US2905452A - Mixer - Google Patents

Description

Sept. 22, 1959 A. I. APPLETONVI MIXER 7 Sheets-Sheet 1 Filed June 28, 1956 lm/entor' ARTHUR LAPPLETON W/W MIXER Filed June 28, 1956 7 Sheets-Sheet 2 Inventor ARTHUR I. APPLETON Sept. 22, 1959 "A. l. APPLETON MIXER Filed June 28, 1956 '7 Sheets-Sheet 3 I nventor ARTHUR I; APPLETON Sept. 22, 1959 A. l. APZPLETON MIXER 7 Sheets-Sheet 4' Filed June 28, 1956 3 PE WWW W TV/ mw Sept. 22, 1959 Filed June 28, 1956 A. l. APPLETON MIXER 7 Sheets-Sheet 6 Inven ARTHUR I. APPLETON Sept. 22, 1959 A. 1. APPLETON MIXER Filed Jun 28, 1956 7 Sheets-Sheet '7 ARTHUR I. APPLETON United States Patent O MIXER Arthur I. Appleton, Northbrook, 111.

Application June 28, 1956, Serial No. 594,574

8 Claims. (Cl. 259-105) This application is a continuation-in-part of my prior application, Serial No. 256,066, filed November 13, 1951, covering a Mixer, now abandoned.

The present invention pertains generally to mixing apparatus and, more specifically, to a novel, power'operated device for mixing various fluid, solid and pulverous materials. It finds particular, but by no means exclusive, utility when embodied in a household appliance for mixing foods. The invention is, however, adapted to serve with equal facility in commercial or industrial applications for mixing other substances as well as foods.

One object of the present invention is to provide a power driven mixer particularly well adapted for household use, being susceptible of operation with far greater ease and convenience than mixers of the type heretofore known, and also being substantially spatter-proof when operating.

Another object is to provide a mixer of the character set forth and wherein the members which contact the mix can be assembled, disassembled and cleaned with exceptional ease and rapidity. A related object is to provide a mixer having mixing elements constructed so as to avoid entrapment of material on the surfaces of such elements.

A further object is to provide a mixer having power driven counter-rotating impellers which together sweep the maximum usable volume of the mixing bowl and provide a better, faster mixing action.

Still another object is to provide an appliance of the foregoing type having a particularly attractive appearance and which, when idle, will be completely closed so as to eliminate the necessity for a plastic dust cover.

Other objects and advantages will become apparent as the following description proceeds, taken in connection with the accompanying drawings, in which:

Figure 1 is a perspective view of an illustrative mixer embodying the present invention;

Fig. 2 is an enlarged, vertical sectional view taken through the longitudinal medial plane 22 of the mixer shown in Fig. 1;

Fig. 3 is an enlarged, vertical sectional view taken through the plane of lines 33 of Fig. 1;

Fig. 4 is a fragmentary plan view of the mixer as shown in Fig. l, certain portions of the casing being broken away to illustrate internal details;

Fig. 5 is an enlarged, horizontal sectional view taken through the plane of lines 5-5 of Fig. 2;

Fig. 6 is an enlarged, vertical sectional view taken through the plane of lines 6-6 of Fig. 2;

Fig. 7 is an enlarged, fragmentary, horizontal sectional view through the plane of lines 77 of Fig. 2, and illustrating the planetary gear drive;

Fig. 8 is an enlarged, exploded perspective view of the power head and beater coupling arrangement embodied in the mixer of Fig. 2;

Figs. 9-12 are sectional views taken through the planes of lines 9-9, 10--10, 11--11, and 12- 12 respectively, of Fig. 8;

Patented Sept. 22, 1959 Fig. 13 is an end elevation showing an alternative form of beaters or impellers for use in the mixer shown in Fig. 1;

Fig. 14 is an enlarged fragmentary vertical sectional view through the power head of the mixer, modified to illustrate an alternative form of the impeller drive connection;

Fig. 15 is a horizontal sectional view taken in the plane of lines 15--15 in Fig. 14;

Fig. 16 is a diagrammatic view showing the impellers of Fig. 13 in horizontal section and just prior to passing each other, such view being taken in the plane of lines 16-16 of Fig. 13;

Fig. 17 is an enlarged plan view of the upper impeller, per se, of the assembly shown in Fig. 13;

Fig. 18 is an enlarged end elevation of the upper impeller;

, Fig. 19 is an enlarged, fragmentary perspective view illustrating the drive connection of t is upper impeller;

Fig. 20 is an enlarged end elevation of the lower impeller, per se, of the assembly shown in Fig. 13;

Fig. 21 is an enlarged plan view of this lower impeller; and

Fig. 22 is an enlarged, fragmentary perspective for illustrating the drive connechon of this lower impeller.

While the invention is susceptible of various modifications and alternative constructions, an illustrative embodiment has been shown in the drawings and will be described below in considerable detail. it should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.

