Mixing apparatus

<img file="AT368073B_D0001.tif" />

AUSTRIAN

PATENT OFFICE

Int.Cl³.: B29H 001/10 ® AT PATENT NOTICE © Nr.368073 @ Patent proprietor: FRENKEL C-0 AKTIENGESELLSCHAFT VADUZ »LIECHTENSTEIN @ Subject: DEVICE FOR CONTINUOUS MIXING WITH A ROTOR © Addendum to patent no.

(62) Elimination from:

Registered on: 1977 07 14 »5103/77 (23) Exhibition priority:

Union Priority: UNITED KINGDOM / UK (GB) 1977 07 01

27623/77 CLAIMED (42) Start of patent period: 1982 01 15 Longest possible duration;

B Issued on: 1982 09 10

Inventor:

@ Dependency:

θ References contemplated by the prior art:

GB-PS 987114

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The invention relates to a device for continuous mixing with a rotor which is rotatably mounted about its axis in a coaxial housing, and having at least one mixing zone, wherein the rotor has an outer screw and the housing an inner screw, the cross-sectional areas of the screw grooves relative to change each other in the opposite direction and the worm threads are in opposite directions.

Such devices are used for processing and / or processing of flowable materials, either alone or mixed with powders, liquids or gases, wherein the flowable materials can have a high viscosity. In particular, the invention is concerned with viscoelastic materials, such as rubber.

From GB-PS no. 987,114 an arrangement of this type is known in which, as can be seen from the regular intersections of the worm grooves and the housing grooves, the pitch angle of both grooves is equal.

Continuous mixing machines have been proposed which include a rotor and a housing; In this case, the rotor has an outer helix and the housing has an inner helical gear, which is opposite to the helix of the rotor and coaxial therewith; the screw flights form mixing zones in which the flight in a component (eg the rotor) changes to a given axial length from the full cross-sectional area to the cross-sectional area zero, while the worm gear in the other component (eg, the housing) changes from the cross-sectional area zero to the full cross-sectional area, and vice versa. During operation of such a mixing device, the material to be transported in a component at the inlet of this mixing region or mixing stage is transferred in layers from one component (the sensor) to the other component (the receiver) into which the entire material has been brought when it reaches the end of this mixing section; As a result, this material is mixed and processed in layers during this transfer according to the conditions of the relative movement between the two components.

For two juxtaposed mixing sections, the roles of the encoder and receiver change for the same component. For example, a rotor that starts with a feed section, such as a normal extruder, in a housing of cylindrical cross-section, in a first mixing section, the slave screw gear sizer in the housing, while in an intermediate mixing section of the sender screw gear, the worm gear in the housing while the slave worm gear is on the rotor. Thus, a device having two planes of shear (one in each mixing section) may be described by which the mass flow is successively processed as it passes through the device before exiting the device through an extrusion head or other outlet unit.

If the worm threads in the donor and slave sections are designed in opposite directions (eg a left-handed or right-handed worm gear in one part and a right-handed or worm gear in the other part), then the relative rotation between the rotor and the housing leads to a transport in the forward direction in the two helical channels, while at the same time the material is transported due to the shearing processing explained above. Thus, each mixing section may be considered as a twin-screw or twin-screw extruder in which the outer (housing) flight is wound around the inner (rotor) flight, the two flights interacting through the material passing over the (imaginary), between them, cylindrical or conical shear plane is transferred '.

This feature represents a significant difference of this system compared to an extruder mixing system having a helical channel rotor rotating in a cylindrical housing. In all of these systems, mixing and shearing work can only be effected by introducing gaps into the helical flights and / or locally increasing the leakage flow, for example, over every other web of a helical flight. This results in a mixture and shear stress only in relatively narrow zones of high intensity; moreover, this mixture runs at the expense of the flow component in the forward direction. So in order to get a certain result with a certain amount of 3

No.368073 to achieve uniformity are high ratios for these backflow systems

Length / diameter required; In addition, the use of these systems is generally very limited, since the risk of overheating of local hot spots and similar adverse

There are effects that can not be avoided despite advanced temperature control.

The above-mentioned feature of the system is also an essential difference to the so-called twin-screw extruders. Essentially, these systems have helical or helical rotors on parallel center lines in a housing with a cross section corresponding to the number 8; the rotors cooperate to create shear forces and / or material transfer and / or increased forward feed at the narrow point of this dual housing. Depending on whether these screws are actually engaged with each other, these systems provide very strong forward feed. However, if a certain overall result with a desired homogeneity or uniformity to be achieved, it is because of the local course of the mixing or shearing a relatively high ratio length / diameter required; moreover, such twin screw systems are extremely complex in mechanical terms compared to single rotor systems and are therefore expensive and complicated.

