Blow molding method and device

Abstract

In a method for producing hollow bodies (H) from preforms (V) by means of blow molding, a) a preform (V) is provided, b) a process gas having a normal formulation is introduced into the internal volume of one of the preforms (V) in a cascade from at least three gas reservoirs (61, 62, 63, 64) with different specified gas pressures (P1, P2, P3, P4) so as to have a correspondingly increasing process pressure, the last gas reservoir (64) used having the highest specified gas pressure (P4), and c) after the blowing process has ended, at least some of the process gas used is returned in a cascade to the gas reservoirs (61, 62, 63) having a lower specified gas pressure (P1, P2, P3). At least at the start of a production process for producing a plurality of the hollow bodies (H), before steps a) to c) are carried out for the first time, a process gas having a special formulation is introduced into at least one first preform (V) in order to produce a hollow body (H) of a similar quality or the same quality as when using the normal formulation, the special formulation differing from the normal formulation. The method according to the invention and the device according to the invention allow a multi-stage blowing process with a multi-stage recuperation while at the same time reducing costs.

Description

[0001] TITLE

[0002] METHOD AND DEVICE FOR BLOW MOLDING

[0003] TECHNICAL AREA

[0004] The present invention relates to a method and a device for blow molding, preferably for stretch blow molding and more preferably for stretch blow molding of plastic hollow bodies such as PP bottles (PP = polypropylene) or PET bottles (PET = polyethylene terephthalate).

[0005] STATE OF THE ART

[0006] Hollow bodies made of thermoplastic materials, especially PP or PET bottles (PP = polypropylene), are typically manufactured using blow molding machines. For this process, a heated blank or preform is held in a mold of the blow molding machine and inflated by blowing in a process gas, usually compressed air, until it reaches its final shape. This final shape is defined by an enclosing mold.

[0007] The process gas is preferably injected in two or more stages, with the process gas pressure differing in each stage. Typically, a pre-injection with a first pressure is performed, followed by a main injection with at least one second pressure. This second pressure is higher than the first pressure.

[0008] Depending on the process, either only blowing is performed, or the blank is also stretched during pre-blowing using a movable mandrel. The individual process steps are controlled by respective valves, referred to here as process valves. The production or shaping of such hollow bodies using blow molding machines takes place within a few seconds, preferably within 1 to 3 seconds.

[0009] Compressed air is produced using a compressor, which requires a correspondingly large amount of electrical energy. The generation of compressed air contributes significantly to the production costs in the manufacture of such hollow bodies. Furthermore, the carbon footprint is relatively large.

[0010] To reduce the consumption of process gas, especially compressed air, the process gas is at least partially recovered, i.e., recuperated. Any remaining process gas, particularly during the venting of the hollow body, is vented to the outside, thus venting the hollow body.

[0011] EP 1 974892 A2 describes a recuperation process using a multi-stage blowing process with a cascade-like main blowing stage and increasing gas pressures. The blowing device has a gas reservoir for each blowing stage, which is filled during the blowing process with recuperated compressed air from the next highest pressure stage. The gas reservoir with the highest pressure is filled from a pressurized gas source. The initial filling of the subsequent gas reservoirs is carried out with gas from the reservoir with the highest gas pressure. A pipeline is provided for this purpose, leading from this highest-pressure gas reservoir to the subsequent gas reservoirs. Pressure reducers are provided for each of these subsequent gas reservoirs to reduce this highest pressure to the desired nominal pressure of the respective gas reservoir. Such pressure reducers are expensive, require space, and are complex to install.

[0012] EP 1 777056 A1 also describes a multi-stage blowing process using several gas accumulators, which are filled via the recuperated pressure of the next higher-pressure stage. The initial filling is carried out using compressors, with each gas accumulator having its own dedicated compressor.

[0013] EP 1 905569 A2 discloses a cascaded blow molding process in which process gas is first introduced into the preform at a low pressure and then, at a higher pressure, the final shape of the hollow body is achieved. Two pressurized gas sources are provided for this purpose. Furthermore, at least one gas storage tank is provided with a pressure between the low and high pressures. This gas storage tank is empty at the beginning of the production process. It serves to recover the high-pressure process gas used. The recovered process gas is used in the production of further hollow bodies together with the process gas at both low and high pressures. The hollow bodies produced before or during the filling of this gas storage tank therefore do not have the same quality as those produced subsequently and must be disposed of as rejects.There is also a risk during production that pressure drops in the gas storage tank will lead to increased waste.

