DE3519291A1 - Process for homogenising and cooling the plastics melt, in particular a plastics melt treated with a blowing agent, and extruder for carrying out the process - Google Patents

Abstract

A process for homogenising and cooling a plastics melt in an extruder is specified which is suitable in particular for influencing a plastics melt treated with a blowing agent and takes place during the helical transport of said plastics melt through the screw barrel effected by the extruder screw. A constantly predetermined volume flow of plastics melt is transported in an even number of melt strands. During the transport movement the cross-sections of in each case two directly adjacent melt strands are varied in an inverse ratio to one another and these cross-sectional changes are effected in repeatedly successive alternation. A corresponding partial amount of melt taken in each case from the melt strand subjected to the cross-sectional reduction is fed to the melt strand undergoing the cross-sectional enlargement and the melt in the melt strands is rearranged by the helical transport movement during its cross-sectional change. The invention also relates to the design of the extruder for carrying out this process.

Description

description

The invention relates to a method for homogenizing and cooling the plastic melt, in particular a plastic melt gassed with a blowing agent, during their screwing transport movement caused by the extruder screw through the screw cylinder or the screw housing.

The invention also relates to an extruder for exercising this process, in which an extruder screw can be driven in rotation in a screw cylinder or worm housing is arranged, which is a paired number, so at least two, separated from each other by webs running helically around a core Has worm flights, which against the inner circumference of the screw cylinder a Corresponding number of channels for transporting the plastic melt to the extruder outlet limited.

In the production of foam sheets, the plastic, e.g. polystyrene, melted, then gassed with a propellant, e.g. Freon 12 and then the liquefied gas is homogenized with the melt.

In the further course of the process, the melt mixture is cooled down and the temperature set so low and the gas mixture so evenly the effect is that there is a uniform foam structure with small pores at the outlet results from the nozzle.

This process sequence is either carried out on tandem systems, at which the cooling extruder is provided with its own drive and is separate from the gassing extruder works, or it takes place in single-screw extruders, in which the plastic gassing and the cooling process can be carried out with a relatively long screw.

In any case, the quality of the plastic foam is determined by the Affects melt temperature; i.e. a uniform foam structure also sets the constant maintenance of a melting temperature that is as uniform and as low as possible in advance.

The necessary cooling of the plastic melt takes place in the extruder essentially over the wall of the screw cylinder or screw housing and can only be partially supported by internal cooling of the extruder screw.

In practice it turns out to be extremely problematic from the Core area and the adjacent layers of plastic melt in the screw channel to dissipate the heat, because namely the melt in the screw channels is a screwing Transport or Executes feed movement that a publishing movement of the melt core area counteracts the metallic cooling walls from the inside to the outside So that the natural, screwing transport or

If the feed movement of the plastic melt is disturbed, it already is known to use extruder screws, which are screwed inside the through the around the core extending webs separated from each other worm threads over the circumference the screw core have protruding pins as mixing elements. These mixing elements cause a redistribution of the plastic melt within the individual screw channels, but only in such a way that the pins rotating in the radial plane are in Axial direction of the extruder screw meandering back and forth displacement movements generate within the plastic melt. The one around the core of the extruder screw However, built-up layers in the helical plastic melt are not broken up and displaced, so that here too those located in the melt core area Plastic layers remain at a higher temperature than that of the walls of the The screw cylinder or screw housing and the screw core adjacent or closer layers of melt.

Also the additional arrangement of breakthroughs in the screw-like The extruder screw webs running around the core have no improvement in the Brought cooling effect.

The invention is based on the object of providing an initially generic More precisely defined process for homogenizing and cooling the plastic melt indicate that a significantly improved, namely evened out, cooling effect guaranteed within the plastic melt and thus its processing, in particular in the production of foam sheets, facilitated.

The solution to this problem is based on the knowledge that the diametrical Layer structure of the plastic melt during the screwing which takes place in strand form Transport or feed movement continuously from the inside to the outside and from the outside must be turned inwards so that all these melt layers on their transport route to the extruder exit over a sufficiently long distance with the walls of the screw cylinder or housing and the worm come into contact.

The invention on which the invention is based is based on this knowledge From a procedural point of view, the object is achieved in that a) a constant preset Volume flow of plastic melt in a paired number of melt strands is transported that b) each cross-section during the transport movement two immediately adjacent melt strands in inverse proportion to one another be changed that c) the cross-sectional changes in multiple successive Changes are effected that d) in each case from the one subject to the reduction in cross-section Melt strand a corresponding portion of the melt that the cross-sectional enlargement underlying melt strand is supplied and that e) the branching and transfer the melt subset in each case on the flow conditions of the screwing Caused transport movement of the melt strand coordinated intervals will.

It has been shown that these procedural measures intensive mixing of the plastic melt is achieved because it is axially parallel Migration movement of the plastic melt layers on an intense diametrical basis or radial shifting movement of the same is generated.

Particularly good results of mixing are achieved. if Branches or transfers of melt subsets each after half Rotation of the screwing transport movement of the melt within the relevant Screw channel can be made.

From a procedural point of view, it is still according to the invention advantageous that the plastic melt in the melt strands during their change in cross-section is rearranged by the screwing transport movement.

It has proven to be particularly useful in practice when after another procedural design of the invention in the melt strand with reduced cross-section one quarter each and three quarters each in the enlarged melt strand of the specified melt volume can be detected and if in a further embodiment the melt strands temporarily between successive changes in cross-section be transported with a constant but different cross-section.

