Method and device for shaping plastic preforms in order to form plastic containers using a machine controller

Abstract

The invention relates to a method for shaping plastic preforms (10) in order to form plastic containers (15). A transport device transports the plastic preforms (10) along a specified transport path, and the transport device has a preferably rotatable transport support (22), on which a plurality of shaping stations (4) are arranged, each shaping station having a respective blow molding device within which the plastic preforms are shaped by supplying a flowable medium to the plastic containers. The plastic preforms are supplied with at least three different pressure stages (P1, Pi1, Pi2, P2) in order to be expanded, wherein the pressure stages are provided by at least three different compressed air reservoirs, and additionally the plastic preforms are stretched in the longitudinal direction (L) thereof by means of stretching rods. The invention is characterized in that compressed air is at least temporarily returned to at least one compressed air reservoir from the plastic containers, and at least one value which characterizes the usage of compressed air is detected.

Description

[0001] Method and device for forming plastic preforms into plastic containers with machine control

[0002] Description

[0003] The present invention relates to a method and a device for forming plastic preforms into plastic containers. Such devices and methods have long been known in the prior art. Heated plastic preforms are formed into plastic containers, particularly plastic bottles, by exposure to a flowable and, in particular, gaseous medium. This process has become increasingly complex over time. In addition to the exposure to air, the plastic preforms are typically also stretched longitudinally using so-called stretching rods, which are inserted into the plastic preforms.

[0004] In the prior art, it is known that this forming process is carried out using multiple compressed air levels or pressures. For example, it is common practice to first subject the plastic preforms to a pre-blow pressure, then to a higher intermediate blow pressure, and finally to a final blow pressure to completely form the container.

[0005] Recently, there has been increasing effort to make such processes and devices cost- and energy-efficient. Compressed air consumption is a key criterion in this regard.

[0006] When the plastic preforms are subjected to pressure, a blowing curve is typically created. In blow molding machines known from the applicant's internal prior art, this blowing curve is recorded but not evaluated. Rather, it is simply presented to the user in a visual format. The user can then set limit values, and if these limits are exceeded, appropriate actions are initiated, for example, a blow molding process is aborted.

[0007] It is also known from the prior art that compressed air recycling is used to save compressed air. After the plastic containers are formed, the high pressure in the containers is returned to compressed air reservoirs with a lower pressure level.

[0008] In the current state of the art, the blow molding process is primarily controlled by timing. For example, at a specific angle of a blow molding wheel, the stretch rod is moved to a point PT 0 (the stretch rod is in contact with the plastic preform), and a blow molding nozzle is placed on the plastic preform.

[0009] After or around this point, a pre-blow valve is opened in a time-controlled manner, and the plastic preform is subjected to an adjustable pressure. To account for any differences between the individual forming stations or the different switching times of the pre-blow valves, offset settings can be made for the different forming stations.

[0010] This is important due to the very high influence on the material distribution of the time "P1 opens", but can change over the years due to wear and tear on the valves and is rarely adjusted after the machine has been put into operation.

[0011] For this purpose, it is known from EP 2 855 114 B1 to detect the P1 time in the blow curve (pressure in the cavity over time). More precisely, the time at which the pressure buildup in the valve block could actually be measured using a pressure sensor is recorded, and the control system automatically adjusts the deviation to the target time.

[0012] The remaining valve switching points are controlled by time. Typically, the intermediate blow valve is opened in the PT10 range (the stretch rod reaches the gap between the bottom of the cup), and after a certain time, the P2 valve is opened at the final blow pressure. After the P2 pressure has been successfully applied in the cavity / bottle, certain pressure fluctuations occur due to the dynamics of the inflowing fluid and the fluctuations of the P2 annular channel of the blow molding machine. From an energy perspective, it would be more sensible to close the P2 valve at one of the minimum pressure fluctuations, as this results in lower pressure in the bottle (the valve closure prevents the backflow of air into the annular channel) and effectively lowers air consumption.

[0013] However, this time (P2 valve closes) is currently also still entered manually and so it can happen that due to changed process parameters the P2 valve no longer closes at the minimum and the air consumption is no longer minimal.

[0014] It would also be more energy-efficient to only retract the stretch rod once the P2 valve is closed, as the displaced volume of the stretch rod also has a positive effect on air consumption. This time is currently also set manually by the machine operator.

[0015] Air recycling is currently designed so that the machine operator sets certain limits. Within these limits, an automatic pressure-controlled control system attempts to find an operating point at which the ring channel pressure can be kept constant by recirculating the air. The limits are set so that there is no adverse effect on bottle quality while still allowing sufficient time for recycling.

[0016] To account for effects such as the dynamic pressure of the fluid in the annular channel, the machine operator selects a pressure level offset after a short adjustment run without a recycling angle. This offset can also change slightly over time, especially with varying process parameters, so it may happen that suboptimal settings are used for certain recipes.

[0017] In addition, different dynamic pressure compensation could also be advantageous for different consumption quantities. The applicant has determined through extensive studies that the offset can deviate even more than expected. The offset should vary depending on the operating situation. Within the scope of the invention, it is proposed to consider several, for example, three, states. The individual value can be set or adjusted via control. However, for reasons of simplification, three fixed values ​​would also be conceivable.

[0018] The discharge pressure is currently indirectly adjusted via the discharge time when the blower nozzle is removed. If a higher discharge pressure is desired, later discharge times must be manually selected.

[0019] State-of-the-art methods and devices have the disadvantage that a very high level of knowledge is required from the machine operators to optimally adjust the system. Furthermore, compensation for deviations from certain setting values ​​is usually only possible manually.

[0020] In addition, there are significant difficulties in ensuring optimal air consumption. If additional blowing stages, such as an additional intermediate blowing stage, are included in the process, this also increases the probability of errors. Furthermore, pressure fluctuations, for example, in a pre-blowing channel, cannot be adequately compensated. This makes it difficult to fully exploit the potential for increased performance, especially through higher relief pressure, and also results in a high probability of errors.

[0021] Another disadvantage of conventional machines is that the efficiency of air recovery or compressed air consumption is not displayed to the user. Furthermore, statements about air consumption are only possible in conjunction with an integrated flow meter. This means that the effectiveness or efficiency of a production program, especially with regard to air consumption, cannot be directly verified.

[0022] Since the blowing process is essentially defined by times set by an operator, further problems arise. While some points are particularly important from a process engineering perspective and therefore still have to be specified manually, there are also points that are of lower priority from a process engineering perspective, but can be particularly relevant for optimal compressed air consumption. To date, it has not been possible to optimally exploit the compressed air consumption potential in this regard.

[0023] There is no formula for an optimal blowing process in the current state of the art. As mentioned above, additional intermediate blowing stages, especially air recovery and the resulting effects, significantly increase the effort required to find an optimal blowing process.

[0024] The present invention is therefore based on the object of making such methods and devices for forming plastic preforms into plastic containers more efficient. These objects are achieved according to the invention by the subject matter of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the dependent claims.

