DE102020109595A1 - Method for classifying a plastic - Google Patents

Abstract

A method for classifying a plastic, wherein the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing a temperature of the plastic from an initial temperature value to an end temperature value, a volume and / or a mass of the plastic and the supplied plasticizing energy are recorded as measured variables, depending on the recorded measured variables, the initial temperature value and the final temperature value, at least one of the following is determined: a heat capacity of the plastic and / or a change in enthalpy of the plastic and / or a variable that can be calculated from the heat capacity and / or the change in enthalpy , and on the basis of the determined heat capacity and / or the determined enthalpy change and / or the variable that can be calculated therefrom, a plastic group containing the plastic is identified.

Description

The present invention relates to methods for classifying a plastic.

In the following, the prior art is described with the aid of molding machines, with the example of an injection molding machine being discussed in particular. In addition to injection molding machines, the class of molding machines also includes injection presses, presses and the like. The following description of the prior art applies analogously to them.

When setting up an injection molding process, in practice, as before, basic settings are generally made by an operator of the injection molding machine. This also applies to settings of the plasticizing process, by means of which a plastic granulate is transformed into a malleable mass, for example using a plasticizing screw.

The operator is limited to his experience and a "trial and error" procedure because the non-linear nature of the plasticizing and shaping process has largely prevented automatic setting of the injection molding machine in the prior art, although efforts have been made for a long time to use injection molding machines to enable an automatic (self-) adjustment. Because of the material dependency of the process and its mentioned non-linear nature, the automated setting of the injection molding machine often fails because the plastic used is not known or the operator inputs cannot be checked automatically.

The object of the present invention is to provide a method by means of which a plastic can be classified and which can also be carried out on or at least in the immediate vicinity of a molding machine with reasonable effort.

1. a) der Kunststoff durch Zuführen einer Plastifizierenergie in Form von mechanischer und/oder thermischer Energie unter Erhöhung einer Temperatur des Kunststoffs von einem Anfangstemperaturwert auf einen Endtemperaturwert plastifiziert wird,
2. b) ein Volumen und/oder eine Masse des Kunststoffs sowie die zugeführte Plastifizierenergie als Messgrößen messtechnisch erfasst werden,
3. c) in Abhängigkeit der erfassten Messgrößen, des Anfangstemperaturwerts und des Endtemperaturwerts zumindest eines der folgenden bestimmt wird: eine Wärmekapazität des Kunststoffs und/oder eine Enthalpieänderung des Kunststoffs und/oder eine aus der Wärmekapazität und/oder der Enthalpieänderung rechnerisch ableitbare Größe, und
4. d) auf Basis der bestimmten Wärmekapazität und/oder der bestimmten Enthalpieänderung und/oder der daraus rechnerisch ableitbaren Größe eine den Kunststoff beinhaltende Kunststoffgruppe identifiziert wird.

In a first embodiment of the invention, this object is achieved by the features of claim 1. This is done by

1. a) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing the temperature of the plastic from an initial temperature value to a final temperature value,
2. b) a volume and / or a mass of the plastic as well as the supplied plasticizing energy are recorded as measured variables by measurement,
3. c) at least one of the following is determined as a function of the recorded measured variables, the initial temperature value and the final temperature value: a heat capacity of the plastic and / or a change in enthalpy of the plastic and / or a variable that can be mathematically derived from the heat capacity and / or the change in enthalpy, and
4. d) a plastic group containing the plastic is identified on the basis of the determined heat capacity and / or the determined enthalpy change and / or the variable that can be calculated therefrom.

This means that the plastic is classified by determining the heat capacity and / or the change in enthalpy. The fact that the type of plastic and thus its properties can be determined - preferably automatically - by the method according to the invention, one is a considerable step closer to an automatic setting of a molding machine, since many of the settings in molding machines are of course strongly dependent on the material used.

• a) der Kunststoff durch Zuführen einer Plastifizierenergie in Form von mechanischer und/oder thermischer Energie unter Erhöhung einer Temperatur des Kunststoffs von einem Anfangstemperaturwert auf einen Endtemperaturwert plastifiziert wird,
• e) eine vom Kunststoff abgegebene Infrarotstrahlung messtechnisch erfasst wird und
• f) auf Basis der erfassten Infrarotstrahlung eine den Kunststoff beinhaltende Kunststoffgruppe identifiziert wird.

In a second embodiment of the invention, this is done by the features of claim 20, namely by

• a) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing the temperature of the plastic from an initial temperature value to a final temperature value,
• e) an infrared radiation emitted by the plastic is detected by measurement and
• f) a plastic group containing the plastic is identified based on the detected infrared radiation.

• a) der Kunststoff durch Zuführen einer Plastifizierenergie in Form von mechanischer und/oder thermischer Energie unter Erhöhung einer Temperatur des Kunststoffs von einem Anfangstemperaturwert auf einen Endtemperaturwert plastifiziert wird und
• g) aus zumindest zwei verschiedenen Quellen Identifikationsinformationen über den Kunststoff bezogen werden, wobei zumindest eine der zumindest zwei verschiedenen Quellen eine Messung an der zum Plastifizieren des Kunststoffs verwendeten Vorrichtung ist, und dass auf Basis der Identifikationsinformationen eine den Kunststoff beinhaltende Kunststoffgruppe identifiziert wird und bevorzugt der Kunststoff identifiziert wird.

