US2450532A - Insulating means and method of making the same - Google Patents

Description

T.TGNOLA Oct. 5, 1948.

INSULATING MEANS AND METHOD OF MAKING 'IHE SAME Original Filed July 9, 1940 Patented Oei. 5, Y

luNrrltnSTATES PATENT oFFi-cla: I asusta' um!) O'F originel application July c, me, serial No.

344,506. Divided and this application' Marc 30, 1942, Serial No. 436.831

l This invention relates to ignition apparatus, and more particularly to spark plugs for internal combustion engines, insulating means adapted for use therein, and the method of making the 7 claim.. (ci. 114-209) A 2 and with parts broken away, showing one form of spark plug embodying the invention;

Fig. 2 is a bottom view of the spark plug shown in Fig. 1; and,

same. Figs. 3, 4, 5, and 6 are views similar to Fig. 1 This application is a division of my copending showing other modifications and embodiments application Serial No. 344,506, flied July 9, 1940, of the invention with the upper portions thereof for Ignition apparatus and method of making broken away.

the same," now Patent No. 2,331,748. Various embodiments of the invention are illus- Spark plugs are quite generally recognized as l0 trated in the drawings, by way of example, in

the weakest links in the ignition systems of modern internal combustion engines, particularly on high lcompression aircraft engines which must operate continuously for long periods of time at high speed and under heavy loads. One of the chief difculties has been in providing proper electrical insulation which will withstand the high heat to which the plugs are subjected during use and yet prevent gas leakage and ilashovers.

the form of radio-shielded spark plugs which are particularly adapted for use on aircraft engines. It will be understood, however, that the invention is also applicable to unshielded spark plugs and other electrical devices. As shown in Fig. 1, one form of spark plug embodying the inven-tion comprises a metallic shell lo which carries a ground electrode I i in the lower end thereof and is externally threaded at I2 for cooperation One oi' the objects of the presen-t invention is 20 with a threaded opening in an engine cylinder to provide a novelly constructed spark plug (not shown) in the usual manner. Threaded wherein the foregoing difficulties are substantially into the outer end of shell i0 is a nut or body obviated. portion i3 having a tubular radio-shielding .barrel Another object of the invention is to provide i4 formed integrally therewith or otherwise suita spark plug where novel means are employed for ably secured thereto and an internal flange il facilitating the conduction of heat fromthe cenintermediate the ends thereof for supporting a ter electrode to the outer metallic parts thereof. novel center electrode assembly. Shell i0 and Still another object is .to provide novel electrical member i3 together form what may be referred insulating means and method of making the to as the body of the spark plug and in some insame, said means being adaptedfor use in spark stances, as shown in Fig. 6, may be formed as one plugs and other devices wherein high heaty conpiece. ductivity is desired. j In the form illustrated, said center electrode A further object is to provide a novelly conassembly comprises a metallic cylindrical spindle structed spark plug employing ceramic insulating I8 provided at its lower end with a head portion means andcushioning means for the latter to il which is shaped and positioned for cooperaminimize breakage thereof during assembly and tion with ground electrode Il in a manner well use. l understood in the art. Spindle i6 is tightly A still further object is to provide a novel spark wrapped in a sleeve IB of sheet mica or other plug and method of making the same whereby the lsuitable insulating lmaterial which yserves to insuheat conductivity from ceramic parts to metal 401 late the center electrode from nut i3 and the parts is enhanced. insulated spindle has a tight sliding flt in the The above and further objects and novel feareduced bore surrounded by internal flange i5. tures of the invention will more fully appear Novel insulating means whereby electrical and from the following detailed description of the gas leaks are minimized and whereby heat coninvention when the latter is read in connection duction between electrode i8, il and nut I3, Il with the accompanying drawings." It is to be is materially enhanced are provided around insuexpressly understood, however, that the drawings lated spindle i8, i8 between the upper surface of are for the purpose of illustration only and are head il and the lower surface of flange i6. Said not intended asa definition of the limits of the insulating means. in the form shown in Fig. l, invention. reference for this latter purpose being comprises a small stack of mica washers i! and hadfprimarily to the appended claims.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Fig. 1 is a side elevation view, partly in section a novelly fabricated insulating sleeve 20. The inner portion 2| oi.o sleeve 20 is constituted by a mixture comprising a suitable ceramic material and nely divided metallic dust,while the outer portion thereof consists of plain ceramic material. The proportions of metal and ceramic material employed in portion 2i are preferably such that the mixture, when molded and baked in the manner hereinafter described, is a non-conductor or at most a very poor conductor of electricity, but is a materially better conductor of heat than pure ceramic material.

