US2095977A - Graphite resistor - Google Patents

Description

Patented a. 19, 1937 PATENT OFFICE GRAPHITE RESISTOR Robert E. Gould, Norris, Tenn.

No Drawing. Application July 27, 1936, Serial No. 92,945

9 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a process for sealing a graphite resistor in a refractory protection tube.

One of the objects of this invention is to increase the life of graphite resistors in high temperature furnaces. Another object of this invention is to provide a means for the exclusion of oxygen from contact with graphite resistors operating at high temperatures. Other objects of this invention include the provision of an economical and effective means for sealing graphite resistor assembly units. 20 I have discovered a process for effectively completing the manufacture of high temperature graphite resistor units by introducing a gas, liquid or solid hydrocarbon in the space between a graphite resistor element, which has been machined to fit snugly into a refractory protection tube, and the protection tube into the resistor assembly heated to a temperature suflicient for the rapid decomposition of the hydrocarbon for the formation of carbon or by heating the entire 30 graphite resistor assembly either internally or externally after the admission of the hydrocarbon until the space between the graphite resistor and the protection tube has been completely sealed for the exclusion of atmospheric air.

One example of the operation of my process is given for the sealing of a graphite resistor element in a carborundum protection tube with butane as the gaseous hydrocarbon. Each end of the graphite resistor, 1%,; inches in diameter and 34 inches long, was threaded into a graphite terminal 3% inches in diameter and 10 inches long. The assembled resistor and terminals were placed in a carborundum tube 5 inches outside diameter, 4 inches inside diameter and 52 inches long and the assembly sealed at both ends. Each graphite terminal had a inch diameter opening which communicated between the external end of the terminal and the space between the resistor and the protection tube. A metal valved line was threaded into the external end of each opening. The butane was admitted to the space between the resistor and the protection tube through one of the valved lines to the pressure of inch of water with the other valved line closed- A current of 1200 amperes and 10 volts was applied to the resistor. This operation was continued until one end of the assembly was completely sealed. The butane was then admitted through the other valved inlet and the operation continued until the other end of the 5 assembly was sealed. The valved inlet was left in place so that the treatment might be repeated as the requirement was indicated by an increase of resistance in the resistor above normal. The graphite resistor assembly so prepared was oper- 10 ated continuously in a ceramic furnace at a temperature of approximately 1420 C. (2588 F.) for a period of 2283 hours.

It is evident that there are numerous factors which will influence conditions for the most satisfactory operation of my invention, the actual limits of which cannot be established except by a detailed study of each set of raw materials and the finished products involved.

Any hydrocarbon may be used for the sealing operation whether it be aliphatic, aromatic or heterocyclic. In fact, any carbon compound which is susceptible to decomposition at elevated temperature with the deposition of carbon may be used with equal satisfaction. However, from the standpoint of availability and particularly economy it is ordinarily most desirable to use petroleum, petroleum products or associated hydrocarbons. The gaseous hydrocarbons which have been found to be particularly effective are 3 commercial propane, C3Hs and butane, C4H10. Liquid hydrocarbon mixtures, such as naphtha and kerosene, perform their function in the sealing operation in substantially the same manner as the gaseous hydrocarbon. Liquid hydrocarbon mixtures, such as gas oil, light lubricating oil and heavy lubricating oil are representative of the type of this material suitable for the sealing operation. Solid hydrocarbon mixtures, such as parafiin wax and asphalt, perform their function in a manner similar to the liquid hydrocarbon mixtures. I

In the case of the gaseous hydrocarbons and low boiling liquid hydrocarbon mixtures it has been found particularly efiective to admit such 1 materials into the space between the resistor and the protection tube with the assembly already at elevated temperature. In the case of the high boiling liquid hydrocarbons and the solid hydrocarbon mixtures it has been found possible to admit the materials into the space between the resistor and the protection tube while the assembly is cool and then apply heat to the assembly. The heating may be accomplished either externally or internally. In those cases in which the liquid hydrocarbon mixture or the solid hydrocarbon mixture is admitted relatively cool to the space between the resistor and the protection tube, it is necessary to leave one 5 valved inlet open with the end of this inlet sealed under oil to provide for a small superatmospheric pressure in the assembly and, at the same time, to provide for an outlet for the excess hydrocarbon as well as the gaseous decomposition prodl0 uct obtained on pyrolysis of that hydrocarbon remaining in the assembly.