Thus, although devices according to the system described above are superior in design to the other illustrated systems, their use for various purposes has resulted in certain disadvantages. These disadvantages will be described below with reference to the processing or preparation and extrusion of rubber compounds; However, similar deficiencies also arise in other applications, for example, the preparation and extrusion of plastic materials, similar operations in process engineering in general and in particular in the so-called earth industries. In addition, these effects are not limited to the heavier, more viscous materials, although for more fluid materials, these disadvantages are not readily apparent; In these cases, these deficiencies must rather be considered as improvements that could not previously be realized.

Continuous rubber mixers or mixer extruders according to the system described are fed either cold or hot; in the cold feed, the material supplied is very stiff, practically a solid; in the hot feed, the feed material is highly viscous although it is usually not homogeneous in composition and viscosity. In both cases, the material supplied can not practically compress and does not flow, so that in a mixing section, the two machine components must not exert any compressive forces that would lead to excessive heating without a corresponding shear machining or mixing action; because this would give the machine one of the functions, as they have just been highlighted above as a difference from the mixing device according to the invention. Therefore, the screw flights in the rotor and housing generally have the same helical angle; besides, they have the same number of helical channels in parallel in each section. For example, a rotor typically starts a single gear (a single channel defined by a flight) in the delivery section; As the cross-section and / or helix angle of the rotor decreases to compress the feed material with respect to possibly entrained air, it maintains the helix angle in the first mixing section at substantially the same point as that helical channel disappears , In the housing, two or four parallel flights (two or four-speed screws) could be arranged; these flights would again maintain virtually the same screw angle throughout the first and second mixing sections. In the second mixing section, the rotor could start as a two or four-speed screw, depending on the application, but always on the same screw angle between 30 and 40 °. For geometric reasons, such a helix angle limits the number of gears of the applicable cross-sectional shape to a maximum of 8.

With regard to the applicable cross-sectional shape, experience has shown that in the first

Mixing section the width of the helical channel, in particular in the slave component,

- 4 No 368073 should not exceed a certain maximum, so that cold or less mixed and more viscous lumps can be avoided, even with much more than one following

Can not remove the mixing section once it has formed.

Geometric considerations for using channels of given widths with equal helix angles in both the donor and the slave have shown that the number of helical parallel channels (the number of flights of a screw) is limited for each such angle. The number of gears or sections is, however, the greater, the greater the worm angle, ie the more it approaches an angle of 90 °, if it is a plurality of parallel splines or Sliding keys or grooves in the rotor or the housing is.

An additional requirement is that the ratio depth / width of each channel for the conditions of forward transport not be allowed to be too large, so that the material transferred by shearing to the shear plane can be held in each channel.

Due to the above conditions, the following has been found in practice:

A) The mixing / processing or the requirements for more complicated cold feed extrusions, such as the extrusion of tough or hard hzw. solid masses or the final mixture and extrusion in one operation on smaller diameter devices, inevitably resulted in a greater number of mixing sections, thus substantially reducing the advantages of the system as compared to the systems described above;

B) It is difficult to geometrically increase mixer extruders, especially cold fed devices, while maintaining the performance that can be achieved with smaller diameter machines; This also again a major advantage of the system described is lost in comparison with the systems explained.

It is therefore an object of the invention to obviate the drawbacks mentioned, for example for cold-fed mixer extruders for rubber, in order to obtain high quality extrudates with a small length / diameter ratio device, as in a two-shear plane design to achieve high throughput units with respect to the screw diameter. Further, in mixer extruders of the type described, the operational advantages are to be realized at low length / diameter ratios, such as a low temperature threshold of the machined material with the attainment of the desired high uniformity even against little or no leakage resistance, thereby providing an approximately necessary , larger or greater specific machining input can be achieved by simple throttling devices to achieve a desired low energy input value, without loss of uniformity, without the risk of overheating and without the need for over-cooling and complex temperature control.

Furthermore, it is intended to enable adiabatic operation to be approached for each required processing so that the devices can run at higher speeds and thereby achieve larger specific throughputs, size by size; In addition, the mechanical structure of such a device is to be simplified and thus the costs are reduced with respect to mechanical reduction gear and heating or cooling devices. Finally, a substantially geometrical scale up of these devices with respect to their essential dimensions, such as length with diameter (constant length / diameter ratio), shall be achieved with no loss of desirable properties as the size increases.