GENERAL ORGANIZATION Referring more specifically to the drawings, the invention is there exemplified in a novel mixing device which, in this instance, is a household food mixer 30. In general, the mixer 30 comprises a base 31 having an upstanding power head 32, a mixing bowl 34 which telescopes over the power head, and a pair of counterrotating impellers 35, 36 drivingly supported from the power head 32. For purposes of description, the impeller 35 will be referred to herein as the upper impeller while the impeller 36 will be called the lower impeller. (See Fig. 3.) The bowl 34 is equipped with a cover 38, which may be of transparent material, having a center handle 39.

The base 31 of the illustrative mixer 30 is assembled upon a bed 40 (Fig. 2) having feet of rubber or similar material to prevent sliding of the mixer on the counter, table top, or other horizontal surface which supports it. The bed 40 is surmounted by a hood or casing with sloping side walls extending upwardly from a peripheral flange 41 and curving gracefully into a top wall. The casing may, for example, be of stamped sheet metal, cast light metal, or molded plastic material, securely fastened to the bed 40. The side walls of the casing may also have external embossments or ribs to serve as stiffeners and enhance its appearance.

The mixing bowl 34 in its preferred form, has a substantially annular shape and may be constructed from a wide variety of materials including aluminum, stainless steel and glass. In the present instance, the bowl 34 comprises a dished or concave bottom 42 merging into an outer side wall 43 which has a slight outward and upward taper, terminating in a peripheral rim adapted to register with the rim of the cover 33. The bowl bottom 42 also merges with a hollow central boss 44, flared out at its base and tapered toward its upper or free end which is situated other twice per relative revolution.

3 at or near the top of the bowl 34. The internal contour of the boss 44 is complementary with the exterior contour of the power head 32. These parts are so proportioned that the bowl boss can be centered on, and telescoped over, the power head 32 with the bottom of the bowl resting upon the top of the base casing 31.

Turning next to the counter-rotating impellers 35, 36, it will be perceived that the same have been constructed and arranged to sweep the entire normally usable volume of the mixing bowl 34. By normally usable volume is meant the maximum volume at which a user would ordinarily fill the bowl while still permitting the same to be handled conveniently and without likelihood of spillage. By the same token, the impellers 35, 36 have been constructed and arranged to sweep exceptionally close to substantially the entire inside wall surface of the bowl 34 included within the normally usable volume of the same.

This avoids the building up of accumulations of unmixed j or poorly mixed substances on the bowl walls and insures a maximum yield of properly mixed materials from the bowl.

In the present instance, the top impeller 35 is driven in a clockwise direction (as viewed from the top in Fig. 4-)

wise direction (also as viewed from the top). Since each impeller is formed with a pair of diametrically opposed portions, this means that each impeller sweeps past the While it is possible to operate the impellers 35, 36 at various individual rotational speeds, it has been found desirable to proportion each impeller and to select its driving speed so that the opposed bowl reactions or bowl drags due to the counterrotation of the impellers will balance out approximately, thus avoiding a tendency toward rotation of the bowl 34 about the power head 32. This balanced condition can readily be determined in the laboratory by loading the bowl with extremely heavy or viscous materials and by varying the individual speeds of the impellers until the bowl no longer tends to turn. An unbalanced bowl reaction may, of course, be dealt with by the straightforward expedient of utilizing a keyed or splined connection between the hollow bowl boss 44 and the power head 32.

The power head 32 includes concentrically mounted and counter-rotating impeller drive shafts 45, 46 powered by a motor 47 mounted within the interior of the mixer .base 31 and coupled to the concentric shafts by means of a transmission disposed within a gear housing, 48.

To complete the description of the general organization and arrangement, beneath the annular mixing bowl 34 for heating the contents, and on the top of the mixer base 31 is an annular heating element 49 supported by a saucer-like pan or baffle plate 50 mounted upon a plurality of insulating buttons spacing the baffle plate 50 from the mixer base. The heating element is connected by means of a power cord to a source of electric current, and may be regulated by means of a switch 51 controlling a rheostat or the like, as shown in Fig. 1 carried on the top of the mixer base.

Impeller construction Turning first to the construction of the impellers shown in Figs. 2 through 12, two individual impellers 35, 36 are employed.

These individual impellers together make up an assembly including the top impeller 35, which comprises a central hub 52 (Figs. 2, 4 and 8) with a substantially flat beater drive shaft 45 of the power head 32. In the illustrative form of drive shown, these inclined or helical driving lands 57 are angled to slope upwardly in the direction of beater rotation. They, in combination with the slots 56 in the opening through the impeller hub, constitute not only a toothed drive to turn the impeller, but additionally obtain the result of positively locking the impeller to the drive shaft while the shaft is rotating. When the drive shaft is stopped, the impeller may easily be removed by lifting the impeller directly, giving it a slight twist in the direction of rotation to separate the elements, or by'lifting the bowl, as an incident to which the impellers are lifted off the drive shafts.