In a third embodiment of the invention, the object is achieved by the features of claim 22. This is done by

• a) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing a temperature of the plastic from an initial temperature value to a final temperature value, and
• g) identification information about the plastic is obtained from at least two different sources, at least one of the at least two different sources being a measurement on the device used to plasticize the plastic, and that on the basis the identification information a plastic group containing the plastic is identified and preferably the plastic is identified.

What these versions of the invention have in common is that, on the basis of recorded information, a plastic group containing the plastic or even the plastic itself is identified on a device for plasticizing the plastic, i.e. as part of the plasticizing process. An example of such a device would of course be a plasticizing unit, such as is e.g. is used with an injection molding machine, or more generally a molding machine.

An indication that a plastic or a group of plastics is identified on the basis of a parameter or other information (e.g. features d), f) or g)) does not mean, within the scope of the invention, that only the specified parameter or other information is used is used to identify the plastic or group of plastics. Rather, further parameters, measured values or additional information can always be used for identification. The identification of the plastic or the plastic group can also relate to mixtures of two or more plastics or to mixtures of plastics with fillers.

The invention offers further advantages. For example, the invention makes it possible to estimate the load on the molding machine that occurs over time, or to provide a further control element by means of which the operation and operational safety can be monitored.

The plastic groups that are used as a classification for the plastic used include, for example, polyethylenes, polypropylenes, polystyrenes, polyamides, polycarbonates, polymethyl methacrylates and the like.

In addition to the identification of the plastic group containing the plastic, the plastic itself can also be determined, i.e. Which plastic is involved in particular (e.g. PE 0.95, possibly even with an indication of its origin (PE X from manufacturer Y)). In the context of the invention, the determination of the plastic itself is also understood as the identification of the plastic group containing the plastic. The determination of the plastic can also be understood to mean that in addition to the classification of the plastic itself, fillers (for example fibers) are identified or their amount in the plastic is determined.

Another advantage of the invention is that the method according to the invention can be implemented in an automated manner, so that a plasticizing unit and / or a shaping machine automatically determines the plastic used.

• - ein Formgebungsverfahren, wobei der mit dem erfindungsgemäßen Verfahren plastifizierte und klassifizierte Kunststoff, insbesondere im Rahmen eines Spritzgießverfahrens, verwendet wird,
• - ein Plastifizieraggregat, welches zur Durchführung eines erfindungsgemäßen Verfahrens eingerichtet ist, sowie
• - eine Formgebungsmaschine, insbesondere eingerichtet zur Durchführung eines erfindungsgemäßen Verfahrens, mit einem erfindungsgemäßen Plastifizieraggregat.

In addition to the method according to the invention, protection is also sought after

• - a shaping process in which the plastic plasticized and classified by the process according to the invention is used, in particular in the context of an injection molding process,
• - A plasticizing unit, which is set up to carry out a method according to the invention, and
• a shaping machine, in particular set up to carry out a method according to the invention, with a plasticizing unit according to the invention.

In a figurative sense, a plasticizing unit according to the invention and / or a shaping machine according to the invention can be used as a calorimeter by determining the heat capacity and / or the change in enthalpy according to the invention.

The use of the expression “final temperature value” does not mean that no further temperature change - in particular an increase in temperature - is made or cannot happen to the plastic. The expression merely indicates that the temperature is essentially at the end of that time interval over which the respective determination of the heat capacity and / or the enthalpy change is carried out. The subsequent thermodynamic processes can of course be carried out and in certain situations are even unavoidable. The same applies to the initial temperature value.

The measured variables (volume and / or mass, plasticizing energy) can be measured directly or indirectly. Of course, this also applies to the start and end temperatures. The values derived mathematically from the heat capacity and / or the change in enthalpy can also be measured either directly or indirectly (i.e. as an independent physical or chemical variable) or the heat capacity and / or the change in enthalpy can be measured and the mathematically derived values can be calculated from these measured values will. In the following, the explicit specification of the variable calculated from the heat capacity and / or the change in enthalpy is partly omitted. However, its meaning is always included when the (determination of) heat capacity and / or the change in enthalpy are discussed.

The metrological detection of the infrared radiation emitted by the plastic (method step e)) can preferably be carried out at the beginning of the plasticizing process according to method step a) if the plastic is still present as granules, for example. However, it is also conceivable to measure the infrared radiation during the plasticizing process or afterwards.

Further advantageous embodiments of the invention are defined in the dependent claims.

Provision can preferably be made for an energy balance and / or a power balance for the plastic to be drawn up on the basis of the measured variables and for the specific heat capacity, the specific enthalpy change and / or the mathematically derived variable to be determined as a function of the energy balance and / or the power balance becomes. Setting up an energy or power balance that at least partially reflects reality can dramatically increase the accuracy of the determined heat capacity and / or enthalpy change - and thus of course also the quality of the classification of the plastic. In principle, however, alternatives consist of various more or less precise approximations or estimates.

It has already been mentioned that further variables can be determined on the basis of the energy balance and / or the power balance, namely, for example, a load spectrum, a state of wear and / or an operating state. A load collective is a measure of the total load over a period of time, preferably over the entire previous service life of the system. This means that the collective load can be used as a direct measure of the system's wear and tear. Of course, other, in particular more specific, wear dimensions, for example for a plasticizing screw or a plasticizing cylinder, can also be determined from the data determined according to the invention. The operating status of the system can also be quantified using the data obtained.

