METHOD OF CLASSIFYING A PLASTIC

Abstract

A method of classifying a plastic, wherein the plastic is plasticized by supplying plasticizing energy in the form of mechanical and/or thermal energy with an increase in a temperature of the plastic from an initial temperature value to a final temperature value, a volume and/or a mass of the plastic and the supplied plasticizing energy is detected as measurement parameters by measurement means, in dependence on the detected measurement parameters, the initial temperature value, and the final temperature value at least one of the following is ascertained: a thermal capacity of the plastic and/or a change in enthalpy of the plastic and/or a parameter which can be derived by calculation from the thermal capacity and/or the change in enthalpy, and a plastic group including the plastic is identified on the basis of the ascertained thermal capacity and/or the ascertained change in enthalpy and/or the parameter which can be derived therefrom by calculation.

Claims

1. A method of classifying a plastic, wherein a) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and/or thermal energy with an increase in a temperature of the plastic from an initial temperature value to a final temperature value, b) a volume and/or a mass of the plastic and the supplied plasticizing energy is detected as measurement parameters by measurement means, c) in dependence on the detected measurement parameters, the initial temperature value, and the final temperature value at least one of the following is ascertained: a thermal capacity of the plastic and/or a change in enthalpy of the plastic and/or a parameter which can be derived by calculation from the thermal capacity and/or the change in enthalpy, and d) a plastic group including the plastic is identified on the basis of the ascertained thermal capacity and/or the ascertained change in enthalpy and/or the parameter which can be derived therefrom by calculation.

2. The method according to claim 1, wherein an energy balance and/or a power balance for the plastic is set up on the basis of the detected measurement parameters and the thermal capacity, the change in enthalpy and/or the parameter which can be derived therefrom by calculation is determined in dependence on the energy balance and/or the power balance.

3. The method according to claim 2, wherein at least one of the following is ascertained on the basis of the energy balance and/or the power balance: load spectrum, wear state, operating state.

4. The method according to claim 2, wherein supplied and/or discharged thermal energy and/or thermal power and/or a progression in the supplied thermal energy and/or thermal power is ascertained and is taken into account for the energy balance and/or power balance.

5. The method according to claim 1, wherein a specific thermal capacity at a constant pressure is determined as the thermal capacity and the plastic group including the plastic is identified on the basis of the specific thermal capacity at a constant pressure.

6. The method according to claim 1, wherein the initial temperature value and/or the final temperature value and/or a temperature progression of the plastic is measured by means of at least one temperature sensor directly and/or indirectly, wherein preferably closed-loop temperature control of the plastic is performed with the supplied mechanical energy and/or the supplied thermal energy as a setting parameter and measurement values of the at least one temperature sensor as actual values.

7. The method according to claim 1, wherein the plastic is plasticized at a substantially constant pressure, wherein the pressure is preferably closed-loop controlled with a constant target value using measurement values of at least one pressure sensor.

8. The method according to claim 1, wherein the thermal energy is supplied by means of a—preferably electrical—heating apparatus.

9. The method according to claim 1, wherein at least one drive sensor is used by means of which the mechanical energy supplied by way of at least one drive and/or a mechanical power delivered by the at least one drive and/or a progression in the supplied mechanical energy and/or the delivered mechanical power is measured.

10. The method according to claim 1, wherein a plasticizing screw and/or a plasticizing piston is used for supplying the mechanical energy.

11. The method according to claim 9, wherein a plasticizing cylinder in which the plasticizing screw is arranged is used and that the plasticizing screw for plasticizing the plastic is moved rotationally and axially by means of the at least one drive in the plasticizing cylinder.

12. The method according to claim 11, wherein a torque exerted on the plasticizing screw and/or a rotary speed of the plasticizing screw is measured for detecting the supplied mechanical energy.

13. The method according to claim 6, wherein the pressure of the plastic is closed-loop controlled as a setting parameter by means of a force exerted on the plastic by the plasticizing screw.

14. The method according to claim 10, wherein a screw position sensor is used by means of which the volume of the plastic plasticized in the plasticizing cylinder is detected.

15. The method according to claim 5, wherein a hopper is used for feeding the plastic to be plasticized into the plasticizing cylinder, wherein preferably a hopper temperature sensor is used in and/or at the hopper.

16. The method according to claim 6, wherein a plurality of cylinder temperature sensors are used that are associated with heating zones axially distributed on the plasticizing cylinder with the heating zones being heated independently of each other, wherein heating in the heating zones is closed-loop controlled respectively using measurement values of the cylinder temperature sensors associated with the heating zones.

17. The method according to claim 16, wherein in order to ascertain the final temperature value, the closed-loop control of a given heating zone—in particular the last one in the direction of conveying movement of the plastic—is shut down and a measurement value of the temperature sensor associated with the given heating zone is used as the final temperature value.

