Document Bjg58Db3zaK461DVq34vpZkj

ASBESTOS A Symposium of Articles by M. S. Badollet, B. S., M. S, Chem. Eng. Papers Presented at Annual General Meetings of THE CANADIAH INSTITUTE OF MINING AND METALLURGY- 1948 to 1961 ' ' UCC 004674 M .5 & cr * 4_ CONTEMTS Research on Asbestos Fibres (1948)' ........ *............. V.............. 1 Filterability of Asbestos Fibres Used in Wet Processes (1949) 5 Processing Asbestos Frbres;' Effect Upon Physical Properties (1950) .............. -1'' .c. * . . " - -- '> 7 -1. ' t: ; Mj-it 1* *,**>#*X *VS- 1:* -. . . Asbestos, A Mineral of Unparalleled Properties (1951)- , 15 Asbestos Floats (1932) * Vi -t ,, 25 Asbestos Fibres: Production and UsageJl953>< , 35 -V - " ' Heat Treatment of Chrysotife Asbestos Fibres* (1955) - : (with W. C. Streib) ,, ... ...............:................ - - v* V "U , , , 31: . : .' : T , . The Role of Asbestos in Plastics (1956) (with M. R. XimenezV 30 . -*. . ....... . ' >" "4- A_ v' v ,,_ Identification of Minerals Associated with Asbestos by X-Ray . - Oiffrection Potterns (1938) (with ). P. McGourty) . 44: &*,: f -V , 't.......... - > - T'` - K ' > * ** ' , Properties of Asbestos Fibre* Imparted into the United States ' 58 Magnetic Content of Asbestos by Magnetic Separation 56 UCC.004675 Research on Asbestos Fibres By M. S. BADOLLET* (Jubilee Annual Meeting, Vancouver, B.C.) (Transactions, Vol. 1,1, 1948) INTRO DU CTIO N ERY little fundamental re V search has been done on as bestos fibre to take maximum vantage of its properties and to determine in what commercial prod ucts it can best be utilized. For the research chemist who is associated with asbestos develop ment work, a thorough study of mineralogical information on asbes tos deposits would furnish reliable information on the rock formations and the mineral impurities closely associated with the asbestos. Furth ermore, he must have an intimate knowledge of the uses of the fibre in various products so that he can visualize the importance of the fibre and the role it plays in industry. Some of the properties of asbes tos fibres such as strength, com position, length, harshness or soft ness, and mineral associates are of considerable importance to the man ufacturer because they are respons ible for many production difficulties. Kibhe Strength It has been known for some time that asbestos filaments have con siderable tensile strength. These strengths have been referred to merely as `u'eak' to `very trong\ X ot until recently have numerical values been applied to the strengths of asbestos fibres. But today we can take a thin fibre filament and mount it between two holders and apply a gradually increasing load or pull until the fibre breaks. By measuring the cross sectional area of the filament and the amount of load applied, we can calculate the tensile strength of the fibre in terms of pounds per square inch. This type of test is slow and rather difficult, but the fundamental data obtained furnish important basic information that can be applied to mechanical processing equipment and to certain asbestos products. ''Johns-Manville Research Center, Manville, New Jersey, U.S.A. During the processes of liberat ing tile fibres from the wall-rock it is necessary to use some type of equipment that will crack the rock aadnd release the fibre. The maximum strength of the fibre is preserved when this type of releasing is gentle and does not produce fractures at right angles to the fibre bundles. It has been possible to submit crude bundles to processing equip ment such as crushers, rolls, fiberizers, etc., and to test the tensile strengths of the fibres before and after processing in order to deter mine which type of equipment is best suited for opening fibre bundles without destroying the fibre strength. Even the speeds at which some pieces of equipment are op erated have a definite effect upon the destruction of fibre strength and a change of several hundred r.p.m. may transform a strong fibre into a weak fibre. When studying the fibre from a new deposit, it is important to know the strength of the fibre in its nat ural form, as `crude', as well as after it has been processed. The basic information gained by thips type of test is important when con sidering the installation of a new mill to process the fibre. If present milling practice is to be used, it may mean that certain pieces of equipment may require by-passing in order to preserve the fibre strength and not destroy the fibre length. The strength of asbestos fibres is also important in certain commer cial products, as for example tex tiles, papers, and asbestos-cement products. If the strength of the fibre is low, the loss in the textile plant will be high due to drops from the cards and willows. In papers, weak fibres will be ground down by the beater roll. Lifting of the roll may be required, or even reducing the beater cycle, in order to obtain a well formed paper where the fibres retain their maximum strength. In asbestos-cement prod ucts, the fibre strength is im portant. As the fibre strength is decreased by a processing method, so also is the modulus of rupture of an asbestos-cement board or sheet decreased. Typical tensile strength values of chrysotile asbestos crudes range from 10,000 to 100,000 pounds per square inch. Sometimes these values are well over 100,000 provided the filaments