Method and device for shaping plastic preforms into plastic containers with machine adjustment

Abstract

The invention relates to a method for shaping plastic preforms (10) into plastic containers (15), in which a conveying device conveys the plastic preforms (10) along a specified conveying path and has a preferably rotatable conveying support (22) on which a plurality of shaping stations (4) are arranged, the molding stations each have a blow molding device in which the plastic preforms are molded into the plastic containers by applying a flowable medium, and wherein at least three different pressure stages (P1, Pi1, Pi2, P2) are applied to the plastic preforms in order to expand the plastic preforms, the pressure stages are provided by at least three different compressed air reservoirs, and wherein in addition, the plastic preform is stretched by means of a stretching rod in the longitudinal direction (L) of the plastic preform, characterized in that the compressed air is returned from the plastic container to at least one compressed air reservoir at least at some time, and at least one value characterizing the compressed air consumption is detected.

Description

[0001] manual

[0002] The invention relates to a method and a device for forming plastic preforms into plastic containers. Such devices and methods are already known in the prior art. The heated plastic preforms are formed into plastic containers and in particular plastic bottles by applying a flowable and in particular gaseous medium. Over time, this process has become more and more complex. In addition to applying air, the plastic preforms are usually stretched in the longitudinal direction of the plastic preform by means of a so-called stretching rod, which is inserted into the plastic preform.

[0003] In the prior art, it is known that such molding is carried out at multiple compressed air levels or multiple pressures. It is common practice to first apply a pre-blow molding pressure, then a higher intermediate blow molding pressure, and finally a final blow molding pressure to the plastic preform in order to fully form the container.

[0004] Recently, increasing efforts have been made to design such methods and apparatuses in a cost-effective and energy-efficient manner. In this process, compressed air consumption is an important criterion.

[0005] During the application of the plastic preform, a blow molding curve is usually formed. In blow molding machines known from the applicant's internal prior art, this blow molding curve is recorded but not evaluated. However, this blow molding curve is easily visualized for the user. The user can then set limit values, wherein, when these limit values ​​are exceeded or fallen below, a response is executed, for example interrupting the blow molding process.

[0006] It is also known from the prior art to perform so-called compressed air recirculation to save compressed air. In this case, after the plastic container has been formed, the high pressure in the container is returned to the compressed air reservoir with a lower compressed air level.

[0007] In the prior art, the blow molding process is mainly controlled via time points. For example, at a specific angle of the blow molding wheel, the stretch rod moves to point PT 0 (stretch rod contacts the plastic preform), and the blow molding nozzle is placed on the plastic preform.

[0008] After or near this time point, the pre-blow valve is opened in a time-controlled manner and an adjustable pressure is applied to the plastic preform. The different molding stations can be set offset to take into account any differences between the individual molding stations or different switching times of the pre-blow valves.

[0009] This is important, because the time point "P1 opens" has a very high influence on the material distribution, but due to wear and tear of the valve this time point may change over time and is rarely readjusted after commissioning the machine.

[0010] For this purpose, EP 2855114 B1 is known to detect the time point P1 in the blowing curve (the curve of the pressure in the cavity over time). More precisely, the time point of the pressure buildup in the valve block can actually be measured by means of a pressure sensor, and the control device automatically adjusts the deviation from the target time point.

[0011] Other valve switching points are controlled via time points. For example, the intermediate blow molding valve usually opens within the range of PT10 (stretch rod reaches the base cup gap), and the P2 valve with the final blow molding pressure opens after a certain time.

[0012] Once the P2 pressure has been successfully applied in the cavity / bottle, certain pressure fluctuations occur due to the dynamics of the incoming fluid and the fluctuations of the P2 annular channel of the blow molding machine. From an energy point of view, it would make sense to close the P2 valve at one of the minima of the pressure fluctuations, since this creates a lower pressure in the bottle (closing the valve prevents air from flowing back into the annular channel) and effectively obtains a lower air consumption.

[0013] However, this point in time (P2 valve closing) is currently still manually entered and it may therefore happen that due to changed process parameters the P2 valve no longer closes at a minimum and the air consumption is no longer at a minimum.

[0014] From an energy point of view, it also makes sense to retract the stretch rod only when the P2 valve is closed, because the displacement volume of the stretch rod also has a positive effect on the air consumption. Currently, this time point is also set manually by the machine operator.

[0015] The air recirculation is currently configured in such a way that the machine operator sets certain limits. Within these limits, the regulation of the automatic pressure regulation tries to find an operating point at which the annular channel pressure can be kept constant with the help of air recovery. The limit values ​​are set so that there is no adverse effect on the bottle quality while at the same time enough time is available for recirculation.

[0016] In order to take into account the influence of the dynamic pressure of the fluid in the annular channel, for example, the machine operator selects an offset of the pressure level after a short setting run without a recirculation angle. This offset may also change slightly over time and, especially under different process parameters, so that it may happen that a non-optimal setting is used for a specific step.

[0017] Additionally, different dynamic pressure compensations may also be advantageous for different predetermined amounts. In extensive studies, the applicant has determined that the offset may deviate even more than assumed. The offset should be varied depending on the operating situation.

[0018] Within the scope of the invention, it is proposed to consider a plurality of (for example three) states. The individual values ​​can be set or adjusted via regulation. However, for reasons of simplicity, three fixed values ​​can also be envisaged.

[0019] The release pressure is currently set indirectly via the release time when the blow molding nozzle is removed. If a higher release pressure is desired, a later release time must be selected manually.

[0020] Prior art methods and devices have the following disadvantages: A very high level of knowledge is required by the machine operator in order to optimally set the system. In addition, compensation for deviations in some set values ​​can usually only be done manually.

[0021] There are also significant difficulties in ensuring an optimum air consumption. If additional blowing stages are provided for the method, such as additional intermediate blowing stages, this also increases the probability of errors. In addition, pressure fluctuations, for example in the pre-blowing channel, cannot be adequately compensated. This makes it difficult to fully exploit the potential for increased performance, in particular through higher release pressures, and also leads to a high probability of errors.

[0022] Another disadvantage of the known machine is that the efficiency of the air recovery or the compressed air consumption is not displayed to the user. In addition, statements about the air consumption are only possible in conjunction with an integrated flow meter. This means that it is not possible to directly verify the effectiveness or efficiency of the production process, in particular with regard to the air consumption.

[0023] A further problem arises because the blow molding process is essentially defined by the time points set by the operator. While some points are particularly important in terms of process engineering and therefore still have to be specified manually, there are also other points that have a lower priority in terms of process engineering but may be relevant in particular for optimal compressed air consumption. Until now, it has not been possible to optimally utilize the compressed air consumption potential.

[0024] In the prior art, there is no formula for the optimum blow molding process. As mentioned above, the additional intermediate blow molding stages (especially air recycling) and the effects resulting therefrom, also greatly increase the effort required to find the optimum blow molding process.

[0025] The object of the present invention is therefore to make such a method and apparatus for forming plastic preforms into plastic containers more efficient. According to the invention, these objects are achieved by the subject matter of the independent claims. Advantageous embodiments and improvements are the subject matter of the dependent claims.

[0026] In the method according to the invention for molding plastic preforms into plastic containers, a conveyor conveys the plastic preforms along a specified conveying path, wherein the conveyor has a preferably rotatable conveying support on which a plurality of molding stations are arranged. The molding stations each have a blow molding device in which the plastic preforms are molded into plastic containers by applying a flowable and in particular gaseous medium, and in particular compressed air (in particular by means of an application device, such as a blow molding nozzle), and wherein at least three different pressure stages (and / or pressure levels) are applied to the plastic preforms in order to expand them, wherein the pressure stages are provided by at least three different compressed air reservoirs. In addition, the plastic preforms are stretched in the longitudinal direction of the plastic preforms by means of a stretching rod.

