Method and apparatus for blow molding a container comprising a removable bottom

Abstract

A method for molding a plastic preform into a plastic bottle comprises: introducing a plastic preform (10) to be expanded into a blow mould, the blow mould comprising at least two side parts (14) and a bottom part (18) movable relative to the side parts (14) in the longitudinal direction (L) of the plastic preform (10). Inserting a rod-shaped body (34) into the interior of the plastic preform (10) through the mouth of the plastic preform (10); applying a first pressure (P1) to the plastic preform (10); applying a second pressure (Pi) to the plastic preform (10), wherein the second pressure (Pi) is different from and preferably higher than the first pressure (P1); applying a third pressure (P2) to the plastic preform (10), wherein the third pressure (P2) is different from and preferably higher than the second pressure (Pi). After applying the third pressure (P2) to the plastic preform (10), pushing the bottom part (18) onto the plastic preform in the longitudinal direction (L) of the plastic preform (10).

Description

[0001] This application is a divisional application of PCT patent application PCT / EP2017 / 082356, which was filed on December 12, 2017, with application number 201780079565.5 and entitled "Method and apparatus for blow molding a container including a removable bottom", and is a divisional application of the Chinese national phase application. Technical Field

[0002] The invention relates to a method and a device for forming plastic preforms into plastic containers, in particular plastic bottles. Background Art

[0003] Such methods and devices have been known from the prior art for a long time. In this case, heated plastic preforms are usually introduced into blow molds and pressure is applied to them in these blow molds, as a result of which plastic containers or plastic bottles can be formed. In this case, different pressure levels are usually applied to the plastic preforms. Thus, for example, it is known to first apply a pre-blowing pressure, which is used for the first expansion of the container, then an intermediate blowing pressure and finally a final blowing pressure. It is also known from the prior art that in order to expand the container, so-called stretch rods are inserted into the container in order to stretch the container. In addition, methods are known from the prior art in which the base of the blow mold is pushed onto the container during the expansion process. These methods are also called active base methods. Summary of the invention

[0004] The object of the present invention is to improve these methods, in particular to improve these methods in the molding of plastic containers. In particular, the molding of the bottom area of ​​such containers should be improved.

[0005] These objects are achieved by the subject matter of the independent claims. Advantageous embodiments and further developments are subject matter of the dependent claims.

[0006] In the method for molding a plastic preform into a plastic bottle according to the present invention, the plastic preform to be expanded is first introduced into a blow mold, wherein the blow mold comprises at least two side parts and a bottom that is movable relative to the side parts in the longitudinal direction of the bottom of the plastic preform. In another method step, a rod-shaped body is inserted into the interior of the plastic preform through the mouth of the plastic preform, in particular in order to stretch the plastic preform in the longitudinal direction of the plastic preform. In another method step, a first pressure is applied to the plastic preform. Further, a second pressure is applied to the plastic preform, wherein the second pressure is different from the first pressure and preferably higher than the first pressure. In another method step, a third pressure is applied to the plastic preform, wherein the third pressure is different from the second pressure and preferably higher than the second pressure.

[0007] In a first embodiment according to the invention, the bottom is pushed onto the plastics material preform in the longitudinal direction thereof before the third pressure is applied to the plastics material preform, in particular at least temporarily during the second pressure applied to the plastics material preform.

[0008] In this embodiment, it is therefore provided that the bottom portion is pushed onto the plastic preform during the application of an intermediate blowing pressure (also referred to herein as second pressure) to the plastic preform. In this case, it is possible and preferred that the entire pushing movement takes place during this phase, i.e. during the application of the second pressure (i.e. intermediate blowing pressure). However, it is also conceivable that at least one time section of the movement takes place in another phase, for example, during the application of the first pressure to the plastic preform and / or during the application of the third pressure to the plastic preform.

[0009] In a second embodiment according to the invention, the bottom is pushed onto the plastics material preform in the longitudinal direction of the plastics material preform during and / or after the application of the third pressure to the plastics material preform, and in particular after the application of the third pressure to the plastics material preform.

[0010] In this embodiment, the pushing of the bottom takes place in particular during the cleaning phase of the plastic container and preferably during a period of time in which the pressure in the container is reduced again. Preferably, the pushing of the bottom onto the plastic preform can be maintained until the end of this cleaning phase. During the cleaning phase, preferably, the pressure in the container is lower than during the application of the third pressure or during the final blow molding. Due to this lower pressure, the bottom can be pushed more easily, because the bottom only has to resist the lower pressure to approach the container.

