Method and device for producing containers by blow moulding

Abstract

The invention relates to methods and devices for blow moulding containers (2), in which a preform (1), after thermal conditioning within a blow mould (4), is formed into the container (2) by the action of blowing pressure, wherein the blowing gas which provides the blowing pressure is fed into the preform (1) in at least two pressure stages via compressed air lines (210, 220) assigned to the pressure stages in each case, and a blowing air valve (215, 225) controlling the feeding is arranged in each of the compressed air lines (210, 220), wherein at least the blowing gas of the highest pressure stage is supplied from an external compressed gas source, preferably from a compressor (229), and in which after a container has been formed at least some of the blowing air used is discharged to ambient pressure via a relief line (230) controlled by a relief valve (235), preferably via a silencer (237), wherein, furthermore, for the purpose of reuse, at least one further part of the blowing air used is conducted via a return line (240), which is controlled by a return valve (245), into a first compressed gas store (AR1), and the stored compressed gas is used for a later forming operation, characterised in that a directional control valve (250) is disposed in the return line (240) between the return valve (245) and the first compressed gas store (Ar1), which directional control valve has at least two outlets and at least one inlet and which, on the outlet side, connects the return line (240) to the first compressed gas store (AR1) or to another, second compressed gas store (AR2), which stores compressed gas at a pressure different from the pressure of the first compressed gas store (AR1).

Description

[0001] KHS GmbH

[0002] Juchostraße 20, 44143 Dortmund

[0003] Method and apparatus for bias-forming production of containers

[0004] The invention relates to a method according to the preamble of claim 1, in particular the invention relates to a method for blow molding containers, in which a preform is transformed into the container after thermal conditioning within a blow mold by the application of blowing pressure.

[0005] The invention further relates to a device according to the preamble of claim 9, in particular the invention relates to a device for blow molding containers, wherein a preform after its thermal conditioning in a heating device of the device is transformed into the container within a blow mold of a blowing device of the device by the application of blowing pressure.

[0006] It is known to form temperature-conditioned preforms made of a thermoplastic material into containers by blow molding. A typical thermoplastic material used is PET. Various methods and devices are known in the prior art for forming preforms into containers by injecting pressurized blowing gas into a temperature-conditioned preform. Temperature conditioning means that the preform is heated to a temperature that allows the subsequent bias forming process. This temperature conditioning of the preforms takes place in heating devices, often also called furnaces. As a rule, a temperature profile is also imprinted on the preform along its longitudinal axis; that is, there are areas along the preform's longitudinal axis that are heated to different temperatures. For example,The area below the neck ring is often heated to a higher temperature to selectively initiate the forming process and material redistribution resulting from radial and axial expansion within the container. It is also known to heat the bottom area of ​​the preform, from which, for example, the bottom or foot structure of the finished container is formed, to a higher temperature, as complex structures, such as a petaloid bottom, are sometimes required. Depending on the application, it is also known to provide areas with different temperatures along the circumference of the preform. Such special cases are known, for example, as "preferential heating" for the production of containers with oval cross-sections from preforms. DE 43 40 291 A1, DE 42 12 583 A1, DE 2352 926, and EP 2 977 184 A1 are cited as representative examples of the prior art for all these aspects.

[0007] In the most common application, compressed air is used as the blowing gas, which can also be supplied as sterile air to achieve sterile forming conditions. However, other compressed gases are also found in the prior art, or compressed air with the addition of other gas components, for example, to sterilize the preform or the resulting container, or to achieve an internal coating in the finished container. For example, the prior art also describes the use of compressed air with ozone or H₂O₂ additives. Without limiting the generality, it is described below that the forming process is carried out with compressed air as the blowing gas and that a compressor is provided for supplying the blowing gas. However, the use of compressed air as the blowing gas, especially sterile air, is considered only as a preferred embodiment of the invention in all its embodiments, which are described below.It is also known that the forming of the preform into the container is assisted by a stretching rod, which is inserted into the preform against its closed bottom and then stretches the preform axially. The timing of the stretching rod movement and the supply of pressurized blowing gas influences the material distribution in the container and is therefore often used in the prior art for controlling or regulating the forming process. The provision of a stretching rod is considered preferred for the invention in all its embodiments, which are described below.

[0008] It is also known to introduce the blowing gas under pressure in several pressure stages. A pressure stage is understood to be a gas pressure of a specific level. The term "pressure stage" is sometimes also used here to describe the devices that introduce the blowing gas into the preform at the level corresponding to the pressure stage. For example, it is known to form a preform into a container in three pressure stages. In a so-called pre-blow stage, the blowing gas is introduced into the preform at an initial low pressure, e.g., at a pressure in the range of 3-10 bar, so that a container bladder is initially formed from the preform. It is also known to switch to a blowing gas with a higher pressure at this stage of the forming process. Prior art refers, for example, to an intermediate blowing pressure, which can be in the range of 12-20 bar, but is in any case higher than the pre-blow pressure. In this pre-blow stage, or...Following the pre-blow phase and the intermediate blowing stage, the container bladder essentially conforms completely to the surrounding outer mold. It is also known, in a third stage or phase, referred to in the prior art as the final blowing phase, to introduce blowing gas at a very high pressure, e.g., in the range of 25-40 bar, but in any case higher than the intermediate blowing pressure, into the almost completely formed container so that the container conforms completely to the outer mold, ensuring, for example, that the bottom area and the finer bottle contours are fully imprinted onto the container by the outer mold. In this final blowing stage, the container should also conform to the outer mold as reliably and completely as possible to ensure that the outer mold's temperature influences the container. If the outer mold is kept at a low temperature, e.g.,By actively cooling the outer mold, the contact with the outer mold is intended to cool and solidify the container material, thus stabilizing the container. However, it is also known to maintain the outer mold at an elevated temperature through active temperature control. In this case, the contact of the container with all its features against the outer mold is intended to further reliably heat the container material, enabling relaxation processes and reducing material stresses. This is known, for example, as the heat-set process.

[0009] It is also known to relieve the pressure in the container after the blowing process is complete, i.e., to reduce the pressure inside the container to ambient pressure. This involves opening a pressure relief valve in a relief line to release the excess pressure, specifically the blowing gas that is under pressure. The term "venting" is also commonly used for this process. A pressure relief valve is therefore installed in such a pressure relief line; the corresponding line and the valve controlling it are subsequently referred to as the relief line and the relief valve, respectively. Pressure relief is generally achieved via a silencer to mitigate the considerable noise generated during the process. It is also known to use the released blowing air in a targeted manner, for example, for cooling or other purposes, such as selectively blowing air onto specific areas.

[0010] It is also known to remove at least a portion of the pressurized blow gas not by pressure relief via the relief line from the container, but rather to route the pressurized gas via a return line before pressure relief, either from the formed container to an additional pressure accumulator or to a storage tank for the blow gas for one of the different pressure levels described above, namely for the pressure levels below the highest pressure level. The pressurized gas thus returned can then be used, for example, in subsequent forming processes or for other processes that also require pressurized gas. In this application, the corresponding return lines are referred to as return lines, and the valve controlling these lines as a return valve, in contrast to other lines, particularly the relief line.In the prior art, terms such as air-back or air-recycling are also used for the recirculation of compressed air. Therefore, the aforementioned recirculation valve is sometimes referred to simply as the AR valve within the scope of this application. Generic methods and devices thus feature a recirculation line controlled by a recirculation valve for the purpose of the aforementioned recirculation and reuse of the pressurized compressed air.

[0011] The blowing gas for the highest of the at least two pressure stages of the blowing process cannot be obtained from recycled gas, and at least this gas must be continuously supplied externally, e.g., by an air compressor providing compressed air at a specific pressure, which is then used directly or, for example, via a pressure reducer as the blowing gas for the highest pressure stage. The blowing gas can also be passed through a filter, for example, to ensure sterility. Blowing gas for at least one pressure stage below the highest pressure stage must also be supplied externally for an initial period, referred to in this application as the start-up period, since no blowing gas can be recycled initially, and the required quantity of recyclable gas only becomes available during the initial forming processes. The supply of blowing gas to a pressure stage below the highest pressure stage is carried out, for example, by...This is achieved by reducing the pressure of the blowing gas from the highest pressure stage to at least one lower pressure stage via a pressure reducer. It would also be possible, of course, to supply blowing gas of the second pressure stage from a second external source, although the first variant is the more common one. This externally supplied blowing gas for the aforementioned at least two pressure stages of the blowing process must be conceptually distinguished from the recirculated blowing gas. Supplied blowing gas is only the gas that was not previously fed into a container for container forming, while recirculated gas refers only to the gas that was previously fed into a preform for a forming process and, after completion of the container, was released from the container and recirculated for further use.