An extruder is used to carry out the process according to the invention for use in which an extruder screw can be driven in rotation in a screw cylinder or housing is arranged, which is a paired number. so at least two, worm flights separated from one another by webs running helically around a core has, which start against the Innenum of the screw cylinder a corresponding Number of channels for transporting the plastic melt to the extruder outlet limited. The extruder according to the invention is characterized according to the invention in The main thing is that a) the core circumference of the extruder screw relative to the Shell of their screw webs and / or to the cylindrical inner circumference of the screw cylinder or housing a different or different from the normal dimension radial distance in the direction of the screw pitch that b) these core peripheral areas different radial distance each over a fraction of a screw pitch or a screw circumference extend, and c) two successive in the pitch direction Core-circumferential areas differing distance from one another have a reciprocal design, that d) the core circumferential regions having the radial spacing differences in two directly adjacent screw flights, each with an offset position are provided to each other, in which the largest distance of the core circumference be rich in one worm thread the smallest distance between the core circumferential area in the other Worm thread is assigned to the worm circumference, and that e) the land between two directly adjacent worm flights in each case in such length ranges is provided with an interruption or a cutout in which - in the transport direction the plastic melt - a core circumference area with itself against the screw circumference towards the decreasing distance a core circumferential area with enlarging towards the screw circumference This configuration according to the invention is assigned to an extruder screw not only ensures that between two adjacent melt strands not only a reciprocal mass exchange is enforced, but with every mass exchange between the adjacent melt strands at the same time there is also a shift in height of the the melt layers subjected to the mass exchange is associated with one another.

Another important design feature for an extruder the invention is that on the extruder screw, the core peripheral areas with a different radial distance in the two directly adjacent screw threads have a different contour. This is namely the advantageous Effect of the mass exchange between two directly adjacent screw flights optimized.

It is also part of the invention that the radial distance differences having core circumferential areas of the extruder screw away the spacing relationships vary between 0.5 and 1.5 of a normal distance and thereby the distance ratio at the beginning and end of each core circumferential area is 1, i.e. the normal distance is equivalent to.

According to the invention, an extruder screw has proven itself at the beginning and the end of the core peripheral regions in the two immediately adjacent one another Screw flights at least approximately matching position on the core circumference of the extruder screw have so that the melt strands each corresponding volumes at these points contain.

According to the invention, it can also prove to be advisable that the ranges of variation of the different radial distances at the screw core in the circumferential direction either over an angular range of 300 or 2/24 of the Screw pitch or an angular range of 600 or 4/24 of the screw pitch extend and that each between two successive sections with differenten Radial distances a section is provided with a constant radial distance.

It is also useful in the context of the invention to use the sections constant radial distance at the core circumferential area of one worm flight each extend over an angular range of 600 and / or 4/24 of the screw pitch, while the sections with constant radial spacing on the core circumferential area of the directly adjacent worm gear each extend over winecl areas, those between a minimum of 300 and a maximum of 750 and / or a minimum of 2/24 and a maximum of 5/24 the screw pitch.

It can also prove to be advantageous within the scope of the invention if the lengths of the sections with a constant, large radial distance to the Lengths of the sections with constant, small radial distance between each other directly adjacent worm threads are in a ratio that is between 0.33 and 1, namely 1 and 0.5 on the one hand and 0.33 on the other.

According to the invention, however, the lengths of the sections with constant, large radial distance of one worm gear to the lengths of their assigned Sections with constant, small radial distance from the neighboring, other Worm gear are in a ratio that is between 0.5 and 0.75, namely at 0.5; 0.66 and 0.75.

It is also of essential inventive importance that the interruptions or cutouts in the web between the two directly to each other adjacent screw flights have a length which is at least equal to the length of the core circumferential area adjacent to them - in the transport direction of the Plastic melt - increasing radial distance is dimensioned.

It has proven to be particularly useful according to the invention, if these interruptions or

Cutouts in the web between the two directly adjacent screw flights have a depth that corresponds to the mean or the normal dimension corresponding radial distance the core perimeter has a ratio between 0.5 and 1.

In the simplest case, the extruder screw is according to the invention designed as a two-flight screw, so that the exchange of mass and the redeployment of the plastic melt only between the two adjacent screw flights changes.

However, if a four-flight extruder screw is used, then It is essential to the invention that on the one hand the first worm gear with the second screw flight and the third screw flight with the fourth screw flight alternately corresponds, while on the other hand also the second worm gear with the third screw flight and the fourth screw flight with the first screw flight are in mutual exchange connection.

With an extruder screw designed as a six-start screw Initially the first corresponds to the second worm gear, the third to the fourth worm gear and the fifth with the sixth worm gear, respectively alternately, while on the other hand also the second worm gear with the third Worm gear, the fourth worm gear with the fifth worm gear and the sixth Screw thread with the first spiral thread in mutual exchange connection is held.

Another important design measure for an extruder but the invention also lies in the fact that there is a different radial distance the core circumference to the envelope of the screw webs or to the cylindrical inner circumference of the screw cylinder or housing having length sections of the extruder screw only over relatively short partial lengths, e.g. at least one incline distance, the same extend and two successive sections with different radial spacing the core circumference to the shell of the screw webs by an intermediate piece of relative large part length, bwp. with ten pitch intervals, connected, of Core circumference a constant, mean or normal radial distance to the shell the screw webs.

However, it is also of essential importance according to the invention also that the webs between adjacent worm threads of the relatively large Partial length having intermediate piece of the extruder screw each about half Incline spacing interruptions on a length approximately corresponding to its height have that separate from one another on successive or adjacent screw flights Bars are offset from one another in the circumferential direction.

Finally, a feature of the invention is also seen in that that the interruptions or cutouts in the webs of the extruder screw Edges have rounded edges. As a result, namely the formation of congestion when taking place Counteracted mass exchange of the plastic melt between adjacent screw flights.

Further features and advantages of the invention are set out below explained an embodiment shown in the drawing. It shows Fig. 1 in a schematically simplified representation and in longitudinal section a single-screw extruder for melting plastic granulate and for homogenizing and cooling the the resulting plastic melt, equipped with a two-flight extruder screw, 2 shows the process sequence during homogenization in a diagrammatic representation and cooling the plastic melt with the single-screw extruder according to FIG. 1, FIG. 3 shows a purely schematic overview illustration of five different length sections a to e of an extruder screw according to the invention, FIGS. 3a to 3e in larger dimensions Scale and in a detailed representation the length sections shown in FIG. 3 an extruder screw according to the invention, FIGS. 4a to 4e show the developments of the Length sections of an extruder screw shown in FIGS. 3a to 3e, FIG. 5 shows a section along the line V-V through the development of the extruder screw 4b and 4d, FIG. 6 shows a section along the line VI - VI through the development the extruder screw in FIGS. 4b and 4d, FIG. 7 in a three-dimensional view and in longitudinal section a section of an extruder screw in the screw barrel which indicated the screwing transport movement of the melt in the screw channel is, while Fig. 8 is a cross-section through a screw channel with the usual Represents the temperature profile of the melt.