The metal dust'employed in insulating. sleeve 20may consist of nickel, tungsten, or other suitable high heat resisting metallic materials, or a mixture of suitable metals. In one embodiment which has proved successful, one part of metallic powder having a flneness of about 200 mesh was thoroughly mixed with three parts of ceramic material, such as aluminum oxide, also in powder form and having a flneness of about 300 mesh. Finer or somewhat coarser powders may be used but the finer the powders the better the contact between adjacent particles and hence the better the heat conducting ability thereof. The relative percentage of metallic and ceramic powders may be varied, depending upon the portion of the plug in which the mixture is used, the highest proportion of metal being limited chiefly by the ability of the ceramic to function as the binding agent therefor.

In the fabrication of sleeve 20, the dry metallic and ceramic powders for portion 2| are first very thoroughly mixed and just enough water added thereto to dampen it or form a stiff paste. The

dampened mixture is then placed in a cylindrical mold around a core corresponding in size to insulated spindle I6, I3 and a plain ceramic paste consisting of dampened ceramic powder is placed in a second and larger cylindrical mold surrounding the first mold which serves as a core therefor. The ilrst or inner mold is then removed and the concentric Vcylinders of different pastes or materials are pressed together to form the unitary sleeve structure 20 which is then removed from. the mold, dried out by heating at a relatively low temperature and then baked or red at a temperature of approximately 2200" F. This baking temperature may, of course, vary but temperatures between 2000 F. and-2,500 F. have been found preferable. After removal of the baked sleeve from the oven, the outer surface thereof may, if desired, be glazed by any suitable method known in the art, andthe insulated center electrode I6, I8 then fitted therein.

Surrounding the upper end oi insulated spindle I6, I8 and interposed between the upper surface of flange I5 and a washer or plate 22 is a stack 23 of mica washers. The latter and stack I9 are tightly compressed in a suitable press and secured in position by peening the countersunk end of spindle I6 outwardly into contact with the upper surface of washer 22. Shielding barrel I4 may be lined with suitable insulating material, such as mica liner 24, to prevent flashovers between the upper end of the center electrode and said barrel. l

During the installation of the center electrode assembly in nut I3, the axial pressure exerted on ceramic insulating 'sleeve 20 is cushioned by mica stacks I9 and 23 which yield under pressure, thereby minimizing the possibility of any cracking, chipping or breaking of said sleeve. 'I'he mica washers also tend to expand radially against nut I3 and sleeve I8 when compressedand hence contribute to the formation of a. tight gas seal to prevent gas leakage along the center electrode or around the insulating parts, Additionally, the mica insulation tends to cushion the ceramic insulator and prevent the 'breaking or crackingy spark plug, the voids or spaces between the variproduct.

ous insulating and metallic parts surrounding the upper end oi' spindle I6 may be illied with a'suitable high heat resistant insulating compound in accordance with a novel method fully described and claimed in my copendlng application Serial No. 344,507, filed July 9, 1940J for Spark plug and method of making the same, now Patent No. 2,348,427. In general, said method consists in placing the spark plug, completely assembled except for washer 22 and, in some instances, spindle I8, in a vacuum chamber and introducing the insulating compound in liquid form into barrel I4. The liquid is thus caused to flow into and fill the minutespaces around and between the upper end of spindle I6, sleeve I8, mica stack 23 and liner 24. One compound which has been found suitable for this purpose is a cashew-nut-shell oil After the compound has been applied to the plug in this manner, the latter is removed from the vacuum chamber, any excess compound is removed therefrom and washer 22 is installed in the manner heretofore described, The assembled spark plug is then baked for various lengths of time at temperatures increasing from approximately 200 F. to 500 F. until the compound is thoroughly dried and sets, said temperature being kept at all times below the boiling point of the compound, which point varies as the compound dries.

