US2145257A

US2145257A - Muffle

Info

Publication number: US2145257A
Application number: US159481A
Authority: US
Inventors: Henry H Harris
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-08-17
Filing date: 1937-08-17
Publication date: 1939-01-31
Anticipated expiration: 1956-01-31
Also published as: FR842225A; FR842224A; US2145256A

Description

1% 31, 1193. H. H. HARRIS 2914159257 MUFFLE- Filed Aug. 17, 193'? rsom s INVENTOR Henry H. Harm's I ATTORNEYS Patented Jan. 31, 1939 UNITED STATES PATET FFlC Application August 1'7,

22 Claims.

My invention relates to mufiles used in heattreating furnaces, and particularly to a muffle or like container suspended or otherwise disposed within a furnace, the articles to be heat-treated being placed within the muffle or passed therethrough for treatment.

Conventional mufiles are made of cast metal alloy, which renders them both heavy and ex pensive. since weight is a cost factor. It is the main object of my invention to make a light and relatively cheap mufiie, and I accomplish this by making the muffle partly of cast alloy metal and partly of sheet alloy metal, preferably nickelchromium-iron alloy metal or steel adapted to resist heat and corrosion.

Sheet metal heats up and cools down much more quickly than does cast metal, with possible development of strains at and near connections as commonly made between the cast and sheet parts. It is a further object of my invention to provide a muffle of cast and sheet metal, the parts of which are so connected that they will heat up and cool down at a fairly uniform rate, especially at and near the regions where cast and sheet parts are interconnected.

The use of cast muilles involves a long heating up period before the heat is transmitted to the mufiie contents. Mufile walls of sheet metal heat up and cool off at a more rapid rate, and it is a further object of my invention to reduce the time required for muffle operation, and I accomplish this by making the greater part of the muffle area of sheet metal, and using only a relatively small proportion of the cast metal which is needed to give the muffle strength and rigidity.

Further objects of my invention will in part be obvious and in part specifically pointed out hereinbelow in connection with the following description of an illustrative embodiment.

40 In the drawing annexed hereto and made a part hereof,

Fig. 1 is a transverse section through a conventional heat-treating furnace, and showing, also in section, one form of muille constructed according to and embodying my invention, suspended therein;

Fig. 2 is a side elevation of the muffle, partly broken away and partly in section on the line 22 of Fig. 3; and

Fig. 3 is a plan view of the muffle, with parts broken away.

Furnace it) comprises side walls l2, l2 and arched roof Hi, defining chamber l 5 within which muflle i8 is suspended by means of

chains

22, 22, secured to

eyebars

24, 24, anchored in and 1937, Serial No. 159,481

through roof It by means of

nuts

26, 29.

Eyebars

24, 24 are preferably angled with respect to each other to distribute the weight load over roof l4 and better support the mufile weight.

Rails

25, 25 are provided on elevated platforms, 29, 29, within the furnace and extending lengthwise thereof, which rails bear at an angle against the underside of muffle l8 and support part of the weight thereof. Roller rails may be used if desired. I support most of the muffle weight preferably from above, and I am thus enabled to utilize the weight of the muffle and of its contents for holding the sheet portions thereof in a state of extension or semi-rigidity and to thereby dispense with need for braces, stiffeners, and the like, for the sheet metal portions. The drawing illustrates one Way of suspending a muflle within the furnace chamber, but this can be done in various ways.

The wall members of mufile l8 comprise

cast portions

28, 28, and 29, 29, and

sheet portions

39, 32, 32, and 3'! of heat and corrosion resisting alloy metal. Cast

portions

28, 28 form the upper corners of the muffle and are provided with upwardly extending

ears

33, 34 to which the

suspending chains

22, 22 are secured. The

upper corner bars

28, 28 are preferably identical, and are provided with a central depression 3i with the inner edges 36 curving down and inwardly and the outer edges 38 curving out and decidedly in a reverse direction from the depressed middle. In cross-section the curvature near the

edges

36 and 38 of bars 28 is almost semi-circular. Sheet 39 is welded on to the upper convex surfaces of the inner parts 35, 3B, of

bars

28, 28, to form the top wall of the muffle ill. The welding is preferably disposed at and near the edge of sheet num-- ber 39 and a wide overlap between the sheet metal and cast metal is provided as hereinafter referred to.

Cast

portions

29, 29, form the lower corners of the muille. The lower corner bars 29 are preferably identical and have a flat central track portion 58, with the inner and outer edges 99, 69 and l9, 79 respectively of bars 29 curving away therefrom in opposite directions. In cross-section, the curvature near the edges of

corner bars

29, 29 is shallower than the curvature of the upper corner bars 22, 2B.