[0014] PRESENTATION OF THE INVENTION

[0015] Therefore, one of the aims of the invention is to enable a multi-stage blow molding process with recuperation that is cost-optimized.

[0016] This problem is solved by a method having the features of claim 1 and a device having the features of claim 9.

[0017] In the inventive method for producing hollow bodies from preforms using blow molds,

[0018] a) a preform is provided,

[0019] b) A process gas is introduced into an internal volume of one of the preforms in a cascade manner from at least three gas storage tanks with different predetermined gas pressures, with a correspondingly increasing process pressure, according to a standard recipe, wherein the last gas storage tank used has the highest predetermined gas pressure, and

[0020] c) After completion of the blowing process, at least a portion of the used process gas is returned in a cascade manner to those gas storage tanks that have a lower predetermined gas pressure.

[0021] Steps a) to c) of the procedure are repeated with at least one further preform of the preforms.

[0022] According to the invention, at least at the start of a production process for the manufacture of several hollow bodies, before the first execution of steps a) to c), the process gas is introduced into at least one first preform according to a special recipe in order to manufacture a hollow body of similar or the same quality as with the normal recipe, wherein the special recipe differs from the normal recipe.

[0023] The predetermined gas pressure is also called nominal pressure or set pressure.

[0024] This process enables the use of a multi-stage blow molding process with simultaneous process gas recuperation, eliminating the need for multiple compressed gas sources or numerous expensive pressure regulators. Furthermore, the amount of unusable blow-molded hollow bodies is minimized. This combination thus minimizes compressed air consumption, CO2 emissions, the footprint of the equipment, and the costs of both the equipment and its operation. Despite this, high-quality hollow bodies can be produced thanks to the cascaded pressure build-up in the preform.

[0025] Preferably in step c) the gas storage tanks are refilled with the process gas used in the order of their predetermined gas pressures, starting with the gas storage tank that has the second highest predetermined pressure.

[0026] Process gas used at a pressure lower than the lowest predetermined gas pressure is preferably fed to a vent.

[0027] Preferably, the special formulation is applied until the gas pressures of the gas storage tanks, which can be filled with recuperated gas (i.e., used process gas), correspond to the respective predetermined gas pressures. Depending on the variant of the process, this may involve several preforms or, if a rotary machine is used, may take one to two revolutions of the blow wheel.

[0028] Preferably, the special formulation uses process gas from at least two gas storage tanks, both of which are preferably filled from the same pressurized gas source. Preferably, this is the sole pressurized gas source. The pressurized gas is preferably compressed air.

[0029] Preferably, one of the two gas storage tanks connected to the pressurized gas source is the one with the highest predetermined gas pressure, i.e., the highest-pressure gas storage tank. The other of these two gas storage tanks is preferably filled by the pressurized gas source only for use with the special formulation. During use of the standard formulation, this other gas storage tank is filled with used process gas. Preferably, the gas pressure in the other gas storage tank is lower when filled by the pressurized gas source than when filled with used process gas, in order to facilitate easy recovery of the used process gas. In other embodiments, the gas pressure in the other gas storage tank is the same as during normal operation. This other of the two gas storage tanks preferably has the lowest gas pressure; it is thus the lowest-pressure gas storage tank. The gas storage tank with the lowest pressure is preferably used for pre-purge.

[0030] The special formulation and the standard formulation are preferably applied using a control system.

[0031] In some versions, the special formula is used exclusively at the start of the production process. In other versions, it is also used if the predetermined pressure drops in one of the gas storage tanks filled with recuperated gas. If this is the same gas storage tank that can also be filled using the pressurized gas source, it can be filled either exclusively or alternatively using the pressurized gas source, depending on the specific design.

[0032] Preferably, at least four, and preferably exactly four, gas storage tanks with different predetermined gas pressures are used. Preferably, at least three, and preferably exactly three, recuperation stages are used. Through the recuperation or recovery of the used process gas, an eight-stage manufacturing process is thus achieved. Eight-stage manufacturing processes enable a significant saving of compressed gas energy thanks to the four stages of blowing and the threefold recuperation.

