Method for manufacturing a fuel tank or filling pipe and use thereof in a hybrid vehicle

Abstract

A method for manufacturing a fuel tank or filling pipe including a wall made of thermoplastics material and a fibrous reinforcement over at least part of the surface thereof, the method including: heating the fibrous reinforcement to bring the fibrous reinforcement into an at least partially molten state; introducing the heated fibrous reinforcement, and the wall in at least partially molten state, into a mold; and welding the fibrous reinforcement to the wall using pressure of a gas which inflates the wall and presses the heated fibrous reinforcement firmly against the wall in the molten state.

Claims

1. A method for welding a fibrous reinforcement when manufacturing an object chosen from an assembly of a tank and a filling pipe, the object including a wall of thermoplastics material, the welding method comprising: heating a fibrous reinforcement to bring the fibrous reinforcement into a molten state, the fibrous reinforcement including both a thermoplastics material compatible with that of the object and chopped fibers or long fibers or continuous fibers which may or may not be woven, the fibrous reinforcement being located on an external face of the object without increasing significantly a thickness of the object and decreasing a useful capacity of the object; and welding, in a mold, the heated fibrous reinforcement to the wall in an at least partially molten state, using pressure of a gas that inflates the wall against the mold.

2. The method as claimed in claim 1, wherein the object is a fuel tank.

3. The method as claimed in claim 1, wherein the object is a filling pipe.

4. The method as claimed in claim 1, wherein the fibrous reinforcement is heated using a heating element that is placed in front of the fibrous reinforcement to heat the fibrous reinforcement by radiation, by convection, or by contact.

5. The method as claimed in claim 1, wherein the fibrous reinforcement is heated outside of the mold to bring the fibrous reinforcement into a molten state and then introduced heated into the mold.

6. The method as claimed in claim 1, further comprising preforming the fibrous reinforcement, the preforming being performed at least partially outside of the mold and/or in the mold.

7. The method as claimed in claim 6, wherein the preforming the fibrous reinforcement on a preforming support is performed outside of the mold after the fibrous reinforcement has been heated and before the fibrous reinforcement is transferred into the mold.

8. The method as claimed in any claim 1, wherein the thermoplastics-material content of the fibrous reinforcement is at least 30%, or 50%, or at least 70%.

9. The method as claimed in claim 1, wherein there are provided, in the mold, at a site intended for the preheated reinforcement, means for keeping the mold at a temperature high enough to prevent the fibrous reinforcement from cooling before the fibrous reinforcement has become welded to the sheet.

10. A method of manufacturing an object chosen from an assembly a fuel tank and of a filling pipe, comprising: introducing a sheet of thermoplastics material in an at least partially molten state into a blow-molding mold; shaping the sheet to a cavity of the mold by blow-molding using a blow-molding gas; and demolding the sheet; the object comprising a wall of thermoplastics material which is formed by the sheet and locally reinforced by a fibers reinforcement comprising both a thermoplastics material compatible with that of the sheet and chopped fibers or long fibers or continuous fibers which may or may not be woven; the method further comprising the method as claimed in claim 1 for welding the fibrous reinforcement to the sheet, the mold of the welding method being the blow-molding mold and the pressure of the gas which inflates the wall against the mold during welding being the pressure of the blow-molding gas.

11. The method as claimed in claim 10, wherein the fibrous reinforcement is introduced into the mold to press the fibrous reinforcement against a face of the sheet opposite to an interior face of the mold.

12. The method as claimed in claim 10, wherein the fibrous reinforcement is introduced into the mold to press the fibrous reinforcement against an interior face of the mold.

13. The method as claimed in claim 10, wherein two sheets of thermoplastics material in an at least partially molten state are introduced into a blow-molding mold of two half-molds and of a core separating the two half-molds, one sheet being introduced between a first half-mold and the core, the other sheet being introduced between the second half-mold and the core, the method further comprising: bonding the two sheets together after they have been shaped, by opening the mold, removing the core from between the two half-molds, and bringing the two half-molds back against one another.

