US2458151A - Circuit breaker - Google Patents

Description

1949- H. D. DORFMAN ETAL 2,453,151

CIRCUIT BREAKER Original Filed June 24, 1941 2 Shee'ts-Sheet 1 16 4t! 39 Insulation Insulation 63 Elihu DIIOUQQUB\B\ WITNESSES: INVENTORS Hz Her 12 Dorfman &

3 M Gerald J. Freese. 7% B R/ 2 ATTORNEY Patented Jan. 4, 1949 CIRCUIT BREAKER Hiller D. Doriman. Forest Hills, and Gerald J.

Freese,

East McKeesport, Pa.,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application June 24, 1941, Serial No. 399,457, now Patent No. 2.419.125, dated April 15, 1947. Divided and this application May 18, 1944, Serial No. 538,138

11 Claims. 1

This invention relates to circuit breakers and more particularly to multipole circuit breakers of.

the type which are tripped instantaneously on overload currents of predetermined magnitude and after a time delay on lesser overloads,

This application is a division of copending application Serial No. 399,457, filed June 24, 1941, by H. D. Dorfman and Gerald J. Freese, and assigned to the assignee of the instant application. Said copending application has resulted in Patent No. 2,419,125, dated April 15, 1947.

One object of the invention is to provide a compact circuit breaker of improved construction which is simple and inexpensive to manufacture, and safe and reliable in operation.

Another object of the invention is to provide a multiploe circuit breaker with improved means for electrically isolating the several poles from each other to prevent flashover between adjacent poles.

Another object of the invention is to provide a multipole circuit breaker with an improved trip member of one piece moulded construction having a plurality of members moulded integral therewith cooperating with a partition wall forming separate compartments for the several poles of the breaker to more completely isolate adjacent compartments against flashover.

Another object of the invention is the provision of a circuit breaker having a trip device operated by a spring actuated trip member which is normally restrained by a thermally responsive bimetal element, also operated by an electromagnet which is arranged so that the air gap of the clectromagnet can be relatively small without limiting or interfering with the resetting movement of the trip device.

Another object of the invention is the provision of a circuit breaker having a rotatably mounted trip element, a spring actuated tripping lever normally restrained by a thermally responsive bimetal element and which is releasable to move the trip element to trip the breaker and which is resettable by a reverse movement of the trip element, in combination with a hinge type elecromagnet operable at times to move the trip element to trip the breaker, the electromagnet having a small air gap and being disposed so that it does not limit or interfere with resetting movement of the trip element.

Another object of the invention is to provide a circuit breaker with an improved magnetic trip device having an armature disposed for operation in a plane parallel to the axis of a trip member and engageable with a projection on said member, said armature being normally out of the path of said projection to permit movement of the trip member to reset the trip device.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as'to structure and operation. togcthcr with additional objects and advantages thereof, will be best understood from the following detailed description of one embodiment thereof when read in conjunction with the accompanying drawings, in which:

Figure 1 is a front elevational view of the breaker with a part of the cover broken away to more clearly show some of the parts;

Fig. 2 is a vertical sectional view of the circuit breaker taken on line 11-11, Fig. 1, and looking in the direcion of the arrows, the breaker being shown in cosed circuit position;

Fig. 3 is a detailed view of the trip device with the trp bar operated in response to operation of the thermal element;

Fig. 4 is a detailed view of the trip device with the trip bar operated by the electromagnetic trip means, and

Fig. 5 is a sectional view taken substantially along the line V-V of Fig. 2 and showing the assemblage of the electromagnets and the trip bar.

Referring to Figures 1 and .2 of the drawings, the circuit breaker includes a base I I of moulded insulating material on which the several elements of tie breaker mechanism are mounted. A cover 12 also of moulded insulating material is removably secured to the base and cooperates therewith to form an enclosing housing for the breaker mechanism.

The circuit breaker is of the multipole type, each pole comprising a pair of terminals l3 and I5, one disposed at each end of the breaker, a stationary contact ll, an arc extinguisher l9, and a movable contact 2|. A common operating mechanism indicated generally at 22 is provided for simultaneously actuating the three movable contacts to open or to closed position, and a trip device indicated generally at 23 serves to effect automatic opening of the three sets of contacts in response to predetermined overload conditions in the circuit through any pole of the breaker.

