US2476121A - Current transformer - Google Patents

Description

July 12, 1949. J. P. SMITH, JR

CURRENT TRANSFORMER 3 Sheets-Sheet 1 Filed Sept. 11, 1946 FIG.

gwue/wbo b JOHN RSMITH J'R.

July 12, 1949. J. P. SMITH, JR 2,476,121

RRRRRRRRRRRRRRRR ER Filed Sept. 11, 1946 5 Sheets-Sheet 2 July 12, 1949.

Filed Sept. 11, 1946 J. P. SMITH, JR

CURRENT TRANSFORMER 3 Sheets-Sheet 3 Patented July 12, 1949 UNITED STATES PATENT OFFICE CURRENT TRANSFORMER John P. Smith, In, Verona, N. J., assignor to Daven Company, Newark, N. J., a corporation of New Jersey Application September 11, 1946, Serial No. 696,136

19 Claims. (01. 175-358) This invention relates to transformers and more particularly to a transformer which may be coupled to an input electrical circuit without cutting the secondary winding or windings are protected from attack by moisture or foreign matter in m stances when the transformer is subjected to adverse weather conditions including salt water spray, or wide variations in climatic temperatures.

More particularly the present invention comprises a transformer of the type specified which includes a core made up of laminated plates. certain of which are pivotly connected to others in such manner as to provide inter-engaging leaves, which may be opened to permit insertion of an electrical input circuit wire into the magnetic circuit and then closed, the said inter-engaging leaves of the core providing a pronged or interleaved joint which not only will provide relative ease of opening and closing the Joint but will provide a wiping action in closing to remove any foreign matter from the leaves or plates and eliminate the interference with the operation of the transformer by such foreign matter.

A further object of the present invention is to provide a novel construction of secondary winding for the transformer whereby the secondary winding is hermetically sealed without providing a short circuited turn of low resistance which would interfere with the operation of the transformer as well as providing complete protection for the secondary winding from moisture, foreign matter. effects of wide climate temperature changes etc.

Another object of the present invention is to provide a novel manner of supporting the transformer coil, so that when the transformer is used in highly amplified audio circuits short circuits between the coil and its enclosing housing are prevented, and further to provide a moisture proof seal for the housing when it is closed and in operation.

With these and other objects inview as may appear from the accompanying specification, the invention consists of various features of construction, and combination of parts, which will be first described in connection with the accompanying drawings, showing a transformer of a preferred form embodying the invention, and the features forming the invention will be specifically pointed out in the claims.

In the drawings:

Figure 1 is a vertical section through the improved transformer.

Figure 2 is a vertical section through the improved transformer taken at right angles to the section shown in Figure 1.

Figure 3 is a perspective view of the openable laminated core showing the hermeticall sealed secondary coil attached thereto and showing the core open.

Figure 4 is a perspective view of the openable laminated core without the secondary coil and showing the core open.

Figure 5 is a detail side elevation of the openable laminated core showing the core open.

Figure 6 is a vertical section of the stationary part of the openable laminated core taken on line S--S of Figure 5.

Figure 7 is a view similar to Figure 5 showing the core closed.

Figures 8, 9, and 10 are views in side elevation showing a slight modification of the openable laminated core.

Figure 11 is a side elevation of a slightly different form of the openable laminated core.

. Figure 12 is an edge elevation of the core shown in Fi ure 11.

Figure 13 is a perspective view of an insulating sleeve employed in the construction of the secondary coil of the transformer.

Figure 14 is an isometric view of the secondary coil enclosed within its container.

Figure 15 is a perspective view of one half of the secondary coil enclosing container.

Figures 16 and 16A are views illustrating the manner of winding the secondary coil.

Figure 17 is a view of the completed, taped secondary coil.

. Figure 18.is a view of the completed enclosed secondary coil showing its relation to the openable laminated core.

Figure 19 is a view similar to Figure 18 but showing the manner of attaching the hermetically Sealed secondary coil to the openable core.

. Figure 20 is a perspective view of a slightly modified form of the transformer, with the cover of its container removed.

To connect the transformer to an electrical input circuit without cutting any wire in the circuit the transformer core I is made so that it may be opened as shown in Figures 4 and 5 of the drawings to permit insertion of a wire or wires 56 of the input circuit within the core. To permit this opening of the core, and to facilitate and reduce the cost of manufacture of the core I, it is built up of a plurality of plates or leaves.

