US2926330A - Terminal bushing assemblies for transformers - Google Patents

Description

Feb. 23; 1960 F. A, NEWCOMBE 2,926,330

TERMINAL BUSHING ASSEMBLIES FOR TRANSFORMERS Filed May 19, 1955 2 Sheets-Sheet l INVENTOR FRANK A. NEWCOMBE Feb. 23, 1960 F. A. NEWCOMBE 2,926,330

TERMINAL BUSHING ASSEMBLIES FOR TRANSFORMERS Filed May 19, 1955 2 Sheets-Sheet 2 S INVENTOR' FRANK A. NEWCOMBE a a 2,926,330 TERMINAL BUSHING ASSEMBLIES F TRANSFORMERS 7 Frank A. Newcombe, Pine Bluff, Ark assignorto. Central, Transformer Corporation, Pine Blntf,.Ark'., a corporation of Arkansas ApplicationMay 19,1955, seriarlsafsiigcu 9 Claims. (Cl. 339-202 This invention relates to certain new and useful im- 2,92%,33d Patented Feb. 23, 196i "ice of the present invention are accomplished and the manner of their accomplishment will readily be understood from the following specification upon reference to the following drawings, in which:

provernents in terminal bushing assemblies for trans formersfor use in effecting connection between incoming cables and leads from'transformer windings. This application is a continuation in part of and improvement upon theinvention disclosed and described in my co-pending application, Serial vNo. 480,206, filed January 6, 1955,

now Patent No. 2,866,173 dated December 23, 1958.

My aforesaid co-pending application and the improved modification thereof embodied in this invention are both directed toward eliminating the difiiculties heretofore encountered in terminal bushings. for transformers.

These difficulties resulted from the use of .a screw-type clamp for engaging the exposed endof the incoming cable, which caused undesired crimping of the cable ends resulting in damage thereto and .attimes contributing to the undesired breakage of the cable ends, interrupting the connection in an unsatisfactory manner,

The present invention is primarily directed to a ne and novel terminal bushing assembly for transformers which obviates the difficulty heretofore encountered and essentially eliminates the use of screw clamps for effecting engagement of a cable end. 1 v

The present invention contemplates the employment of a spring-operated clamping mechanism which is an improved modification of the clamping mechanism disclosed in the aforementioned co-pending application.

I The improved modification contemplates a.-spring-operated clamping mechanism which gives an indication of how tightly the cable is held'by the mechanism, and which is effective to maintain the necessary connecting clamping with aminimum of pressure being exerted upon the wire.

The principal object of the present invention is to i provide a terminal jbushing assembly for transformers uchad v c m a s tnraefie nsa ow esis a ce connection between an incoming cable and leads from transformerwindings. A further object of the invention to;provide a means for guardingagainst accidental contact with themetal of. the assembly, thereby reducing the hazard of electrical shock to a person.

v A further object of the inventionis to generally 'improve the design, construction and efficiency of terminal bushing assemblies for transformers.

The means bywhich the foregoing and other objects stantial portion of the length of the body.

Fig. 1 is a fragmentary view partly in section and partly in elevation of a terminal bushing assembly mounted horizontally in a side wall of a transformer casing.

Fig. 2 is a sectional view taken on a vertical plane along the longitudinal axis of the bushing assembly and illustrating an incoming cable clamped by the clamping means of the assembly.

,Fig. 3 is an enlarged fragmentary end elevational view of the device as viewed from the inside of the transformer casing.

Fig. 4 is a transverse sectional view'taken as on the line IV-IV of Fig. 2.

Fig. 5 is an enlarged fragmentary sectional view taken on a horizontal plane along the longitudinal axis of the bushing assembly.

Fig. 6 is a transverse sectional view taken as on the line VI-VI of Fig. 2 and Fig. 5.

Referring now to the drawings in which the various 'parts are indicated by numerals, the terminal bushing assembly 10 is illustrated as mounted in a circular opening formed in a side wall 11 of a transformer casing 13. The bushing assembly 10 includes a bushing body 15, preferably of porcelain or other suitable nonconductive material.

