Method for forming a welding spout on a parison during the blowing of a tank

Abstract

The invention relates to a tank of plastics material produced by blow-molding of a parison, incorporating a welding spout, of a shape projecting from its outer surface which has an edge configured to be welded to a corresponding edge of an attached part, the welding spout ending axially, on an inside of the tank, in a shape resulting from contact molding between the parison and a molding component, in which the welding spout ends axially on an outside of the tank in a shape resulting from contact molding between the parison and a molding component.

Claims

1. A tank of plastics material produced by blow-molding of a multilayer parison comprising at least a barrier layer, incorporating a welding spout, of a shape projecting from the outer surface of the tank, the welding spout having an external radial shape resulting from contact molding between the parison and a spout mold, the welding spout ending axially, on an inside of the tank, in a shape resulting from contact molding between the parison and a first molding component, and in which the welding spout ends axially on an outside of the tank in a shape resulting from contact molding between the parison and a second molding component, the shape having an edge configured to be welded to a corresponding edge of an external attached part, the second molding component being different from the first molding component, both being configured to contact the multilayer parison during blow-molding allowing the edge to be welded of the welding spout to be distant from the barrier layer of the multilayer parison.

2. The tank as claimed in claim 1, wherein the welding spout ends axially on the inside of the tank in an internal rim in a shape of a ring.

3. The tank as claimed in claim 1, wherein the welding spout ends axially on the outside of the tank in a radial flat surface in a shape of a ring.

4. The tank as claimed in claim 3, wherein the welding spout comprises an internal rim in a shape of a ring set back from the flat radial surface.

5. The tank as claimed in claim 1, wherein the welding spout has a shape.

Description

(1) The invention will be better understood from a reading of the appended figures, which are provided by way of example and are not in any way limiting, in which:

(2) FIG. 1 is a view in elevation of a fuel tank provided with a filling pipe.

(3) FIG. 2 is a view in cross-section of a part II of the tank in FIG. 1, showing a welding spout in a first embodiment.

(4) FIG. 3 is a perspective view of the same part II, seen from above.

(5) FIG. 4 is a perspective and cross-sectional view along the plane III-III in FIG. 3,

(6) FIG. 5 is a view similar to that in FIG. 4, along a plane IV-IV perpendicular to plane III-IIII.

(7) FIG. 6 is a view similar to that in FIG. 2 of another embodiment of the invention.

(8) FIG. 7 is a view similar to that in FIG. 6, in a perpendicular cross-sectional plane.

(9) Reference is now made to FIG. 1, in which a tank 1 of generic shape may be seen. In reality the shape of the tank will depend on the vehicle, but this shape is of no importance in the context of the invention, which applies to tanks of all shapes. This tank will have been manufactured by the blowing of a parison, as is known, within a blowing mold (not illustrated). An example of such manufacture is described for example in EP 1110697 A2, the contents of which are incorporated in this description as a reference.

(10) The tank is a multilayer tank, of high density polyethylene (HDPE) with at least one layer of EVOH (partly hydrolyzed ethylene-vinyl acetate copolymer), which ensures a seal against hydrocarbons and is referred to as a “barrier layer”.

(11) Tank 1 comprises a filling pipe 3 which is intended to connect the fuel cap (not shown) of the vehicle to tank 1. Pipe 3 is connected to tank 1 by welding. For this purpose it comprises a material compatible with the material of which the tank is made, at least in the regions which are in contact with these two welded components.

(12) For welding with pipe 3 the tank has a welding spout 5, which can be seen in FIGS. 3 to 5.

(13) Welding spout 5 projects from the outer surface 7 of the tank, here in the form of a protrusion that is generally flared derived by revolution, which terminates axially in a radial planar surface 9 in the shape of a ring.

(14) Flat surface 9 is a welding surface, to which the end of filling pipe 3 is welded after the parison has been shaped by blowing in order to secure said filling pipe 3 to tank 1 in a strong leaktight manner.

(15) In FIG. 4 it will be seen that in addition to flat surface 9 welding spout 5 has an internal rim 11 on the outside of the tank which, like flat surface 9, faces the outside of tank 1. Internal rim 11 forms a ring of smaller diameters which lies set back from flat surface 9. It is flat and parallel to said surface 9. Because of the presence of internal rim 11, internal surface 13 of spout 5 ends in a shape which is generally flared, with a stepped cross-section. Flat surface 9 and internal rim 11 may have any shape, provided that they allow the welding spout to be used to connect the tank to an external accessory such as pipe 3, but in accordance with the invention these shapes result from contact molding between sheet 18 (or more generally the parison) and a molding element, as will be seen subsequently.