The (for example. By means of a heating device) supplied and / or removed thermal energy and / or thermal power and / or a profile of the supplied thermal energy and / or thermal power is determined and taken into account in the energy balance and / or power balance. The energy or power balance can be drawn up particularly easily in this way.

In addition to supplying thermal energy during the plasticizing process for plastics, in some cases it is also necessary to cool the plastic, e.g. to prevent the temperature of the plastic from becoming so high that it degrades - in the sense of an undesired chemical or physical change occurs if the temperature of the plastic is too high.

The determination of the heat capacity can be particularly simple if it is determined as the specific heat capacity at constant pressure and the plastic group containing the plastic is identified on the basis of the specific heat capacity at constant pressure. Alternatively, the heat capacity can be determined at constant volume or in mixed forms, but this poses challenges in the form of sometimes complex calculations for data evaluation and operating states that are difficult to control.

The initial temperature value and / or the final temperature value and / or a temperature profile of the plastic can be measured directly and / or indirectly by means of at least one temperature sensor, with preferably a temperature control of the plastic with the supplied mechanical energy and / or the supplied thermal energy as the manipulated variable and measured values of the at least one temperature sensor is carried out as actual values. The use of temperature sensors enables a particularly simple and reliable temperature determination, whereby both a direct measurement of the temperature of the plasticized or not yet plasticized plastic can be provided, as well as the indirect measurement via the determination of the temperature of a body which is in thermal contact with the plastic stands. If only one temperature profile is measured, the start and / or end temperature value can of course be taken from the profile.

The plastic can be plasticized at an essentially constant pressure, the pressure preferably being regulated with a constant setpoint value using measured values of at least one pressure sensor. The advantages of performing the method at constant pressure have already been mentioned. A regulation of the (mass) pressure to a constant target value is carried out in many cases in plasticizing units of the prior art anyway, so that the method according to the invention can be easily implemented.

The thermal energy can be supplied by means of a - preferably electrical - heating device, which is a particularly simple embodiment of the invention, wherein a thermal heating energy generated by the heating device and / or a heating power and / or a course of the heating energy and / or the heating power can be detected.

At least one drive sensor can be used, by means of which the mechanical energy supplied via at least one drive and / or a mechanical power provided by the at least one drive (directly or indirectly on the plastic) and / or a profile of the mechanical energy supplied and / or the mechanical performance is measured. This is also used to easily set up an energy or power balance. Losses that occur, for example, due to friction and other resistances, can be taken into account in the energy or power balance by means of correction factors - for example depending on the machine size and efficiency.

Both for the heating power or energy and for the supplied mechanical energy, it is true that measured or otherwise recorded curves can be used to extract the actually desired variables or to calculate them from the curve (e.g. via integration).

In a particularly simple implementation of the invention, a plasticizing screw and / or a plasticizing piston can be used to supply the mechanical energy. Plasticizing screws, in particular, are a widespread design for plasticizing units, as a result of which the invention can be implemented in some cases without any structural changes to the system.

As a rule, a plasticizing cylinder can be provided in which the plasticizing screw is arranged, the plasticizing screw being moved axially and rotatingly for plasticizing the plastic by means of the at least one drive in the plasticizing cylinder. As a result of the rotation of the plasticizing screw, the plastic is sheared, with the axial drive simultaneously maintaining a pressure in the plastic that is preferably constantly regulated, as already mentioned. During this so-called metering-up, the screw moves back axially while maintaining the pressure mentioned.

A pressure sensor can, however, also directly detect the pressure in the plastic, for example in the form of a mass pressure sensor in the plasticizing cylinder.

Provision can be made for a torque exerted on the plasticizing screw and / or a speed of the plasticizing screw to be measured in order to record the mechanical energy supplied.

Both the rotation and the axial movement can be implemented using one or more electrical or hydraulic drives. Torque and axial movement as well as the axial exertion of force can be measured using appropriate sensors. For example, the exerted torque can be determined from the currents and voltages applied to an electrical machine driving the rotary movement. The axial force exerted by a hydraulic drive can be detected, for example, via the pressure of a hydraulic fluid.

A screw position sensor can be used, by means of which the volume of the plastic plasticized in the plasticizing cylinder is recorded. Because of the known (cylindrical) geometry, the volume in the plasticizing cylinder can be recorded from the screw position - for example before and after the plasticizing of the plastic.

A funnel can be used to feed the plastic to be plasticized into the plasticizing cylinder, a funnel temperature sensor preferably being used in and / or on the funnel. The initial temperature value of the plastic can easily be determined by means of such a funnel temperature sensor without the need for significant procedural or constructional expenditure.

Theoretically, it is also conceivable to install a scale on the funnel, by means of which the mass of the plastic to be plasticized can be measured.

Several cylinder temperature sensors can be used, which are assigned to axially distributed heating zones on the plasticizing cylinder, the heating zones being heated independently of one another, the heating in the heating zones being controlled using measured values from the cylinder temperature sensors assigned to the heating zones. Such regulated heating zones are also already present in many existing plasticizing units, which facilitates the implementation of the invention. Similar to the mechanical input of energy, losses can also occur here, which can be taken into account by means of correction factors - for example, depending on the machine size and efficiency. Ultimately, this generally applies to any losses that occur during the introduction (or removal of energy).

