|Publication number||US2849222 A|
|Publication date||Aug 26, 1958|
|Filing date||Dec 4, 1956|
|Priority date||Dec 4, 1956|
|Publication number||US 2849222 A, US 2849222A, US-A-2849222, US2849222 A, US2849222A|
|Inventors||Senger Edwin C|
|Original Assignee||Rolock Inc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (5), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Aug. 26, 1958 E. C. SENGER MUFF'LE Filed Dec. 4, 1956 INVENTOR Sdwon a 5 ATTORNEY United States Patent MUFFLE Edwin C. Sanger, Fairfield, Conn., assignor to Rolock,
Incorporated, Fairfield, Conn., a corporation of Connecticut Application December 4, 1956, Serial No. 626,129
9 Claims. (Cl. 263-47) This invention relates to apparatus useful in the heat treating of metal parts whether tray conveyed or ad vanced in running lengths through a heat treating zone and especially concerns apparatus for processing such work at high temperatures in the presence of a special gaseous medium. Where an open furnace is the source of heat it is common to advance the work through a gas isolating passageway or elongate oven that spans the combustion chamber of the furnace and is open at both ends outside of the furnace walls which serve to support the oven near opposite ends thereof. Such passageway form of oven is commonly termed a muffle. The gaseous mediums employed therein may have a high content of hydrogen or nitrogen and must be dependably guarded against escape or leakage into the combustion chamber of the furnace.
Muflies for the above purpose are long hollow structures of tubular nature in various cross sectional shapes and usually comprise a hood section arched over and joined to an underlying hearth section so as to house a long passageway desired to have gas-tight, heat pervious walls. Because of the high temperatures involved and a requirement that the metal walls be as thin as possible in order to promote even and rapid transfer of heat from the furnace to the muffle interior, muffies as heretofore constructed have lacked sufficient tubular rigidity when weakened by heat to resist inward collapse of the roof wallof the hood section and/or sagging of the muffle as a whole in its span that bridges the combustion chamber of the furnace. Further troubles have resulted from the tendency of the mufile' walls to distort and rupture when subjected to stresses and strains of thermal shock caused by feeding cold work into the receiving end of a mufile while the latter is very hot. The cold work contacts and abruptly cools only the hearth section of the muflle on which it rests such cooling being unaccompanied by simultaneous cooling of the hood section of the mufie. There takes place a sudden contraction of the cooled hearth section both in lengthwise and crosswise directions which is strongly opposed by the still hot walls of the hood section. Means have therefore been needed to compensate for a wide and suddenly occurring difierential of discordant expansion and contraction between the different sections of the muflle. I
While it has been proposed to add external ribbing to the mufile walls to reinforce them against collapse or sagging it adds objectionable weight, and such form of reinforcement has been found to weaken unduly through overheating because of its relatively greater mass exposed to the intense heat of the furnace and to increase the occurrence. of cracks and the breaking of seams in the muffle walls. Internal ribbing of the mufile walls can not be resorted to without sacrificing badly needed cross sectional space in the passageway formed by the muflle and this reduces the rate of work output from a rnufile of given tubular girth.
An object of this invention is to utilize new mechanical principles in the construction of muflies enabling the walls I 2,849,222 Patented Aug. 26, 1958 thereof to be made of sufliciently thin sheet metal to facilitate heat transfer therethrough without sacrificing needed tubular stiffness of the muffle, whereby a very long, light weight muffle capable of eficient heat performance is enabled to bridge the high temperature chamber of a heat treating furnace without sagging under its own weight alone or when augmented by the weight of its contained work load.
Another object is to avoid introducing into the structure of a mufile any strengthening reinforcement that will add materially to the muffle weight or harmfully oppose widely unequal extents of expansion and contraction that take place in different sections of the muflle respectively in response to temperature differentials induced as aforesaid.
The foregoing and other objects of the invention will become clear in fuller detail from the following description having reference to the accompanying drawings wherein:
Fig. 1 is a perspective view of a muffle embodying the present improvements removed from the combustion chamber of a heat treating furnace.
Fig. 2 is a view looking at either end of the muffle of Fig. 1.
Fig. 3 is an elevation showing the rnufille partly in longitudinal section on the plane 33 in Fig. 2.
Fig. 4 is a view taken in cross section on the plane 44 in Fig. 3 looking in the direction of the arrows.
Fig. 5 is a view similar to Fig. 4 showing a modified cross sectional shape of mufile.
Fig. 6 shows a modified corner construction of the muffle of Fig. 4.
In Figs. 1 to 4, inclusive, the mufflle comprises an elongate, open ended, oven forming enclosure the main part of whose length comprises merely the assembly of a hearth section 12 and a hood section 13. The present improvements reside partly in features of construction of the walls of these individual sections and partly in the cooperative reaction between the sections when united and spanning the heat chamber of a furnace.
It has been proposed heretofore to fabricate muffies of suificiently thin sectional sheet metal walls to permit an acceptable rate of heat flow from the combustion chamber of the oven through the walls of the mufile to the interior thereof. But such mufiles have lacked the tubularstrength and rigidity required to prevent sagging or rupture in the high temperatures required for many heat treating processes.
