US1707300A - Annealing furnace - Google Patents

Description

"llatentc'cl Apr. 2, 1929.

.UNITED STATES PATENT CFFICE.

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ANNEALING IUByACE.

Application aled November 7, 1827. Serial No. 231,488.

A removable furnace casing or bell consisting of refractory heat insulating material, sur

l rounds the container. and electric heating,r elc ments are supported'eitber upon rthe inner wall of the furnace casing or upon the walls of the gas-tight container. K Difficulty has been experienced in quickly`and eicieutly lil-i heating the work and at the same time mainn taining a proper heat distribution within the A container.

lt is an object of the present invention, therefore, to provide an anneahn furnace im whereby the work to be heated an the heat ine: elements are so positioned within a gas tight chamber that a circulation of the at mosphere therein is set up ast the .heater and around the work, where y a rapid and 't uniform heating of the work is eected.

in practicing my invention I stack the Work to he heated substantially in the shape of a chimney and mount a resistance heating element within the space defined thereby. The

S@ Work and resistor are surrounded by e hd andmeans are provided vvhereby a gas of desired chemical characteristics 1s permitted to circulate past the heater, through the stach",

I, and down around the outer surface thereof.

lfn the drawings the single figure is a rieur in vertical section of an annealing fun l nace embodying my invention.

Referring more particularly to the dra\v ings., a furnace embodying my invention coni,

no prises a cylindrical furnace casingr 2 and roof i of suitable refractory hcatfineulating;r material enclosed by a metallic shell 6. The shell completely covers the outer surface of the re fractory casing and is provided at the lower l5 peripheral rim 'thereof with an annular ango opted to extend beneathl the refractory 'portion 2 in supporting relation.

' Eye-bolts 10 are secured to the upper pe- :rinhcral rim of the metallic shell 6. and are m adapted to ybe engaged by crane-hooksor othersuitable means to facilitate the handlug of the furnace casing.

The furnace casing is adapted to be supported 1n operative position upon a base of suitable refractory material having conduits l2 and 14 extending therethrough within the arca defined by the casing, as hereinafter de scrlbcd.

Sinuously wound electrical resistance elements 16 are supported upon the inner face of the refractory wall 2 by means of suitable supports and spacers 18, in a well known manner..

'Since the particular details of construction of the furnace casing form no part of the present invention, further description thereof is not deemed necessa CVithin` the chamber defineldv by the casing 2u, when 1n o eratvc position, and substanbelly cao-ama therewith, is a circular plate 20 mounted upon the refractory base and apertured to receive the terminals of the couolunzs i2 and 1.4. AAn annular channel 22 is formed adjacent to the periphery of the plate 2O and is filled witha granular refractory material auch as sand.

A bell or container 24, of low heat-storage capacity and cti-extensive in diameter with the mean diameter of the channel 22, is posi tioncd within said casing with the lower riphcral edge thereof resting in the grano ar material in the channel 22 to form a sand seal. in a well known manner. Althou l1 a sand seal does not constitute a rfect erroctic seal for the container, the ow of air or gaa therethrough is reduced to such a point 'that the container is substantially gas-ti ht.

An eyemholt 26 is secured to the top o the container: "to facilitato the movement thercof duringf the charging and discharging operatons, as hereinafter described.

The work to be annealed comprises, in the present embodiment, circular coils of wire or steel strip 28, su ported upon a s idcr 29 which. is meunier upon the plat in coaxial relation therewith.

The main heating element com rises a resistanco Wire 30 wound to form a ouble helix and is maintained in operative relation by a plurality oil apcrtured blocks 32, of refractory eloctricinsulating material. The electrical connections (not shown) for the heating elements are effected in the usual manner.

Between the heating element 30 and the work 28 and supported upon the base plate 2O is ositioned a cylindrical grid 34 which effectively prevents engagement between the Work being heated and the heating elements.

A suitable non-oxidizing `"as may be forced into the container through t ie conduit 12 and escapes therefrom through the conduit 14 to maintain a chemically neutral atmosphere within the container and to thereby prevent surface oxidization of the material being heated. The gas employed depends upon the final character of the surface desired, so that the gas may or may not be non-orridizmg. On the other hand, in many operations, the use of a gas may be dispensed with, 1n which event the conduits l2 and 14 are closed.

