US2627002A

US2627002A - Bimetallic switch

Info

Publication number: US2627002A
Application number: US95999A
Authority: US
Inventors: Alvares Octavio Jose
Original assignee: MARIA DE REITZES MARIENWERT
Current assignee: MARIA DE REITZES MARIENWERT; MARIA DE REITZES-MARIENWERT
Priority date: 1949-05-28
Filing date: 1949-05-28
Publication date: 1953-01-27
Anticipated expiration: 1970-01-27

Description

Jan. 27, 1953 o, J, ALVAREZ 2,627,002

BIMETALLIC SWITCH Filed May 28, 1949 s sheets-sheet 1 /f f /f INVENToR. laf crqv/@JLVAKEZ Jan. 27, 1953 o. J. ALVAREZ 2,627,002

BIMETALLIC SWITCH Filed- May 28, 1949 3 Sheets-Sheet 2 14.6/ E 34 136 94 156 1 30 26 m 44 30 g4 3f 172 152 f4 l 48 je I if@ .92 l 30 I6 \\\\\&\\\ 64 l /f 136 f we x00 w///////A ,3p A INVENTOR.

00m/10 7.4L vmwfz Patented Jan. 27, 1953 ambos amErALuc swrrcn- Octavio Jose Alvarez, New York, N. Y., assigner, by mesne assignments, of one-fourth to Maria dc Reitaes-Marienwert, New York, N. Y.

Application May 28, 1949, Serial No. 95,999

12 Claims. (Cl. 20o-188) My invention relates to a bimetallic switch, and more particularly to a bimetallic switch for use with water boilers, such as those provided in a coiiee percolator, hot plates or the like.

It is an object of my invention to provide a bimetallic switch in which the contacts are opened suddenly and with great speed.

It is a further object of my invention to provide a bimetallic switch which has no friction contacts and no frictional or pivoting movements in the mechanical parts of the switch.

It is another object of my invention to provide a bimetallic switch with mechanical compression of the contacts while the switch is closed.

It is another object of my invention to adjust the temperature at which the switch works, from the outside of the switch without touching a current-carrying member.

It is another object of my invention to provide a bimetallic switch which is simple in construction and cheap to manufacture.

I achieve these and similar objects by providing a bimetallic strip, a spring arranged for snapping transition from one end position into another end position, a connection between the bimetallic strip and the snapping spring causing the spring tov snap into the other end position when the bimetallic strip is hot, and a contact arranged for actuation by the spring.

In a first embodiment of my invention a member is provided which connects the snapping spring and the contact, the member being arranged for coming into engagement with the contact in the last part of the motion of the spring into the other end position under action of the bimetallic strip.

In one embodiment of my invention a U-shaped strip having a stationary end is provided, and a contact is rigidly connected to the other end of the U-shaped strip; a member shaped as a double stirrup connects the middle portion of the snapping spring to the leg of the U-shaped strip carrying the contact, and a threaded bolt is screwed into a threaded hole in the part of the double stirrup engaging the snapping spring and extends loosely through holes provided in the U-shaped strip and is arranged with its end near the middle portion of the bimetallic strip.

In another embodiment of my invention the bolt makes contact in the closed position of the switch directly with a counter-member and is pressed into contact-making position by an insulating member. If desired, an insulating plate may be arranged for being pushed between the bolt and the counter-member when the switch 2 opens, and resilient means actuated by the member pressing the bolt into contact-making position is provided for pushing and withdrawing the plate into and from operating position.

'I'he novel features which I consider as characteristic for my invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a sectional elevation of one embodiment of my invention with the switch contacts closed at about two to three times the natural sca e;

Fig. 2 is the same embodiment with the contacts open;

Fig. 3 is a sectional elevation of the same elnbodiment with open contacts and the restarting button pressed in;

F1Fig. 4 is a cross-section along the` line 4--4 of Fig. 4a is a perspective view of a part of the devicshovbvn in Figs. 1-4;

g. 4 is a perspective view of the housing the device shown in Figs. l4; of

Fig. 4c is a perspective view of the contacts of the device shown in Figs. 1-4;

Figs. 5 and 6 are sectional elevations of another embodiment of my invention with open and closed contact, respectively, also at about two to three times the natural scale;

F1Fig. 7 is a cross-section along the line 1-1 of Figs. 8 and 10 are sectional side elevations of a third embodiment oi' my invention with the contact closed and open, respectively, and again at about two to three times the natural scales; and

Figs. 9 and 1i are cross-sections of Figs. 8 and 10 taken along the lines l-l and |i-| i, respectively.

