US2214928A - Safety thermostatic device - Google Patents

Description

Sept. 17, 1940. A. J. KLAPPERICH 2,214,923

SAFETY THERMOSTATIC DEVICE Filed Nov. 1, 1939 2 Sheets- Sheet l Sept. 17, 1940. J, L PERICH 2,214,928

SAFETY THERMOSTATIC DEVICE Filed Nov. 1, 1959 2 Sheets-Sheet 2 fm/mfwa JZflredJ/(Zaweric/E 2 flywmww W Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE SAFETY THERMOSTATIC DEVICE Application November 1, 1939, Serial No. 302,355

Claims.

vices which are thermally responsive.

The object of the present invention is to provide a bimetallic temperature responsive device 5 involving a safety feature for insuring that the device will not fail to respond under certain critical temperature conditions.

Bimetallic thermostatic devices as' at present constructed consist generally of two dissimilar metals welded together and rolled into the form of a thin strip which may becurved, coiled or substantially straight. This bimetallic strip generally comprises on one side a cuprous metal having a relatively high coefficient of thermal l6 expansion and on the other side a ferrous metal having a relatively low coefiicient of thermal expansion. Various forms of brass or bronze known in the art constitute the cuprous metal, and various iron alloys usually form a satisfac- 0 tory low coefficient metal. In making up the low expansion metal, it is a common practice to make the same of iron-nickel alloy in which nickel constitutes 30% or more of the analysis of the ferrous alloy.

Where the thermostat is required to respond to a relatively low range of temperatures, as in the order of from room temperature to 500, the lower expansion element may be made of a nickel-iron alloy containing approximately 38.8%

nickel. Where the temperature range runs up to 700 F., the nickel content may, for example, be 42% of' the nickel-iron alloy, and wherethe temperature range runs up to 1000 F., the nickel content of the nickel-iron alloy may be 50%.

For the entire range the shift in position for each of the above will be substantially the same linear dimension. However, it will be observed that the ratio of linear response to each degree rise in temperature will be much higher for the lower percentage of nickel than for the higher. It is the desire of the designer to employ for any particular range of response a bimetallic element in which the linear response per degree rise in temperature is a maximum, and hence for a lower temperature range will select a more rapidly responding combination which means a lower percentage of nickel, as per the examples given above.

Now it has been found that for each nickeliron analysis there is a point in the temperature range where the coefficient of expansion undergoes a radical alteration, i. e., the rate of response changes.

55 I have discovered that these nickel-iron alloys The present invention relates to bimetallic dehave a sharp change in magnetic properties at the critical point at which the coefficient of thermal expansion changes. Thus, for example, a 36% nickel-iron alloy has a change in thermal responsiveness in the neighborhood of 500 F., and I find that the loss of magnetic properties, i. e., the Curie point change, occurs at the same region of temperature. For example, I find that nickel-iron alloy of 36.45 nickel has a range of Curie point change between 490 F. and 512 F. 10 A nickel-iron alloy having a nickel content of 37.22% has a range of Curie point change between 525 F. and 545 F. A nickel-iron alloy of 44% nickel has a range of Curie point change between 770 F. and 785 F. 1

This shift in responsiveness which occurs in the nickel-iron alloy at these critical temperature ranges renders the thermostat unreliable in those same ranges. I have found that the Curie point and the inflection point in the ther- 20 mal expansion curve substantially coincide, and I propose to employ the alterations in magnetic characteristics as a means to provide a safety feature against malfunctioning of the thermostat. This may be done in a variety of ways, but it consists. essentially in subjecting to a magnetic field a piece of the nickel-iron or other low expansion alloy, which alloy is subjected to the same temperature as that to which the thermostat is subjected either by being a part of the 30 thermostat, or by being a separate piece so subjected.

