EP1948416A1

EP1948416A1 - System and method for transferring and cooling molded hollow plastic articles

Info

Publication number: EP1948416A1
Application number: EP05810806A
Authority: EP
Inventors: Hendrik Johan Van Manen; Hendrikus Johannes Theodorus Albers
Original assignee: Tool-Tech Holding BV
Current assignee: Tool-Tech Holding BV
Priority date: 2005-11-17
Filing date: 2005-11-17
Publication date: 2008-07-30
Also published as: WO2007058521A1

Abstract

In a system for transferring molded hollow plastic articles (18) from a mold (1,2) to a discharge location (11) and for cooling the articles (18) an intermediate station (9) comprising cooling pins (12) for cooling the group of the articles (18) arranged over the cooling pins (12) is provided. A robot (7) carries a take-out unit (5) for displacing a take-out unit (5) from the mold (1, 2) to the intermediate station (9) for releasing carried articles (18) at the intermediate station (9) and for engaging another group of the articles (18) at the intermediate station (9) and displacing the engaged other group of the articles (18) from the intermediate station (9) to a discharge location (11). The intermediate station (9) has at least one cooling cavity (31) for cooling the articles (18) received therein from the outside.

Description

Titel: System and method for transferring and cooling molded hollow plastic articles

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a system according to the introductory portion of claim 1 and to a method according to the introductory portion of claim 8. Such a system and such a method are known from

WO2004/054778. In this known method and apparatus, after each operating cycle of the molding apparatus, a group of the molded preforms is taken from a mold by a take-out plate. Preferably the take-out plate has the ability to retain preforms for at least a majority of one molding cycle and preferably more than one molding cycle, such that at the end of each cycle the preforms produced in that cycle are ejected from the cores and received in cooling tubes of the take-out plate while a group of the articles formed in the previous cycle are still retained in another set of the cooling tubes of the take-out plate. The group of the molded preforms that has been taken out of the mold after the previous molding cycle is subsequently transferred to an intermediate station. The cooling tubes of the take-out plate that have become empty thereby become available for receiving a next group of molded preforms. The intermediate station or stations are for further cooling and arranging the preforms. For cooling, upstanding cooling pins for receiving preforms to be cooled such that the cooling pins project into the hollow preforms are provided and are equipped for supplying a cooling fluid, which may be in liquid or gas form, from the tips of the cooling pins into the interior of the preforms positioned over the cooling pins. A problem of such known apparatus and such a method is, that the weight of the take-out member requires a powerful robot to manipulate the articles quickly, in particular if relatively large numbers of small articles are to be manipulated after each molding cycle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a solution in which the requirements regarding the capacity of the robot are reduced.

According to the invention, the object is achieved by providing a system according to claim 1. The invention may also be embodied in a method of operation according to claim 8.

The exterior cooling cavity for bringing a coolant in contact with outwardly facing surfaces of articles at the intermediate station allows to cool the freshly molded articles from the outside. This reduces the extent to which the freshly molded articles need to be cooled from the outside in the take-out member before being transfer to the intermediate station can take place without causing too much deformation of the article. Accordingly, the time during which the articles need to reside in the take-out member and/or the intensity with which the articles are cooled in the take-out member can be reduced, so that a lighter take-out member, manipulatable by a robot of smaller capacity provides sufficient cooling of the articles.

Particular embodiments of the invention are set forth in the dependent claims.

Further aspects, effects and details of the invention are set forth in the detailed description with reference to examples of which some are shown in the schematic drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1-3 are perspective views of an example of a system according to the invention in three successive stages of operation;

Fig. 4-9 are schematic side views of an example of an intermediate station in six successive stages of operation;

Fig. 10 is a view in cross-section of a cooling tube of the intermediate station according to Figs. 4-9; and

Fig. 11 is a view in cross-section of a cooling pin of the intermediate station according to Figs. 4-9.