[0025] In a method according to the invention for forming plastic preforms into plastic containers, a transport device transports the plastic preforms along a predetermined transport path, wherein the transport device has a preferably rotatable transport carrier on which a plurality of forming stations are arranged. These forming stations each have blow molding devices within which the plastic preforms are formed into the plastic containers by exposure to a flowable and in particular gaseous medium and in particular compressed air (in particular by means of an exposure device such as a blow nozzle). The plastic preforms are subjected to at least three different pressure stages (and / or pressure levels) for expansion, wherein these pressure stages are provided by at least three different compressed air reservoirs.Furthermore, the plastic preforms are stretched in their longitudinal direction using stretching rods.

[0026] According to the invention, compressed air is at least temporarily returned from the forming stations and / or the blow-molding devices and / or the containers to a compressed air reservoir and at least one consumption of compressed air is recorded.

[0027] Therefore, within the scope of the invention, it is proposed that, on the one hand, compressed air be returned to the reservoirs, and, on the other hand, compressed air consumption and / or at least one value characteristic of compressed air consumption be recorded. The characteristic value is preferably a measured flow rate (which can be mass or volume), a current relief pressure, or a difference between the highest intermediate blowing pressure and the final blowing pressure.

[0028] Particularly preferably, the plastic preforms are first subjected to a pre-blow pressure for their expansion, then to at least one intermediate blow pressure, and finally to a final blow pressure. Preferably, the intermediate blow pressure is higher than the pre-blow pressure, and the final blow pressure is higher than the intermediate blow pressure. Particularly preferably, the plastic preforms are each subjected to the aforementioned compressed air levels one after the other.

[0029] Preferably, after the application of the final blow molding pressure, the now formed plastic container is again (pressure) relieved, which preferably takes place again in the aforementioned compressed air channels or compressed air reservoirs.

[0030] This return of the compressed air, also known as recycling, preferably takes place in at least two compressed air reservoirs.

[0031] Particularly preferably, the compressed air reservoirs are annular channels, which are particularly preferably arranged on the carrier on which the forming stations are also arranged.

[0032] Particularly preferably, the compressed air reservoirs are fed by a rotary distributor which distributes the air from a stationary compressed air reservoir and / or pressure connection and / or compressor to the transport carrier and in particular to the individual reservoirs.

[0033] Particularly preferably, the aforementioned compressed air reservoirs supply all forming stations. For this purpose, a plurality of line connections can be provided that connect the compressed air reservoirs to the individual forming stations.

[0034] The air consumption of a forming machine, particularly a blow molding machine and especially a stretch blow molding machine, can be determined as a first approximation using the formula (container volume + dead space) x current relief pressure x target output or by the formula (container volume + dead space) x (finished blow pressure - highest intermediate blow pressure) x target output. This applies particularly to standard machines and not to so-called heatset machines, especially if P1 and the intermediate blow pressures are largely recycled.

[0035] Active air recovery reduces this relief pressure. The lower the relief pressure, the lower the total air consumption. It is not easy to determine the final relief pressure, as this depends on several factors, such as the P2 pressure level relative to the P1 pressure level, the duration of exposure to an intermediate blowing pressure (Pi1, Pi2), the container volume, the P1 pressure offset and the Pi1, Pi2 pressure offset, the control behavior, and so on.

[0036] In the context of the present invention, the pre-blowing pressure is designated P1, the final blowing pressure is designated P2, and a first intermediate blowing pressure is designated P1. Any second intermediate blowing pressure used is designated P12. Preferably, additional intermediate blowing pressures P13, P14, etc. may also be present.

[0037] In a preferred method, the invention uses existing measured values ​​to calculate a recycling potential and / or measured values ​​recorded at earlier times are used to determine machine parameters in such a way that the compressed air consumption is minimized.

[0038] Thus, the maximum air consumption is advantageously equal to a relief level equal to pressure P2. Current air consumption should be determined using the measured values ​​of a pressure sensor, particularly at the relief point (i.e., the point at which the container is relieved of pressure after the blow molding is complete). The difference between the two values ​​results in an (absolute) air saving. The ratio of the two values ​​results in a percentage recovery.

[0039] One difficulty lies in how the relief pressure is determined. This can be done, as described in more detail below, for example, by evaluating the blowing curve, possibly by analyzing the curve. However, this requires relatively high computing power. Another option is to record the instantaneous value at the time a relief valve is switched on. In particular, the instantaneous pressure value is recorded at the time a relief valve, which releases compressed air from the container, is measured.

[0040] In a preferred method, therefore, at least one pressure, in particular a pressure of the flowable medium, in particular the compressed air in the container, is determined at a predetermined time, in particular a time at which a valve which relieves the plastic container is opened.

[0041] An advantage of the invention described here is an improved determination of the respective pressure levels and compressed air consumption and thus a better adjustability of the machine.

[0042] Ideally, no additional measuring devices or components are required for this purpose. If the accuracy is sufficiently high, it would even be conceivable to dispense with a flow meter, which is sometimes provided for in the state of the art.

[0043] A preferred method involves detecting leaks using statistical methods. For example, it would be possible to statistically record smaller leaks or basal turnovers for each platform size and use them preferentially as a calculation factor.

[0044] In a preferred method, in particular in addition to visualizing air consumption and / or recycling potential, an air recovery system of the device is optimized. This is preferably done by means of a control device—particularly internal to the machine—which optimizes the air recovery system, preferably using the relief pressure, particularly by selecting suitable operating parameters. In this way, the best possible overall air consumption can be achieved.

[0045] This would be possible either via a complex calculation model or via a learning loop through a variation of individual (working) parameters or a combination of both.

[0046] However, this approach preferably sets and / or takes into account limit values ​​which are not exceeded or undercut by the control system.

[0047] An important question in this context is the control limits, so as not to adversely affect bottle quality. For example, there are parameters (process parameters of the second type) that influence air consumption largely without affecting bottle quality, e.g., the duration of air recovery Pi1, Pi2. However, there are also parameters (process parameters of the first type) that could have a decisive influence on quality, e.g., the duration of pressurization at pressure Pi1 or a target pressure of Pi1 and P2.

[0048] In one embodiment, it is assumed that the operator sets the type 1 process parameters that are decisive for bottle quality. Type 1 process parameters include, for example, a target time-distance curve of a stretch rod until complete stretching, a time at which a pre-blow valve P1 opens, a throttle cross-section of P1 and a target pressure in the pressure reservoir of P1, a closing time of P1 or the time at which the valve of the next higher pressure level opens, a final blow pressure P2, and / or a time at which P2 should be reached.

[0049] In a further embodiment, the number of values ​​to be entered by the operator can be further reduced if the two values ​​of the throttle cross-section and the set pressure of P1 are combined and reduced to a single value characterizing the volume or mass flow.

[0050] The process parameters of the first type basically determine the course of a blowing curve in Fig.3 for a given preform (dimensions, temperature profile and material properties), stretch rod (dimensions) and blow mold (dimensions, material and temperature) up to and including time II as well as the pressure at time IV.

[0051] It is also conceivable to specify so-called Pgo time or Pgo pressure instead of the final blowing pressure P2 and the time at which P2 is reached. These indicate when 90% of the P2 pressure has been reached and then calculate or result in P2 pressure and time.

[0052] The time from time point II in Fig. 3, the time at which the valve of the next higher pressure level opens after pre-blowing, to the time at which P2 is reached (in some cases also just Pgo), is called the pressure rise time and / or pressure build-up time of P2. The course of a blowing curve can preferably also be defined by individual process parameters of the first type mentioned above.

