US2591097A - Base for cover-type annealing furnace with external means for circulating and cooling atmosphere gases - Google Patents

Description

April 1, 1952 2,591,097 NAL H. J. PUGSLEY TYPE BASE FOR COVER ANNEALING FURNACE WITH EXTER MEANS FOR CIRCULATING AND COOLING ATMOSPHERE GASES Filed May 24, 1947 2 SHEETSSHEET l INVENTOR HUGH J. PUGSLEY.

Patented Apr. 1, 1952 BASE FOR COVER-TYPE ANNEALING FUR- NACE WITH EXTERNAL MEANS FOR CIR- CULATING AND COOLING ATMOSPHERE GASES Hugh J. Pugsley, Pittsburgh, Pa., assigncr to Swindell-Dressler Corporation, Aspinwall, Pa., a. corporation of Pennsylvania Application May 24, 1947, Serial No. 750,272

9 Claims. 1

This invention relates generally to metallurgical furnaces and, in particular, to furnaces of the cover or hood type which are extensively used for annealing coils of material piled in stacks.

It is standard practice in the annealing of coils of strip, for example, in hook-type furnaces, to supply an atmosphere of non-oxidizing gases within the inner cover used to protect the charge from oxidation when the heating cover is removed to permit cooling of the charge. A fan isusually installed in the base of the furnace for circulating the special-atmosphere gases to hasten the exchange of heat between the gases and the charge in both the heating and cooling steps of the annealing cycle. Because of the limited space available, however, only a relatively small fan can be employed which produces only a slow circulation of the gases. The maximum cooling rate obtainable, furthermore, is limited by the rate at which the heat of the charge is given up to the inner cover and removed therefrom by natural radiation and convection.

I have invented a novel furnace-base construction which permits rapid circulation of the atmosphere gases with a consequent reduction in the time required for both the heating and cooling of the charge. My invention also contemplates provision for forced cooling of the circulating gases, thereby further shortening the cooling time as compared with that required when cooling is effected solely by natural radiation and convection. In a preferred embodiment, I provide a fan chamber in a location spaced from the base and having connections extending through the base for the outflow and return of the atmosphere gases maintained within the inner cover. The fan chamber is designed to accommodate a fan of sufiicient capacity to effect vigorous circulation of the gases. Preferably, the fan chamber is positioned at a distance below the base. In any event, by locating the fan at a point spaced from the base, I avoid the limitations heretofore imposed on the size and capacity of the fan and I am able to employ a larger and more powerful fan and thereby effect a more rapid circulation of the atmosphere gases. By withdrawing the gases from the inner cover and returning them thereto, furthermore, I gain the opportunity of cooling them artificially by contact with suitable heat-exchange means, with a resultant increase in the rate of abstracting heat from the charge by repeated circulation of the atmosphere gases therearound.

Specifically, I provide an outlet passage through the base of a cover-type furnace communicating with a fan chamber below the base. A fan in the chamber draws the atmosphere gases downwardly from the inner cover through the outlet passage. fan upwardly through the base, preferably coaxially of .the outlet passage. A duct system in the chamber above the fan has spaced inlets leading the gases from the inner cover to the center of the fan and outlets from the periphery of the fan communicating with said return flue.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating a present preferred embodiment. In the drawings,

Figure 1 is a central vertical section through a coil furnace which may be circular or rectangular in horizontal section, including a base incorporating my invention;

Figure 2 is a partial section taken substantially along the plane of line IL-II of Figure 1; and

Figure 3 is a partial section showing the lower portion of Figure 1 to enlarged scale.

Referring in detail to the drawings and, for the present, to Figures 1 and 2, a furnace adapted to accommodate a stack of coils for annealing comprises an open-bottomed heating cover or hood [0 removably disposed on a base I l. The cover comprises a side wall [2 and roof l3 of refractory brick laid up within a binding including structural frame members M and sheath ing [5. The interior of the cover may be provided with any desired form of heating means,

'i. e., radiant tubes, electric resistors or open burners. Since my invention concerns particularly the construction of the furnac base and is independent of the nature of the heating means installed in the cover, the latter have not been shown in the drawings.

The base H rests on beams l6 carried on a suitable foundation and comprises a framework of structural members I8 on which lies a bottom plate IS. A hearth 20 of refractory brick is laid on the plate l9, and a channel 2| serves as an outer wall therefor. A flange 22 together with the channel 2| provides a sealing channel adapted to accommodate a flange 23 depending from the cover ID. The base may be circular or rectangular in plan and the cover is shaped to conform to the base.

A charge support 24 is disposed on the hearth 20 and comprises a bottom plate 25, and a top plate 26 supported thereabove by spaced posts A return flue extends from the 'water, e. g flexible hose.

21. The plates 25 and 26 have central openings or ports therethrough. The charge support is adapted to receive a stack of coils 28 with their central void or eye disposed coaxially with the openings in the plates 25 and 26. An open-bottomed inner cover 29 is disposed over the stack of coils before the heating cover is placed on the base. A sealing channel 38 in the hearth 29 accommodates the lower edge of the inner cover.