A pair of

sheets

32, 32 are provided to form the side Walls of the muffle. The upper edge 39, 33 of

sheets

32, 32 is welded to the convex outer surface of the

outer edge portions

38, 38, of the

upper corner bars

28, 28, and the lower edge 35, of

sheet

32, 32, is Welded to the convex outer surface of

inner edge

60, 60, of lower corner bars 29, as seen in Fig. 1. A fourth sheet 3! is provided to form the bottom of the muffle. In connecting bottom sheet 37 to the lower corner bars 29, the edges 62 of sheet 31 are superposed upon and lapped over the convex upper surfaces of the

inner edge portions

10, 10 of corner bars 29, and the welding is done at the extreme margins of edges 62 of sheet 31.

The floor 40 in the muflie is supported by the

lower corner bars

29, 29. Thus corner bars 29 serve not only as a means of attachment for the sheet metal parts but also for supporting the floor upon which the work is supported in turn. In forming the floor 40 a plurality of cross-beams 42 are disposed transversely within the muffle which serve as a support for work supporting tracks 44.

To help support the mufiie weight and keep same from swinging within the furnace, and putting extra strain on the suspending mechanism, as may occur in loading and unloading, I provide

tracks

25, 25, mounted on

platforms

26, 26, which bear against the underside of the flat central track portion 58 of

corners

29, 29. The height of tracks 25 may be adjusted to compensate for variation of muffle weight, according to the work therein. The weight of the floor members and the contents of the mufile serve to put

sheets

32, 32 under tension, and this tension is taken up and absorbed by the curved surface connections terminating at

welds

52, 53. Thus the sheet wall parts 32 remain substantially rigid without reenforcing or bracing. Sheet 36, comprising the muflle roof or hood, and sheet 3'! comprising the muflle bottom are under no particular tension other than their own dead weight, and may permissibly sag centrally, as shown.

The connections between cast and sheet members comprise broad overlaps as shown, and the welded connections are made at and near the edges of the sheet portions with the principal part of the overlap consisting of the sheet resting freely upon and in contact with a convex surfaced part of cast metal. The cast metal edges as 49 are turned in or away so as to face away from the sheet metal and not to contact the sheet, thus avoiding any injury to sheets from sharp edges of cast metal. The marginal parts of the sheets thus heat up and cool off with the rounded cast metal with which they are in contact. Thus the welded joints between the cast metal and sheet metal are relieved from strains caused by uneven heating and cooling rates of thin sheet metal and thicker cast metal as will be readily understood. When an extra-long muffle is desired, I weld together end to end a plurality of sections, as shown at 56.

My improved muffle is much lighter and cheaper than mufiles made entirely of cast alloy, for example. Increased efficiency is secured by materially reducing the time required for the heat treatment operation, the sheet wall portions heating up rapidly and transmitting heat rapidly to the articles being treated. If desired, brace bars 82 may be welded or otherwise secured to the muffle roof, overlying sheet 30, to keep top 30 from spreading or otherwise changing the predetermined arrangement of the parts within the furnace. I heat the interior of furnace i ll by means of conventional heating tubes through openings in furnace walls I2.

I claim:

1. A muffle for use under suspension within heat-treating furnaces comprising curved cast metal upper and lower corner portions, and sheet metal side walls, top and bottom portions, said sheet portions overlying said cast metal portions in broad, rounded overlaps, and welded to said cast portions at the extreme edges of the overlapping sheet portions.

2. A mufile for use in heat-treating f-l""""" comprising a plurality of sheet metal portions forming the side walls and top and bottom of the muffle, means to secure same comprising a plurality of rigid upper and lower corner portions welded to said sheet metal portions, a floor within the mufiie, and means to support same, said means comprising the lower corner portions.

3. A mufile for use under suspension within heat-treating furnaces comprising curved cast metal upper and lower corner portions and sheet steel top, side walls and bottom portions, said sheet metal portions being welded to the cast corner portions and also extending along and around the curved portions of said bars.

4. A muffle as in claim 3 in which the upper cast steel corner portions curve inwardly of the muifie and the sheet portions overlie said curved cast portions.

5. A muffle as in claim 3 in which the edges of the cast portions curve away from the sheets, and the first points of contact between sheet metal and cast metal are removed from the edges of said cast portions.

6. A muffle as in claim 3, in which broad rounded overlaps are provided where the cast and sheet metal portions meet, and the welding is at the extreme edge of the overlapping sheet portion around the curve of the corner bars.

'7. A mufile for use in heat-treating furnaces comprising a plurality of rigid, self-sustaining cast metal portions forming the upper and lower corner portions of the muffle, a semi-rigid sheet metal portion welded to the upper corner portions forming the roof of the muffle, and a second semirigid sheet metal portion welded to the lower corner portions forming the bottom of the muffle, and a pair of semi-rigid sheet metal portions welded to the upper and lower corner portions forming the side walls of the muffle.