In Fig. 1 of the drawing, a single screw extruder 1 is shown, which not only serves to melt plastic granulate, but also is also suitable for homogenizing and cooling the plastic melt. In particular This single screw extruder 1 is suitable for homogenizing and cooling a with a blowing agent fumigated plastic melt, the plastic melt, for example.

Polystyrene and the blowing agent Freon 12 can be.

A storage funnel 2 is used to receive the plastic granulate, while the propellant is in a storage container 3, which has a Line 4 and a metering valve 5 to the screw cylinder 6 or the screw housing 7 is connected. The worm housing 7 is on its entire length of cooling devices 8 or surrounding heating devices. The extruder screw 9 is a two-flight Executed screw and is connected to a rotary drive 10.

The twin-flight extruder screw 9 has two screw flights 11 and 12, which over the entire length of the screw through the screw flights 13 and 14 are separated from each other, which run helically around the screw core 15.

Due to the constant rotation of the extruder screw 9 within the bounded by the worm housing 7 Screw cylinder 6 is the plastic melt produced by melting the plastic granulate in two volumetrically essentially equal melt strands in the direction of the extruder outlet 16 transported, with constant execution of a screwing transport movement inside the screw cylinder 6.

The constantly rotating extruder screw 9 is the plastic melt inevitably to well above the melting point of the plastic granulate lying temperatures heated, which a perfect processing after application from the extruder 1 is not guaranteed. Therefore it is necessary to melt the plastic on their way to the extruder outlet 16 through the cooling devices 8 to a temperature to bring the best possible results during further processing, e.g. to Foam sheeting, ensures a completely even cooling of the in the two Screw flights 11 and 12 between the screw flights 1; 3 and 14 transported Ensuring melt strands 17 and 18 is a special procedural matter Treatment of the same during their screwing transport movement by the from Screw housing 7 limited screw cylinder 6 is provided, initially based on the diagrammatic representation of FIG. 2 is explained.

At this point it should be mentioned that the explanations given are not only apply to the conditions present in single-screw extruders, but also for the so-called tandem extruders, in which cooling and plasticizing or aeration screws are separated from each other and are each driven separately.

I) ie cross-sections A, B, C, D and E shown in FIG. 2 for the two plastic strands result in the extruder 1, specifically for the two Screw flights 11 and 12 each in the area of the cross-sectional planes identified in FIG. 1 A, B, C; D and E This means that in the area of the cross-sectional planes A of Fig. 1 both melt strands 17 and 18 or both screw flights 11 and 12 coincide Have cross-sectional dimensions.

In the cross-sectional plane B of FIG. 1, the melt strand 17 has or the worm flight 11 containing it only half the cross-section of plane A, while the melt strand 18 in the area of the cross-sectional plane B opposite the cross-sectional plane A has one and a half times the cross-sectional area. It is the other way around in the area the cross-sectional plane C of Fig. 1, i.e. there the melt strand 17 has one and a half times Cross-sectional area opposite the cross-sectional planes A, while the melt strand 18 occupies only a cross-sectional area which is half the cross-section in the cross-sectional planes A of FIG. 1 corresponds. In the cross-sectional planes D of Fig. 1 have again the same cross-sectional ratios between the two melt strands 17 and 18 set as in the cross-sectional planes B, while in the cross-sectional planes E of FIG. 1 again cross-sectional ratios occur which those of the cross-sectional planes A correspond.

In any case, the two worm flights 11 and 12 are constant a fixed, predetermined volume flow of the plastic melt is transported. While the transport movement, however, the cross-sections of the two immediately adjacent ones Melt strands 17 and 18 changed in inverse proportion to one another. These Change in cross section of the melt strands 17 and 18 is caused by the fact that on the one hand, corresponding changes in cross-section within the two screw flights 11 and 12 are provided relative to the screw cylinder 6, and in multiple successive Changes occur, while on the other hand the possibility is created that each from the melt strand subject to the reduction in cross-section, a corresponding one Melt subset of the melt strand underlying the cross-sectional enlargement is fed.

In Fig. 2 it can be seen that the melt strand 17 in the cross-sectional plane A consists of the two subsets T1 and T2, which are superimposed in layers of the same thickness. In a corresponding manner, the melt strand 18 also exists in the cross-sectional plane A consists of two equal subsets T3 and T4, which are also in layers on top of each other.

In the cross-sectional plane B according to FIG. 2, the melt strand contains 17 only the subset Ti, while the subset T2 in the melt strand 18 was transferred from the melt strand 17, so that there the melt strand 18 from consists of subsets T2, T4 and T3, which are superimposed in even layers. In the cross-sectional plane C, the melt strand 18 only comprises the partial amount T2, while the subsets T3 and T4 are transferred from it into the melt strand 17 and are deposited there above the subset T 1. The one in the cross-sectional plane B subset T3 located at the bottom in melt strand 18 is therefore in the cross-sectional plane C deposited as an upper part in the melt strand 17, i.e.

a twisted layer position has set itself, which is caused by curved Is indicated by arrows.

When the cross-sectional plane D is reached, according to FIG. 2 of the melt strand 17 only the subset T3, which was originally, i.e. in the cross-sectional plane A, was deposited in the melt strand 18. On the other hand, includes in the cross-sectional plane D of the melt strand 18, the subsets Ti, T4 and T2, of which only the subset T4 located in the middle originally came from the melt strand 18 originates, as can be seen in the cross-sectional plane A of FIG. The subsets However, T1 and T2 originally come from the melt strand 17, like that in FIG Cross-sectional plane A of FIG. 2 can be seen, however, they take place relative to one another an elevation that is twisted in relation to the cross-sectional plane A and are also separated from each other by the subset T4.