14. A method of manufacturing an object from an assembly of a fuel tank and of a filling pipe, comprising: demolding a sheet in an at least partially molten state from a blow-molding mold in which the sheet has been shaped; introducing the sheet into a post-blowing mold; inflating the sheet against an interior face of the post-blowing mold using a post-blowing gas; the object comprising a wall made of thermoplastics material formed by the sheet and locally reinforced with a fibers reinforcement comprising both a thermoplastics material compatible with that of the sheet and chopped fibers or long fibers or continuous fibers which may or may not be woven; the method further comprising the method for welding the fibrous reinforcement to the sheet as claimed in claim 1, the welding mold being the post-blowing mold and the pressure of the gas which inflates the wall against the mold being the pressure of the post-blowing gas.

15. A core of a mold for implementing the method as claimed in claim 13, comprising mobile means of positioning the reinforcement near the interior face of the mold.

16. A tank or pipe obtained by a method as claimed in claim 10, comprising: a wall of thermoplastics material and a fibers reinforcement welded over at least part of its external surface, the fibrous reinforcement comprising a plastics material of same kind as or compatible with that of an external surface of the tank or of the pipe and continuous fibers.

17. The use of a tank as claimed in claim 16 obtained as a fuel tank of a hybrid vehicle.

18. A method for welding a fibrous reinforcement when manufacturing an object chosen from an assembly of a tank and a filling pipe, the object including a wall of thermoplastics material, the welding method comprising: heating a fibrous reinforcement outside a mold to bring the fibrous reinforcement into a molten state, the fibrous reinforcement including both a thermoplastics material compatible with that of the object and chopped fibers or long fibers or continuous fibers which may or may not be woven, the fibrous reinforcement not increasing significantly a thickness of the object and not decreasing a useful capacity of the object; introducing the fibrous reinforcement heated into the mold; and welding, in the mold, the heated fibrous reinforcement to the wall in an at least partially molten state, using pressure of a gas that inflates the wall against the mold.

Description

(1) The present invention is illustrated non limitingly in the attached figures which schematically depict:

(2) FIG. 1: in cross section, a two-shell mold in the open position,

(3) FIG. 2: in cross section, the same mold in the closed position, before the blow-molding of a sheet,

(4) FIG. 3: in cross section, the same mold in the closed position, after the blow-molding of the sheet,

(5) FIG. 4: view from above of a station for shaping a fibers reinforcement,

(6) FIGS. 5 and 6: view from above of an oven of the installation of FIG. 4,

(7) FIGS. 7 and 8: view in section on VII-VII of a shaping tool of FIG. 4,

(8) FIG. 9: part of the shaping tool of FIGS. 7 and 8 during the transfer of the reinforcement and the placement thereof in a mold,

(9) FIG. 10: in cross section, a two-shell mold during a step of positioning and welding a fibers reinforcement using a mobile element.

(10) FIG. 1 depicts, in vertical section, two opposing shells 1 and 1 of an open mold for the manufacture of a fuel tank.

(11) Each shell 1, 1 here has a simple shape with planar perpendicular walls connected by fillets, but any hollow shape is possible.

(12) As is known, an extrusion die 5 fitted with a forming tool 6 allows a sheet or tubular parison 4 to be produced just above the mold, while the two shells 1, 1 are parted from one another. In place of the tubular parison it would of course be possible to use two planar or sheet-form parisons for example according to the method described in EP1110697.

(13) The terms planar and tubular here refer to objects the shape of which is respectively planar or tubular approximately overall. The actual conditions of extrusion of the sheet are such that the sheet inevitably has irregularities of shape which prevent it from conforming rigorously to the intended geometric shape.

(14) Two reinforcements 3 and 3 have been preheated and introduced into the mold, placing one of them on a fillet of the internal surface of one of the shells 1, and the other 3 on a planar part of the internal surface of the other shell 1. Placement of the reinforcement 3 on a non-planar zone entails shaping this reinforcement. This shaping may have taken place beforehand in a shaping tool or may be performed in the mold, by pressing the reinforcement precisely against the internal wall of the shell at the appropriate point of this shell.

(15) Whatever the method used for the shaping of the reinforcement 3, a means 2 for maintaining the temperature of the part of the shell surrounding the zone at which each reinforcement is positioned has also been provided so that the reinforcements do not cool excessively quickly upon contact with the mold. This is because it is important, according to the invention, for welding to take place between each reinforcement 3 (respectively 3) in the molten state and the parison 4 which is also in the molten state. Any premature cooling of the reinforcement would detract from this welding. This premature cooling can be avoided in various ways, for example by providing such temperature maintaining means 2 or by increasing the temperature to which the reinforcement is heated so that it is still in the molten state at the time of welding or alternatively by reducing the time the reinforcement spends waiting in the mold before welding takes place. Another solution may consist in bringing a heating element up close to the reinforcement positioned in the mold, in order to heat it by radiation or by contact prior to the welding operation.

