US2575987A - Conducting rubber heating element - Google Patents

Description

Nov. 20, 1951 R. A. YORK ET AL 2,575,987

CONDUCTING RUBBER HEATING ELEMENT Filed Aug. 29, 1947 I I ll 'Jnventors Riymazza/ A l ark 3 t lzarleu' H 711 Zor attorney Patented Nov. 29, 1951 CONDUCTING RUBBER HEATING ELEMENT Raymond A. York, Pitman,

and Charles H. Taylor,

Haddonfield, N. J., assignors to Radio Corporation of America,

a corporation of Delaware Application August 29, 1947, Serial N 0. 771,240

4 Claims. (Cl. 219 -46) This invention relates to a novel type of heater element utilizing a heat radiator comprising conducting rubber and to an improved blanket structure utilizing the novel heater element.

Various types of electrically heated blankets have been proposed heretofore. The type most generally used includes a heating element, consisting of a spiral wound wire of copper or cadmium bronze. The spiral is coated with insulation and is either woven into the blanket fabric, threaded through the fabric or stitched to the inner side of the fabric. While these blankets have been successful commercial articles, they have several disadvantages. It is difficult to assemble the heater wire into the blanket; the thin strands of wire eventually Wear out and break if the blanket is folded many times and the safety features to protect against breakage have not received unqualified approval from the underwriters. Since the radiating surface is relatively small, heat is more or less localized and may become excessive should the control circuit not be Working properly and the blanket be folded with the current left turned on and running at full strength. When a strand of Wire breaks,

arcing may occur and the spark may set the blanket on fire. While this is not likely to happen when the blanket is fairly new, the danger becomes increasingly great with the age of the article.

In the present invention, none of the above mentioned disadvantages are present since the heating element is composed of a gridwork of strips of conducting rubber having a broad surface area and carrying a very low current. The rubber being tough and flexible can be folded or bent into any shape innumerable times without danger of tearing or breaking and even if a deliberate attempt is made to cut the blanket with the current on, the ruptured ends of the rubber are blunt and have very low electrical conductivity; hence, no arcing occurs which might cause a dangerous spark. It can be proved, experimentally, that arcs drawn from the ruptured rubber are of such low intensity that even 4 cotton soaked in alcohol cannot be ignited.

Many other advantages will be readily seen in using a heating element constructed according to the present invention and some of these additional advantages will be noted hereinafter in the more complete description of the inventionwhich follows:

One object of the present invention is to provide an improved heating element.

Another object of the invention is to provide an improved, heating element which is very resistant to breaking.

Another object of the invention is to provide an improved heating element which does not add to the bulk of a finished article when used to supply heat to a blanket.

Another object of the invention is to provide an improved heating element which is entirely flexible.

Another object of the invention is to provide an improved heating element having a large radiation surface and, hence, giving necessary amount of heat Without use of high temperatures.

Another object of the invention is to provide a heating element which Will radiate adequate heat but-require a very low current to flow in each 01 its sections.

- Another object of the invention is to provide an improved heating element which Will lend itself to being formed into any desired shape.

Another object of the invention is to provide a heating element which can readily be assembled within a blanket. 5

Another 003661 of the invention is to provide a novel heating element having an improved temperature sensitive element integrally attached thereto.

Another object of the invention is to provide an improved electrically heated blanket.

Another ob ect of the invention is to provide a blanket of the electrically heated type having an improved safety construction. 1

Still another objector the invention is to provide an improved blanket of the electrically heated type having a structure which is not affected by laundering processes.

These and other ob ects will be more readily apparent and the invention will be better understood from the specification, including the following drawings, of which Fig. 1 is a plan view of an improved heater element, I

Fig. 2 is a perspective view of an improved heater element made according to the present invention and inserted within a blanket,

Fig. 3 is a cross section view taken laterally across the article illustrated in Fig. 2, along the line III-III,

- Fig. 4 is a partly cut away view in perspective of one type of heater strip used in the invention.

