Method and device for forming plastic preforms into plastic containers with intermediate blow pressure control

Description

[0001] The present invention relates to a method and a device for forming plastic preforms into plastic containers. Such methods and devices have long been known in the prior art, as described, for example, in DE 10 2012 110023 A1, US 2016 / 136868A1, EP 2 497 619 B1, US 2010 / 171243 A1, and EP 1 974 892 A2. Heated plastic preforms are formed into plastic containers, in particular plastic bottles, by exposure to a flowable medium, in particular compressed air.

[0002] These forming processes have become increasingly complex over time, as the aim is not only to produce satisfactory containers, but also to save compressed air and thus energy wherever possible.

[0003] In the prior art, it is known that plastic preforms are subjected to multiple pressure stages or pressure levels to expand them. For example, it is known that a pre-blow pressure is applied first, followed by an intermediate blow pressure stage, and finally a final blow pressure to completely form and stabilize the container.

[0004] In the current state of the art, an intermediate blowing stage is provided, and the operator specifies a target pressure to be used for this blowing stage. A corresponding pressure reservoir, such as an annular duct, is always connected to a higher-level supply assembly, which can supply fresh air via a dome pressure reducer and a proportional valve. It can also be equipped with a relief unit that can release air from the pressure reservoir to the atmosphere.

[0005] One problem here is that the machine operator does not know the energetically perfect setpoint. In practice, the ideal pressure is usually only approximately determined using a rule of thumb. Furthermore, the current technology requires prefilling all pressure reservoirs, including those for the intermediate pressure stage. It has also been shown that air recovery control for additional intermediate blowing stages is no longer practical. Ideal pressures for the intermediate pressure can only be determined through extensive calculations.

[0006] The present invention is therefore based on the object of making such devices and methods both more efficient and more cost-effective. This is 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.

[0007] 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 rotatable transport carrier on which a plurality of forming stations for forming the plastic preforms into the plastic containers are arranged and wherein the forming stations each have loading devices which apply the flowable medium to the plastic preforms and wherein the device has at least three pressure reservoirs and in particular compressed air reservoirs which store the flowable and in particular gaseous media and which, in a first operating mode, subject the plastic preforms to a first pressure level stored in the first pressure reservoir for their expansion,at least a second pressure level stored in the second pressure reservoir and a third pressure level stored in the third pressure reservoir, wherein the second pressure level is higher than the first pressure level and the third pressure level is higher than the second pressure level.,

[0008] Particularly preferably, the device is operated at least temporarily in a second operating mode, wherein this second operating mode differs from the first operating mode by a pressure level prevailing in the second pressure reservoir.

[0009] It is therefore proposed that two different operating modes are available, or at least two operating modes which differ in particular in the design of the second pressure level, which is preferably an intermediate blowing pressure.

[0010] Particularly preferably, the first pressure level is a pre-blow pressure, hereinafter also referred to as P1, with which the containers are pre-blown at the start of the expansion. The second pressure level is particularly preferably a (first) intermediate blow pressure, hereinafter also referred to as P11, and the third pressure level is particularly preferably a finished blow pressure (hereinafter also referred to as P2), with which the container is completely formed and preferably also held in a formed position for a while. Accordingly, the containers are preferably subjected to a first pressure (pre-blow pressure), a third pressure (finished blow pressure) and at least one second pressure (intermediate blow pressure), or a first pressure (pre-blow pressure), a third pressure (finished blow pressure) and at least one second pressure (intermediate blow pressure) are present.It would therefore be conceivable to have n intermediate blowing pressures (Pi1, Pi2, PiN), so that the container is preferably subjected to several intermediate blowing pressures or the intermediate blowing takes place in several stages.

[0011] In another preferred method, the plastic preforms are also stretched using a stretching unit. For this purpose, a stretching rod is preferably inserted into the plastic preforms to stretch them in their longitudinal direction.

