Document zdOywrB5Gz4pXQG1zqr3kyN2R

Asbestos Floats By AT. S. BADOLLET* {Ottawa General Meeting, January, 1952) {Traniactions, Volume LV, 1352, pp. 185-189) Introduction sbestos floats may be A defined briefly as blends of airborne particles of fibrous asbes tos and dust produced during the milling stages and collected by Cot trell precipitators, dust sheds, or bughouses. The various grades of asbestos floats on the market contain fi brous asbestos particles ranging in length from microscopic to approx imately ^4-inch, The fines or dusts present in the floats are from 40 microns to 2 microns or less in cross section. Airborne asbestos particles are of diverse length because they are collected at numerous places in the mill. There are: (1) dusts removed from dry rock storage bins, (2) dusts removed from rock and fibre screens, (3) particles from the tops of collectors, and (4) fines removed by suction from the processing equipment. Sometimes the airborne particles are kept segregated, so that there is a partial separation by gravity. This is accomplished by a series of dust chambers enclosed in a long, rectangular building. The longest and heaviest particles fall nearest to the air flow entrance, the small * Research Center, Johns-Manville Corporation, Manville, New Jersey, U.S.A. est at a point farthest away and nearest the exit. Sometimes the air from the dust chamber building is passed through a series of baghouses or electric precipitators to collect the extremely fine particles which normally escape to the at mosphere. In other instances, the airborne particles by-pass the dust chambers and are passed through rows of bag collectors. Regardless of the method of col lecting the particles, the milling de partment must select proper fibre sizes for blending, producing uni form floats to meet the requirements of the trade. Sometimes one grade of float can be used successfully in many com mercial products; in other cases, great care must be taken to pro duce a float for use in a specific product. The present total production of all grades of Canadian floats ap proximates 40,000 tons per year and it is possible that this quantity may be greatly increased by the proposed expansion programmes now going into effect in Canada. Since floats are valued at $40 per ton at the Canadian mines, a tonnage of 40,000 has a potential sales value of $1,600,Q00. This di vision of the asbestos industry is a good business, and it is well worth the concentrated effort of research and development engineers to find new uses, and so expand the mar ket, for all available floats. Physical Properties of Floats According to the Quebec Screen classification, there are two general classes of floats, known as 7RF and 7TF. Samples of various commercial floats were obtained on the market and a series of tests were devised to determine the differences in their physical properties. Some of these tests were similar to those made by many manufacturers who use floats in their products. The results of some of these tests are given in Table I. They do not, however, in clude the official Quebec Screen test. Manufacturers using floats usually set up their own specifica tions, based upon requirements for their particular products. Loose Density The loose density of floats can be measured by slowly sifting the pow der into a can or container of defi nite dimensions so that the weight per cubic foot can be calculated. Although in some products the loose density of the floats is not par ticularly important, in others it is critical, so each float must be considered as an individual case. In the present investigation eleven 7RF floats were tested and their loose densities were found to range Table I Identification (1) 7RF. .. . (21 7RF.... (3) 7RF... . (4) 7RF.... (5) 7RF... . (6) 7RF.... (7) 7RF... (8) 7RF... (9) 7RF.... (10) 7RF. . .. (11) 7RF.. . (12) 7TF___ (13) 7TF. . . (14) 7TF.. . Loos: Density !b./cu.ft. 19 20 21 22 22 24 24 20 25 23 14 23 23 26 Material +100 M % 3 4 4 4 3 5 5 6 7 7 1 2 2 3 Fines -200 M % 96 93 93 93 95 90 89 91 84 88 96 96 95 91 Grit +48M % 0.04 0.14 0.24 0.16 0.12 Tr. 0.06 0.12 0.24 0.46 0.04 Tr. 0.06 0.00 Whiskers +48 M % 1.90 2.50 2.26 1.30 0.80 1.16 1.28 4.12 0.70 2.38 0.50 0.30 0.60 0.10 Grit -48 M +80 M % 0.02 0.14 0.12 0.20 0.10 0.04 0.10 0.56 0.46 0.54 0.02 Tr. 0.06 Tr. Whiskers -48 M +80 M % Oil Adsorption c.c./g. fiber 0.04 0.66 1.18 0.94 0.46 0.96 1.12 1.10 1.30 0.92 0.84 0.66 0.74 0.75 0.68 0.65 0.68 0.71 0.66 