US2669649A

US2669649A - Safety housing for electrical apparatus

Info

Publication number: US2669649A
Application number: US91888A
Authority: US
Inventors: Benjamin C Webster
Original assignee: Bryant Electric Co
Current assignee: Bryant Electric Co
Priority date: 1949-05-07
Filing date: 1949-05-07
Publication date: 1954-02-16
Anticipated expiration: 1971-02-16

Description

Feb. 16, 1954 B. c. WEBSTER SAFETY HOUSING FOR ELECTRICAL APPARATUS Filed May 7, 1949 as a,

-50 WITNESSES: 2 I Y 5 INVENTOR 70 BenjominCLWebster.

BY I Q 40 1/ ATTORNE Patented Feb. 16, 1954 SAFETY HOUSING FDR ELECTRICAL APPARATUS Benjamin 01 Webster, Southport, Conn, assignor to The-Bryant Electric Company, Bridgeport, Gonn a corporation of Connecticut Application May 7, 1949, Serial No. 91,888

This invention relates: to" electrical circuits, and-more especially concerns safety apparatus for'use'in" the same.

An" outstanding general object OflthlS invention'is'th provision of 'reliable and eiiective apparatusfor protecting" against access to certain parts of an electrical circuit until those parts have beenrendered safetothe touch.

A further-object of'the invention is that of providinga" simple and'practical safety switch andswitch cover'locking' unit for-electrical cir cuits; the" switch components being well protected" against giving off electrical shocks when fully-'exposedrto the touch.

Another object of 'theinventionisthat of providinga safety unit suited. for opening one electrical circuit with the efiect of deadening an.- other, and. for. preventing access to the la er cl rcuitruntil the deadening" operation isa'chieved.

A still 'further object ofthis invention is the provision of'an electrical circuit controlled by a safety unit; the latter affording protection against iaccess'to ccrtain parts in theJcircuit and for giving access after: the circuitis cut off.

The present invention is of especial importance inithe fluorescent lighting field, as where one or more gaseous electric discharge lamps ofthe.

hazards incident uponexposure of parts which normally,- carry an electrical charge during replacement of the lamps. The. usual control switches in these lighting circuits are of a kind which can easily be ignored, or left turned on with the thought that they are turned off, as during such operations as replacement of burned out.tubes.. The terminal portions, such as electrically. conductive metal pins or caps of the fluorescent tubes, thus occasionally become e2:- posed to the touch before full disconnection from their. sockets. is achieved. Likewise, a existsv in forcing the terminals of replacement tubes'intc -live sachets, especially should connection into the energizing circuit be accom- 9 Claims. (01. Zia-11.4)

plished before shielding of the terminals against electrical shock or the like can be had. Ihen again, an open socket and exposed connections adjacent to the socket in one of these fluorescent lighting systems, sometimes give off shocks and afford other dangers well'recognized as existing in exposed electrical parts which continue to carry a charge.

It is, accordingly, an object of this invention to provide a safety unit for fluorescent lighting systems, by which deadeningvof the secondary circuit of these systems is reliably assured before access can be had to certain normally charged components such as the lamp terminals and sockets for the purpose of replacing the lamp.

A still further object of the invention is that of, providing fluorescent lighting systems, or other electrical systems of thecharacter having a primary circuit and a secondary circuit, embodying circuit safety features.

The precedingobiects and other objects of this invention will become more apparent upon consideration of the. following description of a preferred embodiment thereof, when taken in connection with the attached drawing, in which:

Figure l is a diagrammatic view of a fluorescent lighting system including a safety switch unit in accordance with the invention, the unit appearing in plan View toward the lefthand side of the figure, with the cover omitted;

Figure 2v is an enlarged, fragmentary, plan view of the switch unit appearing in Figure 1, and with part of an interior cover plate broken away and. with, the switch being in circuit closing position;

Figure 3,. is an enlarged sectional view taken substantially along. the line III-III of Figure 2, and further representing the tube socket cover and controller knob of the switch unit; and

Figure lis an enlarged sectional view corresponding to Figure 3, taken substantially at right angles to the section of Figure 3.

