US1862906A - Mechanical stirrer - Google Patents

Description

June 14,193.1 y J, PREgEUTHNER 1,862,906

MECHANICAL STI-RRER a y r 26 Ju//L/.s /Qe/eu/ver JNVENTOR.

ATTORNEY.

June 14,- 1.932. J. PRELl-:UTHNER 1,862,906

MECHANICAL STIRRER Filed Nov. 18, 1950 5 Sheets-Sheet 2 .INVENo/e. u B Y A ATTORNEY`- 6 0 nw 2 6 8 l June 14, 1932- J. PREIQEUTHNER MECHANICAL STIRRER 5 Sheets-Sheet Fviled NOV. 18.

' IN VEN TOR. QJ/dum 'A TTORNEY June 14, 1932. l J. PRELEUTHNER 1,862,906

MECHANICAL STIRRER Filed Nov. 18, 1950 5 Sheets-Sheet 4 BY gl/) @J/44403 A TTORNE Y.

June 14, 1932.

J. PRELEUTHNER MECHANICAL STIRRER Filed Nov. 18, 1930 5 Shset-s`Sheet 5 Patented June 14, 1932 UNITED STATES JULIU'S PRELEUTHNER, OF NEW YORK, N. Y.

MECHANICAL STIRRER Application led November 18, 1930. Serial No. 496,442.

This invention relates to improvements in mechanical stirrers of the impeller type, and it is the principal object of my invention to provide a device of this character in which two stirrers are connected or combined to form a unit using a common, upwardly s lanting discharge lip for the material to be stirred provided with indentations and tooth-shaped projections constituting mixing grids :and

causing frequent changes in the directlons of the discharged currents and irregular commotions within the aifected batches of the stirred material to promote intimate and eficient mixing. l

Another object of my invention is the provision of a separate suction tube attached to the bottom of the unit and an intake tube attached to the top of the unit allowing the bringing together of the independent charges supplied to the stirrer through said tubes and their discharge into a ring-shaped space within the stirrer Where they are impinged upon each other and intimately and eiiiciently mixed prior to their nal discharge into the main charge being injected at various levels to permit additional mixing with the main charge by virtue ofthe velocity of the various currents created in the stirrer. y

'A further object of my invention is the provision of a mechanical. stirrer of the above character the impeller disk of which is provided With a plurality of perforations establishing a communication between the channels above and below the impeller to vary the pressures in the charge and thuseliminating-and reducing axial thrusts in the equipment. l

These and other objects and advantages of -my invention will become more fullyvknown as the description thereof proceeds, and will then be specifically defined inthe appended claims.

vIn'the accompanying drawings forming a material part of this disclosure: l

Fig. 1 is a vertical section through a stirrer constructed according to my invention on line A--A of Figure 2. y

Fig. 2 is a top plan view of the stirrer, Figure 1.

`further modification of my invention. l

Fig. 3 is an elevation in axial section of a modified form of the stirrer. y

Figa is a view similar to Figure 3 of another modification.

Fig. 5 is an axial section through the form, 55 Figure 4.

Fig. 6 shows a modified form of the stirrer housing.

Fig. 7 is an elevation in axial section of a Fig. 8 is an elevation in axial section of another modification, the section being taken on line B-B of Figure 9.

Fig. 9 is a top plan view of the stirrer, Figure 8.

Fig. 10 is an elevation in axial section on line C-C of Figure 11.

Fig. 11 is a top plan View of a still further modified form of stirrer.

Fig. 12 shows in elevation and axial section 70 on line D--D of Figure 13 a further modification of my stirrer.

Fig. .13 is a top plan view thereof.

Fig. 14 shows in elevation and axial section another modification of the stirrer.

Fig. 15 is a view similar to Figure 14 of a further modification.

Fig. 16 illustrates in elevation and axial section a stirrer with horizontal cylindrical tanks. v

5F ig. 17 is an elevation in axial section of another modification of the stirrer.

Fig; 18 shows in elevation and axial section a modification of the stirrer having no impeller vanes.

