DE1298885B - Conveyor and mixing device with screws - Google Patents

Description

The invention relates to a conveying and mixing device for liquid-viscous Mixtures of slowly reacting substances, especially the starting material materials for the production of polyester plastics, with at least two together meshing screws driven in the same direction of rotation.

The continuous mixing with simultaneous promotion of reactive Starting materials of generally higher viscosity poses a particular problem of process engineering. In many cases, they are easily decomposable or thermally unstable starting materials, in which the extent of the expiring Reactions under the prevailing pressure and temperature conditions as a function of time is. For their continuous treatment (to achieve a well-defined Reaction state after the end of the conveying and mixing process) become in practice Screw devices preferred, which are also already in different embodiments are known.

In general, such screw devices, if they are procedural and should work in an economically optimal way, meet a number of special requirements, in particular if the product to be mixed and conveyed, for example consists of reactive raw materials for polyester plastics. These raw materials as is known, react in the form of a polycondensation during conveying and mixing with each other in such a way that progressively longer molecules result which finally, a precisely defined mean length at the outlet end of the device own.

First, care must therefore be taken to ensure that the flanks the snails cannot deposit any residues, otherwise the specified average Residence time does not allow a narrow residence time spectrum to be maintained. The tendency to Adhesion to the screw flanks increases with increasing viscosity (i.e. also with increasing degree of polycondensation) of the mixed substances, in the event that the substances react with each other, there is also the fact that the reaction process in the residues adhering to the flanks in contrast to the bulk of the mixed Substances is completely uncontrolled and even a cracking one getting bigger increasing amount of substance. There is no question that this affects the quality of the mixed product is decisively worsened.

Second, it is necessary to turn the mixing process into a pronounced one Carry out material-friendly manner and in particular mechanical squeezing and kneading processes to be avoided, because otherwise there will be fractures due to the high shear forces that occur in the molecular chains. These continued fractions in turn have the consequence that the desired length of the molecular chains is no longer sufficient This is guaranteed to result in a number of cases (such as when the product is to be further processed into synthetic fibers), in turn, a highly disadvantageous impairment of the product properties.

Third, of course, the mixing process must also be of sufficient intensity to be guaranteed. This third requirement goes without saying. You but is to be especially mentioned here, because their consideration to a certain extent Contrary to the demand for optimal fabric protection.

Fourth, finally, is the achievable filling volume of the mixing and Conveyor of considerable economic importance. This arises reinforced by the fact that screw devices of the type considered here with a filling volume corresponding to the current state of the art in considerable Dimensions need to be built, e.g. B. with a diameter of 60 cm and one Length of about 3 m.

The first to third of these demands are satisfactory from a screw device known from German patent specification 862668 Fulfills. In this device, the intermeshing screws are catchy and their cross-sectional centers of gravity are at a distance from the screw axis of rotation, the flanks of the screws having the shape of an arc in cross section, the radius of which is equal to the center-to-center distance of the screws. The groove of a snail is complete thanks to the counter-worm that engages at the flank contact points or almost completely sealed along a space curve.

During the operation of this screw device can become on the flanks no residues are deposited, as the selected flank shape is a constant mutual Scraping off the screw flanks is ensured by placing an outer edge of a screw flank slides steadily along a flank surface of the counter-worm and then continuously Transition an outer edge of the counter-worm with a corresponding flank surface the first snail intervenes. This kind of alternating snail engagement, which can also be referred to as "edge-to-surface" engagement, ensures at the same time that that the high shear forces are avoided at the point of engagement, therefore z. B. no molecular chain breaks can occur during polyester processing. Farther there is sufficient intensity of the mixing process, since the cross-sectional centers of gravity the screw profiles are at a distance from the axis of rotation. This "eccentricity" causes not only the movement in the axial direction but also a very strong relative movement in the radial or circumferential direction, which leads to an intense, but at the same time extremely Material-friendly mixing of the goods leads.