[0011] In a third embodiment according to the invention, during at least one of the pressures applied to the plastics material preforms, the bottom is pushed onto the plastics material preform in the longitudinal direction of the plastics material preform in at least two time sections spaced apart from one another.

[0012] All three variants according to the invention described here are characterized in that the bottom is pushed onto the plastic preform during the application of compressed air to the plastic preform. However, the corresponding time segments and / or frequencies of pushing the bottom are different. The following description immediately relates to all the aforementioned embodiments, which can be applied accordingly to all embodiments of the present invention. Preferred variants involving the various embodiments are subsequently described. Advantageously, the pressures described here are not constant during the various segments. Preferably, in the course of the various time segments, the first pressure and the second pressure increase. However, in terms of average value, the second pressure is higher than the first pressure. Advantageously, the third pressure is substantially constant within a predetermined time period. Preferably, the second pressure is applied to the plastic preform immediately after the first pressure is applied to the plastic preform. Preferably, the third pressure is applied to the plastic preform immediately after the second pressure is applied to the plastic preform.

[0013] Preferably, the switch to the different pressures is achieved by switching valves. Thus, for example, in order to achieve a change from a first pressure to a second pressure, a first valve regulating and / or influencing the supply of the first pressure to the plastic preforms can be closed instead of opening a second valve regulating and / or influencing the supply of the second pressure. Correspondingly, when switching from the second pressure to the third pressure, a valve influencing the supply of the second pressure (more precisely, the supply of air at the second pressure) can be closed instead of opening another valve influencing the supply of air at the third pressure.

[0014] Preferably, therefore, the changeover between the individual pressures is triggered by switching at least one valve, and preferably by switching a plurality of valves.

[0015] Preferably, the phase of applying the third pressure to the plastic container is followed by a cleaning phase, during which the plastic container is cleaned. In this case, the cleaning phase can also be started by switching valves, in particular by closing the valve providing the third pressure P2 instead of opening the valve allowing the cleaning process. Preferably, the pressure during the cleaning phase is lower than the third pressure.

[0016] Therefore, in the context of the method according to the invention, it is proposed to move the bottom and therefore to move the bottom during the expansion of the plastic preform. It should be noted that, although the above method steps are performed in a certain order, they can also be performed simultaneously and preferably simultaneously. Thus, it is possible, for example, to insert the rod-shaped body into the plastic preform through the mouth of the plastic preform while applying a first pressure to the plastic preform. Furthermore, it is possible that the pressure is not constant, but varies over a period of time, for example increases or decreases.

[0017] In another preferred method, the rod-shaped body is moved linearly and / or at a constant speed. This means that the rod-shaped body is introduced into the plastic container in a linearly moving manner. Preferably, the rod-shaped body is inserted into the plastic preform so that it contacts the bottom of the plastic preform. The rod-shaped body is therefore suitable and intended for stretching the plastic preform in the longitudinal direction of the plastic preform.

[0018] In another preferred method, the bottom is also moved linearly and / or at a constant speed. Advantageously, the bottom is advanced in the direction of the plastic preforms and / or in the direction of the above-mentioned rod-shaped body.

[0019] In a further preferred method, in particular after the application of the third pressure (and preferably after the purging phase and the pressure release phase), the formed plastic container is removed from the blow mold. Preferably, the blow mold is opened so that the plastic preform can be introduced into the blow mold. In this case, it is particularly preferred that the side of the blow mold is pivoted relative to the second side of the blow mold, further preferably relative to an axis parallel to the longitudinal direction of the plastic preform to be expanded. After the plastic preform has been introduced, the blow mold is closed again in the same way by pivoting.

[0020] In a further advantageous embodiment, the plastic containers are moved during their expansion on a predetermined conveying track, in particular a circular conveying track.

[0021] Furthermore, it is possible to apply compressed air to the plastic container via the rod-shaped body. However, it is also possible that the compressed air required for expanding the plastic preform is guided between the rod-shaped body and the mouth of the plastic preform. In a further preferred method, the blow mold is locked before applying the air, and particularly preferably, the blow mold is unlocked again after applying the air and before opening the blow mold.

[0022] In a further preferred method, before or during the advancement of the bottom, the rod-shaped body is at least partially retracted. In this way, a collision between the rod-shaped body and the bottom (possibly, with the wall of the plastic preform in between) is prevented.

