US2689897A - Control apparatus - Google Patents

Description

Sept. 21, 1954 P. R, LEE

FIG.|.

WITNESSES: 46 F 40 44 INVENTOR W PGUI R. Lee

mu. Nuwk TTORNEY Patented Sept. 21, 1954 UNITED STATES ATENT OFFICE CONTROL APPARATUS Application February 16, 1951, Serial No. 211,280

3 Claims.

This invention relates to electrical circuit-controlling switches in general, but more particularly to electrical switches of the unitary type having insulating spacers of a frangible nature for separating and insulating the assembled switch components.

In electrical switches of the unitary type, it has been the practice to assemble the various components in a riveted stack, spacing the current carrying arms from each other and from the other switch components by annular insulators made of various materials. Mica has been preferred, since it withstands high temperatures without deterioration and will not crack under compression. However, it has a variable thickness, is difiicult to obtain in large thicknesses, and is in general diificult to handle.

Currently, mica has been replaced by ceramic spacers which will also withstand high temperatures and may be molded in any shape and thickness desired. Since mica spacers are very thin, several mica spacers were often necessary to properly space the switch components. The use of ceramic spacers has reduced assembly and material costs of the switches, since fewer spacers may be used and their larger size facilitates handling and assembly.

However, ceramic spacers are frangible and often crack under the impact stresses incurred during the riveting of the rivet which holds the stack together. Crackin may occur during the riveting operation or may result subsequently from the induced compressive stresses. Broken fragments of the spacers become dislodged from the stack, rendering the switch unfit for use in some cases, and shifting the relative position of the switch components in other cases. When minor cracking occurs before. the thermostatic switch is calibrated, I have. found that calibration of the switch may be effectively accomplished with no fear of further shifting of the switch components. It appears that the internal strains in the spacers are relieved when the spacers crack. The switch components are shifted to new positions which are substantially permanent and not subject to further rearrangement.

However, when the spacers crack after the thermostatic switch has been calibrated, the switch, if still usable, must be recalibrated; since its former calibration has been destroyed by the shift in the relative positions of the switch components. Here again, I have found that the recalibrated switch will retain its calibration indefinitely, with no fear of subsequent Shifting to a difierent setting. Although the. recalibrated switches will operate satisfactorily, the additional time involved in recalibration increases the cost of manufacture. Also, in many cases, a thermostatic switch may go through the entire manufacturing process without cracking its spacers, only to have them crack after shipment of the appliance. This group of thermostatic switches presents additional problems, since repairs in service involve additional time, labor and expense.

To overcome the above diillculties incident to adoption of ceramic spacers, it has been proposed to reduce the riveting stresses during assembly. Obviously, even if such a procedure could eliminate fracturing of the spacers, many switches would be fabricated with loose stacks, making close calibration impossible.

It has also been proposed to make the spacers larger than necessary in order to reduce the riveting stresses in pounds, per unit area. Spacers, although substantial in size, are nevertheless fractured; and irregular pieces are dislodged when the stack is riveted to the required tightness.

I have found that by providing the spacers with grooves defining a plurality of sectors, the spacer is weakened and will easily crack in radial directions during the riveting operation. The resulting segments are firmly locked and are not. dislodged from the stack, yet the riveting stresses are relieved, making th switch assembly stable.

In view of the above, it is an object of my invention to provide an electrical insulating spacer for spacing the component parts of a unitary switch, which spacer, although of a frangible nature, will not shift the relative position of the stacked switch components after the switch is assembled.

It is another object of my invention, to provide an electrical switch of the above type, in which the strains induced in. the fran ible spacers are relieved prior to adjustment, of the switch to prevent subsequent shifting of the switch components after the adjustment is made.

A more specific object of my invention is to provide a unitary electrical switch in which the component parts are stacked in spaced relation to each other by frangible, insulating spacers, which spacers, although broken during assembly, are prevented from having their iragments dislodged from the stack. These and other objects are effected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. l is a side elevation of a thermostatic switch incorporating my invention;

Fig. 2 is a section, on a larger scale, taken on line II-II of Fig. 1;

Fig. 3 is a section, on the same scale as Fig. 2, taken on line III-III of Fig. 1 showing the manner of mounting the thermostat; and

Fig. 4 is a perspective view of my improved spacer on a greatly enlarged scale, a portion having been removed for clarity.

