Claims
- 1. A self-regulating electrical heater which is suitable for heating the production tube of an oil well and which comprises
- (1) at least two elongate spaced-apart electrodes which can be connected to a source of electrical power;
- (2) at least one elongate heating element which comprises a material having a positive temperature coefficient of resistance and through which current passes when the electrodes are connected to a power source;
- (3) an electrically insulating jacket which surrounds the electrodes and the heating element; and
- (4) a metallic foil which is wrapped around the insulating jacket to form a continuous covering with a continuous metal-to-metal seam, wherein the metal surfaces forming said seam are joined to each other by a continuous layer obtained by curing a composition which comprises a polymeric component comprising
- (i) at least 50% by weight, based on the weight of the polymeric component, of at least one relatively high molecular weight fluorocarbon elastomer having a Mooney viscosity at 121.degree. C. of at least 75, and
- (ii) 5 to 50% by weight, based on the weight of the polymeric component, of at least one relatively low molecular weight fluorocarbon elastomer having a Brookfield viscosity at 100.degree. C. of 1,000 to 5,000 centipoises.
- 2. A heater according to claim 1 wherein the composition comprises 8 to 25% by weight of a reinforcing carbon black.
- 3. A heater according to claim 1 wherein the polymeric component consists essentially of 15 to 25% of a fluorocarbon elastomer having a Mooney viscosity at 121.degree. C. of 130 to 190, 30 to 75% of a fluorocarbon elastomer having a Mooney viscosity at 121.degree. C. of 80 to 110, and 5 to 30% of a fluorocarbon elastomer having a Brookfield viscosity at 100.degree. C. of 1,000 to 4,000 centipoises, the percentages being by weight based on the weight of the polymeric component.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a divisional of copending application Ser. No. 772,287, filed on Sept. 4, 1985, U.S. Pat. No. 4,722,758, the entire disclosure of which is incorporated by reference herein.
US Referenced Citations (6)
Divisions (1)
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Number |
Date |
Country |
Parent |
772287 |
Sep 1985 |
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