The axial extruder with the vane rotor

Abstract

The axial extruder with the vane rotor is designed in such way that at the end of the sleeve (1) of the screw there is the head (3) with the conical axial opening with the top angle up to 60°, on the outer face of which the annular matrix (4) is mounted. In the annular axial opening of the head (3) there is mounted the conical rotor (5), on the larger diameter of which there are the vanes. The vanes are inclined from the face of the conical rotor (5) at an angle of 20° to 90°. The conical rotor (5) with the smaller diameter presses on the end of the screw (2) and the larger diameter with the vanes presses on the inner side of the annular matrix (4). On the outer side of the annular matrix (4), the conical rotor (5) is mounted in the bearing house (12) for rotary mounting of the rotor, followed by the torque sensor (11) for driving the rotor and the rotor drive (10).

Description

[0001] The axial extruder with the vane rotor

[0002] Technical field

[0003] The invention relates to the construction of the axial extruder with the vane rotor. The invention falls within the field of mechanical engineering.

[0004] Background

[0005] The pastes are substances formed from a mixture of powdered material and liquid. These two components are mixed in such ratio as to form a dispersion system capable of flowing under the influence of an external force (e.g. mechanical pressure) through openings in a partition of different geometry.

[0006] The pastes are used for different types of products and in different areas of industry. In the food industry, flour and other similar substances (doughs, ketchups, ...) are prepared into pastes, in the pharmaceutical industry they are used to form the final form of pharmaceuticals (creams, ointments, ...), in the chemical industry they are used to prepare chemicals (catalysts, macromolecular substances, ...), in the building industry they are mixtures of substances for the production of a building materials of different shapes (brick ceramic materials, ...), etc. In order to achieve the desired product shape, the dispersion systems in the paste state are essentially processed by extrusion, i.e. extrusion through matrices of different profiles which have a final shape corresponding to the product shape.

[0007] Sometimes paste injection into closed moulds is also used. In all these cases, the course of the extrusion process itself and the quality of the product are influenced by the rheological properties of the paste. These, together with the geometry of the nozzle openings, are the determining parameter for the magnitude of the extrusion pressure. The most important nozzle parameters are the diameter of the opening, the length of the opening and the ratio of the total area of the nozzle to the area of the opening or openings through which the paste is extruded.

[0008] This is called the free cross-section of the nozzle. The smaller the opening area, the greater the extrusion pressure required, as the rule. The rheological properties of the pastes have a significant influence on the magnitude of the extrusion pressure. The pastes are predominantly non-Newtonian, multiphase fluids whose rheological properties depend primarily on the volume or concentration of the fluid in the paste and also on the rate of shear deformation. The rate of shear deformation and the corresponding shear stress in the material is the set of parameters that describes the rheological properties of the paste. These parameters are displayed in graphs, rheograms, from which it is possible to determine the viscosity of the paste (in the case of Newtonian liquids) or the apparent viscosity (in the case of non-Newtonian liquids). In order to extrude the paste with certain rheological properties through the nozzle with the particular free cross-sectional area of the partition, it is necessary to act on the paste by force effect to induce the necessary extrusion pressure.

[0009] This can be induced, for example, by straight line movement of the piston, or by rotation of the screw, which are located in the sleeve, at the end of which the nozzle or partition with moulded or smooth openings is installed. The critical area of any extruder is just this area, i.e., the place where the sleeve of piston or screw ends and the nozzle is located.

[0010] The free cross-section of the nozzle is always smaller than the free cross-section of the sleeve. This is due to the requirement for uniform pressure distribution in the cross-section. The nozzle almost always has a profiled opening, the shape of which corresponds to the desired shape of the product. This results in a difference in free cross-sections and the creation of zones where the paste does not flow. The reduction of the free cross section at the transition from the sleeve to the nozzle is also important because of the need to create resistance to the flow of the paste, which ensures that extrusion pressure is induced.

[0011] The extrusion pressure has the function of extruding of the paste with suitable rheological properties through the free cross-section of the nozzle, in addition to the so-called paste consolidation. The paste consolidation is a relatively complex phenomenon described by the theory of particle mechanics. Its principle consists in the compression of the skeleton, formed by the grains of the particulate substance (powder), under the effect of the extrusion pressure.

[0012] This skeleton consists of grains, particles that are in random contact with each other. Between the particles arranged in this way there is a free space, called the pores. Compression of the skeleton continues until equilibrium is reached between the mechanical strength, or ductility, of the granular skeleton and the applied extrusion pressure. However, the phenomenon itself is considerably more complex because the pores contain the liquid which, together with the particles, forms two-component system of solid phase-liquid.