have not been deformed by wall-rock movement during the period of crystallization. Other fibres, such as amosite, will have values ranging from 15,000 to 90.000 pounds per square inch, while crocidolite will show strengths from 100.000 to 300,000 pounds per square inch. Some of these values are far greater than the tensile strength of the usual grades of re inforcing steel. Composition op Asbestos Fibres Commercial asbestos fibre, when carefully separated into various fractions, is found to be made up of a number of component parts: crudy fibres, in which the slender threads or filaments are not sepa rated, but remain in bundles; dust, consisting of extremely fine par ticles, either fibrous or granular; fairly small size particles of ser pentine rock or other minerals close ly associated with the fibre de posit; and relatively pure fibres separated into thin threads or fila ments. All of these fractions go to make up a commercial fibre and each component part plays a defin ite role when the fibre mass is used in industry. For example, the crudy bundles improve filtration in wet processes and contribute towards porosity, but they also impart to asbestos papers a rough texture which may be objectionable. Dust acts as a filler which decreases por osity, decreases filtration rates, and increases the density. Rock and other granular material may drop out as a loss during processing or, if it remains with the fibre, it will increase filtration rates, increase --1-- UCC 004676 porosity, and give * rough" surface textile to papers or pressed . prod ucts. If the granular material con sists is part of magnetite particles, this is- considered ' objectionable from the standpoi*Mfe|-ii. the elec trical industry. -Tlielrtfere, each component of an asfiditlM'mass plays a definite part and if is an extreme ly difficult task to separate these materials from the fibre mass com mercially and to eliminate those that may be objectionable. Knowing, then, that commercial grades of fibre contain opened fibres, crudy bundles, fines, and granular materials, it is possible to separate these by a special labora tory technique and express their values in percentages of the orig inal fibre mass. From our experience, it has been noted that certain grades of fibres require certain combinations of the fibre component parts, and that a change of 10 to 15 per cent in these fractions will make a large and noticeable difference in the manu factured product. Likewise, when we know the type of fibre and the percentages of its component parts needed for a product, we can devel op this grade of fibre for this par ticular product. furthermore, when working with asbestos in plastics, the various component parts of a given grade of fibre are extremely important factors. In this case, we are in volved in such physical measure ments as absorption, wetability, fluidity, impact strength, power fac tor, bulking, and surface area. This means that the research chemist must know the effects of crudy bundles, fines, and granular mate rials upon the properties of absorp tion, wetability, fluidity, etc. After these facts have been established, he must understand the effects of various combinations of the fibre component parts (dzM,. crudy bun dles, rock, etc.) upwpi^tesc physical properties. With tMh. fondamental information as a background, it is then necessary to make Up molding powders, press them in molds, and study the properties of the molded material to see if the objective has been attained. The results of all these studies place the producer of asbestos in a position to discuss problems under standingly with the plastics manu facturer and to help him with his problems, particularly in the selec tion of the proper fibre grade. Fibre Length The measurement of the true staple fenigth bff the fibres is prob ably the most difficult of the as bestos producer's jobs. Asbestos is unlike cotton, rayon, or other organ ic fibres that can be combed out and the lengths actually measured in inches or fractions of an inch. The staple lengths of fibres in any given mass vary from those ap proximating l/g in. and longer to those of microscopic size. Methods that have been successfully applied to organic fibres have failed to give satisfactory results when applied to asbestos. Wet screening methods have given fairly good classifica tions providing the fibre surfaces are presented horizontally to the screen opening during the test. If the fibres pass lengthwise through the screen opening, the test loses most of its reliability. A test that can measure the true fibre lengths and can be completed within a few minutes would most certainly be welcomed by the indus try. Further effort should be di rected by the research chemist to the solution of this problem. Harshness and Softness of a Fibre The terms `harsh' and `soft' are often used by the miner and manu facturer in. connection with asbestos fibre. In many cases, the harshness of a fibre is erroneously used to mean crudiness. This point should be clearly defined as the two terms are entirely different. The term `crudiness' means the presence of many hundreds of fibre filaments in bundles that are unopened and are wider than a thirty-second of an inch. The bundles also tend to ap pear stiff and will not bend through a 90 arc without, fracturing. Of conrse, these crudy bundles