Stretching blow molding technique

Abstract

The invention relates to a method and a device for bending a straight preform (3) comprising at least a receptacle (4) for holding the straight preform (3), a mandrel (1), a blow mold (11) and a movable unit (7) which is movable towards and away from the preform (3) held in the receptacle (4) and two mold halves (5), wherein the mandrel (1) enters the preform (3) when the movable unit (7) moves downwards, wherein the mandrel (1) has at least one joint (2, 12) and the device comprises a mechanical actuating element (8) which pivots the mandrel (1) about the joint (2, 12) when the movable unit (7) moves downwards, so that the straight preform (3) is obliquely deformed below the receptacle (4).

Description

[0001] The invention relates to a method for stretch blow molding plastic bottles with an inclined opening surface from straight preforms and to a stretching device required for this method.

[0002] In the well-known process of stretch blow molding, a preform is stretched mechanically in its longitudinal direction by a stretching mandrel (also called a stretching rod or stretching mandrel) and by pressure in the circumferential direction, so that the preform conforms to the contour of the blow mold. The term stretch blow molding here encompasses both the two-stage process, in which the preform is injection-molded on a first machine and subsequently stretch-blown on a second machine, and the single-stage process, in which the injection-molded preform and stretch-blow molding take place on one machine in two consecutive steps. The single-stage process is therefore also referred to as injection stretch blow molding, and the machine used for it is referred to as an injection stretch blow molding machine. DE 3314106 A1 discloses a device for expanding a preform with an expanding mandrel for better material distribution.

[0003] From US 2017239871 A1 another device for expanding a preform with an expanding mandrel for better material distribution is known.

[0004] From US 3278665 A a device for extrusion blow molding is known which has a rotatable mechanical element for pressing against the inner wall.

[0005] JP2009241429A shows a device for producing a plastic container with an inclined opening surface, using an inclined stretching mandrel. However, the stretching mandrel itself is straight.

[0006] JP2008044244A shows a device for producing a plastic container with an inclined opening surface, using a stretching mandrel composed of many small joints. The stretching mandrel can be deformed along with the preform when the blow mold is closed. JP2627944B2 shows a device for producing a plastic container with an inclined opening surface, using a stretching mandrel that has a flexible spring that expands in an arc shape when released, thereby mechanically stretching the preform in the already closed blow mold. The use of a spring appears to be disadvantageous, as it requires precise manufacturing of the spring and seems difficult to adjust later.

[0007] The object underlying the invention is to provide an improved method for forming a plastic bottle with an inclined opening surface from a straight preform.

[0008] To achieve this object, a method according to claim 1 and a stretching device according to claim 8 are proposed. Specifically, a method is proposed for bending a straight preform in a device for stretch blow molding or injection stretch blow molding. This device comprises at least one receptacle for holding the straight preform, a stretching mandrel, a blow core, and a movable unit which can be moved toward and away from the preform held in the receptacle parallel to the longitudinal axis of the straight preform, and two mold halves which can be moved away from and toward one another in a plane transverse to the direction of movement of the movable unit. The stretching mandrel enters the preform upon downward movement of the movable unit, the stretching mandrel having a joint, and the device comprising a mechanical actuating element which is present on the movable unit.During the final part of the downward movement of the movable unit, the mechanical actuating element is activated, whereupon the mechanical actuating element pivots the stretching mandrel located below the joint around the joint, so that the straight preform is deformed at an angle below the holder. The joint is located in the area of ​​the blow core, so that the entire straight preform is deformed at an angle directly below the holder.

[0009] The procedure includes in particular the following steps: - Lowering the movable unit and the stretching mandrel parallel to the longitudinal direction of the straight preform held in the holder, - The mechanical actuating element begins to pivot the stretching mandrel around the joint as soon as it is actuated by a device element against which a relative movement of the movable unit takes place, - Simultaneous stretching and bending of the preform by the stretching mandrel with further downward movement of the movable unit, - closing the mould halves at a time when there is no overlap between the contour of the preform and the blow mould formed by the closed mould halves, - Blowing the bent preform to fit it to the blow mold.

[0010] It is preferred that the joint is located within the preform at the start of the pivoting movement.

[0011] It is preferred that the free end of the stretching mandrel rests against the base of the preform at the start of the pivoting movement. It is preferred that the device element, relative to which the movable unit moves relative to, is a stop, and the distance between the stop and the part of the mechanical actuating element that rests against the stop is adjustable.

[0012] It is preferred that the device comprises a plurality of blow cores, a plurality of stretching mandrels, a plurality of receptacles and a plurality of blow molds, each stretching mandrel having a joint and its own mechanical actuating element, the method being carried out on a plurality of preforms in parallel.

