US2527144A - Smelter and method of smelting frit - Google Patents

Description

f 2 Sheets-Sheet 1 1 3 Q flofdzellfeaclw L/'osepk F. L. MEACHAM ETAL SMELTER AND METHOD v0F SMELTING FRIT Oct. 24, 1950 Filed sept. 21, 1949 Patented Oct. v24, 1950 2,527,144 Y SMELTEB. AND METHOD 0F SMELTING FRIT Floran L. Meacham, River Forest, and Joseph H.

Greenberg, Chicago, Ill., assignors to Chicago Vitreous Enamel Product Co., Cicero,y Ill., a corporation of Illinois Application September Z1, 1949, Serial No. 116,886

1 Claim. (C1. isi- 53) This invention relates to-'a smelter and to a method of smelting frit, or similar vitreous material.

In conventional processes for the manufacture of porcelain enamel frit, the raw material is :fed into a smelter, where it is subjected to hot gase" ous products of combustion to melt and smelt the material. The molten material is then discharged from the furnace into a quenching medium, where it breaks up into friable particles that may be ground and further processed for use in porcelain enameling processes. Different types of frit require different melting and smelting conditions as to time and temperature. While this has been recognized in a general way by prior workers in the eld, the design and construction of heretofore used smelters have not, to the best of my knowledge, been particularly suited to the manufacture of the recrystallizing type of porcelain enamel frit. This particular type of frit comes out of the smelter as a clear vitreous material, like glass, but after it has beenv milled and remelted, it recrystallizes to'give an opaque frit. Usually, such a recrystallizing type of porcelain contains zirconium or titanium compounds that are particularly refractory and, therefore, require a higher temperature in the melting and smelting operations, of the order of 2,200 F. and higher.

In accordance with the principles of the presentinvention, a smelter is provided having a hearth for receiving the raw material at one end and provided with a restricted channel leading off laterally through a side wall of the smelter to 'a quenching tank. Burners are arranged at varying elevations for introducing through the side walls of the smelter burning fuel to supply the heat necessary to melt the raw material and smelt the molten material as it flows along the hearth. The smelter is so constructed that the main flow of gaseous products of combustion is lengthwise of the hearth toward the stack end, there the ow is divided and direct flow to the 'stack is controlled by means of a damper, While indirect flow to the stack is possible only by first traversing the return-bend passages extending beneath the hearth. For this latter purpose, the hearth is supported beneath the smelting zone thereof by piers that extend longitudinally of the smelter and dene the aforesaid return-bend passages. Partitions cooperate at the stack vend of the smelter with the piers and withthe walls of the smelter to direct the flue gases from above the hearth, that do not pass through the damperoontrolled central opening tothe stack, rstalong the lateral portions of the return-bend passages for travel back toward the feeding end of the hearth, and then as the flue gases leave the return-bend pass-ages through the middle passages, upwardly into the stack.

By virtue of the construction described, the smelting portion of the hearth is heated by gaseous products of combustion both from above and below, and that portion of the hearth is maintained at any desired temperature by operation of the damper to control the relative volume of combustion gases directed into the return-bend passages beneath the hearth. The actualtenrperature of the molten material on the hearth, at any suitable point therealong, `is determined by the use of an optical pyrometer, or a thermocouple placed at the desired location. Thus, byfproper regulation of the supply of fuel t0 the burners and by regulation of the damper controlling the main ilo-w of gaseous products of combustion from above the hearth to the stack, and indirectly controlling the proportion of gaseous combustion products lead through the return-bend passages beneath the hearth, the melting Aand smelting temperatures on the hearth can be controlled within narrow ranges that are optimum for the particular type of frit being produced..

It is, therefore, an important object of this invention to provide a smelter of novel and improved construction, wherein the hearth on which the raw materials are melted and smelted'can be heated by gaseous products of combustionboth from above and from below, and wherein damper means are provided for contrdlling the proportional volume of combustion gases circulated rbeneath the hearth so asto control within narrow ranges the temperature of the hearth and,there fore, of the material being processed thereon.

It is a -further important object of this invention to provide a smelter for making porcelain enamel frit, and the like, having a hearth divided into a melting and a smelting zone and supported and arranged to provide return-bend ilue passages beneath the smelting zone of the hearth, together with damper means for controlling the main flow of gaseous products of combustion from above the hearth to the stack and thus indirectly controlling the flow of combustion gasesthrough the yreturn-bend flue passages beneath the hearth, whereby the temperature of the hearth and of the material being smelted thereon'may be maintained within narrow, optimum limits: forV best smelting results. n

Other and further important objects of/this invention will become apparent from the following description and appended claim.

the' drawings:

Figure 1 is a longitudinal sectional view, taken substantially along the broken line I-I of Figure 2, illustrating asmelter embodying the principles of my invention;

Figure 2 is a sectional view taken substantially along the broken line II-II of Figure 1; and

Figure 3 is a sectional view taken substantiaily along the line III- IH of Figure 1.

