System for post-treating and transferring preforms

A system for the post-treatment of preforms (9) produced by means of injection moulding, including a removal element (4) having at least one receiving element (5) for receiving a preform (9), and a device for moving the removal element (4) between two tool halves of an opened injection moulding mould and for moving the removal element (4) out of the opened injection moulding mould, a post-treatment element (6) having at least one post-treatment pin (7) having a pin-shaped passage element (7), of which one end can be connected to the environment or a vacuum or reduced-pressure source and of which the other end has an outlet (18) for a coolant, and a motion device with which the removal element (4) can be reciprocated relative to the post-treatment element (6) between a first position in which the post-treatment pin (7) is positioned within the receiving element (5) and a second position in which the post-treatment pin (7) is not positioned within the receiving element (5), wherein the removal element (4) and the post-treatment element (6) are so designed that in the first position coolant can be introduced by way of the coolant inlet into a preform held in the receiving element (5) in such a way that it can flow between the inside wall of the preform (9) and the outside wall of the pin-shaped passage element (7) to the coolant outlet (18) and can be discharged by way of the passage element (7).

BACKGOUND OF THE INVENTION

The present invention concerns a system for post-treatment of preforms produced by means of injection moulding.

By way of example commercially available PET bottles are generally produced by stretch blow moulding of the hollow body preform. In that case the hollow body preform is produced in a first step by injection moulding. The stretch blow moulding operation which follows the injection moulding operation can be effected either immediately after production of the hollow body preform or at a later time. In the production of the corresponding injection moulding moulds, a high level of complication and expenditure is necessary as the injection moulding mould on the one hand has to be designed for very high pressures and on the other hand it must also have suitable heated and/or cooled passages.

Usually an injection moulding tool for the production of PET preforms comprises a large number of, for example 96, cavities into which tool cores of a corresponding configuration are introduced. When the tool is closed, that is to say when the core is fitted into the corresponding cavity, a space, the so-called mould space, is formed between the core on the one hand and the cavity on the other hand. The plasticised plastic material, for example PET, is then injected into that space under high pressure. As soon as the PET preform has cooled sufficiently the mould can be opened and the preform removed.

To reduce the cycle times, that is to say the time from one injection operation to the next, it is already usual for the preform to be removed from the mould at a very early time at which the preform is already solid at its outside surfaces, but the inner region thereof is still fluid. In that condition the preform is generally transferred on to a receiving element, frequently a so-called receiving plate, which generally comprises a group of receiving cavities, wherein each receiving cavity can receive a preform. Thus for example in the so-called vertical tools, that is to say those injection moulding tools which open by a vertical movement of the one tool portion relative to the other, it is possible for the tool mould to be already opened after for example 10 seconds, for a receiving plate with suitable receiving cavities to be introduced into the mould, for the individual preforms to be allowed to fall into the receiving cavities under the force of gravity, for the receiving plate with the preforms to be moved out of the tool and for the mould to close again and begin the next injection moulding operation. During the next injection moulding operation the previous preforms remain in the receiving cavity which is usually cooled.

The receiving plate thus functions as a removal element which has individual receiving elements for receiving a preform and a device for moving the removal element between two mould halves of an opened injection moulding mould and for moving the removal element out of the opened injection moulding mould.

As the preform must remain in the receiving cavity for a comparatively long time for cooling so that generally the next preform can already be removed from the injection moulding tool before the preform has cooled down in the receiving cavity to such an extent that it can be removed without the risk of damage it is already usual to employ receiving plates which have a plurality of groups of receiving cavities, wherein each group has as many receiving cavities as the injection moulding tool provides preforms per injection cycle. The individual receiving cavity groups are then successively equipped with preforms so that the individual preform can remain in the receiving cavity for longer than an injection moulding cycle.

To further reduce the post-treatment time in the removal plate, it has already been proposed in U.S. Pat. No 6,475,422 that a pin be introduced into the preform, by way of the tip of which cooling fluid is passed into the bottom region of the preform. In that case the cooling fluid issues at the tip of the pin and then flows through the annular gap formed between the cooling pin and the inside wall of the preform, and out of the preform into the environment. The preform is thus cooled not only from the exterior but also from the interior.