[0012] In a further preferred method, the second operating mode is a start-up operation of the device or a startup operation in which it is put into operation. Preferably, at least at the beginning of this second operating mode, i.e. the start-up operation, only the first pressure reservoir and the third pressure reservoir are filled with compressed air and / or only the first and third pressure reservoirs are filled with fresh air. Fresh air is understood to mean air coming from outside, which is supplied, for example, by a compressor or a rotary distributor. The second pressure reservoir is preferably depressurized at the beginning or essentially has the external pressure.

[0013] Particularly preferably, fresh air or air from outside is not supplied to the second pressure reservoir in either of the two operating modes and overall.

[0014] Particularly preferably, in the second operating mode, the plastic preforms are at least temporarily subjected to only the first pressure level and the second pressure level. This means that at the beginning of a process, only the first pressure level, i.e., the pre-blow pressure, and the third pressure level, i.e., the final blow pressure P2, are applied to the container, or the plastic preform is subjected to these pressure levels.

[0015] During this initial period, no compressed air is available in the intermediate blowing pressure reservoir, so that no intermediate blowing can take place.

[0016] Particularly preferably, in at least one operating mode, and preferably in both operating modes, compressed air is at least temporarily fed from the forming stations and / or the plastic containers back into the second pressure reservoir. If two or more intermediate blowing stages are present, compressed air is preferably recycled into each pressure reservoir for the intermediate blowing pressure, or each intermediate blowing stage is supplied with recycled compressed air.

[0017] This preferred method describes a recycling process in which blowing air is redirected from the containers into individual pressure reservoirs, in this case, the second pressure reservoir. In this way, during the start-up phase, the second pressure reservoir can be filled with compressed air, which, however, originates (in particular exclusively) from the containers to be treated or expanded.

[0018] Such recycling of blown air during expansion or during the return of blown air from the containers is known from the prior art. The invention proposes using this recycling to some extent also for the initial filling of the second pressure reservoir.

[0019] This effectively suggests that the second pressure reservoir be filled via recycling or with the help of compressed air recycling.

[0020] In another preferred method, a pressure level in the second pressure reservoir is determined, and depending on this pressure level, the system transitions from one operating mode to another during operation. For example, it can be determined that the pressure behavior in the second pressure reservoir has reached a certain target level and is also stable. In this case, it is possible to switch from only pre-inflating the containers to also inflating them intermediately, or to actively integrate the second pressure reservoir into the container expansion.

[0021] This proposes a (temporal) first phase (which, however, corresponds to the second operating mode mentioned above), in which the first containers are blown without the intermediate blowing pressure. In this phase, the pre-blow pressure P1 is therefore directly followed by the application of the final blowing pressure P2. However, recycling is already taking place in this phase to at least one intermediate blowing pressure level (Pi1). Since only refeeding occurs during this phase, but not removal, the pressure in the respective pressure reservoir or annular channel increases from container to container. If a certain level in the pressure levels is exceeded, the machine switches to "Phase 2."

[0022] In phase 1, pressure build-up takes place with at least one intermediate blowing pressure level and preferably with two intermediate blowing pressure levels.

[0023] As soon as the pressure level in one pressure reservoir and preferably in two intermediate pressure reservoirs is stable, the device can switch to the second operating mode (normal working mode).

[0024] In another preferred method, the plastic preforms are subjected to a further pressure level, wherein this further pressure level is higher than the second pressure level but lower than the third pressure level. In this method, it is proposed that the plastic preforms be subjected to two intermediate blowing pressure levels. Recycled compressed air is preferably also fed into the pressure reservoir of the further pressure level.

[0025] Preferably, an additional pressure reservoir, and in particular an annular channel, is available for this additional pressure level. Preferably, this additional pressure reservoir is also not filled at the beginning of a forming process and / or this additional pressure reservoir is not filled with fresh air and / or with air from outside.

[0026] In a further preferred method, operating parameters for applying the first and / or third pressure levels are specified, in particular by a user. For example, a user can specify the pressure level of the first and third pressure levels and when corresponding valves should open and close to apply pressure to the plastic preforms.

