US2720416A

US2720416A - Snap acting thermostatic elements and methods of making the same

Info

Publication number: US2720416A
Application number: US251489A
Authority: US
Inventors: James F Raleigh
Original assignee: Underwood Electric & Manufacturing Co In
Current assignee: Underwood Electric & Manufacturing Co In; Underwood Electric & Manufacturing Co Inc
Priority date: 1951-10-16
Filing date: 1951-10-16
Publication date: 1955-10-11
Anticipated expiration: 1972-10-11

Description

Oct. 11, 1955 J. F. RALEIGH 2,720,416

SNAP ACTING THERMOSTATIC ELEME AND METHODS OF MAKING THE SA Filed on. 16, 1951 2 Sheets-Sheet 1 Inna-"III...

............ IN V EN TOR.

2a izfii fgi Oct. 11, 1955 J. F. RALEIGH 2,720,416

SNAP ACTING THERMOSTATIC ELEME AND METHODS OF MAKING THE SAM Filed on. 16, 1951 2 Sheets-Sheet 2 46 4/4 tfmwj zg Q a BYffiji United States Patent SNAP ACTING THERMQSTATIC ELEMENTS AND METHODS OF MAKEIG THE SAME James F. Raleigh, River Forest, 11]., assignor to Underwood Electric & Mfg. Co., Inc., Chicago, 111., a corporation of Illinois Application October 16, 1951, Serial No. 251,489

10 Claims. (01. 297-15 My invention relates to circuit breakers and more specifically to bi-metallic elements in such circuit breakers and to methods of making such elements.

An object of my invention is to provide a bimetallic thermostatic element which is specially shaped so as to have a snap action in opening a circuit of which it forms a part.

Another object of my invention is to provide bimetallic reed circuit breakers of simple, compact, and sturdy construction which are dependable and effective in operation and capable of being manufactured with uniformity and economy.

My invention has for a further object the provision of specially shaped portions on a bi-metallic thermostatic element which enable the element to have a sudden and decisive action in opening a circuit. These portions may be limited to small regions of the element and may take the form of dimples or depressions in the element.

Still another object is to provide methods of shaping a bi-metallic thermostatic element in such a way that there is resistance to movement of the element in the direction it is urged under the influence of heat, whereby when sufficient heat is applied the movement is sudden and decisive.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings in which similar characters of reference indicate similar parts throughout the several views.

Referring to the two sheets of drawings:

Fig. 1 is a plan view of a planar bi-rnetallic blank that is to be subjected to a dimpling operation to produce a bi-metallic reed;

Fig. 2 is a sectional view taken on the line 22 of Fig. 1 in the direction of the arrows;

Fig. 3 is a longitudinal edge view of the bi-rnetallic blank;

Fig. 4 is a plan view of one face of the reed formed from the blank of Figs. 1 to 3;

Fig. 5 is a view similar to Fig. 4, of the other face of the reed;

Fig. 6 is a side edge view of the reed, but on a larger scale;

Fig. 7 is a fragmentary view partly in section and partly in elevation, illustrating the method and means by which the blank is dimpled to form the reed;

Fig. 8 is a plan view of a concavo-convex bi-metallic blank that is to be subjected to a dimpling operation to produce any of three types of a bimetallic reed which are different from the reed shown in Figs. 4, 5 and 6;

Fig. 9 is a sectional view taken on the line 9-9 of Fig. 8 in the direction of the arrows;

Fig. 10 is a sectional view taken on the line 1010 of Fig. 8 in the direction of the arrows;

Fig. 11 is a plan view of a bimetallic reed with dimples of a certain type made either from the blank of Fig. 1 or from the blank of Fig. 8;

Fig. 12 is a longitudinal edge view of the Fig. 11;

reed of 2,720,416 Patented Oct. 11, 1955 Fig. 13 is a sectional view taken on the line 1313 of Fig. 11 in the direction of the arrows;

Fig. 14 is a plan view of a bi-metallic reed with dimples of another type made either from the blank of Fig. 1 or from the blank of Fig. 8;

Fig. 15 is a sectional view taken on the line 1515 of Fig. 14 in the direction of the arrows;

Fig. 1 6 is a sectional view corresponding to Figs. 13 and 15, of a bi-metallic reed with dimples of still another kind, which reed may be produced either from the blank of Fig. 1 or from the blank of Fig. 8;

Fig. 17 is a fragmentary view partly in section and partly in elevation of an apparatus for forming dimples of the types illustrated in Figs. 15 and 16; and

Fig. 18 is a sectional view taken through a circuit breaker having a bi-metallic reed that may be of any of the types illustrated in Figs. 1 to 16 inclusive.

