Device for charging a screw lodged in a housing and method for operating a device of this type

ES 2 318 052 T3

DESCRIPTION

Device for filling an endless screw housed in a casing and procedure for the operation of a device of this type.

The present invention refers to a device for filling an endless screw housed in a housing, especially of an extruder for the treatment of previously crushed plastic material, whereby the filling opening of the endless screw housing is it is connected in the flow direction with the lower evacuation opening of a receiving tank, which is in a vertical position and is vacuum-tight, for the material to be processed and whereby in the receiving tank there are tools that rotate around an axis, especially a vertical one, due to a drive, which act on the material introduced from above, through a lock, into the receiving deposit. Furthermore, the invention describes a method for the operation of such a device.

In the current art, the applicants of the present invention know in practice of a device of the aforementioned type in the form of a vacuum funnel for injection molding machines or extrusion machines. But a construction such as the one mentioned cannot be used for all types of plastic, especially not for the types of plastic that require a longer residence time in the receiving tank, such as PET (polyethylene terephthalate), for example ground material from bottles, bottle preforms, sheets or plates. Generally, this material is not previously crystallized and needs a certain temperature and a homogeneous distribution, before it is placed in the worm casing for plasticization. Such devices are known, for example, from WO 00/64654.

It is the task of the present invention to improve a device of the type described above to correspond to the aforementioned requirements, that is, that these special types of plastic, especially the ground PET material, are processed in the receiving tank in such a way that the material is introduced into the filling opening of the worm housing with the desired homogeneous consistency. The present invention solves this task through the arrangement in the receiving tank, in the center of the height of the same and between an upper inner part and a lower inner part of the receiving tank, of at least one tool that rotates rapidly for generate a mixing vortex, whereby in the upper inner part, the processed plastic material, especially PET, rotates in the form of a mixing vortex, while supplying energy and instead, the lower interior part forms a dwelling space so that the heated plastic material that reaches its interior can be thermally homogenized, whereby, in this dwelling space, the rotating tools are shaped purely as mixing tools, without further ado supply of energy to avoid agglutination of the plastic material. The present invention starts from the knowledge that it is difficult to lead, through the lower outlet opening of the receiving tank of the endless screw, the material processed in the receiving tank with a homogeneous residence time. Tests have shown that this difficulty can be overcome if, in the upper area of ​​the receiving tank, the energy necessary to reach the desired temperature range of the material can be achieved relatively quickly by means of the rotating tools in this section. This energy contributed by the rotating tools is less in the lower area of ​​the receiving tank due to the fact that the treatment there is less intensive, and this helps to avoid overheating of the material, although the processed material remains, generally in the lower interior space. of the reception deposit, for a considerable time of permanence. This residence time guarantees a good thermal homogeneity of the material entering the worm casing and thus a high quality of the material conveyed from the worm to the next treatment phase, for example an extruder. The longer the average residence time of the material in the receiving tank, the less likely it is that a plastic particle that is not preheated, dried, or sufficiently pre-crystallized will be driven into the worm housing, which is undesirable. . The lesser effect of the tools arranged in the lower area of ​​the receiving tank also contributes to the fact that the mixed material is conveyed without difficulties, especially avoiding the formation of lumps due to the caking itself towards the filling opening of the worm casing. , which for this purpose, is directly connected to the outlet end of the receiving tank, but which in special cases can also be connected by means of a sleeve. The possibility of evacuating the receiving tank guarantees a better drying of a possibly damp material and keeps atmospheric oxygen away from the preheated material, especially PET, so that this material can be previously crystallized in the desired shape and a high value can be reached. prior crystallization. A wet plastic material can also be processed in the described way (with a humidity percentage of up to approximately 5%), since the highest performance required for drying can be produced without any problems in the upper inner part of the tank, without any the risk of an inhomogeneous treatment of the plastic material.

