US2507360A - Pneumatically operated furnace door seal - Google Patents

Description

y 195@ L. E. WICKS 2,507,360

PNEUMATICALLY OPERATED FURNACE DOOR SEAL Filed Nov. 7, 1945 2 Sheets-Sheet 2 l l I l l p l l I i I l I l l l i l i l l I INVENTOR l ewzs 5 Wicks.

ATTORNEY Patented May 9, 1950 PNEUMATICALLY OPERATED FURNACE DOOR SEAL Lewis Edward Wicks, Cleveland; Ohio, assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application November 7, 1945, Serial No. 627,228

This invention relates to heat treating furnaces, and more particularly to door sealing means therefor. The invention is particularly applicable for perfecting a gastight door sealfor furnaces employing a controlled atmosphere in the heating chamber containing the work undergoing heat treatment, but it also may beusecl to advantage in connection with various other types of furnace.

Herein the invention is described in connection with a car type furnace for the heat treatment of castings or otherarticles of magnesium base alloy. Following common practice, sulphur dioxide is introduced into the heating chamber of the furnace in order to prevent undue oxidation of the metal being heat treated. Conventional sealing means for the furnace door heretofore available has not afforded an effective seal against leakage of the gas even though the door is clamped against the door frame and a sealing gasket is interposed between the contiguous faces thereof. Under differential expansion and warp-- age, surface irregularities and normal service wear, leakage of the furnace atmosphere past the door seal has been experienced. In view of i the obnoxious and'harmful characteristics of the" sulphur dioxide gas, protection against its leakage becomes important.

A primary object of the invention is to providea gastight furnace door seal effective to overcome gas leakage past the seal and capable of automatically accommodating itself to maintain the sealing effectiveness in service.

Another object of the invention is toprovide means for preventinginjury to the sealing mechanism upon door opening and closing operations.

A'further object of the invention resides in the provision of a furnace door sealing mechanism' which is of simple and rugged construction, automatically adjustable, positive in operation under he high temperature conditions and free from the need for excessive maintenance service.

Other objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying Fig. 3 is a schematic plan view illustrating door raising and lowering. mechanism.

7' Claims. (01. 110-173) Fig. 4 is a view on an enlarged scale taken on the line 3-4 of Fig. 1'. r r

Fig. 5'is an enlarged detail view of'an upper corner portion of the door looking at the inner side thereof;

Fi 6 is a detailed cross sectional view on an enlarged scale'showing the door in" sealing rela tionship to the coacting' door frame of the furnace.

Fig; '7 is a perspective view showingv the pressure or bellows element employed, and. v

Fig. 8 is a diagrammatic view showing the piping and'control system. p

In the drawing, particularly Figs. '1 and 2, a

rectangular car type heat treating furnace is At its'charging end the furnace is constructed with a door jamb or frame outlining a'doorway" through which the furnace may becha'rged arid unloaded. The door frame consists of side channels l4 and top and bottom channels IE' prefera bly welded to-the exterior of' the shell I]. Two buck'stays Iiiare located at the respective sides of the door frame and a'door H is disposed between the buckstays for vertical movements-into and outofclos-ing relationship'to the door fra'm'e. The door may: be of any suitable construction and as shown comprises channel edge' members I8 disposed in a common plane and 'joinedto ach other attheir ends by angles l9 (Figs: 5Tand 6),

the joints between the chan'nels beirig welded tol provide leakproof construction. A'cover plateZfl bears against the outer flangesof th'e channels andis welded thereto. Within th'ehollow framework thus formed, suitablexinsulatingmaterial 2.1 is.disposed-toireduceiheat losses through the door." Tiexrods, asindicated at 221m Fig. 6, extend through the insulating material and are welded:

to a plate 23-at theinner side of theidoor thereby to firmly hold the insulating; material in plac'e';