In operation, 'the furnace casing 4. is raised and removed, the container 24 is removed, and the work to be heated is stacked upon the spider 80 substantially in the shape shown. The container 24 is then replaced in operative position with the lower edge there of resting in the sand containing channel 22 and the furnace casing 4 is lowered into operative relation therewith.

Upon energization of the heating element 30, it is clear from the drawing that the portions of the work constituting the inner surface of the chimney are heated directly by radiation thereby, and, as the atmosphere within the stack becomes heated, a circulation is set u as indicated by the arrows, whereby the eat is convected down around the outer vsurface of the stack to materially increase the rate of heating thereof.

In addition, if a gas or desired chemical characteristic is introduced through the conduit 12, a circulation will be set up as indicated by the arrows in the drawing, resu1ting ina more uniform effect of the gas upon the material being heated, and, by continuously convectinp,r heat about the material, more uniform heat distribution within the container is effected. The heating elements 16 carried by the furnace casing 4 may be energized if a relatively high temperature is desired,

When the heating operation has been coinpleted, the furnace casing l is raised and removed to permit the work to cool. Since the container 24 is of relatively low heatstorage capacity, the cooling in air will be relatively rapid and, during the cooling operation, the Work is kept out of Contact with the air, and the non-oxidizing atmosphere, if used, may be maintained in the container.

Clearly, many changes may be inade in the details of construction as described and be within the scope of the present invention. For example, the form of the heating; element 30 may be altered, as desired, and the particular means for sealing the container against the influx of air may be varied, de-

pending upon the temperature added therein. Also, while I have, shown the material to be annealed as constituting coils of wire or strip metal. quite clearly any charge may be heated which can be stacked in the form of a hollow cylinder. Further, by proper reo'ulation of the flow of gas through the conduits 12 and 14,' a. desired pressure may be maintained within the container and any gas of a desired chemical characteristichaving a desired effect upon the heated material may be employed.

By my invention, I have provided an improved arrangement of the heating element and charge in a gas-tight container, resulting in the heatingr of the charge both by radiation and convection, thereby increasing the eiiiciency of the furnace and maintaining a more uniform heat distribution therein.

Modifications may be made in my invention without departing from the s* irit and scope thereof, and I desire, there ore, that only such limitations shall be placed thereon as are imposed by the prior art and set forth in the appended claims.

I claim as my invention:

1. In an annealing furnace, the combination with a gas-tight container and an electrical resistor supported therein, of means for stacking Work of substantially annular form to be heated in said container around said resistor to effect the heating of the inner portions thereof by direct radiation and of the outer portions thereof by convection.

2. In a heat treating furnace, the combination with a heating chamber and a resistor disposed therein, of means for sup orting the Work between said resistor and c amber wall to permit the free circulation of furnace chamber gases therearound, whereby the portions of said charge exposed to said resistor are heated by radiation and the portions thereof adjacent the chamber wall are heated by convection.

3. In an annealing furnace, the combination with a gastight container, an electrical resistor and a charge to beheated disposed therein1 of means for permitting the heating of portions of said charge by direct radiation from said resistor and for permitting the heating.;r of other portions of said charge by convection, said means comprising means for supporting` said charge to constitute a hollow cylinder surrounding said resistor and for permitting free circulation of furnace chamber gases upwardly past said resister and downwardly along the outer surface of said charge.

4. In an annealing furnace, a gas-tight container, an electrical resistor disposed centrally thereof, means for su porting said charge to form a hollowcylmdrical stack about said resistor andfin spaced relation to the base of said container, whereby free 'cirn eulation of furnace chamber gases about said stack axially thereof is effected.

5. In an annealing furnace, a gas-tight container and material in annular form to 5 be annealed stacked therein, an electrical v heating .element surrounded by said stack, ``and Ineens for introducing a non-oxidizing as into said container to cause a circulation t ereof past said heatn element and around the outer surface of sai stack.

In testimony whereof, I have hereunto subscribed In);7 name this twenty ninth day of October, 192

WILLIAM J. DIEDERICHS.

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