[0053] Preferably, the course of a blowing curve can also be defined by any combination of the above-mentioned process parameters of the first type.

[0054] However, to define the complete pressure profile of a blowing curve and thus the complete molding process, additional parameters are necessary. These parameters generally have only a minor influence on container quality and are referred to as process parameters of the second type. Process parameters of the second type include, for example, the times of opening and / or closing of the intermediate pressure valves P1, P1 and P2 and / or, during pressure buildup, the pressure levels of the intermediate blowing pressures and / or the times of opening and closing of the intermediate pressure valves, a P1 valve, and a relief valve.

[0055] The pressure curve of a blowing curve and thus the complete forming process can preferably also be defined by individual process parameters of the second type mentioned above.

[0056] Preferably, the pressure curve of a blowing curve and thus the complete forming process can also be defined by any combination of the above-mentioned process parameters of the second type.

[0057] In a preferred embodiment, after the input of the process parameters of the first type, the process parameters of the second type are preferably suggested to the operator by the device or machine.

[0058] In a further preferred embodiment, the process parameters of the second type are partially or completely determined and / or set by the machine.

[0059] Particularly preferably, the machine determines process parameters of the second type in such a way that certain process parameters are linked to one another. For example, during pressure buildup, the time at which a first valve closes can be virtually identical to the time at which a second valve closes. Only the switching delays, from the application of the electrical switching signal including any bus runtimes, to the pilot's reaction time, the pressure buildup in the main valve, and the movement of the main valve, are taken into account.

[0060] In a further preferred embodiment, the parameters of the 1st and / or 2nd type are determined in a model-based manner with or without a Kl (artificial intelligence) and / or the parameters of the 1st and / or 2nd type are determined by control or iteratively.

[0061] Depending on the application and the technical expertise, the system should or may therefore preferably only change certain manipulated variables and / or process parameters of the second type independently and preferably only within specified ranges.

[0062] Thus, the "simple" machine operator can perform optimization at least at a "moderate" level with the greatest possible process reliability, while the experienced user can potentially achieve greater savings through skillful process control and more extensive control interventions, including in the process parameters of type 2. Ideally, however, the operator is spared the need to manually adjust the air recovery, allowing them to concentrate fully on the actual heating and blowing process and container quality.

[0063] In a preferred embodiment, the machine operator can quickly determine how efficiently air recovery is set based on a display of the recycling potential and / or the air consumption and / or a number characteristic of the air consumption. This can sensitize the machine operator to the influencing parameters P2 and the bottle volume on the achievable air consumption or recycling rate.

[0064] In addition, the present invention describes methods and measures for reducing pressure fluctuations in one of the pressure reservoirs and in particular also in a P1 pressure reservoir, in order to reduce air consumption through closed-loop control and in particular automated control, and optionally also to increase the P2 (this is usually the highest pressure) hold time. In addition, higher output rates are to be achieved in terms of process technology and possible controls for a simpler process. The invention is therefore structured into different points in time and describes possible measures at these respective points in time in order to best achieve the stated objectives. This is explained in more detail with reference to the figures. For many of the ideas described here, an evaluation of the blowing curve evaluation, for example by software, is particularly advantageous.

[0065] In a preferred method, a pressure profile is recorded during the production of the plastic container, and this pressure profile is particularly preferably evaluated. For evaluation, this pressure profile can be analyzed using a curve analysis.

[0066] Preferably, the expansion of the plastic preforms refers to the entire process, i.e., including the final blow molding of the containers under a pressure P2. In particular, the pressure profile is determined over time. Preferably, the analysis is performed using an algorithm and / or software. Information can be derived from the pressure profile, allowing for improved control or regulation of the device.

[0067] Particularly preferably, based on the evaluation of the pressure profile, at least one working parameter, in particular a second-type working parameter, is changed for the expansion of the plastic preforms and / or for the pressure build-up and / or recycling, in particular to reduce the consumption of compressed air. Particularly preferably, this change in the working parameter takes place automatically and / or by a control device of the machine.

[0068] Particularly preferably, certain working parameters, in particular blowing parameters, in particular process parameters of the second type, are generated (fully) automatically, whereby a corresponding device preferably always finds the best possible compromise, in particular from partly contradictory objectives.

[0069] Among the objectives, for example, is to minimize the relief pressure and air consumption. Another goal is to keep the high-pressure phase—that is, the phase in which the final blow molding pressure is applied—as long as possible. A high-pressure phase is understood to mean the application of a pressure of more than 5 bar, preferably more than 10 bar, preferably more than 15 bar, and preferably at the aforementioned P2 pressure level to the plastic preforms.

[0070] Another possible goal is to minimize the pressure build-up time, ie the time from the end of a pressure P1 to reaching a pressure P2 or its end.

[0071] Particularly preferably, the said working parameter is selected from a group of working parameters which includes a pressure build-up time of a pressure level, in particular of an intermediate blow-off pressure level Pi1, a distribution of a pressure build-up time (in particular of a proportion of the pressure build-up time for a pressure P1 and the pressure build-up time for a pressure P2), a ratio between a recycling time and a pressure build-up time, a distribution of recycling stages, a distribution of the recycling time, in particular for the pressure stages Pi1 and Pi2), a start of a stretching process, an end of a stretching process, a stretching speed, a throttling speed of a valve device, in particular of a pre-blow valve, a time of opening and / or closing of valve devices, in particular of a P2 valve device, a target pressure of a pressure level, a time for retracting the stretching rod or the like.

[0072] It is also possible to deactivate individual optional process steps. For example, the print recycling stages can be operated synchronously or asynchronously. It would also be conceivable to deactivate individual recycling stages.

[0073] What these parameters have in common is their multidimensional dependence and interactions. In addition, a change in them influences the three key objective functions mentioned above with varying degrees of importance.

[0074] It is therefore preferable to use a model that can be created based on the causal relationships in the system.

[0075] Artificial intelligence (AI) is particularly preferred for generating this model. Using a large amount of recorded data, it can be determined how a change in a specific parameter affects other parameters and also with regard to the aforementioned goals. Working parameters can be adjusted based on these determinations.

[0076] In a preferred method, this solution is found using mathematical and / or technical approaches. For example, it is possible to systematically explore a specific parameter field, for example, using a DoE (design of experiments), and then evaluate the parameter field, particularly with subsequent multidimensional optimization. Linear regression methods, for example, can be used for this purpose.

[0077] Kl algorithms are also particularly preferred.

[0078] Another preferred method utilizes iteration loops, particularly multi-stage iteration loops. Here, for example, individual values ​​can be partially varied during operation and their impact on the target variables analyzed. Optimum points can then be selected based on predefined rules and / or algorithms, such as PID controllers.

[0079] In another preferred method, a calculation is carried out based on a (complex) physical model.

[0080] A preferred method uses AI models, physical models or optimization methods, which take place, for example, in the machine control system or externally, for example cloud-based, in a dedicated computing environment.

[0081] Once the solution has been found, it is possible to either apply it directly or at least display it as an input suggestion to the user and / or at least suggest a possible direction of movement to the user in order to better fulfill one or more of these goals.

