US3544081A

US3544081A - Apparatus for mixing flowable materials

Info

Publication number: US3544081A
Application number: US713523A
Authority: US
Inventors: Hans A Eckhardt
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-03-15
Filing date: 1968-03-15
Publication date: 1970-12-01
Anticipated expiration: 1987-12-01

Description

United States Patent Inventor 3,251,581 5/1966 Jensen 259/108 55 CMMMMIIMMNW my 3,330,538 7/1967 Gableretal. 259/107 3,358,971 12/1967 Steinbook,.lr.. 259/107 [2 pp 713,523 3,385,568 5/1968 Gray 259/10sx F119! 1511963 3,161,404 12/1964 Jay 259/134 [45] Patented Dec. 1, 1970 Primary Examiner-Edward l... Roberts [54] APPARATUS FOR MIXING FLOWABLE MATERIALS ABSTRACT: An a aratus for mixin flowable materials in chims'zs Dnwhgnp' the form of pow/deg, flake, granules, 5nd of fluids in a wide [52] US. Cl. 259/107, range f viscosities, has in a container 3 frame rotating about a 259/134 vertical axis. The frame comprises impellers for radial movem 7/ ment of the material at the top and at the bottom of the con- Search miner and members in between for vertical movement Flow 0 Cream Haze van), patterns of closed loops in vertical planes are enforced for batch mixing by rotating the frame in one direction, and [56] Cm reversed flow patterns for continuousmixing by reversing the UNITED STATES PATENTS frame rotation, as well as for complete discharge. The impel- 2,269,301 l/ 1942 Anstice 259/107 lers and the members carry vanes oblique to the mixer ele- 2,272,7l5 2/1942 Lindsey ..259/(l.C.F Vert.)UX menis- Patented Dec. 1, 1970 Sheet 1 0:3

Y Z 6 F FIG.4

mm A mH vK mC E 4 A 4 m 4 u a w\ n Z 4 5 4 1 :L a. w EMF. Emu I\ A. w w Fo IN 4 Patented, Dec. 1, 1970 3,544,081

Sheet 3 023 INVENTOR. HANS A. ECKHARDT Patented Dec. 1, 1970 Y 3,544,081

Sheet 3 o! 3 3% B FIG.9C 4. J22 4 INVENTOR. HANS A. ECKHARDT 1 APPARATUS FOR MIXING FLOWABLE MATERIALS The present invention relates to the field of mixing, and more particularly, to apparatus for mixing flowable materials which include particulate materials in the form of powder, flake, granules, and fluidmaterials in a wide range of viscosities. Combined with mixing are often such operations as agitating, stirring, dispersing, shearing, kneading, contacting, drying, devolatilizing, reacting, discharging and wiping of inner surfaces of the apparatus. For the sake of simplicity, for any of such combined operations the term mixing will be used in this specification. q

In the prior art a great number of mixing devices is known, each one usually designed for specific mixing purposes and generally not suitable to solve other mixing problems. Among the vertical mixers there are devices known wherein blades or ribbons are applied which, however, fail to guide the flowable material in a closed loop of flow in radial directions at the top and at the bottom of the mixer vessel, and in vertical directions therebetween.

Vertical mixers as well as horizontal mixers are known wherein helical ribbons are arranged to move the material coaxially to the mixer axis, in the case of vertical mixers vertically. It has been found, however, that particles, including larger and harder ones, are conveyed by the blades which wipe the sidewalls of the receptacle, all the way to one end of the mixer, usually the bottom, where they remain without being intermixedwith other material portions and without being effectively sheared or comminuted, lacking the necessary shearing forces in that location. As a whole, the material carried by the helical ribbon along the receptacle surface receives little intermixing with other material portions.

Other material particles -and especially foreign objects, frequently of metal, stone or ceramics, get sheared and squeezed by, the long helical ribbon along the receptacle wall from where no release or escape is'offered. They cause metal abrasion on the mixer partsand undesirable color development in the case of transparent-or translucent products. With explosives such as solid propellants the consequences of such intensive local shear connected, with heat generation have been disastrous. In addition, a helical ribbon which is to wipe the inner surface of the receptacle with close clearance is expensive to make and difficult to maintain, especially in high shear applications. If the helical ribbons are made sufficiently rigid and heavy, a relatively large portion of the mixer volume is taken up by these mixing elements.