[0033] The special formula can be developed and applied in various ways. It utilizes the available compressed air, but takes into account that some of the gas storage units are not yet available. Thanks to this consideration, it has process parameters that also lead to a high-quality end product that does not have to be disposed of as waste.

[0034] In a preferred embodiment, the special formulation differs from the standard formulation in that, after pre-blowing at the lowest pressure, the main blowing stage at the highest pressure, i.e., usually the last stage, is applied immediately; that is, only gas from the first gas storage tank at the lowest pressure and gas from the gas storage tank at the highest pressure are used. Preferably, the pre-blowing and / or main blowing times according to the special formulation correspond to those of the standard formulation. In a preferred variant of the method, the special formulation uses the steps of the standard formulation, except that it differs from the standard formulation in step b). The difference is as follows:

[0035] Immediately after process gas from the gas storage tank with the lowest predetermined gas pressure has been injected into the first preform, process gas from the gas storage tank with the highest gas pressure is introduced, without opening the other gas storage tanks. The special formulation then proceeds in the same way as the standard formulation, following step c) as described above.

[0036] In other variants according to the invention, for example, different times can be used for the application of the available gas pressures compared to the normal recipe.

[0037] The special formulation determines the duration of the injection of the process gas at the lowest pressure, as well as the timing and duration of the injection of the process gas at the highest pressure. The special formulation also determines the level of the lowest pressure, which is preferably lower than that of the standard formulation. All of these parameters are either the same as or different from those of the standard formulation, depending on the special formulation. Preferably, at least the duration of the injection of the process gas at the highest predetermined gas pressure according to the special formulation is longer than the duration of the injection of the process gas at the highest predetermined gas pressure according to the standard formulation.

[0038] In some configurations, a pressure regulator fills the lowest-pressure gas storage tank with a lower pressure than expected in the standard recipe. This has the advantage that the air supply via the pressure regulator is automatically shut off because a higher pressure is present downstream of the regulator. In other configurations, the pressure in the lowest-pressure gas storage tank is nearly constant in both normal and special operation. This is achieved by setting the lowest-pressure gas storage tank to the target pressure when using the special recipe and then slightly reducing the setting of the pressure regulator located between the pressurized gas source and the lowest-pressure gas storage tank when subsequently using the standard recipe. This results in the lowest-pressure gas storage tank having a reduced target pressure, preventing it from being refilled by the pressurized gas source during normal operation.The pressure reducer setting is preferably changed automatically by the control system when switching from the special formulation to the standard formulation. The device according to the invention for producing hollow bodies from preforms by means of blow molding can preferably, but not exclusively, be used according to the method described above.

[0039] In a preferred embodiment, the device comprises at least three process valves and at least three gas reservoirs with different predetermined gas pressures. A first gas reservoir has a low gas pressure, and another has the highest gas pressure. Each gas reservoir is assigned at least one of the process valves to inject process gas in a cascade manner with increasing gas pressure from the at least three gas reservoirs into an internal volume of the preform and to return used process gas in a cascade manner to the gas reservoirs, with the exception of the gas reservoir with the highest predetermined gas pressure. At least some of the gas reservoirs, which have a predetermined gas pressure lower than the highest gas pressure, can only be filled by returning the used process gas.According to the invention, exactly one pressurized gas source is provided, wherein the first gas storage tank and the other gas storage tank can be filled from the pressurized gas source, and wherein the first gas storage tank can additionally be filled by means of recirculation of the process gas used.

[0040] This device is inexpensive to manufacture and requires little space. This is thanks to the single pressurized gas source and the minimal number of pressure regulators; in fact, pressure regulators can be omitted entirely.

[0041] Preferably, the first gas storage tank has the lowest predetermined gas pressure. Preferably, the gas storage tank with the lowest predetermined gas pressure is a gas storage tank for the main blowing or a gas storage tank for the pre-blowing.

[0042] Preferably, the gas storage tanks, which can be filled via recirculation, can be filled using their associated process valves. This also minimizes costs, as there are fewer valves and only a few, short lines.

