Method and apparatus for forming plastic preforms for plastic containers with curve evaluation

Abstract

Method for forming plastic preforms into plastic containers, wherein a plastic preform is introduced into a blow mould and is expanded into a plastic container by being applied by a flowable medium, wherein the plastic preform is applied by at least two different pressure levels and wherein furthermore preferably a rod-like body is introduced into the plastic preform, in order to expand the plastic preform in its longitudinal direction, wherein a pressure curve and/or a movement curve of the rod-like body being determined by a measuring device during the expansion process, wherein least one of the curves is evaluated by means of a processor device and at least one point or region of this curve which is characteristic of the course is determined.

Claims

1. A method for forming plastic preforms into plastic containers, wherein a plastic pre-form is introduced into a blow mould and is expanded into a plastic container by being applied with a flowable medium, wherein the plastic preform is applied by at least two different pressure levels and wherein furthermore a rod-like body is introduced into the plastic preform, in order to expand the plastic preform in its longitudinal direction, wherein a pressure curve and/or a movement curve of the rod-like body and/or a force curve of the rod-like body being determined by at least one measuring device during the expansion process, wherein at least one of the curves is evaluated by a processor device and at least one point or region of this curve which is characteristic of the curve is determined.

2. The method according to claim 1, wherein said characteristic point or region is selected from a group of points or regions containing extremes or extreme regions of the pressure curve or movement curve, turning points or turning point regions of the pressure curve or movement curve and the like.

3. The method according to claim 1, wherein the plastic preform is transported along a predetermined transport path during its expansion.

4. The method according to claim 1, wherein the curve is recorded as a function of time and/or as a function of a position of the plastic preform.

5. The method according to claim 1, wherein at least two characteristic points of the course are determined.

6. The method according to claim 1, wherein the course curve is evaluated by a curve discussion method.

7. The method according to claim 1, wherein a plurality of plastic preforms are formed into the plastic containers by a plurality of forming stations and at least one characteristic point is determined for each of these forming stations.

8. The method according to claim 1, wherein n-tuples are formed from several characteristic points and these n-tuples are stored in a storage device and/or a cloud.

9. The method according to claim 1, wherein the pressurisation of the containers is controlled by at least one controllable valve device and this valve device is controlled taking into account the determined points and/or areas.

10. The method according to claim 1, wherein data are linked to each process point and/or process area, which in particular allow conclusions to be drawn about the relevant forming station or also conclusions to be drawn about correspondingly used blowing parameters.

11. The method according to claim 10, wherein characterising data are selected from a group of data consisting of a validity of the point, a time, a pressure at said process point, a position of the stretching bar at said process point, a force of a driving device of a stretching bar at said process point and/or a delay time.

12. An apparatus for forming plastic preforms into plastic containers, having at least one forming station which has a blow mould into which the plastic preform can be introduced, and an application device which applies the plastic preform with a flowable, wherein the plastic preform is applied with at least two different pressure levels and wherein the apparatus further comprises a rod-like body which can be introduced into the plastic preform, in order to expand the plastic preform in its longitudinal direction, wherein a pressure curve and/or a movement curve of the rod-like body and/or a force curve of the rod-like body being determined by a measuring device during the expansion process, wherein the apparatus has a processor device which is configured for evaluating at least one of the curves and for determining at least one point or region of this curve which is characteristic of the curve.

13. The apparatus according to claim 12, wherein the apparatus comprises a storage device and/or a cloud configured for storing a plurality of characteristic points together with data characteristic thereof.

14. The apparatus according to claim 12, wherein the apparatus comprises a plurality of forming stations.

15. The apparatus according to claim 12, wherein the apparatus comprises a transport device configured to transport the plastic pre-forms during their expansion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Further advantages and embodiments can be seen in the attached figures:

[0057] In the drawings:

[0058] FIG. 1 shows an overall representation of a pressure curve and a stretching bar curve;

[0059] FIG. 2 shows a detailed representation of a measurement curve;

[0060] FIG. 3a, 3b show two detailed representations of measurement curves;

[0061] FIG. 4a, 4b show two detailed representations of measurement curves;

[0062] FIGS. 5a -5d show four detailed representations of measurement curves;

[0063] FIGS. 6a -6d show four detailed representations of measurement curves;

[0064] FIG. 7a, 7b show two representations of overall courses;

[0065] FIGS. 8a-8d show four representations of measurement curves;

[0066] FIGS. 9a-9e show five representations of measurement curves;

[0067] FIG. 10 shows a schematic representation of an apparatus according to the invention; and

[0068] FIG. 11 shows a schematic representation to illustrate the objects of the control device.

