DE102009060654B4 - Method and device for producing plastic bottles - Google Patents

Abstract

Device (1) for forming plastic preforms (8) into plastic containers with a blow mold (2), within which the plastic preforms (8) can be expanded by applying a gaseous medium to the plastic containers, with a feed device (4) which surrounds the plastic preforms (8) supplies the gaseous medium, and preferably with a stretching rod (6) which stretches the plastic preforms (8) along their longitudinal direction (L), the apparatus having a reservoir (12) for the gaseous medium and a supply line (14) which feeds the gaseous medium from the reservoir (12) to the supply device (4) and between which the reservoir (12) and the supply device (4) a valve device (16) is provided to prevent the gaseous medium from being introduced into the plastic preform (8 ), characterized in that between the reservoir (12) and the feed device (4) is a Zwischenemereinicherunrichtun g (10) is provided for the gaseous medium, wherein a receiving volume (V) of the intermediate storage device (10) is variable.

Description

The present invention relates to an apparatus and a method for forming plastic preforms to plastic containers according to the preambles of claims 1 and 6. It further relates to a system with a plurality of corresponding devices according to claim 5.

From the prior art, it has long been known to produce plastic bottles, such as PET bottles, from plastic preforms, these plastic preforms are first heated and then expanded in blow molds against an inner wall of the said blow mold. This expansion takes place in particular by applying an air pressure. Furthermore, so-called stretch blow molding methods are known in which the plastic preforms are additionally stretched along their longitudinal direction with the aid of a stretch rod.

The actual expansion process is divided into different steps, such as a Vorblasvorgang and an adjoining Hauptblasvorgang. In particular, in the stretch blow molding of plastic containers, the pre-blowing in conjunction with the stretching of crucial importance for the distribution of material of the bottle.

However, this interaction always requires the same time almost independent of the output power. The remaining residence time can be used to cool the material on the mold wall, which is particularly important for the dimensionally stable removal of the container from the blow mold.

More recently, efforts have been made to increase the output of such equipment. In the last nine years, the output of such systems has almost doubled. However, this also means that the residence time of the plastic preform or container in the blow mold is getting shorter and thus significantly reduces the cooling time.

The present invention is therefore based on the object to look for ways to extend in particular the process time or to accelerate the processes during expansion of the container.

An example of this is the reduction in the blind spot required for loading and unloading the blow mold. However, the potential for improvement in this regard is already largely exhausted.

The above object is achieved by the subject matter of the independent apparatus and method claims. Advantageous embodiments and further developments are the subject of the dependent claims.

An inventive device for forming plastic preforms to plastic containers has a blow mold, within which the plastic preforms are expandable by exposure to a gaseous medium to the plastic containers.

Furthermore, a feed device is provided which supplies the gaseous medium to the plastic preforms and, advantageously, a stretching rod is also provided which stretches the plastic preforms along their longitudinal direction. In this case, the device has a pressure supply device such as in particular a reservoir for the gaseous medium and a supply line which feeds the gaseous medium from the reservoir to the supply device. Furthermore, a valve device is provided between the reservoir and the feed device in order to control the supply of the gaseous medium into the plastic preform.

According to the invention, an intermediate storage device for the gaseous medium is provided between the reservoir and the supply device.

In the feeding device, which supplies the gaseous medium in the plastic preform, it is in particular a blowing nozzle which is placed on or around an opening of the preform in order to supply it with the gaseous medium, which is in particular air. The plastic preforms are expanded by the application of compressed air against an inner wall of the blow mold.

An intermediate storage device is understood to be any device which temporarily stores the gaseous medium, so that, if required, rapid delivery of the air stored in the intermediate device is possible. By providing this temporary storage device, it is possible, in particular at the beginning of the pre-blowing to achieve a strong pressure increase without at the same time to maintain this strong pressure increase in the further course of Vorblasens. This makes it possible in this way to reduce the Vorblasdauer and an intermediate volume (hereinafter referred to as booster volume) to use in front of the Vorblasventil.

