Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
1999-05-11
2002-09-17
Hoang, Tu Ba (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S529000
Reexamination Certificate
active
06452138
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to soft and flexible electrical heaters, and particularly to heating elements, which have soft and strong metal or carbon containing electrically conductive threads/fibers.
2. Description of the Prior Art
Heating elements have extremely wide applications in household items, construction, industrial processes, etc. Their physical characteristics, such as thickness, shape, size, strength, flexibility and other characteristics affect their usability in various applications.
Numerous types of thin and flexible heating elements have been proposed. For example, U.S. Pat. No. 4,764,665 to Orban et al. discloses an electrically heated fabric for use in gloves, airfoils and aircraft parts. In this patent the fabric is metallized after being formed in a glove structure, following weaving or arranging in a non-woven format. Copper bus bars are utilized for introduction of electrical current to the metallized textile. Having been made of a solid piece of fabric with metallized coating, this heating element doesn't allow for flexibility in selection of desired power density.
The metallizing of the formed heating element results in a loss of significant economies of scale, only a small number of embodiments can be achieved, thus severely limiting the potential application of this invention. The '665 design is also not conducive to tight hermetic sealing through the heater areas (no gaps inside), which can cause a short circuit through puncture and admission of liquid into the body of heating element. this element can't be used with higher temperatures due to the damage caused to the polyaramid, polyester or cotton metallized fabric, described in the invention.
Another prior art example is U.S. Pat. No. 4,713,531 to Fennekels et al. Fennekels et al. discloses a sheet textile structure having resistance elements combined with it. These resistance elements comprise metallic fibers or filaments with a denier like that of natural or synthetic textile fibers, and with overall cross sectional thickness of 8 to 24 microns. The '531 design suffers from the following drawbacks: being a sheet product, it is not conducive to hermetic sealing through the body of the heater (no gaps inside), only perimeter sealing is possible, which can result in a short circuit due to puncture and admission of liquid into the body of the heating element; yarns, comprising metal fibers, lack consistency of electrical resistance per given length, and their stretching, compression, or both, will result in very wide fluctuations in resistance, thus limiting the use of this technology in embodiments controlled by strict design and where an uncontrollable power output and temperature variability are unacceptable; yarns are very heavy: from 1 to 7 grams per 1 meter of yarn; the use of silver fibers makes these yarns very expensive; individual conductors have a large cross sectional thickness, each having an outer sheath of braided textile or elastomer.
Another prior art example is U.S. Pat. No. 4,538,054 to de la Bretoniere. The heating element of de la Bretoniere '054 suffers from the following drawbacks: its manufacturing is complex requiring weaving of metal or carbon fibers into non-conductive fabric in a strictly controlled pattern; the use of the metal wire can result in breakage due to folding and crushing and it affects softness, weight and flexibility of the finished heater; it can not be manufactured in various shapes, only a rectangular shape is available; only perimeter sealing is possible (no gaps inside), which can result in a short circuit due to puncture and admission of a liquid into the body of the heating element; the method of interweaving of wires and fibers does not result in a strong heating element, the individual wires can easily shift adversely affecting the heater durability; the fabric base of the heating element is flammable and may ignite as a result of a short circuit; it is not suitable for high temperature applications due to destruction of the insulating weaving fibers at temperatures exceeding 120° C.
A heating element proposed by Ohgushi (U.S. Pat. No. 4,983,814) is based on a proprietary electroconductive fibrous heating element produced by coating an electrically nonconductive core fiber with electroconductive polyurethane resin containing the carbonatious particles dispersed therein. Ohgushi's manufacturing process appears to be complex, it utilizes solvents, cyanates and other toxic substances. The resulting heating element has a temperature limit of 100° C. and results in a pliable but not soft heating element. In addition, polyurethane, used in Ohgushi's invention, when heated to high temperature, will decompose, releasing very toxic substances, such as products of isocyanide. As a consequence, such heating element must be hermetically sealed in order to prevent human exposure to toxic offgassing. Ohgushi claims temperature self-limiting quality for his invention, however “activation” of this feature results in the destruction of the heater. He proposes the use of the low melting point non-conductive polymer core for his conductive fabric-heating element, which should melt prior to melting of the conductive layer, which uses the polyurethane binder with the melting point of 100° C. Thus, the heating element of Ohgushi's invention operates as Thermal Cut Off (TCO) unit, having low temperature of self-destruction, which limits its application. U.S. Pat. No. 4,149,066 to Niibe et al. describes a sheet-like thin flexible heater made with an electro-conductive paint on a sheet of fabric. This method has the following disadvantages: the paint has a cracking potential as a result of sharp folding, crushing or punching; the element is hermetically sealed only around its perimeter, therefore lacking adequate wear and moisture resistance; such an element can't be used with high temperatures due to destruction of the underlying fabric and thermal decomposition of the polymerized binder in the paint; the assembly has 7 layers resulting in loss of flexibility and lack of softness.
U.S. Pat. No. 5,861,610 to John Weiss describes the heating wire, which is formed with a first conductor for heat generation and a second conductor for sensing. The first conductor and a second conductor are wound as coaxial spirals with an insulation material electrically isolating two conductors. The two spirals are counter-wound with respect to one another to insure that the second turns cross, albeit on separate planes, several times per inch. The described construction results in a cable, which has to be insulated twice: first, over the heating cable and second, over the sensor cable. The double insulation makes the heating element very thick, stiff and heavy, which would be uncomfortable for users of soft and flexible products such as blankets and pads. The described cable construction cannot provide large heat radiating area per length of the heater as it would be possible with strip or sheet type of the heating element. The termination with electrical connectors is very complicated because of stripping of two layers of insulation. In addition, in the event of overheating of a very small surface area of the blanket or pad (for example several square inches), the sensor may fail to sense very low change in total electrical resistance of the long heating element. Such heating cable does not have Thermal-Cut-Off(TCO) capabilities in the event of malfunction of the controller.
The present invention seeks to alleviate the drawbacks of the prior art and describes the fabrication of a heating element comprising metal microfibers, metal wires, metal coated, carbon containing or carbon coated threads/fibers, which is economical to manufacture; does not pose environmental hazards; results in a soft, flexible, strong, thin, and light heating element core, suitable for even small and complex assemblies, such as handware. A significant advantage of the proposed invention is that it provides for fabrication of heati
Gurevich Arthur
Kochman Arkady
Hoang Tu Ba
Liniak Berenato Longacre & White
Thermosoft International Corporation
LandOfFree
Multi-conductor soft heating element does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-conductor soft heating element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-conductor soft heating element will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2906724