Each of the movable contacts 2| is mounted on a contact arm 25 pivotally supported intermediate its ends on the free end of a pair of switch arms 21 b means of a pivot pin 28. The arms 21 for all of the poles are mounted on a rectangular tie bar 29 of insulating material, andeach pair of the arms 21 are joined by a rectangular sleeve 3| surrounding the tie bar and secured thereto so that said tie bar and all of the switch arms 21 rotate as a unit, the tie bar being pivotally supported in the side walls of the breaker; The tie bar 29 extends transversely across the three poles of the breaker.

A flexible shunt conductor 30 connects the contact arm 25 with an angular terminal 32 secured by a screw 33 to one end of a conductor 35. The screw 33 also serves to secure the conductor 35 to the base The other end of the conductor 35 is' connected by a flexible conductor 31 to a point near the free end of a thermally responsive bimetal element 39. The other end of the bimetal 39 is rigidlysecured to the inner end of a conductor 4|, the terminal being secured to the outer end of said conductor. Each of thestationary contacts I1 is mounted on the inner end of a conductor 43 having its outer end connected to the terminal |3.

The electrical circuit for each of the poles is essentially the same and extends from the terminal I3 through the conductor 43, stationary contact l1, the movable contact 2|, the contact arm 25, the flexible shunt conductor 30, the terminal 32, the conductor 35, the flexible shunt conductor 31, the bimetal element 39 and the conductor 4| to the terminal l5.

Each of the three poles of the breaker is contained in a separate compartment formed by barriers 42 (Figs. 1, 2, and 5) moulded integral with the base H and extending the length of the breaker. These barriers 42 are in alignment .with similar barriers 45 (Fig. 2), moulded integral with the cover l2 so that when the cover is in place the barriers 42 and 45 serve to insulate each compartment from the adjacent compartments and prevent flash-overs.

The tie bar 29, which extends across all three poles of the breaker, is provided with annular flanges -48 disposed in recesses in the sides of the barriers 42 to prevent flashover through the openings in the barriers 42 and 45 provided to accommodate the tie bar.

The operating mechanism for the breaker illustrated generally at 22 (Fig. 2) is disposed in the compartment housing the center pole and is supported on a pair of frames 44 secured to the center part of the base The operating mechanism includes a forked operating lever 41, a toggle comprising links 49 and 5|, a pair of overcenter springs 53 and a releasable cradle 55 controlled by the trip device 23. The cradle 55 is pivotally supported on the frame 44 by a pivot pin 56. The inner ends of the forked operating lever 41 are rounded and are pivotally seated in recesses in the frame 44 as indicated at 51. An insulating shield 59 for covering an opening 6| in the cover I2 is mounted on the outer end of the operating lever 41 and a manual operating handle 63 integral with said shield projects through the opening 6| to permit manual operation of the breaker mechanism.

The toggle links 49 and 5| are pivotally connected together by a knee pin 65. The link 5| is pivotally connected by a'pivot pin 61 to the pair of switch arms 21 for the center pole, and the end of the link 49 is bifurcated and pivotally engages a stud 69 on the cradle 55 being retainedin engagement therewith by the tension exerted .by the overcenter springs 53 between the knee pin 65 and the outer end'of the operating lever 41.

Overcenter springs 11, operatively associated with the contact arms 25, surround contact arm operating members 19 and arecompressedbetween angular brackets 8| secured to the pivoted ends of the arms 21 and shoulders 83 on the members 19. The springs 11 hold the ends of the members 19 in engagement with recesses in the inner ends of the contact arms 25. The members 19 and the contact arms form toggles for operating the contact arms 25. I

As previously mentioned, the trip device 23 includes a bimetal element 39 for each of the poles of the breaker, said bimetal elements being connected in series in the circuit of their respective poles. The trip device also includes a series overload magnet 86 for each pole, and a trip bar 81 common to all of the poles. The trip bar 91 is of one piece moulded insulating material and is pivotally supported by means of pins 89 moulded in axial alignment in the ends of the trip bar and which rotatably support said bar in bearings 9| (Figs. 1 and 5) in the side walls of the circuit breaker housing.