could be soft, silky, or harsh, hot, after they are properly opened, they have lost their crudiness as bundles or aggregates and appear as opened or willowed fibres that can be bent at right angles without breaking. Harsh fibres, on the other hand, are usually weaker than soft fibres and, during a processing method whereby the thin filaments are sep arated and bent at right angles, they have a tendency to fracture easily, with resultant loss of fibre length. Some investigators have attributed the harshness of a fibre to the presence of mineral impurities which have crystallized close to the fibrils (1, 2, 3). Others believe it to be due to the water of crystallization or water of constitution of the as bestos (3). In any case, the degree of harshness of a fibre is an im portant factor in its use in industry. If a harsh fibre is micro-pulver ized and examined under a micro scope, it is noticed that the fibres show an abrupt breakage and the pattern resembles, a needle structure instead of the wavy pattern shown by a soft, silky asbestos fibre. The degree of harshness of a given fibre may be estimated by a number of tests such as: (1) open ing of the fibre in a standardized piece of equipment and measuring the length loss and increase of fines produced; (2) the tensile strength; and (3) its filtration properties be fore and after opening. The results of these tests may be expressed as the percent change and the numer ical values used for comparison purposes. It is interesting to note that a harsh fibre always retains a relative ly fast filtration characteristic re gardless of the type of processing. On the other hand, a so-called soft or silky fibre decreases in porosity at a rate proportional to the de~ gree of opening of the fibre fila ments. ; It is the fast filtering characteris tic of a harsh fibre that makes it attractive to the manufacturer, pro vided the fibre strength is not too poor. This type of fibre is an ex cellent material for `freeing-up' a stock, giving porosity and aiding filtration. However, the manufac turer must be careful in handling harsh fibres or he may destroy the maximum fast filtering properties of the fibre by over processing. Soft, silky fibres are normally difficult to handle by the manufac turer producing wet machine prod ucts. These fibres have a greater surface area than harsh fibres, and are also slower filtering. The de gree of softness of a fibre can also be estimated by the same procedure employed for evaluating a harsh fibre and numerical values can be used for comparisons. Usually, it may be said that the softer and silk ier the fibre, the greater the dif ficulty in handling it during the stages of manufacturing. Therefore, it is necessary for the manufacturer to have some knowledge of the workability of soft fibres before he attempts to use them, and it is usual ly the research man that can deter mine these properties and supply the necessary information. Filtration The filtration characteristic of any fibre mass is an important fac tor to the manufacturer using wet m '4 UCC '004677 ; ' - C"' '4 methods for the production of as bestos products. For example, the rate of removal of water, either by suction or by pressure, when manu facturing asbestos papers, mill boards, shingles, asbestos-cement sheets, etc., will, to a certain extent, govern the production rates. Therefore, in order to understand the problems facing the manufac turer, it has been necessary to de velop a laboratory filtration test that can evaluate fibres as fibre masses, or as fibres in combinations with other ingredients that are used in commercial products. The first step in this type of in vestigation was to determine the ef fects of ail mineral impurities closely associated with commercial asbestos fibres. The next step was to study the filtration properties of asbestos fibres from all parts of the world and also, at the same time, determine the percentage of each mineral impurity. This was followed by studying the effects of electrolytes, wetting agents, soft or harsh fibres, fibre particle size, weathered fibres, blends containing various types of fibre, erudy fibre bundles, and many others upon a standardized fibre in order to show the advan tages or disadvantages as regarding the elimination of water from as bestos slurries. With this type of information available, it has been possible to express the degree of filtration change in percentage and then set up methods of correction so as to obtain the maximum improve ment in filtration. Many production problems involving the elimination of water from fibre slurries have been investigated in the laboratory and the information has been suc cessfully applied to the factory pro cesses. Value of X-Ray Studies Today, X-ray diffraction studies are becoming one of the standard tools of the research chemist. They give the chemist a chance to obtain a preliminary answer to some of his problems within a few hours, whereas a chemical analysis may require weeks of analytical work. Quite often, the chemical analysis of asbestos fibres shows the pres ence of small quantities of mag nesium, silica, or water in excess of the normal amounts found in an average sample of asbestos. When these data are calculated in terms of minerals, they may indicate small amounts of talc, brucite, chlorite, etc. occluded in, or