[0023] In a further preferred method, the bottom is advanced by a distance greater than 5 mm, preferably greater than 10 mm, particularly preferably greater than 15 mm, and / or the bottom is advanced by a distance less than 30 mm, preferably less than 25 mm, particularly preferably less than 20 mm. These respective advancement distances also depend on the container to be produced. However, it has been found that these relatively small advancement distances are particularly suitable for producing or forming the bottom.

[0024] In another preferred method, after the third pressure is applied, the plastic preform or the container made of the plastic preform is again released from pressure. In this way, after the container has been finally blown, the pressure can be released from the container so that the container can finally be removed from the blow mould. In this respect, it should be pointed out that, although from a certain point in time (in any case from the application of the third pressure) there is already a formed container inside the blow mould, for the sake of simplicity, in the context of the present application, it is mainly referred to as applying pressure to the plastic preform.

[0025] In particular, in a first embodiment according to the invention, the bottom is at least temporarily pushed during the application of the second pressure to the plastic preform. It is possible to temporarily also carry out the pushing movement during the application of the first pressure, particularly preferably during the transition from the first pressure to the second pressure.

[0026] Advantageously, the transition between the individual pressures differs by a slight decrease in pressure over time. Thus, preferably, the respective subsequent pressure (ie, for example, the second pressure or the third pressure) is defined from a point in time at which the pressure begins to rise again from its minimum value.

[0027] Advantageously, however, at the point in time at which the third pressure is reached, the bottom part has already been pushed completely onto the plastic pre-form and / or has been moved into the upper position.

[0028] In a further embodiment, the bottom is advanced for a duration of between 1 second and 20 seconds, preferably between 1 second and 15 seconds, preferably between 2 seconds and 10 seconds, more preferably between 2 seconds and 5 seconds. Advantageously, the speed with which the bottom is advanced onto the plastic preform is adjustable.

[0029] In all the above embodiments, the second pressure is preferably greater than 3.5 bar, preferably greater than 5 bar, preferably greater than 7 bar, particularly preferably greater than 10 bar, and particularly preferably greater than 12 bar. In addition, the second pressure is preferably less than 20 bar, preferably less than 18 bar, and particularly preferably less than 17 bar.

[0030] In a further advantageous embodiment, which is particularly suitable for the second embodiment described above, the rod-shaped body is at least partially retracted before the third pressure is applied to the plastic preform. Advantageously, the rod-shaped body is retracted at least to the extent required for the bottom to be pushed forward. Advantageously, in a further method step, the rod-shaped body is completely retracted. Furthermore, in this embodiment, when the third pressure is reached, the bottom is pushed completely into its upper position or upwards in any case. In this embodiment, advantageously, when the third pressure is applied to the plastic preform, the bottom is pushed completely upwards, i.e. onto the plastic preform or onto the now formed container.

[0031] For all embodiments of the invention, it is advantageous if the first pressure is between 1 bar and 12 bar, preferably between 1 bar and 10 bar, particularly preferably between 1 bar and 8 bar.

[0032] The third pressure is particularly preferably between 15 bar and 50 bar, preferably between 17 bar and 40 bar, particularly preferably between 20 bar and 40 bar, particularly preferably between 20 bar and 38 bar.

[0033] In a further advantageous embodiment, which relates specifically to the third embodiment of the invention, the bottom part is at least partially retracted again (in the direction of the lower rest position) between two temporally spaced time intervals during which the bottom part is pushed onto the plastic preform. Thus, in this embodiment, the bottom part is first pushed onto the plastic preform and then at least partially retracted again to push the bottom part onto the plastic preform again. Thus, in this embodiment, a plurality of pushes of the bottom part onto the plastic preform bottom are carried out.

[0034] Advantageously, in the third embodiment, the time section is at least partially after the application of the second pressure. Preferably, at least one time section is after the start of the application of the second pressure to the plastic preform. Thus, for example, it is possible to start a first push movement onto the plastic preform during the pre-blow molding process and to start another push movement after the application of the second pressure or in a time period in which the pressure in the plastic preform drops again.

[0035] Furthermore, it is also possible to carry out the two advancing movements after applying the second pressure to the plastic preform, and particularly preferably after applying the third pressure to the plastic preform. Advantageously, in this embodiment, both advancing movements can be carried out in a (temporal) section in which the pressure in the plastic container drops again.

