Mixing apparatus

Start of patent duration: 1982 05 15 Longest possible duration:

Issued on: 1982 12 27

Inventor:

© dependence:

AT 369 316 © Pamphlets considered as delineated by the prior art:

AT-PS 219838 DE-AS 2143184 GB-PS 1435379 US-PS 2744287

Nr.369316

The invention relates to an apparatus for continuous mixing of rubber or the like. viscoelastic media, comprising a housing member and a screw member rotatably disposed therein with a portion in which the housing member having an inner action surface and the worm member having an outer action surface are coaxial with each other, which action surfaces support mutually opposed helical flights of different pitch defining a passage for form the medium to be mixed, wherein the envelope surface of the crown of the inner flights has a sufficiently small distance to the envelope surface of the crown of the outer flights and coincides with and wherein the cross-sectional surfaces of the grooves in the opposed flights on a certain length in opposite sense between a minimum and change a maximum value.

Continuous mixing machines have been proposed which include a rotor and a housing; In this case, the rotor has an outer helical gear and the housing has an inner helical gear, which is opposite to the helical gear of the rotor and coaxial therewith. One of the screw flights can form part of a feed zone, while the two following screw flights form a mixing zone; On a given axial length, the flight in one of the components (eg rotor) changes from a full cross-sectional area of ​​the worm groove approximately to the cross-sectional area zero of the groove, while the worm gear of the other component (eg of the housing) approximately changes from the cross section zero of the screw groove to a full cross section of the screw groove, and vice versa for an approximately following mixing zone. As a result, the medium, which is located in the entry zone in the worm groove of the one component, from the beginning of the mixing zone continuously from the worm groove of the one, the donor component in the worm groove of the other, the slave component transferred so moved, until the end of the mixing zone most or all of the medium flow has been transferred into the screw groove of the other component and thereby with an intensity which corresponds to the relative movement between the two components, has been mixed and processed continuously in layers - without outlet or multiple action.

Because of this mode of action, a device with at least one such mixing zone is also called transfermix zone. However, the basic mixing action of such a transfermix zone does not depend on relative rotation between the two components, but also acts on stationary components as the medium is pumped or otherwise transported through them.

Thus, for example, a transfer mix zone may be formed by a system of helical vanes in a passage of generally circular cross-section through which the medium is pumped for heat exchange through or with the walls of the passage; The helical guide surfaces then act as secondary heat exchange walls. In such a transfermix heat exchanger, the medium may also be a liquid or a gas, optionally powder-carrying, and when flowing, changes in the state of the medium may take place.

Thus, a transfer mix zone can be more generally defined as:

A continuous mixing apparatus comprising an outer member having an inner action surface forming a flight and an inner member having an outer action surface forming a helical pitch having a pitch other than the helical pitch of the inner action surface but coaxial therewith; these flights are opposite each other and form a passage for a medium to be mixed, the envelope surface of the edge or crown of the inner flight having a sufficient small distance to the envelope surface of the edge or crown of the outer flight or coincides with it; the cross-sectional areas of the grooves in the opposed flights change in a contrary manner between a minimum and a maximum value over a certain length of the mixing passage. When the medium is moved through the mixing passage, its layers are successively transferred between the opposed screw grooves serving as donors and takers, thereby undergoing at least a change in their direction of flow and their relative positions in the overall flow of the medium.

A transfermixing zone may generally be considered as an apparatus for continuously applying a surface or edge effect to a mass flow of a medium to progressively change a state quantity of that mass flow with predetermined uniformity.

In this sense, the heat exchange is an example of a surface effect. The application of shear forces is, depending on the consistency of the medium, an example of an edge effect or a combined edge and surface effect. For example, in plasticizing a rubber compound as a cold solid, there is first a shearing action between intersecting worm edges of the two components. In the shear working of a viscous medium, there is a combined edge and surface effect in that, in addition to the shear action, the edge of one flight crosses the groove of the other flight and transmits the shear stress resulting from adhesion to the surfaces through the medium itself becomes. In such a case, the width / depth ratios of the screw grooves become a factor in the application of the shear stress of the medium and thus, inter alia, in the pumping action of a rotating transfermix zone on the medium.

A mass flow is defined as the totality of flows in both components in each cross section of the transfer mix zone, which is many times greater than the portion (the layer) of the flow which is currently transferring from one component to another in this cross section, the most intense one Movement is suspended. Among other properties, this transfer mix zone differs from other grinders, eg Colloid mills in which the processed flow is essentially identical to the total pumped flow.