[0012] According to the invention, there are at least two pressure stages, meaning that in these at least two pressure stages, operation is carried out with supplied compressed gas during the start-up period. However, in the lower pressure stage(s) of the at least two pressure stages, operation can also be carried out with recirculated compressed gas after the aforementioned start-up period, for example, by recirculating compressed gas from the reshaped containers via the return line into a respective compressed gas reservoir of these lower pressure stages. Depending on the amount of recirculated and actually recirculated compressed gas, the situation may even arise after the start-up period in which no more gas needs to be supplied externally to this lower pressure stage. It is also conceivable, for example, that an external supply of compressed gas occurs when critical conditions are reached and that the external supply of compressed gas ceases when the critical conditions are no longer reached, for example, by opening or closing the valve.Closing of a respective supply valve in a supply line for external compressed gas, through which the external compressed gas can be fed into the respective compressed gas storage tank.

[0013] Regarding the aforementioned compressed gas storage systems, it should be noted that these do not necessarily have to be designed as containers or tanks with a specific volume that are connected to pipelines. The compressed gas pipelines themselves can fulfill the compressed gas storage function if they are of sufficient length and diameter. However, in preferred embodiments, ring mains or storage rings are provided as compressed gas storage systems for certain pressure levels.

[0014] In the forming of preforms into containers, there are linear machines on the one hand and rotary machines on the other, with the latter being considered the preferred variant. It is known in the prior art that the forming of the preforms into containers takes place in blow molding stations, several of which are arranged circumferentially spaced and equidistant on a continuously rotating blow molding wheel. This blow molding wheel corresponds, for example, to a blow molding device according to the claim. Compressed air (or another blowing gas) is supplied, for example, by a stationary compressor and fed to the blow molding wheel via a rotary feedthrough. From the compressed gas supplied by the compressor, compressed gas for the first and second pressure stages is generated, for example, by one or two pressure reducers, unless the pressure supplied by the compressor is to be used. This can take place in the stationary or the rotating part.If there are more than two pressure stages, compressed gas for the third stage would also have to be supplied externally, at least for the start-up period. It is also conceivable that initially the forming process takes place in only two pressure stages, and only when a sufficient quantity of compressed gas for the third pressure stage is available does the forming process then proceed to three pressure stages. Where the present application refers to a two-stage or three-stage blow molding process, this denotes the number of pressure stages that are present at least during the start-up period. It is possible that at a later point in time, namely when pressure accumulators at a different pressure than the pressure stages are filled with recirculated air, the forming process takes place with a further pressure stage. For clarity, this is referred to below as an additional pressure stage. For these additional pressure stages, it is necessary that blow molding gas is recirculated into an associated compressed gas accumulator.For the other pressure stages of the blowing process, in addition to the blowing gas supplied (from externally), blowing gas can also be recycled, so that the amount of blowing gas to be supplied becomes smaller or no supply is required at all.

[0015] It is also known from the prior art to carry out not only the injection of the blowing gas into the preform in several pressure stages during a forming process, but also the return of the blowing gas in several pressure stages. For example, EP 1 974 892 B2 describes not only a cascaded injection of the blowing gas into the preform to be formed in several pressure stages, but also a cascaded return of the blowing gas from the container for reuse in several pressure stages. In this prior art, for example, the preform is formed into the container in five pressure stages, and the blowing gas is returned from the finished container for reuse in the same number of pressure stages.In this state of the art, the large number of pressure stages is considered a disadvantage, as it increases the overall process time of the entire forming process, including the return of the pressurized gas or the depressurization of the container until ambient pressure is reached, in order to then open the surrounding mold and remove the finished container. The large number of return lines with return valves in this state of the art is also considered a disadvantage, as it adversely increases the complexity of the equipment and circuitry.

[0016] It is further known in the prior art that the injection of the blowing gas into the preform, the return of the blowing gas from the finished container, and the pressure relief of the finished container are carried out via a so-called blowing nozzle, and that the associated valves, which control the respective lines for the blowing air, are arranged in a so-called valve block. This valve block thus contains the valves that control the individual pressure stages of the blowing process, the pressure relief valve, and, depending on the number of pressure stages in which the blowing gas is returned for reuse, a corresponding number of return valves. Since pneumatic valves are frequently used in practice, a corresponding number of pneumatic lines must be provided on the valve block, or a corresponding number of pilot valves, usually solenoid valves, to which control lines lead, must be provided in the area of ​​the valve block.Overall, this results in a complex valve block design that offers limited possibilities for subsequent modification or retrofitting. Desired changes typically involve extensive modifications to the valve block, sometimes even requiring a complete redesign.

[0017] The disadvantageous necessity of extensive modifications is further exacerbated by the fact that, for example, a pull-up bar and its movement must generally be taken into account, especially if the pull-up bar is hollow and involved in the supply or discharge of compressed gas, with discharge referring to both the release of pressure and the return of blown gas. When the valve block is modified, the pull-up bar itself and its movement often need to be adapted to the changing valve block design or dimensions. The pull-up bar must be axially displaceable within the blow-off nozzle, so any modification of the valve block generally necessitates changes to the blow-off nozzle and consequently to the pull-up bar and its movement.

[0018] It is therefore an object of the present invention to achieve advantages in the recirculation of the pressurized blown air and to demonstrate ways in which advantages in the amount of recirculated blown air, and consequently in energy savings, can be achieved in a structurally simple manner; energy that would otherwise have to be expended for the regeneration of compressed air. In particular, a further object of the present invention is to demonstrate methods and devices with which existing methods and devices equipped with at least one recirculation line can be retrofitted, and an improvement in the recovery of blown air can be achieved with minimal effort. All embodiments and details of the invention described below are preferably aimed at this retrofitting capability, where the advantages of the present invention are realized in a particularly effective way.Therefore, the present invention relates equally to methods for retrofitting devices for the bias-forming production of containers, retrofitted devices for the bias-forming production of containers, and the use of directional control valves for retrofitting devices for the bias-forming production of containers. The preceding and following explanations thus apply particularly to the methods, devices, and uses mentioned in the preceding sentence.

[0019] According to a first aspect of the invention, the problem is solved according to the invention by a method having the features of method claim 1.

[0020] A generic process is a method for blow molding containers in which a preform, after thermal conditioning, is transformed into the container within a blow mold by the application of blowing pressure. The injection of the blowing gas, which provides the blowing pressure, into the preform takes place in at least two pressure stages, in particular, for example, in two pressure stages. The injection occurs via compressed gas lines assigned to each pressure stage, and each of the compressed air lines is equipped with a blowing air valve that controls the injection. This means, for example, that an open position of the valve enables injection, and a closed position prevents injection. At least the blowing gas of the highest pressure stage should be supplied from an external compressed gas source. If such a process is carried out, for example, on a rotating machine, such an external source would be, for example, a rotary engine.and preferably a compressor arranged in the stationary part of the machine. After container forming, at least a portion of the used blowing air is to be released to ambient pressure via a relief line controlled by a relief valve. A silencer is preferably provided for this purpose, through which the pressure is released to the environment. For the purpose of reuse, at least another portion of the used blowing air is routed via a return line controlled by a return valve to a first compressed gas reservoir. The compressed gas received and stored in this first compressed gas reservoir is used for a subsequent forming process. If, for example, two pressure stages are provided, this return can, for example, be to the lower of the two pressure stages or to a compressed gas reservoir with a pressure that lies between the two pressure stages.Since three pressure stages are provided, the return could be to one of the two or both pressure stages below the highest pressure stage, or to a pressure accumulator with a pressure that lies between two of the three mentioned pressure stages.

[0021] In contrast to the prior art, the inventive method incorporates a directional control valve in the return line between the return valve and the first compressed gas storage tank. This valve has at least two outlets and at least one inlet. On the outlet side, the directional control valve connects the return line connected on the inlet side to the first compressed gas storage tank or to a second compressed gas storage tank that stores compressed gas at a pressure different from that of the first compressed gas storage tank. The switching position of the directional control valve thus determines whether the recirculated blow gas flows into the first compressed gas storage tank or into the second compressed gas storage tank, with both being filled sequentially with recirculated blow gas. In this way, for example, a two-stage recirculation process can be established using only one return line and the aforementioned directional control valve.By installing a directional control valve in the return line of a machine that previously only had single-stage return, a further return stage can be retrofitted, for example, without requiring any modifications to the valve block, the blow nozzle, or the drawbar. All that is needed is the installation of a directional control valve in the return line and the connection of the outlets to compressed gas accumulators, for which several options exist.