[0036] In another advantageous variant of the third embodiment, the two time sections are at least partially after the application of the third pressure. Particularly preferably, in another embodiment, the bottom part remains pushed onto the plastic preform for time periods of different lengths. It is possible that the first time period, during which the bottom part is pushed closer to the plastic preform, is longer, for example, takes place during the entire time period during which the third pressure is applied. Furthermore, the second time period may also be longer. It is also possible that the first time period is pushed only for a very short time, for example, to transport the bottom part upwards and immediately back again.

[0037] In a further advantageous method, the cleaning pressure is applied to the plastic container after the third pressure has been applied to it. At this stage, the pressure in the container drops significantly. Therefore, preferably, the cleaning pressure is comparable to the pressure of the intermediate blowing, i.e., comparable to the above-mentioned second pressure. The extent to which the pressure in the container drops during cleaning depends on whether the blowing air is recirculated. If such compressed air recirculation is provided, the pressure in the container drops to about 15 bar to 20 bar. This corresponds approximately to the level of the second pressure, i.e., the level of the intermediate blowing pressure.

[0038] If no recirculation is provided or if a discharge to the environment is to take place, the cleaning pressure drops to approximately 6 to 10 bar and is therefore in the order of magnitude of the first pressure P1 during the pre-blowing. Advantageously, the container is cooled during the cleaning process, in particular by compressed air escaping from the cleaning process. This cleaning phase is followed by a pressure release phase, during which the remaining pressure is discharged from the container.

[0039] Preferably, these separate pressures or air are provided by at least one reservoir, preferably by a plurality of reservoirs. For example, these reservoirs can be so-called annular channels, which are used to store air. During the application of pressure to the plastic preforms, preferably the highest pressure is present in the reservoir or in the annular channel providing the second pressure. The highest pressure corresponds approximately to the third pressure, however, it can also be higher.

[0040] The present invention also relates to an apparatus for molding plastic preforms into plastic bottles, the apparatus comprising at least one conveying device on which a plurality of molding stations are arranged, wherein each of the molding stations comprises a blow mold, the blow molds respectively comprising a bottom and two side parts, the two side parts being movable relative to each other to open and close the blow mold, the bottom being movable relative to the side parts in the longitudinal direction of the plastic preform and in the closed state of the blow mold, and wherein the apparatus further comprises a control device and at least one applying device, the applying device being used to apply a gaseous medium to the plastic preform to expand it, the control device controlling the application of the gaseous medium to the plastic preform so that a first pressure is first applied to the plastic preform, then a second pressure higher than the first pressure is applied to it, and finally a third pressure is applied to it, the third pressure being preferably higher than the second pressure.

[0041] According to the invention, the device comprises a drive device which is suitable and designed to at least temporarily move the bottom relative to the plastic preform during the application of pressure to the plastic preform, wherein in a first embodiment according to the invention, the bottom can be pushed onto the plastic preform in the longitudinal direction of the plastic preform before the application of the third pressure to the plastic preform and particularly preferably at least temporarily during the application of the second pressure to the plastic preform. According to a second embodiment according to the invention, the bottom is pushed onto the plastic preform in the longitudinal direction of the plastic preform during or after the application of the third pressure to the plastic preform, in particular after the application of the third pressure to the plastic preform.

[0042] In a third embodiment according to the invention, the bottom part is pushed onto the plastic preform in the longitudinal direction of the plastic preform in at least two time sections which are spaced apart from one another in time.

[0043] Preferably, the second advancement is used here to produce the curvature in the base region.

[0044] Advantageously, the device comprises a rod-shaped body which can be inserted into the plastic preform during its expansion in order to stretch the plastic preform. Advantageously, the device also comprises a drive device for driving the rod-shaped body. The drive device can be in particular, but not exclusively, an electric drive device, a hydraulic drive device, a pneumatic drive device or a magnetic drive device. Advantageously, the device comprises a control device which also controls the movement of the rod-shaped body. Advantageously, the movement of the rod-shaped body can be adjusted, at least temporarily, to the movement of the bottom. This means, for example, that the rod-shaped body can be retracted to the same extent as the bottom is advanced.

[0045] In a further advantageous embodiment, the two side parts are pivotable relative to one another and particularly preferably pivotable relative to an axis which is parallel to the longitudinal direction of the plastic pre-form.

[0046] In the context of the present invention, more precisely in the context of the first claim, a process cycle is described in connection with the so-called active bottom method / overstroke method. Here, preferably, the bottom lift is preferably limited to a range between 14.9 mm and 19.9 mm. In the method according to the invention, the plastic preform is first inserted into the blow mould and then the blow mould is preferably closed and locked. In this method part, the bottom or the bottom mould is in its lower end position.

