Document dQK1Q8mMaBb26ywnKamekNBj6

June 1956 i f 3iii !n this issue: Refreshing interlude ... page 4 Basic insulating materials . . . page 13 Fabrication in smaL lots .. . page 18 Who buys, who specifies? . . . page 26 Just out.. . page 36 SC-ELEC-02770 f |- # 'asic Insulating Materials Ulh of o, series of Monthly articles on insulation engineering fundamentals bv Creham Lee Moses. ,\ianager. insulation Development Section. IT estinghouse 'jfiectric Corporation, East Pittsburgh. Pennsylvania. Mr. Moses is widely recog as a leading authority on insulation and is the author of more than 100 finical articles and papers as well as a book on electrical insulation. He has red importantly in many insulation developments. I^There are a number of basic mafenal components which are used either eparalely or as combinations in com posite insulation products. The solid, non-resinous materials will be dejcribed individually in this article. Later articles will present information on liquid and resinous materials and composite products made from them. Cellulose Cellulose is a most important com ponent of many forms of electrical in relation. In some electric equipment, it forms the major insulation while in nany other kinds, it is an essential but minor component used in connection intb a wide variety of other materials. Cellulose is used in the form of papers, jams, cloths, and pressboard. The celWose used in the electrical industry is mainly derived either from wood or cotton [inters. Less important sources include flax. hemp, rice, and numerous other plant stocks. Old rags and rope are important secondarv sources of cel lulose, Wood contains from 4(J to OU percent cellulose, while cotton contains up to 90 percent. Cellulose consists of carbon, hydrogen, and oxygen in re peating polymeric units of a chain-like construction. It is frequentlv described as being a natural high polymer. Cellulose has some very unique and desirable properties which include strength, flexibility, and elasticity. It is low cost and its good electrical and phvsical properties make it a most use ful insulation when properly fabricated and impregnated. The processing is important since cellulose is a "thirsty fiber" and is highly moisture absorb ent. Before it can be depended upon as good electrical insulation, it must be carefully dried and impregnated with oils, resins, or varnishes. Paper is the preferred form over cloth where di electric strength is the primary con sideration. The closely matted fiber structure of paper, when suitable- im pregnated. acts as a barrier to the free movement of ionic charges. On the oilier hand, where great mechanical strength is the primary consideration, the relatively stronger cotton cloths are more desirable. It is important to consider the dis advantages that are inherent in cellulusie materials. These include: la> low thermal stability, especiallv at elevated temperatures: I hi moisture sensitiv ity: and (c) the need for impregnation with a liquid or resin to obtain ac ceptable electrical properties. Moisture sensitivity is perhaps the greatest lim itation, consequently cellulosic ma terials should never be used in im portant electrical applications without very thorough pre-drying followed hv thorough impregnation. Impregnation does more than seal the fibers aiainst moisture absorption. Bv- replacing the air normallv in the fiber interstices, the dielectric strength of all insulation is materially improved. For example, im pregnated paper and pressboard is often found to have short time 60 cvele dielectric strength as high as 1.000 volts per mil with impulse levels several times that value. The poor thermal sta bility of cellulose poses a much more difficult problem. Therefore, cellulose is not usually employed where Class A temperatures of 105 C hot-spot are exceeded except for verv short periods, usually intermittent, of operation. The thermal degradation of cellulose begins with the loss of some of the chemicaljv combined water which embrittles and weakens the fibers. Then carbon dioxide and carbon monoxide are given off. Ali of these products of thermal degrada tion are objectionable. The water is insulation, June PJjh 1 j I harmful electrically and the oxides of quantity of contaminants such as par purified fibers are combined with bin carbon pose toxicity problems. Further ticles of iron oxide will be different as ers and fillers bv new paper make more. the residual carbon is an excel well as their ability to withstand acids processes. The resulting paper-like rr \ lent conductor and only a small amount and he3t. Most asbestos fibers are heat terials have many uses in electrical a oi decomposition in cellulosic insula resistant, but contain small amounts of paratus. These asbestos papers ec\ tion locally can destroy the effective hygroscopic moisture t usually about pare favorably with cellulosic pape ness of a piece of electrical equipment. 