Document Lpo0yMDggKg9OoDGzngnmMEqQ

The Role of Asbestos in Plastics tBy M. S. BADOLLET and M. B. XJMENEZ (Annual General Meeting, Quebec City, April, 1956) (Transactions, Volume LIX, 1956. pp. 283-288) Introduction (6) Increase heat and fire re DlctaicorsngseUmfitidheRoeqeldlrudIaNaibunhnGslgaytesi,tiectsohoaseefmnrvdpoepaodfasuhsbnaeatesdnsscstltiaweeonssethnootahfstuysiebtleefyiiptnbrelceaafrorrisenssrasedsomupinrfsooct(ladv7udneeri)ncefohegdrAasmnllmadofrtlwooiinolmdgnienaojgentrshcdetwiomwanmoriptvohaeologdmfue,ettnahtnedodafncgitomhelder from Canada. It is estimated that Unfilled moldings would be im approximately 14,000 tons of as practical in the cold-molding field bestos fillers varying from Group 4 of bitumens and phcnolics. Because to floats are used by the plastics the filler must produce sufficient industry. handling strength, asbestos, with its The utility of fillers in molding fibrous character, is desirable. compositions has long been known. Binders normally used are asphalts, Their original purpose was to help pitches, gilsonite, polymerizable make molding practical and to re oils, resins, and similar compounds. duce the product cost. In the early Cold-molded products of the bitu days, these fillers consisted of saw minous type are sometimes loaded dust, cotton waste, powdered asbes with as much as 85 per cent of as tos, silica, diatomaceous earth, sand, bestos. Such a product possesses clay, powdered glass, cork, marble good heat resistance and fairly good dust, slate flour, or other materials. electrical insulating properties, and Each filler had certain good char is low in cost. Its strength is not acteristics as well as certain objec equal to that of hot-molded prod tionable ones. ucts; however, it is sufficient for In this presentation it is proposed the type of moldings made with to discuss only asbestos as a filler cold-molding powders. in molding plastics. Cold-Molded Phenolic* Types of Plastics In general, molding plastics can be divided into the following class es: (1) cold-molded, (2) thermo plastics, and (3) thermosetting. Cold-Molded Plastic* Asbestos fillers have the follow ing advantages in the cold-molding field: (1) Lower molding cost (2) Make cold-molding possible by controlling the flow of material under pressure while it is in the cold mold (3) Improve mechanical proper ties (4) Increase hardness (5) Decrease molded shrinkage Johns-Manville Research Center, Manville, New Jersey. tFormerly of Johns-Manville Re search Center; now retired. Viscous solutions of a suitable phenolic resin arc used as hinders in cold-molded phenolics. The ad vantages of this higher-priced type of cold-molding compound are: bet ter surface finish, lighter colours, more dimensional uniformity, and better mechanical and electrical properties. Manufacturing Method Cold-molded compounds are in general made by loading the fillers into a heated internal mixer, after which the hinders and other in gredients are added in liquid form or in solution. This mass becomes somewhat tacky and, after dis charge, it is allowed to 'season'. Later on it is screened to separate lumps, whiskers, and other extran eous material to provide a fairly uniform granular compound for molding. The grades of asbestos used in the cold-molding field are normal ly described as floats and shorts. The quality and physical charac teristics of the asbestos are import ant and should be controlled. The most important and troublesome variables within this field are: (1) Texture and quality of fiber should be as constant as possible so that the moldcr can set up his working formula and not be forced to make repeated changes. (2) Bulking property of fiber should be kept constant. For exam ple, if the fiber is increased in bulk ing properties, more binder is re quired and this increases product cost. On the other hand, if the fiber is too heavy or less bulky, the molding material becomes tacky because it does not absorb the prop er quantity of binder. This condi tion also causes screening and mold ing difficulties, sticking to the molds, increased baking time, and softer moldings. Often, the mechan ical strength of the product is low ered. (3) Excess moisture in the as bestos also can cause trouble, such as sticking and blistering. Normal ly, asbestos as received by the molder contains from one to two per cent of moisture. Under some stor age conditions in customers' plants, the fiber may pick up additional moisture: this is why some plant operators pre-dry their fiber as a protection against any moisture