The lower or bottom impeller 36 is coupled to be driven to the outer impeller drive shaft 46 of the power head 32 in a like fashion. In this case, a sleeve or bushing 59 is mounted on the upper end of this inner drive shaft, presenting helical or inclined lands 6t) on .the peripheral surface, seated within slots 61 formed in the side wall of a substantially central opening 62 machined in the hub 63 of this bottom impeller. Again, the lands 60 slope upwardly in the direction of beater rotation, being of the opposite hand to the lands 57 driving the top beater 35 since the beaters or impellers counterrotate.

For convenience in fastening the bushings 58, 59 on the impeller drive shafts 45, 46 respectively, the upper ends of these shafts are formed square and are received within substantially square openings 64, 65 in the upper and lower bushings 58, 59 respectively, although it will be understood that this particular arrangement may be modified if found desirable. To hold the said upper and lower bushings in place, a cap screw 66 may be employed, threaded into the inner shaft 45 and thus holding the bushings in permanent assembled relation.

It will also be observed that the upper sleeve or bushing 58 when in place on the inner drive shaft 45 serves as a pilot to guide the inner or lower impeller 36 toward toothed engagement with the driving element therefor presented by the lower bushing 59 on the outer impeller drive shaft 46. This pilot effect facilitates placing the lower impeller properly located and in driving relation on the outer drive shaft.

Afl'lXCl to, and preferably integral with the opposed outwardly extending arms of the top impeller 35,.arc drooping blade portions 67, 68 bent to depend in substantially straight relation with the outer side wall of the mixing bowl, the leading edge 6? of the depending portion being substantially straight and located spaced but a short distance throughout its length from the inside of the bowl side wall, while the trailing edge 70 is spaced a larger distance to pitch the blade for deflecting material inwardly.

The lower ends of the depending blades 67, 63 of this upper or top impeller 35, curve inwardly slightly generally following the curvature of the dished bowl bottom.

The lower or bottom impeller 36 nests with the upper impeller and is supported for driving relation by the outer drive shaft 46 of the power head 32 centrally disposed within the mixing bowl. This bottom impeller, has a central hub 63 of substantially cylindrical shape within which the slotted opening 62 constituting one element of the toothed drive is fashioned. Extending downwardly from the under face of this central hub 63, and fixed integrally throughout are a pair of diametrically opposed arms 71 each defining an inner blade 72 (Fig. 2) which merges into a bottom blade 73. As shown in Figs. 2 and 4, the inner and bottom blades are slightly curved to conform to the tapered central boss of the mixing bowl in the case of the inner blades, for increased mixing efficiency, in the case of the bottom blades for the latter reason alone. Thus the inner blades are adapted to nest closely along the central boss of the bowl.

This lower impeller 36 also has, in the illustrative form shown in Fig. 2, a section adapted to sweep through the intermediate portion of the contents within the bowl. Accordingly, each of the opposed inner blades 72 of the lower impeller carries a pair of outwardly extending and downwardly curving impeller elements 74, 75 spaced uniformly apart and joining the bottom blades 73 adjacent the ends. These impeller elements may be constructed of fiat rigid strips of the same material from which the blades themselves are fashioned, brazed or otherwise secured in place on the inner impeller, to occupy an intermediate position in the bowl cross-section. In one sense, the impeller elements 74, 75 may be said to pass between the inner blades of the lower impeller 36 and the downwardly depending and outer blades or blade sections 67, 68 of the top impeller 35. Thus upon counter-rotation of the upper and lower impellers, it will be perceived that the upper impeller tends to deflect material inwardly as the result of the slight pitch of the depending blade sections, while the lower impeller tends to deflect material outwardly from the tapered central boss of the mixing bowl, and as well upwardly from the bottom of the bowl, this same lower impeller also carrying the impeller elements for sweeping through, agitating and mixing the contents in the intermediate sections of the bowl. The counter-rotating impellers pass with respect to the other setting up a plurality of currents in the mix, including some towards the center of the bowl, some away from the center of the bowl, some towards the bottom of the bowl and some away from the bottom of the bowl.

While the impeller assembly just described has been found satisfactory and rapid in the mixing action produced, an alternative form of impeller array or assembly is shown in Figs. 13-22. In this form of the impeller assembly, in place of having the helical camming lands and slots forming a coupling and driving connection between the concentrically disposed shafts of the power head and the impellers, a construction is employed utilizing substantially square driving sections at the upper end of the concentrically disposed power shafts and substantially square openings cut within the central hub portions of the impellers and adapted to be received on the power shafts upper end portions.

