US3068441A - Resistor structure - Google Patents

Description

Dec. 11, 1962 H. LEVY RESISTOR STRUCTURE 2 Sheets-Sheet 1 Filed Sept. 9, 1957 Dec. 11, 1962 H. LEVY 3,068,441

RESISTOR STRUCTURE Filed Sept. 9, 1957 2 Sheets-Sheet 2 INVENTOR.

jerfierilez/ MVM United States This invention relates to an improved wire wound resistor.

Conventional wire wound resistors comprise a hollow ceramic core tube of annular cross sectional form on the outside of which the resistor wire is wound in the form of a coil. Terminal bands including radially extending lugs are clamped around the tube and secured in position at predetermined planes along the core tube, usually at both ends thereof. The ends of the resistance wire coil are electrically and mechanically connected to the terminal bands. The finished resistor includes an outer coating (which may be a vitreous enamel) through which the lugs of the terminal bands project so that the leads to the associated electrical circuit wires can be connected to these lugs.

Conventional Wire wound resistors are customarily supported by brackets made of a flat metal strip bent at right angle to define a first or inner leg and a second or outer leg. The first leg of this bracket has its distal or terminal portion bent back upon its proximal portion to form a spring wedge that is inserted into the end of the resistor core tube. The second leg has its distal or terminal portion deflected at right angle to its proximal portion, away from said inner bracket leg, to overlie a supporting surface for attachment thereto. For the latter purpose, the deflected distal portion of the outer bracket leg may be apertured.

A bracket such as the one described in the preceding paragraph is held in position in a conventional wire wound resistor only by the frictional resistance offered by the edges of the slightly compressed spring wedge-like end of the inner bracket leg against displacement (rotational or axial, with respect to the resistor core tube) over the round interior surface of the resistor core tube. To assure positive holding of the bracket at least against rotational movement (with respect to the resistor core tube), the core tube has sometimes been formed with a transverse groove across a terminal face adapted to receive the outer leg of the bracket. However, the provision of such a groove is a separate and relatively expensive operation, accompanied by frequent breakage of the ceramic tube at the time the groove is formed and also during subsequent processing. The seating of the bracket in such a groove brings the bracket (which is grounded) closer to the resistance wire, with consequently greater likelihood of electrical leakage. Further, in resistors including cores with ends thus grooved, the brackets must be mounted in a single predetermined angular relationship to the lugs of the terminal bands. In other words, there is no possibility of varying the angular relationship between the brackets and the terminal lugs after the terminal bands have been secured to the ceramic core tube.

According to the present invention, the inner surface of the ceramic core tube is formed with a plurality of axially extending serrations. The crests of these serra tions extend radially inwardly. The corners of the free end of the inner bracket leg are seated in these serrations whereby the bracket is held against movement in a direction rotational with respect to the core tube. Similarly, the edges of the proximal portion of the inner bracket leg are also seated in other serrations. Thus, the brackets may be inserted into the ends of the finished resistors in a number of angular relationships to the terminal lugs atet ice

and are thereafter positively held against rotational dis placement from this angular relationship.

Other and further features of this invention will become apparent from the following description and appended claims, as illustrated by the accompanying drawings, wherein:

FIG. 1 is a vertical longitudinal cross sectional view, with parts shown in elevation, of an extrusion device for making ceramic core tubes according to the present invention;

P16. 2 is a fragmentary enlarged cross sectional view taken along line 22 of FIG. 1;

PEG. 3 is a fragmentary enlarged cross sectional view taken along line 33 of FIG. 1;

FIG. 4 is an exploded perspective View of a ceramic core-bracket assembly according to the present invention;

FiG. 5 is a perspective view showing the parts illustrated in FIG. 4 as assembled;

FIG. 6 is an enlarged cross sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is an enlarged cross sectional view taken along line 7-7 of FIG. 6 but with the brackets excluded;

FIG. 8 is a view similar to FIG. 7, but with the brackets included;

FIG. 9 is a fragmentary enlarged perspective view of the end portion of a ceramic core tube having a bracket seated therein, part of said tube being broken away to show the inner bracket leg;

FIG. 10 is a side elevation of a bracket in two different positions of fiexing, part of the outer leg being broken awa P16. 11 is a perspective view of a finished resistor according to the present invention, with parts being broken away to show the inner construction thereof; and

FIG. 12 is a cross sectional view taken along line 12-12 of FIG. 11.