In that embodiment however a considerable amount of cooling fluid has to be supplied under relatively high pressure by way of the cooling pin to ensure that sufficient cooling fluid flows through the annular gap and carries away sufficient heat. To provide sufficient cooling fluid it is necessary to act on the cooling pin with compressed air, which involves the costly provision of suitable air feed lines and suitable compressors. In addition that kind of cooling fluid feed leads to very rapid cooling of the bottom portion of the preform while the wall portions and in particular the neck portions are only relatively slowly cooled down, which leads to large temperature differences within the preform, whereby the quality of the preform can be impaired.

WO 2007/063063 has therefore already proposed that the post-treatment pin should be porous so that the cooling fluid is supplied not only by way of the tip but also along the entire peripheral surface of the cooling pin. The temperature difference within the preform can be markedly reduced by that measure. Porous post-treatment pins however are relatively complicated and expensive to manufacture and have to be supplied with high pressure to ensure an adequate coolant fluid flow.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, a system is provided for the post-treatment of preforms (9) produced by means of injection moulding, includingi) a removal element (4) having:a) at least one receiving element (5) for receiving a preform (9), andb) a device for moving the removal element (4) between two tool halves of an opened injection moulding mould and for moving the removal element (4) out of the opened injection moulding mould,ii) a post-treatment element (6) havinga) at least one post-treatment pin (7)a1) having a pin-shaped passage element (7),a11) of which one end can be connected to the environment or a vacuum or reduced-pressure source anda12) of which the other end has an outlet (18) for a coolant, andiii) a motion device with which the removal element (4) can be reciprocated relative to the post-treatment element (6) between a first position in which the post-treatment pin (7) is positioned within the receiving element (5) and a second position in which the post-treatment pin (7) is not positioned within the receiving element (5),wherein the removal element (4) and the post-treatment element (6) are so designed that in the first position coolant can be introduced by way of the coolant inlet into a preform (9) held in the receiving element (5) in such a way that it can flow between the inside wall of the preform (9) and the outside wall of the pin-shaped passage element (7) to the coolant outlet (18) and can be discharged by way of the passage element (7).

DETAILED DESCRIPTION OF THE INVENTION

Based on the described state of the art therefore the object of the present invention is to provide a system for the pre-treatment of preforms produced by injection moulding, which can be operated inexpensively without the provision of compressed air and minimises the temperature gradient within the preform, which inevitably occurs during the post-treatment.

According to the invention that object is attained by a corresponding system comprising a removal element having at least one receiving element for receiving a preform, and a device for moving the removal element between two tool halves of an opened injection moulding mould and for moving the removal element out of the opened injection moulding mould, a post-treatment element having at least one post-treatment pin having a pin-shaped passage element, of which one end can be connected to the environment or a vacuum or reduced-pressure source and of which the other end has an outlet for a coolant, and a motion device with which the removal element can be reciprocated relative to the post-treatment element between a first position in which the post-treatment pin is positioned within the receiving element and a second position in which the post-treatment pin is not positioned within the receiving element, wherein the removal element and the post-treatment element are so designed that in the first position coolant can be introduced by way of the coolant inlet into a preform held in the receiving element in such a way that it can flow between the inside wall of the preform and the outside wall of the pin-shaped passage element to the coolant outlet and can be discharged by way of the passage element. The tip of the pin-shaped passage element thus functions as a coolant outlet, by way of which the coolant introduced into the preform can be discharged from the preform.

The direction of the coolant flow is thus reversed in relation to the configurations referred to in the opening part of this specification. Basically the post-treatment element does not have to make any cooling fluid available as the pin-shaped passage element can be connected to a vacuum or reduced-pressure source and then the cooling fluid can simply be sucked in out of the environment.

If in contrast the pin-shaped passage element is only connected to ambient pressure the post-treatment element should have a feed for coolant.

Thus the post-treatment element can have for example a coolant inlet arranged outside the pin-shaped passage element, wherein the coolant inlet is preferably in the form of a sleeve surrounding the pin-shaped passage element so that the coolant can be fed by way of a preferably annular gap formed between the pin-shaped passage element and the sleeve. While the coolant outlet serves for discharge of the cooling fluid out of the preform the coolant inlet serves for introducing the coolant into the preform.