Fig. 19 is a sectional elevation of a modied form of the stirrer, Figure 18.

Fig. 20 shows in sectional elevation a still further modiied form of stirrer.

The drawings are partly diagrammatical. 90 Similar` figures have been used in the drawings to denote similar parts.-

Reerring now Ato the drawings, primarily toFigs. 1 and 2: the Hat, circular part 1 and the cupped part 2, referred to hereinafter as 95 the top and bottom, respectively, jointly constitute the housing or casing'3 enclosing the lens-shaped, single, undivided cavity 4.

' .The cupped bottom 2 has an upwardly slanting discharge lilr, terminating in the 10 by a plurality of vanes or shrouds 10, originating Within the cavity 4 in an imaginary circle 11, for convenience of reference called the intake circle, and terminating near the outer periphery of the housing at the aforementioned discharge slot, the iniddleline of which, representing, approximately, the mean eective discharge, is called hereinafter, for convenience of reference, the discharge circle 12.

The vanes are curved so that the hollow or convex surfaces 13 move towards the charge When the stirrer is rotated, as Will be specified later, the vanes, as it were, shipping or scooping'up the liquid.

The inner terminals 14 of the vanes originate in the aforementioned circle 11, preferably tangentially or approximately tangentially, so as to offer the 'least resistance at the intake edge 15, which, for the same reason should be as sharp as possible. Considering the abrasive effect of the continuous impact of the charge at this edge, it is preferable to select for the intake edge angles of from 39 to 60 degrees, the drawings showing angles of 60 degrees.

The outer terminals 16 terminatefat the discharge slot 9 in radial directions, i. e. the terminals intersect the discharge circle 12 previously referred to under right angles or approximately right angles.

While the outer terminals thus have fixed positions at, or in proximity of the outer pei riphery, the inner terminals 14 originate at distances from the axis of the stirrer housing which depend upon the properties of the charge and upon the rotary speed. For practical and general purposes, covering the usual mixtures in chemical processes, also the mixtures in oil refining processes, the distance of the intake edge from the centre of the stirrer should not be less than one half, or more than four-fifths of the radius of the discharge circle previously referred to. If the distance is less than one-half of the discharge circle, the intake, i. e. the scooped up volume is insufficient, the more insufficient the nearer the. intake edge is to the centre and the 'faster the stirrer is rotated. If the intake edge is further from the centre than four-fifths of the radius of the discharge circle, the impact incident -to scooping up material by the vanes is too sudden for a smooth running of the stirrer, causing shocks, vibrations, and as a consequence, loss of power, quick deterioration and, eventually, breakdowns. In the drawings, the distance previously referred to is, approximately, two-thirds of the radius of the discharge circle.

The most efficient curve for the vanes is the involute, theoretically, but for practical purposes parabolic, circular and other curves of the second and fourth order may be adopted. Circular' curves have been shown in the drawings, throughout. Curves of the indicated kind assure a continuous and constant change of the direction of the flow of the liquid While passing in front of the vanes, thus avoiding shocks and vibrations and the disadvantages incident of the stated irregularities of the motion.

Curves designed in accordance with the specified characteristics assure an intake, practically, without resistance, a shockless flow of liquid while passing in front of the vanes, receiving continuously and constantly increasing impulses to a higher velocity, arriving at the discharge terminals in radial directions where they are hit by the moving vanes at right angles to the direction of the flow, thus receiving the highest impulse possible under given conditions, discharging, as a consequence, with the highest velocity obtainable under given conditions.

The stirrer is rigidly mounted upon a rotatable shaft 17 by any convenient means, for instance, keys, or, as is indicated in Fig. l, by shrinking the housing upon the shaft, for which purposes a boss 18 is provided in the centre of the top 1, previously specified.

The stirrer may be actuated by any convenient means, an electric motor, for instance, power being applied either directlyv or by interposed transmissions which are not indicated in Fig. l, being standardized parts of the equipment not constituting parts of the invention.

The rotation is determined by the curvature of the vanes, as has been pointed out hereinbefore, the arrow 19 indicating how the stirrer should be turned with reference to the vanes.

