Document 6R1J8GjL2nmDeEG2RXM368yE3

1, & 11 H'*^f'!i ' .i-jt &.VV'rij" ^v, rV ';, . r r . Asbestos Fibres: ST- yv.'.' * ' % . ^ J> Eects Upon Physical Properties *Ji W` ,, * , 1 'V^ , * ' y "T By M. S. BADOLLET* , ' "- ! U -y-"- (Annual General Meeting, Toronto, Ont., April, 1900) ' :W`r ': (Transactions Volume LIII, 1950) Introduction mand for a particular fibre grade handle the fibre. Since many man- is great enough to warrant special ufactnrers of asbestos products pur ASBESTOS aa received by the milling techniques. In such a case, manufacturer of asbestos prod the mill places this specially pre ucts is in the form of either crudepsared fibre in its regular produc chase their asbestos from more than one source -- Canada United States, . Africa Russia, and Aus or milled fibres processed to differ ent degrees of texture. Frequently, the manufacturer finds that the fi tion line. Each time it decides to produce a special fibre, several im portant points must be considered, tralia -- it is important for them 'to know how to handle the several fibres properly. This is particular bres as he buys them are not adapt such as: (I) Will this special fibre ly true when fibres of the same able to his plant processes, and, require new . processing equipment. grade are purchased from two or therefore, it is necessary for him or can existing equipment be used? more different sources and conse either to contact the mine supply (3) Will the" over-all capacity of quently,, may have entirely different ing the material and request a spe the mill be reduced? (3), Hoes this physical1 `characteristics. cific texture for the fibre or to re special fibre have specific physical To illustrate some of the p|hb- process the fibre in his own plant: properties: that* cannot bc matched' lems facing the manufacturer of?*s- ' When the mine or mill manager is- by present fibres offered; to the bestos products, typical shipments requested to change his milling public? and (4): Gan the extra pro of asbestos have been obtained ffbm equipment to produce a special duction Cost be recovered? different, sources and the effects of grade of fibre with a specific tex-< Fibre milling, is a technique that willowing upoa the physical prop ture, he would like to comply. How ever, if he began to make special fibre grades for each customer, he differs somewhat with: ] each plant.' - esties of these fibres 'have been in AH' predwers are continually mak vestigated.', .,, : ing mechanical changes in order to- would be in the position of con stantly rearranging his milling tech improve their, products while main* tabling thdir production; schedule ArUiesit" Btue, (CaociBoiiTx) nique, adding more equipment, or . building a new mill. In the end,' his mill would be producing hun dreds of different fibre grades of varying degrees of texture, which., This problenr ls no easy one, mid it requires - full - co-operatibi between the Sales staff and the Mill Depart ment, ,J 7 ' ! . This variety of asbestos would be difficult to use in its raw condition, as received in the United States, be cause of its crudy nature, quantities is a difficult accomplishment if he ,, of unopened bundles offlbres, and desires to maintain any quantity of : VnmroiNT of ran'Ct'STOwEit the. - presence oU pieces of roefc . of . production, - J '' varying. si^fe, Therefore,the. ens- Viewpoint of . . " 'lJ&s-.-J thi Minsk.: i The custonierha*' aa established, plant which produces a oertain line of*Tasbestos pruductsami probably ' tomer matt either,',have some type of processing eqnipment to convert thia; fibre .tn: thV groper condition j It is well knowar:^]|||^(ashiifilvi%5 at one time lie _ set up Ms plant' fot use in hi* products or he must,* bres as prcduced^aPBlgi CanadjitlK^' with the minimum of equipment neq- tty to coirviiice the miner in Africa mines fall into swfat^ essary for utilisation af the regu* to pjocess hii fibre to the customer as crudes and Each lay grades, of fibre as produced at . specifications. Years of' experience of these > the mines: After a number of years,, . have shown that the easiest answer sub-divisions, attd;upwj; of-'the fi of competition and new develop- to this problem is for the customer bres have differea^feStfees such as .' merits,his products possibly did not- to re-process the fibre himself, be crudy, semi-crudy, open,, and well meet thenewerspecifications, and cause he knows, exactly what he opened. No donbt these Several de* the first question that came up for wants*,,/, ^ i;' grees of texture have been estab discussion was asbestos fibre; Wait - African Blue* fibre is strong but lished after many years of expert* he using the proper fibre, or should harsh,. nd ,by successive willowing ence based upon the general demand he install equipment.. to re*prOec* aetkm:the. fibrerbeconres: balky and of the customer. Therefore the mill the- fibre in order' t<r chaage; it* loses, length^.