In a particularly preferred embodiment there is provided a flow machine, for example a ventilator or a fan, which at the coolant inlet provides a cooling fluid pressure of between 1 and 3 bars, preferably between 1 and 1.5 bars and best between 1 and 1.2 bars. Uniform post-treatment of the preform is possible with such a low pressure, in addition it is possible to dispense with a compressed air connection as usual flow machines such as for example fans or ventilators are capable of providing the corresponding cooling fluid pressure. By virtue of the cooling fluid direction according to the invention it is possible to dispense with the complicated and expensive provision of compressed air. The use of a flow machine also has the advantage that this involves more uniform cooling of the preform.

Alternatively or in combination there can be provided a flow machine which at the coolant outlet produces a cooling fluid pressure of less than 1 bar, preferably between 0.8 and 1 bar and particularly preferably between 0.9 and 0.99 bar.

In a further particularly preferred embodiment the post-treatment element has at least one transfer element with which a preform can be transferred from the removal element to the post-treatment element.

Such a transfer may be required if the preform is to be taken from the removal element so that a further preform of the following injection moulding cycle can be received in that post-treatment element.

In addition the transfer element can have a transfer sleeve, wherein the transfer sleeve has a through passage, the first end of which can be connected to a vacuum source and the second end of which ends in the first position within a preform received in the receiving element, wherein the second end is preferably arranged at the peripheral surface of the sleeve. The sleeve shape permits simple transfer of the sleeve from the removal element to the post-treatment element, such transfer at the same time handling the preform gently.

In addition the transfer element can have a compressed air connection, by way of which compressed air can be introduced into the preform received in the receiving element to eject the preform from the transfer element. In other words the transfer element only serves to remove the preforms from the post-treatment element. Prolonged residence of the preform on or in the transfer element is not planned.

Basically any fluid can be considered as the coolant, even if gaseous coolants and in particular air are particularly preferred.

In a further preferred embodiment the post-treatment element has a coolant distributor plate including a plurality of post-treatment pins. That has the advantage that a plurality of post-treatment pins can be supplied with coolant with a single coolant distributor plate.

Advantageously the coolant distributor plate can be rotated about an axis of rotation to eject preforms which were transferred from the removal element on to the coolant distributor plate, wherein preferably the coolant distributor plate can be rotated through about 90°.

It is particularly desirable if the flow machine is arranged within or fixed to the coolant distributor plate, wherein the intake of the flow machine is connected to the coolant outlet of the at least one post-treatment pin while the outlet of the flow machine is connected to a coolant distributor plate opening relative to the environment, wherein the coolant distributor plate opening is preferably arranged at the side of the coolant distributor plate, that is opposite to the post-treatment pins. For example the coolant distributor plate can have a pressure chamber to which the fan is connected.

Alternatively thereto the outlet of the flow machine can be connected to the coolant inlet of the at least one post-treatment pin while the intake is connected to the coolant distributor plate opening relative to the environment.

For many situations of use it may be advantageous if the sleeve in the form of the coolant inlet has an outer periphery which approximately corresponds to the inner wall opening of the preform so that, in the first position, the outside of the coolant inlet sleeve is in contact with the inside of the preform.

In a further preferred embodiment the coolant distributor plate has cooling passages for the feed of a coolant for cooling the coolant distributor plate itself. In that case water is preferably used here for cooling the coolant distributor plate. Cooling of the coolant distributor plate provides on the one hand that the sleeve which in some embodiments comes directly into contact with the preform is cooled, for example to less than 10° C., and on the other hand the air fed into the preform is cooled.

In a further preferred embodiment there is provided a closure cap which can be fitted on to the passage element and/or the coolant inlet to close same.

In principle in operation of a PET injection moulding system it can happen that one (or more) of the mould cavities can no longer be operated for some reasons. Thus a tool having 96 mould space cavities for each injection moulding cycle could then only still produce 95 preforms per cycle. A mould space then simply remains empty. To prevent in the post-treatment operation coolant and/or vacuum or reduced pressure being unnecessarily discharged by way of a post-treatment element and/or a transfer element into a receiving element which is not carrying any preform, the closure cap can be used.