in crease due to storage conditions. (4) Non-uniform fibers should be at an absolute minimum. They may be described as those that have `whiskers' or long fibrils in excess of the average fiber length for that particular grade. These 'whiskers' twist and tangle and interfere with the efficiency of the screening pro cess. They also cause sticking to the molds, produce surface blisters, and in most cases affect the finish and the appearance of molded products. Bulletin for July, 1956, Montreal After the molding powders are properly sized hy screening, they arc ready to be placed in the mold. At this point, the bulk factor is extremely important because pre forming and final molding arc one and the same operation. Moreover, positive molds are used, and most molded parts arc each fitted with from one to several metal inserts. The molds arc loaded by means of a small hand rake or mechanical rake. Good pourability and proper bulk of the molding compounds arc indispensable at this step for good and efficient cold-molding. If the molding compound charge is insuf ficient. then the molded part is offsize; and if the charge is excessive, the product is heavy and in some extreme eases may even damage the mold. The cold-molding operator has his own responsibilities. He must de velop a well-balanced compound in which the ratio of hinder to filler is adjusted in relation to the bulk value of the filler. If lie docs this, sticking and off-size products, as well as other troubles, will be mini mized or eliminated. In most cases, the compounds are dusted with a powdered lubri cant before they are loaded into the mold, to prevent any sticking tendency. If the formulation is made correctly, the cold-inolded com pound will flow properly and pro duce good material. The main fac tors the operator must constantly watch are: (1) bulk of the asbestos filler; (2) ratio of binder to filler; (3) proper size of particles of the molding compound; and (4) mold ing pressure as well as baking tem peratures and cycles. In general, it may be stated that cold-molded products arc not suit able for power factor applications of any importance; but they are used extensively as lieater plug parts and as housings for the shield ing of electrical units. High londh)g of asbestos ns a filler imparts the heat and flame resistance re quired. Thermoplastics In tlie thermoplastics field the fillers generally used are zinc oxide, titanium oxide, hlanc fixe (barium sulphate), talc, diatnmaccous earth, and asbestos. The e(minion names of the most familiar thermoplastics are: cellu lose nitrate, cellulose acetate., cellu lose acetate butyrate, ethyl cellu lose, vinyls, polystyrenes, vinylidcnc chlorides, and esters of acrylic acid. The disadvantages of fillers, in thermoplastics may be summarized hs follows: (1) Mineral fillers increase the specific gravity and molding weight of both thermoplastics and thermo setting molding compounds. (2) Killers preclude production of transparent or translucent plas tics (molded, cast, or fabricated). Translueency can be obtained only to a limited extent when the re fractive index of the plastic and the filler are approximately the same; in these cases, however, the mold ings lack quality. (3) Killers decrease water and moisture resistance. (4) Fillers also reduce electrical and mechanical properties. The ex ceptions are resistance to arcing and compressive strength. (r>) Fillers in most cases damage the delicate molding and fabricating equipment. ((>) Fillers frequently introduce new and sometimes complicated problems in the difficult art of col ouring, mottling, and configuration of thermoplastics. (7) Fillers in thermoplastics im pose the need for special types of processing, molds, and methods of molding. (8) Fillers increase the quantity of waste and re-work. (9) Fillers make injection and extrusion molding methods trouble some and wasteful. Consequently, work along these lines is chiefly experimental at present. Asbestos improves the heat re sistance and compressive strength of the thermoplastic moldings. It also reduces the cost and the tend ency to cold-flow, with resultant deformation and warpage. Although hardness is improved, the increase is only moderate. Resistance to flammability and arcing is also im proved by asbestos; however, this is true of all mineral fillers. Incorporation of fillers in ther moplastics is usually handled by one of three different methods, briefly described as follows: (1) Preliminary mixing of the plastic hinder in powdered or flake form with the