.In the particular embodiment of the invention disclosed in the accompanying drawing, a safety unit is is provided at the corresponding, high voltage ends of a bank of fluorescent lighting tubes TI, T2, T3 andiT l, for protecting against access to these ends when the tube energizing current is turned on. It is the housing i i of the an electrical insulating material such as any suitable resin, to protect against electrical shock. Cover It conveniently has at its inner side outout portions for receiving projections lac on base I2, thus to orient the several portions to closed position and afford stable closure thereof. lhe base has openings I2b for receiving screws for mounting as to a ceiling or wall. As a further component of the safety unit ii], there is a circuit control switch I5 having features which will be more fully explained hereinafter. It will be observed that in order to replace a lamp it is necessary to remove cover it of unit ID.

The circuit controller portion of the control switch illustratively includes a shaft I8, which extends through a suitable opening in the cover I E and externally of this cover carries a suitably afiixed knob It for manual operation. Pressing on the underneath side of the knob I9 and against the outside surface of the cover I4 is a coil spring 2t of sufficient strength to urge apart the elements against which it presses. In this vicinity the cover conveniently has a depression 2I, for receiving the inner portion of the knob IS and concealing the spring 223 from outside view and thus contributing to neater general appearance of the safety unit It. For added safety, the knob advantageously is of a material which is electrically non-conductive, such asvan electrical-insulating synthetic resin.

. That portion of the controller shaft I8 which is on the inside of the cover It, is connected to operate a switch terminal contacting member of the controller unit as for example an annulus or washer-like member 25 having diametrically opposite rigid arms 25 and 2'! turned down to provide

contacts

28 and 29, respectively, at the outer ends of the arms. The switch terminal contacting member 25 is made of an electrically conductive material, illustratively copper.

arms

26 and 2? usually have about a 90 angle bend, thus to provide the

contact portions

28 and 29.

Also mounted to rotate with the controller shaft I8 is a lock component 30, for selectively locking and unlocking the base I2 and cover It of the housing II with movement of the switch terminal contacting member 25 to and from electrically conducting position. The lock component 39 conveniently is of a substantially cylindrical shape having an axial bore, and diametrically opposite lugs 3! and 32 extending radially from one end of the main body thereof. This locking member usually is made of an electrically insulating material, as for example of a suitable synthetic resin or hard rubber, and conveniently forms a unit with the switch terminal contacting member 25, the latter being mounted in an annular groove 33 and radial grooves 36 and 3? in the end of the locking member remote from the radial lugs 3| and 32 and covered by the insulating washer 35. The annular groove as advantageously is between the inner and outer cylindrical surfaces of the looking member 35 so that the latter member can afford electrical insulation. The radial grooves 35 and 3! respectively receive the arms 25 and 2'! of the switch terminal contacting member 25 and thus hold these arms and their respective contact portions 23 and 23 against rotation except as a unit with the locking member. An internally threaded bushing 34 extends through the axial bore of the locking member 30 and is cleated at one end against the lugged end of the latter member. The other end of the bush The ing as is spread to retain the insulating washer tightly in its covering position over the switch terminal contacting body 25, and accordingly prevents escape of this body from the annular groove st and

radial grooves

35 and 31. Preferably the arms and 21, as united to the locking member 30, are in about the same angular positions as the radial lugs 3I and32.

The unit comprising the switch terminal contacting member 25 and the locking member 30,. is mounted on the controller shaft as for rotation with the same. Bushing 34 conveniently fits onto that end of the shaft I8 which is inside the cover It, and is internally threaded from one end to about mid-length, to accommodate threads on the shaft. The shaft threads terminate to afford a stop against one direction of relative rotation of the bushing 34-, but leave enough ofthe shaft protruding to receive a lock nut It, or the like, acting against relative rotation in the other direction.

At about the middle, for example, base I2 of the safety unit It has integral therewith, or attached thereto, a substantially rectangular or other suitably shaped casing having an upstanding wall 5!] for confining the switch terminal contacting member 25 and locking member 30. Extending laterally from the inside surface of the wall 59, and illustratively somewhat above the principal top surface of the base I2, is an inwardly protruding locking portion 56 of the wall.

lugged end of the locking member but some what larger than this section for clearance. The.