[0043] In preferred embodiments, at least four, preferably exactly four, gas storage tanks with different predetermined gas pressures are provided.

[0044] In preferred embodiments, several blow molds or valve blocks are provided, with each gas storage tank being assigned process valves from several blow molds or valve blocks. The process valves assigned to a common gas storage tank preferably each lead to its own valve block or blow mold. This minimizes the space requirement of the device and reduces costs.

[0045] Further embodiments are specified in the dependent claims.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Preferred embodiments of the invention are described below with reference to the drawings, which serve only for illustration and are not to be interpreted restrictively. The drawings show:

[0048] Figure 1 shows a schematic representation of a device according to the invention;

[0049] Figure 2 shows a pressure profile of the process gas in the device according to Figure 1 according to a standard recipe;

[0050] Figure 3 shows a pressure profile of the process gas if the standard recipe according to Figure 2 were used at the start of the production process and

[0051] Figure 4 shows a pressure profile of the process gas in the device according to Figure 1 according to a special formula.

[0052] DESCRIPTION OF PREFERRED EXECUTION FORMS

[0053] Figure 1 schematically illustrates a device according to the invention. It comprises a valve block 1 with several process valves 11, 12, 13, 14 and a vent valve 15. The valves are connected via a common main line 85 to a blow nozzle 2, which is arranged on a blow mold 3. The blow mold 3 serves to hold a preform V made of a thermoplastic material, in particular PET or PP. The blow nozzle 2 blows compressed air into the preform V and inflates it into a hollow body H, the final shape of which is determined by the blow mold 3. A pressurized gas source 4 is connected via a first pressure filling line 71 and a first pressure reducer 51 to a first gas storage tank 61. The pressure reducer 51 is not strictly necessary, but advantageous, particularly when used for the lowest-pressure gas storage tank. A first process line 81 leads from the first gas storage tank through a first process valve 11 to the main line 85.

[0054] At least one additional gas storage tank is present that is not directly connected to the pressurized gas source. In this example, two additional gas storage tanks are present, hereinafter referred to as the second gas storage tank 62 and a third gas storage tank 63. From the second gas storage tank 62, a second process line 82 leads through a second process valve 12 to the main line 85. From the third gas storage tank 63, a third process line 83 leads through a third process valve 13 to the main line 85.

[0055] A fourth gas storage tank 64 is connected to the pressurized gas source 4 via a second filling line 72 and a second pressure reducer 52. The pressure reducer 52 is not strictly necessary. The compressor pressure of the pressurized gas source can also be used, particularly for the gas storage tank with the highest pressure. A fourth process line 84 leads from the fourth gas storage tank 64 through a fourth process valve 14 to the main line 85.

[0056] The vent valve 15 connects the main line 85 to a silencer 65 via a vent line 86 and then to the environment.

[0057] The compressed gas source 4 is preferably a compressor. Preferably, it is the only compressed gas source 4. Pressure reducers reduce the gas pressure to a desired, predefined gas pressure. They are known in the prior art.

[0058] The first gas storage tank 61 has the lowest gas pressure, the fourth gas storage tank 64 the highest. The gas pressures of the remaining gas storage tanks 62, 63 are also different, with the second gas storage tank 62 having a higher gas pressure than the first gas storage tank 61 and the third gas storage tank 63 having a higher gas pressure than the second gas storage tank 62, but a lower pressure than the fourth gas storage tank 64. Further gas storage tanks may be present, also cascaded and exhibiting different gas pressures. These further gas storage tanks, like the second and third gas storage tanks 62, 63, can also be filled exclusively via recuperation and are not connected to a pressurized gas source. The process valves 11, 12, 13, 14 are preferably 2 / 2-way valves that allow flow in both directions. The vent valve is preferably also a 2 / 2-way valve, but it allows flow in only one direction.

[0059] Figure 2 shows a blow molding process that forms a preform into a hollow body, in particular a PET or PP bottle. Preferably, the illustration shows a complete blow molding process with pre-blowing and the cascade-like main blowing.

[0060] The abscissa represents the time t during which the process gas is blown into the preform and the time during which the used process gas is discharged from the hollow body. The ordinate represents the gas pressure P of the process gas.