Further advantages, features and possible uses of the present invention will be clearly apparent from the description hereinafter of preferred embodiments and the associated Figures in which:

FIG. 1shows a diagrammatic view of a PET injection moulding system with post-treatment unit. The injection moulding mould comprises two plates1,2movable relative to each other, wherein one plate1is stationary and one plate2is movable in the illustrated embodiment.

The one plate has cores3while the other plate has corresponding cavities (not shown). The two plates can be moved relative to each other from an opened position shown inFIG. 1into a closed position in which the cores3of the movable plate2are arranged in the corresponding cavities of the stationary plate1. The so-called mould space which is filled with plasticised PET to form a preform is then formed between the cavities of the stationary plate1and the cores3of the movable plate2.

As soon as the outer surfaces of the preform have cooled, that is to say become solid, the mould is opened and a removal element4in the form of plates is moved between the opened plates1,2. The preforms sitting on the cores3of the moving plate are then transferred into corresponding receiving elements also in the form of cavities.

In the illustrated example the injection moulding tool has four cores, that is to say four preforms are produced in the injection moulding cycle. The corresponding removal element4has however 12 (3×4) receiving elements5which can each receive a respective preform. The removal element4thus has three groups of receiving cavities which are successively filled with corresponding preforms. As soon as the preforms have been transferred from the cores3on to the receiving elements5of the removal element4the removal element4is moved again into theFIG. 1position and the injection moulding mould comprising the two plates1,2can be closed again. As in the illustrated embodiment the removal element is connected to the stationary plate1the post-treatment element6connected to the moving plate2moves towards the removal element4. The post-treatment element6has a row of post-treatment pins7which, while the mould is closed, engage into the preforms held in the removal element1.

That situation is shown inFIG. 2.

The individual post-treatment pins are mounted on a pin plate. In addition transfer elements8are fixed to the pin plate which serve for transfer of the post-treated preforms from the removal plate4on to the transfer elements8or the post-treatment element6. Fixed to the post-treatment element6is a fan27with which an increased pressure or a reduced pressure can be produced in a pressure chamber26. The entire post-treatment plate6is adapted to be rotatable about the shaft9so that the post-treatment element can be rotated through 90° so that the preforms sitting on the transfer element8can be discharged under the force of gravity.

As can be seen fromFIG. 2air is evacuated both by way of the removal element4and also by way of the post-treatment element6, out of the post-treatment space formed by the receiving element5on the one hand and the post-treatment pin7or transfer element8on the other hand. The former leads to the preforms being securely held in the receiving elements5.

Furthermore it will be seen fromFIGS. 1 and 2that the post-treatment element6has more pins than the removal plate4has receiving cavities. The removal plate can therefore be positioned in a plurality of different positions (in the illustrated example 3) relative to the post-treatment element6. The corresponding positions are assumed successively after a respective new set of preforms has been removed from the injection moulding mould so that the preform set held longest in the removal plate4is respectively positioned with respect to the transfer elements8and can therefore be removed.

FIG. 3shows a view on an enlarged scale. Shown therein are three receiving elements5fastened to the removal element4. Two post-treatment pins7and a transfer element8are fastened to the post-treatment element6in opposite relationship. The post-treatment elements have a pin in the form of a sleeve, one end of which is connected to a vacuum or reduced-pressure source. The fan7is used for that purpose in the illustrated embodiment. That provides that, at the end remote from the post-treatment element6of the sleeve, cooling air is discharged from the interior of the preform9. The tip of the pin-shaped passage element thus serves as a coolant outlet while coolant flows into the preform from the environment at the open side of the preform. The illustrated embodiment provides for a continuous air flow through the interior of the preform, wherein the air flows through the annular gap between the pin-shaped passage element and the inside of the preform9into the bottom region of the preform and leaves same through the coolant outlet at the tip of the pin-shaped passage element7.

To remove the completely post-treated preform, that is to say which has also been cooled in its interior, from the receiving element5the corresponding receiving element is acted upon with increased pressure so that the preform9sitting in the corresponding receiving element5is transferred on to the transfer element8. When the injection moulding tool is opened again, whereby the post-treatment unit consisting of the removal element4and the post-treatment element6is also opened again, the corresponding preform9remains on the transfer element8while the preforms in opposite relationship to the post-treatment pins remain in the corresponding receiving elements. That situation is shown inFIGS. 4 and 5.