Although these three demands are largely different from the one previously known Screw device can be met, the current state of the art can not can be regarded as fully satisfactory, since the achievable filling volume of this screw device is economically unprofitable. This disadvantage must, of course, apply to all screw devices adhere, in which the profile flanks of the individual worm threads of two adjacent ones Keep touching the snails along a space curve.

In order to maintain constant flank contact, is a relatively large screw profile cross-sectional shape in relation to the conveying cross-section necessary. But that always leads to an unprofitable filling volume.

It is therefore the object of the invention to provide a conveying and mixing device to create, in addition to the demands of flank cleaning, the avoidance of Crushing and shear forces and the sufficient intensity of the mixing process in addition, the requirement for an economical filling volume is met.

Based on a conveying and mixing device of the type mentioned at the beginning known type with catchy formed screws, the cross-sectional centers of gravity are at a distance from the screw axis of rotation, the flanks of the screws in Cross-section have the shape of an arc, the radius of which is equal to the center-to-center distance is the screw, this object is achieved in that between contact with one of the mutually facing pairs of flanks of the intermeshing screws exists, while a margin is provided between the remaining pair of flanks is, and both screws are adjustable relative to each other in such a way that the flank contact pairs switch.

The proposal of the invention leaves that so far with self-cleaning Snails used the principle that each snail along a space curve against their Counter screw is sealed. This makes it possible to use the screw profile cross-sectional area compared to the previous self-cleaning screws. this leads to a considerably larger filling volume and thus a decisive one economic advantage.

Despite the margin between one of the pairs of flanks, there is a scrape off of all profile flanks of the screws is guaranteed when both screws are relative to each other are adjustable so that this clearance alternately between the one or the other pair of flanks of the intermeshing screws lies. Appropriately the relative movement of the screws to each other is controlled by a periodic stop one of the screws or made by axial displacement of the screws.

In order to achieve an optimal filling volume of the screw device, the cross-sectional shape of the screw profile is to be selected so that the screw profile cross-sectional area assumes a minimum value. This is the case when the outer surface located on the circumference of the screw profile assumes the shape of a ridge. In practice, however, it is in usually sufficient to give this outer surface a small, finite width, which reduces the filling volume somewhat, but has a positive effect on the strength of the snails.

The invention therefore enables an advantageously large filling volume and at the same time constant cleaning of all profile flanks; Farther is through the "edge-to-surface" engagement, which is the same in the invention As with the known screw device, it is guaranteed to be gentle on the fabric Mixing process ensured. Finally, however, there is also sufficient intensity of the mixing process given because of the possible relative movement of the screw flanks is even better than the known screw device. Satisfied as a result thus the invention to the optimum extent all of the requirements discussed at the beginning to a screw device of this type.

An exemplary embodiment of the invention is described below with reference to the Drawings explained in more detail. It shows F i g. 1 to 4 a cross section through two interlocking screws perpendicular to the axis of rotation, in four different ones Relative positions to explain the sequence of movements during a full revolution.

In the illustrated embodiment are from For reasons of clarity only two screws of the embodiment according to the invention are shown. It is also possible, several augers in one level next to each other or in several levels to be arranged one below the other. Furthermore, in a mixed or. Conveyor usual components such. B. the housing and the drive device, too not shown.

Like F i g. 1 shows, each of the two is synonymous and catchy formed screws 5 and 6, seen in cross section, limited by four circular arcs, namely once through the circular arc of the outer surface 7 or 8 of the screw, the radius r of which corresponds to the radius of the entire screw body, further through the two circular arcs of the screw flanks 9 and 10 or 11 and 12, the radii of which correspond to the distance between the axes of rotation of the screws. Another inner circular arc is formed by the screw core 13 or 14, d. H. the radius of this fourth circular arc corresponds to the core radius of the worm.

However, the screws can also be designed so that when a or the core radius has assumed the value zero for both screws, d. H. that one or both of the snails are seedless.

Furthermore, the two screws can also have different core radii and thus have different screw radii. Alternatively or additionally the outer surfaces 7 or 8 can also be the width of one or both screws Zero, d. H. take the form of a ridge.

