 49 -31 Bomb, 24 hours, Bomb, 48 hours, 49 -16 55 ~ 2 7 84 -12 410 - 5 60' C. 60°C. 65 - 3 84 -24 387 -14 46 -35 Bomb, 48 hours, (500%) 43 - 2 6 76 -19 395 8 55 +26 60°C. Original 137 170 555 134 00 155 - 9 543 2 120 -10 Naturalaging, l y e a r 137 124 -27 Oven.96hours.70°C. 103 -24 550 1 97 -28 Bomb, 24 hours, 60' C. 119 -13 145 -15 550 1 113 -16 Table III-A$Linr? - - Data for Heavily Compounded Stocks Bomb, 48 hours, TEXSIL~ 129 -24 550 60° C. 109 -20 1 101 -25 kXNG MODULES TENSILE ELONGATION PRODUCT (40042) 80 575 66 Kg./sq. % Kg./sn. % 70 % Original cm. change cm. change 5% change change Natural aging, 1year 46 0 55 -31 450 - 2 2 35 -47 Oven,96hours,7O0C. 44 - 4 49 -39 445 -23 31 -53 (500%) Bomb, 24 hours, (1) Original 54 84 600 72 55 -31 525 9 41 -38 60' C. 35 -23 51 -29 506 -16 70 -16 Naturalaging, l y e a r 68 +26 Bomb, 48 hours, 55 -24 66 587 2 -22 -13 47 Oven 96hours 70'C. 48 -41 35 -47 515 -10 60' C. 30 -35 ti6 - 8 76 9 610 2 B o m 6 , 2 4 h o u r ~ . 6 O 0 C . 47 -13 60 -17 70 -16 600 0 Bomb,48hours,6O0C. 44 -19 Original (300€8) 133 520 99 (400%) 63 -36 418 -19 Naturalaging,lyear 75 f 2 6 100 -21 ( 2 ) Original 46 62 500 44 48 -51 355 -32 94 -29 Oven.96 hours,7O0C. 77 +29 20 -54 34 -45 406 -19 33 -28 Xaturalaging, l y e a r Bomb, 24 hours, 41 - 7 72 +16 400 -20 Oven,96hours,7O0C. 71 +53 61 -38 58 3 95 -28 450 -13 60' C. 36 -18 -20 64 3 400 64 +38 Bomb,24hours,60°C. Bomb, 48 hours, 31 -30 400 - 2 0 54 -12 Bomb,48hours,6O0C. 54 +17 56 - 6 86 -35 325 -37 40 -60 60' C.
Kg./sq. % Kg./sq. % cm. change cm. change (600%) (1) Original 133 165 Natural aging, 1 year 158 +18 180 9 0 \ ~ e n , 9 6 h o u r s , 7 O 0 C . 151 f 1 3 152 8 Bomb,24hours,60°C. 144 8 168 1 Bomb,48hours.60°C. 144 8 175 6 (500%) (2) Original 147 204 Naturalaging,lyear 9 8 -33 135 -34 0ven,96hours,7OoC. 147 00 151 -26 Bomb,24hours.60°C. 95 -36 146 -29 Bomb, 48 hours,60° C. 72 -51 110 -46 (600%) 223 (3).;Original 112 Naturalaging, l y e a r 95 -16 219 2 Oven,96hours,7O0C. 95 -16 204 8 Bornb,24hours,6OoC. 70 -37 174 -22 Bomh.48hours.60°C. 77 -31 138 -38
++
+++
--
%
-
%
+ +
AGING
+
++
+
-
-
+ +
-
-
+ -
-
+
+-
-
+
-
-
+
+ -
-
+
-
__
-
+
-
-
+
-
+
-
-
+
-
+
-
-
-
-
-
-
+
+
INDUSTRIAL, AND ENGINEERING CHEMISTRY
November. 1929
Table 111 (Continued)
TENSILE
M O D U L U S TENSILE ELONGATION PRODUCT Kg./sq. % Kg./sq. % % % cm. change cm. change $& change change
AGING
(500%) ~-
Table IV-Coefficients of Correlation between Oven Aging and Bomb Aging OVEN AGING-96 HOCRS BOMBAGING-% HOIJRS BEST APPROXICOEF. COEF. MATION
147 147 156 133 139
0 f 6 -10 6
-
Original 41 Natural aeine. 1 vear 46 'S,7-00 c. Oven. 96 6011; Bomd,24hours,6OoC. B o m b , 4 8 h o u r s , 6 O 0 C 35
+ 10
% 2;; -15
(500%)
Original Naturalaging, l y e a r Oven,96hours,7O0C. Bomb,24hours.60°C. Bomb,48hours,60°C.
65 43 57 45 45
-
4
-11 -22 -17
- 34 -12 -30 -30
562 575 520 535 540
362 375 390
570 -13 556 1 565 -34 550 -55 507
(300%) Orieinal 63 105 NzF&ila&ine. -1 vear 71 1 1 4 94 Oven 96hours 70'C. 90 71 + I 3 B o m 6 , 2 4 h o u r & 6 0 ° C . 64 1 104 8 80 Bomb.48hours,6O0C. 58
425 -10 375 - 1 3 350 1 440 - 2 3 400
- 8 +-30 4 -42
I
+-
(300%) (7) Original 86 Naturalaging, l y e a r 87 Oven,96hours.7OoC. 90 B o m b , 2 4 h o u r s , 6 O 0 C . 89 B o m b , 4 8 h o u r s , 6 0 ° C . 86
+2 + + 053
150 136 127 150 142
-
-
440 9 425 -15 400 0 437 5 443
-
4- :!