Fig. 5 is a partially cut away perspective view of the heater strip as shown in Fig. 4 but with a current supply wire running therethrough.

amass? This grid has transverse strips 4, which may have a structure more particularly shown in Fig. 4, although not limited thereto. As shown in'Fig. 4, these strips 4 are made up of three plies -vul-. canized together. An inner ply 6 is made of conducting rubber, which may be'of a conventional typ v g a large p en g of cetylene black uniformly dispersed throughout a rubber matrix. On either face of the inner conductin ply 6 and extending around its edges so as to completely encase itare vulcanized plies 8 and I0 of non-conducting rubber. One of these outer :plies l0 may have fibrous material incorporated therewith in order to preventundue stretching when the article is in use. Connecting these transverse strips 4 is a central strip l2 and two edging strips l4 ofthreeeplystructure, similar to that. of the transverse strips 4 but having a metal conductor l6 embedded in the central ply [8. .This metal conductor may consist of a fiber core 20, upon which iswound a two-strand copper wire 22. .Embedding the bare copper wire in the ply of conducting rubber provides a v ry ood e ectric l c ntact. and. protects wire fromsharp -bendins.- Transverse en strip 24 is of simi a construction to central strip landecle ns s rips M in that the current conductor It embedded ace t l ly, oi con uct ng ub e Howe the er ply icon-center d simi a to the dicetion s o n, n h s. 7 so. t at ther wires 0 We). be. mbedded in a l l o n nd ti rubber. 'The end strip 24 carries wires 22 and '30 to a single'dead strip 26 of non-conducting ru r 7 Other longitudinal snipers, composed of noncoii'du'cting rubberfh'ave embedded therein the wireseo connecting temperature sensitive'elements 3. in series circuit. These temperature sensitive elements '32 are preferably embedded in non-conducting corner pieces 34 vulcanized to the rubber grid. A' transverse strip 29 similar in construction to the strip "44 shown in Fig. 7 carries the circuit wire 3t to complete thecircuit through thetemperature sensitive elements. The temperature sensitive elements 32 are'connected -to=a control circuit '(not shown) through the conductors 30 embedded inthe lead strip 26 and running to the non-conducting strips 213 through the transverse end stripls, to which the lead strip 2'6 integrallyconnected. A l r The entire rubber gridis preferably'attached to a sheet of loosely woven mesh material 36,.such as cotton net or cheesecloth. The rubber strips "arepreferably loosely sewn or tied to the material withthe stitches Passing around rather than through the rubberstrips. This prevents curling or other permanent distortio of the heater un wb ninuse. i

The heating unit is then inserted within the double :iaces 38 of the blanket envelope, as more partic la l wn rr igan t e er u t support material 36 is stitched to the edges 40, pnly, of the blanket, the'stitches being concealed wi h? o i ns str pe eionm reolthj .t h d s y oyided with a zipper or snap fasteners so that 4 the heating unit may be removed or inspected with facility.

The above described improved construction results in several advantages which will be readily apparent. The rubber gridwork is very light in. weight since the strips may be but /2 inch in width and 9.045 inch in maximum thickness. The strips are moreover preferably tapered at the edges to still less thickness, making a unit adding no noticeable thickness or bulk to the blanket.

The type of construction described also provides a heater unit composed of a large number of parallel heating circuits resulting in the power in any one circuit being so low that if a break should occurdue to injury to the blanket the current will be insufiicient to cause arcing with its ccompanying fir h The use of the'center and side current leads provides means of applying different amounts of power to the two halves of the heater unit grid,

thus allowing the use of a single or dual control circuit. A dual control circuit permits obtaining atemperature difierential between the W9 halves of the heater unit.

