EP1412151A1

EP1412151A1 - Device for granulating a thermoplastic, which is extruded from nozzles

Info

Publication number: EP1412151A1
Application number: EP02764759A
Authority: EP
Inventors: Reinhardt-Karsten Muerb
Original assignee: Rieter Automatik GmbH
Current assignee: Rieter Automatik GmbH
Priority date: 2001-08-01
Filing date: 2002-07-23
Publication date: 2004-04-28
Also published as: TW575486B; CN1537043A; DE10137525A1; US20040258784A1; WO2003011547A1; MXPA04000872A; BR0205822A; KR20040027885A; JP2004535957A; CA2454071A1

Abstract

The invention relates to a device for granulating thermoplastics that are extruded from nozzles, the latter being provided in a nozzle disc in a substantially circular arrangement. Blades, which rotate about a blade carrier shaft and are held by a bell-shaped blade carrier in an oblique position in relation to the radial direction, sweep over said nozzles. The blade carrier shaft runs through the centre of the circular assembly, a cooling medium is fed to the nozzle disc and the blades to cool the granulated plastics and an annular intermediate chamber, traversed by the cooling medium from the interior to the exterior, is located between the blade carrier and the nozzle disc. The cavity (24) of the bell-shaped blade carrier is connected to the intermediate chamber and the cooling medium is supplied to the intermediate chamber from the cavity of the blade carrier.

Description

Device for granulating thermoplastic material emerging from nozzles

The invention relates to a device for granulating thermoplastic plastics emerging from nozzles, which nozzles are provided in an essentially circular arrangement in a nozzle disk and are swept by knives rotating about a knife carrier axis, which are supported by a bell-shaped knife carrier in an inclined position relative to the radial direction are held, the knife carrier axis running through the center of the circular arrangement, a cooling medium is fed to the nozzle disk and the knives for cooling the granulated plastics and between the knife carrier and the nozzle disk there is an annular space through which the cooling medium flows from the inside to the outside. This device is therefore one for carrying out the so-called hot cut, in which the plastic strands emerging from the nozzles are cut directly at the nozzles, that is to say in a still molten state.

Such a device is shown in US Pat. No. 3,317,957. The special feature of this known device is that the cooling medium is also supplied from the side of the feed of the melt of the thermoplastic, which is supplied via channels running parallel to the knife carrier axis and lying radially within the circular arrangement of the nozzles. The knife carrier is also driven from the side of the feed of the plastic melt, so that the entire arrangement with the feeds for the plastic melt and the cooling medium is penetrated by the drive axis which merges into the knife carrier axis. This leads to a construction which is complicated, in particular because of the necessary seals, and because of the limited availability of the cooling medium Space these are formed with a relatively small cross-section, which means that considerable pressures must be used to conduct the necessary amount of the cooling medium.

The invention has for its object to simplify and thus improve the design of the device described above, in particular with regard to the flow conditions, for the cooling medium and in this way to ensure the safe washing around the granules just cut and their rapid removal, so that it thereby there can be no sticking under the granules.

According to the invention, this is done in that the cavity of the bell-shaped knife carrier communicates with the intermediate space between the knife carrier and the nozzle disk and the cooling medium is supplied to the intermediate space from the cavity of the knife carrier.

With this design, the inflow of the cooling medium takes place over an area which is offset from the area of the supply of the plastic melt, so that heat losses or undesired heating of the cooling medium can be avoided without further ado. In the known arrangement, such heat transfers are much more difficult to rule out because, as explained above, the cooling medium is supplied axially within the area of the plastic melt feed. The arrangement according to the invention makes it possible to supply the plastic melt from one side of the device and the supply of the cooling medium from the opposite side of the device, so that these two areas only meet where the granulation takes place, namely in the area of the Knife holder, where an area is then created by the space between the knife holder and the nozzle disk, which, due to its supply from the interior of the bell-shaped knife holder, flows through everywhere with a correspondingly larger volume is, which ensures a correspondingly uniform cooling and safe removal of the granules.

The space between the knife carrier and the nozzle disk can expediently be designed in such a way that the intermediate space is closed off at the side by an annular plate attached to the knife carrier and penetrated by the knives and the nozzle disk arranged opposite it, and the knives are rigid in the space from the ring plate as individual ones Ledges protrude up to the system on the nozzle disk and are guided and held in openings in the ring plate that are directed obliquely towards the nozzle disk.

With this design, a laterally closed area defined by the ring plate and the nozzle plate is obtained, which offers easily manageable conditions for the cooling medium to flow through. The arrangement of the ring plate allows the knives designed as individual rigid strips to be held securely by providing the ring plate with openings at an angle to the nozzle disk, into which the strips are inserted and locked in place.