As the temperature to which the selected piece of magnetic nickel-iron alloy is subjected apis altered, the reaction to the magnetic field is likewise altered, and by taking advantage of this alteration of the magnetic character of the nickel-iron or the like low expansion alloy either a mechanical shift or an electrical shift or other 40 alteration of the effectiveness or cooperative character of the bimetallic thermostat is produced. Thus, for example, the contact spring of the bimetallic thermostat itself may be positioned in accordance with the magnetic or nonmagnetic 'character of the alloy under subjection to temperature changes. Alternatively, the zero point of the bimetallic stri itself may be altered as by a shift of position upon the attainment of a temperature which would render the low expansion element unsatisfactory in its cooperation in the bimetallic thermostat. Alternatively, a separate piece of the low expansion alloy may be subjected to a magnetic field dication only, as in a thermometer or indicating instrument where a pointer cooperates with the scale, the pointer may be shifted relative to the scale, or the scale shifted relative to the pointer, upon the incidence of a temperature which would render the thermostatic response unreliable through the medium of a magnetic field and a body of the low expansion alloy.

Now in order to acquaint those skilled in the art with the manner of practicing and utilizing my invention I shall describe, in conjunction with the accompanying drawings, a specific embodiment of the same.

In the drawings- Figure 1 is a diagram of a thermostat embodying my invention wherein the contact carried by the thermostatic strip is subject to change in position by virtue of loss of magnetic properties of the low expansion alloy;

Figure 2 is a modified form of the same;

Figure 3 is a diagram of a thermostatic control circuit in which the circuit is jointly controlled by the thermostat and by a'body of the low expansion metal responsive to the field of a permanent magnet;

Figure 4 is a diagrammatic illustration of a bimetallic strip in which the zero point or anchorage of the bimetallic strip is altered when the low expansion alloy is subjected to a temperature where its response is unreliable;

Figure 5 is a fragmentary illustration of a means for making the stationary contact responsive to temperature changes which would render the low expansion alloy unreliable;

Figure 6 is a diagrammatic illustration of an indicator or thermometer in which the tail end of the responsive strip is shifted to provide an indication that the thermometer has been subjected to a temperature beyond the point at which reliable response may be obtained; and

Figure 7 is a diagrammatic illustration of a thermometer which the scale is shifted relative to the pointer upon the attainment of a critical temperature as aforesaid.

Referring first to Figure 1, the bimetallic strip I is mounted upon an anchorage 2 which anchorage consists of two relatively movable parts 3 and 4 hinged at 5 so as to be adjustable in angular position with respect to each other. The angular position is controlled by the tension screw 6 and the compression screw I, so that the angular position of the part 3 with respect to the part 4 may be determined and fixed. A frame member 8 mounts in insulated relation the element I and also in insulated relation the contact support 9 carrying the adjustable contact screw III. The element I which is the bimetallic strip comprises a low expansion layer I2, bonded as by fusion to the high coefiicient of expansion metal layer I3. The layer I2 is preferably a nickel-iron alloy of from 36% nickel on up to 78% or more nickel. The nickel in fact may run up to The layer I3 is preferably a cuprous metalsuch as copper, brass, bronze or various other two or three element alloys of copper. The specific analysis of the cuprous layer I3 is not of the essence the thermostat.

of this invention. Suitable alloys for this service are well known.

A contact spring I4 is anchored at I5 to the bimetallic strip and it is held in definite relation to the bimetallic strip I by means of the permanent magnet I6 which is attracted to the nickel-iron alloy layer I2 at all temperatures below the critical.temperature of the said magnetic alloy layer I2. A yoke II which serves as a back stop may be provided for limiting the throw of the spring I4 away from the end of the strip I. I do not intend to limit the invention to nickel-iron alloys but use nickel-iron as an example of a suitable magnetic material having a controllable Curie point and being readily workable and relatively inexpensive.

The device operates as follows: Assume that a relay circuit I8, including a suitable current source I9 and a relay coil 20, controls an electric heater 22 to heat a chamber or oven to maintain a definite temperature under the control of The spring I4 and contact III will be in circuit so long as the oven is cold, and the electric resistance heater or other heater 22 is rendered active by this position of the thermostat.