These regulated heating zones can be used particularly advantageously to determine the final temperature value by temporarily switching off the regulation of a specific heating zone - especially the last one in the sense of conveying the plastic - and using a measured value from the cylinder temperature sensor assigned to the specific heating zone as the final temperature value. If possible, you can wait some time until it can be expected that the specific heating zone is in thermal equilibrium so that the The plasticizing cylinder assumes the temperature of the plasticized plastic in the area of the specific heating zone. As a result, the final temperature value can be measured with a high degree of accuracy, but without the use of a generally relatively expensive mass temperature sensor. The accuracy can be further increased if the plasticizing unit is operated in extrusion mode, ie with the plastic emerging from the plasticizing cylinder continuously and therefore conducive to the thermally steady state.

• - Enthalpie-Temperatur-Kurven für eine Vielzahl von Kunststoffen mittels für diese Kunststoffe bekannten Zusammenhängen zwischen der Temperatur einerseits und dem spezifischen Volumen und/oder der Dichte andererseits korrigiert werden,
• - die Wärmekapazität des Kunststoffs und/oder die Enthalpieänderung des Kunststoffs und/oder die aus der Wärmekapazität und/oder der Enthalpieänderung rechnerisch ableitbare Größe mit den korrigierten Enthalpie-Temperatur-Kurven - insbesondere mit Steigungen der korrigierten Enthalpie-Temperatur-Kurven - abgeglichen werden und
• - auf Basis des Abgleichs die den Kunststoff beinhaltende Kunststoffgruppe identifiziert wird.

The already mentioned alternative of a dedicated mass temperature sensor, which measures the temperature of the plasticized plastic directly, still exists, of course.
It can also be provided that for identification of the plastic group containing the plastic

• - Enthalpy-temperature curves for a large number of plastics are corrected by means of correlations between the temperature on the one hand and the specific volume and / or density on the other hand, which are known for these plastics,
• - the heat capacity of the plastic and / or the enthalpy change of the plastic and / or the variable that can be mathematically derived from the heat capacity and / or the enthalpy change with the corrected enthalpy-temperature curves - in particular with slopes of the corrected enthalpy-temperature curves - are compared and
• - The plastic group containing the plastic is identified on the basis of the comparison.

In particular, the heat capacity can take on the role of a curve slope in (corrected) enthalpy-temperature curves, whereby the computational or graphic comparison of the curves with the determined values for the heat capacity and / or the enthalpy change is particularly easy to carry out.

In those cases in which the density or the mass of the plastic to be plasticized is difficult to obtain, this embodiment of the method according to the invention allows a reliable determination of the plastic or the plastic group containing the plastic.

The method according to the invention can be carried out several times, preferably varying a pressure and / or an applied mechanical power. The latter can be varied, for example, by varying the screw speed. This opens up a particularly simple possibility of varying the test conditions without having to make profound changes in the control of the heating (especially the heating zones).

A near-infrared sensor (NIR sensor) can be used to detect the infrared radiation. In principle, the use of a (NIR) spectrometer is also conceivable.

• - Verfahren nach der ersten Ausprägung der Erfindung unter Bestimmung einer Wärmekapazität des Kunststoffs und/oder einer Enthalpieänderung des Kunststoffs und/oder einer aus der Wärmekapazität und/oder der Enthalpieänderung rechnerisch ableitbaren Größe,
• - Verfahren nach der zweiten Ausprägung der Erfindung unter messtechnischer Erfassung der vom Kunststoff abgegebenen Infrarotstrahlung,
• - Maschineneinstellungen und/oder Messwerte und/oder Maschinenkonfiguration, insbesondere Einspritzdrücke (oder daraus abgeleitete Größen wie Viskositäten oder Fließzahlen), maximale und/oder minimale Verarbeitungstemperaturen, Massezylindertemperaturen an der Spitze oder über den gesamten Verlauf des Plastifizierzylinders, Granulattemperaturen, Kühlflüssigkeitstemperaturen, eine Dichte der Schmelze, Informationen über ein eingesetztes Formwerkzeug,
• - Verfahren zum Bestimmen eines für ein Kompressionsverhalten des Kunststoffs charakteristischen Parameters, insbesondere eines Kompressionsmoduls oder einer Kompressibilität,
• - Kameraabbildung des zu plastifizierenden Kunststoffs, insbesondere Kunststoffgranulats.

Information about the plastic can be obtained from at least one of the following sources and used to identify the plastic group and preferably the plastic:

• - The method according to the first embodiment of the invention, determining a heat capacity of the plastic and / or a change in enthalpy of the plastic and / or a variable that can be calculated from the heat capacity and / or the change in enthalpy,
• - Method according to the second aspect of the invention with the measurement of the infrared radiation emitted by the plastic,
• - Machine settings and / or measured values and / or machine configuration, in particular injection pressures (or variables derived therefrom such as viscosities or flow numbers), maximum and / or minimum processing temperatures, mass cylinder temperatures at the top or over the entire course of the plasticizing cylinder, granulate temperatures, cooling liquid temperatures, a density of Melt, information about a used molding tool,
• - Method for determining a parameter characteristic of a compression behavior of the plastic, in particular a compression module or a compressibility,
• - Camera image of the plastic to be plasticized, in particular plastic granulate.

Parameters characteristic of the compression behavior of a plastic, such as the compression modulus or the compressibility, can, for example, according to one of the DE102016005780 A1 disclosed method can be determined. The determination of amounts of a filler via a determination of the compressibility is in the DE102007030637A1 disclosed.

