DE102004037349B4 - Thread for a screw of a screw extruder - Google Patents

Abstract

thread for one Screw of a screw extruder, in particular a double-snail extruder, for separating liquid Constituents of solid constituents of an extruded product, such as rapeseed, with a thread root (21a, 21b, 71a, 71b, 81a, 81b), one of the thread root (21a, 21b, 71a, 71b, 81a, 81b) radially outwardly extending threaded ridge (23a, 23b, 73a, 73b, 83a, 83b), and one of the thread root (21a, 21b, 71a, 71b, 81a, 81b) radially inwardly extending recess (25a, 25b, 75a, 75b, 85a, 85b), characterized in that in Course of the thread of the threaded ridge (73 a, 73 b) and / or the recess (75a, 75b) at least in thread sections in the thread root (61a, 61b) vanish.

Description

The The invention relates to a thread or a screw profile for a screw or for a screw segment of a screw extruder, in particular one Twin screw extruder, for separating liquid components from solid Ingredients of a Extrudierguts, such as oilseed rape, with a thread root and a radially outwardly extending from the thread root Thread web.

Around high efficiency in separating the liquid components from solid To achieve components of the extruded, it is known that Pressure inside the screw extruder along the conveyor line to vary, in particular to increase and decrease alternately. Usually becomes an increase in pressure realized in that the pitch of the threaded ridge changed, in particular is reduced. With single screw extruders, pressure variations can also with change of the screw core diameter, whereby a crimping and / or kneading space between the extruder wall and the screw to be changed can. However, this measure is not readily transferable to twin screw extruders with parallel screw shafts, because the space between the two waves is not easy enlarged or can be downsized.

From the GB 1,140,237 is a twin-screw extruder with two screw shafts are known, the threads have a machined in the thread root threaded recess. In the course of the thread, the center axis distance of the thread root increases.

It Object of the invention, an alternative to the known measures for varying the extrusion pressure within a screw extruder without the basic structure of a screw extruder, in particular a twin screw extruder to change substantially.

These The object is achieved by the claims 1, 5 and 11 or 12, 14, 18 and 21 and solved.

After that is a screw profile or a thread for a screw of a screw extruder, in particular a twin screw extruder, for separating liquid components from solid components an extrusion material, such as rapeseed, sewage sludge for sludge drying, etc., with a thread root, a radially from the thread root outward extending thread ridge and additionally one of the thread root provide radially inwardly extending recess or groove. Of the Threaded base can be a cylindrical or conical shape or a have any other shape, by a larger Erstrekkung in the axial direction of the screw or in the conveying direction of the extruder as the perpendicular to the axial direction radial directions definable is. The threaded ridge or depression form with respect to the Thread base positive or negative form jumps.

With the measure of the invention is the Thread except a "positive" thread property, characterized by the engagement of the threaded ridge of a first thread in one by the threads opposite Threaded space between two lying on the same circumference Threaded bar sections of a second, the first associated thread also gives a "negative" thread property awarded, which is created with the threaded recess in which that in solid and liquid Can collect components to be divided extruded, with by the penetration of a thread groove adapted to the thread recess combined in the depression extruded material, crushed and can be kneaded.

When particular advantage of the measure according to the invention, a thread with a Provide threaded recess, is that in particular for twin-screw extruder at substantially constant radial dimensions of the screws the center axis distance - the shortest Removal of a threaded area to the longitudinal or medial axis of the screw - indicates the thread base are significantly increased can. In this way, the production process, the usual due to the gripping of the opposing thread ridges of Snails is necessary and through the extruded material is pressed upon rotation of the thread of the respective thread ridge, reducible between the facing sides of the screw. With the free space reduction, the extrusion pressure within the Slug extruder significantly increased become. The now possible by the inventive measure larger center distance of the Thread reason has the further technical advantage that the ways from the thread base to a filter for the liquid component of the extruded material can be and thus the expiration time of the extruded material liquid from the screw extruder is significantly reduced.

