WO2013023789A1

WO2013023789A1 - Method and apparatus for blow molding containers

Info

Publication number: WO2013023789A1
Application number: PCT/EP2012/003500
Authority: WO
Inventors: Michael Litzenberg; Frank Haesendonckx; Michael Linke
Original assignee: Khs Corpoplast Gmbh
Priority date: 2011-08-18
Filing date: 2012-08-17
Publication date: 2013-02-21
Also published as: DE102011110962A1

Abstract

The invention relates to a method and an apparatus for blow molding containers (2). A pre-form (1) is drawn out by a drawing bar (11) within a blow mold (4) following thermal conditioning and is shaped into the container (2) by means of the action of a blowing pressure. Initially, a low blowing pressure provided by a low-pressure supply is used and, after that, a medium blowing pressure provided by a medium-pressure supply and then a higher blowing pressure provided by a high-pressure supply. The blowing air is supplied via at least one blowing pressure valve and, following container molding, at least some of the high-pressure blowing air used is fed into the medium-pressure supply. During the container molding, a changeover time between the supply of the medium blowing pressure and the supply of the higher blowing pressure can be varied. The changeover time is predefined by a blowing air control system as a function of a least one parameter.

Description

Method and apparatus for blow molding containers

The invention relates to a method for blow-molding of containers, in which a preform is stretched after thermal conditioning within a blow mold of a stretching rod and formed by blowing pressure into the container and in which initially provided by a low pressure supply low blowing pressure, then at least one of

Medium pressure supply provided medium blowing pressure and then used by a high pressure supply provided higher blowing pressure and the blowing air is supplied via at least one blown air valve and in which after a container forming at least a portion of the high pressure blowing air used in the middle -

CONFIRMATION COPY pressure supply is fed.

The invention further relates to a device for blow-molding of containers, which has at least one blowing station with a blow mold and at least one stretching rod and in which the blowing station both to a low pressure supply to provide a low blowing pressure, to a medium pressure supply to provide a mean blowing pressure and to a High pressure supply is connected to provide a relatively low and medium blowing pressure higher blowing pressure, and in which a blast air return is used for after a container forming the blowing station escaping high pressure blowing air into the medium pressure supply.

In a container molding by blowing pressure preforms of a thermoplastic material, such as preforms made of PET (polyethylene terephthalate), supplied to different processing stations within a blow molding machine. Typically, such a blow molding machine has a heating device and a blowing device, in the region of which the previously tempered preform is expanded by biaxial orientation to form a container. The expansion takes place with the aid of compressed air, which is introduced into the preform to be expanded. The procedural sequence in such an expansion of the preform is explained in DE-OS 43 40 291. The introductory mentioned introduction of the pressurized gas also includes the introduction of compressed gas into the developing container bladder and the compressed gas introduction into the preform at the beginning of the blowing process.

The basic structure of a blowing station for container molding is described in DE-OS 42 12 583. Possibilities for tempering the preforms are explained in DE-OS 23 52 926.

Within the blow molding apparatus, the preforms as well as the blown containers can be transported by means of different handling devices. In particular, the use of transport mandrels, onto which the preforms are attached, has proven to be useful. The preforms can also be handled with other support devices. The use of gripping tongs for handling preforms and the use of expanding mandrels which can be inserted into a mouth region of the preform for mounting are likewise among the available constructions.

A handling of containers using transfer wheels is described, for example, in DE-OS 199 06 438 in an arrangement of the transfer wheel between a blowing wheel and a discharge path.

The already described handling of the preforms takes place firstly in the so-called two-stage process, in which the preforms are first produced in an injection molding process, then temporarily stored and later conditioned in terms of their temperature and inflated to a container. On the other hand, an application in the so-called one-step process, in which the preforms are suitably tempered immediately after their injection molding production and sufficient solidification and then inflated.

With regard to the blow molding stations used, different embodiments are known. In blow stations, which are arranged on rotating transport wheels, a book-like unfoldability of the mold carrier is frequently encountered. But it is also possible to use relatively movable or differently guided mold carrier. In fixed blowing stations, which are particularly suitable for receiving a plurality of cavities for container molding, typically plates arranged parallel to one another are used as mold carriers.

The recycling of spent blowing air from a high-pressure region into a low-pressure region is already described in US-A 4,488,863. A device implementation for multiple use of blowing air is explained in DE 43 40 291 AI.

In JP 11-207808 already described, blown air is attributed both to a low blowing pressure level and to a mean blowing pressure level. However, there are fixed predetermined Umsehaltpunkte for the gradual construction of the blowing pressure.

