US3102716A

US3102716A - Apparatus for mixing

Info

Publication number: US3102716A
Application number: US113254A
Authority: US
Inventors: Meyer S Frenkel
Original assignee: Frenkel AG C D
Current assignee: Frenkel AG C D; FRENKEL C-D AG
Priority date: 1955-06-22
Filing date: 1961-05-29
Publication date: 1963-09-03
Anticipated expiration: 1980-09-03

Description

Sept. 3, 1963 M. s. FRENKEL 3,102,716

APPARATUS FOR MIXING Filed May 29. 1961 3 Sheets-Sheet 1 I E OR. MEYER sCH dgMy RENKEL BY l mn and Farm/A AGENTS Sept. 3, 1963 M. S. FRENKEL APPARATUS FOR MIXING Filed May 29, 1961 3 Sheets-Sheet 2 INVENTOR. MEYER SCHLIOMA FRENKEL BY Man aw Kenna 4 AGENTS United States Patent 3,162,716 APPARATU Ffilt MKXING Meyer 8. Frenlrel, London, England, assignor to Frenlrel C-D Alrtiengesellschaft, Vaduz, Liechtenstein 'Fiied li lay 29, 1961, Ser. No. 113,254 Claims priority, application Great Britain June 22, 1955 11 Claims. (Cl. 259--3) This invention relates to mixing apparatus, useful for a great variety of media which are capable of some sort of flowing motion, in whatever condition or aggregate state they may be. More particularly, the invention relates to screw or worm type mixers regardless under what name they may be used in order to mince and/ or mix solid lumps or particles or to blend and/or mix liquids or to perform similar function, the principle of the apparatus being even applicable to energy-transfer machines such as heat exchangers and generally to energy-conversion apparatus, such as turbines, pumps and the like, including the extreme case of a dynamic sealing gland for a medium under pressure-difference.

lt is an object of this invention to provide a basic mixer construction in the general sense outlined above, in which all elements of the throughput or input, substantially without exception, should on the path between entry and exit undergo a continuous series of treatments corresponding to their properties in order to produce at the outlet a required degree of homogeneity of mixture and of uniformity of other properties and/or states rather than a mixture representing an average of widely differing extreme properties, of which the worst properties determine the overall characteristics of the output or performance as in many conventional appliances.

It is a further object of this invention to provide a basic mixer construction which provides along the path of the material from entry to exit a series of forces and velocities difiering in magnitude and direction. For instance, for an input of solid lumps, the general mixing forces should manifest the necessary crushing effects, among others; for a fibrous material the mixing forces should have a tearing or mincing effect; for a powder and/or a liquid the general mixing forces should manifest as blending effects, and so on.

It is a further object of the invention to provide a basic mixer construction which offers minimum wear of operating surfaces, easy dismantling for cleaning, easy adjustability of clearances to take up wear and economy of space.

it is a further object of the invention, e.g. for the purpose of injection moulding, to provide a basic construction applicable both for continuous operation and batch operation and both for batchmixing and batchextrusion. t

It is a further object to provide a most eflicient heatexchanger.

It is a further object to provide a dynamic sealing gland of fundamentally improved performance over conventional screw-glands.

According to the present invention, the apparatus for mixing may comprise at least two components, such as an at least partly interiorly threaded barrel and a male threaded member or worm, the one surrounding and being axially shiftable relatively to the other one wherein the grooves of the barrel and worm are generally wider than the lands of the threads forming them, the said grooves of the barrel and worm face one another and define a passage for a medium, the minor radii of the barrel thread convolutions and the major radii of the worm convolutions being respectively located on an internal and external conical envelope. The envelopes are preferably parallel to each other and have their axes 3,102,7l6 Patented Sept. 3, 1963 coinciding with the barrel axis. They taper towards the exit or entry end of the passage so that by a relative axial displacement of the components the radial clearance between the said envelopes can be adjusted. The areas of cross-sections of the thread grooves vary at least over a part of the length of the passage between a maximum and a minimum value, so that the cross-section of the one groove increases while that of the other groove decreases whereby, when in operation a medium moves in the said passage, material is transferred between the grooves in the components as giver and taker.

