-SiliconesSurface arc:&, puiity, pH, moisture content, and uniformity are d l important considerations in the selection of fillers (6). Keiv and improved fillers such as Cab-0-Sil, Hi-Si1 X-303, and Du Pont Fine Silica are being developed specifically for silicone rubber. The author predicts that silicone rubbers will be developed with a mechanical strength equal to the organic mechanical rubber stocks in use today. illthough progress has been made in silicone rubber technology in the past 12 years, with increased interest in compounding, gum improvements, and filler developments, advances will be made cvrn more rapidly in the years to conic. ACKNOWLEDGMENT
The author wishes to thank his many associates of the Silicone
Products Department of the General Electric Go. whose work is described in this paper. LITERATURE CITED
(1) Aeons, ;if. C. (to General Electric Co.), U. S. Patent 2,448,756 (1944). (2) General Electric Co., Waterford, N. Y., “Imagineering with Silicone Rubher,” CDS-3, (3) ?Tavitz,A. E., Eke. M f g . , 52, 126 (February 1954). (4) Jones, H. F. ( t o Goneral Electric Co.), U. S. Patent 2,448,530 (1948). ( 5 ) I’feifer, C. W., Ibid., 2,666,041 (Jan. 12, 1954). (6) Pfeifer, C. W., Savage, 13. A I , , and B. R. White, India Rubber WorZd, 129,481-4 (1954). ( 7 ) Reynolds, 8. I., Elec. M ~ Q .52, . 1:W (February 1954). (8) White, B. R., AeTo Dig., 64, 34 (January 1052). RI:CEIVED for review April 12, 195.1.
ACCEPTEDSeptember 7 , 1964.
Silicones in Naval Shipboard Electrical Equipment H. P. WALKER
AND
G. AI. VAN LEAR
Bureau of Ships, Department of the Nauy, Washington 25, D. C .
Silicone insulation was investigated for possible shipboard applications because By utilizing this new family of materials the electrical designers have been able to achieve 30% savings i n weight and space. The increased moisture resistance of silicone insulated equipment has also resulted i n greater reliability of the equipment. Military specifications have been written to cover silicone materials, as well as cable and equipment utilizing silicones. The availability and utilization of such specifications have done much to allow the military as well as the industrial users to obtain uniform products. of its unique thermal and moisture resistance properties.
HE purpose of this paper is to acquaint the reader with what has been achieved in the application of silicone insulation to naval shipboard electrical equipment and power cables. SILICONE PR0I)UCTION
The year. 1913 should be considered as an iniportant p a r for the electrical industry for, with the development of silicones, a new class of electrical insulation v a s ready for production. This insulation would enable the electrical equipment designer to renew his attack on his two worst enemies-moisture and heat. The total silicone production capacity a t the end of 1951 stood a t 5,000,000 pounds per year. Proposed capacity planned through 1954 pushes t,his output to an estimat,ed 31,000,000 pounds per year for all producers. The electrical industry utilizes only a part of the silicone production. Estimates range anywhere from 15 to 40y0,. Products used cover such things as insulating resins, compounds, silicone rubber, laminating resins, coat,ing materials, fluids, and lubricank These, in turn, are used to make Class H componcnls such as glass-served magnet wire, lead wire and cable, pasted mica, glass-mica combinations, laminates, treated fabrics and t’apes, sleeving, rigid tubes, and molded shapes. Electrical equipment utilizing these silicone products range all the way from small solenoid roils to large transformers. CABLE n E v E L o i w E w
Silicones and silicone insulated materials in various forms have found many applications in the electrical industry and are
November 1954
rapidly finding more. A comprehensive treatise on the subject, citing some 150 references has been written by McGregor ( 7 ) . One of the first and principal applications in the electrical field has been in cables for Navy shipboard use. Since the early silicone materials appeared to be formulated for mechanical purposes, it r a s necessary to develop satisfactory electrical characteristics. This has been accomplished in the low voltage field, and t>herange is expanding. Shipboard cables must be rugged to withstand severe installation handling and must possess the maximum degree of reliability of operation throughout a long life under difficult environmental conditions involving exposure to weather, fresh and salt water, oil, vibration, abrasion, high shock impact, and a wide range of ambient temperat,ure. And this must be accomplished with a reasonable faccor of safety by cables of minimum size and might. I n commercial applications generally the size and weight of the cable installation may not bc so significant. The rapid growth of the shipboard electrical plant and distribution system, including electronics, made it imperative that thc size of cables and wireways be reduced and not allowed to expand. Vessels that were built during World War I1 were xired with Navy-type heat and flame resistant armored (Type HF,\) cables in which the primary insulation mas varnished cambric or synthetic resin reinforced with a cushioning fire wall of asbcst’os. These designs have given entirely satisfact,ory seruicc, but it was hardly practicable to alter the construction of these cables during a large shipbuilding program, so a long-range development was undertaken. A project was established in IO42
