EP2879850A1

EP2879850A1 - Perforated plate for producing granules from thermoplastic material and method for producing such a perforated plate

Info

Publication number: EP2879850A1
Application number: EP13752819.6A
Authority: EP
Inventors: Helmuth Meidhof
Original assignee: Automatik Plastics Machinery GmbH
Current assignee: Maag Automatik GmbH
Priority date: 2012-08-01
Filing date: 2013-07-29
Publication date: 2015-06-10
Also published as: DE102012015257A1; US20150149125A1; JP2015524758A; WO2014019668A1

Abstract

Perforated plate (10) for producing granules from thermoplastic material, comprising a multiplicity of die orifices (30), wherein the die orifices are respectively of such a length that they have a substantially equal throughput of melt material.

Description

HOLE FOR PRODUCING GRANULES FROM THERMOPLASTIC PLASTIC MATERIAL AND METHOD FOR MANUFACTURING SUCH A

HOLE PLATE

The invention relates to a granule well plate, to a method for calculating well lengths of a granule well plate, and to a method for producing a granule well plate.

For the production of granules of thermoplastic material, in particular polymers such. As polyethylene or polypropylene, granulating devices are often used, in which extruded, molten plastic material is pressed through nozzle holes of a perforated plate in a cooling fluid, such as water, which in a

Cutting chamber is located so that the emerging melt material is brought to solidification as quickly as possible by cooling. In the cutting chamber is still a

Knife arrangement with knives, which cover the openings of the perforated plate and separates the material strands, so that Granula tkömer be formed.

Lately find in a variety of applications, such as in the fields

Micro-injection molding, rotational molding, packaging or compounding / masterbatches increasingly microgranules use, indicative of granules with dimensions less than or equal to 1.0 mm. For microgranulation specially manufactured perforated plates are usually used, in which a large number of nozzle bores are formed. The nozzle holes are in

Hole nest, also referred to as cluster, grouped in which a variety of

Nozzle holes are formed in close proximity. A plurality of bore nests is in turn arranged lying on one or more pitch circles of the perforated plate.

Granulating devices of this type are known, for example, as underwater granulators of the SPHERO® series from Automatik Plastics Machinery GmbH.

Due to the different temperatures that prevail on and in the perforated plate, a pronounced temperature profile forms in the perforated plate. Hot zones of the perforated plate, approximately in the immediate vicinity of a heat channel in which circulates a heat transfer oil, for example, 240 ° C for heating the perforated plate, or in the melt supply, in which the melt is supplied, for example, 230 ° C of the perforated plate, are colder zones opposite, as the opening side of the perforated plate, which is in contact with and is rinsed by the cooling fluid, which may for example have a temperature of 70 ° C. The cooling effect of the cooling fluid is particularly pronounced in the area of the nozzle nests or nozzle bores, since there the contact surface of the perforated plate is in particularly intensive contact with the cooling fluid.

It can be observed that the cooling effect on the nozzle holes of a

Düsennestes may have different effects, wherein nozzle bores, which are arranged peripherally in the region of the nozzle nest, may be colder than centrally arranged

Nozzle holes.

Due to the different temperatures that prevail in the areas of different nozzle bores of a nozzle nest, the amount of melt that is located in the respective nozzle bores, cooled accordingly different. As a result, the melt flows more slowly in cooler nozzle bores and has a correspondingly lower throughput than in warmer nozzle bores.

This unevenly distributed throughput of melt material through the holes of a nest leads to the microgranulate produced has a correspondingly wide scattering of the grain sizes.

One way to increase the uniformity of the throughput for different nozzle bores is to arrange them on concentric circular rings, which makes the interaction between adjacent nozzle holes easier to calculate and for the individual circular rings a relatively easy to calculate and there respectively at least substantially uniform temperature results, which Scattering of grain sizes tends to be more desirable. Nevertheless, this positive effect of the annular arrangement is usually insufficient to avoid the described interactions and the associated undesired effects, e.g. on the particle size distribution, to reduce it to a minimum.

It can also happen that melt material in the outer, cooler nozzle bores cools down to such an extent that it no longer flows and hardens. The affected holes "freeze" and it reduces accordingly, the number of nozzle holes of the perforated plate, which are in operation and emerging from the melt material that can be granulated.The freezing of nozzle bores thus leads to a reduction in granulation, or to a undesirable increase in the mean particle size distribution of the granules, since freezing of individual nozzle bores the throughput through the remaining free

Nozzle holes increased. It is therefore an object of the invention to provide a perforated plate which overcomes the above disadvantages.