Referring now to the drawings, and nrst to Figs. 1 and 4, I0 is part of the bottom of an electrically heated vessel, such as the bowl of a coifee percolator, which is heated by an electric current which is controlled by the switch hereinafter described. For a reason to be more fully explained later, the part III of the bottom of the vessel is arranged a little higher than the remaining parts of the bottom such as the parts I2 and Il (Fig. 4) so that the upper part of the switch to be described is situated in a recess of the bottom. The parts of theswitch are arranged in a housing generally denoted by i8 and shown separately in Fig. 4b. The housing, preferably made of aluminum, comprises two end walls I8 and 20, a-

`spring 42 to be more fully described later.

The prong-

like extensions

30 and 32 of the roof of the housing i8 4are in contact with or even spot-welded to the bottom parts i2 and i4 of the vessel as will be clear from Fig. 4. A bimetallic strip 44 rests with its end portions on the

marginal portions

28 and 28 of the roof of the housing I8 and is, while it is cold, in contact with the bottom part i of the vessel (Figs. 1 and 4).

A block 48 of insulating material is carried by the end wall I8 of the housing l5. A substantially U-shaped spring 48 is secured with its end portion 50 to the block 46. The end portion 50 is preferably slightly oi-set with respect to the main body of the spring as will be seen from Fig.

1. The other end portion 52 of the U-shaped spring 48 is shorter than the end 50 and its outer rim 54 is bent at right angles to the end portion 52 so as to provide a seat for a block 56 of insulating material. The block 58 with a counterblock 58, also of insulating material, are secured to the end portion 52 of the spring 48 by means of a rivet 80. Between the blocks 5G and 58 is sandwiched the end of the stem of a T-shaped member 62, preferably of metal and shown separately in Fig. 4c, the outer rim 64 of which is bent at right angles with respect to the main portion of the member 82 so as to provide a proper abutment on the counterblock 58. The member 62 is provided with a hole for the rivet 80. The cross-piece 88 of the T-shaped member 62 carries two

contacts

88 and 10 which are in electrically conductive connection with each other, preferably through the material of the crosspiece. The contacts S8 and 'l0 are in contact, when the switch is closed as in Fig. l, with contact pieces 'l2 and i4, respectively, which are secured to the block 46 and to which the circuit controlled by the switch 9 (not shown) is connected. It will be understood that in the position of the switch shown in Fig. 1 the T-sh-aped member 82 with the

contacts

68 and 10 shortcircuits the

contact pieces

12 and 14, whereas in the position shown in Figs. 2 and 3 it interrupts the electrical connection between them.

In the bottom part of the housing I6 a snapping spring 42 is penetrating with its end ,

portions

38 and 40 into the

apertures

34 and 36, respectively. The snapping spring 42, which is separately shown in Fig. 4a, is naturally slightly convex towards' the interior of the housing l5 as will be seen from Fig. 1 which, however, shows the convexity of the snapping spring at an exaggerated scale for the sake of clearness.

In the center of the snapping spring 42 is provided a hole 18 through which the threaded end 18 of a bolt 80 passes loosely, i. e. at a certain distance of the perimeter of the hole '16. The bolt 80 is screwed with the threaded end 18 thereof into the lowermcst part 82 of a connecting member generally indicated by 84 the shape of which is a double stirrup more clearly shown in Fig. 4. 'It consists of a strip the ends of which are bent into U-shape of different widths. The

. lowermost U-shaped part comprises the

portions

82 and 88 which enclose between them practically without play the snapping spring 42. The lowermost U-shaped part is connected to the uppermost U-shaped part by an intermediate part 88 the length of which .substantially corresponds to the distance between the snapping spring 42 and the lower portion of the spring 48 in the switched-'in position shown in Figs. 1 and 4. The upper U-shaped part of the connecting member 84 comprises the

portions

90 and 82 which enclose between them the lowermost bend of the U-shaped spring 48 and are separated from each other by a certain distance so that in the switched-in position of the switch the lowermost bend of the U-shaped spring 48 is in contact with the portion 90, as shown in Figs. 1 and 4, whereas in the open position of the switch it is in contact with the portion 92 as will be described in more detail hereinafter in connection with Fig. 2. The

portions

88, 90 and 92 of the connecting member and the upper and lower portion of the U-shaped spring are provided with holes through which the bolt or its end portion 'i8 pass with a clearance. The bolt 80 extends upwards so that its rounded end 94 is in the switched-in position shown in Figs. l and 4 a short distance below the bimetallic strip 44.