MODES FOR CARRYING OUT THE INVENTION

Hollow plastic articles are manufactured for several purposes. The articles may for instance be tubes for packaging products or grips for bicycles and the like. A category of hollow plastic articles that is manufactured in particularly large numbers are preforms from which bottles are to be manufactured by blow molding. The preforms typically have a neck area forming the entry to a cavity inside the body of the hollow article, that is shaped in a form suitable for co-operation with a cap, such as a screw cap or a cap that is to be clamped over the opening to the cavity. During blow molding, the neck area is to maintain its form, but the body is blown up to larger dimensions to increase the size of the cavity. The preforms need to meet tight standards, inter alia with respect to dimensional tolerances to ensure that the bottles to be formed reliably meet the requirements with respect to for instance strength, appearance and hermetic sealability of the opening. In the description set forth below, the invention as applied to the manufacture of preforms is described. It will, however, be clear, that the invention is also applicable to the manufacture of other molded plastic articles. In Figs. 1-3, mold halves 1, 2 of an injection molding machine are shown. The mold halves 1, 2 are carried by respective platens 3, 4 of which one platen 3 is movable to and fro for displacing the mold halves 1, 2 in directions indicated by double arrow 19 between an open position (Fig. 1) and a closed position (Figs. 2 and 3).

The system shown in Figs. 1-3 is for transferring freshly molded preforms from the mold half 1 that is equipped with cores 20 to a discharge location, in this case formed by a box 11 in which the preforms are to be packaged for transport. Preforms 18 are shown in Figs. 4-9. To minimize cycle times of the injection molder, the preforms are taken from the mold half 1 while still being too weak to be packaged without damaging the preforms. Therefore the system is also designed for cooling the preforms before packaging to ensure that the preforms become sufficiently solidified before packaging. The main units of the system are a take-out unit 5 for engaging a group of the preforms in the mold half 1, a multi-axis robot 7 carrying the take-out unit 5 and an intermediate station 9.

The robot 7 (or at least a control unit for controlling the robot) is programmable and the robot 7 has an arm 8 carrying the take-out unit 5. The arm is movable and drivable for displacing the take-out 5 unit to a takeout position (Fig. 1) for engaging a group of the preforms in the mold half 1 of the mold, displacing the take-out unit 5 carrying the group of the preforms engaged thereby from the take-out position to the intermediate station 9 for releasing the carried preforms in positions at the intermediate station 9 and for engaging another group of the preforms in the intermediate station 9 and displacing the engaged other group of the preforms engaged thereby from the intermediate station 9 to the discharge location 11 for releasing the carried other group of the preforms in positions at the discharge location 11. The take-out unit 5 is equipped with cooling tubes 6 into which the preforms are received from the mold half 1. In the system according to the present example, the cooling tubes 6 are of the same design as cooling tubes 16 of the intermediate station 9 which will be described in more detail. The cooling tubes 6 start to cool the freshly molded preforms from the outside immediately as the preforms are received from the cores 20 of the mold half 1. This allows the preforms to cool at least to such an extent that placement over the cooling pins 12 can take place without causing damage to the preforms. For the sake of clarity, the number of cores 20 of the mold half is only four, but in practice far larger numbers of cores, for instance 8 to 144 cores are customary. The intermediate station 9 is equipped with cooling pins 12 for cooling the group of the preforms arranged over the respective ones of the cooling pins 12 from the inside. One of the cooling pins 12 is shown in more detail in Fig. 11. As shown in Fig. 11, the cooling pins 12 are mounted to a cooling pin carrier platen 13 equipped with coolant conduits 22 and passages 23 for allowing coolant to flow out of the carrier platen 21 towards cooling pins 12 mounted over the passages 23. A coolant conduit 24 extends in longitudinal direction of the cooling pin 12 through the cooling pin 12, from the foot 25 of the cooling pin 12 to the top 26 of the cooling pin 12. Side ports 27, 28 extend radially from the coolant conduit 24 close to the foot 25 of the cooling pin 12.

Via the coolant conduits 22 and the passages 23 in the carrier platen 13 and via the coolant conduit 24 in the cooling pin 12, a coolant, preferably cool air, may be injected adjacent to to a closed end of the preform as indicated by arrows 29. The air then flows axially towards the foot 25 of the cooling pin 12 through an annular space between the cooling pin 12 and the preform.