0.65 0.65 1.05 0.50 0.70 0.16 0.75 0.65 0.68 -- 25 -- UCC 004648 - friim 1-r tfl zirpotnwB per cu. ft. 0rtt +48 Mesh per cent (No. 9). Tlie heaviest is No, & and the light est No. 11. Nos. 1 to 5, inclusive, and No, 8, all withloose densities between 19 an<i2$ pounds per cubic foot, may be etnt#deied as falling within the saOae/i#|^e, as also may Nos. 6, 7, &, which are slightly heaviest* (8 to 26). Float No. 11 is in a class by itself and is light in weight as well as bulky (loose density 14). If density were tiie only physical property that had to be considered, this record would enable the manufacturer to select the proper one for his purpose. The three TF floats included in the Table differ from the RF floats in degree of particle fineness. Nos. 12 and 13 have identical loose den sity (23) while No. 14 is heavier (26). ' Classification by Wet Washing Fibre and Grit -|-I00 Mesh A classification of the particles can be obtained by a wet-washing method which determines the amounts of fibre and grit plus-100mesh and of fines minus-200-mesh. This information is particularly use ful if the floats are to be used in molding, extrusion, or spraying. The RF float No. 11 contains only 1 per cent of material larger than 100 mesh. In the other RF floats, the content ranges from 3 to In many cases, the grit particles in the floats are of very diverse size. Usually, they are small pieces of serpentine rock and magnetite, or small bundles of asbestos fibre. Complete classification, therefore, requires a further breakdown to de termine the quantities of these ob jectionable particles present in the floats. This test is made by water eiutriation and by careful separation of the grit from `whiskers' of fibre bundles. The amount of grit plus-48-mesh in the eleven 7RF floats ranges from a `trace' to 0,46 per cent. The percentage is lowest in samples. Nos. 1, 6, and 11 and highest in No. 10. Although these quantities of grit seem small, they could cause considerable trouble in a manufac turing process by plugging extrusion apparatus or scoring the walls of expensive molds. The three TF floats are almost free from grit plus-48-mesh. 'Whiskers' +48 Mesh `Whiskers' are short asbestos fi bres that may be valuable or ob jectionable, depending upon the use for which the product is required. The quantity of whiskers in the eleven RF floats ranges from 0.60 per cent (in No. II) to 4.12 per cent (in No. 8). In the TF floats, figures for the TF floats are a low of 0.16 per cent (No. 14) and a high of 0.70 per cent (No, 13). In the manufacture of plasties, the presence of whiskers results in non-uniform pourability of the molding powders. This , necessitates * a re-screening operation so that, ' uniformly coated powders will prop-'+i erly fill the molds. In many ease*,'' the whiskers and erudy fibre bun-' dies are not thoroughly covered by.,, the organic plastic material and).;>1 this increases the water absorption properties of the plastic material, which may result in the formation /-' of blisters. Oil-Adsorptive Capacity The capacity of a float to adsorb oil is important because it gives an , indication of ability to hold an or ganic liquid when manufacturing a plastic or caulking compound. This test, made by manufactur- : ers, consists of titrating a given weight of float with oil until its , - adsorptive capacity is reached. In practice, the adsorptive capacity is considered to have been reached;1 when oil can be released from a ball of the thoroughly mixed float and, oil by applying a small amount of pressure against it. The results of this test are expressed in terms of cubic centimeters of oil per gram of float. j 7 per cent, indicating the presence the range is from 0.10 per cent (No. For the eleven RF floats tested,' of material that is sometimes re 14) to 0.60 per cent (No. 13). the oil adsorptive capacity ranges ferred to as `whiskers'. In the plas from 0.65 to 1.05 cubic centimeters V tics industry, particles plus 100 mesh may be helpful in producing impact strength in the product. The three TF floats contain al most identical amounts of plua-10O- mesh material. In two of them the percentage is lower than in the first ten RF floats. ' Fines ~-209-Merk ' /3++" The fines n^S^tfO-mesh in the RF floats range84 to 00 per cent, and in the TF floats from 91 to 96 per cent. The material between pins 100 mesh (fibre and grit) and minus 200 mesh (fines) would be collected on the 200 mesh screen. Its amount can be obtained by adding