Apparatus and method for forming plastic preforms into plastic containers with adjustable throttle

Abstract

Apparatus for forming plastic preforms into plastic containers, having a forming device which has a plurality of forming stations each having a stretching bar for stretching the plastic preform and an application device act upon the plastic container with a flowable medium. The forming device has at least four pressure reservoirs for the flowable medium, which each have predetermined pressures, and a valve block with at least five process valves. The application device is configured for producing a fluid connection between the valve block and a mouth region of the plastic preform in order to act upon the plastic preforms with the pressurised flowable medium, and the process valves are configured to act upon the plastic preforms with different pressures, wherein at least one process valve is configured for producing a connection between the plastic preform and an environment.

Claims

1. A method for forming plastic preforms into plastic containers, having a forming device which has a plurality of forming stations within which the plastic preforms are formed into the plastic containers, wherein the plastic preforms being stretched in the longitudinal direction by means of a stretching bar and being acted upon by an application device with a flowable medium and at least four pressure reservoirs being provided which have predetermined pressures P1, Pi, P+ and P2, wherein a pressure Pi is smaller than a pressure P+ and the pressure P+ is smaller than a pressure P2 and a valve block with at least five process valves V1, Vi, V+, V2, V.sub.Ex is provided, wherein the application device produces a fluid connection between the valve block and a mouth region of the plastic preform, to act upon the plastic preforms with the pressurised flowable medium and the process valves act upon the plastic preforms with different pressures, wherein the pressures and switching times of the process valves are selected in such a way that an air mass which is vented into the environment per plastic container after a recycling stage can be described with the formula m=x*V, wherein V describes the container volume in litres, m the air mass in grams and x a factor of the container volume as a function of the air mass, wherein 7x15.

2. The method according to claim 1, wherein the application device is raised before the pressure in the valve block falls below an overpressure of 0.1 bar.

3. The method according to claim 1, wherein switching times of the process valves are selected so that a pressure rise time t90 from the moment of switching Pi to reaching 90% of P2 is higher than 180 ms.

4. The method according to claim 1, wherein the pressure P1 is variably adjusted and is preferably less than 8 bar and greater than 3 bar and/or the pressure P2 is variably adjusted and is preferably greater than 16 bar.

5. The method according to claim 1, Wherein the recycling stage which vents the air mass of the plastic container to the environment is the last recycling stage.

6. The method according to claim 5, wherein in the venting carried out in the other recycling stages, the relieved compressed air is used to apply a subsequent plastic preform in the next lower pressure stage.

7. The method according to claim 3, wherein a pressure descent time from the moment of switching a first recycling stage to the moment of switching the process valve V.sub.Ex is higher than 140 ms, wherein P1=y*P1.sub.base, 2<y<5 and P1 is directly proportional to P1.sub.base, wherein P1.sub.base is the lowest pressure after the first pressure increase at P1.

8. The method according to claim 1, wherein the pressure P1 is a pre-blowing pressure, the pressures Pi and P+ are intermediate blowing pressures and the pressure P2 is a final blowing pressure, so that a valve block is provided which has an additional intermediate blowing stage and wherein relief pressures P.sub.Ex are used to apply a next lower pressure stage.

9. The method according to claim 1, wherein the process valves V.sub.Ex and V2 have small switching volumes and are each switched only once during the forming of the plastic container and the process valves V1, Vi and V+ are switched twice, once when the plastic container is applied with the corresponding pressure level and once during the associated recycling stage.

10. The method according to claim 9, wherein the control volume for an entire process cycle of the plastic container to be produced is less than 60 ml.

11. The method according to claim 9, wherein the air consumption for an entire process cycle of the plastic container to be produced is less than 0.6 g.

12. The method according to claim 1, wherein at least one throttle is arranged between the pressure reservoir P1 and the process valve V1, wherein the flow rate of the throttle is determined by an adjustable throttle cross-section, wherein the throttle cross-section is adjustable such that the throttle cross-section is larger than 28 mm.sup.2.

13. The method according to claim 12, wherein the at least one throttle is adjustable between at least two fixed positions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Further advantages and embodiments can be seen in the attached drawings.

[0072] In the drawings:

[0073] FIG. 1 shows a diagram with the course of a compressed air curve according to the state of the art;

[0074] FIG. 2 shows a diagram with the course of a compressed air curve according to the apparatus/method according to the invention;

[0075] FIG. 3 shows a diagram with the curves of the compressed air curve according to the prior art and according to the apparatus/method according to the invention in comparison;

[0076] FIGS. 4a and 4b show a schematic representation of a valve block according to the state of the art;

[0077] FIG. 5 shows a schematic representation of a valve block according to the invention;

[0078] FIG. 6 shows a schematic representation of an arrangement of a silencer and a process valve according to the state of the art;

[0079] FIG. 7 shows a schematic representation of a first embodiment of an arrangement of a silencer and a process valve according to the invention;

[0080] FIG. 7a shows a detailed representation of the seal shown in FIG. 7;