The rods 22 are suitably secured to the plate- 20 (bolts being: shown for the: purpose) At each side, the .door-is provided with" a pair of lugs 25-through which extends a supportin'g" rod ZWhaving attached to its upper end :a chain 21 that passes around sprocket wheel 28. The sprocket wheels 28 are mounted on a shaft 29 that is journalled in suitable bearings secured to the upper ends of the buckstays IS. The other end of each supporting chain 21 is connected as at 30 to a flexible cable 3! which passes around a grooved wheel 32 at the rear end of the furnace and is connected to a weight 33 which serves to counterbalance the door. The grooved wheels 32 are mounted on a shaft 34 supported in bearings mounted on the upper ends of spaced buckstays corresponding to the buckstays l5.

Power operating means is provided for driving shaft 29 to effect raising and lowering of the door. This means comprises a hydraulic cylinder 35 (Fig. 3) suitably supported at the top of the furnace and containing a piston whose piston rod 36 is attached to rack bar 3'! which meshes with gear 38 keyed to shaft 39. The shaft 39 is journalled in bearing brackets 43 mounted on cross beams 4| at the top of the furnace. Keyed to shaft 39 is a sprocket wheel 42 around which passes a chain 43, the chain also extending around sprocket wheel 44 keyed on shaft 29. It will be observed that when fluid pressure is admitted to the rear end of cylinder 35, rack bar 31 is thrust forwardly and causes shaft 29 and its chain sprockets 23 to be rotated in a direction to effect raising of the door. Admitting fiuid pressure to the opposite end of the cylinder 35 results in lowering of the door into a position opposite the doorway, the outer limit of piston travel in cylinder 35 terminating descent of the door. By adjutment of nuts on the lower threaded ends of rods 26, the door in lowered position may initially be adjusted into proper alignment with the door frame.

Normally the door is spaced outwardly from the face of the door frame to an extent of approximately 1 inch so that movement of the door can be effected without scraping the door frame. Hence it is necessary to move the door bodily inwardly when it is to be sealed against the door frame. To this end, cam or eccentric devices 45 are provided for engaging the outer side of the door along each vertical edge thereof. Eccentrics 45 are carried by stub shafts 46 journalled in supporting brackets 4'! secured to the respective buckstays IS. A pinion 48 is secured to the outer end of each stub shaft 45 and meshes with a rackbar 43. At least two camming elements are provided for each side of the door. The respective rack bars 49 thereof are mounted on a vertical bar 50 which is connected at its upper end to the piston rod of a piston working in air cylinder The stroke of the piston in cylinder 5! is sufiicient to effect rotation of the eccentrics 45 through an arc of 180. When the eccentrics are actuated, the door is moved from its outermost position as shown in Fig. 4 to scaling position with respect to the door frame as shown in Fig. 6. The eccentrics clamp or look the door in this latter position and subsequently when the door is to be released preliminary to raising it, the eccentrics are turned to outermost position and the weight of the door causes it to gravitate to outermost position. In this position the supporting chains 21 are vertical, thereby eliminating tendency for the door to swing out of its supporting plane during raising and lowering movements.

To seal the door against the door frame, a continuous packing element of heat resisting material such as asbestos fabric is provided at the inner face of the door adjacent to the outer pc- 4 riphery or rim thereof. This packing or gasket 52 is adapted to engage contact strips 53 secured to the outer face of the door frame channels, but it could, of course, engage directly against the flanges of the door frame members, if desired.

The gasket 52 is mounted on the door 11 in a peripheral recess or pocket 54. This pocket is formed by plates 55 spaced outwardly from the periphery of channels l8 and parallel thereto, and angles 56 that are bolted or otherwise suitably secured to the channels l8, the plates being welded to each other at their ends and welded to the upstanding flange of the angles. The recess 54 is continuous around the periphery of the door. The packing 52 is continuous in the sense that it is coextensive with the peripheral length of the recess although for convenience strips of packing equal to the width of the door are out and inserted into the recess at the top and bottom of the door while other strips of the required length are cut and disposed in the recess at the sides of the door, the side strips at their ends extending across the ends of the top and bottom strips (Fig. 5). The width and depth of the packing are such that it is firmly retained in the recess and affords a seal against gas flow past its sides, but it is displaced outwardly relatively to the recess 54 and to the inner face of the door by application of pressure rearwardly thereof.