18. The method according to claim 1, wherein to identify the plastic group including the plastic: enthalpy temperature curves for a plurality of plastics are corrected by means of relationships known for said plastics between the temperature on the one hand and the specific volume and/or the density on the other hand, the plurality of values for the thermal capacity of the plastic and/or the change in enthalpy of the plastic and/or the parameter which can be derived by calculation from the thermal capacity and/or the change in enthalpy are matched to the corrected enthalpy temperature curves—in particular gradients of the corrected enthalpy temperature curves —, and the plastic group containing the plastic is identified on the basis of the matching.

19. The method according to claim 1, wherein the method is carried out several times with preferably a pressure and/or a supplied mechanical power being varied.

20. A method of classifying a plastic, wherein b) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and/or thermal energy with an increase in a temperature of the plastic from an initial temperature value to a final temperature value, h) an infrared radiation emitted by the plastic is detected by measurement means, and i) a plastic group containing the plastic is identified on the basis of the detected infrared radiation.

21. The method according to claim 20, wherein a near infrared sensor is used for detecting the infrared radiation.

22. A method of classifying a plastic, wherein b) the plastic is plasticized by supplying plasticizing energy in the form of mechanical and/or thermal energy with an increase in 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, wherein at least one of the at least two different sources is measurement at an apparatus used for plasticizing the plastic and that on the basis of the identification information a plastic group containing the plastic is identified and preferably the plastic is identified.

23. The method according to claim 22, wherein information about the plastic is obtained from at least one of the following values and used for identifying the plastic group and preferably the plastic: detected infrared radiation or identification information about the plastic, machine settings and/or measurement values and/or a machine configuration, in particular injection pressures (or parameters derived therefrom like viscosity or flow rates), maximum and/or minimum processing temperatures, mass cylinder temperatures at the tip or over the entire length of the plasticizing cylinder, granulate temperatures, cooling fluid temperatures, a density of the melt and information about a mold tool used, methods of determining a parameter characteristic of a compression behavior of the plastic, in particular a compression module or a compressibility, and camera imaging of the plastic to be plasticized, in particular plastic granulate.

24. A shaping method, wherein the plastic which is plasticized and classified with the method according to claim 1, is used in particular during an injection molding method.

25. A plasticizing assembly adapted to carry out the method according to claim 1.

26. The plasticizing assembly according to claim 25, wherein the plasticizing assembly is adapted on the basis of the identified plastic or identified plastic group: to output indications in relation to improved machine settings and/or improved machine configurations—preferably after previous automatic identification of a current machine setting and/or installed and/or used components —, and/or to automatically alter machine settings, and/or to output warnings and/or indications in relation to inadmissible operating states occurring and/or to be expected, and/or upon inadmissible operating states to output shut-down signals for automatic shut-down.

27. A shaping machine, in particular for carrying out the method according to claim 24, comprising a plasticizing assembly.

28. The shaping machine according to claim 27, wherein the evaluation unit is integrated in a central machine control system of the shaping machine.

29. The shaping machine according to claim 27 for carrying out a shaping method, wherein the shaping machine is adapted to carry out the shaping method in the course of a reference cycle and/or during production.

Description

[0084] Further advantages and details of the invention will be apparent from the Figures and the related specific description. In the Figures:

[0085] FIG. 1 shows enthalpy temperature curves for different plastics,

[0086] FIG. 2 shows a view of a plasticizing assembly with an illustration of a power balance according to the invention,

[0087] FIG. 3 shows a comparison of the enthalpy temperature curves with a given thermal capacity,

[0088] FIG. 4 shows two diagrams to illustrate the plasticizing/metering operation, and

[0089] FIG. 5 shows an example of a known temperature dependency of the specific volume for a given plastic.

[0090] With a given configuration of a plasticizing assembly, on the one hand, the service life of the installed components is to be optimized while, on the other hand, the processing parameters are to be autonomously adapted in regard to the requirements concerning the plastic to be processed or they are to be recommended.

[0091] In order to use optimization algorithms, knowledge of the plastics/plastic groups being processed is absolutely required or at least of substantial use.

[0092] A further benefit of the invention according to the first implementation lies in the calculation of a load spectrum: It is possible to calculate characteristic values which provide information about the appropriate use. Those values can also be used as a calculation basis for a leasing business model.

[0093] The enthalpy (H) diagram in FIG. 1 known from the literature and the power balance of the system of the plasticizing unit (FIG. 2) serve as the basis for the ascertainment procedure.

[0094] The diagram in FIG. 1 describes the energy content/the delivered power of the respective plastic in dependence on the mass temperature T (temperature of the plastic). H=f(T) applies in relation to a kilogram of plastic, the unit is J/g. In addition, the specific volume v with the unit cm.sup.3/g has a physically known relationship to the mass temperature T in ° C. and pressure p as shown in FIG. 5.

[0095] If the values of the functions H are divided point-wise by the values of the specific volume v at the same temperature with the proviso of a constant pressure, then that relationship gives a function H(p.sub.x)=f(T) with the unit J/cm.sup.3. That function is shown in FIG. 3.

[0096] That functional relationship is prepared for selected plastic groups using data technology and is available for controlling the machine.