the plus Grit --48 Mesh +80 Mesh In some special products, the presence of grit smaller than 48 mesh, and even smaller than plus 80 mesh, is considered objection able. Therefore, a further separation is made to determine the quantities of this grit that may be present in these floats. As shown in Table I, the range for the eleven RF floats tested is from 0.02 per cent (Nos. 1 and ll) to 0.66 per cent (No. 8). Two of the TF floats are free from this size of grit and the third (No. 13) contains only 0.06 per cent. `Whiskers' --48 Mesh +80 Mesh per gram. The valne for No. 11 (1.06 c.c./gm.) is much higher than I that for any of the others, which all fall between 0.65 and 0.6$; ; c.c./gm. except Nos. 2, 3, and 7' (0.71 to 0.75 c.c./gm.). Two of the TF floats. Nos. 18 and 14, have closely similar adsorp/./ tive capacity, 0.65 and 0,68 c.c./gm., respectively. No. 12 gave a higher - value (0.75 c.c./gm.). \ Miscellaneous Physical Tests ' Numerous other tests, of import ance to the manufacturer of certain asbestos products, are made on; floats. Data for these are given, in Table II and are summarized in the following paragraphs. 100 mesh and minus 200 mesh val ues shown in the Table and sub tracting the sum from 100. Tiiis test, although useful, does not distinguish between, or give the The presence of whiskers in the sizes of minus 48 mesh and pins 80 mesh is also objectionable because they affect the surface of certain products. Surface Area Study of the surface area of each float was made to obtain data on its covering power as a filler. In this relative amounts of, `whiskers' (as The eleven RF floats tested con test, the surface area is measured bestos fibres) and particles of grit tain whiskers of this size ranging by the air permeability method by that might be present in the floats. from 0.46 per cent (No. 6 to 1,30 means of the Bowen apparatus, fol- -26- UCC 004649 Tablb II IDENTlFfCA- TION SCHVACE Area Density lb. /cu. ft. Compressibility* % Thickness at 200 Compress. Springback, % Thickness at Max. Co MPRESS. cm2 ,'gm. 2,000 3,000 p.s.i. 2,000 p.s.i. 8,000 p.s.i. 2,000 p.s.i. 2,000 p.B.i. <l) 7RF 14,300 80.9 94.7 29 32 2.5 2.8 (2) 7RF 11,300 (3) 7RF 13,000 (4) 7RF 11,800 93.6 93.5 96.5 97.0 99.2 99.1 28 28 29 32 3.1 3.7 32 3.2 3.3 32 3.3 3.4 (5) 7RF 13,000 95.0 98.2 28 31 2.6 3.4 (6) 7RF (7) 7RF i'8) 7RF (9) 7RF (10) 7RF an 7rf 14,000 13,900 12,500 7,500 8,600 20,800 100.0 100.8 102.7 99.6 101.2 93.6 105.4 105.2 107.7 105.8 105.8 99.2 28 28 28 27 28 35 32 3.8 4.0 32 3.4 4.0 32 3.6 4.2 31 3.4 3.9 31 3,0 3.4 39 5.8 6.7 (12) 7TF 15,400 U3) 7TF 11,300 (14) 7TF 15,600 95.0 94.8 96.0 100.0 99.4 99.5 27 27 27 31 3.3 3.7 30 3.5 3.3 29 3,3 3.3 SUPP.COND. of Pressed Specimen Sm'l whiskers & bunndles Gri/t& few whia, & bund. Sm'l amt. of grit & wish. Good smooth ** Grit mostly Good Surface Good surface Large grit Good surface Ionjzable Slats, mhos / cm (10 volts 219 218 222 206 212 379 393 421 190 243 260 221 176 396 Dry Bulk, Vol. OF 100 g. ce. 350 335 340 305 300 320 295 360 255 285 475 295 290 275 Water-SiDLUBLE Solids % 0.16 0.17 0.16 0.17 0.36 0.38 0.26 0.12 0.14 0.16 0.15 0.14 0.36 Chlo rine as Cl % Mag netic Rating* 0.017 4.7 0.029 0.025 0-022 6.3 6.1 6.0 5.7 * 4.1 0.0015 0.022 0.0034 0.16 3.4 3.9 ^Measurements start at 200 p.s.i. aa zero point. lowing the Lea and Nurse tech nique (I). The eleven RF floats tested show a wide range of surface area, from 7,500 cnv/gm. (No. 9) to 20,800 cm'/gm. (No. 11). In other words, float No. 9 has the lowest, and float No. 11 has the greatest, covering power as a filler. In plastics, the surface area of the float governs the amount of filler that can be used successfully prior to pressing in a given mold. Two of the three TF floats (Nos. 12 and 14) have the same surface area, approximately 15,500 cm'/gm. For No. 13 the value is 11,300 cm'/gm. The high value of 15,500 for Nos. 12 and 14 indicates the presence in these floats of a large percentage of fines. Density at 2,000 and 3,000 p.s.i. Ten-gram samples of each float were subjected to pressures of (1) 2,000 p.s.i. and (2) 3,000 p.s.i. and their densities calculated in pounds per cubic foot. These pressures were selected because they correspond to the range of pressures used in the plastic-molding industry, and the data obtained are helpful in select ing the proper asbestos filler for molding powders. At 2,000 p.s.i. the densities range from 89.9 lb./cu. ft. (No. 1) to 102.7 lb./cu. ft. (No. 8). Several of the