The operation of the device so far described is as follows: With the position of the switch shown in Figs. 1 and 4 the T-shaped member 62 with the contacts B8 and 10 is in contact with the contact pieces l2 and 14 and shortcircuits the same. When the current is switched in by any means (not shown) the vessel or hot plate becomes hot and heats through the part |0 the bimetallic strip. The part I0 is preferably somewhat elevated with respect to the remaining parts of the bottom of the vessel so that some liquid will be left within the vessel while the part i0 becomes dry and actuates the bimetallic strip. The bimetallic strip bends in consequence of the heating and eventually reaches the position shown in Figs. 2 and 3. During this process it displaces the bolt 80 and therefore the snapping spring 42 a little whereas the U-shaped spring 48 is not yet aiected. After the snapping spring 42 has passed its mean position in which it is fiat it turns with a snap into the position shown in Fig. 2 in which it is concave with respect to the interior of the housing I6. In the latter part of this motion of the snapping spring 42 the uppermost bend 82 of the connecting member 84 which had followed the motion of the snapping spring 42 owing to its connection with it by its lower U- shaped part comes into contact with the lower bend 52 of the U-shaped spring 48 and suddenly opens the contacts 68-74 (Fig. 2). It will be understood from the foregoing that the temperature at which the switch opens the contacts can be controlled by changing the setting of the bolt 80 within the lowermost bend 82 of the connectingtriember 84 by turning the head 98 of the The parts shown in Figs. 1-4 at the bottom serve for re-setting the switch after it has broken the circuit. A support 98 which is stationary with respect to the housing I8 is provided with a iianged central hole |00 in which a press button |02 is slidably movable. The press button |02 is in contact with a spring member generally denoted by |04 and comprising a metal strip provided with a central hole |06 which is in alignment with a corresponding hole |08 in the press button |02 in order to have access to the head as of ine boit so. .st bom ends the strip m is bent as at and is secured in apertures ||2 of the support 88. About half-way between the bent portions |04 and the hole |08 of the strip |04 the latter is provided on either side with a U-shaped bend I4 turning towards the snapping spring 42.

The operation of this device is as follows:

When .the switch is open and the bimetallic strip 44 has returned to its initial position shown in Fig. l the press button is pressed upwards and the U-shaped bends 4 press the snapping spring into its initial position shown in Fig. 1 whereby the connecting piece 84 is brought back to its initial position and the contacts 68-14 are closed. Then the pressure on the button |02 is relieved so that it returns to the position shown in Fig. l, the switch being ready for use.

If the press button |02 is actuated while the parts of the switch are still in the position shown in Fig. 2, i. e. the bimetallic strip 44 is bent downwards, the snapping spring 42 cannot move upwards with its middle portion because the bolt 80 hits the bimetallic strip 44 and therefore the connecting member 84 cannot move the whole distance upwards. The parts assume then the position shown in Fig. 3 where the snapping spring 42 has a multiple bend and the contacts 68-14 are still open.

Referring now to the embodiment shown in Figs. 5-7, the switch is located inside a structure |20 of insulating, preferably ceramic material. On top of the structure |20 is arranged the heated part |22 such as the bottom of a water boiler and underneath the structure |20 is an insulating plate |24 provided with an aperture |25 .ior a press button |28 which preferably consists of insulating material. The press button |28 is provided with a central aperture |30 in order to render the head |32 of a screw bolt |34 accessible by means of a screw driver (not shown). Parts i 20, i 22 and |24 are held together by any suitable means (not shown).

t 6 the leaf spring |40. In this position of the switch the snapping spring |54 is slightly convex towards the contact piece |42 whereas in the opening position oi' the switch shown in Fig. 5 it is concave with respect to the contact piece |42.