For definitive removal of the preform9carried on the transfer element8there is a compressed air feed shown inFIG. 6, which provides that the preform is ejected from the transfer element8at the correct time.

FIG. 7shows an alternative embodiment of the post-treatment pin. Here the post-treatment pin also comprises a pin-shaped passage element7which however is surrounded concentrically by a sleeve at its end towards the pin plate6. Air is passed into the interior of the preform by way of that sleeve11, by way of a corresponding supply passage12. The sleeve11thus serves as a coolant inlet while the tip of the pin-shaped passage element again functions as a coolant outlet.FIG. 7in the lower view again shows a corresponding transfer element8which is substantially like the post-treatment element7, wherein only the pin-shaped passage element is somewhat shorter so that the preform9can be moved into the transfer position which is also shown at the bottom inFIG. 7without the tip of the pin-shaped passage element encountering the bottom of the preform. In the embodiment illustrated here the transfer element performs a double function as it serves both for transfer of the preform and also for the post-treatment, that is to say the corresponding feed of air.

FIG. 8shows a further alternative embodiment. This differs from theFIG. 7embodiment only in that the sleeve11is of a smaller diameter so that there is an annular space between the sleeve11and the preform9. The result of that is that the air flow divides up when leaving the sleeve11. A part of the air flows outwardly over the screwthreaded region of the preform9while another part of the air flows into the bottom region and there leaves the preform by way of the tip of the pin-shaped passage element.

In the embodiment shown inFIGS. 7 and 8the sleeve11is respectively acted upon with increased pressure. There is therefore no need for the pin-shaped passage element to be connected to a vacuum source at its end towards the pin plate but it can be simply connected to the environment. Alternatively it would also be possible for the end of the pin-shaped passage element, that is at the pin plate side, to be connected to a vacuum or reduced-pressure source, with the sleeve11connected to the environment. In that embodiment however dividing up the coolant flow in such a way that a part is discharged from the preform by way of the pin-shaped passage element and another part by way of the preform opening can generally not be implemented.

FIGS. 9 to 12show a further embodiment of a post-treatment element. Here the sleeve element11is in one piece with a holding element13which in the direction of the preform has a projection having an inner guide surface14and an abutment15for the preform. The element13has an inner bore16, into which the pin-shaped passage element7is fitted. In addition there is a row of recesses17serving for the feed of air. An end view is shown at the right inFIG. 9for further clarification.

FIG. 10shows the embodiment ofFIG. 9with inserted pin-shaped passage element. In the situation here the preform is held in the receiving element by a corresponding vacuum while, by virtue of the reduced pressure at the end of the pin-shaped passage element7, that is remote from the receiving element5, air is sucked through the recesses17into the preform and out of the preform by way of the end18functioning as the coolant outlet.

InFIG. 11the receiving element5is now acted upon with compressed air while the post-treatment element and the receiving element are moved away from each other. The result of this is that the preform9is urged out of the receiving element5until it touches the contact surface15. In that position a suction and vacuum effect by way of the pin-shaped passage element7provides that the preform is held on the transfer element.

In the embodiment shown inFIGS. 9 to 12the post-treatment elements and the transfer element do not differ. Instead, they involve a corresponding dual function. With this embodiment therefore there is no need to provide more post-treatment pins than there are receiving cavities in the removal plate, which not only reduces the costs for manufacture of the post-treatment plate but also reduces the necessary feed flow of coolant as fewer post-treatment pins have to be supplied with coolant.

FIG. 13shows a further embodiment. The pin plate6has two post-treatment elements (shown at the centre and at the bottom) and a transfer element (shown at the top in the Figure). The transfer element8differs from the post-treatment elements in that the pin-shaped passage element is omitted and there is an additional seal19which can come into contact with the preform9during transfer. In theFIG. 13embodiment the transfer element is connected to a vacuum source, which makes it possible for the preform9to be held on the transfer element8when it comes into contact with the seal19as a slightly reduced pressure is then produced within the preform9. The other two pins7are provided for post-treatment of the preform9. Here, air is introduced into the interior of the preform by way of the sleeve11, by way of a fan (not shown), through the feed means20. That air flows out of the preform by way of the tip18of the pin-shaped passage element and into the environment by way of the passages21. In that case the air is deflected by way of corresponding deflection plates29so that the coolant is fed by way of the rear side of the post-treatment plate (the side thereof that is remote from the pin-shaped post-treatment pins), and is discharged again on the front side.