Behind each of the packing strips 52 there is provided a pneumatically actuated pressure element in the form of a metallic bellows 51 by which the packing strips are forced into tight pressed sealing engagement with the outer face of the door frame. Each of the bellows 57 is formed of thin gauge sheet metal bent into a rectangular section and provided with longitudinally extending corrugations 58 at each side of the section. The longitudinal edges of the strip are interlocked as at 59 and suitably soldered or welded to make a gastight connection. The bellows section is closed at its ends by plates soldered or otherwise suitably secured in position so that the completed bellows unit will be perfectly airtight. Preferably the bellows units are made in a length corresponding to the length of the gasket elements with which they cooperate. Near each end each bellows unit 51 is provided with a threaded bushing 60 which is passed through the rear wall of the recess 54 and a nut 6| (Fig. 6) is applied to each of the bushings to retain the bellows in position. A conduit or pipe 62 is attached by suitable fittings 63 to the bushings of adjacent bellows as seen more clearly in Figs. 5 and 6. Similarly, all of the bellows are connected in series as shown in Fig. 1 so that air pressure admitted to one of the bellows flows through the interconnecting pipes 62 into the other bellows so that they expand under the applied pressure. Thereby the gaskets 52 will be forced outwardly to bear against the sealing strips 53.

It will be apparent that by reason of the provision of the bellows 5T, coextensive in length to that of the packing 52, any slight irregularities or crevices which may be present or appear between the packing and the sealing strips when the door is clamped against the door frame'will be positively closed to prevent flow or leakage of gas from the furnace chamber past the seal. Moreover, in case of unequal expansion or warpage of the door resulting from the high temperatures to which it is exposed, the bellows will automatically cause the gasket to move into sealof pressure to the bellows.

in position and to maintain such sealed relae tionship. It is to be appreciated further that in case the clamping mechanism including the eccentrics 45 becomes worn, a tight seal wi l still be effected merely by movement of the gasket under influence of the actuating bellows.

To avoid the possibility that the bellows may inadvertently be subjected to fluid pressure with possible rupture of the bellows when the door is out of clamped position, means are provided to effect correlated operation of the door clamping means and the bellows. In this connection refference is made to Fig. 8. Therein a single con-. trol element which suitably comprises a man-. ually actuated four way valve 65 is provided to control flow of fluid. pressure to and from the bellows and to the operating cylinders 5| of the clamping mechanism. High pressure air from a suitable source is admitted past the valve $5 in its release position as illustrated through con-v duit E6 to the lower ends of the cylinders 5| to effect movement of the clamps 45 to door releasing position. A speed control valve 6'! is connected in this line so that flow of fluid pressure is slow in the direction of releasing the clamps whereby the door under its gravity movement may follow the rotation of the eccentrics. Flow in the other direction is unrestricted since it is not needed to control piston speed. From the opposite ends of cylinders 51 exhaust occurs through conduit 68 which is connected to the other outlet port of valve 65. Line 68 becomes the pressure line when valve 65 is moved to scaling position at which time line 66 becomes the exhaust line. A pressure reducing regulator 69 is connected to the line 68 through conduit 1B and output of the regulator is delivered past speed control valve H to a flexible hose: connection l2 and to an adjustable relief valve 13. A branch connection as indicated at M runs to a door actuated control valve and check valve 16. This latter valve is connected to line 68 and free flow therethrough is in the direction indicated by the arrow, but it checks flow from line 68 in the opposite direction when there is high pressure in the line 68. The valve '15 is spring biased in open position and is closed only when the door is in lowered position. It serves to ex-. haust pressure in lines '12 and It solong. as the door is not fully lowered. The flexible hose 12 is provided at its end with a well known type of snap-on hose connector 11. The one part of this connector is carried by the door as indicated at 1B in Figs. 1 and 2 and is connected through pipe 79 to a fitting corresponding to the bushing 50 with which one of the bellows is provided for admittance and exhaust of fluid pressure. However, if desired, the hose may be permanently attached to the bellows fitting and be made of a length sumcient to accommodate vertical movement of the door.