[0027] According to the invention, compressed air is returned from the molding station and / or the blow molding device and / or the container to the compressed air reservoir at least at certain times and at least one compressed air consumption is detected.

[0028] It is therefore proposed within the scope of the invention that on the one hand the compressed air is returned to the reservoir and on the other hand also the compressed air consumption and / or at least one value characterizing the compressed air consumption is detected.

[0029] The characteristic value is preferably a measured (mass or volume) flow rate, a current release pressure, or the difference between the highest intermediate blowing pressure and the final blowing pressure.

[0030] Particularly preferably, in order to expand the plastic preforms, first a pre-blowing pressure, then at least one intermediate blowing pressure and finally a final blowing pressure are applied to the plastic preforms. The intermediate blowing pressure is preferably higher than the pre-blowing pressure and the final blowing pressure is higher than the intermediate blowing pressure. Particularly preferably, the aforementioned compressed air levels are applied one after the other to each plastic preform.

[0031] Preferably, after the final blowing pressure has been applied, a (pressure) release of the now formed plastic container is again carried out, wherein this is again preferably carried out in the compressed air channel or compressed air reservoir.

[0032] This return of compressed air, also called recirculation, preferably takes place in at least two compressed air reservoirs.

[0033] Particularly preferably, the compressed air reservoir is an annular channel, which is particularly preferably arranged on a support element on which the shaping station is also arranged.

[0034] Particularly preferably, the compressed air reservoir is supplied by a rotary distributor which distributes the air from a stationary compressed air reservoir and / or a pressure connection and / or a compressor to the conveying support and in particular to the individual reservoirs.

[0035] The mentioned compressed air reservoir particularly preferably supplies all molding stations. For this purpose, a plurality of line connections can be provided which connect the compressed air reservoir to the individual molding stations.

[0036] The air consumption of a molding device, in particular a blow molding machine, in particular a stretch blow molding machine, can be determined in a first approximation by the formula (container volume + dead space) x current release pressure x target output or by the formula (container volume + dead space) x (final blow molding pressure - maximum intermediate blow molding pressure) x target output. This applies in particular to standard machines and not to so-called heat-setting machines, in particular if P1 and the intermediate blow molding pressure are largely recirculated.

[0037] Active air recovery reduces this release pressure. The lower the release pressure, the lower the total air consumption. It is not easy to state what the final release pressure is, since it depends on several factors, such as the P2 pressure level, the P1 pressure level, the duration of application of the intermediate blowing pressures (Pi1, Pi2), the container volume, the excursion of the P1 pressure and the excursion of the Pi1, Pi2 pressures, the regulation behavior, etc.

[0038] Within the scope of the present invention, the pre-blowing pressure is denoted by P1, the final blowing pressure is denoted by P2, and the first intermediate blowing pressure is denoted by Pi1. Any second intermediate blowing pressure used is denoted by Pi2. Preferably, there may also be further intermediate blowing pressures Pi3, Pi4, etc.

[0039] In a preferred method, the invention utilizes existing measured values ​​to calculate the recirculation potential and / or uses measured values ​​detected at an earlier point in time to determine machine parameters such that compressed air consumption is minimized.

[0040] The maximum air consumption is therefore advantageously equal to the release level at the P2 pressure level. The current air consumption should be determined via the measured values ​​of the pressure sensor, in particular at the release time point (i.e. the time point at which the container is released again after the final blow molding). The difference between these two values ​​represents the (absolute) air saving. The ratio of these two values ​​represents the percentage recovery rate.

[0041] One difficulty is determining the manner in which the pressure is released. As described in more detail below, this can be achieved, for example, by evaluating the blow molding curve, possibly with the aid of a curve discussion of the blow molding curve. However, this requires relatively high computing power.

[0042] Furthermore, it is also possible to take into account the instantaneous value at the time of switching the release valve, ie in particular to record the instantaneous value of the pressure at the time when the release valve is measuring to release compressed air from the container again.

[0043] In a preferred method, at least one pressure, in particular the pressure of the flowable medium, in particular the compressed air in the container, is therefore determined at a specific time, in particular the time of opening a valve which releases the pressure in the plastic container.

[0044] One advantage of the invention described here is that the determination of the pressure level and the compressed air consumption is improved and thus leads to better adjustability of the machine.

[0045] Preferably, no further measuring devices or components are required for this purpose. With a correspondingly good information value, it is even conceivable to dispense with the flow meter that is sometimes provided in the prior art.

[0046] In a preferred approach, leaks are detected by means of statistical methods. Thus, for example, smaller leaks or substantial turnovers per platform size can be statistically captured and preferably included as a calculation factor.

[0047] In a preferred method, the air recovery system of the device is optimized, in particular in addition to the visualization of the air consumption and / or the recirculation potential. This is preferably achieved by means of a regulating device, in particular an internal machine regulating device, which preferably uses the release pressure, in particular by selecting suitable operating parameters to optimize the air recovery system. In this way, the best possible overall air consumption can be achieved.

[0048] This can be achieved via complex computational models or via learning loops that vary individual (operating) parameters or a combination of both.

[0049] In this procedure, however, limit values ​​are preferably set and / or taken into account which are also not to be exceeded or undershot.

[0050] In this case, the regulation limits are important in order to avoid damaging the quality of the bottle too much. There are parameters that influence the air consumption but have little effect on the quality of the bottle (type 2 process parameters), such as the duration of air recovery Pi1, Pi2. However, there are also parameters that may have a significant impact on the quality (type 1 process parameters), such as the duration of the applied pressure Pi1 or the target pressures of Pi1 and P2.

[0051] In one embodiment, it is assumed that the operator sets type 1 process parameters that are decisive for the bottle quality. Type 1 process parameters are, for example, the target time path curve of the stretch rod until fully stretched, the time of opening of the pre-blowing valve P1, the throttling cross section of P1 and the target pressure in the pressure accumulator of P1, the closing time of P1 or the time of opening of the valve of the next higher pressure level and the final blowing pressure P2, and / or the time when P2 is reached.

[0052] In a further embodiment, the number of values ​​input by the operator can be further reduced if the two values ​​of the throttle cross section and the target pressure of P1 are combined and reduced to a single value characterizing the volume flow or mass flow.

[0053] Type 1 process parameters essentially determine Figure 3 The course of the blowing curve for a given preform (dimensions, temperature distribution and material properties), stretch rod (dimensions) and blow mold (dimensions, material and temperature) up to and including time point II and the pressure at time point IV.

[0054] It is also conceivable to stipulate the so-called P 90 Time or P 90 The final blow molding pressure P2 and the time point at which P2 is reached are replaced by the pressure; the time and pressure indicate when 90% of the P2 pressure has been reached, and the P2 pressure and time point are then calculated or derived therefrom.

[0055] from Figure 3 The time point II in the pre-blow molding process (i.e., the time point at which the valve of the next higher pressure level after the pre-blow molding is opened) to the time point at which P2 is reached (in some cases, only P 90 ) is called the pressure rise time point and / or pressure accumulation time of P2.

[0056] The course of the blowing curve can preferably also be defined by individual parameters of the above-mentioned type 1 process parameters.

[0057] Preferably, the course of the blowing curve can also be defined by any combination of the above-mentioned type 1 process parameters.

