Method for producing a plastic article and blow molding tool

Abstract

The invention relates to a method for producing a plastic article and a blow molding tool for performing the method. The method comprises extruding an approximately tube-shaped preform, dividing the melt flow within the extrusion head or separating the extrudate exiting or already exited from the extrusion head, such that a preform having an approximately C-shaped cross section is obtained, forming the preform into a hollow part within a multipart blow molding tool using differential pressure, wherein an expansion and partial preforming of the preform first takes place with the blow molding tool partially closed, then in a further step at least one insert is inserted into the interior of the partially preformed article between the not completely closed blow molding tool and through the open side of the preform, and in a further step the blow molding tool is completely closed, wherein the article is completely formed, forming at least one at least partially circumferential pinch-off seam.

Claims

1. A blow molding tool for producing a plastic article, comprising: at least two blow mold halves each having a cavity that complement one another to form an impression, wherein the at least two blow mold halves are openable and closeable in relation to one another, wherein at least one blow mold half of the at least two blow mold halves includes a movable mold spacer configured to abut another blow mold half of the at least two blow mold halves, the movable mold spacer comprising a four-sided frame disposed around the cavity and being retractable into and extendable out of a separating plane of the blow mold halves, wherein at least one of the sides of the frame defines at least a portion of at least one recess in the frame configured to provide an access opening to the cavity when the movable mold spacer abuts the other blow mold half, and wherein, when the movable mold spacer is retracted, the access opening is fully closeable by the mold halves.

2. The blow molding tool as claimed in claim 1, wherein: the mold spacer is adapted to a contour of the cavity of the mold half.

3. The blow molding tool as claimed in claim 1, wherein: the mold spacer is temperature controllable.

4. The blow molding tool as claimed in claim 1, wherein: the at least two blow mold halves are arranged to provide a closing movement in two stages, wherein in a first stage of the closing movement the mold spacer is extended, and wherein in a second stage of the closing movement the mold spacer is retracted.

5. The blow molding tool as claimed in claim 1, wherein: the at least one side of the frame which defines at least a portion of at least one recess in the frame configured to provide an access opening to the cavity when the movable mold spacer abuts the other blow mold half further defines at least a portion of a plurality of recesses in the frame configured to provide a plurality of access openings to the cavity when the movable mold spacer abuts the other blow mold half.

6. The blow molding tool as claimed in claim 1, wherein: each blow mold half of the at least two blow mold halves includes a movable mold spacer configured to abut the movable mold spacer of the other blow mold half, each of the movable mold spacers comprising a four-sided frame disposed around the cavity, wherein at least one of the sides of the frame of each mold spacer defines at least a portion of at least one recess in the frame configured to provide an access opening to the cavity when the movable mold spacer abuts the other blow mold half.

7. The blow molding tool as claimed in claim 6, wherein: each mold spacer is retractable into and extendable out of a separating plane of the blow mold halves.

8. The blow molding tool as claimed in claim 6, wherein: each mold spacer is adapted to a contour of the cavity of each mold half, respectively.

9. The blow molding tool as claimed in claim 6, wherein: each mold spacer is temperature controllable.

Description

(1) The invention is explained below on the basis of an exemplary embodiment that is represented in the drawings, in which:

(2) FIG. 1 shows a perspective view of part of an extruder head with the preform emerging from it,

(3) FIG. 2 shows a sectional view along the lines II-II in FIG. 1,

(4) FIG. 3 shows a perspective view of a device for blow molding plastic articles according to the invention, which also illustrates the sequence of the method according to the invention,

(5) FIG. 4a shows a sectional view through the blow molding tool in FIG. 3 and the preform placed between the blow mold halves,

(6) FIG. 4b shows a plan view in the direction of the arrow indicated in FIG. 4a,

(7) FIG. 5a shows a partial section through the blow molding tool with closed blow mold halves before the expansion of the preform,

(8) FIG. 5b shows a section along the lines B-B in FIG. 5a,

(9) FIG. 5c shows a section along the lines C-C in FIG. 5a,

(10) FIG. 5d shows a view corresponding to FIG. 5c with an inserted blowing pin,

(11) FIG. 5e shows a view corresponding to FIG. 5d that illustrates the introduction of the insert into the partially formed article,

(12) FIG. 6a shows the opened blow molding tool with retracted mold spacers,

(13) FIG. 6b shows a partial longitudinal section through the blow molding tool in the state that is shown in FIG. 6a,

(14) FIG. 7a shows a cross section through the blow molding tool in the closed state and

(15) FIG. 7b shows a cross section through the blow molding tool and the article during article removal.