The reference numeral I indicates generally a smelter embodying the principles of my invention and particularly adapted for the preparation of a porcelain enamel frit of the recrystallizing type. As previously explained, such a frit contains high melting point, refractory compounds, such as zirconium or titanium compounds, which require a relatively high temperature during the smelting operation, usually of the order of 2,200 F. and higher. In order to put all of the ingredients into solution during the smelting operation, and also to prevent premature crystallizing out of the more highly refractory compounds contained or formed therein, the temperature must not only be kept relatively high but must be maintained within comparatively narrow limits over all parts of the smelting zone of the hearth as the entire mass of the molten material in the smelting zone, up to the time that the molten material is discharged into a quenching medium.

The smelter I0 is formed with parallel spaced side Walls II and I2, joined at one end by a wall I3, through which raw material, indicated at I4, is fed by means of a screw feed conveyor I5 rotatably mounted axially within a feeding tube I6. The side walls II and I2 are joined at the feeding end of the smelter by an arched top wall I1, and toward the stack end of the smelter by an arched top wall I8 placed on a lower elevation than the wall I1 and connected to said wall I1 by a vertical wall portion I9. The lower, arched top wall I8, at the stack end, cooperates with a raised bottom wall portion (Figure l) to provide a flue 2I opening into the stack (not shown).

The bottom wall of the furnace, indicated generally by the reference numeral 22, is formed with upper surfaces at various elevations. At the feed end of the smelter, the bottom wall 22 abuis the end wall I3 and provides a stepped elevated upper surface 23 for supporting the feed end of a refractory hearth 24. The elevated surface 23 of the bottom wall extends from the end wall I3 for about the distance normally occupied on the hearth above by a mound of rawmaterial, indicated at 25, that is supplied by the feed conveyor. The bottom wall 22, from the elevated wall portion 23, is stepped down to successively lower levels as indicated at 21 and 28, and the` portion of the hearth 24 overlying these bottom wall levels is supported by piers 29 resting upon the lower level 21, and by longitudinally extending piers 39 resting upon the bottom wall level 28. As best shown in Figure 3, there are a plurality of longitudinally extending piers 38, identified by subscript letters as piers 30a and 30h abutting the side walls II and I2, respectively, and intermediate piers 30o, 30d and 30e, all parallel to each other and together providing ue passages 3|, 32, 33 and 34, the arrangement and function of which will be more clearly explained later on.

The hearth 24 extends from the end wall I3 the full width of the interior of the smelter and terminates in spaced relation to the flue 2| at a line indicated by the reference numeral 35, which is also the line at which the supporting piers or 4 abutments 30 also terminate. The hearth 24 is built up of a plurality of refractory bricks, with a raised marginal portion, such as the portions 36 and 31, abutting the side walls Il and I2, respectively, and the raised portion 38 abutting the end wall I3. The hearth 24, as a whole, slopes slightly downwardly from the feed to the stack end thereof, and is provided intermediate its length with inwardly extending shallow Wall poi"- tions 39 and 48 abutting up against the channel side walls 36 and 31, respectively. Said shallow Walls 39 and 40 serve as flow-diverting walls to divert the flow of molten material into a restricted channel having a lengthwise extending section defined by longitudinally extending confining walls 4I ad 42 adjoining said walls 39 and 40, respectively. A continuation of the channeldefining wall 4I extends obliquely as the wall section 43, and then perpendicularly to the side wall I2 as the section 44, which latter section extends into abutting relation to the side wall I2. Similarly, the channel-defining wall 42 is provided with an oblique continuation 45 and with a perpendicular continuation 46, with the latter continuation abutting against the side channel wall 31. Between the channel-defining wall portions 46 and 44, the iiow of molten material is guided into a tap hole 41, which extends through the side wall I2 and discharges into a quenching tank (not shown).

The side walls II and I2 are provided with openings at various elevations, such as the openings 49, 50, 5I and 52 in the side wall II and the openings 53, 54 and 55 in the side wall I2, through which burners, B, extend for the introduction of liquid or gaseous fuel and air into the interior of the smelter. The vertical wall section I9 is provided with two downwardly slanting openings 56 and 56a through which extend burners B directed against the face of the mound of raw material indicated at 25, causing the material on said mound face to melt, as indicated at 25a and flow down in a molten stream 25h that spreads over the hearth 24 for the full width of the hearth between the channel side rails 36 and 31. The portion of the smelter on the feed side of the dividing plane indicated by the dashand-dot line X (Fig. 1) may be considered as the melting zone of the smelter, while that toward the stack side of the dividing plane X maybe considered as the smelting zone of the furnace. The side burners extending through the openings 5I, 52 and 55 direct flaming fuel into the smelting Zone across the molten stream of material owing over the hearth into the restricted chan-- nel defined by the shallow confining walls 4I, 43, 44 and 42, 45 and 46, from the end of which channel the stream is discharged through the tap hole 41 into a quenching medium. Due to the arrangement of burners in the melting zone and ,the higher elevation of the arched top wall lI1 in that zone, there is a more or less swirling action as indicated by the arrows (Figure l), while the flow of combustion gases straightens out somewhat to a generally longitudinal direction, as indicated by the arrows in the smelting zone, due to the lower elevation of the top arched wall I8 over said zone. 4