It is a further object of the invention to provide a perforated plate which allows the production of granules, in particular ikrogranulat, with reduced scattering of the grain sizes.

It is yet another object of the invention to provide a perforated plate in which the occurrence of frozen nozzle bores is prevented or at least reduced as much as possible.

These and other objects of the present invention are achieved with a perforated plate for producing granules of thermoplastic material according to claim 1, a

Computer-implemented method for determining nozzle bore lengths for a perforated plate for producing granules of thermoplastic material according to claim 4, a method for producing a perforated plate for producing granules

thermoplastic material according to claim 14 solved.

Further preferred embodiments of the invention are set forth in the dependent claims.

In a first aspect, the present invention relates to a perforated plate for producing granules of thermoplastic material, having a plurality of nozzle bores, wherein the nozzle bores are each sized in length so that the nozzle bores have a substantially equal throughput of melt material.

According to the invention, an uneven throughput of melt material through

Nozzle holes are substantially compensated by the length of each

Nozzle holes, and thereby caused by the nozzle holes hydraulic

Resistance, is varied. With nozzle holes that are varied accordingly and

have different lengths, the most uniform throughput distribution can be achieved.

In this way, it can also be avoided in particular that individual nozzle bores have a significantly lower throughput of melt material than other nozzle bores, so that the risk of freezing bores due to a lower throughput of melt material is reduced. The perforated plate may preferably be a perforated plate for producing ikrogranulat of thermoplastic material having a plurality of nozzle nests, which are arranged on at least one pitch circle of the perforated plate. Each nozzle nest may have a plurality of nozzle bores, which preferably each have the same

Have bore diameter. The nozzle bores may have a diameter of less than 1.0 mm, preferably in the range of 0.2 to 0.8 mm.

In particular, the bore length can be shortened by introducing a pilot hole of larger diameter, thus lowering the nozzle bore.

Alternatively or additionally, a segment thickness may be altered or otherwise the topology of the nozzle nest may be changed to a shorter nozzle bore

To get nozzle bore length. In particular, the topology may be described by a stepped surface, an aspherical surface, or a spherical surface that describes a side of the nozzle nest that faces away from a knife assembly and / or faces an inlet channel.

The variation of the bore lengths may be a few 1/10 mm.

The length of the nozzle bores can be determined in particular by means of a

Three-dimensional simulation using Computational Fluid Dynamics CFD, wherein the simulation is preferably carried out for a predetermined, desired operating state and / or in a range around the desired operating state.

In a second aspect, the present invention relates to a computer-implemented method for determining nozzle bore lengths for a die plate for producing granules of thermoplastic material, the die plate having a plurality of nozzle bores, comprising the steps of:

Creating a model that describes the orifice plate at least in the region of at least a subset of the plurality of nozzle bores;

Specifying operating parameters for at least one desired operating state;

Performing a computer-implemented calculation and / or simulation of a flow of melt material through the subset of nozzle bores using the model to determine a flow rate of melt material for each nozzle bore of the subset; and changing lengths of the nozzle bores to achieve a more uniform throughput.

The subset may describe a number of nozzle bores which are arranged adjacent in the perforated plate and / or formed in a delimitable region of the perforated plate are. The subset can represent a subset of all nozzle holes of the perforated plate. It is also possible in the process all the nozzle holes of the perforated plate to

take into account, in which case the subset corresponds to the entire plurality of nozzle bores.

With the method, nozzle bore lengths are preferably determined for a perforated plate for producing microgranulate, wherein the perforated plate has a plurality of nozzle nests which are arranged on at least one pitch circle of the perforated plate. The subset of

Nozzle holes can correspond to the nozzle bores of at least one of the nozzle nests.

Preferably, the computer-implemented simulation is performed as a three-dimensional simulation using Computational Fluid Dynamics CFD.

The model can affect the geometry and the heat transfer

Describe material properties of the perforated plate at least in the subset of nozzle holes. The model may be a nozzle nest or may describe multiple nozzle nests as the subset. It is also possible to use a model for the entire perforated plate.

The operating parameters may in particular viscosity parameters for the melt material, a

Temperature of the melt material in a supply area, a

Lochpia ttenheizungstemperatur and / or a cooling fluid temperature include.

