US2254900A

US2254900A - Door seal for furnaces with protective atmosphere

Info

Publication number: US2254900A
Application number: US300380A
Authority: US
Inventors: Gerhard P Lessmann
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1939-10-20
Filing date: 1939-10-20
Publication date: 1941-09-02
Anticipated expiration: 1958-09-02

Description

Sept. 2, 1941. @.P. LEssMNN Y MSRHERE Doof: SEAL FOR FURNACES WITH PROTEGE' Filed oct. 2o. 19395 2 Sheets-'sheet 1 WITNESSESA- nuvENToRA Y f Gerbardlessmanh.

ATTORNEY Sept. 2, 1941.- s. P. LEssMANN DOOR SEAL. FOR FURNACES WITH PROTECTIVE ATMOSPHERE 2 sheets-sheet 2 Filed Oct- 20, 1939 INVENTOR 6 6 lll/(laf 6 4 Gerhard PLesSmarm.

ATTORNEY Patented Sept. 2, 1941 l TIVE ATMOSPHERE Gerhard P. Lessmann, AWilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application Qctober 20, 1939, Serial No. 300,380

6 Claims. (Cl. 263-10) My invention relates broadly to a furnace closure construction of general utility, but of particular application to heat-treating furnaces in which a charge is to be heat-treated while enveloped by an appropriate controlled gaseous atmosphere.

v Treating processes of this character are well known, and the composition or constituents of the controlled gas are determined by the particular charge being heat-treated, and the particular method of heat-treatment to which it is being subjected. Hydrogen, dissociated ammonia, or partially or completely combusted hydrocarbon gases, are among the most common of the controlled atmospheres employed. Where such gases are used, their entire efllcacy would be destroyed if outside air were permitted to leak into the heat-treating chamber or chambers of the furnace, and in order to minimize such leakage. the controlled gaseous atmospheres within the furnace are maintained at a pressure slightly above atmospheric, resulting in a plenum system. The higher pressure of the controlled atmosphere now causes the latter to leak out of the furnace through any cracks, crevices, or

openings that are not perfectly sealed, and a small amount of leakage is generally desired in order to assure that no air nds its way into the furnace, and to continually ush out the heattreatment chamber'or chambers so that a clean and pure atmosphere is always contained in them.

However, leakage is necessarily a source of Y continuous waste and lexpense, and, therefore, furnace structures of the type described seek 4to minimize or decrease the leakage to as small an versa. While cracks between the door and furnace door frame and consequent gas leakage or air infiltration may not be of serious consequence in large furnaces, which on account of their size 'contain a large volume of controlled gas and in which the work when heat treated is relatively far from the entrance, in the small furnaces,

especially small box-type furnaces, small gas,-

leaks or small amounts of air infiltration into the furnace lbecome important in view' of the proximity of the heat-treatment chamber to the furnace entrance and in view of its relatively small cubic content.

Itis an object of my invention to improve the seal between that part of the furnace which requires an opening in a furnace wall and the door therefor to the end that gas leakage either into or out of the furnacel is kept down.

In accordance with the preferred embodiment of my invention, a resilient gasketing material, which is also heat-resistant to a considerable degree, such as, for example, asbestos fabric, is employed as a gasket between the door and the door frame. However, such resilient gasketing materials wear out very rapidly if rubbed repeatedly by the relative motion between it and the door or door frame. Accordingly, following my invention, I provide a Vdoor which rst moves laterally from the door` frame in its openingV movement so that there is no rubbing contact on the resilient gasketing material in the 'subsequent opening movement vof the door.

Accordingly, it is a further object of my invention to provide a gasketing material between the door and the door frame of a heat-treating furnace which will seal the crevices between the two and will have ,long life.

It is an additional object .of my invention to so locate this resilient material that it is not directly exposed to the intense heat of the furnace. To this end the gasketing material is secured to the outer, cooler, rim edges of the door where it is maintained relatively cool.

My invention is especially adapted to high temperature furnaces and to this end lboth the door and the door frame are provided with expansion slots to prevent deformation due to warpage. By use of the gasket I assure a tight seal between the door and frame in spite of any irregularities of the contacting surfaces between the two which become greater with continued use of the furnace. AI, also employ the gasketing material to cover the expansion slots in the door so that there'can be novgas leakage through them. Additionally, the gasket is so secured to the door that it can be readily replaced in the event that it ultimately becomes worn or has lost its efliciency as a seal.

rOther objects and novel features of my invention will be apparent from the following description thereof, taken in conjunction with the draw ings, in which: 1

Figure 1 is a schematic representation, in a of the furnace of Fig. 1;

Fig. 3 is an enlarged. elevational view of the door frame havingrcam means thereon for moving the door laterally in the beginning of its opening movement;

Fig. 4 is a side viewl of the structure of Fig. 3;

Fig. 5 is an enlarged horizontal sectional view through the door and door frame of the furnace;

Fig. 6 is an enlarged side view of the door with parts broken away and its refractory brick lining removed to show the essential features of its construction; and

Fig. 7 is an enlarged view of a detail showing the gasket and the manner :by which it is secured to the door.