Referring to the drawing in detail, and especially Figs. 1 and 3, there is shown a unitary thermostatic switch having an adjustable contact 10 and a mating movable contact I2 adapted to complete an electrical circuit through the heating element of an electrical appliance or the like. Contact I is mounted on one end of a flexible spring arm l4 and contact I2 is mounted on a similarly flexible spring arm [6 in a position to mate with contact 10. Each of the spring arms is anchored in a stack l8 at one end and is biased toward the other at its free end, causing the contacts II] and I2 to normally engage each other.

A creep-acting bimetal bar 26, having one end anchored in the stack I8, is disposed below the arm l4 and is fitted with an insulating pin 22 at its movable end. The high expansion component of the bimetal is on the bottom. Thus when the bimetal is heated, it will warp upwardly, moving the pin 22 into engagement with the movable end of the arm 16 in a manner to move contact [2 out of engagement with contact to interrupt the electrical circuit.

The temperature at which the contacts are separated is determined by the position of adjustable contact It]. An adjusting screw 24, having an insulating terminal portion 26 passing through an opening provided in the arm 46 and abutting the contact arm 14, serves to adjust the position of the contact In. The adjusting screw is threadedly engaged in a nut 28, which in turn is carried by a bracket 30 anchored in the stack I6. To lower the opening temperature of the contacts, the screw is screwed downwardly, thereby lowering the position of the contact l0. Conversely, the opening temperature may be raised by screwing the adjusting screw upwardly to raise the position of the contact l0.

As best shown in Fig. 3, the component parts of the unitary thermostatic switch, including the contact arms l4 and IS, the bimetal bar and the adjusting screw bracket 30, are firmly held together in the stack I8 by a tubular rivet 34 which passes through openings provided adjacent one end of each of the above components. Each of the contact arms l4 and I6 is insulated from the rivet 34 and other metal parts by an insulating spacer 36 made of a refractory material. One of the spacers 36 is inserted in the stack between the bracket and the contact arm I6, while the second spacer 36 is inserted in the stack between the contact arm 14 and the bimetal bar 20.

Since the spacers, as illustrated, are identical, only one will be described. As best shown in Fig. 4, the spacer 36 is annular in shape and is provided with a cylindrical central bore 38 adapted to receive the rivet 34. A annular depending flange 40 is provided adjacent the bore 38. The upper surface 42 and the lower surface 44 of the spacer are preferably flat and parallel to each other. In the upper surface of the spacer, a plurality of radially disposed grooves 46 are provided which define a plurality of sectors 48. A second set of grooves 49 is also provided in the cylindrical wall'of the bore 36. The grooves 49 bar.

4 are substantially normal to the upper surface 42 and lie in radial planes passing through the radial grooves 46, thereby further defining the sectors 48. The thickness of the spacer is materially reduced by the grooves 46 and 49, and the spacer is thus weakened considerably at the grooves.

A fiat steel washer 50 is disposed between the bimetal bar 20 and the lower spacer 36 to accurately control the free length of the bimetal A similar flat steel Washer 5| may be inserted between the adjusting screw bracket 30 and the upper spacer 36 to distribute the pressure exerted against the upper spacer during the riveting operation on the rivet 34. The use of the washers 50 and 5| is advantageous since, due to inherent molding and curing variations, the dimensions and flatness of the spacers 36 are variable.

In assembling the component parts of the thermostat on the rivet 34 to form the stack 16, the parts are mounted in the following order: bimetal bar 20, washer 50, an insulating spacer 36 (in inverted position), contact arm l4, a metallic terminal lug 52, a mica washer 54, a second metallic terminal lug 52, contact arm l6, a second insulating spacer 36 (in upright position), washer 5| and adjusting screw bracket 30. The contact arm I4 is provided with an aperture 56 suiiiciently large to receive the flange 40 of the spacer and, in assembly, care is taken to insure that the arm I4 is properly seated on the face 44 of the spacer. With this arrangement, the contact arm I4 is fixed in the stack in spaced relation to the rivet 34 and danger of grounding is eliminated. The terminal lug 52 is provided with an opening 58 of larger diameter than the flange 40 and is spaced from the rivet in similar fashion. Contact arm I6 is similarly arranged together with its terminal lug 52.

After the above stack is assembled, the rivet 34 is spun over, i. e., flared outwardly as shown at 53 to compress the stack firmly. The spinning operation is continued until the compressive force on the stack becomes great enough to crack the frangible refractory spacers 36. At the instant that cracking occurs, the spinning operation may be terminated, since the sudden yielding of the spacers produces the desired strain relief. Some cracking will usually occur substantially along the grooves 46 and 43, since the spacer is weakened there. However, the cracking does not in all cases occur within the grooves but may originate in regions outside a groove and deviate therefrom to an adjacent groove. Also in some instances, cracks may occur in regions entirely outside of the grooves. In all cases, however, it has been found that the majority of cracks will occur in a generally radial direction and that cracking in a chordal direction is practically eliminated. The segments thus broken have irregular radially disposed edges, whereby they are securely held in the stack and are not dislodged therefrom.