The flow rate of melt material through a nozzle bore can be determined by determining the rate at which the melt material flows through the nozzle bore. In this case, for example, a velocity profile can be determined via the diameter of the at least one nozzle nest and / or the average velocity over the diameter.

The reference value may preferably be a predetermined setpoint for the throughput of

Melt material, a value of the flow rate of melt material determined for a nozzle bore selected as a reference, or an average of the flow rate of melt material of all nozzle bores of the subset of nozzle bores. As a reference nozzle bore may preferably be a centrally located in the nozzle nest nozzle bore can be selected.

The length of a nozzle bore can be shortened if the melt flow rate determined for the nozzle bore is less than the reference value. The length of a nozzle bore can be changed with a fixed predetermined increment. Preferably, the length of a nozzle bore is varied with a varying value.

In particular, in an iterative determination of optimal nozzle bore lengths by repeatedly calculating and / or simulating the flow rate of melt material through the nozzle bores, a step size decreasing for each iteration may be used.

Preferably, a quality measure is determined that is representative of a deviation of

Throughputs of melt material through the nozzle holes of a nozzle nest. The quality measure may in particular be based on a minimum value and / or a maximum value of the determined throughputs of melt material through the nozzle bores; a difference between the maximum value and the minimum value of the determined throughputs of melt material through the nozzle bores; or a sum of the squares of the differences in the determined throughputs of melt material through the nozzle bores to an average of the determined throughputs of the melt material.

The quality measure can in particular be used to be compared with a predetermined criterion in an iterative determination of nozzle bore lengths, wherein the iteration is aborted if the quality measure satisfies the criterion.

The method can be used to appropriate, especially optimal

To determine nozzle bore lengths for a perforated plate.

The method may be part of a method for producing a perforated plate for producing micro-granules of thermoplastic material, wherein the perforated plate is manufactured according to the determined nozzle bore lengths.

The perforated plate may be part of a hot roll pelletizer.

In the applicant's pilot plant investigations were carried out on nozzle length compensation according to the invention. In this case, microgranules of LDPE with 5% Masterbatch white were prepared by means of an underwater pelletizer SPHERO 50 with a material throughput of 16 kg / h through a perforated plate with 20 holes, the associated knife carrier with 6 knives had a speed of 3500 rev / min. The particle size distribution thus obtained was determined by means of a Camsizer from Retsch Technology GmbH.

Various production scenarios were examined under otherwise constant test conditions: Initial situation:

All 20 nozzle bores with nozzle diameter 0.8 mm, cylindrical nozzle length uniformly 5 mm.

It resulted in a mean granule diameter Mv3 = 1201 pm; Standard deviation Sigma3 = 106 pm.

Correction after the first CFD simulation according to the invention:

With 10 nozzle bores, the cylindrical nozzle length was reduced to 4.6 mm, the remaining 10 nozzle bores remained at 5 mm.

This resulted in a mean granule diameter Mv3 = 1214 pm; Standard deviation Sigma3 = 92 pm.

Further correction after renewed inventive CFD simulation:

For 6 nozzle bores, 5 mm cylindrical nozzle length remained, 8 nozzle bores were 4.6 mm cylindrical nozzle length and the remaining 6 nozzle bores were shortened to 4.2 mm cylindrical nozzle length.

This resulted in a mean granule diameter Mv3 = 1219 pm; Standard deviation Sigma3 = 89 pm.

Overall, the following result according to the invention was found:

By shortening the cylindrical nozzle length, the pressure reduction in the corresponding nozzle bore is reduced and the throughput per nozzle bore is slightly increased, thus also the average granule diameter. This could be compensated if necessary by a slight increase in the blade speed. In the sense of reproducible (constant) test conditions, however, this was dispensed with in the present case in order to detect the direct effects of the nozzle length compensation - without any further experimental variables.

The nozzle length compensation according to the invention causes a significant reduction of the standard deviation, i. With almost constant granule diameter, the size distribution of the Granulatkömer is much narrower and thus the throughput per nozzle bore much more uniform.

