Document wKXzdazn3m8dQNnvOYnODJgNV

June 1956 this issue: Refreshing interlude ... page 4 Basic insulating materials .. . page 13 Fabrication in small lots ... page 18 IFho buys, who specifies? ... page 26 Just out... page 36 I ulation Engineering Fundamentals--Ao. 5 1 ! v --,--I >. i il Waste Insulating Materials ith oj a series of monthly articles on insulation engineering fundamentals b\ Graham Lee Moses. Manager. Insulation Development Section. Westinghouse jKctric Corporation, East Pittsburgh. Pennsylvania. Mr. Moses is widely recog`gW as a leading authority on insulation and is the author oj more than 100 {nical articles and papers as veil as a book on electrical insulation. He has red importantly in many insulation developments. ^There are a number of basic ma terial components wnich are used either separately or as combinations in com posite insulation products. The solid, *on-resinous materials will be de scribed 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 with a wide variety of other materials. Cellulose is used in the form of papers, yams, cloths, and pressboard. The celWose used in the electrical industry is mainly derived either from wood or cotton linters. 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 U> 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 "thirstv 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 oiis. 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 suitably im pregnated. acts as a barrier to the free movement of ionic charges. On the other 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 cellulusic materials. These include: lai low thermal stability, especially at elevated temperatures: (bl 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 normally 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 chemicaliv combined water which embrittles am! weakens the fibers. Then carbon dioxide and carbon monoxide are given off. All of these products of thermal degrada tion are objectionable. The water is Insulation, Juno 1o harmful electrically and the oxides of quantitv of contaminants such as par carbon pose toxicitv problems. Further ticles of iron oxide will be different as more. the residual carbon is an excel well as their ability to withstand acids lent conductor and onlv a small amount and heat. Most asbestos fibers are heat of decomposition in cellulosic insula resistant, but contain small amounts of tion locally can ciestrov the effective hygroscopic moisture 'usually about ness of a piece of electrical equipment. 2'b i. When they are dehvdrated by Ceiluiose nils an important place in excessive heating, they are embrittled electrical insulation in spite of these and fragile. Ail asbestos fibers are poor [imitations. Its physical strength, ease electrical insulators unless thev are of fabrication, convenience of use. and thoroughly dry and protected against adaptability to commercial processes re-absorbing moisture. make it a highly desirable material not Chrvsotile asbestos from Canada is onlv bv itself, but for use in combina well suited for spinning because of the tion with higher temperature classes. fineness of the fibers, good tensile Small percentages of cellulosic material strength, and flexibility. It may contain are permitted under AIEE standards in a considerable number of magnetic both Class B and H insulations, with oxides of iron particles which are con tne provision that it must be used only ducting and may cause electrical fail for structural purposes where its deg ures under certain conditions. It is sus radation does not seriously impair the ceptible to attack by sulphuric acid and ability of the composite insulation svs- hydrochloric acid. It is capable of tem to perform its intended function. withstanding temperatures up to 300 C without loss of strength. Above 400 C. as much as three percent water of crystallization mav be lost in one- half hour. At 600 C and above, prac tically ail its water of crystallization will be lost and it will become weak and brittle. Arizona Chrvsotile asbestos contains considerable less magnetic ox ide of iron and is used for certain elec trical grades of asbestos paper. While it can be spun into varn. it is weaker and more brittle than the Canadian Cotton tape used to insulate Reid coils. type. Portable Electric Tools. Inc. Amphibole asbestos is a much more Asbestos heat resistant type: it mav withstand temperatures as high as 1,000 C with Asbestos is a fibrous mineral some times called "serpentine" and "horn blende. * It exists in nianv forms in varying physical and chemical proper ties. Chrvsotile and Amphibole are the more important commercial tvpes from out serious degradation. It is relatively resistant to hydrochloric and sulphuric acids. The electrical resistance of Amphibole mav be improved bv treating it with boric acid solution with dis tilled water. 