The invention relates to an aftercooling apparatus for preforms, with the still dimensionally unstable preforms being removed from the open mold halves of an injection molding machine by means of a removal gripper and allowed to at least partially aftercool in water-cooled removal or cooling sleeves.
The invention further relates to a method for aftercooling preforms with a threaded portion, a blow-molded part and a neck ring which can be at least partially aftercooled in water-cooled cooling sleeves while still being in a hot, dimensionally unstable state.
In practical applications, three aftercooling systems have attained dominance for the production of preforms:
According to recent developments, the injection molding machine cycle time is further shortened by removing the preforms from the molds in a soft state with an unstable shape. However, previously less noticeable problems are now becoming more important. Physical effects cause cooling inside the walls of the preforms to be uneven:
Accordingly, each intervention during aftercooling becomes an extremely delicate task. In the fabrication of injection-molded parts with injection molding machines, the cool-down time is a determining factor for the duration of a full cycle. The first and main cooling effect still takes place in the injection molds. Both mold halves are intensely water-cooled during the injection molding process, so that the temperature of the injection-molded parts, while still in the mold, can be lowered at least in the marginal layers from, for example, 280° C. to a range of about 70° C. The temperature drops in the outer layers very quickly below the so-called glass-transition temperature of about 80° C. The actual injection molding process up to the removal of the injection-molded parts could recently be cut almost in half, while retaining optimal qualities of the preforms. The preforms must be solidified in the mold halves to a degree that they can be gripped by the removal aids and transferred to a removal device. The shape of the removal device matches the outside dimension of the injection-molded parts. The intense water cooling in the mold halves causes, according to physical principles, a time delay of the temperature drop reaching the core region of the preform wall. Accordingly, the aforementioned about 70° C. cannot be uniformly attained across the entire cross-section. As a result, rapid re-heating over the material cross-section occurs from the inside to the outside as soon as the intense water cooling through the molds is interrupted. For two reasons, it is therefore most important to aftercool the preforms outside the mold. Dimensional changes, but also surface damage, such as pressure points, etc., during aftercooling must be prevented. Cooling in the higher temperature range must also be prevented from being too slow to avoid locally detrimental crystal formation caused by reheating. The goal is a uniform amorphous state in the material of the finished preform. The residual temperature of the finished preforms should be so low that no pressure or adhesion damage occurs at the contact points even in large packages with thousands of loosely supplied injection-molded parts. The surface temperature of the finished injection-molded parts must not exceed 40° C. even after slight reheating. Aftercooling after removal of the hot, dimensionally unstable preforms from the injection mold is very important for maintaining dimensional stability.
In WO 2004/041510, the applicant proposes an intense cooling station and an aftercooling station, with the intense cooling station having cooling pins that can be inserted into the preforms for cooling the inside. The interior shape of the cooling sleeves is here matched to the corresponding interior shape of the injection mold, such that the preforms after removal from the molds can be inserted with as little play as possible until completely contacting the cooling sleeves. If the preforms are in a horizontal position in the first aftercooling phase, then they tend to on a corresponding bottom part of the cooling sleeve. The preforms are then cooled more strongly at the bottom due to a more intense cooling contact in the lower region, which induces stress in the preform, causing the preform tends to assume an oval shape. If individual preforms are easily deformed during the first aftercooling phase due to the shortened cooling time in the injection molds, then the corresponding dimensional changes in already solidified preforms can no longer be corrected. According to a preferred embodiment disclosed in WO 2004/041510, an inflation pressure can be generated inside the preforms through targeted control of suction and blow air, and the not yet solidified preform can be brought into complete contact to the entire inner wall surface of the cooling sleeve. After the preforms fully contact the inner wall surface of the cooling sleeve, the contact across this area is maintained during several seconds, producing a calibration effect for each individual preform. The calibration effect produces a high production and quality standard during the production of the preforms that was not attainable with conventional technology. The preforms are thereby brought again to the exact dimensions shortly after being removed from the injection molds. Any dimensional changes introduced after the first critical handling from the injection molds into the cooling sleeves are compensated. Calibration of the preforms allows removal of the preforms from the molds at still higher temperatures, thereby shortening the injection molding cycle time even further.
WO 2004/041510 proposes two different solutions for producing an inflation pressure. According to a first variant, a sealing ring is arranged on a cooling pin or on a blow nozzle, which is brought into contact on the conical transition in the interior of the preform. According to the second variant, the blow nozzle has ring-shaped seals intended for contacting the end face of the open rim of the preform. The inflation pressure hereby operates on the entire preform. Both solutions disadvantageously require in practice and with multiple injection molds having, for example, 100 to 200 mold cavities very high precision for guiding and moving all blow nozzles.
