I S D USTRIAL A N D E,VGINEERING CHEMISTRY
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when vulcanized with rubber. I n some regular tread compounds these differences are not so pronounced. Parts 93 0 35 0 3 0 5 0 0 75
Smoked sheets Carbon black Zinc oxide Sulfur Diphenylguanidine
-_-
136 75
The mix was aged 24 hours, vulcanized a t 141.5' C., and tested after 24 hours' aging. The differences in quality imparted to vulcanized rubber are further illustrated in Figure 5, in which the characteristics of samples A and B are shown. The higher volatilematter content is clearly reflected in the poorer quality of all the tests. The physical tests of rubber compounds containing each of the five samples considered in this paper are given in Table T'II. The same mixing formula is used in each case. T e s t s of Carbon Black S a m p l e s TIME TENSILEELONGATION TGNSILE CURE AT AT AT40070
Table VII-Rubber OF SAMPLE
AT
c.
BREAK ELONGATION HARDNESS Kg.per Per cent sq. cm. 630 141 65 310 613 163 324 68 555 178 301 70 602 225 103 60 128 63 612 273 142 580 66 268 .. 300 675 118 61 308 610 148 65 603 161 69 303 65 52 167 610 82 56 186 580 92 59 193 570 238 610 81 60 101 63 264 603 257 598 110 65 much diphenylguanidine was used with this sample.
141.5'
Minutes 40 60
D
Ea
80 40 60 80 40 60 80 40 60
so
40 60 80 a Four times as
BRBAK
Kg.per sq. cm.
~~
~~
The long blacks of high volatile content show very poorly in these tests. In the case of sample E it was not possible to
Vol. 20, No. 9
get sheets for test with the regular formula a t the usual time of vulcanization because of extreme undercure. Accordingly, a mixture was made using four times the amount of diphenylguanidine as the accelerator. Evidently in the case of highvolatile blacks some side reaction with the accelerator occurs which so diminishes its concentration that there is no longer enough to accelerate the vulcanization react,ion properly. Some technologists who have specialized on the problems in connection with solid tires for motor trucks have expreesed the opinion that the cause of blowouts in solid tires is the evolution of gas from the carbon black. The results as given in Figure 1 are contrary to this conclusion, because no gases are evolved in carbon black until a temperature considerably above that occurring in solid tires when run under heavy load and high speed. It can be fairly safely concluded that the gas which comes from solid-tire blowouts is from the breakdown of the rubber hydrocarbon from the heat generated in the tire, instead of the gas from carbon black. Several instances of the difficulty encountered in the mixing of some lots of carbon black with rubber, especially in internal type mixers, have recently been called to the writer's attention. The temperature of the mix rises so high that the process has to be stopped. One instance has been given when this took place on an open mill. Two samples exhibiting this condition have been examined and found to be abnormally low in volatile matter. Might it not be possible that the gas contained in carbon black acts as a lubricant to assist dispersion into the rubber and when the black is deficient in gas, an excessive amount of heat is generated in the mixing by the lack of lubrication? Acknowledgment
Acknowledgment is due to R. K. Estelow and Jacob Gabry, who did a large share of the experimental work in connection with this investigation.
A Mechanical Agitator' G . N. Quam C O E COLLEGE,
CEDAR
T H E studies of the relative rates of corrosion of various ItoKmetals by certain food products it was found necessary simulate, as nearly as possible, the conditions of liquid motion over metal surfaces observed in practice. A device similar to that suggested by Fetzer* was found quite suitable and inexpensive. Its construction is shown in the accompanying diagram. The agitator (20 X 35 cm.) in which the standard test tubes T(2.5 X 20 cm.) were placed was 2,'made of soft wood. Six test tubes were placed in each side and were equipped with breathing tubes, B, bent so as to keep from tipping down into the water of t h e thermostat. The metal samples (7.5 X 4 em.) w e r e f o l d e d i n order to fit loosely a t the
I
:m
Received April 4, 1928. IND. BNG. C H E M . , 17, 788 (1925). 1
2
Figure 1
RAPIDS,IOWA
bottoms of the tubes containing 50-cc. portions of the corroding liquid. The agitator with the partly filled tubes floated in the water thermostat and could be rocked through an angle of 30 to 35 degrees, thus causing the flow of liquid over the stationary metal strips. The liquid was always in contact with air through the breathing tubes. The hinge, H , attached to the rocker arm prevented the agitator from twisting and the walls of the thermostat restricted its movement parallel to the crankshaft of the motor. With this device the agitation was uniform, quiet, and readily controlled. The device has proved to be very effective in determining relative rates of corrosion of metals exposed to common food products under the conditions of temperature and time in commercial practice. The accompanying table illustrates the agreement of some of the data obtained with pure metals and raw whole sweet milk. Loss of Metal Surface Exposed t o Milk a t 75O C. for 30 M i n u t e s METAL SAMPLE I SAMPLE I1 SAMPLE I 1 1 SAMPLEIV SAMPLE V M g / s q . dm. M p /so dm. M g / s q dm. Mg / s q . dm. Mg / s q dm Copper 1.55 1.378 1.378 1.72 1.55 Zinc 0.689 0.861 0.689 1.03 .... Nickel 6.54 6.02 6.54 6.71 6.54 Tin, block 0 . 0 0.172 0.0 0.0 0 . 1 gain
The extension of the application of the device to other problems can be readily recognized.