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 of 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 and more brittle than Chrvsotile. mercial asbestos fibers obtained from different parts of the world will varv in chemical composition as well as in chemical and ph\siral characteristics, for example. thev Jitter enusiderablv in fievibilily and the ('untamed waters of crystallization, physical properties, and color of the fibers. The nature and In recent years, improved mechani cal and chemical processes have made asbestos fibers available in more de-irable forms. Thev are now used in -mailer dimensions with tremendous reductions in the number of impurities and conducting particles compared to what was feasible in (he past. These purified fibers are combined with bin ers and fillers bv new paper make, processes. The resulting paper-like rr teriais have many uses in electrical a paratus. These asbestos papers co; pare Javorably with cellulosic pace in thickness and flexibility. Thev ca also be treated with organic and >i cone resins which improve their eiectr cal properties. Asbestos in these fore is mainly used for wire covering an. for insulation between the turns c strap coils. Fiber Glass Glass is an excellent electrical insuid tion. but in the forms commercial!' available before 1935. it was not suit able for the insulation of coils am wire, such as used in electric machin erv. In plates, moldings, and castings, glass appears to be 3 hard, brittle, vit reous material and has very definite and rather narrow limits as to where :t can be used as electrical insulation. With the commercial production 0! glass in thin flexible monofilaments, a vast new field was opened to its use as electrical insulation. Fiber glass has manv very desirable characteristics. It possesses great physical strength, mois ture and chemical resistance, and out standing thermal endurance. The sci ence of spinning glass into threads for textiles is not verv new as patents date as far back as 1890 covering the in sulation of magnet wire with glass ft* bers. The mass production of thin glass monofilaments in flexible form mad the present widespread use of fiber glass insulation possible. It was early found necessary to de velop a special formulation of glas^ called "electrical grade'' for use in th^ "* I t Insulation, June !'*.; rs eni|**m**<i a> electrical insulation, characteristics of strength, liexibilitv. suecessfulk in textiio operation-, a I two major form- of filter glas> and fuzziness depending upon the npe -mall amount of lubricant mu-i hr u- lS used for electrical insulation are of filament, number of filament- in in mertiali'U applied j,. tin filament- a- 'cr*ntmuon*- filament \ani and dividual yarn-, and ibr waving and llir\ an- I.nmed. W i|ii tin- in I >m at nn i '`staple fibci' suin', i l><' 'oiitimi- blaming juncr-sc-. Laigoi iliamcici >iii-b girt?-- llbri- ran l>r bandied \ ri \ filament \arn> arf the most corn* filaments can be produced at a higher much as conventional textile materials ,,,iv used for both wire and cable rate and are hence lower in price than ate fabricated. However, if the lubri lations and for woven tabnc prod- the* finer filaments. However. verv thin cant is destroyed, the glass filament- fabrics mav require the use of the will readilv abrade. The abrasion re or continuous varns. the filaments finest filament sizes in order to have sistance of woven fabrics is verv menhanicali\ drawn from molten thinness, flexibility, and strength. The greatlv 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 be considered in the proper some cases, it is necessary to remove Tgjjcr varns are produced from short selection and application of fiber glass the initial lubricant from the filament glass described as "slivers" and yarns and woven products. of a fabric in order to appiv certain "Jre made by drafting and twisting Fiber glass has many excellent char tvpes 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 '^r to the production of cotton yarns, use as electrical insulation. These can of the glass fabrics are frequentiv em jjje individual sliver fibers usually be summarized as follows: ployed before glass cloths are coated "jVe a length of about nine inches and pav be as long as fifteen inches. The ^uple fibers are produced bv the gas Jlast drawing of molten glass which are jjjen collected on a drum and spun into ^unts- Since glass fibers abrade them Selves in their raw state, it is necessary to 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 *nd 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 varn differ in the number and diameter of the indi vidual filaments used in their construc tion. Woven products have different 1. Excellent thermal endurance. Since glass is inorganic and unaffected 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 a* water is not absorbed into the structure of the filaments. Water 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. \o 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 phvsical strength is the primary consideration. 