WO1999012713A1

WO1999012713A1 - Device for discharging and granulating plastic monofilaments

Info

Publication number: WO1999012713A1
Application number: PCT/EP1998/005780
Authority: WO
Inventors: Peter Locker
Original assignee: Rieter Automatik Gmbh
Priority date: 1997-09-10
Filing date: 1998-09-10
Publication date: 1999-03-18
Also published as: DE19739783A1

Abstract

The invention relates to a device for discharging and granulating plastic monofilaments (5) coming out vertically in fusion through discharge nozzles (2), and which, after a short fall, are supplied, while still in fusion, to a granulator located downstream. After having briefly crossed a free area (9), said monofilaments (5) run into vertical receiving channels, into which the cooling water (8) flows together with the plastic monofilaments, said channels being inserted into a horizontal cutting plate (7) which extends over the discharge nozzles (2) and features the counter-cutting edge for a knife device (10) scraping on the side opposite that of the discharge nozzles (2) above the cutting plate (7). Said cutting plate is formed on the side of the knife device (10) by the flat through-cutting surface (11) and extends over the whole set of discharge nozzles (2), and the distance between the cutting surface (11) and the discharge nozzles (2) is so small that the knife device (10) touches the monofilaments (5) while they are still in fusion.

Description

Device for discharging and granulating plastic strands

The invention relates to a device for discharging and granulating plastic strands which emerge vertically in molten form through discharge nozzles and, after passing through a short distance, are still fed to a subsequent granulator in a molten manner.

Such a device is known from EP-PS 229610, in which plastic strands vertically emerging from the discharge nozzles after passing through a short zone formed by a cooling water spray mist are fed to a granulator constructed from a counter knife and a cutting rotor constructed in the manner of a milling cutter. The cooling water sprayed into the zone inevitably comes into contact with the area of the discharge device. Their discharge nozzles continue in an opening contained in an insulating plate, the insulating plate being intended to ensure that little heat is removed from a nozzle plate containing the discharge nozzles. A greater removal of heat could lead to a so-called freezing of the discharge nozzles and thus to a non-uniformity in the discharge of the plastic strands. Because of the use of the milling cutter-shaped cutting rotor, the device has to work with a small distance between the teeth of the cutting rotor and the counter knife, which does not guarantee a clean cut of the plastic strands with certain plastics. This is because the plastic material pulls threads between the individual granules, ie, no clean granules are formed. It is also known from US Pat. No. 4,184,833 to provide a rotating knife arrangement with radially directed knives for carrying out the so-called hot cut, which sweep across horizontal discharge nozzles serving as counter-blades while maintaining a small distance, this arrangement also is equipped with the supply of cooling water. The problem arises that the cooling water also comes into contact with a nozzle plate containing the discharge nozzles, the temperature of which is thereby lowered. This is undesirable because a lowering of the temperature of the discharge nozzles can cause them to freeze, ie that plastic material supplied in a molten state is cooled down to such an extent that it solidifies.

The invention is based on the object of designing the device explained at the outset in such a way that it can carry out the above-described hot cutting of plastic strands, i.e. the granulation of still molten plastic strands enables the discharge nozzles not to run the risk of excessively cooling the plastic material contained in them, so that there is an uneven melt flow in the discharge nozzles. In particular, the complete freezing of discharge nozzles should be avoided.

According to the invention, this is done in that after passing through a short free zone, the strands enter vertical receiving channels into which cooling water flows together with the plastic strands and which are introduced into a horizontal cutting plate which extends over the discharge nozzles and the counter knife for one of the side facing away from the discharge nozzles forms a knife arrangement scraping over the cutting plate, the cutting plate having a continuous, flat cutting surface on the side of the knife extending over all the discharge nozzles. arrangement is formed and the distance between the cutting surface and the discharge nozzles is so short that the knife arrangement meets the still molten strands.

Due to the short distance between the cutting surface, the cutting plate and the discharge nozzles, the strands emerging from the discharge nozzles can cool down only slightly and thus maintain their molten state. The knife arrangement therefore strikes still molten strands and thus acts in the sense of the hot blow-off, whereby due to the presence of the short free zone, cooling from the cooling water flowing into the receiving channels can practically not extend to the discharge nozzles, since the cooling water does not come with the discharge nozzles comes into contact. The vertical guidance of the strands ensures that the water supplied to the receiving channels remains on the cutting plate or the receiving channels, since it is always pulled towards the relevant surface of the cutting plate and the receiving channels due to gravity.