(16) On the inside of the tank the welding spout ends axially in a second internal rim 14, similar to first internal rim 11, that is to say forming a ring of smaller diameters set back from internal surface 8 of the tank. Internal rim 14 may have any shape, but in accordance with the invention it is the result of contact molding between sheet 18 (or more generally the parison) and a molding element, as will be seen subsequently.

(17) As will be seen in FIG. 5, the outer lateral surface 15 of welding spout 5 is cylindrical, except for two diametrically opposite grooves 17 which can be seen in FIGS. 3 and 4.

(18) These grooves 17 are used for positioning a finishing tool in order to perform finishing operations on the tank after it has been molded, and in particular the drilling of spout 5, as will be described subsequently.

(19) Furthermore these grooves 17 prevent the welding spout from having a shape derived by revolution, that is to say one which does not change throughout any rotation about its axis, which provides better mechanical strength for the welding spout according to tests performed by the inventors.

(20) The process as claimed in the invention will now be described through a particular and non-limiting embodiment.

(21) As described in EP 1110697 A2, a parison comprising two sheets 18 of multilayer plastics material is extruded from an extrusion die and is lowered into a mold (not shown).

(22) This mold comprises two matching halves, known as shells or molds or cavities, and a central insert which may be placed between two shells.

(23) In accordance with the known process, once the two sheets of the parison have been lowered between the cavities on either side of the insert, each of the two cavities closes on the insert in such a way as to close the mold for a first time. Excess pressure of gas, generally air, is then established between the insert and each sheet of the parison in such a way as to press the sheet against the internal wall of the cavity and impart shape to it. This stage is described as blowing. As blowing takes place, accessories previously installed on the insert and carried by suitably moving structures are advanced in the direction of one or other of the sheets, applied against the sheet and welded to it. This operation makes it possible to insert various accessories such as ventilation valves and pipes into the tank without having to insert them into the mold after molding. After this shaping the two cavities each bearing a sheet of the parison move away from the insert and the latter is withdrawn from between the two cavities. The two cavities are finally caused to approach each other in such a way as to close the mold for a second time, this time bringing the peripheries of the two sheets into contact, peripheries which weld to each other and form the tank.

(24) The invention to which this application relates is implemented in the course of performance of this known process during its blowing stage.

(25) It may be required to form a welding spout on one or both of sheets 18 of the parison, depending upon the desired functions for the tank. Here the invention only describes a single welding spout and a single sheet 18, but this indication is not in any way limiting.

(26) FIG. 2 illustrates two moving inserts 19 and 21 which will be described as moving plunger 19 and push member 21 on either side of the sheet 18 of the extruded parison. Push member 21 is carried by the insert (not shown, it is located below sheet 18 in relation to FIG. 2), while moving plunger 19 is carried by one of the two cavities (not shown, the cavity bearing moving plunger 19 is located above sheet 18 in relation to FIG. 2). Around moving plunger 19 the shell also comprises a spout mold 23, in two parts, 23A and 23B, which are capable of moving within the plane of the figure between a closed position which may be seen in FIG. 2 and an open position in which each of two parts 23A and 23B is separated from the other by a sufficient distance to allow the spout to be released from the mold after it has been shaped in spout mold 23.

(27) Spout mold 23, in combination with moving plunger 19, delimits a recess 31 for forming a welding spout. This recess 31 has an opening 25 which opens out opposite the insert.

(28) Push member 21 comprises a head 21A and a shoulder 21B. It faces opening 25 of recess 31. It is capable of adopting a first position set back from recess 31, which can be seen in FIG. 2, and a second position shown as a dashed line in FIG. 2 in which it occupies part of the opening 25 of recess 31. The movement of push member 21 from the aforesaid first position to the aforesaid second position is shown by arrow 27.

(29) Moving plunger 19 may also move as indicated by arrow 29 between a set-back position as shown in FIG. 2 and a forward position illustrated by a dashed line.

(30) Thus moving plunger 19 is capable of adopting a first position in which the volume of recess 31 is a maximum and a second position in which the volume of recess 31 is a minimum.