In the space defined by the ring plate and the nozzle disk, there is an outward flow of the cooling medium which, taking the rotation of the knife carrier outwards, increasingly approaches the tangentials. It is then expedient to choose the inclination of the knives protruding into the intermediate space in such a way that when the ring plate rotates they oppose the resulting flow with a low flow resistance. Through this choice of the inclined position of the knives, the cooling medium flows past practically unhindered when the knife carrier rotates. A reverse oblique position would lead to a pumping action of the knife holder with the knives, which is undesirable in the device on which it is based, since on the one hand this creates unfavorable vortices for the removal of the granulate and also the pumping action to a corresponding one Energy consumption on the part of the drive motor leads, which in addition to the energy required for the granulation means an unnecessary loss of energy.

The mounting of the knives consisting of strips in the ring plate advantageously makes it possible to individually store the knives on the ring plate, which is arranged together with the knife holder at a fixed distance from the nozzle disk, the knives being individually operated during operation to compensate for wear by pressure medium Nozzle plate can be pressed. In this case, the knives are slidably mounted in the openings in the ring plate, so that they can be automatically adjusted during operation in the direction of the nozzle disk for wear compensation. The pressure media used here can be elastic, in particular helical springs, but also hydraulically or pneumatically applied pressure.

In order to further reduce the remaining resistance of the knives during the rotation of the knife holder against the cooling medium, the knives are given such a length that their radial expansion only slightly exceeds the cross section of the nozzles, but so far that the cut made by the knives cuts the plastic emerging from the nozzles into insulated plastic granules. A minimum of the knife length is thus achieved, so that when the knife carrier rotates, the knives only exert a slight resistance with respect to the cooling medium flowing through.

It should also be noted that primarily water, but also oil and gaseous media, for example nitrogen, can be used as the cooling medium. The choice of the respective cooling medium depends on the chemical conditions of the plastic to be granulated.

Exemplary embodiments of the invention are shown in the figures. Show it:

1A the device as a whole in section, 1 B shows a section along the line AA from Figure 1,

Fig. 2 is a plan view of the ring plate with these penetrating

Slits for receiving the strip-like knives, namely for three circular arrangements of knives, Fig. 3, the same ring plate with inserted into the openings

knives,

Fig. 4 in a schematic representation of an annular plate with a

Knife when sweeping over the nozzle disc,

5 shows the arrangement according to FIG. 4 in plan view, FIG. 6 shows the attachment of the knife in the opening of the ring plate,

7 shows a section of the ring plate with a spring-loaded knife,

Fig. 8 shows a variant of the arrangement of FIG. 7, in which the

Knife is pressed by a hydraulically actuated piston,

9 the supply of a hydraulic fluid through the knife carrier axis to the ring disk,

10 is a plan view of the nozzle disk with a single ring-like arrangement of nozzles, FIG. 11 is an enlarged view of some of the nozzles according to FIG. 10 with a knife that just exceeds the diameter of the nozzles in the radial direction,

FIG. 1A shows the device according to the invention in section, the constituents not belonging to the invention, namely an extruder for feeding a molten plastic, being omitted. The device contains the melt distributor 1 used in a known manner, which has a plurality of melt channels, here the two channels 2 and 3. The nozzle disk 4 is flanged to the melt distributor 1 by means of fastening means, not shown here, into which the melt channels 2 and 3 open and merge into the nozzles 5 and 6. In operation, the nozzles 5 and 6 in the molten form emerge from the granulate thermoplastic plastic. The nozzle disk 4 has further nozzles, the position of which can be seen in a circular arrangement from FIG. 10. Opposed to the nozzle disk 4 is the ring plate 7, from which the knives 8 and 9 (and further knives not shown) protrude and, in a known manner, sweep over the surface of the nozzle disk 4 facing the ring plate 7 and thereby the plastic strands emerging from the nozzles 5 and 6 cut. With regard to the arrangement and storage of the knives 8 and 9 in the ring plate 7, reference is made to the explanations relating to FIGS. 4 to 6. The ring plate 7 is fastened to the bell-shaped knife carrier 10, which sits at the end of the knife carrier axis 11, which opens into the drive motor 12 shown in principle. The drive 12 sets the knife carrier 10 and thus the ring plate 7 with the knives 8 and 9 in rotation via the knife carrier axis 11, wherein, as explained above, the supplied plastic strands are granulated.

The inner parts of this device are enclosed by the housing 13 which continues into the cover 14 which extends over the area of the nozzles 5 and 6 and the knives 8 and 9. The two areas of the plastic feed and the granulation that belong together are held together by the flange-like projections 15 of the housing 13 and 16 of the melt distributor 1, specifically by means of the screws 17, when the cover 14 is tightened, thus firmly enclosing the whole the device through the housing consisting of parts 13 and 14 extends into the area of the melt distributor 1. As FIG. 2 shows, which will be discussed in more detail below, the device according to FIG. 1 is designed essentially rotationally symmetrical, that is to say essentially the housing 13 with the cover 14 has a circular surface on the outside. The holder 39 is given the necessary centering by the holder 39. The cover 14 belonging to the housing 13 is formed here from plexiglass which, because of its transparency, enables the processes in the area in which the granulation takes place to be observed.