Referring to the aforementioned Figs. 13-22, starting with the top impeller 35, it will be noted that the same comprises a central hub 80 with a relatively flat but substantially convex top contour 81 and a flat bottom face 82. Fixed to, and preferably integral with the hub 80 are a pair of outwardly extending, diametrically opposed arms 84. In this instance, the arms 84 droop downwardly from the hub 80 but initially remain well clear of the bottom impeller 36' to avoid the possibility of pinching the fingers of an inadvertent user. Eventually, the arms 84 terminate in an inner blade 85 and an outer blade 86, connected as by means of a top or cross blade 87. The depending ends 88 of the blades 86 curve radially inward, generally following the curvature of the dished bowl bottom.

The bottom impeller 36', on the other hand, comprises a central hub 89 of substantially cylindrical form and having flat top and bottom faces 90, 91 respectively. Extending downwardly from the lower face 91 of the hub 89, and fixed integrally thereto, are a pair of diametrically opposed arms 92 each defining an inner blade 93, a bottom blade 94 and a reversely bent outer blade 95. The inner blades 93 are adapted to nest closely along the tapered central boss of the mixing bowl and are adapted to pass between the boss and the inner blades 85 of the top impeller 35 upon relative rotation of the impellers. By the same token, the outer blades 95 of the bottom impeller occupy an intermediate position in the bowl cross-section and pass between the inner and outer blades 85, 86 of the top impeller 35' upon relative rotation of the impellers. The bottom blades 94 at the same time pass between the depending ends of the inner "6 blades and the dished bottom surface of the mixing bowl.

Provision is made in the construction of the impellers '35, 36 for facilitating mixing action by setting up a plurality of opposing currents in the mix. Referring in particular to Fig. 16 it will be perceived that each outer blade 86 of the top impeller 35 is pitched so that it will tend to deflect material inwardly as the impeller moves in a clockwise direction. The same is also true of the inner blades 85 of the top impeller 35'. On the other hand, the cross blades 87 of the top impeller are pitched to deflect material downwardly towards the bottom of the bowl. The inner and outer blades 93 and of the bottom impeller 36' are pitched so as to deflect material outwardly as the bottom impeller rotates in a counter-clockwise direction, while the bottom blade 94 is pitched to deflect material upwardly away from the bottom of the bowl.

In view of the foregoing arrangement, it will be appreciated that there will be an impact between deflected material each time the blades of one impeller pass those of the other. Thus material deflected inwardly by the blades 85 will be opposed by material deflected outwardly by the blades 93. Similarly, material deflected inwardly by the blades 86 will be opposed by material deflected outwardly by the blades 95. In like manner, the material deflected upwardly by the bottom blades 94 will be opposed by material deflected downwardly by the cross blades 87. The substantial number of such material impacts per unit time resulting from counterrotation of the impellers 35', 36' results in an extremely rapid and thorough mixing action. Such action is further enhanced in the present instance by fashioning each of the blades 85, 86, 87, 93, 94 and 95 with a sort of reverse airfoil section with respect to its direction of movement. As clearly indicated in Fig. 16, the leading edge of each blade is of substantially knife-edged cross-section while the trailing edge portion of each blade has a rather bulbous cross-section. This creates increased turbulence behind the blade as it moves through the mix.

For the purpose of avoiding spattering of mixed materials which mibht otherwise result from the mixing impacts just described, an ingenious arrangement is built into the impellers 35, 36. This is accomplished by giving the upright blades of each impeller a moderate amount of rake with respect to their direction of movement (Fig. 13). In other words, the upright impeller blades are given a trailing posture or attitude so that their lower ends trail substantially behind their upper ends. By reason of such arrangement, the impacts between the oppositely deflected increments of the material are stretched out over a longer period of time and are applied to a smaller instantaneous area. In addition, the material deflected by each one of the blades 85, 86, 93, 95 is given a slight downward component, while that deflected by the cross blades 87 is given a still greater downward movement. These results may easily be appreciated upon reference to Fig. 13 which shows the impellers 35', 36 in passing position. Due to their rake or trailing posture, the blades pass each other in sort of a progressive, scissoring action rather than passing along their entire lengths at the same instant. Moreover, the angular offset resulting from the raked disposition of the blades will cause the outermost pairs of blades 86, 95 to commence passing ahead of the innermost pairs 85, 93. This means that the impacts of deflected material from each pair of opposed blades 85, 93, on the one hand, and 86, 95 on the other hand, start at different times near the top of the mix and then work downwardly without splashing. Any tendency toward splashing is further minimized due to the downward deflection produced by the upwardly and forwardly inclined attitude of the horizontal blades 87 of the top impeller 35 and which are located at or near the top of the mix.

For completeness in description, reference is here made 7 to Fig. 14 where an illustration appears of the drive between the impellers 35', 36' of Figs. l322 and the power head counter-rotating impeller drive shafts 45', 46'. In this case, these concentric drive shafts are journailed and mounted to make up the centrally disposed power head 32 about which the annular mixing bowl may be supported, with the imepllers depending into the contents of the bowl. Each impeller drive shaft is fashioned with a short square upper section 45", 46" adapted to fit into with some considerable play, the square openings 35", 36" machined in the central hubs of the impellers 35', 36', respectively.