(31) In the second position, referred to as the forward position, moving plunger 19 bears against the plastics material of the parison and by molding imparts to it its final shape delimited by the dashed line on the side of the cavity of the mold.

(32) In the first position, referred to as the set-back position, moving plunger 19 allows the material of the parison to move forward in recess 31 if it experiences a thrust from the direction of the insert in the mold, in particular through the effect of the excess pressure during the stage of blowing the parison.

(33) In order to implement the invention the following stages are carried out during the blowing stage in a process for shaping a tank.

(34) In this stage the parison of two sheets 18 is extruded and each shape 18 is placed between the insert and each of the two cavities of the mold. The mold is closed onto the insert.

(35) Moving plunger 19 and push member 21 are placed in their first positions. Spout mold 23 is closed, in the position in FIG. 2.

(36) Subsequently air is injected under pressure between each sheet 18 and the insert to shape it to the shape of the cavity against which it is thus pushed. This blowing causes the plastics material of sheet 18 to flow towards and into recess 31. Sheet 18 then forms a hollow 18A on the side of the insert.

(37) While the material of sheet 18 is flowing towards the interior of recess 31 push member 21 is advanced into its second position, shown by a dashed line. The head 21A of the push member penetrates recess 31 and shoulder 21B bears against sheet 18. Sheet 18 then adopts a shape corresponding to the side of the insert, as indicated by the dashed line. In particular push member 21 plays the part of a molding component with regard to the sheet and forms a flat portion 30 corresponding to future internal rim 14.

(38) In a second operation, determined in relation to the operating conditions during blowing, which are defined in particular by the thickness of the parison, the duration and pressure of blowing, and the temperatures of the components present, moving plunger 19 is placed in its second position shown by a dashed line.

(39) Sheet 18 thus adopts the corresponding shape, with flat radial surface 9 in the shape of a ring and an internal flat surface 12 corresponding to future internal rim 11 previously described with reference to FIG. 4. In other words moving plunger 19 acts as a molding component with regard to sheet 18.

(40) Once push member 21 and moving plunger 19 have both reached their second position, they remain immobile until the end of the blowing stage. Depending upon the different parameters for molding the tank, the invention may take place throughout the entire blowing stage (in which case it begins at the same time as air is injected under pressure and ends when the blowing pressure ceases) or only part of the blowing stage (for example it may start after air has been injected and/or end before the blowing pressure ceases).

(41) After sheet 18 has been sufficiently cooled to allow the tank to be released from the mold, the two cavities of the mold separate, spout mold 23 opens and the tank is released from the mold.

(42) In a finishing operation the wall of the tank is then drilled out to its entire thickness between flat portion 12 and flat portion 30 so as to cut out the internal surface 13 of the spout and define internal rims 11 and 14. A drilling tool which is fastened onto grooves 17 of spout 5 is used for this purpose.

(43) In the embodiment illustrated in FIGS. 6 and 7 a push member 21′ whose head 21′A is smaller than that 21A of push member 21 previously described is used. Push member 21′ thus leaves lateral play between sheet 18 and head 21′A which makes it possible to control flow of the material in a better way when forming the welding spout.

(44) Having regard to distance A measured in the direction of movement of the push member between head 21′A of the push member and the cavity, distance B measured in a direction transverse to the movement of the push member between head 21′A of the push member and the cavity and distance C measured in the direction of movement of the push member between the shoulder of push member 21′B and the cavity, it will be found that ratio A/B is less than 4 and that the value of C is less than 6 mm.

(45) Measurements made by the inventors on tanks manufactured as claimed in the invention have shown that the barrier layer of the multilayer parison lies at a sufficient distance from surface 9 so that subsequent welding of this surface 9 to an attached part such as a pipe does not damage this barrier layer. This adequate positioning of the barrier layer within the wall of the tank is the result of the action of moving plunger 19, accentuated by that of push member 21, in the course of the blowing stage.

(46) Furthermore, with a multilayer parison comprising virgin material and ground up material (such as for example is obtained from the recovery of rejects), the distribution of the layers of the multilayer parison remains fairly uniform, whereas without the action of plunger 19 it has been found that virgin material tends to be lacking in the welding spout while ground up material tends to be present there in excess quantity.

(47) The invention is not limited to the embodiments presented and other embodiments will be clearly apparent to those skilled in the art.