US 1923815 A
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Description (OCR text may contain errors)
FURNACE Filed Feb. 24, 1931 ATToRwg s Patented Aug. 22, 1933 Frank A. Fahrenwald, Chicago, Ill.
Application February 24, 1931. Serial No. 517,843
This invention relates to roller-hearth furnaces of the type used for heat-treating certain metal articles, such as sheets of steel, brass, etc., and particularly furnaces embodying the structural principle of United States Letters Patent No. 1,791,404, issued February 3, 1931, to the present inventor, which discloses a furnace having non-cooled, hearth-forming roller units with raised sheetsupportin treads producing reentrant outlines to permit interlacing of sheet supporting surfaces, and mounted wholly within and exposed to the full temperature of the furnace chamber by means of two series of rotary driving supports, for instance, stub shafts presented along the inner opposite sides of the chamber; the termination of the hearth units wholly within the heating chamber permitting the elimination of structural complications incident to projecting such units through the furnace walls, and. the freedom of the ends of the units from in-- terference with the walls adapting the units to be assembled with the furnace by passing them through the furnace door and lowering them upon their driving bearings, or disassembled. therefrom, in case of replacement, without cooling down the furnace, by merely raising them from their bearings and passing them out through the furnace door.
The primary object of the invention is to provide new and improved raised tread roller hearth units which, while answering to the condition of replaceability without disturbing the furnace walls or even shutting down a furnace, will not only afford interlaced sheet supporting surfaces guarded against the passing of the forward edge of a sheet down between two rollers, but will afford, in each unit, vertical support that is substantially continuous from tread to tread in the sense that it will prevent articles narrower than the distance between treads from wedging be tween oppositely acting inclined walls of the reentrant portions of the roller, and thus permit narrow articles such as rails, rods and the like to be treated in a furnace primarily designed for sheets; which said units also will provide a roller hearth of lighter weight; one that is more freely open at its ends for the convection of furnace gases through it; and one that is more economical to produce and better safeguarded by its design against internal stresses that cause bulging or other distortion, either at the time of production or at times of taking on or giving oil the high temperature at which the furnace works; and which said units will also be easier to produce with the uniformly thin wall rigid under extreme furnace temperatures, particularly at its bearing points upon its driving supports, and units which will remain more nearly uniform in temperature throughout their walls, as well as more uniform in their influence upon the temperature of wide heat treated objects, such as sheets.
Other objects of the invention willbe apparent from the full disclosure of embodiments selected to illustrate the invention.
In the accompanying drawing 1'. have illustrated certain physical formsin which my inventive idea is embodied. Fig. l is a longitudinal sectional View through a furnace containing my improvements; Fig. 2 is a horizontal sectional view through the furnace shown in Fig. 1; and Fig. 3 is a cross-section of the same furnace.
Such a furnace comprises a pair of spaced side walls 1-1, a floor 2, and roof 3, suitable means of any desired type being employed for generating heat inside the furnace, such for example as gas burners 4 located in suitable apertures 5 formed in the furnace walls at any desired point. Also formed in the side-walls are spaced horizontal apertures 6 in which are located the horizontal rotatable shafts 7 Whose outer ends are journaled in cantilever-bearings 88 located coaxially, one outside the other at unequal distances from the furnace wall. As it passes through the furnace wall each of these shafts comprises a continuous thin wall defining an unobstructed hollow interior, increasing gradu ally in diameter so that the increase in cross-" section may substantially compensate for the weakening effect due to the gradually increasing temperature; and the thin wall of the shaft terminates abruptly at its major diameter to leave a large open and unobstructed end through which its interior space is exposed freely to furnace atmosphere, and by which construction, the only path of heat conduction from the hearth forming units is through these thin walls which, by their outward taper, gradually decrease in total sectional area and thereby impose chokage upon the flow of heat units. These shafts are cause it is easier to make perfect castings that way, and because the cross-sectional area of metal available for the conduction of heat is thereby decreased. These shafts are preferably employed wholly without artificial cooling, which means that it is important to dam up as much as possible of the heat inside the furnace to avoid the occurrence of bearing difficulties. This damming-in is accomplished by restricting the conduction, the convection, and the radiation of heat along this shaft. Conduction is reduced because of the fact that high temperature alloys of the character described generally exhibit a very lim ited specific conductivity for heat, the total conductivity being also reduced as much as possible by constantly decreasing the cross-sectional area of the shaft as the temperature decreases from the interior of the furnace outwardly. Radiation along the interior of such a shaft is practically negligible; and the conveyance of heat along the shaft by movement of hot gases therealong is impeded by employing a suitable packing 9 around the shafts (or otherwise constricting the side openings 6) together with means of some nature for impeding flow of such gases through the bore of the shaft. When the inner ends of the shaft are left open as shown in Fig. 3, the flow of gas therethrough is most easily prevented by plugs 15 in the outer ends thereof, in case the pressure inside the furnace is to be superatmospheric as is oftentimes the case; when the inner end is made without communication with the furnace interior (as shown at 11 in Fig. 2) such plugs may, of course, be omitted. The shafts are retated in any suitable way as by sprockets 12 and chains 13.