portion 55 illustratively is molded integral with the wall and base I2. In the underneath side of the locking portio 5:3 and radiating from opening are

depressions

53 and 54 for holding the radial lugs 3| and 3'2. vent rotation of the knob I9 and switch controller shaft I8 until, by manual operation, the

knob and shaft are rotated and moved longitudinally against the action of coil spring 21! to free the lugs 3| and 32 of the depressions. The longitudinal movement and rotation of the lugs to desired extent, is facilitated for example by a space 58 within the wall 58 and immediately below the locking portion 55. Above the looking portion 56 and within the limits of the wall 59, there is a compartment SI for receiving the switch terminal contacting member. 0n opposite sides of this compartment are terminal contacts 4c and i! of the control switch I5. These terminal contacts are made of electrically conductive material, such for example as copper, or copper alloy, and preferably are in the form of thin flexible and resilient strips, each having both of their ends supported. In this connection the contact to has its ends fitting in grooves 66 and in opposite sides of the casing wall 50, and the terminal M likewise is supported in grooves 65 and 5? of this wall. In the normal or open circuit position of the terminals 4e and M, the lateral distance between these terminals is advantageously less than the distance across the switch terminal contacting member 25 measured from contact portion 28 to contact portion 29. With this arrangement, the terminals 4!! and 4| are susceptible to being bowed apart by the switch terminal contacting member 25, with rotation of knob I9 and the controller shaft I8 for closing the switch I5. To

These depressions are eifective to pre-,

protect-regain; electrical .1 shock: and; also: tozree taimthe terminalblades w and 4-] initheir-end supporting grooves, the switch I5 has an-;ele.c;-. tricalz. insulating. plate; I21 or other. a suitable oasing component overtheterminals and across the top:;of:wa1l.50... The. plate I2 illustrativelyishcld in". place by; lag bolts'ltr1tbreaded into. the; top edge: of w-all150; There: is anopening I5 vinzthe plate: 12 for-ineressand egress-of. the locking member; 30; and. the; switch: terminal: contactin member; 25; This opening preferably is. sub.- stantially in alignment withoneningti andiusuallyv of about; the same: size; and shape: (see Figure-12)..

Assuming: that; the cover; I 4: along: with. the switch: controller; portion; of" the safety unit. I are removed from the base I2, and: that'it'is desired toiclose the: switch I 5, the following-operationsrarezinnorder: The; cover I4 isrseatedon the base I2; with the base projections I ia receiving the cutout portions at the inner :side of thecover: In achieving this-operation, the knob IS-ris; given-a turn should this'beneeded, to align the-locking; member 30 and the switch. terminal contacting-member for insertion through shaped opening I5 in the plate '52. As these latter elementspare inserted,- the locking member 39 passes on down into shaped opening 55 1 and blocks rotationofithe knob I9tby reason of contacting the wallof this opening; During this time'the switch contact" arms 4 26. and. 'l'I take a position (dotted lineiportioningFigure 2.) betweenthe switch terminals lllianddl and arerout: of electrical contact with the same as for example-by being in substantially.- parallel relation to the terminal blades: Then, 'by'pressing the knob I9 inward against thepactionrof coil spring 20, the shaft I8. undergoes a: longitudinal movement" and the lugs 3I and ii'zi accordinglymove clear oi'the underneath surface of locking portion 5810f. the Wall 50. It'will lie-observed that. the lower surface of locking: portion 58 issloped-atfifia (Fig; 4) sothat at this point, the: knob I9 maybe turned for: rotating the shaft I 8 and the: locking memberilso 0 Carry ou forrexample l resented in Figure l, an'energized ortransiormer about a 90 angle" of rotation in a clockwisedirection as viewed-in Fig; 2', and lugs 3| and 32 will ride on the sloped surfaces 55a to cause Ion gitudinal inward movement of'shaft" 18' to finally seat" in the'depressions 53 and-.51 in the surfaces of locking.- portion 55. Coil spring 20 then is effective. to arrest further rotationv of the lugs; Thecover M accordingly is locked'tothe base I2. A further-important operation which occurs in giving theshaft Ia'zthernecessaryz rotationto bring: the lugs" to the: locking: position" just: indicated, is the rotation of therswitch terminalroon tacting: member Thearms 26 and 21in being' fixed'tothe' shaft -I 8, also undergo an angular displacement corresponding to that of the lugs and; accordingly; reach .a lateral or bridging posi tion: with respect to the-switch terminalsttl and 4|; thus: electrically interconnecting the same-Q In approaching this position, the switch contacts 2Ilsand29 of the arms tendtobowrapart the terminals 49' andid I; thusassuring agood; firm-electrical; connection. It follows'that the cover- It and base I2 are, safely locked together while the switch I5 is closed for conducting; electricity.-

