US2671654A - Movable hearth muffle furnace - Google Patents

Description

March 9, 1954 F. w. H ORNBRUCH TAL MOVABLE HEARTH MUFFLE FURNACE Filed Jan. 10, 1951 IlI 1.1

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of@ \o LIN INVENTOR. IM w. um By -FMM GMW Patented Mar. 9, 1954 MOVABLE HEARTH MUFFLE FURNACE Frederick W. Hornbruch, Roselle Park, and Frederick C. Schaefer, Westeld, N. J., assignors to American Gas Furnace Company, Elizabeth,

N. J., a corporation of New Jersey Application January 10, 1951, Serial No. 205,254 v 1 Claim. l

'I'he present invention relates to heat treating machines more especially metal treating furnaces and is concerned with improved means for the continuous feeding of workpieces through the heating zone while maintaining the work enveloped in a protecting or processing atmosphere.

To protect or process work duringy the heat treating process it has been the common practice to transport the work on a conveyor through a mufile, and in some cases, to vibrate the muiiie in such a way as to cause the work to be propelled along its surface. 'I'he prior devices were, however, somewhat complicated. and envolved numerous elements to assemble and maintain in good order, and, in the case of the reciprocable muille type of furnace, necessitated moving the entire heavy muiiie including its attached delivery chute and associated oil cascade mechanism, with the result that considerable power was required to operate the machine to feed relatively small workpieces. The present invention undertakes to construct a heat treating machine in which the massive muiie, its delivery chute and cascade mechanisms, thermocouples, treating gas supply tubes and accessory equipment, remain fixed and immovable, and to provide within the mule, a movable hearth along which the workpieces are caused to travel from a loading station exteriorly of the furnace, through the tunnel-like muille, to the delivery chute and quench tank at the exit of the muilie.

In carrying out the aims of the invention we propose to mount a tubular muiiie in a normally fixed position within the heating chamber of a furnace, and to incorporate within the muiiie a relatively movable hearth. The movable hearth member is fashioned with relatively shallow sides, is open at its delivery end, and extends forwardly beyond the forward open end of the stationary mule. 'Ihe extending portion of the hearth slab forms a receiving tray for the work that is to be fed through the muiile. Suitable means are provided, hereinafter to be explained, to effect reciprocatory movement of the hearth slab within the muiile, slowly in one direction and relatively rapidly in the other 'with an abrupt stop at the end of the latter movement, so that work to be treated is advanced step-by-step along the slab from the receiving end to the delivery end.

Other objects-and advantages will be in part indicated in the following description and in part rendered apparent therefrom in connection with the annexed drawings.

To enable others skilled in the art so fully to apprehend the underlying features hereof that they may embody the same in various ways contemplated by this invention, drawings depicting a preferred typical construction have been annexed as a part of this disclosure and, in such drawings, like characters of reference denote corresponding parts throughout all the views, of which:

Figure l of the drawings is a side elevation, partly in section, of a treating furnace embodying the invention.

Fig. 2 is a transverse sectional view taken along line 2-2 of Fig. 1.

Fig. 3 is a transverse sectional view of the muiiie and hearth on an enlarged scale more clearly to illustrate a preferred construction.

Fig. 4 is a longitudinal view, partly in section, of the muiile and hearth.

In the embodiment illustrated, the furnace per se is of the usual construction and comprises a main frame I0, that supports the brick-work Ii which in turn defines and encloses the elongated heating chamber i 2. A series of burners I3 located in the Walls of the furnace are provided to heat the chamber l2. Pyrometer openings and peep openings are also provided as will be understood.

On the floor of the heating chamber spaced supports, e. g. fire-brick blocks i4 are placed in pairs, and across each pair is placed a heat resisting rod or tube I5. The rods extend transversely of the furnace chamber and support at their medial regions, a heat resisting muiile member I6. In the instant embodiment muflie IB is generally tubular having at upper, lower, and side walls, is open at its forward end Ia and extends a short distance from the front wall of the furnace chamber. Other muilie shapes may of course be used. The rear end of the muiiie is closed, except for treating gas tube l'i, and an observation tube i 8, and is formed with an opening in its lower wall that communicates with a delivery chute I9. Chute i9 carries a quenching cascade mechanism 20 and leads to a quench tank 2| indicated in dotted lines. 'I'he chute I9 extends downwardly through an enlarged opening 22 in the lower wall of the furnace, which opening is normally maintained closed to the entrance or escape of gases by a flange piece 23 carried by the chute. With this construction, the muie, while normally stationary, is free to stretch or contract with changes in temperature. Such movements being unrestrained by virtue of the roller-like action of 3 the horizontal bars l5 between the nat underside of the muilie and the fiat tops of the supports I4.