[0082] In another preferred method, a recommendation for a P2 pressure increase may also be possible as a by-product of the solution finding process, if, for example, this leads to a constant air consumption. In addition, a suggestion to change the P1 pressure would also be possible if this would result in process-related advantages and the pressure consumption or air consumption would also remain essentially the same.

[0083] In another preferred process, the plastic preforms are subjected to at least four different pressure levels. This process involves initial pre-blowing at a first pressure P1. This is followed by two intermediate blowing steps at pressure levels P11 and P2, and finally a final blowing at the highest pressure P2. This increases the recycling potential and thus further increases the difference between P2 and the relief pressure.

[0084] In another preferred method, at least one value characteristic of compressed air consumption and / or a compressed air curve is visualized. For example, the pressure curve can be output via a display device such as a monitor, in particular including limit values, allowing a user to very quickly check the efficiency of the control system.

[0085] In another preferred method, an inspection of the manufactured plastic containers takes place. It is also possible to incorporate the data from this inspection into the machine control system. For example, changing certain parameters can result in adverse development of the plastic containers. Priority is given to producing a precisely desired container. This makes it possible to verify changes to working parameters made by a control system against the target quality of the manufactured containers.

[0086] Preferably, the wall thickness of the plastic containers is measured during the inspection. The wall thickness of the plastic preforms is preferably measured in several areas of the finished plastic containers. In another preferred method, the transparency and / or crystallinity and / or optical change of the wall of the plastic container due to cold stretching is measured. In another preferred method, mechanical properties such as top load or burst pressure are measured.

[0087] Particularly preferably, the plastic preforms are inspected contactlessly and / or optically. In another preferred method, the starting time of a stretching process is adjusted and / or changed. Preferably, the plastic preform is subjected to a pre-blowing pressure and (at least temporarily) simultaneously

[0088] It is known from the prior art to change the starting time of the P1 valve depending on a switching time difference between the valve devices. Within the scope of the present invention, it is now proposed to change the starting time of the stretching process.

[0089] Preferably, in the case of certain deviations in the pressure curve at a given point on the pressure curve, the stretch start is adjusted so that a constant time elapses between pressure buildup and the blow curve and the stretch start, particularly across all forming stations.

[0090] This time is preferably set by the machine operator for one station and applied to all stations! Deviations due to different switching times between stations are preferably compensated for by changing the stretch start.

[0091] Alternatively, it would be possible to monitor a current stretching position or a position of a stretching rod at a time of a pressure increase, in particular a P1 pressure increase, and to preferentially control the stretching start, ie the beginning of the stretching process.

[0092] In this way, it is achieved that at each station the valve opens at the same position, speed and acceleration of the stretch rod in the plastic preform.

[0093] Changing the stretching speed or accelerating the stretching rod up to this point would also be conceivable to achieve this goal. However, it should be ensured that the stretching speed at the time "tP 1 opens" is constant across all forming stations.

[0094] In a preferred method, an application device, such as a blowing nozzle, is placed at the mouth of the plastic preforms to apply compressed air to them. Preferably, the movement of this application device is decoupled from the movement of the stretching rod. This makes it possible to provide different drive devices for the movement of the application device and the movement of the stretching rod.

[0095] Furthermore, it would be possible to use a position of the stretch rod as a reference value for the individual movements and / or the determination of the process parameters, for example to specify a stretch in mm or in % which the stretch rod has already carried out from a point in time PO and / or at the start of the pre-blowing process.

[0096] In this case, the position of the stretch rod is preferably used as the control variable, which allows the interaction between the stretch rod movement and / or stretch rod position and the pre-blowing start to be better taken into account.

[0097] The present invention is further directed to a device for forming plastic preforms into plastic containers, comprising a transport device which transports the plastic preforms to be formed along a predetermined transport path, wherein the transport device comprises a preferably rotatable transport carrier on which a plurality of forming stations are arranged, wherein the forming stations each comprise blow-molding devices within which the plastic preforms can be formed into the plastic containers by being subjected to a flowable and in particular gaseous medium, and the forming stations each comprise application devices for applying the flowable medium to the plastic preforms, wherein the forming stations each comprise stretching devices,for stretching the plastic preforms in their longitudinal direction, and these stretching devices each have at least one stretching rod movable in the longitudinal direction of the plastic preforms, which can be inserted into the plastic preforms, and wherein the device has at least three compressed air reservoirs in order to subject the plastic preforms to at least three different pressure levels.

[0098] According to the invention, compressed air can be returned at least temporarily from the forming stations and / or the plastic containers into at least one compressed air reservoir, and a detection device is provided which at least temporarily detects a value characteristic of the consumption of compressed air.

[0099] It is therefore also proposed in terms of the process to feed compressed air from the forming stations and in particular the containers back into another pressure reservoir and to further record compressed air consumption or a value characteristic thereof by means of a recording device.

[0100] In an advantageous embodiment, the device has a control device that controls the device taking into account a detected compressed air consumption. In particular, the control device controls valve devices of the individual forming stations, stretching units of the individual forming stations, and the like. For example, the times and periods at which the plastic preforms are subjected to the individual pressure levels can be controlled.

[0101] In a further preferred embodiment, the control device is suitable and intended to change working parameters for the forming process, particularly taking into account a detected compressed air consumption. These working parameters are preferably changeable within predetermined limits.

[0102] Particularly preferably, the device comprises a plurality of measuring devices suitable and intended for detecting parameters or values ​​characteristic of compressed air consumption. For example, one or more flow measuring devices can be provided with which the flow of compressed air can be measured. For example, the flow between a reservoir and the individual forming stations can be measured, or the flow of compressed air supplied to the containers or plastic preforms can be measured.

[0103] In a preferred embodiment, a plurality of pressure measuring devices is also provided. For example, each forming station can be assigned such a pressure measuring device. Such pressure measuring devices can also be assigned to the aforementioned reservoirs.

[0104] In a preferred embodiment, at least one of the compressed air reservoirs has a larger capacity for compressed air than at least one other and preferably the remaining compressed air reservoirs.

[0105] Furthermore, it is possible that at least two compressed air reservoirs that can be brought into direct flow connection with each other are available, in particular for a specific pressure level.

[0106] In particular, this is the compressed air reservoir for the first pressure P1 or the pre-blowing pressure.

[0107] Preferably, the capacity of this compressed air reservoir is at least 26%, preferably at least 30%, preferably at least 40% and preferably at least 50% larger than the capacity of the remaining compressed air reservoirs.

[0108] To reduce pressure fluctuations, a larger compressed air reservoir can be provided, or alternatively, an additional annular channel or volume with a downstream throttle or connection can be created. This creates a larger reservoir volume or annular channel volume.

[0109] This idea is based on using the compressed air reservoir, specifically the annular channel, as a type of compressed air storage device. Due to the increased volume, smaller flow differences between the downstream stations or cavities have a smaller impact on the pressure within the reservoir. The increased volume also smooths out these differences.

[0110] In addition, this pressure fluctuation could also be reduced by an additional P1 ring channel and, in particular, a P1 compressed air reservoir combined with a connecting line, preferably also with an adjustable throttle. Thus, an additional reservoir, in particular an additional ring channel, could be provided, which preferably has a connection to the forming stations, and in particular to each forming station, to a main channel. In this way, air would be immediately replenished at every point where air is currently being removed.