crystallized be tween, the fibrils. In such cases, a careful X-ray investigation shows the typical ring structure of the minerals and the data can then be recalculated showing the percent ages of the mineral impurities pres ent in the fibre. X-ray studies, along with petro graphic investigations, have fur nished valuable clues to chemical reactions that may take place not only in asbestos fibres themselves, but in finished products. Knowledue of Geology of Deposit as an Aid to the Manufacturer If the manufacturer purchases fibre at random, the material he ob tains may include asbestos from several different deposits, and the mineral formations of each locality will contribute some important fac tor to the fibre that may or may not be objectionable to his process. For example, suppose a certain asbestos-cement manufacturer for a number of years purchased his fibre supply from one mine, where the rocks were very little faulted and hence there was very little fault fibre, and where such minerals as brucite, picrolite, and magnetite were present in only small amount. This manufacturer would have all of his processes well standardized on the fibre from this mine and everything operating in a satisfac tory manner. Now suppose that he decided to change his source of fibre supply and the fibre came from a deposit in another locality where there was considerable fault ing, and considerable amounts of fault fibre, brucite, picrolite, mag netite, and other minerals. What would happen? First, if he did any re-process ing of the fibre in his factory, such as willowing, he would notice a loss in fibre due to formation of dust or fines caused by the wil lowing action on the fault, fibre, brucite, and minerals present. Second, the fibre, having a total overall lower strength, would have a tendency to lose length during any processing stage. Third, the surface area of the processed fibre would be increased and it would have a tendency to re quire more binding agent. Fourth, the fibre, when wet, would be slimy and difficult to handle. Fifth, the porosity of the fibre would decrease and the removal of water by normal filtration means, either by suctionor by pressure, would be slowed down, thus result ing in a decreased output of the products. Sixth, the strength of the final products would probably show a decided decrease in modulus of rupture. If these changed conditions were suddenly thrust upon the manufac turer, without any forewarning, he would be in a difficult position. Consequently, today, the research chemist studies all of these prob lems long before the manufacturer needs to make the fibre change. He first consults the geological litera ture of the locality in which the fibre occurs and becomes familiar with the rock formations. With this information as a background, he ob tains large representative samples of the fibre and studies its physical properties in the laboratory. This is followed by pilot-plant tests, where products are made under con ditions similar to regular manufac turing procedures. When all of this work is completed he is ready to make a recommendation to the manufacturer as to the value of the fibre and as to whether it can be used successfully, and, if so, what changes in processing will be nec essary. It may be urged that these tests are time consuming and may not be worth the expense, but, if a manu facturer loses production in his factory for any length of time, his financial loss is considerably greater than the cost of the surveys and tests made by the research and de velopment chemist. Future of the Asbestos Industry The asbestos industry appears to have reached a stage where consid erable expansion of output of fibre is necessary. In making this state ment it is, of course, assumed that there will be no displacement of asbestos by other materials in the products for which it has been used in the past and also that the many new developments now in progress will materialize commercially in the near future. The demand for asbestos today far exceeds the supply, and it has been necessary for many producers of asbestos products to curtail pro duction because of the shortage of fibre. The situation has been relieved somewhat as a result of many re finements in extraction at the mills which have made it possible to in crease recoveries and throw away less fibre in the tailing product. Developments in the plastics in dustry in Canada and the United States during the past few years open up an estimated potential --3-- UCC 004678 i djT shortage of. materlalj, to expand iite present $todbet*-ril> '. factory equipment. -in toe Research Center, where' regular products are made on a semi-commercial scale. *Y- edii 200y0tt> ton*. j*f year. The asphalt, til^pmmtryv which uses short asbestos fibre, has shown considerable expansion daring the past few years, and this consump tion may he estimated at 120,000 tons of asbestos per year. There is also an increasing pro -1`CflurcwJsioNs ; .. k. ^ \ T' - .. - , la' concluding, the writer wishes to point out that, i& our' work on asbestos fibres in the Research Ceh- ter, we have set up - a procedure to be followed during our fundamental and development investigations. This plan of investigation includes the following types of approach: . , I toe problem involves very large. L tonna^ of atoestoa i^ - ,T'; is transfer|eK^|P;l