By providing a threaded recess locally limited pressure peaks can be caused in the depression, which leads to an increased efficiency in the separation of solid and liquid components of an extruded material and allows better tuning of the screw extruder to certain extrudates.

Of Another can with the measure according to the invention, the conveyor passage enlarged between the facing sides of two adjacent screws and be scaled down, where by the screw extruder without much design effort a further degree of freedom for adjusting certain extruding pressures along the Delivery direction provided is.

According to the invention Center-axis distance of the thread root smaller than that of the thread ridge and bigger than the depression. It should be clear that the center distance the thread base, the threaded ridge and the recess certainly change in the course of the thread can.

at an execution The invention takes in the course of the thread of the center axis distance the thread base too. It takes the center axis distance of the threaded ridge essentially equivalent the increase of the center pitch of the thread root. When increasing the center pitch of the thread root takes the radial depth the depression in the course of the thread to by either the center axis distance the depression increases less in the course of the thread than the center axis distance of the thread root or the center axis distance the depression remains constant over the course of the thread. To one Increase of the center pitch of the root can be a center pitch decrease continuously connect the thread root.

The Basic shape of the thread of an extruder screw, which is essentially through the radial outer dimension is defined by the thread ridge is cylindrical or conical, wherein Other shapes without circular symmetry, such as elliptical shapes in cross-section, according to the invention into consideration to be drawn.

at an execution of the invention can in Course of the thread at least thread sections, the recess go into the thread base and / or the threaded ridge in the thread root. In this case, the center axis distance of the thread root can either at the substantially constant center distance of the threaded ridge increasingly approaching, or the center-to-center distance of the thread ridge decreases in size to the thread base diameter. The same applies to the center axis distance the depression, which increases the center axis distance of the thread root approaches, or the center-to-center distance of the thread root fits the center-to-center distance decreasing the depression.

at a special design the invention, the center axis distance of the thread root, the Recess and / or the threaded ridge in the course of the thread at least in sections, periodically, in particular sinusoidal, increase and decrease.

Preferably extends the thread-like depression helical, in particular substantially parallel to the thread ridge, d. H. the depression has the same Thread pitch like the thread ridge. That's the way it is simple, screws with thread according to the invention with another To combine screw to form a twin-screw extruder.

The Thread does not have to be complete wind around the central axis of the snail. Preferably, the surrounds Recess the central axis of the thread at least in a peripheral portion of at least 90 °, in particular at least 180 °, being a complete one Surround the central axis or multiple full environments for long conveyor lines high extrusion pressure is / are preferred.

at another embodiment the invention, the axial width of the recess to vary, for another option an alternating, locally limited pressure build-up and dismantling within short conveyor lines to induce. This is particularly appropriate when the kneading volume be enlarged in the depression should, but the permissible Radial depth of the recess is limited. Similar effects are caused by change the width of the threaded ridge reached in the course of the thread.

Of Furthermore, the invention relates to a screw part or segment with a thread according to the invention or worm profile, which worm part on a worm shaft Can be mounted over a transmission can be driven by a motor of an extruder. Preferably, for mounting the worm member to the worm shaft a shaft-hub connection provided, which is realized for example as a keyway structure.

Preferably is the screw part sleeve-shaped, so that it's easy on one usually cylindrical worm shaft mounted and fixed axially and radially can be. Especially with very large extruders it can be an advantage be the desired one To realize snail thereby that several snail parts to an already mounted in an extruder housing screw shaft be put on. To the desired Change the screw configuration to be able to the worm parts are removable and by differently designed worm parts replaceable.