At least one of the components may comprise a section extending throughout at least a part of the length of the passage and being rotatable about the barrel axis. Furthermore, at least one of the components may comprise at least two rotatable sections in axial sequence of one another wherein the angular velocities of the sections are adjustable independently of oneanother.

Furthermore, the apparatus according to the invention may comprise means for intermittently opening and closing the passage exit, and other means for cyclically shifting one of the components relatively to the other one in the axial direction wherein the shifting stroke may be adjustable.

In such apparatus the variations of the areas of facing groove-cross-sections along the length of the passage may form at least one cycle in that the cross-sectional areas of the groove in one component varies from a maximum value to zero and back again to a maximum value, while in the other component the cross-sectional area of the groove facing the first one varies from zero to a maximum value and back again to zero whereby when a medium moves in the passage, material-transfer takes place from the one component as giver to the other component as taker and back again from the other component as giver to the first mentioned component as taker in a complete cycle.

Apparatus according to the invention, arranged to set up the pumping or extruding effect of the threads against the high-pressure side of a vessel is adapted to form dynamic sealing glands in order to retain fluids under pressure.

Further objects and details of the invention will be apparent from the description given hereinafter and the accompanying drawing illustrating several embodiments thereof by way of example. In the drawing,

FIG. 1 is a section of a first embodiment, applied for instance as rnixer-extruder, having sections of the female screw with independently adjustable angular velocities.

FIG. 2 is a section through another embodiment with a valve at the outlet for application as batch-mixer, and with cyclic axial adjustment of the inner screw to provide variation of the clearance.

FIGS. 3 and 4 show examples of different male screws.

FIGS. 5 and 6 show examples of different female screws to be used in various combinations with the male screws.

The general mixing apparatus according to this invention shown iii FIG. 1 comprises an inner component or worm 1 and an outer component or barrel consisting of two sections 2 and 3. The worm is provided with a male helical thread 12 and the barrel with a female thread 13. The threads which face one another defin'e with their grooves 15 and 16 which are wide compared to the narrow lands shown a passage for a medium to be mixed between the entry funnel 6 and a suitable and conventional exit means depending on the application of the mixing apparatus and here indicated as an extrusion head or dieplate 7.

Both components are rotatably mounted in casing 4, the inner component 1 on a bearing and drive assembly I on.

8, the drive for the worm 1 being indicated at 9. The sections 2 and 3 of the barrel are mounted in ball bearings in casing 4 and driven by individual drives ll and 11 mounted in casing 4, so that sections 2 and 3 can be driven at different and adjustable speeds. The glands indicated at 17 may be of a type according to this invention, or any suitable type.

The operating surfaces of components 1 and 2, Le. the

helical threads

12 and 13 are of opposite pitch and the I barrel and worm are adapted for opposite rotation so as to effect transport in both screws towards the common exit. From the entry funnel 6, the worm 1 comprises a feed section 18 in which the thread extends with its lands closed to the inner surface of the casing 4, which in the range of section 18 is substantially cylindrical. This section is followed by at least one mixing cycle 192ii, wherein the first section 19 the cross-sectional area of the groove of the worm decreases from the initial maximum to zero, whereas the cross-sectional area of the barrel groove 16 facing groove 15 increases from zero to maximum in complementary fashion, so that in operation the material originally in the inner screw groove is transferred into the outer screw-groove at the end of section 19. In section 20, the cross-sectional area of outer groove 16 decreases from maximum to zero, while the inner groove 15 increases from zero to maximum so that in this sector material will be transferred back from the outer to the inner screw. All this material transfer between the oppositely rotating screws coincides with a mixing of thematerial which to a considerable extent takes place in transit-zones 21. The changes in groove cross-section may be effected by variation of the characteristics of pitch, pitch circle diameter, groove-depth and profile shape of the thread either singly or in any combination. The profile-shape can be adapted to the particular use for which the apparatus is destined, for example the shape here shown with sharp edged lands of the

threads

12 and 13 is adapted for blending, dispersal extrusion and other applications. The number of threads of the screw will also be adapted to the application although double-threaded screws are here shown, and change in the number of threads may also be used in the variation of the groove-cross-sectional area.