The present invention contemplates an improvement in apparatus for mixing a wide variety of flowable materials, such as finely divided solids, for example, in powdery, flaky, granular form or liquids from low to high viscosities.

It is an object of this invention to provide an improved, more effective and at the same time simpler, less expensive mixing apparatus which is easy to clean and to maintain.

It is a further object to provide a mixing apparatus enforcing flow patterns in form of closed loops by moving the material radially at the top and at the bottom of the apparatus, and to move it vertically along the inner surface of the apparatus as well as in the center, however, in opposite'directions.

It is another object to provide a mixing apparatus suitable for continuously discharging and replenished hoppers wherein a closed loop flow is established by forcing the material at the top of the apparatus radially outward, along the sidewalls of the apparatus downward, at the bottom of the apparatus radially inward, and at the center of'the apparatus upward.

It is a further object to provide a mixing apparatus especially suitable for certain types of flowable materials wherein a closed loop flow is established by forcing the material at the bottom of the apparatus radially outward, along the sidewalls of the apparatus upward, atthe top of the apparatus inward and in the center of the apparatus downward.

It is another object to provide a mixing apparatus which establishes a closed loop flow in one direction'advantageous during the mixing period of a batch mixing cycle, and which establishes a closedloop flow in the opposite direction by reversing the direction of rotation of the mixing element, advantageous during the discharge period of the batch mixing cycle.

It is a further object to provide a mixing apparatus which breaks up strata of materials by interspersing portions of strata into portions of other strata in vertical and radial directions.

It is a further object to provide a mixing apparatus which subjects particles, especially harder and larger ones, intermittently toshearing forces in individual areas which are succeeded by other areas provided for releasing, interspersing and intermixing such particles into other material portions, before they are subjected again, to shearing forces in other individual areas. i

It is a further object to provide a mixing apparatus which rejects and releases foreign objects from shearing forces thus avoiding metal abrasion and frictional heat generation, and which permits the release and rejection of larger foreign objects by resilient opening and contraction of the passages for such release and rejection.

, It is another object to provide a mixing apparatus which has an inner surface completely wiped by mixing elements with close clearance.

It is another object to provide a mixing apparatus with mixing elements which resist distortion and bending, which at the same timeare of light weight and of small volume, and which are simple to manufacture and to maintain.

These and other objects, novel features and advantages will be more apparent from the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view of one embodiment with parts broken away;

FIG. 2 is an elevation of the same embodiment, partly in section;

FIG. 3 is a perspective view of another embodiment, with parts broken away;

FIG. 4 is an elevation of an embodiment similar to that of P16. 3;

' FIGS. 'SA, 513, and 5C shows plan and cross-sectional views of elements from FIGS. 1, 2, 3, 4;

FIGS. 6A, 6B and 6C, FIGS. 7A, 7B, and 7C, FIGS. 8A, 8B, and 8C, FIGS. 9A, 9B, and 9C, FIGS. 10A, 10B, and 10C, FIGS. 11A, 11B, and 11C, and FIGS. 12A, 12B, and 12C are plan and cross-sectional views of other elements which may be used with the apparatus of the invention.

Referring to the drawings, FIGS. 1 and 2, there is shown an apparatus for mixing flowable materials comprising a container 12 having a substantially vertical axis and

inner surfaces

14, 15 and 16 symmetric to this axis, a feed opening 18 and a discharge opening 19, both shown as being closed. A frame 20 is mounted for rotation by the shaft 21 which has an axis coinciding with the axis of the container 12, and by drive means (not shown). The frame 20 comprises a top impeller 22 which extends in the upper part of the container 12 from the shaft 21 outward toward the inner surfaces 15 and which is shaped to move material in an inward direction having a component radial of the shaft 21, and to wipe the inner surface 14 of the container 12 with close clearance.

The frame 20 includes the outer member 23 which extends from the outward endof the top impeller 22 downward along the inner surface 15 and which is shaped to wipe the inner surface 15 with close clearance, and to move material in an upward direction having a vertical component.

The frame 20 also comprises a bottom impeller 24 which extends in the lower part of the container 12 from the axis outward, and is connected to the lower end of the outer member 23. The bottom impeller 24 is shaped to wipe the inner surfaces 16 with close clearance and to move the material in an outward direction having a component radial of said axis.