* - * 'V. * ; . tries to maintain a set of standard characteristics ?: At this' point, the A., normai ^nebecrscreen tcst,. af fibre mixtures, with gaps between Research and Development Engi ter one witlowji% flsrtioii, shows that the different grades for future ex neer should step in and review the approximately 13 ounces of the total pansion if the demand is sufficient. entire problem , with the production 19: ounce* remaiift. oh the top screen. In gome instances, the customer de- department and decide whether the Successive, .WtRowingstages do not fibre must be changed, tp fit exist* change thls result,,- sufficiently to * Research Centre, Johns-Manville ing equipment, or whether the show what is happening to the phys Corporation, Manville, N.J. equipment should be modernised to ical. properties of this fibre. ., _ _ -- 10 -- UCC 004669 By a careful water elutriation method, a definite indication can be obtained of reduction in fibre length after each willowing action. Figure 1 shows that, for five willowing ac tions, the +14 mesh fibre dropped from 52.6 per cent to 30.6 per cent, a length reduction of 40 per cent. Coincident with decrease in fibre length, there is also an increase of fines ( --200 mesh) from 30.4 per cent to 45.4 per cent or an increase of 49 per cent. Therefore, to wil low this fibre successfully, a mini mum amount of willowing action should be used in order to avoid a loss in length of fibre and the for mation of fines which would be lost in later stages of processing or product formulation. In the production of asbestos products by wet methods, the den sity of the opened fibre as well as its ability to remain in suspension are important factors. The buoy ancy of a fibre can be determined from a slurry of fibre in water, with a definite weight of fibre in a constant and definite volume of wa ter. After thorough mixing, the slurry is allowed to settle, and the rate of settling is read in cubic cen timeters for a given time. In most rases, the settling reaches equili brium after one hour. The density can be determined by filling a stand ard measure with a capacity of say, a cubic foot, and obtaining the weight of its contents. The results are then expressed as pounds per cubic foot. Figure 2 shows that the buoyancy of the Blue fibre increases rapidly for the first willow pass, and that after the second pass the slope of the curve decreases. Conversely, the curve for the density values shows that the density decreases rapidly for the first pass and after the sec ond pass changes only slightly. An interpretation of the buoyancy and density curves indicates that this particular Blue fibre reached a high degree of opening at two pass es through the willow and that further willowing, at added expense, would effect relatively little im provement in the quality of the fibre. During the process of willowing a fibre there is another important change taking place in its surface area. This change, also, is indi rectly reflected in the buoyancy and the density measurements. Samples of the Blue fibre were measured for surface area by the air permeability method, using the Bowen apparatus and following the Lea and Nurse technique (1). A number of methods have been advo cated for determining the surface area of solids and each has advan tages and disadvantages. However, after considerable experimentation, it is thought that the method used in this investigation, while not giving absolute values, shows the general trend and indicates physical changes to the fibre after each processing action. Since it is known that wil lowing action on a fibre will open bundles into thinner cross-sections, reduce length, and create fines, there should result a cumulative measure of these effects by obtain ing the surface area measurements. Figure 3 shows the surface area measurements of the Blue fibre in its original state and after each willowing action. The results are expressed in square centimeters per gram of fibre, and the data, ex pressed graphically, yield a curve which shows that: (1) the surface area is increased after each willow action; and (2) this measurement shows a greater change per willow pass than the tests for buoyancy and density, because of the change in fibre length and the formation of fines. The conclusions that can be drawn from these test data on open ing African Blue are: (1) the fibre length decreases after each willow ing pass, with resulting increase of fines; (2) the buoyancy and density values of the fihre show only small changes after two passes through the willow; (3) surface area meas urements show that, after each wil low pass, the area is increased; (4) a total of two passes through this particular willow would be the maxi mum treatment to produce a fibre for use in a plant; (5) one willow pass would be acceptable, since it produced a fairly open fibre with the minimum of length loss and creation of fines. Rhodesian Fibre (Chhysotile) This particular grade of fibre as received in the United States would also be difficult to use in most wet processes for the production of as bestos products, because of the pres ence of crudy