[0111] If such a connection is provided at only one point, for example, with a throttle, the air will, in the worst case, move over an arc of 180°. Such a larger reservoir or an additional reservoir can be arranged at various points in the device, but in particular in flow connection with the second or actual compressed air reservoir.

[0112] In a further preferred embodiment, it is possible for smaller pressure differences to be filled or released through the described additional annular channel, in particular without requiring the opening of a dome pressure valve, which introduces increased pressure fluctuations into the annular channel.

[0113] In a further preferred embodiment, the device comprises a control device that controls at least one process parameter based on measured pressure profiles. This control device can, in particular, also utilize artificial intelligence to effect this control.

[0114] In a further preferred embodiment, the control device is suitable and intended to change movement parameters of the stretching rod and in particular a speed of the stretching rod movement.

[0115] In a further preferred embodiment, the control device is suitable and intended to change the flow rate of the blowing air between at least one compressed air reservoir and the individual forming stations, in particular the flow rate of the blowing air between the P1 compressed air reservoir and the individual forming stations. The device preferably has at least one and preferably several throttle devices by means of which the flow rate can be changed.

[0116] If the stretching speed and / or the stretching acceleration were increased and at the same time the P1 flow rate were also increased, the same amount of air could be ensured in a shorter time with the same stretching in the longitudinal direction and thus have more P2 holding time.

[0117] However, a reduction in the speed of the stretch rod movement would also be conceivable, since a lower P1 pressure also enables lower air consumption. A maximum stretch rod speed is preferably more than 1.0 m / s, preferably more than 1.5 m / s, preferably more than 2.0 m / s, preferably more than 2.5 m / s. The stretching units preferably have electric motor drive devices and, in particular, linear motors for moving the stretch rods.

[0118] Preferably, a maximum horizontal bar acceleration of more than 40 m / s 2 preferably at more than 45m / s 2 preferably at more than 50m / s 2 .

[0119] The control device preferably enables control of working and / or process parameters relating to the P1 compressed air reservoir and / or the supply of the forming stations via the P1 compressed air reservoir. This also preferably achieves independent control of the process parameters for the lowest possible air consumption and the lowest possible P1 pressure reservoir fluctuations.

[0120] Preferably, working parameters can be changed here which are selected from a group of working parameters which includes an intermediate blowing pressure or its level, an intermediate blowing time (with a predetermined number, however, at least one intermediate pressure level), a recycling time of a pre-blow pressure, a pre-blow recycling time (this is particularly relevant for the pressure fluctuations), a recycling time of an intermediate blowing pressure, a time for closing a finished blow (P2) valve, or a time for a return stroke of the stretch rod from a P10 position, ie the position in which the stretch rod is extended into the bottom cup of a blow mold and / or contacts the tip of the plastic preform.

[0121] In addition, valve overlap times can be changed.

[0122] These changes are based on several considerations:

[0123] The applicant has determined that a pressure level between the final blowing pressure and the pre-blow pressure effectively reduces compressed air consumption. For this purpose, a so-called intermediate blowing pressure with a pressure level between 30% and 70%, preferably between 40% and 60%, of the final blowing pressure is advantageously used. Preferably, an additional 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 air consumption complex, and there is no longer a practical rule of thumb.

[0124] Even now, there are already process points where the above specification of the intermediate blowing pressure does not result in the ideal air consumption and additional costs arise due to a higher compressed air requirement!

[0125] 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 influence of possible fluctuations in the annular channel pressure and can lead to poorer process stability.

[0126] Preferably, each station on a rotary molding machine feeds air into the annular channel during air recycling and requires air from the annular channel during the molding process. The annular channel is preferably a circumferential channel, preferably with several stations arranged along it and connected by lines of approximately the same length. However, the annular channel does not necessarily have to be designed as a ring, so a central distributor or a central volume with a distributor can also be used.

[0127] By carefully selecting the timing of the feedback, peaks in the pressure curve in the annular channel can be absorbed and fluctuations reduced

[0128] Further advantages and embodiments are shown in the attached drawings, which show:

[0129] Fig. 1 is a schematic representation of a device according to the invention;

[0130] Fig. 2a-c three views illustrating an enlarged compressed air reservoir;

[0131] Fig. 3 shows a representation of a pressure curve;

[0132] Fig. 4 shows a diagram illustrating a stretch rod movement; Fig. 5a-c shows three diagrams illustrating valve switching times;

[0133] Fig. 6a, b two representations to illustrate a valve control;

[0134] Fig. 7 shows a pressure curve;

[0135] Fig. 8 is a diagram illustrating switching times; and

[0136] Fig. 9a, b a pressure curve during recycling.

[0137] Fig. 1 shows a device 1 for forming plastic preforms 10 into plastic containers 15. This device comprises a rotatable support 22 on which a plurality of forming stations 4 are arranged. These individual forming stations each have blow molding devices 82, which form a cavity within them for expanding the plastic preforms.

[0138] Reference numeral 84 denotes a loading device used to expand the plastic preforms 10. This can be, for example, a blow nozzle that can be placed against a mouth of the plastic preforms to expand them. It would also be conceivable for the blow nozzle to seal the blow molding device. This loading device is preferably movable in a longitudinal direction, and preferably exclusively in a longitudinal direction, of the plastic preforms.

[0139] Reference numeral 90 denotes a valve arrangement such as a valve block, which preferably has a plurality of valves that control the application of different pressure levels to the plastic preforms. Preferably, each forming station has such a valve block.

[0140] In a preferred method, the plastic preforms are first subjected to a pre-blow pressure P1, then to at least one intermediate blow pressure Pi1 or Pi2 that is higher than the pre-blow pressure, and finally to a final blow pressure P2 that is higher than the intermediate blow pressure Pi1 or Pi2. After the plastic containers have expanded, the pressures or compressed air are preferably returned from the container to the individual pressure reservoirs. Preferably, a further pressure stage, in particular a further intermediate blow pressure, is provided.

[0141] Reference numeral 88 denotes a stretching rod, which serves to stretch the plastic preforms in their longitudinal direction. Preferably, all forming stations have such blow molds 82 and stretching rods 88. This stretching rod is preferably a component of a stretching device designated 30. The stretching rod is movable (preferably also exclusively) in the longitudinal direction of the plastic preforms 10.

[0142] Preferably, the number of these forming stations 4 is between 2 and 100, preferably between 4 and 60, preferably between 6 and 40.

[0143] The plastic preforms 10 are fed to the device via a first transport device 62, such as, in particular but not exclusively, a transport star. The plastic containers 15 are removed via a second transport device 64.

[0144] Reference numeral 7 denotes a pressure supply device, such as a compressor or a compressed air connection. The compressed air is conveyed via a connecting line 72 to a rotary distributor 74, from which it is fed via a further line 76 to the compressed air reservoir 2a, which in this case is an annular channel. Thus, this rotary distributor preferably serves the purpose of conveying air from a stationary part of the device to a rotating part of the device.

