Geer Oven Research Articles

Correlation and acceleration of a Geer oven test to natural exposure

In order to find a correlation of air oven tests with natural exposures—indoor exposure, sheltered exposure and direct outdoor exposure—we carried out tests using ASTM standard rubbers (NR, CR, SBR, BR and EPDM). We determined the percent elongation at break and the hardness of test pieces before and after exposure under the condition of a constant load. After good correlation between the natural exposure and the oven test has been found in terms of change in elongation and hardness, acceleration factors of the oven test to the natural exposure were calculated.

Some Results Obtained in a Study of the Development of Stickiness by Vulcanized Rubber

Abstract The experiments described in the present paper show the possibility of reproducing artificially the stickiness which appears during natural aging, and the results show the experimental conditions which are most favorable to a study of the phenomenon. The indications are that it is best to use an oxygen bomb of small capacity, at a temperature of 60–70° C, and with a pressure of 1–4 kg. per sq. cm. of oxygen. The factor which under no conditions must be disregarded if almost certain failure is to be avoided is unquestionably the problem of ventilation. The Geer oven does not seem to be of any service in such experimentation. The appearance of stickiness during aging is not indicative of an advanced stage of deterioration, but is a manifestation of one form or type of aging rather than the consequence of an extreme state of deterioration. Finally, the influence of certain factors has been established. As far as factors inherent to the rubber mixtures themselves are concerned, the accelerator-vulcanizing agent system plays a determinant part. The character of the phenomenon depends on the aging conditions, particularly on the rate of oxidation. The tendency of a vulcanizate to become sticky on aging is particularly great when the temperature is relatively low and the pressure of oxygen is likewise low.

Accelerated Aging of Vulcanized Rubber. Factors Determining the Relation between Oven and Bomb Aging

Abstract A study has been made of the influence of the following factors on the relative rates of tensile deterioration of natural rubber vulcanizates in the Geer oven and oxygen bomb, both at 70° C : period of vulcanization, sulfur ratio, nature of accelerator. Expressing this relation as the oven/bomb ratio, i.e., the ratio between oven and bomb aging periods that give the same deterioration, the following conclusions are drawn. (1) Varying the period of vulcanization of a given mix over a moderate range (2:3) around the optimum does not noticeably alter the oven/bomb ratio, except in unaccelerated mixes, where overvulcanization gave an abnormally low ratio, owing to the rubber perishing very rapidly in the oven. (2) The effect of varying the sulfur ratio within the usual limits for soft rubbers is small, and appears to result from the quicker vulcanization of the mixes richer in sulfur. (3) The nature of the accelerator profoundly affects the ratio, values ranging from 3 to 27 being found among the present mixes ; this effect is believed to be exerted through the influence of the accelerator both on rate of vulcanization and on the oxidizability of the vulcanizate. Theoretical considerations indicate that a rubber which vulcanizes quickly and (or) oxidizes slowly should give a low oven/bomb ratio, whereas one that vulcanizes slowly and(or) oxidizes quickly should give a higher ratio. The experimental data are generally in accord with this, and there is evidence that both rate of vulcanization and oxidizability can have an important effect, but the data do not enable the separate effect of each to be assessed exactly. The bearing of the results on the use of the oven and bomb tests is briefly discussed. It is shown that they demonstrate the fallacy of using a single factor for converting oven to bomb aging periods or vice versa, and that the relative natural aging resistances of widely different vulcanizates cannot be reliably assessed by either test, a limitation arising from the fact that the relative importance of oxidative decay and aftervulcanization varies from one type of mix to another, and that the temperature coefficients of these processes are not necessarily the same. These facts are very important in relation to the choice and application of accelerated aging tests for specification purposes, since these usually have to be applied to rubbers of unknown compositions, which are likely to vary widely in their relative response to different aging conditions.

Influence of Exposing Vulcanized Rubber to Light on Its Subsequent Aging in the Dark

Abstract The present experiments confirm the observations of Morgan and Naunton by showing that exposure of vulcanized rubber to light may affect the results of oxygen-bomb aging tests made some days, or perhaps even weeks, afterwards. They show also that a few days' exposure to even diffused daylight may noticeably lower the tensile strength of unaged rubber. With normal, i.e., not transparent, rubbers the effect of light on subsequent aging is small, and indeed does not seem to be noticeable at all in relatively slow aging tests, such as that in the Geer oven. Nevertheless, it is clearly advisable, as a precaution, to avoid unnecessary exposure to light of rubbers that are to be subjected to accelerated aging tests.