The lower or stationary section 2 of the core I is built up of a plurality of U-shaped plates 3. One leg 4 of each of the U-shaped plates 3 is shorter than the other leg 5. In building up the stationary section 2 one or more of the U-shaped plates 3 are placed in flat side wise engagement with their long legs 5 and their short legs 4 engaging one another to form sets. Any desired number of these sets of the U-shaped plates are then arranged in flat sidewise engagement with the long legs of one set lying flat against the short legs of the adjacent set thus forming alternate slots or spaces 8 and projections 'I at the upper ends of the assembled stationary section 2 of the core I. The various plates 3 of each set and the setsof plates making up the core I are held in proper assembled position by bolts 8.

The upper moveable section 9 of the core I, is made up of a pluralityot L-shaped plates III, and in building up the moveable section 9 one or more of the L-shaped plates I are placed in fiat side wise engagement. The same number of L-shaped plates are arranged in each set as the number of u-shaped plates 3 in the sets of the stationary section 2, and the sets are arranged alternately as clearly shown in Figure 4 of the drawings so as to provide alternate depending prongs II and spaces I2. The L-shaped plates II) are bolted or held together by suitable bolts I3, and the movable section 8 of the core I is pivotly connected to the stationary section 2 by a suitable bolt I4 which extends through the interengaging prongs or legs III of the L-shaped plates I0 ani legs 5 of the U-shaped plates 3, so that when the core I is closed to engage a wire of an input electrical circuit, the tree prongs or legs I6 will engage in the spaces 6 formed in the upper end of the outer side of the stationary section 2 as indicated in Figure 5 of the drawmgs.

The outer corners of the prongs or legs I6 of the L-shaped plates II and the outer corners of the projecting ends of the legs 4 forming the stationary plates 2 are rounded as shown at I1 so as to facilitate the pivotal movement of the movable section 9 and the free and relatively easy movement of the prongs or legs l8 into or out of the slots or spaces 6.

The provision of the U-shaped plates 2 and the L-shaped plates III and their manner of assembly permits all of the U-shaped plates to be exactly alike as well as all of the L-shaped plates, thus simplifying and cheapening the cost or manufacture of the core structure.

In the form of the core I shown in Figures 5, 6 and '7 of the drawings the pivoting bolt I4 is shown located centrally of the side edges of the plates 2 and III while in the forms shown in Figures 8, 9 and 10 of the drawings the pivot bolt I3 is shown as off the center of the plates.

By placing the pivot bolts I3 of! center the area 4 is reduced to a minimum, and a joint which is not subject to extreme accuracy of fit or closing. The joint can be slightly open without appreciably afiecting its reluctance and small particles of foreign material in the bottoms of the spaces -6 will not adversely affect its operation as might be the case in the modified form of core shown in Figures 11 and 12 of the drawings.

Figures 11 and 12 of the drawings show, diagrammatically a simplified modified form of the openable core structure. In this form of the core the stationary section 20 of the core is composed of a plurality of U-shaped members 2| arranged in flat sidewise engagement. The legs 22 of the U-shaped members 2I' are all of equal length forming in effect two spaced flat surfaces 23 against whichthe lower surface of the movable section 24 of the core abuts. The movable section 24 of the core is made up of a plurality of rectangular strips 25 of flat metal lying in side to side engagement. The movable section 24 is pivoted at 26 to any suitable support (not shown) so that it may be swung into open position (as shown in Figure 11) to permit engagement of the core with an input wire or conductor of an electrical circuit. In this form of the core as well as in the forms shown in Figures 5, 7, 8, 9 and 10 of the drawings the input wire is received in the space between the legs of the stationary section of the core. The input wire is so shown in Figures 1 and 2 of the drawings. In the transformers of the present invention it is not satisfactory to pot the secondary coils as specified which will operate sufiiciently under adverse weather conditions a novel construction of hermetically sealed secondary coil is provided. To prevent short circuiting oi the secondary coil through its containing can, the wire of which the secondary coil 30 is formed is threaded through the longitudinal bore 3| of a glass insulating sleeve 32.

Figure 16 illustrates one manner of threading .the wire through the insulating sleeve 32, in

which operation a needle 33 (see Figure 16A) having splits 34 in its ends, and on which needle the wire 35 employed for making the coil 30 is wound, is passed a number of times through the insulating sleeve 32 until sufllcient wire to form the coil 30 is unwound from the needle 33.