The construction described above is more or less conventional in the art of coil-annealing furnaces. My invention is particularly concerned with means for circulating the atmosphere of non-oxidizing gases usually maintained inside the inner cover 29. Such gases are supplied through a suitable inlet pipe (not shown), provision being usually made for purging atmospheric air trapped by the cover as it is lowered over the charge before the heating cover is placed on the base.

In accordance with my invention, I provide an outlet'passage 3| extending downwardly through the base to a fan chamber 32 located at a distance therefrom. This chamber may be located at any'convenient point but, for convenience, it is preferably suspended in a pit 33 below the base. The chamber is defined by a wall of suitable thermal insulation laid up within a shell of metal plate and having a lining of similar material.

:An expansion 'joint 34 may be installed between the passage 3| and the chamber 32.

A fan 35 is mounted on a shaft 35a extending vertically through the bottom of the chamber 32. The shaft 35a may be connected to a driving motor (not shown) directly or by a belt-andpulley'drive. Immediately-above the fan a duct system 36 fabricated from metal plate is installed in the chamber 32 to guide atmosphere gases'from the inner cover 28'to the fan inlet and conduct them from the periphery of the fan to a return flue 31. The flue 31 is preferably disposed coaxially of the passage 3| and extends upwardlyto approximately the level of the top plate 26,-of the charge support 24. The duct system 36 will be describedin greater detail with reference to Figure 3.

The duct system 36 includes a pair of partitions 38 spaced inwardly from the side walls of the chamber 32defining therebetween a space for accommodating a heat exchanger 39. A reducing-duct section 40 extends from the .upper edges to-enclose itv when retracted. The exchanger comprises a series of water tubes 42 of hairpin shape extending from aheader box 43 to which extend inlet and outlet connections-for cooling The exchanger preferably includes bottom 'rails 44 traveling on rollers 45, journaled in the chamber 32 and extension 4|. The exchanger has a refractory wall '46 at the inner end thereof serving when the exchanger isretracted, substantially to close the opening, in the side wall of the chamber through 'which'the exchanger is advanced into operative position. The exchanger, of course, is retracted 'during'the heating stage of the annealing cycle and advanced to the solid-line position only duringthe cooling stage, if it is desired to cool the charge at a rate greater than that obtainable -'by'natural radiation and convection aided by forced circulation of the atmosphere gases.

The-'duct-system '38 is generally box-likehaving a bottom horizontal wall 48 with a central opening 49 directing atmosphere gases toward the eye of the fan 35. The wall 48 is notched at 58 on opposite sides. Spaced vertical walls 5| extend upwardly from wall 48 and meet to form a ridge 52 of inverted V-shape. The walls 5| and ridge 52 terminate at partitions 38. The partitions extend upwardly from the wall 48 forming spaced inlet passages 53 conducting gases into the eye of the fan as indicated by arrows. Partitions 38, walls 5| and ridge 52 also define outlet passages 54 conducting gases flowing from the periphery of the fan upwardly through the notches 59 and the space between f the partitions 38, on the outside of walls 5|. The

gases then flow through the heat exchanger 39 and are conducted to the flue 31 by the reducing section 48.

Gases flowing downwardly through the passage 3| are confined to the inlet passages 53 until they pass through the fan after which they return by Way of the outlet passages 54. In other words, the down-flowing gases divide into two spaced streams and the up-fiowing gases are likewise divided into two streams alternating with the down-flowing streams. All the streams, however, are maintained separate below the level of the top of the duct system 38.

During the heating stage-of theannealing cycle, the circulation of the atmosphere gases within the inner cover downwardly along the outsideof the charge,v through the charge support, passage 3| to the chamber 32 and then through the duct system to the return flue 3'1, tends to equalizethe distribution of heat't-hroughout the height of the charge. Without such circulation, the top of the charge is usually heated to a higher temperature than the bottom. The fan 35 and its driving motor should have sufficient capacity to maintain vigorous circulation of the gases in order to accelerate the exchange of heat between the inner cover and the Charge. The inner cover, of course, is heatedby the heating means of the heating cover, whatever their nature, and serves to heat 7 the charge by radiation and convection. Rapid forced circulation maintained bythefan greatly increase the rate of heat transfer by convection.

The return flue 31, as previouslystated, terminatesat about the level of the top plate .25- of the charge support. As shown in the drawings, it is somewhat smaller 'in diameter than the port in this top plate. As a result, the-updraft of gases from theflue through the eye of" the stacked coils induces a portion of the gases ,flowing radially "throughthe charge supportand causes them to flow upwardly through the charge again. The remainder 'of the inwardlyv flowing gases, of course, turnsidownw'ardly'through the 'passage 3|. Whenthe chargehas been'heatedtothe desired annealing temperature, the cover 18 is removed and placed on another base to heat a. charge piled thereon. The cooling of the charge ;which has been heated may be accelerated,by'continuingthe circulation of the atmosphere gases. Theheat exchanger 39, furthermore, maybe-advanced into operative position to effect even-more rapidoooling of the charge than would result from natural radiation and convection; By passing, cooling water through the pipes 42,'the atmosphere gases withdrawn from the inner cover .29 by the. fan are artificially cooled before being returned whereby they absorb a greater amount. of heatfromthe charge when passing therearound than would otherwise be possible.