[0022] If the initial forming process involved only two pressure stages, an additional pressure accumulator would need to be provided, representing a third pressure stage, an auxiliary pressure stage. Once this auxiliary pressure accumulator is sufficiently filled with compressed gas, the forming process could be carried out with a third pressure stage: the original two pressure stages plus the newly added auxiliary pressure stage supplied by recirculated blown gas, with the lower of the two original pressure stages also being supplied by recirculated blown gas and connected to the outlet of the directional control valve.

[0023] In the example of the original two pressure stages, the return flow does not necessarily have to occur in the lowest of the two original pressure stages. Instead, the two pressure accumulators connected to the outlet of the directional control valve could also operate at a pressure between the two original pressure stages, thus providing compressed gas for four pressure stages: two original pressure stages and two auxiliary pressure stages. Once the compressed gas accumulators for the returned blown gas are sufficiently filled—that is, the accumulators for the auxiliary pressure stages—a conversion process could take place with compressed gas across a total of four pressure stages. It is also conceivable that one of the additional pressure stages could have a pressure below the lowest original pressure stage. The compressed gas stored there could, for example, be used for purposes other than conversion.In a forming process with three original pressure stages of blown gas, the blown gas could be returned from the containers via the return line to those pressure accumulators belonging to the two lowest original pressure stages, according to the invention. Accordingly, a pressure accumulator of each of the two lower pressure stages would be connected to the two outlets of the directional control valve. However, it is possible and preferred that at least one of the two pressure accumulators connected to the outlet side of the directional control valve for the returned blown gas is at a pressure stage that does not correspond to the original pressure stages, i.e., that an additional pressure stage is implemented. This simply means that a further pressure stage is added to the original pressure stages, namely the aforementioned additional pressure stage.This preferred embodiment is further preferably characterized in that the pressure difference between the pressures of adjacent pressure stages is essentially the same. "Essentially" here means with a deviation of plus or minus 3 bar (+ / - 3 bar), more preferably + / - 1 bar. Thus, if the highest original pressure stage is, for example, 35 bar and the lowest original pressure stage is, for example, 5 bar, then the two intermediate additional pressure stages could, for example, be at 15 bar and 25 bar.

[0024] The aforementioned compressed gas accumulators could, for example, be designed as storage containers, preferably arranged on a rotating blow wheel, which offers advantages in terms of short pipe runs and small dead volumes. Preferably, these compressed gas accumulators, especially the ones connected on the outlet side of the directional control valve according to the invention for the recirculated blow gas, are designed as ring lines or accumulator circuits, which are further preferably arranged rotationally symmetrically or even concentrically to the geometric axis of rotation of the blow wheel. This allows comparable pipe run lengths and dead volumes to be achieved for all blow stations arranged on the rotating blow wheel, which is advantageous for ensuring consistent tank quality in all blow stations, thus avoiding differences between the stations.However, especially for the highest pressure stage, it is also conceivable that the pressure accumulator is formed from the lines leading from the compressor to the blowing stations, including one or more rotary distributor tracks, in order to transfer the pressurized gas from the stationary to the rotating part of the blowing wheel.

[0025] As explained above, the solution according to the invention allows the number of recirculation stages to be increased easily, either retroactively or during the manufacturing of a machine. It was also explained that, in principle, it is possible for the compressed gas to be recirculated in all recirculation stages into compressed gas accumulators that are already present and / or that are supplied with compressed gas externally, for example, before and / or during the start-up phase of a forming machine. The compressed gas accumulators of the lower pressure stages would thus be connected on the output side of the directional control valve, for example, the compressed gas accumulators of the two lowest pressure stages of a three-stage forming process. However, it is preferred that at least a portion of the blown gas is recirculated into a compressed gas accumulator, which, for example,During a start-up period and throughout the forming process, the pressurized gas reservoir is filled exclusively with recirculated compressed gas, but no recirculated compressed gas is released. Only after this start-up period would the recirculated compressed gas from the reservoir be fed into a preform to be formed, thereby transforming, for example, a three-stage forming process during the start-up period into a four-stage forming process after the start-up period. In this preferred variant, at least a portion of the compressed gas should therefore be fed into the pressurized gas reservoir of an additional pressure stage.With regard to the forming process, this corresponds to a preferred method of supplying the preform with compressed gas from at least one gas reservoir of an additional pressure stage during the forming process, after a start-up period and after the preform has been pressurized with compressed gas from the lowest pressure stage, but before the preform is pressurized with compressed gas from the highest pressure stage. This method thus follows, for example, and preferably, a start-up period. In this respect, the invention provides that during a start-up period, a first phase of a forming process with at least two pressure stages takes place, and outside the start-up period, a different phase of the forming process takes place, namely with the addition of one or more additional pressure stages, whose gas reservoirs are filled by recirculated compressed air during a start-up period.However, the invention does not preclude the possibility that the additional pressure stage accommodates compressed gas that is not used for forming processes but is supplied for another purpose. The pressure of this compressed gas in such an additional pressure stage may also be below the P1 pressure if this is a suitable pressure level for the other use. Preferably, however, the additional pressure stage also leads to an additional forming stage.

[0026] A preferred method therefore provides that, for a start-up period and for the forming processes within this start-up period, at least one compressed gas accumulator of at least one additional pressure stage, whose pressure lies between the pressures of the at least two pressure stages, is only filled, but no compressed gas is fed from it into the preforms during the forming process. In this way, it is possible, for example, to fill this compressed gas accumulator of an additional pressure stage exclusively with recycled gas. If this compressed gas accumulator were also integrated into forming processes from the outset, it would have to be filled with externally supplied compressed air before the start of the first forming processes. It is advantageously provided that the start-up period ends as soon as and to the extent that a predetermined pressure has been established in the at least one compressed gas accumulator. The compressed gas accumulator can, for example,The system must have a corresponding pressure sensor that transmits pressure readings to a control unit. The control unit could, upon reaching a predetermined pressure, alter the sequence of the forming processes, and in this altered sequence, compressed gas from at least one compressed gas reservoir could be fed into the preform for forming a preform, thus adding at least one additional pressure stage to the existing at least two.

[0027] The start-up period refers to the time during which the very first forming processes are carried out on the very first preforms, which are transferred, for example, to a blowing wheel, e.g., after an initial start or after a restart following standby or an interruption. During this period, the return valve and the directional control valve can, for example, assume an open position after completion of the blowing process but before the vent valve opens, thereby continuously allowing recirculated blowing gas to flow into a connected pressure gas reservoir. Simultaneously, a valve on the outlet side of this pressure reservoir can be in its closed position to prevent gas withdrawal.

[0028] It is possible to implement more than one additional recirculation stage according to the invention, particularly to implement them retroactively. Two alternative approaches are advantageously proposed for this purpose. It is proposed that either a further directional control valve with at least one inlet and at least two outlets be arranged between the recirculation valve and the directional control valve, wherein one of the outlets leads to the other directional control valve and the other outlet leads to a third compressed gas reservoir. In this way, the number of compressed gas reservoirs into which blow gas can be recirculated can be successively increased by arranging at least two directional control valves in series. An alternative approach provides that the directional control valve has at least one inlet and at least three outlets, wherein each of the outlets leads to a compressed gas reservoir.In both alternatives, all output-side connected compressed gas accumulators store compressed gas at different pressure levels. It is also possible that one of the accumulators stores compressed gas at a pressure level not intended for the forming process, i.e., below the lowest pressure stage, but which could be used for other purposes, such as switching air or for blowing preforms, containers, or machine areas for cooling, cleaning, or shielding purposes.

[0029] The advantage of the two alternative approaches described above is that neither requires any modification of the blow nozzle or the valve block, thus significantly simplifying retrofitting. Of course, appropriate valves, additional lines, and an additional compressed gas reservoir are necessary. Implementing the invention as part of a retrofit also requires an adjustment to the control unit that governs the forming process, in particular the switching of the individual valves. Compared to the modifications that would be required to a blow nozzle, a valve block, and possibly the drawbar and drawbar movement, this still represents a considerable reduction in effort, especially since the control unit would also need to be adapted there.

