US3164375A - Apparatus for intensive mixing - Google Patents

Description

Jan. 5, 1965 M. s. FRENKEL 3,164,375

APPARATUS FOR INTENSIVE MIXING Filed May 29, 1961 4 Sheets-Sheet 1 INVENTOP MEYER 4. HEWEL 39 Wm I 83mm krmwy Jan. 5, 1965 M. s. FRENKEL APPARATUS FOR INTENSIVE MIXING 4 Sheets-Sheet 2 Filed May 29, 1961 Fla. 4.

INVENTQQ.

Jan. 5, 1965 M. s. FRENKEL 3,154,375

APPARATUS FOR INTENSIVE MIXING Filed May 29, 1961 4 Sheets-Sheet a Fucs.7.

Jan- 5, 1 6 M. s. FRENKEL APPARATUS FOR INTENSIVE MIXING 4 Sheets-Sheet 4 Filed May 29, '1961 vw E 8 lww AGENTS United States Patent Ofifice 3,164,375 Patented Jan. 5, 1965 Claims. (Cl. 259-3 The present application is a continuation-in-part of my application Serial No. 592,472 filed on June 18, 1956.

This invention relates to mixers, process machines and extruders both with continuous operation and with intermittent operation on some predetermined cycle of operation, as occurs for example in injection moulding of plastics. Similarly it relates to chemical process machines in which reactions take place under controlled conditions of shear-working, heating or cooling through the walls of the machine, pressure, and the like.

In considering mixing, distinction is made between extensive mixing which covers dispersal of materials in any aggregate state; and on the other hand intensive mixing which covers shear working mainly. Intensive mixing is generally applied to media in the liquid, plastic or semisolid state which are already at least in part dispersed among themselves or have admixtures say of powders, such as for example, plastics, clays, filter cakes, doughs and the like. As far as solids are concerned, for instance, powders already inter-mixed to some degree or some granular or powdery aggregate by itself, the equivalent of such intensive mixing will be considered to be shear grinding between suitable surfaces of a machine.

While both extensive and intensive mixers in general comprise a casing and a component or components inside it adapted for relative motion, the distinction between machines for these two purposes is clear. An extensive mixer is built so as to have no zones where operative surfaces of components pass one another at close clearances and/ or at high relative speeds. Where due to the nature of the machine such zones are unavoidable, they are made as small as possible (for example where screws are involved, their lands will be made as narrow as possible). For intensive mixers, on the contrary, zones in which operative surfaces pass one another at small clearances and/ or at high relative speeds are made as large as possible relative to the operative volume of the device as a whole.

The present invention more particularly relates to intensive mixers.

Intensive mixers at present available are essentially of two kinds: firstly, colloid mills which have a very substantial proportion or all of their hold-up volume forming the zone of intensive working. This makes them suitable only for very high rates of shear application if worthwhile throughputs are to be obtained, or more generally speaking, this feature of their construction ties up the throughput with the rate of application of shear work. This restricts their field of operation to materials of relatively low viscosity, emulsification applications and the like, while for example the intensive working of doughs or filter cake cannot be contemplated in colloid mills unless it is intended to liquefy them. Secondly, there are intensive mixers in which a larger proportion of the holdup volume does not form a zone of intensive mixing, such as Sigma-Blade Mixers (essentially batch mixers), various screw type devices mainly with two screws on parallel shafts (which may be batch or continuous devices) or mixers having eccentrically moving rubbing components, to form travelling zones of intensive mixing with the suitably shaped wall of the casing. These mixers all operate statistically in the application of the shear work they do on the throughput, that is, some layers of the throughput have far too much work done on them, other layers get too little work done on them, and in order to achieve a required average or to make sure that all layers have had at leastsome intensive mixing, far more mechanical work has to be done than would be required to give every layer the predetermined amount of shear mixing. In these mixers, in consequence, the layers which have been least worked prove the weak spot in the resulting material while the layers which are worked many times prove the limiting factors on operating conditions which can be applied, for example on account of local over-heating.

To illustrate this, consider a conventional or a high speed plastics extruder although this is only an intensive mixer unintentionally in the zones of very small clearance between the lands of the screw and the barrel surface. In running such an extruder adiabatically (without external heat input), it has not proved possible to obtain a melt of a practically useful uniformity which has not also a temperature considerably in excess of the minimum melt temperature, so that such extruders cannot be run cool, as is useful for certain applications. Furthermore attempts to control the output temperature materially affected the rate of output. All these factors prove severe limitations on practical operation. 1

Objections'of a similar nature apply to much of the mixing proceeding in the chemical industry generally,

where often a batch mixing step is interposed into otherwise continuous process lines when intensive mixing or working is required, to the detriment of the process as a whole.