8. A mufile as in claim 7 in which the cast metal upper corners are curved, and curve inwardly of the muffle.

9. A muffle as in claim '7, in which the cast metal corner portions are curved, and the upper corner portions curve inwardly of the muffle, and the lower corner portions curve inwardly and outwardly from the furnace.

10. A muffle as in claim '7 in which the cast metal lower corners have a fiat central portion and curved outer edge portions.

11. A muffle as in claim '7 in which the cast metal lower corners have a flat central portion, and curved outer edge portions having reverse curvatures, one of which is within the muffle and the other of which is outside the mufile.

12. A muille as in claim '7, with means to place the sheet metal portions forming the side walls of the muille under tension.

13. In a heat-treating furnace comprising a floor, walls and roof, a muflie comprising a pair of rigid cast metal bars forming the upper corner portions of the muffle, a semi-rigid sheet metal portion welded thereto forming the roof of the muffle, a second pair of rigid cast metal bars forming the lower corner portions of the muffle, a second semi-rigid sheet metal portion welded to said last referred to cast portions forming the bottom of the muffle, a pair of semi-rigid sheet metal portions welded to the upper and lower cast portions forming the side walls of the muiiie, and means to suspend said muffle within the furnace to permit the weight of muffle and contents to place said last referred to semi-rigid sheet metal portions under tension and keep same from buckling.

14. A heat-treating furnace as claimed in claim 13, in which the means to suspend said mufiie comprises ears on said cast upper corner bars secured to chains and eyebars anchored in the roof of the furnace, the chains and eyebars diverging upwardly from the muffle toward the roof.

15. In a heat-treating furnace comprising a floor, walls and roof, at muffle comprising a pair of rigid cast metal bars forming the upper corner portions of the muffle, a semi-rigid sheet metal portion welded thereto forming the roof of the muffle, a second pair of rigid cast metal bars forming the lower corner portion of the muffle, a second semi-rigid sheet metal portion Welded to said last referred to cast bar portions forming the bottom of the muffle, and means to sustain the muffle within the furnace comprising a suspending connection from the roof thereof and a supporting connection from the floor thereof.

16. In a heat-treating furnace comprising a floor, side walls and a roof, a muffle comprising a pair of rigid, self-sustaining cast metal bar portions defining the upper corners of the muflle, a sheet metal portion welded thereto forming the roof of the muffle, a second pair of rigid selfsustaining cast metal bar portions defining the lower corners of the muffle, and a sheet metal portion welded to said lower east bar portions and forming the bottom of the muiiie, a pair of sheet metal portions welded to said upper and lower corner portions forming the side walls of the muffle. means to place said last referred to sheet metal portions under tension comprising a suspending connection of the muffle within the furnace, and a floor within the muffle supported by said second referred to pair of cast metal sheet portions, the weight of the floor and muffle contents serving to keep said side wall sheet metal portions under tension.

17. In a heat-treating furnace comprising a floor, side walls and roof, defining a chamber, a muffle maintained within said chamber, and means to support the weight of the muffle partly from the floor of the furnace and partly from the roof thereof.

18. In a heat treating furnace comprising a floor, side walls and a roof, a mufiie made partly of rigid metal upper and lower corner portions, and partly of flexible sheet metal side walls top and bottom portions, means for suspending the muffle attached to the upper corner portions and means for supporting the muffle bearing against the lower corner portions.

19. In a heat-treating furnace comprising a floor, walls and roof, a mufiie comprising cast metal upper and lower corner portions and top, bottom and side walls sheet metal portions welded to said cast corners, elevated rails within and on the floor of the furnace bearing against the lower east corner portions of the mufile serving to support part of the weight thereof, and ears on the upper cast corner portions secured to chains anchored in the roof of the furnace serving to support the rest of the muflie weight.

20. A heat-treating furnace as in claim 19 in which the muffle is provided with a plurality of cross beams serving as a bed for a floor within the muffle, the beams resting directly on the lower corner portions, and the elevated rails extending longitudinally of the furnace bear directly against the underside of said lower corner portions.

21. A mufiie comprising rigid metal parts at the upper and lower corners and flexible sheet metal roof, wall and bottom parts between and welded to the said rigid metal parts, the bottom sheet and side sheets respectively being welded to opposite faces of the lower corner rigid metal parts.

22. A muffle as in claim 21 for use under suspension within heat treating furnaces in which certain of the cast metal corner bars are curved and curve inwardly of the mufiie and the sheet portions overlie said curved corners and are welded thereto at the extreme edges of the overlapping sheet portions.

HENRY H. HARRIS.