Referring now to FIGS. 1-3, an extrusion device for making ceramic core tubes is generally indicated by the reference numeral it This device includes a hollow cylinder 12 having a screw type conveyor 14 rotatably arranged therein and adapted to be driven by any suitable source of power (not shown). A hopper 16 is provided for feeding a plastic clay composition to the conveyor 14. The right end of the cylinder 12 is closed except for an aperture 18 serving as a journal for the cylindrical right end of the conveyor 14. The left end portion of the cylinder 12 has seated therein an elongated mandrel 20 tapering to the left and having its surface serrated axially at the left end of the mandrel, as indicated at 22. Specifically, the mandrel 2G is supported by radial members or spokes 24 attached to a ring 26 fitting the inside of the left end of the cylinder 12. An annular die 28 is fixed in the left end of the cylinder 12. A tube 30 extruded between the mandrel 20 and die 28 is deposited on a belt conveyor 32.

In the operation of the extrusion device 10, a plastic clay mass 31 is fed through the hopper 16 to the screw conveyor 14 and, by the action of the latter, forced between the mandrel 20 and the die 28 in the form of a tube 30 having a serrated inner surface. The extruded tube 39 is deposited on the belt conveyor 32 and cut into suitable lengths, which then are fired. The resulting hollow ceramic resistor core tubes are illustrated in FIGS. 4-7 and there indicated by the reference numeral 34. As shown, the inner surface 36 of these core tubes are axially serrated.

FIGS. 4-7 also illustrate supporting brackets generally indicated at 38. These brackets are of identical construction, comprising a fiat metal strip bent at right angle to define an inner leg 40 and an outer leg 42 having its end portion 44 deflected at right angle, away from the inner bracket leg (described herein below) to overlie a supporting surface. The end 44- of the outer bracket leg may be apertured, as at 46, to admit a screw or other attaching device therethrough. The end 43 of the inner leg 40 is bent back upon itself.

The cooperation between the serrated inner surface 36 of the core tubes 34 and the brackets 38 is illustrated in FIGS. 7-l0. As there shown, the serrations of the inner tube surface 38 define alternating axial notches '9 and ribs 52. The edges of the inner bracket legs 48 are seated in a pair of notches 50. The latter are preferably rounded or formed without sharp interior angles, to eliminate the formation of stress cracks in the tube. The shape of the notches 50 is also of importance in the vitreous enameling operation. The adjacent ribs 52 hold the leg 40 from rotation with respect to the tube 34. When the inner bracket leg is inserted into the end of the tube 34, the bracket leg end 48 is slightly and resiliently bent to-- ward the leg portion 40, from the position shown in FIG- 10 in full lines to the position shown in broken lines. Further, when so inserted, the corners at the end of the end leg portion 48 are seated in a pair of notches 5t and the adjacent ribs 52 hold the leg portion 48 from rotation with respect to the tube 34.

The slight resilient compression of the spring wedgelike bracket portion defined by the inner leg 40 and the inner leg end portion 48 is easily brought about merely by inserting the bracket portion 40, 48 into the tube. Frictional resistance against withdrawal is established by the resilient pressure of the bracket portion 40, 48 against the inside of the tube 34. However, this frictional resistance is only suificient to hold the brackets against accidental withdrawal, and is not suflicient to prevent deliberate, desired withdrawal.

If desired, the inner leg portion 48 may originally be bent into the position shown in FIG. 10 in broken lines. Then the wedge- like bracket portion 40, 48 may be inserted into the tube 34 without being resiliently bent. In other words, the bracket portion 40, 48 will fit within the tube 34. For many conditions, such a construction of the brackets 38 is quite satisfactory.