It is an object of this invention to provide apparatus for intensive mixing which is free from some or all of the above drawbacks.

It is an object of this invention for intensive mixers having a hold-up volume which is generally larger than the zone or zones of intensive mixing, to provide a mixer in which all or a predetermined proportion of flow layers of a predetermined thickness are subjected to shear mixing of a required intensity in one pass.

It is a further object of the invention to provide such apparatus in which'the rate of shear working can be adjusted, possibly during operation of the device, with minimal influence on the rate of throughput.

To achieve some or all of these objects, the present invention provides for the method having the steps of transporting a medium which may consist of a plurality of constituents, in a first helical groove, the step of exuding the said medium continuously over one side of the said elical groove, the said groove thus acting as a giver groove and the side surface of said giver groove forming a land of some width to the adjacent turn of the same or another giver groove, the step of sweeping the said layer between the said land of said giver groove and a relatively moving land of a second helical groove facing the said first groove and forming a taker groove, the step of intensively shear-working the said layer between the said relatively moving lands, the step of discharging said layer into the said taker groove and the step of transporting the said medium in the said helical taker groove, characterized in that the said lands of said helical giver and taker grooves are of at least the same order of width as the said grooves themselves, whereby to work substantially all the layers exuded from the said giver groove through the preset gap between the saidco operating lands.

I Apparatus to carry the said invention into effect may comprise an exterior component having an internal operating surface provided with a helical thread and an interior component having an external operating surface provided with a helical thread of different direction but substantially co-axial with said helical thread on said internal operating surface, the said helical threads facing one another and defining a passage for a medium to be mixed; the envelope defined by the crown of the thread on the interior component being within the envelope defined by the crown of the thread on the exterior component and at a clearance therefrom, and the cross sectional areas of the grooves of the said facing threads varying in opposite senses between a maximum and a minimum value for each of the said threads along substantially the same length of the said passage; whereby when in operation the said medium moves along the said passage, portions thereof are successively transferred between the grooves of the said facing helical threads as giver and taker respectively; the said apparatus being characterized in that the crowns of the said threads conform at least in part to sections of frusta of cones having substantially the same apex angle, the said crown or land being individually of a width at least equal to the width of the corresponding helical groove, whereby substantial surface areas at predetermined clearance'for shear work on portions of the said medium are formed between the said lands. Such apparatus may comprise means for effecting adjustment of relative position along the said common axis of the helixes between the two components, for adjusting the clearance between said lands.

In such apparatus the minimum values of groove cross sections for each of said helical threads may be zero and the said threads may be of opposite hands. One or the other or both of the said components may be mounted to be rotatable and means maybe provided for driving the same, orat least asection of one or both of said components may be mounted to be rotatable and driven.

Such apparatus may comprise an exit means with a valve-means for intermittent opening and closing of the said exit and it may generally be provided with entry and/ or exit means adapting it for continuous or for batch operation.

In alternative embodiments the said envelope to the crowns or lands of the said threads may be cylindrical for permitting axial relative displacement of the said components without change of clearance.

In yet another embodiment the conical interface between the lands of the said helical may have an apex angle approaching 90 or even equal to 90 so that the said conical interface becomes a flat plane.

In preferred embodiments of this invention, the helix angle of the helical'groove in the rotating and driven component, at least, is'between 45 and 90, where by helix angle is meant the angle between a tangent to the helix and a plane through the axis of the helix at this tangent position.

This invention also comprises systems of cooperating male and female screws generally as described above, but modified in that one screw has lands which are narrower than the groove or grooves thereof. In that case the co-operating screw, having land or lands broader than the groove-or grooves thereof, is specifically adapted for heat transfer therethrough, on account of its broad lands being continually swept by the narrow lands of said cooperating screw to provide intensified heat transfer with each layer of the material being transferred from giver t-o taker.

The invention will be described by way of example and in some detail with reference to the accompanying drawing, in which:

FIG. 1 is a diagrammatic section through an intensive shear-working machine of this invention.

FIG. 2 is an alternative detail of the embodiment of FIG. -1 showing a single start male screw configuration.

. FIG. 3 is an alternative detail of the embodiment of FIG. l-showing a double-start male screw configuration.

FIG. 4 is an alternative detail of the embodiment of FIG; 1, showing a single-start female screw configuration.

FIG. 5 is an alternative detail of the embodi FIG. 1 showing a double-start female screw confi sraticn.

PEG. 6 is a diagrammatic section of screws a modification of the machine of PEG. 1 showing the relative position of the screws for a large clearance.