[0081] FIG. 7b shows a further schematic representation of the first embodiment according to the invention;

[0082] FIG. 7c shows a further schematic representation of the first embodiment according to the invention;

[0083] FIG. 8a shows a schematic representation of a second embodiment of an arrangement of a silencer and a process valve according to the invention;

[0084] FIG. 8b shows a further schematic representation of the second embodiment according to the invention;

[0085] FIG. 9 shows a schematic representation of a third embodiment of an arrangement of a silencer and a process valve according to the invention;

[0086] FIG. 10 shows a schematic representation of an embodiment of an arrangement of adjustable throttles according to the invention; and

[0087] FIG. 11 shows a schematic representation of a further embodiment of an arrangement of adjustable throttles according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0088] FIG. 1 shows a diagram 100 with the course of a compressed air curve according to the state of the art. The diagram 100 shows the pressure curve P as a function of time t. The three columns on the left side of the figure, marked P1, Pi and P2, represent the pressures P1, Pi and P2 applied to the plastic container. The three columns on the right show the relief phases in which a relief pressure P.sub.Ex is released from the plastic containers.

[0089] The arrows A show that the pressure released in the first (upper) relief phase is used to apply a subsequent plastic container in the next lower pressure stage Pi and the pressure released in the second (middle) relief phase is used to apply the subsequent plastic container in pressure stage P1. Accordingly, the relief pressure of a preceding container of a higher pressure stage is preferably used to feed the blowing air consumption of the following container in the next lower pressure stage. New compressed air is (idealised) only supplied when pressure P2 is applied. This compressed air then passes through the pressure stages in stages, in different containers and is then vented at the last container (lower relief phase).

[0090] The third (lower) relief phase should be as small as possible with regard to pressure and energy consumption, but it must also be higher than the pressure P1, as otherwise it would not be possible to recycle the air without an additional compression unit.

[0091] FIG. 2 shows a diagram 110 with the course of a compressed air curve according to the apparatus/method according to the invention. In contrast to the diagram in FIG. 1, there is an additional intermediate stage here in which the container is additionally applied with the pressure P+.

[0092] It can also be seen again that the relief pressures P.sub.Ex are used to apply a next lower pressure stage. The additional pressure stage P+can significantly reduce the last relief phase and thus reduce compressed air consumption.

[0093] The reference sign P1.sub.base identifies the lowest pressure after the first pressure boost when pressure P1 is applied.

[0094] FIG. 3 shows a diagram 120 with the curves of the pressure curve according to the prior art 130 and according to the apparatus/method 140 according to the invention in comparison. It can be seen that with the apparatus according to the invention, the application begins earlier and ends sooner, so that the forming process takes place more quickly. At the same time, the container quality is improved by a longer holding time at the maximum pressure P2.

[0095] The time t90 characterises the moment when the pressure P1 is applied until 90% of the pressure P2 is reached. This time should preferably be as short as possible.

[0096] FIGS. 4a and 4b show a schematic representation of a valve block 50 according to the prior art. The valve blocks 50 here have four or five process valves V1, Vi, V2, V.sub.Ex. However, due to the arrangement of the valves V1, Vi, V2, V.sub.Ex, the dead space T.sub.R is relatively large here, which leads to a high installation space and a higher relief pressure.

[0097] FIG. 5 shows a schematic representation of a valve block 50 according to the invention. Here, the valve block 50 also has five valves V1, Vi, V+V2, V.sub.Ex, however, in comparison to FIG. 4b, an additional valve V+ is present for an additional intermediate stage. Compared to FIGS. 4a and 4b, the dead space T.sub.R is also reduced due to the arrangement of the valves V1, Vi, V+V2, V.sub.Ex.

[0098] FIG. 6 shows a schematic representation of an arrangement of a silencer 15 and a process valve V.sub.Ex according to the state of the art. The valve V.sub.Ex is responsible for relieving the internal pressure of the container, wherein the relieved air is fed to the environment through this valve and the downstream silencer.

[0099] The silencer 15 and the valve V.sub.Ex are arranged on different sides of the valve body 52 of the valve block 50, so that the axes of the silencer 15 and the valve V.sub.Ex are at a 90 angle to each other. The compressed air must therefore be diverted, which leads in particular to a high flow path of the air. The reference sign 12 indicates a pilot air supply for the valve.

[0100] FIG. 7 shows a schematic representation of a first embodiment of an arrangement of a silencer 15 and a process valve V.sub.Ex according to the invention. Unlike in the prior art, the silencer 15 and the valve V.sub.Ex are here arranged in one axis or coaxially on the valve body 52 of the valve block 50. Such an arrangement considerably shortens the flow path of the compressed air in particular. The reference sign 20 indicates a valve seat or a sealing device, which is designed here as an example of a flat-sealing soft seal, and the reference sign 21 indicates a valve piston, which is designed here as a hollow piston.