[0013] It is preferred that the blow cores, stretching mandrels and mechanical actuating elements are arranged on a common movable unit.

[0014] The invention also relates to a stretching device comprising a blow core, at least one mechanical actuating element and a stretching mandrel for bending a straight preform in a device for stretch blow molding or injection stretch blow molding of the preform, wherein the stretching mandrel adjoins the lower end region of the blow core and has a joint at its end facing the blow core and the free region of the stretching mandrel adjoining the joint is pivotable about the joint, wherein for this purpose the mechanical actuating element is attached to the stretching mandrel and extends upwards through the blow core.

[0015] The stretching mandrel does not extend through the blow core and is not movable relative to the blow core in the axial direction within the blow core.

[0016] It is preferred that the mechanical actuating element is a pull rod.

[0017] It is preferred that the stretching mandrel comprises a first joint and a second joint, which are present at the same end region of the stretching mandrel, wherein the mechanical actuating element is attached to the first joint and the stretching mandrel is articulated to the blow core via the second joint.

[0018] It is preferred that the stretching mandrel or the free end region be connected to a pull rod via a first joint and to the blow core via a second joint. A movement of the pull rod in the direction of the blow core facing away from the stretching mandrel causes a pivoting movement of the stretching mandrel about the first and second joints.

[0019] The drawbar runs inside the blow core from its starting point on the stretching mandrel to the opposite end of the blow core and penetrates it there.

[0020] A lever is preferably attached to the free end of the pull rod.

[0021] The invention is illustrated by a preferred, but not restrictive, embodiment variant shown in the drawings: Fig. 1-4: schematically illustrate the components of the device essential for the invention and the sequence of the method according to the invention. Fig. 5-6: schematically illustrate a prior art device, which preferably represents the starting basis of the subject device.

[0022] In the figures, the devices for stretch blow molding are shown in a highly simplified and schematic manner.

[0023] The illustrated part of the device is the stretching and blowing station of a stretch blow molding machine or an injection stretch blow molding machine.

[0024] Those known components of such devices which are not essential for understanding the present invention, such as the injection station and the ejection station of an injection stretch blow molding machine, are not shown and described.

[0025] A well-known process for the production of straight bottles by stretch blow molding is described in the Fig. 5 and Fig. 6. A straight preform 3 is held by a holder 4 so that a stretching mandrel 1 can be inserted in a straight line from above into the preform 3. The stretching mandrel 1 is moved downward by or together with a movable unit 7. The movable unit is a blow core assembly having at least one blow core 11. The blow core 11 is penetrated by the stretching mandrel 1 at the upper end, forming a seal at this point. In this prior art, the movable unit 7 is first moved downwards so that the stretching mandrel 1 enters the preform 3 and the blow core 11 into the receptacle 4. The lowermost section of the blow core 11 projects into the threaded area of ​​the preform 3. When the blow core 11 rests against the receptacle 4, the stretching mandrel 1 is moved further downwards independently of the movable unit 7 and stretches the preform 3 vertically downwards in its longitudinal direction.Subsequently (or already during stretching), pressure is applied to the preform 3 between the lowermost section of the blow core 4 and the stretching mandrel 1, so that it is molded transversely to the inner contour (blow mold) of the two mold halves 5 (only one is visible in the figures). Since, in this known process, the unstretched preform 3 fits into the space enclosed by the two mold halves 5, the blow mold can already be closed when the stretching mandrel 1 is inserted.

[0026] The present invention preferably adopts the basic structure of this prior art, as it is proven and already present in many existing machines. The present invention can be advantageously retrofitted to such existing machines.

[0027] In the Fig. 1-4 schematically illustrate the method for producing a bottle with an inclined opening. Like the prior art device, the device comprises two mold halves 5, which can be moved away from each other in a plane transverse to the direction of movement of the movable unit 7, wherein both mold halves preferably undergo a movement when a change of state from closed to open and vice versa occurs. The movement can comprise a translational movement and / or a pivoting movement. Like the prior art device, the device comprises a holder 4, which receives the preform 3 and holds it during stretch blow molding. The holder 4 can, in particular, be part of the injection mold of the preform 3, wherein the holder 4 is moved from the injection station to the stretch and blow molding station. The holder 4 encompasses the threaded area of ​​the preform 3.Like the prior art device, the device comprises a movable unit 7 which is movable parallel to the direction of movement of the stretching mandrel 1 and parallel to the longitudinal axis of the straight preform 3. The movable unit 7 preferably comprises a horizontally arranged element which, as illustrated, is moved along two vertical guides, in particular guide columns. At least one blow core 11 is present on the movable unit 7 and is firmly connected to the movable unit 7. Pressure can be introduced into the blow core 11 via channels in the movable unit 7. A nozzle is present at the lower end of the blow core 11. The lowermost section of the blow core 11 or the nozzle, which reaches the inside of the threaded section of the preform 3, is in the . Fig. 1-4 are shown in section. This section preferably extends (unlike the illustration) over the entire length of the threaded section. As in the prior art, the blow core 11 is moved in the longitudinal direction of the preform 3, i.e., parallel to the longitudinal axis or exactly along the longitudinal axis of the preform 3. The stretching element and its arrangement or attachment are designed differently from the prior art.