Bushing body 15 is provided with a substantially cylindrical inner bore or chamber 17 which extends from the inner end of the bushing body throughout a sub- At the opposite or outer end body 15 is provided with an additional bore or chamber 19 which is outwardly open and substantially frusto-conical in shape. The chambers 17, 19 are preferably co-axial and are separated by a shoulder 21, which is preferably centrally bored axially of the bushing body to provide communication between the inner and outer chambers 17, 19. Externally the inner end portion 23 of body 15 is preferably cylindrical and of a slightly smaller diameter than said circular opening in side wall 11, thereby closely fitting in said opening. Body 15 is provided with an annular flange 25 with. lock nuts'39 and lock washers 41. plate- 33 is provided with a central opening having an annular recess 35 formed adjacent thereto which closely adjacent the outer end of inner end portion 23, said annular flange being adapted to seat in adjacency to casing side wall 11. A longitudinal groove 26 is provided in inner end portion 23 and extends from the distal end of said inner end portion to flange 25. Said longitudinal grove provides access to spring 31 in the event it becomes necessary to remove the spring. A suitable sealing gasket 27 is interposed between flange 25 and side Wall 11 to effect seal of the bushing entrance into the casing side wall.

Inner end portion 23 is provided with a peripheral groove 29 in which is seated a retainer spring 31 engaging and retaining a plate 33, which surrounds body 15, against removal from said body. Plate 33 is substantially triangular in shape and is apertured adjacent each of the apices to receive bolts 37, which are provided Additionally fits spring 31. The bushing body is anchored to the casing side wall 11 by bolts 37,- which extend through ring 33 into engagement with the inner face of side wall 11 and bear thereagainst, pulling flange 25 and gasket 27 into tight sealing engagement with the side wall.

Mounted in bushing body 15 is an integral connector element 43 which is formed of suitable conductive metal,

such as a suitable grade of silicon bronze or the like and which is adapted to have a transformer lead connected to it and to engage an incoming cable to effect electrical communication between the cable and lead. Connector 43 includes an outer terminal portion 45 and an inner em portion 47 which is of reduced diameter relative to the diameter of the terminal portion. Internally, adjacent its outer end, terminal portion 45 is provided with a chamber 49 which extends from the outer end of the terminal portion throughout a substantial portion of the length of connector element 43.

Chamber 49 includes a longitudinal guideway 51 having a. horizontal top and bottom, and having concave sides. Said guideway extends throughout the length of said chamber.

Chamber 49 is internally threaded along a portion extending from the outer end of the chamber throughout a substantial length of said chamber. Guideway 51 longitudinally cuts across and blanks out a portion of the internal threaded portion to form interrupted threading in said chamber, the portions of threading existing only at the top and bottom of the chamber. Terminal 45 is transversely bored to provide opposite cable openings 53, the cable openings communicating with chamber 49 and extending through the material of terminal 45.

At the junction between terminal 45 and stem 47 connector 43 includes a disc-like annular flange 55 which is annularly grooved as at 57 to receive and retain a sealing gasket 59. Preferably connector 43 includes a pair of diametrically opposed minor length ribs 61 which lie along a minor portion of stem 47. At its distal end stem 47 is externally threaded as at 63 and the stem includes an internally threaded socket 65 in its distal end.

Threadedly engaged with said interrupted threading of chamber 49 is an externally threaded, hollow cylindrical sleeve 67, having peripheral knurling adjacent its outer end and having an inwardly extending shoulder 69 adjacent its inner end, said sleeve being formed of suitable conductive metal, such as brass or the like. A solid insert 71, as preferably formed of steel, is threadedly engaged in the outer end of sleeve 67, thereby blocking the end of the sleeve. Insert 71 is provided with a cylindrical outer end portion 73 having a transverse slot 75. A proacaasso v tective cap 77 is fixed to the outer end portion 73 and the knurled portion of sleeve 67. Said cap is preferably of a non-conductive material, such as one of the suitable phenolic plastics or other suitable material. Preferably the cap 77 is of a size to extend radially beyond the outer end of chamber 19, and the cap is provided with an inwardly extending rim 79, which substantially blocks the said outer end, thereby protecting persons against electrical shock, and additionally providing protection to the bushing assembly against the weather. It should be noted that in the extended position, as shown in Fig. 5, the inner edge of rim 79 is substantially in alinement with the outer end of chamber 19 the periphery of rim 79 is inwardly sloping to permit entry into frusto-conically shaped chamber 19.