The lands of

threads

12 and 13 approach from either side the frusto-conical interface or transit-zone 21 which is co-axial with the barrel and worm. The clearance between opposite lands is denoted by 23. On account of the f usto-conical shape of this interface, or more generally of the shape of the interface whose radius varies in one direction along the passage defined between the grooves of the barrel and worm, the axial relative position of the two components can be changed, whereby the magnitude of the clearance 23 is adjustable in order to compensate wear, and for other purposes described later The arrows 24 indicate the direction of the material-transfer in

sections

19 and 20.

The bearing assembly 8 for worm 1 is mounted on a carriage 25 which, by means of the screw provision 26 is movable along the base 27 of the machine, and remains fixed in any set position thereon. 28 denotes a hand wheel for setting the carriage and 29 a pointer and scale graduated to indicate the setting of the clearance 23. Such devices are well known for example as motor bases and they are therefore not described in any detail. The barrel sections 2 and 3 are seen to be mounted and driven to be rotatable independently of one another.

.Means for the adjustment of the angular velocities of one another by an internal shaft drive and internal hearing provision, which would also include dynamic gland sealing to prevent material, say extrudate, from getting into the bearing.

In this example, the lands of the

helical threads

12 and 13 of the barrel and worm respectively are formed flat with sharp corners, as required for example for mincing.

Two-start threads are shown of opposite hand on the.

barrel and worm which in operation are rotated in opposite directions in order to transport the material being mixed and advanced towards the common exit, diagrammatically shown as extrusion head 7.

' The interface 21 between the crests of the lands is shown frusto-conical, though it may be of other convenient shape permitting adjustment of the axial relative positions of the screw-components to adjust the clearance.

This embodiment permits, by a simple variation of the angular velocities of the independently rotatable sections of the barrel the adjustment of required states of temperature, pressure, and the like along the axis, in order to ensure desired states at the outlet over a very wide range, with stability, and uniformity.

In the operation of the apparatus according to FIG. 1, the medium or material to be Worked is supplied through the funnel or hopper 6 to the worm in section 18. From there the material is conveyed into section 19 in which the material, while being taken along towards the exit, is gradually urged into the barrel groove 16 until practically all the material has been transferred from groove 15 to the groove 16. Subseqeuntly, while the axial movement of the material continues, it is now urged from groove 16 back into groove 15 from where it can reach the exit through an extrusion head or the like. Prior to the starting of the apparatus the clearance between the crests of the lands of the threads will have been adjusted, depend ing on the kind of the medium. to be worked, by a slight axial shift of the worm in relation to the barrel so that the gap between the crests of the threads will be increased or decreased owing to the conical form of the interface or the envelopes on which the crests of the. barrel land-s and worm lands, respectively, are located. in most instances it is preferred that the frusto-conical interface 21 tapers towards the exit end of the apparatus. In consequence of such tapering the peripheral velocity of particles in the interface is progressively decreased and the extruding pressure correspondingly increased. However, structures are also useful in which the taper extends in the reversed direction.

Now it will be clear that in section 19, groove 15 can be denoted as the giver groove whereas groove 16 is the taker groove. In section 24) the function of the grooves are reversed so that groove 16 becomes the giver and groove 15 the taker. During the operation of a the apparatus a continuous extrusion over all of the helical giver groove takes place and the particles are taken up and separated from the giver groove by the oppositely rotating threads flanking the taker groove. This separation may proceed in various forms depending on the properties of the material involved, e.g. crushing of lumps, mincing of fibers blending of powders or free flowing fluids, shear-mixing of viscous fluid and the like, wherein the size of the separated particles depends on the adjustment of the clearance between the barrel and worm or the distance of the conical envelopes of the two threads from each other which, as stated hereinbefore, can be varied by an axial shift of the worm in relation to the barrel. An extremely thorough mixing of the particles will take place and no particle can escape the interaction of the giver and taker grooves. The particles form vortices in three mutual normal planes in the one groove and are compelled to change over into other vortices when transferred from the one into the other groove, which rotates in the opposite direction. A dual pumping or extruding efiect takes place owing to the two screws into the taker groove. The heat input by mechanical working, can be made large and can also be kept small, as may be required. In addition, particularly in the embodiment illustrated in FIG. 1, the adjustability of the velocity of the sectionwise sub-divided barrel portions greatly aids to maintain desired output conditions.