The present improvements overcome this and other problems by providing the hearth and hood sections with cooperative patterns of corrugations related so as not only to impart rigidity but also to compensate for the hereinbefore mentioned wide differentials of expansion and contraction between the sections due to powerful discordant forces of expansion and contraction in the mufile walls.
To this end each of the corrugations 14 in hood wall 13 extends throughout the arched shape of the wall crosswise the mufile fully to and terminating at downward directed bottom edges of the hood Wall between points on opposite sides of the latter where the hood wall meets rim portions of the hearth sections 12 comprising parts 16 and 17. Thus corrugations 14 strengthen the ability of hood wall 13 to support its own arched formation crosswise of the muffle without collapsing while imparting to the hood section an ability to stretch lengthwise of the muffle in accordion fashion and thus accommodate expansion and contraction of the hearth wall 12 lengthwise-of the muffle occasioned by temperature changes.
Corrugations 15 extending lengthwise in the floor wall 12 of the hearth section help to stiffen it lengthwise against sagging while at the same time because they are separate from corrugations they can flex to permit mechanical expansion and contraction of the hearth section crosswise of the mufile instead of imposing stresses and strains on the hood section of the muffle tending to flex the arched hood Wall. Such'corrugations 15 in the floor wall 12 of the hearth section are disposed lengthwise of the mufile between the opposite lateral rim portions of the hearth section. They also form upstanding work supporting ridges serving as the sole points of support presented to cold work metal when introduced into the mufile for heat processing, and thus prevent the work from extracting as much heat from the metal of the hearth wall as would be the case if the floor wall 12 were fiat and in surface contact with the work metal over a larger area,
From the foregoing description and in all figures of the drawings it will be seen that the ends of corrugations 14 are in edgewise contact along an undulating course with the upward facing relatively broad substantially plane surfaces of rim portions 17, 23 of hearth section 12, practical and differing cross sectional shapes of which rim portions are shown in Figs. 4 and 6 respectively. In Fig. 4 the sheet metal of the hearth section is bent throughout the length of its marginal portions to extend first upward forming a vertical web 16 rising from floor wall 12 and then laterally inward of the mufl'le to form a shelf-like lip 17 against whose upward facing surface the downward directed edges of the corrugated hood wall 13 abut in the aforesaid undulating cause at a height above the level of the floor wall 12 equal to the vertical extent of web 16. All points of meeting or joinder of the hood wall to the hearth section throughout the length of the muflle may now be welded continuously along the said undulating cause from the outside of the muffle as at 18 to form a gas-tight seal and to unify the hood wall and the hearth section into an elongate tubular structure having the following advantages.
The corrugations 15 in the floor wall 12 of the hearth section reduce the amount of floor surface area with which the work resting on or sliding through the muffle comes in contact. These corrugations in conjunction with the web 16 acting as a diaphragm provide flexibility in the hearth section capable of absorbing expansion and contraction thereof crosswise the muffle without forcefully transmitting distortive forces to the hood wall 13. Corrugations 14 in the hood wall increase its rigidity in directions radial to the arch of the hood wall and thus fortify it against inward or downward collapse without the need of extraneous reinforcement. Cor-rugations 14 further permit accordion-like expansion and contraction of the hood wall lengthwise of the muffle so that it does not forcefully resist longitudinal expansion and contraction of the hearth section.
From the foregoing cooperative functions of the corrugations in the hood wall and in the floor wall of the hood section combined with lateral flexibility of web 16 there results a muffle of minimum weight, high heat permeability and maximum strength against sagging as well as sufficient relief from the distortive effects of heat to impart long life and increased endurance without the rupture and leakage heretofore occurring at sectional joints and elsewhere in the sheet metal walls of muffles as formerly constructed.
At each end of a muffle section constructed as above, there may be appended a terminal or throat section 19. Such throat section may comprise a sheet metal work entrance or discharging passageway 19 whose dome wall has downward directed edges welded to the shelf 17 as are the edges of the hood wall 13 and having its rear edges welded to the forward end of the hood wall. If the height of throat section 19 is less than that'of the hood wall 13, as is shown to be the case in Figs. 1, 2 and 3, the open gap that results will be closed by a crescent shaped vertical plate 20 having its edges welded to both the hood wall and the throat Walls to complete gastight closure therewith,
At extreme ends of hearth wall 12, which project beyond and in outboard relation to the length of hood wall 13, there may be a vertical flange plate 21 bordering the open end of throat section 19 and welded fixedly thereto, plate 21 sometimes containing holes 22 to receive bolts for fastening the flange plate 21 to mating pieces of equipment (not shown).
In Fig. 6 the hearth wall 12 differs from hearth section in Fig. 4 by presenting a shelf-like lip 23 protruding from the web 16 laterally in an outward direction rather than an inward direction otherwise like shelf 17 with respect to the muflle. The hood wall 13 is then welded in edgewise abutting contact with lip 23 in the same manner as with shelf 17 in Fig. 4.