The carrying elements or hearth-forming units consist of hollow drums 14 of high-temperature alloy which bridge the furnace chamber but lie wholly within the same and rest at their ends upon the extremities of the shafts 7, one drum between the extremities of each two adjacent shafts. Each of these drums is, according to the present invention, formed with spaced circumferential enlargements l5 alternating with portions 16 of reduced diameter, the enlargements of all rolls being of the same size, and the enlargements of each roll being located opposite the narrow portions of the adjacent rolls. All the rolls are preferably formed exactly alike, being merely shifted in position as necessary to cause each to interfit with its neighbors; and each is made with a continuous thin side wall of substantially uniform thickness throughout in order to diminish casting strains and to reduce thermal stresses in operation, in other words, maintain the walls against buckling, bulging or other forms of distortion, both at the time of production and when alternately attaining and giving up extreme temperatures incident to their use. But while their surfaces are corrugated to insure the structural integrity referred to and provide the necessary reentrant lines to permit the usual interlacing of adjacent hearth units, the rolls are free from internal radial or approximately radial walls, flanges or the like which develop destructive stresses under heat expansion; the grooves are relativel shallow and their salients spaced such distance apart relatively to the depth of the corrugations as will present the side walls of the raised sheet supporting portions at an angle 'of depression relatively to the horizontal which is so largely less than a right angle that the roller surface between the salients sufficiently approaches, in effect, a continuous supporting surface as to admit of passing through the furnace, elements having transverse dimensions less than the distance between sheet supporting treads or salients.
In the design illustrated, assuming the roll to be about thirteen inches in diameter, which is a desirable size for some standard furnaces, the sheet supporting treads or salients of the corrugations would be eight inches on centers and the depth of the grooves two inches. In other words, as illustrated in the drawing forming part of this specification, the depth of the grooves is so much less than the spacing of the treads that the inclined side surfaces of these raised portions lie at about 50 depression from the horizontal. This measures the ratio of lateral thrust to vertical support of an article too narrow to bridge the space between the supporting treads and imposes too small a force to bend the narrow article, besides afl'ording a surface which approaches con tinuity with respect to vertical supporting effect; and two such surfaces extending in opposite directions each at the angle illustrated in the drawing (around 50 depression from the horizontal), while providing a trough-like support, will define an angle of around 86, so that in addition to being a very favorable design as to safeguarding structural integrity under extreme temperatures, there is no tendency of the narrow article, when treated in a furnace primarily designed for sheets, to wedge down into the trough or to receive lateral force sufficient to bend it when opposed by like surfaces acting in the opposite horizontal direction. In this design of hearth. unit, the tread or enlargement 15a at each extreme end of a roller constitutes a roller bearing tread through which the unit is received by the supporting stub shafts '7 and, because of the relatively thin wall with which the unit is constructed, these end treads preferably include internal radial flanges 15?) which may approximately equal the depth of the grooves 14 in dimension, so that said flanges leave a relatively large, unobstructed, 'open end for free convection of gases. This opening may also be said to prevent direct conduction of heat across the end of the unit.
