US2145256A

US2145256A - Muffle

Info

Publication number: US2145256A
Application number: US159480A
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; US2145257A

Description

H. H. HARRIS MUFFLE Filed Aug. 17, 1937 INVENTOR rw WM ow 6 H ATTORNEY-5 Patented Jan. 31, 1939 UNETEB ears FEE

Application August 17,

13 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 heattreated 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 muffle, 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.

It is also well known in heat-treating practice that sheet metal heats up and cools down much more quickly than does cast metal, and it is also an 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 regions where cast and sheet parts are interconnected.

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 In the drawing annexed hereto and made a part hereof,

Figure l is a transverse section through a conventional heat-treating furnace, and showing, also in section, one form of mufile 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; and

Fig. 3 is a plan View of the muflie, with parts broken away. Furnace It comprises side walls l2, l2 and arched roof l4, defining chamber H5 within which muffle I8 is suspended by means of

chains

22, 22, secured to I-bars 24, 2t, anchored in and through roof M by means of

nuts

26, 26.

Eyebers

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

By suspending the muffle preferably from above, 50 I am enabled to utilize the weight of the mufile and of its contents for holding the sheet portions thereof in a state of extension or semirigidity and to thereby dispense with need for braces, stiffeners, and the like, for the sheet metal portions. The drawing illustrates one way 1937, Serial No. 159,480

of suspending a mufile within the furnace chamber, but this can be done in various ways.

The wall members of mufile I8 comprise cast

portions

28, 28 and

sheet portions

30, 32, of heat and corrosion resisting alloy metal. Cast 5

portions

28, 28 form the upper corners of the muflie and are provided with upwardly extending ears 3 3, 34 to which the suspending chains 22,

22 are secured. The

corner bars

28, 28 are preferably identical, and are provided with a central l0 depression 29 with the inner and outer edges curving down and inwardly in a reverse direction from the depressed middle. In cross-section the curvature near the edges of bars 28 is almost semi-circular, and the cars 3 34 are dis posed in the central depression 29. Sheet 30 is welded on to the upper convex surfaces of the

inner parts

36, 36, of bars 23, 28 to form the top wall of the muffle All. A preferably continuous sheet 32 is welded to the convex outer surfaces of the

other side portions

38, 38 of

corner bars

28, 28, and serves in the form shown to form the sides and bottom walls of the mufile.

The floor ill of the muffle is disposed within and supported by the side and bottom wall sheet 32. In forming the floor 40 a plurality of crossbeams 42 are disposed transversely within the muffle. Each beam :12 has a semi-circular notch 44 at the end thereof to receive a tube 48 extending lengthwise of the muffle. Tubes 46 are supported by the sheet wall member 32 and in turn support the cross-bars 52 and floor 40. Thus an extended rounded engagement is provided at $8 between sheet 32 and the outer rounded surfaces of tubes to thereby avoid any possibility of producing a crack or break in the sheet member 32 at the region where it serves to support the floor 40.

The weight of the floor members and the contents of the muflle serves to put sheet 32 under tension, and this tension is taken up and absorbed. by the curved sin-face weld connection 52. Thus the sheet wall parts 32 remain substantially rigid without reenforcing or bracing. Sheet 311, comprising the muffle roof or hood is under no particular tension other than its own 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 55 are turned in 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. To keep the muflle from swinging within the furnace, and putting extra strain on the suspending mechanism, as may occur in loading and unloading, I provide a pin or pins 58 on the underside thereof to be received within a track or channel (not shown) on the furnace floor. The floor 40 preferably contains the work-supporting tracks 40a.

My improved muflle is much lighter and cheaper than mufiies 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.

I claim.

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

2. A muflle as in claim 1 in which the cast steel corner bars curve inwardly of the muffle and the sheet portions overlie said curved cast portions.

3. A muflle as in claim 1 in which the edges of the cast bar portions curve away from the sheets, and the first points of contact between sheet metal and cast metal are removed substantially in from the edges of said cast bar portions.

4. A mufile as in claim 1 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.

5. A mufiie for use in heat-treating furnaces comprising a pair of rigid, self-sustaining cast metal bar portions forming the upper corners of the muflle, a semi-rigid sheet metal portion welded thereto forming the roof of the muffle, and a second semi-rigid sheet metal portion welded to said cast portions and forming the sides and bottom of the muflle.

6. A muflle as in claim 5 in which the cast metal upper corners are curved, and curve inwardly of the muffle.

'7. A muflle for use under suspension within heat-treating furnaces comprising a pair of rigid,

self-sustaining cast metal bar portions forming the upper corners of the muffle, means secured to said cast upper portions whereby the muflle may be supported within a furnace, a semi-rigid sheet metal portion welded to said cast portions and forming the sides and bottom of the muflle, and means to place said second referred to sheet portion under tension.

8. In a heat-treating furnace comprising a floor, walls and roof, a muflle comprising a pair of rigid cast metal bars forming the upper corners of the mufile, a semi-rigid sheet steel portion welded thereto forming the roof of the muflle, a second semi-rigid sheet steel portion welded to said cast portions forming the sides and bottom of the muflle, and means to suspend said muflle within the furnace to permit the weight of muffle and contents to place said second semi-rigid sheet steel portion under tension and keep it from buckling.

9. A muiiie as in claim 8 for use under suspension within heat treating furnaces in which the cast metal corner bars curve inwardly of the muflle and the sheet portions overlie said curved corners and are welded thereto at the extreme edges of the overlapping sheet portions.

10. A heat-treating furnace as claimed in claim 8, in which the means to suspend said muflle comprises ears on said cast corner bars secured to chains and eyebars anchored in the roof of the furnace, the chains and eyebars diverging upwardly from the muflle toward the roof.

11. In a heat-treating furnace comprising a floor, sides and a roof, a muflle comprising a pair of rigid, self-sustaining cast metal bar portions defining the upper corners of the muffle, a sheet metal portion welded thereto forming the roof of the muflle, a second sheet metal portion welded to said cast bar portions and forming the sides and bottom of the muflle, means to place said first referred to sheet metal portion under tension comprising a suspending connection of the muffle within the furnace, a floor within and supported by said second referred to sheet steel portion, the weight of the floor and muflle contents serving to keep said second sheet metal portion under tension.

12. In a heat-treating furnace as claimed in claim 11 wherein the transverse beams have notched ends, and a tube is disposed within said notches, which tube extends lengthwise of the furnace, whereby the second referred to sheet will pass around a curved edge.

13. In a muflle comprising a suspended sheet metal wall and bottom portion, a floor structure within said sheet metal portion and said floor comprising round sectioned parts at its edges, and said floor being supported by said sheet metal portion by engagement thereof with the rounded edge portions.

HENRY H. HARRIS.