Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-08-10
2001-07-10
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S532000
Reexamination Certificate
active
06259070
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrical resistance insulator for supporting a heater coil in a heater assembly.
BACKGROUND OF THE INVENTION
Various types of electrical insulators have been constructed in the past to support heater coils within an electric heater assembly suitable for use in many applications and in particular for use in an electrically heated clothes dryer. In such heater assemblies, the heater coils are mounted directly to supporting arms of the insulator which in turn is mounted to a heater assembly support.
One example of an insulator is disclosed in U.S. Pat. Nos. 4,531,017issued Jul. 23, 1985 and 4,675,511 issued Jun. 23, 1987, both by Jimmy Sherrill. These patents disclose an electrical insulator having two support arms spaced apart and that extend from a base. The arms have inclined outer guide surfaces that provide the shape of an arrowhead for the insulator. The outside inclined guide surfaces have inwardly directed notches. The arrowhead insulator also has a central slot between the arms with a notch at the bottom of the slot adjacent the base and horizontally aligned with the two side notches. The insulator supports the coil at three consecutive coil convolutions. An important feature of this insulator is that the upper ends of the guide surfaces are smaller than the distance between the outer convolutions of the coil and the distance between the bottoms of the notches in the sidewalls. This allows the coil to be firmly placed into the elongated slot and adjacent coil convolutions to be spread over the inclined outer guide surfaces and sprung back into place in the inwardly directed side notches. While this arrowhead design provides a support for a heater coil that may be readily mounted to the insulator, there is a problem associated with the coil flexing relative to the insulator during operation. This occurs due to the cyclic heating and cooling of the heater coil during operation. When the heater coil is heated it has a tendency to expand. This expansion places stresses on the coil at the insulator. Consequently, the heater coil has a tendency to flex upwardly or outwardly between the insulators causing the adjacent convolutions of the heater coil diametrically opposed to those convolutions supported by the insulator to flex toward each other during a heating cycle. During repeated heating cycles the coils have a tendency to be mechanically fatigued and break at locations adjacent the insulator. Also, the heater coil has a tendency to expand touching adjacent metallic parts and then breaking.
Another similar insulator is shown in U.S. Pat. No. 4,628,189which issued Dec.9, 1986 to Michael Danko. The electrical resistance insulator is similar to that disclosed in the aforementioned U.S. Pat. Nos. 4,531,017 and 4,675,511, however the slope or arcuate angle of the side guide surface relative to the side notch is greater than that disclosed in the aforementioned U.S. patents. Further, the central slot is tapered. Danko discloses that preferably the distance between the tips of the arrowhead and the ends of the sidewall notches is somewhat greater than half the diameter of the coil. The central slot is located to be slightly off center from the horizontal direction of the convolutions of the coil held in the side slots. This creates a reverse bending in the coil which counteracts any bowing in the heater coil outwardly during a heating cycle. However, the heater coil is still supported at three locations relative to the insulator on one diametrical side of the coil which allows stresses to be placed on the outer convolutions of the heating coil adjacent the insulator causing them to flex and provide a localized area on the coil that is subject to fatigue and failure.
There is a need to provide an electrical resistant insulator that supports a helically wound heater coil and prevents the heater coil from moving at the convolutions of the heater coil diametrically opposed from the convolutions of the heater coil normally supported by the electrical insulator while still permittng for simple assembly of the is heater coil onto the insulator.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrical resistant insulator that supports a helically wound heater coil and reduces bowing or flexing of the coil about the insulator.
In accordance with the present invention an electrical insulator has a body portion having a pair of supporting arms that extend outwardly from the body portion. The body portion is mounted to a support structure and the arms support the coil at seven coil locations relative to the insulator. This is accomplished by supporting the coil at adjacent convolutions of the coil that are diametrically opposed and interleaved with coil convolutions that are also supported by the insulator. The coil is supported at three adjacent convolutions at one diametrical side of the coil and the coil is supported at four adjacent convolutions at the other diametrically opposed side of the coil. The three supported coil convolutions are interleaved with the four supported diametrically opposed coil convolutions.
In accordance with the invention, the pair of arms have confronting inside surfaces spaced apart from each other that define an elongated central slot that extends outwardly from the base. The central slot supports the coil at a first coil supporting location between the arms and adjacent the base. The arms also further have inclined outside surfaces that extend outwardly from the base and taper inwardly towards the slot. The arms each have an inwardly directed notch extending in from the inclined outside surface adjacent the base for receiving and supporting the coil at second and third coil supporting locations. It should be understood that the first, second and third coil supporting locations are located on the same diametrical side of the coil, are adjacent to each other as adjacent convolutions in the coil, and are separated approximately by the pitch of the coil. The arms of the insulator further include a stepped out shoulder that is formed in the confronting inside surface and extends away from the central slot to define a widened slot portion. Each shoulder may be sloped upwardly and outwardly from the slot. The arms have extending beyond the shoulder a lug portion that includes the confronting inside surface of the arm, extends towards an outer end of the lug portion and continues to extend back along the inclined outside surface. The lug portion has a width between the confronting inside surface and the inclined outside surface that corresponds to the pitch of the coil such that two adjacent convolutions of the coil abut the lug portions whereby the lug portions support the coil at four additional coil supporting locations. These four additional coil supporting locations support four consecutive convolutions of the coil which are located diametrically opposed or opposite from the first, second and third coil supporting positions. The four additional coil supporting locations have the first, second and third coil supporting locations interleaved between them at one half coil turn. In this manner, the coil is supported at diametrically opposed and interleaved convolutions of the coil such that the insulator supports the coil from contracting, expanding or bowing over the insulator due to the coil cycling through heating and cooling cycles.
Preferably, each of the arms has a first length between the inwardly directed notch and the outer end of the lug portion that is greater than the diameter of the coil. The arm preferably has a second length between the inwardly directed notch and the shoulder that is less than the diameter of the coil.
Preferably, the lug portion tapers outwardly or widens along the inclined side surface as the lug portion extends from the outer end towards the base such that the width of the lug portion increases. Preferably, the coil is supported on the lug portion between the inwardly directed notch and the outer end of the lug adjacent the shoulder.
Camco Inc.
Paik Sang
LandOfFree
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