According to an improvement of the present invention, the tool that rotates in the central area of ​​the receiving tank is housed on the upper side of a disk, the edge of which is located a short distance from the inner wall of the receiving tank. In the context of the present invention, this distance is at least 20 mm. Through this distance, an annular pass opening is generated around the edge of the disk for the plastic material processed in the upper inner part of the receiving tank, through which this material can gradually pass from the inner part. top towards the inside bottom of the tank. The convenient distance for the formation of this annular passage depends on the type of plastic material processed and also on the degree of crushing of the same. The higher the density of the processed material, the smaller the size of the aforementioned annular passage can be. In order to be able to adapt to different relationships, within the framework of the present invention, it is convenient if the size

ES 2 318 052 T3 of the distance can be adjusted, which from the construction point of view can be realized without problems by a suitable displacement of the disc edge sections.

The introduction of the processed material, which is in the receiving tank, towards the introduction opening of the worm housing is facilitated if the receiving tank has an upper cylindrical section and a lower conical section that tapers to the opening filling of the worm housing. Such a construction method also has the advantage that the tools arranged in the conical section of the receiving tank are shortened more and more from top to bottom, so that if a sufficient mixing effect is maintained, the energy input to the material processed is negligibly reduced. For this, it is advantageous if, within the framework of the present invention, the tool that produces the mixing vortex is located in the area of ​​the upper end of the conical section, since this favors the formation of the mixing vortex through the sections of sloping wall.

It has been found that the favorable ratios of the height of the cylindrical section to the height of the conical section are in the range between 3: 1 and 1: 3.

The tools arranged in the lower inner part of the receiving tank are, as mentioned, only mixing tools. This can also be valid for the tools that generate the mixing vortex in the upper inner part of the receiving tank, since generally it is not necessary to grind the plastic material introduced into the receiving tank, which most of the time anyway. of the times it is entered in a pre-shredded state. However, if desired, at least one tool arranged in the upper section of the receiving tank can be designed as a crushing tool, preferably equipped with blades, especially if these crushing tools are held by the disk that separates the two inner parts of the tank.

In terms of construction, it is advantageous to close the vacuum-tight receiving tank with a lid on the upper part, which has an opening for the introduction of the material and to which a chamber is connected, which can be closed at the top and bottom with valves they close vacuum-tight, especially gates, and to which an evacuation conduit is connected, whereby an additional evacuation conduit is connected to the reception tank itself. The chamber acts as a sluice, which can be evacuated, for the material to be introduced into the receiving tank, so that no atmospheric oxygen enters the receiving tank during filling. The cover can be used to hold the drive, especially an adjustable drive, and possibly also a gear. Such a drive makes it possible to modify the number of revolutions of the tools and thus adapt them to the conditions present in each case. A finer setting of the desired working conditions in the receiving tank results, according to a refinement of the invention, because the tools housed in the lower section of the receiving tank and the tools housed in the upper section of the receiving tank are Driven by coaxial shafts independently of each other. With this, the objective pursued can be achieved in a favorable way, precisely because it is none other than supplying the energy as quickly as possible to the material that is in the upper section of the receiving tank. However, in the lower area of ​​the receiving tank, it is sought to thermally homogenize the material to maintain the desired outlet temperature at the outlet opening of the receiving funnel, and for this it may be sufficient with a slower turn, in comparison, of the tools.

In order to achieve the desired effect, it is convenient to arrange, according to the invention, in the upper and lower section of the receiving tank, at least one temperature sensor in each case and to control the working process depending on the heat states determined by these. temperature sensors, of the processed material. To avoid heat losses to the outside, the receiving tank has heat-insulating walls. Another possibility for influencing the temperature conditions in the receiving tank is that the receiving tank has at least one double-walled cladding section, the hollow space of which is connected to a conduit for a temperature regulation means, which can be a liquid or a gas. In this way, for example, the heating of the material in the upper section of the receiving tank can be accelerated by conducting additional thermal energy through the temperature control means, and / or obtaining, through the medium temperature regulation, a cooling of the material that is in the lower section of the receiving tank.