To cool the granules cut by the knives 8 and 9, a cooling medium, here cooling water, is supplied to the housing 13 and the area in which the granulation takes place, namely through the coolant inlet 18. The coolant inlet 18 opens practically tangentially into the interior 19 of the housing 13, which results in a rotational flow in the housing 13, the rotational speed of which can be adjusted by the amount of water supplied. The cooling water passes from the interior 19 via the throughflow openings 20, 21 and 22 into the cavity 24 of the bell-shaped knife carrier 10. The knife carrier 10 rotates at the rotational speed given by the drive motor 12. In order to design the supply of the cooling water via the flow openings 20, 21 and 22 to the cavity 24 in the knife carrier 10 in such a way that the cooling water rotating in the interior 19 can flow into the passage openings 20, 21 and 22 largely without turbulence, the supply speed of the cooling water and thus the speed of rotation of the cooling water in the interior 19 is regulated such that the cooling water in the interior 19 rotates in the area of the passage openings 20, 21 and 22 with the same rotation speed as the passage openings 20, 21 and 22. In this way, energy losses are avoided at this point due to different rotational speeds. This type of adaptation of the rotational speeds is made possible by the tangential supply of the cooling water via the coolant inlet 18.

The cavity 24 of the knife carrier 10 is now, as can be seen, in direct connection with the knives 8 and 9 and the area of the nozzle disk 4, since the bell-shaped knife carrier 10 opens towards the nozzle disk 4, so that it enters the cavity 24 of the knife carrier 10 Cooling water that has entered past the knives 8 and 9 and out over the surface of the nozzle disk 4. can flow out. This outflow is facilitated by the likewise tangentially arranged coolant outlet 25, which leads out of the intermediate space 26 between the nozzle disk 4 and the ring plate 7. In this intermediate space, the cooling water circulates due to the rotation of the knife carrier 10 and the knives 8 and 9, in a direction that goes directly into the tangential direction according to the coolant outlet 25. A direction and a transition from area to area is thus created for the entire flow of the cooling water, which opposes the lowest possible resistance to the coolant flow and thus has a correspondingly energy-reducing effect on the drive motor 12.

FIG. 1B shows a section along the line A-A from FIG. 1A, which therefore runs along the side of the nozzle disk 4 facing the knives. This results in a top view of the ring plate 7 with the knives 8 and 9 in FIG. 1B. The ring plate 7 is held by the knife holder 10, in which the throughflow openings 20, 21 and 22 are provided (the fourth drawn throughflow opening is in FIG. 1) not visible). FIG. 1B also shows the cover 14, which runs from the location of the coolant outlet 25 in a spiral around the ring plate 7, the space between the ring plate 7 with the knives 8 and 9 continuously decreasing to the outer wall of the cover 14 or in the direction of flow (see Arrow) expanded, so that in this area the flow rate of the cooling water remains practically constant with increasing diameter of this space, which is important for a turbulence-free flow of the cooling water, which accordingly removes the granulate evenly after cutting via the coolant outlet.

In Figure 2, the ring plate 7 attached to the knife carrier is shown individually without a knife, namely in a top view of the side with the exit of the knife.

2 shows the openings of the individual openings 27, into which, as will be explained in more detail below, the individual knives are inserted. overall 2 is a ring plate with three circular arrangements 28, 29, 30.

The same ring plate 7 is shown in FIG. 3, but a knife 8 is inserted in each of the openings 27. As can be seen, these knives 8 protrude from the openings 27 at an angle to the surface of the ring plate 7 and at an angle to the direction of rotation. The knives 8 assume an inclined position with respect to the direction of rotation, which is selected such that due to the inclined position when the ring plate rotates, there is only a slight flow resistance to the flow of the cooling water that occurs. The cooling water flows from the inside to the outside (see illustration for FIG. 1A), the flow of the cooling water not spiraling radially outwards. The respective oblique position of the knives 8 is adapted to the respective angle of this spiral, so that they oppose this only with a slight flow resistance in relation to the cooling water passing through. The direction of rotation of the ring plate 7 is indicated by the arrow shown.

The arrangement of a knife 8 in relation to the nozzle disk 4 with the nozzle 5 is shown schematically in FIG. The knife 8 is inserted into an opening 27 in the ring plate 7 and fastened in this, as explained below. The nozzle plate merges into the bell-shaped knife carrier 10 which is fastened on the knife carrier axis 11 indicated by the dash-dotted line.