Referring now again to the drawings;

Fig. 3 is a modification in which the top l is domed and the bottom 2 is flat, the stirrer discharging under a downward slant. The suction tube 7 is supposed to be attached to the intake 6 by the shrinking method, as suggested at 22. Here, as well, as in the drawings throughout, the direction of the inflow is indicated by arrows 20 and of the discharge by arrows 21.

Fig. 4 indicates a modification in which all parts are cast in a unit with the intake tube 7.

Fig. 5 is a modification indicating a-housing composed of two parts rigidly held together by strips 23 and bolts 24, also shown in a plan detail in Fig. (i.

Fig. 7 indicates a modification in which the cupped bottom part 2 of the housing and the suction tube 7 are cast as a unit. The manner of attaching theafore named parts to the tank 27, of which a part of the bottom is only shown, is also indicated by members 25 and bolts 26.A In this modification, as well, as in all previously considered forms, the impeller disk is replaced by the top of the housing. In the present case the top of the housing, which is provided with a plurality of vanes 10, is rigidly attached to the rotatable shaft 17,

constituting the only operable member of the modification, the bottom of the housing, forming in conjunction with the suction tube, what may be called a suction cup, being stationary.- In this modification the parts constituting the stirrer are reduced to a possible minimum; so are also the movable parts, the top of the housing, or to be more correct, the

impeller being the only movable member.

The power needed to operate the present modification is thus also reduced toaJ possible minimum.

Figs. 8 and 9 show the combination of two stirrers in a composite unit, the several pieces, namely the fiat top 1 and the cupped bottom 2 constituting, respectively, the top of an upper or first stirrer housing and the bottom of a lower or second stirrer housing, being rigidly attached to each other and also to cross beams atop the tank by hangers 28, members 29 and bolts 30 and 31. The details of.at taching the aforementioned hangers to crossbeams on top of the tank are not shown in the drawings being known members of tank equipment not constituting parts ofthis invention. The members 29 and 31 are also omitted in Fig. 9.

Between the afore specified parts l and 2' is the shaft mounted. rotatable impeller comprising the impeller disk 32, which in the present instance, constitutes, respectively, the bottom and the top of the afore mentioned first and second stirrer housing. The impeller disk is provided with a plurality of vanes 10. All members of this modification, as previously referred to, constitute two stirrers combined in a single unit, each of these two stirrers conforming in most details to the modification shown in Fig. 7. or in a wider sense to the stirrer shown in Figs. l and 2.

In studying the modification disclosed in Figs. 8 and 9, it may be observed that both, combined stirrers utilize a common, upwardly slanting discharge lip 5 which is a part of the cupped bottom 2, the lip projecting above the level of the discharge which, in the present form is the upper edge 35 of the vanes 10. Impeller type stirrers of known design in which two stirrer units are combined use for each stirrer unit a separate discharge lip. The advantage of a common, slanting discharge lip has been previously pointed out.

The lip 5, in this modification is provided with indentations 36 and teethshaped proing grids. Such grids formed by irregularities in the continuity of the discharge lips or rims, elther of the cupped or of the flat or of both parts constituting the housing may be incorporated inthe lstirrers by manufacturing t e stirrers accordingly, or they-may be attached as separate members as will be specified later and as shown in Figs. 10 and 11.

The modification indicates also a separate suction tube 7 attached to the bottom of the unit by bolts 8, and a suction or intake -tube 42 attached 'to the top of the stirrer unit by bolts 43, both tubes suggesting the intake of portions of the charge by suction from the top and the bottom levels, respectively, also the addition of material during operation directly into the cavity of the stirrer trough the afore specified tube 4t2.l The affected portions of the charge drawn from widely distant parts of the tank or added independently are brought together within the cavities of the two combined stirrer units being discharged primarily into the ring shaped space 89 within the stirrer housing where they are impinged upon each other and intimately and efficiently mixed prior to their final discharge into the main charge, being injected here into various levels promoting additional mixing within the main charge by virtueof the velocity of the currents.