Assuming that the clamps are released and the door is in raised position, a suitable charge of magnesium castings to be heat treated are loaded on to a car, for example, and pushed along floor tracks and into the heating chamber of the furnace, the latter being provided with tracks 80 for movement of the car in the furnace. Then by operation of the power cylinder 35 the door will be lowered into position opposite the doorway. As the door completes its lowering movement it effects closure of valve 15 thereby conditioning the pneumatic circuit for application This feature prevents delivery of air pressure to the bellows asoaseo when the door: is. elevated. By' movement of the control valve 65- to: door sealing position, pressure is admitted to line 68 and the pistons in. cylinder 51 descend. to actuate the eccentrics and force the door inwardly against the door jamb. In the meantime the hose T2 is connectedby the operator to the fitting on the door. The air pressure from the line 68. is reduced by the regulator 69 to an appropriate valuev and then passes slowl through valve H and through the hose to the bellows to expand the same and thereby perfect a gastight seal between the packing 53 and sealing strips 54 as heretofore described. In case the air pressure exceeds a predetermined amount, the relief valve operates to bleed. off the excess pressure.

Sulphur dioxide gas is introduced into the furnace so that oxidation of the metal undergoing heat treatment may be prevented. The heat treatment of magnesium alloy articles is usually carried out at temperatures of between about 700 F. to 850 F. During the heat treatment it has been found the sealin means has proven effective to prevent seepage or leakage of the gas out of the furnace chamber.

In order to release the door, the valve-65 is operated to release position whereby fluid pressure is admitted to line 66 and the pistons in cylinders 5| move upwardly. Responsively to actu'ation of the bars thereby the eccentrics move to their outer position and the door gravitates away from the door jarnb. At this time, incase the operator fails first to disconnect the flex-- ible hose I2, exhaust of pressure from the beilow takes place through the line 14 and check valve 16. Therefore, the bellows cannot bemaintained in an extended position or be subjected to expanding pressure when the door and its gasket move away from the door jamb, thus preventing danger of rupturing the bellows. Since the door is required to be first released before it can be raised, dangerof rapid wear of the packing through its rubbing on the sealing strips is avoided.

The invention as hereinabove set forth is embodied in a particular form, but may be variously embodied within the scope of the appended claims.

What is claimed is:

1. In a furnace having a doorway in one wall thereof, a door frame outlining said doorway, a door for closing said doorway, a gasket of heat resistant materialv carried by the door in position to engage with said door frame, means for holding the door in closing position against said door frame, and pneumatically actuated metallic press sure devices bearing against the side of said gasket remote from said door frame and effective along substantially the entire length of said gas ket to force the same towards and into sealing relationship with said door frame.

2. .A door sealing mechanism for furnaces. and the like comprising a door frame in one wall of the furnace outlining a charging opening therethrough, a movable door cooperating with said door frame to cover and uncover said doorway, means forming a continuous recess along the periphery of said door, with the recess open at the furnace confronting face of the door, heat resistant gasket members disposed in said recess and coextensive with the peripheral length thereof, a. pluraltiy of elongated metallic bellows in said recess behind said gasket members and operable to press said gasket members outwardly at said recess along substantially the entire length thereof into sealing engagement with said door frame, and means for admitting fluid pressure to said bellows.