Deterioration of Vulcanized Rubber by Copper and Manganese Compounds

Abstract The deterioration of vulcanized rubber containing increasing percentages of copper and manganese compounds and the extent of the protection given to the stocks by a secondary naphthylamine have been investigated. Jones and Craig showed that the addition of copper stearate made no difference to the type of aging of stocks containing various percentages of antioxidant when measured by decrease in tensile strength, and the results of Taylor and Jones indicate that the decrease is proportional to the time of aging in the Geer oven. Preliminary work.—Experiments were made on the base mix to determine its suitability and its optimum cure. The optimum cures of the base mix plus copper or manganese compounds after storage for six weeks in the dark at normal room temperature and of the base mix plus sym. di-β-naphthyl-p-phenylenediamine also were obtained. The following compounds A, B, C and D were mixed on a laboratory mill having 12 × 6 in. rolls.

Wanted—A New Aging Test

Abstract For many years rubber manufactures have been tested by artificial as well as natural aging tests. Of the former, the heat aging test by means of the Geer oven (an electric oven held at 70° C) was the first to be adopted and remains probably, the widest used. The correlation between the Geer oven and natural aging varies according to the type of goods and their conditions of service, but a rough and ready guide is that one day in the oven at 70° C is approximately equivalent to six months of natural life. Other heat-aging tests subject the rubber goods to air or oxygen at elevated temperature and pressure, with proportionate reduction of the time of test necessary for practical results. Apart from heat, light has a great deteriorating effect on rubber and some use has been made of this in testing rubber manufactures which are subject to light aging in service. The purpose of this article is to draw attention to the difficulty of accurately simulating natural light, particularly in reference to the conditions obtaining in direct summer sunlight, which has been found to have a far faster deteriorating action than that of ultraviolet light on rubber. For instance, it has been found that about 10 days of summer sunlight, partly deprived of its ultraviolet fraction by passage through window glass, is sufficient to completely destroy a plain rubber film which will stand up to weeks of light aging by a mercury vapor lamp or of ordinary heat aging at 70° C.

Applications of the Manometric Method for Measuring the Oxidizability of Rubber. Oxidizability and Aging in the Geer Oven

Abstract In summary, the changes which take place in the mechanical properties of a rubber mixture when it is aged in a Geer oven, and which are evident by dynamometric measurements, are closely related to the proportion of oxygen absorbed by the sample. It is therefore much more practical and convenient to measure its oxidizability after only a few minutes' aging, using a sample of any shape whatsoever, and a weight of approximately one gram. As far as any particular standard industrial mixture is concerned, there is no good reason for not conforming to the customary practice of rubber technologists of expressing aging on the basis of loss in tensile strength. In this case the only thing necessary to do is to calibrate the manometer in kg. per sq. cm. after having established the curve relating oxygen absorbed to loss in tensile strength.

The Direct Determination of Oxygen in Rubber. The Adaptation of the Ter Meulen Method to Rubber and Its Application to the Study of Aging

Abstract The ter Meulen method for the direct determination of oxygen has been adapted, with modifications, to the analysis of raw and vulcanized rubbers. Raney nickel has been found to be quite effective as the reducing catalyst and to be satisfactorily resistant to sulfur poisoning. The method has been applied to the study of the aging of vulcanized rubber in the Geer oven and oxygen bomb. From this study the following conclusions may be drawn: (1) The increase in combined oxygen is greater in the oxygen bomb than in the Geer oven. (2) Deterioration of rubber in the oxygen bomb involves oxidation primarily, whereas that occurring in the Geer oven involves not only oxidation but also thermal decomposition followed by volatilization of oxidation products. (3) The effectiveness of an antioxidant in retarding the absorption of oxygen in oxygen-bomb aging agrees well with its ability to maintain the physical properties of the stock in which it is present. (4) The deterioration in physical properties of a rubber stock in the oxygen bomb during the early stages of aging is a linear function of the increase in combined oxygen. For stocks containing antioxidants and diphenylguanidine as the accelerator, an increase in combined oxygen of approximately 1.2% corresponds to a decrease in tensile strength of 50%. (5) The relationship of increase in combined oxygen to decrease in tensile strength seems to be affected not only by antioxidants, but also by accelerators of vulcanization.