[0028] Unlike the prior art, the stretching element comprises a joint 2 and a mechanical actuating element 8, which causes a pivoting movement of the lower, free section of the stretching element about the joint 2.

[0029] The stretching element is designed in two parts, with the upper section extending through the upper end of the blow core 11, as in the prior art, and this passage point being sealed. This upper section is referred to below as the tension rod 10. The upper section is connected to the lower section via a joint 2, with the lower section representing the actual stretching element and is referred to below as the stretching mandrel 1.

[0030] More precisely, the stretching element itself preferably comprises a single joint 2, in which the section of the stretching element above the joint 2 is straight and rigid, and the section of the stretching element below the joint 2 is also rigid in the form of the stretching mandrel 1. This makes the production of the stretching element simpler than the solutions with springs and joint members mentioned in the introduction to the description, and its movement is more predictable and consistent.

[0031] The stretching mandrel 1 preferably has a second joint 12, the pivot axis of which is located on the blow core 11. An upward movement of the pull rod 10 causes the stretching mandrel 1 to pivot simultaneously about the first joint 2 on the pull rod 10 and the second joint 12 on the blow core 11. Preferably, there is also a stop for the stretching mandrel 1 on the blow core 11, against which the stretching mandrel 1 rests at one of the two end points of the pivoting movement. The blow core 11 can also have two stops, for both end positions of the stretching mandrel 1. A first stop can thus specify the angle or the end position of the stretching mandrel 1 pivoted obliquely about the joint. The stretching mandrel 1 can rest against a second stop when it is in the at least approximately vertical position of the Fig. 1 is.

[0032] Less preferably, instead of the second joint 12 on the blow core 11, only a guide and a stop for the stretching mandrel 1 may be provided. In this case, upon upward movement of the pull rod 10, the stretching mandrel 1 would be pulled along the guide until it reaches the stop.

[0033] The mechanical actuating element 8 is in the Fig. 1-4 is shown in simplified form and is intended to illustrate that a mechanical coupling exists between the part of the mechanical actuating element 8 at which the actuation takes place and the stretching mandrel 1. The mechanical actuating element 8 is actuated upon movement of the movable unit 7, in particular by a device element relative to which a relative movement of the movable unit 7 takes place.

[0034] The mechanical actuating element 8 is moved along with the movable unit 7 and preferably comprises a rod 9 or another component which projects downward from the movable unit 7 but is movable relative to the movable unit 7. The rod 9 interacts with a stop 6 located below the movable unit 7. The movable unit 7 is moved towards the stop 6 during lowering. The stop 6 can be an existing component of a known device, or alternatively, a stop 6 can be placed on the device.

[0035] The rod 9 preferably acts on a lever 13 to which the pull rod 10 is hinged.

[0036] When the rod 9 hits the stop 6, the mechanical actuating element 8 causes the stretching mandrel 1 to pivot about the joint 2. The joint 2 is preferably a hinge joint. The rear section of the stretching element in the form of the pull rod 10 remains essentially vertical, although the lower end may experience a slight lateral movement. The lever 13 of the mechanical actuating element 8 can, in particular, be a toggle lever.

[0037] The distance between the tip of the rod 9 and the movable unit 7 is preferably adjustable, for example, by changing the length of the rod 9. Alternatively, the position of the stop 6 relative to the movable unit 7 can also be adjusted.

[0038] This makes it possible to adjust the point at which the pivoting movement of the stretching mandrel 1 begins during the lowering process.

[0039] As shown, the joint 2 is located within the preform 3 at the beginning of the pivoting movement. Relative to the blow core 11, the joint 2 is preferably located below that portion of the blow core 11 that is located in the threaded portion of the preform 3. The second joint 12 is also located below that portion of the blow core that is located in the threaded portion of the preform 3.