At Athe stack end ofthe hearth 24, spaced, parallel partitions 51 and 58 extend from the bottom floor level 28 to join the arched top wall,l8 to divide the space between the end of the hearth and the innerface 6D of the wall 2Q into a main gas passage M leading directly into the exhaust flue 2l and two side auxiliary gas passages A and A1 (Figure 2). An abutment arch 6I, supported upon the end of the hearth 24, is positioned in alignment with the partitions 51 and 58 to provide an entrance to the main gas passage M. The arched top wall I8 is slotted, as at 63, adjacent the abutment 6I and on the stack side thereof, in order to provide an entrance for a vertically adjustable damper, or door, E4 for closing the entrance into the main ilue passage M from the smelting zone. The damper 64 extends between the partitions 51 and 58 and lies against the stack side of the partitioning abutment 6 I.

When the damper 64 is open, the gases of combustion above the hearth 24 are free to pass directly through the central opening provided by the partitioning abutment 6| into the main flue provided by the spaced partitions 57 and 58 and thence through the flue 2| to the stack, and will do so, since this is the path of least resistance. By regulating the opening of the damper 6ft, however, the proportion of gases forced to travel under the hearth can be regulated, and in this way the furnace pressure and the under-hearth temperature can be regulated. Also, more of the heat content of the gases of combustion can be utilized and stack temperature kept lower. Thus, When the damper 64 is closed, the entire ilow of gases of combustion from above the hearth is diverted into the return-bend passages 36 beneath the hearth before entering the main gas nue passage M for discharge through the ilue 2| into the stack. By controlling the position of the damper 64, and, therefore, the area of the opening into the main gas passage M, the operator can control the proportional volume of gaseous products of combustion owing through the return-bend passages beneath the hearth, and thus control the temperatures of the hearth and of the molten material flowing thereon.

An optical pyrometer, or other temperature measuring device or devices, may be used to determine the temperature of the molten material either in the iiow of molten material 25a, over the surface of the mound 25 or in the flow of molten material 25h over the smelting zone of the hearth, or at any point in the smelting zone. Thus, for a given composition of frit, the temperature may be maintained within the optimum range by proper control of the various burners and by proper adjustment of the damper 64. Since the flue gases conducted into the returnbend passages below the hearth are almost as hot as they are in the furnace proper, the underside of the hearth is maintained at a temperature almost as high as the upper surface, thereby reducing heat losses through the hearth to a minimum. By regulating the opening of the damper door I64, the proportion of ilue gases forced to travel under the furnace hearth can be regulated, since when the door is opened, the gases will take the path of least resistance and go directly into the main gas space M and thence to the stack, whereas when the door 64 is closed,

the gases will be forced to travel through the auxiliary gas spaces A and A1 into the returnbend passages beneath the hearth. Since the hotter ue gases travel i'lrst through the outer passages 3l and 34 of the return-bend passages, heat losses through the side Walls Il and I2 are somewhat compensated for, with the result that the hearth 24 is maintained at a substantially uniform temperature throughout its width and extent.

It will be understood that modications and variations may be effected without departing from the scope of the novel concepts of the present invention.

We claim as our invention:

A smelter for the making of porcelain enamel frit, comprising a housing having continuous parallel side walls, an end wall, a top wall having a portion at one elevation cooperating with said end and side walls to define a melting zone and having a portion at a lower elevation dening a smelting zone, a refractory hearth extending between said side walls beneath said top wall portions, means for feeding raw material through said end wall onto said hearth in said melting zone, burner openings through said side walls for introducing burning fuel into said melting and smelting zones, said hearth having raised portions dening a channel of less width in said smelting zone leading to one side `wall for discharge of molten material therethrough, said hearth terminating in a free end beyond said channel, a stack for exhaust gases beyond the free end of said hearth, supports under said hearth defining lengthwise extending returnbend flue passages beginning adjacent said stack along said side walls and terminating adjacent said stack toward the median line of said housing, wall partitions cooperating with housing walls to define a central opening above said hearth at the free end thereof leading to said stack and to define lateral openings down to the beginning ends of said flue passages and from the terminating ends of said flue passages upwardly into said stack, and a movable damper for said central opening directly controlling the flow therethrough to said stack and indirectly controlling the ilow to the beginning ends of said flue passages of gaseous products of combustion from said smelting zone.

l FLORAN L. MEACHAM.

JOSEPH H. GREENBERG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 363,292 Howell May 17, 1887 576,734 Ludford et al Feb. 9, 1897 839,220 Speer et al Dec. 25, 1'906

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