samples have substantially identical density, but for the gToup as a whole the differences in density are such as would influence the selection of the filler to be used for certain products. At 3,000 p.s.i., the densities range from 94.7 lb./cu. ft. (No. 1) to 107.7 lb./cu. ft. (No. 8), The in crease in density for the additional1 (1) For references see end of pa per. 1.000 p.s.i. pressure ranges from 3.2 to 6.2 lb./cu. ft. Compressibility of Floats at 2,000 and 3,000 p.s.i. In this test, a 10-gram sample of the float is compressed at 200 p.s.i. and its thickness measured. It is then compressed at (I) 2,000 p.s.i. and (2) 3,000 p.s.i. and its thickness again measured. The re duction in thickness, expressed as a percentage, gives a measure of the compressibility for each float. Thirteen of the fourteen floats test ed show about the same percentage of compressibility (27 to 29). For No. II, the value (35) is appreci ably higher. This is an important property and must be taken into consideration when pressing a molding powder to a definite size after the molding cavity has been properly filled. Uniform compressibility is impor tant as a bulky fibre will also ex hibit poor dimensions after press ing. Springback After .Release of Pressures The amount of 'springback' of a molding powder is another im portant property considered by plastics manufacturers. If the springback is too great, it will be difficult to obtain the proper di mensions for a molded product. Too much emphasis' cannot be placed upon this property. All fourteen floats were tested for springback at pressures of both 2.000 and 3,000 p.s.i. As will be noted from the data in Table II, the springback factor is uniformly low for all of them except No. 11 which, also, is the sample with the highest percentage of compressibil ity. To use float No. 11, with a springback of 5.8 and 6.7 per cent, allowance must be made for its com pressibility or the plastics manu facturer cannot control the di mensions of his product. Surface Condition of Pressed Blocks The surface characteristics of pressed blocks of the floats are noted in Table II. The surfecas usual ly show long `whiskers', short stub by fibre bundles, and grit, which generally are considered poor prop erties from the viewpoints of ap pearance and water adsorption. A smooth surface is desirable, provided the molded product meets all other specifications of the manu facturer. Five of the floats give good smooth surfaces and probably will be satisfactory for use in mold ing powders, provided other proper ties are acceptable. Ionisation Salts For the manufacture of some spe cial types of molding powders, it is essential that the asbestos fibre have low electrical conductivity. In this case, some plastics companies make a test on water-soluble material leached from floats. Apparently, all floats contain a certain quantity of water-soluble material. Its conduc tivity is determined, and the re sult of the test is expressed in terms of micromhos per centimeter per 10 volts. For the eleven RF floats tested, this factor ranges from 190 (No. 9) to 421 (No. 8). For the TF floats. Nos. 12, 13, and 14, the values are, respectively, 221, 176, and 396. It is not known at present which values are objectionable, but it ap pears that a conductance of 300 mi cromhos or higher per centimeter -- 27 -- UCC 004650 per 10 volts may cause trouble, with the molded plastic product having a low dielectric strength. Dry Bulk The bulking values of floats are sometimes considered Important fac tors in plastics as well as in drywall joint fillers. By some manufacturers, the bulk ing value is expressed as the vol ume, in cubic centimeters, of a given weight, say LOO grams, of the float. Some fillers should have high drybulk value while others should not; this depends entirely upon the in tended application. The eleven RF floats have dryhulk values ranging from a low of 255 (Vo. 9) to a high of 475 (No. II). For the three TF floats. Nos. 12, 13, and 14, the values are, re spectively, 295, 290, and 275---dif ferences that may lie within experi mental error. Water-Soluble Material All floats were analzed for wat er soluble materials by allowing a sample of each to stand in distilled water for 03 hours and filtering off the clear water. Aliquots of the fil trates were dried and weighed to determine total solids, and these were then analyzed for chlorides. The amount of water-soluble ma terial in the eleven RF floats ranges from 0.12 per