July, 1923
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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NOTES AND CORRESPONDENCE The Resilient Energy and Abrasion Resistance of Vulcanized Rubber Editor of Industrial and Engineering Chemistry: Referring to the paper on “The Resilient Energy and Abrasion Resistance of Vulcanized Rubber,” by H. W. Greider, published in THISJOURNAL, 15 (1923), 504, I beg to submit a few remarks, especially since the entire field of investigating the wear resistance of all our materials used under certain kinds of friction-metals, building materials, textiles, rubber, etc.-has been sadly neglected in this country, although the property of resistance to abrasion is in a great many cases of far greater practical importance than strength, hardness, and other properties usually covered by routine tests. First of all, abrasion tests of materials are of practical value only if they are undertaken in such manner that the particular form of friction which the material has to bear in practice is exactly reproduced. There are great differences, for instance, in the kind of friction encountered in a ball or roller bearing, in a locomotive wheel against the rails, and in a shovel or plow blade. Running metal or rubber against an arbitrarily selected abrasive material is in most cases no duplication of service conditions, and the value of such tests for the classification of materials is questionable. I believe that Fig. 11 in the paper shows clearly that something else is “going on” with the surface of a tire than what has been done to the rubber specimens in the laboratory investigation. In other words, the stresses encountered in practice are of a different nature. It is regrettable that the author does not give any information on the method he used to measure the “resilient energy” of rubber compounds. On page 508 the author states: “It has long been recognized that in metals, concrete, stone, and other engineering materials, resistance to abrasive wear is intimately associated with the hardness of the material, and i t is not clear why hardness has not previously received more consideration as a factor in the toughness of rubber.” As far as metals are concerned, all investigators-such as Robin, Nusbaumer, Stanton, Saniter, Brinell-have found that no relation exists between “hardness” and resistance to abrasion. One of the most careful investigations ever carried out on this important subject was undertaken by the Institution of Mechanical Izngineers, London, and the results were published in the 1916 “Report of the Hardness Tests Research Committee” of this institution. Some of the difficulties encountered in all researches of this kind are a t present unsurmountable. “Hardness” of metals is usually defined as “resistance to permalzent deformation,” but no means have yet been found to determine this resistance. What we are doing is to investigate the resistance of progressively deformed metals to gradually increased deformation, taking a n entirely arbitrary end-point. If we would apply our metalhardness testers (Brinell or scleroscope) to hardness tests of vulcanized rubber, we would find that rubber is harder than iron. Hardness of rubber is something entirely different from hardness of metals, and I do not believe that hardness of rubber has ever been determined; this depends, of course, on how we decide to define “rubber hardness.” Instruments like a durometer or plastometer compare properties of elastic compressibility by means of arbitrarily shaped and dimensioned tools, which, however, do not produce a permanent indentation or penetration of the rubber. These tests are carried out below the elastic limit
of the material, and are therefore of a nature entirely different from that of the usual mechanical hardness tests of metals. Mr. Greider’s paper is of great interest, and his results are undoubtedly of considerable value to the industry, but he uses his terms of mechanical properties-such as resilient energy, resilience, toughness, hardness, etc.-in a manner which would tend to indicate that he is speaking of “standard” units and recognized values of properties of the material, which-as everybody must regret-is by no means the case. Unfortunately, we do not yet know anything regarding resilient energy, toughness, or hardness of rubber.
HERMAN A. HOLZ 17
MADISON
AVE.
N C W Y O R K , N. Y .