The screws 5 and 6 are shaped so that between one of each other facing pairs of flanks of the intermeshing screws perpendicular to the plane of the drawing a margin remains. For the entire device has the presence of one Such leeway has the advantage that additional usable space for the promotion and Mixture of reacting substances has been obtained.

When the two screws 5 and 6 rotate in the in F i g. 1 to 4 in the direction indicated by arrows slides in each case a profile edge on the profile edge facing it along the counter-worm (edge to surface engagement) and thereby cleans this part of the snail.

The in F i g. 1 shows the front position in the direction of rotation outer profile edge of the screw 5 at the beginning of the scraping of the screw flank 11 the screw 6 moving synchronously with the screw 5 the in F i g. 1 further rotated position indicated by dashed lines, it is located the front outer profile edge in the direction of rotation of the screw 5 at the end of its cleaning contact with the flank 11 (indicated by dashed lines).

While now the screw 6 is a relatively large rotation up to the in F i g. 2 excellent position has to be performed by the snail 5 only a slight rotation up to its in F i g. 2 to carry out the position shown, d. H. the movement of the screws is now asynchronous. Such an asynchronous Rotational movement of the screws 5 and 6 can be, for. B. can be achieved by one of the The worm moves axially relative to the other or the worm 5 continues to rotate the screw 6 stops for a moment.

In Fig. Figure 2 shows the excellent position again the Beginning and the position indicated by dashed lines is the end of the scraping process, at which is now the rear outer profile edge of the screw 5 in the direction of rotation, the flank 12 of the screw 6 cleans.

The rotation of both screws takes place during this scraping process again synchronously.

In the transition from the in F i g. 2 position indicated by dashed lines of the two screws in the in F i g. 3 excellent position remains the rotary movement synchronously, as is the case with the scraping process that now follows, in which the in the direction of rotation front outer profile edge of the screw 6, the flank 9 of the screw 5 cleans. That The end of this scraping process is again indicated by dashed lines in FIG. 3.

In Fig. 4 is fully excellent the beginning of scraping the Flank 10 of the screw 5 through the rear outer edge of the Profükante in the direction of rotation Screw 6. This position can, starting from that indicated by dashed lines in FIG Position can only be reached if the screws 5 and 6 are asynchronous Carry out rotary movement in such a way that either the screws are axially relative to one another shifted or this time the screw 6 with further rotation of the screw 5 for stopped for a moment.

The end of the scraping off of the flank 10 is shown in FIG. 4 dashed indicated. When moving from this position to the one shown in FIG. 1 fully excellent In the starting position, both worms perform a synchronous rotary movement again.

Thus, despite the leeway between each one of each other facing pairs of flanks of the intermeshing screws a cleaning of all Worm flanks are given during a full revolution, with of a screw with a screw core, the outer surface of the screw profile located on the circumference cleaned by removing each outer surface of one auger during one revolution once slides along the core 13 or 14 of the other screw.

The inventive design of the cross-sectional shape is of the The pitch of the screw is independent.

Claims (5)

Claims: 1. Conveying and mixing device for liquid viscous Mixtures of slowly reacting substances, especially the starting materials for the production of polyester plastics, with at least two intermeshing, Screws driven in the same direction of rotation, designed as single-flight screws and their cross-sectional centers of gravity are at a distance from the screw axis of rotation, the flanks of the screws having the shape of an arc in cross section, the radius of which is equal to the center of the axis from the worm, characterized in that that between one of the mutually facing pairs of flanks of the interlocking There is screw contact, while there is a margin between the remaining pair of flanks is provided, and both screws are adjustable relative to one another in such a way that that the edge contact pairs change. 2. Apparatus according to claim 1, characterized in that the rotating Screws are adjustable relative to one another by stopping one of the screws. 3. Apparatus according to claim 1, characterized in that the screws are adjustable relative to each other by axial displacement. 4. Device according to one of claims 1 to 3, characterized in that that the screws have different diameters. 5. Apparatus according to claim 4, characterized in that some of snails with a core and others without a core.