[0058] However, in order to define the complete pressure course of the blowing curve and thus the complete forming process, further parameters are required. These parameters usually have only a minor influence on the container quality and are referred to as type 2 process parameters. Type 2 process parameters are, for example, the points in time at which the intermediate pressure valves Pi1-Pin and P2 are opened and / or closed and / or the pressure level of the intermediate blowing pressure during the pressure build-up and / or the points in time at which the intermediate pressure valve, the P1 valve and the release valve are opened and closed.

[0059] The pressure course of the blowing profile and thus the complete forming process can also preferably be defined by individual parameters of the above-mentioned type 2 process parameters.

[0060] Preferably, the course of the blowing curve and thus the complete forming process can also be defined by any combination of the above mentioned type 2 process parameters.

[0061] In a preferred embodiment, after the type 1 process parameters have been entered, the device or machine preferably suggests type 2 process parameters to the operator.

[0062] In a further preferred embodiment, the type 2 process parameters are partially or completely determined and / or set by the machine.

[0063] Particularly preferably, the machine determines type 2 process parameters in such a way that certain process parameters are related to one another.

[0064] For example, during pressure buildup, the first valve may close at almost the same time as the second valve. Switching only delays pressure buildup in the main valve until movement of the main valve from application of the electrical switching signal including any bus run time via the pilot response time.

[0065] In a further preferred embodiment, the type 1 and / or type 2 parameters are determined on the basis of a model with or without AI (artificial intelligence) and / or are determined by adjustment or iteration.

[0066] Depending on the application and technical expertise, the system should or can therefore preferably only change certain control variables and / or type 2 process parameters independently and preferably only within a specified range.

[0067] This means that an "average" machine operator can perform optimization at least on a "medium" level with the greatest possible process reliability, while experienced users are also able to achieve greater savings through clever process control and more extensive regulatory interventions in the process parameters of Type 2. Ideally, however, the operator does not have to adjust the air recovery manually, so that the operator can fully concentrate on the actual heating and blowing process and container quality.

[0068] In a preferred embodiment, the recirculation potential and / or air consumption and / or a digital display characterizing the air consumption allows the machine operator to quickly identify the set efficiency of the air recovery. This allows the machine operator to be aware of the influencing parameter P2 and the bottle volume for the achievable air consumption or recirculation rate.

[0069] Furthermore, the invention describes methods and measures for reducing pressure fluctuations in one of the pressure accumulators and also in particular in the P1 pressure accumulator, reducing the air consumption by means of regulation and in particular automatic regulation, and optionally also increasing the holding time of P2 (which is usually the highest pressure). In addition, higher output rates are to be achieved in terms of process engineering and simpler process regulation is possible.

[0070] Therefore, the present invention is divided into different time points and describes possible measures at these time points in order to achieve the stated objectives in the best possible way. This will be explained in more detail with reference to the accompanying drawings. Particularly preferably, the evaluation of the blow molding curve evaluation, for example by software, is advantageous for a number of the ideas described here.

[0071] In a preferred method, a pressure course is recorded during the production of the plastic container, and particularly preferably, the pressure course is evaluated. For evaluation, for example, a curve analysis can be performed on the pressure course.

[0072] Preferably, the expansion of the plastic preform is understood to mean the entire process, i.e. also the final blowing of the container at the pressure P2. In particular, the pressure course is a course determined over time. Preferably, the evaluation is performed with the aid of an algorithm and / or software. In the process, information can be obtained from the pressure course that allows an improved control or regulation of the device.

[0073] Particularly preferably, on the basis of the evaluation of the pressure course, at least one operating parameter, in particular a type 2 operating parameter, for the expansion of the plastic preforms and / or for the pressure build-up and / or recirculation, in particular in order to reduce the compressed air consumption, is changed. Particularly preferably, this change of the operating parameter is carried out automatically and / or by a regulating device of the machine.

[0074] Particularly preferably, certain operating parameters, in particular blow moulding parameters, in particular type 2 process parameters, are generated (fully) automatically, wherein the corresponding device preferably always finds the best possible compromise, in particular between partially conflicting objectives.

[0075] One of these goals is, for example, to keep the release pressure or the air consumption to a minimum. Another goal is to maintain the high pressure phase, i.e. the phase in which the final blowing pressure is applied, for as long as possible. The high pressure phase is understood to mean that a pressure of more than 5 bar, preferably more than 10 bar, preferably more than 15 bar and preferably at the above-mentioned P2 pressure level is applied to the plastic preform.

[0076] Another possible goal is to minimize the pressure build-up time, ie the time to reach the end of pressure P1 to pressure P2 or the end of pressure P2.

[0077] Particularly preferably, the mentioned working parameters are selected from a group of working parameters, which include the pressure level, in particular the pressure accumulation time of the intermediate blowing pressure level Pi1, the distribution of the pressure accumulation time (in particular the ratio of the pressure accumulation time of pressure P1 to the pressure accumulation time of pressure P2), the ratio between the recirculation time and the pressure accumulation time, the distribution of the recirculation level, the distribution of the recirculation time (in particular the distribution of the recirculation time of the pressure levels Pi1 and Pi2), the start of the stretching process, the end of the stretching process, the stretching speed, the throttling speed of the valve device (in particular the pre-blowing valve), the time point of opening and / or closing the valve device (in particular the P2 valve device), the target pressure of the pressure level, the time point of retracting the stretching rod, etc.

[0078] Individual optional method steps can also be deactivated. For example, the pressure recirculation stages can be operated synchronously or asynchronously. It is also conceivable to deactivate individual recirculation stages.

[0079] What these parameters have in common is their multi-dimensional dependencies and interactions. In addition, changes affect the three basic objective functions mentioned above to varying degrees.

[0080] Therefore, it is preferred to use a model that can be created based on the interdependencies in the system.

[0081] Artificial intelligence (AI) is particularly preferably used to generate the model. Using a large amount of recorded data, it can be determined what effect a change in a specific parameter has on other parameters and the above-mentioned goals. Based on these determinations, the operating parameters can be adjusted.

[0082] In a preferred method, mathematical and / or technical methods are used to find the solution. For example, a certain parameter field can be systematically traversed, for example by means of DoE (Design of Experiments), and an evaluation of the parameter field can be performed, in particular with subsequent multidimensional optimization. For example, a linear regression method can be used here.

[0083] Particularly preferably, AI algorithms are also used.

[0084] In a further preferred method, an iterative loop, in particular a multi-stage iterative loop, is used. Here, for example, individual values ​​can be partially changed during operation and their influence on the target value is analyzed. The optimal point can then be selected based on predefined rules and / or algorithms (e.g. PID controllers).

[0085] In a further preferred method, the calculation is performed using a (complex) physical model.

[0086] In a preferred method, AI models, physical models or optimization methods are used, which are performed, for example, in the machine control or externally, for example in a cloud-based manner, in a computing environment provided for this purpose.

[0087] Once a solution is found, it can be directly applied or at least displayed to the user as an input suggestion and / or at least possible directions of movement can be suggested to the user to better achieve one or more of these goals.

[0088] In a further preferred method, an increase in the P2 pressure can also be recommended as a byproduct of finding a solution if, for example, an increase in pressure results in the air consumption remaining constant. In addition, a recommendation to change the P1 pressure is also possible if a change in the P1 pressure can bring process-related advantages and the pressure consumption or air consumption also remains essentially the same.