[0061] The upper graphic shows the overall system; the four graphics arranged below show the times of the withdrawal and the duration of the withdrawal of the process gases from the individual gas storage tanks 61, 62, 63, 64.

[0062] Figure 2 shows normal operation. That is, operation when all gas storage tanks 61, 62, 63, 64 are filled and ready for the stepwise blow molding of hollow bodies.

[0063] In a first step, the first process valve 11 is opened, and process gas from the first gas storage tank 61 enters the main line 85 and thus the preform V. This process gas has a pressure P1, which is the lowest of the four gas pressures.

[0064] In a second step, the first process valve 11 is closed and the second process valve 12 is opened. Process gas with a higher pressure P2 now flows from the second gas storage tank 62 into the main line 85. In a third step, the second process valve 12 is closed and the third process valve 13 is opened. Process gas with an even higher pressure P3 now flows from the third gas storage tank 63 into the main line 85.

[0065] In the fourth step, the third process valve 13 is closed and the fourth process valve 14 is opened. Process gas with the highest pressure P4 flows from the fourth gas storage tank 64 into the main line 85.

[0066] After this fourth step and after closing the fourth valve 64, the hollow body H is fully formed. By opening the third process valve 13 in the reverse direction, used process gas from the main line 85 and from the hollow body H enters the third gas storage tank 63. A first recuperation R1 takes place. This is the fifth step. After closing the third process valve 13 and opening the second process valve 12 in the reverse direction, used process gas, now at a lower pressure, enters the second gas storage tank 62. This is the sixth step and the second recuperation R2. In a seventh step, the second process valve 12 is closed and the first process valve 11 is opened to allow an analogous third recuperation R3 into the first gas storage tank 11.In an eighth step, the process gas, now significantly depressurized, is released into the environment via the vent valve 15 and the silencer 65. This step is designated EXH in Figure 2.

[0067] The process valves 11, 12, 13, 14 thus switch twice each during a blowing process, i.e., a cycle for producing the hollow body H. Once when blowing into the preform V, and once when reducing the gas pressure in the main line 85 and in the hollow body H.

[0068] In this normal process, the fourth gas storage tank 64 is filled to the predetermined pressure level as needed using the pressurized gas source 4. The remaining gas storage tanks 61, 62, 63 are supplied exclusively with recovered used process gas. In the event of a pressure drop in the first gas storage tank 61, it is also possible in some embodiments to raise it back to the desired predetermined gas pressure using the pressurized gas source 4.

[0069] The standard recipe specifies the duration and timing of the supply of process gas from the individual gas storage tanks. Pressure sensors monitor the pressures in the gas storage tanks 61, 62, 63, 64. A control unit (not shown) controls the opening and closing of the process valves 11, 12, 13, 14, the check valve 15, and the two pressure reducers 51, 52 according to the standard recipe.

[0070] Figure 3 illustrates what would happen when using this standard recipe if it were also applied at the start of the manufacturing process, i.e., before the second and third gas reservoirs 62, 63 are filled. The gas pressures according to Figure 2 are shown as dashed lines. The actual gas pressures present are shown as solid lines. The process pressure from the first gas reservoir 61, filled by means of the pressurized gas source 4, would enter the preform V at pressure P1. Opening the second and third gas reservoirs 62, 63 would lead to a pressure reduction in the preform V.

[0071] The pressure would therefore only rise above level P1 with a delay and remain at the highest level with gas pressure P4 for a shorter time, as can be clearly seen in Figure 3. This results in hollow bodies H that do not meet the quality requirements. For example, because they are not sufficiently formed or because their shape is not sufficiently uniform. They are scrap and must be disposed of.

[0072] Figure 4 therefore shows a special formulation that can be used before the normal formulation, i.e., when the second and third gas storage tanks 62, 63 are still empty. It can also be used during normal operation if high pressure drops occur in the second and / or third gas storage tank 62, 63 or even in the first gas storage tank 61.

[0073] The special formulation also ensures that the first and fourth gas storage tanks 61, 64 are filled by means of the common pressurized gas source 4 and brought to their predetermined gas pressure levels. Preferably, the gas pressure level of the first gas storage tank 61 when filled by means of the pressurized gas source 4 is somewhat lower than the predetermined gas pressure level when supplied by recuperation.