2G i. When they are dehydrated by in thickness and flexibility. They ca Ceiluiose ftlls an important place in excessive heating, thev are embrittled also be treated with organic and si electrical insulation in spite of these and fragile. All asbestos fibers are poor cone resins which improve their eiectr limitations. Its physical strength, ease electrical insulators unless they are cal properties. Asbestos in these fore of fabrication, convenience of use. and thoroughly dry and protected against is mainiv used for wire covering an. adaptability to commercial processes re-absorbing moisture. for insulation between the turns c make it a histblv desirable material not Chrysotile asbestos from Canada is strap coils. uiilv bv itself, but for use in combina well suited for spinning because of the Fiber Glass i tion with higher temperature classes. fineness of the fibers, good tensile Small percentages of cellulosic material strength, and flexibility. It may contain Glass is an excellent electrical insula are permitted under AIEE standards in a considerable number of magnetic lion, but in the forms commercial!' both Class B and H insulations, with oxides of iron particles which are con available before 1935, it was not suit toe provision that it must be used only ducting and may cause electrical fail able for the insulation of coils am for structural purposes where its deg ures under certain conditions. It is sus wire, such as used in electric rnachin radation does not seriously impair the ceptible to attack by sulphuric acid and erv. In plates, moldings, and castings, ability of the composite insulation sys hydrochloric acid. It is capable of glass appears to be a hard, brittle, vit tem to perform its intended function. withstanding temperatures up to 300 reous material and has very definite C without loss of strength. Above and rather narrow limits as to where it 400 C. as much as three percent water can be used as electrical insulation. of crystallization may be lost in one- With the commercial production o! half hour. At 600 C and above, prac glass in thin flexible monofilaments, a tically ail its water of crystallization vast new field was opened to its use as will be lost and it will become weak and electrical insulation. Fiber glass has brittle. Arizona Chrysotile asbestos martv very desirable characteristics. It contains considerable less magnetic ox possesses great physical strength, mois ide of iron and is used for certain elec ture and chemical resistance, and out trical grades of asbestos paper. While standing thermal endurance. The sci it can be spun into yarn, it is weaker ence of spinning glass into threads for and more brittle than the Canadian textiles is not vctv new as patents date Coilon tape used to insulate field coils. type. as far back as 1890 covering the in Portable Electric Toots. Inc. Asbestos Asbestos is a fibrous mineral some times called "serpentine'* and "horn blende,'' It exists in nianv forms in varying physical and chemical proper ties. Chrysotile and Amphibole are the more important commercial tvpes from Amphibole asbestos is a much more heat resistant typer it may withstand temperatures as high as 1,000 C with out serious degradation. It is relatively resistant to hydrochloric and sulphuricacids. The electrical resistance of Am phibole may be improved bv treating it with boric acid solution with dis tilled water. sulation of magnet wire with glass fi bers. The mass production of thin glass monofilaments in flexible form made the present widespread use of fiber glass insulation possible. ' * It was early found necessarv to de velop a special formulation of glas^ called "electrical grade"' for use in ths; ^* which asbestos insulation is fabricated. Crocidolite asbestos From Africa The first is essentially a compound of is different in chemical composition silicate of magnesium, iron, calcium, from either of the other tvpes ol as and frequently some manganese. The bestos described and is much more re second is similar except that it usually sistant to sulphuric acid, but harsher contains aluminum in addition. Com ami more brittle than Chrvsotile. mercial asbestos fibers obtained from rn recent years, improved mechani different parts of the world will varv cal and chemical processes have made in chemical composition as well as in asbestos fibers available