EP 900 135 proposes a concept similar to the aforementioned second variant. Sealing of the open rim presumes a certain pressing force and also sufficient dimensional stability of the threaded part. To prevent dimensional changes of the threaded part, the preforms must be left in the injection molds until reaching a higher dimensional stability. However, this works against shortening the injection molding cycle time.
Based on extensive investigations, it was recognized that calibration of the still hot, dimensionally unstable preforms immediately after withdrawal of the removal robot from the open mold halves has significant advantages. However, this success was not observed with all types of preforms. For example, with preforms having an unsupported threaded region in relation to the cooling sleeves, the problems with dimensional stability could not be solved. The inventor has recognized that with increasingly shorter machine cycle times, the entire open end side can be subject to a significant handling risk during aftercooling, and not only because the threaded portion protrudes from the cooling sleeve and can therefore no longer be cooled by the cooling sleeve. This happens regardless if the preform is calibrated or not.
It is therefore an object of the invention to develop a method and an apparatus which ensures highest quality parameters and maximal dimensional stability of the preform during aftercooling, in particular with respect to handling, at least with typical preforms, and provides the shortest possible cycle time.
The aftercooling apparatus according to the invention is characterized in that blowing devices are integrated in the cooling sleeves in the region of the outer open end sides of the preforms, through which the outer skin, at least of an unsupported region of the preforms, can be solidified with cooling air.
The method of the invention is characterized in that the outer skin, at least of a part of the outer open unsupported end sides of the preforms, are cooled with cooling air through air blowing devices integrated in the cooling sleeves and thereby solidified.
The inventor has recognized that calibration after insertion of the hot preforms into the cooling sleeves with a substantially cylindrical or slightly conical blow-molded part results in significant progress in the manufacture of conventional preforms. The interior space of the preform, at least of the blow-molded part, must be mechanically sealed for calibration. However, the force of the compressed air used for the calibration, as well as the mechanical sealing force, creates new problems, if the region of the open end of the preform wall sections is not supported by the inner wall of the cooling sleeves. It is also important to note that the outside of the open end of the preform can already be solidified immediately after transfer from the open mold halves to the cooling sleeves, as soon as the air cooling is integrated in the cooling sleeves. This produces a time improvement of, for example, 1 to 2 seconds to make the respective threaded region dimensionally stable by additionally cooling the outside with cooling air. Cooling the blow-molded part immediately from the outside could be disadvantageous because the calibration would then require a higher air pressure. Water-cooling the cooling sleeves has an immediate effect in the cylindrical region of the neck ring due to the direct wall contact, which turned out to be successful from the beginning. The entire region of the neck ring should be air-cooled and solidified from the outside until the mechanical forces can no longer impair dimensional stability due to the sealing forces. In a particular preferred embodiment, the outer air cooling location for calibration is selected to be located approximately vis-à-vis the inside sealing force of the compressive or sealing rings.
The novel aftercooling solution for calibration and/or handling starts preferably with the concept of a Thermos bottle closure. Both applications have a sensitive wall material. In one case, the material is glass, in the other case an easily deformable plastic. With the solution according to the invention, the sealing location need not be defined with the highest precision. The substantial advantage of the novel invention is that the entire cycle time can be substantially reduced, while meeting all quality criteria and while the efficiency of the injection molding machine can be increased by between 15% and 20%. The preforms can be unmolded sooner, i.e., when the preforms are still substantially dimensionally unstable.
In practice, there are a large variety of preforms which may require special treatment.
With the new invention, dimensional stability can be fully maintained even when the dry cycle time is significantly shortened. This means that a reserve remains for a still shorter machine cycle time when the particular air cooling of the outer, open end side is employed. Field tests have shown that the machine cycle time can be reduced by 15% with clear preforms and by 20% with colored preforms.
The novel invention enables a number of particularly advantageous embodiments. Reference is made here to claims 2-17 and 19-29.
Advantageously, when calibrating, the pressure of the compressed air increases continuously from the start of the calibration. In this way, shrinkage can be continuously compensated even when the preform continues to solidify. Preferably, the compressed air supply can be reproducibly controlled by a programmed increase of the control voltage of a control valve and a corresponding increase of the calibration pressure.