[0089] In a further preferred method, at least four different pressure levels are applied to the plastic preform. In this method, pre-blowing is first carried out at a first pressure P1. This is followed by two intermediate blowing steps at pressure levels Pi1 and Pi2 and finally final blowing at the highest pressure P2. In this way, the recycling potential can be increased and the difference between P2 and the release pressure can therefore be further increased.

[0090] In a further preferred method, the compressed air consumption and / or at least one characteristic value characterizing the compressed air route is visualized. For example, a display device such as a monitor can be used to output the pressure route, in particular the pressure route including the limit values, and the user can thus very quickly check the efficiency of the control.

[0091] In a further preferred method, the manufactured plastic containers are inspected. The data from this inspection can also be incorporated into the machine control. For example, changes in specific parameters can lead to unfavorable development of the plastic container. Priority is given to manufacturing the desired precise container. In this way, changes in operating parameters made by the control can also be checked against the target quality of the manufactured container.

[0092] Preferably, the measurement of the wall thickness of the plastic container is performed as part of the inspection. Preferably, the wall thickness of the plastic preform is measured in a plurality of regions of the manufactured plastic container. In a further preferred method, the transparency and / or the crystallinity and / or the optical changes in the wall of the plastic container are measured by cold stretching. In a further preferred method, mechanical properties such as top load or burst pressure are measured.

[0093] Particularly preferably, the plastic pre-forms are inspected contactlessly and / or optically.

[0094] In a further preferred method, the starting point in time of the stretching process is adjusted and / or varied.Preferably, the pre-blowing pressure is applied to the plastic preform and (at least at a certain time) is performed simultaneously.

[0095] It is known from the prior art to vary the start time of the P1 valve as a function of the switching time differences of the valve arrangements. Within the scope of the present invention, it is now proposed to vary the start time of the stretching.

[0096] Preferably, if there is a certain deviation of the pressure course at a given point on the pressure curve, the start of stretching is adjusted so that there is a constant time between the pressure build-up and the blowing curve and the start of stretching. In particular, all molding stations are included.

[0097] This time is preferably set by the machine operator for one station and adopted for all stations! Deviations due to different switching times between stations are preferably compensated via a modified stretching start.

[0098] Alternatively, the current stretching position or the position of the stretching rod at the point in time of the pressure increase, in particular the P1 pressure increase, can be monitored and the stretching start, ie the start of the stretching process, preferably regulated.

[0099] This ensures that at each station the valve opens at the same position, speed and acceleration of the stretch rod in the plastic preform.

[0100] It is also conceivable to vary the stretching speed or acceleration of the stretching rod up to this point in time in order to achieve this goal. However, it should be ensured that the stretching speed at the point in time "tP1 on" is constant in all forming stations.

[0101] In a preferred method, an application device, such as in particular a blow moulding nozzle, is placed on the mouth of the plastic preform in order to apply compressed air to the plastic preform.

[0102] Preferably, the movement of the application device is separated from the movement of the stretching rod. Therefore, different drive devices can be provided for the movement of the application device and the movement of the stretching rod.

[0103] Furthermore, the position of the stretch rod can be used as a reference variable for individual movements and / or for determining process parameters, for example specifying in mm or in % the stretching that the stretch rod has already carried out since time P0 and / or at the beginning of the pre-blowing process.

[0104] In this case, the position of the stretch rod is preferably used as a controlled variable, which means that the interaction between the stretch rod movement and / or the stretch rod position and the start of pre-blowing can be better taken into account.

[0105] The present invention further aims to provide an apparatus for molding plastic preforms into plastic containers, the apparatus comprising a conveying device which conveys the plastic preforms to be molded along a specified conveying path, wherein the conveying device has a preferably rotatable conveying support on which a plurality of molding stations are arranged, wherein each of the molding stations has a blow molding device in which the plastic preforms can be molded into plastic containers by applying a flowable and, in particular, gaseous medium, and each of the molding stations has an application device in order to apply the flowable medium to the plastic preforms, wherein each of the molding stations has a stretching device for stretching the plastic preforms in the longitudinal direction of the plastic preforms, and each of the stretching devices has at least one stretching rod which is movable in the longitudinal direction of the plastic preforms and can be inserted into the plastic preforms, and wherein the apparatus has at least three compressed air reservoirs in order to apply at least three different pressure levels to the plastic preforms.

[0106] According to the invention, compressed air can be returned from the molding station and / or the plastic container to at least one compressed air reservoir at least at a certain time, and a detection device is provided which detects a value characterizing the compressed air consumption at least at a certain time.

[0107] Therefore, a method is also proposed in which compressed air is returned from the molding station, in particular the container, to a further pressure accumulator and also the compressed air consumption or a value characterizing the compressed air consumption is detected by means of a detection device.

[0108] In a preferred embodiment, the device has a control device which controls the device taking into account the detected compressed air consumption. In particular, the control device controls the valve devices of the individual forming stations, the stretching units of the individual forming stations, etc. For example, the time and period at which the individual pressure levels are applied to the plastic preforms can be controlled.

[0109] In a further preferred embodiment, the control device is adapted and intended to vary operating parameters for the forming process and in particular to vary these operating parameters taking into account the detected compressed air consumption.Preferably, these operating parameters can be varied within specified limits.

[0110] Particularly preferably, the device has a plurality of measuring devices which are suitable and intended to detect parameters or values ​​characterizing the compressed air consumption. For example, one or more flow measuring devices can be provided which can be used to measure the flow of compressed air. For example, the flow between the reservoir and the individual molding stations or the flow of compressed air supplied to the containers or plastic preforms can be measured.

[0111] In a preferred embodiment, a plurality of pressure measuring devices are also provided. For example, each molding station can be assigned such a pressure measuring device. Such a pressure measuring device can also be assigned to the above-mentioned storage.

[0112] In a preferred embodiment, at least one of the compressed air accumulators has a larger storage volume for compressed air than at least one other, and preferably a further, compressed air accumulator.

[0113] Furthermore, in particular for a given pressure level, there may be at least two compressed air reservoirs which can be directly flow-connected to one another.

[0114] In particular, this is a compressed air reservoir for the first pressure P1 or pre-blowing pressure.

[0115] Preferably, the storage volume of the compressed air reservoir is at least 26%, preferably at least 30%, preferably at least 40% and preferably at least 50% greater than the storage volume of the other compressed air reservoirs.

[0116] In order to reduce the pressure fluctuations, a larger compressed air reservoir can be provided, or alternatively an additional annular channel or volume with a downstream throttle or connecting device can be provided. In this way, a larger reservoir volume or annular channel volume can be formed.

[0117] The idea is that the compressed air reservoir, ie in particular the annular channel, acts as a kind of compressed air storage and that due to the increased volume, smaller flow differences at the receiving station or cavity have a small effect on the pressure in the reservoir. The increased volume also smoothes out the differences.

[0118] In addition, such pressure fluctuations can also be reduced by an additional P1 annular channel and in particular a P1 compressed air reservoir in combination with a connecting line, preferably also in combination with an adjustable throttle valve. For example, an additional reservoir, in particular an additional annular channel, can be provided, which has a connection to the main channel, preferably to the molding station, and in particular to each molding station. In this way, air will be added again immediately at each point where air is removed.

[0119] If such a connection is provided at only one point, for example with a throttle valve, then in the worst case the air moves over an arc of 180°.

[0120] Such a larger reservoir or an additional reservoir can be arranged at different points in the system, but in particular in flow connection with the second reservoir or the actual compressed air reservoir.