[0030] In all the above methods, it is further advantageously proposed that at least one of the compressed gas accumulators receives the compressed gas of the lowest pressure stage of the at least two pressure stages and that this compressed gas accumulator is supplied, at least until the end of a start-up period, with compressed gas from a higher pressure stage, in particular with the compressed gas from the highest pressure stage of the at least two pressure stages, which is reduced to compressed gas of the lower pressure stage via a pressure reducer. This can and preferably should take place even before the first forming operations on first preforms, so that the at least two pressure stages of the preamble of claim 1 are available, and should continue until sufficient recirculated blowing air is available. Of course, it is also possible that blowing air from a higher pressure stage is supplied at a reduced pressure even after the end of a start-up period, e.g.If the amount of recirculated compressed air is insufficient, for example due to a malfunction or other reasons, a shortage of available compressed air at this pressure level would be imminent, thus jeopardizing the consistent quality of container production. During the start-up phase and thereafter, compressed gas should be recirculated into the compressed gas storage tank containing compressed gas at the lowest pressure level. This recirculation should preferably occur on the side of the pressure regulator facing away from the storage tank, with the recirculated compressed gas flowing through the pressure regulator into the compressed gas storage tank. Since the recirculated compressed gas is routed back to the compressed gas storage tank via the pressure regulator in this way, pressure spikes that would occur with direct injection into the storage tank without passing through the pressure regulator can be avoided.

[0031] It is further proposed, with advantage, for all the aforementioned methods that the injection of pressurized gas at the lowest pressure level into the preform is stopped when a P1 pressure is reached in the preform or in the resulting container bladder, wherein the P1 pressure is selected from a range between 2 and 5 bar, particularly at approximately 3 bar. In this context, "approximately 3 bar" means 3 bar ± 0.5 bar. Subsequently, pressurized gas at a higher pressure is injected into the preform.

[0032] It is also advantageously proposed for all the aforementioned methods that the highest pressure stage be at a P2 pressure, with the pressures in the compressed gas accumulators, into which the blow gas is returned, being in steps with approximately equal intervals between the P2 pressure and ambient pressure or P1 pressure. Thus, if, for example, the P2 pressure is 30 bar and blow gas is returned to two compressed gas accumulators, these could be at 20 bar and 10 bar, respectively. Similarly, if, for example, the P2 pressure is 30 bar and the lowest blow pressure of the multiple pressure stages is 5 bar, and the blow gas is returned to two intermediate compressed gas stages or their associated compressed gas accumulators, their pressures could be, for example, 22 bar and 14 bar. In this context, "approximately" means + / - 1 bar.

[0033] According to a further aspect of the invention, this problem is solved according to the invention by a device with the features of device claim 9. Advantageous embodiments of the device are specified in the dependent claims.

[0034] The device according to the invention is a device for blow molding containers from thermally conditioned preforms, comprising a device for thermally conditioning the preforms and a forming device for forming the thermally conditioned preforms. The forming device has at least one forming station with a blow mold, a blow nozzle, and a valve block. In particular, it is intended that the forming device is designed in the form of a blow wheel on which several such blow stations are arranged at circumferential intervals, the blow wheel being driven to continuous rotation during operation.The blow molding station is designed to transform a preform within the mold into a container by applying blowing pressure. The blowing gas, which provides the blowing pressure, is introduced into the preform in at least two pressure stages via compressed air lines assigned to each pressure stage. Each of these compressed air lines contains a blowing air valve that controls the injection. It has been previously described, or is known in the prior art, that, for the purpose of introducing the blowing air, a blowing nozzle is lowered onto the preform, sealing it in place. Subsequently, by actuating the valves involved, blowing air at different pressure levels is introduced into the preform in a specific sequence. This is preferably supported by a stretching rod that is guided axially into the preform and against the base of the preform, thus stretching the preform axially.

[0035] The device has a relief line and is configured and designed to release at least a portion of the used blowing air to ambient pressure via the relief line, which is controlled by a relief valve, after container forming, preferably via a silencer of the device. The device further has a return line controlled by a return valve and a first compressed gas reservoir connected thereto, and is configured and designed to guide at least a further portion of the used blowing air via the return line into the first compressed gas reservoir for reuse, and to guide the stored compressed gas from the compressed gas reservoir into a preform for a subsequent forming process.This setup and configuration is primarily expressed in the provision of appropriate lines with switchable valves located within them, and in a control device that, in a time-coordinated manner, moves the switchable valves to an open and a closed position. For example, to recirculate compressed air, the valve in the return line must open before the vent valve and close before the vent valve opens. To recirculate the largest possible quantity of compressed air, the vent valve must remain closed during the recirculation process to prevent valuable energy contained in the compressed air from escaping through the vent line. The vent and return valves must also be controlled in a time-coordinated manner with the valves in the compressed air lines.The return and relief valves should only be opened once the forming process of the container is complete. As a rule, the valves in the compressed air lines are then closed. "As a rule" does not preclude the possibility that a compressed air line might remain open. For example, it is known that after the forming process is complete, the finished container is purged with compressed air for cooling purposes; this is common practice in so-called heat-set processes. This purge air could advantageously be stored in one of the aforementioned pressure accumulators via a return line. However, with regard to the blowing air used for the actual forming process, which flows in for the actual forming operation, the return and relief valves are closed so that the necessary pressure can build up in the preform, the developing container bladder, or the container itself.This setup and design is also reflected in the fact that the recirculated compressed air, stored in a pressure accumulator, can be fed back into a preform at a later time via a corresponding line. This line, which leads from the pressure accumulator through the nozzle into a preform and is also valve-controlled, allows the recycled compressed gas to be reused as desired. In the simplest way, this is achieved, for example, via the return line, which is thus filled with compressed gas flowing from the accumulator towards the pressure accumulator during a recirculation process, and conversely, during the forming process, with recycled compressed gas flowing from the accumulator towards the container.

[0036] According to the invention, a directional control valve is arranged in the return line between the return valve and the first compressed gas storage tank. This valve has at least two outlets and at least one inlet and connects the return line on the outlet side to the first compressed gas storage tank or to another, second compressed gas storage tank that stores compressed gas at a pressure different from the pressure of the first compressed gas storage tank. This directional control valve can, for example, be a 3 / 2-way valve. On the inlet side, the return line leads to the directional control valve or is connected to the inlet of the directional control valve. On the outlet side, two return lines lead to compressed gas storage tanks. In a first switching position of the directional control valve, for example, the first compressed gas storage tank is pressurized with recirculated compressed air, and in a second switching position, for example, a second compressed gas storage tank is pressurized with compressed gas. In the case of a 4 / 3-way valve, for example, the output side could be...A third pressurized gas storage tank with a third pressure stage may also be connected.

[0037] By arranging such a directional control valve in the return line according to the invention, no modification of the nozzle or the valve block is required; the modification takes place in the return line itself. Compared to a modification, for example, in the relief line, the arrangement in the return line has the advantage that as much blown gas as possible is returned. If, for example, such a directional control valve were arranged in the relief line, a pressurized gas reservoir could indeed be arranged at one of the outlets, and a portion of the blown air could be returned via this reservoir.However, this would result in a loss of blown gas compared to the arrangement in the return line, because the switching positions of a directional control valve have brief overlaps, which does not mean any energy loss in the arrangement in the return line, since in each of the switching positions there is a return to a pressurized gas storage tank, but in the arrangement in the vent line a usable proportion of blown gas would be vented unused.

[0038] The advantages of the device subclaims correspond to the advantages stated for the analogous method subclaims, so that a repetition can be omitted here.

[0039] A device according to the invention can in particular be designed and configured to carry out one of the methods specified in the method claims.

[0040] The preferred embodiments of the method discussed above can also be implemented in the apparatus in a mirror image. Conversely, the preferred embodiments of the apparatus discussed above can also be implemented in the method in a mirror image. The advantages of the method and the apparatus mentioned above are, in a mirror image, also advantages of the apparatus and the method, respectively. For the advantages, embodiment variants, and embodiment details of the various aspects of the solutions described here and their respective possible developments, reference is also made to the descriptions of the corresponding features, details, and advantages of the other aspects and their developments.

[0041] The invention is explained in more detail below with reference to preferred embodiments and the accompanying figures. The drawings are not necessarily to scale. In the figures, identical or essentially functionally identical or similar elements are designated with the same reference numerals. They show:

[0042] Fig. 1 is a sketch illustrating the basic structure of a device for the forming production of containers, using the example of a rotary blow molding machine.

[0043] Fig. 2 shows a schematic representation of the pipes and valves involved in a forming process;

[0044] Fig. 3 shows a principled sectional view through an outer form of a forming station with a preform and developing container bladder.