Power head and transmission The outside shaft 46, on the other hand, is journalled within a centering cone 96 which may be built up out of plastic, metal, or hard rubber material, and has a tapered stepped section 96 towards the lower end, externally threaded for securing within the upper end of a gear housing 48 or the like enclosing the impeller drive shafts transmission or gear drive assembly.

The taper of the centering cone 96 is preferably complemental to that of the inside of the mixing bowl boss, so that the cone is adapted to serve as a centering means for the bowl. The upper ends of the drive shafts 45, 46 are each provided, as has hereinbefore been described in detail, such that the impellers may be instantaneously detached from these drive shafts, either individually or as an incident to lifting the bowl off the mixer base. The arrangement also serves to enable the impellers to be connected to their drive shafts with utmost ease and speed.

In the present instance, the outer drive shaft 46 is turned directly by the motor 47, and by means of a planetary drive means contained within the housing 48,

counter-rotation is imparted therefrom to the inside shaft 45. The outside shaft 46, thus is journalled within the centering cone 96, and is connected by means such as threads or the like, at its lower end, with a sleeve 99 machined to receive a worm wheel 100. This sleeve 99 at its very lower end is milled with outwardly extending gear teeth forming a sun gear 101. The outer concentric shaft 46, sleeve, worm wheel and sun gear assembly, nest within a planetary gear array 102, the downward thrust on the shaft 46 being taken up as by means of a lower gear disc 103 supported within an internal ring gear housing 104 pinned (as by a pin 105) to the inner impeller drive shaft 45. The internal ring gear housing 104 is constructed to present a lower stepped section, seating within a recess 106 formed in the housing cover 107 closing the transmission or drive gear housing 48. The shoulders 108 presented by the lower stepped bearing surrounding the inner drive shaft 45, serve to take up downward thrust on this shaft, bearing against a horizontal annular bearing seat 109 provided laterally of the recess 106 within the housing cover.

The sun gear 101 drives, as shown in Fig. 7, the assembly of planet gears 102, which through the internal ring gear housing 104 imparts rotation in a counterdirection to that of the sun gear, to the inner impeller drive shaft 45. Speed reduction of this inner shaft is also effected by the transmission shown in the drawings, the particular speed ratio being somewhat a matter of choice as hereinbefore described.

It has been found relatively simple with this transmission to obtain improved mixing action with the counter-rotating beaters by selecting a speed ratio at which the points where the oppositely moving heaters pass, constantly rotate but slowly about the power head; If the speed ratio between the outer and inner impeller drive shafts is a whole number, the points at which the blades-pass will remain. stationary within the mixing bowl. If on the other hand, the speed ratio is some fractional number, these points will move constantly about the power head in one direction or the other, depending upon the particular speed ratio. It has been found that a slow rate of travel of these points uniformly in one direction produces an improved mixing action.

Counter-rotation. of the shafts 45, 46 is effected by means of the worm wheel, sun gear and planetary gear drive contained within the transmission housing 48. In the present instance the worm wheel is driven by means of. a worm gear 110 carried by a motor shaftv 111 powered by the motor 47 supported within the interior of the base 31 of the mixer.

Referring to Figs. 5 and 6 more particularly, in the present instance the motor 47 is fastened, as by'bolts 112, to a mounting bracket which is affixed to the bed 40. The worm and worm gear comprise a primary speed reduction means and may be encased within the transmission housing 48 and the motor housing 113, which latter housing may be cast or otherwise formed as a part separate from the transmission housing 48, or made integrally therewith. In either event, the transmission housing 48 is fastened as by means of bolts 115 through feet 116, to the bed 40, to provide a firm and stable structure for mounting the power head and the motor within the base 31 of the mixer. Within the motor housing 113, the motor 47 is mounted for rotation, commonly an electric drive motor of the Universal type, and is equipped with a cooling fan 118 at the motor shaft end remote from the worm gear 110. The motor housing has openings such as 119 for the passage of air through and by the motor windings. The motor fan 118, thus causes a constant movement of air through the interior of the mixer base 31, this constant movement or circulation of air having for a first purpose, the cooling of the motor 47.

For driving the impellers 35, 36 at selectively variable speeds corresponding to the requirements for the substances being mixed in the bowl 34, the motor 47 may be equipped with an adjustable governor 125. While the present invention is not particularly concerned with the details of the governor, it might be noted that, in this instance, the governor is constructed as a component part of the motor assembly and is provided with an upstanding adjusting stem 126 terminating at its upper end in a speed control dial, which is actually a calibrated manual adjusting dial 128. To preclude spilled material from entering the casing via the opening through which the adjusting stem 126 extends, the top wall of the casing has an embossment or raised island 129 formed therein and disposed in underlying relation with the speed control dial 128. Power for the motor 102 may be supplied as by means of a power supply cord 130 which enters the back wall of the casing or base 31 of the mixer.