[0013] As the porosity decreases with the compression of the skeleton due to the extrusion pressure, the liquid fills these pores more, thus increasing the so-called paste saturation. If the saturation value exceeds S = 1, the pressure in the paste volume causes the excess liquid volume to be displaced and the paste to be drained. This is a phenomenon where the pores are filled with liquid and the granular skeleton is further compressed by the extrusion pressure, the excess liquid flows through its pores and flows through the extruder nozzle outside the device. This phenomenon is called liquid phase migration and is characterized as the displacement of the liquid phase in the pores of the granular skeleton in the direction of least resistance away from the paste skeleton itself. This phenomenon is undesirable because it causes a decrease in the liquid content in the pores, resulting in a change in its rheological properties and an enormous increase in extrusion pressure. In critical cases, this pressure can reach such high values that the shutdown or crash of the device occurs due to the stoppage of the extrusion process when the nozzle becomes clogged. The main cause of fluid migration and changes in extrusion pressure is the static area of the extruder working zone, i.e. the area where the sleeve ends and the extrusion nozzle begins. Because the geometry of the extruder working zone changes in this area, the paste must, in accordance with the continuity equation, change the speed and direction of the flow.

[0014] In accordance with the paste rheogram and with its non-Newtonian liquid properties, this can result in either the formation of the static zone in this area, thus changing the cross section and geometry of the transition zone, which is more or less the standard phenomenon in well-working extruders, or the situation arises where, due to unsuitable rheological properties of the paste and too large reduction of the ratio of free cross-sections of the sleeve and nozzle, the critical pressure increase in this area occurs, resulting in the aforementioned migration of the liquid phase with the critical change in the rheological properties of the paste and the consequent interruption of extrusion or breakdown of the device.

[0015] This adverse phenomenon can be eliminated in several ways. Most often, the rheological properties of the processed pastes are modified so that they can be extruded on the type of extruder used. This method often encounters problems associated with the selection of a suitable additive, a lubricating agent whose main role is to limit the migration of liquid in the paste, reduce interparticle friction and thus positively affect the rheological properties of the paste as it passes through the various parts of the extruder, especially the zone between the end of the sleeve and the inlet to the matrix, and the flow through the openings of the matrix.

[0016] The problem is that an additive is a substance that is generally not desirable in the final product in terms of the composition of the system being processed and has only the function of improving the rheological properties. Its presence can therefore often have a negative effect on the quality of the final product and increase the price of the product. Therefore, efforts are made to reduce its presence in the paste to a minimum by selecting the suitable type or directly exclude it. However, this often runs into a very difficult problem, which lies in the relatively narrow range of extruder types that can be used, differing in principle in their construction and in the implementation of the extrusion process. The well-known is the piston extruder. The basic principle of extrusion is based on the extrusion of paste by means of the cylindrical piston, which is movably mounted in the sleeve, at the end of which there is the nozzle. The advantage of this type is the constructional simplicity of the device. For pastes with suitable rheological properties, it allows trouble-free extrusion through nozzles of different profiles and lengths. The great advantage is the uniform pressure distribution in front of the piston face and the formation of the so-called piston flow, which prevents the flow of paste in the radial or tangential direction, but only up to the area of the static zone formation, where radial flow is added in addition to the axial flow. Thus, if the paste is suitably prepared in the mixer and homogeniser, and has a homogeneous structure throughout its volume, there is no, or only a limited, disturbance of its homogeneity in the transverse cross-section in the piston extruder.

[0017] The disadvantage is that the above mentioned device generally cannot operate in continuous mode, because after the piston passes from the hopper towards the nozzle, the volume is emptied and the piston must return to the starting position behind the hopper. If mixing of the paste during extrusion must also be ensured, e.g. due to the addition of an additive, this cannot be performed precisely because of the piston flow. This also causes that in the area of the transition of the paste from the sleeve to the nozzle, the paste is compressed mostly by normal stresses, while the rheological properties are mainly influenced by the presence of shear stresses, which significantly affect the rheological properties of the paste. If these are not sufficiently generated, the paste is compressed only under the influence of the normal stresses, causing leakage of the liquid phase and the critical change of the rheological properties that will cause the stopping of extrusion or the shutdown or breakdown of the device.