Heat-Resisting Inner Tube Stocks

Abstract A large number of laboratory tests were carried out which showed that to resist deterioration due to heat in an inner tube stock successfully, the following points should be observed: 1. Sulfur ratios should be very low. One per cent on the rubber content is sufficient for most stocks; some will require 1.2 per cent. This is true provided no sulfur-producing material is present. 2. When P33 Black or a similar soft black is used, 20 to 25 volumes are necessary. In the case of zinc oxide, blanc fixe, barytes, and the like, lower volumes will be necessary to obtain satisfactory resistance to tear. 3. The stocks should not be markedly overcured, especially if the cure is carried out at 50 pounds steam pressure (298° F.) or above. This is the opposite of former practice with stocks of higher sulfur ratio. 4. The accelerator chosen must be strong enough to combine practically all of the sulfur present, and yet should not be too scorchy to handle safely in the plant. 5. Tests showed that the use of 2 per cent of a good anti-oxidant was justified. One per cent gave good results, but especially when agings longer than 18 hours were carried out the stocks containing 2 per cent were markedly superior. 6. Zinc oxide, blanc fixe, barytes, or precipitated whiting can be successfully employed in stocks of this type. The modulus and tensile figures are lower than when P33 Black is used, but the losses in tensile strength due to air-bomb aging are comparable to P33 Black, and these fillers would permit the manufacture of colored tubes such as red, green, and yellow. 7. Heat-resisting inner tube stocks of this type compared to the ordinary tread, carcass, and tube stocks will necessarily be more scorchy, and care must be taken to cool the stocks properly in processing through the factory. The possibility of the migration of sulfur from the carcass stocks to the inner tube, or the migration of accelerator from the inner tube stock to the carcass stock must be taken into account. Today tire manufacturers are using as low as 2 per cent sulfur in the carcass stocks of bus and truck tires. These low sulfur ratios in the carcass stock tend to prevent the migration of sulfur. The usual Geer oven migration tests were carried out on stocks containing Ureka C as accelerator. The Geer oven was maintained at 93.3° C. (200° F.) for 14-day periods, and in no case did these tests show appreciable migration of sulfur or accelerator. Controls were run during the migration tests and alone.

Impure Iron Oxide as a Rubber Pigment. I. Effect of Ferric Sulfate on Cure and Aging of Rubber

Abstract 1. Traces of ferric sulfate in oxide of iron will accelerate aging of rubber. 2. Traces of ferric sulfate in oxide of iron will cut down the rate of cure of rubber. 3. The Bierer-Davis bomb aging tests and the Geer oven tests lead to the same conclusions, although the stocks perform differently in each case. 4. By changing the ferric sulfate to ferrous carbonate with sodium carbonate in solution and washing out the residual sodium sulfate, the ferric sulfate is neutralized to an inactive salt. 5. Iron oxide aggregated by ferric sulfate will not break down on milling in rubber. 6. Increased aggregation reduces the specific surface and the coloring or tinting value of the pigment.

Studies in the Oxidation of Rubber Mixings

Abstract In a former communication (Trans. Inst. Rubber Industry, 4, 493 (1929)) some results were presented of studies on the changes of rubber samples oxidized to an intense degree. For that investigation the oxidation temperature used was 70° C. (Geer Oven), while in the present paper results are given of experiments made at 100° C. and their relation to the results at the lower temperature are discussed. The experimental procedure was similar to that previously used, the preliminary stage being the sheeting out of small portions of the samples by passing them through the tightly closed cold rolls of a laboratory mill. The weighed samples were then suspended by strings in an ordinary steam oven fitted with an air inlet near the bottom and an outlet at the top. The progress of oxidation of each sample was noted from time to time by (a) determining the increase in weight, and (b) removing and estimating the amount of resinous matter present by extraction with acetone for 24 hours. In some instances the acetone extraction was preceded by an extraction with chloroform.