While my invention is applicable to any suitable type of furnace, in Figs. l` and 2 I show a box-type furnace comprising the usual bottom wall 2, top wall 4, back end wall 6, front end wall 8, and side walls III and I2, these walls being constructed in the customary manner of a refractory inner lining backed by heat insulating brick or material.

The walls define a heat-treatment chamber I4 in which a charge is adapted to be heattreated by suitable energy-charging means in the form of electrical resistors, radiant gas tubes, or any other suitable heating means. A gas inlet pipe I6 is adapted to convey a controlled atniosphere to the back end of the heating chamber I4 and passes through the brick work of the end wall 6 and also 4any outer, gas-tight, metallic shell which may be, employed to encasethe furnace, as is customary in the art. Charges are inserted into and removed from the furnace through a suitable opening I8 in the front wall I of the furnace. The front wall 8 is provided with a door frame or :lamb 20 against which a furnace door 22 is adapted to abut for closing the opening I8. It may be observed that the front wall 8 is so constructed that the door frame is at a slight angle to the vertical for the purpose of having the weight of the door itself press its edges against the door frame.

Referring more particularly to Figs. 3 through '1, it may be perceived that the door comprises a plurality of channel members 24 which form the outer sides or edges of the door, the channel members having legs 26 on the side farthest from the furnace opening I8, and legs 28 on the side toward the furnace :"bpening which are adapted to abut the door frame 20. The door in this lparticular embodiment is generally rectangular sothat four channel members 24 are employed for the edge sides of the door with abutting corners being suitably welded together to form a gas-tight joint. The back of the door may comprise a sheet or plate of metal 30 welded or otherwise gas-tightly secured to the legs 28. Suitable refractory and insulating brick 40 fills the space within the metallic door casing `formed by the channels 24 and plate 30, and may be anchored in positionby well known expedients. A peep hole 42 may be provided in the door covered by a swinging plate 44 pivoted to the door at46. Additionally, the bottom of the door may be provided with a plurality of spaced, reinforcing gusset plates 4I. The door 22 is of a larger size than the opening 50 in the door frame which is aligned with the furnace opening I8 in the front wall 8, and the door legs 28 are at all points spaced outwardly a short distance from the edges of the opening 50 when the door is in its closing position.

For high. temperature furnaces it is preferable to provide expansion slots in boththe door frame and the door. To this end the door frame slots 52 extending from its outer edges for a is provided with a plurality of spaced expansion short distance inwardly of the frame, and the channels 24 are similarly provided with expansion slots 54 extending from the inner rim, or the edge that is closest tothe door frame, for a short distance towards its outer edge, preferably less than half the distance, these slots vbeing provided in all of the channels 24 con stituting the metallic edges of the door.

It is the main purpose lof my invention to provide a suitable seal between the door and the door frame when the door is in closing position and to this end I secure gasketing material I8 to the outside surface of the door channels 24. This gasketing material is preferably asbestos fabric and is placed completely around the door edges, vbeing held in place by angle members 58 bolted to the channel members 24 by a plurality of spaced bolts 6l screwed into suitable threaded holes 6I in the channels 24. The top and bottom angles 58 are substantially the same length as the corresponding horizontal edges of the door while the vertical angles 58 are of the same length as the vertical edges. of the door.

As may be observed in Fig. 7, the gasketing than the length of the slots 54. having an edge 62 outwardly of the slots so that the slots are effectively covered by this material, and an additional edge 64 beyond the inner edge of the door for a purpose to be subsequently described. 'I'he angles 58 are formed with legs Bl somewhat longer than the slots 54 so that they will securely clamp the gasketing material 5B to the channels 24 beyond the ends of the slots .54 to prevent or at least minimize gas leakage through them. The other legs 68 of thenangles It are placed slightly outward of the inner rim of the door so that they do not abut the door frame when the door is closed.

With the structure thus far described, with the door in closing position the edge 84 of the gasketing material 50 is compressed against the door frame 20 by virtue of the weight of the door itself and, where necessary, additional clamping means may be employed to force the door more tightly against its door frame. Accordingly, the edge 64 of the gasketing material provides a suitable gas seal between the rim of the door and the door frame which will follow irregularities inthe abutting surfaces of the door frame or door, or both. Moreover, it may be observed that this gasketing material is fairly well shielded from the direct heat of the furnace and is substantally exposed to the outer, cooler, atmosphere about the door.

However, a compressible material suitable for gasketing as a rule wears very rapidly if rubbed and, accordingly, my invention further includes provisions for raising the door to opening position by first laterally moving the door away from `the door frame so that the gasketing edge 84 is moved laterally away from the surface of the door frame and thereafter the,q door may be moilfe fully to open position without rubbing the gas e To obtain this operation with a vertically- 2,254,900 14 between the points B and C and 18 between.

the points D and E. V-

The door is provided on each of its vertical sides with a pair of spaced cam shoes which ride on the surfaces of the corresponding cam bars 12. 'I'hese shoes comprise a cam shoe 18 fitting the cam indent 14 and a cam shoe 88 fitting the cam indent 16. The shoes are suitably fastened to bars 82, in turn welded or otherwise secured to the vertical channel members 2l and reinforced by gusset plates 84 for securing a rigid assembly.