[0047] Subsequently, the rod-shaped body or stretch rod is inserted into the plastic so that it contacts the ridge of the plastic preform. Subsequently, the first pressure application, i.e. the pre-blowing, begins. It is also possible here to already start applying pressure before the rod-shaped body is inserted. In this way, the blow-molding or blow-molding process can be controlled at low pressure.

[0048] In a further method step, in an embodiment according to the invention, in particular before starting the bottom lifting and / or applying the second pressure, the rod-shaped body or the cleaning rod is lifted upwards and in particular moved into the bottom position which is in or reaches the end position.

[0049] Subsequently, the bottom is preferably pushed onto the plastic preform or moved into the upper end position of the bottom. In a further method step, the final blow molding is carried out with a third pressure. This method of moving the bottom into its uppermost position is preferably carried out during the intermediate blow molding with the second pressure. After the end of the third pressure phase (final blow molding), the bottom is preferably in its uppermost position. In a further method step, cleaning is carried out, wherein here, particularly preferably, the cleaning rod or the rod-shaped body is in the retracted position. Finally, the rod-shaped body is moved back again.

[0050] In particular, in the second embodiment, after the pre-blowing and stretching, an intermediate blowing takes place, ie a second pressure P2 is applied to the plastic preform. Advantageously, in this method stage, the rod-shaped body is at least partially moved back.

[0051] In this embodiment, after applying the third pressure and particularly during cleaning, the bottom is moved to the upper position. However, this can also be started shortly before starting cleaning.

[0052] In this embodiment, preferably, until the end of the application of the third pressure, a standard process is carried out, or a process is carried out which differs from the standard process only in terms of the stretching path, i.e. the movement path of the rod-shaped body. Advantageously, during the intermediate blowing, i.e. during the application of the second pressure, the rod-shaped body moves back, for example, to a position described in more detail below. Preferably, after the application of the third pressure to the plastic container, a cleaning phase is carried out, in which the pressure is reduced again, in particular cleaning of the container occurs. During this phase, the bottom moves upwards to the so-called boxing phase.

[0053] Advantageously, the internal pressure of the container or the cleaning pressure at this stage is between 4 and 20 bar, preferably between 6 and 12 bar.

[0054] In another preferred method, after the cleaning is completed, the bottom is moved upwards again.

[0055] This embodiment also offers the advantage that less force is required to push the bottom. Moreover, less pressure is required in the overtravel unit in this way. Finally, wear on the entire system (seals and stops) can also be reduced. In addition, since the profile is completely blown out, better control can be achieved. Finally, stresses can be reduced, since the material can relax for longer, so tension can also be reduced.

[0056] In another preferred method, which relates in particular to the third embodiment according to the invention, during the intermediate blowing, i.e. during the application of the second pressure, the bottom is moved to a high end position, thereby stretching the bottom of the container. Subsequently, a cleaning process is carried out and the bottom is moved again to its highest end position and subsequently to its lowest end position to provide a bending point at which the bottom can be folded more easily. The end of the blowing process is again carried out as known from the prior art.

[0057] In a second variant, the standard method as described above is performed until the end of the final blow molding. This means that the bottom remains in its lowest end position until the application of the third pressure ends. As described above, this lowest end position can be located again between 14.9 mm and 19.9 mm below the position of the stretch rod. Subsequently, during the cleaning process, the bottom moves to its highest end position, thereby stretching the bottom of the container. After the final stretching, the bottom moves back to its lowest end position. The process of producing the bend is now carried out. To this end, the bottom is moved again to its highest end position and then moved back to its lowest end position, thereby producing the bend. The production of the bend can also be accomplished by repeatedly moving the bottom mold several times. Subsequently, the bottom and the stretch rod are moved to their process end positions, and the finished containers are distributed and transferred to other processing facilities.

[0058] After this method step, a pressure release cycle is performed in all embodiments, after which the bottom is moved or moved to its lower position again. Finally, after opening the blow mold, the plastic container (as a final blow-molded bottle) is taken out. Through the present invention, an improved control of the blow molding speed is achieved. Preferably, further control can be performed by adjusting the second pressure P2. In addition, since the blow molding can be carried out more slowly, a larger process window can be achieved. In this way, a higher container quality is also achieved. Moreover, an improved control of the wall thickness can be performed, in particular a more constant wall thickness can be achieved. This second pressure P2 is sometimes referred to as the intermediate blow molding pressure (Pi).