FIG. 14shows a further alternative embodiment of the invention. The post-treatment situation is shown at the top inFIG. 14, functioning as in theFIG. 13embodiment.

The post-treatment elements however all have a corresponding seal19, which makes it easier for the pins to be used both for the post-treatment operation and also for the transfer. In principle however the transfer can also be effected without a corresponding seal19. Although the pins have different functions they are of an identical structure, which reduces the costs of storage, as there is not any need to store both transfer elements and also post-treatment elements.

The transfer situation is shown at the bottom inFIG. 14. Here the sleeve11is connected to a vacuum source, which provides that the preform9is drawn on to the sleeve11, thereby permitting transfer of the preform.

FIG. 15shows a sectional view of a further embodiment. In this case also a transfer element8and two post-treatment elements7are fixed to the pin plate6. TheFIG. 15situation also shows the receiving element5which is cooled by way of the cooling passages22, by way of spiral-shaped passages. Compressed air or vacuum can be selectively supplied by way of the feed means23at the bottom of the receiving element5to either hold the preform9within the receiving cavity5or expel it therefrom. The pin-shaped passage element7is surrounded concentrically by a sleeve11, by way of which cooling air is passed into the interior of the preform, being discharged by way of the tip19of the pin-shaped passage element7. There are also cooling passages28, by means of which the post-treatment plate can be cooled, preferably water-cooled.

The pin-shaped passage element7is shown on an enlarged scale inFIG. 16. It will be seen that in the illustrated situation the cooling air which is fed by way of the sleeve11is both passed into the bottom region of the preform9in order then to be discharged there by way of the tip of the pin-shaped passage element7, and it can also leave the preform9by way of the preform opening as a gap is arranged between the outside of the sleeve11and the inside of the preform9.

FIG. 17shows an enlarged view of the corresponding transfer element8. That transfer element8has a central bore which can be acted upon selectively with vacuum or compressed air to hold or expel the preform9.

FIG. 18shows a corresponding transfer element8, a closure cap24here being fitted on to the through bore. More specifically, during operation of an injection moulding mould, it can happen that, for some reason, one of the plurality of mould cavities with which the corresponding preforms are produced, can no longer be used. Nonetheless the mould can continue to be used, in which case one preform less is then produced in each injection moulding cycle. As however the post-treatment element generally has a plurality of transfer elements8which at the same time are intended to take over preforms from the removal element and are therefore acted upon with compressed air, it is advantageous for all transfer elements8to be connected to one and the same vacuum source. If however a corresponding preform is missing at a transfer element, it is not possible for a reduced pressure to be built up there. Instead here air unimpededly flows in so that possibly even in relation to adjacent transfer elements, it is not possible for a sufficiently great reduced pressure to be produced, so that adjacent preforms cannot be transferred. In the case of the transfer element8in question therefore a corresponding closure cap24is applied to minimise the pressure loss.

FIG. 19shows a further embodiment of the invention. That essentially differs from the preceding ones in that the sleeve11here is of such a configuration that it substantially corresponds to the inside contour of the preform9so that the inside of the preform9is in contact with the sleeve11in the opening region, that is to say in particular in the region of the screwthread. If the sleeve11is additionally cooled then the screwthread region which generally has particularly thick portions and therefore contains a correspondingly large amount of heat can be very effectively cooled down. In addition the complete air flow is then available for the pin-shaped passage element7.

FIGS. 20 and 21show perspective views of the post-treatment element (FIG. 20) and the transfer element (FIG. 21) respectively.

An alternative embodiment of the post-treatment element7is shown as a perspective view inFIG. 23and a plan view from above inFIG. 22. Here the post-treatment element comprises a pin-shaped passage element7which is fitted in a sleeve11provided with a through bore, with milled grooves25. The through bore in the sleeve11is of a configuration corresponding to the outside diameter of the pin-shaped passage element7so that the pin-shaped passage element7and the sleeve11are in contact. The groove-shaped milled recesses25then serve for the feed of air. The configuration according to the invention of the post-treatment system permits inexpensive and at the same time highly effective post-treatment of the preforms.

List of References