PEG. 7 is a diagrammatic view of a similar modii cation with the female screw transparent to enable the operation of the device to be visualized.

FIG. 8 shows a modified embodiment of the invention in side elevation and partly in axial section.

The shear working device shown in FIG. 1 comprises a sh ft l. which is rotatably mounted in a casing Z, by means of a bearing and drive shaft assembly 8, the whole being mounted on a common base 17. The apparatus comprises a feed section 3 and the shear-working section 2 as well as a convenient outletsection, say an extrusion die 5, following the working section In this example, the feed-section is shown to comprise the helical thread 6 on shaft 1 while the casing 2 provides the cylindrical surface for helix s to rotate in, and also the hopper 7 for feeding a material to be worked. The whole feed-section is mounted and operated as is, for instance, well known in plastics extruder practice.

The working section 4- according to this invention comprises a screw-thread 9 on screw 1 which has land iii which is wider than the groove 11 and which from the entry to the exit of section 4 reduces from a maximum groove cross-sectional area to substantially zero groove cross-sectional area. Corresponding to this, the casing 2 has a female screw-thread l2, likewise having land 13 which is wider than groove 34 and which is of opposite hand to the thread 9 of the male screw. The female thread increases from Zero groove cross-sectional area to a maximum groove cross-sectional area from the entry to the exit of the working section 4. The interface 15 between the male and female threads is of frusto-conical shape and there is a clearance 16 between opposite lands of the male and female helix. The screw bearing assembly 8 is mounted on a carriage 1'8 which can be screwed along the base 1'7 by screw device 19, actuated by hand wheel 29. Drive 21 is also adapted to permit axial displacement of shaft 1 whereby the clearance in between the screws can be adjusted.

PlG. 2 shows an alternative detail of screw 9 in working section 4 having land 28 and groove 2? whose ratio of widths (landto-groove) is larger than shown for the land 1% and groove if. of FIG. 1 and in which the groove is of more rounded profile. As in the embodiment of FIG. 1, the helix is a single-start one of pitch FIG. 3 shows a male screw 9 in the working section 4 which is a second alternative detail for FIG. 1. Here the natio of widths of lands 34 to groove 3} is the same as it is in FIG. 2, but in which the helix is a two-start one whereby the pitch t of each single helix is double the pitch of FIG. 2.

FIG. 4 shows an alternative detail of part of the casing 2 of PEG. 1, comprising a half of the working section 4 which is split longitudinally along flange 22 so that two halves can be bolted together through bolt-holes 23 to form a complete section 4. The two halves are so shaped as to form a continuous single-start female helix 12 having a land 34 and groove 35 of the same width-ratio as the male screw of FIG. 2, to which it is opposite handed and with which it is intended to co-operate.

FIG. 5 shows an alternative detail similarly as FIG. 4, but in which the female helix 12 is double-start, having lands 36 and grooves 37 of the same width-ratio as the male screw of FIG. 3 to which it is of opposite hand and with which it is intended to co-operate.

FIG. 6 shows a detail of the operative parts of a modification of the machine of PEG. 1 with the male screw withdrawn axially in order to provide a large clearance 16.

FIG. 7 shows diagrammatically a working section 4.

comprising double-start male and female screws, such as for example those of FIGS. 3 and 5, but where for the sake of clarity the view is drawn as if the casing 2 were transparent, the grooves of the female screw being shown dotted.

Considering now the different parts of the screws which lie opposite one another: 38 represents the crossing of the land 28 of the male screw and of the land 34 of the female screw; 39 represents the crossing of the male groove 29 and of the female groove 35; 4% represents the crossing of the groove 29 of the male screw with the land 34 of the female screw; and 41 the crossing of the land 28 of the male screw with the groove 35 of the female screw. The crossing areas 38, 39, 40 and 41 thus represent all the combinations, and recur all along the frustoconical interface 15 between the screws.

In operation, with the inner screw 1 rotating as Indicated, the .direction of flow in its helical grooves 18 as indicated by the black arrows, while the direction of flow in the helical grooves of the stator (female) is as indicated by the dotted arrows. As the grooves in the rotor (male) reduce in cross-sectional area, the material, say a viscous fluid, in these grooves has to enter the clearance 16 and in the narrow slot formed by the clearance between the opposite lands it has to flow by drag-flow in the circumferential directions, as indicated by the small arrows.