DETAILED DESCRIPTION OF THE INVENTION

[0069] FIG. 1 shows a representation of several measurement curves. The reference sign BL refers to a (blowing) pressure curve. The left coordinate shows the position of the stretching bar in millimetres and the right coordinate shows the blowing pressure in bar. The time in seconds is plotted on the ordinate.

[0070] The reference sign PR indicates a position of the stretching bar or the above-mentioned movement curve. The reference signs V1 to V3 indicate the switching positions of three (blow) valves. The left two reference signs V1, V2 indicate the opening of the valves for application of the preform with compressed air and the right two reference signs V1, V2 indicate the opening of the valves for the purpose of recycling (of blowing air).

[0071] FIG. 2 illustrates the determination of a first process point P1 Start, i.e. the point at which the plastic preforms are applied with the first pressure P1. It can be seen that the valve V1 is switched at a slightly earlier point in time. Advantageously, the point P1 is determined by means of a difference quotient method. By determining or specifying the point P1, the valve delay time of the first valve V1 can be determined. In addition, process values and process experience can also be collected through this point.

[0072] FIG. 3a shows the determination of a second process point P2, which represents a local maximum. It is possible to search for the first 0-pass in the difference quotient (the derivative) and thus for P2. Advantageously, an additional median smoothing is carried out here.

[0073] Point P2 defines the point at which the plastic preform starts to flow, i.e. actually starts to expand. FIG. 3b shows a problem case in determining the point P2. In this case, it is possible to specify a range or limit a range in which this point is to be found (for example, in the range limited by a certain maximum slope). It would also be possible to estimate this point or to specify a range of points. Also, the centre of this range could be specified as the point.

[0074] The point P3 (cf. FIGS. 4a and 4b) marks a local minimum. The second 0-crossing in the difference quotient (the derivative) after P1 is searched for, wherein a median smoothing can also be carried out here. This point P3 defines the point at which the plastic preform rests against the blow mould and the pressure in the mould rises accordingly.

[0075] These points P2 and P3 are also used to set blowing parameters and also to gain process experience.

[0076] FIGS. 5a to 5d show the determination of a further process point P4 (here the detection of the starting point with the application by the pressure PI). This can also be determined by means of a difference quotient method. In this way, the start of application with a second pressure PI can be detected. Again, it is possible to determine a valve delay time. The blowing parameters can also be set in this way and process values and process experience can again be collected. Preferably, an overflow safety of PI to P1 can be reduced with this procedure.

[0077] FIG. 6a shows the detection of a further relevant point P5 (here the detection of the start of application with the pressure level PI plus). This can also be done using a difference quotient method. Also in this way a determination of the valve delay time is possible, as well as an adjustment of the blowing parameters. FIGS. 6b, 6c and 6d each show problem situations in which the evaluation of the measurement curves is difficult and, if necessary, areas must also be identified.

[0078] In a further preferred method, a first local maximum of the pressure is searched for. It is possible to limit the search to, for example, the area where 95% of a certain pressure, such as the ring channel pressure of the maximum pressure P2, is reached. Then a local maximum of the pressure curve can be searched for. Based on this point, the cooling time can be recorded, i.e. the situation in which the already expanded bottle is completely in contact with the blow mould. The total pressure rise time can also be determined.

[0079] FIGS. 7a and 7b show the determination of the point at which the P2 valve closes. A certain time can be added to the valve delay, for example 60 ms (two times the average valve delay). This point, shown in FIG. 7b, can be used to detect leaks when the pressure drop is too high with a closed P2 valve.