[0145] In addition to the annular channel 2a shown, further annular channels are preferably provided, which, however, are concealed by the annular channel 2a in the illustration shown in Fig. 1, for example, they are located beneath it. Reference numeral 32 denotes a connecting line that delivers the compressed air to a forming station 4 or its valve block 90. ​​Preferably, each of the annular channels is connected to all forming stations via corresponding connecting lines. This connecting line is preferably arranged in the rotating part of the device.

[0146] Reference numeral 8 schematically indicates an optional clean room, which is preferably annular in shape here and surrounds the transport path of the plastic preforms 10. A (geometric) rotation axis, relative to which the transport carrier 22 is rotatable, is preferably arranged outside the clean room 8. The clean room is preferably sealed from the non-sterile environment by a sealing device, which preferably has at least two water locks.

[0147] Furthermore, the device has a cover device (not shown in Fig. 1) which defines the upper boundary of the clean room 8. This cover device is preferably arranged on at least one of the stretching devices 30.

[0148] The device has a plurality of measuring and / or sensor devices that serve to control the device. Reference numeral 14 denotes a pressure measuring device that measures the air pressure within the compressed air reservoir 2a. Preferably, the other compressed air reservoirs also have corresponding pressure measuring devices.

[0149] Reference numeral 16 denotes a further pressure measuring device, which measures an air pressure, in particular an internal pressure of the plastic preform to be expanded. Preferably, such a pressure measuring device is assigned to each forming station.

[0150] Reference numeral 18 also schematically denotes a flow measuring device which determines the flow of the blown air from a compressed air reservoir to the valve block 90 of a forming station 4. Preferably, corresponding flow measuring devices are arranged between a compressed air reservoir and all forming stations.

[0151] Additional flow measuring devices can also be assigned between the other compressed air reservoirs and the respective conversion stations.

[0152] Furthermore, position detection devices are preferably also provided which can detect the positions of the stretching rods of the individual forming stations.

[0153] Reference numeral 24 denotes a control device which controls and, in particular, regulates the device 1. This control device is preferably also capable of changing the device's working parameters. For example, the control device controls, in particular, the individual valves and thus the application of the individual pressure levels to the plastic preforms. In addition, the control device preferably also controls a movement of the stretching rods of the individual forming stations. The control device preferably also controls movements of the application devices, i.e., the blow nozzles. The control device is therefore preferably suitable for controlling the times at which the application devices are applied to the plastic preforms and / or the times at which the blow molding devices are lifted off the plastic preforms again, and in particular also for changing these times.

[0154] Reference numeral 26 denotes a storage device in which measured variables, in particular pressure values ​​and flow values, but also corresponding operating parameters, are recorded. These respective values ​​are preferably stored with a time assignment.

[0155] Preferably, these values ​​can be stored continuously, especially over long periods of machine operation. The control device also controls or regulates the device taking these recorded measured values ​​into account.

[0156] Reference numeral 28 schematically designates an inspection device for inspecting the manufactured containers. Preferably, an assignment device is also provided, which is suitable and intended to assign to a specific inspected container the working parameters that were used to manufacture this container.

[0157] Reference numeral 25 denotes a display device that serves to output information to a machine operator. This display device can be used to output measured pressure curves.

[0158] Figs. 2a-2c show an embodiment of the invention with an enlarged annular channel. Fig. 2a shows the prior art situation, in which a conventional annular channel 2a is provided.

[0159] In the situation shown in Fig. 2b, it can be seen that the volume of the annular channel 2a, which represents the compressed air reservoir for the P1 pressure level, is significantly increased. This allows the effects of pressure fluctuations to be reduced. In the situation shown in Fig. 2c, a second annular channel 3a is provided in addition to the annular channel 2a. Several flow connections, in particular throttles 5, are provided between the two annular channels.

[0160] The embodiments shown in Figs. 2b and 2c are based on the idea that the annular channel serves as a type of compressed air reservoir. Due to the increased volume, smaller flow differences in the downstream forming stations 4 or cavities have a smaller influence on the pressure in the annular channel. These differences are smoothed out by the increased volume.

[0161] In the situation shown in Fig. 2c, as mentioned, an additional P1 annular channel 3a is provided, along with a plurality of connecting lines with adjustable throttles 5, through which pressure fluctuations can be reduced. Smaller pressure differences can be filled or released through this additional annular channel 3a without requiring the opening of a dome pressure regulator 30, which would introduce increased pressure fluctuations into the annular channel.

[0162] In this case, different configurations regarding the installation location of the dome pressure regulator 30 and the connection positions of the connections 5 of the ring lines may prove to be effective.

[0163] Fig. 3 shows a pressure curve DK plotted over time. The left coordinate represents the pressure in bar, and the right coordinate represents a force in Newtons and a bar position in millimeters.

[0164] The reference symbol RK denotes a stretching curve or a stretch rod movement. The reference symbols l-IX show different states during the expansion process. For example, the reference symbol I denotes the start of the blow molding process with pre-blowing. At time II, the command with an intermediate blow pressure is activated and at reference symbol III a finished blow pressure. At time IV, the pressure in the container has reached its maximum value and at time V the valve that supplies the finished blow pressure is closed again. The reference symbols Sv1 denotes a switching time or a switching of an intermediate blow valve and the reference symbol Sv2 a switching time or a switching of the P2 valve. At time V the P2 valve is closed again.

[0165] At time VI, the pressure in the container drops sharply as a result of further opening of the valve SV1 to initiate a recycling process.

[0166] At time VII, this valve is closed again, thus completing the recycling process. At time VIII, the (complete) depressurization of the now-formed container begins, which is completed at time XI. The pressure measured at time VIII allows for a conclusion about air consumption in standard processes.

[0167] Fig. 4 shows an illustration of an improved control of a stretch rod 82. It can be seen that the stretch rod is first fully inserted into the plastic preform and is already serving to stretch it. In the fourth partial image, valve P1 is opened and pre-blowing begins. In this state, the stretch rod rests against the bottom of the plastic preform.

[0168] Within the scope of the invention, it is now proposed to adjust this stretch start so that a constant time elapses between the pressure buildup of the blow curve and the start of the stretch, particularly across all forming stations. As can be seen in Fig. 4, the process begins with a stretching phase, and only then is the pre-blow pressure applied.

[0169] Figs. 5a-5c illustrate measures for valve switching. Reference numeral 42 refers to electrical switching signals for switching the valves, as does reference numeral 44. In Figs. 5b and 5c, reference numeral 43 denotes a mechanical position of the valve, for example, a first valve, and reference numeral 45 denotes a mechanical position of a second valve. It can be seen that certain dead times occur in each case.

[0170] Figures 5b and 5c show the switching and pressure build-up times of the pre-blow valve and an intermediate blow valve. These are switched to ensure the most energy-efficient pressure build-up in the container.

[0171] As shown in Figs. 5a-5c, there are specific rules for switching the pre-blow pressure to the intermediate blow pressure. First, an electrical signal 42 is output, which causes valve P1 to close. A certain dead time then occurs. Then, valve P1 is opened with another electrical signal.

[0172] The dead time “eit” shown is a fixed time that is maintained in principle, regardless of wear or the actual switching time of the respective valves.

[0173] In a preferred embodiment of the method according to the invention, this valve overlap time or dead time can be monitored and possibly improved using a sensor system. In an ideal process, a switching curve could look like that shown in Diagram 5b. Here, it would be impossible for the higher pressure level to flow back to the lower pressure level.

