US2562940A - Shielded resistor unit - Google Patents

Description

Aug. 7, 1951 e. w. PACKER SHIELDED RESISTOR UNIT Filed Nov. 3, 1949 mm hum NW Wm Y M mm 6m Gm HIIIIII QVVENTOR. Glenn 14 Packer BY a ig A TTOQNE v Patented Aug. 7, 1951 SHIELDED RESISTOR UNIT Glenn W. Packer, Chica go, 111., assignor to Goodman ManuiacturinglsCompany, Chicago, Ill., a

corporation of Illino Application November 3, 1949, Serial No. 125,191

4 Claims.

This invention relates to an improved resistor of the kind used with heavy duty electric motors, as for example, with motors for electric mining locomotives which may be operated in explosive atmospheres.

Resistors for motors used in gassy mines must be completely shielded or enclosed to reduce the hazard of explosion. As a practical matter to withstand the shocks of rough usage, as well as to dissipate heat generated by the resistance unit, the shell or enclosure will usually be made of metal such as steel. Enclosing the resistance unit greatly complicates the problem of heat dissipation, causing the resistance unit to run at a very high temperature at times, which in turn causes it to distort and may eventually lead to failure by shorting against the metal case. In the'past, such failures have been tolerated as unavoidable in heavy duty equipment and replacement of resistor units at frequent intervals has been commonplace.

An object of the present invention, therefore, is to provide an improved heavy duty resistor unit which is entirely enclosed for use in gassy mines, yet which will dissipate heat rapidly enough to prevent failure through warping or distortion.

An important feature of the present invention is that the heat generating resistor element is resiliently mounted within the casing in such a manner that the mounting will lend itself flexibly to distortional movements of the element during heating and cooling. This is a great improvement over conventional rigid mountings which tend to crumble or break when the element is distorted.

Other objects and advantages will be apparent from the following description taken in connection with the drawings in which:

Figure 1 is a longitudinal sectional view of one embodiment of a shielded resistor unit made in accordance with the present invention;

Fig. 2 is an outside end view of Figure 1;

Figure 3 is a sectional view of Figure 1, taken along the line 9-4 and Figure 4 is a fragmentary view similar to Fig ure 1, showing how the mounting means for the resistance element may deflect to accommodate distortion of the latter.

Referring now more specifically to the drawings, the embodiment illustrated comprises a casing generally designated 2| and consisting of a tubular shell 22 and a pair of identical closure members 22. The shell will preferably be of heat conductive material, such as steel; the closure members will preferably be of brass. A shown in Figure 2, the closure members are square in section and have at each corner a tie bolt 24, effective to press the closure members tightly against the opposite ends of the shell.

To facilitate stacking multiple units, where more than one are required, aligning pins 26 and holes 21 are provided in opposite edges of the cover plates. Thus, multiple units may be stacked (and externally interconnected) to suit the requirements of a particular installation. Internally of the casing and protected thereby from the atmosphere, is a resistance element 29, in this case an iron coil. Each end is welded to the outer edge of a steel washer 29, which in turn is welded to the underside of the head of a steel electrode bolt 31. The shank 32 of the electrode bolt is square (for instance, Figure 3) and is engaged within a star-shaped opening 33 in a washer 34. The star-shaped opening permits a plurality, in this case eight, of rotative positions of the electrode bolt 3|. To maintain the washer 94 against rotation during tightening of the electrode bolt. its periphery is flattened in two places, as at 26, and these flats are engaged by a correspondingly formed seat 31 in a ceramic insulating disc 38.

which is seated against the inner face of the end wall 23. An inwardly extending peripheral skirt 3!, formed on each closure member, defines a socket for the corresponding disc 38. To prevent rotation of each ceramic disc 38 relative to its end wall, a pin 4| carried in the latter engages a slot 42 formed in the former.

Each electrode bolt 3| is electrically insulated from its corresponding closure member and its washer 44, by means of a bushing 43 and an annular disc 46, the latter two members being made of a suitably heat resisting material, as for example, mica.

The electrodes are held fast in place by means of nuts 41. Terminals 48 held on by nuts 49 may suitably connect the resistance coil element 28 into an external circuit, as for example, the starting circuit of a series motor in any well known manner.