EP 2298534 describes a method for the recovery of blown air, in which a multi-stage pressure curve is provided both in the region of the pressure reduction and in the region of the pressure build-up. When returning the blown air is in a first step used blast air of the highest pressure returned to the return area for the lowest blowing pressure. Respective switching points both in the area of pressure reduction and in the area of pressure build-up are fixed.

The hitherto known methods and devices are not yet sufficiently suitable for achieving an optimization of the blown air return in such a way that both the largest possible return quantity is ensured and an undesired process time extension is avoided.

The object of the present invention is therefore to improve a method of the aforementioned type such that within a permissible working range the largest possible return amount of blast air is achieved.

This object is achieved in that in the container forming a UmschaltZeitpunkt between the supply of the mean blowing pressure and the supply of the higher blowing pressure is variable and is set by a Blasluftsteuerung depending on at least one parameter.

Another object of the present invention is to construct a device of the initially mentioned type such that an optimized blown air return is supported. This object is achieved in that control valves for selectively connecting the blowing stations with the low pressure supply, the medium pressure supply and the high pressure supply to a blast air control are ^¬ closed, a variable UmschaltZeitpunkt between the supply of the mean blowing pressure and the supply of the higher blowing pressure in dependence specifies at least one parameter.

The variability of the temporal position or the pressure level for switching between the supply of the mean blowing pressure and the supply of the higher blowing pressure enables a process optimization taking into account different by a user specified constraints. For example, it is possible to adaptively change the position of the switching point in such a way that a maximum return quantity of blown air is achieved and thus only a smaller compressor is required for an external compressed air supply of the blow molding machine. It is also possible to carry out the method described above under the constraint of a maximum process time to be maintained. Other possible constraints include, for example, the specification of a minimum time for pending a maximum blowing pressure within the blown container or the prevention of pressure drops during the concern of the maximum blowing pressure.

Pressure fluctuations can be reduced by using a storage volume at least for the mean blowing pressure. High quality blast pressure control is supported by measuring the blowing pressure applied to the blowing station.

A further homogenization of the pressure supply can take place in that the recycled blown air is supplied to a buffer.

To further optimize the usable recirculation amount of blowing gas, it is proposed that at least part of the recirculated blast air is supplied to the low-pressure supply.

An optimization of the blown air return is supported by measuring a volumetric flow provided by a compressor.

An optimization of the entire blowing process is supported by the fact that an optimization of the amount of recycled blowing air is performed taking into account a predefinable process time to be observed.

A typical procedure is that a connection of the higher blowing pressure takes place when reaching about 40 percent of the pressure forming in the container end pressure.

In the drawings, embodiments of the invention are shown schematically. Show it:

Fig. 1 is a perspective view of a blowing station for producing containers from preforms,

Fig. 2 is a longitudinal section through a blow mold in which a

Preform is stretched and expanded,

3 shows a sketch to illustrate a basic structure of a device for blow-molding containers,

Fig. 4 shows a modified heating with enlarged

heating capacity

5 is a block diagram for illustrating the pneumatic functional components in the blown air return,

6 is a blow pressure curve for illustrating a three-stage pressure build-up with blown air return,

Fig. 7 is a diagram similar to Figure 6 for

Illustration of the variable position of the switching point between the mean blowing pressure and the higher blowing pressure,

8 shows a further blow-pressure curve for illustrating a shifted switch-over time for a temporally shortened use of the average blowing pressure.

9 shows a further blow pressure curve for a process with prolonged use of the mean blow pressure. The basic structure of a device for forming preforms (1) in container (2) is shown in FIG. 1 and in FIG. 2.

The device for forming the container (2) consists essentially of a blowing station (3), which is provided with a blow mold (4) into which a preform (1) can be inserted. The preform (1) may be an injection-molded part of polyethylene terephthalate. To allow the preform (1) to be inserted into the blow mold (4) and to allow the finished container (2) to be removed, the blow mold (4) consists of mold halves (5, 6) and a bottom part (7), which is a lifting device (8) is positionable. The preform (1) can be held in the region of the blowing station (3) by a transport mandrel (9) which, together with the preform (1), passes through a plurality of treatment stations within the device. But it is also possible to use the preform (1), for example via pliers or other handling means directly into the blow mold (4).

To allow a compressed air supply line below the transport mandrel (9), a connecting piston (10) is arranged, which feeds compressed air to the preform (1) and at the same time performs a seal relative to the transport mandrel (9). In a modified construction, it is basically also conceivable to use solid compressed air supply lines.