By arranging transfermix zones one after the other, one can obtain the required intensity of the edge or area effects on a mass flow or expose a mass flow of a series of different effects in succession, u.zw. each with a uniformity determined by the particular geometry. As one of many examples, a rubber or plastic compounding extruder may be cited which provides plasticization or fusing in one or more mixing zones, with shear and heat exchange, and with mixing action and pressure build-up for extrusion in these or subsequent mixing zones. Another example of an edge effect would be chemical contacting with a catalyst, wherein the catalyst may be attached, for example in the form of a wire, to one or both screw edges.

The surface and edge effects are so called because their intensity is a maximum at the surface or edge of the direct application and this intensity decreases with increasing distance in the direction of the mass flow into it. The edge-encircling surface of revolution through which the transfer of the medium from one to the other component takes place in a transfer-mix zone³⁵ is divided by the crests or edges of the intersecting flights. The more threads are present in one or both components, the smaller are the redistributions of the transfer surface, and the more uniform the application of the

Edge or surface effects.

However, there are limits to the duplication of the flights in each component, because 40 each screw for strength reasons must have a minimum crown width, u.zw. depending on

Application; and the more worm grooves are offered for the mass flow, the closer each individual worm groove, until the flow conditions are impaired and it also does not go purely geometrically. In cases where the relative rotation between the components provides the pumping action, ie in all extruders, results in screw grooves with too small Behhält45 widths / depths insufficient transfer of shear stress in the depth of the grooves, so that there stagnation or reflux occur. In a non-rotating transfer mix zone, the resistance to the pumping action may become too great.

The extreme depths of the screw grooves result in a transfer mix zone at opposite ends of the mixing zone in each component, but with the effect of such a limitation ⁵⁰ makes no less effective by an excess number of flights.

Such limiting effects are easily understood by means of larger size transfer mix zones which have been extrapolated from smaller versions that fit the particular purpose.

Nr.369316

For example, when the diameter and length as well as the depth of the annular passages of a transfer mix zone are doubled, the transfer area is quadrupled. If one equals the number of flights in each component, as it corresponds to a geometric enlargement, then the number of subdivisions of the transfer surface per unit area is thereby quartered.

On the other hand, when the number of flights in each component is doubled, the number of divisions of the transfer area per unit area is restored to the same value as in the small transfer mix, but the width / depth ratio of the individual flights is halved. This then leads to the above-indicated loss of pumped throughput or general aggravation of the flow characteristics.

The above considerations explain difficulties encountered in increasing transfer mix units, particularly when used as cold feed extruders, as well as limiting the performance of smaller transfer mix units in this and other applications. Such limitations are not only present in highly viscous media, but also occur in flowable media; they may not be considered as such, but rather as opportunities for improvements that were not yet feasible.

This invention is intended to provide a transfermixing zone with which the uniformity, ie the uniform effect, can be increased with the application of edge and / or surface effects, as indicated by the number of subdivisions of the transfer surface, without that the mass flow of the medium is reduced by unfavorable ratios of width / depth of the individual screw grooves.

In addition, a transfer mix zone is to be proposed which, while maintaining the desired uniformity, ie quality, can be geometrically enlarged in its main dimensions, as indicated by the subdivision per unit area of ​​the transfer surface, without causing a disproportionate reduction of the mass flow through unfavorable ratios width / depth of individual screw grooves results.

In addition, transfer mix zones for rubber and plastic extruders, especially with cold feed, are proposed with which a plasticization and / or melting with low length / diameter ratios (L / D) can also be achieved for those media that were previously only in In some cases extruders with high L / D ratios and in single screw mixers could not be processed at all without the risk of general or local overheating.

In particular for such applications, enlargements are to be made possible without losses in quality and throughput occurring.

According to the invention, this is achieved by a device of the type mentioned, which is characterized in that the number of worm threads on each of the two components within the transfer mix zone changes in the opposite direction to the change in the cross section of the worm grooves on the relevant component, wherein the Worm grooves with a larger cross-sectional area have a greater width than the worm grooves with a smaller cross-sectional area.

According to a preferred embodiment, it is provided that the worm threads of the housing part and the worm threads of the worm member within the transfer mix zone, as known per se, are formed in opposite directions, and that the product of the number of flights of the housing part and the number of flights of the worm member in each Cross section of the transfer mix zone is approximately constant.

In such a continuous mixer, it is also expedient that the housing part and the screw part in a conventional manner of individual rings, within which the number and pitch of the flights is constant, are constructed, wherein the flights of adjacent rings are offset from each other discontinuously.

Another feature of the invention provides in order to increase the number of flights of the screw member to more than the double team input into the transfer mix zone, a first additional flight closer to the pressure side than to the vacuum side of the existing flight begins with gradually increasing height and further additional screw flights from the pressure side of the original existing screw further Start stepping into the depth of the transfermix zone.