A slidable plate |12 of insulating material is arranged at' right angles to the snapping spring |64 and the leaf spring |40 (Figs. 5 and 6) which in the opening position of the switch shown in Fig. 5 enters between the screw bolt |84 and the contact piece |42 thus interrupting any arc which might occur during the switching operation. The structure |20 is provided with a strip |14 of insulating material at the spot turning towards the forward edge of the plate |12, so as to provide a complete separation of the screw bolt |34 and the contact piece |42 in the open position of the switch.

In order to close the switch the press button |28 is moved upwards until it reaches the position shown in dotted lines in Fig. 6. The button is provided with a bevelled upper surface |16 which during this motion comes into engagement with a spring |18 the shape of which will be seen from Figs. 5 and 6. The spring |18 is secured to the structure |20 by means of a bolt with nut |82 and one of its ends is shaped as guide |84 for the plate |12. The other end |86 of the spring |18 engages a hole |88 in the plate |12. The natural position of the spring |18 is shown in Fig. 5 where it holds the plate |12 in the arc-interrupting position. When the switch is closed by means of a pressure on the button |28 the spring |18 is brought by the bevelled end |16 of the button into the position shown in Fig. 6 where it retracts the plate 12 and holds it in retracted position so that the screw bolt |34 can make contact with the contact piece |42. When the button |28 is relieved from pressure and returns into the position shown in full lines in Fig. 6, the plate |12 abuts against the screw bolt |34 and the spring |18 remains in the position shown in Fig. 6.

The operation of this device is as follows:

With the switch being open and the parts being in the position shown in Fig. 5, in order to close the switch, the press button |28 is raised into the position shown in dotted lines in Fig. 6. Thereby the plate |12 is retracted as described above and the screw bolt |34 brought into contact with the contact piece |42 thus establishing an electrical connection between the current lead |10 and the end |48 of the heating winding as more fully described hereabove. The pressure on the press button |28 is then relieved and the parts are in the position shown in Figs. 6 and 7.

The heating of the part |22 now begins and the bimetallic strip |36 bends downward displacing the leaf spring |40, the contact piece |42, the screw bolt |34, and the snapping spring |54. When the latter has passed its neutral position 1t snaps suddenly into its other end position thereby interrupting the contact between the screw boit |34 and the contact piece |42. When this happens the plate |12 is moved forward from the position shown in Fig. 6 into the position shown in Fig. 5.

Referring now to Figs. 8-11, an embodiment of my invention is shown which on the whole is similar to that shown in Figs. 5-'7 with the exceptions described hereinafter. First of all the plate |12 and the spring |18 are omitted. The bimetallic strip is a double one but its parts |80 and |82 bend under the influence of heat in op- 7 v posite directions as clearly shown in Fig. l1. The leaf spring i is not provided with a contact piece but it is extended so as to abut with its end ist on the structure mi in the open position of the switch shown in Fig. 10. Finally the 'connection of the screw bolt i3d with the snapwhich the bolt its is screwed.' The clamping member ist is bent into U=shaped parts 28d and 2s@ adjoining the fiat portion 202 and clasping iirmiy the snapping spring ld establishing with the latter a mechanical connection as well as an electrical contact. The ends 203 and 2id of theclamping member i9@ are bent so as to clamp between them the pressing button 2HE which is provided with a circumferential groove iid' forengagement by the ends 219sand 2id of the clamping member its. The upper end of the button 252 is bevelled as at tit so that it can be pressed into position between the ends 2t@ and 2id. Inthis embodiment the bolt 34 is set for a certain temperature by adjusting its position in the clamping member i9@ by turning the bolt with a screw driver (not shown) attacking at the slot 2id. After the setting the press button M2 is pressed into position between the ends 2053 and il@ ofthe clamping member its after which the setting of the switch can be still changed through the opening in the switch button.

The operation of this device is essentially th e same as that of the device shown in Figs. 5-7. When the switch is in closing position the parts have the position shown in Figs. 8 and 9, the connection between the current lead il@ and the end ist of the heating winding being established through the snapping spring i565, the clamping member 898, the bolt i3d, and the leaf spring Mil. When the bimetallic strip becomes hot it assumes the position best shown in Fig. ll, in which its parts i90 and is? are bent with the sides having the smaller coefiicient of thermal expansion facing each other. Therefore the bolt i3d is pressed vdownwards and in the last part of its-motion, which is accelerated by the snapping of the spring iSd, interrupts the current. The parts are now in the position shown in Figs. 10 and 11. In order to reset the switch the press button 2|2 is pressed upwards. It should be noted that in this embodiment the press button 2l2 is at a definite distance .from the bolt 34 owing to the provision of the clamping member ISB.