Arcing hazard due to strip breakage may be still further reduced, if desired, by providing extra conducting rubber ribbons it parallel to the side conducto s t and tak n the p ac i rib ons 25 shown in Fi s. 1 and 2- h s e ablishe e ua potential lines at /2 or /3 line vol a hes extra conducting r bbons. 44 may b? i the lIlQQlfied fornrshown in F in order o. t th some tim c ntain the cir uit wires 3 connecti h temperature sen it eelemehts 32,. shown in the figu e. a conducti pl 41 ma b encased between two n-conduct n p s 8 and 5% ith he centr ply 46 bein positioned f ent r to as to al w room to em ed the circ it i e 3% alone one side of one of t e nononduc e pli s 48- There has hus be n des ri ed a novel ype of electri ally heated blanket having an m o ed heat r unit desi ned ior maximu durab i y and ffiticiency an e ha in saf ty icatures not f nd n prev ou rt cles of h so os It will be r ily ap arent to one sk lled t e art t a certain hanges may he madei l hou depar ng rom the sol t of th inv ntion.- For-eraroplc. the h ater uni c uld e used W thin ther fabr c truc ures such as aviators suits; the rubber gridwork could take orm o her han. tha i lu t a e u h as diaechal trips or cell lar honeycom st uc ures ondthe mo e, o tta hmen o the fabric m h be y oth r means, as by th rm e e obber ce ntsrio ls ype of p ratu "sensitive el ment could, a so be u ed in c nj nction there'- Wc aim as our n enti n:

, l. A self-supporting heating element comprise ing a plurality of ribbons of electrically conduct.- ing-rubber, means "for connecting said ribbons in parall o a s urce of cur ent, a plurality of mm rer ture ensiti e res st rs. in heat transfer rela on tosaid ri bons, nd means necting said resist rs in circuit, said nne tin means comp g a me all c co ductor embed ed within a ribbon of non-conducting rubber integrally secured o said electric lly co d cti g rubber ribbons.-

.A self-su por g h at elemen c mpris ihg a eridwork of relatively narrow.- thin ible ribbons of electrically conducting rubber, said arid o hcomprisine a plurality of lon itudi ally extending ribbons and a plurality of transversely extend ng i bon all s d bbo s be ng in grally united at their crossover points, and means longitudinal strips of said grid having outer plies .1

of non-conducting rubber and an inner ply of electrically conducting rubber having embedded therein flexible metallic electric conductor, and others of said longitudinal strips being of nonconducting rubber having a flexible metallic electrical conductor embedded therein, a plurality of temperature-sensitive resistors positioned adjacent said other longitudinal strips and connected in circuit with said last mentioned electric conductor, means including said some longitudinal strips connecting said transverse strips to a source of current, and means connecting said temperature-sensitive resistors to a control circuit for regulating the supply of current to said heater element.

4. A heater unit comprising a se1f-supporting heating element and an envelope of loosely woven, non-conducting, filamentous material for said heating element, said heating element comprising a gridwork of relatively narrow, thin, flexible ribbons of electrically conducting rubber, said grid- Number 6 work comprising a plurality of longitudinally extending ribbons and a plurality of transversely extending ribbons, all of said ribbons being integrally united at their crossover points, and means for connecting said ribbons in. parallel to a source of electrical current.

RAYMOND A. YORK.

CHARLES H. TAYLOR.

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

UNITED STATES PATENTS Name Date 416,360 Dewey Dec. 3, 1889 1,073,926 Pollak Sept. 23, 1913 1,577,981 Otto Mar. 23, 1926 2,255,376 Bull et al :Sept. 9, 1941 2,277,772 Marick Mar. 31, 1942 2,340,097 Woodman Jan. 25, 1944 2,386,095 Edgar et a1. 1 Oct. 2, 1945 2,404,736 Mariok July 23, 1946 2,456,463 Theodore Dec. 14, 1948 2,473,133 Watson i June 14, 194.9 2,503,457 Speir et al. Apr. 11, 1950 FOREIGN PATENTS Number Country Date 49-0546 Great Britain Aug. 17, 1938

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