From the foregoing, it will be seen that the present invention contemplates roller hearth units having longitudinally undulating or corrugated continuous thin walls providing raised sheet supporting treads with intervening grooves'having a depth that is small (preferably not more than a fourth) relatively to the distance between treads; so that the raised treads and reentrant portions of the units are free from acute angular changes in direction between their supporting ends, and because of the shallowness of the reentrant portions relatively to the diameters of the units, do not greatly differ in their radial distance from the axis of the unit and thus maintions are more disk-like in form; the wall portions defining the sides of the raised portions are presented at such small angles to the axis of the unit that they afford vertical support to narrow articles resting between the treads and impose low angles of incidence to such articles under lateral thrust; the said walls form the confines of relatively large non-cooled interior spaces free from objectionable obstruction by deep reentrant portions, thereby not only favoring the aforesaid approximate uniformity in temperature throughout the unit but the more nearly uniform influence upon the entire area of the treated sheet; the length of these units is such that they are wholly within the furnace chamber and can be supported without interference with the walls of the furnace by mere gravity engagement with their supports, thus facilitating assembly, disassembly and replacement; the ends of the units preferably stand in unobstructed open communication with the atmosphere of the furnace chamber; and the heat conduction between these ends and their driving supports may be limited to their contacts on major circumferential parts of their thin walls, heat losses being minimized by the long path of travel around the relatively large circumference of the unit. The inner ends of the shafts '7 at one side of the furnace are made cylindrical as shown at 17 and of sufficient length to contact with the terminal enlargements of the two rolls which contact therewith, one of which rolls upon a track which is axially displaced from the track occupied by the other. The shafts at the opposite wall of the furnace are formed with two separate tracks 18, defined between suitable circumferential ridges 19 in order to hold the rolls against longitudinal shifting. These ridges are also formed by casting, and the shafts like the rolls are formed with uniform wall thickness. An easy way to handle these rolls into and out of the furnace is to form the roof 3 with apertures 2525 through which chains or hooks can be lowered to grasp in lifting relation the ends of any roll which is to be removed. A carrier sheet is then sent through the furnace on the remaining rolls, on which the removed roll is rested for removal from the furnace, while a replacement roll is brought to position by the said or another carrier plate, and lowered into position by a reversal of the process. The parts here described exhibit a maximum of lightness and cheapness, they can be made with a minimum of machine work, and the contacting portions since they exhibit merely a rolling contact with each other, exhibit no wear but on the contrary maintain smooth running tracks which if anything are improved rather than injured by particles of dust or scale falling thereon which become rolled to a kind of surface layer.
The invention resides in a roller hearth structure embodying various combinations of the foregoing characteristics as set forth in the sub-joined claims.
It will be understood that many changes of design, appearance, and construction can be made in the elements of my improved furnace and I therefore do not limit myself to details herein shown except as the same are specifically recited in my several claims which I desire may be construed each in accordance with its own limitations and independently of limitations contained in other claims.
Having thus described my invention what I claim is:
1. In a roller hearth furnace, a heating chamber with spaced side confines, rotary supports distributed along the inner surfaces of said confines,
and roller hearth units resting upon said supports; said units having relatively thin continuing walls undulating longitudinally of the units and without internal flanges or radially or approximately radially extending walls and providing raised tread portions alternating with reentrant portions, and the portions of the walls forming the sides of the raised portions being at angles of depression from the horizontal supporting plane of the treads, not exceeding about 50 and the included angle between two such inclined surfaces being not less than about 2. A roller hearth furnace as described in claim 1, in which the supports constitute rollers extending through the furnace walls, having outer ends of reduced diameter through which they are supported, and having inner portions consisting of a thin annular Wall flared to substantially its hearth unit supporting circumference, terminating adjacent the inner surfaces of the furnace walls providing relatively large supporting surfaces for the hearth units and having their enlarged inner ends freely open to the atmosphere of the furnace.
3. As a new article of manufacture, a roller hearth unit comprising a large, hollow, thin walled roller with unobstructed open ends adapted for support, through its external cylindrical surfaces, upon appropriate bearing members and having its said thin wall free from internal flanges or radial or substantial radial walls and longitudinally undulated to provide raised treads alternating with reentrant portions but with the angle of depression forming its reentrant portions not materially greater than 50, and with the portions of the unit which form the sides of the raised portions forming included angles of not less than about 80 and thereby affording a large component of vertical support to a narrow object and small lateral thrust to such an object passing over the unit.
4. As a new article of manufacture, a roller hearth support consisting of a shaft of relatively small diameter adapted to extend through a furnace wall and be received in external bearings, and a relatively short unit-receiving inner end consisting of a thin wall flared from the reduced end to the diameter of a relatively larger unitsupporting surface, said flared end being open to substantially the full diameter of its roll-supporting wall and in unobstructed communication with surrounding atmosphere.
5. A roller hearth support as described in claim 4, in which the enlarged inner end of the support is provided with a plurality of axially aligned roll-receiving grooves whereby it is adapted to receive two parallel rolls axially offset one relatively to the other.
FRANK A. FAHRENWALD.