Attention is called here to the particular novel design of combinations in a single operative unit of two impeller type stirrers. Combinations of this type incorporating two stirrers in a unit, but usually specified as a single stirrer are known. They have in common with the present modification a housing comprising a top and a bottom part and an impeller intermediate of the aforementioned two parts of the housing, the impeller comprising a circular disk and, integral thereof, a plurality of vanes. In designs known heretofore, each of the stirrers incorporated in the combination use a separate discharge lip while the present design utilizes for both discharges a common, slanting discharge lip as has been pointed out before. Additionally, in stirrers of known design the vanes terminate in close proximity of the periphery of the housing, while in the present modification the vanes terminate somewhat short of the inner surface of the housing in proximity of the discharge lip, thus leaving a ringshaped space, the aforementioned mixing chamber 89, wherein the respective discharges from the upper and the lower stirrer are impinged upon each other with unreduced velocity, prior to their final discharge into the main charge. In stirrcrs of known design, having vanes terminating at the discharge opening the discharge is direct into the main charge and although the affected portions are mixed with each other and also with the main charge at the discharge opening but outside of the cavity the mixing is considerably less intimate than in the prescnt forms in which first mixing of the diS- charged portions is effected and subsequently the mixing of this mixture with the charge, in the process tank.

This modification indicates also a method of attaching a shaft composed of a steel core 17 and a protecting cover of lead 38, attached, preferably homogeneously, to the core by any convenient method, to the stirrer, in a manner assuring protection of the steel core from contact with corrosive charges, as, for instance, used in oil refining processes. For this purpose, the steel core is exposed at the lo .'er terminal by removing therefrom the lead, and after the steel core is secured in the stirrer body by any suitable method, for instance, by a key 39, the'recess at the lower surface of the impeller disk and the ringshaped gap above the impeller disk are filled with lead by the so-called lead burning process, as is indicated at 40 and 41 in Fig. 8.

The modification shows also perforations in the impeller disk, these perforations 90 establishingT a communication between the chambers above and below the impeller, contributing the occasionally different pressures in the affected portions of the charge, thus eliminating or reducing axial thrusts in the equipment.

In Fig. 9 the relative paths of portions of the liquid while passing from central to peripheral sections within the cavity 4 of the stirrer are indicated by arrows 33 and 34. The arrows 33 suggest the path with reference to the vanes, relatively, the stirrer assumed not to rotate, the particles, however, moving as if the stirrer were in rotation. The arrows 34 show, approximately the actual path, the stirrer supposed to rotate.

Attention is here called to the omission in Fig. 9 of the parts 29, 31, 38, 39, and 42, for simplicity.

Figs. 10 and 11 indicate a modification resembling the one shown in Figs. 8 and 9, all

parts, however, being cast in a single unit.

The modification incorporates also a separate mixing grid 44 provided with indentatioiis 36 and teethshaped projections 37 along the circumference, and the manner of attaching this grid to the top 1 of the housing by bolts 45. The impeller disk 32 shows also pressure equalizing perforations 90.

Figs. 12 and 13 indicate in operable relation the combination of; a stationary suction tube 7 attached by members 46 and 47 to the cone bottom 4'8 of the tank 27, a part of the bottom being shown only, a cupped bottom 2 of the housing rigidly attached to the tank by the partly shown members 49, a rotatable stirrer unit comprising .the top 1 and cast therewith ina unit an impeller comprising a perforated im eller disk 32 and a plurality of double acting vanes 10, a stationary tube 42 provided with a branch tube 50 wherethrough material may be added into the cavity of the stirrer, as indicated by the arrows 5l, a shaft 17 projecting downwardly into the tube 7 and a bearing 52 secured in the tube 7 by braces 53 and bolts or rivets 54, the bearing indicating a method of steadying the impeller shaft in the suction tube 7. The upwardly projecting lip 5 of the stationary, cupped part 2 is provided with indentations 36 and teethshaped projections 37, and a small, ringshaped mixing chamber 89 is indicated in proximity of the slanting discharge lip 5. In operation, the actions of the double vanes of the impeller cause portions of the charge to enter the chambers below and above the impeller, forcing them into the mixing chamber 89 where they are impinged upon each other and finally discharged into the main charge, similar, as has been specified previously, with reference to other modifications. f