tj pilot pWt;'st' ttei^i^;ait';. tos, Qtie,, where large si tion milling equipment to i _ In this manner, we are able- to, follow the fibre from the earliest stages in the crude or mill roci^v"^^ throughout all its investigations in the laboratory and pilot plants, and" duction of asbestos papers,, mill (1) Obtain the complete history of during the time when the fibre is ... boards, brake linings, clutch fac the source of the fibre. incorporated into the final product. ings, pipe coverings, roofings, black (2) Study its physical and chemi This procedure gives the research : line, etc., that require asbestos cal properties. man full responsibility for the re fibres of various grades. The total . (3) Improve the physical or chemi search and development work until amount'of fibre used in these proto cal properties of the fibre so the factory accepts the material and ucts in Canada and the United that it will be better suited for takes over the production job. ' , States might be estimated at 130, its specific use. 000 tana per year.. . . .. (4) Study the processing technique References " Therefore, it may be said that the potential volume of asbestos that could be consumed in Canada and and develop the best method in the' pilot plant' for handling ' - the: fibre and then recommend Allen, M. A. and Butler, G. If., Univ. of Arizona Bull. No. 113, Mineral Technology Series No. 24, the United States might reach, atotal of 450,000. to 500,000 tana per year for the next few year* provided- toe fibre is available and toe asbestos products mannfactu*- the procedure to be followed in : toe factory. - , . ' , (5) After the" preliminary invest!- gationa ',;are completed, the processed fibres are submitted June 1st, 1921, pp. 1-29. '. KEEP, F: E., Geology of Skabani Mix- ' anti Belt; Geol. Surv. Khodia,- BuH. No. 1?, 1929. f- Cooke, H. C., Geol. Surv. Can., No. 12, 1937. . i * ' - '!>+ '-**v *.;.-..V*:' ' *' -...vi.;-. . e-4--' .UCC- 004679 *' A' ; *'v Filterability of Asbestos Fibres Used in Wet Processes By M. S. BADOLLET* [Annual General Meeting, Montreal, Que., April, 1949) [Transactions, Volume LII, 1949, pp. 2(>0-'2(i4) Introduction by mechanical equipment with a minimum reduction of fibre length. THE manufacture of some as The many physical properties bestos products involves the use peculiar to asbestos fibres (1) of asbestos in combination withshould be well understood by the water, cement, and granular fillers. This type of production is often called the wet or semi-wet process manufacturer. They may be briefly enumerated as follows: fibre strength, fibre composition, slimi and requires the use of either pres sure or vacuum to eliminate the excess water in the fibrous blend so that the product may develop the proper strength during the cur ing stage. ness, length, harshness, softness, and filterability or porosity. This last named property is important and it is the purpose of this paper to present some basic studies on filtration as applied to production Asbestos-cement products avail problems. able today are numerous and are a valuable contribution to the build ing industry. Their production in Filtration Studies quantity depends upon the type of The term filtration is used here equipment employed, the speed at to designate the removal of water which it can be operated, and the from a slurry or wet matte of as factors involving the blending of bestos fibre by applying pressure asbestos cement, water, and fillers. or vacuum. Assuming that all mechanical A simple laboratory procedure troubles at a plant have been elim has been devised for accurately inated or are under control, it is still advisable to study the basic properties of the raw materials used in the asbestos-cement products. The type of cement used is an important factor, but usually the manufacturer of the cement is will ing to work with the asbestos de velopment engineer and' recommend the proper type to be used for the product. The source of the water should not be overlooked as a general fac tor involved in the production cycle. Waters containing a high percentage of contamination such as silts, hu mus, or soluble salts may adverse ly affect the setting of the cement or cause a slowing down of the production rate in the factory. Asbestos in combination with ce ment is an ideal material for build ing products. It is inorganic, will not deteriorate, and can be handled measuring the filterability of as bestos in water, or of asbestos in combination with water and ce ment. The apparatus (Figure 1) consists of a vertical bomb or cylin drical iron pipe threaded at each end so that it may be capped. The bottom cap is fitted with a screen and outlet so that the filtration proceeds on this disc of a definite area. The water or filtrate which passes through the filter matte is passed up vertically through a rotometer which accurately measures the rate of flow. Pressure is applied gradually by the use of a pressure regulator so that a constant rate of flow is maintained throughout the filter cycle. Slight agitation is maintained within the bomb by al lowing the entering air to percolate (1) See Badollet, M.S., Research on Asbestos Fibres; C.I.M., Trans., Vol. LI, 1948, pp. 131-134. ^Research Centre, Johns-Manville Corporation, Manville, New Jersey. Figure 1.