The course of circulation described,'i. e.,-downwardly around the outside of the charge and upwardly through the interior thereof, is to be preferred for annealing certain kinds of material. Circulation of the atmosphere in the reverse direction may be effected if desired. In such cases, the duct system 36 is unnecessary. The return flue 31 becomes the outlet passag and should extend downwardly to the eye of the fan 35. The gases from the fan would then flow upwardly through the passage 3! and the top of the flue 31 should have a bell mouth to deflect the ascending gases radially outward through the charge support.

It will be apparent from the foregoing description and explanation that the invention provides an improved furnace base particularly advantageous for use in the annealing of coils in stacks. The fan chamber 32 being spaced from the base permits the use of a fan large enough to maintain rapid circulation of the atmosphere gases. By withdrawing these gases to a point spaced from the furnace, furthermore, I am able to subject them to artificial cooling before returning, in order to shorten the COOIiIlg stage of the annealing cycle. The invention, of course, makes possible a marked reduction in the overall time of a complete annealing operation and thus permits a substantial increase in the production obtainable from a given amount of furnace equipment. The invention does not materially increase the cost of the equipment, furthermore, and does not necessitate any change in the normal annealing procedure as usually practiced except, of course, that the time for heating and cooling the charge is greatly reduced.

l h I have illustrated and described a preferred embodiment of the invention, it will be recognized that changes in the construction disclosed may be made without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. In a base for a cover-type furnace, a charge support spaced above the base having a central port, a passage extending downwardly through the base coaxial with said port, a flue extending upwardly through the passage to about the level of said support, and a fan spaced from the base for circulating the atmosphere surrounding a charge on said support through said passage and flue.

2. A base for a cover-type furnace as defined by claim 1 characterized by means for cooling the atmosphere before it enters said flue.

3. A base for a cover-type furnace as defined by claim 1 characterized by a heat-exchanger movable into and out of said passage.

4. In a coil heating furnace of the cover type, a base comprising a charge support, a passage through the base, said passage forming a cham ber below the base, a flue extending upwardly through ,the passage to about the level of said support, and a fan spaced from the base for circulating the atmosphere surrounding a charge on said support through said passage and flue.

5. In a coil heating furnace of the cover type a base comprising a charge support, a passage through the base, said passage forming a chamber below the base, a heat exchanger movable into and out of said passage, a flue extending upwardly through the passage terminating adja cent the support, and a fan spaced from the base for circulating the atmosphere surrounding a charge on said support through said passage and flue.

6. In a base for a cover-type furnace, a charge support spaced above the base having a central port, a passage extending downwardly through the base coaxial with said port, a flue extending upwardly through the passage to about the level of said support, the discharge end of said flue being smaller than said port whereby to induce upwardly a portion of the atmosphere flowing toward said passage, and a fan spaced from the base for circulating the atmosphere surrounding a charge on said support through said passage and flue.

7. In a base for a cover-type furnace, a charge support, an outlet passage through said base for the atmosphere surrounding a charge on said support, a heat exchanger movable into and out of said passage, said passage having an opening admitting said exchanger, a closure on said exchanger substantially filling said opening when the exchanger is withdrawn, a flue extending through the base, and a fan spaced from the base for circulating said atmosphere through said passage and flue.

8. In a base for a cover-type furnace, a charge support, an outlet passage through said base for the atmosphere surrounding a charge on said support, a flue extending through the base, a fan spaced from the base for circulating said atmosphere through said passage and flue, removable means between the fan and the flue for cooling the atmosphere before it enters said flue, said removable means having mounted thereon a closure at each end whereby the connection between the flue and fan is automatically continued upon either insertion or removal of the cooling means and a chamber substantially sealed against the atmosphere connected to the connection between the flue and fan receiving the removable means when withdrawn.

9. In a base for a cover-type furnace, a charge support spaced above the base having a central port, a passage extending downwardly through the base coaxial with said port, a flue extending upwardly through the passage to about the level of said support, the discharge end of said flue being smaller than said port whereby to induce upwardly a portion of the atmosphere flowing toward said passage, a heat exchanger movable into and out of said passage, said passage having an opening admitting said exchanger, a closure on said exchanger substantially filling said opening when the exchanger is withdrawn, and a fan spaced from the base for circulating the atmosphere surrounding a charge on said support through said passage and flue.

HUGH J. PUGiSLEY.

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

UNITED STATES PATENTS Number Name Date 1,689,042 McGee Oct. 23, 1928 1,727,192 Bailey Sept. 3, 1929 1,794,151 Cope Feb. 24, 1931 1,938,306 Webb Dec. 5, 1933 2,226,986 Wechsberg et a1. Dec. 31, 1940 2,276,971 Hoak Mar. 17, 1942 2,277,592 Keener et al Mar, 24, 1942 2,414,312 Lee Jan. 14, 1947 2,439,127 Dailey, Jr., et al. Apr. 6, 1948 2,502,204 Cole Mar. 28, 1950

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