Cold Resistance of Synthetic Rubber W. J.
MCCORTNEY AND
J. V. HENDRICK
Chryrler Corporation, Detroit, Mich.
UMMOBILES must A etart and perform at temperatures as low as
-40"
c.
with the UBB of
modern acxderatore and presant-dsy sulfur ratiw,
A n accurate method for detennining the cold nsistance of rubber has been developed. It is used to check the cold resistance of synthetic rubbers, compounds of these rubbers, and effects of different methods of processing. All tests a n tun at -40" C. The results show that mall variations in processingand compounding &ow up greatly in stiffening characteristia at low temperatures.
it is possible to compound M t U d rubber Bo that it will remain quite flexible at eubsero tempmtures. previously we used the T-50 test' and cheages in durometer hsrdnees as a means of determining mld resistance for natural and synthetic rubber parte. These measurements p r o d to be qualitative but failed to show the exact charaobrintioa de8i&i for automobile rubbr parte subject to flexing and deformation at subzero temperatures. The Tbo test also p r o d dow and cumbemme for checks in an automobile laboratory where speed is erulential. Am& T-50teat WBB tried, which consisted of elongating the m e a s d inch of a standard tensile dumbhell from 1 to 3 inches. Theae ssmples were mounted in an apparatus (Figum 1) and plaoed in a Ioom refrigerated to -40' C. The dumbbelh were then r e l d , and the length of the marked d o n wm measured witbin 30seconds. The amount the sample failed to retunlinthis time WaE expreased as per cent hibility. Thia test also p r o d to be inconsistent and a poor meammment of the qualities sought.
. TLBLBI. N ~ P ~ C N o E y m ~ M*tai.l. put.by r e t N w - e tmE N w - e m Q N
5
t Mlain# 6 rood Imp Nexxone D emyW-msphthyhmhd
a t
zino * d e ( N ~ W J-
.
Lithuge
... 100 ... .... .. .... .. .._ ... iw .,_ ... ...0.25 ._. ... _ . ... IO 4 IO ...
1w
~a0pre.e mP D - m Newrene tms I
NO.a)
Temp.ol o w fer 40 min..
C.
il
30 10
"2
30 6
... ...
153 141
" 'a
' 'a_
... 141
168
30 10
I
were then relewd at the upper end of the mandrel, and the time r e q u i d for them to return to a horisontal position was used as an index of mld resistance. Extremely good synthetic rubber compounds return to their original Bhape witbin 0.5 second; poor samples I%quire approximately 60-70 seconds. This test was promising but after considerable work showed inmnsistentresults.
Teat Procedure With the 1941 models,the Cbryder .Corporation introduced . vacuum-activated automatic trmenmmom. It WBB newsssry for these tnmsmiasion% to function at subzero as well as
at normal or elevated temperatures. Cold-resistant measur+ mente developed to date fdd to simulate the low-tempereon the diaphragms used in these tranmhiom. ture &e& AB a result, we were f o r d to test the diaphragm themeelves in the actimting mechanism at -40' C. When such teste were found to be extremely Sensitive and of repducible accuracy, it was decided to adopt this test as the stsndard measur8ment of freeae resistanoe in our laboratories. In this teat the activating mechanism was stripped of all the parts that were not neoeessry for the rubber maawemen& (Figure3). The frmis&ce of the vsrioua rubberlike materiakwere recorded as the vacutwn, in millimeternof mercury, required to r e m the diaphragm completely @lgure 4). The activating mechslusm ' and diaphragm to be tested as illustrated in Figure 3 are connected to a manometer and v~mumpump. The pump is started, and the manometer anddiaphgmareobservedsimultsnaously. Atthemoment
30 10
10
TABLE II. COLDR ~ S I S T ~ COFE N B O P ~ NCoyponmhe E 8oltSnW
Cold Faaktanq Mm. of H. E G N PD-163 I
1NDU"""IAI.
A N D ENGINP!!!?ING
CHEMISTRY
Vol. 33, No. S
TO VAWUM LINE
--
81
CUP
"gure 3. Aclivating Mechanism and Diaphragm
Figure P. Apparatus for Drop Ted
when the dmphragm remm, winch happens q u w y , the manometer is read. This reading gives an indica-
tion of the stXnes of the material at room temperture (25' C.). In most caw, except those which will be r e f d to la*, 65-65 durometer synthetic N b h r compounds remrea at mom temperature betwem 38 and 43 mm. of mercury. The activating diaphragm asembly is then d i a o o n n e o t e d from the v~cuumsystem, and ita frictional parta are lubricated with kerosene. This premta condensation of moisture and freezing of the frictional parta which would give erroneou~multa. The n b l y m treated io then placed in the cold room at -40' C. to free= for one hour. ~ r e d o u atests indicated thstmastsJmthetcrubbercom~~dsraachtheir optimum freezing Eharaoteristica after one hour; natural N h k V l d C d Z ~ qh U k 0 aPPlDXiUlSt8lY 2 weeks to reach maximum hard-.) The -bly left in the cold room in reconnected to the vacnum aystem which is m located that it may funotion outside of the cold room. The diaphragm is
.