[0040] The pivoting movement only occurs after the stretching mandrel 1 rests against the bottom of the preform 3. This causes the preform 3 to bend, guided by the stretching mandrel 1.

[0041] Preferably, the two mold halves 5 are open while the stretching mandrel 1 is moved into the preform 3.

[0042] Preferably, the straight shape of the preform 3 overlaps with the shape contour of the mold halves 5, so that the mold halves 5 can only be closed when the preform 3 has been bent by the stretching mandrel 1. In the Fig. 1 and Fig. 2, the mold halves 5 are thus moved apart, since otherwise the preform 3 could not be positioned as shown. Because the mold halves 5 are closed only after the preform 3 has begun to bend, there are no restrictions regarding the length and shape of the straight preform 3. Preferably, the extent of the pivoting of the lower section of the preform 3 increases the further the movable unit 7 is moved toward the stop 6.

[0043] The closing of the mold halves 5 can begin as soon as the preform 3 has been bent sufficiently to fit into the mold or after the preform 3 has been completely bent and stretched.

[0044] The stretching and bending of the preform 3 occur simultaneously, as the pivoting movement of the front section of the stretching mandrel 1 is mechanically coupled to its downward movement. Depending on the point of the downward movement at which the pivoting movement begins, the stretching and bending of the preform 3 can occur at different times. In one variant, the preform 3 is first slightly stretched in the longitudinal direction, which supports centering of the base of the preform 3 on the stretching mandrel 1. After centering, further stretching occurs simultaneously with the bending of the preform 3.

[0045] The device can comprise a plurality of stretching mandrels 1, blow cores 11, receptacles 4, and mold halves 5 (or two mold halves 5 with a plurality of blow molds), so that a plurality of bottles can be produced simultaneously or in parallel. It is preferred that each stretching mandrel 1 has its own mechanical actuating element 8. It is preferred that each stretching mandrel 1 has its own mechanical actuating element 8, wherein the trigger point, in particular the distance between rod 9 and stop 6, is adjustable for each mechanical actuating element 8 independently of the others. This advantageously ensures that the starting point of the pivoting movement of the respective stretching mandrel 1 is adjustable independently of the others.

[0046] Preferably, the mechanical actuating elements 8 are arranged on a common movable unit 7. The device preferably has a common stop 6 for the rods 9 of the mechanical actuating elements 8.

[0047] The stretching mandrel 1 can have any cross-sectional shape. As shown, the stretching mandrel 1 can have a wider area at the upper end, where the first joint 2 to the drawbar 10 and the second joint 12 to the blow core 11 are located. Due to the articulated connection of the stretching mandrel 1 to the blow core 11, there is no downward movement of the stretching mandrel 1 independent of the blow core 11 and the movable unit 7.

[0048] In a preferred embodiment, the stretching mandrel 1 has a widened head at its lower end, i.e., opposite the joint 2, for example, a spherical head or a disc-shaped head with rounded edges. The pivotable stretching mandrel 1 is preferably actuated by a rod assembly inside the blow core 11, so that the mechanical actuating element 8 actively pivots the pivotable section of the stretching mandrel 1 in both directions. The rod assembly inside the blow core 11 is preferably in the form of a pull rod 10, with an upward movement of the pull rod 10 causing the stretching mandrel 1 to pivot from a vertical orientation to an inclined orientation.

[0049] As shown, the mechanical actuating element 8 can comprise a lever 13, one end of which is located at a first pivot point on the movable element 7 and the other end of which is connected to the rod 9 via a second pivot point, wherein the lever 13 is attached to the pull rod 10 at a point between the two pivot points. The rod 9 is preferably guided parallel to the pull rod 10 located in the blow core 11.

[0050] A less preferred possibility would be a push rod which, when moving downwards, causes a pivoting movement of the lower section of the stretching mandrel 1 from the vertical orientation to an oblique orientation, wherein the said first pivot point in this case would be located between the attachment point of the lever 13 on the push rod and the second pivot point.

[0051] Another less preferred option is a cable pull. In the case of a cable pull or a push rod, joint 2 could be omitted and only joint 12 would be present. However, at least one of the two joints 2, 12 is present, so that the stretching mandrel 1 has at least one joint 2, 12.

[0052] The mechanical actuating element 8 preferably comprises a return element which causes the rod 9 to be pressed in the direction of the stop 6 and causes a relative movement of the rod 9 towards the stop 6 when the movable unit 7 is moved away from the stop 6.

[0053] A return element can be present at any point of the device and act on any element (selected from pull rod 10, lever 13, rod 9 or stretching mandrel 1) and in particular can be present as a spring.