FIG. 5 shows a plan view of the area of the ring plate 7 shown in FIG. 4 with the knife 8, from which the knife 8 protrudes. The knife 8 is inserted into the opening 27 indicated by the dashed lines. It is attached to the ring plate 7 by the screw 31.

FIG. 6 shows a side view of the illustration according to FIG. 5, which clearly shows how the knife is inserted into the knife holder 7, and in the opening 27 provided for this purpose. The screw 31 then clamps the knife 8 in the opening.

FIG. 7 shows, similar to FIG. 6, a section of the ring plate 7 with the opening 27 into which the knife 8 is inserted. The knife 8 ends here in the central region of the ring plate 7, where the rear side of the knife 8 meets the helical spring 32, which is supported against an abutment 33. The helical spring 32 presses the knives 8, which are displaceably and thus adjustably mounted in the ring plate 7 and thereby constantly press against the nozzle disk 4 with a corresponding pressure. When the knife 8 wears, which shortens it, the helical spring 32 automatically pushes the knife further in the direction of the nozzle disk 4, which completely compensates for the wear that has occurred.

FIG. 8 shows a variant of the embodiment according to FIG. 7, in which the rear side of the knife 8 is mounted in a piston 34 which is guided in a corresponding bore 35. The bore 35 continues to a certain extent the opening 27 to the rear of the nozzle disk 4. A pressure exerted either by a liquid or a gas acts on the piston 35 and is supplied to the bore 35 via a special feed 36. The compensation of the wear on the knife 8 takes place here in the same way as described in connection with FIG. 7 above.

FIG. 9 schematically shows the supply of a printing medium, as is required in the arrangement according to FIG. 8. The pressure medium passes here via the knife carrier axis 10 into a central distributor 37, from which the pressure medium reaches the ring plate 7 via the knife carrier 10 via a bore 38.

FIG. 10 shows the nozzle disk 4, which here are only provided with a circular arrangement of nozzles 4, 5. The nozzles 4, 5 are with holes circular cross-section formed the same average, they are, as will be explained with reference to Figure 11, swept by the knife 8.

FIG. 11 shows a section of the nozzle disk 4 with three nozzles 5, plus the knife 8 arranged obliquely with respect to the radial direction. The radial extent R of the knife 8 is shown in FIG. It can be seen that it is slightly larger than the diameter D of the nozzles 5. This has the consequence that the knives 8 provide just enough to cut through plastic melt supplied via the nozzles 5, the granules being cut individually and independently of one another, since the knives are only slightly larger in terms of their radial expansion R than the diameter D, so that when the knives 8 rotate, there is only minimal resistance to the cooling water flowing around them.

Claims

claims

1. Device for granulating thermoplastic plastics emerging from nozzles (5, 6), which nozzles (5, 6) are provided in a nozzle disk (4) in an essentially circular arrangement and of knives rotating about a knife carrier axis (11) (8, 9) are swept, which are held by a bell-shaped knife carrier (10) in an inclined position relative to the radial direction, the knife carrier axis (11) running through the center of the circular arrangement, a cooling medium

Nozzle disc (4) and the knives (8, 9) for cooling the granulated plastics is supplied and between the knife carrier (10) and the nozzle disc (4) there is an annular space (26) through which the cooling medium flows from the inside, characterized in that the cavity (24) of the bell-shaped knife carrier (10) with the intermediate space (26) in

Connection is established and the cooling medium is supplied to the intermediate space (26) from the cavity of the knife carrier (10).

2. Device according to claim 1, characterized in that the intermediate space (26) is attached to the knife carrier (10) by the knives (8,

9) penetrated ring plate (7) and the nozzle plate (4) arranged opposite to it is laterally closed and in the space (26) from the ring plate (7) the knives (8, 9) as individual rigid strips until they rest against the nozzle plate (4) protrude and are guided and held in openings (27) in the ring plate (7) which are directed obliquely onto the nozzle disk (4).

3. Device according to claim 1 or 2, characterized in that the inclination of the knife (8, 9) projecting into the intermediate space (26) is chosen so that when the ring plate (7) rotates it opposes the resulting flow a low flow resistance.

4. Device according to one of claims 1 to 3, characterized in that the knives (8, 9) on the ring plate (7), which is arranged at a fixed distance from the nozzle disc (4), individually adjustable and for wear compensation by pressure medium ( 32, 34) can be pressed individually onto the nozzle plate (4) during operation.

5. Device according to one of claims 1 to 3, characterized in that the radial extent of the knives (8, 9) only slightly exceeds the cross section of the nozzles (5, 6), but so far that that of the knives (8, 9 ) cut cuts the plastic emerging from the nozzles (5, 6) into isolated plastic granules.