The invention also relates to a set of snow ckenteile or segments, of which at least one is designed as a screw part according to the invention. The worm parts should be designed to be mountable on a worm shaft in a specific sequence. Preferably, a complete screw with a thread is thus to be formed, which is provided with a continuous thread transition from one screw part to the other. In the case of a continuous transition, attention must be paid not only to the transition of the thread ridge or threads, but also to a substantially uninterrupted transition of the thread depression.

at a development of the invention, the set of screw parts at least a Schnekkenteil having a certain main conveying direction provides at a fixed rotational drive direction of the screw. To high pressures Within an extruder, creating at least one more Be provided snail part in the sentence according to the invention, the a thread with a opposite direction for the same rotational drive direction conveying direction having. This can be realized simply by the fact that relevant Schnekkenteil in opposite conveying orientation on the worm shaft is mounted.

Of Furthermore, the invention relates to a screw with at least one thread according to the invention. In a special design the invention is the screw forming part of the screw and a Worm shaft in one piece manufactured, in particular forged. Preferably, the screw have multiple thread configurations, of which at least one by the thread according to the invention is formed. The thread configuration can be with one or more Gewindesteg- and / or recess-free sections along the Be provided snail.

Farther can the screw according to the invention at least three substantially continuously merging into each other Having threaded portions: a threaded portion includes a conventional Thread without recess; another threaded section has one conically increasing thread root, one being gradually in the course of the thread the thread root penetrating recess is provided and the Center distance of the thread ridge gradually with that of the thread root increases; and a cylindrical threaded portion is with a recess provided with a constant radial depth in its course, in particular, the center distances of the threaded ridge and the Thread bases are constant.

at A preferred embodiment of the invention is a threaded portion the snail to conveying of the product in a first direction, while another threaded configuration, the in certain circumstances is well-insulated, executed is to push the product counter to the first direction the extruding pressure upstream to increase the further thread configuration.

In addition concerns the invention an arrangement of two screws to form a Twin-screw extruder. The snails each comprise at least an inventive thread. there the threads are so assigned to each other, that upon rotation of the Schnekken the threaded ridge of a thread in the recess of engages other thread. Preferably, the roots of both Snails in such a way that between them a narrow gap is formed. Between the threads, large areas of kneading are created, of which the set under pressure Extrudiergut in the circumferential direction the snails can dodge.

at a development of the arrangement of two screws are at least thread-forming sections of the screw structurally associated with a filter, in particular of a plurality of substantially parallel to each other Consists of plates which extend substantially in a radial direction extending away from the snail.

Around in particular the extrusion pressure within a screw extruder to be able to vary without The basic structure of a screw extruder to change in essence, there is an independent one Invention aspect therein, the diameter or the center axis distance to increase the thread root, wherein the thread pitch in particular substantially equivalent is reduced to the center axis distance increase of the thread root. In this way, the space between them can be opposite Reduced sides of two screws of a twin-screw extruder be without having to provide a depression in the thread root.

Around the installation of such a screw with magnifying To simplify thread reason, the conveying direction end of the screw extruder housing with a removable cover over which the screw forward out of the case (in conveying direction) can be removed. Preferably, the twin-screw extruder a housing which varies according to the increase in center pitch the thread root of the screw along opening the conveying direction, essentially the distance of the facing sides of the screw and the housing to keep substantially constant.

Further Advantages, characteristics and features of the invention are achieved by the following description of preferred embodiments with reference to the drawings clearly, in the show:

1 a perspective view of a twin-screw arrangement with a known and a thread or screw according to the invention for comparison;

2 is a side view of the twin screw according to 1 ;

3 a cross-sectional view of the twin-screw arrangement along the sectional vectors III-III according to 2 ;

4 a plan view of another embodiment of a twin-screw arrangement with thread according to the invention; and

5 a perspective, schematic view of the internal organs of a twin-screw extruder according to the invention.

In the 1 to 3 is a twin screw arrangement 1 represented, in which two mutually parallel screws 3 . 5 are provided. The snails 3 . 5 each comprise a wave 7 . 9 on the outside of which a wedge profile is designed for a shaft hub connection.