According to the invention, the device of the type mentioned above is characterized in that the mutually different pitch angles of the flights are complementary to each other, with a pitch angle between 45 and 90 °, when the other pitch angle is between 0 and 45 °. Considering the level of the shear plane, a subdivision is achieved which is sufficient for the requirements for mixing and processing.

Appropriately, the slave component for the case of a mixing section, in which the

Encoder component has a worm gear with a screw angle α &lt;45 °, essentially the

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- 5 complementary worm angle (90 ° - α). Since the transport of the material in a helical channel, as far as it is influenced by the screw angle, proportional to the

Product (sin α χ cos α), the transport factor will be the same for the two components, while the number of gears in the slave may be greater than that in the encoder.

For example, if a rotor with a helix angle of 32 ° 30 min and a catchy construction is used as the donor followed by a feed section, then a slave housing with the same worm angle could have a maximum of eight courses. However, at a complementary helix angle of 57 ° 30 min, it can have a maximum of well over 30 gears, going up to the same effective cross-sectional area as the transducer, to avoid over-compression.

When scaled up according to the proposal of the invention, the actual dimensions of the cross-sectional grooves of a smaller device need not necessarily be reproduced exactly on a larger device. For example, in the conditions for scale enlargement, which apply to rubber machines, ie that for all sizes, the peripheral speed of the rotors is the same, which means that the speed must be reduced in proportion to the rotor diameter, the residence time with the size of the device to. Thus, for example, if a 120 mm diameter device had a housing with 20 gears at the beginning, then a device with a diameter of 250 mm, ie approximately twice the diameter, would not necessarily have 40 gears at the beginning, but could, for example, also 32 gears are sufficient for use in plasticizing.

It could also be found in use of the device according to the invention that the magnification factors change, for example for rubber machines, perhaps in the direction of larger unit throughputs, ie to a power slightly higher than the square of the diameter, as at present, but with falling standards of quality, which is the case with conventional devices.

However, the proposals of the invention can make the necessary subdivisions for maintaining the quality of increasing diameter possible for the devices with different magnification factors, eg for a rotor with a constant angular velocity, which provides a flow rate which increases with the third power of the diameter, such as it is the case with less viscous materials. In any case, the proposals of the invention are required so that the potential of the continuous mixer of the type described above can be reached even closer, u.zw. both in terms of more difficult mixing tasks for smaller diameter devices and in terms of some performance standard at a series of scaled magnifications of geometrically similar substantial dimensions.

As throttle devices conventional types, such as breaker plates or Siebbzw. Umbrella packs are used for the gradual adjustment of the flow resistance or continuously adjustable needle valve devices that operate with a relative axial movement 40 for the regulation. Suitably, an adjustable throttle flange is provided, in which one or more flow restrictors are introduced in the radial direction in order to achieve a continuous adjustment during operation.

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the schematic drawings. FIG. 1 is a side elevational view of the rotor 45 of a conventional two-level cold feed extruder used in conjunction with the housing sections shown in FIGS. 5-8, with one screw channel in the first and two screw channels in the first and second screw channels second shear plane; Figure 2 shows a similar rotor according to a simple embodiment of the invention, wherein a gradual change to two screw channels in the first shear plane is used; 3 shows a similar rotor SO of an alternative change to four screw channels in the first shear plane and four channels in the second shear plane; Fig. 4 shows a similar rotor showing in the first shear plane a change from one to eight screw channels according to this invention; 5 shows a longitudinal section through a housing bush, which the first and second shear plane of a conventional,

No. 368073 continuous mixer, wherein a three-flighted screw channel is shown at substantially the same screw angle as the rotor; Fig. 6 is a longitudinal section through an eight bushing housing bushing, ie the maximum number of parallel flighting channels, which can be received at the same worm angle as in Fig. 5 without too great maximum depth of the channel relative to its width; FIG. 7 a longitudinal section through a housing bush, showing how the use of the complementary screw angle 12 allows parallel passageways or screws with low depth / width ratio of the channel cut; Fig. 8 is a longitudinal section through a housing bush illustrating how the use of the complementary worm angle 20 allows for parallel flights or worms without too great a maximum depth / width ratio of the channel cut; Figures 9 and 10 are enlarged sections of the maximum groove cross-sections in the housing in the plane of the drawing and at right angles to the axis of the groove; FIGS. 11A and 11B show the simplest version of a continuously adjustable throttle flange with a radially movable limiter, and FIGS. 12A and 12B show a version of a continuously adjustable throttle flange with four radially movable limiters.

As can be seen from Fig. 1, a main portion -1- of the rotor has an entrance portion, a compression portion -3- in a cylindrical housing portion (not shown), a first scissor plane portion -4- and a second scissor plane portion -5- which is one the cross-sections shown in Figures 5 to 8 can be adapted from housings with two planes of shear; In addition, a conventional outlet section -6- is still provided in a cylindrical housing (not shown).