[0045] Fig. 4 shows a schematic representation of the pressure profile within the preform or within the developing container bladder or within the container during the forming process, once according to a prior art, once according to the invention, and

[0046] Fig. 5 shows a schematic representation of the temporal sequence of a forming process according to the invention.

[0047] The following section first explains the basic structure of a machine for forming preforms (1) into containers, e.g., bottles, using the preferred example of a rotary blow molding machine, which is designed to rotate continuously because this is considered a particularly preferred design, e.g., compared to intermittently rotating blow molding machines or linear blow molding machines. However, the basic supply and recovery of blowing air according to the invention would remain unchanged if the less preferred blow molding machine designs, which are therefore not shown or described, were chosen.

[0048] To illustrate the technical context of the invention, Fig. 1 shows the basic structure of a rotary blow molding machine (B) equipped with a heating unit (H) with a circulating section (20) and a rotating blow wheel (25) as a forming unit. Starting from a preform input (26), the preforms (1) are transported by transfer wheels (27, 28, 29) into the heating unit (H) and into the circulating section (20). In a transfer area, the preforms (1) are transferred from a transfer wheel (29) to a transport unit (33). Heating units (30), e.g., heating boxes known in the prior art, and optionally blowers (31) are arranged along the circulating section (20) to maintain the temperature of the preforms (1). The preforms are temperature-conditioned as they pass through the heating device (H) so that subsequent forming on the blow wheel (25) is possible.The section of the circulation path (20) that runs alongside the heating units (30) is referred to in this application as the heating section (24). After sufficient temperature conditioning of the preforms (1), they are transferred to the blowing wheel (25), in the area of ​​which blowing stations (3) are arranged. For the transfer to the blowing wheel (25), a transfer wheel (35) removes the preforms from the transport devices (33) in a removal area. The finished blown containers (2) are fed by further transfer wheels to an output section (32).

[0049] In order to transform a preform (1) into a container such that the container possesses material properties that ensure a long shelf life for foodstuffs, especially beverages, filled within the container, specific process steps must be followed for heating and orienting the preforms (1). Furthermore, advantageous effects can be achieved by adhering to specific dimensioning requirements. Various plastics can be used as thermoplastic materials. For example, PET, PEN, or PP are suitable.

[0050] In the chosen example, without loss of generality, the expansion of the preform (1) during the orientation process is achieved by supplying compressed air. The compressed air supply is, for example, divided into a pre-blowing phase, in which compressed air is supplied at a low pressure, and a subsequent main blowing phase, in which gas is supplied at a higher pressure. During the pre-blowing phase, compressed air with a pressure P1, for example, in the range of 5 to 10 bar (e.g., 7 bar), is typically used, and during the main blowing phase, compressed air with a pressure P2, for example, in the range of 25 to 40 bar (e.g., 35 bar), is supplied. A forming process sequence according to the invention is explained with reference to Figures 2-5.

[0051] In this example, the forming process takes place in two pressure stages. However, it is also possible and known to include an additional pressure stage between these two stages, a so-called intermediate blowing phase. During pressure release, the P2 pressure could be returned to an associated pressure reservoir to be used for the intermediate blowing phase in the next forming process. To enable such an intermediate blowing phase even during the initial forming processes, this pressure reservoir can be pre-filled with compressed air before the first forming operations begin. This can be achieved, for example, by feeding the P2 compressed gas into the reservoir in a pressure-reduced form, i.e., via a pressure reducer. The pressure reservoir for P1 pressure is also pre-filled with the P2 blowing gas in a pressure-reduced form before the first forming operations begin.The principle according to the invention requires only a forming process with two pressure stages and can be applied analogously to forming processes with any number of pressure stages greater than two. However, according to the invention, a return line is required, in the sense of at least one, through which blow gas is returned to a pressure accumulator in order to use the returned blow gas for subsequent forming processes. This return via a return line can, for example, be made into the P1 pressure accumulator. The aforementioned pressure gas accumulator for the intermediate blow pressure could then, for example, be retrofitted or added in the manner according to the invention, which will be described in more detail later, and the pressurized gas stored therein could, for example, only be used for forming processes when the intermediate pressure gas accumulator is sufficiently filled by returned blow gas.

[0052] As can be seen from Fig. 1, in the illustrated embodiment, the circular track (20) is formed from a plurality of circulating transport devices (33) arranged in a chain-like fashion and guided along deflection wheels (34). The chain-like arrangement is intended to create a substantially rectangular basic contour. In the illustrated embodiment, a single, relatively large deflection wheel (34), the head wheel, is used in the area of ​​the circular track (20) facing the feed wheel (29) and a discharge wheel (35), while two comparatively smaller deflection wheels (36) are used in the area of ​​adjacent deflections. However, any other circular track contour is also conceivable in principle.

[0053] To enable the feed wheel (29) and the discharge wheel (35) to be arranged as close as possible to each other, the arrangement shown proves to be particularly advantageous, since in the area of ​​the corresponding extension of the circular path (20) three deflection wheels (34, 36) are positioned, namely the smaller deflection wheels (36) in the area of ​​the transition to the linear circular sections of the circular path (24) and the larger deflection wheel (34, head wheel) in the immediate transfer area to the feed wheel (29) and to the discharge wheel (35).

[0054] The chain-like connected support devices (33) rotate around the described deflection wheels (34, 36) and along the circular track (20). For this purpose, one of the deflection wheels, e.g., the head wheel (34), or several of the deflection wheels can be rotaryally driven, e.g., by a motor driving the head wheel (34), or e.g., by a mechanical coupling to the rotation of the blow wheel (25), which can, for example, have a rotary drive (41). The feed wheel (29) transfers preforms (1) onto support devices (33), which arrive without preforms in a feed section of the circular track. From this feed section, the support devices (33), now equipped with a preform (1), guide the preform (1) clockwise along the circular track (20), first towards the distant deflection wheel (34), then around this deflection wheel (34), and then back towards the discharge wheel (35).As soon as a carrying device (33) with a preform (1) enters the removal area of ​​the circulation track (20), the preform (1), which at this point has undergone the heating required for forming, is removed from the carrying device (33) or transferred to the removal wheel (35) and guided by the wheel, rotating around its axis, towards the blowing wheel (25). The carrying device (33), now without a preform after this removal process, travels along the circulation track (20) from the removal area to the feed area to pick up another preform (1). The illustrated feed and removal wheels (29) and (35) can, for example, have pincer-like feeding and removal elements. Since these wheels, collectively referred to as transfer wheels, are not significant for the present invention, further description is omitted. For the same reason, the blowing wheel (25) also requires no detailed description.These wheels can be designed in a wide variety of ways, as is known in the prior art.

[0055] After the containers have been blown, they are removed from the area of ​​the blowing stations (3) by a removal wheel (37) and transported via the transfer wheel (28) and a discharge wheel (38) to the discharge line (32).

[0056] The heating section (24) shown in Figure 1 can be modified, for example, by providing a larger number of heating units (30) in order to, for example, temper a larger quantity of preforms (1) per unit of time. The heating units (30) described above are, for example, designed as heating boxes in which, for example, NIR emitters are arranged. This is merely an example of usable heating units. A multitude of designs are known in the prior art that serve the temperature conditioning of preforms and can thus be described as heating devices. Other heating methods besides irradiation with IR or NIR radiation are also known in the prior art, e.g., heating the preforms by microwave irradiation. The invention is independent of the specific appearance of the heating units (30) and also of the specific appearance of the heating section (24) and the circulation section (20).

[0057] On the blowing wheel (25), which is rotated by the rotary drive (41), several blowing stations (3) are arranged circumferentially. In these stations, the temperature-conditioned preform (1) is to be formed into a container (2) by pressurizing it with a blowing gas, as will be shown and described later. A rotary distributor (50) supplies the blowing stations (3) not only with the required blowing fluid, in this specific example compressed air, but also with other media required on the rotating blowing wheel, such as temperature control fluids for the blowing stations (3) or the like. The rotary distributor (50) can also be used, for example, to transmit electrical energy or to facilitate data exchange between the machine control and the blowing station (3), and between sensors on the blowing wheel (25) and the machine control.Such rotary distributors (50) are known to the skilled person in a wide variety of designs and therefore do not require further description.