Nr.369316

It is preferably provided that two transfer mix zones are arranged adjacent to each other, whereby in the first transfer mix zone the number of screw flights increases and in the second transfer mix zone the number of screw turns decreases; It is expedient that in the boundary region between the two transfer mix zones, the total cross-sectional area of ​​the grooves on the screw part is equal to zero.

A particular embodiment is that the number of flights on the screw part in successive sections of the transfer mix zone each doubled and the number of flights in the opposite sections of the housing part is halved in each case. It is advantageous that, after the beginning of the first transfer mix zone, the number of screw flights on the screw part is increased more than twice by new starts of screw flights shifted stepwise from the pressure side of the existing screw flight, and in a further section by evenly doubling increased to the maximum number where the screw groove cross section has its minimum value, and then decreases by evenly distributed halving, and that the number of flights in the housing part in the first transfer mix zone decreases by evenly distributed halving and increases in the second transfer mix zone by evenly doubling, these doublings and halves of the flights being opposed to each other Cross sections of the housing part and the screw part done.

In the following the invention will be explained in more detail by embodiments with reference to the drawings. Show it: Fig.l in cross-section, an application of the invention as cold-feed rubber extruder with two transfer mix zones, Figure 2 is a sectional view of an alternative embodiment of the transfer mix zone of the rotor of Fig.l, Figure 3 is a sectional view of the housing insert, the 4 shows, in a schematic form, a development of a rotor with two transfer zones and many passages in comparison to the example according to FIGS. 1 to 3, FIG. 5 shows in schematic form a development of a housing insert for the transfer mix zones with much more gears than in the example according to Fig.l to 3, Figure 6 in schematic form Fig.4 and 5 superimposed to explain a transfer mix Zone in two parts with many more gears than in the examples Fig.l to 3, for improved uniformity or an enlarged version of the examples of Figures l to 3 without loss of uniformity. and Fig. 7 shows in schematic form a development of a housing insert similar to Fig. 5, but composed of a series of separately manufactured ring members, each having a different number of gears with different pitch angles.

In the cold feed extruder of Fig. 1, the rotor -21- is mounted in the housing -22- in the usual way. This has a feed opening -23- and an outlet flange -24-; Both rotor and housing are equipped with the industry standard heating and cooling devices. Known exit devices, such as an extrusion head, a screen pack, a pelletizing head or fixed cutting knives, could be connected to the exit flange.

The rotor comprises a feed and compression zone -25- with a single-flight screw -27- leading to the first transfer mix zone -A-, and a discharge zone -26- with a double-flight screw -28- directed towards the second transfer mix zone -B- follows. Both rotor zones -25 and 26- are located in cylindrical bores of the housing. The feed zone -25- may be provided with known devices for assisting forward transport, such as longitudinal grooves in the housing, etc.

In the first transfer mix zone -A-, the housing insert -29- has a first section with a 20-speed screw -30- and a second section with a single-speed screw -31- while in the second transfer mix zone -B- one Section with a continuous worm -32- a section with a 20-speed worm -33- follows, as shown below the drawings.

The rotor extends in the first transfer mix zone -A- with a single-flighted screw -34- in a first section and is built up in this section to the four-start screw -35-, which as such runs in a second section to the point, where the grooves with the cross-section zero at the end of the transfer zone -A- leak. In the transfer mix zone -B-, the rotor starts with a section with four-flight screw -36- and ends with a branch cut -37- which passes over the end of the transfer zone -B- as the double-flighted section Snail -28- the discharge zone continues to run.

The number of flights indicated for the rotor above and for the housing below Fig. 1 will be understood to vary in a complementary manner throughout the length of each transfer mix zone according to this invention.

The first section of Zone -A- of the rotor shows the gradual build-up from the single-speed to the four-speed auger. According to this invention, this structure starts near the pressure edge of the single-flighted screw; the new flights -38- rise gradually into the zone -A- and transverse to the groove cross-section shifted beginnings, which are smooth transitions to full flights. This prevents stagnation of the un-plasticized rubber that would occur if the three additional flights were to start at the same height and with less smooth transitions.