The invention will be described below with reference to preferred embodiments, with reference to the drawings: Fig. 1 shows a Mikrogranulatlochplatte according to an embodiment;

Fig. 2 shows schematically a section of a perforated plate in the region of a nozzle nest;

3 shows an exemplary temperature profile in a section of a perforated plate in the area of a nozzle test in the case of identical nozzle bore lengths;

Fig. 4 schematically illustrates a first distribution of melt flow velocities through nozzle bores of a nozzle nest in the case of equal nozzle bore lengths;

Fig. 5 schematically illustrates a second distribution of melt flow velocities through nozzle bores of a nozzle nest in the case of equal nozzle bore lengths;

Fig. 6 shows schematically a nozzle bore with adapted bore lengths of

Nozzle holes according to one embodiment;

Fig. 7 schematically illustrates a distribution of velocities of melt flows

Nozzle holes of a nozzle nest in the case of adapted nozzle bore lengths according to an embodiment;

8 shows an exemplary temperature profile in a section of a perforated plate in the area of a nozzle nest for the case of adapted nozzle bore lengths according to an embodiment;

FIG. 9 shows a method for determining nozzle bore lengths for a die plate according to an embodiment; FIG. and

10 schematically shows a section of a perforated plate in the region of a nozzle nest according to a further embodiment.

A perforated plate 10 for producing micro-granules of thermoplastic material according to an embodiment is shown in FIG. 1 in a plan view of a melt outlet side of the perforated plate 10.

As shown in Fig. 1, in the perforated plate 10, a plurality of nozzle bores 30 are formed, which are in Bohrungsnestem 20, also referred to as clusters, grouped. The Bore nests 20 are arranged lying on one or more pitch circles of the perforated plate 10.

FIG. 2 shows a section in the region of a nozzle nest 20 of a perforated plate 10 for producing ikrogranulat from thermoplastic material according to another

Embodiment shown. As shown in FIG. 2, a plurality of nozzle bores 30 are formed in the nozzle nest 20. The nozzle bores 30 each have a same bore diameter, which may be in the range between 0.1 mm and 1.0 mm. The nozzle bores 30 are formed in the nozzle nest 20 in close proximity. Thus, the distance between two adjacent nozzle bores may be less than 7 times, preferably less than 5 times, more preferably less than 3 times the bore diameter of the nozzle bores 30. In this way, a compact package is achieved and it can be formed in the perforated plate 10 a very large number of nozzle nest 20 with a large number of nozzle bores 30. As further illustrated in FIG. 2, the nozzle nest 20 may be formed as an insert 22 which is inserted into a perforated plate body to form the perforated plate 10. It is ebeno possible to form the perforated plate 10 in one piece and form the nozzle nest in the one-piece body of the perforated plate 10.

The nozzle bores 30 may be arranged in the nozzle nest 20 irregularly or regularly distributed, for example, regularly distributed on concentric circles, or in a triangular, quadrangular or hexagonal arrangement.

As further illustrated in FIG. 2, a feed channel 40 can be provided in the perforated plate 10, by means of which hot melt material is supplied to the nozzle nest 20. In Fig. 2 further channels 50 are shown, which are formed in the perforated plate 10 and which serve to guide a heat transfer fluid to temper the perforated plate 10.

In operation of the orifice plate 10, the hot melt material supplied via the supply passage 40 to the nozzle nest 20 is forced through the plurality of nozzle bores 30 of the nozzle nest 20 to be forced through the outlet side openings of the nozzle bores 30 into a cooling fluid, such as water to become.

The outlet-side surface of the perforated plate 10 is therefore in particular in the area of

Nozzle nests 20 in intimate contact with the cooling fluid, which may for example have a temperature of 70 ° C. This causes a flow of heat energy from the hot perforated plate 10 into the cold cooling fluid, which locally cools the perforated plate 10, in particular in the area of the nozzle nests 20, which has an effect on the temperature of the nozzle bores 30 in particular. The nozzle bores 30 of the nozzle nests 20 are at the same time in intimate contact on their inner walls with the hot melt material flowing through the nozzle bores 30, which emits a portion of the heat energy contained via the inner wall to the respective nozzle bores 30. It should be noted here that a nozzle bore 30 arranged in the center of the nozzle nest 20 is completely surrounded by further nozzle bores 30, while no further adjacent nozzle bores exist to the outside for a nozzle bore 30 arranged at the edge of the nozzle nest 20.

It is now assumed the case that the nozzle bores 30 all have a same geometry, in particular a same diameter and a same length. In this case, the heat given off by a nozzle bore 30 arranged in the center of the nozzle nest 20 therefore feeds a smaller volume of the nozzle nest 20, and therefore heats it more strongly than does a nozzle bore 30 arranged at the edge of the nozzle nest 20. At the same time, the proportion of the surface in contact with the cold cooling fluid, which is dispensed with a nozzle bore 30 arranged at the edge of the nozzle nest 20, is smaller because of the smaller number of neighboring holes

As a result, the nozzle bores 30 at the edges of the nozzle nest more strongly cool and have a lower temperature than nozzle bores 30 in the center of the nozzle nest 20.