The geometry of the screw can be so calculated, including a certain value of the clearance 16, that the circumferential drag-flow between the lands in areas 38 equals or exceeds by a required amount the total forward flow in the screw-system. Thereby it is made certain that every layer of the flow through the working section 1s sub ected to the intensive shear-working which the material is given in the areas 38 between opposite lands. this shear-working can be controlled firstly by the speed of rotation of the male screw, and secondly, by the adjustment of the clearance. This second adjustment is more important as it permits regulation of the shear work input to some degree independently of speed and hence of throughput.

As the shear-working proceeds in enforced order, every layer of a predetermined thickness (i.e. of clearance as set) being given a predetermined amount of shearworking and no more, this enables the total shear work to be put in for a required purpose to be kept to a minimum, thus leading to most economical operation and also permitting minimum heating, as is required for many applications. This has been proved in practice on plastics extruders operating adiabatically, ie without external heat being put in. In these extruders, an intensive working section corresponding to section 4 on FIG. 1 was provided following a screw section adapted for melting the plastics granules to a large degree. In this application, it proved possible and practicable to vary the outlet temperature of the molten plastic by practically useful amounts only by adjusting the clearance, leaving the rotational speed of the screw unchanged.

If the co-operating male and female screws do not vary between full and zero groove cross-section, but between some maximum and minimum values thereof, only a predetermined part of the flow is subjected to intensive mix- Between the different male and female screws shown in FIGS. 25, 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. 2 and of the female screw of FIG. 4, as also the combination of the male screw of FIG. 3 and of the female screw of FIG. 5, 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 starts.

However, combining the double start male screw of FIG. 3 with the single start female screw of FIG. 4 will result in considerable compression as the double start The intensity of p 6 male screw of bigger pitch transports in its groove considerably more material than the single-start, smaller pitch female screw, for the same relative rotational speed.

Conversely, combining the single start male screw of FIG. 2 with the double start female screw of FIG. 5 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.

FIG; 8 shows a modification of the apparatus of FIG. 1 in a side-elevational, partly axially sectional view. The internally threaded barrel of the mixer seen in FIG. 8 consists of four sections 61, 62, 63, 64. Section 61 is stationary and includes a hopper 65 so that it constitutes a feed section. The annular sections 62, 63 are rotatable about the common axis of the several barrel sections and are equipped with respective circumferential worm gears 66, 67 meshingly engaging Worms 68,69. The shafts 70, 71 of the worms permit the barrel sections 62, 63 to be individually driven in the same direction, preferably the direction of the leads of their threads, but at different peripheral speeds.

Annular glands 72, 73, 74 arranged on the feed section 61, the rotatable section 63, and the axially terminal stationary section 64 provide seals between the several adjoining sections.

The screw of the mixer is mounted on a shaft 81 by means of which it may be rotated. The portion of the screw 30 within the feed section 61 defines a substantially cylindrical envelope, and the grooves of its threads are of uniform depth, and of substantially uniform cross sectional area over a major portion of the feed section length. In the annular rotatable barrel section 62, the cross sectional area of the threads on the screw 80 varies in an axial direction away from the hopper 65 from a maximum to substantially zero, while the thread grooves on the barrel vary in cross sectional area from substantially zero to a maximum in the same direction. Within the second rotatable barrel section 63 and the terminal section 64, this relationship is reversed.

The thread grooves on the barrel sections 61, 62, 63,

64 and on the screw 80 complement each other to form a continuous passage for a medium to be mixed. The entrance of the passage is at the hopper 65, and the exit end at a flange 82 to which a discharge conduit may be attached in a manner apparent from FIG. 1.

The shaft 81 together with the worm 841 may be shifted axially in the manner evident from FIG. 1 to vary the spacing of the substantially conical faces of the screw 80 and of the barrel section in a different manner in a first portion of the barrel consisting of sections 61, 62, and in a second barrel portion consisting of sections 63, 64, the feed-section provides a cylindrical surface on the casing 2 for the screw 1 to rotate in and also the hopper 7 for feeding the material in. The whole feed-section is mounted and operated as, for example, is well known in plastics extruder practice.

The heat transfer section 44 comprises a screw-thread on screw 1 which has narrow lands 50 and relatively wide grooves 51. From the entry to the exit of section 44 the grooves reduce from a maximum cross-sectional area to substantially zero cross-sectional area in the screw 1. Corresponding to this, the casing 2 has a screw-thread 52, having contrariwise lands 53 which are wider than the grooves 54 and which thread is of opposite hand to the thread of the male screw 1. The interface between the male and female threads is of frusto-conical shape and there is a clearance 56 between opposite lands of the male and female helices. A device as shown, for example on FIG. 1 enables the screw 1 to be displaced axially relative to casing 2 whereby the clearance 56 can be adjusted.