A stretching of the preform (1) takes place in this embodiment by means of a stretching rod (11) is positioned by a cylinder (12). According to another embodiment, a mechanical positioning of the stretch rod (11) is carried out over curve segments, which are acted upon by Abgriff rollers. The use of curve segments is particularly useful when a plurality of blowing stations (3) are arranged on a rotating blowing wheel

In the embodiment shown in Fig. 1, the stretching system is designed such that a tandem arrangement of two cylinders (12) is provided. From a primary cylinder (13), the stretch rod (11) is first moved to the area of a bottom (14) of the preform (1) before the beginning of the actual stretching operation. During the actual stretching process, the primary cylinder (13) with extended stretching rod together with a carriage (15) carrying the primary cylinder (13) is positioned by a secondary cylinder (16) or via a cam control. In particular, it is intended to use the secondary cylinder (16) in such a cam-controlled manner that a current stretching position is predetermined by a guide roller (17) which slides along a curved path during the execution of the stretching operation. The guide roller (17) is pressed by the secondary cylinder (16) against the guideway. The carriage (15) slides along two guide elements (18).

After closing the mold halves (5, 6) arranged in the region of carriers (19, 20), the carriers (19, 20) are locked relative to one another by means of a locking device (40). To adapt to different shapes of a mouth section (21) of the preform (1), the use of separate threaded inserts (22) in the region of the blow mold (4) is provided according to FIG.

Fig. 2 shows in addition to the blown container (2) and dashed lines drawn the preform (1) and schematically a developing container bladder (23).

Fig. 3 shows the basic structure of a blow molding machine, which is provided with a heating section (24) and a rotating blowing wheel (25). Starting from a preform input (26), the preforms (1) are transported by transfer wheels (27, 28, 29) into the region of the heating path (24). Heater (30) and fan (31) are arranged along the heating path (24) in order to temper the preforms (1). After a sufficient temperature control of the preforms (1), they are transferred to the blowing wheel (25), in the region of which the blowing stations (3) are arranged. The finished blown containers (2) are fed by further transfer wheels to a delivery line (32).

In order to be able to transform a preform (1) into a container (2) in such a way that the container (2) has material properties which ensure a long usefulness of foods filled inside the container (2), in particular beverages, special process steps must be taken the heating and orientation of the preforms (1) are maintained. In addition, you can advantageous effects are achieved by adhering to special dimensioning regulations.

As a thermoplastic material different plastics can be used. For example, PET, PEN or PP can be used.

The expansion of the preform (1) during the orientation process takes place by compressed air supply. The compressed air supply is in a pre-blowing phase in which gas, for example compressed air, is supplied at a low pressure level and subdivided into a subsequent main blowing phase in which gas at a higher pressure level is supplied. During the pre-blowing phase, compressed air is typically used at a pressure in the interval of 10 bar to 25 bar and during the main blowing phase compressed air is supplied at a pressure in the interval of 25 bar to 40 bar.

From Fig. 3 it can also be seen that in the illustrated embodiment, the heating section (24) from a plurality of revolving transport elements (33) is formed, which are strung together like a chain and guided by Umlenkrädern (34). In particular, it is envisaged to open a substantially rectangular basic contour by the chain-like arrangement. In the illustrated embodiment, in the region of the transfer wheel (29) and an input wheel (35) facing extension of the heating section (24) a single relatively large-sized guide wheel (34) and in the range of adjacent deflections two comparatively smaller dimension- ied deflecting wheels (36) used. In principle, however, any other guides are conceivable.

To enable a possible dense arrangement of the transfer wheel (29) and the input wheel (35) relative to each other, the arrangement shown to be particularly useful, since in the region of the corresponding extent of the heating section (24) three deflecting wheels (34, 36) are positioned, and Although in each case the smaller deflection wheels (36) in the region of the transition to the linear curves of the heating section (24) and the larger deflection wheel (34) in the immediate transfer area to the transfer wheel (29) and the input wheel (35). As an alternative to the use of chain-like transport elements (33), it is also possible, for example, to use a rotating heating wheel.

After a finished blowing of the containers (2) they are led out of the area of the blowing stations (3) by a removal wheel (37) and transported via the transfer wheel (28) and a delivery wheel (38) to the delivery line (32).