In operation the door 22 may be raised or lowered through the medium of a hydraulic or pneumatic cylinder 86 having a piston rod 88 to which one end of a sprocket chain 9D is secured, the chain passing over a sprocket wheel 92, with its other end secured to the upper bar 82 on the vertical side of the door, it being understood that two such chains are provided for each side of the door. Accordingly, in the closed position of the door, the cam shoes 18 are disposed in the cam indents Hand the cam shoes 88 are disposed in the cam indents 16. the size of the cams and the depth of the indents being so chosen that the door presses against the door frame to compress the edge portions 64 of the gasket material 56. -The cam guides may be further provided with additional protuberances 9| to position *the door.

Inasmuch as the anglemembers 58 are 'secured to the outside of the door, it is necessary to dispose the cam shoes 18 and 88 at some distance from the door, and this means that the cam guide bar 12 must be correspondingly disposed. Accordingly, the door guide and cam means 'HI further comprises vertically disposed bars 98 inward of the cam bars 12 and welded or otherwise secured thereto in any suitable manner, these guide bars being spaced outward somewhat from the door frame 20 and extending toward the door but beneath the cam shoes so that the door can be raised or lowered without excessive side play `tending to displace the cam shoes from alignment'with the cam guide bars 12.

In operation, if it is assumed that the door is in closed position, during initial upward movement of the door, the cam shoes 18 and 80 ride on the inclined surfaces 98 and i8() of their respective cam indents, the shoes having corresponding inclined surfacesto permit ready movement of the door. -In riding on these inclinedl surfaces, the door is moved away from the door frame so that the edge-portion 84 ofthe gasketing material 58 is moved laterally away fromthe door frame. After this initial movement of the door, the cam shoes 18 and 80 ride on the dat surfaces of the cam bar 12 between the points A and B, and C and D, respectively, until the door reaches its fully open position. In lowering the door, the reverse, however, takes place, that is, the shoes ride first on the higher flat surfaces of the cam bars and finally lodge in their cooperative cam indents. In this last movement,

. the weight of the door forces it against the door frame, thereby compressing the gasket edge 84 between it and the door frame for a tight seal.

It may be observed that I provide two shoes. on each side of the door, the purpose of thisbeing tov prevent rocking of the door which might plied thereto, which would come within the scope of my invention. Q

I 4claim as'my invention: f

1 A- heat-treatment furnace having a heattreatment chamber in which acharge is adapted to be heat-treated while enveloped by a special atmosphere, said furnace including walls defining a heat-treatment chamber, a metal shell about y said walls, means to convey a special atmosphere into said chamber, said furnace being provided with an opening through which 'a charge may pass, a door frame about said opening, a door cooperating with said frame for closing said opening, said door, having an exposed outer metallic casing provided with expansion slots extending" from the face ofsaid door which is adjacent said door frame, a resilient gasketing material, means for mounting said gasketing material for sealing the adiacent surfaces between the edge of said door and said door frame, said gasketing material having a sufficient extent to cover said slots, means for raising and lowering said door including cooperative devices on said door and door frame for moving said door to and from covering position for said opening withv said gasketing material out of contact with said door frame except in extreme door closing position, and for laterally moving said door to or from its extreme closed position whereby to avoid rubbing contact of said material on said door frame.

2. A furnace closure means, preferably for a metal-encased furnace of the type in which a charge is to undergo heat-treatment while enveloped by a controlled gaseous atmosphere, comprising a door having a-face adapted to face the furnace proper, said door having an outer metal casing with an open end at said face and a nonmetallic refractory brick within saidcasing, said casing having spaced expansion-slots extending from said face inward of said door, and a resilient gasketing material secured about the outside .of said casing to cover said slots.

3; A furnace closure means, preferably for a metal-encased furnace of the type in which a charge is to undergo heat-treatment while encasinghaving spaced expansion slots extending from said face inward of said door, and a resilient gasketing material removably secured ,about the outside of said casing to cover said slots, with an overlap extending slightly beyond said face.

4. A furnace closure means, adapted to be used for a metal-encased furnace of the type having vsaid door having an outer metal casing with an open end at said face and a non-metallic refracoccur if one shoe only were used, which would.

for covering and uncovering an opening in sy metal-encased furnace of the type s chamber in which a. charge is to undergo'heettreatment while enveloped by a controlled stmosphere, comprising a door having metal casing having a substantially open end facing said opening and a non-metallic refractory substantially enclosed furnace-chamber having an opening in one wall thereof, a door-frame for said opening and a rnqvable door for covering 15 y said opening, characterized by said door comprising a refractory wall-portion and a metallic portion enclosing at least the side edges of the refractoryv wall-portion, said metallic portion of the door having expansion slots therein extending from the surface thereof which is presented towards the furnace-chamber when the door is inr'its closed position, a gasket-member, and nieans for mounting said gasket-member so that it substantially seals the space between said door and said door-frame when the door is closed, said gasket-member having a sufficient extent to cover said expansion slots.

GERHARD 1". LEssMANN.