Reference is made to FIGS. 11 and 12 showing finished resistors generally indicated at 54 and including a core tube 34, brackets 38, a coil 56 of resistance wire, terminal bands having radial lugs 58, an outer coating of vitreous enamel. As shown, the brackets 38 are aligned diametrically with the lugs 58. However, the brackets 38 may be disposed as desired with respect to the lugs 58, as by being originally inserted into the tube 34 at some desired angle, or by being withdrawn from the position shown in FIGS. 11 and 12 and reinstated at some other desired angle with respect to the lugs 58.

Many details may be varied without departing from the principles of this invention. Various types of brackets, flat or otherwise shaped, and various types of through bolts or other fastening devices may be used. It is therefore not my intention to limit the patent granted on this application otherwise than necessitated by the following claims.

The invention is claimed as follows:

1. A resistor structure comprising a ceramic core tube having an axially serrated inner surface, and supporting brackets having their ends seated in said core tube, each bracket consisting of a strip of fiat sheet material having inner and outer leg portions, said inner bracket leg portion being disposed within one end of said core tube, edges of said inner leg portion being seated in said serrations on the inside of said tube and held thereby against rotational displacement with respect to said tube, said tube having an opening therethrough having transverse dimensions greater than the transverse dimensions of said inner legs so that the inner legs of the brackets avoid completely plugging said opening.

2. A resistor structure comprising a ceramic core tube having an axially serrated inner surface, and supporting brackets, each bracket consisting essentially of a flat metal strip bent to form an inner and an outer leg, the end portion of said inner leg being bent back on the remainder of said inner leg into wedge-like configuration, said inner bracket leg being received in one end of said core tube, edges and corners of said inner leg being seated in serrations on the inside of said core tube and thereby held against rotational displacement with respect to said tube.

3. A resistor structure comprising a ceramic core tube having an axially serrated inner surface, said serrated inner surface presenting a plurality of axially extending notches and ribs around the inner circumference thereof such as to provide relatively closely spaced plural notches and ribs along hemispherical sections thereof, supporting brackets connected to the ends of the ceramic core tube, each bracket comprising essentially a flat metal strip formed with inner and outer leg portions, the inner end of the inner leg portion being reversely bent into wedgelike configuration, at least an edge of the inner leg portion and a corner of the reversely bent end of the inner leg portion being seated in notches on the opposite side of a chord of the ceramic core tube to prevent relative rotation between the bracket and tube, and terminal lugs on said ceramic core tube, and said plural notches and ribs permitting placement of said brackets in various angular positions of relationship with respect to said terminal lugs and leaving an open passage through the core tube.

4. A resistor structure comprising a ceramic core tube having an axially serrated inner surface, said serrated inner surface presenting a plurality of axially extending notches and ribs around the inner circumference thereof such as to provide relatively closely spaced plural notches and ribs along hemispherical sections thereof, supporting brackets connected to the ends of the ceramic core tube, each bracket comprising essentially a flat metal strip of a transverse width less than the diameter of the ceramic core tube and formed with inner and outer leg portions, the inner end of the inner leg portion being reversely bent into wedge-like configuration, the edges of the inner leg portion being seated in a pair of notches on one side of a diameter of the core tube and the corners of the reversely bent end of the inner leg portion being seated in a pair of notches on the opposite side of the same diameter of the core tube, and terminal lugs on said ceramic core tube, and said plural notches and ribs permitting placement of said brackets in various angular positions of adjustment with respect to the terminal lugs and leaving an open passage through the core tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,942,496 Siegel Ian. 9, 1934 2,151,799 Richter Mar. 28, 1939 2,487,057 Kohring Nov. 8, 1949 2,537,061 Kohring Jan. 9, 1951 2,538,977 Mucher Jan. 23, 1951 FOREIGN PATENTS 498,332 France Jan. 8, 1920 408,449 Italy Dec. 30, 1944

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