[0027] In another preferred method, operating parameters for applying the second pressure level are determined by a control device. This makes it possible to specify a pressure start or end point, or a pressure duration. Therefore, the control system particularly preferably determines, for example, ideal pressure levels and pressure times for the intermediate blowing pressure stages.

[0028] It is therefore particularly preferred to no longer specify a target pressure for the intermediate blowing pressure stages PI1 and Pi2. Instead, the device itself preferably finds an optimum for these pressures (and / or application times).

[0029] The preferred framework conditions for this are constant air extraction and air recovery times. In the initial development step, these can preferably be assumed to be fixed. In further embodiments, controlled pressure rise and recycling times would also be conceivable.

[0030] An advantage of this design is that pressure reducers and prop valves for the respective pressure reservoirs Pi1 and Pi2 are omitted.

[0031] However, in a preferred embodiment, a single valve may be available for service or diagnostic purposes or for pre-filling the channel.

[0032] The following describes a start-up operation for such a device, divided into several phases: In the first phase (Phase 1), the first bottles are blown without Pi, i.e., without the intermediate blowing pressures. P1 is therefore immediately followed by P2. On the recovery side, however, Pi2 and Pi1 are recycled. Since only refeeding occurs, but not removal, the pressure in the annular channel increases from bottle to bottle. If a certain level is exceeded in the annular channels, the machine switches to the second phase, i.e., "Phase 2."

[0033] The second phase ("Phase 2") is initiated when certain starting conditions are met, for example the intermediate blowing pressure Pi1 is greater than 1 / 3 of the finished blowing pressure P2 and the intermediate blowing pressure Pi2 is greater than 2 / 3 of the finished blowing pressure P2.

[0034] As soon as the ring channel pressures reach or exceed the start condition, the control system switches to phase 2. Here, for the first time, Pi1 and Pi2 are switched on in addition to P1 and P2 during pressure buildup. On the recovery side, Pi2 and Pi1 continue to switch on. Due to the fixed pressure buildup and recycling times, a certain Pi1 and Pi2 pressures stabilize. This second phase is preferably a transition phase between the second operating mode described above and the first operating mode.

[0035] Preferably, therefore, the device is operated in at least three different operating modes, wherein the third operating mode is preferably a transition mode between the second operating mode and the first operating mode and / or the third operating mode is temporally located between the second operating mode and the first operating mode.

[0036] The second phase is preferably followed by a third phase ("Phase 3").

[0037] A starting condition is also preferably defined for this third phase. This can, for example, consist of the intermediate blowing pressures Pi1 and Pi2 being stable and the intermediate blowing pressure Pi1 being greater than the pre-blowing pressure P1. In addition, the above conditions for the start of phase 2 can also apply here.

[0038] The machine transitions to Phase 3 when the annular channel pressures for Pi1 and Pi2 have stabilized. However, the prerequisite is that Pi1 is still above P1. If all conditions are met, P1 recycling comes into play in Phase 3. The P1 recycling control operates as is known in the state of the art. In Phase 3, the machine is in full operation and / or the aforementioned first operating mode.

[0039] Ideally, the entire process from phases 1 to 3 generally takes place in just a few seconds. The steady state is thus reached relatively quickly.

[0040] If a start condition is no longer met, the system automatically switches back to the previous phase. This switchover can occur at any time in real time and preferably represents a response to a specific machine situation. This method makes it possible to counteract disruptive influences such as leaks, bottle bursts, the rejection of pre-blow bottles, or shut-down stations.

[0041] The invention now also makes it possible to use Pi pressures, i.e., intermediate blowing pressures, that are lower than P1. The relief pressure is thus independent of the P1 pressure, although it is still advantageous for air consumption to feed P1 entirely via recycling.

[0042] In addition, the method according to the invention offers an effective method for dealing with interference.