It will be understood that each of the elements described above, or two or more together, may also find a. useful application in other types of bimetallic switches differing from the types described above.

While I have illustrated and described the invention as embodied in bimetallic switches for water boilers I do not intend to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of my invention.

Without further analysis, theforegoing will so fully reveal the gist of my invention that others can by applying current knowledge readily adapt it for various applications without omitting feaor specific aspects ofthis invention and,therefore.

tures that, from the standpoint of prior art, fairly constitute essential characteristics o! the generic such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What I claim as new and desire to secure by Letters Patent is:-

1. A bimetallic switch comprising in combination: a bimetallic strip; a spring arranged for snapping transition from' oneend position into another end position; a connection between said bimetallic strip and said snapping spring causing said spring to snap into the other end position when said bimetallic strip is hot; e contact disposed between said bimetallic and said spring; `said contact having a circuit-breaking position and a circuit making position; a connection between a first portion of said snapping spring and said contact causing to move said contact into circuit-breaking position when said snapping spring has moved into the other end position under actionof said bimetallic strip; and manu-1 ally operated means adapted to engagesaid snapping sprlng at a second portion thereof distant from said irst portion of said snapping spring for bending the same from said other into said one position, operation of said manually operated means while said snapping spring is prevented from returning into said one position resulting. however, in bending of said snapping spring with out its return in said one position and without consequent closing of said contact.

2. A bimetallic switch comprising in combina tion: a frame; a bimetallic strip; a strip-shaped snapping spring having two ends abutting against said frame; said spring being arranged for snapping transition from one end position into another end position; a connection between said bimetallic strip and said spring causing said spring to snap into the other end position when said bimetallic strip is hot; -a contact disposed between said bimetallic strip and said spring; a connection between a first portion of said spring and said contact; and manu-ally operated means adapted to engage said snapping spring at a second portion thereof distant from said rst portion of said snapping spring for bending the same from said other into said one position, oper= ation of said manually operated means while said snapping spring is prevented from returning into said one position resulting, however, in bending of said snapping spring without its return in said one position and without consequent closing of said contact.

3. A bimetallic switch comprising in combination: a frame; a bimetallic strip having ends resting against a surface adapted to be heated; a strip shaped snapping spring having two ends abutting against said frame; said spring being arranged for snapping transition from one end position into another end position; a connection between the middle portion of said bimetallic strip and said spring causing said spring to snap into the other end position when said bimetallic strip is hot; a contact disposed between said bi metallic strip and said spring; and a connection between a rst portion of said spring and said contact; and manually operated means adapted to engage said snapping spring at a second portion thereof distant from said iirst portion of said snapping spring for bending the same from said other into said one position, operation of said manually operated means while said snapping spring is prevented from returning into said one position resulting, however, in bending of said snapping spring without its return in said one -position and without consequent closing of said contact.

4. A bimetallic switch comprising in combination: a frame; a bimetallic strip; a strip-shaped snapping spring having two ends abutting against said frame; said spring being arranged for snapping transition from one end position into another end position; a connection between said bimetallic strip and said spring causing said spring to snap into the other` end position when said bimetallic strip is hot; a contact carrier; and a member shaped as a double stirrup and connecting the middle portion of said spring with said contact-carrier; and manually operated means for closing said contact.

5. A bimetallic switch comprising in combination: a frame; a bimetallic strip; a strip-shaped snapping spring having two ends abutting -against said frame; said spring being arranged for snapping transition from one end position into another end position; a connection between said bimetallic strip and said spring causing said spring to snap into the other end position when said bimetallic strip is hot; a contact carrier; and a member shaped as a double stirrup and connecting the middle portion of said spring with said contact-carrier said double stirrup engaging said contact-carrier with play; and manually operated means for closing said contact.