[0097] In the metering operation in an injection molding process the plasticizing screw 4 is rotated at a speed n. In that situation the torque M is provided by the drive 3. At the same time, the screw is withdrawn, thereby setting a melt cushion in the screw pre-chamber. The withdrawal speed in that case is closed-loop controlled in such way that the pressure in the screw pre-chamber p.sub.x remains constant (see FIG. 4).

[0098] The power introduced mechanically into the plasticizing process is proportional to the product of the torque M and the rotary speed n. That can be ascertained on the injection molding machine by virtue of evaluation of the electrical or hydraulic drive parameters.

[0099] In relation to FIG. 2 it should also be mentioned that, for example, the following parameters which occur in the plasticizing operation can be set from the exterior: pressure p.sub.x (dynamic pressure), temperature profile (predetermined for open-loop or closed-loop control of the heating apparatuses), moisture content at the hopper 6, additives in the plastic (that is to say, for example, in the plastic granulate), temperature of the material, temperature in the hopper, rotary speed of the screw. The remaining parameters (for example, torque, stroke, mass flow) are then set during the plasticizing operation.

[0100] FIG. 4 shows a plasticizing assembly 1, namely in the state during injection (above) and in the state during or after the metering operation (below). Granulate, for example, is fed to the plasticizing cylinder 5 by way of a hopper 6 and plasticized by means of the plasticizing screw 4. Provided on the plasticizing cylinder 5 is a heating apparatus 2, by means of which the plasticizing cylinder 5 is heated zone-wise. Additional temperature sensors can also be provided (not shown) for zone-wise closed-loop control of the heating power. In regard to the arrangement of the drive 3 of the plasticizing screw 4, reference is to be made to FIG. 2. A hopper temperature sensor 7 and a near infrared sensor 8 are provided on the hopper 6.

[0101] In addition, the heating power Q is taken into account in the power balance of FIG. 2. The proportion of the heating power is also ascertained and added to the mechanical power input. In order to be able to ascertain the increase in enthalpy, the power introduced is reduced by the pressure build-up power. That is calculated from the product of the volume flow V ascertained in relation to the stroke movement and the pressure px which is kept constant over the screw stroke movement. The power input into the plastic, ascertained in that way, can now be compared to the curve families available in the control system. Now, if the mass temperature T is known from a measurement on the machine, it is possible to calculate an intersection of the energy content with the mass temperature in FIG. 3, said intersection is also brought into conformity with a curve from the data set. That curve is assigned to a plastic or a plastic group. Therefore, the requirements for a plastic-specific mode of operation or monitoring are provided.

[0102] In relation to the third implementation of the invention four embodiments by way of example are also set forth hereinafter. It is generally the case that the plastics or plastic groups are identified in accordance with the invention by way of a logical combination of the per se known chemical and physical properties. [0103] 1. Besides 30% glass fibers the plastic sought, also contains ‘carbon black’ as a black coloring agent. Determining the chemical structure of the plastic by means of an NIR sensor is not unambiguous, as the fillers (in particular graphite) absorb the radiation in the near infrared range and the plastic thereby becomes invisible for that characterization method. Some plastics can be excluded by virtue of further process parameters like the processing or drying temperature. Common plastics like polyolefins (polyethylene, polypropylene) are not pre-dried and are processed at below 260° C. Other plastics like polyamides are pre-dried at at least 80° C. and processed at over 260° C. With characterization methods like energy absorption (enthalpy) or compression capability (bulk modulus) it is possible to deduce a given filler content from calibration curves or the plastic group can be further restricted. [0104] 2. The plastic being sought contains a specific structure of the molecular chains like, for example, with PA6 or PA66. With PA66 the carbonamide groups are always opposite each other in such way that each functional group can form a hydrogen bridge without deformation of the molecules. With PA6, however, that is possible only at every second carbonamide group. The higher melting point of PA66 and the lower degree of water absorption can be explained by the different molecular structure. By means of a conventional NIR sensor which is calibrated to individual wavelengths the distinction between PA6 and PA66 is not unambiguous and it is necessary to revert either to an NIR spectrometer or another characterization method. Evaluation of process data like the processing temperature and energy absorption in dependence on temperature on the basis of calibration curves can be used here for distinction purposes. [0105] 3. The plastic being sought has a known chemical structure and a specific density like, for example, PE-HD (high density) and PE-LD (low density). The basic structure can be recognized by means of an NIR sensor. Evaluation of process data like the processing temperature and the energy absorption in dependence on temperature on the basis of calibration curves as well as characterization methods like determining the compression modulus can be used here in addition. [0106] 4. The plastic being sought has a known chemical structure and a specific viscosity, like for example, a polypropylene with a melt mass flow rate MFR=5 g/10 min and a different polypropylene with 50 g/10 min (measured in accordance with DIN EN ISO 1133). The basic structure can be recognized by means of an NIR sensor. For determining the viscosity differences more precisely it is possible to use characterization methods like the flow number which is ascertained from the injection pressure progression. In addition, it is possible to deduce a plastic group in a specific viscosity range from the ratio of energy absorption by dissipation (power requirement of the metering drive) and energy absorption by thermal conduction (power requirement of external heating/cooling).