By continuingrotationof the'knob I 9,. in .thesame 1 directionthe; lugs 31 and -32 Y againride; on sloped surfaces 560 to movenclear ofthe depressions 53. and. back-to tree exit position (dotted line-p051:- tion in Figure; 2) leaving, the; switch; terminals. and I. electrically. disconnected} The: cover .I Azthemmax: bezlifte'd jmmtheebasei I2; .ati whlch time, the switch; terminal; contacting. member 25 is. int suitable alignment-with. openings. 15-: torremoval, as; is :the locking: member 30. in: alignment withopeningsi'iand.15.. With. the removal of cover I4; and the knob:- I9; shaft I8, SWitCh'=COX1v tacting member 25 and lockingmember 3.0; all supported by the cover; theterminals 40: and 41. arezprotected. against touch by: thezplate- I2. The;- removed': controller portions of. the switch I 5. are; electrically dead.

Now in applying-the safety unit In to: a. fluorescenta lighting system, it1-is advantageouszto house the corresponding adjacent: ends. of the lighting tubes TI, T-2;. T3' and T4 wlthimthe housing-1 II formed by the base I2 and cover: I4 In the illustrative embodiment represented: in Figure l of. the accompanying drawing. the-.fl'ucrescent lighting system includes a step-up transformer'of which the energizing orprimarywindings PI. and P2. are connected at and 8| in parallel to a line source of'alternating current electricalsupply. Beginning at junction 8Il-with the line supply, one ofthe parallel primary cir cuitsincludes leadsBS and 82, primary winding PI; leads 83 and 84, control switch I5 (and more particularly contact 40, switch terminal contact:- ing'body 25 and-contact ll thereof, seeFigure -2) and lead'fifi baclr to the line'connection 8!. The other parallel primary circuit includes leads 86 and s2, primary winding P2; leads 83 and 8!". contact 49, switch terminal contacting body 25; contact H, and lead'85-to connectionBI.

The base'oi'the safety'unit IIIhas mounted thereon, for shielding by the cover H, a plurality of sockets or other suitable lampholders; such as electrically conductive clips 90,- 9'I, 92', and 93, respectively receiving the adjacent'terminal ends of tubes TI T2, T3 andTfl.

Secondary ooilsSI and 520i the transformer are, for example, in autotransformer connection across the coils PI 'andPZ, the tubes-TI and T2 accordingly being connected in parallel with coils PI and SI. Thus; in the cmbodiment rep secondary circuit mayb traced from' the lefthand side of coiLPI, through this coil and'the secondary coil SI- to junction 95,- thence along lead I fiI-to reactor RI and" condenser-CI, lead I533 to lampholder terminal a, across the lamp TI and thence along loads :79 and 82' back to the lefthand side ofthe coil PI. A circuit-parallel to thisfis traceable from the lefthand side-of: the coil P I; through this coil and secondary S I 1 along lead IO'I andthrough reactor B2. to terminal'SIa oi'f the lampholder 31, across the tube, T2, and back" along leads l9 and'M to the lefthand' side of'coilPi. Thereactors RI and'BZ conveniently serve to limit the current supply once, the serially associated'tubes .Ti and Tlhavebecomecondirctive. The condenser CI eiiects phase displace: ment of the operating currents thronghtube TI as eomparedwith.theourrentthrough T2, thus reducing stroboscopic eiiect in the-emitted and blended light ofthe two tubes.

Similarly, tubes T3. TII-are connected... in parallelivithcoils F2 an.dlS2.. Acir'cuit maybe traced from the-lefthand side ofcoiLPi (Fig are i.) through ooiland secondary coiLSl; junction 94,- along-lead Hi2, throughreaotorBJ and. condenser C3, and along lea-c1425 to terminal Mootthe Iarnpholder s2, thence acrosstube -Til, andhack-over loads '59 and 821:0 the lefthand side of .coil E2; Coils-P2; arnifiZ also are-incircuitincluding lead; I 02, reactor-R4, lead 405:, terminal 93aof lampholder 33, tube T4" and leads illand 82 back to the coils. Reactors R3 and Eli limit the current in their respective circuits once the tubes T3 and T4 are energized. The condenser C3 effects phase displacement so as to reduce stroboscopic effect in the light emitted from tub s T2 and T4.

