US2038376A - Automatic thermostatic switch - Google Patents

Description

April 21, 1936. E. B. MOORE AUTOMATIC THERMOSTATIC SWITCH Filed Sept. 11, 1934 2 Sheets-Sheet l INVENTOR EDMUND BMooRE "ATT RNEY April 21, 1936. E7 5 MOORE 2,038,376

AUTOMATIC THERMOSTATIC SWITCH Filed Sept. 11, 1954 2 Sheets-Sheet 2 li l Ill HII INVENTCR EDMUND BMOORE.

ATTORNEY Patented Apr. 21, 1936 UNITED STATES PATENT "OFFICE 9 Claims.

This invention relates to heat controlling devices, and is particularly concernedwith improvements in high temperature thermostatic electric switches.

It lsknown that the use of bi-metallic temperature responsive strips in electric switches is old. Such devices comprise broadly a bi-metallic strip anchored at one end and capable of movement at the other end by virtue of the different coeflicients 10' of expansion of the two metals forming the strip. The free end of the strip, then, may move toward orv away from an electrical contact whereby an electric circuit is completed or broken in response to the temperature of the strip. For breaking or making circuits involving very small current intensity, such switches are satisfactory, but when the thermostat is called upon to break currents of larger intensity, the simple thermostats of the character mentioned fail, since the movement of the bi-metallic strip is so slow that arcing, pitting and sparking of the contact points occurs whenever the circuit is made or broken, resulting in rapid wear and deterioration of the contact points. Such simple thermostats have been improved by incorporating springs in conjunction with the bi-metallic strip, whereby a snap action of the strip is produced. By the snap action, the circuit may be quickly made or broken whereby the nibbling action of the strip and contact is 3 obviated and a clean break or make is established for the circuit. Such an organization permits of long life in the contact points. Thermostats of this second character are satisfactory for very moderate temperatures, but are quite useless 35 when applied in high temperature devices such as soldering irons, inciting pets, irons and the like, by reason of the fact that the temperatures developed in the heating element are of suificiently high degree to draw the temper from the springs- 40 on which the snap action of the switch depends. In addition, those thermostatic switches involving snap springs and the like are inclined to be bulky and extremely sensitive to adjustment, and do not lend themselves to rugged and compact con- 45 struction which is desirable for portable apparatus and apparatus which must stand rough usage. If the spring type of thermostatic snap switch is utihzed for relatively high temperature apparatus, it is essential to isolate the spring ele- 50 merits from the region of high temperature, which still further tends to make the apparatus more bulky than necessary.

An object of this invention is to provide a thermostatic snap switch capable of utilization in high 55 temperature portable heating apparatus.

Another object is to provide a positive thermostatic snap switch obviating the use of resilient spring elements upon which the snap action normally depends.

A further object is to provide a thermostatic 5 snap switch capable of compact and unitary construction, whereby the switch unit may be readily applied to various types of electrical heating apparatus.

A still further object is to provide a thermo- 10 static switch which will be positive in operation and will obviate frequent replacement of the switch contact elements due to arcing and pitting,

etc.

Still another object is to provide a thermostatic ]5 switch capable of making and breaking electrical circuits, either alternating or direct current, involving relatively high voltage and amperage.

Generally, my invention comprises an insulating and/or refractory support upon which a 101- 20 metallic switch strip is fixedly mounted. A contact is provided in the support with which a free end of the strip may engage to make or break an electrical circuit. A second bi-metallic element is pivotally mounted in the support and has a 25 pivotal connection with the free end of the first strip whereby, when the temperature is raised, the second strip exerts a biasing force upon the first strip to hold it either in or out of engagement with the switch contact. The axes of the first and second strips are so organized with respect to each other that the force exerted on the first strip by the second strip is at a maximum when the first strip is either fully in engagement with, or fully out of engagement with the contact. In intermediate positions, the resultant force tending to urge the first strip into or out of engagement with the contact is of lesser degree than in either of the extreme positions.

It will be apparent that a thermostat of this character may be applied to a variety of electri cal heating appliances, such as constant heat electric soldering irons, melting pots, and other industrial and household heating appliances.