This reinforcing effect comes from the fact that the booster volume with the pre-blow pressure set (which is generally between 10 and 16 bar) is available and introduced very quickly into the container or into the plastic preform can be. Thus, a comparatively large cross-section of the valve device to the blow piston is preferably provided, so that the air flow is not throttled in this area. In particular, at the beginning of the Vorblasvorgangs a rapid increase in pressure is desirable to simultaneously avoid constriction of the plastic preform by stretching and thus possibly a concern of the plastic preform to the stretch rod. In the further period of Vorblasens the rapid increase in pressure is no longer desired, since otherwise it may come during expansion to blistering of the plastic preform and can create areas of the plastic preform too early to the wall of the blow mold. The volume of the temporary storage device therefore serves to change the pre-blowing pressure and not to recycle air.

In a further advantageous embodiment, the intermediate storage has a receiving volume which corresponds at least to the internal volume of the plastic preform to be expanded. Particularly preferably, the receiving volume of the intermediate storage corresponds to at least two-thirds of the inner volume of the preform and very particularly preferably corresponds to the receiving volume of at least half of the inner volume. In this further advantageous embodiment, the temporary storage device has a receiving or internal volume which corresponds at most to the internal volume of the container to be produced. Preferably, the maximum storage volume of the intermediate storage corresponds to half the internal volume of the container to be produced, and most preferably the maximum storage volume corresponds to one third of the internal volume of the container to be produced.

So here the booster volume is adapted to the plastic preform. The intermediate storage device may be, for example, a tubular body whose internal volume is particularly preferably adaptable. Advantageously, the geometric internal volume of the temporary storage device does not change during the expansion process.

Advantageously, the device further comprises a throttle device for the gaseous medium, which is arranged between the reservoir and the temporary storage device. This throttle device serves to avoid an excessive increase in pressure at the beginning of the blowing process and in this way to prevent the above-mentioned blistering. At the same time, however, the temporary storage device ensures that a high pressure increase is available immediately after the start of the blowing process.

It is possible that the temporary storage device is integrated with check valves, which allow only an air flow to the container.

In the current state of the art, the above-mentioned large cross-section to the valve is not possible because all the air has to flow through the Vorblasdrossel and therefore the resulting pressure in the blowing chamber builds up only slowly. In the underlying idea of the invention results in a relatively sudden pressure build-up in the preform, but due to the comparatively small booster volume only comes up to a certain pressure level. This pressure level depends on booster volume, pre-blowing pressure and preform volume. After the said booster pressure has been compensated, the blow-by air flow predetermined by the blow-by throttle flows through the blow-by blower as usual and the blowing process continues as usual.

By inventively proposed device, a rapid pressure build-up is possible to reduce Vorblastotzeit. Furthermore, in this way a Reckstangenkontakt can be avoided and overall process window can be increased.

In a further advantageous embodiment, a receiving volume of the temporary storage device is variable. In this way, adaptation to different preform and container volumes is possible. Thus, the user can set how the pressure increase should proceed at the beginning of the process.

The present invention is further directed to an apparatus for forming plastic preforms into plastic containers having a plurality of devices of the type described above, wherein at least a portion of these devices are supplied with the gaseous medium through the same reservoir. The reservoir can be, for example, an annular channel which serves for supplying compressed air to the device or even to a plurality of devices.

The present invention is further directed to a method of forming plastic preforms into plastic containers. The plastic preforms are expanded within a blow mold by exposure to a gaseous medium to the plastic containers and the gaseous medium is supplied to the plastic preforms via a feeder, wherein the gaseous medium is supplied from the reservoir via a supply line of the feeder and wherein via one in the supply line arranged valve means the supply of gaseous medium is controlled in the plastic preform.

According to the invention, the gaseous medium is at least partially fed before the expansion process to an intermediate storage device, which is arranged between the reservoir and the supply device.

Therefore, it is also proposed in terms of the method that the blast air or a part thereof is first supplied to said intermediate storage device, in which case the actual blow molding process initially causes an acceleration of the preblowing process by the gaseous medium stored in the intermediate storage.

Advantageously, the gaseous medium in the intermediate storage device is at least temporarily before the expansion process under a pressure which is greater than 1 bar, preferably greater than 5 bar, more preferably greater than 7 bar and more preferably greater than 10 bar.

In a further advantageous method, the plastic container is stretched during the expansion process by means of a stretch rod in its longitudinal direction. Thus, the method is in particular a so-called stretch blow molding method.