Regarding machine settings and / or measured values and / or machine configuration: For example, certain plastic groups have very special minimum or maximum processing temperatures. If such special processing temperatures occur, the plastic group or plastic can already be determined or at least restricted. Data from other components or external devices can be used to identify the plastic or the Plastic group can also be used. Relevant data can arise, for example, in dryers, material conveyors and / or storage. Each plastic group has a certain characteristic with regard to all of the above parameters. Together with the invention according to the first characteristic (determination of a heat capacity of the plastic and / or a change in enthalpy of the plastic and / or a variable that can be calculated from the heat capacity and / or the change in enthalpy) and / or the second characteristic (metrological detection of the amount emitted by the plastic Infrared radiation) and / or a parameter characteristic of a compression behavior of the plastic, the existing plastic group can be determined according to an exclusion process and in many cases the plastic including the load (fillers) can be identified.

To create the camera image of the plastic to be plasticized, in particular plastic granulate, a camera arranged in or on a funnel of a plasticizing unit can be provided in order, for example, to recognize the granulate shape of the plastic granulate.

The granulate form (or other form, such as powder) can be determined - preferably automatically - by means of image recognition software. For example, rod granules (long glass fibers) can be differentiated from conventional granules (e.g. cylindrical cold cut, as is typically the case with engineering plastics, or, for example, round or lenticular granules that result from underwater granulation, typically with polyolefins) or powder (e.g. PVC dry blend).

To carry out method steps for acquiring and / or calculating parameters and identifying the plastic or the plastic group containing the plastic, the plasticizing unit and / or the shaping machine can contain an evaluation device.

• - Hinweise in Bezug auf verbesserte Maschineneinstellungen und/oder verbesserte Maschinenkonfigurationen - vorzugsweise nach vorheriger automatischer Identifizierung einer vorliegender Maschineneinstellungen und/oder verbauter und/oder verwendeter Komponenten - auszugeben und/oder
• - Maschineneinstellungen automatisch zu verändern und/oder
• - Warnungen und/oder Hinweise in Bezug auf eintretende und/oder zu erwartende unzulässige Betriebszustände auszugeben und/oder
• - bei unzulässigen Betriebszuständen Abschaltsignale zum automatischen Abschalten auszugeben.

The evaluation device can be designed to initiate specific steps based on the identified plastic group, for example:

• - to output and / or notices relating to improved machine settings and / or improved machine configurations - preferably after prior automatic identification of an existing machine setting and / or installed and / or used components
• - to change machine settings automatically and / or
• - to issue warnings and / or notices regarding occurring and / or expected impermissible operating states and / or
• - output shutdown signals for automatic shutdown in impermissible operating states.

The evaluation unit can be integrated into a central machine control of the molding machine. Alternatively, the evaluation unit can be arranged remotely from the molding machine and / or the plasticizing unit and connected to it, for example, via a remote data transmission connection (keyword: cloud computing).

The method according to the invention can be carried out both in the context of a reference cycle and during production. If the plastic group is known before the start of production, the correct automatic setting of the molding process can be ensured. However, the method according to the invention can also be used advantageously during operation, for example to check that the processing material (the plastic) has not changed.

The reference cycle can be carried out with a certain plastic to be identified before the start of production. For this purpose, special settings can also be made on the machine in order to be able to carry out the measurements under conditions defined in relation to certain aspects.

• 1 Enthalpie-Temperatur-Kurven für verschiedene Kunststoffe,
• 2 eine Darstellung eines Plastifizieraggregats mit einer Verdeutlichung einer erfindungsgemäßen Leistungsbilanz,
• 3 einen Abgleich der Enthalpie-Temperatur-Kurven mit einer bestimmten Wärmekapazität,
• 4 zwei Diagramme zum Verdeutlichen des Plastifizierens / Aufdosierens sowie
• 5 ein Beispiel für eine bekannte Temperaturabhängigkeit des spezifischen Volumens für einen bestimmten Kunststoff.

Further advantages and details of the invention emerge from the figures and the associated description of the figures. Show:

• 1 Enthalpy-temperature curves for various plastics,
• 2 a representation of a plasticizing unit with an illustration of a power balance according to the invention,
• 3 a comparison of the enthalpy-temperature curves with a certain heat capacity,
• 4th two diagrams to clarify the plasticizing / dosing and
• 5 an example of a known temperature dependence of the specific volume for a certain plastic.

With a given configuration of a plasticizing unit, on the one hand the service life of the installed components should be optimized and on the other hand the processing parameters should be autonomously adapted or recommended with regard to the requirements of the plastic to be processed.

In order to be able to use optimization algorithms, knowledge of the plastics / groups of plastics that are being processed is essential or at least of considerable benefit.

Another benefit of the invention according to the first embodiment lies in the calculation of a collective load: characteristic values can be calculated which provide information about the intended use. These values could also be used as a calculation basis for a leasing business model.

The enthalpy (H) diagram in, known from literature, serves as the basis for the determination 1 as well as the power balance of the plasticizing unit system ( 2 ).

The diagram out 1 describes the energy content / the performance of the respective plastic as a function of the melt temperature T (temperature of the plastic). The following applies: H = f (T) based on one kilogram of plastic; the unit is J / g. Furthermore, the specific volume v with the unit cm ³ / g has a physically known relationship with the melt temperature T in ° C. and pressure p nach 5 .

If one divides the values of the functions H point by point with the values of the specific volume v at the same temperature under the condition of a constant pressure, this results in a function H (p _x ) = f (T) with the unit J / cm ³ . This feature is in 3 shown.