For further objects and for a more complete understanding of the details of my invention, ref-= erence may be made to the following description and claims, and to the drawings, in which:

Fig. l is an elevation, partly broken away, showing an electric soldering iron embodying the ther mostat of this invention;

Fig. 2 is an enlarged fragmentary portion, partly broken away, of Fig. 1;

Fig. 3 is a section on the line 3-3 of Fig. 2;

Fig. 4 is a section on the line 4-4 of Fig. 3; 5

Fig. 5 is a section on the line 6-6 of Fig. 3:

Fig. 6 is an end view of the thermostat as shown in Fig. 3;

Fig. 7 is a diagrammatic view showing the elements of the thermostat in different positions of adjustment;

Fig. 8 is a diagrammatic view showing the capable positions of adJustment of certain elements of the thermostat;

Fig. 9 is an elevation, partly broken away, showing the thermostat arranged in a cartridge of similar size and shape to cartridge type electric heating elements;

Fig. 10 is a view similar to Fig. 9 showing the thermostat in combination with an electric heating element encased in a cartridge;

Fig. 11 is a small scale section showing the adaptability of the cartridge type thermostat and heating elements to a melting pot;

Fig. 12 is a circuit diagram as applied to a plurality of heating elements with a master thermostat; and

Fig. 13 is a section showing a method of applying a thermostat as a control unit in a metal block,

In the figures, l5 designates the thermostat as an assembly. In Figs. 1 and 2, the thermostat is shown as applied to an electric soldering iron having a handle l8 to which a metallic sleeve i1 is attached. Within the sleeve l1, the thermostat l5 is enclosed, toward the handle end thereof, and a heating element 18 occupies the opposite end of the sleeve. The soldering tip 13 is preierably screwed into the core 26 of the heating element as at 2|, and the soldering tip, heating element and thermostat are held within the sleeve l1 by means of screws or the like 22. 23 designates the electric cord for supplyingcurrent to the apparatus. In Fig. 2, the wires 24 and 26 extend through the handle from the cord 23, one of the wires such as 26, being attached directly to the resistance heating wire 26 of the heating element l8, and the other wire 24 being attached to one binding nut 21 of the thermostat ii. The other end of the heating wire 28, designated as 28, is attached to a binding screw 29 forming part of the thermostat. The heating ele-- ment is of more or less conventional construction compr ming the metallic core 28 wrapped with a layer of mica 31, over which the wire 26 is wound. A second layer of mica 32 is wrapped over the wire 26, forming a suitable insulating layer between the heating element l8 and the sleeve I1.

The thermostat l6 comprises a cylinder 33 formed of suitable insulating and/or refractory material. This cylinder is provided with a central slot 34, one end thereof being covered by a disc 36 to facilitate the assembling oi the unit. Within the slot 34, a pillar- 38 is mounted by means of the binding screw 29 and a second screw 81, these screws anchoring one end of a bi-metallic strip 38 which forms the primary element of the thermostat. The upper free end of the strip 38 is provided with a contact 33 of silver, platinum, tungsten or the like, which is adapted to engage a contact 48 of similar material, formed on the end of an adjustable screw 41 threaded into the cylinder 33. The screw 4|, in conjunction with the binding nut 21, serves as one element of the switch and as a terminal for the wire 24, as

previously mentioned. The cylinder is provided .with an auxiliary bore 42 to accommodate the other apparatus, to accommodate the wire 28. The cylinder likewise is provided with a slot 44 opposite the heads of the screws 28 and 31, through which said screws may be assembled. Likewise, the wire 28 from the screw 28 comes through this-slot 44 and extends from the cylinder through a groove 46 formed in the outer surface thereof. The upper end of the strip 38 is provided with a cross pin 46, which is engaged by the upper ends of a U-shaped bi-metallic strip 41. The lower part of this strip 41 abuts the top surface of the disc 36, and is held thereagainst by means of a screw 48 passing through the strip 41 and threaded into the disc 35. The disc 35 is crowned as at 49 to permit rocking of the strip 41 during operation. It will be noted that the strip 38 is embraced by the sides of the strip 41, and that the plane of said first strip is normal to the plane of the sides of the strip 41. Adjusting screws 58 and 51 are let through the sides of the cylinder 33, these screws being capable of contact with or adjustment with respect to the strip 38 for adjusting the thermostat to properly respond to temperature conditions of desired magnitude.

