INDUSTRIAL AND ENGINEERING CHEMISTRY
868
E Stock Permanent Stretch elongation Tensile Lbs./sq. in. Per cent Per cent Before oxygen aging Before working 370 16 1266 0.5 360 21 1147 340 20 1049 1 390 24 1072 1.5 2 330 23 952 370 27 925 2.5 Oxygen aging a1 60’ c. for 16 hours 350 15 1103 Before working 360 20 981 0.5 370 22 953 1 . ~ . 370 i.5 23 889 340 23 823 2 25 703 360 2.5 Hours worked
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The data indicate a marked deterioration as the working is increased. 3-The last stock is the C stock which was previously referred t o as showing decided changes in quality with the cure. Samples were prepared in the same manner and the following tests were obtained before and after oxygen aging, the cure being 25 minutes at 50 pounds steam pressure: C Stock Permanent elongation Tensile Stretch Per cent Per cent Lbs./sq. in. Before oxygen aging Before working 540 39 1479 0.5 540 43 1404 1 540 43 1334 1.5 530 47 1315 2 530 48 1265 540 50 1176 2.5 Oxygen aging a t 60’ C . for 16 hours 520 Befor’e working 0.5 530 1 380 1.5 240 2 60 2 329 2.5 70 0 335 Hours worked
This stock in particular shows the very decided effect which may be obtained with oxygen aging and which does not show up in the original cure. It will be noted that the tensile has only dropped from 1479 pounds on the original milled stock to 1176 pounds on the stock which was milled an extra 2.5 hours, but in the oxygen aging test it has dropped from 1308 pounds t o 335 pounds.
Conclusion It can readily be seen from all these data that the oxygen aging test affords an excellent method of determining: (1) the proper compounding materials; (2) the presence of impurities in compounding materials; (3) the correct cure; and (4)whether the stock has been overworked. Although it may be possible t o determine some of these factors successfully on high-grade stocks by means of the heat aging test, as far as the writers’ experience goes and in accordance with the general opinion, i t is not possible to rely on the heat test for low-grade stocks. This is now perfectly possible with the oxygen aging test. Moreover, the heat aging test, which takes two weeks t o complete, is eliminated in many cases on account of the time required. The oxygen aging test provides a ready means of determining every night whether the work is progressing satisfactorily.
Application to Tire and Tube Stocks By H. B. Pushee THE GENERALTIRE & RUBBERCo., AKRON,OHIO
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H E oxygen bomb aging test has been applied in the writer’s laboratory t o a number of tire and tube stocks that have been under observation for several years, so t h a t their age-resisting qualities are well known. The results of the bomb test check the results of natural aging very satisfactorily. Furthermore, the effect of variation of the state of cure on the ageresisting properties of these stocks has been correctly indicated by the results of the bomb test.
Vol. 17, No. 8
Value in Testing Rubber Tubing and Rubberized Fabrics By Hugh L. Thomeon AEOLIANCo., MERIDEN, CONN.
H E following remarks about the Bierer-Davis aging test are solely from the standpoint of a user of rubber products. For about twenty-five years the Aeolian Company has been a large-scale consumer of rubber tubing and rubberized fabrics. The properties of the rubber products necessary in the manufacture of player pianos make the requirements difficult t o meet, and these requirements are further complicated by the numerous sizes, shapes, and weights of material necessary for each instrument. It has been possible, however, t o obtain rubber products entirely suitable except in one respect-the assurance of satisfactory aging. Experience has shown that certain rubber compounds and types of material fail consistently after a comparatively short time, and furthermore there has been no certainty that other and supposedly better materials would stand up for a longer period. When it is considered that the ability of a few pounds of rubber to age well is vital t o the successful performance of a n instrument which costs several thousand dollars, the desirability of advance assurance for every lot of material is self-evident. Many methods have been tried in the effort t o foresee in a reliable manner the aging of tubing and rubberized fabrics, varying all the way from simple exposure to light and air-in which case the deterioration has been accelerated by subjecting the rubber t o stress-to the forced air oven. This latter method, though doubtless valuable for some compounds, d o 9 not seem applicable to the class of rubber materials used by this company. On the other hand, results with the Bierer-Davis aging test have been most encouraging. The company has accurate data on the “expectation of life” of certain grades of rubber compounds, and the oxygen aging test apparently checks these results in all cases. It is surely of immense value in comparing one material with another. At the present time 12 hours’ exposure in the bomb under 300 pounds per square inch pressure of oxygen a t 60” C. is considered t o be equivalent to one year in darkness under the conditions prevailing in the piano. I n the tests by this company compounded rubber materials always last longer than so-called “pure-gum” products. Furthermore, the equivalent time of 12 hours in the bomb and one year of aging under ordinary exposure is not correct when the material is exposed to light of any intensity. For this reason experiments were started with a quartz bomb in the hope of checking more accurately the effect of light in addition t o t h a t of oxygen. The danger of ignition of rubber samples in the oxygen bomb has been emphasized and illustrated by Bierer and Davis in their original paper. A similar but much less serious explosion has recently occurred in this company’s laboratory. Heating is carried on in a conditioning oven having an intermittent heater of 300 watts and two continuous heaters of 400 and 500 watts, respectively. The 300-watt intermittent heater alone is used for the oxygen bomb aging test. On a recent occasion the 500watt heater was inadvertently turned on, resulting in a rise of temperature sufficient t o ignite the rubber samples in the bomb. These samples had a total weight of about 48 grams. The standard safety valve, with which the Emerson bomb is now equipped, gave way, relieving the pressure without damage to the bomb itself. The flame was of sufficient intensity, however, t o burn away a large portion of the brass safety device. The pressure inside the oven forced open the door but did not break the mica