(16) In FIG. 1, first of all the step of extruding an approximately tube-shaped preform according to the invention is illustrated. Firstly, a tube-shaped preform made of thermoplastic material is discharged in the molten hot state from the extruder head denoted by 1, to be precise in a known way through an annular die of the extruder head 1. The extrusion may take place continuously or discontinuously. In the exemplary embodiment represented, the preform tube 2 is separated along one side of the length by means of a separating device 3, so that it is given the cross-sectional form represented in FIG. 2 over its entire length, i.e. is provided with a longitudinal slit 4. Coming into consideration, for example, as the separating device are a hot knife, a movable blade, a laser or the like.

(17) As in the exemplary embodiment represented, the separation of the preform tube 2 may take place outside the extruder head after and during the emergence of the preform tube 2 from the extruder head 1 or from the annular die (not shown). Alternatively, separation of the preform tube 2 may also take place inside the extruder head 1, with a flow divider provided there.

(18) Finally, as a further alternative, the preform tube 2 may first be discharged to its full length and then separated by means of a gripper and a separating device.

(19) In the case of the exemplary embodiment represented, it is envisaged to take the preform tube 2 from the extruder head 1 by means of a gripper 5 and bring it to the blow molding tool 6, as schematically illustrated in FIG. 3.

(20) The gripper 5 is represented in a greatly simplified form in the drawings. It does not necessarily have to have a circular-segmental gripper element, but rather it may have gripper segments arranged in a circular arc or a polygon, with suction cups provided for taking over the preform tube 2. As already mentioned at the beginning, such a gripper is described, for example, in DE 102 05 524. The taking off of the preform tube 2 may be supported by a further separating device for the preform tube 2. Alternatively, by constricting the die gap of the extruder head, a thin location can be produced in the preform tube 2, which makes it possible for said tube to be torn off by means of a gripper 5.

(21) During the manipulation of the preform tube 2 with the gripper 5, the preform tube 2 can be expanded in the circumferential direction or radially, in order to achieve a corresponding overlapping of the cavities 7 of the blow molding tool 6. At its lower end, in the direction of gravitational force, the preform tube is additionally gripped and clamped in the regions adjacent the slit 4 respectively by a spreading element 22. The spreading elements 22 may be formed, for example, as pneumatically operable tongs, which may be formed such that they can be moved in relation to one another in the sense of spreading out the preform tube 2.

(22) In the exemplary embodiment represented, a single-cavity tool is shown, i.e. the cavities 7 that complement one another of the blow mold halves 8a, 8b form a single impression. The blow molding tool 6 according to the invention may equally well be formed as a multi-cavity tool.

(23) While the gripper 5 is bringing the preform tube between the opened blow mold halves 8a, 8b of the blow molding tool 6, at the same time an alignment of the longitudinal slit 4 of the preform tube 2 takes place in such a way that the longitudinal slit 4 is brought into line with the parting plane 10 or separating plane of the blow molding tool, to be precise in the direction of the side facing the viewer in the case of the exemplary embodiment that is represented in FIG. 3.

(24) Each of the blow mold halves 8a, 8b of the blow molding tool 6 is provided with slides 9a, b, c, d, which are preferably formed such that they can be hydraulically extended out from the parting plane of the blow molding tool 6 and retracted into it. These slides 9a, b, c, d serve during the closing movement of the blow mold halves 8a, 8b as mold spacers and are referred to correspondingly hereafter.

(25) As can be seen in particular from FIG. 3, the mold spacers 9a, b, c, d respectively frame the cavities 7 of the blow mold halves 8a, 8b, the arrangement that is represented in the figure not being adapted to the contour of the cavities 7 for reasons of a simplified representation. In fact, the mold spacers (slides) consist of a number of segments 9a, b, c, d, which are respectively adapted to the contour of the cavities 7, in order to keep the occurrence of flash as little as possible. The mold spacers may also be of a one-part form.

(26) Once the preform tube has been brought into the position shown in FIG. 3 and correspondingly aligned, the blow mold halves 8a, 8b of the blow molding tool 6 with the mold spacers 9a, b, c, d extended out from the parting plane 10 are moved toward one another in such a way that the mold spacers 9a, b, c, d assume the position shown in FIGS. 5a and 5b. They clamp the preform tube 2 circumferentially between them, while forming flash 11. In this position, the blow mold halves 8a, 8b are not completely closed, but are kept at a distance from one another by means of the mold spacers 9a, b, c, d.