This functional relationship is processed in terms of data for selected plastic groups and is available to the control of the machine.

When the injection molding process increases the dosage, the plasticizing screw 4th rotated at a speed n. The torque M from the drive 3 provided. At the same time, the screw is withdrawn, creating a cushion of melt in the antechamber. The retraction speed is regulated in such a way that the pressure in the screw antechamber p _x remains constant (see 4th ).
The power mechanically introduced into the plasticizing process is proportional to the product of the torque M and the speed n. This can be determined on the injection molding machine by evaluating the electrical or hydraulic drive parameters.

In relation to 2 It should also be mentioned that, for example, the following variables occurring during the plasticizing process can be set externally: pressure p _x (dynamic pressure), temperature profile (specified for control or regulation of the heating devices), moisture on the funnel 6th , Additives in the plastic (ie for example in the plastic granulate), temperature of the material, temperature in the hopper, speed of the screw. The other variables (e.g. torque, stroke, mass flow) are then set during the plasticizing process.

In 4th is a plasticizing unit 1 shown once in the state during injection (top) and once in the state during or after dosing (bottom). Via a funnel 6th For example, granulate becomes a plasticizing cylinder 5 fed and by means of the plasticizing screw 4th plasticized. On the plasticizing cylinder 5 is a heating device 2 provided by means of which the plasticizing cylinder 5 is heated in zones. Additional temperature sensors (not shown) can also be provided for zone-wise regulation of the heating power. For the arrangement of the drive 3 the plasticizing screw 4th be up 2 referenced. At the funnel 6th are a hopper temperature sensor 7th and a near infrared sensor 8th intended.

The heating power Q is also included in the power balance. The proportion of heating power is also determined and added to the mechanical power input. In order to be able to determine the increase in enthalpy, the power introduced is reduced by the pressure build-up power. This is calculated from the product of the volume flow V determined over the stroke and the pressure px, which is kept constant over the screw stroke. The power input into the plastic determined in this way can now be compared with the families of curves available in the control. If the mass temperature T is known from a measurement on the machine, an intersection of the energy content with the mass temperature can be in 2 which is also brought into agreement with a curve from the data set. This curve is assigned to a plastic or a plastic group. This is the prerequisite for a plastic-specific mode of operation or monitoring.

1. 1. Der gesuchte Kunststoff enthält neben 30% Glasfasern noch „Carbon-Black“ als schwarzen Farbstoff. Die Bestimmung der chemischen Struktur des Kunststoffes mittels eines NIR-Sensors ist nicht eindeutig, da die Füllstoffe (insbesondere Graphit) die Strahlung im Nahinfrarot-Bereich absorbieren und der Kunststoff dadurch für diese Charakterisierungsmethode unsichtbar wird. Durch weitere Prozessgrößen wie die Verarbeitungs- oder Trocknungstemperatur können manche Kunststoffe ausgeschlossen werden. Gängige Kunststoffe wie Polyolefine (Polyethylen, Polypropylen) werden nicht vorgetrocknet und bei unter 260°C verarbeitet. Andere Kunststoffe wie Polyamide werden bei mindestens 80°C vorgetrocknet und bei über 260°C verarbeitet. Mit Charakterisierungsmethoden wie der Energieaufnahme (Enthalpie) oder dem Kompressionsvermögen (K-Modul) kann aus Kalibrierkurven auf einen bestimmten Füllstoffgehalt geschlossen oder die Kunststoffgruppe weiter eingeschränkt werden.
2. 2. Der gesuchte Kunststoff enthält einen spezifischen Aufbau der Molekülketten, wie z.B. bei PA6 oder PA66. Bei PA 66 liegen sich die Carbonamidgruppen immer so gegenüber, dass jede funktionelle Gruppe ohne Deformation der Moleküle eine Wasserstoffbrücke bilden kann. Bei PA6 ist dies nur bei jeder zweiten Carbonamidgruppe möglich. Der höhere Schmelzpunkt von PA 66 und die geringere Wasseraufnahme sind auf den unterschiedlichen Molekülaufbau zurückzuführen. Mittels eines konventionellen NIR-Sensors, der auf einzelne Wellenlängen kalibriert ist, ist die Unterscheidung zwischen PA6 und PA66 nicht eindeutig und es muss entweder auf ein NIR-Spektrometer oder eine andere Charakterisierungsmethode zurückgegriffen werden. Die Auswertung von Prozessdaten wie der Verarbeitungstemperatur und der Energieaufnahme in Abhängigkeit der Temperatur auf Basis von Kalibrierkurven kann hier zur Unterscheidung genutzt werden.
3. 3. Der gesuchte Kunststoff weist einen bekannten chemischen Aufbau und eine spezifische Dichte auf, wie z.B. PE-HD (high density) und PE-LD (low density). Die Grundstruktur kann mittels eines NIR-Sensors erkannt werden. Die Auswertung von Prozessdaten, wie der Verarbeitungstemperatur und der Energieaufnahme, in Abhängigkeit der Temperatur auf Basis von Kalibrierkurven sowie Charakterisierungsmethoden wie die Bestimmung des Kompressionsmoduls können hier ergänzend verwendet werden.
4. 4. Der gesuchte Kunststoff weist einen bekannten chemischen Aufbau und eine spezifische Viskosität auf, wie z.B. ein Polypropylen mit einer Schmelze-Massefließrate MFR = 5 g/10 min und ein anderes Polypropylen mit 50 g/10 min (gemessen nach DIN EN ISO 1133 ). Die Grundstruktur kann mittels eines NIR-Sensors erkannt werden. Für die genauere Bestimmung der Viskositätsunterschiede können Charakterisierungsmethoden wie die Fließzahl, die aus dem Einspritzdruckverlauf ermittelt wird, verwendet werden. Des Weiteren kann aus dem Verhältnis der Energieaufnahme durch Dissipation (Leistungsbedarf des Dosierantriebs) und der Energieaufnahme durch Wärmeleitung (Leistungsbedarf der externen Heizung/Kühlung) auf eine Kunststoffgruppe in einem spezifischen Viskositätsbereich geschlossen werden.