[0018] The well-known is also the screw extruder. The basic principle of extrusion in this type of device is based on the extrusion of paste by one or more screws, which are placed in the cylindrical sleeve at the end of which the nozzle or matrix is located. The advantage is that the device can operate in continuous mode. The paste is filled continuously through the hopper, with the screw conveying the paste towards the nozzle. The screw rotates and its shape causes the paste to be axially conveyed towards the nozzle, in addition, the paste rotates tangentially about the axis of the screw with a speed different from the rotational speed of the screw due to friction against the wall of the housing and the surface of the screw.

[0019] It is this friction that causes mixing of the paste and its compression in the screw. Therefore, it is also possible to use the screw to homogenize the additives added to the extruder during the extrusion. Another advantage is the fact that the extrusion pressure caused by the screw at its end pushes the paste into the nozzle with normal tension, however, the rotary motion of the screw causes shear stresses in the paste (compared to the piston extruder), which has a positive effect on the rheological properties of the paste and the extrusion process itself. The ratio between the normal and shear stresses in the paste corresponds to the geometry of the screw.

[0020] Increasing the frequency of rotation of the screw increases the shear stress of the paste, which is positive in terms of improving its rheological properties, but at the same time the amount of the extruded material increases and with it the extrusion pressure, i.e. also the normal stress, causes compression of the paste and associated negative phenomena such as leakage of the liquid phase.

[0021] The disadvantage of this type of device is the fact that the presence of mixing may cause inhomogeneity of the paste for some types of materials. In the case of strongly adhesive materials, this tends to stick on the screw and starts to rotate with it, causing the extrusion process to stop. This problem can be adequately solved by twin-screw extruders. Further disadvantages are that if an increase in extruder performance is required, this can be achieved, for example, by increasing the frequency of rotation of the screw, i.e. increasing the amount of material conveyed.

[0022] However, this results in increased extrusion pressure. This is the consequence of the ratio between the normal and shear stresses in the paste, where the normal stress increases due to the increase in the conveyed quantity, while the increase in shear stress is not so pronounced and is mainly affected by the increase of the frequency of rotation of the screw. The construction of conventional extruders does not allow this pressure to be reduced to an optimum value otherwise than by changing the rheological properties of the paste, which is usually by adding a larger volume of liquid or by increasing the free cross-section of the nozzle. However, these two methods are not suitable in terms of the final product properties and the pressed extrudate tends to be dimensionally unstable.

[0023] Also known is the screw extruder with the nozzle in the shape of a dome. The principle of operation of this extruder is based on the extrusion of the paste by screw with a specially adapted vane-shaped end of the screw through the matrix in the shaped nozzle, e.g. hemispherically shaped nozzle. The modification of the end of the screw consists in placing vanes at the end of the screw which, when moved, copy the inner surface of the matrix. The greatest amount of extrudate is extruded near the edge of the vanes. The main advantage of this solution consists in the specially modified end of the screw, which has the shape of vanes moving on the inner surface of the matrix. This solution makes it possible to induce in the paste a significant shear stress close to the inner surface of the matrix, which is caused precisely by the vane-shaped end of the screw. So the screw itself conveys the paste into the hemispherical extruder head, compresses it and the vanes then push it through the matrix. In the process itself, this is reflected by reducing the required extrusion pressure and by limiting unwanted extrusion phenomena that occur with higher extrusion pressures in standard devices. The disadvantage is the fact that the vane(s) are located at the end of the screw and rotate with it at the same frequency of rotation. This solution does not allow simultaneous control of the amount of paste extruded and extrusion pressure. Pressure regulation is only possible by changing the moisture content of the paste being processed.

[0024] The well-known is also the radial extruder. The extruder has the matrix in the shape of cylinder, on the surface of which several vanes move, which are inclined towards the inner surface at certain angles. The narrowing wedge gap is formed between the matrix and the vane. In this gap, the paste is compressed by friction against the surface of the matrix and the vane. When the necessary extrusion pressure is reached, the paste begins to flow through the openings in the matrix, thus forming the extrudate with the shape corresponding to the shape of the openings in the matrix. The advantage of this type of device is the fact that the shape of the vanes together with the matrix create the narrowing wedge gap in which the paste is compressed and at the same time intensively stressed by shear stresses, which are the most significant in terms of the rheological properties of the paste and the extrusion process itself. This solution allows a very efficient passage of the paste from the extruder chamber to the matrix openings. The disadvantage is that since the extruder chamber is not closed, it is not possible to create a pressure other than atmospheric pressure on the paste surface in the extruder.

[0025] The extrusion of the paste is performed only under the effect of the mechanical pressure created in the narrowing wedge gap between the vane and the matrix. If this design does not allow the necessary extrusion pressure to be generated, the paste will not be able to flow through the nozzle openings. Another disadvantage is that the matrix geometry is mostly limited to cylindrical openings and relatively thin matrices, for which a low-value extrusion pressure is sufficient.