As soon as the thermostat is subjected to'a temperature where the bimetallic strip I responds by producing the necessary movement to open the circuit at the contacts I I], I4, the relay circuit will in turn open the heating circuit and shutoff further application of heat. Since the thermostat may be working very close to its critical temperature, the response of the strip I may not be sufficient when the oven has been heated to the desired temperature, and in order to insure that the contacts I0, I4 will not remain closed because of the layer I2 passing through or into the critical temperature range, the magnet I6 will detect a change in the character of the nickel-iron or other magnetic layer I2 and will be released by failure of the nickel-iron or other magnetic alloy to retain its magnetic qualities, whereupon the spring II will spring upwardly against the yoke I1 and open the circuit at the contacts I4, I 0.

In Figure 3 I have indicated a magnetic relay 24 for providing the safety feature. The bimetallic thermostatic strip I carries a contact spring I4 which cooperates with the stationary contact III, or alternatively with a contact III on the back side, if desired.

The circuit of the relay 20 is controlled by the safety element 24 which consists of an armature 25 made of the same nickel-iron or other magnetic alloy as the layer I2 of the bimetallic strip I, and the layer I2 and the element 25 are subjected to the same temperature at all times. The permanent magnet 26 normally holds the armature 25 against the stationary contacts 21, 21 and the circuit remains operative. This condition prevails until a temperature is attained where the nickel-iron alloy which comprises the layer I2 and the armature 25 passes into the region of its critical change in responsiveness to expansion and magnetic properties' The armature 25 thereupon drops, opening the circuit at the contacts 21, 21 and rendering the thermostat ineffective to control the circuit further. Upon cooling down of the thermostat and the armathe thermostatic strip in a predetermined position. Upon exposure of the layer I2 to a temperature which brings it to the critical point in respect to its expansion properties and magnetic properties, the permanent magnet 29 loses its attraction upon the layer I2 and the spring 30 then swings the strip I about the pivot 28 to engage the stop 32. Thereby the strip I loses control of the circuit at the contacts I 4', I until the thermostat cools down to a point where the layer I2 is again attracted by the permanent magnet 29 and the thermostatic strip I is swung into the position shown in Figure 4.

In Figure 5, the stationary contact 32 is carried upon an armature 33 which is made of the same alloy as the low expansion layer I2 of the strip I. This armature is pivoted at 35 and is normally held under the influence of the permanent magnet 34 against the stop 35 so that the contact I4 and the stationary contact 32 may cooperate to control the heater circuit or other controlled circuit.

Upon the attainment of the critical temperature by the bimetallic strip I and the armature 33, both being subjected to the' same temperature, the magnet 34 loses its power to hold up the armature 33 and the same drops against the stop 31, whereupon the contacts I4 and 32 lose control of the heater or other controlled circuit.

As shown in Figure 2, the thermostat may close a circuit upon reaching a certain high temperature, but it may be desirable to open the circuit if the temperature exceeds the critical responsive point of the layer I2. This is done by mounting the spring l4 and magnet I6 in such relation to the magnetic layer I2 that the circuit will be opened at I0, I4 in the event that too high a temperature should be reached.

In Figure 6 I have indicated the operative element of a thermometer or temperature indicator in which a bimetallic element 38 anchored on a pivoted anchor pin 39 carries at its free end a pointer 49 cooperating with a scale 42. The part of the scale which is within the working range of the bimetallic strip 38 is graduated, and beyond the range of the accurate response of the bimetallic strip 38 the scale chart may carry blank indications as at 43, 44. blank or variously colored as desired. The anchor pin 39 carries an arm 45 normally resting against an adjustable stop 46 and it is held in this position by means of a pin 41 urged in a clockwise direction by a fork 48 carried on a strip 49 made of the same nickel-iron alloy as the layer I2 of the thermostatic bimetallic strip 38. This strip 49 is hinged at 50 and is subjected to the tension of the spring 52 which tends to swing the fork 48 to the left in Figure 6 and thereby to swing the indicator 49 over into the nonindicating part of the chart 43, 44. The permanent magnet 53 acting upon the nickeliron alloy strip 49 holds the parts in the position shown so long as the nickel-iron strip 49 is below the critical temperature at which its character as to expansion and as to magnetic properties changes. So long as the thermometer is subjected to changes within its range, it will accurately indicate on the graduated scale 42 the temperature which prevails. If, however, it is subjected to temperatures which exceed the range for which it is accurate, the needle or pointer 40 will be swung over into the non-indicating field 43, 44 by release of the armature 49 from the permanent magnet 53. A stop pin 55 They may be may limit the throw of the armature 49 to the left.

