ES2881199T3 - Device for producing a flowable mortar composition - Google Patents

Abstract

Device for producing a fluid mass, in particular a fine-grained mortar mass, such as a plaster mass, comprising a main mixer for mixing the dry mortar with water, a post mixer (1), and a rotary displacement pump ( 8), in particular an eccentric screw pump, for transporting the premixed mass to the post mixer (1), in which the rotary displacement pump (8) comprises a transport rotor (9), in particular an eccentric helical rotor , which is rotatable in a stator, in particular in a transport tube (10), with a transport thread (17); and the rear mixer (1) has a mixing rotor (2) with an active surface (3) arranged in particular on the outer surface of the mixing rotor (2) and a mixing tube (4) with a counter surface (5) arranged in particular on the inner surface of the mixing tube (2), in which the mixing rotor (2) can be driven via the conveying rotor (9) so that the active surface (3) of the mixing rotor (2) can rotate around a central axis (A) of the mixing tube (4) along the counter surface (5), in which the mixing rotor (2) is designed in such a way that the mixing rotor conveying direction of the mixer back is, at least in sections, opposite to the conveying direction of the conveying thread of the conveying rotor, whereby, in particular, a turbulence is generated in the mass and/or in which the mixing rotor (2) has a mixing thread (16) or a mixing propeller or mixing rotor blades that is or are shaped to rotate in a direction opposite to a direction of rotation of the transport thread (17), characterized in that the stator, in particular the transport tube (10), of the rotary displacement pump (8) has a diameter greater than the downstream mixing tube (4) in terms of flow rate.

Description

DESCRIPTION

Device for producing a flowable mortar composition

The invention relates to a device for producing a flowable mortar composition, in particular a fine-grained mortar composition, such as a putty.

In the case of fine-grained mortar masses, such as plaster masses, which are used to fill holes and cracks or to completely plaster plasterboard, the mortar mass is mixed by so-called sinking. The dry mortar is spread over the water, which absorbs it, and then the mortar mass is mixed. In particular, in the case of fine-grained mortar masses, nodules and small lumps form which make continuous mixing and transport difficult. In practice, these fine-grained mortar mixes are first mixed in a separate mixer and, after a longer mixing period, fed to a pump for transport. Thus, in the prior art, only batch operation is possible.

From DE 19754969 A1 a device is known with which it is possible to continuously produce a low viscosity foamed grout or a low viscosity foamed mortar mass with a homogeneous consistency without nodules and with which a high capacity is achieved. Of transport. The device comprises a main mixer for mixing the dry mortar with water and an eccentric screw pump arranged downstream from the main mixer to convey the premixed mortar mass to a secondary mixer. The rear mixer is arranged at an outlet of the eccentric screw pump and has a vane rotor that is centrally arranged in a housing. The water is introduced into the shell and mixed with the mortar mass via the paddle rotor to produce a low viscosity mortar mass. However, the smallest nodules or lumps are barely captured by the vane rotor as they can avoid it.

Document EP 1721 717 B1 discloses a device for producing a fluid mortar mass, in particular a fine-grained mortar mass. The mixing rotor of the rear mixer is eccentrically coupled to a delivery rotor of an eccentric screw pump. The mixing rotor is essentially rod-shaped and is used to remove lumps or nodules contained in the mortar mass between an active surface of the mixing rotor and a coupling surface, in particular the inner surface, of a mixing tube.

From DE 102009 047 717 A1 an eccentric screw pump is known for conveying fluids, in particular liquid mortar, with a stator consisting of an elastomer and having a two-step steep screw-shaped pump cavity. or multiple starts, and with a motor driven rotor that passes through the pump cavity with radial eccentricity and has a steep thread shape. At the pressure end of the stator, the pump cavity opens into a mixing chamber in which a mixing element is coupled, which is non-rotatably connected to the rotor. The mixing element is provided with turbine blades that form a turbine insert, which are directed against the direction of fluid flow for a certain direction of rotation of the rotor. The mixing chamber with the mixing element has a larger inside diameter than the pump cavity. The mixing element is separated from the inner wall of the mixing chamber. With the help of this rear mixer of this well-known eccentric screw pump, a better mixing quality and an increase in the proportion of empty air is achieved. The pumped fluid is effectively mixed and the void air content is increased, thereby achieving better performance and processability of the mortar.