The frame 20 further includes an inner member 25 which extends from the top impeller '22 to the bottom impeller 24 and which has a smaller radial distancefrom said axis at its upper end than at its lower end. The inner member 25 is shaped to move the material in an upward direction having a The top impeller 22, the outer member 23 and the bottom impeller 24 comprise as a rigid profile a strip 26, and along the periphery thereof toward the inner surfaces l4, 15, 16 a plurality of vanes 27. The edges on one side of the vanes 27 are connected to the rigid strip 26, and the edges on the opposite side are oblique and in close proximity to the

inner surfaces

14, 15, 16, the vanes 27 being disposed oblique to the strip 26. The inner member 25 consists of an elongated rigid strip 28 to move through the material with its front rim 28' first, and a plurality of vanes 29, each vane connected on the edge 29 to a flat side of the strip 28, the vanes 29 being disposed oblique to the strip 28.

In operation, when the shaft 21 is rotated in clockwise direction as seen in a plan view, as indicated, the bottom impeller 24 moves the flowable material from the center outward, the outer member 23 and the inner member 25 move the material upward and the top impeller 22 moves the materi al inward which then moves downward in the center by gravity. The downward movement in the center is improved by the smaller distance of the inner member 25 from the axis at the top impeller 22 than atthe bottom impeller 24. The inner member 25 cuts out a conical-body of material which sinks down by gravity toward the bottom where it is sliced into thin layers and plowed to the outside by the bottom impeller 24. A closed loop flow of the material in vertical planes through the axis is thus achieved.

The vanes 27 wipe the

inner surfaces

14, 15, 16 with close clearance. Undispersed particles are subjected to shearing forces between the wiping edges of the vanes 27 and the

surfaces

14, 15, 16 and, after having passed the vanes 27, are interspersed into other material portions, until they receive subsequent shear work by other vanes 27. Foreign objects, after having travelled along a vane 27, are then rejected into other material portions. In many instances, for example, for complete discharge, it is advantageous to reverse the rotation of the shaft 21; the outer member 23 will then wipe the material downward and the bottom impeller 24 inward and downward.

FIG. 2 shows the same embodiment, with the frame 20 in the diametral position indicated in dotted lines. The flow directions of the material advantageous for the first phase of, the mixing cycle are indicated with solid arrows, the flow directions in the second-phase, for complete discharge, with the direction of rotation reversed, with dotted arrows.

FIG. 3 illustrates another embodiment particularly suitable for continuous mixing in a hopper or container 32 with con: tinuous discharge through a discharge opening 39 in the bot-, tom surface 36, shown as being open, into a discharge duct 37, and continuous or intermittentfeeding through a top opening 38, shown as being open. The other inner surfaces are designated with 35.

The frame 40 is mounted for rotation by the shaft 41 and by drive means (not shown) around an axis coinciding with the axis of the container 32. A top impeller 42 consists-of the long top impeller arms 42' defining the top impeller perimeter, and the short top impeller arms 41", both extending in the upper part of the container 32 from the shaft 41 outward toward the inner surface 35 and shaped to move the material outward, when rotated in clockwise direction as seen in a plan view, as indicated. From the outer ends of the long top impeller arms 42, the outer members 43 extend downward aLong the inner surface 35 shaPed to wipe the inner surface 35 with close clearance and to move the material downward.

In the lowest part of the container 32, a bottom impeller 44 consists of the long bottom impeller arms 44' defining the bottom impeller perimeter, and the short bottom impeller arms 44", which extend from the axis outward and are shaped to move the material outward. The long bottom impeller arms 44 connect to the lower ends of the outer members 43; the short bottom impeller arms 44' connect to the inner members 45 which extend to the ends of the short top impeller arms 42", and are shaped to move the material upward. The lower ends of the inner members 45 have a smaller radial distance from the axis than the upper ends.

The outer members 43 consist of rigid profiles, in this case of strips 46 and along their periphery toward the surface 35 a plurality of vanes 47, their edges on one side being connected to the strips 46, their edges on the opposite side being oblique and in close proximity to the-inner surface 35, and oblique to the strips 46.