[0043] Furthermore, perfect ring channel pressures (especially for intermediate blowing) can be provided for each blowing process, especially for blowing processes with two or more intermediate blowing stages.

[0044] The present invention is further directed to a device for forming plastic preforms into plastic containers, comprising a transport device that transports the plastic preforms along a predetermined transport path P. The transport device comprises a rotatable transport carrier on which a plurality of forming stations for forming the plastic preforms into the plastic containers are arranged. The forming stations each comprise application devices (in particular blowing nozzles) that apply the flowable medium to the plastic preforms, and the device comprises at least three reservoirs or pressure reservoirs that store the flowable and in particular gaseous medium.

[0045] Furthermore, in a first operating mode, the plastic preforms can be subjected to a first pressure level stored in the first pressure reservoir, at least a second pressure level stored in the second pressure reservoir and a third pressure level stored in the third pressure reservoir for their expansion, wherein the second pressure level is higher than the first pressure level and the third pressure level is higher than the second pressure level.

[0046] According to the invention, the device can be temporarily operated in a second operating mode, wherein this second operating mode differs from the first operating mode by a pressure level prevailing in the second pressure reservoir. In a further embodiment of the invention, the device has a fresh air supply device designed to supply fresh air to the first and third pressure reservoirs, but not to the second pressure reservoir.

[0047] Particularly preferably, the fresh air supply device comprises a compressor or a pressure connection. Furthermore, the device preferably comprises a distribution device that directs the compressed air from the fresh air supply device to the rotatable support and, in particular, to the pressure reservoirs. The distribution device is preferably designed as a rotary distributor.

[0048] In a further preferred embodiment, the pressure reservoirs are annular channels. These pressure reservoirs are particularly preferably arranged on the rotatable support.

[0049] In a further advantageous embodiment, the device comprises a plurality of sensor and / or measuring devices for determining operating parameters. Particularly preferably, at least one pressure measuring device is assigned to each pressure reservoir. Particularly preferably, one or more flow measuring devices are also provided, which determine the flow rate of air flowing from a pressure reservoir to the respective forming stations.

[0050] In a further advantageous embodiment, the device comprises a control device for setting a pressure in the pressure reservoirs. This is particularly the case for the first and third pressure reservoirs. The control device is particularly preferably a dome pressure regulator.

[0051] In a further advantageous embodiment, the device comprises an additional pressure reservoir, which is suitable and intended for applying a further pressure level to the plastic preforms. In particular, this is an additional intermediate blowing pressure level. Particularly preferably, this additional pressure reservoir is also not supplied with fresh air.

[0052] Particularly preferably, compressed air can be guided or recirculated from the plastic containers into at least one pressure reservoir. Particularly preferably, this is at least the second pressure reservoir for an intermediate blowing pressure and / or the further pressure reservoir for the further intermediate blowing pressure and / or the pressure reservoir for the above-mentioned first pressure.

[0053] Further advantages are evident from the attached drawings, which show: Fig. 1 is a schematic representation of a device according to the invention; Fig. 2 is a representation of pressure curves in the different phases; and Fig. 3 is a representation illustrating the transition between the phases.

[0054] Fig. 1 shows a device 1 for forming plastic preforms 10 into plastic containers 15. This device has 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 in their interior for expanding the plastic preforms.

[0055] 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 an opening 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.

[0056] 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.

[0057] In a preferred method, the plastic preforms are first subjected to a pre-blow pressure P1, then to at least one intermediate blow pressure Pi 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. Particularly preferably, the plastic preforms are subjected to a further intermediate blow pressure Pi2 that is higher than the pressure Pi1 but lower than the pressure P2.

[0058] After the plastic containers have expanded, the pressures or compressed air are preferably returned from the container to the individual pressure reservoirs.

[0059] 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.

[0060] Preferably, the number of these forming stations 4 is between 2 and 100, preferably between 4 and 60, preferably between 6 and 40.

[0061] 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.

[0062] 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 supplied 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.