Because the preform has relatively thick-walled portions in the area adjacent to to its open end while on the other hand the dimensional stability of the preforms is least adjacent to to the open end of the preform, effective cooling is particularly desirable close to the foot 25 of the cooling pin 12. Moreover, an enhanced cooling effect adjacent to to the foot of the cooling pin 12 is further desirable, because the air arriving in the area of the foot 25 of the cooling pin 12 has been warmed up by heat received from the hot preform and therefore has become less effective at cooling the preform. To improve the cooling of the preforms in the area adjacent to to the foot 25 of the cooling pin 12, the cooling pins 12 have a larger-cross- section over a portion (preferably at least 5 % and more preferably at least 10 %) of the length of the pins 12 adjacent to the feet 25 thereof than adjacent to a top end thereof. This causes the cross-sectional surface of the annular space between the preform and the cooling pin 12 to be relatively small adjacent to the foot 25 and the flow speed of the coolant to be accordingly high so that its cooling effect is enhanced.

The cooling of the preforms in the area adjacent to the foot 25 of the cooling pin 12 is further enhanced by a portion of the coolant (arrows 30) exiting the side ports 27, 28 in an area closely adjacent to the foot 25 of the cooling pin 12.

At the intermediate station 9, cooling cavities 31 (see Fig. 12) for cooling preforms from the outside at the intermediate station 9 are provided. According to the present example, the cooling cavities 31 are located in the cooling tubes 16 of a cooling rack 10. The cooling tubes 16 are carried by arms 32. A pneumatic conduit 33 and cooling conduits 34, 35 extend through each one of the arms 32. Passage 36 communicates with the pneumatic conduit 33 and passages 37, 38 communicate with the coolant conduits 33, 34. The pneumatic conduit 33 communicates via the passages 36 with respective cavities 31 of the tubes 16 mounted over the passages 36 for transferring a vacuum to the cavities 31 for retaining preforms, or at least closed end portions thereof, in the cavities 31.

Because the exterior cooling cavities 31 are located in cooling tubes 16 and the cooling pins 12 and the cooling tubes 16 are displaceable relative to the other between a cooling position in which the cooling pins 12 each project into one of the cooling tubes 16 and a charge and discharge location allowing preforms on the cooling pins 12 to be engaged by the take-out unit 5 for removal from the intermediate station 9, the still weak preforms can be reliably transferred from the take-out unit 5 to the cooling cavities with very little risk of damage and, for a portion of the cooling time at the intermediate station 9, the preforms can be cooled simultaneously from the inside (by the cooling pins 12) and from the outside (by the cooling tubes 16). Moreover, the cooling tubes 16 can also support the preforms during cooling so that deformations can be counteracted and in some cases even reversed, before the preforms harden to their final shape.

The cavity 31 is bounded by a lining 39 through which a cooling channel 40 extends. The cooling channel 40 communicates via the passage 37 with the coolant supply conduit 34 and communicates via the passage 38 and a discharge channel 41 with the coolant return conduit 35. Preferably coolant supplied via the coolant supply conduit 34 and returned via the coolant return conduit 35 is a liquid. The lining 29 is preferably of a soft material, such as rubber, so that the interior surface of the cavity 31 contacting the preform is resilient. The resiliency of the interior surfaces of the cavities 31 ensures that it contacts the preforms in the cavities 31 over a large surface, which is advantageous for effective heat transfer. The resiliency of the interior surfaces is also advantageous for reliable retention of the preforms by the vacuum, since effective sealing of the interior surfaces of the cavities 31 against the outside of the preforms helps to counteract leakage of air between the preforms and the interior surfaces.

The cooling pin carrier platen 13 is displaceable along rails 14, 15 between a loading and unloading position shown in Fig. 2, 4, 5 and 9 where space above the cooling pin carrier platen 13 is available for maneuvering the take-out unit 5 into a position with the cooling tubes in line with a group of the cooling pins 12 for the transfer of preforms to and from the cooling pins 12 and a hand-over position shown in Figs. 1, 3, 7 and 8, where the cooling pins 12 are in line with the cooling tubes 16 of the intermediate station 9 for the transfer of preforms 18 to and from the cooling tubes 16 of the intermediate station 9. The cooling tubes 16 of the intermediate station 9 are displaceable between an uppermost position as shown in the drawings, leaving sufficient clearance from the cooling pin carrier platen 13 to allow the platen 13 with preforms 18 located on one or more of the cooling pins 12 to move between the loading and unloading position and the hand-over during which movement underneath preforms 18 located on one or more of the cooling pins 12 pass underneath preforms 18 held in the cooling tubes 16. To this end, the arms 32, carrying the cooling tubes 16 of the intermediate station 9, are carried by a bridge 17 that is displaceable along posts 48, 49.