[0058] Fig. 3 shows a schematic sectional view through an outer form (4) of a forming station (3), while Fig. 2 illustrates, in a schematic diagram, the lines, valves, and pressurized gas storage or sources involved in a forming process. In the illustrated example, the outer form (4) consists of a base form (5), which defines a bottom contour, and two side shells (6), which define the wall contour of a container to be produced. These form elements (5, 6) of the outer form (4) enclose an inner cavity (9). In the illustrated example, a preform (1), shown in an already stretched and radially slightly expanded state, is located in the cavity (9) and held by the outer form (4). In this application, it is referred to as the container bladder (8), and the original preform (1) is shown with a dashed line.Not shown is a finished container, which is formed by the continued expansion of the depicted container bladder (8) until it has completely conformed to the outer mold (4). A stretching bar (7) holds the stretched preform (1) against the bottom mold (5), meaning that the closed bottom (11) is pressed against the bottom mold (5) by the tip of the stretching bar (12). As can be inferred from the depicted and developing container bladder (8), the stretching process generally takes place with the simultaneous introduction of the forming fluid under pressure. A so-called stop plate (14) is located in the opening area of ​​the preform (1), the developing container bladder (8), and the finished container. The schematic shows how a blow nozzle (10) was lowered in a sealed manner onto the mouth edge of the preform (1) in order to inject blowing gas into the preform (1) and into the resulting container bladder (8).In alternative embodiments, it is also known that the blow nozzle (10) is not sealed against the mouth edge, but is, for example, sealed against the neck ring or sealed against the blow mold or the stop plate (14). In any case, all these types of sealing aim to ensure that the desired forming pressure can be generated within the preform (1).

[0059] This blow nozzle (10) is also shown schematically in Figure 2, together with a schematically depicted container (2). A compressed gas line (210) for the so-called P1 pressure, i.e., for compressed gas with the lowest pressure level of P1, runs to this blow nozzle (10). This compressed gas line (210) is controlled by a first blow gas valve (215), which is subsequently also referred to as the P1 valve. On the side of the P1 compressed gas line (210) opposite the blow nozzle, an associated compressed gas reservoir (217) is shown, which is supplied with compressed gas, e.g., from an external compressed gas source, but in the example shown, by a second compressed gas reservoir (227) via a pressure reducer (219), wherein this second compressed gas reservoir (227) has a blow gas pressure of P2, where P2 is higher than P1.This second compressed gas storage tank (227) is supplied by a compressed air compressor (229), and a pressure reducer may also be arranged between the compressor (229) and the compressed gas storage tank (227).

[0060] The blow gas at pressure stage P2 flows from this second pressurized gas reservoir (227) via the P2 pressurized gas line (220) and, controlled by and via the P2 valve (225), also to the blow nozzle (10). In the illustrated embodiment, a two-stage blow molding process is thus originally implemented. In contrast, in a three-stage blow molding process, for example, a P3 pressurized gas line and a PS blow valve would exist, and the P3 pressurized gas would also be directed to the blow nozzle (10) and, with appropriate switching of the aforementioned valves, introduced into the preform (1).

[0061] In addition to these compressed gas lines (210) and (220), a so-called exhaust line (Exh, 230) extends from the blow nozzle (10). The exhaust valve (235) is opened by a control device (100, not shown) when any compressed gas remaining in the container (2) needs to be released. With the exhaust valve (235) open, the compressed gas flows towards and through the silencer (237) and then escapes into the environment, allowing ambient pressure to equalize inside the container (2).

[0062] In accordance with the invention, a return line (air recycling, AR, 240) is also provided, which is likewise controlled by a valve, in this case by the return valve (245). According to the prior art, the return line (240) would, for example, lead to the P1 storage tank (217) and fill it with recirculated compressed air, so that during operation and possibly after a start-up period, only a small amount or even no compressed air would need to be supplied to the P1 storage tank (217) from external sources via the pressure reducer (219). It is also known in the prior art, in a manner not shown, to provide a third pressure stage with P3 pressure. In this case, it is also known to provide a second return line in addition to the return line (240) shown, which is also controlled by a return valve. For example, the air would be supplied via one of these two return lines.First, pressurized gas is returned to the P3 reservoir, with the pressure at P3 being higher than the pressure at P1. Subsequently, a further quantity of pressurized gas is returned to the P1 reservoir via the other return line. This is followed by venting.

[0063] In contrast, the example shown provides for a directional control valve (250) in the return line (240), e.g., retrofitted. If more than one return line is provided, such a directional control valve can be provided in one or both of the return lines. Without limiting generality, the following description focuses solely on the case where there is only a single return line.

[0064] In the illustrated case, the directional control valve can assume two switching positions, thus it is a 3 / 2-way valve. On the side of the directional control valve (250) facing away from the nozzle, i.e., connected to the outlets of the directional control valve (250), two return lines (242) and (244) run to pressure accumulators (246) and (248), respectively. The recirculated compressed air is stored in these two pressure accumulators (246) and (248) at different pressures. Accumulator (246) can, for example, store recirculated compressed air AR1 at a pressure AR1, where the AR1 pressure lies between the P1 and P2 pressures. Pressure accumulator (248) can, for example, store recirculated compressed air AR2 at a pressure AR2, where the AR2 pressure also lies between the P1 and P2 pressures. In the case shown, the AR1 pressure should be lower than the AR2 pressure, resulting in pressure levels P1, AR1, AR2 and P2 in ascending order.The distances P1 to AR1, AR1 to AR2, and AR2 to P2 can preferably be substantially the same, so that the pressure difference P1 to P2 can be achieved in three equal steps via the intermediate pressure stages AR1 and AR2. "Substantially" in this context means that the distances do not have to be exactly the same, but can vary by + / - 1 or + / - 2 bar.

[0065] In the illustrated example, two compressed gas accumulators (246) and (248) for recirculated blow gas are provided on the opposite side of the blast nozzle from the directional control valve (250). If, for example, a return line (240) leads to the P1 compressed gas accumulator in an existing machine, blow gas could continue to be recirculated into this P1 compressed gas accumulator via the directional control valve (250) in its first position. With a change in the directional control valve position, an additional compressed gas accumulator for recirculated blow air could be connected via the second available output of the directional control valve, thus transforming the originally single-stage blow air recirculation process into a two-stage blow air recirculation process. Similarly, a directional control valve with more than two outputs could be arranged in the return line (240) to connect, for example, three compressed gas accumulators to three outputs. These three compressed gas accumulators could, for example,It could be a P1 and a P3 pressure reservoir, and an additional Air Recycling (AR) pressure reservoir. These reservoirs could also be a P1 pressure reservoir, an AR1 pressure reservoir, and an AR2 pressure reservoir.

[0066] As can be clearly seen in Figure 2, no modifications to the blow nozzle (10) are required for this change, which is made possible by the installation of the directional control valve (250), particularly when it is retrofitted to an existing forming machine. No modifications are required to the valve block, schematically designated by reference numeral (200), in which the described blow valves, return valves, and relief valves are arranged. This block can be located, for example, on the blow nozzle or on a drawing bar (not shown) or on a drawing bar movement device (also not shown), with the advantage of short pipe runs. The directional control valve (250) shown can be positioned at any point in the return line (240) without requiring any modification to the valve block (250).

[0067] Figure 4 illustrates the basic process of a forming operation according to the prior art (curve 410 represents the pressure profile inside the preform over time) and according to the present invention (curve 420 shows the modified pressure profile over time according to the invention). According to the prior art, for example, the P1 valve opens first while the vent valve (235) is closed. Accordingly, the measured pressure initially rises until a first pressure plateau is reached. The pressure curve up to this point is explained, among other things, by the fact that the pressure in the preform initially rises until a certain threshold value is reached, at which point the container bladder ruptures, causing the pressure to drop briefly, and then the container bladder continues to expand. The P1 valve is then closed and the P2 valve is opened. The pressure increases abruptly because the P2 pressure is higher than the P1 pressure.Referring to Figure 3, the switch from P1 to P2 pressure takes place, for example, after the stretching bar has fully stretched the preform and the container bladder (8) has at least partially reached the outer walls.

[0068] Switching to the P2 pressure causes the container bladder (8) to conform completely to the surrounding walls, and in particular, even finer contours are imprinted. After complete conformity to the outer shape, the internal pressure eventually reaches the P2 pressure. The pressure is maintained for a certain period of time so that the container achieves stability through cooling. In heat-set processes, conformity to the surrounding shape would not lead to cooling; instead, the container wall would be kept at an elevated temperature. In contrast to Figure 4, it would then be purged and cooled, for example, with purge air, before the pressurized gas is released. According to Figure 4 and a prior art, this release of the pressurized gas occurs in one step by opening the relief valve.Therefore, the depicted curve (410) is not the pressure curve of the prior art, which defines the generic form of the technology, because according to the prior art, pressure relief via the relief valve is preceded by a return step via a return valve. Pressure curve 410 thus shows a simplified pressure curve, also so that pressure curve 420 can be more clearly distinguished from it.