plasticizers, fillers, ami other ingredients in ball mills or in internal mixers. (2) Wending of the ingredients, including binders, plasticizers, and fillers, with or without solvents, in heated kneaders. Hot-rolling is fol lowed by calendering, stamping, or by molding. (3) Incorporation of the fillers and plasticizers on the lint rolls after the plastic binder has been consolidated into a plastic sheet. This procedure is used for blnnking and/rr fabricating and/or molding. To obtain a good product requires considerable good judgment on the part of the operator. This is in fluenced by: (1) method of incor poration; (2) time of mixing; (3) temperature of mix; (4) percentage of filler; (5) type of filler; (6) mixing technique; and (7) type and condition of the plastic binder. Because of the conditions under which hot-rolling is practical in the thermoplastics industry, and be cause the binders arc plasticized, the operation is a safe and efficient one for the operator. Binders re main fusible indefinitely, and this permits perfect blending hy pull ing the filled compound in fairly thin sheets over and over as re quired. Filler loadings arc usually on the low side. In most eases, a well-formulated compound can be processed and molded without sticking to hot steel; however, in some special cases lu bricants are used to minimize pos sible difficulty. Most of the thermoplastics used for regular molding can be produced in a large variety of molding flows, because the plastic base and the plasticizer content, or their ratios, can be changed within wide limits. In thermoplastics, the molder must give close attention to: (1) nature, grade and flow of the base; (2) nature of the plasticizer, wheth er it is a solid or liquid; (3) per centage of plasticizer; (4) nature and percentage of fiber; (5) pre heating; (6) molding temperature; and (7) molding pressure. Special techniques have been de veloped by the trade for tlic drill ing and machining of each par ticular type of thermoplastic, filled or unfilled. Asbestos, especially light-coloured fibers, can be used in moderate percentages in the manufacture of thermoplastic molding or calender ing materials bused on ethyl cellu lose, vinylchloridc acetate, and vinylchloride (polyethylene has been tried experimentally). The as bestos filler improves the hardness, heat resistance, burning rate, com pressive strength, and arcing resist ance of the product but it affects 486 The Canadian Mining and Metallurgical adversely such characteristics as specific gravity, translucciicy. ap pearance. depth of colour, other col our possibilities, flexibility, shock and flexural strength, water resist ance, and electrical properties. In the thermoplastics field, the use of fillers is very limited. Vinyl cldoride acetate and vinvlehloridehnse floor tiles, however, constitute a very important and growing field. Work is also being done on floor coverings. Asbestos is used in some types of shellac-base compounds also, but not to the extent it was in the past. One manufacturer in the United States has been producing injection moldings in very large quantities with a compound made with miner al fillers, asphalts of high purity, pitches, plasticizers, and hardening or strengthening agents such as as bestos or other fibers of short or medium length. We understand that the cost of these moldings ranges from $20 to $200 per ton. Thermosetting Plastics The thermosetting field of plas tics is large, and use of fillers has many advantages. Filled moldings are cheaper, and the fillers control the flow of the molding compound. In addition, they improve the me chanical strength and dimensional uniformity, they make the moldings more dependable and durable, and' they decrease the shrinkage and warping tendencies of moldings after their ejection from the hot mold. Fillers shorten the curing time and increase hardness; they im prove heat, fire, and arcing resist ance. Some of the disadvantages in the use of commercial fillers in these plastics are: increase in specific gravity and molded weight; de crease in water and moisture resist ance; lowering of electrical proper ties; increase in wear and tear on equipment and molds. Moreover, as bestos introduces grit, rock, and magnetite. These impurities increase deterioration of equipment; they make drilling and machining opera tions difficult. In the production of thermoset ting plastics it is generally accepted that, if the compound has a tend ency to stick to the hot-mixing rolls, it will also stick to the molds and cause rejections, expensive