--Apparatus for measuring the filterability of asbestos. UCC 004680 upward from a point or several' points above the filter disc. This prevents settling of the slurry and allows a gradual deposition of the fibre upon the filter disc. The data obtained by such' filter tests are plotted Of., .co-ordinate paper and the areas" under the curves are measured in square inches so that the values can be compared directly with each other. Procedure is as follows: The top of the filter unit is removed and a small sample of the fibre un der study, made up as a slurry in water, is poured into the bomb and the cap replaced. A low pressure is applied and the entire amount of fibre in the bomb is allowed to deposit on the filter disc or leaf to form a thin pre-coat. A larger sample of the fibre is now made up as a slurry and placed in the bomb for the actual test. By means of a pressure regulator, the float in the rotometer is maintained at a standard rate of flow {in terms of c.c. per minute). The pressure is continually applied so that the flow rate is kept constant. Pressure read ings are recorded every 30 seconds and the pressure values are plotted against time in order to present the data graphically. Table I--Effect of Asbestic Fines Area Designation (See Figure 2) Percentage of Fines in Sample E.................. D................ C -1- D................ B + C +D.......... .. A + B + C -f- O. 0% 10% 20% 3U% 40% Area Under Curve at 6 Min. 10.326 sq. in. 12.148 sq. in. 15.989 sq. in. 22.655 sq. in. 27.373 sq. in. Percent Decrease in Porosity Due to Presence of Fines _ 17.64% 54.84% 119.40% 165.10% Calculation (example): 12.148 - 10.326 X 100 10.326 17.64% ence of asbestic fines is objection able sinee they adversely affect the filtration characteristics of an as bestos fibre. The manufacturer ob jects to the presence of asbestic fines because they slow down the wet process machines and also in crease his overall fibre losses by as slow filtering, poor saturation, and increased density, and, finally, will give a brittle product. Effect of Temperature of Water In many wet processes, the water temperature is an important fac tor and production rates can be in creased by taking advantage of this fact. A series of four tests were con ducted at temperatures (F.) of Effect of Asbestic Fines A quantity of commercial asbes tos fibre was first cleaned to re move all dust, rock, and asbestic fines. This clean fibre was then set aside for the filtration studies. The asbestic fines or dusts used in these studies were obtained from an asbestos-mill dust house. A micro scopic examination of the dust showed that the particles ranged in size from 0 to 40 microns and were of irregular shape with practically no fibrous structure. , Blends of these f*W*` with the clean fibre were madfe vp, contain ing, respectively, 10, 20, 30 and 40 per cent fines. Filtration studies were made on each of these blends and also on the clean fibre. The results of the tests are given in Table I and are shown graphically in Figure 2. The data, when plotted graph ically (Figure 2), give typical fil tration curves and from these we are able to measure the area under each curve and calculate the effect of the fines upon filtration. It will be quite evident from in spection of Figure 2 that the pres- msSI 4, .KearJSM):* Figura 2,--Effect of fines on filterability of asbestos. passing through the equipment screens into, the waste water. It is known that commercial fibres contain various amounts of admixed asbestic fines and that, if these form a high percentage of the total fibre mass, they will cause serious manufacturing troubles such Figure 3,--Effect of water temper` attire on filterebility of asbestos. 50, 72.5, 86 and 122. In each case the same fibre was used, so that the only variable was the tem perature of the water. The results of the tests are pre sented in Table II and, graphically, in Figure 3. Table II.--Effect of Water Temperature Temperature F. Area Under Curve at 6 Min. 59................................................ ....... 72.5"..................................................... 86.................................................. ... 122........................................................ 25.918 sq. in. 21.629 sq. in. 18.481 sq. in. 13.295 sq. in. Increase in Filtra tion Rate 16.6% 28.9% 48.7% Calculation (example): 25,918 - 21.629 X 100 25.918 16.6% UCC 004681 These, tests show that, by in Table III --Effect of Serpentine Rock creasing the water temperature, it is possible to remove the water from an asbestos fibre slurry in a shorter Screen Size of Rock Calc. Specific Area Under Surface Area Curve at 6 Min. Improvement in Filtration ' time and thereby give the manufac turer an opportunity to increase his production rate. In some plants, warm water is used SO as to gain 0................. - 8+10 mesh....... -- 10 + 14 mesh____ - 20 + 35 mesh....... __ 11.8 cm2/gm. 16.8 cnWgm. 37.4 cnWgm. 