In operation, after the mold 1, 2 containing freshly molded preforms has been opened, the take-out unit 5 is brought to a take-out position, for instance as is shown in Fig. 1. In the take-out position, the take-out unit 5 engages the group of the preforms that is ejected from the mold half 1. While the mold 1, 2 closes again for carrying out a next injection molding cycle (Fig. 2), the take-out unit 5 carries the group of the preforms engaged thereby from the take-out position to the intermediate station 9, where the take-out unit 5 releases the carried group of the preforms in positions 12 at the intermediate station 9. At the intermediate position 9, the group of preforms that has been released is cooled from the inside by the air expelled from the cooling pins 12 and from the outside by contact with the linings 29 of the cooling tubes 16.

The take-out unit 5 then engages another group of the preforms in the intermediate station 9 that has been transferred to the intermediate station during an earlier operating cycle. The take-out unit 5 is subsequently displaced from the intermediate station 9 to the discharge location 11 where the carried other group of the preforms is released, so that the preforms are received in a box 11 at the discharge location.

Because the preforms are cooled from the outside at the intermediate station 9, less cooling of the preforms from the outside in the take-out unit 5 is required. Accordingly, the preforms may be released from the take-out unit earlier and/or the required cooling power of the take -out unit 5 is reduced. In turn, this allows the take-out unit 5 to be of a lighter construction, so that the requirements with respect to the robot 7 are reduced. A particularly low weight of the take -out unit 5 is achievable if, as in the present example, the robot 7 is adapted for each time releasing all preforms carried by the take-out unit 5 at the intermediate station 9. According to the present example, the mold 1, 2 has a number of mold cavities equal to the number of preforms that can be carried simultaneously by the take-out unit 5. The mold cavities are each for molding one of the preforms at a time and the mold is arranged for simultaneously molding the preforms.

The capacity of the intermediate station 9 is preferably at least two times and more preferably at least three times the number of preforms that can be carried by the take-out member 5, so that the preforms can be left to cool at the intermediate station 9 for an extended period of time.

In Figs. 4-9 groups of preforms 18 that have been molded during successive molding cycles A to D are each represented by a single preform 18A to 18D respectively. As is shown in Figs. 4-9, each time after a group of the preforms 18D is released at the intermediate station 9, two next groups of the preforms are released at the intermediate station 9 before the group of preforms 18D is engaged by the take-out unit 5 for removal from the intermediate station 9, so that the preforms are effectively cooled, even if molded at short cycle times. In Fig. 4, the release of a group of preforms 18D from the cooling tubes 6 of the take-out unit 5 to the cooling pins 12 in the loading and unloading position also shown in Fig. 2. The take-out member 5 is lowered by the robot arm 8 in a direction as indicated by the arrow 44, preferably until the preforms 18D rest on the platen 13. Then, the preform clamps 42 engage the preforms 18D, vacuum in the cooling tubes 6 is released and the take-out unit 5 is lifted again leaving the group of preforms 18D retained at the cooling pin 12 by the preform clamps 42. Ejection of the preforms 18D from the cooling tubes 6 may be supported by air pressed into the cavities of the cooling tubes 6. Another group of preforms 18A released three cycles back is at the intermediate station 9 in positions over a cooling pin 12, but ready to be engaged by the take-out unit 5. Two other groups of preforms 18B, 18C released two respectively one cycle back is retained in the cooling tubes 16 of the intermediate station 9. These groups of preforms 18B, 18C are held in cooling tubes 16 of the intermediate station 9 and are being cooled from the outside by contact with the cooled inner surfaces of the cavities 31.

