L. T. WORK R. H. SNOW
ANNUAL REVIEW
Size Reduction This year’s literature rgects continued progress with some novel developments somewhat less than the usual amount of new A lthough material on size reduction equipment has been reported in the past year, there is extensive literature of a review nature and on other aspects in this field, as well as in the related fields of size enlargement, classification for size, collection, and particle size measurement. Such a state of affairs can well be understood in the light of the many new devices in these fields reported last year (57). Among the books in these areas are: “Particulate Clouds,” by Green and Lane (22); “Particle Size,” by R. D. Cadle (8); and the contribution by R. D. Cadle from the National Center for Atmospheric Research a t Boulder, Colo., entitled “Particles in the Atmosphere and Space” (9). Supplementing these are a number of published symposia, extensive review papers, and reports of specialized conferences. Examples of these are A.I.Ch.E.’s Fluid Particle Technology ( 7 7) ; Chemical Processing’s ‘‘Size Reduction and Classification” (74); and Chemical Engineering’s article by Gluck, “Vibrating Screens)’ (27). At the 58th Annual Meeting of the American Institute of Chemical Engineers in Philadelphia on December 7, 1965, there were several papers on grinding fundamentals. An IIT Research Institute project on particle size measurement, supported in joint effort by 20 companies, will soon be operating. I t is a companion to the basic project at I I T R I on size reduction, which is under way and making progress. As the International Standards Organization is making progress with sieves, it is now including measurement in fine sizes, by sieve or otherwise, in its program.
AUTHORS Lincoln T. Work is a Consulting Chemical Engineer in New York City. Richard H. Snow is a Senior Engineer, Chemical Engineering Research, Illinois Institute of Technology, Chicago.
Scientific trends include more on surface treatment and imperfections, nucleation, agglomeration, and shape-particularly of whiskers. I n grinding, new attention is being given to fracture and to resultant fineness. Particles and Their Measurement
I n recent years, penetrating knowledge has been obtained as to how crystals form and grow, what is the effect of imperfections and of films on their surfaces, and the formation of high length-to-diameter shape particulates commonly known as whiskers. There are symposia on nucleation (26)) coalescence (49)) and whiskers (56); a book titled “Ceramic and Graphite Fibers and Whiskers” (38))and an article pointing out how electron diffraction in surface chemistry reveals adsorption and rearrangement (47). A review article in Analytical Chemistry (October 1965) summarizes recent studies in single crystal growth. Special attention is currently being given to the use of sieves for analytical separation by sizes, particularly in the low micron dimensions. The Allen-Bradley Co. of Milwaukee offers a sonic sifter, although actually vibration combined with air pulses may be yielding the results in fine sizes. Zwicker (58) tells of the use of micromesh sieves to below 2 microns using the Alpine suction knife method. A wet technique being demonstrated by Dr. Brian Kaye at IIT Research Institute combines sieve cloth and elutriation for rapid, accurate separation. I n other techniques for fine particle measurement, Kaye and Treasure (30) stress the importance of thermal stability of the suspension for sedimentation testing; Ramakrishna and Rao (50) describe the mechanism of sedimentation. Pigment dispersions are analyzed using the disk centrifuge ( 3 ) . The annual reviews of Analytical Chemistry (April 1966) treat electron microscopy, x-ray diffraction, and light scattering. I n the July 1966 (Part 11) issue of the same journal, the listing of producers of sampling and particle size measurement is impressive. Truly, with the present tools, particle size measurement to fine sizes is becoming more rapid and more VOL. 5 8
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certain as to accuracy, or at least reproducibility. The factors of shape and surface configuration are still not definite. Size Reduction