[0174] In reality, however, wear or a process change may result in a change in the mechanical switching time of the valves, and in this way, overlapping valves would occur beyond a reasonable level, as shown in Fig. 5c.

[0175] Preferably, an inflow of the higher pressure level into the ring channel could be detected by a sensor in the ring channel or between the ring channel and the valve block and the dead time could be set to an optimum with regard to air consumption and P2 high pressure phase and, in particular, could be set automatically.

[0176] Figures 6a and 6b illustrate this situation. The annular channels 2A and the valve block 90 are shown again. The sensor system can be arranged between these devices.

[0177] The current state of the art involves switching a pressure level after a set time. However, the gradient of the pressure curve or pressure graph could also allow for automatic switching to the next pressure level, for example, after a predetermined proportion of the annular channel pressure in the blowing curve is reached. This could simplify the adjustment process and simultaneously compensate for different switching times and the associated different pressures.

[0178] As mentioned above, the time at which the P2 pressure in the container is to be reached (in particular the delta from points II and IV in Fig. 3) can preferably be used by the control for the optimal air consumption.

[0179] At point V shown above, the P2 valve could close prematurely, thus advantageously enabling leak detection. Extensive tests have shown that a certain pressure peak is necessary to achieve excellent container formation. The holding pressure required to press the container against the cold mold and ensure cooling has a certain level that should not be exceeded. However, this level is well below the aforementioned pressure peak.

[0180] In addition, it has been shown that despite several recycling stages, the air consumption still depends very much on how much P2 pressure (finished blow molding pressure) has to be used for the container.

[0181] For these reasons, it is preferable to try to reduce the pressure peak during the build-up of the P2 pressure subsequently (i.e. in the pressure maintenance phase) in order to minimize air consumption.

[0182] Fig. 7 shows another diagram for reducing pressure consumption. Here, too, the pressure curve over time is shown in a simplified manner. It shows a maximum pressure P-peak and a minimum pressure P-min. Furthermore, it can be seen that the pressure fluctuations in this high-pressure range decrease over time.

[0183] In a preferred method, the point in time at which the P2 pressure in the container is to be reached is set, and in particular, automatically adjusted. Preferably, the delta between points II and IV is used by the control system to determine the maximum or optimal air consumption.

[0184] In a preferred process, the P2 valve is closed when the pressure fluctuations are minimal. This is achieved in Fig. 7, approximately in the right-hand area of ​​the pressure curve. Due to the dynamic nature of the fluid as it flows into the container, with the sudden deceleration of the fluid flow at the mold wall upon successful molding, fluctuations in the pressure curve occur during the first phase of the final blow molding pressurization. Therefore, if the pressure curve exhibits fewer fluctuations, this can be interpreted as a sign that the container is now fully formed and stabilized.

[0185] It would therefore be possible to detect by means of the pressure curve on a pressure sensor that the formation of the container is now complete, so that at this moment the P2 valve can, for example, be closed again.

[0186] Preferably, the P2 valve is also closed prematurely for leak detection. If the container bursts, air would escape and the pressure would drop below an adjustable minimum. Such containers can be detected and ejected in this way.

[0187] In another preferred method, the P2 valve is closed in a valley of pressure fluctuation. In this case, the effective P2 pressure for this container can be minimized and air consumption reduced.

[0188] Within the scope of the invention, it is further preferably proposed to find a minimum and to carry out the closing of the valve in this range automatically after an adjustable holding time.

[0189] However, it is preferable that a minimum holding time for the plastic containers to be subjected to the P2 pressure level is not exceeded. This time is particularly necessary to maintain the dimensional stability of the plastic container.

[0190] In another preferred method, the stretch rod is retracted only when the P2 valve is closed. This allows for lower air consumption while maintaining a constant pressure.

[0191] The effect of closing the P2 valve during this minimum pressure fluctuation can be further enhanced if the stretch rod returns to the zero position after the P2 valve has closed. The air displaced by the stretch rod causes the pressure to drop during the holding phase.

[0192] If the stretch rod were to be pulled back before the P2 valve was closed, a dome pressure regulator would actively adjust and supply fresh air to replace the displaced volume with compressed air.

[0193] Preferably, the stretch rod is automatically retracted only after the P2 valve has closed or closed in order to reduce air consumption.

[0194] Preferably, however, the automatic control is also limited to the extent that a minimum holding time is maintained under which the P2 pressure remains stored in the container.

[0195] It would be particularly advantageous to retract the stretch rod only after all pressure stages and all recycling stages have been completed, in order to achieve greater recycling potential and to provide more compressed air for the recycling processes more quickly. In this case, it would also be conceivable to retract the stretch rod to the zero position in parallel with the unloading. This would result in faster unloading and a faster and more effective recycling process.

[0196] Further potential for the recycling process also arises in point 6 shown in Fig. 3. This point in time can be determined by calculating backwards from a relief point in time or a relief pressure (a forced relief).

[0197] Control via a feedback angle or a time is also preferably possible. Pressure control and time control are preferably proposed here in order to achieve minimal air consumption and low fluctuations in the P1 compressed air reservoir. Preferably, each control or regulation independently controls the required feedback angle and the required pressure level.

[0198] Another preferred method proposes automated offset adjustment via a calibration or adjustment run. This allows the 0° recycling angle and the target and actual pressure of a pressure reservoir to be compared. To adjust the air recycling system as precisely as possible, an offset should be adjusted beforehand. This indicates the extent to which the target and actual values ​​of the annular channel pressure differ under production conditions when recycling the pre- and intermediate blowing pressure.

[0199] To do this, the controller factor should be set to 0% and the state to manual operation. During ongoing production, the actual value should be compared with the setpoint. If the difference exceeds a specified tolerance range, such as + / - 0.1, the offset values ​​should be adjusted.

[0200] Preferably, the state is then set to automatic and the control factor is set above 0% again. This should preferably be checked before activating the recycling system.

[0201] Since these procedures are always the same and an incorrect offset selection has a significant impact on air consumption, it is best to adjust this offset through regular calibration runs (e.g., once a month or when loading a new recipe). For this purpose, the control of an air recycling system is temporarily switched off, and the actual and setpoint values ​​of a pressure sensor are compared. If deviations occur, an offset is adjusted.

[0202] A further potential for compressed air savings arises from point VII in Fig. 3, i.e., the start of recycling for pressure stage P1. It is proposed here that the recycling start be performed after an optimal overlap between recycling and a simultaneous air discharge (from another forming station) to reduce pressure fluctuations.

[0203] This is illustrated in Fig. 8. In a system with multiple forming stations, for example in Fig. 8, eight forming stations, compressed air is fed from a pre-blow ring channel 2a at a certain angle or time into the longitudinally stretched plastic preform, and the pressure in the ring channel 2a drops. In another forming station, for example station 4' in the figure, air is pressed into the ring channel 2a at a certain time during recycling, and the pressure in this ring channel 2a rises again. The resulting pressure fluctuations are shown in Fig. 9a. These times can be selected independently of one another in the prior art or result from the process-related setting parameters. By advantageously adjusting the feedback time during air recycling, the pressure fluctuation can be minimized by simultaneous recycling and pressurization of the plastic preform (see Fig.9b) and the pressure in the annular channel P1 can be better maintained.