INDUSTRIAL AND ENGINEERING CHEMISTRY
2345
t o make a close study of the materials and const,ruction of the Type HFA cables for the purpose of determining the extent to which the thickness of insulation and coverings might be reduced without a significant sacrifice in performance and with retention of a reasonable factor of safety. The qualified suppliers assisted in this work and a specification was actually w i t t e n for smaller Type HFA cables using thinner walls of essentially the saine component materials. Homver, this specification was not used for purchase, partly because the end of large shipbuilding programs was in sight, and partly because it was realized that a substantially greater reduction in cable size could be accomplished by employing superior component materials and new design prineiples. IO6 10'
I d !
I INSULATION RESISTANCE AS A - FUNCTION OF DAYS HUMIDIFIED -1
I
2
:
;
k
6
J7
DAYS HUMIDIFIED
Figure I
Although t h k development was aimed primarily a t size and weight reductions, it was suspected that better operating characteristics could be secured a t the same t,ime. Beginning in 1943 and 1944 a thorough study vas inade of all available insulating and other component materials. A mass of information was available from continuing research and developmental programs that the Bureau conducts in Naval Laborat,orics to evaluate component materials for the purpose of ensuring that equipmeiits will utilize to best advantage the most suitable and latest combination of components in designs that are fitted to the peculiar operating conditions on shipboard. About this time the silicones appeared as a possible cable insulation. The early data indicat,ed that these promising materials should be given the highest priority tom-ard developnient of suitable grades for cable insulation, in the same manner that the Kavy took the initiat,ive in developing production facilit,ies in t,he field of polyethylene insulation and polyvinyl chloride type nonmetallic sheath components. It was decided to develop new cable designs based on silicone insulations, largely because of their demonstrated &ability, and because it was suspected that compound formulations, based on the unique molecular Rtructure of the silicones might be developed that would not char or carbonize and that might be capable of suEtaining rated voltage and performing normal Lunct'ions during a fire. This feature has been developed successfully, although close manufacturing controls are essential. The initial work with silicone rubber indicated that, its physical properties although poor compared l.0 other insulations, might be made into a sufficiently rugged cable. The early compounds
2346
appeared to be formulated for mechanical applications. Some improvement in electrical properties was desired, and a largc improvement in speed of extrusion and cure was necessary from t,he standpoint of insulating t,he miilions of conductor-feet required for Kavp cables. I t took several years of intensivc work to produce a silicone rubber formulation with reasonably acceptable extrusion speeds and finished cable characteristics. The rccommended cure of 24 hours or more a t 480' F. was impractical for Kavy planning. It was necessary to develop compounds for relatively rapid cont,inuous vulcanization. The starting point was a noiiiinal 20-mil xvall on KO. 18 American vire gage (AWG) strand. Currently this development has progressed t'o ahout 500 feet per minute, or a cure of less than l/2 minute t o produce acceptable physical and electrical properties, quite in contrast to 24 hours. Perhaps the insulation will improve aftcr years of service instead of showing a progressive deterioration as ordinary insulations do. This tender cure of lees than one minute leaves the insulation susceptible t o contamination by other cable components, and presents a major problem that has t o be matched carefully. A containing Kava1 laboratory project checks the compatibilit'y of any proposed new material with the silicone insulation and, if further investigation is ivarranted, t,hen a completed cable mupt shoiv satisfactory performance before the new component can be used in production. This procedure has been found to be a necessity with both the power and control cables. This compat,ibility problem was one of the most serious obstacles to overcomc, alt'hough a considerable iiuinber of other lesser but new and 1111foreseen obstacles were encountered and overcome concurrently during the development. Another continuing laboratory project, operates to construct and test hand taped cable models, insulated with varying combinat,ions of selected tape materials. Inicrior materials are discarded wit,hout further testing expense. T h r superior materials or combinations are incorporated in developmental contracts for factory made cable samples for evaluat,ion tests in Saval laboratories. C4BLE APPLICATIOV S