This is illustrated by way of example in FIG. 3, which is the result of a simulation of the

Temperature course in the nozzle 20 and the nozzle 20 surrounding the surrounding part of the perforated plate 10 shows. It can be seen in FIG. 3 that the central region of the nozzle nest 20 has a higher temperature than the edge region.

The different temperatures of the nozzle bores 30 cause melt material, which flows through a nozzle bore 30 arranged at the edge of the nozzle bore 20, to be cooled more strongly than is the case for melt material which is arranged in the center of the nozzle nest due to the relatively colder inner wall Nozzle bore 30 flows, due to the relatively warmer nozzle bore there.

The different cooling leads to the fact that the melt material in the different nozzle bores assumes different viscosities and accordingly flows at different rates. This is illustrated by way of example in FIG. 4, which shows the result of a simulation of the flow of melt material through the nozzle nest 20, in the representation of FIG. 4 for each nozzle bore 30 the vectors of the velocity are shown, with the Melt material flows through the respective nozzle bores 30 and exits therefrom. In Fig. 4 it can be seen that the speed at which the melt material by a

Nozzle bore 30 flows, highest for centrally located in the nozzle nest 20

Nozzle holes and the speed decreases towards the edge of the nozzle nest 20, as can be seen by the different length and width velocity vectors.

FIG. 5 shows a further result of a further simulation of the flow of melt material through the nozzle nest 20, in which case those lying on the edge of the nozzle nest 20

Nozzle holes 30 have cooled down to such an extent that the melt material no longer flows and the peripheral nozzle bores 30 are "frozen";

Representation of FIG. 5 for the affected nozzle holes 30 no speed vector to see. Towards the center of the nozzle nest 20, the speed of the melt material continues to increase, showing a large difference in the speed at which melt material flows through and exits the individual non-frozen nozzle bores.

According to the invention, it is therefore proposed to vary the lengths of nozzle bores and to adapt them so that a substantially uniform throughput of melt material is achieved.

Thus, for example, as shown in FIG. 6, the nozzle bores 30 can be countersunk with pilot bores, such that the pilot bores extend the nozzle bores 30 to such an extent that different nozzle bore lengths result for different nozzle bores 30.

In particular, as shown in FIG. 6, located at the edge of the nozzle nest 20

Nozzle holes 20 may be made with a deeper pilot hole, so that there is a shorter nozzle bore length for the located at the edge of the nozzle nest 20 nozzle bores 30 than for centrally located in the nozzle nest 20 nozzle bores.

By shortening the nozzle bore length, the hydraulic resistance of the affected nozzle bore 30 is reduced, so that it presents a smaller flow resistance to the melt flow. The melt flow can therefore flow faster through the shortened nozzle bore 30. Ideally, the nozzle bore length is dimensioned such that the resulting, adjusted hydraulic resistance compensates for the influence resulting from the temperature differences as optimally as possible. By a suitable choice of nozzle bore lengths for the nozzle bores 30 of a nozzle nest 20 can be achieved so that for all nozzle bores 30 of the nozzle nest 20, a substantially equal throughput of

Melt material through the nozzle bores 30 results. This is shown by way of example in FIG. 7, which adjusts a distribution of melt flow velocities through nozzle bores of a nozzle nest in the case

Represents nozzle bore lengths. As can be seen in FIG. 7, the velocity vectors of the melt material are essentially the same for all nozzle bores 30 of the nozzle nest 20. This was achieved in that, as can also be seen in FIG. 7, the nozzle bore lengths, in particular those at the edge of the nozzle nest 20 lying nozzle bores 30 have been lowered accordingly far, so that the nozzle bore lengths of the peripheral nozzle bores 30 are adjusted and shortened so that the best possible compensation results.

As shown in the temperature profile of FIG. 8, with customized nozzle bore lengths, a flatter temperature gradient also occurs through the nozzle nest 20; the

Temperature differences between the edge region and the center of the nozzle nest 20 are lower than in the case illustrated in FIG. 3 without compensation by adaptation of

Nozzle bore lengths.

In order to determine what lengths the individual nozzle bores 30 should have to achieve the desired compensation, a method for determining

Nozzle bore lengths are used for a perforated plate shown in FIG.