delays, and cleaning jobs. Moreover, the mirror polish of the cavities may be damaged, and internal lubrication of the molding compounds is indis pensable. the compound flows poorly, Production is decreased. Also, mold ings are mechanically weak, untrue, and defective dimensionally, and electrical and other properties are erratic. On the other hand, if the com pound flows immoderately and too rapidly, it causes excessive case hardening, excessive and wasteful flash, lack of dimensional accuracy, decreased mechanical and electrical strength, and upsetting of pins, re movable parts, inserts, and the like. It also interferes with the efficiency of the ejecting devices. Chrysotile asbestos as a filler has a number of advantages, some ofwhich are common with other fill ers. Advantages of chrysotile are: (1) it is mineral in nature; (2) it is available in large quantities; (3) it is low or moderate in cost; (4) it is fibrous in structure; (5) it is pos sible to adjust percentages used in relation to fiber length; (6) it is easy to process and mold in com pounded form; (7) it retains the binders; (8) it is inert to reactions involving rolling, molding, and cur ing of the compounds; (9) it per mits the manufacturer to use high percentages of filler, e.g., 65 to 70 per cent; (10) it allows the molder to vary the percentage and fiber length to achieve desired mechanical strengths; (11) it imparts tough ness; (12) is provides better surface finish than soft wood flours, barytes, or mica; (13) it retards the burning rate; (14) it supplies heat and fire resistance; (15) it in creases hardness; (16) it reduces the natural shrinkage of the resins and plastic binders; (17) it allows blending with mineral and organic fillers; and (18) it increases the moisture resistance of moldings partly filled with cellulose fillers. Compared with other mineral fillers, chrysotile has the following advantages: (l) it is fibrous and available in lengths desired; (2) it has excellent binder retention; (3) it is easy to process and mold; (4) it may be loaded at higher levels than other mineral fillers; and (5) it produces the hardest and tough est moldings at loadings impossible with other fillers. Asbestos - filled thermosetting moldings excel all others in heat re sistance, up to temperatures of 450F., because asbestos loadings can be made at higher percentages than is possible with other mineral fillers. The impact .strength can lie varied within wide limits by vary ing the quantity and length of as bestos. Chrysotile asbestos has some dis advantages however. Chief of these arc: (1) Combined Water Combined water is present as a part of the chrysotile structure. If temperatures of molded products reach 450F. or higher and some of the combined water in the asbestos is liberated, the molding will blister and crack. This difficulty is par ticularly significant when heater plugs and other electrical and heat ing appliances are involved. (2) Fiber Length Fiber lengths of asbestos used in plastics vary, depending upon the grade. The molder must understand the type of fiber and something about its properties, especially the specific gravity, bulk, molded weight, mechanical and electrical properties, water and moisture re sistance. In addition, he must under stand mixing techniques, colouring, surface finish, molded shrinkage, and percentage of fiber available in the asbestos grade used. (3) Dust or Fines The so-called `dust' or `fines' in asbestos may be granular, fibrous, or talcy. Variations in the ratio of dust to fiber, and its degree of fine ness, will affect all those properties mentioned under the heading of fiber length. For example, surface quality of the molding will improve as the percentage of dust increases; however, all other conditions -being equal, the surface quality of the molding will be lowered as the fibrous structure of the dust, or as the particle size of the dust, in creases. In other words, a fine gran ular dust will impart the best sur face finish. (4) Talcy Dust Talcy dust adheres to the surfaces of the fibers, producing what is called the `talcose' effect. It re tards, and in extreme cases pre vents, adhesion of the resin binder to the asbestos filler and adhesion of the blending charge to the hot ter of the mixing rolls. This often results in increased rolling time, sticking, fouling, irregularities, poor detail, inferior surface finish, and increased rejections or waste. (5) Rock The so-called `rock fraction' in asbestos, which is mostly ground serpentine, is usually present