On the waves 7 . 9 are for illustrative comparison each a known pair of threads or Schneckenprofilpaar 8th and an inventive pair of threads or Schneckenprofilpaar 10 fixed in place. The spiral profile pair 8th has identical threaded parts (profile parts) 13a . 13b conventional design with a thread root (screw core) 15a . 15b and one of the thread reason 15a . 15b radially outwardly extending threaded ridge (helix) 17a . 17b which extends radially in a substantially tapered manner. The threaded parts 13a . 13b known type are associated with each other such that the threaded ridge ( 17a ) of a threaded part ( 13a ) substantially in the axial direction A in the middle in between two thread ridge portions of the other opposing thread ( 13b ) lying kneading room 14 engages what works best in 3 is apparent. The kneading room 14 is in the radial direction R by the roots 15a . 15b limited, wherein the kneaded Extrudiergut in the circumferential conveying direction of the kneading space 14 can escape.

The threaded parts 13a . 13b are as essays for the wave 7 . 9 executed.

The threaded pair according to the invention 10 includes two identical, cooperating threaded parts (profile parts) 11a . 11b that have a thread root (screw core) 21a . 21b and one of the thread reason 21a . 21b extending thread ridge (helix) 23a . 23b includes. The threaded bar 23a . 23b runs helical or thread-like with constant pitch. Parallel and essentially with the same thread pitch is a thread recess (Wendelnut) 25a and 25b provided that slightly wider b _v in the thread root 21a . 21b is introduced as the axial width b _{s of} the threaded ridge 23a . 23b ,

As in particular in 3 can be seen, engages the threaded bar 23b of the threaded part 11b in the threaded recess 25a of the thread 11a , thereby freeing the space 31 That is, by opposing sides of the threaded parts 11a . 11b is limited, between the snails 3 . 5 clearly opposite the kneading room 14 the known thread pair 8th is reduced, which not only higher extruding pressures can be generated but also the way for the expiry of the liquid component of a Extrudierguts (not shown) is shortened. In addition, a combined squeeze and kneading zone 33 formed in the threaded recess, which zone through the engaging threaded ridge 25b and the side walls 35 the thread recess 25a is partially limited in the radial direction R and in the axial direction A.

With the possibility according to the invention, the threaded ridge 23a . 23b in the threaded recess 25a . 25b meshing becomes another effective combined crushing and kneading range 37 created by the small gap between the facing sides of the thread root 21a of the thread 11a and the thread root 21b of the thread 11b results. With the thread according to the invention, a thread root of large diameter can be created for twin-screw extruder with a relatively small distance between the extruder screw axes.

In 4 is a twin screw arrangement 41 shown in the two substantially parallel waves 43 . 45 with circumferential spline a set on the shaft 43 . 45 mounted worm parts or segments 51a . 51b . 53a . 53b . 55a . 55b both stationary in radial (R) and axial direction A.

The snail parts 51a to 55b include a non-visible Innennutprofil that for localized mounting of the screw parts 51a to 55b on the worm shafts 43 . 45 cooperates with their spline.

The snail parts 51a . 51b are from her conventional design and have a common thread with a thread root (screw core) 61a . 61b in the axial direction of constant diameter and from the thread root 61a . 61b radially outwardly extending threaded ridge (helix) 63a . 63b , The thread ridges 63a . 63b have a constant thread pitch in the course of the thread.

It should be clear that to increase the extrusion pressure and the thread pitch in the conveying direction both in the thread of the screw part 51a as well as the threads of the screw parts 53a . 53b . 55a and 55b can lose weight. It may also be provided to gradually increase the thread pitch in the conveying direction after a thread pitch reduction in order to provide in this way a periodic thread pitch increase and decrease along the conveying direction.

The central scroll parts 53a . 53b are so on the waves 43 . 45 mounted on the transition 65 to the conventional screw parts 51a . 51b connect and that in each case the Gewindesteg 63a . 63b of the screw part 51a . 51b continuously in the associated thread ridge 73a . 73b of the central scroll part 53a . 53b passes.