'I'he forward end of the muilie is anchored to the front of the furnace by means of bolts 24 that connect with a furnace mounted ange 25 and a muiile mounted flange 25. Compression springs 21 encircle the bolts and react against the respective flanges to keep the forward end of the mufiie in a normally fixed but yieldable position relative to the forward end of the furnace.

The floor of the muiile I8, is constructed to support a reciprocable hearth slab 30 which extends 'from a point adjacent the delivery opening in the muiiie to a point exteriorly of the furnace beyond the forward end of the mufile. The slab extends substantially the width of the munie and is formed with shallow sides 30a, illustrated more clearly in Fig. 2. 'Ihe receiving end 30h of the slab may be open at its end or closed on three sides as illustrated and functions as a tray, whereas the delivery end is open so that the work may discharge into the chute I9. Where the hearth slab 30 leaves the open end of the muiiie a curtain IGa which may be a flame curtain or an adjustable plate, is provided to prevent ingress of unwanted gases and to permit escape of treating gases.

With reference more particularly to Figs. 3 and 4, it is preferred to support the hearth slab 30 on a plurality of rollers firstly to minimize friction and the power factor envolved in reciprocating the slab, and secondly to minimize wear between relatively moving surfaces, the latter being very pronounced when the parts are hot. The rollers are constructed of heat resisting metal and in the embodiment illustrated comprise a plurality of groups of round rod pieces 20?' arranged on parallel axes extending transversely and at spaced intervals along the mufiie. The rollers of each group are confined against undue creep lengthwise along the muiile by means of restricting lugs 30;* carried by the hearth slab at either side of the groups of rolls, adequate clearances being provided between cooperating lugs to allow the rolls to revolve as needed. Lateral movement of the rolls may be prevented by providing longitudinal channels or depressions iSd in the floor of the muiile, the side walls of which function as curbings for the individual rollers. 1f desired, however. the rollers may be a continuous rod and extend from one side wall o1 the muiiie to the other, in which case the side walls of the muiiie will function to restrain the rods against undue lateral shifting. In the construction disclosed however, relatively large rollers may be employed because the lower portions are submerged in the channels in the munie. The iioor of the hearth slab is not therefore elevated from the floor of the munie an excessive distance.

As the hearth slab is reciprocated, the several groups of rollers revolve forwardly and reversely and support the slab throughout its length in substantially frictionless manner.

The provision of groups of rollers or rods between the hearth slab and muftie constructed and arranged in accordance with this invention embody a floating characteristic in that they freely permit either the hearth or muiiie to elongate and contract in response to temperature changes and take up new positions accordingly, as well as anti-friction bearings between the normally relatively movable elements.

The side of the Aouter and exposed end of the hearth slab is provided with n'xed pairs of outwardly projecting flanges 20c and d disposed at either side of a ball ended lever Il. For aligning purposes and wear compensation adjustable wedges ila are inserted between the ange c and the ball end of the lever ll. Screws 2lb are provided to lock the wedges in adjusted position. The lever 2i may, if desired, be constructed as ayoke to straddle both sides of the hearth slam and is pivoted as at 32, to bearing blocks 23 securely mounted to a cross bar I4. The bar 34 forms part of an auxiliary stand 3l that houses power means for imparting oscillatory movement to the lever 3|. Lever Il is provided with an extension 38 that is urged in one direction about the pivot 32, by an adjustable compression spring 31 and in the opposite direction by a hammer cam I8. The spring 22 is mounted upon a pull rod 39 whose effective length is made adjustable by a wing nut 40. The cam 38 is mounted upon the driven shaft 4| of a power transmission, here indicated as a variable speed transmission 42, and is formed with an ascending portion 38a and an abrupt descending portion 38h. As the cam is revolved counterclockwise, in Fig. l. the lever 36 is caused to move slowly to the left and quickly to the right, at the frequency at which the cam is driven. These movements are transmitted to the hearth slab 30 through the intermediary of lever 3|. In consequence the hearth slab is caused to move quickly forward into the muiiie and slowly out of the muiile. The forward motion of the slab is brought to an abrupt stop by means of a bumpe 50, ilxedly carried by the slab, engaging a pad i mounted to a spring tensioned bumper block 52. The block 52 is slidably mounted upon the top of the auxiliary stand 35 and held against lateral movement by screws 53 operating in slots 54 formed in flanges at its base. The forward end of the abutment block 52 is provided with a screw threaded extension 55. Jam nuts 5S are positioned on the screw at either side of an angle bracket 58 and opposed springs 51, operating between the jam nuts and the angle bracket. tend normally to constrain the abutment block against movement, but operate to absorb the shock when the slab bumper 50 strikes.