In a further advantageous method, at the beginning of the expansion process, a gas volume is transferred from the intermediate storage device into the plastic preform in order, as mentioned above, to achieve a faster increase in pressure at the beginning of the blowing process.

In a further advantageous method, the supply of the gaseous medium into the plastic preform is throttled by means of a throttle device, which is arranged between the reservoir and the intermediate storage device. In this way, in particular after the emptying of the gaseous medium stored in the intermediate storage device with the aid of the throttle device, the expansion process is carried out. This throttle device may be, for example, an aperture.

The increase in pressure of the gaseous medium (as a function of time) into the plastic preform at the beginning of the expansion is therefore advantageously increased by the use of the intermediate storage device. In this way, in particular, the entire expansion process can be shortened in time and thus, in turn, more time is given to cool down the blown within the blow mold container.

Further advantages and embodiments will become apparent from the accompanying drawings.

• 1 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung zum Umformen von Kunststoffvorformlingen zu Kunststoffbehältnissen;
• 2 eine schematische Darstellung zur Veranschaulichung des erfindungsgemäßen Prinzips;
• 3 eine Darstellung zur Veranschaulichung der erfindungsgemäß geänderten Druckkurven;
• 4a-4b zwei Darstellungen zur Veranschaulichung eines änderbaren Volumens der Zwischenspeichereinrichtung.

Show:

• 1 a schematic representation of a device according to the invention for forming plastic preforms to plastic containers;
• 2 a schematic representation for illustrating the principle of the invention;
• 3 a representation to illustrate the invention modified pressure curves;
• 4a-4b two illustrations for illustrating a changeable volume of the temporary storage device.

1 shows an inventive device for forming plastic preforms to plastic containers. In 1 the reference number refers 2 on a blow mold, which here consists of two side parts 2a and 2 B as well as a bottom part 2c composed. In a closed state, this blow mold forms a cavity in its interior 28 from, which serves to expand the plastic preform to the plastic containers. For this purpose is over a muzzle 8a supplied to the plastic preform using a blow nozzle compressed air and so the plastic preform expands against the inner wall of the blow mold.

In addition, the device has a stretching rod 6 on, also in the longitudinal direction L the plastic preform is moved so as to stretch the plastic preform in its longitudinal direction. It is possible that the supply of the blowing air and the movement of the stretch rod take place simultaneously, but preferably starts first the stretching process and shortly thereafter, the blowing air is supplied.

The reference number 22 refers to a blow mold, in which case the two blow moldings 2a and 2 B are each arranged on carriers and can be folded in this way. Likewise, the bottom part 2c be pulled down to open the blow mold.

2 shows a rough schematic representation for illustrating the device according to the invention 1 , Again, here is a plastic preform 8th shown by means of a feeder or a blowing nozzle 4 is subjected to a gaseous medium to be expanded in this way. The reference number 16 denotes a valve device and in particular a Vorblasventil, which controls the compressed air supply, in particular to a beginning of the expansion process. This valve device 16 is from a reservoir 12 supplied, which may be, for example, a channel in which the blown air is stored. As a reservoir in this context, all means are understood which are suitable to provide compressed air available, so for example, compressor devices and the same.

Downstream of the reservoir 12 there is a throttle device 18 , which the supply of Vorblasluft to the preform 8th throttles. In this way it can be achieved that the Vorblasdruck is not supplied abruptly over the entire Vorblasvorgang, but is braked or throttled.

Between the valve device 16 and the throttle device 18 is a temporary storage device 10 intended for the blowing air. The reference number 14 indicates in its entirety a conduit which supplies the compressed air from the reservoir 12 to the tuyere 4 leads. This temporary storage device 10 can be filled advantageously before the actual blowing process or the blown air can under a certain pressure in this latching device 10 be filled. At the beginning of the blowing process, first the volume of the temporary storage device 10 emptied into the plastic preform and only then via the throttle 18 the Vorblasvorgang continued.

3 shows a schematic representation for illustrating the device according to the invention. In this case, the reference numeral refers K1 on a normal pressure curve, which arises without the device according to the invention. The reference number K2 refers to a pressure curve using the temporary storage device 10 , One recognizes that in particular in the range 42 the pressure increase is steeper than with the normal pressure curves. Overall, the curve is on the timeline T shifted slightly further to the left, which means that the entire blowing process can be somewhat shortened compared with the prior art. At the same time, however, you can also see the area 44 with decreasing pressure, which is caused by the use of Vorblasdrossel.

