Electric heating – Heating devices – With heating unit structure
Patent
1986-04-30
1988-06-07
Goldberg, E. A.
Electric heating
Heating devices
With heating unit structure
219552, 219528, 338212, H05B 308
Patent
active
047498447
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrical heating devices.
BACKGROUND OF INVENTION
U.S. patent applications Ser. No. 181,974, filed Aug. 28, 1980 and now abandoned, Ser. No. 295,000, filed Aug. 21, 1981 and now U.S. Pat. No. 4,485,297 issued Nov. 27, 1984, Ser. No. 487,080, filed Mar. 23, 1983, now abandoned and Ser. No. 572,678, filed Jan. 20, 1984, now U.S. Pat. No. 4,523,085, issued June 11, 1985 all of which, together with Ser. Nos. 580,742, now abandoned, and 646,688, now U.S. Pat. No. 4,542,285, are owned by the assignee of the present application and are here incorporated by reference, disclose flexible sheet heaters including a pair of longitudinally-extending (typically copper) conductors, and a semi-conductor pattern extending between and electrically connected to the conductors. The heaters there disclosed provide generally superior performance and substantially even heat distribution, and are useful in a wide range of applications.
There are circumstances, however, in which the heater may be subjected to unusual or extreme conditions. For example, Ser. No. 580,472 discloses that heaters may be used as, for example, firing range targets. When used as a target for small arms, there is a very real chance that a bullet may strike and sever one of the longitudinally-extending conductors, and render the heater inoperative. Similarly, the shock of a large calibre shell, when for example the target is used on an anti-tank weapons range, may cause partial delamination or other structural damage, even when the "hit" is wholly in the area between conductors. High stresses or risk of breakage may be presented in other environments or applications; and other potential difficulties are presented by the need, in some applications, to operate using relatively high voltage or current levels.
SUMMARY OF INVENTION
The present invention provides an electrical sheet heater which has greater structural strength and integrity and in which the risk of failure from breaking or cutting of a conductor is significantly decreased. The invention also provides for a higher current carrying capability, and, particularly in those embodiments the semi-conductor pattern between conductors is an essentially solid layer, for more even heat distribution adjacent the inner edges of the conductors.
In general, I have discovered that a sheet heater including a substrate, a semi-conductor pattern (typically of colloidal graphite) having a pair of spaced-apart conductor contact portions and a heating portion electrically connected thereto and extending therebetween, and a pair of conductors one of which overlies and engages each of the conductor contact portions, will provide the above advantages if each conductor includes transversely-spaced, longitudinally-extending strip portions and a plurality of longitudinally-spaced openings therebetween. The strip portion along one edge of each conductor overlies and engages a respective conductor contact portion, and the openings and the strip portion along the other edge of the conductor overlie portions of the substrate that are not covered with the semi-conductor pattern. A sealing layer of insulating material overlies the respective conductor and is sealed to the substrate through the longitudinally-spaced openings.
In preferred embodiments in which the heating portion of the semi-conductor pattern includes a plurality of longitudinally-spaced areas free from semi-conductor material along the inner edge of the conductor and in which the sealing layer is sealed to the substrate in such areas, the conductor includes two rows of longitudinally extending openings, each generally rectangular and not less than about 1/4 inch on a side, and there is a solid strip portion about 1/8 wide provided between the two rows of openings and along the inner and outer edges of the conductor. In other preferred embodiments, the conductor includes but a single row of longitudinally-extending openings, there is a solid strip portion about 1/8 inch wide provided along one edge of the row of openings and a solid
REFERENCES:
patent: 4542285 (1985-09-01), Grise
Donovan Lincoln
Goldberg E. A.
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