This application is a continuation-in-part of my copending application, Serial No. 14,467, filed March 12, 1948 and relating to Circuit Breakers, which application has now issued as Letters Patent No. 2,619,564.

The drawings illustrate exemplary embodiments of my invention which are depicted for illustrative purposes.

The reference character 20 designates a bi-metallic blank, illustrated in Figs. 1, 2 and 3, which is suitable for use in making a thermostatic reed or element of a circuit breaker. A hole 21 in the blank is provided and is to receive an attaching element to hold the thermostatic reed to be made from the blank 29. When the reed is to have its contact riveted thereon, the blank is desirably provided with a second hole 22 illustrated in dotted lines in Fig. l, which hole is to receive the contact rivet. When the contact is to be welded to the reed, as is often the case, aperture 22 is unnecessary. Aperture 22 may be formed either before or after the blank 21 is subjected to dimpling operations, but aperture 21 desirably is formed before dimpling.

The blank 20 comprises two thin metallic sheets or

layers

23 and 24 which are bonded to one another and which have respectively a relatively high coeificient of expansion and a relatively low coefiicient of expansion.

To give the reed 25 of Figs. 4, 5 and 6 snap action, I form a plurality of dimples 26 in the blank 26, which lie near the long edges of the reed at approximately equal distances from a line drawn between the centers of the attaching hole 21 and a contact rivet 27. Four dimples may be provided which lie in substantially rectangular arrangement as shown. The dimples are formed by pressure applied to the high-coefiicient side 23 of the blank so that conical protuberances extend from the low-coefiicient side 24. A result of the formation of the dimples is that the reed 25 is made concave-convex in longitudinal and transverse directions, the high-coeflicient side being concave, and the low-coeflicient side being convex. The dimples may be formed as illustrated in Fig. 7, a block 28 supporting the blank 20 and punch 29 being applied to deform a portion of the blank lying over an opening 30 in the block into a dimple 26.

It is important that the several dimples 26 be formed in the reed successively and not simultaneously. The order of dimple formation is not critical, but it is important that the reed blank be unconfined when the dimples are being formed therein. This same procedure should be followed in forming the dimples in the modified forms of reeds that are about to be described.

Figs. 8, 9 and 10 illustrate a modification of the above in which a blank 31 is employed which is concavo-convex in longitudinal and transverse directions before the dimpling operatons are performed, the high-coefficient side 23 being concave and the low-coefficient side 24 being convex. Apparatus like that shown in Fig. 7 may be used to form two dimples 32 which lie adjacent the lon gitudinal edges of a reed 33, which results from the dimpling operations, at equal distances from a line joining the centers of the contact 27 and the attaching hole, and with a line joining the dimple centers being perpendicular to the aforesaid line.

Fig. 18 illustrates the use of either the reed of Figs. 4 to 6 or the reed 33 of Figs. 11 and 12 as part of a circuit breaker 34, which otherwise comprises a mounting base of non-conducting material, a cover 36 which may be of metal, a contact screw 37 and amounting post 38. The mounting post 38 has an enlarged portion 39 which serves as a spacer for supporting the reed relative to the base, and at the end of which a portion 39a extends through the opening 21 in the reed and is riveted to secure the reed thereto. The head on the contact screw 37 comprises a contact 40 engageable with the contact 27 on the reed. The concave side of the reed is toward contact 40. With this arrangement, and when the current passing through the contact screw 37 and mounting post 38 and through the reed exceeds the predetermined value for the circuit breaker for a period of time, the heat produced by the current flow is suflicient to make the high-coefiicient layer 23 of the reed expand enough more than the low-coefficient layer 24 that the reed will snap suddenly away from the contact 40. Then, upon cooling sufiiciently, the reed may snap back to close the contacts.

Figs. 14 and 15 illustrate a modified form of reed 41 which is characterized by two dimples 42 which are only partial dimples because, in the form disclosed, they are intersected by the longitudinal edges of the reed and, as a further variation from the other forms depicted, the dimples are joined to the body of the reed through annular projections 43 which surround the dimples. The regions directly opposite the annular projections 43 on the face of the reed opposite the annular projections are shaped as partially annular depressions or channels. The high-coefficient layer 23 is on the side of the reed on which the dimples 42 and the projections 43 are located, and this side is concave. The opposite side where the low-coefficient layer 24 is located is convex. The centers of the dimples lie generally on a line perpendicular to a line between the centers of the contact 27 and the hole 21 and at about equal distances from the latter line.