The machine operates as follows: the furnace is brought up to the heat required and the workpieces to be treated are placed in a chute-like tray 60 mounted above the leading end 30h of the hearth slab. The power transmission 42 is set in operation and through the linkages and connections mentioned, the hearth slab is caused to reciprocate within the stationary muiiie I6. As the workpieces drop from the tray 60 upon the reciprocating hearth, the forward motion of the latter generates sufficient motion in the workpieces as to cause them to start forward also. However, when the forward motion of the hearth is abruptly stopped by the bumper striking the cushion 5I, the inertia of the workpieces causes them to slide a short distance further relative to the hearth. On the relatively slow rearward movement of the slab the Workplaces are carried bodily therewith and at the end of the next forward movement they are again jolted forward. In this way the work is advanced step-by-step through the heated muille until they are caused to slide forward oil." the delivery end of the slab into the delivery chute and quench medium. The rate of advance of the work along the hearth slab may be varied by regulating the length of the stroke of the slab and the force with which it strikes the bumper l, the speed of rotation of the hammer cam, and the tension of the compression spring 31. By properly coordinating these adjustments with-the unit mass of the workpieces, the lattermay be caused to move along the hearth at the rate best suited to the character of the heat treating process to be carried'out. And inasmuch as only the floor of the muiile is actuated, the smaller mass may be stopped more readily, with less wear and destruction, than is occasioned with other designs in which the entire muiile is reciprocated.

Without further analysis, the foregoing will sofully reveal the gist of this invention that others can, by applying current knowledge, readily adapt it for various utilizations by retaining one or more of the features that, from the standpoint of the prior art, fairly constitute essential characteristics of either the generic or specific aspects of this invention and, therefore, such adaptations should be, and are intended to be, comprehended within the meaning and range of equivalency of the following claim.

' Having thus revealed this invention, we claim as new and desire to secure the following combinations and elements, or equivalents thereof, by Letters Patent of the United States:

In combination, a heat treating furnace having an elongated heating chamber defined by connected upper, lower and end walls, said chamber having Aan entrance opening in one of the end walls thereof and an exit opening in the lowei` wall at the end of the chamber remote from the entrance opening, a relatively stationary tubular muille within the heating chamber of the furnace adapted to surround the work to be treated and to exclude the furnace combustion gases of the chamber from the work, said muffie having its open end portion extending through said entrance opening and a contiguous tubular portion at its other end projecting downwardly through the said exit opening in the lower wall of the heating chamber and providing an exit for the work, means for conducting work to be heat treated through the interior of the relatively fixed tubular muiil'e comprising an elongated movable slab member telescopedA within the tubular muiiie, said slab member having one end portion projecting from the open end of the muiile that extends through the entrance opening of the furnace to receive Work pieces and its other end terminating adjacent the said downwardly extending portion of the muilie, means for imparting lengthwise reciprocating motion to the slab relative to the stationary mufile to cause the Work placed on the slab at the entrance end of the furnace to move along the slab within and relative to the muiile toward the said down- Wardly projecting portion and eventually off the end of the slab into said downwardly projecting portion of the muiile that projects through the exit opening in the furnace Wall, and means for supporting said relatively stationary muie'in spaced relation from the lower wall of the heating chamber comprising a series of non-combustible supports upstanding from the lower wall of the heating chamber, said supports being arranged in spaced pairs lengthwise the chamber and having relatively fiat and coplanar upper surfaces, a roller element across on the tops of each pair of said supports for supporting the weight of the muiiie in a manner affording unconstrained freedom of expansion and contraction thereof in a lengthwise direction incident to changes in furnace temperature.

FREDERICK W. HORNBRUCH. FREDERICK C. SCHAEFER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,011,680 Wall Dec. 12, 1911 1,695,950 Carpenter Dec. 18, 1928 2,021,072 Machlet Nov. 12, 1935 2,447,393 Campion, Sr. Aug. 17, 1948 2,600,401 Gilbert June 17, 1952 2,608,289 Holzworth Aug. 26, 1952

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