5. Improvement in space factor for insulation is attainable because of the with silicone varnish. This is impor tant. for the original filament lubri cants do not have comparable thermal stability to the silicone varnishes and processing varnishes over these lubri cants may result in an interior prod uct. 2. Glass fabric? must be recognized 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 dielectric 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 type 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. No new material such as fiber glass is completely free from limitations. It is desirable therefore, to understand some of the problems which face the insulation designer and must be con sidered in its use. Recently, numerous synthetic fiber textiles have been introduced as elec trical insulation. These are either con tinuous monofilaments of resins, or short fibers made of resins, that are 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 ''dper developed by National Bureau of standards. 1. Glass filaments without anv lubri cant or resinous treatment are abrasive and may cut each other under phvsical 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 15 than upon their own characteristics for Mica is a unique material which has which permits fabrication into tin their life expectancy. great value as electrical insulation be flexible splittings with inlriusicai f. cause of its electrical, mechanical, high dielectric strength. As it occurs Mica and chemical properties and the form, nature, mica is a crvstalline structu: .Mica includes several forms of min in which u is available as an engineer capable of being split into thin d eral silicates which were crystallized ing material, i.e., thin flexible films of lectric barriers which lend the:: during their formation under tremend 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 mic 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 timr Mica derives its outstanding electrical petitive conditions against the inroads the breakdown strengths of the equivr 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 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 whethr varieties of mica, only muscovite and beyond its safe temperature limit (well thin flexible splittings, thick films. i> phlogopite are of industrial impor above 500*0) 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 found in a mechanical strength and dielectric forms in combination with the paper 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 be 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 usirs- except that it is associated with lime (except sulphuric and hvdro-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 electrical insulation. There are con separation and splitting. Mica pos economical trained labor for splittin- siderable deposits of muscovite in the sesses high shear and tensile strength it in the Western Hemisphere. It ! United States. Mexico, and South in a direction perpendicular to the being used in special capacitors, a' America. Phlogopite is a hvdrogen laminae, but is weak in the opposite in mica-filled glass molded par1' 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 develop*1- 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. Book form mica splittings being lahrirated it*10 flexible mica wrappers. 16 Insulation, Jit nr l'1 >> j^jca platelet* using eseutialk arentionaI paper making: machines. r ! A CTl platelets arc produced by three \ ferent systems: Hv0raulic pulsing jet. GLASS PLASTIC [i,) Mechanical grinding and roast ing to partial dehydration. ELECTRICAL Grinding, chemical treatment, and roasting to a higher level COMPONENTS of dehydration. [jsuallv the platelets are O.OOOo jehes thick or less, and less than 0.1 in their largest dimension. Until sin treated, these are verv fragile and difficult to handle. Their physical and "^ectrical characteristics are completeK "yjjependent upon the resins used for ponding and coating. Products made Sjom mica papers are now in com mercial production: and are under going trial use in service and functional "^valuation in numerous laboratories. SEPIA CE SAG PHENOLIC Summary ^ The basic solid insulating materials "Reviewed herein have individually peculiar characteristics which make them well suited to specific use? 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 carefullv, 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 svstems as a whole are now con sidered the major factors in electric equipment design. Article Ao. 6 to appear next issue One-Sided Conversation . The defendant acknowledged that he hadn't spoken to his wife in five years, and the judge put in a question. "What explanation have vou?" he asked severely. "A our honor." replied the husband. "I didn't like to interrupt her." --Reichhold Chemicals. Inc. SEP LACE WCA-GIASS Take Advantage of the No. I 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 impoct strength, greater stability, increased arc resistance, trimmed manufacturing costs and improved end product. Giastic's specialized engineering contribution and long experience are yours to command. ASK FOR GLASTIC GRAPHIC NO. 3-M THE GLASTIC CORPORATION 431? GLENRtOGE ROAD CLEVELAND 21-, OHIO GLASTIC FIRST! Glass premix molding materials were originated by Glastic---the result of o discovery by o Glastic engineer during cooperative study of a customer's insulating problem in 1947. Glastic 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 Int. 9 on Reader Service Card Insulation, June 1956 IT