It is the task of the invention to further develop a device of the type mentioned above in such a way that the mixing effect is preferably improved.

This task is solved in particular by a device having the characteristics of claim 1. Advantageous further developments and developments emerge in particular from the dependent claims.

In one embodiment, a device for producing a fluid mass, in particular a fine-grained mortar mass, such as a plaster mass, comprises a main mixer for mixing dry mortar with water and a rotary displacement pump, in particular a pump. eccentric screw, to transport the premixed dough to a secondary mixer. The rotary displacement pump comprises a conveyor rotor rotating in a stator, in particular an eccentric screw rotor, with a conveying thread. The rear mixer has a mixer rotor with an active surface, in particular arranged on the outer surface of the mixer rotor, and a mixer tube with a counter surface, in particular arranged on the inner surface of the mixer tube. The mixing rotor can be driven through the conveyor rotor such that the active surface of the mixing rotor can rotate about a central axis of the mixing tube along the counter surface.

In one embodiment of the invention, the mixer rotor is designed in such a way that the conveying direction or the conveying direction or the flow of material conveyed from the mixing rotor of the rear mixer is, at least in sections or also in general, opposite to the conveying direction or conveying direction or the flow of conveyed material from the conveying thread of the conveyor rotor. In this way, turbulence is generated in the material flow, which improves mixing.

In one embodiment of the invention, the mixing rotor comprises a mixing thread (or: a mixing spiral), which is designed to rotate in the opposite direction to a direction of rotation of the transport thread. If the transport thread of the conveyor rotor is designed as well as a right-hand thread (also: right-hand rising thread), the mixing thread of the mixing rotor is correspondingly designed as a left-hand thread (also: left-hand rising thread). In the opposite case, if the conveying thread of the conveyor rotor is designed as well as a left-hand thread (also: left-rising thread), the mixing thread of the mixing rotor is correspondingly designed as a right-hand thread ( also: right-hand rising thread). In this way, an opposite conveying effect or conveying direction or conveying direction or material flow of the mixing rotor compared to the conveying thread is achieved at least partially.

In principle, the device is designed to guide the mortar mass in the rear mixer between an active surface and a counter-surface in such a way that the latter is conveyed in the transport direction along the counter-surface and the surface. The active surface moves along the counter-surface, the active surface in particular making a rotational or orbital motion about a central axis of the rear mixer along the counter-surface. It has now been discovered that the grinding of the lumps between the active surface and the counter surface can be improved if the mixing rotor itself is provided with a mixing thread, which is formed in the opposite direction to the transport thread of the conveyor rotor. The mixing thread thus generates a material flow movement which is directed against the conveying direction of the conveying thread. In this way, a strong turbulence of the material flow is generated which is effectively transferred in the conveying direction.

Due to the aforementioned turbulence, the lumps or nodules of the transported mortar mass increasingly reach the area between the active surface and the counter-surface. There they are exposed to comparatively high pressure, friction and shear forces and are crushed and pulverized between the active surface and the counter surface, so that the mortar mass is effectively homogenized. The rotary or orbital movement of the active surface continuously presses and grinds the mortar mass, thus ensuring the continuous production and transport of a substantially homogeneous mortar mass.

In one embodiment, the active surface is formed by the outer surface of the rotating mixing thread. In particular, in the case of contact surfaces with cylindrical symmetry, this means that the contact area between the active surface and the contact surface is essentially in the shape of a helix. This structural formation of the active surface further favors the transport of the material in the direction of the comminution area between the active and opposite surfaces.

By means of the rotary or orbital movement of the active surface, the mortar mass is pressed and crushed, so as to ensure that a substantially homogeneous mortar mass is produced and conveyed. In this way, both fine-bodied and thick-bodied mortar masses can be effectively homogenized without the need for additional measures to alter the consistency, such as the supply of water or compressed air. Since the mixing thread itself moves the material against the conveying direction, more mortar mass is effectively pressed into the area between the active and counter surfaces, thus improving the homogenization of the mass flow.

Furthermore, the stator of the rotary displacement pump, in particular a transport tube through which the mortar mass is conveyed, has a larger internal diameter than the mixing tube located downstream. In this way, a sufficient conveying effect in the conveying direction is ensured. In addition, the mass flow is compressed in the area of the rear mixer, so that the lumps are possibly already pulverized by internal friction.