From the transition 65 takes the center axis distance - defined as the distance of a threaded area surface to the central axis M of the worm shaft 43 . 45 - the thread root 71a . 71b the snail parts 53a . 53b tapered slightly too, while in a central area of the thread root 71a . 71b between two axially juxtaposed Gewindestegabschnitten a depression (helical groove) constant center distance m _v , defined as the distance of the recessed bottom to the central axis M of the screw shafts 43 . 45 , and increasing depth t gradually according to the increase of the center pitch m _{g of} the root 71a . 71b in the snail part 53a . 53b penetrates. The depression (Wendelnut) 75a . 75b of the threaded screw part 53a . 53b begins at the transition 65 and reaches its greatest depth t at the transition 67 between the central parts of the scroll 53a . 53b and the slug parts 55a . 55b to the further course of the screw part 55a . 55b to stay constant. The center axis distance m _s remains in the course of all three screw parts 51a . 51b . 53a . 53b . 55a . 55b constant. However, that takes in the course of the screw part 51a . 51b constant ridge height h continuous due to the conicity of the thread root 71a . 71b of the screw part 53a . 53b to a web height h, which in the course of the screw part 55a . 55b remains constant.

The thread of the screw parts 55a . 55b comprises a cylindrical, defined by the threaded ridge basic shape with a thread root 81a whose center axis distance m _g in the axial direction A of the shaft 53 . 55 essentially does not change. From the thread reason 81a . 81b extends radially outward of the threaded ridge 83a . 83b that compared with the threaded ridges 73a . 73b the central scroll parts 53a . 53b and the thread ridges 63a . 63b the usual scroll parts 51a . 51b has the same thread pitch and the same outer diameter. However, the thread pitch in the axial direction A may change. From the transition 67 runs helically, equal to the thread pitch 83a . 83b a threaded recess 85a whose depth t in the course of the thread of Schnekkenteile 55a . 55b is constant.

As in 4 can be seen, which shrinks through the opposite sides of the screw parts 51a . 53a . 55a , and 51b . 53b . 55b in the radial direction R limited free space 14 from the transition 65 continuously tapering, until at the threaded parts 55a . 55b only a small gap between the threads 81a . 81b and between the wells 85a . 85b and threaded ridges 83a . 83b is formed. With the decrease of the free space 14 the extrusion pressure can be increased considerably. In addition, the distance is reduced to lying around the Schnekkenteil components, so that the liquid component of the extruded material can run faster due to the shorter paths.

With the set according to the invention snail parts 51a to 55b for a twin-screw extruder is also achieved that within a very short conveyor lines a considerable Extrudier pressure increase is provided. With the creation of a threaded recess 75a . 75b . 85a . 85b , in which the thread ridge 73a . 73b . 83a . 83b engages the opposite screw part, the distance d of the opposing roots is reduced to a minimum.

To simplify the manufacture of the set of screw parts 51a to 55b to realize corresponds to the center axis distance m _{v of} the threaded recess 85a . 85b of the screw part 55a . 55b and the gradually forming threaded recess 75a . 75b of the middle scroll part 53a . 53b the center axis distance mg of the thread root 61a . 61b the conventional screw part 51a . 51b ,

It is conceivable the sentence snail parts 51a to 55b with two or three further parts of the screw, which are symmetrical to the screw parts 51a to 55b sitting on the shafts, ie after the screw parts 55a . 55b may again be arranged a screw part with a conical root with gradually disappearing depression to reduce the extrusion pressure. The set of snail parts could be compared to a conventional one Complete the screw section.

At the in 4 shown twin screw arrangement is schematically only one-sided a plate-like filter 91 indicated, whose plates are in the axial direction A of the waves 43 . 45 extend. The filter 91 is used for cleaning and directed draining of the liquid component of the product to be extruded.

Such filters are particularly adjacent to the set of scroll parts 51a to 55b to arrange, because there the separation rate of liquid and solid components is highest. With the increase of the thread root according to the invention, the distance of the screw part from the filter can be reduced, which results in shorter drain times and an increased yield rate.

