Abstract
The invention relates to a method and a device for producing large-volume container trays of plastic. A tubular preform is guided over a mold frame which is facing two blow molds. During the closure of the blow molds, an encircling flange is formed on the outer edge of the container trays. After blow molding, the container trays are cut free from the mold frame along said mold frame.
Claims
1. A method for producing large-volume container shells from plastic material, in which a tube-shaped preform of plastic material in a thermoplastic state is passed over a mold frame which faces at least one blow mold in the open state, the blow mold is closed, wherein the mold frame forms a circumferential flange at the edge of the blow mold and thus at the outer edge of the container shell, the container shell is formed in the blow mold by plastic blow molding, and in which, afterwards, the container shell is cut free from the mold frame along this mold frame.
2. The method according to claim 1, in which the mentioned blow mold faces a further blow mold, the mold frame is arranged between the two blow molds, during blow molding, one container shell each is formed simultaneously in the two blow molds, and in which, afterwards, the container shells are cut free from the mold frame along this mold frame.
3. The method according to claim 1, characterized in that the flange is formed by pressing the thermoplastic preform between the blow mold and the mold frame.
4. The method according to claim 3, characterized in that the mold frame is made up of several retractable and extendable mold elements so that, as viewed in the transverse direction of the tube of the preform upon guidance of the tube-shaped preform the mold frame has a smaller dimensional size than the inner diameter of the preform and that during plastic blow molding the mold frame assumes a spread-out state.
5. The method according to claim 1, characterized in that high-molecular polyethylene is used as a plastic material.
6. The method according to claim 1, characterized in that the preform is a multilayer preform and at least one layer presents a foam structure.
7. The method according to claim 6, characterized in that for forming the foam structure the respective blow mold is designed such that a vacuum acts on the preform.
8. The method according to claim 1, in which during the formation of the flange, screw holes and a circumferential groove a circumferential projection are formed as well.
9. The method according to claim 1, in which the respective container shell has a capacity from 250 to 5000 I, in particular from 1000 to 4000 I.
10. A device for producing large-volume container shells from plastic material, in which an extrusion device ejects from a molten material head, a tube-shaped preform of plastic material, which is passed in a thermoplastic state over a mold frame which faces at least one blow mold in the open state, the blow mold is closed, wherein the mold frame forms a circumferential flange at the edge of the blow mold and thus at the outer edge of the container shell, the container shell is formed in the blow mold by plastic blow molding, and in which, afterwards, the container shell is cut free from the mold frame by a cutting device along this mold frame.
11. The device according to claim 10, in which the mentioned blow mold faces a further blow mold, the mold frame is arranged between the two blow molds, during blow molding, one container shell each is simultaneously formed in the two blow molds, and in which, afterwards, the container shells are cut free from the mold frame along this mold frame.
12. The device according to claim 10, characterized in that the mold frame is made up of several retractable and extendable mold elements so that, as viewed in transverse direction of the tube of the preform, during guidance of the tube-shaped preform, the mold frame has a smaller dimensional size than the inner diameter of the preform, and that during plastic blow molding the mold frame assumes a spread-out state.
13. The device according to claim 10, characterized in that for forming the foam structure the respective blow mold is designed such that a vacuum acts on the preform.
14. The device according to claim 10, in which during the formation of the flange, screw holes, and a circumferential groove and a circumferential projection are formed as well.
15. The device according to claim 10, in which the respective container shell has a capacity from 250 to 5000 I, in particular from 1000 to 4000 I.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Embodiments of the invention are explained in the following on the basis of the drawings:
[0014] FIG. 1 shows a cross-section of open container shells with a respective circumferential flange.
[0015] FIG. 2 shows a perspective view of container shells.
[0016] FIG. 3 schematically shows the arrangement of two blow molds with a mold frame arranged therebetween.
[0017] FIG. 4 shows an illustration with spread-out mold frame.
[0018] FIG. 5 shows an illustration with closed blow molds.
[0019] FIG. 6 shows the state after cooling the plastic molding material and open blow molds.
[0020] FIG. 7 shows a view of the mold frame in the closed and in the open state.
[0021] FIG. 8 shows a side view of the mold frame in the retracted and in the spread-out state.
[0022] FIG. 9 shows a top view of the mold frame in the closed and the spread-out state.