In Fig. 3, there is illustrated a spark plug which is identical with the above-described structure, except for the construction of ceramic insulating sleeve 20 and the provision of a ceramic sleeve 23 which replaces the upper portion of the stack of mica washers 23. Sleeve 20', as shown, comprises a lower porti-on of plain ceramic material and an upper portion 2 I constituted by the novel metal impregnated ceramic heretofore described. Said upper and lower portionsare prepared in the same mold while damp and. hence, form an integral unitary sleeve structure. It will be noted that in the embodiment of Fig. 3 the metallic and ceramic mixture is well removed from the otherwise uninsulated portion of center electrode I6, I1 and has direct contact with nut I3, thereby materially facilitating the conduction of heat from the center of the plug to the outer air-cooled surfaces thereof to obviate overheating while minimizing the possibility of fiashovers. In this form, the metallic content in portion 2| may be somewhat greater than in the embodiment of Fig. 1.

In the embodiment of Fig. 4, a molded insulated sleeve 25. extends substantially -the full length of spindle I6 and through the reduced bore of a nut I 3 which corresponds with nut I3 of Fig. 1. The upper and lower portions of sleeve 25 are composed of plain ceramic material, while the central portion 2B thereof. preferably that portion which contacts nut I3', consists of a mixture of ceramic material and metal of the character above-described. Insulator 25 is preferably molded in a single mold as a unitary sleeve and machined to fit tightly into nut I3', an external shoulder 21 on the'insulator being adapted to seat on an internal shoulder 28 on the nut. Surrounding4 the upper end of insulator 25 in the space formed by the latter, insulating sleeve 24 and 'assassin washer Il, there is provided suitable insulating means, such as a stack of mica washers Il. In

other respects, 'the spark plug shown. in Fig. 4\

is the same as that shown in Fig. 1. In the embodiment of Fig. 5, an insultingsleeve Il .consisting primarily of a suitable ceramic material, such as porcelain or aluminum oxide, sur

rounds the lower end of spindle IB between head i1 and a metallic sleeve or liner Il in body mem.

ber il'. Both of the sleeves 30 and 3| have a tight nt around mica cigarette I8 which surrounds spindle I8, and sleeve Il has a tight sliding fit in the bore of member I3', shoulder 2B on the latter being engaged by an external shoulderl'l on the lmetal sleeve.

. Amanner to provide good contact between rela tively large engagingsurfacs. Preferably, the

c upper end of sleeve I is conical and ilts into a similarly shaped recess in the lower end of sleeve Il, thereby providing a relatively largecontact area for heat transfer. In assembling sleeves Il and 3| on insulated electrode Il, i8, the same are placed end to end and pressed together while one is moved angularly with respect to the other until the relatively hard ceramic material grinds for itself a perfect seat inl the relatively soft metal of sleeve il I, the latter being made of copper or similarly soft metal having high heat conductivity. Good contact between sleeves 30 and Il and, hence, a good heat conducting joint therebetween is thus formed, whereby heat from electrode i6 may be readily conducted to body i3'. If desired, the conical end of ceramic sleeve I0 may be provided with a surface consisting of metal coating oi' suitable metal, such as copper, applied thereto under a llame by a method known commercially as the Schori process." The upper end of metallic sleeve 3l is preferably flush with an internal shoulder 33 in nut i3' and a cushioning stack of mica washers 23 is seated against the same and said shoulder. That portion of the plug which is broken away may berof the same construction illustrated in Figs. l orv 3. It will be understood. however, that shielding barrels Il are not necessary parts 'of any of the embodiments and may be dispensed with, if desired.