,z DIAM., 6 HDLES EQMLLY SPACED
Figure 4.
Details of Diaphragm for Freeze-Resistanc* T e h (Dimensions in Inches)
d v a t e d by means of muum, and the number of millimeters of mercury q u i d to reverse it under theee conditions is read.
Resdtn w i t h Synthetic R u b h Tablee I to V contain the formulaa of variow synthetic r u b k compounds h t e d and their freeze reainhcfm. The rubber control stock given with thw tables is a hydraulic
TAB= In. T ~ O X O Cofmmram' L Put.by Weight
M.tsri.l
... 1w .5. .100 .5. . 100 . 6. . 1. 5w. . 100 . 6. . 5
1w
0.5 0.1 0.5
30 1 P0l.r IC4 a
0.2 0.5
a0
0.5
o.a
0.5
45
0.0
o.a
0.5 0.2
0.5 0.2
0.6 0.6 0.6 45 45 46
.... .. .. .. .. .. .. ...........15.... .18 .............. . . . . . . . . . . . . 6.a ... ...............
oil
Curd 40 minu-
0.5
at 148' F.
0.5
B& compound Burstt No. 10 Ethplsne diehiode KEIP O l U Ice oil
194 87 114 143 151
206
... ... ... ...
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
May, 1941
.
581
As discussed in the first part of this paper, 40 mm. of merCpld Recury weresubtracted from the sistance DUfigures of Table 11, IV, and V. Dimensional Changea at rometer HardTensile,In. Elonga96 72 hr., 72 hr., -40° F., The relative weights of the tion, % Modulus (300%) S O hr., OF. 158’ F. 250’ F. Mm. Hg Material ness 1Lb./Sq. p l a s t i c i z e r s added to the Neoprene I + Circo light 56 oil 1680 433 908 -1.71 -1.49 Stiff Thiokol FA compounds (Table .... ... ... . .0. . .... .... Stiff 55 Ameripol 111) vary. This is due to the 685 283 ... .... .... .... 206 69 Thjokol S Thiokol Fa + Barrett .... .... .... fact that only the above 63 827 463 654 87 No. 10 amount of plasticizers could Neoprene G N + dibutyl 675 812 -0.40 0.0 4-3.23 87 2160 63 aebacate be practically milled into the NeoDrene E 4- dibutvl 2000 716 622 52 sgbacate - 1.... .70 .0. ..4.8 4-4.47 .... 74 77 given compound. From pre1870 510 ... 67 Chemigum vious tests on the physical Neoprene PD 263 + di59 1093 316 637 -2.5 -3.28 8.38 36 butyl sebacate properties of these compounds, Natural rubber brake-cup .... ... ... .... .... .... 55 stock 36 40 minutes at 298” F. was a I n 8. A. E. 20 oil (aniline point, 108’ e.). chosen as the best cure for these materials. Table IV gives the cold resistance of the compounds. No work was done t o determine the effect of various softenbrake-cup material and the most freeze-resistant natural ers on either Chemigum or Ameripol. However, sample rubber compound developed in this laboratory. diaphragms of both materials were tested for cold resistTo each of the basic compounds of Table I were added 15 ance. We have no information as to their chemical composiparts of channel black and 15 parts of each (in turn) of the tion other than that they contain Chemigum and Ameripol. softeners listed in Table 11. The cures were the same as for The latter tested “stiff”, and the former, 74 mm. of mercury. the basic compounds. From previous tests on the physical Table V contains the freeze resistance of the best coldproperties of these compounds it was decided that 40 minutes resistant synthetic compounds derived from results of this a t the above temperatures was the best cure for these mapaper, along with the cold resistance of our natural rubber terials. Table I1 gives the cold resistance of these combrake-cup stock. pounds. TABLEV.
PHYSICAL PROPERTIES OF BESTCOLD-RESISTANT COMPOUNDS
’
End of
IN
1875 Col. S. Taylor Suit of Prince George’s County, Maryland, was diitilling “Standard Whiskies for the Drug Trade” on his
plantation called “Suitland”, which whiskies were examined and approved by the Boards of Health of the District of Columbia and Washington City. Col. Suit owned a painting of an alchemist, here reproduced as No. 125 in the Berolzheimer Series of Alchemical and Historical Reproductions. This was lithographed in color on a business card for use by pharmacists, there being a small rectangle for the insertion of the name and address.
Symposium
On the back of the card are found the endorsements of these whiskies by the Health Officer of the District (October 1, 1875) and by the President of the Board of Health (August 22, 1875). Obviously the artist, name unknown, has taken his inspiration from some older painting of an alchemist, although some of his equipment is unusual, particularly the tall apparatus resembling a modern coffee percolator. D. D. BEROLZHEIMER 50 East 41st Street New York, N. Y.
The lists of reproductions and directions for obtainin copies appear BB follows: 1 to 96. Janua 1939?isaue, page 124: 97 to 120, fanuary, 1941. page 114. adQtional reproduction appears each month.
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