- The coil of wire, forming the coil 30 is then taped in the usual manner as shown in Figure 17 of the drawings.

The glass insulating 'sleeve 32 has annular bands 36 of metal around its circumference at each end and these annular metal surfaces provide for soldered engagement of the sleeve 32 with the sealing can or housing 31 which encloses and hermetically seals the secondary coil 30.

The housing 31 is formed of two halves 33,

channeled, as shown at 39 in Figure 15, of the drawings, to receive therein the coil 30. The halves 38 of the can or housing 31 are approximately rectangular in shape with a central open portion 40 and the bottom cross portion of the halves 38 are cut away as shown at H to receive the glass insulating sleeve. After the coil 30 is placed in the halves of the housing or can 31,

with the glass insulating sleeve 62 in proper position, the halves are soldered together and to the metalized ends of the sleeve 32, thereby forming a hermetically sealed housing for the secondary coil 30. The leads 42 and 43' are brought out through the housing 31 through tight sealing insulators 44, which are preferably of glass, but may be made of any other suitable sealing insulating material.

The opening 40 in the housing 31 is sufllcient size to permit the secondary coil assembly to be threaded on the stationary section 2 of the coil I as shown in Figures 3, 1 and 2 of the drawings.

When the transformer is employed in highly amplified audio circuits it is necessary to support the secondary coil assembly in such manner that only one of the plates 2 of the laminated core I is shorted to the coil assembly. If the coil assembly is permitted to touch or short the core I at more than one of the plates 2, transients are set up in the windin of the secondary coil 30 which interfere with the proper and clear reception of the audio signal.

To provide for proper and secure support of the secondary coil assembly with contact of only one plate 2 of the core structure a spider or frame 45 is provided which is preferably made of brass, and has three lengths or sides 46, as clearly shown in Figure 19 of the drawings. The two side arms 46 have ears 41 thereon which are soldered to the housin or can 31 as shown at 48. The spider or frame 45 is securely fastened to one side of the core I with the other sides of the core spaced to provide insulating air spaces as clearly shown in Figure 19. This construction not only eliminates the setting up of transients in the transformer but gives rugged mechanical support to the secondary assembly.

Figures 1 and 2 of the drawings show the core assembly and secondary coil assembly as applied to the design of an audio pickup.

In this construction the core I and hermetically sealed secondary coil structure attached thereto are enclosed in a container 50 including a main body 5| and a cover 52 which is hinged at one side, to the body 52 as shown at 53.

The secondary coil assembly and the stationary section 2 of the core I are located in the body 5I and are surrounded by a shield 54 of high permeability which will minimize the picking up of unwanted audio signals such as power line hum, etc.

To insure proper operation of the transformer it is necessary to so mount it in the container 50 that the pressure on the laminating plates 2 of the core will not be so great as to render the opening operation of the movable section 9 of the core I too stiff or cause such pressure between the plates to produce undesirably increased eddy currents while at the same time a certain amount of pressure on the plates 2 must be exerted so as to prevent weaving or slipping of the plates 2 and I0 over each other thus producing unwanted and undesirable noises in the pickup. A too loose mounting also produces mechanical difliculties such as imperfect matching of the prongs I6 with the corresponding spaces 6 thereby preventing proper closing of the core I.

To secure the proper pressure on the plates 2 and I0 of the core the core and coil assembly are supported on two studs 55 and 56. The studs 55 and 56 are the same as the bolts or studs 8 shown in Figure 4 of the drawings and hereinafter referred to, and consequently they extend through the core I, and their size is kept as small as practical so that the magnetic path through the core will not be unduly restricted.

Sleeves 51 are threaded upon the protruding threaded ends of the studs or bolts 55 and 56 and they receive in their threaded bores outwardly of the ends of the studs 55 and 56, the threaded shanks of screws 58. Spacer washers 59 are positioned between the shield 54 and the wall of the container 50 and are held in place by the screws 58. Looking washers 60 are mountable on the studs or bolts 55 and 56 and engage the coil I.

In assembly the transformer in the container 50 of the sleeve 51 on the right in Figure 1 is threaded on the protruding threaded end of the stud or bolt 55 and is soldered to the spider or frame 45 as shown at 6|. A locking nut 62 is then threaded on thelei't protruding end of the stud or bolt 55 against the washer 60 until the desired pressure on the plates 2 is provided. The sleeve on the right is then backed off the stud or bolt 55 until the core and coil assembly fits snugly in proper position within the shield 54. The lock washer 60, lock nut 62 and sleeve 51 at the left in Figure l are then fixed in position by soldering all three together as indicated at 64. The complete unit is then assembled using the space washers 59 and screws.