[0080] FIGS. 8a to 8d show the detection of relevant points for the start of the recycling of blown air. Again, the search can be done using the difference quotient method. These process points can be used, for example, to reduce air consumption or to set shorter process times.

[0081] FIGS. 9a to 9e show five representations of measurement curves in which the start of the air outlet process from the container is determined. Here, too, the respective process points can be determined using the difference quotient method.

[0082] The following table shows relevant points of the pressure curve and, if applicable, their significance:

TABLE-US-00001 Process points Pressure curve Meaning or physical significance P1 Start  Effect of opening the P1 valve for pre-blowing pressure P1 Turning point 1 The plastic of the plastic preform begins to flow or the plastic preform begins to expand P1 Turning point 2 The plastic preform or its material is in contact with the inner wall of the blow mould. PI Start.sub.*1 Effect of opening the PI valve on the pressure curve PI Plus Start .sub.*1 Effect of opening the PI plus valve on the pressure curve P2 Start .sub.*1 Effect of opening the P2 valve on the pressure curve P2 Max .sub.*3 P2 Ende .sub.*4 Effect of closing the P2 - valve for HPZ End .sub.*1 PI Plus Recycling Start Effect of opening the PI Plus valve for compressed air recycling PI Recycling Start .sub.*1 Effect of opening the PI valve for compressed air recycling P1 Recycling Start .sub.*1 Effect of opening the P1 valve for compressed air recycling External Recycling Start Exhaust Start .sub.*1 Effect of opening the exhaust valve Exhaust end? Effect of closing the exhaust valve

[0083] FIG. 10 shows a roughly schematic representation of an apparatus 1 according to the invention for forming plastic preforms 10 into plastic containers and in particular plastic bottles 20. In particular, the apparatus is a stretch blow-moulding machine. The reference sign 2 indicates a transport device such as a so-called blowing wheel, on which a plurality of forming stations 25 are arranged. These forming stations are preferably designed in the same way or have the same components. For reasons of clarity, however, this is only shown for two forming stations.

[0084] The reference sign 32 indicates a feeding device such as a transport starwheel which feeds plastic preforms 10 to the forming device 1 and the reference sign 34 indicates a removal device which removes the blown plastic containers or plastic bottles 20 from the forming device 1.

[0085] The forming stations each have an application device 14, such as a blow nozzle, which applies the plastic preforms with compressed air. The reference sign 12 schematically indicates a blow mould within which the plastic preforms are formed.

[0086] The reference sign 8 roughly schematically indicates a measuring device, more precisely a pressure detection device, which records the actual (air) pressure (in particular within the containers to be expanded). The reference sign 16 indicates a rod-like body or a stretching bar which stretches the plastic preforms 10 in their longitudinal direction. The pressure curves shown above can be recorded by means of the measuring device

[0087] The reference sign 26 indicates a smoothing device which smooths the recorded pressure curves or the movement curves. A processor device 22 determines the relevant process points from the course curves, as mentioned above. A control device 28 is used to control the individual valve devices of the forming stations.

[0088] The determined process points are stored in a memory device 30.

[0089] FIG. 11 is a schematic representation to illustrate the objects of the control device 28. The control device 28 is preferably a central control unit, in particular for the higher-level control of the blow-moulding machine components.

[0090] The control device 28 preferably controls a control device of the blowing machine (SBC) for blowing curve evaluation, in particular the processor device 22 and/or also control devices 24 for the container transport (SDC), for example for the position detection of the containers or the like. The control devices of the blow moulding machine (SBC) are preferably the control of the forming stations 25n 1 . . . X, the b ow moulds with valve block and/or the stretching unit.

[0091] The control device 28 also controls, for example, a heating device 5 connected upstream of the feed device 32. Preferably, the control device controls the heating actuators, lamps, heating devices, cooling devices, etc. of the heating device 5.

[0092] The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are individually or in combination new compared to the prior art. It is further pointed out that the individual figures also describe features which may be advantageous in themselves. The skilled person immediately recognises that a certain feature described in a figure can also be advantageous without adopting further features from this figure. Furthermore, the skilled person recognises that advantages can also result from a combination of several features shown in individual figures or in different figures.