US2480166A - Resistor for thermogauges - Google Patents

Description

Aug. 30, 1949. K. scHwARTzwALDER ETAL 2,480,166

RESISTOR FOR THERMOGAUGES Filed Jan. 8, 1945 Inventors Patented Aug. 3o, 1949 2,480,166

UNITED STATES PATENT RESISTOR FOB, THERMOGAUGES Karl Schwartzwalder, Holly, and Alexander S.

Rulka and Robert W. Smith, Flint, Mich., assignors to General Motors Corporation, Detroit,

Mich., a corporation of Delaware y Application January 8, 1945, Serial No. 571,812

(Cl. 20L-76) Claims. l This invention relates generally to a thermogauge or temperature indicator and more particularly to the composition and manufacture of an improved resistor which varies in resistance or electric conductivity with temperature changes to operate an indicating instrument such as a differential galvanometer.

Although shown herein as employed in an indicator system for the temperature of the water fil battery 24 having a ground connection `26 to the vehicle frame.

As shown in Figure 2,the unit I6 includes an adapter shell 28 which is threaded into an opening in a Wall of the engine head il and supports an inwardly extending metal sleeve 30 having a closed inner end 32 and an open outer end with a flange 34 to engage the shell 28. The resistor 36, which may be in the form of a rod cooling system of the internal combustion enl0 having flattened sides as shown in Figure 3, is gine of an automotive vehicle, it will be apparent mounted Within the Sleeve 30 with e Spring 38 that the resistor is adapted for use in other engaging the outer end of the resistor and holdtypes of temperature indicator systems or any ing the inner end of the resistor in contact with electrical circuits wherein a predetermined varithe sleeve end 32. Both the spring 33 and Sides ation in electricl conductivity is desired in re- 0f the leSiStOr 35 are insulated IOm iShe Sleeve sponse to temperature changes, by means of insulation 40 such as sh paper. According to the present invention, the re The spring 38 is interposed between the outer sistor is in the nature of a ceramic oxide which end 0f the resistor 3s and the inner nd 0f a may be composed primarily of magnete and contact stud 42 which is threaded at its outer ferrie oxide in combination with glass phase that 20 end to recewe securing means such as the nuts acts as a med bond M for the end of the conductor I8. The stud The preferred composition With certain modi- 42 1s Insulated from trae dapter she? 28 md cations thereof and the method of manufacturle ange 34 of 'SI.eEVe y means o .was ers and 48 of Bakelite or similar insulating mateing the resistor to he described hereinafter have n 1 d l. k t 5u f bb th rk been found to produce a resistor which satises "5 ma an a' Sea mg gas e o ru er or e 1 e` such desired physical requirements as arelatively The outer Washer 48 may be pressed over a knurled portion of the stud into contact with a large and substantially uniform temperature .coshoulder 52 on the stud and the several parts emcient of resistance, electrical and chemical of the unit I6 may be held together by turning stability, 'no appreciable change 1n resistance on 30 over a flange 54 at the outer end of the Shell changes in applied voltage, arelatively low re- 2s in the manner shown in Figure 2 SP'StIVlty to url lmlze se1 fhea'tmgf a9@ nodlrec' From the foregoing description it will be seen tional eiects 1n electrical conductivity 1n the that one end 0f the resistor 36 will be grounded range of voltages and currents encountered in through the 31181130 and adapter 23 to the enpractlcegine head I4 whereas the opposite end of the In i"he dlaWmgS resistor is electrically connected through the Figure 1 is a diagrammatic view of a part of an spring 38, stud 42 and conductor I8 to the indiauiOmObile ShOWiIlg an engine temperature indicator 20. The heat from the water cooling syscator system. tem of the engine will be transmitted through the Figure 2 is an enlarged sectional view showing 4,) shell 30 to the resistor 3s which, as will be dethe mounting of the resistor of the present inscribed hereinafter, has the characteristic of vention. changing its electrical conductivity with a change Figure 3 is a perspective View of the resistor. in temperature, and the differential galvanome- Referring ISii t0 Figure 1, there has been ter 20 will be calibrated, as known in the art, shown a part of a conventional automotive vehito indicate the temperature of the water cooling cle including the usual body 4 with the windsystem in response to the amount of current flow. shield 6, the hood 8, and the instrument panel Referring now to the composition of the relil. The engine block l2 is provided with the sistor 3E and the manufacture thereof which isY head it in which is installed a thermostatic unit the subject matter of the present invention, the llt for mounting the resistor of the present invenresistor consists generally of a ceramic oxide comtion which is connected by the conductor I8 posed primarily of magnetite and ferrie oxide in' to a temperature indicator 20 such as a differcombination with glass phase that acts as a red ential galvanometer of known type Which'may bond. The composition which has been found to be connected in accordance with conventional be most suitable for the use described hereabove practice through the ignition switch 22 to the 55 consists of approximately 71.1% of magnetite (FeJOt), 8.9% of ferric oxide (FezOs), 10% borosilicate glass, and 10% magnesium borate glass.`

In the foregoing composition the borosilicate glass may be that known as Pyrex and the magnesium borate glass may be made from. 95% B20: and 5% MgO, but it should be understood that the glasses can vary considerably in composition and the invention is not limited to use of these particular compositions.