[0121] In a further preferred embodiment, smaller pressure differences can be filled or relieved via the described additional annular channel, in particular without the need to open a dome pressure valve which would introduce increased pressure fluctuations into the annular channel.

[0122] In a further preferred embodiment, the device has a control device, which controls at least one process parameter based on the measured pressure process. In particular, the control device can also use artificial intelligence to realize the control.

[0123] In a further preferred embodiment, the control device is adapted and intended to vary movement parameters of the stretching rod and in particular the speed of the stretching rod movement.

[0124] In a further preferred embodiment, the control device is suitable for and intended to change the flow rate of the blowing air between at least one compressed air reservoir and the various molding stations, in particular the flow rate of the blowing air between the P1 compressed air reservoir and the various molding stations. Preferably, the device has at least one and preferably a plurality of throttling devices, by which the flow rate can be changed.

[0125] If the stretching speed and / or the stretching acceleration increases and the P1 flow rate also increases at the same time, the same amount of air can be ensured in a shorter time point at the same stretch in the longitudinal direction, thus with more P2 holding time.

[0126] However, it is also conceivable to reduce the speed of the stretching rod movement, since a lower P1 pressure also enables a lower air consumption.

[0127] Preferably, the maximum speed of the stretching rod is greater than 1.0 m / s, preferably greater than 1.5 m / s, preferably greater than 2.0 m / s, preferably greater than 2.5 m / s. Preferably, the stretching unit has an electric drive and in particular a linear motor for moving the stretching rod.

[0128] Preferably, the maximum stretch rod acceleration is greater than 40 m / s 2 , preferably greater than 45m / s 2 , preferably greater than 50m / s 2 .

[0129] Preferably, the control device makes it possible to control operating and / or process parameters that influence the P1 compressed air reservoir and / or the supply of the P1 compressed air reservoir to the molding station. Preferably, in this way, an independent control of the process parameters for the lowest possible air consumption and the lowest possible P1 pressure reservoir fluctuations is also achieved.

[0130] Preferably, an operating parameter can be changed here, which is selected from a group of operating parameters, which group of operating parameters includes the intermediate blowing pressure or its level, the intermediate blowing time (for a specified number but at least one intermediate pressure level), the recirculation duration of the pre-blowing pressure, the pre-blowing recirculation time point (this is particularly related to pressure fluctuations), the recirculation duration of the intermediate blowing pressure, the time point for closing the final blow (P2) valve, or the time point for the return stroke of the stretch rod from the P10 position (i.e. the position where the stretch rod extends into the bottom cup of the blow mold and / or contacts the top of the plastic preform).

[0131] The valve overlap time can also be varied.

[0132] These changes are based on several considerations:

[0133] The applicant has determined that a pressure level between the final blowing pressure and the pre-blowing pressure effectively reduces compressed air consumption. Advantageously, a so-called intermediate blowing pressure is used for this purpose, the pressure level of which is between 30% and 70% of the final blowing pressure, preferably between 40% and 60%.

[0134] Preferably, another intermediate pressure is added between the intermediate blowing pressure level and the final blowing pressure level. This makes the relationship between the individual pressure levels and the air consumption complex, and there is no longer an effective approximate figure.

[0135] Even now, there are already process points at which the above-mentioned regulation of the intermediate blowing pressure does not lead to the ideal air consumption and results in additional costs due to the higher compressed air requirement!

[0136] It has also been shown that lower P1 pressure levels are more efficient in terms of air consumption. However, lower P1 pressure levels increase the impact of any fluctuations in the annular passage pressure and may result in poorer process stability.

[0137] Preferably, each station on the rotary machine feeds air into the annular channel during air recirculation and requires air from the annular channel during the molding process. The annular channel is preferably a circumferential channel, on which a plurality of stations are preferably arranged and connected with approximately the same line lengths. However, the annular channel does not necessarily have to be designed as a ring, so that a central distributor or a central volume with a distributor can also be used.

[0138] By carefully selecting the timing of the return feed, peaks in the pressure path in the annular channel can be absorbed and fluctuations reduced.

[0139] Further advantages and embodiments emerge from the accompanying drawings, in which:

[0140] Figure 1 is a schematic diagram of an apparatus according to the present invention;

[0141] Figure 2a to Figure 2c are three schematic diagrams of enlarged compressed air storage;

[0142] Figure 3 is a schematic diagram of the pressure curve;

[0143] Figure 4 is a schematic diagram showing the movement of the stretch rod;

[0144] Figure 5a to Figure 5c are three schematic diagrams showing valve switching time points;

[0145] Figure 6a , Figure 6b are two views showing a valve control device;

[0146] Figure 7 It is a pressure route;

[0147] Figure 8 is a schematic diagram showing switching time points; and

[0148] Figure 9a , Figure 9b is the pressure curve during recirculation.

[0149] Figure 1 The device 1 for molding plastic preforms 10 into plastic containers 15 is shown. The device has a rotatable support 22, on which a plurality of molding stations 4 are arranged. These individual molding stations each have a blow molding device 82, which forms a cavity in its interior for expanding the plastic preform.

[0150] Reference numeral 84 denotes an application device for expanding the plastic preform 10. This can be, for example, a blow-moulding nozzle which can be placed on the mouth of the plastic preform in order to expand the plastic preform. It is also conceivable that the blow-moulding nozzle is sealed to the blow-moulding device. Preferably, the application device is movable in the longitudinal direction, and preferably exclusively in the longitudinal direction of the plastic preform.

[0151] Reference numeral 90 denotes a valve device, such as a valve block, which preferably has a plurality of valves which control the application of different pressure levels to the plastic preforms. Preferably, each molding station has such a valve block.

[0152] In a preferred method, first a pre-blowing pressure P1, then at least one intermediate blowing pressure Pi1 or Pi2 higher than the pre-blowing pressure, and finally a final blowing pressure P2 higher than the intermediate blowing pressure Pi1 or Pi2 is applied to the plastic preforms. After the plastic container has been expanded, the pressure or compressed air is preferably returned from the container to the respective pressure accumulator. Preferably, a further pressure level, in particular a further intermediate blowing pressure, is provided.

[0153] Reference numeral 88 denotes a stretching rod, which serves to stretch the plastic preform in its longitudinal direction. Preferably, all molding stations have such a blow mold 82 and a stretching rod 88. The stretching rod is preferably part of the stretching device denoted by 30. The stretching rod is (preferably also exclusively) movable in the longitudinal direction of the plastic preform 10.

[0154] Preferably, the number of such forming stations 4 is between 2 and 100, preferably between 4 and 60, preferably between 6 and 40.

[0155] The plastic preforms 10 are fed to the device via a first conveying device 62 , such as in particular but not exclusively a conveying star wheel. The plastic containers 15 are conveyed via a second conveying device 64 .

[0156] Reference numeral 7 denotes a pressure supply device, such as a compressor or a compressed air connection. The compressed air is delivered to a rotary distributor 74 via a connecting line 72 and from there to a compressed air reservoir 2a, which in this case is an annular channel, via an additional line 76. Thus, preferably, such a rotary distributor serves the purpose of supplying air from a stationary part of the device into a rotating part of the device.

[0157] In addition to the annular channel 2a shown, further annular channels are preferably provided, which are however arranged in a Figure 1 In the schematic diagram shown in FIG. 1 , the annular channel 2a is hidden by the annular channel, for example, because it is located below the annular channel 2a. Reference numeral 32 denotes a connecting line for delivering compressed air to the molding station 4 or its valve block 90. ​​Preferably, each of the annular channels is connected to all molding stations via a corresponding connecting line. The connecting line is preferably arranged in the rotating part of the device.