In the modified heating section (24) shown in FIG. 4, a larger amount of preforms (1) per unit time can be tempered by the larger number of radiant heaters (30). The fans (31) introduce cooling air into the region of cooling air ducts (39), which in each case oppose the associated radiant heaters (30) and emit the cooling air via outflow openings. The arrangement of the outflow directions, a flow direction for the cooling air is substantially transverse to a transport direction realized the preforms (1). The cooling air ducts (39) can provide reflectors for the heating radiation in the area opposite the radiant heaters (30), and it is likewise possible to realize cooling of the radiant heaters (30) via the discharged cooling air.

Fig. 5 shows schematically a block diagram of the pressurized gas supply. The drawn preform (1) was simultaneously represented on behalf of the container (2) and the container bladder (23). A high pressure compressor (41) provides pressure of an output pressure level, for example, about 40 bar. About one or more pressure transducers (42, 43) takes place in the illustrated embodiment, a pressure reduction to two different supply pressure levels. A mean pressure level here is about 10 to 25 bar, the lower pressure level about 5 to 15 bar and the high pressure level about 20 to 40 bar. The pressure transducers (42, 43) are designed as Reduzierverteilstationen and provided with silencers for derived in the environment of compressed air.

About boiler (44, 45, 46) is provided a reservoir volume for the respective pressures, so that even with a clocked pressure removal, the respective pressure level is maintained at least approximately. The controlled compressed gas supply takes place using valves (47, 48, 49). The valves (47, 48, 49) are connected to a controller (50) which coordinates the respective switching times of the valves (47, 48, 49). According to a typical procedure, first after opening the valve (47) blowing of the container (2) with the lower blowing pressure and then after closing the valve (47) and opening the valve (48), a further blowing with the medium pressure. After closing the valve (48) and opening the valve (49), a finished blowing with the higher blowing pressure. After reaching a sufficient stability of the container (2) within the blow mold (4) opens a return valve (51) after a previous closing of the valve (49) and there is a return of out of the container (2) flowing out blast air in the region of the medium pressure supply and / or the low pressure supply. After completion of the recovery process opens a vent valve (52) and the internal pressure in the container (2) is lowered to an ambient pressure.

Blowing air flowing back from the region of a blowing station (3) back into the region of the medium-pressure supply is reused via the valve (48) at a blowing station following in the course of the process. Depending on the return quantity and the consumption quantity, a pressure variation varying within a tolerance band occurs in the region of the vessels (44, 45).

According to the exemplary embodiment in FIG. 5, the blown air returned via the return valve (51) is first stored in a boiler (53). The boiler typically has a pressure level above the pressure level provided for the medium pressure supply. Preferably, a connection is made between the return valve (51) and the boiler. (53) a check valve (54) is inserted, which allows a flow of gas only in the direction of the boiler (53).

Further non-return valves (55, 56) are respectively inserted between the boilers (44, 45) and the valves (47, 48) in order to provide a direction of flow only from the boilers (44, 45) in the direction of the valves (47, 48). to enable.

To assist in operation, the boiler (53) is connected to the compressor (41) via a valve (57) to assist in initial filling. Preferably, the compressor (41) is arranged stationarily outside the blowing wheel (25) and connected via a rotary coupling (58) to the pneumatic components on the blowing wheel (45). In the stationary area outside the blowing wheel (25), an air supply unit (59) is also positioned.

To support a sequence control, the controller (50) is connected to pressure sensors (60, 61). The pressure sensor (60) detects the pressure prevailing in the region of the blowing station (3). The pressure sensor (61) measures the pressure in the area of the boiler (53) and thus the currently recirculated pressure.

A controlled transfer of pressure from the boiler (53) in the region of the medium pressure supply via a valve (62), which is also connected to the controller (50).

The venting valve (52) preferably delivers the blast air to the environment via a muffler (63). Likewise preferred is the blowing station (3) with a pneumatic Formhaltung (64) equipped. A supply pressure for this pneumatic form-locking device (64) is preferably branched off from a pneumatic supply line of the blowing station (3). In order to optimize the return of the spent blowing air such that there is the least possible demand for fresh air supplied by the compressor (41), the actual output of the compressor (41) can be determined with a flow meter (65). The optimization of the blown air return can be set, for example, such that the smallest possible volume flow per unit of time to fresh blown air from the compressor (41) must be provided.

Fig. 6 shows an example of a blow pressure curve (66). Plotted is the pressure within the preform (1) or the container (2) or the developing container bladder (23) over time. At a start time, the low blowing pressure (PI) is activated. Typically, in this case, a pressure level of about 10 percent of the final value is reached. At a second time, the mean blowing pressure (PB) is activated. After reaching a typical value of about 40 percent of the final pressure, the higher blowing pressure is activated.