In a particularly preferred embodiment, a cooling aggregate is associated with the aftercooling apparatus for producing low-temperature air, in particular at a temperature below 0° C. A pressure generator for the cooling air is associated with the aftercooling apparatus, which generates a cooling air pressure of less than 2 bar, preferably less than 1.2 bar. Advantageously, the application is controlled, wherein the aftercooling apparatus includes a controller by which the air blowing device can be activated immediately, from the moment the preform is transferred to the removal or cooling sleeves. Application of low-temperature air has two significant advantages: firstly, immediately after transfer of the preforms, which are removed from the molds while still hot, an immediate and more intense solidification of the outer skin can be attained in the region of the opening. This means that before any mechanical intervention through handling or calibration, this region which is especially at risk, is solidified to a degree so as to prevent an oval shape or local swelling. The low-temperature air advantageously also reduces the quantity of cooling air. The air pressure can be reduced, for example from 4 bar to only 1 bar. Accordingly, the same effect can be attained with a much smaller air quantity than with ambient air. In particular, the quantity and temperature of the low-pressure air can be purposely controlled.
According to a particularly advantageous embodiment of the novel invention, it is proposed that the air blowing device is implemented as air channels directed to the outer, open-ended side of the preforms. Preferably, the aftercooling apparatus includes a controller for switching the apparatus on and off, by which the air blowing device can be activated from the moment the preform is transferred to the removal or cooling sleeves as well as during the calibration phase. The solution of the invention can be applied in the field of aftercooling wherever there is a risk of handling-related damage.
In a particularly advantageous embodiment, a gripper has a plurality of nipples with a corresponding insertion part into the preforms, wherein the insertion parts of the nipples have radially expandable compressive or sealing rings which can be inserted into the preforms. The compressive rings are preferably implemented as a radially expandable sealing rings, by which a sealing force can be generated via a bore in the nipples in the interior of the blow-molded part of the preforms directed towards the inner wall of the preforms for building up an inflation pressure. In a particularly preferred embodiment, the inflation pressure is controlled by starting with a minimum pressure, which then increases to the optimal pressure.
According to another important concept of the invention, the nipples can be inserted into the preforms, with control of their position, to a selectable optimal sealing location in the region between the threaded part and the blow-molded part. Different shapes of the transition between the threaded part and the blow-molded part can then be taken into consideration. The best sealing location is identified at the beginning of each production. After insertion of the nipples, the outer wall of the entire blow-molded part of the preform must be in wall contact with the corresponding inner wall of the removal sleeve. Preferably, the preforms are already inserted into the removal sleeves during transfer with the removal sleeves until a complete and full inner wall contact of the entire blow-molded part, including the closed bottom part, is attained. During the duration of several injection molding cycles, the preforms are aftercooled in the water-cooled cooling sleeves of an aftercooling, wherein the calibration is performed during the time of a single injection molding cycle or limited by the duration of a single injection molding cycle. The preforms can be removed from the cooling sleeves without any problems.
With respect to the apparatus, each nipple has two tubular parts which can move relative to one another. A support shoulder is fixedly attached at each end. With the two aforedescribed solutions, each nipple includes air channels through which compressed air can be controllably supplied into the interior space of the blow-molded parts of the preforms. The actuating plate is moved by controlled actuating means with respect to the platform for synchronous activation of the compressive or sealing rings. The actuating means have only a supporting function during the calibration. The compressive or sealing rings, when compressed, are held at the inside of the preform. A small force of the actuating means for the actuating plate is already sufficient for providing a good seal. Advantageously, the nipples are arranged on a platform by way of a common actuating plate, by which the nipples are inserted in or withdrawn from the preforms as well as positioned inside the removal sleeves. To this end, controlled drive means are associated with the platform for positioning the compressive or sealing rings with an optimal insertion depth or at an optimal location.
According to a preferred embodiment, the preforms are removed from the removal sleeves and transferred to cooling sleeves of an aftercooling when reaching sufficient dimensional stability, but within the time of a single injection molding cycle. After calibration, the compressive or sealing rings can be released and the pressure relieved from the interior space of the blow-molded parts. A vacuum can be generated via the air channels and the nipples, with the preforms being transferred to the aftercooling by way of the nipples. The nipple does not have a cooling function. Preferably, during the short calibration time, no air is exchanged between the interior of the preform and the ambient air. The nipples are provided with air channels, through which a vacuum can be generated in the preforms for removal of the preforms. The air channel for compressed air and suction can be identical inside the nipple. Preferably, the tubular sections are movable inside one another, wherein the inner tubular section has at least one air channel. For the concept of the first solution approach, the apparatus has a controllable removal gripper with a number of removal sleeves, with the number of removal sleeves corresponding to at least the number of injection positions of the injection mold. The apparatus has an air connection for controllable admission of compressed air to produce an inflation pressure inside the preforms for calibrating the preforms, as well as a fitting to control suction, whereby after switching from inflation pressure to vacuum the preforms can be removed from the removal sleeves with the help of the nipples. With this concept, the apparatus includes, in addition to the removal gripper, an aftercooling and a transfer gripper for transferring or switching the preforms from the removal gripper to the aftercooling, for finish cooling of the preforms, independent of the injection molding cycle.