The inner members 45, the top impeller 42 and the bottom impeller 44 consist of rigid strips 48 to move through the material with their front rims 48' first, and a plurality of vanes 49, each vane connected on one edge 49 to a flat side of the strip 48 and disposed oblique to that strip 48.

In operation, when the shaft 41 is rotated in clockwise direction, as seen in a plan view and as indicated, the top impeller 42 moves the flowable material as it enters through the top opening 38 outward, the outer member 43 moves the material downward along the inner surface 35. The material is moved inward at the bottom by the bottom impeller 44, and upward in the center by the inner members 45. The upward movement in the center is improved by a smaller radial distance of the inner member 45 from the axis at the bottom than at the top of the container 32, essentially decreasing the tendency of the material to move downward in the center.

Closed loop flow patterns of the material in vertical planes through the axis are thus achieved, which has been found to be advantageous for most mixing operations. Many materials tend to flush and rathole through the center, leaving the peripheries toward the inner surface 35 more or less stagnant, and this drawback has been eliminated by this development.

FIG. 5 shows a mixing and wiping element similar to that used in FIGS. 1, 2, 3, 4 in more detail. A is a plan view, B is a section along the lines B-B of A, C is a section along lines C-C of A. This element for wiping a surface with close clearance and for transversely moving and diverting flowable material comprises as a profile a rigid strip 56 and along the periphery thereof toward the surface 55 a plurality of vanes 57, their edges on one side being connected to the strip 56 and their edges on the opposite side oblique and in close proximity to the surface 55, the vanes 57'being disposed oblique to the strip 56. As shown at the right side of A and B, the vanes 57 overlap as projected in the direction of their movement indicated by a solid arrow, so that the vanes 57 wipe the surface 55 completely. The flow of material is indicated by dotted arrows, in this as well as in all subsequent figures.

At the left side of A and B, the element is shown as produced from an elongated L-shaped profile 50 comprising the rigid strip 56' and the strip-shaped ribbon 51 having one edge, the wiping edge 52, in close proximity .to the surface 55, by machining from the wiping edge 52 a plurality of slots 53 in directions transverse and parallel to the center line of the profile 50. By bending the portions of the ribbon 51 between the slots 53 out of the plane of the ribbon 51, the vanes 57 are formed.

The vanes 57 and 57' are constructed to be resilient by using resilient material and by having only part of their edges adjacent to the

rigid strips

56,56 attached thereto, for example by welding or soldering only the right portions of the vanes 57;57' to the strips 56;56' and by machining the slots 53 between the vanes 57' and the rigid strip 56' sufficiently far to the right. As an essential feature, the vanes57;57' are thus constructed'and attached so that they bend under forces imposed by the material toward the direction of such forces, as indicated by the vane 57" in dotted lines, and after decrease of such forces resile back toward their initial position.

FIG. 6 shows a different element for wiping a surface and transversely moving material. A is a plan view, B is a section along the lines B-B of A, C is a section along the lines C-C of A. The element is produced from a longitudinal L-shaped profile 60 which comprises the strip-shaped ribbon 61 having one edge, the wiping edge 62, in close proximity to the surface 65, by machining from the wiping edge 62 a plurality of slots 63, and by bending the

portions

67 and 67 of the ribbon 61 between the slots 63 out of the plane of the ribbon 61 thus forming the vanes 67. The vane portions 67" are attached to the rigid strip 66 by welding or soldering, while the vane portions 67 are resilient.

FIG. 7 illustrates another element for wiping a surface and transversely moving material. A is a plan view, B is an elevational view along the lines B-B of A, C is a section along the lines CC of A. The element is produced from a T-shaped profile 70 comprising two strip-shaped

ribbons

71,71 by machining from the wiping edge 72 and the edge 72' a plurality of

slots

73,73 and by bending portions of the

ribbons

71,71 between the slots 73 on one side out of the plane of the

ribbons

71,71 thus forming the

vanes

77,77. In order to have the wiping edges 72 extending in close proximity to the surface 75, the wiping edges 72 are machined to run parallel and concentric to the surface 75.