Rate of Cure of Reclaimed Rubber—II

Abstract Residual alkali in reclaim is chiefly responsible for the faster rate of cure of stocks containing reclaimed rubber as compared with those containing new rubber only. Reclaim prepared in water can be made to cure as fast as alkali reclaim by the addition of sodium hydroxide to the extent that this is present in the alkali reclaim. The determination of residual alkali requires a very long extraction, in this case approximately 60 days. Of five possible theories accounting for the rapid rate of cure of reclaim, only that of residual alkali is tenable. There still remains in certain cases, however, a difference in rate of cure between stocks containing new rubber and those containing water-cooked reclaim for which no explanation has been found. Sodium hydroxide of itself is not deleterious to rubber compounds, for, in addition to its value as an accelerator in certain cases, it tends to improve physical properties and aging resistance, as judged by the Geer oven test.

Correlation between Geer Oven and Natural Aging of Selected Tire Compounds

Abstract In standard guanidine tread and carcass compounds, test results obtained from the 4- and 8-day periods in the Geer oven at 70° C. correspond approximately to 1 and 2 years of natural aging. Data obtained from the 12-day period correspond with 3 years of natural aging for tread compounds, but results showed no relation between these same periods for carcass stocks. The tensile product is the criterion which shows the best correspondence between Geer oven tests and natural aging tests on the tread and carcass compounds used.

Aging of Mechanical Rubber Goods Stocks by Various Methods

Abstract THIS 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; 24 hours and 48 hours in the oxygen bomb at 60° C. and 300 pounds (21 kg. per sq. cm.) 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 physical 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 is recorded. (Tables I to III) Figures 1 to 6, inclusive, show graphically the changes in the physical properties studied on each of the three lightly compounded stocks, using several different methods of presenting the data.

Studies in the Oxidation of Rubber Mixings

Abstract The rubber airbags used for inflation purposes during the vulcanization of motor covers gradually change during use, and a hard, brittle material forms inside. The bags can, however, be kept in use long after the rubber or, at any rate, the inside rubber, is in an entirely perished condition. The ordinary physical testing methods used for following the changes in rubber are, therefore, not available under conditions where the deterioration is very intense; but the changes can be satisfactorily followed by chemical methods. In the present paper are given briefly some of the results obtained during extensive studies of rubber submitted to prolonged oxidation in a Geer oven at 70° C. Experimental.—The samples were vulcanized for varying periods, and after vulcanizing were sheeted out thin and placed in small beakers in the Geer oven. The progress of oxidation was noted from time to time by measuring the increase in weight and by removing and analyzing portions of the samples. In the early experiments rubber-sulfur mixings were used for simplicity, but later the work was extended to accelerated mixings. In order to obtain a theoretical insight into the changes taking place, the rubbers were in some cases extracted with acetone before oxidation (aging); also the aging of rubber previously extracted with first acetone and then chloroform was studied. In some series samples were submitted to repeated aging and extraction, that is, after the extraction following aging the samples were again returned to the oven. After a further period of aging they were again extracted, and so on repeatedly.

Correlation between Geer Oven and Natural Aging of Selected Tire Compounds

Correlation between Geer Oven and Natural Aging of Selected Tire Compounds

Aging of Stretched Rubber

Abstract Sunlight aging under tension of many compounds including the following has been investigated: tire tread shoe upper, tube stocks, golf ball thread, jar rubber, solid tire, bathing cap stock, channel rubber. With some of these stocks the sunlight aging as been compared with unstretched samples by Geer oven, Bierer bomb, and ultra-violet light methods. The stretching of the test strips accelerates deterioration in sunlight, ultra-violet light, and Geer oven. Stretched samples have not yet been tested in the Bierer bomb. The rate of deterioration was not proportional to the degree of stretch in any of the stocks in the early stages of exposure. In sunlight there is a critical elongation for each stock at which the deterioration progresses more rapidly than at any other in the early stages of aging. No direct relationship was found between the results of sunlight aging and the other methods employed. Stretched strips aged in ultra-violet light were found to give softer stress-strain curves than the unaged samples, whereas sunlight aging under the same conditions stiffens the stress-strain curve.