M a y 7 , 1923
............ Editor of Industrial and Engineering Chemistry: The principal point a t issue, as I interpret the comments of Mr. Holz, is my use of the term “hardness” with reference to a physical property of vulcanized rubber. I am quite aware that “hardness” of rubber is not identical with “hardness” of metals. I have used the term in the sense recognized by every rubber technologist, as measured by instrument in common use in the rubber industry to determine this property. For a further description of these instruments (durometer, densimeter, and plastometer) and a study of their measurements and of the nature of “hardness” in vulcanized rubber, I must refer Mr. Holz to the paper by Gurney, on “The Modulus of Hardness of Vulcanized Rubber” [THISJOURNAL, 13 (1921), 7071. While I have not attempted to define “hardness” in my paper, I have shown that, a t least with respect to the influence of added pigments, the property measured by the durometer, and termed hardness, is substantially identical with the rigidity (stiffness) of the rubber, as determined by the stress load required to produce 300 per cent elongation (compare Figs. 8 and 9 in my paper). Wherever I have used the word “hardness” in the paper I have usually included in parentheses, as synonymous, the word “rigidity.” I have no desire to appear controversial with respect to the physical properties of metals, of which I claim no special knowledge. Nevertheless, it should be permissible to point out that, even in the case of metals, the property of “hardness” lacks exact definition. Upon this definition hinges the assertion of Mr. Holz that numerous investigators have found no relation between hardness and abrasion resistance in metals. As ordinarily used with reference to metals, the term “hardness” embodies several concepts: scratch hardness (the WIoh scale and its modifications), indentation hardness (Brinell), elastic impact or rebounding hardness (Shore scleroscope), cutting hardness (micro-sclerometer), tensile hardness or resistance to permanent deformation. The Brinell hardness number measures the resistance of the metal to plastic deformation. I n writing this paper, I had in mind a possible analogy between the abrasion resistance of rubber and that of bearing alloys. I would call Mr. Holz’s attention to a recent paper by Bierbaum in Chemical and Metallurgical Engineering, 28 (1923), 304, in which he uses the term “hardness” as practically synonymous with cutting or abrasion resistance, and devises a “micro-cut’’ method of determining the hardness of metals used in bearing alloys.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Mr. Holds remark t h a t the durometer and plastometer measure “elastic compressibility” signifies nothing t o a rubber physicist. Rubber is substantially incompressible, b u t i t is readily deformable. The stress-strain curve of rubber may be determined either in compression or tension, b u t what these instruments really measure seems t o be the property of rigidity, a characteristic of all solid substances. To say, therefore, t h a t rubber has greater “hardness” (rigidity) than iron, cannot correctly characterize the material. Rubber probably has no elastic limit except its rupture strength; i t does not follow Hooke’s law, and every stress, however slight, produces some permanent deformation, and i t is, therefore, quite impossible to measure “hardness” above the elastic limit of the material. The “resilient energy” capacity, regarding the measurement of which Mr. Holz asks t o be informed, was determined by the previously published methods of Wiegand [ C a n . Chem. J., 4 (1920), 1601 and of Gurney and Tavener [THISJOURNAL, 14 (1922), 1341, a planimetric determination of the area between the stress-strain (tensile) curve and the elongation axis. The energy capacity m a y also be determined from compression stress-strain curves. I have not attempted t o define “toughness” of rubber further than t o say t h a t i t is usually considered t o be an optimum combination of tensile strength, abrasion
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resistance, endurance of flexing, resilience, and relatively low permanent set. Resilience m a y be defined as t h e ability of the material t o return t o its original conformation and dimensions following t h e application of a deforming stress, and in rubber i t has at least two elements-high rate of return and absence of great permanent deformation (permanent set). While these quantities are perhaps not as yet accepted “standard” units, they are, at any rate, generally recognized by rubber technologists. I s$all not undertake t o defend laboratory tests of abrasion resistance ; their value is already sufficiently appreciated in the rubber industry. Mr. Holz is correct in saying t h a t laboratory abrasion tests do not exactly duplicate road conditions, b u t i t is neither necessary nor desirable t h a t they should. I a m heartily in accord with his emphasis on the desirability of further investigations in t h e field of abrasion resistance, b u t find myself unable t o agree with the claim t h a t “we do not yet know anything regarding the resilient energy, toughness, or hardness of rubber.” H. W. GREIDER MELLON INSTITUTE OF INDUSTRIAL RESEARCR PITTSBURGH, PA. M a y 14, 1923