Then, as shown in Fig. 5, the take-out unit 5 is laterally shifted relative to the platen 13 in the direction of arrow 43 so that the cooling tubes 6 are brought in positions in line with the cooling pins 12 carrying the group of preforms 18A and the preform clamps 42 engaging the group of preforms 18A are disengaged from the group of preforms 18A. The take-out unit 5 is lowered in a direction indicated by arrow 45 and the cooling tubes 6 thereof engage the group of preforms 18A. Then, as shown in Fig. 3, the take-out unit 5 is displaced by the robot arm 7 to the discharge location 11, where the preforms are discharged. To avoid damage to the still relatively warm, and accordingly vulnerable preforms, the robot 7 and preferably the take-out unit 5 is preferably equipped with sensors, and the control unit of the robot preferably programmed to be responsive to signals from the sensors such that the preforms 18 can be lowered until very close to the previously discharged preforms in a box or other container. Thus, the preforms can be discharged in a box without dropping the preforms over a substantial height into the box, thereby reducing the risk of damage to the finished preforms. Meanwhile, as shown in Figs. 3 and 6, the cooling pin carrier platen 13 is shifted along the rails 14, 15 in the direction of arrow 46 to a position under the arms 32, such that the cooling pins 12 carrying the group of preforms 18D are in-line under a group of free cooling tubes 16, the preform clamps 42 disengage from the preforms 18D, the cooling tubes 16 are moved towards the cooling pins 12 and vacuum applied to the free ones of the cooling tubes 16 causes the group of preforms 18D to be engaged by these cooling tubes 16 and lifted from the cooling tubes 16 as the cooling tubes 16 are moved away from the cooling pins 12 again.

Next in turn to be discharged to the discharge location is the group of preforms 18B that was molded during the molding cycle following the cycle during which the group of preforms 18A was molded. As shown in Fig. 7, the platen 13 is shifted in the direction of arrow 48 to bring a group of cooling pins 12 in line with the group of preforms 18, the preform clamps 42 being in a position ready for receiving the preforms 18B. Then, the bridge 17 is lowered (arrow 49) so that the group of preforms 18B is lowered over the cooling pins 12 in line therewith and the preforms 18B are released by the cooling tubes 16 by removing the vacuum exerted via the passages 36. To further facilitate the ejection of the preforms 18B, air pressure may also be applied via the passages 36. Then, the group of preforms 18B is engaged by the preform clamps 42 associated to the cooling pins 12 over which the group of preforms has been positioned and the cooling tubes are lifted again, resulting in the situation shown in Fig. 9.

In the meantime, a next group of preforms is being taken out of the mold 1, 2 as is illustrated by Fig. 1 and moved to the intermediate station 9. In Fig. 8 a preform 18E of the next group of freshly molded preforms held by the cooling tubes 6 of the take-out unit 5 is shown. The platen 13 carrying the cooling pins 12 is shifted back to the loading and unloading position shown in Figs. 2, 4, 5 and 9 and the take-out unit 5 is lowered as shown in Fig. 9 so that the preforms 18E held in the cooling tubes 6 of the take-out unit 5 are positioned over the free cooling pins 12 where the preforms of the newly arrived group of preforms 18E (arrow 50) are released. Then, the take out unit 5 is lifted again and a situation similar to the situation shown in Fig. 4 is obtained, except that the newly arrived preforms 18E and the cooled group of preforms 18B are located on other groups of the pins 12 than the newly arrived preforms 18D and, respectively, the cooled group of preforms 18A in Fig. 4.

Since the take-out unit 5 is equipped with a plurality of cooling tubes 6 forming the take-out members that each time engage a single preform from the mold each time after an injection molding cycle is completed and each engage a single preform at the intermediate station 9 each time after the freshly molded preforms have been released at the intermediate station, the same take-out unit members 6 can carry out both the transfer from the mold 1, 2 to the intermediate station 9 as the transfer from the intermediate station 9 to the discharge station 11. From the foregoing, it will be clear to the skilled person, that within the framework of invention as set forth in the claims also many variations other than the examples described above are conceivable. For instance, the cavity for the cooling of the preforms from the outside may also be a cavity such as a hood in which a plurality of preforms is received an cooled simultaneously. Further, the number of cooling pins may be larger than twice the number of preforms the take-out unit can hold for instance to also contribute to the cooling of preforms held at the intermediate station that are not to be released at the time the cooling pins are moved into a position projecting into the preforms. The capacity of the cooling cavity or cavities at the intermediate station may be more than two or three times the capacity of the mold and the take-out unit, so that preforms can be held in the cooling cavity of cavities during a plurality of cycles.