It is known per se from DE-AS 1,542,405 to cut solid strands into granules after a correspondingly long cooling zone. So it is not a hot tee. The cooling zone contains, after the receiving channels for the strands filled with the cooling water, adjoining pipes into which the outputs of the receiving channels end while leaving an opening gap, wherein cooling water is introduced under pressure in the opening gap, so that the strands under the influence of the under pressure Tubes of water fed a train is exerted. The pipes are so long that the strands are solidified at their end and cut into granules there. In the device according to the invention, the supply of the cooling water can expediently be designed so that the cutting plate is flushed by the cooling water. In this case, the receiving channels represent the processes for the cooling water supplied to the relevant surface of the cutting plate.

After the strands emerge from the discharge nozzles, there is a certain stretching of the strands due to the force of gravity acting on the strands, which stretching can advantageously be influenced by adjusting the distance of the cutting plate from the discharge nozzles. As the distance increases, there is a correspondingly increased stretching of the strands, which leads to a reduced granule diameter. In this way, the size of the granules can be influenced.

The individual recording channels can be designed so that they take up several strands. In this case, the strands are guided in the receiving channels so that the knife arrangement does not push the strands onto one another, i.e. , the force exerted on the strands by the knife arrangement presses them directly onto an edge of the receiving channel in question, without this force containing an essential force component which presses the strands against one another. This prevents the still molten strands from sticking together. The knife arrangement is expediently designed as a rotor with essentially radially arranged knives.

Shown in the figures of the embodiment of the invention. Show it: Figure 1: In principle representation of the invention, a discharge nozzle with a cutting plate and a knife scraping over the cutting plate;

Figure 2: A nozzle plate with 4 nozzles and a knife rotating over the cutting plate in longitudinal section in the direction of the axis of the rotor;

Figure 3: The rotor arrangement with the rotating knives according to Figure 2 in an axial view;

Figures 4a to 4d: Different receiving channels in the cutting plate for receiving different numbers of strands.

The device for granulating plastic strands shown in FIG. 1 in principle contains the nozzle plate 1 with the discharge nozzle 2, to which a stream of molten plastic 3 is fed, for example from an extruder or an autoclave. The plastic 3 leaves the discharge nozzle 2 in the form of the plastic rod 4, which initially expands somewhat here and then stretches into a thinner strand due to the force of gravity acting on it. This thinner strand enters the receiving channel 6 in the cutting plate 7, which widens in a funnel shape in the direction of the nozzle plate 1 in order to take up a film of cooling water 8 which is fed to the cutting plate 7 on its side facing the nozzle plate 1. The funnel-like expansion of the receiving channel 6 also facilitates the safe flow of the plastic strand 5 into the receiving channel 6 of the cutting plate 7. It should also be pointed out that the behavior of the molten plastic after leaving the nozzle plate 1 depends on which plastic material it is . It are also plastics that stretch immediately after leaving the nozzle plate 1 and thus become thinner.

Between the nozzle plate 1 and the cutting plate 7 there is a short drop distance, which is designed here as a short free zone 9, in which the strands 4 are only flushed with air until they come into contact with the cooling water 8. This short free zone 9 ensures that the high temperature of the nozzle plate 1, which is normally above 200 ° C., cannot affect the cutting plate 7 in the sense of heat removal. The short free zone thus effectively forms an insulation between the nozzle plate 1 and the cutting plate 7 without requiring any special technical effort. The cooling water film 8, which is applied to the relevant surface of the cutting plate 7, in particular, as shown here, overflows the cutting plate 7, ensures that the still molten plastic strands 4 and 5 cannot adhere to the receiving channel 6 of the cutting plate 7. In the case of the introduction of several plastic strands into a receiving channel of the cutting plate, the cooling water film also ensures that the strands cannot stick together, which is explained in more detail below.

The cutting plate 7 forms the counter knife for a knife arrangement, of which only one knife 10 is shown here. The knife 10 is in touch contact with the side 11 facing away from the nozzle plate 1, that is to say the knife 10 scrapes over the side 11 of the cutting plate 7, the individual knives of the knife arrangement resting against the side 11 only with slight pressure, that is to say the cutting surface the insert 7 forms. The cutting plate 7 extends over the entire area of the discharge nozzles 2 in the nozzle plate 1, so that there is a uniform cutting effect over all the receiving channels 6 in the cutting plate 7. In FIG. 1, a cutting knife 12 and a strand 13 (also shown in dash-dotted lines) falling approximately in the middle of the receiving channel 6 are shown in dash-dot lines, which indicates the beginning of the cutting process in which the cutting knife 11 points to a still molten strand 13 in the sense of the so-called hot cut. The distance between the cutting surface 11 and the discharge nozzle 2 is so short that the strands 13 maintain their molten state until the cutting surface 11 is reached. These are lengths that can be in the range of approx. 1 cm to 20 cm, in which the strands hardly cool in the air and therefore remain in their molten state, in which they can also be cooled by the small amount of cooling water Cooling water film 8 is supplied, can hardly be quenched. In FIG. 1, the knife arrangement with the knife 10, which is in a position just after the cutting of a granulate 14, is also shown in a normal manner of representation.

