US2421482A - Furnace - Google Patents

Description

Patented June 3, 1947 FURNACE Percival B. Crocker, Foxboro, Mass., assignorfto The Sentry Company, Foxboro, Mass., a corporation of Massachusetts Appueeuen september zo, 1944, serle1Ne.ss4,9os

4 claims. (c1. 26a- 41) This invention relates to furnaces for the heat treatment oi metals and more particularly to one wherein the work is heated in a metal container (conveniently in the form of a metal tube traversing the furnace) within which container a suitable atmosphere is maintained about the work. The type of furnace with which the invention is primarily concerned is one wherein the work. is heated at temperatures in the neighborhood or 2000 F. and ilnds a wide field of application in the treatment of compacted metal powders in the practice of powder metallurgy, so called, but also useful for other purposes, as,

for instance, brazing, silver soldering or bright annealing. An object of the invention is to provide such a. furnace so constructed that the workreceiving containers and other parts of vthe furnace are not liable to rapid deterioration.

My invention will be Well understood by reference to the following description taken in connection with the accompanying drawings, where- Fig. I1 is a diagrammatic side elevation of' a furnace;

Fig. 2 is a central longitudinal section, the drawing being simplied by the omission of a showing of details of construction not of importance to an understanding of the invention; and.

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

Referring to the drawings, the furnace there shown embodies a main enclosure it constructed of :refractory brickwork on a suitable metallic frame, not .illustrated in detail, and which is divided by a tubular member l2 of ceramic refreintory material traversing the same between opposed walls thereof and preferably, as hereinafter more fully described, extending for a substantial distance beyond said walls. This reiractory tubular member I2 divides the interior of the enclosure into an outer chamber which .may be traversed by heating elements I4 in the form of resistorrods of silicon carbide and an inner chamber I6 corresponding to the space within the tube. Through the inner chamber and in spaced relation to the walls thereof extends a metal tube I8 (which for reasons of economy may be ordinary mild steel), the interior of which forms a work-treating chamber in which the pieces of work to be treated may be placed, conveniently being traversed therethrough on boats or trays. Suitable sealing means tting the tube I8 closes the ends of the inner chamber It. f

The tube I-8 may be provided with entrance and exit doors 2U and 22 atits ends respectively which may be fitted with gas curtains diagrammatically indicated at 24. A portion of the tube between the furnace proper and the exit door 22 may form 'a cooling chamber provided with a water jacket 28. Hydrogen or cracked ammonia gas consisting of a mixture of hydrogen and nitrogen may be supplied to the interior of the tube I8 at a point 21 adjacent the exit door 22 to flow through the tube from `left to right, viewing Fig. l, to be exhausted through a suitable port in or adjacent the entrance door 2li and serving to maintain a desired atmosphere around the pieces of work during'their treatment. The features referred to in this paragraph are in themselves conventional.

Referring now particularly to Figs. 2 and 3 of the drawing, I have there shown the refractory tube I2 as provided with an interior lining' 28 of carbon. This lining may be in the form of a sleeve or a tube having a sliding nt on the interior of the refractory tube I2 to permit its easy application or renewal. The lining may be sectional and I have herein in Fig. 1 illustrated it as iff it were made of two sleeves, an openjoint 30 being illustrated at the center of the furnace. A small exposure of a portion of the inner surface of the refractory tube I2 may be tolerated so long as it is free from cracks at the point of exposure. The drawing, Fig. 3, may be taken as showing a carbon sleeve lining about 1/2 inch thickin a refractory tube about 9 x 7 inches interiorly, which is an example of a practical embodiment.

In 'the operation of the furnace the carbon, under the heat of the resistance elements It, is subject to partial combustion and generates a gaseous mixture of nitrogen and the oxides of carbon, chiefly the monoxide, which lls the closed space I6 surrounding the tube t8 forming a stag nant atmosphere therein substantially neutral to the metal and which therefore protects it from deterioration.