[0054] The return element causes the stretching mandrel 1 to return to the Fig.1 returns to the straight starting position shown before the next preform 3 is processed in the station shown.

[0055] The mechanical actuating element 8 preferably comprises the pull rod 10, the lever 13, and a rod 9. However, the mechanical actuating element 8 is not limited to this embodiment and could also comprise fewer or more components. It is important that the mechanical actuating element 8 mechanically couples the downward movement, particularly the final part of the downward movement, of the movable unit 7, and the pivoting movement of the stretching mandrel 1. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 3314106 A1

[0002] US 2017239871 A1

[0003] US 3278665 A

[0004] JP 2009241429A

[0005] JP 2008044244A

[0006] JP 2627944B2

[0006]

Claims

[1] Method for bending a straight preform (3) in a device at least comprising a holder (4) for holding the straight preform (3), a stretching mandrel (1), a blow core (11) and a movable unit (7) which is movable towards and away from the preform (3) held in the holder (4) parallel to the longitudinal axis of the straight preform (3) and two mold halves (5) which are movable away from and towards each other in a plane transverse to the direction of movement of the movable unit (7), wherein the stretching mandrel (1) enters the preform (3) during the downward movement of the movable unit (7), characterized byin that the stretching mandrel (1) has at least one joint (2, 12) and the device comprises a mechanical actuating element (8) which is present on the movable unit (7), wherein during the last part of the downward movement of the movable unit (7) the mechanical actuating element (8) is actuated, whereupon the mechanical actuating element (8) pivots the stretching mandrel (1) present below the joint (2, 12) about the joint (2, 12), wherein the joint (2, 12) is located in the region of the blow core (11), so that the entire straight preform (3) is deformed obliquely directly below the holder (4). [2] Method according to claim 1, characterized by the steps: - lowering the movable unit (7) and the stretching mandrel (1) parallel to the longitudinal direction of the straight preform (3) which is present in the holder (4), - the mechanical actuating element (8) begins to pivot the free end region of the stretching mandrel (1) around the joint (2, 12) as soon as the latter is actuated by a device element relative to which the movable unit (7) moves relative to it, - Simultaneous stretching and bending of the preform (3) by the stretching mandrel (1) with further downward movement of the movable unit (7), - closing the mould halves (5) at a time when there is no overlap between the contour of the preform (3) and the blow mould formed by the closed mould halves (5), - Blowing the bent preform (3) to fit it to the blow mold. [3] Method according to one of claims 1 to 2, characterized by that the joint (2, 12) is located within the preform (3) at the start of the pivoting movement. [4] Method according to one of claims 1 to 3, characterized bythat the free end of the stretching mandrel (1) rests on the bottom of the preform (3) at the start of the pivoting movement. [5] Method according to one of claims 2 to 4, characterized by that the device element, relative to which a relative movement of the movable unit (7) takes place, is a stop (6) and the distance between the stop (6) and the part of the mechanical actuating element (8) which comes into contact with the stop (6) is adjustable. [6] Method according to one of claims 1 to 5, characterized by that the device comprises a plurality of blow cores (11), stretching mandrels (1), receptacles (4) and blow molds, wherein each stretching mandrel (1) has a joint (2) and its own mechanical actuating element (8) and the method is carried out on a plurality of preforms (3) in parallel. [7] Method according to claim 6, characterized bythat the blow cores (11), stretching mandrels (1) and mechanical actuating elements (8) are arranged on the one movable unit (7). [8] Stretching device comprising a blow core (11), at least one mechanical actuating element (8) and a stretching mandrel (1) for bending a straight preform (3) in a device for stretch blow molding or injection stretch blow molding of the preform (3), characterized by in that the stretching mandrel (1) adjoins the lower end region of the blow core (11), wherein the stretching mandrel (1) does not extend through the blow core (11) and is not movable in the axial direction in the blow core (11) relative to the blow core (11) and has at least one joint (2, 12) at its end facing the blow core (11), and the free region of the stretching mandrel (1) adjoining the joint (2, 12) is pivotable about the joint (2, 12), wherein for this purpose the mechanical actuating element (8) is attached to the stretching mandrel (1) and runs upwards through the blow core (11). [9] Stretching mandrel (1) according to claim 8, characterized by that the mechanical actuating element (8) is a pull rod (10). [10] Stretching mandrel (1) according to one of claims 8 to 9, characterized by in that the stretching mandrel (1) comprises a first joint (2) and a second joint (12), which are present at the same end region of the stretching mandrel (1), wherein the mechanical actuating element (8) is attached to the first joint (2) and the stretching mandrel (1) is articulated to the blow core (11) via the second joint (12).

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