[0158] Reference numeral 8 schematically denotes an optional clean room, which is preferably formed in an annular shape here and surrounds the conveying path of the plastic preforms 10. Preferably, the (geometric) axis of rotation about which the conveying support 22 can rotate is arranged outside the clean room 8. Preferably, the clean room is sealed from the non-sterile environment by a sealing device, which preferably has at least two water locks.

[0159] Furthermore, the device has a covering device ( Figure 1 ), which delimits the clean room 8 upwards. The covering device is preferably arranged on at least one of the stretching devices 30.

[0160] The device has a plurality of measuring and / or sensor devices, which are used to control the device. Reference numeral 14 denotes a pressure measuring device, which measures the air pressure in the compressed air reservoir 2a. Preferably, the other compressed air reservoirs also have corresponding pressure measuring devices.

[0161] Reference numeral 16 denotes a further pressure measuring device which measures the air pressure, in particular the internal container pressure of the plastic preforms to be expanded. Preferably, such a pressure measuring device is assigned to each forming station.

[0162] Reference numeral 18 also schematically designates a flow measuring device which determines the flow of blowing air from the compressed air reservoir to the valve block 90 of the molding station 4. Preferably, a corresponding flow measuring device is arranged in each case between the compressed air reservoir and all molding stations.

[0163] A further flow measuring device can also be distributed between a further compressed air reservoir and the corresponding forming station.

[0164] Furthermore, position detection devices are preferably provided, which can detect the position of the stretching rods of the individual forming stations.

[0165] Reference numeral 24 denotes a control device which controls and in particular regulates the device 1. The control device is preferably also able to change operating parameters of the device.

[0166] In particular, the control device controls the individual valves and thus the individual pressure levels applied to the plastic preforms. In addition, the control device preferably also controls the movement of the stretch rods of the individual molding stations. Preferably, the control device also controls the movement of the application device, i.e. the blow molding nozzle. The control device is therefore preferably suitable for controlling and in particular also changing the point in time at which the application device is placed on the plastic preform and / or the point in time at which the blow molding device is lifted again from the plastic preform.

[0167] Reference numeral 26 denotes a storage device in which in particular measured variables, in particular pressure values ​​and flow values, and corresponding operating parameters are stored. Preferably, these corresponding values ​​are stored together with a time allocation.

[0168] Preferably, these values ​​can be stored continuously, in particular over a long period of time while the machine is in operation. The control device controls or regulates the device while also taking into account these recorded measured values.

[0169] Reference numeral 28 generally and schematically indicates an inspection device for inspecting manufactured containers. Preferably, an assignment device is also provided, which is suitable and intended to assign the working parameters used for manufacturing a specific inspected container to that container.

[0170] Reference numeral 25 denotes a display device, which is used to output information to the machine operator. For example, the display device can be used to output a measured pressure (course) curve.

[0171] Figure 2a to Figure 2c An embodiment of the invention with an enlarged annular channel is shown. Here, Figure 2a A situation according to the prior art is shown, in which a conventional annular channel 2a is provided.

[0172] exist Figure 2b In the case shown, it can be seen that the volume of the annular channel 2a representing the compressed air reservoir for the pressure level P1 is greatly increased. In this way, the influence of pressure fluctuations can be reduced. Figure 2c In the case shown, a second annular channel 3a is provided in addition to the annular channel 2a. A plurality of flow connections, in particular throttle valves 5, are provided between the two annular channels.

[0173] according to Figure 2b and Figure 2c The embodiment of is based on the idea that the annular channel acts as a kind of compressed air storage and that due to the increased volume, smaller flow differences of the receiving forming station 4 or cavity have a small effect on the pressure in the annular channel. The increased volume smoothes these differences.

[0174] exist Figure 2c In the case shown, as mentioned, an additional P1 annular channel 3a is provided, and here a plurality of connecting lines with adjustable throttle valves 5 are provided, by means of which pressure fluctuations can be reduced. Smaller pressure differences can be filled or released via this additional annular channel 3a without opening the dome pressure regulator 30, which introduces increased pressure fluctuations into the annular channel.

[0175] Various configurations with regard to the installation position of the dome pressure regulator 30 and the connection position of the connection piece 5 of the annular line may prove to be advantageous.

[0176] Figure 3 A schematic diagram of the pressure curve DK over time is shown. The left scale shows the pressure in bar, while the right scale shows the force in Newtons and the stretch rod position in millimeters.

[0177] Reference symbol RK denotes the stretching curve or the stretching rod movement. Reference symbols I-IX show different states during the expansion process. Reference symbol I denotes the start of the blow molding process with pre-blowing. At time point II, the application of the intermediate blow molding pressure is activated, and at reference symbol III the final blow molding pressure is activated. At time point IV, the pressure in the container has reached its maximum value, and at time point V, the valve supplying the final blow molding pressure is closed again.

[0178] The reference symbol Sv1 denotes the switching time or switching of the intermediate blow molding valve, and the reference symbol Sv2 denotes the switching time or switching of the P2 valve. At the time V, the P2 valve is closed again.

[0179] At time VI, the pressure in the container drops sharply due to the further opening of valve SV1 in order to start the recirculation process.

[0180] At time point VII, the valve is closed again, thereby completing the recirculation. From time point VIII, the (complete) release of the now formed container begins, which is completed at time point XI. The pressure measured at time point VIII allows conclusions to be drawn about the air consumption in the standard process.

[0181] Figure 4 A schematic diagram showing an improved control of the stretch rod 82 is shown. It can be seen that the stretch rod is first fully inserted into the plastic preform and has been used to stretch the plastic preform. In the fourth partial image, the valve P1 is opened and pre-blowing begins. In this state, the stretch rod touches the bottom of the plastic preform.

[0182] Within the scope of the invention, it is now proposed to adjust the start of stretching in such a way that a constant time elapses between the pressure build-up in the blowing curve and the start of stretching, in particular including all molding stations. Figure 4 As can be seen in FIG. 1 , the first step here is to start with stretching and only then to apply the pre-blowing pressure.

[0183] Figure 5a to Figure 5c The reference numeral 42 in each case refers to an electrical switching signal for switching the valve, as does the reference numeral 44. Figure 5b and Figure 5c In FIG. 4 , reference numeral 43 denotes a mechanical position of a valve, for example a first valve, and reference numeral 45 denotes a mechanical position of a second valve. It can be seen that a certain dead time occurs in each case.

[0184] Figure 5b and Figure 5cThe switching times and pressure build-up times of the pre-blow valve and the intermediate blow valve are shown. These valves are switched to ensure that the pressure build-up in the container is as energy-efficient as possible.

[0185] As in Figure 5a to Figure 5c As shown in , there are certain rules for switching the pre-blowing pressure to the intermediate blowing pressure. First, an electrical signal 42 is output, which causes the valve P1 to close. Then a certain dead time point occurs. The valve Pi1 is then opened with another electrical signal.

[0186] The dead time "t 停滞时间 ” is a fixed time which is generally maintained regardless of the wear of the corresponding valve or the actual switching time.

[0187] In a preferred embodiment of the method according to the invention, the valve overlap time or dead time can be checked and possibly improved by means of a sensor system. Under ideal process control, the switching curve can look like Figure 5b In this case, it is not possible for the higher pressure level to flow back to the lower pressure level.

[0188] In practice, however, wear or process-related changes may result in changes in the mechanical switching time of the valve, and this may lead to a greater than reasonable degree of valve overlap, as in Figure 5c As shown in .