The trip bar 81 extends across the three poles of the breaker through openings provided therefor in the barriers 42 and 45. In order to more completely insulate the compartments, the trip bar 81 is provided with a plurality of flanges 8B moulded integral with said trip bar and disposed one on each side of each of the barriers 42 and 45. These flanges are positioned close to the barriers and effectively prevent flashover through the opening provided in the barriers for the trip bar 81. Each pole of the breaker is provided with a trip member 93 pivotally supported on a U-shaped frame by a pivot pin 91. The frame 95 of each pole is suitably secured to the base and is separate from the frames 95 of the other poles. The pivot pin 91 which supports the trip member 93 is mounted in a pair of ears |0| formed on a projection 03 of the frame 95. A spring I05 compressed between a bar I01, supported in openings in the legs of the frame 95, and the trip member 93 biases said member in a clockwise or tripping direction. The trip member 93 is normally prevented from rotating in a tripping direction by engagement of the latch end thereof with a latch |09 on the free end of the bimetal 39.

A latch member secured to projections ||3 moulded integral with the trip bar 81 normally engages the latch end of the cradle 55 and thereby restrains the cradle in operative position.

When the bimetal element 39 for any one pole is heated a predetermined amount in response to an overload current, it flexes in a direction to move the free end thereof toward the left (Fig. 2) and after a time delay unlatches the trip member 93, whereupon the spring I05 rocks said trip member in a clockwise direction. During this movement the end of the trip member 93, disposed above a projection ||5 moulded integral with the trip bar, strikes said projection and rocks the trip bar 81 counterclockwise causing the latch III to release the cradle 55. This permits the over-center springs 33 to actuate the operating mechanism and open the contacts as will be more fully described later.

The trip device is also operated electromagnetically by means of the electromagnet 86 to instantaneously trip the breaker upon the occurrence of a heavy overload for instance, 1000% or more of rated current or on short circuits in the circuit of any pole of the breaker.

For this purpose each pole of the breaker is provided with an electromagnet 86 including a U-shaped magnet core II1 (Fig. 5) mounted between the barriers 42 moulded integral with the base II. A U-shaped magnet frame I2I spaces. the core II1 from the base II and, at its upper ends, forms a mounting for an armature I23.

The conductor 35, which is secured to the base II by means of the screw 33 and a screw I23, extends through the U-shaped core H1 and thus secures the'magnet unit to the base, the inner surface of the base being recessed to receive core 1 andmagnet frame I21 as shown in Fig. 2. A spacer I25 is provided to space the conductors 35 from the magnet core and a channel-shaped length of insulation 121 between the conductor 35 and the spacer I25 insulates the core II1 from the conductor. Since the current flowing through the circuit of each of the poles traverses the conductors 35 said conductors serve to energize the electromagnets 85.

The armature I23 is pivotally mounted by means of a reduced portion I3I thereof projecting into an opening in one leg of the U-shaped magnet frame I2 I. A spring I35, having one end connected to a member I33 on the armature and its other end anchored on the one leg of the magnet frame, biases the armature I32 to its unattracted position. A cam I33 on the member I33 is adapted to engage an arm I moulded integral with the trip bar 81 upon energization of the electromagnet and cam the trip bar 31 counterclockwise (Fig. 2) to release the cradle 55.

The armature I23 is disposed for operation in a plane parallel to the axis of the trip bar 31 and when in its unattracted position the cam I39 thereon is disposed to one side and out of the path of movement of the projection I on the trip bar, as shown in Fig. 5, in order to permit clockwise rotation of said trip bar (Fig. 2) for the purpose of relatching the trip member 93. This arrangement of the parts permits a shorter tripping stroke of the armature and makes possible a smaller air gap which results in improved operating characteristics of the trip device and yet despite the relatively small air gap the electromagnet does not limit orinterfere with resetting movement of the trip bar 31.

A wire or leaf spring I43, disposed in a recess I42 in one of the barriers 42 and supported at each end in the recess of the barrier, is tensioned against a flat surface I52 on the trip bar 81 to bias the trip bar in both directions toward its normal position. The spring I43 also prevents tripping of the breaker due to shock or jar. By enclosing the spring I43 in the recess I42 in the barrier 42 it is protected against the heat and flame of the arc incident to the rupture of the current.