It has been shown that particularly favorable operating ratios can be achieved if the usable volume of the receiving tank corresponds to at least half, preferably all or three times the flow rate of the endless screw per hour. For this, it is convenient, if all the tools contribute to the processed plastic material every 100 kg of flow of the worm of the extruder, a mixing energy of between 3 to 12 kWh. This is also sufficient for the treatment of wet plastic material. Most of this mixing energy is provided by the tools arranged in the upper interior part of the receiving tank.

The method according to the present invention for the operation of a device according to the invention is characterized in that the energy supplied to the material in the receiving tank is regulated by adjusting the number of revolutions of at least one of the supporting shafts. to tools. In this way, optimal results can be obtained. This regulation of the number of revolutions of the tools takes place, conveniently, depending on the temperatures of the processed material, measured in the lower and upper sections of the receiving tank. A possibly additional tempering of the processed plastic material can be obtained by introducing a temperature regulating means in at least one of the tools. Of

ES 2 318 052 T3 alternatively or additionally, a tempering of the material that is in the receiving tank can be carried out by introducing a temperature regulation means in the hollow space of at least one of the cladding sections , made up of double walls, of the reception tank.

Exemplary embodiments of the object of the invention are schematically represented in the drawing. Fig. 1 shows a first embodiment in vertical section. Fig. 2 is a section on the line II-II of fig. 1. fig. 3 shows a second embodiment in section, similar to fig. 1. fig. 4 shows a detail in horizontal section. Fig. 5 shows a third embodiment in vertical section. Fig. 6 shows a fourth embodiment in vertical section. Fig. 7 is a vertical section through a detail of a variant of the embodiment of FIG. 6 and fig. 8 is a section on the line VIII-VIII of FIG. 7. fig. 9 shows in section, similar to figs. 6 and 7, another variant and fig. 10 is a section along line XX of FIG. 9.

In the embodiment according to FIGS. 1 and 2 the device has a receiving tank 1, fixed in place, for the plastic material to be processed, and this is made up especially of previously crushed PET material, that is, granulated. Usually this material comes from crushed bottles, especially ground, bottle preforms, sheets or PET plates. The vertical receiving tank 1 has a vertical axis 62 and has an upper section 2, which is essentially cylindrical, and a truncated cone-shaped section 3 that connects to the lower part of section 2. These two sections 2, 3 they limit an upper inner part 68 and a lower inner part 69 of the reservoir 1. The entire reception tank 1 has a large volume, in order to be able to process large quantities of material so that all the particles of material to be processed remain for a certain time, sufficiently extended, in the reception tank 1, to be sufficiently preconditioned before the material in question enters from the lower outlet opening 4 of the receiving tank 1 towards a vacuum-tight filling opening 5 of the casing 6 of an endless screw 7. The volume of the tank of Reception 1 is chosen, for example, in such a way that the material there achieves an average machining time through tank 1 of approximately one hour. The housing 6 forms, most of the time, an extruder with the endless screw 7, here it can be a single screw extruder or a multi-screw extruder. In the housing 6 the material led through the filling opening 5 of the worm 7 is plasticized by the worm 7 and in known manner is pressed through an extrusion head 8 to form a wire. A granulating device not shown or another forming tool can be connected to the extrusion head 8. However, the worm 7 can also be a simple transport or dosing worm, which guides the material conveyed by it to any machining device, for example an extruder. Suitably the filling opening 5 is directly and vacuum-tight connected to the filling opening 4, only in special cases can there be an indirect connection, for example via a vacuum-tight tube connection.

The endless screw 7 is driven via the shaft 10 by a drive not shown in the direction of the arrow 9, which passes through a vacuum-tight end of the front side 11 of the housing 6 and is connected with continuous rotation to the core 12 worm gear 7. As shown, this core 12 can have different diameters in the axial length of the worm gear 7. In the exemplary embodiment shown, the diameter of the core increases towards two expansion zones 13, 14, respectively, in front of which the conveyed material is compressed and plasticized, in each case, and is then released under pressure in a reduction zone pressure 13 or 14. Through this pressure reduction, gaseous inclusions contained in the material carried by the endless screw 7 can be dissolved and these can escape from the housing 6 in the direction of the arrows 17 through the gas escape holes 15 or 16. These gases are conveniently collected and eventually led to recycling. At the connection to the second pressure reduction zone 14 the diameter of the worm core 12 increases again, so that the material conveyed by the worm 7 reaches the extrusion head 8, or the outlet nozzles arranged inside, in a sufficient state of plasticization.