With regard to the third embodiment of the invention, four further exemplary embodiments are specified below. In general, the plastics or groups of plastics are identified within the scope of the invention via a logical combination of the chemical and physical properties known per se.

1. 1. In addition to 30% glass fibers, the plastic we are looking for also contains “carbon black” as a black dye. The determination of the chemical structure of the plastic by means of an NIR sensor is ambiguous because the fillers (especially graphite) absorb the radiation in the near-infrared range and the plastic is therefore invisible for this characterization method. Through other process variables such as Processing or drying temperature can be excluded for some plastics. Common plastics such as polyolefins (polyethylene, polypropylene) are not pre-dried and are processed at temperatures below 260 ° C. Other plastics such as polyamides are pre-dried at at least 80 ° C and processed at over 260 ° C. With characterization methods such as energy absorption (enthalpy) or compressibility (K-module), calibration curves can be used to infer a specific filler content or to further restrict the plastic group.
2. 2. The plastic you are looking for contains a specific structure of the molecular chains, such as PA6 or PA66. In PA 66, the carbonamide groups are always opposite each other in such a way that each functional group can form a hydrogen bond without deforming the molecules. With PA6, this is only possible for every second carbonamide group. The higher melting point of PA 66 and the lower water absorption are due to the different molecular structures. Using a conventional NIR sensor that is calibrated to individual wavelengths, the distinction between PA6 and PA66 is not clear and either a NIR spectrometer or another characterization method must be used. The evaluation of process data such as the processing temperature and the energy consumption depending on the temperature on the basis of calibration curves can be used here to differentiate.
3. 3. The plastic we are looking for has a known chemical structure and a specific density, such as PE-HD (high density) and PE-LD (low density). The basic structure can be recognized by means of an NIR sensor. The evaluation of process data, such as the processing temperature and the energy consumption, depending on the temperature on the basis of calibration curves as well as characterization methods such as the determination of the compression modulus can be used here in addition.
4. 4. The plastic we are looking for has a known chemical structure and a specific viscosity, such as a polypropylene with a melt mass flow rate MFR = 5 g / 10 min and another polypropylene with 50 g / 10 min (measured according to DIN EN ISO 1133 ). The basic structure can be recognized by means of an NIR sensor. Characterization methods such as the flow number, which is determined from the injection pressure curve, can be used for a more precise determination of the viscosity differences. Furthermore, from the ratio of the energy consumption through dissipation (power requirement of the metering drive) and the energy consumption through heat conduction (power requirement of the external heating / cooling), conclusions can be drawn about a plastic group in a specific viscosity range.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102016005780 A1 [0048]
• DE 102007030637 A1 [0048]

Non-patent literature cited

• DIN EN ISO 1133 [0069]

Claims (29)

