April, 1024
INDUSTRIAL A N D ENGIhTEERING CHEMISTRY
INVEXTORY CHARGE-In order to insure continuous operation, an ‘average of 1 month’s coal supply and 2 months’ supply of cobs must be maintained the year around. Allowing 25 working days per month, 1150 tons of coal and 2500 tons of cobs will be needed for this reserve. An inventory charge vf 8 per cent, including interest on investment, taxes, and insurance is allowed for this item. OPERATIXGCHARGES-The estimated labor requirements are given in Table I, which shows a total labor charge of $208 per day. An item of $20 per $1000 of wage paid is included for employees’ compensation insurance. Undei- the item of fuel, the unit price of $2.00 per ton may seem low, but is within the average price which has prevailed in normal years at the mine mouth in the section for which this plant is planned. Since the main consumption of steam is in the digestion and rectification process, only a relatively small amount of condensed steam can be returned to the boiler. At 85,000 B. t. u. per pound of furfural, 74 pounds, or approximately 9 gallons, of boiler feed water will be required per pound of furfural, or 81,000 gallons per day. A standard charge of
369
$5.35 per 100,000 gallons is allowed for this item. During the process a quantity of solution equivalent (at the maximum) to about 50 times the weight of furfural formed must be condensed. Assuming a 50” C . heat rise in the condensing water, about six hundred times the weight of furfural would be necessary as condensing water, a total of 650,000 gallons per day. For a plant located on a river, the condensing water could be pumped directly from and discharged into the river. The charge for condensing water will then be distributed over the items of fixed charges, labor, fuel, and maintenance. As customary in estimates for plants of about this size, an allowance of 2 per cent of the total operating charges for oil and supplies and of 6 per cent for maintenance is made. RAWMATERIAL-The unit price set for the cobs is $2.50 per ton, although in certain localities adequate supplies have been offered as low as $2.00 per ton. TOTAL PRODUCTION CosT-The various items entering into the cost of production are assembled in Table 11. The total estimated cost of production for the plant handling 50 tons of cobs per day is 6.15 cents per pound of furfural produced.
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The Influence of Certain Compounding Ingredients in Hard Rubber’ By W. E. Glancy HOODRUBBERCo.. WATERTOWN,MASS
H
iiRD vulcanized rubber has been a common, everyday
material nearly as long as has soft vulcanized rubber, for it was back in 1851 that a patent was granted to Nelson Goodyear, a brother of Charles Goodyear, as a result of his investigation on the vulcanization of rubber. Yet, although one new use after another has developed for this material, the volume of business is still only a matter of a few mi1;ions of dollars a year, or only a small fraction of the amount that is spent for soft rubber goods. This means that there are relatively few companies interested in hard rubber and a correspondingly small number of technicril men who have devoted much time to the subject. From time to time articles have appeared in the journals dealing with certain phases of hard rubber manufacture; yet almost nothing has appeared which might be considered a discursion of hard rubber compounding. Two years ago North2 contributed an exceedingly comprehensive and thorough paper dealing with the effect of certain compounding ingredients upon the physical properties of soft rubber. One could certainly visualize a rubber stock if data on all the properties of the mix as considered by North could be obtained. .In the case of hard rubber, however, some of the physical properties usually given, such as permanent set, resiliency, etc., may be neglected. The purchaser may require certain standards of electrical and acid resistance, as well as finish and type of fracture, depending upon the use of the material in question. Often, however, he ill only ask: “Is it of proper hardness; what is the proportion of filling materials; is the tensile strength satisfactory; is it properly vulcanized?” It is the writer’s purpose to make a beginning in this field by showing the effect of certain compounding ingredients upon the physical prop1 Prer>ented before the Division of Rubber Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. Received October 24, 1923. 2 India Rubber World, 63, 98 (1920).
erties of hard rubber. The data obtained consist of only the breaking strength and ultimate elongation of various hard rubber stocks, and while the data are not so complete as Korth’s, nevertheless, they do give some conception of the action of the materials in question, as properties such as hardness and ductility seem to change with the breaking strength and ultimate elongation. Investigators who have attempted to obtain reliable data when testing soft rubber goods know that it is difficult t o get consistent, trustworthy results. The same applies to hard rubber testing, but more so. It is known that when a piece of hard rubber,is dropped into hot water it becomes soft and pliable. If it is tested under these conditions, the ultimate elongation and breaking strength are found to be vastly changed. These differences, to a lesser extent, occur with smaller differences of temperature. Likewise, the rate of separation of the clamps on the testing machine has a considerable influence. Other factors, such as milling conditions, age of stock, type of test piece, etc., have their influence. EXPERIRIENTAL The results of the tests discussed herein were obtained under conditions as nearly identical as possible. A standardized method of handling all mixings was followed, and the tests were carried out a t 21” C. on a horizontal Scott tester, the clamps separating a t the rate of 0.5 cm. per minute. (These conditions, as well as the shape of the test piece, are as recommended by the Hard Rubber Division of the War Service Committee in its report of August, 1918.) In order to eliminate the cutting and grinding of each test piece down to accurate dimensions, a three-cavity mold was constructed, so that the only cutting necessary was that of separating the thin overflow from the test piece. Results recorded are the average of at least three tests. They do not represent
360
ISDUSTRIAL AhTDENGINEERING CHEMISTRY II
absolute values, but are of comparative value only, showing general tendencies. Compounds were mixed to show something of the mass action of sulfur, the accelerating or hardening effect of lime and magnesia, the filling effects of mineral rubber and tire reclaim and of a commercial resin. These compounds contained rubber from the same lot of smoked sheets, which were washed and kiln-dried under usual factory conditions. The rubber was broken down until it was smooth and ready to receive the compounding ingredients, the same breaking time being given each batch. A standard laboratory mill 30.5 em. long and 15.2 em. in diameter was used. Vulcanization was carried out in press a t 170" C.