The material to be processed is led to the receiving tank 1 through a chamber 18 (fig. 2) of a sluice, which can be evacuated, 60, which is designed in a vacuum-tight manner and which p is provided for this above and down with 19 or 20 valves. Conveniently these valves 19, 20 are designed as gate valves, the gate plates 21 or 22 of which pass through the chamber walls 18 in a vacuum-tight manner and can be moved to one side by means of pneumatically or hydraulically actuated cylinders 23,24. and towards the other. Connected to the filling opening 25 of the chamber 18 is the outlet end of a funnel 26, through which the conveyed material is introduced into the device. The lower outlet end of the chamber 18 is connected in a vacuum-tight manner to an opening 27 of a lid 28, with which the receiving tank 1 is closed upwards in a vacuum-tight manner. To this cover 28 is connected an evacuation conduit 29, through which the interior space of the receiving tank 1 can be evacuated. Through another evacuation conduit 61 the lock 60 can be evacuated.

In the receiving tank 1, tools 30, 31 shaped like radial blades circulate around the vertical axis of the tank 62. These tools 30, 31 are fixed to a vertical shaft 32 coaxial with the axis of the tank 62 and can extend from it towards out in an essentially horizontal direction. The shaft 32 is housed in the cover 28 in a vacuum-tight manner at point 33 and is driven in its rotational movement through a motor 34, optionally through a gear 35. The guide lines for this are identified with 36 The tools 30 are housed in the area of ​​the height of the receiving tank 1, in which the lower funnel-shaped section 3 meets the upper cylindrical section 2. These tools 30 extend almost to the wall of the section 2 of the receiving tank 1 and therefore, with their high peripheral speed, cause an intensive removal of the material introduced into the receiving tank 1. If necessary these tools 30 can be equipped

ES 2 318 052 T3 with blades 70, so that the processed material is also shredded. In the case of this processing, the material found in the upper interior part 68 of the receiving tank 1 is stirred in the form of a mixing vortex 71. The energy used for this is transmitted mostly as thermal energy to the processed material and this way heats it up. As can be seen, the tools 31 found in the lower interior part 69 of the receiving tank are shorter than the tools 30 housed in the upper cylindrical section 2 of the receiving tank 1. Therefore, due to their lower peripheral speed , the lower tools 31 contribute less energy to the processed material than the upper tools 30. For this reason, in the upper section 2 of the receiving tank 1 a rapid supply of energy takes place to heat the cold plastic material that enters from above, which thanks to the evacuation, which takes place thanks to the endless screw 7 through from the outlet opening 4, gradually descends and reaches the area of ​​the shorter tools 31. These tools 31 only mix the plastic material found in their area, for this reason the lower interior part 69 of the tank 1 forms a dwelling space for the processed and heated material, in which compensation is made for all possible inhomogeneities. thermals. At the same time, a caking of the heated plastic material is avoided. Especially when the lower inner part 69 of the receiving tank 1 is higher than the upper inner part 68, the desired residence time, which is considerable, of the processed and stirred plastic material takes place in the inner part 69. Conveniently the relationships They are presented in such a way that the entire usable volume of the receiving tank 1 corresponds at least to the flow rate that the endless screw 7 produces in half an hour. The temperatures of the plastic material processed in sections 2 and 3 of the receiving tank 1 are conveniently monitored through temperature sensors 37 or 38, to which the lines leading to a control unit (not shown) are connected. through which appropriate control signals are emitted to guide lines 36 of motor 34. The ends 39 of the tools 31, which become shorter and shorter in the downward direction, can be chamfered, as shown in fig. 2, to fit the funnel shape of the tank section 3. Conveniently, the tools 31 are very thin to provide as little energy as possible to the material.