FIG. 2 shows an example of a mixer-extruder with provision for adjusting the clearance between the worm and barrel threads, cyclically, for example, as part of a working cycle as in batch mixing or injection of plastics, or simply foradjusting the clearance in ordinary continuous mixing, crushing, or the like, without cyclic axial motion.

The apparatus is similar to that shown in FIG. 1 with like numerals denoting like parts. As distinct from FIG. 1 the barrel 32 is stationary and in one piece with the casing. It is provided with heat exchange elements 33 which are diagrammatically indicated, to be utilised for heating or cooling, as may be required.

Following the mixing cycle, a 'valving means for opening and closing the exit-aperture is digra-mmatically shown as a sliding gate 36, with a ratchet-mechanism 58 for its operation. I

The frusto-conical interface 21 between the inner and outer screw components enables the inner screw component to be moved axially for altering the clearance in the mixing cycle, e.g. in order to adjust the heat input by mechanical working into the medium being mixed or to adjust the pressure generated by the apparatus, while keeping the clearanceat the same minimum value in the mixing cycle. It will be understood that mixing cycles with continuously conical interfaces, or otherwise shaped interface, may equally well be provided in this kind of machinery.

An adjustable eccentric 34 actuates reciprocating motion of the worm 1, e.g. when the mechanism is intended for use as a batch-mixer or as an injection machine. The carriage 25 is mounted on a slide 35 which is guided in a slot 30 of the base 27 for movement parallel to the axis of the worm 1. The eccentric 34 is linked to the slide 35 by a connecting rod 31 so that the carriage 25 reciprocatcs in the direction of the worm axis when the eccentric rotates. When the drives of the gate 36 and of the eccentric 34 are connected the closing of the clearance accompanied by an increase of the pump pressure may be caused to coincide with the opening of the exit-valve, and the opening up of the clearance with the closing of the exit-valve. I

In operation as a batch mixer or as injection apparatus, e.g. for transfer moulding of plastics, a circulation will take place in each of the mixing cycles when the exitvalve is closed which causes thorough mixing and heat input by mechanical Working. The heat input which is often excessive, can be kept low by opening up the clearance and by adjusting the speed of rotation of the screw components, without detracting from the fundamental completeness and thoroughness of the compounding and mixing, whereby a required degree of uniformity of the output can be obtained. The output can be easily brought under a required pressure for ejection by closing the clearance, and cycles of operation for e.g. injection with greater speed and greater contents of each discharge can be better adjusted than hitherto possible.

FIG. 3 shows a detail of a section of male screw adapted for half a cycle of material trans-fer, i.e. to act as giver only, which may be mounted as an alternative screw in the examples already shown. It has a single helical thread 12 with grooves 40 and narrow lands 41, coming practically to a sharp edge, and has a rigid handed pitch t FIG. 4 shows an alternative male screw, having a quadruple helical thread, with a groove 42 and land 43 of similar shape as shown in FIG. 3

FIG. shows a half of a female screw, with its helical thread 13' having grooves 44 and lands 45 matching those of the male screw of FIG. 3.

FIG. 6 shows a half of a female screw whose quadruple helical screw thread has grooves 46 and lands 47 matching those of the male screw of FIG. 4.

The female screw sections of FIGS. 5 and 6 have flanges 48 with bolt holes 49 for bolting together and to a fixed casing as in FIG. 2, or to a rotatable part of a casing, as would correspond to FIG. 1.