STANDARD TESTPIECE
1
-
UINERRL RUBBER R U B B E R - S U L f U R R E S I N - RUBBER-SULFUR
RESULTS Proportions of rubber and sulfur were chosen within limits which might be considered as the hard rubber field, as shown in Table I. Attention is called to the very rapid increase in breaking strength between cures of 35 minutes and 45 minutes for all the mixings, and to the high breaking strengths which are attained. It is also noted that there is an actual decrease in strength when the amount of sulfur is increased from 66.7 per cent to 100 per cent by weight on the rubber. As the length of cure is increased, the ultimate elongation decreases much as the breaking strength increases. Tests completed on specimens which are only soft cured are less consistent than tests on the harder cured pieces. These results are expressed graphically on Plate I.
. .. . .
The quality of the materials used was such as is usually found in rubber factories. The bulk of the powders will pass through a 150-mesh screen and all through a 120mesh screen. The lime was a commercial hydrated lime, approximately 92 per cent Ca(OH)2 with the usual small quantities of carbonate and oxide. The magnesia contained 97 per cent MgO. The mineral rubber was a standard grade with softening point of 161" C. (ball and ring method). The tire reclaim was made by the alkali process and had a specific gravity of 1.26. The commercial resin melted a t 81' C. and blended well with the mix.
Vol. 16, S o . 4
Time of cure.. Per cent Cam- Sulfur to uound Rubber A 100.0 B 68.7 C 42.8 D 33.3
A B
C D
100.0 66.7 42.8 33.3
TABLE I-RUBBER-SULFUR 35 Min. 40 Min. 45 Min. 60 Min.
90 Min.
-Tensile Strength-Kg.- per _ Sa. Cm.60.4 302.7 424.9 538.3 209.3 442.7 501.3 603.1 29.3 121.8 237.8 519.0 37.5 69.4 130.0 417.2 -Ultimate Elongation-Per cent4.1 66.9 3.7 3.0 5.0 98.0 4.0 3.0 77.0 31.0 6.0 58.0 77.1 74.1 6.5 88.8
564.9 621.2 580.4 516.1 5.5 5.0 6.0 5.3
Table I1 shows the diluent effect of mineral rubber and resin with quantities up to 13 per cent by volume when added to a 700:300 rubber-sulfur mixture. These figures are shown graphically in Plate 11. The curves are not unlike those for similar tests on soft rubber goods, a maximum tensile strength being obtained a t about 7.5 volumes when the stock is cured 45 minutes.
INDUSTRIAL A N D ENGIXEERING CHEMISTRY
April, 1924
.
TABLEI1 (Base mixing: 700 rubber, 300 sulfur) Tensile Strength Ultimate Elongation Kg./Sq. Cm. Per cent 40 Min. 45 Min. 40 Min. 45 Min. Mineral Rubber-Sulfur-Rubber Volumes Mineral Rubber to 100
36 1
COh’CLUSIONS
1-There is a critical point in the process of vulcanization of hard rubber, and if the curing is interrupted previous to this point a flexible, leathery material is produced. If the curing is continued beyond this point, a sharp increase in breaking strength and corresponding reduction in ultimate elongation occur together with the hardening of the rubber-a specific case showing an increase from 500 pounds per square inch to 5500 pounds per square inch in the 10minutes near the critical point. 2-As the proportion of sulfur is increased, a point is Resin-Sulfur-Rubber Volumis Resin reached where further increase in sulfur no longer causes to 100 Volumes an increase in breaking strength, but an actual weakening Rubber due to dilution occurs. 3-Under the vulcanizing conditions described, materials of the mineral rubber type can be used with advantage up t o about 7.5 volumes, when a weakening of the compound occurs. 4-Lime and magnesia, which possess accelerating propTable I11 shows the influence of magnesium oxide and lime in :t base mixing of 700 parts of rubber and 300 parts erties in soft-cured rubber, also decrease the time required of sulfur. by weight. The quantities used of these two in- to harden the compound and increase the breaking strength organic rtccelerators are small, but as large as is common in when used in small quantities. 5-Resin may be used to actual advantage up to about soft rubber goods, and the figures show a decided hardening effect wjth the introduction of these materials and answer 5 volumes. 6-Tire reclaim of the grade described, in quantities up to 6 the question as to whether hard rubber compounds are influenced by inorganic accelerators. The graphs (Plate 111) volumes, causes a large increase in breaking strength and decrease in ultimate elongation, and in larger quantities reduces shown bring out this point more clearly. the breaking strength and increases the ultimate elongation. TABLE I11