cent (No. 9) to 0.38 per cent (No. 7). In the TF floats the range is about the same, with a maximum of 0.36 per cent for No. 14. No good correlation exists be tween the ionizable salt values and the quantity of water-soluble mate rial. The percentage of chlorine in the residues also was determined. For the eleven RF floats it ranges from 0.0015 to 0.16 per cent, and for the three TF floats from 0.0034 to 0.16 per cent. Magnetic Rating Since many floats are used as fil lers in products employed by the electrical industry, it may be impor tant to learn something about their magnetic ratings. The test, an adap tation of the Mapes (2) test, meas ures the amount of magnetic pres ent. Ratings of the eleven RF floats range from 3.4 (No. II) to 9.6 (No. 10). The other nine RF floats have ratings between 4.1 to 52? with an average of 5.4. The three TF floats range from 3.9 to 5.0, averaging 4.3. The maximum magnetic rating value for a successful float is not known precisely, but it is believed that the manufacturer would prefer the lowest rating available. It is known that the smallest trace of magnetite can be easily detected in a magnetic field and it may result in the rejection of the plastic ma terial. Use of Asbestos Floats Asbestos floats have a definite use in such industrial products as automobile body coatings, adhesives, caulking compounds, dry-wall joint filler, lubricating greases, asphalt and cold-water paints, plastics, molding powders, welding rods, in secticides, radiator scaling com pound, acoustical plasters, cements, and many others. Asbestos floats offer to manufac turers the advantages of being a low-cost inorganic filler, which will improve impact strength and pro vide good workability, good binding qualities, heat resistance, fair acid and alkali resistance, large surface area, and availability in commercial quantities. A recommendation for the best grade of asbestos floats for a par ticular product should be made care fully, since each product has its own requirements and specifications. Automobile Body Undercoating A float for automobile body coat ing to be applied by spray gun may require the absence of `whiskers' and large particles of gTit. If the coating is to be applied by brush, however, the presence of whiskers and grit would not be objectionable. Therefore, the selection of a float for this job depends upon the meth od of application and such other factors as bulk and fluidity when incorporated in a binder. Adhesive* The use of floats in adhesives depends upon the type and appli cation of the adhesive product. The proper recommendation can be made only after knowing the desired prop erties of the adhesives and the meth od of application. The amoont of floats in adhesives (3) varies be tween 9 and 40 per cent of the mix, depending upon the product. Caulking Compound* Caulking compounds may be sen sitive to changes in grade of floats. For example, a gun grade of caulk ing compound may require a float relatively free from whiskers and grit, while, for a caulking compound applied by knife, a float containing whiskers and some grit could be used. In general, the use of floats in caulking compounds (3) may range from 4 to 15 per cent by weight of compound. Wall Joint* The manufacturer of dry-wall joint filler is very careful in his selection of floats. His specifica tions for asbestos fibre are rigid and he insists upon good bulking value, freedom from grit, good cov erage, and no whiskers. Very few natural floats on the market today fulfill these requirements and, therefore, a special float must he made for this job. The amount of floats (3) required for this use may vary between 5 and 20 per cent of the dry mix ready for the market. Lubricating G reate* ' Various types of floats have been used in some grades of lubricating greases, but in most greases grit is objectionable. Whiskers may be permitted unless the customer's spe cification indicates otherwise. The amount of float used in greases var ies between 10 and 25 per cent of the product (3). Paint* Paints, with either asphalt or cold-water base, may require a gritfree and whisker-free float if smooth surface is demanded- Other wise, some grit and whiskers are allowable. Paints may contain from 5 to 11 per cent of floats. Plastics and Molding Powder* Floats, with specifications vary ing from customer to customer, are used extensively for plastics and molding powders. The general opinion of the plas ties manufacturer is that fibrous float structure increases impact strength, allows a wide range for adjusting quantity of floats as filler, furnishes good binder retention and workability, imparts hardness and toughness to the moldings, increases heat and fire resistance, reduces natural shrinkage of resins and binders, reduces warpage and de formation, makes cold-molding pos sible by controlling the flow under pressure in the molds, allows blend ing of mineral and organic fillers, imparts good finish, improves the -- 28 -- UCC 004651 .... 