In one embodiment, the mixer rotor has a circular, oval, or elliptical cross section.

In one embodiment, the mixing rotor of the subsequent mixer is arranged in a final area of the conveyor rotor associated with the subsequent mixer, in particular it is formed in one piece with the conveyor rotor, or is materially connected to the conveyor rotor by welding. These designs, particularly one-piece ones, have the advantage of greater stability.

Alternatively, the mixing rotor is connected to the conveyor rotor through fixing means, in particular by means of a screw connection. The mixing rotor thus forms an extension of the conveyor or screw rotor of the rotary displacement pump. The removable connections allow, in particular, advantageously, to interchange the mixing rotors according to the needs or the application, in particular, as a function of the viscosity of the fluid mass to be produced.

In one embodiment, the active surface of the rotor lies substantially close to the mating surface of the mixer tube or is at least slightly pressed against the mating surface, wherein the active surface and / or the mating surface are made of a elastic material, such as a wear resistant rubber comprising synthetic or natural rubber. By using rubber, better adhesion and friction of the mortar mass to the respective formed rubber surface is achieved. Furthermore, the rubber is ductile enough that the mortar composition can pass between the surfaces and be greatly squeezed out.

According to an advantageous embodiment, the contact surface is elastic and the active surface is comparatively inelastic or rigid, so that only the contact surface yields elastically when the mortar mass is driven through and compressed. Due to the elastic counter-surface and the inelastic or rigid active surface, the pressure on the mortar mass increases markedly with the simultaneous compression of the mortar mass between the surfaces, so that even the smallest lumps or nodules are pulverized.

According to another advantageous embodiment, the elastic and inelastic behavior of the surfaces is reversed, in which the active surface is elastic and the counter surface is comparatively inelastic or rigid, so that only the active surface yields elastically when driving through and the mortar mass is compressed. Also in this embodiment, the mortar mass is squeezed between the surfaces and at the same time is subjected to increased pressure. In a preferred embodiment, the active surface of the mixing rotor and the engagement surface of the mixing tube are each formed of materials having different elastic properties, the pair of materials chosen being an elastic material, such as rubber, and a material comparatively inelastic, like metal, preferably steel. Thanks to this choice of material, a greater pressure is exerted on the mortar mass and, at the same time, a sufficient elastic conformity of the surface formed by the rubber is achieved.

According to a possible embodiment, the coupling surface of the mixing tube is formed of rubber, the mixing tube comprises an outer tube and a rubber insert which is attached to the inner side of the outer tube and the inner surface of which forms the coupling surface, and the active surface of the rotor, in particular, is formed of metal, preferably steel. Using a rubber insert and placing it in the outer tube, a counter-surface is created that yields elastically and is resistant at the same time.

In the embodiments described above, it is sufficient, in terms of the compression, friction and shear forces acting on the mortar mass, that the active surface moves along the engaging surface in a tight or substantially gap-free manner.

Alternatively, both the active surface and the counter-surface can be elastic, in which case it is particularly advantageous if the active surface is further pressed against the counter-surface to exert or maintain a greater pressure on the mortar mass.

In particular, in embodiments comprising mixing rotors having an elliptical or oval cross section, a space is provided in a circumferential portion between the mixing rotor and the mixing tube. In other words, the mixing rotor does not rest completely on the mixing tube.

In one embodiment, the mixing tube of the rear mixer is integrally formed with a transport tube of the rotary displacement pump, wherein the outer tube and the rubber insert of the mixing tube are each formed in one piece. with an outer tube and an inner rubber insert of the transport tube. The post mixer and eccentric screw pump are combined by these constructive measures to form a compact construction unit that can be manufactured at low cost.

According to an alternative embodiment, the mixing tube of the rear mixer and a transport tube of the eccentric screw pump are formed as separate parts and are connected to each other through fixing means, such as a flange or a clamping flange, while the flange has an annular collar projecting radially inward and which is disposed between the rubber insert of the mixer tube and an internal rubber insert of the transport tube and bears hermetically against them. By shaping the mixing tube and the transport tube as separate parts, the mixing tube can be inserted as required and removed again, for example, for cleaning. The sealing collar of the flange prevents the mortar from penetrating between the two rubber parts.