Fig. 14 indicates the use of a stirrer unit in the top levels of a charge and the manner how material may be pumped into the cavity of the stirrer from the bottom levels through a stationary suction tube 7 attached by members 46 and 47 to the cone bottom 48 and by members 55 and 56 to the cylindrical shelly of the vertical tank 27, a circular plate rigidly attached to the upper terminal of this tube 7 constituting the stationary flat bottom 2 of the stirrer equipment. The cupped or d omed member 2 provided on the convex inside with a plurality of vanes 10, and rigidly attached to the rotatable shaft 17, said member 2 constituting-in this case the rotatable top of the impeller housing, is mounted coaxially and in operable relation to the said tub-e 7, the methodof deriving power being indicated, diagrammatically, by bevel gears and pulleys 76, 77 and 78, operably mounted upon the crossbeam 60 on to of the tank.

In operation, material Willpbe pumped, primarily, from the low levels of the charge through the suction tube 7 into the cavity of the stirrer and finally ejected therefrom in a slanting direction into the top stratas of the charge, the downwardly slanting, either continuous or irregular discharge lip 5 causing the discharged batches to be expelled in diagonal directions, as indicated by the arrows 21. Considerable heights may be negotiated, the counterpressure of the liquid in the tank assisting and facilitating the lift. ,Fig 15 indicates an equipment comprissecured in the impeller disk,

ingFa unit resembling the modification shown in igs. 12 and 13 namely, a stirrer unit 57 provided with a downwardly slantin discharge lip 5, operably mounted upon t e rotatable shaft 17, in combination with an intake tube 59 attached to the crossbeam 60 on top of the tank 27 by braces 61 and bolts 62, a supply tube 63 controlled by a valve 64 and a hand-wheel 65 connecting a supply tank 66, rigidly mounted upon the aforespecified crossbeams 60, with the intake tube 59 previously specified. This equipment is in co-axial disposition with the lower part of the housing formed by the cupped bottom 2 provided with a suction tube 7 and stationary attached to the bottom 48 of the tank 27.

In operation, portions of the charge entering the stirrer through the tubes 7 and 59 are mixed within the housing and finally discharged into the main charge in directions indicated by the arrows 21.

Fig. 16 indicates a cylindrical tank 67 placed with the axis horizontally, in combination with a horizontally discharging stirrer 68 mounted upon a horizontal shaft 17. The shaft is supported in a known manner, by the brackets 69 of which only one 1s shown and power is derived through pulleys 70. A bent tube 7 attached to the tank 67 by brackets 71 and bolts 72, terminating 1n operable relation to the stirrer 68 indicates how material may be sucked into the stirrer from the lower levels of the charge.

Fig. 17 indicates the co-operative use of two stirrers or impellers rotating in opposite directions, namely, the stirrer 57 rigidly mounted upon the hollow shaft 73, and the impeller 58 rigidly mounted upon the solid shaft 17 which is co-axially disposed to and within the hollow shaft 73. The shafts may be driven in opposite directions byv a system of bevel gears and pulleys 74, 75, 76, 77, 7 8 and 79 which are adequately mounted upon the top of the tank. Each pair of bevel gears is assigned to drive one of the shafts, the

gears 74 and 75, for instance, the hollow shaft- 7 3, the gears being suitably secured to their respective shafts, or instance, by keys.