In the method of FIG. 9, which is executed as software on a computer, a model is first provided in a step 110. The model used as a computational and / or

Simulation model describes the geometry and properties of the perforated plate.

In particular, the model describes the number and spatial arrangement of the nozzle bores 30 in the nozzle nest 20, as well as the geometry of the nozzle bores 30 themselves, such as diameter and length of the nozzle bores. The model can further describe the thermal behavior of the materials of the perforated plate. It is possible that the model describes only the area of a nozzle nest. This may be possible in particular if all the nozzle nests 20 of the perforated plate 10 are subject to the same conditions, for example if all the nozzle nests 20 are arranged on the same pitch circle of a rotationally symmetrical perforated plate 10. Alternatively, it is also possible that the model describes the entire perforated plate 10, or that the model describes a region of the perforated plate 10 with a plurality of nozzle nest 20.

In a further step 120, the parameters necessary for the calculation and / or simulation are provided. In particular, this can be parameters of a desired

Operating state, for which the perforated plate is to be designed. Predeterminable parameters can be, in particular, viscosity parameters for the melt material, a temperature of Melting material in a supply area, a perforated plate heating temperature or a ühlfluidtemperatur include.

Based on the model and on the parameters, computer-aided calculation and / or simulation is performed in step 130 to determine how the melt material flows through the nozzle nest 30. Preference is given to a three-dimensional simulation using

Computational Fluid Dynamics executed. In this way, it is determined for each nozzle bore, which throughput of melt material results through the individual nozzle holes. The throughput can be determined directly as a calculated value or derived from the flow rate of the melt material.

Based on the result of the calculation and / or simulation, in a step 160, the lengths of the nozzle bores are adjusted. In this case, for nozzle bores 30 which have a low or too low throughput of melt material, the nozzle bore lengths can be shortened. Alternatively or additionally, for nozzle bores 30 which have a high or too high throughput of melt material, the nozzle bore lengths can be extended. The calculation process would then be with a corresponding new (e.g., longer) bore

perform. This can be done for all nozzle bores 30 or only for a part of the nozzle bores 30. Also changing the length of only one nozzle bore 30 is possible.

To determine which nozzle bore 30 is to be changed in length, a reference value can be used. If the flow rate of melted material determined for a nozzle bore deviates from the reference value by more than a predetermined amount, it is determined that the length of the nozzle bore is to be changed. As a reference, for example, a predetermined setpoint for the flow rate of melt material, a value of the throughput of

Melting material determined for a nozzle bore located centrally in the nozzle nest, or an average of the throughput of melted material of all nozzle bores of the nozzle

Nozzle nesting be used.

In step 160, the nozzle bore lengths may be changed at a predetermined pitch. In an iterative procedure, the step size can preferably be reduced with each iteration. Alternatively, the change in length, at a nozzle bore 30th

also be calculated depending on how much the flow rate through the nozzle bore 30 deviates from the reference value.

From step 160, the method may return to step 130 to re-calculate and / or simulate the changed nozzle bore lengths. In this way it is possible in an iterative manner, by means of repeated simulations and changes, to determine step by step the most optimal determination of the nozzle bore lengths.

In the method of FIG. 9, furthermore, in a step 140, a quality measure can be determined that is representative of a deviation of the throughputs of melt material by the

Nozzle holes of a nozzle nest. The quality measure may be based on a minimum value and / or a maximum value of the determined throughputs of melt material through the nozzle bores, a difference between the maximum value and the minimum value of the determined throughputs of melt material through the nozzle bores, or a sum of the squares of the differences determined throughputs of melt material by the

Nozzle holes to an average of the determined throughputs of melt material. The quality measure can thus be a measure of how good the compensation made by the change in length. Thus, in a step 150, a comparison of the quality measure with a predeterminable criterion can be made to determine whether the compensation provided

Requirements fulfilled sufficiently well. If not, then steps 160, 130, 140 and 50 are iteratively repeated until the criterion is met or the method is aborted by a user.

If it is determined in step 150 that the quality measure satisfies the predetermined criterion, the method goes to step 170 and ends. The determined nozzle bore lengths can now be output, for example to produce a perforated plate on the basis of the data obtained.