FIG. 8 shows a different element for wiping a surface and transversely moving material. A is a plan view, B is an elevation in the directionB-B of A, C is a s section along the lines C-C of A. The element is produced from a T-shaped profile 80 comprising two strip-shaped ribbons 81, 81' by machining from the wiping edge 82 and the edge 82' a plurality of slots 83, 83' and by bending portions of the ribbons 81, 81' between the

slots

83, 83 on opposite sides in opposed directions out of the plane of the

ribbons

81, 81 thus forming the vanes 86, 86'. To have the wiping edges 82 extending in close proximity to the surface 85, the wiping edges 82 are machined to run parallel and concentric to the surface 85.

It is apparent that the elements shown in FIGS. 7 and 8 have greater resistance to bending, torque and twist than the elements of the FIGS. 5 and 6 and it is practical to improve their mechanical resistance and the capacity to mix and to move material transversely by providing

vanes

57, 67 on the opposite sides of the

rigid strips

56, 66. Advantageously, for increased mechanical stability, the vanes on one side of the rigid strip should be staggered in relation to the vanes on the op posite side of that strip, as FIGS. 7 and 8 show.

It is also to be noted that of the wiping elements shown, only those in the FIGS. 5, right side, and 9 wipe a surface completely and are recommended for use in a mixer as shown in FIGS. 1 and 2, where only one outer member 23 wipes the inner surface 15. In this mixer, wiping elements as in FIGS. 5, left side, 6, 7, 8 would leave stripes of the surface unwiped and they are therefore suitable for a mixer as shown in FIGS. 3 and 4 wherein the surface 35 is wiped by two outer members 43. It is understood that the vanes 47 along one outer member 43 are staggered in relation to the vanes 47 along the diametral outer member 43.

FIG. 9 illustrates a further element for wiping a surface and transversely moving material. A is a plan view, B is a section along the lines 13-13 of A, and C is a section along the lines C-C of A. The element comprises a rigid strip 90 which is oblique to the surface 95 and has along its periphery toward the surface 95 a plurality of vanes 97, their edges 91 on one side being connected to the rigid strip 90, and the edges along the opposite side, the wiping edges 92, oblique and close proximity to the surface 95, the vanes being disposed oblique to the rigid strip 90. The vanes 97 overlap as projected in the direction of movement, so that they wipe the surface 95 completely.

In the FIGS. 5, 6, 7, 8, 9 elements for wiping a surface and transversely moving material have been presented, suitable for the top impeller 22, the outer member 23 and the bottom impeller 24 in FIG. 1, and for the outer members 43 in FIG. 2. For the same applications the elements described in the following FIGS. 10, ll, 12 can be successfully used,'although they have been developed particularly for transversely moving material without wiping a surface, like the inner member 25 in FIGS. 1 and 2, the top impeller 2, the bottom impeller 44, and the inner members 45 in FIGS. 3 and 4.

FIG. 10 shows an elongated element for travelling through flowable material transversely to its center line, for moving material in the direction of that center line. A is a plan view of this element, B is a section along the lines 13-3 of A, and C is a section along the lines C-C of B. The element comprises the two

rigid strips

102, 103 moving through the material with the front rims 102', l03'first, and a plurality of vanes 105, each vane connected on one edge 106 to a flat side of the strip 102, and connected on the opposite edge 107 to a flat side of the strip 103, said vanes being disposed oblique to the

strips

102, 103. The element is shown at the left side as produced from a U-shaped profile.

FIG. 11 illustrates another element for moving material transversely to its center line. A is a plan view, B is a section along the lines B-B in A, and C is a section along the lines C-C in B. The element comprises two

rigid strips

112, 113 moving through the material with their front rims 1121.113 first, and a plurality of vanes 115, each vane connected on one edge 116 to the flat side of the strip 1 12, and connected on the opposite edge 117 to a flat side of the strip 113, with portions of the vanes being disposed oblique to the

strips

112, 113. The element is shown as produced from an H-shaped profile.

FIG. 12 pictures a further element for moving material transversely to its center line. A is a plan view, B is a section along the lines B-B of A, and C is a section along the lines C-C of B. The element comprises two oblique

rigid strips

122, 123 moving through the material with their front rims 122' 123' first, and a plurality of vanes 125, each vane connected on one edge 126 to an oblique flat side of the strip 122, and on the opposite edge 127 to an oblique flat side of the strip 123, the vanes being disposed oblique to the element. The vanes 125 may be flush with the front rirns 122', 123 or may remain below, or may extend beyond, as shown.

