Method of producing a hollow body from thermoplastic material

Abstract

The invention relates to a method for producing hollow bodies from thermoplastic material comprising the shaping of at least one tubular preform or at least two two-dimensional, web-like preforms of plasticated thermoplastic material into a substantially closed hollow body, for example in the form of a fuel tank for motor vehicles.

Claims

1. A method for producing a hollow body from thermoplastic material, comprising: providing at least one preform of thermoplastic material on a multipart blow molding tool, introducing the at least one preform into cavities of the blow molding tool, molding the at least one preform into shells within the blow molding tool, joining at least one insert to at least one shell of the shells within the blow molding tool, the insert defining a part-volume that is closed off with respect to a main-volume of the hollow body to be produced, joining together the shells by closing the blow molding tool, forming the hollow body with the insert enclosed within the hollow body between the shells, applying pressure to the main-volume enclosed by the hollow body, wherein a pressure equalization with the part-volume is brought about parallel to the pressure applied to the main-volume, wherein the pressure equalization takes place by the part-volume within the closed blow molding tool being connected initially for a time to the main-volume by at least one bypass line and by at least one inflation needle or an inflating mandrel, with which a wall of the insert and/or of the hollow body is pierced.

2. The method as claimed in claim 1, wherein the connecting of the part-volume to the main volume takes place by the at least one inflation needle being connected to the at least one bypass line, the inflation needle being made to pierce through the wall of the insert and/or of the hollow body.

3. The method as claimed in claim 1, wherein the at least one inflation needle comprises at least two inflation needles, and the connecting of the part-volume to the main volume takes place by the at least two inflation needles being connected to one another by the at least one bypass line, one inflation needle of the at least two inflation needles being made to pierce through the wall of the insert and a further inflation needle of the at least two inflation needles being made to pierce through a wall of the hollow body.

4. The method as claimed in claim 3, wherein the inflation needle being made to pierce through the wall of the insert is made to pierce through the wall of the hollow body from the outside.

5. The method as claimed in claim 1, wherein the at least one inflation needle or inflating mandrel comprises at least two inflation needles or inflating mandrels, and, before the joining of the insert, a wall of at least one shell which provides the wall of the hollow body is pierced with the at least two inflating mandrels or inflation needles, which communicate with one another by at least one bypass line, and in that during the joining of the insert, the insert is pierced by one of the inflation needles or inflating mandrels by using a joining movement.

6. The method as claimed in claim 5, wherein an application of pressure to the hollow body takes place in two stages, including a first, preliminary blowing pressure being applied before the joining of the insert, by the inflation needles communicating with one another by the bypass line.

7. The method as claimed in claim 4, wherein the inflation needle piercing the insert is made to pierce through the wall of the hollow body from the outside in a region of a connection opening to be produced in the wall of the hollow body after removal from the blow molding tool.

8. The method as claimed in claim 1, wherein the insert is part of a venting system.

9. The method as claimed in claim 1, wherein the insert comprises a valve.

10. The method as claimed in claim 1, wherein the insert comprises a venting line.

11. The method as claimed in claim 1, wherein the insert comprises a bubble vessel.

12. The method as claimed in claim 1, wherein the insert comprises an expansion tank.

13. The method as claimed in claim 1, wherein the pressure equalization avoids destruction of the insert by the pressure applied to the main volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure hereinafter will be described with reference to the accompanying drawing in which:

(2) FIG. 1 shows a hollow body 1 in the form of a fuel tank according to the present invention directly after the joining together of shells 2 within a blow molding tool 3.

DETAILED DESCRIPTION

(3) FIG. 1 shows a hollow body 1 in the form of a fuel tank according to the present invention directly after the joining together of shells 2 within a blow molding tool 3. The blow molding tool 3 is represented in a highly schematically simplified form. Within the hollow body 1, parts of a venting system are represented in the form of a bubble vessel 4 and a valve 6 connected to the bubble vessel 4 by way of a venting line 5. Both the bubble vessel 4 and the valve 6 have been welded to a shell 2 directly after the shaping of the shells 2 in part-cavities 3a, 3b of the blow molding tool 3. After removal of the hollow body 1 from the blow molding tool 3, the bubble vessel 4 is connected by way of a lead-through in the wall of the hollow body 1 to a venting line laid outside the hollow body 1.

(4) The hollow space enclosed by the hollow body 1 is referred to hereinafter as the main volume 7, the volume enclosed by the bubble vessel 4 is referred to hereinafter as the part-volume 8.

(5) In the region of an inspection opening 9, which is represented in an indicative manner in FIG. 1 and is obtained by cutting out a circle after removal of the hollow body 1 from the blow molding tool 3, the hollow body 1 is provided with a molded-in metal flange ring, which is not represented. The molding-in of this flange ring in the region of the inspection opening takes place in the last method step of the production method by applying a gas pressure to the main volume 7 of the hollow body 1 at an increased internal pressure of approximately 6 to 10 bar. This final blow molding of the hollow body 1 takes place by way of at least one inflation needle 10, which is fired into the still warm-plastic hollow body 1 within the blow molding tool in the region of the inspection opening 9. The venting system comprising the bubble vessel 4, the venting line 5 and the valve 6 is of course thereby likewise subjected to pressure if this venting system in the installed state is formed as a self-contained part-volume 8, the connecting of which does not take place until after removal of the hollow body 1 from the blow molding tool 3.

(6) In order to achieve a pressure equalization during the final blow molding of the hollow body 1, it is therefore envisaged to fire into the hollow body 1 a second and third inflation needle 11, 12, which communicate with one another by way of a bypass line 13. The second inflation needle 11 penetrates the shell 2 as well as the wall of the bubble vessel 4 joined onto the shell 2. The third inflation needle 12 is fired into the hollow body 1 in the region of the later inspection opening 9 through the wall of the hollow body 1 or through the shell 2. A pressure equalization between the main volume 7 and the part-volume 8 takes place by way of the bypass line 13, so that in this way collapsing, for example of the bubble vessel 4, is reliably prevented. The firing in of the second and third inflation needles may in this case take place directly after the joining together of the shells 2.

(7) As an alternative to the variant of the method described above, it may be envisaged to fire in the second and third inflation needles 11, 12 already directly after the shaping of the shells 2 in the blow molding tool 3 and to bring about a preliminary blow molding of the not yet joined shell 2 by way of the bypass line 13. In this stage of the method, the halves of the blow molding tool are for example respectively sealed off from a tool divider, a core or a central frame.

(8) It goes without saying that the invention should be understood as meaning that the pressure equalization between a part-volume 8 and the main volume 7 of the hollow body 1 may take place at any desired location and at multiple locations of the hollow body 1, for example including on both shells 2.

(9) After the preliminary blow molding, the bubble vessel 4 for example can then be joined onto the shell 2 concerned by the already fired-in second inflation needle 11 piercing through. Then, the shells 2 can be joined together and an application of gas pressure to the hollow body 1 can take place for the purpose of final blow molding.

(10) The introduction of the third inflation needle 12 in the region of the later inspection opening 9 is not detrimental to the finished hollow body 1 as long as cutting out of a circle in the wall of the hollow body is performed there.

LIST OF DESIGNATIONS

(11) 1 Hollow body 2 Shells 3 Blow molding tool 3a, 3b Part-cavities of the blow molding tool 4 Bubble vessel 5 Venting line 6 Valve 7 Main volume 8 Part-volume 9 Inspection opening 10 Inflation needle 11 Second inflation needle 12 Third inflation needle 13 Bypass line