The input wire of an electrical circuit is shown at 65 and it is located within the opening within the core I when the movable section 6 is in closed position. The input line wire 65 is held out of contact with the core I by insulating sleeve 66, carried by suitable supports 61.

A resilient skirt 68, made preferably of synthetic rubber or similar material is carried by the hinged cover 52 and is pinched along the upper edge of the body 5| of the container 50 just above the hinge 53, as clearly shown in Figure 2 of the drawings, thus providing substantially water tight joint at this point. The skirt or seal 68 also extends through the openings 69 in the cover 52 and engages about the wire 65 adjacent the points where it extends through the openings 69. The skirt 68 further extends downwardly over the connecting joint between the free edge of the cover 52 and the body 5| as shown at 16. i

The free edge of the cover 52 has an apron 1I formed thereon which overlaps the corresponding upper edge of the body 5| and this apron "II is perforated to receive a locking button 12. The locking button 12 is carried by a sprin tongue 13 which in turn is carried by the body 5 I. When the cover 52 is in closed position the looking button 12 will snap into locking position and hold the cover closed. To release the locking button 12, an operating button 14 is attached to the spring 13 for moving the spring 13 to move the button 12 out of locking position with respect to the cover 52.

When the cover 52 is closed the interior of the container and the transformer parts therein will be effectively protected from weather conditions.

The lead wires 42 and 43 are connected to suitable ports 16 carried by the container 50.

The construction shown in perspective in Figure 20 of the drawings differs only in minor features from the structure shown in the other figures of the drawings, such diflerences consisting mainly in the provision of insulated holdons for the live wire, the greater cutting away or rounding of the comers of the protruding ends of the U-shaped plates and the L-shaped plates as shown at 8| and the changed latch construcgamma 7 tionemployedlorholdingthecoverottbecontainerin closed position.

As shown in Figure 20 the spring tongue or strip llispositionedexterlorlyof thecontaincr SI and has a semi-pyramidal latch block ll carried thereby. This view also clearly shows the supports 85 for the insulating sleeves G6 which correspond tofliesleevesii,andsti'ipsofinsulation It which prevent contact of a live wire with the supports 05 and container II.

It'will be understood that the invention is not tobelimitedtothespeciflcconstructionorarrangement oi partsshowmhutthattheymaybe widely modified within the invention defined by the claims.

What is claimedis:

1. A split core current transformer comprising, a core including a stationary section and a movable section cooperating to provide a conductor receiving passage through an annular magnetic circuit when closed. said movable section movable to permit insertion oi. a conductor through said passage. a secondary coil assembly including an insulating sleeve,acoilofwirepasedthrough saidsleeveinsuchamannerastoformacontinuous open center annular coil with said sleeve enclosing one portion of the coil, a substantially horseshoe shaped housing enclos'ng all of said coil except that portion contained within said insulating sleeve, said insulatin sleeve being located betweenthelegsofthehousingandbonded to the housing to form a hermetically sealed housingforthewirecoiLtheportionofsaidcoiland housing opponte to said insulating sleeve extendingthroughsaidpasageandmeansforrigidly;

connectin said housing to said core.

2. A split core current transformer as claimed inclaim lincluding acontainerforthecoreand secondaryeoiLandinsulatingmeanscarriedby the container to prevent a conductor which may extend through said passage from contacting said core.

3. A split core current transformer as claimed in claim 1 wherein said core is made up of a plurality of laminated plates, a container for enclosing said core and secondary coil, means for connecting the stationary section of said core to said container, said means including means to regulate the pressure of the plates of said stationary section one the other.

4. A split core current transformer comprising, a core having two separable sections cooperating to provide a conductor receivin passage through an annular magnetic circuit when con:

nected together, a secondary coil asemhly comprisinganinsulating sleeve,acoilofwirepassing through said insulating sleeve, a housing enclosingall of said coil except that portion extending through said insulating sleeve, said housing having ends abutting and bonded to the ends of said insulating sleeve to form a. hermetically sealed enclosure for said coil, the portionof saidcoil andhousing oppositetosaidinsulating sleeve extending through said passage, and means for rigidly connecting said housin to said core.