In FIG. 2, the device is shown with a nozzle plate 1, in which four discharge nozzles 2 are contained next to one another in a radial row, from which four plastic strands 5 emerge and are collected together by a receiving channel 6 in the cutting plate 7. The receiving channel 6 is designed like an elongated hole here, which is explained in more detail with reference to FIG. 3. Due to the larger number of plastic strands 5 to be cut next to one another, the device according to FIG. 2 results in a correspondingly high throughput.

The device is an essentially radially symmetrical arrangement with the rotor 15, which is driven via the axis 16 in a manner not of interest here. The rotor 15 has individual arms 17 which are provided with essentially radially directed knives 18. The knives 18 scrape over the cutting surface 11 of a cutting ring 19, in which the receiving channel 6 continues, so that the strands 5 pass through the cutting ring 19 and can be gripped by the knives 18. The cutting ring 19 is used here because, for reasons of material savings, it is advantageous to restrict the high-strength material of the cutting ring 19 essentially only to the cutting area. In particular for smaller devices, however, it is of course also possible, as shown in connection with FIG. 1, to provide the cutting plate 7 directly with the cutting surface on its side facing away from the nozzle plate 1, that is to say to form the cutting plate 7 in one piece.

The cutting plate 7 together with the rotor 15 is mounted in the housing 20, which rests on the two support screw connections 21 and 22 which are supported with respect to the stationary base plate 23. Due to the rotation of the two support screw connections 21 and 22, the housing 20 and with it the rotor 15 and the cutting plate 7 can be raised and lowered with all other organs of the cutting device, as a result of which the short free zone 9 can optionally be set. In this way, the device can be adapted to the conditions of different plastics to be granulated.

In FIG. 3, the device according to FIG. 2 is shown in an axial view in dash-dot lines, only the cutting ring 19 and several of the radially arranged knives 18 being shown. The knives 18 here sweep over the receiving channels 6, which, as shown in FIG. 2, each take four plastic strands 5. In order to give the plastic strands 5 a secure position at the time of the cut, the receiving channels 6 have individual bulges 24, which capture the respective plastic strand to a certain extent and thus support it with regard to lateral movement. FIG. 4 shows different embodiments of receiving channels in the cutting insert.

FIG. 4 is a round receiving channel 25, with which only one strand 5 is cut at a time (see FIG. 1).

FIG. 4b shows an elongated receiving channel 26 in which two strands 5 are cut.

FIG. 4c shows an arrangement similar to that shown in FIG. 3, in which four strands 5 are cut in an elongated hole as a receiving channel with bulges 27 arranged in a step-like manner.

Of course, it is also possible to cut a larger number of strands 5 in each case with the receiving channels shown in FIGS. 4a and 4b.

Claims

claims

1. Apparatus for discharging and granulating plastic strands (5) which melt vertically emerge through discharge nozzles (2) and, after passing through a short drop distance, are still fed to a subsequent granulator in a molten state, characterized in that the strands (5) after passing through a short free one Zone (9) enter vertical receiving channels (6) into which cooling water (8) flows together with the plastic strands (5) and which are introduced into a horizontal cutting plate (7) which extends over the discharge nozzles (2) and the counter knife for a knife arrangement (10, 18) scraping over the cutting plate (7) on the side facing away from the discharge nozzles (2), the cutting plate (7) having a continuous, flat cutting surface (11) extending over all discharge nozzles (2) the side of the knife arrangement (10, 18) and the distance between the cutting surface (11) and the discharge nozzles (2) is so short is that the knife assembly (10, 18) meets the still molten strands (5).

2. Device according to claim 1, characterized in that the cutting plate (7) from the cooling water (8) is washed over.

3. Apparatus according to claim 1 or 2, characterized in that the distance (9) of the cutting plate (7) from the discharge nozzles (2) is adjustable.

4. Device according to one of claims 1 to 3, characterized in that the individual receiving channels (6) receive a plurality of strands (5) which are guided in relation to the knife arrangement (10, 18) in the receiving channels (6) that the knife arrangement (10, 18) does not push the strands (5) onto one another.

5. Device according to one of claims 1 to 4, characterized in that the knife arrangement (18) forms a rotor 150 with substantially radially arranged knives (18).