The reed 41 of Figs. 14 and 15 may be produced by the apparatus of Fig. 17. This apparatus comprises a stationary anvil 44, a movable ring die 45, and a movable plunger die '46; the plunger die 46 being positioned Within the ring die and aligned with the anvil 44. The anvil 44 has a beveled edge 47 and a rounded and somewhat conical recess 48 which generally corresponds in shape and size to the adjacent end of the plunger die 46. The other end of the plunger die is secured in a head 49, which has a bore 50 into which the plunger die 46 extends with an annular space between the bore and the plunger die. This annular space receives one end of a sleeve 51 which has its other end threaded into the ring die 45. A lock nut 52 which is also threaded on the sleeve 51 lies against the ring die 45. The lock nut is engaged by a washer 53 which is in turn engaged by one end of a coil spring 54 which surrounds the sleeve 51 and has its other end in engagement with the head 49. The exterior of the sleeve 51 at the portion lying within the head 49 has a recess 55 with a flat bottom. A pin 56 which projects through the head 49 lies in the recess. ment with the ends of the recess 55, limits movement of the sleeve 51 into and out of the head 49 and thus limits relative axial movement of the ring die 45 and the plunger die 46. The pin 56, by engagement with the bottom of the recess 55, prevents relative rotative movement of the sleeve 51 and the head 49, and thus relative rotative movement of the ring die 45 and the plunger die 46. The spring 54 resists movement of the plunger die 46 out of the ring die 45. Adjustment of the lock nut 52 and the ring die 45 on the sleeve 51 will adjust the axial position of the plunger die 46 within the ring die 45.

The pin 56, by engage-.

The stationary anvil 44 lies within a support 57 which may be movable into and out of the plane of Fig. 17 to carry a blank from which the reed 41 is to be formed. The support may index the blank with rsepect to the anvil 44 so that the dimples 42 are properly located relative to the edges of the reed 41 and have the right longitudinal position or distances between the attaching hole 21 and the contact 27.

When a dimple 42 is to be formed in the blank, the blank is properly placed on the support 57 so as to extend across the anvil 44. Then the head 49 is moved to bring the ring die 45 toward the anvil 44 into engagement with the blank. The ring die presents a narrow annular edge that, in cooperation with the bevel 47 on the anvil 44, forms the annular projection 43 and its opposed channel. As the projection 43 is being formed, the plunger die 46 is moving out of the ring die 45 and into engagement with the blank and into the recess 48 in the anvil 44. Thus, the dimple 42 is formed. The blank that is processed in the fashion just described may originally be planar like the blank 20 of Figs. 1 to 3 or concave-convex like the blank 31 of Figs. 4 to 6. The high-coeflicient layer 23 will face the ring die 45 and the plunger die 46 during the dimpling process.

Fig. 16 illustrates still another modified form of reed 58 .in which dimples 59 are formed from the high-coefficient side 23 of the blank, but the dimples are sufliciently inward of the longitudinal edges of the reed so that neither the dimples nor annular projections 60 surrounding the dimples are intersected by the longitudinal edges of the reed. The result is that the projections 60 are complete and completely surround the dimples 59. Like the dimples of the preceding reeds, the centers of these dimples are between the contact and the attaching hole generally on a line perpendicular to a line between the centers of the contact and hole and at about equal distances from the latter line. The reed 58 may be formed by the apparatus of Fig. 17 by a process as described for forming the reed 41, from a fiat blank or a concavo-convex blank.

The thermostatic reed 41 or the thermostatic reed 58 may be used in a circuit breaker like the circuit breaker 34 in place of the reed 21 or the reed 33.

I have discovered that the currents at which the various thermostatic reeds of my invention will open the circuits in which they are placed depend on a number of factors. The stiffer the reed, the more current it will carry before snapping. The thicker the reed, the stiffer it becomes and the more current it carries before the reed reaches a given elevated temperature. My reeds may also be coated with a highly conductive metal, such as copper, to provide an increase in their current-carrying capacity.