[0101] The left-hand illustration of FIG. 7 shows an enlarged view of the outlet openings 18, which are kidney-shaped here as an example.

[0102] In this embodiment, the valve piston 21 and in particular the hollow piston is designed in such a way that it is actively kept closed via control air and opens when the load is relieved. The compressed air then flows through the kidney-shaped outlet openings 18 and the valve piston 21 into the silencer 15 and is supplied to the environment via the latter.

[0103] In this illustration, the process chamber 19 is closed against the outlet via the valve V.sub.Ex and a control air chamber (not shown) for the control air supply is pressurised so that the valve V.sub.Ex is actively kept closed.

[0104] FIG. 7a shows a detailed representation of the sealing device 20 shown in FIG. 7. The sealing surface of this sealing device 20 is offset inwards so that the valve is opened with the support of the pressure prevailing in the process chamber when the control pressure is released. The ratio of the sealing surfaces is such that the valve can be kept closed with control pressure.

[0105] FIG. 7b shows a further schematic representation of the first embodiment according to the invention. In particular, the coaxial arrangement of the silencer 15 and the valve V.sub.Ex can be seen again from this figure. The reference sign 18 again indicates the kidney-shaped outlet opening.

[0106] FIG. 7c shows a further schematic representation of the first embodiment according to the invention. In this figure, the flow path of the air stream L from the valve V.sub.Ex to the silencer 15, marked by arrows, can be seen when the valve V.sub.Ex is open.

[0107] FIG. 8a shows a schematic representation of a second embodiment of an arrangement of a silencer 15 and a process valve V.sub.Ex according to the invention. In this embodiment, the silencer 15 and the process valve V.sub.Ex are again arranged coaxially to each other. The reference sign L again indicates the air flow from the valve V.sub.Ex into the silencer 15 as indicated by the arrows.

[0108] Unlike in FIG. 7, the valve piston 21 is not a hollow piston here, but an internally guided or internally centred piston which is partially pressure compensated. The valve piston 21 is again opened by the compressed air and actively held closed with control pressure.

[0109] FIG. 8b shows a further schematic representation of the second embodiment according to the invention. The kidney-shaped outlet opening 18 is again illustrated in the enlarged right-hand illustration.

[0110] FIG. 9 shows a schematic representation of a third embodiment of an arrangement of a silencer 15 and a process valve V.sub.Ex according to the invention. Here, the silencer 15 is not arranged axially to the valve V.sub.Ex, but is at an angle to it. Preferably, the angle between the valve axis and the silencer axis is less than 50.

[0111] FIG. 10 shows a schematic representation of an arrangement of adjustable throttles 60, 62 according to the invention. Two throttles 60, 62 are arranged which can be moved along the arrows on a piston rod 70. Depending on the arrangement of the throttles 60, 62, either more or less air volume 69 of the air volume 68 present in the valve block 50 enters the plastic container 10.

[0112] The reference sign 65 indicates a drive, such as a motor, by means of which the throttles 60, 62 can be moved along the piston rod 70. The reference sign 66 indicates a compressed air supply line for the valve block 50.

[0113] The arrangement of the throttles 60, 62 shown in FIG. 10 is particularly advantageous for small plastic preforms and plastic containers.

[0114] FIG. 11 shows a schematic representation of a further embodiment of an arrangement of adjustable throttles 60, 62 according to the invention. The arrangement corresponds to the arrangement shown in FIG. 10. However, the position of the throttles 60, 62 shown here is particularly advantageous for larger plastic preforms and plastic containers.

[0115] The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided they are individually or in combination new compared to the prior art. Furthermore, it is pointed out that the individual figures also describe features which may be advantageous in themselves. The skilled person immediately recognises that a certain feature described in a figure can also be advantageous without adopting further features from this figure. Furthermore, the skilled person recognises that advantages can also result from a combination of several features shown in individual figures or in different figures.

LIST OF REFERENCE SIGNS

[0116] 10 plastic container [0117] 12 control air supply [0118] 15 silencer [0119] 18 outlet opening [0120] 19 process room [0121] 20 valve seat, sealing device [0122] 21 valve piston [0123] 50 valve block [0124] 52 valve body [0125] 60 throttle [0126] 62 throttle [0127] 65 drive [0128] 66 compressed air supply line [0129] 68 air volume [0130] 69 air volume [0131] 70 piston rod [0132] 100 diagram [0133] 110 diagram [0134] 120 diagram [0135] 130 state of the art pressure curve [0136] 140 pressure curve according to the apparatus/method of the invention [0137] A arrow [0138] T.sub.R dead space [0139] L air flow [0140] R arrow [0141] P1 pressure P1, pre-blowing pressure [0142] Pi pressure Pi, intermediate stage [0143] P+pressure P+, intermediate stage [0144] P2 pressure P2, finish blowing pressure [0145] P.sub.Ex relief pressure [0146] V1 process valve [0147] Vi process valve [0148] V+process valve [0149] V2 process valve [0150] V.sub.Ex process valve