Volumes MgO
(Base mixinn: 700 rubber, 300 sulfur) Tensile-Strength Ultimate Elongation Kg./Sq. Cm. Per cent 40 Min. 46 Min. 40 Min. 45 Min. Magnesium Oxide-Suljuv-Rubber
to 100 Volumes
Rubber 0.0 0.42 0.83 2.08 3.11
121.8 281.0 310.6 338.7 415.9
Volumes Lime
237.8 368.0 381.0 469.0 486.2 Lime-Su1.f~-Rubber
77.0 16.0 30.0 17.0 7.0
31.0 3.0 6.0 3.0 4.0
77.0 25.0 8.0 7.0 6.0
31.0 9.0 7.0 5.0 4.9
to 100 Volumes
Rubber 0.0
0 1 2 4
5s 16 91 37
121.8 288.2 350.0 468.4 485.3
237.7 386.1 430.1 451.7 450.2
Table IV and Plate IV show the influence of tire reclaim. A small quantity of reclaim acts as a hardening agent, as shown hy the increase in breaking strength and decrease in elongation. Increasing the quantity used, however, causes a softening of the specimens cured under like conditions, probably due to the rubber in the reclaim which does not have sufficient sulfur available to harden it. TARLEIV-TIRE RECLAIM-SULFUR-RUBBER (Base mixing: 700 rubber, 300 sulfur) Volumes Reclaim Tensile Strength Ultimate Elongation Kg./Sq. Cm. Per cent t o 100 Volumes Rul~ber 40 Min. 45 Min. 40 Min. 45 Min. 0 0 121.8 237.8 77.0 31.0 5.11 372.8 480.4 7.3 4.5 10 22 335.2 428.2 16.9 7.5 20 44 329 4 404.9 35.4 8.8 40 88 221.8 289.8 68.9 57.2
A coniparison of the results obtained shows that lime and magnesia act much more rapidly than asphalt and resin and may be properly considered accelerators or hardening agents. Lime seems to be slightly more active than magnesia. Asphalt and resin may be considered as plastic diluents, their hardening effect within the limits considered being due to their bulk. Tire reclaim contains sufficient basic materials to act ab an accelerator when used in small proportion. Large quantities bring so much additional rubber that there is an insufficient quantity of sulfur in the base mix to produce hard rubber.
ACKNOWLEDGMENT The writer wishes to acknowledge his indebtedness t o W. H. Moore, who supervised the testing, and D. D. Kright, who assisted witb the graphs.
Nichols Medal Award Charles A. Kraus, director of research a t Clark University, Worcester, Mass., was awarded the seventeenth impression of William H. Nichols Medal of the New York Section of the AMERICANCHEMICALSOCIETY in recognition of his splendid researches on the properties of nonaqueous solutions. The medal was presented by Marston T. Bogert a t the regular March meeting of the New York Section on March 7, 1924. The Nichols Medal was founded in 1902 through the gift of William H. Nichols, and is awarded annually by a jury of the New York Section to that investigator whose contribution, published in the journals of the AXERICANCHEMICAL SOCIETY, shall have been judged of outstanding merit. It has been awarded to E. B. Voorhees, C. L. Parsons, M. T. Bogert, M. B. Bishop, W. H. Walker, W. A. Noyes and H. C. P. Weber, L. H. Baekeland, M. A. Rosanoff and C. W. Easley, Charles James, Moses Gomberg, Irving Langmuir (twice), C. S. Hudson, T. B. Johnson, G. N. Lewis, and Thomas Midgley, Jr. F. G. Cottrell, director of the Fixed h’itrogen Research Laboratory of the Department of Agriculture, following the introductory remarks of Clarke E. Davis, chairman of the New York Section, spoke interestingly of the personal side of the medalist, calling attention to his intense love of research, his interest in unusual phenomena and his method of coordinating everything to the end which he has in view. Perhaps the most important point brought out by Dr. Cottrell was the joy to be had from research in pure science which is often overlooked by chemists in these days of intense commercialism. Dr. Kraus has contributed fifty-four journal articles, two books, and twenty patents to the literature, as a result of his many researches in the field of liquid ammonia solutions and related problems. After fitting remarks of presentaten by Dr. Bogert, Dr. Kraus delivered his medal address on The Theory of Radicals as Applied to Modern Chemistry.” After reviewing the changes in the conception of chemical combination from the time of Berzelius, he discussed the theory of radicals in the light of modern investigation, showing that radicals could be placed in an electromotive series similar in all respects to that of the elements. His investigations of the complex alkyl tin radicals and their properties in liquid ammonia solutions formed the basis Tor the discussion, which will later be published in full in the Journal of the American Chemical Society, where most of his previous work has appeared.