5. A split core current transformer as claimed in claim 1 including a container enclosing said core and coil, and insulating means carried by said container to prevent a conductor which may extend through said passage from contacting said core.

6. A split core current transformer as claimed in claim 1 wherein said connecting means is constructed and arranged to provide contact of the coilhousingwithsaideoreatonlyonesideotthe core and to provide insulating air spaces between thecoreandhousingatallotherapproxilnate parts thereof.

'1. Aspiit core current transformer as claimed inclaimlwherelnsaidcoreiscomposedoia plurality of laminated plates, a container enclosing said core and coil, means for connecting one section of said core to said container, said core and container connecting means being adjustable and constructed and arranged to regulate the pressure of the plates of the core section one against the other.

8. In a transformer for coupling to an input electrical circuit without necessitating the cutting of a wire, a core including a stationary section and a movable section cooperating to provide a conductor receiver passage through an annular magnetic circuit when closed, said movable section movable to permit insertion of a live conductorthroughthepasageacoil assembly including an insulating sleeve, a coil of wire passed through said sleeve, a housing enclosing said coil and connected to said sleeve to hermetically seal said secondary coil within the housing, a portion of said housing and coil extending through said conductor receiving said core made up of a plurality of plates in flat sidewise engagement, means for rigidly attaching said secondary coil housing to said core in such manner as to provide contact between the housing and only one plate of said core and provide insulation air spaces between all other parts of the core and housing, a container for enclosing said core and secondary coil, means for connecting said core and coil to said container, said connecting means extending through and connecting the plates of said core, and means cooperating with said connecting means to regulate the prasure of the plates of the core one against the other.

9. In a transformer for coupling to an input electrical circuit without necessitating the cutting of a wire, a core including a stationary section and a movable section cooperating to provide a conductor receiver passage throug an annular magnetic circuit when closed, said movable section movable to permit insertion of a live conductor through the passage, a secondary coil including an insulating sleeve, a coil of wire pased through said sleeve, a housing enclosing said coil and connected to said sleeve to hermetically seal said secondary coil within the hous'ng, a portion of said housing and coil extending through said conductor receiving passage, said core made up of a plurality of plates in flat sidewise engagement, means for rigidly attaching saidscoilhousingtosaidcoreinsuch manner as to provide contact betwmn the housing and only one plate of said core and provide insulation air spaces between all other parts of the core and housing, a container for enclosing said core and secondary means for tingsaidcoreandeolltosaid container,saidccnnecting means extending through and connecting the plates of said core, means cooperating with said connecting means to regulate the pressure of the plates of the core one against the other, and insulating means carried by said container for preventing contact of a live wire with said core.

10. In a transformer for coupling to an input electrical circuit without necessitating the cutting of a wire, a core including a stationary sectionandamovablesectioncooperatingtoprovide a conductor receiving passage through an annular magnetic circuit when closed, said movable section movable to permit insertion of a live conductor through the passage, a secondary coil including an insulating sleeve, a coil of wire passed through said sleeve, a housing enclosing all of said coil except the portion enclosed in said sleeve, said insulating sleeve connected to said housing in such manner as to form a break in the housing, said housing and sleeve constructed and arranged to hermetically seal said secondary coil within the housing and the insulating sleeve, said core made up of a plurality of plates in flat sidewise engagement, means for rigidly attaching said secondary coil housing to said core in such manner as to provide contact between the housing and only one plate of said core and provide insulation air spaces between all other parts of the core and housing, a container for enclosing said core and secondary coil, means for connecting said core and coil to said container, said connecting means extending through and connecting the plates of said core, means cooperating with said connecting means to regulate the pressure of the plates of the core one against the other, a cover for said container, a resilient moisture proof skirt carried by said cover to protect the interior of the container when the cover is closed, said skirt extending over the joint between said container and said cover and provided with openings for receiving therethrough an input wire.