In Figure '7 I have shown the bimetallic strip 38 with a coil 55 anchored upon a stationary pin 51 and carrying an indicator 40 over a chart member 58, the lower part of which is held in registration with a window or opening 59 in the case or cover. A permanent magnet 60 cooperates with a piece of nickel-iron or other magnetic alloy 62, which alloy 62 forms an armature for the magnet 50, and is made of the same analysis as the low expansion layer I2 of the strip 38.

In the event that a temperature is attained which renders the nickel-iron alloy subject to change in its magnetic and expansion properties, the armature 62 will be dropped, and the upper part of the chart 58 which may be differently colored, or may be blank, comes opposite the window 59, indicating that the instrument is no longer responsive with sufhcient accuracy to make it dependable.

The above are but examples of the application of my new principle of utilizing the loss in magnetic properties of the low expansion alloy to take the control of the control apparatus away from the expansion characteristics of the thermostatic strip.

I do not intend to be limited to the details herein shown or described, as they are but explanatory.

I claim:

1. In combination, a thermal responsive device comprising the combination of a bimetallic element consisting of a body of metal of a relatively high coefiicient of thermal expansion and a body of magnetic metal of a relatively low coefficient of thermal expansion, and a cooperating safety device comprising a magnet having magnetic attraction for said second body of metal, said second body of metal being released by said magnet upon the attainment in said second body of metal of a temperature which would alter materially the responsiveness of said thermal responsive device to changes in temperature.

2. In combination, a bimetallic thermal responsive element including a body metal having a relatively high coefficient of thermal expansion and a cooperating body of magnetic metal having a relatively low coefficient of thermal expansion, said magnetic metal comprising a nickel-iron alloy of 30% or more nickel content, and safety means comprising a magnet cooperating with said latter body of metal for releasing said body of metal upon the subjection of said body of metal to a temperature at which its rate of expansion is materially changed, said safety means disabling said thermal responsive element upon the occurrence of said latter temperature.

3. A safety bimetallic thermostat comprising a bimetallic thermal responsive element consisting of two bodies which are of dissimilar metals, one of which metals has a relatively low thermal coeflicient of expansion and which consists of a nickel-iron alloy of 25% or more nickel and a stationary cooperating element relative to which said thermal responsive element has movement, and a permanent magnet cooperating with said one body of metal for altering the cooperative r'elations'hip between said cooperative elements upon the attainment of a temperature at which the coefficient of thermal expansion of said alloy is altered.

4. In combination a bimetallic thermal responsive element consisting of two bodies which are made of dissimilar metals, one of which metals has a relatively low thermal coefiifiicient of expansion, and which consists of a nickel-iron alloy of 25% or more of nickel, an electric circuit controlled by said element, and a permanent magnet cooperating with an armature of said alloy for altering the control of said circuit by said element when said element attains a temperature at which the coemcient of thermal expansion of said alloy is materially altered.

5. A safety thermostatic device comprising a control circuit, means to control said circuit in response to temperature changes comprising a bimetallic element consisting of one metal of a relatively high rate of expansion, and a second metal of a relatively low rate of expansion, which rate of expansion is altered at substantially a predetermined temperature, said second metal having magnetic properties which also are altered at substantially said predetermined temperature, and means for altering the control of said circuit by said element, said means comprising a permanent magnet having an armature of said second metal exposed to said temperature changes.

ALFRED J. KLAPPERICH.

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