In the cross-sectional plane E, both melt strands 17 and 18 have again matching cross-sections, the melt strand 17 being its original Subset T2 and the original subset T3 from the melt strand 18, while the melt strand 18 there from its original subset T4 as well the original subset T1 consists of the melt strand 17. Also in the cross-sectional plane E has again, as the curved arrows indicate, a positional rotation of the Melt layers formed by the subsets took place.

The relocation and reallocation of the subsets T 1, T2, T3 and T4 within the melt strands 17 and 18 is due to the in the screw flights 11 and 12 provided different cross-sectional changes inevitably by the screwing transport movement of the screw flights 13 and 14 made by namely the screw flights 13 and 14 are determined by the different cross-sectional changes Place Have interruptions or excerpts that cause an exchange of mass between the two adjacent screw flights 11 and 12 of the extruder screw 9 allow.

Since by the respectively between the cross-sectional planes A and E according to Fig. 1, multiple mutual mass exchanges that have taken place between the two Melt strands 17 and 18 and the simultaneous multiple mutual Shifting the subsets Ti, T2, T3 and T4 is achieved that all of these Subsets T1 to T4 corresponding layers of the plastic melt are sufficiently intense in the boundary surfaces of the screw cylinder 6 in the screw housing 7 in contact arrive and are consequently also evenly cooled by the cooling devices 8 can. This ensures an optimal melt temperature at the extruder outlet 16.

In Fig. 2 of the drawing, in addition to the feed direction, the exchange direction and the direction of rotation for the subsets T1 to T4 indicating the individual arrows Subsets T 1 to T4 or melt layers are assigned special flags, which characterize the sequence of movements from the inside to the outside, which occurs in the Melt redistribution through a certain interaction of decreasing and increasing Cross-sectional dimensions in the screw flights 11 and 12 and the simultaneous Melt exchange between the adjacent screw channels 11 and 12 results.

The changed position of these flags within the individual cross-sectional planes A to E makes it clear that all long cross-sectional side surfaces of the melt layers determined by the individual subsets T1 to T4 during the helical transport movement of the melt strands 17 and 18 to any one Point in time with the inner boundary surfaces of that formed in the worm housing 7 Screw cylinder 6 come into contact and thus influencing the cooling be subjected. An even cooling of the whole of the extruder screw 9 conveyed melt volume is ensured.

The structural design is shown below with reference to FIGS. 3 to 6 an extruder screw that enables the type of process described above to be carried out 109 explained, which is shown only schematically in Fig. 3 of the drawing, in the Figs. 3a to 3e, however, are shown in full detail.

The extruder screw 109 according to FIG. 3 is shown in FIGS. 3a to 3e as four-start extruder screw shown, i.e. it has four helically over worm flights 111, 112, 113 and 114 running the entire length around its core, which are laterally bounded by the screw flights 115, 116, 117 and 118, as inner ones Limit the screw core 110 and the outer limit of the screw cylinder 106 in the worm housing 107 are limited.

In FIGS. 3 a to 3 e, those comprising the worm housing 107 are also shown Cooling devices 108 shown.

The length ranges of the extruder screw shown in FIGS. 3a, 3c and 3e 109 have, with one important exception, the usual structure of a four-course Extruder screw. The screw core 110 is there over its entire length a cylindrical outer surface 119, while the screw flights 115, 116, 117 and 118 have an outer contour which runs concentrically to this and which is only relatively little Play to the inner boundary surfaces of the screw cylinder 106 in the screw housing 107 has.

The exception is that each of the screw webs 115,116,117 and 118 at specific angular intervals around the longitudinal axis of the extruder screw 109 staggered interruptions or cutouts 121, 122, 123 and 124 are provided, in such a way that each screw flight 115,116,117 and 118 two interruptions or

Recesses 121, 122, 123 and 124 are present, and their angular spacing from each other is around 1800.

The length sections of the extruder screw shown in FIGS. 3b and 3d 109 have in terms of process technology, i.e. for homogenizing and cooling the plastic melt, the same meaning as the two sections of the extruder screw 9 according to FIG. 1, which are delimited by the cross-sectional planes A and E, respectively.

Its operating principle is therefore such that there is at least the the same processes with regard to the mass exchange between adjacent melt flows as well as the subset rearrangement within the same, as shown in FIG. 2 shown in the drawing and explained in detail with reference to diagrams A to B. have been.

The length sections described above with reference to FIGS. 3a, 3c and 3e of the extruder screw 109 are separate or independent of those in FIGS. 3b and 3d shown length portions thereof produced. The connection of the different Length sections together to form the complete extruder screw 109 can be done using screw couplings. This can prove to be beneficial prove that the coupling parts having the internal thread each in the ends incorporate the length sections shown in Figs. 3a, 3c and 3e, while the coupling parts provided with the external thread are at both ends on the length sections of the extruder screw 109 are provided, which are shown in Figs. 3b and 3d.

A comparison of FIGS. 3b and 3d shows that there Length sections of the extruder screw shown have at least the same length dimension have, but preferably have an overall identical design.

The effective part of the length sections shown in Figures 3b and 3d the extruder screw 109 has such a length dimension 120 that on it all the screw flights delimited from one another by the screw flights 115, 116, 117 and 118 111, 112, 113 and 114 extend at least a full pitch distance.

However, such a configuration is also important for all of the 3a to 3e shown length sections that they are when assembled to complete Let the extruder screw 109 join one another without any gaps; i.e. that their helical threads 110, 111, 112, 113 and 114 as well as their screw flights 115, 116, 117 and 118 are suitable let join together.

The main distinguishing feature of the in Figs. 3b and 3d Length sections 120 shown for the extruder screw 109 compared to those in FIGS 3a, 3c and 3e shown length portions thereof lies in the fact that their screw core 110 in the area of the individual screw flights 111, 112, 113 and 114 does not have a cylindrically limited lateral surface 119 is equipped, but rather in the individual worm threads 111, 112, 113 and 114 different has designed outer surfaces 125, 126, 127 and 128.

It should already be pointed out that on the one hand the contour of the Jacket surfaces 125 and 126 between the two immediately adjacent Screw flights 111 and 112 as well as the lateral surfaces 127 and 128 in the two again directly adjacent screw flights 113 and 114 different are contoured, but the contours of the lateral surfaces 125 and 127 on the one hand and the contours of the lateral surfaces 126 and 128 on the other hand coincide with one another can.