Between the different male and female screws shown in FIGS. 3-6, different effects of compression and decompression can be achieved together with the mixing for the case of viscous fluids being dealt with.

For example, the combination of the male screw of FIG. 3 and of the female screw of FIG. 5, as also the combination of the male screw of FIG. 4 and of the female screw of FIG. 6, will not result in any particular compression or expansion effects as the screws are of matched pitch and in each case of the same number of threads.

However, combining the quadruple threaded male screw of FIG. 4 with the single thread female screw of FIG. 5 will result in considerable compression as the quadruple threaded male screw of bigger pitch transports in its groove considerably more material than the single thread, smaller pitch female screw, for the same relative rotational speed.

Conversely, combining the single thread male screw of FIG. 3 with the quadruple threaded female screw of FIG. 6 will result in decompression in the female screw grooves, as they tend to transport more material for the same relative speed of rotation between the screws.

In all examples of mixer described, the helix angle at least in the rotating component is between 45 and 90.

The glands 17 in FIG. 1 have inner and outer helical threads with a conical interface, generally according to this invention.

I claim:

:1. In an apparatus of the type described, a barrel component and a worm component coaxial with said barrel, said barrel having an inner and said worm having an outer helical thread each with lands between adjacent thread groove convolutions so that the lands of the worm face the lands of the barrel, the lands of each thread being narrower than the groove formed therebetween, said threads being of opposite pitch, the cross-sectional areas of opposite thread groove portions varyingj the one from a maximum to a minimum value and the other one from a minimum to a maximum value so that said portions complement each other to form a continuous passage having an entrance and an exit end axially spaced from each other, the lands of said barrel thread being located on a first conical surface and the lands of the worm thread being located on a second conical surface parallel to the first one, said worm being axially shiftable in relation to said barrel thereby to vary the spacing of said surfaces from each other, said barrel and said worm being rotatable in the directions of the pitch of their threads, respectively.

2. In a mixing apparatus, a barrel component and a worm component coaxial with said barrel, said barrel having an inner and said worm having an outer helical thread each with lands between adjacent thread groove convolutions so that the lands of the worm face the lands of the barrel, the lands of each thread being narrower than the groove formed therebetween, said threads being of opposite pitch, the cross-sectional areas of opposite thread portions varying the one from a maximum to substantially zero and from substantially zero to another maximum value and the other one from substantially zero to a maximum value and from that maximum value to substantially zero so that said portions complement each other to form continuous passage having an entrance and an exit end for the medium to be mixed, the lands of said barrel thread being located on a first conical surface and the lands of the worm thread being located on a second conical surface parallel to the first one, said Worm being axially shiftable in relation to said barrel thereby to vary the spacing of said surfaces from each other, said barrel and said worm being rotatable in the directions of the pitch of their thread-s, respectively, so as to convey the medium towards said exit end.

3. An apparatus as in claim 2, said barrel being composed of a plurality'of conical sections, a plurality of driving means for rotating said sections respectively in the same direction but with different peripheral speeds, and a gland between each two adjoining sections of the barrel.

4-. 'An apparatusas in claim 2, said barrel being composed of a stationary section including a feeding hopper, and a plurality of rotatable sections in coaxial alignment, a plurality of driving means for rotating said rotatable sections in the same direction but with different peripheral speeds, and a gland between the stationary section and the adjoining rotatable section, and another gland between each two adjoining rotatable sections.

5. An apparatus as in claim 2, wherein said conical surfaces taper towards said exit end.

6. An apparatus as in claim 2, wherein two of the said portions are connected in coaxial alignment of one another in each of said components.