In the differing constructions of Figs. 4 and 6 there is the advantage that the extreme lower and outermost corners 24 of the muffle are entirely free from joints and consist solely of a smooth bend of the sheet metal of the hearth wall 12 wherefore there are no snags, as from welded joints, to become disrupted in handling the muflle nor seams to give way at this very vulnerable point in the construction.
The appended claims are directed to and intended to cover the foregoing and all other equivalents differing from the particular shapes and arrangements of parts herein disclosed which fairly come within a board interpretation of the definitions of the invention a worded in the claims.
1. A muflle having walls highly pervious to heat adapted to bridge a high temperature chamber in a heat treating furnace without sagging, comprising in combination, a channel-shaped sheet metal hearth section including a floor wall and marginal rim portions each presenting a relatively broad substantially plane surface continuous lengthwise of the muflie, and a sheet metal hood wall arched over the width of said hearth section and having corrugations running crosswise of the muffle disposed to form alternate ridges and grooves each following the arch of said hood Wall and extending fully to and terminating at downward directed bottom edges thereof in a manner to impart undulating contour thereto in a line of meeting with said plane surface, said undulating bottom edges being united respectively withsaid plane surface in a manner to form a gas-tight joint therebetween.
2. A mufile as defined in claim 1, together with a hollow throat structure forming a continuation of the passageway through said muffle secured rigidly to both the said hearth section and to the said hood wall including flanges outwardly bordering said continuation of the passageway for anchoring the muffle to mating pieces of equipment.
3. A muflle as defined in claim 1, in which the said marginal rim portions of the said hearth section each comprises a laterally extending shelf-like lip portion having an upward facing relatively broad substantially plane surface extending straight and continuous lengthwise of the muflle spaced above the said floor wall.
4. A muffle as defined in claim 3, in which the said downward directed edges of the said hood wall abut against the said plane surfaces of the said lip portions and are secured fixedly thereto.
5. A muffle as defined in claim 3, in which the said rim portions of the said hearth section each comprises a bent formation of continuous sheet metal of the said hearth section including a flexible web portion rising from the said floor wall and a shelf-like lip portion having an upward facing relatively broad substantially plane surface extending laterally from said web portion inward of the mufl le.
6. A muflle as defined in claim 5, in which the said undulating edges of the said hood wall abut in an undulating course against said plane surfaces .of the said shelflike lip portions respectively and are secured fixedly thereto.
7. A muffle as defined in claim 3, in which the said rim portions of the said hearth section each comprise a bent formation of continuous sheet metal of the said hearth section including a flexible web portion rising from the said floor wall and a shelf-like lip portion having an 5 upward facing relatively broad substantially plane surface extending laterally from said web portion outward of the muffle.
8. A muflie as defined in claim 7, in which the said undulating edges of the said hood wall abut in an un dulating course against said plane surfaces of the said shelf-like lip portions respectively and are secured fixedly thereto.
9. A mufiie having walls highly pervious to heat adapted to bridge a high temperature chamber in a heat treating furnace without sagging, comprising in combination, a channel-shaped sheet metal hearth section including a floor wall having corrugations of continuous linear extent in the sheet metal thereof running lengthwise of the muffle between opposite lateral margins of said floor 10 a gas-tight joint therebetween.
References Cited in the file of this patent UNITED STATES PATENTS 951,556 Bossingham Mar. 8, 1910 1,268,583 Knox June 4, 1918 2,144,374 Hofiman Jan. 17, 1939 2,381,538 Harris Aug. 7, 1945 2,783,987 Gilbert Mar. 5, 1957
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US951556 *||Sep 24, 1909||Mar 8, 1910||John E Bossingham||Annealing-box.|
|US1268583 *||Dec 31, 1917||Jun 4, 1918||Blaw Knox Co||Annealing-pot.|
|US2144374 *||Oct 21, 1937||Jan 17, 1939||American Brake Shoe & Foundry||Carburizing box|
|US2381538 *||Jul 3, 1942||Aug 7, 1945||Harris Henry H||Muffle|
|US2783987 *||Apr 4, 1952||Mar 5, 1957||Hayes Inc C I||Super-hearth construction for heat treatment furnaces|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3744964 *||May 28, 1971||Jul 10, 1973||Texas Instruments Inc||High temperature diffusion tube|
|US4767104 *||Apr 2, 1987||Aug 30, 1988||Honeywell Bull Inc.||Non-precious metal furnace with inert gas firing|
|US7598477 *||Feb 7, 2005||Oct 6, 2009||Guy Smith||Vacuum muffle quench furnace|
|US20060175316 *||Feb 7, 2005||Aug 10, 2006||Guy Smith||Vacuum muffle quench furnace|
|USRE43717 *||Mar 1, 2011||Oct 9, 2012||Saint-Gobain Ceramics & Plastics, Inc.||Interconnecting muffle|
|U.S. Classification||432/249, 266/255|