It be clear that the set of screw parts either as an essay on Shafts of a screw mountable or integrally formed with the respective shaft is.

In 5 are the internal organs of a twin-screw extruder according to the invention 101 represented by two snails 103 . 105 includes that from a worm shaft 107 . 109 and screw parts mounted thereon according to the invention 111 . 113 that exists in 5 are only indicated. The snail parts 111 . 113 determine a conveying direction F, which at a change of direction of the screw shafts 107 . 109 can be reversed.

With not according to the invention shown in more detail Thread, the distance of the center axes can be greatly reduced, or it can be snails can be used, whose roots have larger center distances can.

In the illustrated embodiment are screws with a screw land diameter of about 160 cm and a distance between the center axes M of the screw shafts 103 . 105 used by about 132 mm.

The main components of the filter 121 are in the conveying direction and in the radial direction R extending plates with a plate thickness of about 1 cm, which are arranged parallel to each other with a plate spacing of 2 cm.

The plates 123 are stacked in packages, with a filter plate package 125 . 127 one snail each 103 . 105 assigned. The snail 103 . 105 facing side of the filter plate package 125 . 127 is formed complementary to the shape defined by the thread ridge basic shape of the screw or screw parts.

The filter plate packages 125 . 127 are through a partition 129 separated. Outside are storage walls 131 . 133 provided, which the filter plate packs 125 . 127 carry H in a horizontal radial direction. carrier plates 135 that erstrek ken in the horizontal radial direction H hold the filter plate packs 125 . 127 stationary in the radial direction, wherein for the carrier plates two carrier bases 137 . 139 below the carrier plates 135 are arranged, the tapered for the rapid flow of the liquid component of the extruded edge portions 141 exhibit.

The Internal organs of the twin-screw extruder do not become one illustrated housing surrounded by an entrance for the extruded material and outputs for the liquid Component of the extruded material and the solid part of the extruded material having.

The in the above description, in the drawing and in the claims disclosed features of the invention can both individually and also in any combination for the realization of the invention in its various embodiments be essential.

1

Twin screw arrangement

3, 5, 43, 45, 103, 105

slug

7, 9, 107, 109

wave

8th

known pair of threads

10

Thread pair according to the invention

11a, 11b

threaded parts

13a, 13b

threaded parts

14

kneading space

15a, 15b, 21a, 21b

thread base

61a, 61b

thread base

71a, 71b, 81a, 81b

thread base

17a, 17b, 23a, 23b, 63a, 63b

thread web

73a, 73b, 83a, 83b

thread web

25a, 25b, 75a, 75b, 85a, 85b

thread groove

31

free space

33

crushing and Knetzone

35

Side wall

37

crushing and kneading area

41

Twin screw arrangement

51a, 51b, 53a, 53b, 55a, 55b

screw part

65, 67

crossing

75a, 75b, 85a, 85b

thread groove

91

filter

101

Twin-screw extruders

111, 113

screw part

121

A filter assembly

123

plates

125 127

Filter plate pack

129

partition wall

131 133

bearing walls

64356

135

carrier plates

137 139

support bases

141

edge sections

A

axially

F

conveying direction

H

horizontal radial direction

M

central axis

R

radial direction

b _s

axial Width of threaded ridge

b _v

axial Width of the recess

m _v , m _s , m _g

Center axial distance

d

distance

H

Thread web height

t

depth

Claims (22)