Fig. 2 shows an alternative embodiment of a rotor -21-, wherein like numerals denote the same parts; In the transfer mix zone -A-, seven additional screw flights -38'- begin gradually along and across the original groove and continue as an eight-flight screw -39- until the end of the transfer mix zone -A-. In contrast to the embodiment according to FIG. 1, the grooves of the eight-speed worm do not reduce to the cross-section zero but only to a minimum value, and increase again in the transfer zone B- as a continuation of the eight-start worm -41- the transfer mix zone -B-. In the second section, every second flight proceeds symmetrically, leaving the four-flight screw -42- to the end of the transfer mix zone -B-. After that, the second-flighted screw -43- of the discharge zone -26- remains due to further leakage of every second gear. The number of flights in the various sections is shown in Fig.2.

Fig. 3 shows the case insert of Fig.l outside this device and without rotor to illustrate its structure. The same numbers indicate the same parts as in Fig.l; the number of flights and their sections are also shown.

In use, an unvulcanized rubber compound in the form of strips (skins), chunks (pellets) or powder is introduced into the feed opening -23- and brought to the first transfer zone -A- by the rotor -21-, whereby compression may occur for venting.

Upon entering the transfer mix zone -A-, the outermost layers of media flow in the rotor are transferred to the twenty grooves of the housing screw, which become deeper in that section until they reach a width / depth ratio of about 1 (in the plane) the drawings). During this transfer, these layers are divided and sheared by the relative rotation for plasticization, while in the shallow grooves, effective forward transport occurs as a result of the same relative rotation. From the beginning there are 1 χ 20 - 20 points of intersection of worm crests or cutting points for a shearing action.

In the worm groove of the rotor, the newly developing worm -38- penetrates into the rubber flow near the pressure edge of the original catchy worm -27-, subdivides the hitherto hardly plasticized material and also displaces it over the worm groove, as in the other two other developing screw flights -35- do. Thus, the forward flow in the screw groove is not held on, but distributed to the negative pressure side of the original screw, where, depending on the original degree of filling, still room for filling can be free.

After the gradual emergence of the three auxiliary scrolls -34-, the flow in the rotor proceeds in four helical grooves -35- which have been fully running and begun at their lowest points with a width / depth ratio of approximately one, thereby ensuring good forward transport ,

During development work on this invention, only three helical flights -34- formed at the same level at the beginning of transfer zone -A- were tested, but this greatly reduced throughput. The same thing happened when an additional flight was started in the middle of the original worm groove and the other two later in the middle of the two grooves. This led to additional staircase-shifted initial layers

- 7 Nr.369316

Worm threads in the case of plasticization of rubber. The same applies to the melting of plastics, but does not have to be for a medium which reaches the transfer mix zone -A- even in a relatively good flowable state.

Compared to the four-speed screw -35- in the second section then the ten-course 5-screw -31- is arranged, which is due to the elimination of every second flight of the twenty-speed screw and thereby at the beginning again has a greater groove width than depth, ie the favorable condition for the forward transport. As can be seen, on each circumference of the transfer surface 4 χ 10 = 40 overlap points of the screw cores and thus cutting points for a shearing effect. This results in both a good uniformity in the application of the. Shear work and also good forward transport achieved. At the end of the transfer mix zone -A-, all layers of the rubber flow from the screw groove of the rotor have been transferred into the 10 screw grooves of the housing and thereby processed to a uniformity which is mainly determined by the number of cutting points distributed over the transfer surface. the more cutting points, the more uniform.

Analogously, for the transfer mix zone -B-, because of the changes in the screw flights according to the invention, there are 4 χ 10 = 2 χ 20 = 40 cutting points in each cross section of the transfer zone, which also ensure the uniformity of shear processing to a certain extent there.

With the rotor of Figure 3 in place of the four-speed rotor of Fig.l is the number of 20 cutting points in each cross section:

χ 20 - 8 χ 10 = 10 x 8 = 20 χ 4 = 80 for all parts of the transfer mix zones -A and B-, where we can look at the average value of the eighth-starting screw in the first section of the rotor as a four-start screw.

It has been determined experimentally that for a small transfer mix unit with a rotor diameter of 82 mm (from zone -B-), in which even without the inventive change in the number of flights a geometry with 80 cutting points / circumference by means of a housing insert with 20 flights and a 4-speed rotor for 4 χ 20 - 20 χ 4 - 80 cutting points / circumference, the extrusion results were significantly worse for a blend containing more than 50% natural rubber. When using the device 30 according to the invention there was a more than 50% increase in throughput of sufficiently smoothly extruded treads from less than 400 to 630 kg / h at a temperature of the extrudate that was more than 5 ° C lower, although the screw speed could be increased from 86 to 108 rpm.

Within certain limits, the number of cutting points / circumference serves to distinguish between Transfer35 mix geometries of the same diameter. For transfermix geometries of different sizes, it is advisable to take a subdivision length of the circumference as a characteristic size. For example, for 80 cutting points to the extent of a 82 mm diameter transfer mix, this results in 3.24 mm. This subdivision length of the circumference gives an indication of achieving equivalent performance in a larger cold feed extruder 40, at least for the plasticizing zone -A-.