Preferably, the supply tube and the mixing tube are arranged coaxially with each other. In such an arrangement, it is provided in one embodiment that the fixing means, in particular the clamping flange or flange, is non-positively clamped between the transport tube and the mixing tube through clamping means that act axially, in particular, tie rods. The axial bracing serves to increase stability, so that the forces that arise during the transport of highly viscous masses can also be compensated. Preferably, the rubber insert of the mixer tube is materially connected to the outer tube of the mixer tube by vulcanization, thereby achieving a firm fit of the rubber insert to the outer tube. Alternatively or additionally, the internal rubber insert of the transport tube is preferably materially connected to the transport tube of the displacement pump by vulcanization.

In embodiments, the pitch of the mixing thread or mixing helix may be axially constant or it may vary axially. Instead of a mixing thread, in all embodiments individual mixing thread sections and / or individual mixing rotor blades or mixing rotor blades spaced apart, which likewise have a direction of rotation, may also be provided on the mixing rotor. opposite to the thread of transport and whose outer surfaces form individual active surfaces of the mixing rotor in the subsequent mixer.

The invention will also be explained in more detail below with respect to other features and advantages by means of exemplary embodiments and with reference to the accompanying drawings.

These show:

FIG 1 a schematic representation of a device according to the invention according to a first embodiment, in sectional view,

FIG 2 a schematic representation of the device according to the invention according to a second embodiment in sectional view, and

FIG 3 a schematic representation of the device according to the invention according to a third embodiment in sectional view.

In FIG 1, a schematic diagram of a device according to a first embodiment is shown in sectional view. The device comprises a main mixer for mixing the dry mortar and water (not shown). A rotary displacement pump 8 in the form of an eccentric screw pump was arranged downstream of the main mixer for conveying the premixed mortar mass, in particular a fine-grained mortar mass, such as a plaster mass, in the conveying direction. F to a downstream mixer 1. The displacement pump 8 has a transport tube 10 comprising an outer tube 11 and an inner rubber insert 12 arranged on the inner side of the outer tube 11. The inner rubber insert 12 forms a channel of helical transport 13, through which the mortar mass is pumped to the rear mixer 1 by means of a conveyor rotor 9 that rotates in the transport channel 13 and which is formed by an eccentric helical rotor.

The rear mixer 1 is arranged at an outlet 14 of the rotary displacement pump 8 and comprises a mixer tube 4 and a mixer rotor 2 arranged coaxially with the conveyor rotor 9. The mixer rotor 2 is arranged in a final area 25 of the conveyor rotor 9 associated with the rear mixer 1, and is fixed to it by means of a screw connection that is not shown in more detail.

In an alternative embodiment, the mixing rotor 2 and the conveyor rotor 8 are formed in one piece. The mixing rotor 2 of the rear mixer 1 extends from the conveyor rotor 9 in the conveying direction F or parallel to a central axis A of the mixing tube 4 over the length L of the mixing tube 4.

The mixing tube 4 comprises an outer tube 6 and a rubber insert 7, which is attached to the inner face of the outer tube 6 and is materially connected to the outer tube 6 by vulcanization. The mixing rotor 2 of the rear mixer 1 and the conveyor or screw rotor 9 are made of metal, suitably made of steel. The rubber insert 7 and the outer tube 6 of the mixer tube 4 are integrally formed with the inner rubber insert 12 and the outer tube 11 of the transport tube 10, so that the rear mixer 1 forms an integral part of the displacement pump 8.

The mixing rotor 2 has a helical mixing thread 16, the outer surface of which forms an active surface 3 that is substantially tight, that is, substantially free of voids, against the cylindrical inner surface of the rubber insert 7. The inner surface of the rubber insert 7 it forms an elastic counter-surface 5 that cooperates with the inelastic or rigid active surface 3 of the mixing rotor 2. Furthermore, the rotor 2 can have its active surface 3 pressed against the counter-surface 5 of the mixing tube 4.