It has also been found through actual practice that the preferred composition specified above can be varied as to both glass content and magnetite and ferric oxide contents. Addition of other metallic oxides such as chrome oxide, manganese oxide, nickel oxide, etc., have been made but for the present purpose, the above composition has thus far been the most suitable. In all cases some glass as a bond has been found to be desirable.

In the manufacture of the resistor, the constituents are first milled together for about one' half hour, preferably in a porcelain lined mill with porcelain balls. Then about 8% of a binder such as Dritcx, which is a hydrogenated oil, is added and the mixture ground for about fifteen minutes.

The mixture is then removed from the mill, admixed with water, and granulated through a 20-mesh screen. It is dried in a steam drier and preferably again granulated through a further screen such as 14-mesh since when passed through the .20-mesh screen in a Wet condition the length of some parts may be greater than 20- mesh and the mixture also swells to some extent after being pressed through this first screen.

The granulated mixture is then pressed in metal dies into the desired shape and form, such as the rod of Figure 3, and placed in a furnace at a temperature of about 700 F. for thirty minutes to burn out the Dritex. It has been found desirable to put the formed rods into stainless steel trays covered with calcined alumina during this heating operation and the alumina cleaned from the rod surface after cooling. The rods are then heated in a nitrogen atmosphere to about 1600 F. in a continuous belt type furnace on a forty-three minute cycle to melt the glasses and bond the materials together.

The ends of the rods are coated with copper, as indicated at 56 in Figure 3, in any known manner such as by spraying, and the resistance checked at 200 F. The rods may then be copper sprayed or coated in some other known manner to give the resistance desired for the particular application. In the present instance the resistor is formed into a strong, hard and relatively nonporous rod about one inch long and one-quarter inch in diameter which has the following properties.

Its resistivity at 25 C. is approximately 27 ohm-cm and its temperature coeicient of resistance is 3% per degree centigrade. This low resistivity minimizes self-heating and allows the resistor to carry higher currents without excessive self-heating. The resistor is chemically stable and unaffected by contact with ethylene glycol, alcohol, oil or grease. It is slightly soluble in water and must be protected when used under conditions of vhigh humidity or where there is danger of contact with Water or steam. For applications, however, where it is not feasible or desirable to avoid contact with water it appears from preliminary experiments that the eliminaoxide, 10%

tion of the magnesium borate glass and use of only Pyrex as the glass phase in our composition may provide a resistor whose stability is not affected by humidity.

The electro-resistive effect is almost entirely absent in this resistor over the range of voltages encountered in practice, and for the range relevant to the present application, such as from 4 to 24 volts the change of resistance with voltage is negligible. The electrical conductivity also exhibits no directional effects in the range of voltages and currents encountered in practice and the resistor may be used in D. C. or A. C. circuits interchangeably without special precautions because of volume rectification effects. Since the resistor is formed in a slightly oxidizing atmosphere at a temperature much higher than that encountered over its operating range, it is electrically stable and requires no pre-aging or protection from direct contact with air or other oxidizing atmospheres.

It will be apparent that certain variations from the preferred method of manufacture described herein may be made by those skilled in the art, as well as modifications in the composition of the resistor, within the scope of the present invention as defined in the appended claims.

We claim:

1. A thermally sensitive resistor consisting of approximately 70% magnetite, 10% ferric oxide, and the remainder glass phase.

2. A thermally sensitive resistor consisting of approximately 70% magnetite, 10% ferrie oxide, and a glass bond consisting of approximately equal amounts of borosilicate glass and magnesium borate glass.

3. A thermally sensitive resistor consisting of a bonded mixture of 71.1% magnetite, 8.9% ferric borosilicate glass and 10% magnesium borate glass.

4. A thermally sensitive resistor comprising a glass bonded composition consisting of at least about 70% magnetite with a glass phase including magnesium borate glass.

. 5. A thermally sensitive resistor comprising a glass bonded composition having a substantially uniform temperature coefficient of resistance consisting of at least about 70% magnetite with a glass phase including borate glass.

KARL SCHWARTZWALDER. ALEXANDER S. RULKA. ROBERT W. SMITH.

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

UNITED STATES PATENTS Number Name Date 860,997 Steinmetz July 23, 1907 2,027,413 Andres Jan. 14, 1936 2,106,578 Schwartzwalder et al. Jan. 25, 1938 2,152,286 Schoenmaker Mar. 28, 1939 FOREIGN PATENTS Number Country Date 231,335 Switzerland June 1, 1944 OTHER REFERENCES Ser. No. 377,578, Bieeld (A. P. C.), pub. May 18, 1943.

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