[0026] The well-known is also the screw radial extruder. The principle of its operation consists in conveying the paste to the head by means of screw or pair of screws. At the end of the screw are placed vanes, inclined to the matrix surface. This creates the narrowing wedge shaped gap between the face of the vane and the surface of the matrix with the openings. The paste, which is under the force effect of the screw, is under certain pressure and passes under the vanes, where the effect of the screw is taken over by the vanes. In this narrowing wedge gap, the stress state changes significantly. If the normal stress prevails in the screw and the shear stress is less significant and arises due to the decomposition of forces from the screw action, the normal stress decreases in the wedge gap due to friction against the matrix and vane surface, but mainly due to the flow of the paste towards the openings in the matrix and through these openings, and the shear stresses start to prevail, which has a positive effect on the rheological properties of the paste.

[0027] The advantage is that this principle is the combination of extruders with dome shaped nozzle and radial extruder. The screw creates the necessary extrusion pressure, thus ensuring the performance of the device, while the inclined vanes ensure the shear stress of the paste, thus positively influencing its rheological properties. As a result, high pressures are not required for extrusion as in other types of devices.

[0028] The disadvantage is again the fact that the vanes are located at the end of the screw, their frequency of rotation is the same as the frequency of rotation of the screw. This means that the vanes can only push through as much paste as the screw conveys. Thus, two cases of operation can occur that are significantly different from the optimum operation of the device. In the first case, it is the paste with good flow properties, where the paste conveyed by the screw flows easily through the openings in the matrix, i.e. no high extrusion pressure is required. If the screw is not sufficient to convey the paste into the head, the vanes push it through the matrix, and the extruder head is not filled, there is insufficient pressure in the device, which may cause the resulting product behind the matrix not to have the desired properties.

[0029] The opposite situation occurs if the paste that has poor flow properties is extruded. If the screw conveys the same amount of paste as in the previous case, but the rheological properties do not allow the necessary flow through the matrix openings, the head fills with paste, the extrusion pressure builds up, a leakage of the liquid phase usually occurs, the extrusion stops, and the device shuts down or crashes.

[0030] The extruder with separate drive of the screw and the rotating head is also known. This type of device is described in document WO2015159198 Al. It is based on the principles of previously known extrusion devices for extruding pastes, but with significant technical improvements. It consists of screw sleeve with hopper, which comprises the screw, driven by drive with the possibility of control of the rotation frequency. The end of the screw is conical in shape with grooved surface in the axial direction.

[0031] The sleeve is finished with the head of special construction. It has a conical shape, with grooves in the axial direction. The conical end of the screw and the head are of such geometry as to form the narrowing inter-cone space. The base of the cones should consist in one plane, but this is not necessary. The conical head has the extrusion nozzle fixed at the top of the cone. The cone head itself and the nozzle are arranged so that they rotate together about the axial axis. This rotary motion is provided by separate drive with the possibility of independent control of the rotation frequency. It is necessary that the frequency of rotation of the screw and the frequency of rotation of the head and nozzle can be controlled completely independently of each other.

[0032] Summary of the invention

[0033] In order to control the extrusion pressure while maintaining the constant mass flow of paste through the extruder with separate drive of screw and vane rotor for processing of bulk materials, powders in the form of paste, which is formed from them by the addition of liquid in the optimum ratio, the axial extruder with vane rotor has been designed.

[0034] The extruder uses the screw drive and the screw itself of common design for different types of extruders. The screw is used to convey and consolidate the paste, thus creating extrusion pressure that can no longer be controlled. In conventional extruders, this pressure ensures the extrusion of the paste through the nozzle openings. The bearing house for rotary fitting of the screw and torque sensor for driving the screw follow the screw in the sleeve.

[0035] The essence of the solution according to the invention consists in the fact that it uses two separate drives. One is designed to drive the screw to consolidate the paste and create extrusion pressure, and the other to drive the rotor with vanes. The head is mounted at the end of the screw sleeve with the inlet circular axial opening either conical in shape with top angle up to 60°, or cylindrical in shape. At the outer face of the end of the head is fitted the annular matrix with openings through which the paste is extruded by the extrusion pressure generated, and regulated by the combination of the speed of screw and rotor.