fibre bundles. The same procedure has been ap plied to this fibre as was used with the African Blue. The same equip ment and rates of feed were adopt ed for all tests, so that the mechan ical processing was constant in all cases. This particular fibre was given a total of eight passes through the willow in order to determine the maximum opened condition of the fibre. The Quebec-screen tests increased slowly to the maximum value of 12.6 ounces on the second screen at four passes, and then decreased to 11.7 ounces on this screen at the eighth pass. The water elutriation procedure for length indicated a decrease in fihre length ( + 14 mesh) after each pass, and a small increase in fines (--200 mesh). Figure 4 shows the two curves, which are entirely dif ferent from those for the African Blue fibre and which do not inter sect at any point. The slope of the curve for the + 14 mesh fraction begins to level off after six passes while the curve for the --200 mesh fraction shows only a small increase in fines after six passes. In other words, the + 14 mesh fibre decreased in length 61 per cent, but increased only 24 per cent in the objectionable --200 mesh fines. The buoyancy of the fibre con tinues to increase rapidly after each pass. Figure 5 indicates that the slope of the buoyancy curve would begin to level off at some point after eight passes. Density measurements show that the density of the Rhodesian fibre decreases rapidly for the first two passes and thereafter at a lesser rate, with indications that it would probably reach its minimum density after eight passes. Surface area measurements made on this fibre show that it has less surface area than the African Blue after each pass through the willow. The curve (Figure 6) has a lesser slope than that for the Blue fibre, which would indicate that this fibre does not break down into shorter fibre lengths as rapidly as the lat ter. In other words, it resisted de structive action better than the Afri can Bine under identical tests con ditions. Canadian Chrysotile -- Semi-Harsh A quantity of Canadian semiharsh fibre was obtained and sub jected to numerous willowing actions to determine its resistance to fibre length destruction. This particular fibre contains considerable quanti ties of crudy fibre bundles that should be opened before it is usable in an asbestos product; therefore, it was subjected to a total of ten wil low treatments. The Quebec-screen test indicated -- 11 -- UCC 004670 a large Increase on the second screen for the first pass, and onlysmall increases for each succeeding pass Up to six. From that point up to ten passes, the test indicated minor changes only. The water elutriatfeHl - test indi cated an 18% per cent decrease in length for the +14 mesh fibre for the first two passes. Examination of the curve (Figure 7) reveals that the remaining willowing actions from two passes to ten had only minor effects upon the destruction of the fibre length. The fines (--200 mesh) show a 14 per cent increase for the first two passes and only a slight increase for the re maining treatments. From these data it can be concluded that this fibre resists destructive action and remains in good condition even after ten passes through the willow. The buoyancy value of this fibre, as shown by Figure 8, increases rapidly for the first four passes, and then the slope of the curve begins to decrease. The density values (Figure 8) show a large change for the first two passes and only minor changes for the remaining tests. Surface area measurements are not increased as rapidly as in the case of either the Rhodesian or the Blue fibre. Figure 9 illustrates the increase in surface area and, as will be noted, the slope of the curve is less than for the two African fibres. From the test data obtained on this Canadian fibre, it can be stated that willowing action is not detri mental to its physical properties and that it resists destructive action bet ter than the African Blue or the Rhodesian fibre. Canadian Soft Chrysotile Fibre A typical Canadian, soft, silky fi bre was wiliowed atfttal of sixteen times in order to its re sistance to the action ot a willow. The Quebec-screen test indicated a change on the second screen after the first pass. This same screen began to indicate a decrease after nine passes and, at sixteen passes, had decreased to a value slightly above that at the starting point. The water elutriation curves (Figure 10) show that this fibre, although it lost length and some pul verizing took place, did not disin tegrate; therefore, it can be con sidered highly resistant to process ing equipment. It would probably be satisfactory for use in its orig inal state unless an increased fibre buoyancy was desirable for some specific usage. The +14 mesh fibre decreased 20 per cent after sixteen passes, and the --200 mesh fines increased 14% per cent for the same number of passes, a further proof that this fibre resisted the destructive action of the mechanical equipment. The buoyancy of this fibre, as