According to another advantageous embodiment, the apparatus has an aftercooling constructed as a removal robot with a plurality of cooling positions in relation to the injection positions of the injection molds. The preforms to be transferred hot are here inserted into respective unoccupied cooling positions, calibrated, intensely cooled and ejected after finish cooling. The nipples can here support, with controlled and compressed air, the ejection of the finish-cooled preforms from the removal sleeves as well as the transfer to a conveyor belt. According to the second embodiment, the press or sealing rings can likewise be relieved after calibration, the pressure in the interior space of the blow-molded parts can be vented, the nipples withdrawn and held in a waiting position, until the aftercooling is repositioned for a new charge of preforms of the subsequent injection molding cycle.
In both embodiments, the preforms are calibrated with compressed air and the calibration time is limited by the injection molding cycle. Pressing and calibration of the still soft preforms has significant advantages:
According to another particularly preferred embodiment of the apparatus, the water-cooled removal sleeves have in the region between the threaded portion and the blow-molded part ventilation channels for a corresponding outside cooling of the corresponding preform region, also an air fitting for the ventilation channels. Depending on the geometrical shape of the preforms, the ventilation channels are arranged in the transition region between the threaded portion and the neck ring and/or in the transition region between the neck ring and the blow-molded part. Preferably, the water-cooled removal sleeves are constructed from standardized parts, such that depending on the particular situation, customized guide rings for the ventilation channels for cooling the transition region between the threaded portion and the neck ring and/or the transition region between neck ring and blowing portion can be implemented.
With respect to the method, it is also proposed to employ outside cooling of the preforms with air in the region between the threaded portion and the blow-molded part immediately after transfer of the preforms to the cooling sleeves of the removal gripper until the end of the calibration. Compressive or sealing rings are attached to the nipples for the calibration and preferably introduced in a position-controlled manner into the preforms up to the transition region between the threaded portion and the neck ring or up to the transition region between the neck ring and the blow-molded part. In combination, the preforms are already cooled from the outside after insertion into the cooling sleeves and during the calibration, also from the outside, to the transition region between the threaded portion and the neck ring and/or up to the transition region between the neck ring and the blow-molded part, and solidified. Advantageously, the outer skin of the preforms is more strongly solidified immediately after transfer from the open mold halves to the cooling sleeves, and before the calibration on the critical unsupported portions of the preforms, so that the mechanical gripper forces do not adversely affect on the corresponding regions. With preforms having a widening neck, the transition region between the threaded portion and the neck ring is air-cooled from the outside. The preforms are hereby inserted until the neck rings contact the front face of the cooling sleeves, wherein the cooling sleeves are configured so that a minimum gap, preferably in a range of hundredths of millimeters, remains between the bottom part of the preforms and the corresponding bottom part of the cooling sleeves, which can then be eliminated by the calibration.
The invention will now be described in more detail with reference to several exemplary embodiments.
a shows a nipple optimally inserted in a preform in the region of the open end side of the preform;
b shows on an enlarged scale a nipple with a floating compressive or sealing ring;
a shows outside cooling of the transition region between threaded portion and blow-molded part of the preforms;
b shows a partial section of
a shows an enlarged portion of external air cooling;
b shows external air cooling in a preform with a widening neck section;
a,
5
b and 5c show once more in schematic diagrams an optimal location for applying the compressive or sealing rings and the exterior cooling, wherein in
a shows a differently constructed thick-wall preform with corresponding positioning of the nipple and the sealing ring, respectively;
b shows the solution of
c shows removal of a preform with the nipple operating as a support nipple;
a shows an exemplary test of a preform calibration; and
b shows a defective preform, wherein the transition region that was not supported in the cooling sleeve, is not solidified according to the invention.