in more de chemical and phisical characteristics, sirable forms. Thev are now used in for exampic, thrv differ cousiilerabK smaller dimensions oilli tremendous in flexibiid y ami the contained waters reductions in tbe number of impurities of crystallization, physical properties, and conducting particles compared to and color of the fibers. The nature ami what was feasible in ihe past. These M Insulation* June /">' irs employed a,- electrical insulation, characteristics of strength. liexibilin. successlulh in textile operation?. a I tvn> major form? of filler gla? and fuzziness depending upon the H pe Mnatl amount of lubricant mu?i i- im ? used for electrical tu-uiatmn are of filament, number of filament? in in mediately applied to tin- likiment- a "rnnl ill umi? fi la menl UIII' and dividual yarn?. and ihc mm ms; and Li ie \ mi- Ifitmed. it i|h till- in I-I n h| n ii l y "staple filin' iHiii'. I In' > iri 111) ii. blaming p m KC-.se?. l.aigei itiainotci ?nrii gia?- Siiiei - can lie handled \m filament varn? are the most com- filaments can be produced at a higher much as conventional lexlile matenal- ,njv used for both wire and cable rate and are hence lower in price than are fabricated. However, if the luiiri- lations and for woven fabric prod- the finer filaments. However, very thin cant is destroyed, the glass filaments fabrics mav require the use of the will readily abrade. The abrasion re for continuous varns. the filaments finest filament sizes- in order to have sistance of woven fabrics is very aechanicallv drawn from molten thinness, flexibility, and strength. The greatly improved further when the fab and can be compared in appear- yarn characteristics and their effect on rics are treated with varnishes. In to natural silk or linen, Staple cost must he considered in the proper some cases, it is necessary to remove TJj^r varns are produced from short selection and application of fiber glass the initial lubricant from the filament ^jjffth glass described as "slivers'' and yarns and woven products. of a fabric in order to apply certain 'fit made by drafting and twisting Fiber glass has many excellent char type? of resinous treatment to the doth. jj^se slivers together in a fashion simi- acteristics which make it desirable for Heat cleaning and chemical cleaning '-jj to the production of cotton yarns, use as electrical insulation. These can of the glass fabrics are frequently em jhe individual sliver fibers usually be summarized as follows: ployed before glass cloths are coated "jj^ve a length of about nine inches and 1. Excellent thermal endurance. with silicone varnish. This is impor Jay be as long as fifteen inches. The Since glass is inorganic and unaffected tant, for the original filament lubri Japle fibers are produced by the gas Uast drawing of molten glass which are jiien collected on a drum and spun into prns- Since glass fibers abrade them selves in their raw stale, it is necessarv J add a small amount of lubricant to the fibers to permit their subsequent processing without damage. The lubri cants added to glass fibers correspond to the natural oils present in organic fibers in minimizing friction between fibers, thereby reducing fiber breakage and abrasion. Staple fiber and continuous filament glass yams are made with fibers of sev eral different diameters, but with rela tively good control of the specific diam eters. Various types of yarn differ in the number and diameter of the indi vidual filaments used in their construc tion. Woven products have different by normal operating temperatures in electric machines, the basic fibers have no established temperature limit. The limit of operating temperature of fin ished products is dependent upon the type of resinous treatment employed. 2. Moisture resistance is outstanding as water is not absorbed into the structure of the filaments. W ater will collect on the faces and between the filaments and its exclusion is a prob lem of selection and application of resinous treatment. 3. Great chemical resistance is in herent in electrical grade fiber glass. So other fibrous material has compara ble general chemical resistance. 4. Superior mechanical strength is comparable with that of steel on an in dividual fiber basis. This permits the use of thinner fabrics where physical strength is the primary consideration. 