(16) A retaining means for keeping each reinforcement in position against the wall of the shell is also provided. This means (not depicted) may be suction of air through a duct provided for this purpose in the shell or even mechanical retention (for example using grips or rods, which may or may not pass through) of the external edge or of the reinforcing medium.

(17) A length of parison 4 equivalent to the height of the mold has also been lowered either during the positioning of the reinforcements or beforehand or afterwards.

(18) The mold is next closed by bringing the two shells 1, 1 thereof together, as can be seen in FIG. 2. The parison finds itself trapped to its lower end between the two shells and at the exit from the extrusion head 5 between the two shells and the forming tool 6.

(19) The blow-molding of the parison is then commenced, by injecting into it air at a pressure varying from 5 to 10 bar, depending on the dimensions of the mold.

(20) The pressure of the air presses the parison against the walls of the shells 1 and 1 and brings the parison to the geometry of the tank that is in the process of being manufactured.

(21) An additional effect of the air pressure is that of pressing the parison in the molten state against the reinforcements in the molten state held in the mold. This results in the reinforcements becoming welded to the parison.

(22) A heating station that can be used for preforming the reinforcement and a method for handling the reinforcement using a vacuum gripper will now be described with reference to FIGS. 4 to 9.

(23) The steps in the method are as follows:

(24) FIG. 4: The reinforcement 3 is loaded onto a mesh 10 by an operator 12. This mesh comprises a succession of metal rungs 10A which are parallel in just one direction. It is mounted on a rail (not depicted) and progresses automatically toward an oven 14 after it has been loaded.

(25) The rungs of the mesh need to be able to raise the reinforcement 3 from beneath. To do this, the rungs need to have suitable spacing to provide the reinforcement with an appropriate support even when the reinforcement has reached a molten state.

(26) FIG. 5: The reinforcement is heated in the oven 14. For preference, the two faces of the reinforcement are heated simultaneously, so as to reduce the cycle time.

(27) Regarding the oven: The use of heating metal strips emitting in the infrared as a heating element of the oven yields good results. This use is non limiting. Further, these heating elements are insensitive to vibration and have a life compatible with the envisioned application, namely the manufacture of tanks (estimated at 8000 h at optimal use according to the manufacturer). If necessary, the heating power may be regulated (pyrometer with control loop) so as to reduce the sensitivity of the heating to variations in workshop temperature (drafts, etc.).

(28) FIG. 6: Once heating is complete, the mesh on which the reinforcement is laying leaves the oven and is positioned in a cavity of a 3D shaping tool 16 to shape the reinforcement in the molten state to a three-dimensional shape. The shell of the forming tool constitutes a preforming support and comprises two jaws, a lower jaw 18A capable of moving vertically, and an upper jaw 18B, as may be seen in FIG. 7.

(29) FIG. 7: The upper jaw 18B performs a second function: it is a gripper. This gripper 18B positions itself over the reinforcement.

(30) FIG. 8: The lower jaw 18A presses against the lower face of the reinforcement and compresses it against the gripper 18B. This operation shapes the reinforcement to the desired 3-dimensional shape.

(31) The lower jaw 18A is made up of vertical plates 18C which slide between the rungs 10A of the mesh on which the reinforcement 3 rests. The plates have top edges that form a layer (which is imaginary and embodied in FIG. 7 by a discontinuous line 20) that coincides with the three-dimensional shape that it is desired to be imparted to the reinforcement.

(32) For preference, retaining rods (not depicted) are mounted on actuators (not depicted) and prevent the reinforcement from slipping between the jaws as they close, by holding it in place during this closing. In the case of a reinforcement measuring 340 mm109 mm, two actuators 3 mm in diameter are enough to maintain the positioning. The stroke of the actuators is adjusted so that efficient pressure is applied to the reinforcement without damaging it. This retention is preferably located in the zone of the first contact during closure of the jaws.

(33) FIG. 9: The three-dimensionally shaped reinforcement is picked up by a robot 22 bearing the gripper 18B under partial vacuum.

(34) The vacuum is preferably obtained using a Venturi-type system. The level of vacuum is adjusted so as not to cause excessive deformation of the reinforcement. The inventors have found that a vacuum of 266 mbar provides effective retention of the reinforcement on the gripper.