(27) On one of the end faces of the blow mold halves 8a, 8b, i.e. those sides that extend transversely in relation to the parting plane 10 of the blow molding tool 6, recesses 12 that respectively complement one another are provided in the mold spacers 9a, b, c, d, and when the spacers 9a, b, c, d are moved together, as represented in FIG. 5a, respectively form openings 13, through which the parting plane 10 of the closed blow mold halves 8a, 8b extends. These openings are respectively arranged symmetrically with respect to the (imaginary) parting plane 10. The longitudinal slit 4 of the preform tube 2 likewise ideally extends in the parting plane 10 of the blow molding tool.

(28) After the mold spacers 9a, b, c, d have been moved together, for example caused (enforced) by the closing movement of the blow mold halves 8a, 8b, the preform tube is pinched together, while forming the flash 11 only outside the opening 13. In the region of the openings 13, the longitudinal slit 4 of the preform tube 2 remains open.

(29) In a further method step, which is illustrated in FIGS. 5b and 5c, a blowing pin 14, attached to a blow mold half 8b, is respectively inserted into the openings 13. The blowing pins 14 each have an approximately circular cross section in a way corresponding to the openings. The invention should be understood in the sense that the contour of the openings 13 as well as the number of openings 13 and the corresponding number of blowing pins 14 are not critical for the invention.

(30) In the case of the exemplary embodiment represented, the blowing pins 14 are attached to a blow mold half 8b in a pivotably movable manner; the invention should be understood in the sense that the blowing pins 14 may also be provided on a separate device.

(31) As revealed by FIGS. 5c and 5d in particular, the blowing pins 14 are each provided with a sealing collar 15, which seals them from the mold spacers 9a in the region of the openings 13.

(32) In a further method step, which is illustrated in FIGS. 5d and 5e, the preform tube is placed against the cavities 7 while introducing blowing air and is formed against said cavities. After expansion and partial formation of the preform tube 2 into the semifinished article 16, the blowing pins 14 can be pivoted out from the openings 13. Said pins respectively clear the openings 13 completely, so that a manipulator 17 with an insert 18 can be inserted into the semifinished article 16, as is shown in FIG. 5e.

(33) Once the inserts 18 have been joined onto the wall of the semifinished article 16, the openings 13 are once again closed by the blowing pins 14. Then the performs are once again subjected to blowing pressure in order to prevent any folding of the preform tube in the region adjacent the mold spacers 9a, b, c, d or to smooth out any folds occurring there.

(34) At this point it should be mentioned once again that the number and position and the type of inserts are not critical for the invention. In the present case, for example, the article may be a fuel tank into which a surge chamber is introduced as an insert.

(35) In the case of the exemplary embodiment that is shown in FIG. 3, the manipulator 17, which is formed as a three-axis robot arm, and the likewise three-axis gripper 5 are arranged on respectively opposite sides of the blow molding tool 6. They may alternatively be arranged on one side of the blow molding tool 6.

(36) Once the insert 18 has been introduced into the semifinished article 16, the blowing pins 14 have possibly been inserted into the openings 13 and the preform tube 2 has been post-molded, the mold spacers 9a, b, c, d are retracted (see FIG. 6a) and the blow mold halves 8a, b perform a closing movement, in which the wall material of the semifinished article extending over the width of the gap 19 between the blow mold halves 8a, b is pinched together to form further flash 20. For reasons of a simplified representation, the gap 19 is shown in the drawings larger than it actually is. The finished article is given the shape shown in FIGS. 7a and 7b. The blow mold halves 8a, b open, or are moved apart in the direction of the arrows shown in FIG. 7b, and the finished article 21 can be removed by means of a removal device. It goes without saying that the flash 20 is removed.

LIST OF DESIGNATIONS

(37) 1 Extruder head 2 Preform tube 3 Separating device 4 Longitudinal slit 5 Gripper 6 Blow molding tool 7 Cavities 8a, b Blow mold halves 9a, b, c, d Slides (mold spacers) 10 Parting plane 11 Flash 12 Recesses 13 Openings 14 Blowing pins 15 Sealing collar 16 Semifinished article 17 Manipulator 18 Insert 19 Gap 20 Flash 21 Finished article 22 Spreading elements