A plunger 81, having a flange 83 at its outer end, extends through the opening in the inner end of sleeve 67, said plunger being spaced from the walls of chamber 49 and formed of suitable conductive metal, such as brass or the like. Interposed between the plunger and insert 71 is a compression spring 85 urging movement of the plunger away from the insert, the plunger being limited in travel by flange 83 seating against shoulder 69.

The inner end of plunger 81 terminates in a cylindrical portion 87 having a smaller diameter than the main body of the plunger. A contact 89, preferably of a good conductive material, such as bronze or the like, is provided with a cylindrical socket which is rotatably fitted onto the cylindrical portion 87. Contact 89 is of a size and shape to closely and slidably fit guideway 51 and the contact is vertically bored, which boring intersects one side of the cylindrical socket of contact 89 and is in communication therewith. The contact is fastened onto plunger 81 by means of a pin 93 inserted in said vertical boring,

which pin extends from top to bottom of contact 89 and seats in a peripheral groove 95 provided in inner end portion 87 substantially in tangential contact therewith, thus providing in effect a key against separation of the contact and end portion, while permitting relative rota tion between the contact and the end portion. The distal end of contact 89 is knurled and transversely recessed in the shape of a V, thus the distal end being adapted to engage an incoming cable 97. It should be noted that contact 89 by being shaped to fit guideway 51, as heretofore described, is thereby transversely elongated which provides a substantially long contacting surface to engage the incoming cable.

In the assembly of the device the plunger 81 is inserted through the cylindrical sleeve 67 so that the plunger extends outwardly through the inner end of the sleeve and flange 83 abuts shoulder 69. Compression spring 85 is inserted in sleeve 57 behind plunger 81 and insert 71 is threadedly engaged in the outer end of the sleeve. Protective cap 77 is then preferably molded onto the knurled outer end of the sleeve 67 and outer end portion 73 during the cap molding operation. Contact 89 is fitted onto the cylindrical portion 87 of plunger 81 and secured thereto in the manner heretofore described. Thus the sleeve, the contact, the insert and the spring-operated plunger, togetherwith the protective cap, are assembled together. Sleeve 67, with the aforementioned assembly, may then be engaged with the interrupted threading of chamber 49. The cap 77 and sleeve 67 may be rotated and run down to the closed position in which contact 89 engages the inner vertical face of chamber 49. A pair of retaining pins 99 then may respectively be inserted in transverse openings bored in the opposite sides of the terminal 45, said openings communicating with chamber 49 and extending through the material of the terminal. Said openings are positioned so that they enter the chamber at points which are spaced from and behind contact 89 when the contact is in the closed position. Retaining pins 99 extend into the space between plunger 81 and the walls of chamber 49, and are engaged by the contact 89 at its position of maximum outward travel, thereby limiting further outward travel of contact 89 and sleeve 67, and preventing accidental removal of protective cap 77 from the assembly.

Connector 43, together with the sleeve and its related said assembly, is then inserted through the central bore formed in shoulder 21, the bore being preferably radially undercut from the chamber 19 throughout a substantial portion of the length of the central bore, as at 100, to accommodate terminal ribs 61, the ribs effectively keying the connector to the bushing body against relative rotation. Gasket 59 is brought into engagement with the outer face of shoulder 21. A washer 101 is passed over the threaded end of stem 47 and a nut 103 is engaged with the external threads of stem 47 and is moved into tight fitting engagement with the inner face of shoulder 21, thus fixing the connector to the bushing body against withdrawal.

The threaded end of a lead stud 105, to which is attached a transformer lead 107, is then threadedly engaged with the threaded socket 65 formed in the distal end of stem 47, thus electrically connecting lead 107 to terminal 45. Bushing body 15 is preferably provided with a pair of diametrically opposed cable apertures 109 which are in transverse alinement with terminal cable openings 53 for selective introduction of a cable end to the connector from the exterior. Preferably bushing body 15 is additionally provided with a further aperture 111 disposed substantially ninety degrees from the cable apertures 109 and providing for the reception and housing of a suitable spark rod 113, the wall of terminal 45 being apertured substantially ninety degrees from the cable openings 53 as at 115, the aperture 115 being internally threaded and engaged therewith.