The 4a and 4b show two different states of the device. In this case, these representations differ in particular with regard to a state of the temporary storage device 10 , At the in 4a shown situation is a piston 26 along the arrow P2 retracted so that a small volume V the temporary storage device 10 is formed. In the right part of the picture is the piston 26 extended, so here's the volume V the temporary storage device 10 is relatively large. In this way is an adjustment of the volume V possible on different boundary conditions. However, the volume is nevertheless V _T in the actual work operation preferably constant.

All disclosed in the application documents features are claimed as essential to the invention, provided they are new individually or in combination over the prior art.

LIST OF REFERENCE NUMBERS

1

device

2

blow

2a, 2b

side panels

2c

the bottom part

4

Blowing nozzle, feeding device

6

stretching rod

8th

Plastic preform

8a

muzzle

10

Latch means

12

reservoir

14

management

16

valve means

18

throttling device

22

blow mold

26

piston

28

cavity

42, 44

Area

K1, K2

pressure curve

L

longitudinal direction

T

timeline

V

Volume of the buffer device

V _T

volume

P2

Direction of movement of the piston

Claims (10)

Device (1) for forming plastic preforms (8) into plastic containers with a blow mold (2), within which the plastic preforms (8) can be expanded by applying a gaseous medium to the plastic containers, with a feed device (4) which surrounds the plastic preforms (8) supplies the gaseous medium, and preferably with a stretching rod (6) which stretches the plastic preforms (8) along their longitudinal direction (L), the apparatus having a reservoir (12) for the gaseous medium and a supply line (14) which of the Feeding means (4) supplying the gaseous medium from the reservoir (12) and wherein between the reservoir (12) and the feed means (4), a valve means (16) is provided to control the supply of the gaseous medium in the plastic preform (8) , characterized in that between the reservoir (12) and the feed device (4) is provided a temporary storage device (10) for the gaseous medium, wherein a receiving volume (V) of the temporary storage device (10) is variable. Device (1) according to Claim 1 , characterized in that the intermediate storage device (10) has a receiving volume (V) which corresponds to at least half of the internal volume of the plastic preform (8) to be expanded. Device (1) according to Claim 1 , characterized in that the intermediate storage device (10) has a receiving volume (V) which corresponds at most to the inner volume of the container to be produced. Device (1) according to at least one of the preceding claims, characterized in that the device (1) comprises a throttle means (18) for the gaseous medium, which is arranged between the reservoir (12) and the temporary storage device (10). Plant with a plurality of devices (1) according to at least one of the preceding claims, wherein at least part of these devices (1) are supplied with the gaseous medium by the same reservoir (12). A method for forming plastic preforms (8) into plastic containers, the plastic preforms (8) being expanded within a blow mold (2) by applying a gaseous medium to the plastic containers, and supplying the gaseous medium to the plastic preforms (8) via a feed device (4) is, wherein the gaseous medium from a reservoir (12) via a feed line (14) of the feed device (4) is supplied and via a in the feed line (14) arranged valve means (16) the supply of the gaseous medium in the plastic preform (8) is controlled, characterized in that the gaseous medium is at least partially supplied prior to the expansion operation of a buffer device (10) which is arranged between the reservoir (12) and the feed device (4), wherein a receiving volume (V) of the buffer device (10) is changeable. Method according to Claim 6 , characterized in that the plastic preform (8) during the expansion process by means of a stretch rod (6) in its longitudinal direction (L) is stretched. Method according to Claim 6 , characterized in that at the beginning of an expansion process, a gas volume from the temporary storage device (10) in the plastic preform (8) is spent. Method according to one of Claims 6 to 8th , characterized in that by means of a throttle device (18) which is arranged between the reservoir (12) and the intermediate storage device (10), the supply of the gaseous medium in the plastic preform (8) is throttled. Method according to one of Claims 6 to 9 , characterized in that by the use of the temporary storage device (10) the pressure increase of the gaseous medium in the plastic preform (8) is increased at the beginning of the expansion.

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