[0074] Subsequently, process gas at pressure P1 is blown from the first gas storage tank 61 into the preform V. After a predetermined time, the first process valve 11 is closed and the fourth process valve 14 is opened immediately. This means that the fourth gas storage tank 64 now supplies the preform V with process pressure P4, i.e., the highest process pressure, directly after the first gas storage tank 61. The pressure in the preform V rises more quickly and can be maintained at the highest level for the necessary time. This is clearly visible in Figure 4. The special formulation determines the timing and duration of the application of the fourth process pressure P4 to the interior of the preform V. This duration is preferably longer than in the standard formulation and begins earlier.In a preferred variant, the pre-blowing according to the special recipe and the normal recipe takes exactly the same amount of time, and the main blowing also takes the same amount of time, whereby in the special recipe, the gas from the highest pressure gas storage is used immediately after the pre-blowing during the main blowing, i.e., no cascade is used in the main blowing.

[0075] The recuperations R1, R2, R3 preferably take place in the same way as in the normal process, whereby the second gas storage tank 62 and the third gas storage tank 63 are filled to their predetermined gas pressure levels.

[0076] Depending on the embodiment, the special formulation must be carried out on more than one preform so that the two middle gas storage tanks 62, 63 are ready for use with the standard formulation. During the repetition of the special formulation, depending on the embodiment, refilling the first gas storage tank 61 using the pressurized gas source 4 may or may not be necessary.

[0077] When using the special recipe, the first process valve 11 still switches twice per blowing cycle, but the second and third process valves 12, 13 only switch once, namely for the first and second recuperation R1, R2 respectively.

[0078] Switching between the standard and special recipes can be carried out, for example, by time control or by means of pressure monitoring of the individual gas storage tanks, at least the second and third gas storage tanks 62, 63. The switching is preferably carried out automatically by means of a control system.

[0079] This device and the associated process can be used with both rotary and linear blow molding machines. Large gas storage tanks can be used, which simultaneously supply the process pressure required for the production of several preforms V.

[0080] The inventive method and device enable multi-stage blowing with multi-stage recuperation while simultaneously reducing costs. REFERENCE MARK LIST

[0081] 1 valve block

[0082] 11 first process valve

[0083] 12 second process valve

[0084] 13 third process valve

[0085] 14 fourth process valve

[0086] 15 Vent valve

[0087] 2 blow nozzles

[0088] 3 blow mold

[0089] 4. Compressed gas source

[0090] 51 first pressure reducer

[0091] 52 second pressure reducer

[0092] 61 first gas storage facility

[0093] 62 second gas storage

[0094] 63 third gas storage facility

[0095] 64 fourth gas storage

[0096] 65 silencers

[0097] 71 first filling line

[0098] 72 second filling line

[0099] 81 first process management

[0100] 82 second process management

[0101] 83 third process management

[0102] 84 fourth process management

[0103] 85 Main line

[0104] 86 Vent line

[0105] EXH vent

[0106] H Hollow body P Gas pressure

[0107] P1 first process pressure P2 second process pressure P3 third process pressure P4 fourth process pressure R1 first recuperation R2 second recuperation R3 third recuperation t time

[0108] V preform

Claims

PATENT CLAIMS 1. Method for producing hollow bodies (H) from preforms (V) using blow molding, wherein a) a preform (V) is provided, b) wherein a process gas according to a standard recipe is introduced in a cascade manner from at least three gas storage tanks (61, 62, 63, 64) with different predetermined gas pressures (P1, P2, P3, P4) into an internal volume of one of the preforms (V) with a correspondingly increasing process pressure, wherein the last used gas storage tank (64) has the highest predetermined gas pressure (P4), and c) wherein, after completion of the blowing process, at least a portion of the process gas used is returned in a cascade manner to those gas storage tanks (61, 62, 63) which have a lower predetermined gas pressure (P1, P2, P3), and wherein steps a) to c) of the process are repeated with at least one further preform (V) of the preforms, characterized by that at least at the start of a production process for the manufacture of several of the hollow bodies (H) before the first execution of steps a) to c) the process gas is introduced into at least one first preform (V) according to a special recipe for the manufacture of a hollow body (H) of similar or the same quality as with the normal recipe, wherein the special recipe differs from the normal recipe.