Each of the armatures I23 (Fig. 5) has mounted thereon a contact I44 electrically connected to the conductor H by a flexible shunt conductor I45. Upon the occurrence of an overload in excess of a predetermined magnitude or a shortcircuit, the armature I23 is attracted by the magnet core H1 and moves the contact I44 into engagement with a contact I48 mounted on one end of a resilient contact blade I50 (Figs. 2 and 5) secured to the conductor 35, thereby shunting the current around the bimetal element 39. This prevents undue heating of the bimetal and aids in preserving the calibration thereof. The arrangement of the armature I23 and of the contacts I44 and I48 is such that operation of the armature, upon energization of the magnet provides a wiping contact.

The circuit breaker mechanism is shown in Fig. 2 in the closed circuit position with the trip device 23 in untripped position. when the trip bar 81 is rocked in unlatching direction in response to an overload in the circuit through any one of the poles, the latch III disengages the cradle and permits the overcenter springs 53 to rotate the cradle clockwise about its pivot 56. At the start of this rotation of the cradle 55,

a projection 53 on the cradle 55 engages a stud on the toggle link 5| and starts the toggle 495I in the direction to cause its collapse. Continued movement of the cradle 55 causes the center line of the toggle link 49 to move to the right of the line of action of the springs 53 which act to complete the collapse of the toggle. This rocks the arms 21 counterclockwise carrying the contact arms 25 and the movable contact 2I therewith to open the circuit of the breaker. This operation of the mechanism also causes the handle 53 to be moved to an indicating position intermediate the open and closed positions. In the closed circuit position (Fig. 2) the line of action of the overcenter spring 11 is above the pivot 26 of the contact arm 25 and biases the contact arm in a clockwise direction about its pivot providing pressure for the contacts. When the arms 21 are rotated counterclockwise, as above described, a tail I45 on the toggle member 19 strikes a projection I41 on the base II causing the toggle 19--25 to move overcenter. This rocks the contact arm 25 counterclockwise about its pivot 26 which opens the contacts a greater distance than would be possible if the movable contact were mounted directly on the arms 21.

Following each automatic operation of the breaker due to operation of the trip device 23 in response to an overload current, it is necessary to reset the mechanism to operative condition before the contacts can be reclosed. This is effected by rotating the manual lever 41 from its tripped position to its extreme counterclockwise or open position. This movement of the lever 41 is transmitted to the cradle 55 by a hooked projection I5I engaging a portion I53 of the cradle. As the cradle 55 is rotated in a counterclockwise direction, the latch end thereof passes the latch member I and engages a projection I55 molded integral with the trip bar 81, rocking the trip bar clockwise slightly past its normal position to relatch the cradle 55. During the clockwise resetting movement of the trip bar 81, the projections II5 thereon engage the ends of the trip members 33 and rock said members counterclockwise to relatch them with the latches I09 on the bimetal elements 39.

After the cradle 55 has been relatched, thecontacts can be closed manually by moving the lever 41 clockwise to its closed circuit position.

During this movement the line of action of the overcenter springs 53 crosses to the right of the pivot 69 of the toggle link 49 causing the toggle 49-5I to move overcenter and rock the arms 21 quickly clockwise to close the contacts. As the switch arms 21 approach the closed position, the arm 25 strikes a projection I51 on the base II at a point to the left of the pivot 26 (Fig. 2) causing clockwise rotation of the contact arm 25 about its pivot 25 moving the spring 11 overcenter above the pivot 25. This causes the contacts to close with a snap action and applies pressure to the closed contacts after they are closed.

The contacts are opened manually by moving the lever 41 in a counterclockwise direction about its pivot to the open position. This movement carries the line of action of the springs 53 to the clockwise or open position, this force becomes '5 suiiicient to cause the toggle to quickly collapse, and since the toggle link is pivotally connected to the switch arms 21 for the central pole, these arms are rotated counterclockwise causing opening of the contacts for all of the poles. The

contacts are closed manually in the manner previously described.

The circuit breaker is trip free, i. e., operative automatically in response to predetermined abnormal circuit conditions in any one of the poles thereof irrespective of the position of the operating lever 41. 1

The are extinguishers [9, there being one provided for each pole of the breaker, are of the spaced plate type and comprise, generally, a stack of slotted plates of magnetic material positioned adjacent the paths of movement of the movable contacts 2|. plates causes the arc resulting from the rupture of the circuit to be drawn in the direction toward the ends of the slots where the arc is broken up into a plurality of short arcs, and these short arcs are quickly cooled and extinguished.