I have found that best results are obtained if the refractory tube I2 extends for a substantial distance beyond the walls of the main enclosure i0 to regions of relatively low temperature, say about 1000" F. i

'I'he arrangement just described of a refractory tube projecting a substantial distance beyond the furnace walls also facilitates the sealing of the chamber IS. Ordinary asbestos packing 32 may be tted to the outside of the metal tube I8 and pressed against the end of the tube I2, as by means of a clamping collar 3B, and will be effective andV long lasting'. 'I'he lining 2S may be terminated a short distance from the ends of the refractory tube to yprovide for heat dissipation adjacent the seal.

Refractcries such as are practical for use in constructing the tube I2 are likely to develop cracks in use. In the construction shown the refractory tube may continue in service although cracked if not too much damaged. The atmosphere generated within the chamber I6 ls stagnant and under substantially no pressure which would cause it to seep through small cracks. Furthermore in normal use there is a layer of unconsumed carbon lining the tube which tends to seal cracks and passages therethrough. A long service from a given refractory tube may thus be obtained.

If gas should leak from the closed chamber i6 through the refractory tube l2 either because of the porosity of the latter or of slight cracks,the gas, as contrasted, for instance, with hydrogen, will not harm the silicon carbide resistors. The construction therefore permits the use of these highly satisfactory means for developing a high degree of heat.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and l therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive, as is in fact clear in several matters from the description itself. Reference is to be had to the appended claims to indicate those principles of the invention exemplified by the particular embodiment described and which I desire to secure by Letters Patent.

I claim: y

l. A furnace of the class described comprising an enclosure which is divided by a refractory tube extending between opposite walls thereof into an outer chamber in which heat is developed and an inner chamber, a metal tube extending through said inner chamber to provide a work-treating chamber in which work may beheated in a suitable atmosphere, means for sealing the ends of said inner chamber about the metal tube, the refractory tube having a sleevelike lining of carbon wherefrom is generated Within the refractory tube and about the metal tube a stagnant atmosphere consisting substantially of nitrogen and oxides of carbon and substantially neutral to the metal tube.

2. A furnace of the class described comprising an enclosure which is divided by a refractory tube extending between opposite walls thereof into an outer chamber in which heat is developed and an inner chamber, a metal tube extending through said inner chamber to provide a work-treating chamber in which work may be heated in a suitable atmosphere, means for sealing the ends of said inner chamber about the metal tube, the refractory tube extending substantially beyond the walls of the enclosure to regions of relatively low temperature, the refractory tube having a substantially coextensive lining of carbon wherefrorn is generated within the refractory tube and about the metal tube a stagnant atmosphere consisting substantially of nitrogen and oxides of carbon and substantially neutral to the metal,

3. A furnace of the class described comprising an enclosure which is divided by a refractory tube extending between opposite walls thereof into an outer chamber in which heat is devel,- oped and an inner chamber, a metal tube extending through said inner chamber to provide a worktreating chamber in which work may be heated in a suitable atmosphere, means for sealing the ends of said inner chamber about the metal tube, and a lining for the refractory tube comprising one or more movable sleeves of carbon slidably fitting the same, from which lining is generated Within the refractory tube and about the metal tube a stagnant atmosphere consisting substantially of nitrogen and oxides of carbon and substantially neutral to the metal.

4. Heat treating apparatus wherein the work is enclosed in a metal container to be heated in a suitable atmosphere therein and comprising a closed chamber with refractory walls Within which the container is enclosed in spaced relation to said walls, the chamber having a lining of carbon, and means for heating the walls of said chamber exteriorly to provide about the container a stagnant atmosphere of nitrogen and oxides of carbon generated from the lining.

PERCIVAL B. CROCKER.

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

UNITED STATES PATENTS Number Name Date 2,290,551 Gier July 21, 1942 1,700,942 Lederer Feb. 5, 1929 2,057,518 Fraser Oct. 13, 1916 2,375,463 Berger May 8, 1945

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