[0036] The matrix can be made of sheet metal of a different thickness with different number of openings and shape. It can also be the sieve with different opening sizes and wire thicknesses. The axial opening of the head includes the conical rotor with the smaller diameter pressing on the end of the screw and with the larger diameter with the vanes pressing on the inner side of the matrix. The larger diameter of the conical rotor has the vanes inclined toward the face of the matrix surface at an angle of 20° to 90°. On the outer side of the matrix, the conical rotor is mounted in the bearing house for rotary bearing of the rotor, followed by the torque sensor for driving the rotor.

[0037] The advantages of the vane rotor axial extruder according to the invention are apparent from its outwardly manifested effects. The effects consist in the fact that by combining the rotational frequency of screw, rotor and matrix geometry it is possible to control the performance of the device, i.e. the amount of material extruded, the strength and surface quality of the extrudate, and it also allows the extrusion pressure to be controlled while maintaining constant mass flow of paste through the device. Overview of figures on the drawings

[0038] The axial extruder with the vane rotor according to the invention will be further explained in the drawings, wherein

[0039] Fig. 1 shows an assembly of the axial extruder with separate drive of screw and vane rotor. Fig. 2 shows a detail of the assembly.

[0040] Fig. 3 shows the extruder head.

[0041] Fig. 4 shows the extruder rotor in two views.

[0042] Examples of embodiment

[0043] It is understood that the various embodiments of the invention are presented for purposes of illustration and not as limitations of solutions.

[0044] In this example of the specific embodiment, the structural assembly of the vane rotor extruder according to the invention is described as illustrated in Figs. 1 and 2. It comprises the extruder sleeve 1 with the screw 2, which is mounted in the bearing house 9 for rotary fitting of the screw. Further, there follows the torque sensor 8 for driving the screw 2 and the drive 7 of the screw 2 itself. At the end of the extruder sleeve 1 with the screw 2, the pressure sensor 6 is located and the head 3 with conical axial opening having top angle of 60° as shown in Fig. 3 is mounted. Alternatively, the head 3 has the cylindrical axial opening. The annular matrix 4 with the set of openings is mounted on the outer face of the head 3. The circular axial opening of the head 3 comprises the conical rotor 5, on the larger diameter of which are the vanes, which are inclined at angle 45° from the face of the conical rotor 5 as illustrated in Fig. 4. The conical rotor 5 with the smaller diameter presses on the end of the screw 2, and the larger diameter with the vanes presses on the inner side of the annular matrix 4. On the outer side of the annular matrix 4, the conical rotor 5 is mounted in the bearing house 12 for rotational fitting of the conical rotor 5, followed by the torque sensor 11 for driving the conical rotor 5 and driving the rotor 10.

[0045] Industrial applicability

[0046] The axial extruder with the vane rotor according to the invention is applicable in the field of industry where the processing of bulk materials in paste form is used, e.g. ceramic industry for extrusion of semi-finished products such as catalyst carriers, bricks, etc., pharmaceutical industry for preparation of microgranulate for tableting or encapsulation, etc., chemical industry for treatment of chemicals into a compact form, e.g. multicomponent fertilizers, food processing industry, etc.. List of reference numbers

[0047] 1 extruder sleeve

[0048] 2 screw

[0049] 3 head

[0050] 4 annular matrix

[0051] 5 conical rotor

[0052] 6 pressure sensor

[0053] 7 separate drive

[0054] 8 torque sensor

[0055] 9 bearing house for rotary fitting of the screw

[0056] 10 rotor drive

[0057] 11 sensor

[0058] 12 bearing house for rotational fitting of the rotor

Claims

CLAIMS1. An axial extruder with a vane rotor, wherein a bearing house for rotary fitting of a screw, a torque sensor for driving the screw and the screw drive are connected to the screw in a sleeve, characterized in that at an end of the sleeve (1) of the extruder with the screw (2) there is mounted a head (3) with a circular axial opening, on an outer face of which an annular matrix (4) is mounted; in the circular axial opening of the head (3) a conical rotor (5) is mounted, on the larger diameter of which the vanes are mounted; the smaller diameter conical rotor (5) presses on the end of the screw (2) and the larger diameter with vanes presses on the inner face of the annular matrix (4); on the outer side of the annular matrix (4), the conical rotor (5) is fitted in the bearing house (12) for rotational fitting of the rotor, followed by a torque sensor (11) for driving the rotor and a rotor drive (10).

2. The axial extruder with the vane rotor according to claim 1, characterized in that the circular axial opening of the head (3) is cylindrical.

3. The axial extruder with the vane rotor according to claim 1, characterized in that the circular axial opening of the head (3) is conical with top angle up to 60°.

4. The axial extruder with the vane rotor according to any one of claims 1 to 3, characterized in that the vanes are inclined from the face of the conical rotor (5) at an angle of 20° to

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