Features of the circuit breaker contact means construction shown and described in this application are fully disclosed and claimed in United States Patent No. 2,318,298, issued May 4, 1943, to Hiller D. Dorfman and Gerald J. Freese, and assigned to the assignee of this invention. Having described the preferred embodiment of the invention in accordance with the patent statutes, it is to be understood that various changes and modifications may be made in the structural details disclosed without departing from some of the essential features of this invention. It is, therefore, desired that the language of the appended claims be given as reasonably broad interpretation as the prior art permits.

We claim as our invention:

1. A trip device for a circuit breaker comprising a trip bar movable from a normal position in one direction to trip the breaker and in another direction from said normal position to reset the trip device, means biasing said trip bar to said normal position, a projection on'said trip bar, and an electromagnet having a pivoted armature for engaging the projection to operate said trip bar and trip the breaker, said armature in its unattracted position being disposed out of the path of said projection to permit movement of the trip bar to reset the trip device.

2. A trip device for a circuit breaker comprising a trip bar of one-piece molded insulating material movable from a normal position in one direction to trip the breaker and from normal position in another direction to reset the trip device, said trip bar being provided with a plurality of projections molded integral therewith,

an electromagnet having a pivoted armature, said 65 electromagnet being responsive to overload conditions above a predetermined value to cause the armature to engage one of said projections and operate the trip bar to trip the breaker, a separately supported trip member biased in a tripping direction and releasable for engaging another of said projections to operate the trip bar, a bimetal element operable when heated a predetermined amount to release the trip member, said armature in unattracted position being out of the path The presence of these of the first projection to permit movement of the trip bar to reset the trip member.

3. A trip device for electrical control apparatus comprising a trip bar movable from a normal position to a tripping position and from said normal position to a resetting position, said trip bar being provided with a projection, a pivoted armature including a member for engaging the projection on the trip bar to move the trip bar totripl0 ping position, said armature being disposed for movement in a plane parallel to the axis of the trip bar, an electromagnet responsive to predetermined circuit conditions for operating the armature, said member being disposed out of the 'path of movement of the projection on the trip bar when the armature is in its unattracted position to permit movement of the trip bar to resetting position. 7

4. In a circuit breaker, relatively movable contacts, actuating means for opening the contacts,

a trip device comprising a trip bar solely of onepiece molded insulating material, said trip bar having a normal position for releasably restraining the actuating mechanism and being movable in one direction from said normal position to release said actuating mechanism and in another direction from said normal position for resetting the trip device, a pluralit of projections molded integral with said trip bar, electromagnetic means responsive to circuitconditions above a predetermined value for engaging one of said integral projections to cause release of the actuating mechanism, a spring biased trip member mounted separately from said trip bar for engaging another of said integral projections and moving the trip bar to cause release of the actuating mechanism, a bimetal element operable when heated a predetermined amount to cause release of said.

trip member, and means engageable with a third integral projection on said trip bar for resetting said trip member.

5. In a circuit breaker, relatively movable con tacts, actuating means to cause opening of the contacts, atrip device including a trip bar movable from a normal position in one direction to trip the breaker and in another direction from said normal position to reset the trip device, a projection on said trip bar, and an electromagnet having a pivoted armature for engaging the projection to trip the breaker, said armature in its unattracted position being disposed out of the path of the projection to permit movement of the trip bar to reset the trip device.

6. In a circuit breaker, relatively movable contacts, actuating means operable to cause opening of the contacts, a trip device including a trip bar movable from a normal position in one direction to trip the breakerand in another direction to reset the trip device, said trip bar being provided with a plurality of projections, an electromagnet having a pivoted armature, said electromagnet being responsive to overload conditions above a predetermined value to cause the armature to engage one of the projections and operate the trip bar to trip the breaker, a separately supported trip member biased in a trippin direction and releasable for engaging another of said proj ections to operate the trip bar, a bimetal element operable when heated a predetermined amount to release the trip member, said armature in unattracted position being out of the path of the first projection to permit movement of the trip bar to reset the trip member.