[0069] According to pressure curve 420, the release of pressurized gas from the finished container occurs in three steps, two of which are a recirculation step for purged gas and the third step is a venting step. In the recirculation step designated R2, the recirculation valve (245) is open, the P1 valve, the P2 valve, and the venting valve are closed, and the directional control valve (250) is switched so that purged gas flows from the finished container into the AR2 pressurized gas reservoir. The directional control valve (250) then switches, and the recirculation stage designated R1 is activated, in which purged gas can flow into the AR1 reservoir. Finally, the recirculation valve (245) is closed and the venting valve (235) is opened, allowing the internal pressure in the container to drop to ambient pressure. For example...Since the AR1 and AR2 accumulators are not supplied with external pressurized gas, but exclusively with recirculated blown gas, the forming process cannot yet utilize pressure stages AR1 and AR2 for initial forming operations, during which the aforementioned accumulators may not yet be filled with recirculated blown gas. During this period, referred to in the present application as the start-up period, the forming process would proceed as shown in curve (410), but the pressure relief would proceed as shown in curve (420). When sufficient recirculated blown gas is available in the AR1 and AR2 pressurized gas accumulators, this pressurized gas can also be used for the forming operations, allowing the process described below in pressure curve 420 to begin. For example, a control device can switch between the different forming processes described.when a connected pressure sensor in the compressed gas storage tank AR1 and / or AR2 indicates sufficient filling by reaching a certain pressure.

[0070] As already described for curve 410, the P1 pressure stage is executed first. However, the process does not switch to the P2 pressure stage. Instead, the recirculated blowing gas from the AR1 pressure reservoir is first fed into the preform. Accordingly, this section is designated Z1 in pressure curve 420: Z because an additional pressure stage is present, and the number 1 because recirculated blowing air, which was stored in recirculation stage R1, is used. Afterward, blowing gas from the AR2 pressure reservoir is fed into the preform, indicated in pressure curve 420 by the designation Z2: the number 2 because blowing gas from recirculation stage R2 is used in this phase. The original two-stage forming process with pressure stages P1 and P2 has now become a four-stage forming process by adding or integrating the two additional pressure stages AR2 and AR1. For example...By retrofitting the directional control valve (250), a two-stage forming process can be easily converted into a four-stage forming process. This example can be applied analogously to originally three-stage forming processes (and to processes with any number of pressure stages) and to cases where the directional control valve merely adds an additional compressed gas reservoir for recirculated blowing air. Accordingly, the forming process then only involves one additional pressure stage compared to the original pressure stages.

[0071] Figure 5 schematically illustrates the sequence in which, for example, a control device 100 opens and closes the valves involved to carry out a multi-stage forming process and a multi-stage return process for blown gas. In the first step 110, the exhaust valve or the vent valve in the vent line is closed. At this point, a preform 1 is located in the blowing station 3 belonging to the exhaust valve 235, and the blowing nozzle 10 of this station is sealed against, for example, the preform 1. The stretching of the preform 1 by the stretching rod 7 of the station may have already begun. Subsequently, in step 120, the control device 100 opens the P1 valve 215. The P1 pressurized gas flowing into the preform 1 leads to a pressure increase in the preform, as shown, for example, in Figure 4. After reaching a desired pressure value or after a certain period of time, e.g.,Upon reaching a specific rotational angle of the blow wheel 25, the P1 valve 215 closes at 130° and the return valve 245 opens at 140°, while the directional control valve 250 is in the position where the AR1 pressure accumulator 246 is flow-connected. Therefore, the blowing gas stored in the AR1 pressure accumulator 246 can now flow into the preform 1 or into the already formed container bladder 8 and effect further deformation. The AR1 pressure accumulator 246 may have been previously filled with recirculated blowing air. The AR1 pressure is thus the second pressure stage of the forming process, possibly implemented as an additional pressure stage, whereby the P1 pressure is always lower than the AR1 pressure.

[0072] In step 150, the control unit 100 switches the directional control valve 250 to the AR2 pressure gas accumulator 248. The return valve 245 remains open, meaning the AR2 pressure gas accumulator 248 is fluidically connected to the meanwhile further developed reservoir bladder 8. The AR2 pressure gas accumulator 248 is therefore a pressure gas accumulator of a third pressure stage, where the AR2 pressure is higher than the AR1 pressure. The AR2 pressure stage can also be designed as an additional pressure stage and may, for example, have been pre-filled exclusively with recirculated blow gas. By the end of the AR2 pressure stage, the reservoir bladder 8 may, for example, have largely conformed to the contour defined by the outer shape 4.

[0073] In a final forming step, in step 160, the control unit 100 closes the return valve 245. This interrupts the flow of AR2 compressed gas. The directional control valve 250 can remain in its last position. In step 170, the P2 blow-off valve is opened, and compressed gas at P2 pressure flows into the almost fully formed container, pressing the container walls firmly against the outer mold. This creates even fine details and allows the container to cool, if necessary, through contact with the outer mold. After a certain period of time, the forming process is complete; that is, the preform 1 has become a finished container 2. After a certain period of time, the control unit 100 closes the P2 valve 225 in step 180, and the phase of releasing the compressed gas begins. This phase starts with the return of the blow-off gas, followed by venting.

[0074] To recirculate the blown gas, the control unit 100 first opens the return valve 245 in step 190, while the directional control valve 250 remains in its last position, thus maintaining a fluid connection between the interior of the container and the AR2 pressure accumulator 248. The blown air from container 2, which corresponds approximately to the P2 pressure, flows into the AR2 accumulator 248. Then, in step 192, the control unit 100 switches the directional control valve 250 to its second position, establishing a fluid connection to the AR1 pressure accumulator 246, allowing blown gas to flow into the AR1 pressure accumulator 246. Subsequently, in step 194, the control unit 100 closes the return valve 245, while the directional control valve 250 remains in its last position, thus already in the position it must be in for the next forming process.With the closing of the return valve 245, the return phase is completed and no more blown gas is discharged via the return line 240.

[0075] The pressure relief phase then begins via the relief line 230. In step 196, the control unit 200 opens the exhaust valve 235, allowing the remaining pressurized gas to escape from the container to the environment via the silencer 237. The pressure in the container 4 reaches ambient pressure, so the finished container 4 can now be removed from station 3 and a new preform 1 inserted, allowing the preceding process to be repeated.

[0076] The described process assumes that sufficient compressed gas of both pressure stages is available in the AR1 pressure accumulator 246 and the AR2 pressure accumulator 248. If these two pressure accumulators 246 and 248 are filled exclusively with recirculated blown air, a modified sequence of steps would occur at the start of production of a forming machine or blow molding machine B, which is also executed by the control unit 100. The control unit 100 would therefore initially initiate one sequence of steps and later a different sequence. In these two different process sequences, the valves mentioned above would be opened and closed in a different order, and the durations of being open and closed would also be different.However, this primarily concerns the sequence for supplying blown gas to the preform 1, while the discharge of the blown gas, i.e. the recirculation phase and the venting phase, does not need to be changed, but could remain the same in both mentioned step sequences.

[0077] In Figure 5, a dashed arrow indicates that steps 140-160 are not executed or are skipped during a start-up period, specifically when there is not yet a sufficient quantity of compressed gas in the AR1 pressure accumulator 246 and the AR2 pressure accumulator 248. During this start-up period, no recirculated gas can be used for forming processes. It is possible for the control unit 100 to automatically determine, for example, by monitoring the pressure values ​​in the two accumulators (which may be equipped with pressure sensors), when there is sufficient charge to integrate the recirculated compressed air accumulators into the forming process and when skipping the associated steps is no longer necessary. Alternatively, an operator may input a signal indicating that the start-up period has ended.It is also conceivable that a time-controlled switch from one type of process control to another could occur, for example, by switching between the two after a certain number of blow wheel revolutions with the associated forming processes. Alternatively, the number of containers produced could be used as a criterion for when this switch can be made.