Theory. Whereas energy requirements have for years been dominant in developing theories about size reduction, increasing attention is being given to the nature of fracture and to the distribution of sizes in the reduced solids. It is a natural answer to the question of what can be accomplished rather than what is the cost. It is accompanied by an increasing tendency to understand how the attainable distribution of sizes affects the properties of a product. In a study of the fracture of individual particles of glass spheres, quartz, limestone, barytes, and cement under both compression and impact, Rumpf (52) presents data on fracture probability and size of products. Arbiter and H a m s (2, 23) propose a three-dimensional weightsize-time frame of reference for comminution theory and also review energy considerations. Mempel and Patat (42, 43, 48) have a new approach to measuring the resistance of materials. This they define in terms of the
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INDUSTRIAL AND ENGINEERING C H E M I S T R Y
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rate of breakage in a ball mill, relative to the distribution of ball energies. Kiesskalt and Dahlhoff (37) relate grindability in a vibratory ball mill to the speed of sound in the materials. The “laws” for product sue distribution and production rate continue to be advanced. Reid (57) has a form for batch grinding, easily adaptable to continuous. This is said to have an advantage over the equation of Bass (4). Liberation of mineral grains (S), thermal stress fi-acture (29, $o), chemical change (7,36),and grinding limits (33) are the subjects of other work. A pictorial presentation of mill action and of factors bearing on size reduction is given in “Handbook of Crushing” put out by Pennsylvania Crusher Division, Bath Iron Works, Broomall, Pa. Many producers of size reduction equipment have small mills for laboratory scale operation. Data obtained on these, although not too easily scaled up to large plant sizes, are still so used. Among recent announcements of small mills are those by Reitz Manufacturing Co. of Santa Rosa, Cali. ( 2 3 , the Megapact laboratory jar mill of Pilamer, Ltd. (28), “Little Jake” by Jacobson Machine Works of Minneapolis, Minn. (72), and the Mini-Mill, a miniature colloid mill by Gifford-Wood, Inc., of Hudson, N. Y.
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Practice. In an extensive review article, Jay W. Gossett (27A) points out that progress in size reduction is evolutionary, not revol~tionary. He also stresses the growing importance of fine grinding and of classification to ensure freedom from grits in products. The relative merits of small scale and large scale testing are presented, with the observation that, although sample weight for test is large, the plant unit test results are generally better duplicated in the customer's plant. The discussion in this paper ranges from consideration of large equipment for mining, cement, and related industries to the special problems of smaller scale operation on special products of the chemical industry. It places much of sue reduction in a perspective not possible in these year-to-year reviews. There is a special note of novelty in jet milling, which has been advanced noticeably by a couple of mill producers. Perhaps the marked increase in fluid pressure, which makes possible the grinding of hard materials in a properly designed system, stands out among the author's citations. Broadly speaking, the author has noted that progress is made by small adjustments in structure, in materials, in operating characteristics, and the l i e , rather than by new designs and new principles.