Ordinarily the initial sealing of the assembly is sufficient to secure adequate production for a long period of use. However, under some circumstances, particularly when it has been necessarily alternately cooled down and reheated, it may be found necessary to repeat the sealing operation. It has previously been proposed to maintain an inert atmosphere in the space between the graphite resistor element and the protection tube. This has been found to be particularly expensive where no provision has been made for sealing the space between the ends of the resistor element and the protection tube. When such space has been sealed in accordance with my invention disclosed herein, it is ordinarily not necessary to supply an inert atmosphere to the above mentioned space. However, if it be deemed necessary to maintain a very slight positive pressure of inert gas on this space after the space around the ends of the resistor element have been sealed, this may be done by supplying inert gas to the inlet mentioned above for use in connection with the sealing of the resistor assembly when using gaseous 35 or highly volatile liquid hydrocarbons. Even under these circumstances a very small quantity of inert gas is required.

It will be seen, therefore, that this invention actually may be carried out by the modification 40 of certain details without departing from its spirit or scope.

I claim: 1. Process of sealing a graphite resistor into a refractory protection tube using a gaseous hydro- 45 carbon, which comprises, heating the graphite resistor assembly to a sufficient temperature to effeet a rapid pyrolysis of the gaseous hydrocarbon subsequently admitted with the formation of carbon, and admitting the gaseous hydrocarbon into 50 the space between the graphite resistor and the refractory protection tube.

2. Process of sealing a graphite resistor into a refractory protection tube using a liquid hydrocarbon, which comprises, heating the graphite re- 55 sistor assembly to a sumcient temperature to effect a rapid pyrolysis of the liquid hydrocarbon subsequently admitted with the formation of carbon, and admitting the liquid hydrocarbon into the space between the graphite resistor and the 60 refractory'protection tube.

3. Process of sealing a graphite resistor into a refractory protection tube using a liquid hydro carbon, which comprises, admitting the liquid hydrocarbon into the space between the graphite resistor and the refractory protection tube, and heating the graphite resistor assembly to a sulficient temperature to effect a rapid pyrolysis of the liquid hydrocarbon with the formation of carbon.

4. Process of sealing a graphite resistor into a refractory protection tube using a solid hydrocarbon, which comprises, heating the graphite resistor assembly to a sufficient temperature to effect a rapid pyrolysis of the normally solid hydrocarbon subsequently admitted in a melted state with the formation of carbon, and admitting the melted solid hydrocarbon into the space between the graphite resistor and the refractory protection tube.

5. Process of sealing a graphite resistor into a refractory protection tube using a solid hydrocarbon, which comprises, admitting the solid hydrocarbon into the space between the graphite resistor and the refractory protection tube, and heating the graphite resistor assembly to a sufficient temperature to effect a rapid pyrolysis of the solid hydrocarbon with the formation of carbon.

Y 6. Process of sealing a graphite resistor into a refractory protection tube using a hydrocarbon, which comprises, heating the graphite resistor assembly to a sufiicient temperature to effect a rapid pyrolysis of the hydrocarbon subsequently admitted with the formation of carbon, and admitting the hydrocarbon in the space between the graphite resistor and the refractory protection tube.

'7. Process of sealing a graphite resistor into a refractory protection tube using a hydrocarbon, which comprises, admitting the hydrocarbon into the space between the graphite resistor and the refractory protection tube, and heating the graphite resistor assembly to a sufficient temperature to effect a rapid pyrolysis of the hydrocarbon with the formation of carbon.

8. Process of sealing a graphite resistor into a refractory protection tube using a carbon compound which forms carbon on pyrolysis, which comprises, heating the graphite resistor assembly to a suificient temperature to effect a rapid pyrolysis of the carbon compound subsequently admitted with the formation of carbon, and admitting the carbon compound into the space between the graphite resistor and the refractory protection tube.

9. Process of sealing a graphite resistor into a refractory protection tube using a carbon compound which forms carbon on pyrolysis, which comprises, admitting the carbon compound into the space between the graphite resistor and the refractory protection tube, and heating the graphite resistor assembly to a sufiicient temperature to effect a rapid pyrolysis of the carbon compound with the formation of carbon.

ROBERT E. GOULD.