The mixing rotor 2 is driven by the rotary displacement pump 8, so that it rotates with its active surface 3 in accordance with the rotational movement of the conveyor or screw rotor 9 about the central axis A along the counter surface 5 The mortar mass, which is conveyed along the counter-surface 5 of the mixing tube 4 in the transport direction F, is passed, pressed and rubbed between the non-elastic or rigid active surface 3 of the mixing rotor 2 and the Elastic counter-surface 5 by the rotational or orbital movement of the mixing rotor 2, the elastic counter-surface 5 yielding elastically when the mortar mass is passed through and pressed. The mixing thread 16 is formed opposite a transport thread 17 of the conveyor rotor, that is, the mixing thread 16 and the transport thread 17 are formed opposite each other with respect to their direction of rotation or direction of rotation. . In the exemplary embodiment the conveying thread 17 is upward to the right and the mixing thread 16 is upward to the left. Since the conveyor rotor 9 and the mixing rotor 2 are fixedly rotatably connected to each other, they rotate at the same rotational speed in the conveying operation. Counter-rotation of the thread pitches causes opposite conveying movements in the conveying operation. Due to the dimensions of the conveyor rotor 9 compared to the mixing rotor 2, the resulting mass flow is directed in the conveying direction F, but is strongly swirled, that is, turbulent. In this way, the lumps can already be pulverized by the increase in internal friction or between the active and opposite surfaces 3, 5.

The rubber insert 7 and the internal rubber insert 12 are formed of a wear resistant elastomer of synthetic or natural rubber, for example, NR (natural rubber) and / or SBR (styrene butadiene rubber).

In FIG. 2, an alternative embodiment of the device of FIG. 1 in sectional view. The mixing tube 4 of the rear mixer 1 and the transport tube 10 of the rotary displacement pump 8 are formed as separate parts and are connected to each other by an annular flange 15. The flange 15 has an annular collar 19 projecting radially towards the interior and that is arranged between the rubber insert 7 of the mixing tube 4 and the internal rubber insert 12 of the transport tube 10, and that seals it. Collar 19 ends approximately flush with rubber insert 7 and inner rubber insert 12, thus forming a continuous transition from inner rubber insert 12 to rubber insert 7.

In all other respects, reference is made to the explanations indicated with reference to FIG 1.

In FIG. 3, a schematic representation of another embodiment of the device is shown in sectional view. The mixing tube 4 of the rear mixer 1 and the transport tube 10 of the rotary displacement pump 8 are - as in the embodiment of FIG. 2- separate components, which are connected to each other through a clamping flange 18. The clamping flange 18 also has an annular collar 19 that projects radially inward and that engages tightly between the rubber insert 7 of the mixing tube 4 and the internal rubber insert 12 of the transport tube 10. In addition, the clamping flange 18 has two retaining elements 20 projecting diametrically outward and to which the clamping rods 21 are attached. The clamping elements 21 are supported at each end at one end of the conveying tube 10 and at one end of the mixing tube 4, respectively, by means of retaining elements 22. Along the clamping rods 21 axial forces can be exerted by means of the screws 23 and thus the components attached to them can be axially braced with respect to each other in the axial direction, that is, in the direction of the central longitudinal axis A.

In all other respects, reference is made to the explanations with reference to FIG 1.

In the exemplary embodiments depicted in FIGS. 1 to 3, the active surface 3 is formed in each case of an inelastic material, such as metal, in particular steel. The contact surface 5 is formed of a relatively elastic material, such as rubber.

Alternatively, the contact surface 5 can, for example, be formed of a metal and the active surface 3 can be formed of a relatively elastic material, such as rubber. For this, the mixing rotor 2 with the mixing thread 16 can be provided, for example, with a rubber coating. Alternatively, both the active surface 3 of the mixing rotor 2 and the coupling surface 5 of the mixing tube 4 can be formed elastically, while the mixing tube 4 has the rubber insert 7 and the mixing rotor 2 is additionally provided with a rubber cover. .

The mixing screw or mixing screw can have a constant pitch or a variable pitch.

Instead of a continuous mixing thread, individual mixing thread sections and / or individual mixing rotor blades or mixing rotor blades spaced apart may also have been provided on the mixing rotor in embodiments not shown, which likewise have an opposite conveying direction. to the transport thread and whose outer surfaces form individual active surfaces of the mixer rotor in the downstream mixer. List of reference signs

1 rear mixer

2 mixer rotor

3 active surface

4 mixer tube

5 counter-surface

6 outer tube

7 rubber insert

8 displacement pump

9 conveyor rotor

10 transport tube

11 outer tube (transport tube)

12 internal rubber insert

13 transport channel

14 departure

15 flange

16 mixing thread

17 transport thread

18 clamping flange

19 collar

20 retainer 21 tie rods 22 retainer 23 screw

25 final area

To central axis

F direction of transport L length

Claims (10)