(35) Use will preferably be made of a number of orifices 24 to create the vacuum. This is because use of a single orifice causes flows of air that cool the reinforcement in the vicinity of this orifice.

(36) The gripper may have an edge following the final shape of the reinforcement. This edge may be embodied by a flat surface a few millimeters wide.

(37) This edge may be covered with PTFE (or some other non-stick coating) to prevent molten material from being deposited, something which could occur over the long-term.

(38) In addition, regulating the temperature of the gripper makes it possible to avoid excessively rapid cooling of the reinforcement during transfer to the blow-molding mold. In particular, a water-based (or oil-based) control system or a system involving an electric heater installed on a metallic element of the gripper makes it possible to ensure that the temperature of the fibrous reinforcement is effectively maintained.

(39) Conversely, the control system needs to make it possible to avoid the temperature of the gripper increasing as a result of repeated contacts with the reinforcement in the molten state. One alternative is to place the gripper on a heating or cooling station during standby phases. However, temperature regulation is less straightforward in that case.

(40) As already explained with reference to FIGS. 1 to 3, the surface of the mold in contact with the reinforcement may be equipped with suction systems (of the vent type), not depicted.

(41) The size of these vents needs to be sufficiently small to prevent the reinforcement from entering there as a result of the high pressures applied during the blow-molding of the parison against the mold.

(42) For preference, retractable rods are positioned on the surface of the mold in contact with the reinforcement. These rods pass through the reinforcement as it mates with the surface of the mold, thereby assisting with the transfer of the reinforcement between the gripper and the mold.

(43) For preference, regulating to a specific temperature (higher than the average temperature of the mold) makes it possible to avoid excessively rapid cooling of the reinforcement (for example: zone at 60 C. whereas the rest of the mold is at 11 C.)

(44) The robot thus places the reinforcement at the surface of a blow-molding mold.

(45) During a next step (not illustrated), the tank is blow-molded, causing the reinforcement to be overmolded by contact and pressure with the molten parison.

(46) In the embodiment of FIG. 10, the two same shells 1 and 1 as before are depicted spaced apart, under an extrusion head 5 that produces a sheet or tubular parison 4.

(47) The two shells 1 and 1 are used to carry out a method of manufacturing a fuel tank.

(48) According to this method, the sheet 4 of thermoplastics material leaves the extrusion head 5 in an at least partially molten state. It enters between the two shells 1 and 1, namely enters a blow-molding mold consisting of these two shells and possibly of a core (not depicted).

(49) The sheet 4 is intended to be blow-molded in the blow-molding mold (when the two shells have been brought together) by blow-molding using a blowing gas.

(50) In the step depicted in FIG. 10, this blow-molding has not yet taken place.

(51) A fibers reinforcement 3 comprising both a thermoplastics material compatible with that of the sheet 4 and chopped fibers or long fibers or continuous fibers which may or may not be woven is introduced into the blow-molding mold using a mobile element 30 which may be borne by a robot external to the mold (not depicted) or by a core of the mold (not depicted). The mobile element may for example be an actuator fixed to the core. The mobile element 30 ends in a shape 32 which in this instance is planar but more generally is adapted to suit the part of the interior face of the shell 1 against which the sheet 4 will be pressed under the pressure of said shape 32.

(52) The mobile element comprises means of gripping the fibrous reinforcement, which means are not detailed here.

(53) In this instance, the fibrous reinforcement has been heated beforehand to bring it into the mold in a molten state. However, this heating could take place while the reinforcement 3 is being transported by the mobile element 30 or prior to this transporting. An optional means 2 maintains the temperature of the region of the shell 1 near to the fibrous reinforcement 3.

(54) As can be seen in FIG. 10, the mobile element 30 has the function of pressing the reinforcement 3 against a face of the sheet 4 opposite to the interior face of the shell 1.

(55) During this pressing, the fibrous reinforcement 3 becomes welded to the sheet 4 which is in an at least partially molten state.

(56) Welding may be complete right from this stage of operations. As an alternative, welding is perfected by applying the pressure of the blow-molding gas to the sheet 4 when the latter is being shaped by blow-molding against the two shells.

(57) In another alternative form that is compatible with the preceding one, the fibrous reinforcement 3 is pressed against the sheet 4 after the step of blow-molding the sheet 4.