When the thermostat is cold or at room temperature, the strip 38 will be deflected so that the contacts and 48 are in engagement to complete the electrical circuit through the device. At the same time, the sides of the strip 41 will be straight, as shown in solid lines at 52 in Fig. 8, whereby no stress other than that inherent in the strip 38 causes engagement of the contacts 39 and 40. As the current is applied from an external source, the heating element 18 will rise in temperature, the heat being gradually transmitted to the thermostat, causing the strips 38 and 41 to deflect.. The strip 41 is so organized that when its temperature is raised, it will tend to assume a position such as that shown at 63 (in dotted lines) in Fig. 8. Actually, this curvature of the sides of the strip 41 takes place in only a very small degree, but the tendency for curvature is transferred to the pin 46 to exert a force tending to hold the contacts 39 and 48 in engagement. By virtue of the alignment of the screw 48, the anchorage of the strip 38, and the pin 48, the tension of the sides of the strip 41 tends to hold the strip 38 to the left of the central axis 54 shown in Fig. 7. Upon a further increase in temperature of the thermostat, the strip 38 will build up a force tending to separate the contacts 33 and 48, this force gradually becoming suilicient to overcome that force imposed by the strip 41 tending to hold said contacts in engagement. 'I'hereupon, the strip 38 will move to the right and upon initiation of such movement, the substantially horizontal component of the forces imposed by the sides of thestrip 41 decreases as the strip 38 approaches a position coincidental with the axis 54. Since the initial force in the strip 38 must be sufiiicient to overcome that horizontal component imposed by the sides of the strip 41, the strip 38 will separate the contacts with a snap, passing by the axis 54, whereupon the horizontal component of the force imposed by the strips 41 will reverse and tend to hold the strip 38 in the oif position. Upon breaking of the switch, current ceases to flow to the heating element, permitting cooling thereof to a point where an opposite force builds up in the strip 38 tending to remake the circuit. The same ac-- tion then occurs as has been previously described, the force in the strip 38 gradually overcoming the horizontal component of the force exerted by the sides of the strip 41 until the strip 38 will snap to the left to remake the circuit.

By suitable adjustment of the screws 5| and 4|, the characteristics of the strip 38 may be altered to permit of changing the temperature range within which the thermostat will act.

It is apparent from the above, that the thermostat of this invention provided a device capable of operation at high temperatures without dependence upon springs or the like, to effect a snap switch action. The strip 41, broadly, acts as a spring to eifect the snap action, but its characteristics are independent or the material limitations of springs, since its action-is wholly dependent upon the action of a bi-metallic strip, and is not dependent upon the elasticity of the material comprising the strip. The strips 38 and 41 will operate properly over wide temperature ranges, and no dependence is placed upon temper or hardness of the materials thereof, such hardness and temper characteristics being very sensitive to temperatures beyond a rather limited range.

Fig. 9 shows'the thermostat l5 encased in a cartridge 60, the lead wires GI and 62 extending from one end thereof. Such a cartridge is similar in size and shape to certain forms of standard heating elements and, where a plurality of such heating elements are used, the thermostat may take the place of one and serve as a master temperature control for all. Fig. 10 shows the thermostat l5 encased with a heater G3 in a cartridge 64, so that a unitary temperature control heating element is provided.

Figs. 11 and 12 show an organization wherein a plurality of cartridge type heating elements are used in a melting pot or the like, one of the cartridges comprising a device such as that shown in Figs. 9 or 10, the circuit being organized so that the thermostat IS in one of the cartridges serves to control the current applied to all of the heaters. In Fig. 12, for instance, the thermostat |5 is connected to one leg 65 of thesupply circuit, the other wire 66 from the thermostat being connected in parallel to one terminal of each of the several heating elements 61. The other terminals of the heating elements 61 are connected in parallel and in turn are connected to the other leg 68 of the supply circuit. The thermostat I 5, shown in Fig. 12, may be embodied in a cartridge of the type shown in Figs. 9 or 10. Fig. 13 shows the applicability of the cartridge type thermostat and/or heating element to a mass 69 having a bore Ill therein, within whichbore the cartridge may be inserted.