in dif- Bulletin for July, 1956, Montreal 487 fcring percentages. This fraction has a tendency to segregate when the ingredients forming the molding compound arc given the prelimin ary dry- and cold-mixing. Accumu lation of rock on the bottom of tlie mixer or ball mill unbalances the disposition of the ingredients. Pres ence of this rock in a molding com pound will tend to scratch the deli cate mirror polish of the mold, which is costly to repolish. (G) Pencil* of Fiber `Pencils' are defined as fiber bundles not well opened, and thin in cross-section. These pencils cause the charge to stick to the hot rolls and molds as a result of the pencils being crushed between the friction rolls or under the molding pressure. When this happens, tire newly ex posed fiber surfaces remain partly coated and do not ride with the charge on the rolls or within the mold. When the pencils remain uncrushed tlrey are enclosed by the binder, and. when opened by the grinding operation, they appear as poorly bound units, or as uncoated fibers or specks that show on the exposed surface of the moldings and throughout their mass. These pen cils may also be blamed to a cer tain extent for blistering of mate*, rial within the mold or in service. (7) Lump* of Fiber If the fiber is lumpy before the molding powder is made it will cause about the same trouble as pen cils. Lumps must be Temoved to en sure good disposition. The fiber product as produced from the mine should be void of lumps; if not, it should be screened or lightly fluffed before use. (8) IVhislcer* Small percentages of long fibers in an extremely short fiber product are called `whiskers'. Although these whiskers may be only a frac tion of an inch longer than the main makeup of the fiber grade, they cause sticking and affect sur face quality and appearance. (9) Grit Grit is usually smaller in particle size than the rock discussed earlier; it is harmful, however, and can damage the molds. (10) Magnetite Magnetite, an iron oxide having magnetic properties, is usually present in most grades of chryso lite asbestos. Its removal is diffi cult. The effect of magnetite on electrical properties has been the subject of much discussion, partic ularly when it is coated by a resin. Its black colour is objectionable in moldings of light colour or shade. Electrical properties of the mold ing may or may not be affected by the presence of magnetite. (11) Alkalinity Chrysotilc asbestos has a high al kalinity because of the nature of the molecular grouping of its ele ments, which, in the presence of water, combine to form a small per centage of Mg(OH)j. The pH is usually around 9.3 to 9.7. In many molding powders this alkalinity is not objectionable; in others, such as urea formaldehyde, alkalinity is troublesome. However, asbestos is not used to fill resins of this type. (12) Capacity for Moitture Absorption Asbestos, unfortunately, 1ms a high capacity for absorbing mois ture. This effect can be counter acted, however, by oven-drying be fore the molding powders ire made. (13) Surface Finish Imparted by Asbestos Floats of good grade impart good finish as well as the desired tough ness and mechanical strength. As the result of considerable experi mentation, floats of excellent qual ity are now available. (14) Phenolic Molding Compounds Phenolic resins include the con densation products resulting from the controlled reaction of phenol with formaldehyde or with furfuraldehyde. The ratio of the reactants can be varied. The variations as well as the type of condensing agents, modifiers and/or additives used determine the characteristics of the resultant resin. One- and twostep resins and variations are made; they are used within the field dis cussed, the type selected being based on the properties desired in the end product. Phenolic molding com pounds are made by blending shortfibered asbestos and/or floats and subjecting the mixed ingredients (including fiber) to some type of mechanical or heat treatment while the mass is in motion. Chief among these treatments arc: (1) prelimin ary drv-mixing in ball mills or in internal mixers followed by hotblending in friction rolls, and fin ally grinding of the mass to pow ders of the desired fineness; (2) preliminary dry-inixing in ball mills or in internal mixers followed by hot-friction blending in Danbury mixers, and grinding to powders of the desired fineness, lly this meth od of treatment, fiber length is sometimes reduced, and consequent ly the toughness and mechanical strengths of the moldings are de creased. However, good