FR2690376A1 - Plastic hollow parts assembled from two half shells - obtd. by pressure over-moulding along their assembled flanges to form reinforcing channel ensuring consistent mechanical strength - Google Patents

Abstract

A hollow plastic part (1), that has to have mechanical resistance, is made by pressure moulding two half shells (2,3) each with assembly flanges (4,5) and joining them along these flanges. After assembly a second pressure moulding step is carried out to form a reinforcing channel (15) around the two assembled flanges (4,5). ADVANTAGE - A simple, quick, low cost mfg. method c.f. lost core moulding. Also overcomes weakness of bonding or welding half shells that can reduce strength to 15-20% in joint area and gives consistent mechanical strength.

Description

 The present invention relates to a method for manufacturing a hollow plastic body, and more particularly to a method for manufacturing a hollow plastic body intended to have a predetermined mechanical strength.

The present invention also relates to a hollow body produced by implementing the above method
It is known to produce by molding plastic material under pressure a hollow body of a single piece of simple shapes having a predetermined mechanical strength. This plastic material is molded by injection or compression in the molding space provided between an inner core and an outer mold consisting, for example, of two parts which are assembled around the core.

 This simple and economical method is only suitable for hollow bodies of simple shapes, for example tanks, cans, vases, etc. It does not allow hollow bodies of complicated shapes to be produced.

 It is also known to make hollow bodies from a single piece of complicated plastic shapes by implementing a pressure plastic molding process using a fusible or soluble core, which is made to disappear after the operation. molding itself. This process gives satisfaction to its users, but its implementation is relatively long, delicate and expensive, because it requires high investments.

 We also know, to produce a hollow plastic body, the method comprising the steps which consist in producing, by molding plastic material under pressure, at least two half-shells each provided with an assembly flange, and assemble these half-shells along their respective flanges.

The assembly of the flanges can be carried out, for example, by gluing or by welding. The implementation of this process is simple, quick and economical, and allows hollow bodies of complicated shapes to be produced.

 It is known that, in a hollow body obtained by this latter process, the admissible mechanical stress of the assembly zone, constituted by the flanges welded against each other, is only equal to a small percentage, of on the order of 15 to 20%, of the admissible stress for the rest of the hollow body. It is even lower in the event of sticking.

 This process therefore does not make it possible to produce hollow bodies intended to have a high mechanical strength.

 The object of the present invention is to remedy the drawbacks of known methods and to propose a method of the aforementioned type making it possible to produce hollow bodies made of plastic material having a predetermined mechanical strength, while being simple, rapid and relatively inexpensive to use. expensive.

 Another object of the invention is to provide a hollow plastic body of complicated shapes, having a predetermined mechanical strength while being simple, quick and relatively inexpensive to produce.

 According to the invention, the method of the aforementioned type is characterized in that it further comprises, after the assembly step, a step consisting in carrying out a second plastic molding operation under pressure on the assembled hollow body for forming a reinforcing cord covering the two assembled flanges along at least part of the length thereof.

 The reinforcing cord, which covers the two flanges assembled in the manner of a hoop, reinforces the assembly area. It can be easily designed to give this assembly zone, which constitutes the zone of least resistance of the hollow body thus produced, the predetermined mechanical resistance desired for this hollow body.

 The assembly area, which is essentially peripheral, is easy to access and relatively simple in shape.

 In addition, the quantity of plastic material necessary to produce this reinforcing bead, the thickness of which remains small, is small. On the other hand, the external shape of the bead is generally unimportant, so that one can use for the second molding operation molds machined relatively easily and relatively simple shapes.

The second molding operation is therefore a simple, rapid and inexpensive operation.

 Furthermore, a calculation of the resistance of the structure of the hollow body makes it possible to optimize the design of the hollow body by taking account of the second molding operation. We can thus give this hollow body a relatively regular mechanical resistance in all its points, and minimize the total amount of plastic material used and therefore the final cost of producing said hollow body.

 According to a preferred embodiment of the invention, there is provided, in the second molding operation, an additional quantity of plastic material at locations in the hollow body other than the flanges proper to reinforce or complete said hollow body.

 It is thus possible to mold, under excellent conditions of implementation and cost, protruding elements such as ribs, reinforcements of all kinds, legs, etc. to reinforce or complete the hollow body.

 This is particularly appreciable in the abovementioned perspective of optimizing the structure and the final cost of the hollow body considered: in fact, specialists in this field will appreciate that such elements are not easy to produce economically in a single molding operation. .

 It is thus possible to design and optimize a hollow body, not only according to the sole conditions of its production by molding, but also according to the conditions of its insertion in a complex technical environment.