Puichase specification MIL-C-2194 for silicone insulatrd cab1t.s mas drafted in the latter pait of 1948. Throughout this development the Bureau worked closely with the material suppliers in developing the components, and with the cable manufacturers in obtaining several hundred experimental cable samples that Aere fabricated and evaluated. Some 30 odd industry technical committee meetings have been held since 1942. It n a s only thiough the full cooperation of all parties that these cable designmere advanced to a stage suitable for practical use in about half the normal time required foi a major development of this scope The control cables, insulated with Class E (extruded silicone lubber) dielectric, contain from 1 to 44 conductors in sizes Iris than Xo 10 AWG and the following essential features LTithout detail. 1. St'randed conductor of bare copper, xvvatertight. 2 . Class E dielectric 3. Closely woven glass braid, lacquered 5. Insulated conductors cabled, watertight 0. With or without binder over core 6. Impervious sheath i. Braided wire armor and paint
The power and lighting cables, insulated with Class 1 ' ' (taprd silicone treated glass cloth) dielectric, contain from 1 to 1 conductors in sizes larger than No. 10 AVG up to 808,000 circular mils. The essential features are the mine as thosc in contyol cables except that the extruded Class E dielectric and lacquercd glass braid are replaced with the taped Class T dielectric. Thew new cable designs can be fabricat,ed with existing mariufacturirig facilitiea. The special equipment for applying asbestos roving or felted asbestos and saturating it) are not required.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 46,No. 11
-SiliconesSpecification MIGC-2194 contains practical testing procedures that are used in qualificat,ion evaluations and in inspecting material offered for delivery under contracts. Several of the unusual tests that were developed are described briefly as follows: Qualification Cold working S bend on 12X mandrel a t -2OQ
c.
180° Cold bend on 12X mandrel at --20° C. Current loading 400 hr. a t 128' C. copper Current loading 18 hr. at 126' C . sheath 960' C . Gas flame a t rated voltage, hr.
Inspection
.-
N o damage
. . ... ..
No damage No damage 3
., .,..
N o damage
......
N o damage
1
These reduced diameter silicone insulated cables have been installed on all new construction vessels contracted for since 1948 with the exception of several auxiliary ships which used standard Type HF.4 cables from Naval stores. These cables supply power and lighting, interior communication (except telephone) and fire-control circuits comprising about 85% of the total cable. Telephone cable and a number of special purpose types will be converted to silicone from time to time. These cables are being installed also when changes and additions are made to electronic equipment during activation, alteration, and conversion work on combatant vessels where space is a t a premium. But, in general, all work except new construction is done with the types of cable that were originally installed, largely to avoid changing the fittings. The silicone insulated, reduced-diameter cables, as they are called, are handled and installed exactly as are the older Type HFA cables, using the same type of hangars and fittings. Excellent reports are received from installing activities as to relative flexibility and ease of handling compared to Type HFA cables. One improvement in installation handling is that Type HFS cables are required to be preheated before installation when the temperature is below freezing, a requirement which has been carried forward from many years ago when thermoplastic sheaths were young, whereas the silicone insulated cables will withstand severe handling down to -20" C. Bolted, squeeze-on, or other mechanical connectors are applied with no attempt to clean the water sealing compound from the strands. No solid conductors are used. Bare, uncoated copper is used in all cables. The same current ratings are assigned to Type HF-4 and reduced diameter cables of the same number and size of conductors. This did not result in a higher operating temperature for the smaller cables because of the better heat dissipating qualities of the insulation and coverings. Control cables are rated a t 600 volts a.c. or 1000 volts d.c.; all other cables are rated a t 1000 volts a x . or d.c. Some of the advantages of reduced diameter shipboard cables can be summarized as: 1. Greater reliability of operation under adverse conditions such as emergency overloads and fire 2. Reduction of 30% in space requirements 3. Reduction of 20% in weight 4. Better electrical properties a t operating temperature 5 . Elimination of critical domestic and imported materials
