US2676195A - Protecting tube for thermocouples - Google Patents

Description

April 20, 1954 J. v: HART PROTECTING TUBE FOR THERMOCOUPLES Filed Oct. 18, 1950 INVENTOR JOH N V. HART ATTORNEY.

Patented Apr. 20, 1954 UNITED ATENT OFF ICE PROTECTING TUBE FOR THERMOCOUPLES poration of Delaware Application October 18, 1950, Serial No. 190,895

6 Claims. 21

This invention relates to wells for holding heat sensitive elements such as-thermometers or thermocouples in substances of various kinds undergoing treatment involving temperature change. This invention relates more specifically to an improved corrosion-resisting well which is alsoresistant to the adherence of metallic oxides or zcokey deposits. This invention is useful particularly with molten aluminum, which rapidly destroys the well or protecting tube which sur rounds the temperature-measuring element, or with substances. containing other corrosive components or coke-forming constituents, for example, hydrocarbon oils undergoing cracking.

In measuring the temperature of molten aluminum and in the cracking of hydrocarbon oils where corrosive compounds are present, which, in the most prevalent forms, are particularly destructive of pure iron or steel of which the bulk of the apparatus in this sort of equipment is composed, it is necessary to protect the walls of the vessels and pipes from these compounds.

In addition to the comparatively short life, due to corrosion, of the hitherto known thermometer wells in the presence of molten aluminum or corrosive compounds, another objection presents itself in that metallic oxides or cokey or carbonaceous constituents tend to adhere to ordinary thermometer wells made of iron or steel. A coating or mass of the carbon-like material is thus formed upon the thermometer well which mass, since it is a poor conductor of heat, renders the thermometer much less sensitive to temperature changes of the substance under observation.

The particular object of this invention is therefore to provide a suitably constructed well of durable material which will not only be resistant to corrosion but will also repulse the adherence of oxides or metal or cokey or carbon- 1 like constituents of hydrocarbons.

More specifically, it is an object of this invention to provide a protecting well or tube composed of welded steel pipe closed at one end with a plug punched out of steel and covered with a layer of gray iron cast over the outer surface of the steel pipe and steel plug and adhering thereto and of a uniform thickness.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying 2 drawings and descriptivematter in which is illus trated and described a preferred embodiment of the invention.

In the drawings:

Fig. l is a side elevation with parts broken away in vertical, longitudinal cross section.

Fig. 2 is a vertical, transverse cross section on line 2-2 of Fig. l as viewed in the direction of the arrows.

A heat sensitive element generally indicated at I is formed of a helical coil of wires 2 and 3 of different metals or different metallic compositions joined at one'end to form a hot junc tion 4. These wires pass through ceramic insulators 5 to a terminal head, generally indicated at 6, whence they are connected to lead wires which are led off through a pipe I to a suitable indicating instrument.

In order to protect the heat sensitive element I from mechanical damage or the ruinous effects of heat or corrosion, the temperature sensitive element l is surrounded by a protecting tube, sheath, or well, generally indicated at 8. Well 8 is composed of a welded steel pipe 9 which is closed at its outer or immersed end (surrounding temperature sensitive element I) by a plug [0 punched from a sheet of steel. Steel pipe 9 and steel plug ID are covered on their outer surface with a gray iron casting !2 of uniform thickness.

Attempts were made to form the well of cast iron by casting with a sand core in a sand bed. It was found that sand cores of this type tended to warp and shift, which produced finished castings whose wall thickness was not uniform, thereby reducing the life expectancy of the finished well. Where the iron layer I2 is cast directly on the surface of the wall tube 9 and the steel plug in the result is an integral tube whose walls are of uniform thickness. The outer or open end of the tube is screw threaded at i3 to interfit with the terminal head ii.

While, in accordance with the provisions of the statutes, I have illustrated and described the best form of the invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I 3 claim as new and desire to secure by Letters Patent is as follows:

1. A protective casing for a temperature sensitive element including, a hollow tube, a plug closing one end of said tube, and a protective coating cast on the outer surface of said tube and said plug to resist oxidation or corrosion or adhesion of deposits from the material Whose temperature is being measured and in which the closed end of the casing is immersed.

2. A protective casing for a temperature sensi-- tive element including, a welded steel pipe, a plug punched from steel closing at one end of said pipe, and a layer of gray iron cast on and adheringto the outer surface of said pipe and said plug so as to form therewith an integral casing for insertion in the material whose temperature is to be measured.

3. A well for a heat sensitive element including, a tubular member having a closed end adapted to protrude into the material whose temperature is being measured and composed of an inner layer of steel and an outer layer of cast iron adherent thereto by reason of the shrinkage of the outer layer of cast iron upon cooling in contact with the inner layer from a molten state.

1. A protective well for a heat sensitive element including, a metal tube, a closure for one end of said metal tube, and a layer of cast gray iron adhering to the outer surface of said tube and said member, the bond between said layer of cast grey iron and the outer surface of said tube and said member being a shrink fit resulting from depositing molten grey iron directly upon the outer surface of said tube and said member and allowing said layer of grey iron to harden by cooling in direct contact with the outer surface of said tube and said member.

5. A protective casing for heat sensltiveelemerits including, a metal pipe, a metal plug closing one end of said pipe, and a layer of cast gray iron of uniform thickness cast from a molten state directly on and adhering to the outer surface of said pipe and said plug.

6. A protecting tube adapted to extend through an opening to be exposed to the heat ofa space whose temperature is to be measured, said protecting tube being adapted to enclose a thermocouple and having an open end from which the thermocouple wires are led and a closed end adapted to be immersed in the material whose temperature is to be measured, said tube being composed of a welded steel pipe, a steel plug closing the end of said pipe, and a layer of gray cast iron of uniform thickness adhering to the outer surface of said pipe and of said plug, said pipe and said plug forming a core on which said layer of grey iron is cast directly from a molten state.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Foxboro Company, Bu1letin l98, page 19 (1937). Bristol Company Catalog 1402, pagesv 48-49 Brown Instrument Company, Catalog #1102 (1937) pages 4445. a

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