Thread for a screw of a screw extruder, in particular a double-screw extruder, for separating liquid constituents from solid constituents of an extruded product, such as rapeseed, with a thread root ( 21a . 21b . 71a . 71b . 81a . 81b ), which differs from the thread ( 21a . 21b . 71a . 71b . 81a . 81b ) radially outwardly extending threaded ridge ( 23a . 23b . 73a . 73b . 83a . 83b ), and one of the reasons ( 21a . 21b . 71a . 71b . 81a . 81b ) radially inwardly extending recess ( 25a . 25b . 75a . 75b . 85a . 85b ), characterized in that in the course of the thread of the threaded ridge ( 73a . 73b ) and / or the recess ( 75a . 75b ) at least in thread sections in the thread root ( 61a . 61b ) vanish. Thread according to claim 1, characterized in that the thread root ( 21a . 21b . 71a . 71b . 81a . 81b ) extends more in an axial direction (A) of the thread than in a radial direction (R) of the thread, in particular substantially in the axial direction (A) of the thread. Thread according to claim 2, characterized in that in the course of the thread, the center axis distance (m _v , m _g , m _s ) of the thread root, the recess and / or the threaded ridge changed or change at least in thread sections. Thread according to one of claims 1 to 3, characterized in that in the course of the thread of the center axis distance of the thread root ( 71a . 71b ), wherein the center distances of the threaded ridge ( 73a . 73b ) and / or the recess ( 75a . 75b ) remain substantially constant over the course of the thread. Thread according to the preamble of claim 1 or according to one of the claims 1 to 3, characterized in that in the course of the thread of the center axis distance the root of the thread increases, with at least the center-to-center distance of the thread ridge decreases in the course of the thread honey and the Center pitch of the recess increases in the course of the thread. Thread according to one of claims 1 to 3, characterized in that in the course of the thread of the center axis distance of the thread root ( 71a . 71b ), the depression ( 75a . 75b ) and / or the thread ridge ( 73a . 73b ) increases and decreases periodically at least in thread sections. Thread according to one of claims 1 to 4, characterized that it has a substantially conical basic shape. Thread according to one of claims 1 to 4, characterized in that the thread root ( 21a . 21b . 71a . 71b . 81a . 81b ) is at least partially conical and / or cylindrical. Thread according to one of claims 1 to 8, characterized in that the recess ( 25a . 25b . 75a . 75b . 85a . 85b ) has a helical course. Thread according to one of claims 1 to 9, characterized that the recess has a longitudinal axis the thread at least in a peripheral portion in particular surrounded by at least 180 °, preferably completely surrounds. Thread according to the preamble of claim 1 or one of claims 1 to 10, characterized in that in the course of the thread a width (b _v , b _s ) of the recess and / or the threaded ridge changes, in particular increases or decreases. Screw part for mounting on a worm shaft a screw extruder with one according to one of claims 1 to 11 trained thread. A screw member according to claim 12, which is sleeve-shaped. Set of snail parts, of which at least one after one of the claims 12 or 13 is formed. A set according to claim 14, in which the screw parts ( 53a . 53b . 55a . 55b ) are arranged in series on a shaft ( 7 . 9 . 107 . 109 ) to be mounted. A set according to claim 15, in which the screw parts ( 53a . 53b . 55a . 55b ) form at least one continuous screw thread. Set according to one of claims 14 to 16, wherein at least one by at least one screw part ( 53a . 53b . 55a . 55b ) formed thread in a rotational main direction has a first conveying direction (F) and another thread formed by at least one screw part in the rotational main direction has a second, the first opposite conveying direction (F). A screw with at least one according to one of claims 1 to 11 trained thread. A screw according to claim 18, which is a combination from at least one thread with recess and an adjoining and this includes separate recess-free thread. A screw according to one of claims 18 or 19, in which a Thread portion in a rotational main direction a first conveying direction having a threaded portion is provided, in the main direction of rotation comprises a first opposite conveying direction. A twin-screw extruder comprising a pair of screws each according to any one of claims 18 to 20, wherein the threads of the screws are associated with each other such that, upon rotation of the screws, the threaded ridge (15) 23a . 23b . 73a . 73b . 83a . 83b ) of the one thread in the recess ( 25a . 25b . 75a . 75b . 85a . 85b ) engages the other thread. Twin-screw extruder according to claim 21, characterized in that the screw-forming sections of the screw are a filter ( 91 ) assigned.