128 



THE INDIA RUBBER WORLD 



[December 1, 1916. 



gree. Although both an under and an over-cured sample can be 

 tested, an under-cured sample, he said, does not pass the test. 

 The temperature of the oven is a factor. 



Later, during the discussion relative to insulated wire, par- 

 ticularly in regard to compounds containing a large amount of 

 accelerator, he expressed the opinion that the temperature of an 

 accelerated aging test vifould make no difference in the physical 

 resuhs obtained. This is limited by reducing the total amount 

 of sulphur when accelerator is used. By "type of compound" he 

 explained that he meant compositions in relation to tensile 

 strength and physical quality. This life test will show whether 

 the product is going to stand up or not. It is a practical service 

 test to accelerate the conditions which the compounds would have 

 in ordinary use, not compounds subjected to very bright light, 

 nor for articles to be subjected to a great deal of steam. 



Regarding a suggestion that the permanent elongation of steam 

 hose may be caused by the cold flow of the water which follows 

 the hot injection of steam while exposed to daylight. Dr. Geer 

 said that, bearing in mind that permanent elongation is dependent 

 somewhat upon tensile, it will be found that after three days of 

 elongation the tensile will have fallen off. If the ratio of the 

 tensile and elongation could be worked out it w-ould indicate 

 what the limit ought to be. 



C. R. Boggs then discussed a series of experiments begun 

 seven years ago to determine the value of the various short life 

 tests which had been proposed up to that time : 



These tests included various dry heat and steam tests and what 

 is known as the acetone peroxide test. On none of the tests 

 tried did we obtain results which were at all promising. Acetone 

 pero.xide certainly does not o.xidize rubber in the same manner 

 as air does under ordinary conditions. We then imported a 

 quartz tube mercury vapor light in the hope that the ultra-violet 

 light might cause the natural oxidation, but at a greater speed. 

 Oxidation does take place rapidly, but it is similar to that ob- 

 tained on a sunracking test rather than that obtained by the 

 natural aging of rubber. The ultra-violet light, therefore, might 

 be used as a standard light for a sunracking test, but not for a 

 life test, as the two tests are not similar by any means. 



We had had so many disappointments that when we heard of 

 Dr. Geer's heat test we practically refused to try it. Later, how- 

 ever, we did try it and the results were sufficiently promising so 

 that about three or four years ago we made a comparatively 

 thorough study of it. As we have tested samples regularly which 

 h«ve been exposed to the light and air of an ordinary room after 

 regular intervals of time over the entire life of the samples, we 

 *"1<new what the life of our samples should be and consequently it 

 did not take long to find out that the test was very valuable. We 

 have used the test since then. Duplicate samples of those tested by 

 the Geer test. When kept and tested after ordinary deterioration, 

 showed the same characteristics in practically every case. Sam- 

 pies which, by the Geer test, had shown decrease in tensile but 

 not in ultimate elongation, showed the same thing after natural 

 ai;ing. Other samples which maintained their tensile but de- 

 creased in elongation, and still others which increased in tensile, 

 all showed the same results by the two tests. The time in days 

 that corresponds with a certain number of hours of the Geer test 

 varies with different grades of compounds, but does not seri- 

 ously detract from the value of the test. 



There are at present many specifications which call for a defi- 

 nite compound of certain chemical and physical characteristics 

 which are based on the assumption that there exists no reliable 

 short life test and that, therefore, the next best insurance is to 

 demand something which has been known to have had a satisfac- 

 tory life. When the purchaser has taken this position we have 

 assisted him in trying to see that he obtained what he specified. 

 n<owever, if we have a satisfactory short life test in Dr. Geer's 

 heat test, it would be much better for both the purchaser and 

 manufacturer to use this test. The purchaser would be insured 

 of a permanent compound and the manufacturer allowed to use 

 his ingenuity to advance the art of the trade. It is now time for 

 the purchaser to satisfy himself that the test is what it is claimed 

 to be. 



Up to the present time, I have not found any samples which 

 were not correctly represented by the Geer test, but I have lately 

 heard of a compound with an organic accelerator which was said 

 to pass the test, but which did not stand up on natural aging. I 

 am now trying to duplicate this result. 