5. Improvement in space factor for insulation is attainable because of the cants do not have comparable thermal stability to the silicone varnishes and processing varnishes over these lubri cants may result in an inferior prod uct. 2. Glass fabric? must be recoanized as primarily providing spacing insula tion just as cotton cloths do. There is no inherent dielectric barrier effect in the glass cloth. Like cotton cloth, fiber glass cloth can only become a dSelectnf barrier when it is suitably impregnated and coated with a resin. Thus the dielec tric barrier action of fiber glass fab rics must be attributed to the resin treatment selected and the technique of processing used. Furthermore, the thermal end-urance of such a fiber glass cloth is likewise dependent upon the resinous treatment and not upon the glass fabric itself. Therefore, in all glass cloth for high temperature insula tion. care and thought must be given to the tvpe of treatment and processing. improvements in physical characteris Synthetic Textiles tics. This is often a distinct economic advantage in comparison with both cel lulose cloth and asbestos cloth. Mo new material such as fiber glass is completely free from limitations. It is desirable therefore, to understand Recently, numerous synthetic fiber textiles have been introduced as elec trical insulation. These are either com linuous monofilaments of resins, or short fibers made of resins, that are some of the problems which face the insulation designer and must be consiaered in its use. spun into threads and woven into fab rics. They have the dielectric limitation of all fabrics--not being dielectric bar Electron micrograph of glass fiber aper developed by National Bureau of ''landards. 1. Glass filaments without any lubri cant or resinous treatment are abrasive and may cut each other under physical pressure or movement. To handle them riers unless varnish coated. Thermally. these materials lie between celiulosic fabrics and glass fabrics, and depend on the nature of the resin coating more Insulation, June JO.Vi 15 than upon their own characteristics lor Mica is a unique material which has which permits fabrication into tlri their life expectancy. great value as electrical insulation be flexible splittings with intrinsicai is cause of its electrical, mechanical, high dielectric strength. As it occurs Mica and chemical properties and the form nature, mica is a crystalline structu: .Mica includes several forms of min in which it is available as an engineer capable of being split into thin m eral silicates which were crystallized ing material, i.e., thin flexible films of lectrie barriers which lend the:: during their formation under tTemend- high dielectric strength and great selves to processing into composi ous pressure while cooling very slowly thermal stability. It is one of the insulating structures. These composi: from the molten state. There is preferen earliest materials used for insulation in insulating products made of mir tial orientation of the crystalline struc the electrical industry and has main splittings frequently have dielectr! ture producing thin parallel laminae. tained its position under severe com strengths equal to 10 or more time Mica derives its outstanding electrical petitive conditions against the inroads the breakdown strengths of the equivc and physical properties from the ex of other natural materials and many lent air spacing. Such high dielectr: istence of these laminae which permit modern synthetics. Mica splittings have strengths can be maintained througr its fabrication into these exceptionally high dielectric strength and low die out severe thermal aging when the mic thin, flexible, elastic members. The lectric loss combined with very high splittings are properly combined wii. mineral mica is found in many forms surface and volume resistivity, being suitable backing and bonding me and qualities, and exists in many parts infusible and r on-inflammable. Mica is terials. of the world mixed with clay, feldspar, one of the very best insulating materials The name mica is often applied \ and quartz. Of the seven recognized in thermal endurance. When heated all of the various forms of mica whethi- varieties of mica, only muscovite and beyond its safe temperature limit (well thin flexible splittings, thick films, o phlogopite are of industrial impor above 500C) mica dehydrates and powder. The simple term mica is ah tance, especially in electric equipment. subsequently calcines, thus becoming frequently extended to cover mic. Muscovite mica is commonly called opaque and silvery and losing its products which contain anv of the> white or ruby mica and is iound in a mechanical strength and dielectric forms in combination with the papers coarsely crystalline intrusive igneous properties. ' cloths, resin films, and bonds. It rock known as pegmatite. Phlogopite Chemically, mica is relatively inert therefore desirable to differentiate