, Theefiect of safety unit it on the fluorescent lighting system just described, is to close th parallel primary circuits or" the windings PI and P2 by means of the switch 55. so long as the locking'member so locks together the cover M and base l2. Under these conditions, the cover l4 not only prevents'access to live parts of the switch itself, but also to such components as the lampholders 9G, 3!, 92 and 533, including their termi-- nals, and the ends of tubes Tl, T2, T3 and T4 supported therein; vWhen the cover 34 is unlocked by rotation of knob 15, the switch 25, and more particularly the switch terminal contacting member 25 of the controller, opens the transformer primary energizing circuits of the fluorescent lighting system, and the secondary or energized circuits including the lamps TLTZ', T3 and T4 are rendered'electrically dead. Upon removal of the cover it from the base i2, as for example to replace one of the lamps therefore, any components of the secondary circuits may be safely touched without danger of electrical shock or short-circuit. The terminal contacts 46 and 4| connected in the primary circuits of the transformer are the only parts in unit Ill which may be energized when cover I4 is removed, but these are at a relatively low potential, and are not readily accessible in view of being housed within the insulating wall 59 and beneath the insulating plate 12.

:At the other ends of tubes Tl, T2, T3 and TA. remote from the safety unit It, is a suitable enclosure 59, for closing 01? these tube ends and such related parts as their supporting sockets, or other suitable holders and the electrical connections needed in this vicinity for giving the tube operating circuits described above. A fastener 68 such as for holding together a base and cover of the enclosure 69, advantageously is not moved to open the enclosure until after operation of knob 19 to open the unit ill. If desired, the enclosure 69 may be replaced by another unit it! for added safety I Having described a preferred embodiment of the invention in accordance with the patent statutes, it is desired that the invention be not limited to this particular structure,' 'inasmuch as it will be obvious to persons skilled in the art that many modifications and changes may be made in this particular structure without departing. from the broad spirit and scope of this invention. Accordingly, it is desired that the invention be interpreted as broadly as possible and thatit be limited only as required by the prior art.

I claim as my invention:

1. An electrical safety unit, comprising, a housing having relatively movable portions for admitting access tothe inside thereof; an electrical switch inside said housing and including relatively movable contacts respectively supported by said relatively movable housing portions forcoming apart with the same, one of said contacts being mounted for movement 'relative to its housing portion, manually operable means for said one contact operative from outside said housing for effecting opening and closing' of the switch by movement relative to said housing portions with said housing portions 8 closed; and locking means for preventingac'ce'ss to' the inside of said housing while the switch is closed.

2. An electrical safety unit, comprising, a housing having relatively movable portions for admitting access to the inside thereof; an electrical switch inside said housing and including spaced contacts and a movable bridging contact respectively supported by said relatively movable housing portions for coming apart with the same, said bridging contact being operative from outside said housing for selectively affording a bridge across said spaced contacts with said housing portions closed; and locking means 0perative with said bridging contact for preventing access to the inside of said housing while the switch is closed.

3. An electrical safety unit, comprising, a housing having relatively movable portions for admitting access to the inside thereof; an elec trical switch inside said housing and including relatively movable contacts respectivelysupporF ed by said relatively movable housing portions for'coming apart with the same, one ofisaid contacts being mounted for movement relative to its housing portion, manually operable means for said one contact operative from outside said housing for opening and closing the switch by movement relative to said housing portions with said housing portions closed; and locking means cooperative with said one contact for locking the latter at switch closing Position and for preventaccess to the i -side of said housing While the switch is closed. Y

4. An electrical safety unit, comprising, a housing having relatively movable portlonsfor admitting access to the inside thereof; an electrical switch inside said housing and including laterally spaced'fiexible terminal strips supported at the ends thereof to one'of said housing portions, and a terminal bridging member'rotatably supported by another of said housing portions and operable by a controller from the outside thereof, for'rotation between said terminals for con-.- necting and disconnecting the same when the housing is closed; and a lock operative with said controller for preventing access to the inside of said housing while the switch is closed and for giving access when the switch is open.