It will be noted that the screw threads are both singlestart, but that the female screw thread 52 has a much larger pitch.

58 indicates heating or cooling elements arranged in casing 2.

In operation, the material to be'heated or cooled, having entered through hopper '7, is transferred in the heat transfer section 44 from the male into the female screw. This proceeds layer by layer, which layers are each individually smeared across the wide lands 53 of the female screw where they take intensive part in the heat transfer, and then collect in the grooves 54. Grooves 54, having a large pitch, transport the material-ifit is viscous-forward at a greater speed of flow than in the male screw, so that its contact with the heated or cooled sides of the grooves is minimised, and it is quickly discharged. For granular material, such as plastics being melted, the broad lands of the female screw also impose a certain compression which aids melting. The layer by layer treatment makes the heat transfer uniform, and by keeping up the temperature-difference through the wall, makes the heat transfer more intensive than it could be if the layer just having taken part in the heat transfer was not removed from the wall. The adjustability of the clearance makes it possible to adjust for the thickness of layer being taken off the wall. Alternatively, in case of wear, it enables increases of clearance to be taken up so that a required thickness of layer can be removed from the heat transferring lands.

I claim:

1. In apparatus for intensive mixing, a barrel component and a worm component co-axial 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 are of at least equal width as said grooves and the lands of the Worm face the lands of the barrel, said threads being of different lead at least in direction, 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 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 adapted to be axially shifted in relation to said barrel thereby to vary the spacing of said surfaces from each other, at least one of said components being rotatable in the direction of the lead of its thread, so as to convey the medium towards said exit end.

2. In apparatus for intensive mixing, a barrel component and a worm component co-axial with said barrel, said barrel having an inner and said. worm having an outer helical thread each with lands between adjacent thread groove convolutionsso that the lands are of at least equal width as said grooves and the lands of the worm face the lands of the barrel, said threads being of opposite leads, the cross sectional areas of opposite'thread groove portions varying the one from a maximum to substantially zero-and from substantially zero to a maximum value and the other one from substantially zeroto a maximum value and from that maximum value to substantially zero so that said portions complement each other 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 spacing of said surfaces from each other, at least one of the components being rotatable in the direction of the lead of its thread so as to convey the medium towards said exit end.

3. An apparatus as in claim 1, said barrel being composed of a plurality of annular sections axially adjoinmg one another, 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 apparatus as in claim 1, said barrel being composed of a stationary section including a feeding hopper and a plurality of rotatable sections in co-axial alignment, a plurality of driving means adapted to rotate 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 1, wherein said conical surfaces taper towards said exit end.

6. An apparatus as in claim 1 wherein respective portions of the threads on said components are connected in co-axial alignment to one another.

7. An apparatus as claimed in claim 1 wherein said barrel and said worm are rotatable in the directions of the leads of their threads, respectively, so as to convey said medium towards said exit end.

8. An apparatus as claimed in claim 1 wherein said barrel and said worm are rotatable in the directions of the leads of their threads, respectively, said barrel being composed of a plurality of annular sections axially adjoining one another, 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.

9. An apparatus as claimed in claim I wherein the helical thread whose groove portion is first of reducing cross-sectional area and which is rotated has a greater pitch than said helical thread of said other component, whereby to effect compression of said medium being intensively mixed.

10. An apparatus as claimed in claim 1 wherein the thread whose groove portion is first of reducing crosssection and which is rotated has a smaller pitch than said helical thread of said other component, whereby to effect decompression of said medium being intensively mixed.

References Cited by the Examiner UNITED STATES PATENTS 2,183,959 l2/39 Dunsheath. 2,547,151 4/51 Braeseke 25-44 X 2,744,287 5 56 Parshall et al.

WALTER A. SCHEEL, Primary Examiner.

I. S. SHANK, Examiner.

Claims (1)

1. IN APPARATUS FOR INTENSIVE MIXING, A BARREL COMPONENT AND A WORM COMPONENT CO-AXIAL 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 ARE OF AT LEAST EQUAL WIDTH AS SAID GROOVES AND THE LANDS OF THE WORM FACE THE LANDS OF THE BARREL, SAID THREADS BEING OF DIFFERENT LEAD AT LEAST IN DIRECTION, 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 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 ADAPTED TO BE AXIALLY SHIFTED IN RELATION TO SAID BARREL THEREBY TO VARY THE SPACING OF SAID SURFACES FROM EACH OTHER, AT LEAST ONE OF SAID COMPONENTS BEING ROTATABLE IN THE DIRECTION OF THE LEAD OF ITS THREAD, SO AS TO CONVEY THE MEDIUM TOWARDS SAID EXIT END.

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