Eventually, the bars that extend outward from the shaft 32 of the upper tools 30 can also be provided with mixing blades, to increase the friction effect on the material in the tank 1 and thus reinforce the transmission of energy to the processed material.

To avoid heat loss to the outside, the walls of the liner 42, and advantageously also the cover of the receiving tank 1, are thermally insulated.

In the embodiment variant according to FIGS. 3 and 4, the tools 30 or 31, housed in the upper section 2 and in the lower section 3 of the receiving tank 1, can be operated independently of each other. For this, the tools 31 are attached to a central shaft 32 and the tools 30 to a hollow shaft 43 that surrounds this shaft 32 in a coaxial manner. The two shafts 32, 43 are driven through toothed rings 44 or 45 of two gears 35, both of which can be driven by a common motor 34. Both gears 35, 46 can be adjusted, through guide lines not shown , conveniently depending on the temperatures of the processed material, measured through the temperature sensors 37, 38 (fig. 1,2). The motor 34 and the gears 35, 46 can be supported by the cover 28.

The upper tools 30 are here made up of a disk 72, which on its outer perimeter houses the blades 70. This disk can rotate in the same direction as the tools 31 (arrow 41, fig. 4) found in the part Lower interior 69 of the receiving tank 1. However, both drive shafts 32, 43 offer the possibility of selecting different directions of rotation.

Fig. 4 shows a particularly convenient form of the tools 31 for the lower section 3 of the tank

1. As can be seen, the tools 31 have a curved shape towards their direction of rotation (arrow 41) to transport the material to be processed from the outer edge towards the center, resulting in a special mixing effect.

A further influence of the temperature relationships in the two tank sections 2, 3 can be achieved if the tempering of the material in the respective sections 2 or 3 is carried out through the hollow spaces 47 of the tools 30 or 31. Feeding lines 48 are connected to these hollow spaces 47, through which a temperature regulation means is introduced into the hollow spaces 47. Through suitable rotary couplings, the introduction of the temperature regulation means into the supply lines 48 takes place from the sources 49 provided for this. The temperature regulation means must not be the same for all tools 30 and 31; It is possible, for example, to additionally heat the disk 72 that forms the tools 30 by means of the temperature regulation means to bring the material processed by it, or by the blades 70, quickly to the desired temperature, while on the contrary, the tools 31 are cooled by another temperature regulating means or a temperature regulating means which is at another temperature. The temperatures of the temperature regulating means led to the tools 30, 31 can be suitably regulated.

Another possibility for influencing the temperature of the material found in the receiving tank 1 derives from the tempering of the interior space of the receiving tank 1 through a double-walled conformation of its lining 42. This is represented in FIG. 3, whereby the hollow space 52 between the two walls 50, 51 of the lining 42 is subdivided by intermediate walls 53 into two facing sections

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54, 55, which in each case are connected to a conduit 56 or 81 for the supply or evacuation of a temperature regulating medium, which can be a gas or a liquid. Both lines 56 are connected to a source 59 for the temperature control means via the control units 57 or 58. Possibly, different sources of the temperature control means can supply the two control units 57, 58. The control units 57, 58 can regulate the quantity and / or the temperature of the corresponding temperature control means and can be influenced by the temperature sensors 37, 38 (fig. 1, 2). As can be seen, by selecting the location of the intermediate wall 53 the temperature behavior in the two sections 2, 3 of the receiving tank 1 can be influenced. Therefore, the intermediate walls 53 can, but should not, be housed in the transition zone between the funnel-shaped section 3 and the upper cylindrical section 2.

Between the edge of the disk 72 and the inner wall 51 of the receiving tank 1 an annular passage 73 is formed, the width of which is generally at least 20 mm, so that the material that circulates and is heated in the inner part 68 it can gradually pass to the lower interior part 69 of the receiving tank 1. In order to prevent the processed material from penetrating too quickly through this annular passage 73, its width should not be too large, generally it is less than 30 mm. An adaptation to the different consistencies of the processed material is possible, if the width of this annular passage 73 can be modified. For this, the disk 72 or the inner wall of the reservoir can be shaped in such a way that the corresponding edge sections of the disk 72 or the wall can be displaced in the radial direction.