With the terminal bushing assembly mounted on cas ing 13 in'a manner heretofore describedfincoming cable 97 is to be introduced thereto. In doing so cap '77 is rotated, running the cap, the sleeve'67 and its related reversely rotated, running the sleeve 67 inwardly along threaded terminal 45, the sleeve carrying with it compression spring 85, plunger 81 and contact 89. The cap turns freely until the distalend of the contact engages'the incoming cable 97 and the spring 85 begins to compress. Further rotation of the cap compresses the springwhich urges the contact carried by the plunger into tight clamping engagement with the inserted cable, which effectively tightly clamps the cable between the vertical inner face of the chamber 49 and the contact 89. As the rotation of the cap progresses the increased compression of the spring causes increased resistance to rotation which gives an indication of how tightly the incoming cable is clamped. Thus the rotation of the cap may be ceased at the desired degree of clamping tightness. It will be understood that since the plunger fil is rotatably mounted in the socket of contact 89, the plunger is adapted to rotate freely with the spring 85, thereby preventing any binding between the spring and the plunger, which particularly would occur with the spring under tight compression were it not for he plunger being rotatable.

As shown in the drawings the entire clamping of the cable end is eifected by the action of spring 85. As is apparent in the event of wear or other change in the conditions of the inserted cable end, the spring is fully eifective to maintain firm clamping engagement and electrical contact with the cable end and that the same is accomplished without effecting crimping or other deformation of the cable end.

it will be further observed that since the elements of connector 43, contact 89, plunger 81 and sleeve 67 are all formed of conductive material, a' superior electrical connection is effected between incoming cable 97 and transformer lead 107.

I claim:

1. In a terminal bushing assembly for transformers which includes a non-conductive bushing body adapted for morning in a transformer casing, a conductive con nector Within said body extending from an outer portion of said body to an inner portion of said body and including means for electrically coupling a lead, said connector in said outer portion including an internally threaded hollow terminal having a vertical inner face, an externally threaded hollow sleeve having an inner end and an outer end, said inner end of said hollow sleeve extending into the outer end of said terminal and threadedly engaging the internal threading therein, an inwardly extending shoulder provided adjacent the inner end of said sleeve to form a reduced opening at the inner end thereof, a plunger having a reduced cylindrical portion at one end thereof and a flange at the other end thereof, said reduced cylindrical portion being formed with a peripheral groove therein, said plunger extending through said opening with the flange thereof limiting inward movement of said plunger, cap means fixedly attached to said sleeve adjacent the outer end thereof, spring means interposed between said cap means and the outer end of said plunger to urge said plunger away from said cap means, a contact slidably mounted in said terminal for movement longitudinally of said terminal, said contact being bored to provide a cylindrical socket in the "outward side"tl'iereof,said reduced cylindrical'portion of garages said plunger extending in said cylindrical socket, apin carriedby said contact and extending substantially tangentially in said peripheral groove to rotatably connect said plunger and said contact, means limiting outward travel of said cap means for preventing removal of said cap means from said terminal, said terminal being transversely apertured inwardly from said contact to provide cable openings for receiving endwise insertion of an incoming cable end, threaded advancement along said terminal of said cap means being effective to slide said contact into engagement with a cable end inserted into said cable openings, said cap means being freely rotatable along said inward advancement, further threaded advancement after engagement of said contact and cable being effective to compress said spring means, said spring means upon said further threaded advancement being effective to urge said contact into tight engagement with said incoming cable, thereby effectively clamping said cable between said contact and said inner face.

2. in a terminal bushing assembly for transformers which includes a non-conductive bushing body adapted for mounting in a transformer casing, a conductive connector within said body extending from an outer portion of said body to an inner portion of said body and including means for electrically coupling a lead, said connector in said outer portion including an internally threaded open-ended hollow terminal having a vertical inner face, an externally threaded hollow sleeve having an inner end and an outer end, said inner end of said hollow sleeve extending into the open end of said terminal and threadedly engaging the internal threading therein, an inwardly extending shoulder provided adjacent the inner end of said sleeve to form a reduced opening at the inner end thereof, a plunger having a reduced cylindrical portion at one end thereof and a flange at the other end thereof, said reduced cylindrical portion being formed with a peripheral groove therein, said plunger extending through said opening with the flange thereof limiting inward movement of said plunger, cap means fixedly attached to said sleeve adjacent the outer end thereof,