This modification indicates also a method of steadying the stirrer shafts without the use of the usual bearing brackets which are preferably avoided in the present case, in view of the comparatively considerable height required. The solid shaft 17 rigidly secured in the bevel gear 76 and in the impeller 58 is supported in a bearing 8( conveniently attached in a manner not shown in the drawings to the partly shown cone bottom 48 of the partly shown tank 27 preferably provided with an exchangeable wearing plate 81 of suitable material, and also in a bearing 82 secured within the hollow shaft 73 in any convenient manner, so as not to obstruct entirely the clear opening of said hollow shaft. The hollow shaft 73 is steadied against transverse motions by the antifriction ball race 84, the shaft being rotatably admitted in the central bore ofthe afore mentioned ball race 84 andthe ball race being secured against side motions by the vertical sde of the circular race pan 85 conveniently attached to the top beams 60 of the tank, details of this attachment omitted in the drawings. This hollow shaft 73 is also secured against vertical motions, partly by its own weight and partly by the bevel gear to which it is rigidly attached as previously stated, said gear being held in position, considering an upward motion, by the bevel 74 previously referred to.

'lhe drawings show also a stationary intake tube 59 attached in a suitable manner to the top beams 60 across the tank 27 having a similar object as the tube 59 specified with reference to the modification shown in Fig. 15, namely, the adding of material during operation, either continuously or intermittently, through this tube directly into the cavity vof the stirrer, so as to save time and power otherwise necessary. The tube 59 is provided with a branch tube 50 wherethrough material may'be added as suggested by the arrows 51 and in addition to such material as added through said tubes from the ou'tside, portions of the charge may enter the tube 59 through apertures 87.

Here, as well as in previously specified modifications, the upwardly slanting discharge lip 5, projecting above the discharge level of the combined stirrers 57 and 58 is an outstanding feature assuring ecient mixing. This lip is in the presently discussed modification provided with irregularities, the indentations 36 and the teethshaped projections 37 which contribute to the promotion of numerous irregular currents, in proximity of the discharge from the stirrer.

This modification permits the disposition of the rotatable parts of the equipment in any level of the charge, assuring as well a supply of material within the stirrer from the outside, as from the bottom strata and from the top strat-a of the charge. Material may be added from the outside also through the small tubes 86 and 88, diagrammatically indicated in the drawings, operably terminating at the upper terminals of the intake tube 59 and the hollow shaft 7 3, respectively.

In operation, material entering the stirrer as suggested previously, being either charged from the outside, or drawn into the cavity of e stirrer equipment from the bottom and top strata of the main charge, is mixed, primarily, within the cavity of the stirrer, subsequently discharged with impinging force into the aforespecified mixing chamber 89, wherein intimate mixing takes place, whereupon the mixed batches are discharged and forcibly injected into the main charge where additional mixing is accomplished, not

onl in the neighborhood of the discharge an in the level of the stirrer but, in consideration of the slanting and irregular currents, in all levels and distant portions of the tank.

Considering also that the impellers of the equipment rotate in opposite directions, the portions are impinged upon each other withm the mixing chamber in opposite d1rect1ons, utilizing the velocities imparted to them by the vanes of the stirrer exclusively for mixing, discharge bein accomplished by the radial components on the discharge currents therefore having ra ial directions, not, as 1n stirrers of known design, tangential directions, the latter currents causing Within the main charge an inefficient rotation of the charge in concentric currents.

Fig. 18 indicates a, modilication without vanes, cro-rotation of the liquid within the cavity of the stirrer with the stirrer being promoted by frictional impulses. Stirrers of this type may be advantageously utilized for the production of emulsions. They have to be rotated at higher speeds than stlrrers for mixing purposes and in consideration of the higher speeds required the stirrers have to be balanced more carefully than others. Balancing comprises the tests and the corrections of the stirrers with regard tp an accurate mass distribution around the axis. Balancing ma be accomplished easier and with greater egrees of absolute concentricity if the stirrers are cast without vanes.

Fig. 19 indicates a similar modification having no actual vanes, the cupped bottom 2 provided with a continuous slanting lip 5 projecting above the discharge level which in the present instance is the level of the flat, rotatable top 1, however, is rigidly attached to the partly shown bottom 48 of the process tank by members 25 and bolts 26.

In operation, the rotating top 1 replacing the impeller, causes the co-rotation of the portions of the char e entrained within the cavity of the stirrer housing, discharging the affected portions by virtue of the centrifugal force developed, discharge being accomplished through the ringsha ed discharge slot 9 in directions suggested the arrows 21, replacement of the dlssipate volumes being accomplished by suction from the main charge into the stirrer through the intake opening 6 in directions indicated by arrows'20.