11. In a transformer for coupling to an input electrical circuit without necessitating the cutting of a wire, a core including a stationary section and a movable section cooperating to provide a conductor receiver passage through an annular magnetic circuit when closed, said movable section movable to permit insertion of a live conductor through the passage, a secondary coil assembly including an insulating sleeve, a coil of wire passed through said sleeve, a housing enclosing said coil and connected to said sleeve to hermetically seal said secondary coil within the housing, a portion of said housing and coil extending through said conductor receiving passage, said housing rigidly attached to said core at only one point to fix the position of said secondary coil to said core, said housing being constructed of two halves channeled to receive the wire coil and provided with curved portions on each half to receive the ends of said insulating sleeve, said housing halves attached to each other and to said sleeve at its ends to form a hermetthrough an annular magnetic circuit when connected together, a secondary coil assembly comprising an insulating sleeve, a coil of wire passing through said insulating sleeve, a housing enclosing all of said coil except that portion extending through said insulating sleeve, said housinghaving ends abutting and bonded to the ends of said insulating sleeve to form a hermetically sealed enclosure for said coil, the portion of said coil and housing opposite to said insulating sleeve extending through said passage, means for rigidly connecting said housing to said core, and tight sealing insulators carried by said housing at opposite ends of said insulating sleeve, the lead wires of said secondary coil extending through said sealing insulators.

14. A secondary coil assembly for current transformers having an opening therethrough for cooperative engagement with the core portion of said transformers comprising, an insulating sleeve, a coil of wire passing through said sleeve in such manner as to form a continuous open center annular coil with said sleeve enclosing one portion of the coil, a substantially horseshoe shaped housing enclosing all of said coil except that portion contained within said insulating sleeve, said housin and said insulating sleeve ically sealed housing for containing said secondall of said coil except that portion contained within said insulating sleeve, said insulating sleeve being located between the legs of the housing and bonded to the housing to form a hermetically sealed housing for the wire coil, the portion of said coil and housing opposite to said insulating sleeve extending through said passage, and means for rigidly connecting said housing to bonded together to form a hermetically sealed housing for said wire coil. Y

15. A secondary coil assembly for current transformers having an opening therethrough for cooperative engagement with the core portion of said transformers comprising, an insulating sleeve, a coil of wire passing through said sleeve in such manner as to form a continuous open center annular coil with said sleeve enclosing one portion of the coil, a substantially horseshoe shaped housing enclosing all of said coil except that portion contained within said insulatin sleeve, said housing being constructed in two halves and provided with curved portions in each half to receive the ends of said insulating sleeve, said housing halves attached to each other and to said sleeves at its ends to form a hermetically sealed housing for containing said secondary coil.

16. A secondary coil assembly for current transformers having an opening therethrough for cooperative engagement with the core portion of said transformers comprising, an insulating sleeve, a coil of wire passing through said sleeve in such manner as to form a continuous open center annular coil with said sleeve enclosing one portion of the coil, a substantially horseshoe shaped housing enclosing all of said coil except that portion contained within said insulating sleeve, said horseshoe-shaped housing having its ends engaging and bonded to the ends of said insulating sleeve to form a hermetically sealed enclosure for said coil and tight sealing insulators carried by said housing at opposite ends of said insulating sleeve, the lead wires of said secondary coil extending through said sealin insulators.

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17. A split core current transformer as claimed in claim 13 including a container enclosing said core and coil, and insulating means carried by said container to prevent a. conductor which may extend through said passage from contacting said core.

18. A split core current transformer as claimed in claim 13 wherein said housing and core connecting means are constructed and arranged to provide contact of said housing with said coreat only one side of the core and to provide insulating air spaces between the core and housing at all other approximate parts thereof.

19. A split core current transformer as claimed in claim 13 wherein said core is composed of a plurality of laminated plates, 8 container enclosing said core and coil, means for connecting one section of said core to said container, said core and container connecting means being adjustable and constructed and arranged to regulate the pressure of the plates of the core section one against the other.

. 7 JOHN P. SMITH, J1.

REFERENCES CITED.

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

UNITED STATES PA'I'ENTS Number Name I Date 826,283 Schmidt July 17, 1906 854,309 Reed May 21, 1907 1,555,066 Lines Sept. 29, 1925 1,765,913 Fischer June 24, 1930 1,935,426 Acly Nov. 14, 1933 2,058,362 Smalley Oct. 20, 1936 2,175,934. Wentz Oct. 10, 1939 2,251,373 Olsson Aug. 5, 1941 2,273,534 Mitchell Feb. 17, 1942 2,350,029 Glass, Jr. May 30, 1944 3,380,300 Gaston July 10, 1945 2,403,340 Camilli 'July 2, 1946 FOREIGN PATENTS Number Country Date 344,575 Great Britain Mar. 12, 1931

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