spring means interposed between said cap means and the outer endof said plunger to urge said plunger away from said cap means, a contact slidably mounted in said terminal for movement longitudinally of said terminal, said contact being bored to provide a cylindrical socket in the outward side thereof, said reduced cylindrical portion of said plunger extending in said cylindrical socket, a pin carried by said contact and extending substantially tangentially in said peripheral groove to rotatably connect said plunger and said contact, said terminal being transversely apeitured inwardly from said contact to provide cable openings for receiving endwise insertion of an incoming cable end, threaded advancement along said terminal of said sleeve by rotation of said cap means being effective to slide said contact into engagement with a cable end inserted into said cable openings, further threaded advancement after engagement of said contact and cable being effective to compress said spring means, said spring means upon said further threaded advancement being effective to urge said contact into tight engagement with said incoming cable, thereby effectively clamping said cable between said contact and said inner face.

3. In a terminal bushing assembly for transformers which includes a non-conductive bushing body adapted for mounting in a transformer casing, a conducting connector within said body, said connector including an internally threaded open-ended hollow terminal having a vertical inner face, an externally threaded hollow sleeve having an inner end and an outer end, said inner end of said hollow sleeve extending into the open end of said terminal and threadedly engaging the internalthreading therein, an inwardly extending shoulder provided adjacent the inner end of said sleeve to form a reduced open- "ing at the inner end thereof, a plunger having a'reduced cylindrical portion at one end thereof and a flange at the other end thereof, said plunger extending through said opening with the flange thereof limiting inward movement of said plunger, cap means fixedly attached to said sleeve adjacent the outer end thereof, spring means interposed between said cap means and the outer end of said plunger to urge said plunger away from said cap means, a contact slidably mounted in said terminal for movement longitudinally of said terminal, said contact being rotatably mounted on and carried by the cylindrical portion of said plunger, said terminal being transversely apertured inwardly from said contact to provide cable openings for receiving endwise insertion of an incoming cable end, threaded advancement along said terminal of said cap means being effective to urge said contact under pressure of said spring into tight engagement with a cable end inserted into said cable openings, thereby effectively clamping said cable between said contact and said inner face, and means for coupling said connector to an electrical lead.

4. In a terminal bushing assembly for use with transformers, including an electrically non-conductive body, an elongated electrically conductive connector mounted in and extending longitudinally inwardly from the outer end of said body, a longitudinally extending non-circular guideway in said connector, said connector being transversely apertured to provide a cable receiving aperture intersecting said guideway, a transversely disposed contact having a shape complementary to said guideway, non-rotatably and slidably fitted in said guideway, a plunger rotatably connected to said contact, said connector having internally threaded portions adjacent and communicating with said guideway, a threaded sleeve engaged with said threaded portions for inward advancement and outward retraction of said sleeve therealong, the outer end of said sleeve being closed, said plunger being slidable relative to said sleeve, said sleeve having an internal shoulder adjacent its inner end, a radial flange on said plunger engageable with said shoulder to limit separation of said sleeve and plunger, compression spring means seated against said flan e and being compressible by said sleeve outer end under sleeve advancement along said threaded portions to urge said plunger and contact inwardly along said guideway toward said aperture, said shoulder engaging said flange upon outward retraction of said sleeve to eifect retraction of said plunger and contact away from said aperture against the action of said spring, and limit means projecting into said guideway outwardly from said contact for limiting said plunger and contact retraction, whereby to limit sleeve retraction under said shoulder and flange engagement.

5. In a terminal bushing assembly for use with transformers, including an electrically non-conductive body, an elongated electrically conductive connector mounted in and extending longitudinally inwardly from the outer end of said body, a longitudinally extending non-circular guideway in said connector, said connector being transversely apertured to provide a cable receiving aperture intersecting said guideway, a transversely disposed contact non-rotatably and slidably mounted in said guideway, a plunger connected to said contact, said connector having internally threaded portions adjacent and communicating with said guideway, a threaded sleeve engaged with said threaded portions for inward advancement and outward retraction of said sleeve therealong, the outer end of said sleeve being closed, said plunger being slidable relative to said sleeve, said sleeve having an internal shoulder adjacent its inner end, a flange on said plunger engageable with said shoulder to limit separation of said sleeve and plunger, compression spring means seated against said flange and being compressible by said sleeve outer end under sleeve advancement along said threaded portions to urge said plunger and contact inwardly along said guideway toward said aperture, said shoulder engaging said flange upon outward retraction of said sleeve to effect retraction of said plunger and contact away from said aperture against the action of said spring, and limit means projecting into said guideway outwardly from said contact for limiting said plunger and contact retraction, whereby to limit sleeve retraction under said shoulder and flange engagement.