As described above with reference to FIG. 6, the nozzle bores 20 can be adjusted in length by mounting pilot holes which are the

Countersink nozzle bores 30 so far that the nozzle bores 30 provided for the respective nozzle bores result. Alternatively or additionally, it is also possible to change a segment thickness of a nozzle nest or otherwise to change the topology of the nozzle nest. This will be described below with reference to FIG. 10.

10 shows a section in the region of a nozzle nest 20 of a perforated plate 10 for producing micro-granules of thermoplastic material according to a further embodiment. As shown in FIG. 10, the nozzle nest 20 may be formed by an insert 22 which may be inserted into a perforated plate main body to form the perforated plate 10. In the insert 22, the plurality of nozzle bores 30 of the nozzle nest 20 are formed. The insert 22 is formed in the example of FIG. 10 so that the insert 22 on the side facing the blade assembly plan and on the inlet channel 40 side facing is convex. This results in a topology of the insert 22, on the basis of which nozzle bores 30 in the center have a length which is greater than the length of

Nozzle holes formed on the edge of the insert 22.

In this case, the insert 22 can be processed, for example, on the side facing the inlet channel 40 by a processing center which processes the affected area as a free-form surface in order to obtain the corresponding determined nozzle lengths. The surface may have a stepped profile, or as shown in Fig. 10, a substantially lenticular profile. The profile can be described by an aspherical surface. Alternatively, the profile may also be described by a spherical surface, wherein the parameters of the spherical surface may be chosen so that the determined adapted lengths of the nozzle bores to be achieved are approximated as well as possible. In particular, in the case of a spherical surface machining can also be done by grinding.

In this way, the nozzle bores 30 can be adapted in the nozzle nest 20

Nozzle bore length can be formed without interfering with the affected nozzle bores

Vorbohrungen would have to be introduced.

As described above, by changing and adjusting the lengths of the nozzle bores, the uniformity of the flow rate of melt material through the

Nozzle holes can be improved.

Alternatively, it is also conceivable to increase the uniformity of the throughput for different nozzle bores, to change the nozzle diameter of individual nozzle bores or to adapt them to the temperature profile accordingly. Thus, for example, a respective adapted bore diameter can be determined for all nozzle bores of a nozzle nest by a corresponding simulation analogous to the method described with reference to FIG. 9, such that an optimally uniform or at least sufficiently uniform throughput of melt material is established through the nozzle bores. Since already a change of the

Diameter in the range less 1/100 mm a very strong change of the respective

Hydraulic resistance of the affected nozzle bore can cause the parameter of the nozzle diameter is very sensitive in terms of adjustability. For a customized

Perforated plate, it would therefore be necessary to produce the nozzle holes precisely with a large variety of adapted, only slightly different diameters. As this

production technology is much more difficult to implement than a production technology easily controllable change and adjustment of the nozzle bore lengths, is the change and Adjustment of nozzle bore lengths against change and adjustment of

Nozzle diameters preferred.

Particularly in the case of large nozzle nests with a large number of nozzle bores and / or in the case of perforated plates which are designed to be relatively thin in the region of the nozzle bores and their nozzle bores correspondingly short nozzle bore lengths, it may be advantageous both the diameter and the length of the respective Adjust nozzle bores. So it is possible, for example, starting from an initial diameter of a

Nozzle hole to determine an adapted length of the nozzle bore. If the determined length assumes a value that is greater than a desired maximum length of a nozzle bore, or a value that is smaller than a minimum length of a nozzle bore, the

Output diameter can be increased or decreased and based on it emeut an adjusted length of the nozzle bore can be determined. In this way it can be achieved that the nozzle bores do not differ in their length in a possibly undesirably large extent. If only a limited number of differing diameters are provided for the possible diameters of the nozzle bores, for example 2, 3, 4 or 5 different diameters, it is possible to provide corresponding tools such as drills for this limited number of diameters, which allow precise production of these allow limited number of different diameters. That's the way it is without too much

production engineering effort possible to produce perforated plates, the nozzle bores are adjusted accordingly both in their diameter and in their length in order to achieve the most uniform throughput of melt material through the nozzle bores.

While the invention in the above with respect to perforated plates for the production of

Microgranulate was described, the present invention is not limited in this way. Rather, the invention can also be applied to other types of perforated plates having a plurality of nozzle bores, which need not be arranged in the nozzle nest.

Claims

claims

Perforated plate (10) for producing granules of thermoplastic material, with a plurality of nozzle bores (30), preferably with a respective same bore diameter;

characterized in that

the nozzle bores (30) are each dimensioned in their length so that the

Nozzle bores (30) have a substantially equal throughput of melt material.