6. A bimetallic switch comprising in combination: a frame; a bimetallic strip having ends resting against a surface adapted to be heated; a strip-shaped snapping spring having ends abutting against said frame; said spring being arranged for snapping transition from one end position into another; a contact carrier; a member shaped as a double stirrup and connecting the middle portion of said snapping spring to said contact-carrier; said double stirrup engaging said contact-carrier with play; aligned holes in said double stirrup, said contact carrier and said snapping spring; a screw thread in said hole in the part of said double stirrup engaging said snapping spring; and a screw bolt screwed into said threaded hole and extending loosely through said other holes; said screw bolt having an end arranged near the middle portion of said bimetallic strip when the latter is cold and being engaged by the middle portion of said bimetallic strip when the latter becomes hot.

7. A bimetallic switch comprising in combination: a frame; a bimetallic strip; a strip-shaped snapping spring having two ends abutting against said frame; said spring being arranged for snapping transition from one end position into another end position; a connection between said bimetallic strip and said spring causing said spring to snap into the other end position when said bimetallic strip is hot; a U-shaped strip having a stationary end; la contact rigidly connected t the other end of said U-shaped strip; and a member shaped as a double stirrup and connecting the middle portion of said spring with the leg of said U-shaped strip carrying said contact.

8. A bimetallic switch comprising in combination: a frame; a bimetallic strip having ends resting against a surface .adapted to be heated; a

strip-shaped snapping spring having ends abut-` 10 middle portion of said snapping spring to the leg of said U-shaped strip carrying said contact; said double stirrup engaging said leg of said U-shaped strip carrying said contact with play; aligned holes in said double stirrup. said U-shaped strip and said snapping spring; a screw thread in said hole in the part of said double stirrup engaging said snapping spring; and a screw bolt screwed into said threaded hole and extending loosely through said other holes; said screw bolt having an end arranged near the mid dle portion of said bimetallic strip when the latter is cold and being engaged by the middle portion of said bimetallic strip when the latter becomes hot.

9. A bimetallic switch comprising in combination: a bimetallic strip; a strip-shaped snapping spring having stationary ends; a bolt connected to the middle portion of said spring and having an end arranged near said bimetallic strip for axial displacement of said bolt by said bimetallic strip when said bimetallic strip becomes hot; a contact arranged for actuation by a first portion of said spring, said contact being disposed between said birnetallic strip and said spring; and manually operated means adapted to engage said snapping spring at a second portion thereof distant from said iirst portion of said snapping spring for bending the same, operation of said manually operated means while said snapping spring is prevented from returning into the position in which said bolt is not axially displaced by said bimetallic strip resulting, however, in bending of said snapping spring without a consequent closing of said contact.

. 10. A bimetallic switch comprising in combination: a bimetallic strip arranged in a bottom recess of an electrically heated vessel; a stripshaped snapping spring having stationary ends; a bolt connected to the middle portion of said spring and having an end arranged near said bimetallic strip for axial displacement of said bolt by said bimetallic strip when said bimetallic strip becomes hot; a contact arranged for actuation by a first portion of said spring, said contact being disposed between said bimetallic strip and said spring; and manually operated means adapted to engage said snapping spring at a second portion thereof distant from said first portion of said snapping spring for bending the same, operation of said manually operated means while said snapping spring is prevented from returning into the position in which said bolt is not axially displaced by said bimetallic strip resu1ting, however, 1n bending of said snapping spring without a consequent closing of said contact.

n 11. A bimetallic switch comprising in combination: a bimetallic strip; a strip-shaped snapping spring having stationary ends; a bolt connected to the middle portion of said spring and having an end arranged near said bimetallic strip for axial displacement of said bolt by said bimetallic strip when said bimetallic strip becomes hot; a. contact arranged for actuation by a rst portion of said spring; and manually operated means adapted to engage said snapping spring at a second portion thereof distant from said iirst portion of said snapping spring for bending the same, operation of said manually operated means while said snapping spring is prevented from returning intov the position in which said bolt is not axially displaced by said bimetallic strip resulting, however, in bending of said snapping ng without a consequent closing of said con- REFERENCES CITED The following references are of record in the le of this patent:

A Number 12 UNITED STATES PATENTS Name Date Hook Dec. 11, 1928 Behringer Aug. 6, 1929 Thomas Oct. 22, 1929 Simmons Jan. 7, 1930 Livingston Feb. 4, 1930 Thomas Mar. 24, 1931 Kuhn et al. Feb. 16, 1937 Clark June 18, 1940 Aitken Dec.24, 1946