2. Method according to claim 1, wherein the special formulation uses process gas from at least two of the gas storage tanks (61, 64), wherein both gas storage tanks (61, 64) have been filled from the same pressurized gas source (4).

3. Method according to claim 2, wherein one of the two gas storage tanks (61, 64) is the gas storage tank (64) with the highest predetermined gas pressure and wherein the other gas storage tank (61) of the two gas storage tanks (61, 64) is filled only for the use of the special recipe by means of the pressurized gas source (4) and is filled with used process gas during the use of the normal recipe, wherein the gas pressure when filled by the pressurized gas source (4) is preferably lower than when filled with used process gas.

4. Method according to claim 3, wherein the other gas storage tank (61) of the two gas storage tanks (61, 64) has the lowest gas pressure (P1).

5. Method according to one of claims 1 to 4, wherein in the event of a drop in the predetermined pressure in one of the gas storage tanks (62, 63) which have a lower gas pressure (P1, P2, P3) than the highest gas pressure (P4), process gas according to the special recipe is again introduced into the internal volume of the next preform (V) in the production process.

6. Method according to any one of claims 1 to 5, wherein at least three, preferably exactly three, recuperation stages (R1, R2, R3) are used.

7. Method according to any one of claims 1 to 6, wherein the special formulation in step b) differs from the normal formulation in that, immediately after process gas from the gas storage unit (61) having the lowest predetermined gas pressure (P1) has been introduced into the internal volume of at least one first preform (V), process gas from the gas storage unit (64) having the highest gas pressure (P4) is introduced, wherein the special formulation then carries out step c) in the same way as the normal formulation.

8. Method according to claim 7, wherein the duration of the injection of the process gas with the highest predetermined gas pressure (P4) according to special recipe is longer than the duration of the injection of the process gas with the highest predetermined gas pressure (P4) according to normal recipe.

9. Device for producing hollow bodies (H) from preforms (V) by means of blow molding, preferably using the method according to one of claims 1 to 8, wherein the device has at least three process valves (11, 12, 13, 14) and at least three gas storage tanks (61, 62, 63, 64) with different predetermined gas pressures (P1, P2, P3, P4), wherein a first gas storage tank (61) has a lowest gas pressure (P1) and another (64) gas storage tank has a highest gas pressure (P4), wherein each gas storage tank (61, 62, 63, 64) is assigned at least one of the process valves (11, 12, 13, 14), to extract process gas in a cascade-like manner with increasing gas pressure from the to inject at least three gas storage units (61, 62, 63, 64) into an internal volume of the preform (V), and to return used process gas in a cascade manner to the gas storage tanks (61, 62, 63, 64), with the exception of the gas storage tank (64) with a highest predetermined gas pressure (P4), wherein at least a part of the gas storage units (62, 63), which have a predetermined gas pressure lower than the highest gas pressure (P4), can be filled exclusively by means of recirculation of the process gas used, characterized by that exactly one pressurised gas source (4) is present, that the first gas storage tank (61) and the other gas storage tank (64) can be filled from the pressurized gas source (4) and that the first gas storage tank (61) can also be filled by means of recirculating the used process gas.

10. Device according to claim 9, wherein the gas storage tanks (61, 62, 63) which can be filled by means of recirculation can be filled by means of the process valves (11, 12, 13) associated with them.

11. Device according to one of claims 9 or 10, wherein the first gas storage tank (61) has the lowest predetermined gas pressure (P1) and the other gas storage tank (64) has the highest predetermined gas pressure (P4).

12. Device according to claim 11, wherein the gas storage (61) with the lowest predetermined gas pressure (P1) is a gas storage for the main blowing or a gas storage for the pre-blowing.

13. Device according to one of claims 9 to 12, wherein at least four, preferably exactly four gas storage tanks (61 , 62, 63, 64) with different predetermined gas pressures (P1, P2, P3, P4) are provided.

14. Device according to one of claims 9 to 13, wherein each gas storage (61, 62, 63, 64) is assigned to several check valves (11, 12, 13, 14), wherein each check valve (11, 12, 13, 14) leads to its own blow mold (3).

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