blends are made and the curing cycles are re duced. The purpose of the hot-rolling or hot-blending in Banburys is two fold, (1) to ensure thorough blend ing of the resin, fillers, dyes, and lubricants, and (2) to facilitate the advance of the resin in order to de crease molding time. Moreover, re duction in the amount of condensa tion produced in the mold favours production of perfect, blisterless moldings and tends to reduce mold ing flash. Thermoset flash is prac tically useless. On the other hand, the thermoplastics type can be re worked and mixed with virgin com pound, with or without the addi tion of plasticizers to compensate for volatilization in molding. Preforming.--Phenolic molding compounds are usually preformed in suitable equipment. Preforms produced with the original powders are made in various forms and sizes or pellets, or in shapes approximat ing the final molding. This method accelerates production, assures uni formity of the molding charge, and reduces waste and flash to a mini mum. Preheating.--Molding preforms are usually preheated in special ovens to bring them to the proper degree of plasticity. Preheating re duces molding time. When long or very long asbestos fibers are used in phenolic molding compounds they are mixed with the finely powdered resins and other ingredients in internal mixers, or by spraying liquid resins, or in solu tions. The resultant mixture, al though not very uniform, is used for molding. Mechanical mixing does not affect fiber length, but it does create a problem of loading the mold because of the high-bulk factor. Toughness and mechanical strengths are improved, but flow within the mold is retarded. Conse quently the molding cycles are long er, more internal lubricant is usual ly needed, surface quality is poor, and the molded mass is not so uni form as that resulting from short asbestos grades. Tire furan resins include the products resulting from the reaction of furfuryl alcohol and furfural; 488 The Canadian Mining and Metallurgical ASBESTOS-FILLED PLASTIC MOLDING COMPOSITIONS (1) TilfcRMOSETTING TYPES Phenolics Molded Cast Specific gravity.................................................................... 1.52-2.00 1.70 18.2-13.8 0.0006-0.006 16.3-- 4,000 6,500 3 000-6 000 16,000-36.000 10.500-12.600 Flexural strength................................................................ 7,000-16,000 Impart strength. ft. lb.;in. of noteh-Itod teat..................... 0.27-3.5 Hardness, Rockwell............................................................. M95-MU6 5,000-8.000 IU10 Thermal conductivity, 1(M cal/sec/aq. cm per l*C/cm........ Resistance to heat (continuoua), F.................................... Heat distortion temp., *F.................................................... 8-16 350-400 290-350 8.4 800 "" Dielectric strength, in, thickness, short time, volts per mil..................................................-........................... 100-350 Dielectric strength, H in. thickness; step by step,---volts per mil........................................................................ Dielectric constant, 10* cycles............................................ Dissipation (power) factor, 10* cycles................................. Arc resistance, seconds........................................................ 76-325 5-7 0,10-0.50 Track, -- -- -- ---- W.Ur .brorption, 24 hr., H in. thick, %...... .................. 0.10-0.50 Burning rate....................................................................... Nil ---- Almost nil Effect of weak acida........................................................... None to alight Same as Effect of strong acids.......................................................... Decorap. by molded oxidizing acids; others si./none Effect of weak alkalies........................................................ Depends on al- Effect of strong alkalies...................................................... kalinity; si. or marked Effect to organic solvents.................................................... None on bleed* proof mate- Machining qualities......................................................... Molded qualities.................................................................. Fair to good In mold In mold 11' Data taken from Modtrn Enryclofitdia, 1956 edition. Fukans Molded 1.76 15.80 3,000-4,600 10,000-13,000 6,000-9,000 imo 265-330 ---- -.. . -" - 0.01-0.2 Slow Same as phenolics Melamine Fokmaldkhydb Colo >ifOLDEO Molded Organic Inorganic 1.70-2.00 16.3-13.8 0.005-0.007 