[0059] Another advantage is that during the so-called boxing (i.e. during the displacement movement), less force is required, since it is not necessary to move against the highest third pressure. In this way, the entire molding station can also be designed for pressures below 30 bar. Less pressure is required and the components are less stressed.

[0060] Preferably, it is possible to move the bottom and the bottom lifting unit with different pressures, thereby influencing the lifting speed. It is also possible to influence the blowing speed or the speed of the blowing process with a second pressure. In this way, a larger process window can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Further advantages and embodiments can be derived from the drawings.

[0062] In the attached picture:

[0063] Figure 1 is a crude schematic diagram of an apparatus for making plastic containers;

[0064] Figure 2 is a schematic diagram of the molding station;

[0065] Figure 3 are two diagrams for explaining the manufacture of the container;

[0066] Figure 4 is a diagram of a method according to a first embodiment of the present invention;

[0067] Figure 5 is a diagram of a method according to the invention in a second embodiment of the invention;

[0068] Figure 6 is a diagram of a method according to the invention in a third embodiment of the invention;

[0069] Figure 7 is a diagram of a method according to the present invention in a third embodiment; and

[0070] Figure 8 is another illustration of the method according to the invention in a third exemplary embodiment. DETAILED DESCRIPTION

[0071] Figure 1 A schematic diagram of a device 1 for producing plastic containers according to the invention is shown. The device comprises a support 2 which is rotatable relative to an axis of rotation Z and which is configured here as a so-called blow wheel. A plurality of forming stations 20 are arranged on the blow wheel. During the transformation of the plastic preforms into plastic containers, these forming stations move along a conveying path P, i.e., along a circular path.

[0072] Figure 2 A schematic diagram of a molding station 20 or half of such a molding station is shown. The molding station comprises two side supports, but only one side support 4 is shown. These side supports are respectively used to hold the blow mold sides, of which only the blow mold side 14 is shown here. These blow mold sides form a cavity 15 together with the bottom 18, in which the plastic preform 10 can be blown into a plastic container. The reference number L refers to the longitudinal direction of the plastic preform. Between the side support 4 and the blow mold side 14, a blow mold carrier shell 16 is arranged (and correspondingly also between the second side support (not shown) and the second blow mold side (not shown)).

[0073] Reference numeral 32 denotes a blow-molding nozzle, which is used to apply compressed air to the plastic preforms. This application device can be used to apply a separate air pressure to the plastic preforms. Reference numeral 34 denotes a rod-shaped body or stretch rod, which can be inserted into the container. The bottom 18 can be moved relative to the side in the longitudinal direction L by a drive device 36, which is only shown schematically. Figure 1 In the present invention, a movement towards the plastic preform is understood to be an upward movement.

[0074] Figure 3 Two views of a plastic container are shown. In this case, the left image shows the geometry of the container during cleaning before the boxing stage. The right image shows the situation after the boxing stage, where the bottom 10a of the container is pushed upwards to create the bend.

[0075] Figure 4 A first diagram of the method according to the invention is shown. In this case, reference numeral 52 denotes a blowing curve or a pressure profile.

[0076] Reference numerals P1, Pi, P2, Sp and E and corresponding vertical lines indicate respective time periods, each of which uses a new pressure level. The second pressure Pi is also referred to as the intermediate blow molding pressure. It can be seen that from a time point of about three seconds, a specific pressure P1 (pre-blow molding pressure) is applied to the plastic container. At the same time, the stretch rod moves into the container. Reference numeral 54 indicates the direction of the stretch rod movement. At the end of the phase of applying the first pressure P1, the rod-shaped body is slightly retracted and briefly offset, and the bottom also moves to the upper position.

[0077] The entire pressure curve preferably includes several inflection points (in the mathematical sense, i.e., points at which the second derivative of the corresponding function will change sign). Preferably, by definition, the first pressure P1 changes to the second pressure Pi in the region of the inflection point WP1 of the pressure, and the second pressure Pi changes to the third pressure P2 in the direction of the inflection point WP2. The transition from the third pressure P2 (also called the final blowing pressure) to the purge pressure Sp occurs shortly before the sharp drop in pressure, and the transition from the purge pressure Sp to the release pressure occurs again before the sharp drop in pressure.