28.9 sq. in. 14.8 sq. in. 11.8 sq. in. 9.0 sq. in. 48.8% 59.2% 68.8% this added advantage. -- 65 + 100 mesh....... 154.0 crua/gm. 16.1 sq. in. 44.3% . - 150 + 200 mesh....... 294.0 cma/grn. 17.6 sq. in. 39.1% Effect of Serpentine Rock of Different Sizes Serpentine rock relatively free from asbestos was ground in a ballmill and screened for size by siev ing on a rotap apparatus. A con stant weight of each screen fraction was then added to a constant weight of asbestos in order to determine which size is the most effective in improving filtration. The assump tion was made that the rock par ticles were perfect spheres and that the average diameter of each particle was the average of the screen open ings, Although it is realized that this involves a certain amount of error, the method does give a rough comparison of the specific surface area in terms of cm2 per gram. Calculation (example): 28.9 - 14.8 X 100 28.9 48.8% upon filtration and upon the qual ity of the manufactured products. A quantity of crudy fibre was selected and fractions of various screen sizes were separated on a rotap apparatus so that a constant weight of these bundles could be added to a constant weight of fibre. greatest effect upon speeding up the filtration properties of an as bestos fibre (see Table IV and Fig ure 5). As the surface area of the bundles increased, the tendency was for filtration to be slowed down, thus indicating that, if all the bundles were completely opened, It was found that, of the several screen sizes of serpentine rock used in the tests, the most effective in improving the filtration characteris tics of the asbestos fibre was the --ifO-f-35 mesh material. The larg er sizes apparently do not give as good a porous structure to the fibre, and with the smaller sizes, also, the filtration rate is lower, due to decrease in the porosity of the fibre mass (see Table III and Fig ure 4). Figure 4.--Effect of rock particle* on filterability of asbestos. Figure 5.--Effect of crudy fibe bundles on filterability of asbestos. Although the presence of some suitably sized serpentine rock is beneficial in improving the filterability of asbestos fibres, care must be taken not to use an excessive amount, which would adversely af fect the physical structure of the asbestos-cement products. If the percentage of grit : dr serpentine rock exceeds that normally present in commercial grades of asbestos, then the asbestos-cement products will have lower strengths and in creased densities. Effect of Crudy Bundles or Pencils Milled fibres as sold to custom ers frequently contain crudy bundles that are not properly fiberized. Tile presence of these bundles, if not further opened by re-processing, will have certain adverse effects In this case it was necessary to make the assumption that the fibre bundles were perfect cylinders. The lengths and diameters of these bundles were measured under the microscope and then averaged for each screen fraction. The erndy handles with the small est specific surface area had the the filtration rate of the fibre would approach that of a normal fibre and would be classed as slow. Screening of the crudy bundles on the 10 mesh screen indicated that the grading for size was not ac curate, as the specific surface area of these bundles should have been between 102 and 127 cm2 per gram. Table IV.--Effect of Crudy Fibre Bundles Screen Size Original..................... -- 4+ 8 mesh......... --10 + 14 mesh......... -14+28 mesh......... -- 28+35 mesh......... Calc. Specific Surface Area 0 102.0 ems/gm. 168.0 cmj/gm. 127.0 cma/gm. 164.0 cm2/gm. Area Under Curve at 6 Min. 28.9 sq. in. 7.1 sq. in. 9.4 sq. in. 11,6 sq. in. 13.2 sq. in. Improvement in Filtration -- 75.5% 67.5% 59.8% 54.3% 28.9 - 7.1 X 100 Calculation (example):--------------- -----------------= 75.5% 28.9 UCC 004682 f'tJs*$/nnatrift;' li microns) general trend Sad indicate a decrease' in the fibre lynidie, cross-section. . As shawm;,) 5, thfe* " creased tb&i did the Uy in Figure hnndlea in ! rate more than bundles. From the vfdlkpbiiit of the manu facturer, the presence of the crudy fibre bundles would be considered Identification Filter- v . ' CURVE, ' Area. Under i ABILITY (Figured! , , Curve. (Can. soft - 1 V n : AT 4 Mm. .. ,/ - 100%) , Arizona soft:...___ ...... Canadian soft............ ............... . Italian slip----- ----------- ................ Cyprus.......................................................... Canadian semi-harsh.................................. Arizona harsh___`........ ............................... A. - C ' &50sq, m. D 6.40sq. in. F 3.30-aq. in. E ' 1.78 sq. in. B 0,24 sq. in. 37.6% : 100.0% 124.7% 161.2% 179,0% 197.2%. satisfactory -- particularly if he did any reprocessing -- as he would have more effective fibre present to compare the curves we have taken . harshness, the fibre will filter fast in his product. It might even en the Canadian soft fibre as the er. able him to reduce the quantity of standard. By this method we are fibre used and make a superior product at a reduced fibre cost. However, the presence of crudy fibre bundles has a detrimental ef able to express the filterabillty of each fibre as a percentage, with Ca nadian soft fibre taken as 100 per cent. Since the Arizona soft fibre Application of Technological In formation to Manufacturing Processes fect in some products because they was so slow filtering it was impos The importance of the filtration impart a rough surface, and any sible to measure the area of its curve characteristics of asbestos fibres subsequent sanding or polishing at the end of six minutes. As a con should not be overlooked by the would result in the product having sequence, the area measurements in manufacturer of asbestos products an uneven texture. these tests were all made at the end which are made by wet or semi-wet methods. In, the manufacture of. Fibres From Different Deposits paper, millboard, shingles, pressed For these tests, samples of as bestos crudes from a number of sheets, or pipe, the ease of the re-.. moval of die water will t$ a cer tain extent affect the production sources were carefully processed so as to avoid contamination with par ticles of the wall-rock, and, after a preliminary opening by hand, were passed through a laboratory-type rate.