The immediately current trends being noted in the literature point toward the choice of circuit or flow sheet, the characteristics of some newer type mills, and control means for automatic operation and for consistent product quality. Concerning flow sheets and equipment, the Proceedings of the 7th International Mineral Processing Congress are most informative (7). Coyle (75) reports on a simplified flow sheet for processing an iron ore using only two steps of autogenous grinding to reduce gyratory crusher product to -500 mesh. Thompson and Olsen (55) compare the economies of open-circuit rod milling with closed-circuit single-stage ball milling of ores. Lynch (37)shows how grinding circuits can be simulated with mathematical models and the digital computer. For the newer trends in mill design and operation, increased size of units and the perennial quest for wearresistant materials stand out. In particular, thew include: jet mills with substantially increased fluid pressures, previously mentioned; the increased use of pin breakers and rotor throwing devices in high speed m i l l s ; the effect of sonic and of short length frequent stresses in fracturing smaller particles, an attribute of
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vibratory pebble mills. These appear to dominate this year’s news either as innovations or a sreports of progress. The concept of designing impactors for better performance (53) and of crushing rock between vibrating plates (17) and the use of supercritical speeds in the operation of autogenous mills as reported by Hukki (25) are currently of moment. Fahrenwald (78) gives data on his “space” mills which are oscillatory ball mills; and he reports appreciably higher capacities and substantially better energy efficiency than with ball mills. Lesin and Lokshina (34) have presented an analysis of the characteristics of vibratory mills. Among variants of the stirred ball mill, the attritor type is the subject of reports (46, 54). The trend to larger mills for the tonnage industryjaw, gyratory, roller, ball and rod, and hammer millsis justified by Dettmer (76) who points out that this trend is based upon lower capital cost per unit of capacity, the use of less space, and greater efficiency in operation and maintenance, along with more economical auxiliary equipment including instrumentation for automation. There are many references to controls as a means of reducing operating manpower and of ensuring steady capacity operation and uniform product quality. Sonic and flow devices are commonly used (20, 39). In operations on phosphate rock, a 1500-horsepower unit can grind 101 tons per hour under sound intensity control. The title portrays it-“Sonics Plus ComputerPushbutton Ball Mill” (44). Information on particle size distribution of products, particularly the finer ones, is becoming general knowledge; and mill makers have to use classifiers to control “top size” or to ensure freedom from grit. Classifiers are being improved to provide for separation of coarser sizes without having them carry much useful fines or to produce grains essentially free of dust. Some are being built into the mills, while others are used separately. There has been a resurgence of interest in sieves, with a tendency to use them in the finer mesh sizes. With proper vibrating, air flow, or fluid washing procedures, this is feasible. The Gluck article (27) gives an extensive review of this field. Typical references may be cited (5, 70, 13). Structures which embody some of the most significant of the current developments are:
1. Sonic-Sifter, The Allen-Bradley Co., Milwaukee, Wis. Figure 1 2. Vortec impact mill, Vortec Products Co., a division of Douglas Aircraft Co., Inc., Torrance, Calif. Figure 2 3. Vertical impact pulverizer, Pennsylvania Crusher Division of Bath Iron TVorks. Figure 3 4. Centridyne mill, Entoleter, Inc., New Haven, Conn. Figure 4 5. Hosakawa mikron separator, Pulverizing Machinery Co., Summit, N. J. Figure 5 6. Alpine air jet sieve, Alpine American Gorp., Natick, Mass. 01762. Figure 6 66
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Applications