[0063] In addition to this ring channel 2a shown, further ring channels are preferably provided, which are shown in Fig. 1 However, in the illustration shown, they are concealed by the annular channel 2a, for example, they are located underneath. Thus, a pressure reservoir is preferably provided for storing the pressure P2 as well as the intermediate blowing pressures Pi1 and Pi2 and the pressure P1.

[0064] 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.

[0065] 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.

[0066] Furthermore, the device has a (in Fig. 1 not shown) which delimits the clean room 8 at the top. This cover device is preferably arranged on at least one of the stretching devices 30.

[0067] 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.

[0068] Reference numeral 16 denotes a further pressure measuring device, which measures an air pressure, in particular an internal container pressure of the plastic preform to be expanded. Preferably, such a pressure measuring device is assigned to each forming station.

[0069] Reference numeral 18 also schematically denotes a flow measuring device which determines a 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.

[0070] Additional flow measuring devices can also be assigned between the other compressed air reservoirs and the respective conversion stations.

[0071] Furthermore, position detection devices are preferably also provided which can detect the positions of the stretching rods of the individual forming stations.

[0072] Reference numeral 24 denotes a control device that controls and, in particular, regulates the device 1. This control device is preferably also capable of changing the device's operating parameters.

[0073] 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 blowing 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, and in particular also for changing these times.

[0074] 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 temporal assignment.

[0075] Preferably, these values can be stored continuously, particularly over long periods of machine operation. The control device also controls or regulates the device taking these recorded measured values into account.

[0076] The reference numeral 28 roughly schematically designates an inspection device for inspecting the manufactured containers.

[0077] 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 (progression) curves.

[0078] Fig. 2 shows a representation of pressure curves. Reference symbol P2 denotes pressure P2 or its temporal progression in the individual phases 1, 2, and 3. It can be seen that the P2 pressure reservoir is already filled with pressure P2 at the start of production. During production, this pressure P2 fluctuates during the final blow molding phase because the plastic preforms are pressurized in each forming station, but compressed air continues to be supplied from the outside.

[0079] The reference symbol P1 indicates the pre-blowing pressure, which is already present at the corresponding pressure reservoir at the beginning of production.

[0080] At the beginning of production, the two intermediate blowing pressures Pi1 and Pi2 are still at the level of the external pressure. It can be seen that these two pressures slowly build up during phase 1.

[0081] In phase 2, the intermediate blowing pressures continue to build up and are then essentially constant in phase 3.

[0082] Fig. 3 shows the phases Fig. 2 , but here interrupted by the respective starting conditions. It can be seen that when the starting conditions Pi1 = 1 / 3 P2 and Pi2 = 2 / 3 P2 are met, the transition from the first phase to the second phase occurs.

[0083] In the first phase, the containers are only pressurized to the first pressure P1 and the third pressure P2, meaning no intermediate blowing takes place. However, during the compressed air return, the pressure reservoirs for the intermediate blowing pressures are also filled, and thus, pressure slowly builds up in these pressure reservoirs.

[0084] In phase 2, the two intermediate pressure levels are also used in the blowing phase.

[0085] Recycling takes place here into the intermediate blowing pressure levels Pi1 and Pi2.

[0086] When further starting conditions are reached (Pi1 stable and Pi2 stable as well as Pi1 greater than P1), phase 3 is triggered. In phase 3, which preferably represents the above-mentioned first operating mode or normal working operation, compressed air is now also returned to the P1 compressed air reservoir.

[0087] The system also responds preferentially to different disturbances, reacting in different ways depending on the pressure reservoir.

[0088] With regard to the P2 pressure reservoir, compensation is carried out via a control device, in particular a dome pressure regulator.

[0089] With regard to the intermediate blowing pressures Pi1 and Pi2, it is preferable to alternate between the individual phases 1 - 3 depending on the presence or absence of the starting conditions.