6. In a terminal bushing assembly for use with transformers, including an electrically non-conductive body, an elongated electrically conductive connector mounted in and extending longitudinally inwardly from the outer end of said body, a longitudinally extending non-circular guideway in said connector, said connector being transversely apertured to provide a cable receiving aperture intersecting said guideway, a transversely disposed contact non-rotatably and slidably mounted in said guideway, a plunger connected to said contact, said connector having internally threaded portions adjacent and communicating with said guideway, a threaded sleeve engaged with said threaded portions for inward advancement and outward retraction of said sleeve therealong, the outer end of said sleeve being closed, said plunger being slidable relative to said sleeve, cooperable means on said sleeve and plunger engageable to limit separation of said sleeve and plunger, compression spring means seated against said plunger and being compressible by said sleeve outer ,end under sleeve advancement along said threaded portions to urge said plunger and contact inwardly along said guideway toward said aperture, said cooperable means engaging upon outward retraction of said sleeve to effect retraction of said plunger and contact away from said aperture against the action of said spring.

7. In a terminal bushing assembly for a transformer, an electrically non-conductive body, an electrically conductive connector mounted in and surrounded by said body, said connector extending longitudinally inwardly from the outer end of said body and at its inner end Within said body including means for receiving a transformer lead, said connector being chambered inwardly from its outer end and being internally threaded to provide an internally threaded chamber which opens outwardly, said connector inwardly of said outer end being apertured to provide openings communicating with said chamber for the reception of a cable end, a non-conductive cap covering the outer end of said body, a hollow sleeve fixed to said cap, said sleeve being externally threaded and threadedly engaged with said internally threaded chamber, a plunger slidably mounted in and extending inwardly beyond the inner end of said sleeve, a contact mounted on one end of said plunger inwardly from said sleeve inner end, said contact slidably engaging said chamber for movement toward and away from said openings, and a compression spring housed within said hollow sleeve between said cap and the other end of said plunger, said spring urging said plunger to move said contact toward said openings.

8. In a terminal bushing assembly for a transformer, an electrically non-conductive body, an electrically conductive connector mounted in and surrounded by said body, said connector extending longitudinally inwardly from the outer end of said body and at its inner end within said body including means for receiving a transformer lead, said connector being chambered inwardly from its outer end and being internally threaded to provide an internally threaded chamber which opens outwardly, said connector inwardly of said outer end being apertured to provide openings communicating with said chamber for the reception of a cable end, a non-conductive cap covering the outer end of said body, a hollow sleeve fixed to said cap, said sleeve being externally threaded and threadedly engaged with said internally threaded chamber, a plunger slidably mounted in and extending inwardly beyond the inner end of said sleeve, a contact mounted on one end of said plunger inwardly from said sleeve inner end, said contact slidably engaging said chamber for movement toward and away from said openings, a compression spring housed within'said hollow sleeve between said cap and the other end of said plunger, said spring urging said plunger to move said contact toward said openings, and stop means projecting into said chamber into the path of movement of said contact away from said openings to limit said movement away from said openings.

9. In a terminal bushing assembly for a transformer, an electrically non-conductive body, an electrically conductive connector mounted in and surrounded bysaid body, said connectorextending longitudinally inwardly from the outer end of said body and at its inner end within said body including means for receiving a transformer lead, said connector being chambered inwardly from its outer end and being internally threaded to provide an internally threaded chamber which opens outwardly, said connector inwardly of said outer end being apertured to provide openings communicating with said chamber for the reception of a'cable end, a non-conductive cap covering the outer end of said body, .a hollow sleeve fixed to said cap, said sleeve being externally threaded and threadedly engaged with said internally threaded chamber, a plunger slidably mounted in and extending inwardly beyond the inner end of said sleeve, a

References Cited in the file of this patent UNITED STATES PATENTS 2,447,324 Fox Aug. 17, 1948 2,456,246 Berg Dec. 14, 1948 2,664,457 Joublanc Dec. 29, 1953 2,672,595 Barr Mar. 16, 1954 2,740,100 Broverman Mar. 27, 1956 FOREIGN PATENTS 824,504 Germany Dec. 13, 1951

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