Through the sections -2 to 4-, the one screw -7-, which forms a single helical channel -8-, whose cross-sectional area decreases in the first shear plane -4- to zero extends. The shear plane -4- also has a conical wrap surface. In the second shear plane -5- and the outlet section are two screws -9-, which the helices or form spiral channels -10- of these sections, which emanate from the cross section zero at the beginning of the second shear plane.

In Fig. 2, like reference numerals designate the same parts as in Fig.l; In addition, a second worm -11- is additionally provided in the first scissor plane section -4-. This screw gradually rises from the bottom of the single helical channel -8- to subsequently form the two helical channels -12-.

According to the invention, this additional screw land begins its rise in the first shear plane section -4- and continues for some time or a certain distance as a sub-screw before it assumes an equivalent size and shape to the original screw -1-.

In the embodiment according to Fig. 3, similar reference numerals denote the same parts as in Fig. 1; there are three sub-screws -13- rising from the bottom of the original single channel -8- in the first scissor plane section -4-. The shape of these screws gradually changes to form four helical channels -14- for the last part of the shear plane -4-.

In the second shear plane -5-, in addition to the two original screws -9-, two screws -15- are provided, which together form four helical channels -16-. Since all of these screws or channels start from zero, the development of the screws -9 and 15- is quite symmetrical, as is of course also true for the development of the four helical channels -16-.

At the end of the second shear plane -5- the two webs -15- terminate relatively abruptly and the outlet section -6- has only two helical channels -10-.

In the embodiment according to FIG. 4, the same reference numbers also designate the same parts as in FIG. seven additional screws are provided, rising in the first shear plane -5- to define eight helical channels -18-.

Fig. 4 shows a preferred embodiment with which the division of the original one channel -8- into the eight helical channels -18- can be achieved.

The first additional screw -17- begins near the leading edge of the screw -7- shortly after the beginning of the first shear plane -4-; shortly thereafter follows the second screw -17-, etc. This causes the material flow, which in front of the front edge of the screw -7- zusammeni

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7, while it may be loose and lumpy at the trailing edge of the screw -7-, distributed in compressed form across the channel -8-, and driven in an impeller-like manner to flow to the helical channels in the tube Stator to be convicted.

In the second plane of shear -5- the eight screws -19- symmetrically form the eight helical channels -20- and then reduce quite abruptly to the two screws -9- for the outlet section -6-.

5 shows the shear plane housing bushing -31- as a mixing part of the extruder housing, whose cylindrical sections or sections corresponding to the inlet section -2-, the compression section -3- and the outlet section -6- of the rotor (see FIG. correspond, not shown. Three helical screws -32- form a three-flight helical channel -33 --- with a width / depth ratio much greater than one, with a cross-sectional shape that is very well suited for transporting rubber; In this case, a screw angle of approximately 32 ° 30 min is used. This corresponds to the conventional construction in which the rotor has a similar screw angle.

In Fig. 6, like reference numerals designate the same parts as in Fig. 5; eight augers -34- are provided, which still form an eight-turn helical channel -35- with the same screw angle of 32 ° 30 '. It can be seen that no more than eight channels can be received in parallel, while at the same time using the same cross-sectional area as in Fig. 5, unless the ratio width / depth of the maximum channel cross-section (viewed in the drawing plane) is reduced below one.

In Fig. 7, like reference numerals designate the same parts as in Fig. 5; twelve screws -36-, but now at a complementary helix angle of 90 to 32 ° 30 ', ie 57 ° 30', form a twelve-way helical channel structure -37- according to the invention when combined with one of the rotors according to the Fig.l to 4 are used. It can be seen that the new, complementary worm angle makes it possible, analogous to the embodiment according to FIG. 5, to use a large ratio width / depth for the maximum cross section of the channels.

In the embodiment of Figure 8, like reference numerals designate the same parts as in Figure 5; 20 screws -38- on the worm angle 57 ° 30 'form a 20-turn helical channel structure -39-. The ratio width / depth of the maximum cross-section is approximately 1, similar to the embodiment of Figure 6, while because of the complementary screw angle, the number of screws and thus channels is increased by 2.5 times.

For manufacturing reasons, irrespective of whether the production takes place by casting or by machining, the number of gears should be divisible by four, ie the section perpendicular to the center line should be symmetrical about two right-angled axes. Such an embodiment is considered useful and possibly even necessary.