TOKYO .LETTER B y K.KASHIMA, 994 Ikebukuro, near Tokyo, Japan
ANNUAL MEETINGS April is the month of cherry blossoms and general meetings. On the 1st and 2nd, the annual meeting of the Mathematical and Physical Society of Japan was held in Tokyo. On the 7th and 8th, t h e 45th annual meeting of the Chemical Society of Japan was held at the chemical laboratory of the Faculty of Science of the Tokyo Imperial University. The Sakurai Medal was awarded t o Shintaro Kodama for which the medalist read a paper on amino acids and aldehydes. Professor Katayama gave the presidential address, on stoichiometry. T h e general meeting of the Pharmaceutical Society of Japan was held at the City of Tokushima on the 14th and 15th of April. The 26th annual meeting of the Society of Chemical Industry was held in Tokyo on the 5th and 6th of May. Shuichiro Nagai, of the Faculty of Applied Chemistry of t h e Tokyo Imperial University, was awarded with the society’s medal for the work on safrol from camphor oils. K. Saegi gave the presidential address. SYIiTHESIS O F
PETROLEUM
Petroleum in this country is not abundant. For some time chemists have been conducting experiments t o investigate the origin of petroleum. Kiuhei Kobayashi, of Waseda University, has made studies on Japanese acid clay (fuller’s earth), and has published a book, “Acid Clay,” which is the only book on this subject. On distilling a mixture of sodium chloride and the clay, he obtained hydrochloric acid. This curious fact led him t o seek further facts. Fish oil was then used instead of salt. H e distilled a mixture of t h e oil and the clay, covered with the same amount of the clay. A petroleum-like oil having greenish fluorescence was distilled over. After washing with sulfuric acid, caustic soda solution, and water, as in the petroleum industry, the insoluble oil was fractionally distilled into gasoline (about 30 per cent), lamp oil (50 per cent), and middle oil (10 per cent). He claims t h a t the petroleum which he has prepared from fish oil has physical properties which are almost identical with those obtained from the natural petroleum, the yields being about 60 per cent of the oil. The product is mainly composed of naphthenic hydrocarbons containing a comparatively large amount of olefinic hydrocarbons. Based on these results, he proposes an hypothesis on the cause of formation of natural petroleum, Other chemists have also engaged in this work and many papers have been published in Chemical Industry ( J a p a n ) , T h e Journal of
the Chemical Society of J a p a n , and the Patent Journal; readers will be able t o get their outlines through Chemical Abstracts. As material, fish oils of different origin-vegetable oils, calcium salts of fatty acids from soy bean, pine resin, sodium salts of f a t t y acids from herring oil, pupa oil, etc., were used. Acid clay is a curious substance; when a mixture of the clay a n d camphor is heated, petroleum is formed. N o t only Fare fish oils used for the manufacture of petroleum, b u t also calcium or sodium salts of fatty acids. When treated with lime, glycerol is produced from the oil, the yield of this material being about 10 per cent. This reduces the price of the oil by 13 t o 45 per cent and also t h a t of the petroleum. The process has now passed the period of laboratory experiment. When t h e writer had a chance t o journey through Echigo for inspection of the petroleum industry two years ago, one company was manufacturing petroleum from fish oil in apparatus with a capacity about 10 koku (1koku = 180.39 liters). The annual production of fish oils in this country is not clearly recorded, b u t i t is estimated t o be about 3,000,000 kan (1 kan = 3.75 kg.). Some of this is used for lubricating oils, etc., but a large p a r t may be used for the manufacture of petroleum. J. Takahashi in his book, “A New Treatise on the Mineral Deposit of Petroleum,’’ reports a comprehensive and complete investigation of the mineral deposit in the petroleum fields of Japan. GASOLINE FROM NATURAL GAS This subject is a n internationally popular one. The drying material of Dr. Ikeda, mentioned in a previous letter and now called “adsole,” has proved t o be a powerful drying agent and is now being used in many industries. Fish are easily dried b y this material. It has also been found t h a t adsole will absorb gasoline from natural gas, from which the gasoline is recovered. T h e T B y B Gas Laboratory has been founded for t h e utilization of adsole, manufacture of gasoline and other connected works, being connected with the Rikwagaku Kenkyujo (Institute of Physical and Chemical Research). A plant was built in Echigo, a famous petroleum field in Japan, and the work is now progressing. I n the future some report will be written on the work of this plant. May 26, 1923