[0078] Correspondingly, reference numeral 56 represents the movement trend relative to the bottom. It can be further seen that in this embodiment, during the entire stage of applying the third pressure P2 to the container, the bottom remains in an upwardly propelled position. The third pressure P2 first rises to a specific level of about 35 bar and maintains a predetermined time period (about 12 seconds here) in this stage. In this time period, the container is formed in the circumferential direction. After the final blow molding, the container is cleaned (pressure Sp), wherein the pressure drops to a level of about 10 bar again. Finally, in the last stage E (or during the application of the release pressure E), the container is released from pressure and the stretch rod is retracted upwardly. In this stage, the bottom is also reset again, as can be seen from the last part of the curve 56.

[0079] Figure 5 A further embodiment of the method according to the invention is shown. The pressure curve 52 is as described in the previous method, i.e., there are no changes here. Figure 4 As in the embodiment shown in , during the application of the first pressure P1 to the container, the stretching rod is slightly retracted again. Reference numeral P10 indicates the position in which the stretching rod is retracted. Reference numeral P0 indicates another position of the stretching rod.

[0080] Different from Figure 4 In the embodiment shown, Figure 5 In the embodiment shown, the bottom is pushed upwards only during the cleaning phase and the pressure Sp and is reset again during the pressure release phase E. In this method, the bottom thus remains pushed (upward) onto the plastic bottle for the entire duration of the pressure applied to the plastic preforms or plastic bottles.

[0081] With regard to the pressure trend curves, it can be seen in all embodiments that, as described above, these pressure trend curves are adjacent to each other in each case. However, in any case, the average pressures in the various stages (pre-blowing, intermediate blowing and final blowing) are different, that is, the pre-blowing pressure is less than the average value of the intermediate blowing pressure here, and the intermediate blowing pressure is less than the average value of the final blowing pressure. In other words, the average pressure between the vertical lines P1 and Pi will be less than the average pressure between the vertical lines Pi and P2, and the average pressure between the vertical lines Pi and P2 will be less than the average pressure between the vertical lines P2 and Sp. The average pressure E between the lines Sp and is again less than the average pressure between the lines P2 and Sp.

[0082] exist Figure 6In the method shown, the bottom is first pushed onto the plastic preform before or during the application of the second pressure and is kept in this upward position until the application of the third pressure P2 is completed. Subsequently, in the area between the vertical lines Sp and E, the bottom is briefly reset to its starting position and then pushed back onto the plastic preform. This is performed in the area of ​​the pressure release phase E. Finally, the bottom is moved back to its original position during the pressure release phase. The stretch rod movement preferably does not follow the movement of the bottom described last, but remains in a partially retracted position. Therefore, in this method, the bottom is pushed onto the plastic preform exactly twice and is also retracted again. However, the bottom can also be pushed onto the plastic preform more than twice (for example three or four times) and retracted again (at least partially).

[0083] Figure 7 Shown as Figure 6 Another embodiment of a variant is shown. In this embodiment, the bottom is also pushed in and retracted twice, but only after the third pressure P2 is applied. It can be seen that here the bottom is temporarily pushed onto the plastic preform and immediately retracted, so that the bottom is then pushed again onto the plastic preform or onto the now formed plastic container. In this embodiment, too, at the end, the bottom is moved back to its original position again.

[0084] Figure 8 Shows Figure 6 Another embodiment of the method is shown in . It can be seen that here the bottom is first pushed in during the phase P1 and the phase to be started Pi. Subsequently, during the application of a third pressure P2 to the plastic preform, the bottom is temporarily withdrawn and pushed onto the plastic preform again. The bottom is withdrawn a third time during the cleaning phase Sp in order to push the bottom onto the plastic preform (or the then formed container) again during the pressure release phase. Thus, in Figure 8 In the method shown, the bottom is pushed onto the plastic preform three times and withdrawn. In this method, the blowing speed can also be better controlled. In particular, this can be controlled by adjusting the second pressure Pi (i.e. the intermediate blowing pressure). The container quality can also be improved in this way. Moreover, the wall thickness can be better controlled.

[0085] The applicant reserves the right to claim all features disclosed in the present application documents as the essence of the present invention, as long as the features are novel with respect to the prior art, either individually or in combination. In addition, it should be noted that features that can be advantageous in themselves are also described in the various figures. It should be immediately recognized by those skilled in the art that a particular feature described in a figure can also be advantageous without adopting other features in the figure. In addition, it should be recognized by those skilled in the art that advantages can also be obtained by combining more features shown in individual figures or in different figures.