7. In a mixing apparatus, a barrel component and a worm component coaxial with said barrel, said barrel having an inner and said-worm having an outer helical thread eachwith lands between adjacent thread groove convolutions so that the lands of the worm face the lands of the barrel, the land-s of each thread being narrower than the groove formed therebet-Ween, said threads being of opposite pitch, each of two adjoining groove portions of the thread of one of said components varying in crosssectional area from a maximum to substantially zero and from zero to another maximum, and each of two adjoining portions of said other component and coextensive with said first mentioned portions varying in cross-sectional area from substantially zero to a maximum and from that maximum to substantially zero, so that the portions of the one component complement the portions of said other component to form a continuous passage having an entrance and an exit end for the medium to be mixed, the lands of said barrel thread being located on a first conical surface and the lands of the worm thread being located on a second conical surface parallel to the first one, said worm being axially shiftable in relation to said barrel thereby to vary the spacing of said surfaces from each other, at least one of said components being rotatable I in the direction of the pitch of its thread so as to convey the medium towards said exit end.

it 8. An apparatus as in claim 7, further comprising means for cyclically reciprocating said worm in its axial direction, said means including guide meansfor guiding an end portion of said worm in said axial direction and an eccentric drive connected to said end portion of said worm.

9. In a mixing apparatus, a barrel component and a Worm component coaxial with said barrel, said barrel having an inner and said Worm having an outer helical thread each with lands between adjacent thread groove convolutions so that he lands of the worm face the lands of the barrel, the lands of each thread being narrower than the groove formed therebetween, said threads being of opposite pitch, and cross-sectional area of a groove portion of said barrel thread varying from substantially zero to a maximum, and the cross-sectional areaof a groove portion of said worm thread which is co-cxtensive with said portion of said barrel thread groove verying from a maximum to substantially zero so that said groove portions of the one component complement said groove portions of the other component to form a continuous passage having an entrance and anexit end for the medium to be mixed, the interface between the lands of the barrel thread and the lands of the worm thread being frusto-conical, said worm being shiftable in the axial direction, and at least one of said components being rotatable in'the direction of the pitch of its thread.

10. An apparatus as in claim 9 in which'the component reducing from maximum to zero groove cross-section has a helical thread of larger pitch than said other component having a groove cross-section increasing from zero ma maximum value whereby to effect a compression of the material being mixed.

11. An apparatus as claimed in claim 9 in which the component having a groove cross-section reducing from maximum to zero area has a helical thread of smaller pitch than said other component having a groove crossseotion increasing from zero to maximum, whereby to effect a decompression of the material being mixed.

References Cited in the file of this patent UNITED STATES PATENTS Parshall et al. May 8, 1956

Claims

1. IN AN APPARATUS OF THE TYPE DESCRIBED, A BARREL COMPONENT AND A WORM COMPONENT COAXIAL WITH SAID BARREL, SAID BARREL HAVING AN INNER AND SAID WORM HAVING AN OUTER HELICAL THREAD EACH WITH LANDS BETWEEN ADJACENT THREAD GROOVE CONVOLUTIONS SO THAT THE LANDS OF THE WORM FACE THE LANDS OF THE BARREL, THE LANDS OF EACH THREAD BEING NARROWER THAN THE GROOVE FORMED THEREBETWEEN, SAID THREADS BEING OF OPPOSITE PITCH, THE CROSS-SECTIONAL AREAS OF OPPOSITE THREAD GROOVE PORTIONS VARYING THE ONE FROM A MAXIMUM TO A MINIMUM VALUE AND THE OTHER ONE FROM A MINIMUM TO A MAXIMUM VALUE SO THAT SAID PORTIONS COMPLEMENT EACH OTHER TO FORM A CONTINUOUS PASSAGE HAVING AN ENTRANCE AND AN EXIT END AXIALLY SPACED FROM EACH OTHER, THE LANDS OF SAID BARREL THREAD BEING LOCATED ON A FIRST CONICAL SURFACE AND THE LANDS OF THE WORM THREAD BEING LOCATED ON A SECOND CONICAL SURFACE PARALLEL TO THE FIRST ONE, SAID WORM BEING AXIALLY SHIFTABLE IN RELATION TO SAID BARREL THEREBY TO VARY THE SPACING OF SAID SURFACES FROM EACH OTHER, SAID BARREL AND SAID WORM BEING ROTATABLE IN THE DIRECTIONS OF THE PITCH OF THEIR THREADS, RESPECTIVELY.