-
- 4k
-
410
95 83 95 63 43
_.-_.
72 67 75 51 42
190 183 169 149 158
-E!
--
-
!I if
2 I. 4:
-11
.-1:I -1s
+- 4 €0
+
3 $1
I 1
152 150 125 113 122
-
1
-18 -26 -20
.- .,29 -24 24
25
-37 -34
78 66 76 49 31
-
63 50 45 65 46
-21 -29 3 -27
94 82 72 93 90
OF
OF
,I,
Original Naturalaging, 1 year Oven,96hours,70°C. Bomb,24hours.60°C. Bomb,48hours,60°C.
1015
-15 3 -37 -60
+
-13 -23 1
-- 4
CORRE- PROBABLE CORREPROPERTY LATION ERROR LATION Lightly Compounded Stocks Modulus 0.610 t0.24000 0.940 Tensile 0.990 *0.00074 0.900 Elongation 0.470 *0.34000 0.390 Tensile product 0.950 =+0.03500 0.890 Mediam Compounded Stocks Modulus 0.410 t0.12500 0.500 0.420 0.770 Tensile *0.18400 0.760 0.550 Elongation *0.06300 0.740 *0.06100 0.845 Tensile product Heavily Compounded Stocks Modulus -0.830 *0.07900 -0,570 Tensile -0,720 *0.12200 -0.147 Elongation 0 440 *0.22000 0.380 Tensile product 0.072 t0.25000 0.200
TO
PROBABLE NATURAL ERROR AGING +0.04600 *0.07400 *0.33000 *0.07700 t0.11600 * O 09200
Bomb Oven
.,,
Oven Bo'mb
=tO 10800
Oven Bomb
tO.17300 t0.25000 t0.22000 *0.25000
Oven Oven
t0.03800
... .
..
Acknowledgment
Grateful acknowledgment is made of the assistance of
H. A. Braendle, of Binney & Smith, for outlining the method of working out the coefficient of correlation, and to J. M. Ball, of R. T. Vanderbilt Company, for help in drawing up the graphs.
Some Notes on Artificial Aging Tests for Rubber w. w. vogt GOODYEAR 'CIRE & RUBBERCOMPANY, AKRON,OHIO
ROM a strictly yuautitative point of view we should
F
expect an artificial age test to duplicate in all respects the changes that take place on natural aging. I n other words, all of the measurable physical and chemical properties should be changed in the same direction and to the same degree for all types of compounds. If we are looking for such performance from an artificial aging test, then in the writer's opinion none of the present tests fulfil these conditions to a sufficient degree f,o warrant any extensive use of correlation factors. It must, moreover, be realized that the present methods of artificial aging seek only to duplicate the natural aging of rubber on shelf storage in the dark. If we wish information that will predict aging of rubber products under their normal service condifions, then we must get into the field of specialized testing wherein the conditions with respect to light, temperature, humidity, etc., may be made to approach more nearly those of the actual service. Limitations of Present Aging Methods With these points in mind we may now consider a few of the more serious limitations of present methods. LIMITATION1-All of the measurable properties should change in the same direction and to the same degree as in natural aging. I n this connection the writer wishes to present a few data by C. R. Park. The formula is-rubber 100, ZnO 12.5, PbO 6.25, and sulfur 6.25. This stock was used for several years as a tube stock. General experience and records over a long period have shown that it stiffens on aging and that the tensile qualities hold up fairly well. From the data given in Table I we find: (1) On natural aging the tensile product decreases and the stiffness index increases. (2) I n the Geer oven the tensile product decreases and the stiffness index decreases very strongly. (3) I n the
Bierer-Davis bomb the tensile product increases slightly, but the stiffness index decreases quite markedly. Table I
TENSILESTIFFNESS PRODUCT^ INDEX^ Original 150 85 76 76 3 days Geer oven a t 70' C. 6 days Geer oven a t 70' C. 65 70 9 days Geer oven a t 70' C. 60 64 16 hours Bierer-Davis bomb (at 50' C. and 400 Ibs. per sq. in. or 28.2 kg. per dq. cm.) oxygen pressure I55 77 6 months natural 140 95 12 months natural 120 102 a Tensile in kg. per sq. cm. X elongation + 1000. b Difference in kg. per sq. cm. of the moduli a t 650 and 450 per cent. AGINQ
This behavior is typical of several similar types of litharge stocks and one is forced to conclude that it is rather hopeless to attempt their evaluation by present methods of accelerated aging. LIMITATION 2-Another question that is constantly being asked is-how many hours in the oven or the bomb does it take to equal a given period of natural aging? I n other words, what is the equivalence factor? Park (1) and Vogt (6)have shown that to produce changes equivalent to those produced by a given period of natural aging the times required for both the oven and the bomb test vary as much as tenfold depending upon the type of stock. This extreme variation can only force us to the conclusion that in the present state of the art accelerated aging cannot be said to be a quantitative method. Even under the most ideal conditions one can get very diversified results as to the equivalence factor, depending upon what property one chooses upon which to make the comparisons. The data given in Table I1 also bear directly upon Limitation 2. They represent the average of the results obtained on nineteen stocks which differed from one another only in the percentage and kind of softener, all other conditions being fixed.
