Process and Device for the Extrusion/Moulding of Thermoplastic Hollow Bodies

Abstract

A process and device for extrusion/molding of thermoplastic hollow bodies using at least one extruder and at least two molds and including the extrusion of a flow of material, its cutting into parisons, and the molding of the parisons to produce the hollow body, alternately in the first mold and then in the second mold. The process may work in parallel for certain of its operations. The process and the device are well suited for producing hollow bodies of complex three-dimensional geometry with a high productivity.

Description

EXAMPLE

The example that follows is given by way of illustration of the invention, without wishing to limit its scope.

In one specific method of implementing the process, the device described in FIG. 1 is used. A multilayer extrusion head (2) is fed by the extruder (1). After a useful length of a flow of molten material has been expelled, a parison is cut off and then taken hold of in its upper part by the robot (3), which deposits it in the preforming tool (6). After the deposition, the preforming tool is introduced by a horizontal movement into a moulding machine so as to place the parison in the lower part of the blow moulding mould (4). At the end of the cycle, the article, maintained in the upper cavity while the mould (4) is being opened, is extracted by means of an extraction device (8) (this is in general an extractor inside the mould) and is received in the receiving device (7).

While the parison is being moulded in the mould (4), the preforming tool (6) returns to its base position in order to receive a new parison that the robot (3) is holding and deposits on the preforming tool (6) before the latter transfers the preformed parison to a second mould (5). The transfer of the new parison into the mould (5) takes place only when the latter is open, the hollow body moulded during the preceding cycle being extracted from the upper cavity of the mould (5). After the second parison has been deposited in the mould (5), the preforming tool (6) again returns to its base position in order to receive another parison, which will follow the same manufacturing cycle as that described in the case of the first parison. The preforming tool (6) used in FIG. 1 is provided with a rotary gripper (9), this being illustrated in FIG. 2. This gripper grips the bottom (lower end) of the parison when the latter is brought in by the robot (3) and, while the robot is moving and depositing the parison in the tool (6), the said gripper takes hold of this end while performing a 90° rotation (in the direction indicated by the arrow) in order to accompany the deposition movement. Without this rotation movement, the end held by the gripper (9) could not be aligned with the rest of the parison and a shape heterogeneity could remain in the final hollow body moulded since, if this movement were not present, a small end of the parison would remain substantially vertical, whereas most of the parison is positioned so as to be approximately horizontal. This (the small vertical end) makes it markedly more difficult to transfer the parison from the preforming tool into the lower half-mould.

Claims

1-12. (canceled)

13. A process for extrusion/molding of thermoplastic hollow bodies, using at least one extruder and at least first and second molds, comprising: extruding a flow of at least one molten thermoplastic through an extrusion head of the extruder;cutting the flow of material so as to create parisons;molding each of the parisons into a hollow body, alternately in the first mold and then in the second mold, each of the molds including moving parts that cannot be positioned beneath the extrusion head; andusing a preforming tool and a mechanical handling device, the handling device being separate from the preforming tool, such that the handling device takes hold of the parison and deposits the parison in the preforming tool, the same preforming tool transferring the preformed parison to one or other of the molds to mold a hollow body.

14. The process according to claim 13, wherein the preforming tool includes a rotary gripper that takes hold of the parison via its bottom and accompanies its deposition in the preforming tool, preforming a 90° rotation between a position approximately perpendicular to the preforming tool and a position approximately parallel to the preforming tool.

15. The process according to claim 13, comprising a cycle of: a) extruding the tubular flow of molten thermoplastic through the extrusion head in a vertical direction to flow out downwards under effect of its own weight, until a useful length has been obtained;b) cutting off a parison corresponding to the useful length of the flow of extruded material, then taking hold of and transferring the parison vertically by the mechanical handling device;c) depositing the parison by the handling device in the preforming tool to obtain a preformed parison;d) opening the first mold and a remaining hollow body molded during the preceding cycle of operations from the first mold;e) transferring the preformed parison by the preforming tool above a lower part of the first mold;f) depositing the preformed parison by the preforming tool in the lower part of the first mold;g) moving the preforming tool away from a closure zone of the first mold and sending the preforming tool back to a base position beneath the extrusion head;h) closing the first mold and molding the preformed parison into a hollow body;the closing h) comprising: 1) extrusion/molding of a next hollow body from a next parison, the extrusion of which was started after the parison was cut, by repeating operations a) to h) with the second mold; and2) extrusion of a next further parison, the extrusion of which was started after the next parison was cut, being carried out, the sequence of operation being such that, at the end of 1), the preforming tool returns to the base position so as to receive the next further parison, a) to h) then being repeated on the next further parison.

16. The process according to claim 13, wherein the preforming tool comprises, at least on the surface, a material that prevents the parison from sticking.

17. The process according to claim 13, wherein an extraction device for extracting the hollow body is actuated to drop under gravity into a receiving device.

18. The process according to claim 13, wherein the preforming tool is temperature-conditioned.

19. The process according to claim 13, wherein the hollow bodies that are extruded and molded are tubings for fuel.

20. A hollow body extrusion/molding device for carrying out the process according to claim 13, comprising: at least one extruder,one extrusion head;at least first and second molds used alternately, each of the molds comprising moving parts that cannot be positioned beneath the extrusion head; anda mechanical handling device, provided with an arm, and a preforming tool separate from the mechanical handling device acting as a robot.

21. The device according to claim 20, wherein the preforming tool includes a rotary gripper that can take hold of the parison by the bottom and preform a 90° rotation between a position approximately perpendicular to the tool and a position approximately parallel to the tool.

22. The device according to claim 20, wherein the preforming tool includes means for transferring the preformed parison into a part of at least one open mold.

23. The device according to claim 20, wherein the mechanical handling device, the preforming tool, and the parts of at least one mold can move at a same time.

24. The device according to claim 20, further comprising a receiving device for receiving a molded hollow body when the mold is opened.