The structure shown is only illustrative of one arrangement of elements-the principlesv involved may be utilized in other ways. For instance, the biasing force on the switch element might be imposed by other temperature responsive means, the stress therein being either tensile or compressive or both. The biasing might also be arranged to place-the switch element in tension rather than in compression. It should be particularly noted that the biasing force is not a potential force such as that imposed by a spring or resilient means, but is a force only active and responsive to temperature conditions.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications andchanges.

What is claimed is:

1. A thermostatic switch comprising a support, a bi-metallic temperature responsive strip fixed in said support, a switch element mounted in said support, said strip having its normal straight line axis spaced from said switch element and said strip being organized to deflect toward and away from said switch element in response to temperaturechanges, and a defiectable element pivoted to said support along said strip axis and pivoted to said strip, said deflectable element comprising bi-metallic means organized when heated to exert a compressive force upon said strip.

2. In a thermostatic switch of the type including a bi-metallic strip and a switch element 7 wherein the strip is adapted to engage and disengage the switch element in response to temperature changes, means to apply a force for holding said strip in engagement with said element, said means being organized to apply said force in diminishing magnitude as said strip disen a es said element in response to temperature changes, said means comprising bi-metallic temperature responsive means attached respectively to said support and to said strip, dependent for its force exerting characteristic upon stresses imposed therein by changes in temperature thereof.

3. In a thermostat having a temperature responsive bi-metallic leaf organized for movement between two extreme positions, means pivoted between said two positions adapted to apply a force tending to restrain said leaf to one or the other said position, said leaf, in response to temperature changes, being capable of overcoming said force and moving from its then current extreme position, said means comprising a bi-metallic strip dependent for its force exerting characteristic upon temperature changes therein.

4. A thermostatic switch comprising an insulating support, a bi-metallic, normally straight strip mounted thereon, a second bi-metallic strip lying principally in a plane normal to the plane of said first strip, said second strip being pivoted' to said first strip and to said support. said pivots being in the plane of said first strip, and said second strip being of such character that the force exerted thereby per unit oi! temperature change is less than the force exerted by said first strip per unit of temperature change.

5. In a thermostatic snap switch, a primary temperature responsive bi-metallic switch strip,

a contact with which said strip is adaptedto engage in response to temperature changes thereof, and a temperature responsive bi-metallic element adjacent said strip and subjected to the same temperature conditions organized to impose a force on said strip, said strip being capable, by virtue of suflicient temperature change thereof, of overcoming said force.

6. In a thermostatic snap switch, a movable primary temperature responsive element, switch means operated upon by said element for opening and closing a circuit, and a second temperature responsive element adjacent said primary element and subject to the same temperature conditions organized when heated to impose a biasing force on said first element, said biasing i'orce being capable of being overcome by said first element under certain temperature conditions.

7. A thermostaticsnap switch comprising a support, a bi-metal strip anchored thereto and carrying a contact, a contact on said support with which said strip contact at times engages, a bi-metal strip bodily oscillatable with respect to said support lying substantially parallel to said first strip, and a pivot connection between the unsupported ends of both said strips.

8. In a thermostatic snap switch, a bi-metal switch strip anchored to a support, a second bimetal biasing strip longitudinally parallel to said first strip, said biasing strip being pivoted to said support for oscillation in a plane parallel to the plane of movement of said switch strip under the influence of changes in temperature, and a aoaaeve pivotal connection between the unsupported ends 01' both oi said strips.

9. Ina thermostatic snap switch, a support having a switch element, a bi-metal strip anchored at one end to said support and having means toward its other end for engaging said switch element, and a temperature responsive element pivoted at one end to said support adjacent said strip element anchorage and pivoted at its other end to said strip other end, said element being organized to exert a compressive force on said strip proportional to the temperature oi! said switch.

EDMUND B. MOORE.

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