il lustrated by Figure 11, shows a rapid increase for the first two to three willowings and only a gradual increase by subsequent treatments. However, the buoyancy values are all lower than those for the three fibres previously discussed, which shows that this fibre is relatively free from crudy fibre bundles and is fairly well opened. The density values decrease for the first two to three passes and then practically level off, with only minor changes brought about by further processing. A total of two willow passes would probably be sufficient to place this fibre in good open condi tion. From the curve obtained (Figure 10), it can be concluded that this number of willowing ac tions did little harm as regards de stroying fibre length or pulverizing the fibre. The curve also indicates that the quantity of unopened bun dles was small and that the fibre was fairly well opened at the asbes tos mill prior to shipment to the customer. Therefore, this fibre can be used in its original condition as received from the mine, without further processing on the part of the purchaser. Surface measurements on the Canadian soft fibre are given in Figure 12. The fibre in its condition as received presents a greater sur face than any of the other fibres discussed in this investigation. This would indicate that the combination of fibres of various lengths and fines created a large surface area. The surface area of this fibre at any given pass is greater than that of any of the other fibres so far dealt with. Therefore, if a manu factured product requires a fibre of great surface %rea, this one should fit the specification. However, since this physical property is only one of many to be recognized, we must balance it against the other factors before reaching a final conclusion. Canadian Chrysotile Harsh Fibre This harsh fibre of the chrysotile variety has some interesting char acteristics from the viewpoint of its physical properties. It was subjected to a total of six passes through a willow, and, in the Quebec-screen test, each pass indicated an increase on the second screen. The crudy fibre bundles opened easily and became fairly bulky, so that most of the fibre re mained on the second screen. Water elutriation tests indicated a definite length loss in the +14 mesh fibre after each pass through the willow (see Figure 13). After six passes, this decrease in length amounted to 81 per cent and the quantity of fines ( -- 200 mesh) showed an increase after each wil low action. However, the amount of this increase is only 22 per cent, which would not be considered alarming. These data indicate that the long fibre will not resist flexing ation by willowing, and that shorter lengths were produced without pul verizing to dust. Therefore, any mechanical re-processing of this fi bre after shipment to a customer should be extremely mild, or the fibre should be used without addi tional processing. The buoyancy value of this fibre (see Figure 14), while showing Rn improvement after each pass, does not equal that of the other fibres discussed up to this point. The density shows a rapid im provement for the first two willow passes and only minor changes after subsequent passes. Therefore, for re-processing of this fibre, from the viewpoint of buoyancy or density, a minimum of two passes, or even one pass, would be considered sufficient. However, there is an important loss of length after one or two passes, and it might be advisable to avoid any further processing of this fibre. Surface area measurements on this harsh fibre, shown graphically in Figure 15, indicate a smaller in crease in area than for any of the other fibres tested in this investi gation. In other words, this fibre maintains low surface area and low buoyancy, although it loses length, in processing. For certain products these properties are important and should not be overlooked; for other products, great care must be exer cised in handling the fibre before and during its use. The surface areas of all fibres tested are charted in Figure 16, which enables a direct comparison to be made between the several fi bres for the same number of passes through the willow. The two ex treme fibres are the soft, silky chrysotile of large surface area, and -- 13-- UCC 004672 ' Cfc-te * 0* ' ' ,3vT:^.-J*'* n*na ' *jfLj T'j ' ^S>g>i. 1 i* 1 " li Figure 16.--Effect of willowing on airfare area, various fibre*. the harsh chrysolite,' having- small surface area. Effects of Willowino Upon FniERiBiLin of Fibre : When a fibre is opened by mech anical means, a fibre of greater surface area results. Figure 17 shows, for each of the fibres inves tigated, the effects of four willow passes upon its filterability. . : The soft, silky chrysotile fibre rapidly becomes more difficult to de-water after each opening process, with the result that plant produc tion is retarded1. ,' The Rhodesian fibre remains fast filtering up to four passes through the willow, at which point it begins to show a trend toward more diffi cult filtration. However, after .this number of willow passes, the fibre - would still be considered , satisfac tory for any wet process. //. ' Of all the fibres tested'- in 'this 1 investigation, the filtration charac teristics of the two identified: as "semi-harsh' and 'harsh' arelCaat affected hy the widowing process. Both would be considered ideal/ for sweetening poor Mterii even if they had been hi by mechanical procesaei^ The filterabil fibre is only the willowing passes it is si filtering fibre. <' ----i--i--t--j-- Z--r Mtmbi ` Figure 17.