3. A door sealing mechanism for furnaces and the like comprising a rectangular door frame in a vertical wall of the furnace outlining a charging doorway therethrough, a rectangular door movable horizontally into position against said door frame to close said doorway, means to lock said door in said closing position, means forming a continuous recess along the periphery of said door with the recess open at the furnace confronting face of the door, elongate packing strips in said recess at the top and bottom of the door, elongate packing strips in said recess at the sides of the door, the ends of said side strips extending across the adjacent ends of said top and bottom strips, said strips being formed of heat resisting material, a metallic bellows for each of said packing strips substantially coextensive in length therewith and positioned in said recess behind said strips for expanding said strips outwardly of said recess into sealing relation with said door frame, and means for supplying pneumatic pressure to said belllows.

4. In a furnace having a doorway in one wall thereof, a door frame outlining said doorway, a door for closing said doorway and normally spaced outwardly therefrom, means for raising and lowering said door, pneumatically actuated clamping means operable to force said door inwardly into closing relation with said doorway, a pcripherally continuous sealing gasket of heat resistant material carried by said door in position to engage the outer face of said door frame, a plurality of metallic bellows units associated with said gasket for pressing the same into sea-ling relationship with said door frame, conduit members connecting said bellows units serially for pneumatic pressure intercommunication therebetween, means including a single control element for admitting fluid pressure to said pneumatically actuated clamping means to actuate the same and to one of said bellows for expanding all of them thereby to effect sealing engagement of said gasket with said door frame, and means for effecting exhaust of pressure from said bellows units upon actuation of said control element to effect release of said clamping means.

5. In a furnace having a doorway in a vertical wall thereof, a door frame outlining said doorway, a vertically movable door normally spaced outwardly from said door frame, means for raising and lowering said door relatively to said door frame, pneumatically actuated clamping devices engageable with the outer side of the door along the vertical edges thereof for moving said door inwardly and clamping it in closing relationship to said door frame, means carried by the door forming a continuous peripheral recess open at the furnace confronting face of the door, a heat resistant gasket in said recess, a plurality of metal bellows behind said gasket for pressing the latter outwardly of said recess into sealing relation with said door frame along substantially the entire length thereof, means for delivering fluid pressure to said pneumatically actuated clamping devices and to said bellows to actuate the same, and means controlled by said door for preventing delivery of fluid pressure to said bellows until said door is in fully lowered position.

6. In a furnace having a door frame in one wall thereof outlining a charging doorway, a door movably mounted on said furnace for movement into and out of closing relation with said door frame, clamping means for holding said door in closing position against said door frame, said door having a marginal portion overlapping the door frame along the entire length thereof and being provided in said marginal portion with a continuous recess open at the inner furnace confronting face of the door, a gasket of heat resistant material disposed in said recess and adapted to be forcibly projected past said inner face of the door into pressure sealing contact with the outer face of said door frame, a plurality of pneumatically actuated metallic pressure devices secured in said recess behind said gasket to move the same into said sealing contact with said door frame, a valve controlled conduit for conducting fluid pressure to said pressure devices to actuate the same, and door controlled means comprising a valve connected to said conduit and operable to exhaust pressure from said pressure devices continuously until said door is in position to be clamped against said door frame.

7. A door sealing mechanism for furnaces and the like comprising a door frame in one wall of the furnace outlining a charging opening therethrough, a movable door cooperating with said door frame to cover and uncover said doorway, means forming a continuous recess along the periphery of said door, with the recess open at the furnace confronting face of the door, a gasket of heat resistant material disposed in said recess and coextensive with the peripheral length thereof, a plurality of metal bellows in said recess behind said gasket and operable to press said gasket outwardly of said recess along substantially the entire length thereof into sealing engagement with said door frame, and means for admitting fluid pressure to said bellows.

LEWIS EDWARD WICKS.

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

UNITED STATES PATENTS Number Name Date 871,421 Koppers Nov. 19, 1907 2,040,387 Van Ackeren May 19, 1936 FOREIGN PATENTS Number Country Date 430,436 Great Britain Feb. 0, 1934

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