Method for classifying a plastic, wherein a) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing the temperature of the plastic from an initial temperature value to a final temperature value, b) a volume and / or a mass of the plastic as well as the supplied plasticizing energy are recorded as measured variables by measurement, c) at least one of the following is determined as a function of the recorded measured variables, the initial temperature value and the final temperature value: a heat capacity of the plastic and / or a change in enthalpy of the plastic and / or a variable that can be mathematically derived from the heat capacity and / or the change in enthalpy, and d) a plastic group containing the plastic is identified on the basis of the determined heat capacity and / or the determined enthalpy change and / or the variable that can be calculated therefrom. Procedure according to Claim 1 , characterized in that an energy balance and / or a power balance for the plastic is drawn up on the basis of the measured variables and the specific heat capacity, the specific enthalpy change and / or the mathematically derived variable is determined as a function of the energy balance and / or the power balance. Procedure according to Claim 2 , characterized in that at least one of the following is determined on the basis of the energy balance and / or the power balance: load spectrum, state of wear, operating state. Procedure according to Claim 2 or 3 , characterized in that supplied and / or discharged thermal energy and / or thermal power and / or a course of the supplied thermal energy and / or thermal power is determined and taken into account in the energy balance and / or power balance. Method according to one of the preceding claims, characterized in that a specific heat capacity at constant pressure is determined as the heat capacity and the plastic group containing the plastic is identified on the basis of the specific heat capacity at constant pressure. Method according to one of the preceding claims, characterized in that the starting temperature value and / or the end temperature value and / or a temperature profile of the plastic is measured directly and / or indirectly by means of at least one temperature sensor, preferably temperature control of the plastic with the supplied mechanical energy and / or the supplied thermal energy is carried out as a manipulated variable and measured values from the at least one temperature sensor are carried out as actual values. Method according to one of the preceding claims, characterized in that the plastic is plasticized at an essentially constant pressure, the pressure preferably being regulated with a constant setpoint value using measured values of at least one pressure sensor. Method according to one of the preceding claims, characterized in that the thermal energy is supplied by means of a - preferably electrical - heating device (2). Method according to one of the preceding claims, characterized in that at least one drive sensor is used, by means of which the mechanical energy supplied via at least one drive (3) and / or a mechanical power provided by the at least one drive and / or a course of the supplied mechanical energy and / or the performed mechanical power is measured. Method according to one of the preceding claims, characterized in that a plasticizing screw (4) and / or a plasticizing piston is used to supply the mechanical energy. Procedure according to the Claims 9 and 10 , characterized in that a plasticizing cylinder (5), in which the plasticizing screw (4) is arranged, is used and that the plasticizing screw (4) is rotated and axially moved for plasticizing the plastic by means of the at least one drive in the plasticizing cylinder (5). Procedure according to Claim 11 , characterized in that a torque exerted on the plasticizing screw (4) and / or a speed of the plasticizing screw (4) is measured in order to detect the supplied mechanical energy. Procedure according to Claim 6 and Claim 11 or 12 , characterized in that the pressure of the plastic is regulated as a manipulated variable by means of a force exerted on the plastic by the plasticizing screw (4). Method according to one of the Claims 10 to 13 , characterized in that a screw position sensor is used, by means of which the Volume of the plasticized plastic in the plasticizing cylinder (5) is recorded. Procedure according to Claim 5 and one of the Claims 11 to 14th , characterized in that a funnel (6) is used to feed the plastic to be plasticized into the plasticizing cylinder (5), a funnel temperature sensor (7) preferably being used in and / or on the funnel (6). Procedure according to Claim 6 and Claim 8 and one of the Claims 11 to 15th , characterized in that several cylinder temperature sensors are used which are assigned to axially distributed heating zones on the plasticizing cylinder, the heating zones being heated independently of one another, the heating in the heating zones being controlled using measured values from the cylinder temperature sensors assigned to the heating zones. Procedure according to Claim 16 , characterized in that to determine the final temperature value, the regulation of a specific heating zone - in particular the last one in the sense of conveying the plastic - is temporarily switched off and a measured value from the temperature sensor assigned to the specific heating zone is used as the final temperature value. Method according to one of the preceding claims, characterized in that, to identify the plastic group containing the plastic, enthalpy-temperature curves for a large number of plastics are corrected by means of correlations known for these plastics between the temperature on the one hand and the specific volume and / or density on the other - the multiple values for the heat capacity of the plastic and / or the enthalpy change of the plastic and / or the variable that can be mathematically derived from the heat capacity and / or the enthalpy change with the corrected enthalpy-temperature curves - in particular with slopes of the corrected enthalpy temperature -Curves - are compared and - on the basis of the comparison, the plastic group containing the plastic is identified. Method according to one of the preceding claims, characterized in that the method is carried out several times, with preferably a pressure and / or an applied mechanical power - being varied. Method for classifying a plastic, wherein b) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing a temperature of the plastic from an initial temperature value to a final temperature value, h) an infrared radiation emitted by the plastic is measured and i) a plastic group containing the plastic is identified on the basis of the detected infrared radiation. Procedure according to Claim 20 , characterized in that a near-infrared sensor (8) is used to detect the infrared radiation. Method for classifying a plastic, wherein b) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and / or thermal energy while increasing a temperature of the plastic from an initial temperature value to a final temperature value, and j) identification information about the plastic is obtained from at least two different sources, at least one of the at least two different sources being a measurement on the device used to plasticize the plastic, and that based on the identification information, a plastic group containing the plastic is identified, and preferably the Plastic is identified. Procedure according to Claim 22 , characterized in that information about the plastic is obtained from at least one of the following and used to identify the plastic group and preferably the plastic: - Method according to one of the Claims 1 to 19th - Procedure according to one of the Claims 20 or 21st - Machine settings and / or measured values and / or machine configuration, in particular injection pressures (or variables derived therefrom such as viscosities or flow numbers), maximum and / or minimum processing temperatures, mass cylinder temperatures at the top or over the entire course of the plasticizing cylinder, granulate temperatures, coolant temperatures, a density the melt, information about a used molding tool, method for determining a parameter characteristic of a compression behavior of the plastic, in particular a compression module or compressibility, camera imaging of the plastic to be plasticized, in particular plastic granulate. Molding process, the plastic plasticized and classified by a process according to one of the preceding claims, in particular in the context of an injection molding process, being used. Plasticizing unit, which is used to carry out a method according to one of the Claims 1 to 23 is set up. Plasticizing unit after Claim 25 , characterized in that the plasticizing unit is designed to, on the basis of the identified plastic or identified plastic group - indications regarding improved machine settings and / or improved machine configurations - preferably after prior automatic identification of an existing machine setting and / or installed and / or used components - and / or - to automatically change machine settings and / or - to issue warnings and / or notices in relation to occurring and / or expected impermissible operating conditions and / or - to output shutdown signals for automatic shutdown in impermissible operating conditions. Shaping machine, in particular set up to carry out a method according to Claim 24 , with a plasticizing unit Claim 25 or 26th . Forming machine according to Claim 27 , characterized in that the evaluation unit is integrated into a central machine control of the molding machine. Forming machine according to Claim 27 or 28 , which for performing the molding process according to Claim 24 is set up, characterized in that the shaping machine is designed to perform a method according to one of the Claims 1 to 23 to be carried out as part of a reference cycle and / or during production.

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