This invention is primarily concerned with thermostatic reeds provided with dimples of a shape, size, depth and disposition on a reed such that their effect is to resist deformation of the reeds with heat, and to cause such reeds to snap suddenly and decisively when the heating is sufficient. By varing the size, shape, and location of the dimples I can vary the current the reeds will carry before snapping. For example, I have found it to be generally true that the greater the diameter of the dimples for a given depth the softer the reed will be, and the more readily it tends to snap. The shallower a dimple of a given diameter is made, the softer the reed becomes. The reed tends to snap more readily as the distance of the dimples from the longitudinal center line of the reed is increased. The provision of projections around the dimples, as shown in Figs. 14, 15 and 16, makes the reed snap more readily.

The positions of the dimples both laterally and longitudinally of the reed relative to the positions of the attaching opening and the contact have some eifect upon the stiffness of the reed and its snap action, so that such positions thereby affect the current limits within which the switch is effective.

It is possible to produce a thermostatic reed that will snap away from the stationary contact to open the circuit upon sufiicient heating and which will not close automatically upon cooling. Such an arrangement is desirable when the reed is to act as a fuse and the manual return of the reed to close the circuit will presumably not take place until someone has inspected the circuit to find out and remedy whatever caused the overloading resulting in snapping of the reed. The above action can be made to occur if the reed is sufficiently stitf for a snap action and yet retains an appreciable degree of softness.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. A bi-metallic reed adapted to flex with snap action in response to temperature changes within predetermined limits and comprising a bi-metallic sheet of symmetrical shape relative to a center line and having a contact mounted thereon and a mounting hole therein, said contact and mounting hole being located on the center line at opposite ends of the sheet, said bi-metallic sheet having dimples of like configuration and of circular shape in a plane parallel to the general plane of the sheet formed therein at spaced and corresponding positions on opposite sides of the center line adjacent opposite side edges of the sheet and intermediate the contact and mounting hole, and said sheet being somewhat bowed in sectional shape on a line extending laterally of the center line between the centers of the dimples.

2. A bi-met'allic reed as specified in claim 1, and wherein the dimples intersect the opposite side edges of the bimetallic sheet.

3. A bi-metallic reed as specified in claim 1, and Wherein the dimples extend into one surface of the lei-metallic sheet and the marginal portions of the sheet immediately adjacent and surrounding the dimples are oppositely de pressed so as to project an amount less than the depth of the dimples on said one side of the sheet.

4. A bi-metallic reed as specified in claim 1, and wherein the bi-metallic sheet is bowed somewhat in section along said center line, and said dimples extend inwardly on the concave face thereof.

5. A bi-metallic reed as defined in claim 1, and wherein said bi-metallic sheet has two dimples therein on each side of the center line, which dimples on each side of the center line are spaced in a direction substantially parallel to the center line.

6. The method of making a bi-metallic reed from an elongated bi-metallic blank and which comprises the steps of individually and successively punching a plurality of dimple-like indentations into one surface of the blank at positions in the mid-portion of the longer side margins of the blank and spaced at approximately equal distances from opposite sides of a longitudinal center line of the blank while the portion of the blank surrounding the area being punched is relatively free to flex normally in a direction opposed to the direction of punching.

7. The method of making a bi-metallic reed as defined in claim 6, and further characterized by the formation of a ring-like indentation adjacent and surrounding each dimple-like indentation at the same time each dimple-like indentation is punched and from the surface of the reed opposite that in which each of the dimple-like indentations are punched.

8. The method of making a bi-metallic reed as defined in claim 6, and wherein the dimple-like indentations are punched into the blank at positions such that they intersect the longitudinal side edges of the blank.

9. The method of making a bi-metallic reed from an elongated bi-metallic blank and which comprises the steps of individually and successively punching a plurality of spaced dimple-like indentations into one surface of the blank at positions in the mid-portion of and near each longitudinal edge of the blank and spaced approximately equal distances from opposite sides of a longitudinal center line of the blank while the portion of the blank surrounding the area being punched is relatively unrestrained from normal fiexure.

10. The method of imparting snap action to an elongated bi-metallic reed having a contact and a mounting aperture located on a longitudinal center line and which comprises the steps of individually and successively punching the reed at separated and opposite positions adjacent opposite side edges and in the same direction to form therein a plurality of dimple-like deformations of substantially similar shape and each having their points of deepest impression equally spaced on opposite sides of the longitudinal center line and within the longitudinal edges of the reed.

References Cited in the file of this patent UNITED STATES PATENTS 2,148,221 Schneider Feb. 21, 1939 2,289,131 Layton July 7, 1942 2,340,615 Rath Feb. 1, 1944 2,400,412 Hawn May 14, 1946 2,487,684 Smith Nov. 8, 1949