Point over the full pitch of a worm thread the lateral surfaces 125 and 127 of the worm flights 111 and 113 are those in FIG. 5 as a development shown contour, while the lateral surfaces 126 and 128 of the worm threads 112 and 114 have the contour shown in FIG. 6, also as a development.

The beginning of a complete worm gear lies in the Representations of FIGS. 5 and 6 on the right, while the end of the same is on the left.

From Fig. 5, the normal depth of the worm flights 111 and 113 is opposite the inner circumference of the screw cylinder 106 at the right and left ends of the illustration each identified by the reference number 129. The normal depth 129 for the However, worm flights 112 and 114 are also entered in the same places in FIG. 6.

From Fig. 5 it can be seen that at the beginning of the worm gear 111 and 113 of the length section 120 of the extruder screw 109 has the normal depth 129 thereof prevails. By forming the in the circumferential direction of the screw core gradually Reduced to a larger diameter increasing circumferential surface section 130a the depth of the worm threads 111 and 113 to a level 131, which is half corresponds to normal depth 129. The lateral surface section connects at an angle of 600 130a of the lateral surface section 130b, over which the worm flights 111 and 113 the depth 131 which is reduced by half compared to the normal depth 129 maintained.

The lateral surface section 130b is then connected via a Angle range from 600 away a lateral surface section 130c, which in the circumferential direction takes such a course that at its end the screw flights 111 and 113 one Has depth 132 which is greater by half than the normal depth 129 or the Three times the reduced depth 131 corresponds. To the lateral surface section 130c then closes, again over an angular range of 60 °, a lateral surface section 130d, along the length of which the depth 132 of the screw flights 111 and 113 is maintained will.

Adjacent to the jacket surface section 130d is a jacket surface section 130e is provided, which corresponds to the lateral surface section 130c, but is a mirror image runs to this and to a reduced depth 133 for the screw length 111 and 113 leads, which in turn corresponds to the depth 131 and, like this, extends over a Angular range extends from 600 and limited by a lateral surface section 130f whose contour matches the contour of the lateral surface section 130b.

A reciprocal, in turn, adjoins the lateral surface section 130f to the jacket surface section 130a running jacket surface section 130garn, the themselves Extends over an angular range of 300 and has such a position that at his At the end of the normal depth 129 for the worm threads 111 and 113 is reached again.

The contour of the lateral surfaces 126 and shown in FIG 128 for the screw core 110 in the area of the screw flights 112 and 114 settles composed of a larger number of lateral surface sections 134a to 134h, which extends over a full angle range of 3600 or over a full screw pitch string together in a certain way.

From Fig. 6 it can be seen that the lateral surface section 134a to the preceding lateral surface section, which is the normal depth 129 for the Screw flights 112 and 114 limited, connects over an angle of 300 away. It has such a profile that the depth of the worm threads 112 and 114 gradually enlarged by half to depth 135 compared to normal depth 129. Over an angle of 300 this depth 135 becomes the worm flights 112 and 114 bounded by a lateral surface section 134b. This is then followed by over an angle of 600 the lateral surface section 134c, which in turn extends so that a depth 136 of the screw flights 112 and 114 reaches at its end which is equal to half of the normal depth 129 and equal to one third of the maximum depth 135 for these worm threads.

The minimum depth 136 for the worm flights 112 and 114 is about an angular range of 900 is limited by the lateral surface section 134d, at which a lateral surface section is then again over an angular range of 600 134e, which corresponds to the lateral surface section 134c, but to this runs reciprocally.

At the end of the lateral surface section 134e there is again a depth 137 for the worm flights 112 and 114 reached three times the minimum depth 136 corresponds and is equal to the maximum depth 135. The maximum depth 137 of the screw flights 112 and 114 extends over an angular range of 450 through the lateral surface section 134f is determined, to which then over an angular range of 300 the lateral surface section 134g, which corresponds to the lateral surface section 134a, but one takes to this reciprocal course. At the end of the lateral surface section 134g is for the worm flights 112 and 114 the normal depth 129 is reached again, namely about 150 before the end of a full screw pitch, so that the angular range of 150 up to the full screw pitch from a lateral surface section 134h is determined, the normal, cylindrically limited core circumference of the extruder screw 109 corresponds.

FIGS. 5 and 6 also make it clear which relative position the jacket surface sections 130a to 130g of the lateral surface 125 of the screw flight 111 in the direction of the screw pitch to the lateral surface sections 134a to 134h of the lateral surface 126 of the worm flight 112 to each other. But they also make the corresponding relative position of the lateral surfaces 127 and 128 in the screw flights 113 and 114 are clear to one another.

The relative position of the lateral surface sections is particularly clear 130a to 130g in the screw flights 111 and 113 to the jacket surface sections 134a to 134h in the worm flights 112 and 114 from the developed top views can be seen in FIGS. 4b and 4d. But also in FIGS. 3b and 3d, the lateral surface sections are 130a to 130g or 134a to 134h can be seen at least partially, in particular there the different depths of the screw flights 111 to 114 compared to the inner circumference of the screw cylinder 106 in the screw housing 107 become clear.

For carrying out the process for homogenizing and cooling the plastic melt However, it is not enough to use the circumferential surfaces 125, 126, 127 and 128 of the Screw core 110 in the area of screw flights 111, 112, 113 and 114 by lining up of lateral surface sections 130a to 130g and 134a to 134h, respectively, which are relatively to the cylindrical inner circumference of the screw cylinder 106 or to the envelope of the Screw flights 115, 116, 117 and 118 have different radial distances. Rather, it is also necessary to do this in the screw flights 115,116,117 and 118 between two directly adjacent screw flights, so for example. at least in the screw flight 116 between the screw flights 111 and 112 and the Screw flight 118 between the screw flights 113 and 114 special interruptions or cut-outs to be provided.

Such interruptions or excerpts can, however, additionally and at other locations also on the one hand in the screw flight 117 between the screw flights 112 and 113 and, on the other hand, in the screw flight 115 between the screw flight 114 and the screw flight 111 can be provided.