1. Device for producing a fluid mass, in particular a fine-grained mortar mass, such as a plaster mass, comprising a main mixer to mix the dry mortar with water, a post mixer (1), and a rotary displacement pump (8), in particular an eccentric screw pump, to transport the premixed mass to the post mixer (1), in wherein the rotary displacement pump (8) comprises a transport rotor (9), in particular an eccentric helical rotor, which is rotatable in a stator, in particular in a transport tube (10), with a transport thread (17); and the rear mixer (1) has a mixer rotor (2) with an active surface (3) arranged in particular on the outer surface of the mixer rotor (2) and a mixer tube (4) with a counter surface (5) arranged on particularly on the inner surface of the mixing tube (2), in which the mixing rotor (2) can be driven through the conveyor rotor (9) so that the active surface (3) of the mixing rotor (2) can rotate around of a central axis (A) of the mixing tube (4) along the counter-surface (5), in which the mixer rotor (2) is designed in such a way that the transport direction of the mixing rotor of the rear mixer is, at least in sections, opposite to the transport direction of the transport thread of the transport rotor, therefore that, in particular, turbulence is generated in the mass me wherein the mixing rotor (2) has a mixing thread (16) or a mixing propeller or mixing rotor blades that are or are shaped to rotate in the opposite direction to a direction of rotation of the transport thread (17), characterized in that the stator, in particular the transport tube (10), of the rotary displacement pump (8) has a larger internal diameter than the post-connected mixing tube (4) with regard to the flow rate. Device according to claim 1, in which the mixing rotor (2) has a circular, oval or elliptical cross section. Device according to one of the preceding claims, in which the mixing rotor (2) of the rear mixer (1) is arranged in a final area (25) of the conveyor rotor (9) associated with the rear mixer (1), in particular it is formed in one piece with the conveyor rotor (9) or is connected to the conveyor rotor (9) by welding or through fixing means, in particular by means of a screw connection. Device according to one of the preceding claims, in which the active surface (3) of the mixing rotor (2) substantially abuts against the counter surface (5) of the mixing tube (4) or is pressed at least slightly against the counter-surface (5), in which the active surface (3) and / or the counter-surface (5) are made of an elastic material, such as a wear-resistant rubber produced from synthetic rubber or natural, and / or the active surface (3) of the mixing rotor (2) and the counter-surface (5) of the mixing tubes (4) are each formed by materials with different elastic properties, in which they are selected as a material pair an elastic material, such as rubber, and a comparatively inelastic material, such as metal, preferably steel. Device according to one of the preceding claims, in which the counter-surface (5) of the mixing tube (4) is formed of a rubber, in which the mixing tube (4) comprises an outer tube (6) and a rubber insert (7) that is attached to the inner face of the outer tube (6) and whose inner surface forms the counter-surface (5). Device according to claim 5, in which the mixing tube (4) of the rear mixer (1) is integrally formed with a transport tube (10) of the displacement pump (8), while the outer tube (6) and the rubber insert (7) of the mixing tube (4) are each formed in one piece with an outer tube (11) and an internal rubber insert (12) of the transport tube (10) . The device according to claim 5, wherein the mixing tube (4) of the rear mixer (1) and a transport tube (10) of the displacement pump (8) are formed as separate parts and are connected to each other by fixing means, such as a flange (15) or a clamping flange (18), in which the flange (15) has an annular collar (19) projecting radially inward, arranged between the insert of rubber (7) of the mixing tube (4) and an internal rubber insert (12) of the transport tube (10) and that seals it. Device according to claim 7, in which the transport tube (10) and the mixing tube (2) are arranged coaxially with respect to each other and the clamping means are non-positively clamped between the transport tube (10) and the mixing tube (2) by means of clamping means of axial action, in particular, by means of clamping rods (21). Device according to any one of Claims 6 to 8, in which the rubber insert (7) of the mixing tube (4) is materially connected to the outer tube (6) of the mixing tube (4) by vulcanization and / or the internal rubber insert of the transport tube (10) is materially joined to the transport tube (10) of the vulcanization displacement pump. Device according to any one of the preceding claims, comprising a mixing screw or mixing screw, in which the mixing screw or mixing screw has a constant pitch or a variable pitch.