--Effect of willowing on filterability of various fibre*. ' * ? * CoRnri.+-rK>N o* Test Data In general, there is good correla tion between buoyancy and surface area values at a given number of willow passes. When the surface area data,,and buoyancy values are expressed graphically, most of- the points fall upon a straight line, in dicating that either test can be used as a guide for determining the de gree of opening of a given grade of fibre. ' When the surface area measure ments and the decrease in -(-14 mesh fibre expressed in percent are shown graphically for each willow pass for each kind of fibre, there ap pears to be a fairly good correlation, since most of these points also fall upon a straight line. This is an indication that the surface area of processed fibres is greatly influ enced by. the destructive action of willow hammers. Application on Tear Data The manufacturers. of some as bestos products require that ashestos fibres meet certain specifications as to date of filtration, . fibre strength;, length, buoyancy, density, and surface area. In a previous pa per on filtration, presented at the. 194& - AnnpaJ, General Meeting of this it was pointed out thatj? bjr opning r fibre, the. rate of filfctation.is decreased. In all of the ipsrestigatiOns discussed in the present paper, each fibre shows a trend to become more difficulty to filter after each willowing action.. Therefore,., some decision must be made on- the-! basis of the general awer-all, effect a willowing. action has upon physical properties of the fifcnu _ -v - ' .. " Fibre;strength (3) is important/ 'and softjs;silky, fibres retain , their strengths, better than harsh fibres when ' processed, by mechanical equipment. ."/". , , , : , . If fixation is the most Impor tant factor government the produc tion rate, of an asbestos product, then, given a, fibre of satisfactory strength, a minimum amount of wil- lowing should be useih : If'a low density or a high buoy ancy value is required and filtra tion is not important, then the fibre should be well opened to obtain its roaximam fluffing condition.. If a fibre is required- to' have strength and high surface area with a minimum loss of fibre length and minimum formation of fines by a - willowing' action, then it is neces sary to select a fibre or a blend of fibres that will meet these require- raent8` UCC 004673 _ ...... ......... The Research or Develi Engineer should make a thorough1? study of the available fibres. The%^ knowing the fibre specifications re?!'.: quired for a given , asbestos^ uct, he should makedefinite n mendations tw tb*:ingnnfsetnre^ i to. the kind of fibre and ty^pe of ] processing necessary to obtain/*} maximum value of the. fibre/fOtt specific utilization./ , , Conclusions (1) Asbestos fibres as received by the manufacturer of asbestos pro nets usually require some type o| re-processing before they can nsed to best advantage in a product.^ (2) Any fibre re-processing mctifi|i od adopted by a manufacturer wil produce changes in physical prop*: erties, such as a lowering , of fibre strength, loss in length, formatio of fines, different degrees of buey-r ancy, changes in density, increase ja surface area, and a tendency to comb more difflcnlt to filter. . () The soft chrysotile fibtgt ; sist the destructive action of j*T' low fairly, well, but have the n est surface area and are the? difficult to filter at any given*hui^ her of willow passes. `' (4) African, Bine fibre'll length, increases: rapidly in area, becomes relatively buoy after each willow pass,1 apd rapidly. - \ - (5) Rhodesian fibre loses le increases in buoyancy has less < face area than either the Cans soft fibre or the African Blah-: and its filtration1 characteristic*:;) main good even after-four, passes, J : /t . () The semi-harsh fihre/i the destructive action of th^. low fairly well,* but is less to willowing action, than dian soft fibre, increases rapidly/j buoyancy, is rapid filtering, aSd'! less surface - are*: than the Rhodesian, or Canadian soft ! (.7) The harsh fibre loses rapidly, increases in buoyanCy/s ly, has the "lowest; surface * all fibres studied in this it tion, and- remains fast' filter&g^iffj each willow stager -^ Rmxiscn (1) Lea, F. M.. and Kftras*,'-' Specific Surface of fw/l ers; Soe. Cheto. Ind^l Sept., IS*, p- 277-283. / (2/ BADOtxsrr, M. S., Fitterab Asbestos FHhrsftj -C.LSfv 'I... Vol, LUV 1949, pp, (3) Badoluet, M. S., Research Asbestos Fibres; Can. Min. Jo April 1948, pp. 213-216. ' ' --^14-- -