7? 7r "v , njtv; '?*: b- *;; , \. electrical propertied and reduces' the cost of moldings. Molded plastics are carefully checked for specific gravity, flex ural strength, tensile strength, com pressive strength, impact' strength, water absorption, diefcctfic .strength. power factor, shrinkage, heat re sistance, visual observations of molding qualities, and ejection from the mold. It is important, therefore, that the plastics manufacturer select asbestos floats with care so that molding powder and molded prod uct have the desired properties. The asbestos floats used as a filler in these materials generally form from dO to 80 per cent of the mix (3). JVelding Hods The welding rod manufacturer desires a float wliich will produce good coating as a filler, and which lacks whiskers and. grit that might clog extrusion equipment. Floats also should be free from any sul phide mineral, or at least should contain less than the 0.01 per cent of sulphur that would produce ob noxious gas during welding. The amount of floats used for coating rods varies between 8 and 10 per cent*. Insecticides Floats sometimes are used as fill er for insecticides to be dusted or sprayed onto flowers, weeds, and other plants. In this case, the float should be a fine dust so that it will impart large coverage. Floats for ffi'RV-Ci 1 - J' this purpose must compete with such other powders as talc and diatomaceous earth. The amount of float in a ready-to-use insecticide is approximately 4 to 5 per cent. Radiator Sealing Compound Various combinations of mate rials, including fine asbestos, are used in sealing compounds for au tomobile radiators. The asbestos forms from 1 to about 6 per cent by weight of the solids content of the mixturet. Acoustical Plasters Based upon the weight of the dry compound, some acoustical plasters contain from 6 to IS per cent of asbestos floats. In this ap plication, the floats function as a filler to provide bulk and fire re sistance. Whiskers and grit are not objectionable unless a spray gun is used. Cements Cements and adhesives are con sidered similar by some authorities, and the amount of floats needed for adhesives would apply also to cements. Depending upon the type of cement and the application, the asbestos floats content ranges from 9 to 40 per cent (3). In many cases, whiskers and grit are permitted. r- Conclusions (1) Fourteen asbestos floats pro duced in Canada have been exam ined in tests similar to those made '"British Patent 535,355; Canadian Patent 365,792. tU. S. Patents 2,391,737, 2,315,321. by customers in their own labora tories. (2) Many of these floats have almost identical characteristics; however, one float, No. 11, differs considerably from all the others and has many unique properties. (3) . The type of float required for a particular product depends upon the use for which the product is manufactured, and each manu facturer has his own specifications and methods for testing the float, (4) Float characteristics such as grit, whiskers, compressibility, springback, and magnetite rating are usually carefully checked by the plastics manufacturer, since these qualities affect bis products. (5) Bulk, surface area, and den sity values of floats are considered important factors in such products as wail joint fillers, caulking com pounds, some pressed products, and acoustical plasters. (6) The amount of ionizable salts, water-soluble solids, and chlorides in the floats is a matter of importance and frequently is checked by plastics manufacturers interested in improving the elec trical properties of their products. References 1. Lea, F, M,, and NURSE, R. W., Specific Surface of Pine Powders; Soc. Chem. Inc., Trans., Sept., 1939, pp. 227-283. 2. A.S.T.M., Standards for Textile Materials, D118-50T, Oct., 1950, pp. 197-202. 3. Bennett, H., The Chemical Form ulary, Vol. IX, 1951. HENLEY, Normann, Henley's Twen tieth Century Book of Formulas, Processes, and Trade Secrets, 1947. -29- UCC 004652