From time to time, some special aspects of applications appear. Some, like the startling growth of new metal powders, are not due to grinding but to other means of size control (24). Some show how choice of mill type has an important bearing on product quality and cost of production (45). Others show new applications of old powdered material-for instance, pulverized coal in the blast furnace (47). Others show change of properties-the enhanced activity of ball-mill alumina (35). Then again, new techniques are shown such as freeze-drying for making fine metal powder (32). These are but a few examples of the changing trends of progress in this field. REFERENCES ( 1 ) .4rbiter, N . , ed., Proc. 7th International Mineral Processing Congress, Columbia University, X e w York, N . Y . , 1964 (pub]. 1965). (2) Arbiter, N., Harris, C. C., Brit.Chem. Eng. 10 (4), 240 (1965). (3) Atherton, E . , T o u g h , D.,Soc.DwsCol. J . 81,615, 624 (1965). (4) Bass. L . , Z . Angew. Math. Phjs. 5 (41, 283 (1954). (5) Berg, D . B., Chem. Proc. 28 (131, 74 (1965). (6) Bodziony, J., Bull. Acnd. Polonais Sci. Ser. Sci. Tech. 13 (9), 459, 469; (lo), 883 (1965). (7) Burton, T. G., Trans. Inst. Chem. Eng. (London) 44 (2), T37 (1966). (8) Cadle, R. D., “Particle Size,” Reinhold, New York, 1965. (9) Cadle, R . D., “Particles in the Atmosphere and Space,” Reinhold, New York, 1966. (10) Cizem. Eng. 72 (26), 60 (1965). (11) Ckem. Eng. Prog. Simp. Ser. 62 (1966). (12) Chem. Equip. 4 ( l o ) , 3 (February 1966). (13) Chem. Proc. 27 (16), 63 (1964). (14) Ihzd., 29 (7), 29 (1966). (15) Coyle, S., University of Minneqota School of Mines and Metallurgical Engineering Center, Mining Symposium Proc.. p p . 9-13 (January 1965). (16) Dettmer, P . B., Mining En$. 17 (4), 57 (1965); 17 (5), 68 (1965). (17) Eng. Hews 175, 48 (Sept. 2, 1965). (18) Fahrenwald, A. W., M e t a l M i n . Pmc. 2 (31, 30 (1966). (19) Fitch, B., IND.ENG. CHEY. FUNDAMENTALS 5 ( I ) , 129 (1966). (20) Gillis, A. E . , Can. M i n . J . 87 (31, 48 (1966). (21) Gluck, S. E., Chem. Eng. 72 (3). 151 (1965). (21A) Gossetr, Jay W., Chem. Proc. 29 (?), 29 (1966). (22) Green?H . L . , Lane, W.R . , “Particulate Clouds,” 2nd ed., Spon, Ltd.,London, 1964. (23) Harris, C . C., Ins?. &fin. M a t . Trans. 75 (31, C37 (1966). (24) Hausner, H. H., ed., “Modcrn Dcveloprnents in Powder Metallurgy,” Plenum Press, New York, 1966. (25) Hukki, R . T., iMm. Congr. J . 51, 120 (September 1965). (26) IND. ENG.CHEM.57 (9), 17 (1965). (27) f h i d . , 57 (12), 83 (1965). (28) Ibid.,5 8 (8), 87 (1966). (29) Jones, M. P.; Fullard, R . J., Insi. M i n . M e t . Trans. 75 (3), C127 (1966). (30) Kaye, B. H.,Treasure, C. R. G., M a ? . Rer. Std. 5 (ll), 568 (1965). (31) Kieaskalt: S., Dahlhoff, B., Chem. Ing. Tech. 37 ( 3 ) ,277 (1965). (32) Landsberg, A . , Campbell, T. T., J . M e t . 17, 856 (August 1965). (33) Leopold, B., Fujii, J . S., J . Poljmer Sci. C11, 149 (1965). (34) Lesin, A , , Lokshina, R . V., Brif. Chem. Eng. 11 ( l ) , 44 (1966). (35) Lewis, D., Lindley, M. TV., Am. Ceram. SOC.J . 49, 49 (January 1966). (36) Liberti,A.,DeVito;F. G.,Stoub25 (4), 161 (1965). (37) Lynch, A . ,J., Chem. Eng. N e w s 43,40 (Dec. 20, 1965). (38) McCreight, L. R . , ”Ceramic and Graphite Fibers and Whiskers,” Academic Press, New York, 1965. (39) Marcotte, E . J . , Can. “din, J . 87 (3), 50 (1966). (40) Marovelli, R . L . , Chen, T. S., Veith, K. F., Trans.A I M E 235, 1 (1966). (41) hfay, J. I V . , IND.ENO.CHBM.59 (7): 18 (2965). (42) Mempel, G . , Chem. Ing. Tech. 37 (11), 1146 (1965). (43) Ibid., 37(12), 1259 (1965). (44) Meinhold, T. F., Chem. Proc. 28 (111, 62 (1965). (45) Meinhold, T. F., Beggs, F. L . , Ibid., (6), p. 70. (46) Nordeman, H . V., Tappi 49 (21, 95.4 (1966). (47) Ostrowski, E. J., Dietz, J . R., Iron Steel Eng. 42, 116 (December 1965). (48) Patat,F., Mempel, G., Cham. Ing. Tech. 37, 933 (1965). (49) “Processing with Coalescence,” Chem. Eng. Progr. 61 (IO), 51 (1965). (50) Rarnakrishna, V., Rao, S. R . , J . Appl. Chem. (London) 15 (lo), 473 (1965). (51) Reid, K. J . , Chem. Eng. Sci. 20 (111, 953 (1965). (52) Rumpf, H . , Chem. Ing. Tech. 37 (31, 187 (1965). (53) Schatz, M‘., Rock Producls 68, 57 (September 1965). (54) Stanczyk, M , H., Feld, I. L., U. S. Bur. Iviines Rep. Invest. 6694 (1965). (55) Thompson, J. V., Olsen, K . E., Rock Products 69 (S), 89 (1965). (56) “Whiskers, Making and Use,” Chern. Eng. Progr. 62 (3); 51 (1966). (57) Work, L. T., IND.E m . CHEM.57 ( I l ) , 125 (1965). (58) Zwicker, J. D., Ceram. Buil. 45 (81, 716 (1966).
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