[0023] FIG. 10 shows a side view with different states of the blow molding process.
[0024] FIG. 11 shows a side view with partly open and fully open blow mold.
DETAILED DESCRIPTION
[0025] FIG. 1 shows in a cross-section the open container shells 10, 12 produced in a blow molding machine, each of which with a circumferential flange 14, 16. Through holes 18 are formed in the respective flange 14, 16 and a circumferential groove 24 is formed in the flange 16. The container shells 10, 12 are transported from the place of production to the point of destination in the open state and, thereat, are connected to one another along the flanges 14, 16 in a fluid-tight manner by means of a screw connection. The large-volume closed container formed in this way serves at the point of destination as a drinking water tank, waste water tank, fecal matter container, rain receiving tank, fire-fighting reservoir etc. In the upper container shell 10, an access opening 20 is formed.
[0026] FIG. 2 shows a perspective view of the container shells 10, 12, each of which having reinforcing elements 22. The flange 16 includes the circumferential groove 24 into which a sealing element 26 for the fluid-tight connection of the flanges 14, 16 is inserted.
[0027] FIG. 3 schematically shows the arrangement of two blow molds 26, 28 with a respective corresponding cavity 30 for forming the container shells 10, 12. Here, the blow molds 26, 28 are shown in the open state spaced from each other and a mold frame 32 is arranged between them. From a molten material head 34 of the blow molding machine a tube-shaped preform 36 is ejected in a still thermoplastic state. Preferably, high-molecular polyethylene is used as a plastic material. Its inner diameter D is larger than the width d of the entire mold frame 32 in its retracted state so that the preform 36 can be freely passed downward over the mold frame 32 and thus fully surrounds the mold frame 32. The mold frame 32 comprises mold elements 35 extendable and retractable in transverse direction.
[0028] In FIG. 4, the preform 36 is passed downward so far that its lower end at least extends up to the lower dimension of the facing blow molds 26, 28. The mold frame 32 is laterally extended with its mold elements 35 and in doing so spreads the preform 36 surrounding it. In this extended state of the mold frame 32, external portions of the mold elements 35 face frame portions 40 of the blow molds 26, 28 on all four sides.
[0029] In FIG. 5, the blow molds 26, 28 are closed, wherein the mold elements 35 of the mold frame 32 form the flange 14, 16 at the edge of the respective blow mold 26, 28 and thus at the outer edge of the container shells 10, 12 to be formed on each side of the blow mold 26, 28 by pressing between the respective blow mold 26, 28. By blowing air into the mold frame 32, the respective container shell 10, 12 is formed in the cavities 30 of the blow molds 26, 28.
[0030] FIG. 6 shows a state after cooling down the plastic molding material in the blow molds 26, 28. The two container shells 10, 12 are cut free along a line 41 from the mold frame 32 surrounded by plastic material, and the containers 10, 12 with a respective circumferential flange 14, 16 are removed from the blow molding machine.
[0031] FIG. 7 shows a view of the mold frame 32 in two states. To the right of a center axis 44, the mold frame 32 with associated mold element 35 is illustrated in the retracted state in which the preform 36 is passed downward so as to surround the mold frame 32. To the left of the center axis 44, the mold frame 32 is in the extended state, wherein it spreads the tube-shaped preform 36 outwards. Within the mold frame 32, four hydraulic or electric linear drives 46 are arranged which move the mold elements 35 of the mold frame 32 into the extended or the retracted state. At the lower end of the mold frame 32, a blowing air supply 50 is provided, via which the blowing air for blow molding can be blown in. As can be seen, the preform 36 extends beyond the lower edge of the mold frame 32 to have enough plastic material present in the closed state of the blow molds 26, 28 in order to form the circumferential flanges 14, 16.
[0032] FIG. 8 shows a side view of the mold frame 32. To the right of the center axis 44, a state is shown in which a closing element 48 keeps the blow mold 26 in the open state. The preform 36 is passed over the retracted mold frame 32. To the left of the center axis 44, a state can be seen in which a further closing element 49 has moved the associated blow mold 26 from an open position illustrated in broken lines into the closed position. The mold frame 32 is in the extended state and its mold elements 35 press the preform 36 against the edge portions 40 of the blow mold 26 in order to form the flange 16. Via the blowing air supply 50 blowing air is blown in and the wall of the preform 36 places itself against the inner side of the cavity 30 of the blow mold 26, as a result whereof the associated container shell 10 is formed. The mold frame 32 is held from below by a fixture 33.