6,600-7.000 30,000 9,000-11,000 0.28-0.40 MU0 13-17 260-400 266 1.87-2.16 14.8-12.9 0.010-0.017 1,400-3,000 6,000-16.000 3,700-10,000 0.40 M80-M90 -- -- 600 ^ 400 1.60-2.2 17.3-12.7 0.000-0.010 2.200 18,000 2,000-7,600 0.40 M76-M98 -- n. 900-1300 ; 400 360-400 86-116 45 320 60--76 6.1-6.7 6.0 0.041-0.060 0.07 120-140 78-200 0.08-0.14 6.5-2.0 Nil Nil None to alight Slight Decomposes Decomposes 50-80 - 100-600 0.6-16 Nil Slight Decomposes None None to alight Completely resistant Fair to good Good Is mold or oven Very light att'k None ` Slight attack Decomposes None on bleed- Attacked by proof colours some Fair Good In mold Poor to fair Fair to good In oven None None None Poor Fair to good In oven furfuryl alcohol with formaldehyde; furfuryl alcohol and ketones, and finally the product resulting from the polymerization of furfuryl al cohol. Resins made by reacting phenol and furfural also belong to the furan group, but their properties place them with the phenolics. (15) Melamine -- Formaldehyde Molding Compounds Calcium cyanamide, a fertilizer prepared by heating calcium carbide with nitrogen under pressure, is the starting point in the synthetic prep aration of melamine. This watersoluble material reacts with formal dehyde adjusted to a pH of 7.2 to 9.0 by means of caustic soda. The primary advantages of melamine formaldehyde resins compared with cheaper urea formaldehyde types are increased stability to heat and hot water, and greater resistance to alkalies and fruit juices. Moreover, the melamine formaldehyde resins permit use of alkaline fillers, such as asbestos. Such fillers cannot be used with the urea resins because they would inhibit setting. Molding powders are prepared by mixing the liquid resin with the desired percentage of filler. Doublearm open mixers provided with ducts to remove the formaldehyde fumes are used. The damp mass is dumped onto a screener provided with a device to break up the damp resin-filler mixture. From this screener, the compound is conveyed to the oven drier. The galvanized iron shell of the driers must be acidproof. The continuous convey ing belt should be chromium plated. The compound, spread in thin lay ers, is dried under very closely con trolled temperature and humidity conditions. During the drying cycle the water content drops from 50 to 1 per cent and chemical condensa tion of the resin proceeds. Cutting and grinding are the next steps. Grinding is done in ball mills where pigments, lubricants, and catalysts are added. The catalysts develop acidity when the compounds are heated to molding temperatures. These curing agents reduce the cur ing time and make the molding op eration faster and more economical. The compound taken from the ball mills is ground to a fine powder to provide a more uniform molding powder. If a molding compound of higher density is desired, tlie material is heated from 120 to 220F. in Ban bury mixers. The partial fusion thus obtained reduces the volume of the molding compound. Powders must be kept in cold storage under controlled conditions. (16) Colour of Thermosetting Moldings For most phenolic molding com pounds used for industrial and many other applications, the colour is not important. Colours other than black and brown are available today, how ever, and the filler has to be select ed accordingly. (17) Textures Asbestos of the chrysotile variety, whether in the form of shorts or floats, should be of soft texture. Semi-harsh and harsh chrysotile fibers have a tendency to pulverize during the processing cycles and are more difficult to coat with re sins than are the soft chrysotile fibers. Likewise, the molder will have less trouble in formulation if he knows that the physical proper ties of his fibers are not altered during his processing. In the paper, Heat Treatment of Chrysotile Asbestos Fibers (1), it was stated that this kind of fiber in the form of floats is very good for use in plastics because of its im proved physical properties. Considerable research is being done in the fields of polyester and epoxy resins with asbestos in vari ous forms. These fields may be very important in the not-too-distant fu ture. (18) Physical Properties of FiberContaining Moldings The accompanying Table, taken from the Modern Plastics Encyclo- (1) Badollet, M. S., and Streib, W. C., Heat Treatment of Chrysotile Fibers; C.I.M., Trans., Vol. LVIII, 1955 pp. 33-37. Bulletin for July, 1956, Montreal JPQ pedia for 1.055, shows the various properties of , the asbestos-filled molded compositions of the thermo setting type. Conclusions