For the rotor of FIG. 1 and the stator housings of FIGS. 5-8, it will be seen that the features of the invention are required to achieve a density of screw-cut points / unit area of ​​the shear plane surface which is greater than the combination of the eight-speed housing with the different rotors when the screw angles for the rotor and the housing are approximately the same.

It must be emphasized that with this greater density of screw cutting points, and thereby the subdivision of the streams, a very substantial progress is achieved with respect to the difficulty of the mixing tasks that can be performed. For example, without the use of the features of the invention, it is quite impossible to achieve the final compound plus the extrusion of the rubber composition in the form of usable tire treads in one pass when starting with carbon blacks from a carbon black masterbatch previously mixed or pre-dosed with vulcanizing chemicals in powder form. The same applies to the mixture / preparation of powdered rubber or Rubber with carbon black, fillers and vulcanizing chemicals in one go. These findings relate to achieving a high quality result on a device

- 8 No.368073 given size with a throughput that is characteristic of this size, as opposed to results with atypically small output powers that can be achieved on small diameter machines with various conventional mixers / extruders substantially cylindrical housings; because it is virtually impossible to copy such devices on a much larger scale.

In Fig. 11, a flange -50- in a sectional view (Fig.llA) and in a side sectional view (Fig.llB) is shown. This flange -50- should be installed at the end of the housing, ie between the outlet flange of the housing, which may terminate flush with the end of the rotor, and the extrusion head, cutter or other outlet device.

The inlet portion -51- of the obturator or the valve has a parallel, cylindrical bore with a smaller diameter than the outlet bore of the housing, whereby a tight restriction is achieved, which amounts to about 60% of the outlet cross-section of the housing. The end portion -52- of the throttle flange has a conical bore which makes the end diameter of the throttle flange equal to that of the housing; This achieves a certain continuity with an extrusion head to which the housing is adapted directly.

The restricting element -53- in its simplest form may be a relatively fine-threaded screw so as to provide a seal against the rubber under pressure; For example, if the screw is made of steel, it would be mounted in a brass sleeve (not shown) to avoid binding. Both the throttle element -53- and the flange -50- can with holes or Be provided grooves so that a heating / cooling medium can be performed in a conventional manner in circulation through these parts.

The throttle element -53- has a spherical end -55- with the same radius as the bore of the inlet portion -51- of the throttle valve, so that there is a close fit when the throttle element has been fully inserted. In this case, the flow of the medium is limited to two symmetrically arranged segments -56- of the flow cross-section. For a cold feed rubber extruder, the combined area of ​​these segments may be less than 5% of the cross sectional area of ​​the exit bore of the housing, still providing satisfactory tread extrusion that is five times the width of the bore of the housing, as tests have shown.

In the embodiment according to FIGS. 12A and 12B, the throttle flange -60- has a rectilinear, continuous bore -61- with the same diameter as the outlet bore of the housing.

Four restrictor elements 62 are arranged symmetrically on radial axes; each throttle element -62- has a conical tip -63-. The solid lines show the throttle elements in the fully inserted position, while the dashed lines show the throttle elements in the fully retracted position. In the latter case, the maximum opening then has a cross shape bounded at the outer ends by wedges 64 formed in the small segments defined by the cylindrical parts of the throttling elements when fully inserted. Although these wedges are not essential, it is a preferred embodiment, because the best or can perform most control when the throttle elements have been introduced quite far, so that in the other case, the four open segments leave too large a cross-sectional area for the flow.

In order for a predetermined flow rate to be distributed throughout the bore, semicircular or otherwise shaped grooves may be provided in the conical ends of the throttling elements so that when closed they produce the action of a breaker plate.

Compared with the embodiment of Fig. 11, wherein only a single throttle element is used, in this embodiment of Fig. 12, in which four throttle elements are provided, a much smaller radial movement of the throttle elements between the open and the closed positions required. Since in the setting, according to a preferred Ausge- 9

No.368073 during operation, the throttle element must penetrate into a rubber flow under pressure, large forces can occur. Therefore, a screw with a relatively fine pitch is selected for mechanical reasons, so that a large number of rotations and thus a longer period is required to produce an equivalent effect in the embodiment with a single Drossel5 element as in the embodiment with four throttle elements.

The following relationship applies: The more throttle elements are installed, the faster the device can be adjusted and the more evenly the openings for the restricted flow are distributed over the flow cross-section, resulting in a better flow in the

Extrusion head results.

The throttling action for achieving a higher specific processing degree on a medium can be more effective, the more the flow in the preceding mixing section or sections has been divided. If only very few subdivisions or virtually none have been made, as is the case with a conventional extruder, this throttling leads to a backflow in the screw grooves, which counteracts the desired uniform treatment.