[0033] FIG. 9 shows a top view of the mold frame 32. Two states of the mold frame 32 are illustrated. In one state, the mold frame 32 is in the retracted state, in which its mold elements 35 are arranged within the tube of the preform 36 ejected by the molten material head 34. In this state, the preform 36 is passed downward over the mold frame 32. Moreover, an extended state of the mold frame 32 is illustrated, in which the mold elements 35 are moved outward by means of the linear drives 46. In doing so, the mold elements 35 also move the wall of the preform 36 and spread the preform. After forming the container shells 10, 12 in the blow molds 26, 28 and the forming of the flanges 14, 16 on the outer portions of the mold elements 35, the container shells 10, 12 are cut free from the mold frame 32, for which a cutting device 54 with a rotating knife is arranged.
[0034] FIG. 10 shows a top view of two states above and below a center line 57. The blow molds 26, 28 are each in the closed position with the mold frame 32 arranged in the center. In the upper image part, it is shown that the blowing air fed via the blowing air supply 50 expands the preform 36 so that it is forced into the cavity 30 of the blow molds 26, 28. At the same time, a vacuum is applied to the cavities 30 of the blow molds 26, 28 in this embodiment, which vacuum supports the expansion of the preform 36 and the latter places itself against the inner wall of the cavities 30. In this example, the preform 36 is a multilayer preform and includes a foam structure as medium layer. For forming this foam structure, a reduced blow pressure is required, which is made possible by the application of the vacuum. In doing so, the preform 36 is circumferentially tightly pressed against the outer portions of the mold elements 35 of the mold frame 32 so that the vacuum can build up between the blow molds 26, 28 and the preform 36.
[0035] As can be seen, the blow molds 26, 28 are designed such that in the outer portion of the mold elements 35 a flash 58 results. Along this flash 58, the flash 58 is cut free circumferentially by means of the cutting device 54 and associated knives 56, this flash 58 being waste material. The blow molds 26, 28 are formed such at their edge portions that the circumferential flat flanges 14, 16 are formed with through holes 18.
[0036] FIG. 11 shows a side view of two states. To the left of the center axis 44, the state with partly open blow mold 26 is illustrated. The container shell 10 is cut free from the mold frame 32. In the right-hand image part, the blow mold 28 is in the open final position and the container shell 12 can be removed and the parts of the flash 58 can be fed to the waste. By means of a circumferential groove molding element 60 on the mold frame 32 the circumferential groove 24 for the later reception of a seal is formed in the flange 14. The flanges 14, 16 are formed by pressing between the outer portions of the mold frame 32 and the edge portions 40 of the blow molds 26, 28. A flange measure F in the blow molds 26, 28 is at least 20% smaller than the thickness of the preform 36.
[0037] The described method and the device can be modified in many ways. The mold elements 35 can be designed foldable or movable by means of drives. It is advantageous when the mold elements form a flat surface in the spread-out state. It is also advantageous when in the case of several blow molds in one blow molding machine the respective hollow body molds are designed differently. Further, it is advantageous when after cutting the container shells free from the mold frame this mold frame is pulled downward or upward away from the blow molds before removing the container shells. When using a co-extrusion machine, the tube-shaped preform can also include several different plastic layers.
LIST OF REFERENCE SIGNS
[0038] 10, 12 container shells [0039] 14, 16 flange [0040] 18 through holes [0041] 20 access opening [0042] 22 reinforcing elements [0043] 24 groove [0044] 26, 28 blow molds [0045] 30 cavity [0046] 32 mold frame [0047] 34 molten material head [0048] 36 preform [0049] D inner diameter of the preform [0050] d width of the mold volume [0051] 35 mold elements [0052] 41 line [0053] 44 center axis [0054] 46 linear drive [0055] 50 blowing air supply [0056] 48 closing element [0057] 49 further closing element [0058] 54 cutting device [0059] 56 knife [0060] 57 center line [0061] 58 flash [0062] 60 groove molding element [0063] F flange measure