The role of asbestos in plastics has been reviewed from the view point of its usage in the cold-mold ing, thermoplastic and thermosetting fields. The advantages and disad vantages of ehrvsotile asbestos in tliesc fields have been discussed, as well as general methods of com pounding the fillers with the resins. The use of asbestos in plastics is important to both the plastics man ufacturer and the asbestos indus try, and it will continue so for a long time. Today, in the competitive market, it is necessary for the asbestos fib er salesman to understand the us age of asbestos in plastics and to be able to help the manufacturer wher ever possible. Ilis contacts furnish the leads for future development by the mines of the proper grades of asbestos for the plastics industry. The closest possible co-operation between the mines and the plnstics manufacturer is essential to assure the success of the product by keep ing variations in quality within the narrowest limits. Ontario Mining Association THE Thirty-Seventh Annual Meeting of the Ontario Min ing Association, which represents the producing mines of the Prov ince, was held in Elgin House on lake St. Joseph, Muskoka, in mid June. M. L. Uuouhaut, Manager for McIntyre Porcupine Mines, Limi ted. was elected President of the Association for 195(5-57, and M. S. Fotiierixoham, President of Steep Bock Iron Mines, Limited, was re elected Vice-President. Eleven of the fifteen Directors of the Association were re-elected for the ensuing year. To replace the four retiring Directors -- J. Beattie, B. W. Lang, G. A. McKay, and H. L. Roscoe -- the following new Directors were elected for 1956-57: J. M. Cunningham-Dunlop, President, Nipissing Mines Com pany, Limited. J. A. H. Paterson, General Man ager, Mining Corporation of Can ada. Limited E. A. Perry, Manager, Hollinger Consolidated Gold Mines, Lim ited R. V. Porritt, Director, Pamour Porcupine Mines, Limited Guest-speaker at the annual din ner, held on June 18th, was Dn. R. L. Hearn, Chairman of the HydroElectric Power Commission of On tario. He reviewed the electric pow er needs of Ontario, both present and future, and the- Province's place in the present world-wide de velopment of nuclear electric pow er. Concerning the latter, he stated 1 t 1 I1 M. L. Urquhart that construction will commence this summer on a 20,000 kilowatt experimental nuclear electric pow er plant adjacent to the Des Joa chims station through the joint ef forts of the Federal Government, the Canadian General Electric Com pany, and Ontario Hydro. It is planned to have this plant operating by 1959. The fuel will be natural uranium, possibly enriched with plutonium, and heavy water for the moderator of neutrons. It will be in the form of about 200 rods of uranium sheathed in zirconium to prevent its corrosion by the heavy water and to retain fission prod ucts. A second heavy-water system flowing through tubes surrounding the fuel rods will carry the heat given off by the fissioning uranium to steam generators, where ordin ary water will be converted to steam to drive a turbine which will, in turn, drive electric generators. From the experience gained in de signing and operating this experi mental plant, plans for stations of 100,000 kilowatt capacity or high er can be made. Field Conference, Alta Soc. Petr. Geologists AS WAS ANNOUNCED in our June Bulletin (p. 395), the Sixth Annual Field Conference of the Alberta Society of Field Geo logists will be held on August 23rd, 24th. and 25th in the CalgaryBanff area, centring .in the Canmore-Kananaskis region. The papers to be presented and discussed at technical sessions on the first day of the Conference were listed in the June Bulletin. Since that list was published we have learned that the author of the pap er on Belly River Formation Strati graphy, not known at that time, is Keith Williams. Also, an addi tional paper, on The Panther River Structure, by C. W. Hunt, has been definitely promised, and it is hoped that others will be offered before the opening of the Conference. The geology to be seen and stud ied in the field trips will range from the Palaeozoic to the Cenozoic and will include classic thrust faulting. Members planning to join the Conference should send their ap plications immediately to Mr. Gra ham Gammell, Registration Chair man, 406 Canadian Bank of Com merce Building, Calgary. Reserva tions for accommodations should be made through Mr. M. F. Teskey, Accommodations Chairman, 307 Sixth Avenue West, .Calgary. 490 The Canadian Mining and Metallurgical