[0204] This approach has also proven successful in extensive experiments conducted by the applicant.

[0205] This procedure has direct process-technical advantages with regard to the material distribution of the container, since the P1 pressure in the ring channel 2a has a significant influence on the container quality and small fluctuations in the ring channel 2a also reduce the fluctuations in the material distribution.

[0206] 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 specifically controlling a time for a recycling process. This is illustrated here in Fig. 9b.

[0207] In another preferred method, a feedback angle or a feedback time is controlled. Both pressure control and time control are possible. This also minimizes compressed air consumption.

[0208] In another preferred method, for example, a calibration run is performed prior to commencing operation to set offsets and, if necessary, limit values. In particular, an automated offset adjustment is preferably performed via a calibration run. This allows a 0° recycling angle and the target and actual values ​​for the compressed air reservoir pressures to be compared.

[0209] In another preferred method, a relief pressure is set. In methods known from the applicant's internal prior art, a relief time at which the remaining compressed air is released from the container is set as a process-related variable. The pressure prevailing in the cavity, i.e., the blow mold, at this time and the time result in a forced relief pressure that prevails when the pressurizing device is lifted off.

[0210] A later release time would result in a longer high-pressure phase, but could lead to excessive forced release pressure due to process-related changes (e.g., higher pressure in the cavity due to a changed recycling setting), and the device could even suffer mechanical damage.

[0211] However, since a relief time should be chosen as late as possible in order to keep the high pressure phase as long as possible, it is proposed to select the maximum relief pressure as a process-related variable and to carry out an automated control of the time.

[0212] The present invention simplifies the operation of such devices and can also be carried out more easily by less trained personnel.

[0213] Furthermore, air consumption is reduced, especially while maintaining container quality. Errors are also minimized.

[0214] Furthermore, the described process also allows for the introduction of an additional intermediate blowing pressure. Finally, an improved automation concept is also presented.

[0215] The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are novel, individually or in combination, over the prior art. It is further noted that the individual figures also describe features that may be advantageous in and of themselves. The skilled person will immediately recognize that a particular feature described in a figure may be advantageous even without the adoption of further features from that figure. Furthermore, the skilled person will recognize that advantages may also arise from a combination of several features shown in individual or different figures.

Claims

A method for forming plastic preforms (10) into plastic containers (15), wherein a transport device transports the plastic preforms (10) along a predetermined transport path and the transport device has a preferably rotatable transport carrier (22) on which a plurality of forming stations (4) are arranged, wherein these forming stations each have blow molding devices within which the plastic preforms are formed into the plastic containers by being subjected to a flowable medium, and wherein the plastic preforms are subjected to at least three different pressure stages (P1, Pi1, Pi2, P2) for expansion, wherein these pressure stages are provided by at least three different compressed air reservoirs, and wherein the plastic preforms are further stretched in their longitudinal direction (L) by means of stretching rods, characterized in thatthat compressed air is at least temporarily returned from the plastic containers to at least one compressed air reservoir, and at least one value characteristic of the compressed air consumption is recorded. The method according to claim 1, characterized in that the characteristic value is a measured flow rate, a current relief pressure, or a difference between the highest intermediate blowing pressure and the final blowing pressure. The method according to claim 1, characterized in that the pressure curve is recorded during the production of the plastic container, and preferably this pressure curve is evaluated. Method according to at least one of the preceding claims, characterized in that, on the basis of the evaluation of the pressure profile, at least one working parameter, in particular a working parameter of the second type, for the expansion of the plastic preforms and / or for the pressure build-up and / or the recycling is changed, in particular in order to reduce the consumption of compressed air. Method according to at least one of the preceding claims, characterized in that, after the process parameters of the first type have been entered, the process parameters of the second type are suggested to an operator by a device. Method according to at least one of the preceding claims, characterized in that the process parameters of the second type are partially or completely determined and / or set by a device. Method according to at least one of the preceding claims, characterized in that the parameters of the first type and / or the second type are determined in a model-based manner with or without a classifier.Method according to at least one of the preceding claims, characterized in that the parameters of the first type and / or the second type are determined by closed-loop control or iteratively. Method according to at least one of the preceding claims, characterized in that the parameters of the first type and / or the second type are determined model-based, with or without a control element, and by closed-loop control. Method according to the preceding claim, characterized in that the working parameter is selected from a group of working parameters which includes a pressure build-up time of a pressure level, in particular an intermediate blowing pressure level, a distribution of a pressure build-up time, a ratio between a recycling time and the pressure build-up time, a distribution of recycling times, a deviation from synchronicity, a type of operation of recycling stages, a start of a stretching process, a stretching speed, a throttle cross-section of a valve device, in particular a pre-blow valve, a time of opening and / or closing of valve devices, a target pressure of a pressure level, a time for retracting the stretching rod and the like.Method according to at least one of the preceding claims 1-4, characterized in that a change is made taking target specifications into account, wherein these target specifications are preferably selected from a group of target specifications which includes a minimization of the relief pressure and / or the air consumption, a maximization of a high-pressure phase and a minimization of a pressure build-up time and / or a minimization of the pressure fluctuation of a pressure level. Method according to at least one of the preceding claims 1-4, characterized in that a specific parameter is changed within a predetermined range and the effect of this change is recorded. Method according to at least one of the preceding claims, characterized in that the plastic preforms are subjected to at least four different pressure levels.Method according to at least one of the preceding claims, characterized in that at least one value characteristic of a compressed air consumption and / or a. Compressed air flow is visualized. Device (1) for forming plastic preforms (10) into plastic containers (15), comprising a transport device (2) which transports the plastic preforms to be formed along a predetermined transport path, wherein the transport device (2) comprises a preferably rotatable transport carrier (22) on which a plurality of forming stations (4) are arranged, wherein these forming stations (4) each comprise blow-molding devices (82) within which the plastic preforms (10) can be formed into the plastic containers (15) by being subjected to a flowable medium, and the forming stations (4) each comprise application devices (84) for applying the flowable medium to the plastic preforms (10).wherein the forming stations (4) each have stretching devices (30) for stretching the plastic preforms in their longitudinal direction (L), and these stretching devices (30) each have at least one stretching rod movable in the longitudinal direction (L) of the plastic preforms (10), which can be inserted into the plastic preforms, and wherein the device has at least three compressed air reservoirs in order to subject the plastic preforms to at least three different pressure levels. characterized in that compressed air can be fed back from the forming stations into at least one compressed air reservoir at least temporarily, and a detection device is provided which at least temporarily detects a value characteristic of the compressed air consumption. Device (1) according to the preceding claim, characterized in that the device (1) has a control device,which controls the device (1) taking into account a detected consumption of compressed air. Device according to the preceding claim, characterized in that the control device is suitable and intended to change working parameters for the forming process and in particular taking into account a to change the measured compressed air consumption. Device (1) according to the preceding claim, characterized in that one of the compressed air reservoirs has a larger compressed air intake volume than the remaining compressed air reservoirs and / or at least two compressed air reservoirs that can be brought into direct flow communication with one another are available. Device (1) according to the preceding claim, characterized in that the device has a control device that changes at least one process parameter based on measured pressure profiles.

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