[0086] Reference numerals list

[0087] 1 Equipment

[0088] 2 Bracket

[0089] 4 Side brackets

[0090] 10 Plastic bottles (also plastic preforms)

[0091] 10a Container bottom

[0092] 14 Blow mold side

[0093] 16 Loading shell

[0094] 18 Bottom

[0095] 15 Cavity

[0096] 20 Forming stations

[0097] 32 Blowing nozzle

[0098] 34 Rod-shaped body, tensile rod

[0099] 36 A driving device for moving the bottom 18

[0100] 52 Pressure trend curve

[0101] 54 Movement direction of stretching rod

[0102] 56 Bottom moving direction

[0103] P1 First pressure, pre-blow pressure

[0104] Pi Second pressure, intermediate blowing pressure

[0105] P2 Third pressure, final blow molding pressure

[0106] Sp cleaning pressure

[0107] E Release (pressure)

[0108] P0, P10 stretch rod position

[0109] z Rotation axis

[0110] P Conveyor path

[0111] WP1, WP2 are the inflection points of the pressure trend curve.

Claims

1. A method for forming a plastic preform into a plastic bottle, the method comprising the following steps: - introducing the plastic preform (10) to be expanded into a blow mould, wherein the blow mould comprises at least two side parts (14) and a bottom (18) which is movable relative to the side parts in the longitudinal direction (L) of the plastic preform (10); - inserting the rod-shaped body (34) into the interior of the plastic preform (10) through the mouth of the plastic preform (10); - applying a first pressure (P1) to the plastic preform, the first pressure (P1) being a pre-blowing pressure; - applying a second pressure (Pi) to the plastic preform, wherein the second pressure (Pi) is different from and higher than said first pressure (P1), and wherein said second pressure (Pi) is an intermediate blowing pressure; - applying a third pressure (P2) to the plastic preform, wherein the third pressure (P2) is different from and higher than said second pressure (Pi), and wherein said third pressure (P2) is a final blowing pressure; Therein, only after the third pressure (P2) has been applied to the plastic preform (10), the bottom portion (18) is pushed towards the plastic preform (10) in the longitudinal direction (L) of the plastic preform (10).

2. The method according to claim 1, It is characterized in that Before or during advancement of the base (18), the shaft (34) is at least partially retracted.

3. The method according to claim 1 or 2, It is characterized in that The distance the bottom portion (18) is advanced is greater than 5 mm, and / or the distance the bottom portion (18) is advanced is less than 30 mm.

4. The method according to claim 1 or 2, It is characterized in that After the third pressure (P2) has been applied, the plastic preform (10) is again released from pressure.

5. The method according to claim 1 or 2, It is characterized in that After the third pressure (P2) has been applied to the plastic preform, the bottom (18) is retracted again.

6. The method according to claim 1 or 2, It is characterized in that Before applying the third pressure (P2) to the plastic preform, the rod-shaped body is at least partially retracted.

7. The method according to claim 1 or 2, It is characterized in that The duration of advancing the base (18) is between 1 second and 20 seconds.

8. The method according to claim 1 or 2, It is characterized in that The second pressure is greater than 3.5 bar, and / or the second pressure is less than 20 bar.

9. The method according to claim 1 or 2, It is characterized in that After the third pressure (P2) is applied, a cleaning pressure (Sp) is applied to the plastic container.

10. A device for molding plastic preforms into plastic bottles, the device comprising at least one conveying device (2) on which a plurality of molding stations (20) are arranged, wherein: Each of the molding stations comprises a blow mold, each of the blow molds comprises a bottom (18) and two side parts (14), wherein the two side parts (14) are movable relative to each other to open and close the blow mold, the bottom (18) is movable relative to the side parts (14) in the longitudinal direction (L) of the plastic preform (10) and in the closed state of the blow mold, and wherein the device (1) also comprises a control device and at least one application device, the application device is used to apply a gaseous medium to the plastic preform to expand it, the control device controls the application of the gaseous medium to the plastic preform so that a first pressure (P1) is first applied to the plastic preform, the first pressure (P1) is a pre-blowing pressure, then a second pressure (Pi) higher than the first pressure (P1) is applied to it, the second pressure (Pi) is an intermediate blowing pressure, and finally a third pressure (P2) is applied to it, the third pressure (P2) is a final blowing pressure, and the third pressure (P2) is higher than the second pressure (Pi), Characterized in that the device comprises a drive device (36) which is suitable and intended to at least temporarily move the bottom (18) during the application of pressure to the plastic preform (10), wherein the bottom (18) can be pushed towards the plastic preform (10) in the longitudinal direction (L) of the plastic preform (10) only after the third pressure (P2) is applied to the plastic preform.

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