[0189] Preferably, a sensor system in the annular channel or between the annular channel and the valve block can be used to detect the inflow of a higher pressure level into the annular channel and to set the dead time to an optimum value with regard to air consumption and the P2 high pressure phase, and in particular automatically.

[0190] Figure 6a and Figure 6b This is shown. The annular channel 2A is shown again, as is the valve block 90. ​​The sensor system described above can be arranged between these devices.

[0191] In the prior art, the current pressure level is switched after an adjustable time. However, in the gradient of the pressure curve or pressure diagram, an automatic switch to the next pressure level is also possible, for example after reaching a specified proportion of the annular channel pressure in the blowing curve. In this way, the adjustment process can be simplified and at the same time different switching times and therefore different pressures can be compensated.

[0192] As mentioned above, the time point at which the pressure P2 in the container is reached (especially from Figure 3 The increments of points II and IV in ) can preferably be used by regulation for optimal air consumption.

[0193] At point V, as shown above, the P2 valve can be closed prematurely, thus advantageously enabling leak detection. Numerous experiments have shown that a certain pressure peak is required to achieve a very good shape of the container. The holding pressure (which is required to press the container against the cold mold and ensure cooling) has a certain level that should not be lowered. However, this level is much lower than the mentioned pressure peak.

[0194] It has also been shown that, despite multiple recirculation phases, the air consumption still depends strongly on how much P2 pressure (final blowing pressure) the container has to use.

[0195] For these reasons, the preferred approach is to reduce the pressure peak when the P2 pressure is subsequently built up (ie, during the pressure holding phase) in order to thereby minimize air consumption.

[0196] Figure 7 Another schematic diagram of the reduction in pressure consumption is shown. Here too, the course of the pressure change over time is shown in simplified form. Here the maximum pressure P 峰值 and minimum pressure P 最小值 Furthermore, it can be seen that the pressure fluctuations in this high pressure range decrease over time.

[0197] In a preferred method, the point in time at which the pressure P2 is reached in the container is set and in particular automatically set. Preferably, for this purpose, the regulation uses the increments from points II and IV to determine the maximum or optimum air consumption.

[0198] In a preferred method, the P2 valve is closed when the pressure fluctuates only minimally. Figure 7 The pressure course is approximately achieved within the right range of the pressure course. Due to the dynamics of the fluid flowing into the container with the sudden deceleration of the fluid flow at the mold wall in the case of successful molding, fluctuations in the pressure course occur in the first phase of the final blow molding pressure application. Therefore, if the pressure course has smaller fluctuations, this can be interpreted as a sign that the container is now fully formed and stable.

[0199] Thus, for example, the pressure course at the pressure sensor can be used to recognize that the formation of the container is now complete, so that the P2 valve can be closed again at this moment.

[0200] Preferably, the P2 valve is also closed in advance to detect leaks. If the container ruptures, air will escape and the pressure will drop below an adjustable minimum value. Such containers can therefore be detected and ejected.

[0201] In a further preferred method, the P2 valve is closed in the trough of the pressure fluctuation. In this case, the effective P2 pressure for the container can be reduced to the greatest extent, and air consumption is reduced.

[0202] It is further preferably proposed within the scope of the invention to find a minimum value and to automatically close the valve in this range after an adjustable holding time.

[0203] However, it is preferred that a minimum holding time, during which the pressure level P2 is applied to the plastic container, should not be fallen below. This time is necessary in particular for maintaining the dimensional stability of the plastic container.

[0204] In a further preferred method, the stretch rod is retracted earliest when the P2 valve is closed. In this way, lower air consumption can be achieved while maintaining the shape.

[0205] The effect of closing the P2 valve at this minimum of the pressure fluctuation can be further increased if the stretching rod returns to the zero position after the P2 valve has closed. The air expelled by the stretching rod causes the pressure to drop during the holding phase.

[0206] If the stretch rod is retracted before the P2 valve closes, the dome pressure regulator will actively readjust and supply fresh air in order to replace the displaced volume with compressed air.

[0207] Preferably, the stretch rod is therefore automatically retracted only after or when the P2 valve is closed, in order to reduce the air consumption.

[0208] Preferably, however, the automatic control is here also limited to the extent that a minimum holding time is maintained during which the P2 pressure remains stored in the container.

[0209] It is particularly advantageous to retract the stretch rod only after all pressure stages and all recirculation stages have been completed in order to achieve a higher recirculation potential and to provide more compressed air for the recirculation process more quickly. In this case, it is also conceivable to return the stretch rod to the zero position at the same time as the release. This will lead to a faster release and a faster and more efficient recirculation process.

[0210] exist Figure 3 There is further potential for a recirculation process at point 6 shown in . This time point can be determined by calculating back from the release time point or the release pressure (forced release).

[0211] Preferably, control via feedback angle or time is also possible. Preferably, pressure control and time control are proposed here in order to achieve minimum air consumption and low fluctuations in the P1 compressed air reservoir. Preferably, each control or regulation independently controls the necessary feedback angle and the necessary pressure level.

[0212] In a further preferred method, an automatic offset setting via a calibration or setting run is proposed. This allows the 0° recirculation angle and the target and actual pressure of the pressure reservoir to be adjusted.

[0213] In order to be able to adjust the air recirculation system as precisely as possible, an offset should be set in advance. This offset indicates how much the target value and the actual value of the annular channel pressure differ under production conditions when recirculating the pre-blowing pressure and the intermediate blowing pressure.

[0214] To this end, the adjustment factor should be set to 0% and the state should be set to manual mode, and during ongoing production, the actual value should be compared with the target value. If the difference is greater than a specified tolerance range, such as + / - 0.1, the offset value should be adjusted.

[0215] Preferably, the state is then set to automatic and the adjustment factor is again set above 0%. Preferably, this is checked before the recirculation system is activated.

[0216] Since the procedures are always the same and an incorrect choice of the offset has a greater influence on the air consumption, it is advantageous to adjust the offset via regular calibration runs (e.g. once a month or when a new recipe is loaded). For this purpose, the regulation of the air recirculation is briefly switched off, the actual value and the target value of the pressure sensor are compared with each other and the offset is adjusted in the event of a deviation.

[0217] Further potential for compressed air savings can be found in Figure 3 The point VII in , ie the start of the recirculation for the pressure level P1 , is found. It is proposed here to carry out the start of the recirculation according to an optimal overlap between the recirculation and the simultaneous discharge of air (of another molding station) in order to reduce pressure fluctuations.

[0218] This is Figure 8 In a system having multiple forming stations (e.g. Figure 8 In a system with eight molding stations in the figure, compressed air is supplied, for example, from the pre-blow molding annular channel 2a at a certain angle or time point into the longitudinally stretched plastic preform, and the pressure in the annular channel 2a decreases. In another molding station, for example, station 4' in the figure, air is pressed into the annular channel 2a at a specific time point during the recirculation, and the pressure in the annular channel 2a increases again. The resulting pressure fluctuations are Figure 9a Shown in.

[0219] In the prior art, these times can be selected independently of one another or result from process-related setpoints. By carefully adjusting the feedback times during air recirculation, pressure fluctuations can be minimized (see Figure 9b), and better maintain the pressure P1 in the annular channel by simultaneously recirculating and applying pressure to the plastic preforms.

[0220] This procedure has also been demonstrated in a large number of experiments conducted by the applicant.