Mixer bowl heating In order to broaden the utility of the mixer 30, provision is made to adapt the same for use in even the most delicate cooking operations and also for direct cooking or warming of one or more of the ingredients to be mixed or beaten. This is accomplished by equipping the mixer with a controllable heating means, such as a tubular or annular heating element 49 of the type sometimes referred to as a Calrod unit.

Accordingly, the top wall of the mixer base is cut away to form a generally circular opening 131, Within this opening and mounted by means of a mounting plate 132, a saucer-like pan or baffle plate 50 is carried spaced from the mixer base to provide a troughed annular section constituting a support means for the annular heating element 49. In the present instance, for the purpose of lending rigidity to the structure, the bafile plate in the central portion thereof is formed with a turned up central rim 133 which is press-fit onto an indexing collar 135. The collar 135 in turn fits comparatively snugly within a groove formed about the outside of the centering cone 96.

The mounting plate 132, as mentioned before, constituting the mount for the bafile plate 50, is carried on the upper flat surfaces presented by oppositely disposed vertical ribs 136, formed as shown, integral with the transmission housing (48) casting. These ribs 136 laterally projecting and rigid (Fig. 4) form a stable and firm support for the mounting plate 132 and likewise the baflle plate 50.

The baflle plate 58 is provided towards its outer edge with a section bent to slope gently upwardly and presenting a substantially fiat annular part 140 and at its very outer periphery with a reverse curved section or down wardly turned rim 141. The relative size of the opening 131 in the base of the mixer and the baflle plate 50, is such as to provide for substantial clearance between the opening and the plate. Thus the baffle plate is supported level by means of the mounting plate 132, on a plurality of insulating buttons 142, these insulating buttons also serving to mount the annular heating element 49 itself. In the present instance, each of these buttons 142 is made of bonded mica, and is generally cylindrical in shape with a raised shoulder 143 substantially centrally thereof, the opposed cylindrical end portions of each of the buttons being received in like sized alined openings cut in the baffle plate 50 and mounting plate 132. The shoulder 143 serves as a spacer separating the mounting and baflle plates. For securing the heating element 49 within the troughed annular section of the baffle plate 50, the heating element shell on the underside has secured to it a plurality of downwardly extending split pins 144 sized to fit snugly within a central cylindrical bore in the mica insulating buttons 142.. For facilitating entry of the pins in the bores, the upper and lower ends of the bores (the button is reversible) are chamfered. In this case, frictional engagement of the pins 144 within the openings in the insulating buttons 142, holds the pins against endwise movement, and thus the heating unit 49 in place. Nevertheless it is relatively simple to remove the heating unit, which may be done by forcing the pins from the insulating buttons.

The heating unit, as described hereinbefore, is of conventional construction, including a circular array of solidconductor heating wires 145, surrounded by insulating material 150 within a steel, or other like material, shell. For convenience, the heating unit may be connected through the same power cord 130 providing current for the mixer drive motor 47, but for regulating the heat output it is preferable to connect the unit to the source of current through a variable rheostat or the like, controlled by an adjusting dial 51, for regulating the current supplied to the heating unit and thus the heat developed.

The saucer-like pan or baffle plate 50 not only supports the heating unit 49, but also forms a base with the said heating element for supporting the mixing bowl 34. In addition, the baffle plate 50 functions to reflect heat upwardly towards the mixing bowl, focusing of the heat being aided by the flat upwardly sloping section 140 and rim 141 on the outer edge of the baffle plate.

This same downwardly turned rim also functions to deflect downwardly and away from the bowl, air moving by convection through the gap between the underside of the baflle plate and the edge of the opening 131 within the base of the mixer. As has been described hereinbefore, air is constantly being circulated within the interior of the base of the mixer by the motor fan, this movement of air and circulation of warm currents of air through the housing creating temperature differential be tween various points in the housing and resulting in the development of convection air currents. One such series of currents also accompanies use of the heating element for heating contents within the mixing bowl. Since heat is transmitted to the baffle plate 50, which is transmitted directly to the air immediately adjacent the under surface of this plate, the layer of air under the baffle plate being warmer than the surrounding air tends to flow outwardly towards the gap between the baflle plate and the opening in the mixer base. This movement of air may be observed as constant, flowing upwardly through the space or gap and being diverted downwardly and away from the mixing bowl by the concave curved under surface of the baffle plate rim itself.

This constant circulation of air through the gap between the baffle plate 50 and mixer base opening 131, also serves to insulate the mixer base housing or casing walls from heat generated by the heating unit. In other words, the material of the base of the mixer being plastic, metal or the like, if subjected to excessive heat from the heating unit may warp or be stressed, becoming too hot to touch, or in the case of plastic, bending and deforming in an undesirable manner. The constant circulation of air and the movement of air through the gap between the bafile plate 50 and the mixer base by convection air currents, reduces the heat transferred to the mixer base substantially. Furthermore, the heating element is located about the central power head and passes over the motor 47 supported within the base of the mixer. Heat generated in the heating element and transferred by conduction, radiation or convection downwardly affects the temperature of air surrounding the motor. By use of the convection currents causing the constant flow of air beneath the pan or bafile plate 50, the motor is insulated from the heating unit.