Perforated plate (10) according to claim 1, characterized in that the length of

Nozzle holes (30) are determined according to a three-dimensional simulation using Computational Fluid Dynamics.

Perforated plate (10) according to one of the preceding claims, characterized in that the perforated plate has a perforated plate (10) for producing micro-granules

thermoplastic material,

wherein the perforated plate has a plurality of nozzle nests (20) which are arranged on at least one pitch circle of the perforated plate (10),

each nozzle nest (20) having a plurality of nozzle bores (30) each having the same bore diameter; and

wherein the nozzle bores (30) have a diameter of less than 1.0 mm, preferably in the range of 0.2 to 0.8 mm.

A computer-implemented method for determining nozzle bore lengths for a die plate (10) for producing granules of thermoplastic material, the die plate (10) having a plurality of nozzle bores (30), comprising the steps of:

a) providing (110) a model which describes the perforated plate (10) at least in the region of at least a subset of the plurality of nozzle bores (30); b) providing (120) operating parameters for at least one desired one

Operating condition; c) performing (130) a computer-implemented calculation and / or

Simulation of a flow of melt material through the subset of

Nozzle bores (30) using the model to determine a flow rate of melt material for each nozzle bore (30) of the subset; and d) changing (160) lengths of the nozzle bores (30) to achieve a more uniform throughput.

A method according to claim 4, characterized in that in step c) a

Three-dimensional simulation using Computational Fluid Dynamics is performed.

Method according to claim 4 or 5, characterized in that the model is the

Geometry and the material properties of heat transfer

Perforated plate (10) at least in the region of the subset of nozzle bores (30) describes.

Method according to one of claims 4 to 6, characterized in that the

Operating parameters Viscosity of the melt material, a temperature of the

Melt material in a supply area, a Lochpia ttenheizungstemperatur and a cooling fluid temperature include.

Method according to one of claims 4 to 7, characterized in that the flow rate of melt material through a nozzle bore (30) is determined by determining the speed at which the melt material flows through the nozzle bore (30).

Method according to one of claims 4 to 8, characterized

in step d), the throughput determined by the nozzle bores (30) of

Is compared with a reference value and the nozzle bore (30) is changed in length when the flow rate deviates from the reference value by more than a predetermined amount,

where the reference value is one of:

a predetermined setpoint for the flow rate of melt material;

a value of the throughput of melt material selected for one as a reference

Nozzle bore (30) is determined; and

an average of the flow rate of melt material of all nozzle bores (30) of the subset of nozzle bores (30).

10. The method according to any one of claims 4 to 9, characterized in that in step d) the length of the nozzle bore (30) is shortened when the determined flow rate of melt material is less than the reference value, preferably in step d) with the lengths be changed by a predetermined step size.

11. The method according to any one of claims 4 to 10, characterized in that

the perforated plate has a perforated plate (10) for producing micro-granules

thermoplastic material,

wherein the perforated plate has a plurality of nozzle nests (20) which are arranged on at least one pitch circle of the perforated plate (10), and

wherein the subset of nozzle bores (30) corresponds to at least one of the nozzle nests (20).

12. The method according to any one of claims 4 to 11, further comprising

Determining (140) a measure of quality representative of a deviation of

Throughputs of melt material through the nozzle bores (30) of the subset of nozzle bores (30), the quality measure being based in particular on one of:

a minimum value and / or a maximum value of the throughputs of melt material determined in step c) through the nozzle bores (30); a difference between the maximum value and the minimum value of the melt material throughputs determined in step c) through the nozzle bores (30); or

a sum of the squares of the differences in the determined flow rates of melt material through the nozzle bores (30) to an average of the determined throughputs of melt material; and that

the steps c) and d) are carried out repeatedly until the quality measure a predetermined

Criterion fulfilled.

13. perforated plate (10) according to one of claims 1 to 3, characterized in that the

Nozzle lengths are determined by the method according to one of claims 4 to 12.

14. A method for producing a perforated plate (10) for producing granules

thermoplastic material, with the steps:

Creating a perforated plate construction;

Determining nozzle bore lengths by the method of any of claims 4 to 12; and

Finishing the perforated plate (10) according to the determined nozzle bore lengths.

15. Hot Dump Granulator, comprising

A perforated plate (10) according to any one of claims 1 to 3 or 13, or a perforated plate (10) made by the method according to claim 14.