4 shows the developed schematic view of a rotor -50- with a feed section with a single-flighted worm -51-, which after the start of the transfer mix zone -A- merges into an eight-start worm -52- with a stepwise start -53-, as already described for Fig.l and 2. In another section of the Transfermixing Zone -A- 45, the eight-flighted screw is subdivided into the sixteen-speed worm by evenly doubling the flights --54- and, in a third section, again into the thirty-two-speed worm-55-, corresponding to the reducing groove depths Zone -A-.

In the transfer mix zone --B-, the thirty-two-speed worm -56- starts at depth zero of the grooves and halves for two more sections to one sixteen-speed 50 -57 and eight-speed worm -58- to the end of the two Transfer mix zone -B- to run as a double-flighted screw -59- in the discharge zone.

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In Fig. 5 there is shown, in a developed schematic view, a corresponding housing insert -60- which, at the beginning of the transfer mix zone -A-, begins with a forty-speed worm -61- of practically zero depth, in the second section into a twenty-worm worm -62- and then into a ten-speed screw to the end of the transfer mix zone -A- passes. In the transfer mix zone -B-, conversely, first the ten-start screw -64- of maximum screw depth is placed, followed by the twenty-start screw -65 and the forty-odd screw -66- of zero-reducing groove depth.

Fig. 6 shows Figs. 4 and 5 superimposed. This figure shows that except for the resulting eight-speed screw of the rotor at the beginning of transfer mix zone -A-, where the interfaces increase from 40 to 320 / circumference, the remaining transfer mix Zones -A and B- each have 320 interfaces / extent, u.zw. with worm grooves becoming wider with increasing depth, and vice versa, in order to maintain the conditions for good forward pumping.

Using the subdivision length of 3.24 determined above, the circumference of the large 320 interface transfer mix for the same geometric plasticization conditions is calculated as 320 x 3.24 = 1036.8 mm and the diameter as 330 mm equal to about 13 ,

Considering that rubber extruders are usually driven at the same peripheral speed for all sizes, so that the residence time increases proportionally with size, this factor causes a larger transfer mix to be effectively built with this geometry then the same plastication quality as the 82 mm diameter transfer mix with the size corresponding throughput.

Figure 7 shows schematically five separate rings -71, 72, 73, 74 and 75- which are assembled to form a housing insert 70-. These, like insert -60-, are installed in a housing, whereby the individual rings can be locked to the housing or to each other in order to absorb the torque that is exerted by the medium during use.

Ring -71- has a forty-odd flight outgoing from zero depth -76- with helix angle 68 °, ring -72- a twenty-flighted helix -77- with helix angle 59 °, ring -73- a ten-speed helix -78- with helix angle 50 ° and rings -74 and 75- each have ten-flight screws -79 and 80- with pitch angles of 59 and 88 °, respectively.

It follows that, depending on the type of surface effect to be applied to the flow of mass, for example shearing a medium whose viscosity (toughness) quickly approximates with the plasticization, a change in the pitch angle in the direction of 45 °, the angle greatest pumping action (sin 45 ° x cos 45 ° is a maximum), to build the screw grooves with a reduced maximum value and thus additionally to keep the ratio width / depth smaller.

In case insert -70-, the transfer mix zone -B- has only a ten-speed worm, but with gradually changing pitch angle from ring to ring. Accordingly, one could use together therewith a rotor having a geometry of 320 interfaces / perimeter in the plasticizing transfermixing zone -A- and a geometry of 80 interfaces / perimeter in the transfermixing zone -B-, in order to achieve less intensive processing to carry out the already plasticized medium.

Similar to the case inserts, rotors can also be composed of rings, which then have the screws on their outer sides and are fitted together on an axle and keyed together with this or together to transmit the torque.

The manufacture of rotors or housing inserts from single rings is particularly advantageous for larger transfer mix units, since such rings are easier and in particular to produce with smaller machine tools, which can easily compensate for the necessary multi-processing due to the mating and the seal.

Furthermore, one can then manufacture rotors and housing inserts of different transfermix geometries from standardized rings from stock.

When assembling Transfermix zones of single rings, these can also be arranged in different angular positions, so that possibly continuous flights under 9

No.369316 broken and more or less symmetrically arranged. If the screw threads are arranged so interrupted, additional flow-splitting properties are introduced into the mode of action. These could also be installed in transfer mix components that were not originally made of rings, but were manufactured in one piece.