hr is commonly referred to as amber mica as it is unaffected by conventional tween the various forms of mic and occurs in somewhat similar rock solvents, water, alkalies, and acids materials as well as the products usin. except that it is associated with lime (except sulphuric and hydro-fluoric them when using the term "mica". stone and is basic in chemical reaction. acids). Mica should be protected from Mica was synthesized during Work India is the primary source of mus many oils as they may be absorbed War II, but the cost is excessive fo covite mica for commercial use in into the laminae and produce further most uses. Furthermore, there is n- electrical insulation. There are con separation and splitting. Mica pos economical trained labor for splitting siderable deposits of muscovite in the sesses high shear and tensile strength it in the Western Hemisphere. It i- Lnited States, Mexico, and South in a direction perpendicular to the being used in special capacitors, am America. Phlogopite is a hydrogen laminae, but is weak in the opposite in mica-filled glass molded parl' potassium magnesium silicate. Both plane and may easily be split into very where a rigid, brittle structure i- contain water of crystallization with thin flakes and platelets. Electrically, acceptable. about 4.9% in muscovite and 3,2% mica owes its outstanding properties to Three processes have been developer in phlogopite. the form in which it occurs in nature for making paper-like sheets from Left, Raw mica splittings being inspected before any processing. Right. Booh form, mica splittings being ,'nbrirated in10 flexible mica wrappers. 1 f> Junr l1i: jpjca platelet using essentially nvehtional paper making machines. rr \ platelets are produced bv three jerent systems: Hvdraulic pulsing jet. GLASS PLASTIC tj,) Mechanical grinding aTM roast ing to partial dehydration. ELECTRICAL Grinding, chemical treatment, and Toasting to a higher level COMPONENTS of dehydration. jsualh' the platelets are 0.0003 fches thick or less, and less than 0.1 jn their largest dimension. Until sln treated, these are very fragile and JfifScult to handle. Their physical and "^ectrical characteristics are completely "^ipendent upon the resins used for ponding and coating. Products made `"llroin mica papers are now in com- TJjercial production: and are under going trial use in service and functional 'evaluation in numerous laboratories. REPLACE HAG PHENOLIC Summary ^ The basic solid insulating materials "reviewed herein have individually peculiar characteristics which make them well suited to specific uses and limit their use in other applications. None of the materials discussed are precisely interchangeable. In substi tuting one for another, their advantages and disadvantages must be considered carefully, and weighed in the light of engineering objectives and economic considerations. Processing of the materials into their simplest commercial form is of great importance, but fabrication into fin ished insulation products and combina tion with resinous treatments is usually -even more significant in producing the best insulations. The early predominance of insulating materials is giving way. since insula tion systems as a whole are now con sidered the major factors in electric equipment design. - Article A o. 6 to appear next issue One-Sided Conversation : The defendant acknowledged that he hadn t spoken to his wife in five vears. and the judge put in a question. "What explanation have vou?" he asked severely. ""i our honor," replied the husband. "I didn't like to interrupt her." --Reichhold Chemicals. Inc. REPLACE MICA-GLASS Take Advantage of the No, 7 Essential,.. - GLASTIC ENGINEERING We know what glass-reinforced plastic con do. We understand electrical requirements. We can help you take advantage of our material and knowledge to improve your position in your field. Benefits: less material, less weight, higher impact strength, greater stability, increased arc resistance, trimmed manufacturing costs and improved end product. Glastic's specialized engineering contribution and long experience are yours to command. ASK FOR GLASTIC GRAPHIC NO. 3-M THE GLASTIC CORPORATION 4319 GLENRIDGE ROAD CLEVELAND 21, OHIO GLASTIC FIRST! Glass premix molding materials were originated by Glostie--the result of a discovery by a Giastic engineer during cooperative study of o customer's insulating problem in 1947. Giastic has since extended this experience over literally thousands of electri cal applications. Let this pioneer ing spirit and specialized back ground work for you! . . Print /m, 9 on Reader Service Card Insulation, June 1956 1 7