The heating unit 49 is thus enabled to operate for extended periods for the generation of heat and heating contents within the mixer bowl, without deleteriously affecting the operation of the drive motor for the power head of the mixer, or raising dangerously the temperature of the walls of the mixer base.

Further facilitating the circulation of air within the mixer base 31, and furnishing a source of cooling air, is accomplished by a relatively narrow air gap or spacing 152 between the peripheral edge of the bed 40 of the mixer base, and the adjacent lower edge of the walls of the base. This narrow air gap extends completely around the mixer base, interrupted at only a few points (shown as four) by rubber feet 159 which serves both to mount the bed and also to mount the housing of the mixer base. As shown in Figs. 2 and 5, the inner side and end walls of the mixer base housing are fashioned with curved ribs 160, under which the rubber feet 159 are fastened as by threaded bolts 161 or the like. The bed 40 is notched, as at 162, to embrace the rubber feet 159 in the region of a peripheral groove, thus effectively locking the bed and feet together. These plurality of feet support the bed 40, and since they are mounted directly under the ribs formed on the inside of the walls of the mixer base casing, also support this casing.

I claim as my invention:

1. A mixer for food products and other substances and comprising, in combination, a hollow base, a driving motor fixed to said base, an upstanding power head on said base including a fixed hollow casing, a pair of concentric drive shafts journaled within said power head casing and having drive connections at their upper ends, means interposed between said motor and said drive shafts for rotating the latter in opposite directions, a removable annular bowl having a hollow central boss and a bottom and an outer wall, said bowl being adapted to rest on said base in substantially concentric relation with said power head casing, a cover for said bowl, and a pair of counter-rotating impellers each detachably connected with a respective one of said concentric drive shafts by means of its drive connection, each said impeller being substantially symmetrical about its associated drive connection and depending into said bowl, said impellers together being disposed to sweep through substantially the entire maximum usable volume thereof, one of said impellers having at least one pair of radially spaced blades nested against said boss of said bowl with relatively little clearance, to deflect material outwardly relative to said boss and also having a bottom blade to deflect material upwardly from the bottom of the bowl, and the other of said impellers having radially extending arms each terminating in depending upright blades disposed with relatively little clearance against the outer wall of said bowl, said depending upright blades being formed to deflect material inwardly and down wardly' in opposition to the deflection effected by the blades of the first impeller.

2. A mixer for food, products and other substances and comprising the combination of a hollow base, a variable speed driving motor housed within said base, an adjustable speed control means for said motor, a power head column on said base, a pair of concentric drive shafts journaled within said power head column and having direct positive drive connections at their upper ends, gear means interposed between said motor and said drive shafts for rotating the latter in opposite directions, an annular bowl having a hollow boss adapted for complemental engagement with said power head column, said bowl being mountable on said base in substantially concentric relation with said power head column, and a pair of counter-rotating impellers disposed in close- 15 nested relation with the upper. portion of said power head column and each detachably connected with a re spective one of said concentric drive shafts by means of a direct positive drive connection complemental with a respective one of said shaft drive connections, each said impeller having blades depending into said bowl, said blades of one of said impellers having relatively little clearance with the bowl boss and being formed to deflect material outwardly, and said blades of the other impeller having relatively little clearance with the outside wall of the bowl and being formed to deflect material in opposition to the deflection efiected by said blades of the first impeller, said impellers together sweeping substantially the entire surface area defined by the hollow boss, the bottom, and the outer wall of said bowl.

3 In a device for mixing fluid, solid, and pulverou's materials, the combination comprising, an annular mixing bowl having a hollow central boss therein, a power head housed within said boss in concentric relation therewith and having a pair of concentric drive shafts journaled within said power head having drive connections at their upper ends, means for rotating said drive shafts in opposite directions, a pair of counter-rotating impellers each detachably connected at their hubs with a respective one of said concentric drive shafts by means of its drive connection, each said impeller being substantially symmetrical about its associated drive connection and depending into said bowl, said drive connections including helical threads on the upper ends of said drive shafts and means cooperating with said threads carried by the hubs of the corresponding impellers, the helical threads of one shaft being of opposite hand to the threads of the other shaft and inclined in the direction to positively lock the impellers upon rotation to the power head, said drive connections providing for bodily removing said impellers from said power head with said bowl as an incident to lifting said bowl ofi of said power head.