In the developments according to FIGS. 5 and 6, the shape and The position of the cutouts to be provided in the screw flights 115, 116, 117 and 118 is shown.

It can be seen that over a full screw pitch in four interruptions or cutouts 138a, 138b at certain distances from one another, 138c and 138d exist. These interruptions or sections 138a, 138b, 138c and 138d are, however, also in the developed plan views of FIGS. 4b and 4d indicated.

In Fig. 4b it can be seen that the interruptions or Cutouts 138a, 138b, 138c and 138d in the screw flights 116 and 118, respectively which are formed between the worm flights 111 and 112 or 113 and 114 are. On the other hand, it can be seen from FIG. 4d that the interruptions or recesses there 138a, 138b, 138c and 138d are provided in the screw flights 115 and 117, respectively which lie between the worm flights 112 and 113 or 114 and 111.

It is particularly clear from FIGS. 5 and 6 that the individual Interruptions or cutouts 138a, 138b, 138c and 138d different from one another Have shape and are tris in the longitudinal direction of the relevant screw flights, 116, 117 and 118 also extend over different angular ranges. It is It can be seen that the interruptions or cutouts 138a and 138d are each over extend an angular arc of 300 and have a mirror image position to one another. The interruption or the cutout 138b extends over an angular arc of about 75 °, while the interruption or the cutout 138c over an angular arc The outline shape for the individual interruptions or cut-outs runs from about 680 138a, 138b, 138c and 138d is decisive for the mass exchange of the plastic melt, which during the screw-like transport movement of the plastic melt between the melt strands should take place, which according to FIGS. 3b and 4b on the one hand in the screw flights 111 and 112 and on the other hand in the screw flights 113 and 114 are transported. According to FIGS. 3d and 4d, however, this applies to the mass exchange the plastic melt between the melt strands, on the one hand in the screw flights 112 and 113 and, on the other hand, transported in the screw flights 114 and 111 will.

If one compares the representations of FIGS. 5 and 6 with the diagrams A to E of FIG. 2 relates and, for example, in connection with the worm flights 111 and 112 considered, then prevails at the right end of FIG. 5, the same state as on the left side of diagram A of Fig. 2. At the right end of Fig. 6 is the same as in the right part of diagram A of FIG. 2. Since, e.g. in the screw flight 116 between the two screw flights ttt and 112 the interruption or the cutout 138a is located through this or this the subset T2 from the melt strand located in the screw flight 111 into the in the screw flight 112 located melt strand transferred. This process takes place takes place over an angular range of 300, within which in the worm threads 111 and 112, the lateral surface sections 130a and 134a are adjacent to one another.

Then while the melt strand within the screw flight 111 according to diagram B of FIG. 2 only comprises the subset T 1, the melt strand became increased in volume in the worm gear 112 by the subset T2, whereby he comprises the subsets T2, T4 and T3 according to diagram B of FIG. 2.

The portion T 1 of the melt strand remaining in the screw flight 111 becomes in the direction of the slope over an angular arc of 600 without any further influence transported. On the other hand, the subsets T2, T4 and T3 in the melt strand of the screw flight 112 without any influence and only via an angular arc of 300 in the direction of the slope.

Subsequently, however, the screw flight is made from the melt strand 112 the two subsets T4 and T3 with the help of the interruption or the excerpt 138b transferred into the worm gear 111, so that then in the worm gear 112 only the subset T2 still remains. When converting subsets T4 and T3 into the worm gear 111 is caused by the contours of the interruption respectively.

of the cutout 138b rotated during its transfer, so that according to the diagram C of FIG. 2, the subsets T3 and T4 above the Subset T1 come to rest, while in the worm gear 12 only the subset T2 is transported further.

If now the melt strand in the screw flight 111 the interruption or the cutout 138c are reached by their contour and the screw movement conditionally from this melt strand according to the diagram D of FIG. 2, the subsets T1 and T2 transferred into the melt strand of the screw flight 112, which there only consists of the subset T2 and was previously also rotated in itself. Even when transferring of melt strands T1 and T4 through the interruption or the cutout 138c a rotation of the same takes place so that the subsets T1 and T4 are above the subset T2 come to rest. There is thus in the melt strand of the screw flight 111 according to diagram D of FIG. 2, only the subset T3, while the melt strand in the screw flight 112 now comprises the three subsets T1, T4 and T2.

Finally, the strand of melt arrives in the worm gear 112 Area of interruption or

of the cutout 138d, then the subset T2 is branched off from it and fed back into the screw flight 111, which previously only comprised the subset T3 Has.

In this case, there is not only a rotation of subset 2, but rather at the same time, the subsets T1 and T4 are also rotated, so that at the end of the screw pitch the situation according to diagram E of FIG. 2 results, after which the melt strand in the screw flight 111, the subsets T2 and T3 of the Melt strand in the screw flight 112 comprises the subsets T4 and T1.

It is obvious that this forced transport process the plastic melt within the melt strands an optimal cooling of the melt can be achieved because all layers of melt are at some point in time come into contact with the inner periphery of the screw cylinder 106, and hence exposed to the action of the cooling devices 108 surrounding the screw housing 107 are.

This cooling effect is also optimized by the fact that within the Length section 120 of the extruder screw 109 shown in FIGS. 3d and 4d the process sequence corresponding to the diagrams A to E of FIG. 2 between those Melt strands takes place, on the one hand at the screw flights 112 and 113 and on the other hand, are conveyed by the screw flights 114 and 111.

The passage cross-sections of the interruptions or

Cutouts 138a, 138b, 138c and 138d in the screw flights 116 and 118 or 115 and 117 are each coordinated so that they can be easily traversed the Schmel # e subsets from one spiral to the other and also back again vice versa is guaranteed. The respective opening cross-section is always at least as large as the decrease in cross-section in the screw thread from which the relevant melt subset or subsets is or will be discharged.