As described in connection with the drawings, a versatile mixer suitable for batch mixing as well as for continuous mixing, both with complete discharge, is thus obtained. The change from batch to continuous operation and vice versa usually requires merely to reverse the rotation of the mixer elements. Furthermore, a mixer as described in this specification offers a considerable reduction in mixing time and an essential improvement of product quality.

While the present invention has been described in connection with preferred embodiments in an illustrative and not in a limiting sense, it is apparent that modifications and variations may be resorted to without departing from the spirit and the scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

Iclaim:

1. Apparatus for mixing flowable materials comprising:

a container for receiving and containing material, having a substantially vertical axis and inner surfaces symmetric to said axis;

a frame in said container mounted for rotation around an axis coinciding with said axis of said container, said frame comprising:

a top impeller extending in the upper part of said container from said axis outward toward inner surfaces of said container and shaped to move said material in a direction having a component radial of said axis;

' at least one outer member extending from the outward perimeter of said top impeller downward along inner surfaces of said container, shaped to wipe said inner surfaces with close clearance, and to move said material in a direction having a vertical component.

2. Apparatus for mixing flowable materials as described in claim 1, wherein a bottom impeller extends in the lower part of said container from said axis outward and connects to the lower end of said outer member, said bottom impeller being shaped to wipe inner surfaces with close clearance. and shaped to. move said material in a direction having a component radial of said axis.

3. Apparatus for mixing flowable materials as claimed in claim 2, wherein at least one inner member extends from a within the perimenter of said bottom impeller.

4. Apparatus for mixing flowable materials as claimed in claim 3, wherein said innei member is shaped to move said material in a direction having a vertical component.

5. Apparatus for mixing flowable materials as claimed in claim 3, wherein the upper end of said inner member has a smaller radial distance from said axis than the lower end of said inner member.

6. Apparatus for mixing flowable materials as claimed in claim 3, wherein the lower end of said inner member has a smaller radial distance from said axis than the upper end of said inner member.

7. Apparatus for mixing flowable materials as claimed in claim 1, wherein the top impeller is shaped to wipe inner surfaces of said container with close clearance.

8. Apparatus for mixing flowable materials as claimed in claim wherein said top impeller is shaped to move material radially outward, said outer member shaped to move the material vertically downward, and said bottom impeller shaped to move the material radially inward, with said frame rotated in one direction, whereas, with said frame rotated in 2 a rigid profile and along the periphery thereof toward said surfaces a plurality of vanes, their edges on one side being connected to said profile, their edges on the opposite side being oblique and in close proximity to said inner surfaces, said vanes being disposed oblique to said profile, and wherein said inner member shaped to LII move said material vertically, and said top impeller shaped to move said material radially, comprise at least one rigid strip to move through said material with its front rim first, and a plurality of vanes, each connected on one edge to a flat side of said strip, said vanes being disposed oblique to said profile. v .1 a: 10. An element for wiping a surface with close clearance and for transversely moving flowable material comprising a T- shaped profile consisting of a base rib and two side ribbons, each side ribbon having along the periphery thereof a plurality of vanes, their edges on one side being connected to said profile, and. their edges on the opposite side oblique and extending in one side ribbon towardsaid surface in close proximity to said surface, said vanes being disposed oblique to said profile.

11. Apparatus for mixing flowable materials as claimed in claim 9 wherein said vanes overlap as projected in the direction of movement, so that they wipe said surface completely.

32. Apparatus for mixing flowable materials as claimed in claim 9, wherein said member is produced from an elongated profile comprising at least one strip-shaped ribbon having one edge, the wiping edge, in close proximity to said surface, by machining a plurality of slots extending from said wiping edge into said ribbon, and by bending portions of the ribbon between said slots out of plane of said ribbon thus forming said vanes.

13. Apparatus for mixing flowable materials as claimed in claim 12, wherein said slots extend into the ribbon from said wiping edge in directions transverse and parallel to the center line of said elongated profile.

14. Apparatus for mixing flowable materials as claimed in claim 13, wherein the vanes are constructedto be resilient and to bend under forces imposed by said material toward the direction of said forces, and after a decrease of saidforces to resile back toward their initial position.