At times in heavy duty service the resistance element 28 may actually run at red heat. This may soften and distort the element so it sags, twists, and warps. An important feature of the present invention lies in the improved means for resiliently supporting the resistance element intermediate its ends and preventing it from shorting out against the steel shell 22 under such conditions.

The improved supporting means for the resistance element 28 includes a plurality of elecascaaeo J 3 trically insulating elements Bil in this case ceramic rings disposed at intervals along the shell 22, each having a central aperture 52 in which the resistance coil is supported.

The supporting elements are resiliently mounted at intervals along the axis of the casing by resilient means, in this case coil springs 53, compressibly interposed between the end rings El and their corresponding closure members 23, and between adjacent rings 5|, all as shown in Figure 1. The free length of the coil springs 53 will preferably be greater than their assembled length so they will normally be under compression in the assembly, and their free diameter will preferably be greater than their assembled diameter so that they will normally press outward into contact with the shell 22 to facilitate heat dissipation. Normally, the springs 53 will run at a considerably higher temperature than the shell 22, and in order that they maintain a usable measure of their strength and resilience under operating conditions, they will preferably be made of some heat resisting material such as stainless steel.

Figure 4 illustrates how, under severe warping conditions, the individual ceramic supporting elements 5| will tilt to accommodate distortion of the resistance element 28, instead' of cracking or chipping as would be the case if the supporting elements were rigidly mounted. To accommodate this desirable tilting, when needed, some clearance should be left between the elements 5! and the shell, as shown at 54 in Figure 1.

While one form of the improved resistor unit has been illustrated and described, other modifications thereof will be apparent to those skilled in the art as falling within the scope of the invention as defined by the appended claims.

I claim as my invention: I

1. A shielded resistor unit comprising a casing consisting of a tubular metallic shell having closure members at opposite ends thereof, a resistance element extending along the interior of said casing, electrodes outside of said casing and means for connecting opposite ends of said resistance element to said electrodes, and means for supporting said resistance element intermediate its ends including at least one member made of electrically insulating material tiltably supported within said shell and itself supporting said resistance element out of contact with said shell, and resilient means effective to maintain said member at a predetermined position along the resistance element.

2. A shielded resistor unit comprising a casing consisting of a tubular heat conductive shell having closure members at opposite ends thereof, a resistance element extending along the interior of said shell, electrodes terminating outside of said casing and being connected to opposite ends of said resistance element; and supporting means for said resistance element intermediate its ends including an electrical insulating element disposed within said shell and embracing said resistance'element to maintain the latter spaced from the shell, said electrically insulating element being resiliently urged to a predetermined disposition along the resistance element by resilient means reacting against at least one end of the casing, said resilient means being disposed in heat conducting relationship with said shell whereby the latter will be efiective to dissipate heat absorbed by the resilient means from the resistance element when hot.

3. A shielded resistor unit comprising a casing consisting of a tubular heat conductive shell having closure members at opposite ends thereof, an elongated resistance element extending along the interior of the shell between the closure members, exterior electrodes connected respectively to opposite ends of said resistance element; and supporting means for said resistance element including a plurality of apertured spacers of electrically insulating material each tiltably supported within said shell at predetermined positions along the interior of said shell and eifective to support said resistance element to maintain it out of contact with the shell, and metallic helicalshaped separating members in heat-conductive contact with said shell and interposed between adjacent of said spacers and between the end spacers and their corresponding closure members to retain the spacers in their said predetermined positions.

4. A shielded resistor unit comprising a casing consisting of a tubular heat conductive shell having closure members at opposite ends thereof, a resistance element extending along the longitudinal axis of the shell interiorly thereof, exterior electrodes connected respectively to opposite ends of said resistance element; and supporting means for said resistance element including a plurality of ceramic members tiltably supported at intervals along the interior of the casing, each having an aperture embracing said resistance element to tilt with distortion of the latter and effective to maintain the latter out of contact with the shell, and a plurality of coil springs in heat-conductive contact with the shell being compressibly interposed between the end ceramic members and the corresponding ends of the casing and between adjacent ceramic members to maintain the latter resiliently disposed at their said intervals along the interior of the casing.

GLENN W. PACKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,154,417 Kuhn Sept. 21, 1915 1,963,328 Holinger June 19, 1934 2,397,291 Robertson Mar. 26, 1946

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