The reduction of a ship's worth of cable is important. On a prototype destroyer it nieam nearly 9 tons and on a large aircraft carrier it means 100 tons of distributed weight. This results in better military efficiency, safety a t sea, and habitability. -4nd the cable designs are such that these advantages are being realized a t no increase in cost for a ship's worth of cable. To date more than 17,000,000feet of cable or about 80,000,000 conductorfeet at a cost of over $12,000,000 have been installed on Naval vessels. The installing activities report favorably regarding space saving and ease of handling. EQUIPMENT APPLICATIONS
Bureau of Ships engineers are constantly faced with three probl e m in the design and procurement of electrical equipment aside from the special operational requirements for shipboard applications. Present aln-ays are the problems of size and weight,
November 1954
moisture and heat. Silicone insulation, when correctly applied, can and does help in solving these problems. A review of the Bureau's participation in silicones should give the reader an opportunity to appraise his own proposed application of silicone insulation in the light of these findings. Although some direct purchases of silicone products are made such as varnish, grease, compounds, and stock components, the Bureau's main purchases involving silicones are end use items of electrical equipment. Thus Class H motors, generators, or transformers are usually purchased directly from the electrical equipment manufacturer or subcontracted for by the machine builder. Therefore, in order to exploit the silicones to their full advantage it was necessary, very early in the program, to obtain the assistance of a group of manufacturers to help plan and participate in programs
I
c
DISSIPATION FACTOR AS A FUNCTION OF DAYS HUMIDIFIED
DAYS HUMIDIFIED Figure 2
of building and testing Class H equipment proposed for shipboard we. The results of some of this work ( B ) as well as much of the commercial equivalent testing has been reported in the literature ( 2 , 4, 6). The advent of silicone insulation was a stimulant to the electrical industry and indeed a new era of testing and re-evaluation of all insulating materials began. As a result of the initial motor tests the Bureau of Ships in 1946 adopted a maximum temperature limit of 200" C. for Class H insulation. Commercial standards, however, were established a t the more conservative figure of 180" C. The final results of accelerated life testing of Class H motors reported by one group of investigators indicate a t least 7 years of continuous operation a t a hot spot temperature of 220" C. ( 5 ) . Thus, the Bureau's adoption of 200" C. was justifiable. FUNCTION4L TESTING 4ND DESIGN LIMITS
Functional type of testing has appealed to many investigators and in many cases has been adopted as the only practical method of evaluating insulation-on a system basis rather than by the chemical structure of individual materials. Mathes of the General Electrical Co. reported on this new concept of functional evaluation of insulating materials in 1948 (8). Today many test programs are under way involving silicone insulation as well as conventional materials using these n e v test principles with the objective of realigning the temperature limitations of all insulating materials based on where they are used and how they
INDUSTRIAL AND ENGINEERING CHEMISTRY
2347
'are used ( 1 , 3). Unt(i1the result,s of these current investigations are available and new standards adopted, i t is considered that the present standards should be followed. The Bureau of Ships adheres to the following deqign criteria for shipboard elect,rical equipment: 1. For a normal life expectancy ( 7 . 5 to 10 years or' continuous operation) silicone insulated electrical equipment should be designed so as not to exceed a hot spot temperature of 200" C. This for each increase of 12' C. in temthermal life is reduced by perature. 2. Insulation quality should be det,ermined by subjecting the silicone insulat,ed equipment (or coil structure) t o a 1-week humidification test using 100% relative humidity. Daily measurements of insulation resistance and dissipation factor should reveal faulty material or applicat'ion technique. Figure 1 shows insulation resistance as a function of days humidified. -4value of 2 megohms should be considered as borderline betrveen good and poor quality insulation. Figure 2 sliows dieiipation factor (tan 6 ) as a function of days humidified. A value of 25% should be considered as a danger point.