Since each of the two length parts shown in FIGS. 3b and 3d 120 of the extruder screw 109 has the length sections shown in FIGS. 3a, 3c and 3e are upstream and / or downstream, the achievable homogenization and / or cooling result even further improved because there in the screw flights 115, 116, 117 and 118 the Breakthroughs 121, 122, 123 and 124 are present, the offset position against each other and each have a melt exchange between the immediately adjacent ones Force worm gears 111, 112, 113 and 114. At the same time is due to the presence the openings 121, 122, 123 and 124 a pressure equalization between all four screw flights 111, 112, 113 and 114 ensures and thus a uniform melt conveyance ensured in all worm gears.

To favor the melt base through the interruptions, cutouts and openings, it is important that their boundary edges are at least well rounded be, but preferably form guide surfaces, which are in the direction of the desired Extend melt flow.

How the melt of the melt strands changes when the extruder screw rotates 9 shifted within the individual screw flights 11 and 12 with helical flow, is shown qualitatively clearly in Fig. 7 of the drawing. It can be seen that within the individual NEN screw flights 11 and 12 in the direction of the screw pitch a screw-like transport movement of the melt takes place, which is transverse to the screw flight has directed motion components, each in the core and the cylinder Cross-sectional zones have mutually opposite directions of movement.

In Fig. 8 of the drawing, so-called isotherms are schematically simplified shown. It can be seen that normally in the core area K of each melt strand there is practically no cross-flow and consequently the layers of melt stored there also at the high temperature Tmax. remain while those at the helical flow participating melt layers are constantly cooled towards the temperature Tmja will.

By the type of procedure described above as well as the special Design of the extruder intended for their execution, however, it is guaranteed that that also the melt layers located in the core area K of each melt strand relocated and brought up to the available cooling surfaces.

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Claims (22)