7. In a circuit breaker, relatively movable contacts, actuating means operable to cause automatic opening of the contacts, a trip device including a trip bar movable from a normal position to a tripping position and also movable in an opposite direction from the normal position to reset the trip device, said trip bar being provided with a projection, a pivoted armature including a portion for engaging the projection to move the trip bar to tripping position, said armature being disposed for movement in a plane parallel to the axis of the trip bar, an electromagnet responsive to predetermined circuit conditions for operating the armature, an independently supported trip member biased to a tripping position to engage and move the trip bar to cause automatic opening of the contacts, a thermal element operable when heated a predetermined amount to release the trip member, said engaging portion of said armature being disposed out of the path of the projection when the armature is in unattracted position to permit movement of the trip bar to reset the trip member.

8. In a circuit breaker, relatively movable contacts, operating mechanism for said contacts including a manual operating member movable to cause opening or closing of said contacts, and a member releasable to cause opening of said contacts, a trip device including a trip bar of onepiece molded insulating material having a normal position for releasably restraining the releasable member and being movable in one direction to release said releasable member and in another direction for resetting the trip device, said manual member being operable to cause movement of the trip bar in resetting direction, a plurality of projections molded integral with said trip bar, an electromagnet responsive to current conditions above a predetermined value and having a pivoted armature for engaging one of said insulating projections for moving said trip bar to cause release of the releasable member, a spring biased trip member mounted independently of said trip bar and operable to engage another of said insulating projections to move the trip bar to cause release of the releasable member, a bimetal element operable when heated a predetermined amount to cause release of the trip member, and means engageable with a third insulating projection on said trip bar for resetting the trip member, said armature in its unattracted position being disposed out of the path of its cooperatin projection on the trip bar to permit resetting movement of the trip bar.

9. In a circuit breaker, the combination of a conductor connected in the circuit of the circuit breaker, a U-shaped magnetic member around said conductor, a, trip bar rotatable about its longitudinally extending axis generally perpendicular to said conductor, an armature pivoted adjacent one leg of said magnetic. member and movable toward the other leg thereof upon the now or a predetermined current through said conductor, and seigi a rniature being pivoted for rotation in a direction extending longitudinally of said trip bar and being operable to cause rotetion of the trip bar about its longitudinal axis.

'10. In a multipole circuit breaker, relatively movable contact means for each pole, actuating means including a spring biased member releasable to cause opening of said contact means, a trip device comprising a rotatable trip bar or one piece molded insulating material common to all of the poles for normally restraining said releasable member, said trip bar being rotatable in one direction to release said releasable member and in another direction to reset said trip device, a plurality of projections molded integral with said trip bar, a spring biased trip member for each pole, each trip member being independently mounted and being releasable in response to predetermined abnormal conditions in its associated pole and independently of the other poles to engage the associated projection on said trip bar and rotate said trip bar to effect release of said actuating means, electromagnetic trip means for each pole, each of said electromagnetic trip means including a pivoted armature disposed for rotation in a direction longitudinally of the trip bar, each of said armatures being operable in response to predetermined conditions in its associated pole to engage another of said projections and operate the trip bar to release the actuating means, each of .said armatures in unattracted position being disposed out of the path of the cooperating projection on the trip bar to permit movement of the trip bar in resetting direction to reset any of the spring biased trip members of the other poles that are tripped.

11. In a multipole circuit breaker, relatively movable contact means, operating mechanism for opening and closing said contact means, trip means comprising a trip bar common to all of the poles operable in one direction to effect operation of the operating mechanism and in another direction to reset the trip means, a plurality of projections on said trip bar, a plurality of releasable trip members each operable independently of the others and when released engaging one of the projections on said trip bar and operating said trip bar to effect operation of said operating mechanism, an electromagnetic trip means for each pole each having a pivoted armature, and means on each armature for engaging a corresponding projection to operate the trip bar to effect operation of said operating mechanism, each of said means being normally disposed out of the paths of its cooperating projection so as to permit movement of said trip bar to reset the I trip members for the other poles.

HILLER D. DORFMAN. GERALD J. FREESE.

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

UNITED STATES PATENTS Number Name Date 864,027 Pearson et al Aug. 20, 1907 1,023,102 Badeau Apr. 9, 1912 1,271,558 Francis July 9, 1918 1,448,383 Brown June 28, 1923 2,043,306 Sandin June 9, 1936 2,050,285 Dorfman Aug. 11, 1939- 2,178,083 Sandin Oct. 31, 1939 FOREIGN PATENTS Number Country Date 199,526 Great Britain June 28, 1923

Images