After a sufficiently long concern a maximum blowing pressure is carried out at a further time, a beginning of the return of the spent blowing air. After a sufficiently long return period, the residual pressure is vented to the environment. This is typically done at a pressure level of about 60 percent of maximum blowing pressure. The return time is about 40 degrees with a total process angle of 360 degrees and thus about one ninth of the available process time.

FIG. 7 is a graph similar to FIG. 6 illustrating the variability of the high pressure (P2) connection timing. The shift of the Zuschaltpunktes can be done according to different criteria. For example, it is possible to define a minimum supply of fresh blown air as an optimization criterion, which must be provided by the compressor (41). This can be done, for example, under an additional secondary condition of a maximum permissible total process time.

Another way to optimize is to change the timing of the beginning of the blown air return. In general, advancing the corresponding time point leads to a shortening of the cooling time for the containers (2). An operator can manually or automatically set an allowable earliest possible beginning of the blown air return via an optical bottle monitor.

Fig. 8 shows, starting from the diagram of FIG. 7, a time advance of the ZuschaltZeitpunktes for the higher pressure (P2). The advance leads to the fact that a smaller amount of blown air can be reused. On the other hand, a shorter process time and an extended cooling time for the container (2) can be expected. Fig. 9 also shows, starting from the diagram of FIG. 7, a shift of the connection time for the higher blowing pressure (2) to a later date. In this way, the amount of recirculated blown air can be increased, but the time provided for the shaping or cooling of the container (2) is shortened or the overall process time is extended at a predetermined fixed corresponding time.

Claims

Patent claims

A process for blow molding containers in which a preform is stretched after thermal conditioning within a blow mold of a stretching rod and formed by blowing pressure into the container and in which initially provided by a low pressure supply low blowing pressure, then at least one provided by a medium pressure supply Medium blowing pressure and then used by a high pressure supply provided higher blowing pressure and the blowing air is supplied via at least one blowing air valve and in which after a container forming at least a portion of the high-pressure blowing air used in the middle pressure supply is fed, characterized in that in the container forming a switching time between the supply of the mean blowing pressure and the supply of the higher blowing pressure is variable and is predetermined by a Blasluftsteuerung depending on at least one parameter.

2. The method according to claim 1, characterized in that at least for the mean blowing pressure a storage volume is used.

3. The method according to claim 1 or 2, characterized in that at the blow station (3) applied blowing pressure is measured.

4. The method according to any one of claims 1 to 3, characterized in that the recycled blown air is supplied to a buffer.

5. The method according to any one of claims 1 to 4, characterized in that at least a portion of the recycled blown air is supplied to the low pressure supply.

6. The method according to any one of claims 1 to 5, characterized in that one of a compressor (41) provided volume flow is measured.

7. The method according to any one of claims 1 to 6, characterized in that an optimization of the amount of recycled blowing air, taking into account a specifiable process time to be complied with.

8. The method according to any one of claims 1 to 7, characterized in that a connection of the higher blowing pressure when reaching about 40 percent of the container (2) forming end pressure takes place.

9. A blow molding apparatus comprising at least one blowing station having at least one blow mold and at least one stretching rod and wherein the blowing station to a low pressure supply to provide a low blowing pressure, to a medium pressure supply to provide a mean blowing pressure and to a high pressure supply to provide a is connected to the blower pressure relatively high and low blower pressure to the medium pressure supply, characterized in that the control valve for selectively connecting the blow station with the low pressure supply and the high pressure supply to a blown air control connected which are a changed switching timing between the supply of the average blowing pressure and the supply of the higher blowing pressure in response to at least one specifies the parameter

10. The device according to claim 9, characterized in that at least one storage volume is arranged in the region of the medium-pressure supply.

11. The device according to claim 9 or 10, characterized in that the blowing station (3) is connected to at least one sensor for measuring a blowing pressure.

12. Device according to one of claims 9 to 11, characterized in that the Blasluftrückführung comprises at least one intermediate memory.

13. Device according to one of claims 9 to 12, characterized in that the Blasluftrückführung is coupled to the low pressure supply.

14. Device according to one of claims 9 to 13, characterized in that in the region of a from a compressor (41) to the blowing station (3) extending flow path, a flow meter (45) is arranged.

15. Device according to one of claims 9 to 14, characterized in that a controller (50) for the Blasdruckzuführung controls the Blasluftrückführung in response to at least one process time to be observed.

16. Device according to one of claims 9 to 15, characterized in that the controller (50) the blowing station (3) with the high pressure supply upon reaching about 40 percent of a maximum in the container (2) pending blow pressure connects.