Claims 1. A method for homogenizing and cooling the plastic melt, in particular a plastic melt gassed with a blowing agent, during its brought about by the extruder screw, screwing transport movement through the screw cylinder or the worm housing, characterized in that a) always a predetermined Volume flow of plastic melt in a paired number of screw strands (e.g. 17 and 18; Fig. 2) is transported that b) during the transport movement the cross-sections of two immediately adjacent melt strands (e.g. 17, 18; Fig. 2) are changed in inverse proportion to each other (A, B, C, D, E; Fig. 2), that c) causes these cross-sectional changes in multiple successive changes are (Fig. 2) that d) in each case from the subject to the reduction in cross-section Melt strand (e.g. 17 or 18) a corresponding portion of the melt (e.g. T2 or T3, T4 or Ti, T4 or T2) the melt strand underlying the cross-sectional enlargement (e.g. 18 or 17) is supplied (Fig. 2), and that e) the branch and overpass the melt subset (e.g. T2 or T3, T4 or T 1, T4 or T2) in each case the flow conditions of the screwing transport movement of the melt strand (e.g. 17 or 18) coordinated intervals. 2. The method according to claim 1, characterized in that the melt in the melt strands (e.g. 17 and 18; Fig. 2) during their change in cross-section shifted by the screwing transport movement w.rd (A, B, C, D, E; Fig. 2). 3. The method according to any one of claims 1 and 2, characterized in that that in the melt strand with reduced cross-section (e.g. 17 - T 1 or 18 - T2 or 17 - T3; Fig. 2) each a quarter and in the enlarged cross-section of the melt strand (e.g. 18 - T2 / T4 / T3 or 17 - T3 / T4 / T1 or 18 ~ TilT4 / T2) three quarters each the predetermined volume of a channel pair can be detected (Fig. 2). 4. The method according to any one of claims 1 to 3, characterized in that that the melt strands (e.g. 17 and 18; Fig. 2) between successive changes in cross-section temporarily each with a constant but different cross-section are transported (Fig. 5 and 6r 5th extruder to carry out the process according to one or more of claims 1 to 4, in which an extruder screw can be driven in rotation is arranged in a screw cylinder or screw housing, which has a paired Number, i.e. at least two, by webs running helically around a core has separate screw flights, which against the inner circumference of the Screw cylinder or screw housing cinc corresponding number of channels limited for the transport of the plastic melt to the extruder outlet, characterized in that a) the core circumference (125, 126, 127, 128) of the extruder screw (109) relative to the Envelope of their screw flights (115, 116, 117, 118) and / or to the cylindrical Inner circumference of the screw cylinder (6) in the direction of the screw pitch a different respectively. Radial spacing (130a to 130g, 131 to 133; 134a to 134h and 135 to 137) (FIGS. 5 and 6) that b) these Core circumferential areas with different radial spacing (130a to 130g, 131 to 133 or 134a to 134h, 135 to 137) each over a fraction of a screw pitch or a screw circumference, and c) two successive ones in the direction of the pitch Core circumferential areas differ from or differ from normal dimensions (129) have a mutually reciprocal design (Fig. 5 and 6) that d) the radial Core circumferential regions (130a to 130g or 134a to 134h) in two directly adjacent screw flights (111 and 112 or 113 and 114) are each provided with an offset position to one another (Fig. 5 and 6), where the greatest distance (132 or 135 and 137) is in a worm gear (111, 113 or 112, 114) the smallest distance (131 and 133 or 136) of the core circumferential area assigned in the other worm gear (112, 114 or 111, 113) on the worm circumference is (Fig. 5 and 6, and that e) the screw flight (116, 118 or 117, 115) between two directly adjacent screw flights (111, 112 and 113, 114 or 112, 113 and 114, 111) each in such length ranges with an interruption or a cutout (138a, 138b, 138c and 138d) are provided in which - in Transport direction of the plastic melt ~ a core peripheral area (130a, 130e respectively. 134c, 134g) with itself against the screw circumference or the screw cylinder (106) reducing the distance a core circumferential area (134a, 134e or 130c, 130g) with increasing distance to the screw circumference or screw cylinder (106) is assigned (Fig. 5 and 6). 6. Extruder according to claim 5, characterized in that the core peripheral areas (130a to 130g or 134a to 134h) different or different from the normal size (129) Radial distance in the two directly adjacent worm flights (111 and 112 or 113 and 114 or 112, 113 or 114, 111) of the extruder screw (109) have a different contour (Figs. 5 and 6). 7. Extruder according to one of claims 5 and 6, characterized in that that over the core circumferential areas having the radial spacing differences (130a to 130g or 134a to 134h) the distance ratios between 0.5 and 1.5 of the normal distance (129) variicrcll (131, 132, 133 or 135, 136, 137) and the out-of-country ratio at the beginning and end of each th Core circumferential area at a (dimension 129) is (Fig. 5 and 6). 8. Extruder according to one of claims 5 to 7, characterized in that that the beginning and end of the spaced-apart core circumferential areas (130a to 130g or 134a to 134h) in the two directly adjacent screw flights (111, 112 or 113, 114 or 112, 113 or 114, 111) at least approximately matching Position on the core circumference (125, 127 or 126, 128) of the extruder screw (101) (Fig. 5 and 6). 9. Extruder according to one of claims 5 to 8, characterized in that that the variation ranges of the different radial distances at the screw core (110) in the circumferential direction either over an angular range of 300 or 2/24 of the screw pitch or an angular range of 600 or 4/24 of the screw pitch extend and that in each case between two successive sections (130a, 130c, 130e, 130g or 134a, 134c, 134e 134g) with different radial distances Section (130b, 130d, 130f or 134b, 134d, 134f) with constant radial distance (131, 132, 133 or 135, 136, 137) is provided (Figs. 5 and 6). 10. Extruder according to one of claims 5 to 9, characterized in that that the sections (130b, 130d, 130f) with a constant radial distance (131, 132, 133) on the core circumferential area (125 or 127) of one screw flight (111 or 113) each over an angular range of 600 and / or 4/24 of the screw pitch extend (Fig. 5), while the sections (134b, 134d, 134f) with constant Radial distance (135, 136, 137) on the core circumference area (126 or of the immediately adjacent screw flight (112 or 114), respectively Extend over angular ranges between a minimum of 300 and a maximum of 900 and / or a minimum of 2/24 and a maximum of 6/24 of the screw pitch lie (Fig. 6). 11. Extruder according to one of claims 5 to 10, characterized in that that the lengths of the sections (132 or 135, 137) with a constant, large radial distance (132 or 135,137) to the lengths of the sections (130b, 130f or 134d) with constant, small radial distance (131, 133 or 136) in the adjacent worm flights (111 and 112 or 113 and 114) are in a ratio between 0.33 and 1, namely on the one hand at one and 0.5 and on the other hand at 0.33 (Fig. 5 and 6). 12. Extruder according to one of claims 5 to 11, characterized in that that the lengths of the sections (132 or 135, 137) with a constant, large radial distance (132 or 135,137) of one worm gear (111 or 113) or (112 or 114) to the lengths of the sections assigned to them (130b, 130f or 134d) with constant, small radial distance (131, 133 or 136) of the adjacent, other worm flight (112, 114 or 111, 113) are in a ratio between 0.5 and 0.75, namely at 0.5; 0.666 and 0.75. 13. Extruder according to one of claims 5 to 12, characterized in that that the interruptions or cutouts (138a to 138d) in the web (116 or 118 or 115 or 117) of the two immediately adjacent Worm threads (111, 112 or 113, 114) have a length that is at least equal the length of the core circumferential area adjacent to them (130a, 130c, 130e, l30g or 134a, 134c, 134e, 134g) with it - in the transport direction of the plastic melt - Increasing radial distance is dimensioned (Fig, 5 and 6). 14. Extruder according to one of claims 5 to 13, characterized in that that the interruptions or cutouts (138a to 138d) in the web (116 or 118) or (115 or 111) between the two directly adjacent screw flights (111, 112 or 113, 114) have a depth which to the mean radial distance (129) of the core circumferential areas a ratio between 0.5 and 1 (Figures 5 and 6). 15. Extruder according to one of claims 5 to 14, characterized in that that the extruder screw (9) is designed as a two-flight screw. 16. Extruder according to one of claims 5 to 14, characterized in that that the extruder screw (109) is designed as a four-start screw on the one hand the first screw flight (111) with the second screw flight (112) and the third The worm thread (113) corresponds to the fourth worm thread (114) (Fig. 3b and 4b), while on the other hand the second screw flight (112) with the third screw flight (113) and the fourth screw flight (114) with the first screw flight (111) in exchange connection stands (Fig. 3d and 4d). 17. Extruder according to one of claims 5 to 14, characterized in that that the extruder screw is designed as a six-start screw on the one hand the first spiral with the second spiral, the third spiral with the fourth worm gear and the fifth worm gear with the sixth worm gear corresponds, while on the other hand the second spiral with the third spiral, the fourth worm gear with the fifth worm gear and the sixth worm gear is in exchange connection with the first worm gear. 18. Extruder according to one of claims 5 to 17, characterized in that that there is a different or varying radial distance of the core circumference (125, 126, 127, 128) to the shell of the screw flights (115, 116, 117, 118) or to the cylindrical inner circumference of the screw cylinder (106) having length sections (120) of the extruder screw (109) only over a relatively short part of the length, e.g., at least one pitch distance extending the extruder screw (109) and two successive sections (120) through an intermediate piece of relatively large size Part length, for example. With at least ten pitch intervals, are connected to the Core circumference (119) a constant, mean radial distance (129) to the shell the screw flights (115, 116, 117, 118) or to the cylindrical inner circumference of the screw cylinder (106) (Fig.3a to 3e and 4a to 4e). 19. Extruder according to one of claims 5 to 18, characterized in that that the screw flights (115, 116, 117, 118) between adjacent screw flights (111, 112, 113, 114) each about half the pitch on one of their Height corresponding length interruptions (121, 122, 123, 124) have, those on successive webs (115,116,117,118) in the circumferential direction to one another are offset (Fig. 3a, 3c, 3e and 4a, 4c and 4e). 20. Extruder according to one of claims 5 to 19, characterized in that that the interruptions or cutouts (138a to 138c and 121 to 124) in the webs (115 to 118) of the extruder screw (109) delimiting edges rounded or have guide surfaces. 21. Extruder according to one of claims 5 to 20, characterized in that that it is designed as a single-screw extruder for foam film production. 22. Extruder according to one of claims 5 to 20, characterized in that that it is a tandem system with a separate drive for the gas supply extruder and cooling extruder is designed.