4. In a mixer for solid, liquid and pulverous substances, the combination comprising a base, a power head, an annular mixing bowl having a bowl boss adapted to fit over said power head and a bottom adapted to rest on said base,

a first power driven impeller carried by said power head and having a plurality of spaced apart blades at least one of which is disposed against the outer side of the bowl and adapted to deflect material inwardly and downwardly, a

second power driven impeller carried by said power head and having a plurality of blades disposed in alternate spaced relation with the blades of said. first impeller and connected by cross blades, said blades of said second impeller being disposed against the bowl boss and the bowl bottom and adapted to deflect material outwardly and upwardly in opposition to the action of said blades of said first impeller means including said power head for counter-rotating said impellers the blades of each said impeller having a substantial rake with respect to its individual direction of rotation, whereby said blades pass each other with a progressive scissoring action.

5. In a mixer forv foods and other substances, the combination comprising, a power head, a bowl having a hollow central hub therein adapted to fit over said power head, support means for said bowl, a first impeller carried by said power head for rotation in said bowl having a plurality of substantially symmetrical radially extending arms each terminating in a pair of depending upright blades connected by a cross-blade the outermost blade of each pair of upright blades being disposed with relatively little clearance against the outer side wall of said bowl to sweep the bowl area adjacent thereto, a second impeller carried by said power head in said bowl and having a por* tion disposed against said hub and a plurality of substantially' symmetrical axially extending reversely bent. arms each defining a pair of upright blades connected by a bottom blade, said upright blades of said second impeller being radially spaced from the outer side wall of said bowl and disposed in alternate series relation with said upright blades of said first impeller for sweeping the bowl area intermediate the hub and outer side wall, and means including said power head for driving said impellers in opposite directions through said bowl.

6. In a mixer for solid, liquid and pulverous substances, the combination of a mixing bowl, a support for said bowl, a first impeller carried for rotation in said bowl having at least one pair of radially spaced blades pitched to deflect material outwardly relative to said bowl and raked to impart a downward component to the deflected material, said first impeller also having a bottom blade pitched to deflect material upwardly, a second inrpeller carried for rotation in said bowl having at least one pair of blades with alternate radial spacing relative to said blades of said first impeller, said blades of said second impeller being pitched and raked to impart an inward and downward deflection to material within said bowl in opposition to the deflection etfected by the blades of said first impeller, a cross-blade on said second impeller pitched to deflect material downwardly, and power driven means for effecting counter-rotation of said impellers.

7. In a mixer for foods and other substances, the combination comprising a bowl having a bowl boss and having a hollow central hub therein, support means for said bowl, a first impeller having a plurality of substantially symmetrical radially extending arms terminating in depending upright blades, a second impeller closely nested against said hub and having a plurality of substantially symmetrical axially extending and angularly bent arms carrying upright blades, said upright blades of said first impeller being raked to impart a downward component to the deflected material, said upright blades of said first impeller being spaced from said hub and disposed with relatively little clearance against the outer side wall of said bowl, sweeping the area of the bowl adjacent the said side wall, said axially extending and angnlarly bent arms of said second impeller being disposed with relatively little clearance against the bowl boss and bottom and being formed to impart an outward. and upward component to the deflected material, said upright blades of said second impeller being disposed in series relation with said'up' right blades of said first impeller for sweeping the bowl area intermediate the hub and the side walls, and means for driving said impellers in opposite directions through said bowl hub.

8. In a mixer for solids, liquid and pulverous: substances, the combination comprising, a base, a power head, an annular mixing bowl having a bowl boss adapted to fit over said power head in concentric relation therewith and having a bottom adapted to rest on said base, a first impeller detachably carried by said power head in said bowl and having a symmetrical arrangement of radially extending arms each terminating in an outer depending blade disposed with relatively little clearance against the outer side wall of said bowl, said depending blades being pitched to deflect material inwardly relative to said bowl and raked to impart a downward component to the deflected material, a second impeller detachably carried by said power head and having a symmetrical arrangement of axially extending arms disposed with relatively little clearance against the boss and each merging with a horizontal blade disposed with relatively little clearance against the bottom of the bowl, said bottom blades terminating adjacent the Zone swept by the outer blades of the first impeller and carrying an upright blade intermediate the boss and the outer side wall, and power driven means journaled in said power head for efiecting counter-rotation of said impellers.

References Cited in the file of this patent UNITED STATES PATENTS Capek Mar. 14, 1893 Pratts Sept. 12, 1905 Cranston et a1. Oct. 2, 1906 Ashby May 24, 1910 Osher May 31,1910 Miller Sept. 24, 1912 Minney Sept. 25, 1923 Martinet Dec. 8, 1936 Simpson July 23, 1940 Gunther Jan. 21, 1947 Schwarz-Kast Feb. 7, 1950 Savage et a1. June 27, 1950 Davis Jan. 13, 1953 iWeygand et a1 May 12, 1953 Hause Jan. 18, 1955 FOREIGN PATENTS Great Britain Apr. 27, 1949

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