If these criteria are used, successful equipment ~ h o u l diwult. T-Towever, unless the correct materials and application techniquw are used trouble will followr. EQUII'\.IEN'I' Pt~RCII.ASES
Psiiig the criteria as a guide the Bureau has to date purchased the following silicone insuhted shipboard type equipment:
for all insulation problems. Class A and €3 insulated electrical equipment when correctly applied should give inany years oi satisfactory eervice. \Then severe service conditions prevai:, siliconc ius5dation may help solve t,he application prolilem. COYCLCYION
Silicone insulation ivhen correctly applied to shiphoard c!lcctrical equipment, and cable has resulted in 307, savirig? in wcight and space. Improved moisture resistn:ice resulting in inore r ~ liable equipment has heeri achieved by the upe of silicon(>inwlntion in man\- c a m . LITERATURE CITED
Cypher, G. d.,and Harrington, It.. Tmns. A m . Illst. Eluc. E J ~ Q I . S . , 71, pt. 111, 251 (1952). De Kiep, J.,Fiill, L. R.. a n d Moses. G . L., I W . , 64, 94 (1945). ine, E., presented at Ani. Inst. Eler.
Dexter, !J. F., Manning, 11. I. .. and Kalker. 11. P.. E k r . TVo,ld, 130 (Aug. 14, 1948). Grant, G . , Moses, G. L., Kaiippi. T. *i,, and Gibson (>.T. ., T r a n s . Am. Inst. Elm. Enyrs., 68, p t . 11, 692 (1949). Iiauppi, T.A , , Grant, G.. l\loseq, C lioi~seEngr , 5, 135 (Septeinher 19 MeGregor, 12. I{., "Silicones and Xew York, 1954. 1\Iat,hes, K. N.,T m m . Am. I n s f . E k e . Z g g r . , 67, p t ~11, 1 2 X (1943i.
Walker. 11.
P,, Ibid.,
66, S i 7 (1917).
1. 406 generators totaling 150,000 l w . in sizes from 60 to 1500 ~kw.On one class of destroyer; t,he generators \rere rewound with silicone insulation, increasing the rating by 40%) thus saving the Iurcliase of new equipment. 2. 2069 transformeis totaling 26.700 h a . in sides from i . 5 to 37 .5 lcvn 3: 1882 motors for surface chips totaling 42,000 hp. in sizes iron1 1 to 125 hp. 4. 338 motois for submaiine totaling 3098 hp. in sizeq from t o 55 hp. PREC%UTIOKS
Experience gained as a result of these purchases has indicated that. the following mat,erial and technique lactors are importmit,:
1. Prehaking peveral hours at 300" to 400" 3'. before vmiisli dipping the equipment ensures removal of moisture from tlic winding and ensures curing of any undercured component. 2. Dipping time should be miiiimum to prevent solvcnt softening of the silicone film. 3. A minimum of three dips and bakes is considered i i r c c s sary. Kever use air-dry type silicone products on lvindings. a. Silicone resins will give off vapors, under van-ing degrccs of temperature depending on the type of resin used, n-hich may interEere with normal commutation on d.c. machines at the brush face thus causing excessive brush !Tear ivith possible ultimak failt of the machine from coiitaminated surfaces. This condition aggravated by either an illcrease in temperature or restrict ventilation. Volatiles are given off a t about 150" C. for t baked silicone resins and a t room temperatwe for thr air-dry ty silicones. 6. Silicone varnished glass cloth, tape, and sleeving slio,uld bc used with caution. nIica-glass-silicone composites or siliconc rubber glass combinations are preferred due t o better htmdliny and performance characteristics.
4.
1
From an application standpoint silicone insulated electrical equipment has been inatalld on aircraft carriers, submarines, destroyers, mine sweepers, landing rriiftl and auxiliary vessels. Ships Pervice and emergency power generators, special scrvicr power dist,ribution transformem, fire and flushing pumps, ventilating fans, anchor windlass, Forced draft blowr; fuel oil serviw pumps, bilge pumps, and numerous other motor applicat,ionshave utilized silicone insulation. Some uses have been t o reduce size and weight; others have been to irnprove moisture resistance. High nmbient temperatures, more reliabihy, and longer life have been other factors influencing the selection of silicone insulation for many applications. However, silicone insulation is not, a cure-all 2348
C3JRIESY
oow
C O A N I N ( I GORP
Use of Silicon Fluid in Dafihpots of Regulntors in Stearii Generating Plants
INDUSTRIAL A N D ENGINEERING CHEMI.STRY
V O ~46, . No. 11