a illustrates the direct relationship between the function of the nipples 30 as calibration nipples and the conical section 47 of a preform 10. The corresponding conical outer part of the preform 10 is specially cooled immediately after removal from the open mold halves 8, 10, and the unsupported outer wall layer is solidified inside the cooling sleeve 21 (
b shows the insertion part of the nipple 30 according to
a and 3b show outside cooling of preforms 10xx in the not-uncritical transition 47 between the threaded portion 44 and the blow-molded part 43. Many preforms 10xx have an outer conical taper 110 in this region. This conical taper 110 is disadvantageous because the region 47 of the taper vis-à-vis of the cooling sleeve 21 is unsupported, so that there is no contact with the inner wall 111 of the cooling sleeves. Cooling air can be blown in through an air fitting 112 and vented to the outside through a cooling channel 113. This additional cooling has the significant advantage that it can be effectively used from the first instance when the preforms 10 are transferred to the cooling sleeves 21 and additionally during the entire calibration time. The additional solidification of the outside of the affected preform counteracts a possible deformation caused by the pressing force of the compressive or sealing ring 56. The most striking structural difference to a “normal” cooling sleeve is that an air guiding ring 114 is arranged in the open mouth region. An annular cooling channel is arranged around the corresponding preformed part on the inside of the air guiding ring 114 from the location of the air fitting 112 to the vent location 113′. Cooling air then flows intentionally across the entire conical outside of the preforms to the end face of the neck ring 137.
a and 4b show a preform 10x with a conically widened neck piece 136. With this type of preform, the widened neck piece is already part of the blow-molded part and contacts during calibration the inner wall of the cooling sleeve 130. The inner wall of the cooling sleeve provides the preform 10x with the defined exterior shape. The entire blow-molded part of the preform 10x makes contact with the neck ring 137. The optimal sealing location of the compressive or sealing ring 56 is in the region of the cylindrical section in the region of the neck ring 137 (
b shows another interesting conceptual embodiment. The cooling sleeve is constructed of standardized components and consists of an inner cooling sleeve 130, an outer cooling sleeve 131 and a jacket sleeve 132, as well as a head ring 133 which is used to form the air channels (gap Sp). The inner cooling sleeve 130 is designed commensurate with the shape of the preform 10, 10x, 10xx, with a corresponding head ring 133 or 114 being applied. Reference symbol 138 indicates the lowest thread pitch, 134 the base of an actuating plate, and 135 the sealing rings. According to
Frequently, as shown in
b shows a preform having an increased diameter in the region of the open end. This preform is no longer supported in the cooling sleeve in the region of the neck ring 137 and the thread. Advantageously, the outer skin of the aforementioned region is solidified with cooling air immediately after transfer from the injection molds to a removal gripper.
c shows a solution intended to prevent deformation, in particular bulging of the affected section, when the corresponding blow-molded part is tapered (
As seen from the foregoing, the preforms 10, 10x, 10xx have from the moment of the removal from the open mold halves:
An effect with maximum intensity is produced by optimizing the design of the water cooling loops
This leads to substantial advantages:
a,
6
b and 6c show calibration and removal of the preforms 10 from the removal sleeves 40 with the nipples 30 operating as holding nipples. Vacuum can be applied to the interior space of the blow-molded part through the nipple 30 (
a illustrates schematically regulation of the compressed air supply. The compressed air supply for calibration is adjusted via a voltage-controlled control valve 35, 38 by way of the voltage in Volt with controller 39, wherein a continuous increase of the inflation pressure is contemplated, preferably from the start of the calibration. The shrinkage of the preform 10 due to the cooling effect from the cooling sleeve 21 can hereby be compensated and rapid solidification of the outer skin can be attained. The preform 10 can be pressed in an optimal manner against the inner wall of the cooling sleeve for the entire duration of the calibration, without causing bulges in the region of the unsupported regions or damage resulting from handling of the preforms.
Referring back to
The discussions above make reference to the entire disclosure of WO 2004/041510 and PCT 2007/000319.
In the positions illustrated in
The aftercooling device according to
a shows an exemplary test where the preform 10xx is calibrated with cooling air. The temperature distribution is in a much narrower range of only 3.9° C., whereby the cycle time was reduced from 13.5 seconds to 11.5 seconds. The eccentricity of the oval shape was only 0.05 mm instead of 0.2 mm. This shows that with the invention, more precise preforms can be produced with a shorter cycle time.
b shows a preform 10xx, where outside cooling according to the invention was not employed. The calibration pressure was too high, so that the preform bulged in the unsupported conical region.
Number | Date | Country | Kind |
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121/07 | Jan 2007 | CH | national |
757/07 | May 2007 | CH | national |
1452/07 | Sep 2007 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/050840 | 1/25/2008 | WO | 00 | 7/16/2009 |