[0221] Since the P1 pressure in the annular channel 2a has a significant influence on the container quality and small fluctuations in the annular channel 2a also reduce fluctuations in the material distribution, this procedure has direct process-related advantages in terms of material distribution of the container.

[0222] Therefore, in a preferred method, pressure fluctuations in at least one compressed air reservoir and in particular in the P1 compressed air reservoir are minimized by purposefully controlling the timing of the recirculation process. Figure 9b Shown in.

[0223] In a further preferred method, the feedback angle or the feedback time is controlled. Both pressure control and time control are possible. This also minimizes the compressed air consumption.

[0224] In a further preferred method, a setting operation is performed, for example before the start of operation, in order to set the offset and, if necessary, the limit value. In particular, an automatic offset setting is preferably performed via the setting operation. The recirculation angle of 0° and the target value and the actual value can be adjusted depending on the pressure of the compressed air reservoir.

[0225] In a further preferred method, the release pressure is set. In a method known from the applicant's internal prior art, the release time point at which the remaining compressed air is released from the container is set as a process-related variable, and the pressure prevailing in the cavity (i.e. the blow mold) at this time point and at this time point leads to a forced release pressure that prevails when the application device is lifted.

[0226] A later release point in time will result in a longer high-pressure phase, but due to process-related changes (e.g. higher pressure in the cavity due to a change in the recirculation setting) may lead to a forced release pressure that is too high and the device may even suffer mechanical damage.

[0227] However, since the release time point should be selected as late as possible in order to maintain the high-pressure phase for as long as possible, it is advisable to select the maximum release pressure as a process-dependent variable and to carry out an automatic adjustment of the time point.

[0228] The present invention facilitates machine operation of such equipment and may also be more easily performed by less trained personnel.

[0229] Furthermore, the device achieves lower air consumption, especially while maintaining container quality. In addition, errors are minimized.

[0230] Furthermore, the method described also allows the introduction of a further intermediate blowing pressure. Finally, an improved automation concept is proposed.

[0231] The applicant reserves the right to claim all features disclosed in the application documents that are essential to the invention, provided that they are novel with respect to the prior art, either individually or in combination. It should also be noted that the various drawings also describe features that may be advantageous in themselves. A person skilled in the art will immediately recognize that a particular feature described in a drawing may be advantageous even without employing additional features from that drawing. Furthermore, a person skilled in the art will recognize that advantages may also result from a combination of several features shown in a single drawing or in different drawings.

Claims

1. A method for forming a plastic preform (10) into a plastic container (15), wherein: A conveyor device conveys the plastic preforms (10) along a specified conveying path and has a preferably rotatable conveying support (22) on which a plurality of molding stations (4) are arranged, wherein each of the molding stations has a blow molding device in which the plastic preforms are molded into the plastic containers by applying a flowable medium, and wherein at least three different pressure levels (P1, Pi1, Pi2, P2) are applied to the plastic preforms in order to expand them, wherein the pressure levels are provided by at least three different compressed air reservoirs, and wherein, in addition, the plastic preforms are stretched in the longitudinal direction (L) of the plastic preforms by means of stretching rods, It is characterized in that At least at a certain time, compressed air is returned from the plastic container to the at least one compressed air reservoir and at least one value characterizing the compressed air consumption is detected.

2. The method according to claim 1, It is characterized in that The characteristic value is the measured flow rate, the current release pressure, or the difference between the highest intermediate blowing pressure and the final blowing pressure.

3. The method according to claim 1, It is characterized in that The pressure course is recorded during the production of the plastic containers and preferably evaluated.

4. The method according to at least one of the preceding claims, It is characterized in that On the basis of evaluating the pressure course, at least one operating parameter, in particular a type 2 operating parameter, for expansion of the plastic preforms and / or for pressure buildup and / or recirculation is changed, in particular in order to reduce the compressed air consumption.

5. The method according to at least one of the preceding claims, It is characterized in that After the Type 1 process parameters have been entered, the device suggests Type 2 process parameters to the operator.

6. The method according to at least one of the preceding claims, It is characterized in that The type 2 process parameters are partially or completely determined and / or set by the device.

7. The method according to at least one of the preceding claims, It is characterized in that The determination of the type 1 and / or type 2 parameters is performed on the basis of the model with or without AI.

8. The method according to at least one of the preceding claims, It is characterized in that The determination of the type 1 and / or type 2 parameters is performed by adjustment or iteration.

9. The method according to at least one of the preceding claims, It is characterized in that The determination of the type 1 and / or type 2 parameters is performed on the basis of the model with or without AI and by means of adjustments.

10. The method according to the preceding claim, It is characterized in that The working parameters are selected from a group of working parameters, which include: the pressure accumulation time of the pressure level, in particular the intermediate blowing pressure level; the distribution of the pressure build-up time; the ratio between the recirculation time and the pressure build-up time; the distribution of the recirculation time; the deviation from synchronization; the way of operating the recirculation phase; the start of the stretching process; the stretching speed; the throttling cross-section of the valve device, in particular the pre-blowing valve; the time point when the valve device is opened and / or closed; the target pressure of the pressure level; the time point when the stretching rod is retracted, etc.

11. The method according to at least one of the preceding claims 1 to 4, It is characterized in that The changes are made with objectives in mind, wherein these objectives are preferably selected from a group of objectives including minimizing the release pressure and / or air consumption, maximizing the high pressure phase and minimizing the pressure build-up time and / or minimizing pressure fluctuations in pressure levels.

12. The method according to at least one of the preceding claims 1 to 4, It is characterized in that Varies a specified parameter within a specified range and detects the effect of the change.

13. The method according to at least one of the preceding claims, It is characterized in that At least four different pressure levels are applied to the plastic pre-forms.

14. The method according to at least one of the preceding claims, It is characterized in that At least one characteristic value for the compressed air consumption and / or the compressed air route is visualized.

15. A device (1) for forming plastic preforms (10) into plastic containers (15), the device comprising a conveying device (2) for conveying the plastic preforms to be formed along a specified conveying path, wherein: The conveying device (2) has a preferably rotatable conveying support (22), on which a plurality of molding stations (4) are arranged, wherein each of the molding stations (4) has a blow molding device (82) in which the plastic preforms (10) can be molded into the plastic containers (15) by applying a flowable medium, and each of the molding stations (4) has an application device (84) in order to apply the flowable medium to the plastic preforms (10), wherein each of the molding stations (4) has a stretching device (30) for stretching the plastic preforms in their longitudinal direction (L), and each of the stretching devices (30) has at least one stretching rod which is movable in the longitudinal direction (L) of the plastic preforms (10) and which can be inserted into the plastic preforms, and wherein the device has at least three compressed air reservoirs in order to apply at least three different pressure levels to the plastic preforms, It is characterized in that Compressed air can be returned from the molding station to at least one compressed air reservoir at least at a certain time, and a detection device is provided, which detects a value characterizing the compressed air consumption at least at a certain time.

16. The device (1) according to the preceding claim, It is characterized in that The device (1) has a control device which controls the device (1) taking into account the detected compressed air consumption.

17. The device according to the preceding claim, It is characterized in that The control device is suitable and intended to change operating parameters for the forming process and in particular to change said operating parameters taking into account the detected compressed air consumption.

18. The device (1) according to the preceding claim, It is characterized in that One of the compressed air reservoirs has a larger storage volume for compressed air than the other compressed air reservoir, and / or at least two compressed air reservoirs are available which can be directly flow-connected to one another.

19. The device (1) according to the preceding claim, It is characterized in that The device has a control device which changes at least one process parameter on the basis of a measured pressure curve.

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