As illustrated, the spacers 36 are cracked along two sets of the grooves 46 and 49 and in a plurality of regions intermediate the grooves 46, thereby separating the spacer into a plurality of substantially radial segments. The flange 40, although broken and separated, is securely locked in the apertures 56 and 58 of the contact arm and the terminal lug 52, respectively. The separated segments are therefore positively and permanently locked in the stack l8 and cannot be dislodged therefrom.

The thermostatic switch may now be calibrated in accordance with well-known practice and affixed in an electrical appliance or other device. As illustrated in Fig. 3 the thermostat may be mounted on the surface of a member 55 (shown in fragmentary section) and held in firm contact therewith by a mounting screw 51 passing through the tubular rivet 34. The member may be the soleplate of a sadiron or the grid of a waffle iron or the like, the temperature of which is to be controlled. Since the component switch parts are securely held in a permanent position by the rivet 34, the likelihood of a subsequent shift in their relative position, by the compressive force of the mounting screw 51, is eliminated.

Scrap losses due to dislodging of broken spacer fragments is eliminated, since the breaking occurs either along controlled lines where the spacer has been weakened by a reduction in cross-section by the grooves or in a generally radial direction within the sectors 48. In the drawing, the grooves have been shown as disposed in the upper surface 42 of the spacer and in the bore 38. However, in accordance with the teachings of my invention, the grooves may be placed on other surfaces of the spacer. The grooves may be continuous or discontinuous as desired and the depth of groove may be varied to suit the particular spacer design. The number of sectors may be varied also, without departing from the spirit of the invention.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

What I claim is:

1. A unitary thermostat comprising a currentcarrying contact arm, said arm having an opening in one end, a frangible spacer disposed adjacent said arm and having a central bore in registry with said opening, a bimetallic member for actuating said contact arm, said bimetallic member having an opening at one end, said spacer having an annular flange surrounding said bore and extending into the opening in said contact arm, a clamping metal member passing through the opening in said arm, the bore in said spacer and the opening in said bimetallic member, thereby forming a stack, said stack being under a compressive stress imposed by said clamping member, said spacer having a plurality of grooves at least partially defining a plurality of segments, said spacer being broken into a plurality of portions, each of said portions including a portion of said flange and being interlocked in said stack by said contact arm.

2. A unitary electrical switch comprising a plurality of current-carrying contact arms, each of said arms having an opening in one end, a substantially annular insulating spacer disposed adjacent at least one of said arms in registry with said opening, a clamping member passing through said arms and said spacer and forming a stack, said stack being under a compressive stress induced by said clamping member, each said opening being of larger dimension than said clamping member, said spacer having an annular flange extending into the opening of its adjacent contact arm and insulating said arm from said clamping member, said spacer having a plurality of grooves at least partially defining a plurality of sectors, said spacer being broken into a plurality of segments, each of said segments including a portion of said flange and being interlocked in said stack thereby.

3. A unitary thermostat comprising a currentcarrying contact arm, said arm having an opening in one end, a frangible spacer disposed adjacent said arm and having a central bore in registry with said opening, a bimetallic member for actuating said contact arm, said bimetallic member having an opening at one end, a clamping metal member passing through the opening in said arm, the bore in said spacer and the opening in said bimetallic member and forming a stack; said stack being under a compressive stress imposed by said clamping member, said spacer having an annular fiange extending into the opening of the adjacent contact arm and insulating said arm from said clamping member, said spacer having a surface disposed normal to its axis and having a plurality of grooves in said surface, said grooves extending outwardly from said bore and defining, at least in part, a plurality of sectors, said spacer being broken into a plurality of segments, at least one of the breaks being along one of said grooves, each of said segments including a portion of said flange and being interlocked in said stack thereby.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 917,031 Eveleth Apr. 6, 1909 1,983,347 Daley Dec. 4, 1934 2,008,163 Walder July 16, 1935 2,188,596 Hobert Jan. 30, 1940 2,317,033 Dafforn Apr. 20, 1943 2,566,335 Joerren Sept. 4, 1951 2,613,461 Welland Oct. 14, 1952

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