[0090] With regard to the pressure reservoir P1, depending on the state of the pressure levels Pi1 and Pi2, this reservoir can be supplied with recycled air or fresh air. Depending on the type of supply, the valve circuits can also be offset and / or a synchronous supply or pressure extraction can be implemented.

Claims

1. A method for forming plastic preforms (10) into plastic containers (15), wherein a transport device (2) transports the plastic preforms (10) along a predetermined transport path (P), wherein the transport apparatus has a rotatable transport carrier (22) on which a plurality of forming stations for forming the plastic preforms (10) into the plastic containers (15) are arranged, wherein the forming stations each have application devices (84) which apply the plastic preforms with the flowable medium, and wherein the apparatus (1) has at least three pressure reservoirs which store the flowable and in particular gaseous medium, and, to expand them, the plastic preforms are applied in a first operating mode with a first pressure level (P1) stored in the first pressure reservoir (2a), with at least one second pressure level (Pi1) stored in the second pressure reservoir, and with a third pressure level (P2) stored in the third pressure reservoir, wherein the second pressure level (Pi1) is higher than the first pressure level (P1), and the third pressure level (P2) is higher than the second pressure level (Pi1), characterized in that the apparatus is operated temporarily in a second operating mode, wherein this second operating mode differs from the first operating mode by a pressure level prevailing in the second pressure reservoir and that the second operating mode (B1) is a starting mode of the apparatus, and, at a beginning of this starting mode, only the first pressure reservoir and the third pressure reservoir are filled with compressed air, and only the first pressure reservoir and the third pressure reservoir are filled with fresh air.

2. The method according to claim 1, characterized in that, in the second operating mode, the plastic preforms are at least temporarily applied only with the first pressure level (P1) and the second pressure level (P2).

3. The method according to at least one of the preceding claims, characterized in that, in at least one operating mode and preferably in both operation modes, compressed air is at least temporarily guided from the forming stations and / or the plastic containers back into the second pressure reservoir.

4. The method according to at least one of the preceding claims, characterized in that a pressure level in the second pressure reservoir is determined, and, depending upon this pressure level, there is a transition from one operating mode to the other operating mode.

5. The method according to at least one of the preceding claims, characterized in that the plastic preforms are applied with a further pressure level (Pi2), wherein this further pressure level is higher than the second pressure level (Pi1), but lower than the third pressure level (P2).

6. The method according to at least one of the preceding claims, characterized in that working parameters for application with the first and / or third pressure levels are specified, and / or working parameters for application of the second pressure level are determined by a control device.

7. An apparatus for forming plastic preforms (10) into plastic containers (15) with a transport device (2) that transports the plastic preforms (10) along a predetermined transport path (P), wherein the transport device has a rotatable transport carrier (22) on which a plurality of forming stations for forming the plastic preforms (10) into the plastic containers (15) are arranged, wherein the forming stations each have application devices (84) which apply the plastic preforms with the flowable medium, and wherein the apparatus (1) has at least three pressure reservoirs which store the flowable and in particular gaseous medium, and, to expand them, the plastic preforms can be applied in a first operating mode with a first pressure level (P1) stored in the first pressure reservoir (2a), with at least one second pressure level (Pi1) stored in the second pressure reservoir, and with a third pressure level (P2) stored in the third pressure reservoir, wherein the second pressure level (Pi1) is higher than the first pressure level (P1), and the third pressure level (P2) is higher than the second pressure level (Pi1), characterized in that the apparatus (1) can be operated temporarily in a second operating mode, wherein this second operating mode differs from the first operating mode by a pressure level prevailing in the second pressure reservoir, and the apparatus has a fresh air supply device which is designed such that it applies the first and the third pressure reservoirs, but not the second pressure reservoir, with fresh air.

8. The apparatus (1) according to the preceding claim, the apparatus (1) has a further pressure reservoir which is suitable and intended for applying a further pressure level to the plastic preforms.

9. The apparatus (1) according to at least one of the preceding claims 7-8, characterized in that compressed air from the plastic containers can be guided into at least one pressure reservoir.