The usable capacity, in kilograms, of the material to be processed in the large volume receiving tank 1 corresponds to at least half, conveniently to all or three times the flow rate in kilograms of the endless screw 7. The drive (motor 34) for the upper tools 30 contributes to the material to be processed, conveniently, 3 to 12 kWh of mixing energy every 100 kg / h of flow of the endless screw. These examples of working conditions have proven to be favorable, but the particular working conditions depend on the consistency and detailed status of the material entered, in each case, in the receiving warehouse 1.

The shaft 32 (or also the hollow shaft 43) does not necessarily have to be arranged exactly vertically, inclined positions are possible. However, the more inclined the tree is, the more material in the receiving tank 1 will be transported up or down to a greater extent. Generally, in the lower inner part 69 such a transport in the vertical direction is not desired, since there the material only has to be mixed and not heated.

In the embodiments according to FIGS. 1 to 4, the filling of the housing 6 of the endless screw 7 is carried out in the radial direction, relative to the axis 63 of the endless screw 7. The axis 62 of the receiving tank 1 coincides with this radial direction. Furthermore, the housing 6 of the endless screw 7 can be filled with material from the front of the receiving tank 1. As shown in fig. 5, a tangential connection of the casing 6 to the receiving tank 1 is also possible, so that the tank axis 62 runs in the distance a along the axis of the endless screw 63. This makes it possible to divide the shaft that supports the tools 30, 31 and actuated from above or below, in each case, by an adjustable motor 34 or 66, to the two shaft sections 64, 65. For this, it is convenient to shape the lower end of the upper shaft section 64 as a sleeve 67 that surrounds the lower shaft section 65, so that the two shaft sections 64, 65 are centered and housed relative to each other. other. This tangential connection of the worm housing 6 in the reservoir 1 also makes it possible to achieve a complete filling of the worm 6 through the tools 31, which rotate around the vertical shaft 62 and which are arranged in the area of ​​the lateral outlet opening of the tank 1 or of the filling opening 5 of the worm housing.

In this embodiment the tools 30 are also formed as blades 70 housed in a disk 72. This disk 72 is arranged a little deeper than the upper edge of the lower section of the funnel-shaped magazine 3. This favors the formation of the mixing vortex 71, since the material processed by the blades 70 is expelled from the disk 72 in a radial direction and reaches the sloping parts of the lining wall of the tank section 3, so that the colliding material receives an upward motion impulse.

In the embodiment according to FIG. 6 the disk 72, which houses the blades 70, is approximately halfway up the height of the receiving tank 1 and considerably lower than the transition line between the two tank sections 2, 3. As mentioned before, the tools 31 arranged below the disk 30 only mix the processed material, but do not give it a mixing vortex, so that an almost flat "mirror" material 40 results on the inside 69.

The lower end of the funnel-shaped tank part 3 opens into the filling opening 5 of an extruder worm 7, which is driven through a gear 74 with a motor 75. A hermetic thread 76 prevents leakage of processed material at the end of the drive side of the endless screw 7.

As shown in fig. 7 and 8, the receiving tank 1 can open at the bottom into the filling opening 79 of a group of dosing augers 77, which for example has two dosing augers 78 arranged parallel to each other and driven by a motor common 75. This array of dosing augers conveys the material towards a radially arranged filling opening 5 of an extrusion auger 7.

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The figs. 9 and 10 show a variant of the aforementioned. Here, the double dosing screw 78 transports the material, which is conveyed to it through the receiving tank 1, towards a tank 80, where it falls from above towards the extrusion screw.

Through the execution examples described, an average residence time of at least half an hour can be achieved for each pre-crushed plastic particle introduced into tank 1. This residence time is calculated from the entry of the plastic particle into the airlock. upper 60 to the outlet of tank 1 through outlet opening 4.

The outlet opening 4 of the tank 1 can also lead the material to an installation of another type than those represented, for example, through a transport apparatus towards a silo or an installation for a subsequent treatment of any other type, also towards a dosing apparatus.