Claims

1. A system for transferring molded hollow plastic articles (18) from a mold (1,2) to a discharge location (11) and for cooling the articles (18), comprising: a take-out unit (5) for engaging a group of the articles (18) in the mold (1,2), an intermediate station (9) comprising cooling pins (12) for cooling the group of the articles (18) arranged over the cooling pins (12); and a robot (7) carrying the take-out unit (5) for:

- displacing the take -out unit (5) to a take-out position for engaging the group of articles (18) in the mold (1,2);

- displacing the take -out unit (5) carrying the group of the articles (18) engaged thereby from the mold (1, 2) to the intermediate station (9) for releasing the carried articles (18) at the intermediate station (9) and for engaging another group of the articles (18) at the intermediate station (9); and

- displacing the engaged other group of the articles (18) engaged thereby from the intermediate station (9) to a discharge location (11) for releasing the carried other group of the articles (18) at the discharge location (11); characterized in that the intermediate station (9) further comprises at least one cooling cavity (31) for cooling the at least one article (18) received therein from the outside of the at least one article (18).

2. A system according to claim 1, further comprising at least one coolant conduit (34, 37, 40) arranged for causing a coolant flow in contact with or closely along the outside of the at least one article (18) at least partially received in the cooling cavity (31).

3. A system according to claim 1 or 2, wherein the robot (7) is adapted, for each time releasing all articles (18) carried by the take-out unit (5) at the intermediate station (9).

4. A system according to claim 3, wherein the take-out unit (5) has a capacity of a first maximum number of articles (18) to be carried simultaneously thereby and wherein the intermediate station (9) has a capacity of a second maximum number of articles (18) to be carried simultaneously thereby, said second number being at least three times said first number.

5. A system according to any one of the preceding claims, wherein the robot is a programmable multi-axis robot (7).

6. A system according to any one of the preceding claims, wherein a plurality of the exterior cooling cavities (31) are each located in a cooling tube (16), wherein the cooling pins (12) and the cooling tubes (16) are displaceable relative to each other between a cooling position in which the cooling pins (12) each project into one of the cooling tubes (16) and a charge and discharge location (11) allowing articles (18) on the cooling pins (12) to be engaged by the take-out unit (5) for removal from the intermediate station (9).

7. A system according to any one of the preceding claims, wherein the take-out unit (5) comprises a plurality of take-out members (6), each for each time engaging a single one of the articles (18) from the mold (1,2) and for each time engaging a single one of the articles (18) from the intermediate station (9).

8. A system for manufacturing articles (18), including a mold (1,2) having a number of mold cavities, each for molding one of the articles (18) at a time, the mold (1,2) being arranged for simultaneously molding the articles (18) and a system according to claim 4, wherein the number of mold cavities is equal to the first maximum number of articles (18) to be carried simultaneously by the take-out unit (5).

9. A method for transferring molded hollow plastic articles (18) from a mold (1,2) to a discharge location (11) and for cooling the articles (18), comprising:

- displacing a take-out unit (5) to a take-out position;

- the take-out unit (5) in the take-out position engaging a group of the articles (18) held by the mold (1,2);

- displacing the take-out unit (5) carrying the group of the articles (18) engaged thereby from the take-out position to an intermediate station (9);

- the take-out unit (5) releasing the carried group of the articles (18) at the intermediate station (9);

- the take-out unit (5) engaging another group of the articles (18) at the intermediate station (9);

- displacing the take -out unit (5) carrying the other group of the articles (18) engaged thereby from the intermediate station (9) to the discharge location (11); and

- releasing the carried other group of the articles (18) in positions at the discharge location (11); characterized by cooling the articles (18) from the outside in at least one cavity (31) at the intermediate station (9).

10. A method according to claim 9, wherein the cooling of the articles

(18) from the outside includes causing a coolant flow in contact with or closely outside the articles (18).

11. A method according to claim 10, wherein the take-out unit (5) each time releases all articles (18) carried thereby at the intermediate station (9).

12. A method according to claim 11, wherein each time after a group of the articles (18A) is released at the intermediate station (9), at least two next groups of the articles (18B, 18C) are released at the intermediate station (9) before said group of articles (18A) is removed from the intermediate station (9) by the take-out unit (5).