A smaller type of spark plugwhich is commercially known as a 10 mm. plug is illustrated in Fig. 6. In this type, a one-piece metallic body Il is employed with-ground electrodes 35 installed in the lower end thereoffor cooperation with the lower end of a center .electrode IB'. The latter has a collar or enlarged portion |1' above which it is surrounded by an insulating sleeve Il'. Surrounding spindle IB' between collar I1' anda shoulder 36 in body 34 is a cushioning stack of mica washers 31 and a ceramic insulating sleeve 38the latter having a portion 39 with an enlarged bore extending downwardlyvbeyond collar il' to a point adjacent ground electrodes Il. 'I'he upper portion of the spark plug shown in `Fig. 6 is illustrated as being similar tothe corresponding structure in Fig. 3. It will be under- .stood that portions oi' ceramic insulators II and 2l may, if desired, be impregnated with metallic dust or powder for increasing the heat conducting ability thereof.

There is thus provided a novel spark plug wherein use is made of ceramic materials for insulatiing means and wherein said means are novelly combined with other insulating materials which serve to cushion the brittle ceramics and thereby obviate breaking and cracking of the latter during assembly of the plugs and during,

actual use thereon There is also provided novel metallic impregnated ceramic insulating means and method i'or making the same. the heat conductivity of which is relatively greater than that of plain ceramic material, while the electrical insulating qualities thereof are not materially less than those oi plain ceramic materials. A novel spark plug and method of making the same are also provided whereby good heat conductivity be'' tween ceramic and metallic parts is assured. Additionally, the features of the present invention may be incorporated in simply constructed spark plugs at relatively low cost.

Although a limited number of embodiments of the invention are illustrated and above-described, it will be understood that the same is not limited thereto but that various other modifications embodying features of the invention may be made. fllor example, sleeves 20 and 20', shown in Figs.' 1 and 3, are interchangeable in the types ot plugs illustrated in said-figures, and one or both ofthe stacks of cushioning washers shown inthe several embodiments may be dispensed with, if desired. The shape of the engaging faces of sleeves In and li in Fig, 5 may also be varied.

las being suitable, may also be' made wit out departingfrom thev spirit and scopeoi the nvention. as the same will now be understood by those skilled in the art. For a definition of the limits oi the invention, reference is had prima rily to the appended claims.-

What is claimed is:

1. The method of making electrical insulators which includes the steps of mixing powdered electrical insulating material, such as ceramic material, and metallic powder in a dry state, dampening said powdered mixture, separately placing said mixture and a quantity of dampened insulating powder in different'portions of a mold, compressing the contents of said mold, and baking the -contents of said mold until the same is dried.

2. sa integral rigid tubular electrical insula tor for ignition apparatus or the like, said integral insulator having longitudinally arranged portions of ditlerent composition one oi which is composed of a mixtureof insulating material and ing a central longitudinal portion consisting of a mixture of molded insulating material and iinely divided metallic particles, and end portions consisting solely of molded insulating material.

5. An integral rigid tubular electrical insulator for spark plugs or the like comprising an inner portion consisting essentially of-a mixture of molded insulating material and finely divided metallic particles and an outer portion comprised of said molded insulating material free from metallic particles.

6. A tubular insulator containing metallic partlcles and undivided insulating material, said metallic particles being dispersed within a portion o! the insulatng materal, the remander of said insulating material being free of said particles.

'7. A unitary insulator containing metal particles evenly dispersed within hardened insulating materiahsaid particles being within part of said insulating material, the remainder of said insulating material being free of said particles.

TULLIO TOGNOLA.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 335,160 Thomson Feb. 2, 1886 669,130 Vogt Mar. 5, 1901 1,116,631 Schisler Nov. 10, 1914 Number OTHER REFERENCES A catalogue numbered 4, entitled Lapp, In-

sulators for 1928, copyright 1928 by Lapp Insulator Co., Inc. ot LeRoy, N. Y., U. s. A., page 3.

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