- If a fibre is difficult to de water, then the manufacturer eith' er changes- hi* process mechanical ly, changes his grade of fibre, or uses some fibre blend that will al micro-pulverizer so as to obtain fibres of approximately the same size. The pulverized fibres were low him. to maintain the production rate.".".,;,.,,; \ ... ' . . .' measured under the microscope and By adding a fast filtering fibre were then tested for filterabillty. to a slew filtering fibre it is poa- The cross-section measurements indicated that, for each prepared sample, the widths ranged from 1 to 5 microns and the lengths from 10 to 200 microns. sible to step Up production rates, but the manufacturer must be csre-J fal not to~ overdo . this mixing for fear of Ibshig strength in the prod- uct, ,. ... . . .., . Figure 6 shows graphically the' results of filtration tests. The slow est filtering fibre tested !* die.' Arizona soft fibre (curve A). The Figure 6.--Filtration characteristics . .. of chrymtiU fibre from various V- tocaHtwi. ,,/ prepared Canadian sofk fibre (curve C) is-j of four1 minutes Instead of six, min the Arizona The Italian utes. ' _ " ' ; / slip chrysotl%*j filtering th fibre. i D) is faster Canadian soft On thin basin. of comparison, the Arizona soft fibrin (curve AJ is 62.4 per cent slower filtering, and the It fa usually considered ' thatr *; fibres ranging, from semi-fcarshto harsh <rc fast, filtering and like wise that the fibre strengihdeereaaes with its degree of harshness.- Therefore the manufacturer must exetcisecare in selecting his fibre, or the ratio of.soft to. harsh fibre inhis fibre blend must be well plain#, ned, in order to obtain the best fibre for bis particular process. The Cyprus ehrysotile (curve F), which has a semi-harsh feel to the hand, would be considered fair ly fast filtering in comparison with the other soft fibres. Curve E rep resents a typical Canadian semi- harsh fibre and it would be consid ered fast filtering. Curve D was ob tained for a very harsh fibre from Arizona; this is extremely fast fil tering. Italian slip fibre (curve X>) is 24.7 per cent raster filtering, than die Canadian soft fibre (curve C>. For the Cypres, Canadian semi-harsh, and Arizona harsh .fibres, the filtra tion rate is faster than for the soft ehrysotiles. ' A physical examination of each of these fibres would, show that the softer and silkier a fibre, the more difficult it Is to filter. As the soft ^ At the present time. United Stater? manufacturers of asbestos products ; who employ the wet or semi-wet process .consume approximately' 340,000 tons of asbestos per year.' This- includes approximately 11,000 tops.'of fibres: from countries other than Canada and the United States: This immediately raises the question as to why these foreign fibres are used. ,'Would they be used if Can- . The area measurements of each ness of texture decreases and the ads 'could supply the total tonnage curve are given in Table V. In order fibre assumes a certain degree of required ? The answer to this ques- 8-- -- . UCC 004683 tioii i0 not so much concerned with the availability of the fibre as with the particular physical properties of the foreign fibres that give the manufacturer the effects desired in his operations. These foreign fibres have the required free filtering properties and at the same time have strength. They also give the manu facturer sufficient latitude for blending, so that he can sweeten his slow filtering fibres with strong fibres that are fast filtering. Conclusions (1) The presence of asbestic fines or shorts decreases the filterability of a fibre mass in proportion to the of fines or shorts present in the mixture, (2) By increasing the water tem perature it is possible to increase the filterability of a fibre mass and thus improve the operation of the process. (3) The presence of serpentine rock will increase the filterability of a fibre mass provided the rock is not too small in particle size. In the tests made, --20-)-35 mesh ma terial gave the maximum improve ment in filtration; with smaller sizes, the filtration rate began to decrease, due to decreasing poros ity of the mixture. (4) Crudy fibre bundles will im prove filtration. As the cross-sec- tibn of the bundles is decreased, the filtration rate is slowed down. The presence of large quantities of crudy bundles may also affect the surface texture of the [ product, a factor which must be taken into con sideration. (5) Fibres from different depos its show considerable diversity in filtration characteristics. Soft, silky fibres are difficult to filter; semiharsh to harsh fibres filter easily. (6) By knowing the filtration characteristics of different fibres it is possible to select those that fil ter rapidly or to blend fibres to obtain the desired filtration results to fit the manufacturing process concerned. s *t t ) r i - !. ei 1