5. An electrical safety unit, comprising, a hous me having relatively movable portions for ad-' mitting access to the inside thereof; an electricalswitch inside said housing and including/a circuit controller supported through the wall of one of said housing'portions and having a bridging contact portion inside said Wall for rotation by operation from the outside, and spaced contacts within a casing supported inside another of said housin portions, said casing having an access opening for admitting said bridging contact portion of the controller; and a lock for closing said'housing against access, comprising, a locking portion within said contact casing below the access opening thereof, and a logged component fixed for movement with said controller through said access opening for rotation to underneath said locking portion with rotation of said bridging contact portion to closed position of the switch. x

6. An electrical safety unit, comprising, a hous ing having relatively movable portions for ad--' mittin access to the inside thereof; an electri cal switch inside said housing and including, a shaft through the wall of one of said housing portions and carrying an operating knob on the outside and a switch terminal-closing portion inside for unitary longitudinal movement and rotation relative to the supporting housing portion, and terminals in a casing which is supported inside another of said housing portions, said casing having a shaped access opening through the casing thereof for admitting said terminalclosing portion at one rotative position thereof; and a lock for closing said housing portions against access including, a locking component fixed on said shaft and shaped to fit through said shaped opening at said one rotative position for subsequent rotation to position corresponding to terminal-connecting position of the terminalclosing portion, a corresponding locking portion within said casing for flanking said shaped look-- ing component during rotation of the latter and affording an interlock with the same against rotation at its position corresponding to terminalconnecting position of said terminal-connecting portion, and a sprin biasing said shaft longitudinally toward the outside of said housing and thus urging said shaped locking component retractibly into interlocking relation with the corresponding locking portion,

7. An electrical safety unit for transformeroperated gaseous electric discharge lighting systems,comprising, in combination,a closed housing having relatively movable portions for admitting access to the insidethereof; at least one lampholder within said housing for receiving transformer secondary current supply and the end of a gaseous electric discharge lamp, an opening in said housing of a size to receive one end of a gaseous electric discharge device for engagement with said holder; an electrical switch inside said housing and including, separate terminals for transformer primary circuit connection, and controller means respectively supported by said relatively movable housing portions for coming apart with the same, said controller means being permanently movably mounted in and extending through its housing portion so as to be operative from outside said housing for effecting electrical connection and disconnection of said switch terminals with the housing portions closed; and locking means for preventing access to the inside of said housing while said switch is closed.

8. Supporting means for gaseous electric discharge lamps comprising, spaced hollow supporting housings each having openings for receiving the corresponding end of a lamp, said housing being spaced apart a distance considerably less than the length of a lamp to be supported thereby so that a substantial portion of each end of the lamp extends into the respective housing when supported thereby, one of said housings having relatively movable portions for admitting access to the inside thereof; at least one lampholder within said housing for receiving transformer secondary current supply and the end of a gaseous electric discharge lamp and being spaced from its corresponding housing opening; an electrical switch inside said housing and including, se arate terminals for transformer primary circuit connection, and controller means respectively supported by said relatively movable housing portions for coming apart with the same, said controller means being operative from outside said housing for eifecting electrical connection and disconnection of said switch terminals with the housing portions closed; and locking means for preventing access to the inside of said housing while said switch is closed.

9. Supporting means for gaseous electric discharge lamps comprising, a hollow housing having at least one opening of a size to closely surround the glass envelope of a lamp with the ad- Jacent end and terminal of the lamp completely received within the housing, said housing having relatively movable portions for admitting access to the inside thereof, an electrical switch and contact means for engaging a lamp terminal in said housing, said contact means being spaced from said housing opening, a circuit controller supported through the wall of one of said housing portions and having a non-circular shaped contact bridging portion inside said wall for rotation by operation from the outside, and said switch including spaced encased contacts supported inside another of said housing portions and having a noncircular shaped access opening into the casing thereof for admitting said contact bridging portion of the controller at one rotative position of the latter for subsequent rotation to switch closing position where said contact bridging portion of the controller cannot escape through said casing opening.

BENJAMIN C. WEBSTER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 978,841 Buckton Dec. 20, 1910 1,629,089 Beckmann May 17, 1927 1,675,837 Beckmann July 3, 1928 1,731,417 Hartwig Oct. 15, 1929 2,042,680 Pontis June 2, 1936 2,127,473 Sacco Aug. 16, 1938 2,313,983 Yost Mar. 16, 1943 2,401,555 De Reamer June 4, 1946 2,406,104 Ranney Aug. 20, 1946 2,430,336 Hathaway Nov. 4, 1947 2,434,576 Mcshane et al Jan. 13, 1948 2,449,820 Seaman Sept. 21, 1948 FOREIGN PATENTS Number Country Date 244,851 Great Britain Dec. 31, 1925 333,551 Great Britain Aug. 11, 1930 393,721 Great Britain June 15, 1933 597,173 Great Britain Jan. 20, 1948