Mr. Boggs later expressed himself of the opinion that the 



value of the test might increase upon further investigation, adding 

 that most compounds tested by the rapid aging method con- 

 tained an increased amount of accelerator, and that while suc- 

 cessful results are the rule, care must be taken particularly to 

 avoid over-curing. 



Mr. Whipple's address carried the discussion a step farther 

 tlian that of Dr. Geer : 



Among the interesting points brought out by Dr. Geer, his dis- 

 cussion of the nature of curves obtained and their interpretation 

 brings to my attention one type of curve which he has omitted. 

 namely, one with an upward tendency from the beginning of the 

 test and not falling below its starting point during the period of 

 the test. Such a curve has been obtained in three instances on 

 tests conducted for Committee D 11. I have not seen the results 

 of the other members of this committee, but if they are in agree- 

 ment with mine and the curves obtained were to be interpreted 

 in a broad way as indicating service value, it brings out the in- 

 teresting conclusion that the general run of the code wire is bet- 

 ter than the general run of the 30 and 40 per cent grades on the 

 market to-day, as the code wires consistently gave this upward 

 curve. 



One test, for instance, showed 102, 106 and 108 per cent, re- 

 spectively, after 12, 24 and 48 hours' exposure to the test, and at 

 the end of the hours the curve had dropped to its starting point 

 of 100 per cent and did not fall below this after 144 hours, at 

 which time the test was discontinued, whereas three of the 30 per 

 cent wires after 144 hours had fallen to 56, 58 and 58 per cent, 

 respectively. 



We have, of course, tried out this aging test on samples of 

 known life, starting with a knowledge of most of the conditions 

 under which the original compounds were made and vulcanized, 

 and although the conditions may not have been exactly the same, 

 the results should have been inore nearly comparable, as in the 

 accelerated test the curve was a decreasing one from the begin- 

 ning and in the actual life test there was a decided increase 

 from the beginning, and at the end of ten years the value was 

 150 per cent of the original. 



Other compounds on which we have a better check have shown 

 i" a year and a half an increase from 1,200 to 1,800 pounds tensile 

 strength and at the end of three years were still 1,800 pounds or 

 above, representing an increase to 150 per cent, whereas in the 

 accelerated tests these have shown a downward curve from the 

 beginning. 



I am decidedly of the opinion that this accelerated test is of 

 value to the manufacturer in determining the best time and tem- 

 perature to be used in vulcanizing compounds of the same general 

 type, and I am also of the opinion that it is of great value to the 

 manufacturer in passing judgment on the relative value of many 

 of the ingredients used in rubber compounding, and while not 

 prepared to state any relative values, I am quite sure that after 

 further experiments we shall be able to arrive at an interpretation 

 of results which will be of value to the consumer as well as to 

 the manufacturer. 



Referring to Mr. Tuttle's description of tests after which the 

 tensile strength of the articles had fallen down, Mr. Whipple 

 said: 



We bad some cable made in 1906 which was furnished to the 

 government, and was stored under water at Fort Wadsworth. 

 There were about ten reels, one mile each, and those ten reels 

 continually went down on the electrical test. Now, after nearly 

 ten years, they are entirely defective electrically. The tensile 

 strength of the insulation is over 1,800 pounds and the elongation 

 over 12 inches after ten years. You cannot find an apparent 

 mechanical defect anywhere; they are simply water-logged. This 

 experience is just the opposite of the one mentioned by Mr. Tuttle. 

 but it also shows that both methods of testing must be considered. 



P. L. Wormeley then spoke of the work being done at the 

 Bureau of Standards along the lines of Dr. Geer's investiga- 

 tions : 



I have been conducting the test which has just been described 

 for something over four years, and would say that in a general 

 way the diagrams which Dr. Geer has put on the board illustrate 

 vfery well the results obtained at the Bureau of Standards. Our 

 first tests were made with 12 compounds furnished by Dr. Geer 

 and in some cases sufficient time has not elapsed to show their life 

 under normal aging conditions. The results that we have ob- 

 tained would indicate that the effect of dry heat at 160 degrees F. 

 on the physical properties of rubber compounds is indicative of 

 the probable life; but these results have not exhibited any definite 

 relation between the effect of the heat test and the effect of 

 aging under normal atmospheric conditions. When our tests 