[0078] In general terms, it can be said that the control device 100 can perform two operating modes in all previously described variants of the invention: firstly, by including the original pressure stages and bypassing further pressure stages during the forming of the preform 1 in the container 2, and secondly, by including the further pressure stages during the forming of the preform 1. According to the terminology of the present application, the further pressure stages are so-called additional pressure stages, in contrast to the original pressure stages, and in the preceding example relating to Figure 5, pressure stages AR1 and AR2 are such additional pressure stages. Without needing to describe this in detail, it is also possible that only one of the two pressure stages AR1 or AR2 is designed as an additional pressure stage, while the other pressure stage is pre-filled externally, e.g., via the P2 compressed gas reservoir (227), before the start of the first forming processes.This is achieved by installing a pressure reducer and a valve in an intermediate connecting line. This allows for the supply of compressed gas at reduced P2 pressure, while also enabling the fluid connection to be closed, for example, when no further compressed gas replenishment is required due to recirculated compressed air from an external source. In this case, this pressure stage would not be skipped; only the other pressure stage would be bypassed.

Claims

Claims 1. A method for blow forming containers (2), in which a preform (1) is transformed into the container (2) after thermal conditioning within a blow mold (4) by the application of blowing pressure, wherein the supply of the blowing gas, which provides the blowing pressure, into the preform (1) takes place in at least two pressure stages via compressed air lines (210, 220) assigned to each pressure stage, and a blowing air valve (215, 225) controlling the supply is arranged in each of the compressed air lines (210, 220), wherein at least the blowing gas of the highest pressure stage is supplied from an external compressed gas source, preferably from a compressor (229), and in which, after container forming, at least a part of the blowing air used is released to ambient pressure via a relief line (230), which is controlled by a relief valve (235), preferably via a silencer (237).wherein, for the purpose of reuse, at least a further portion of the blown air used is fed via a return line (240) controlled by a return valve (245) into a first compressed gas storage tank (AR1), and the stored compressed gas is used for a subsequent conversion process, characterized in that a directional control valve (250) is arranged in the return line (240) between the return valve (245) and the first compressed gas storage tank (AR1), which has at least two outlets and at least one inlet and which connects the return line (240) on the outlet side to the first compressed gas storage tank (AR1) or to another, second compressed gas storage tank (AR2) which stores compressed gas at a pressure different from the pressure of the first compressed gas storage tank (AR1).

2. Method according to claim 1, characterized in that the pressure of the first compressed gas storage tank (AR1) and / or the pressure of the second compressed gas storage tank (AR2) lies between the pressures of the at least two pressure stages, wherein preferably the pressure difference between the said pressures is substantially the same.

3. Method according to claim 1 or 2, characterized in that the first and / or the second compressed gas storage (AR1 , AR2) is designed as a ring main or storage circuit.

4. Method according to one of claims 2 or 3, characterized in that, for a start-up period and for the forming processes in this start-up period, at least one compressed gas storage tank (AR2) is filled by at least one additional pressure stage, the pressure of which preferably lies between the pressures of the at least two pressure stages, but no compressed gas is fed from it into the preforms (1) during the forming process, wherein preferably the start-up period is ended as soon as and to the extent that a predetermined pressure has been established in the at least one compressed gas storage tank (AR2), and from then on compressed gas from the at least one compressed gas storage tank (AR2) is fed into this preform (1) for the forming of this preform, so that at least one additional pressure stage is added to the at least two pressure stages.

5. Method according to one of the preceding claims, characterized in that either a further directional control valve with at least one inlet and at least two outlets is arranged between the return valve (240) and the directional control valve (250), wherein one of the outlets leads to the other directional control valve (250) and the other outlet leads to a third compressed gas storage tank, or the directional control valve has at least one inlet and at least three outlets, wherein each of the outlets leads to a compressed gas storage tank, wherein for both alternatives all compressed gas storage tanks store compressed gas at different pressure levels.

6. A method according to one of the preceding claims, characterized in that at least one of the compressed gas storage tanks (217) receives the compressed gas of the lowest pressure stage of the at least two pressure stages and this compressed gas storage tank (217) is supplied at least until the end of a start-up period with a compressed gas of a higher pressure stage, in particular with the compressed gas of the highest pressure stage of the at least two pressure stages, which is reduced to compressed gas of the lower pressure stage via a pressure reducer (219), wherein both during the start-up period and afterwards, blow-off gas is returned to the compressed gas storage tank (217) containing compressed gas of the lowest pressure stage. and wherein the recirculation preferably takes place on the side of the pressure reducer (219) facing away from the storage tank and the recirculated blow gas flows through the pressure reducer (219) into the pressure gas storage tank (217).

7. Method according to one of the preceding claims, characterized in that the injection of blown gas of the first pressure stage into the preform (1) is terminated when a P1 pressure is reached in the preform (1) or in the resulting container bladder (8), wherein the P1 pressure is selected from a range between 2 and 5 bar, in particular at about 3 bar, and then pressurized gas with a higher pressure is injected into the preform (1).

8. Method according to one of the preceding claims, characterized in that the highest pressure stage is at a P2 pressure, wherein the pressures in the compressed gas accumulators (AR1 , AR2), into which blow gas is returned, are in steps with approximately equal step spacing between the P2 pressure and ambient pressure or P1 pressure.

9. Device (B) for blow forming containers (2) from thermally conditioned preforms (1), comprising a heating device (H) for thermally conditioning the preforms (1) and a forming device (25) for forming thermally conditioned preforms (1), wherein the forming device (25) has at least one forming station (3) with a blow mold (4) and a blow nozzle (10) and a valve block (200) and is configured to form a preform (1) within the blow mold into the container (2) by applying blow pressure, wherein the supply of the blow gas, which provides the blow pressure, into the preform (1) takes place in at least two pressure stages via compressed air lines (210, 220) each assigned to the pressure stages, wherein a blow air valve (215, 225) controlling the supply is located in each of the compressed air lines (210, 220). is arranged, wherein the device (B) has a relief line (230) and is set up and designed,After container forming, at least a portion of the blown air used is released to ambient pressure via the relief line (230), which is controlled by a relief valve (235), preferably via a silencer (237) of the device (B), wherein the device (B) further comprises a return line (240) controlled by a return valve (245) and, a first compressed gas storage tank (AR1) connected thereto and is designed and configured to guide at least a further part of the used blowing air via the return line (240) into the first compressed gas storage tank (AR1) for the purpose of reuse, and to guide the stored compressed gas from the compressed gas storage tank AR1 () into a preform (1) for a later forming process, characterized in that a directional control valve (250) is arranged in the return line (240) between the return valve (245) and the first compressed gas storage tank (AR1), which has at least two outlets and at least one inlet and which connects the return line (240) on the outlet side to the first compressed gas storage tank (AR1) or to another, second compressed gas storage tank (AR2), which stores compressed gas at a pressure different from the pressure of the first compressed gas storage tank (AR1).

10. Device according to claim 9, characterized in that the pressure of the first compressed gas storage tank (AR1) and / or the pressure of the second compressed gas storage tank (AR2) lies between the pressures of the at least two pressure stages, wherein preferably the pressure difference between the said pressures is substantially the same.

11. Device according to claim 9 or 10, characterized in that the first and / or the second compressed gas storage (AR1 , AR2) is designed as a ring main or storage circuit.

12. Device according to one of claims 10 or 11, characterized in that the device (B) has a control unit (200) which controls the forming processes taking place on the device, wherein this control unit (200) is configured to control the forming in two operating modes, namely in a first operating mode for a start-up period and a second operating mode outside the start-up period, wherein the forming takes place in the at least two pressure stages during the start-up period, wherein at least one additional pressure stage is added to the at least two pressure stages during the forming outside the start-up period.

13. Device according to one of the preceding claims 9-12, characterized in that either between the return valve (240) and the directional control valve (250) a further directional control valve with at least one inlet and at least two outlets is arranged, wherein one of the outlets leads to the other directional control valve (250) and the other outlet leads to a third compressed gas storage device, or the directional control valve has at least one inlet and at least three outlets, wherein each of the outlets leads to a compressed gas storage device, wherein for both alternatives all compressed gas storage devices store compressed gas at different pressure levels.

14. Device according to one of the preceding claims, characterized in that at least one of the compressed gas storage tanks (217) is arranged and configured to receive the compressed gas of the lowest pressure stage of the at least two pressure stages and is at least temporarily supplied with a compressed gas from a higher pressure stage, in particular with the compressed gas from the highest pressure stage of the at least two pressure stages, which is reduced to compressed gas of the lower pressure stage via a pressure reducer (219) of the device, wherein a return line for returning blown gas to this compressed gas storage tank (217) of the lowest pressure stage opens on the side of the pressure reducer (219) facing away from the storage tank, so that the returned blown gas flows through the pressure reducer (219) into the compressed gas storage tank (217).

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