Fig. 20 indicates a modiiication utilizing nozzles or tuyres screwed in the housing or secured in other suitable manner, the nozzles being disposed at the outer periphery of the stirrer, replacing the aforespecified discharge slot 9. The modification shows also a piece of piping used as a suction tube 7 this member being stationary and yrigidly attached to the partly shown bottom 48 of a I tank by braces and bolts 25 and 26.

Nozzles are advantageously utilized for the production of emulsions, the material being discharged from the stirrer into the main charge in line, impinging streams, in a manner similar to the one specified previously.

While the invention has been illustrated in its basic form and in modifications and-va rious applications in what are considered preferable forms, it is pointed out that the examples shown may be additionally variously modified without departing from the spirit of the invention which is not limited to the structures disclosed and which is maintained as long as the novel features shown in the most primitive form in Figs. 1 andy 2 and in more elaborate forms in other illustrations accompanying this specification are incorporated. These improvements may be summ'arized as follows:

stirrer comprising a rotatably shaftmounted housing enclosing a vaned or vaneless, single, undivided, lensshaped cavity, the lensshaped housing composed of a flat and a domed part, a central intake aperture in one of the two parts constituting the housing one of the two parts of the housing replacing the impeller disk, the domed part of the housing provided with a continuous or irregular slanting discharge lip terminating either in or beyond the level of the discharge, the flat part of the housing provided with a continuous or irregular, circular rim, pressure equalizing holes in the imp eller disk or in the impeller disk replacing element, vanes of a special curvature, stationary or co-rotating suction tubes disposed below or superimposing the stirrer housing, the use of said suction tubes as means for charging material directly into the cavity of the stirrer, the cooperatlve use of two stirrers in close proximity of each other, the use of two stirrers in close proximit of each other, so as to rotate in opposite irections, the use of hollow shafting for the transmission of power in stirrer equipment, the use of hollow shafts for charging material therethrough 'into the cavity of the stirrer housing, the use of bearings within members of the equipment for the support of the shaft, the use of horizontally discharging stirrers, the use of bent and inclined suction tubes, the use of a part of the housing as a common discharging element for two or more stirrers in combination, the provision of an internal mixing chamber within said common dischar ng element wherein the batches discharged fgrlom two'stirrers operating in close proximity of each other are mixed prior to their discharge into the main tank, the manner of supporting shafts and hollow shafts without the use of bearing brackets, finally the use of discharge nozzles.

Having thus described my invention what claim as new and desire to secure by Letters Patent is: A

1. A mechanical stirrer comprising two iic stirrer units, a housing for one unit, a dat top for said housing, constituting an impeller disc, and a cup-shaped element, said Hat disc and said cup-shaped part constituting the housing for the second unit, a means` for rotating said disc, a common upwardly slanting discharge lip forming part of said cupshaped element provided with a plurality of indentations for causing frequent changes in the direction of the discharge currents and irregular commotions therein to promote intimate and eicient mixing, means for uniting the units, and separate inlet or suction tubes for each unit. 2. A mechanical stirrer comprising two integrally formed stirrer units, the bottom part of one and the top of the other unit formed by a rotary implement constituting an impeller, a cup-shaped member forming with said impeller one unit housing, a slanting discharge lip on said member projecting above the level of the discharge, common to both stirrer units, said impeller having a plurality of pressure equalizing openings, irregular elements formed on the rim of said disc, a

ring-shaped mixing chamber within said cupshaped member, and separate inlet tubes for said units.

3. A mechanical stirrer comprising two integra-l stirrer units a cup-shaped bottom member for one unit having an upwardly slanting discharge lip common to both units, the bottom of one unit and the top of the other unit formed by an impeller disc having pressure equalizing openings formed therein, a mixing grid attached to the top unit provided with a plurality of teeth forming indentations, and an inlet tube formed with each unit.

Signed at New York, in the county of New York, and State of New York, this 28th day of October, A, D. 1930.

JULIUS PRELEUTHN ER.

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