 According to another aspect of the present invention, the hollow body of the aforementioned type is characterized in that it is produced by implementing the method of the invention.

 According to a preferred embodiment of the invention, this hollow body is an air intake manifold for an internal combustion engine.

 Other features and advantages of the present invention will appear in the detailed description below.

In the accompanying drawings, given only by way of nonlimiting examples
- Figure 1 is a top view of a hollow body according to a preferred embodiment of the invention;
- Figure 2 is a side elevational view of the hollow body of Figure 1
- Figure 3 is an enlarged partial view in section on III-III in Figure 1
- Figure 4 is a view similar to Figure 3 according to IV-IV in Figure 1 of an alternative embodiment of the present invention
- Figure 5 is a view similar to Figure 3 schematically a mold for the implementation of the second molding operation;
- Figure 6 is a view similar to Figure 3 of another alternative embodiment of the present invention.

 In the embodiment shown in FIGS. 1 and 2, an air intake manifold for an internal combustion engine is generally identified by the reference number 1. This manifold 1, intended in this example for a diesel engine (not shown), is intended to be placed above the rocker cover (not shown) of this engine. Such a collector is subjected to mechanical, vibratory, chemical, thermal stresses.

The collector 1 is produced, in a known manner, in the following manner
at least two half-shells 2, 3 are produced by molding plastic material under pressure, each provided with an assembly flange 4, 5, and
- these half-shells 2, 3 are assembled along their respective flanges 4, 5.

 The half-shells 2, 3 are produced by molding plastic material according to the techniques of hot injection or compression.

 The plastic material can be a thermoplastic material, or a thermosetting material, or another suitable material, for example bakelite. It can be loaded with fibers, for example glass fibers, and include a mineral filler, for example talc. The glass fiber load can be between 15% and 50%, or exceed 50%.

 The assembly is carried out by known techniques, for example by welding by linear or angular friction or by ultrasound, by thermal welding by conduction or induction, by gluing, in particular when the material used is not weldable.

 In the example considered, the plastic material is of the thermoplastic, polyamide, PPS (phenylene polysulfide) or all other polymers type, loaded with glass fibers: it is known that polyamide, for example nylon 6-6, has good mechanical characteristics, but poor resistance to temperature. On the contrary, PPS has, compared to nylon, superior mechanical characteristics and excellent thermal resistance for a higher price.

 As shown in the figures, the manifold 1 comprises a section of central tube 6 for air intake, intended to be connected to an air filter and, if necessary, to a compressor (not shown). The section 6 opens into a transverse distribution pipe 7 from which four curved conduits 8, 9, 10, 11 leave, intended to supply air respectively to the four cylinders of the engine in question.

 The upper half-shell 3 carries the central section 6. The lower half-shell 2 carries the tubular sections 8a, 9a, 10a, 11a for connecting the conduits 8, 9, 10, 11 downstream, as well as spacers of stiffening 12, 13, 14, located respectively between the tubular sections 8a and 9a, 9a and lova, 10a and lla.

 The spacers 12, 13, 14 are each pierced with a hole, respectively 12a, 13a, 14a, allowing for example the fixing of the manifold 1 to an azl member not shown.

 There are thus two flanges 4, 5 of relatively simple shapes in space, and two half-shells 2, 3 of relatively complex shapes which can be produced easily by conventional molding.

 According to the invention, after the step of assembling the half-shells 2, 3, a second plastic molding operation was carried out under pressure on the collector 1 assembled to form a reinforcing bead 15 covering the two flanges 4, 5 assembled along at least part of the length thereof.

 It can thus be seen that the cord 15 comprises, in the example shown, the sections 15a, 15b, 15c, 15d, 15e, placed around the sections of the flanges 2, 3 situated respectively at the periphery of the transverse tube 7 and around downstream ends of the conduits 8, 9, 10, 11.

 It can also be seen in the figures that, in the same second molding operation, an additional quantity of plastic has been added to locations in the manifold 1 other than the flanges 4, 5 proper to reinforce or complete the manifold 1: fixed on the upper part of the tubing 7 a lug 16 pierced with a hole 16a; similarly, the cord 15 comprises, at one end of the tubing 7, an outward projection 17 constituting another hooking tab pierced with a hole 17a.

 Another example would consist in coming to report in a hole to come to the molding the arrival of a pipeline, for example the arrival of the pipeline intended for the recycling of exhaust gases.

 We know that it is not easy to produce in a single molding operation a half-shell provided with a tab such as the tab 16 extending in the direction of the thickness of said half-shell: in fact , a molded part is all the more regular and homogeneous as its thickness is itself regular and homogeneous or varies only very gradually.

 It is therefore entirely desirable to carry out, during the second molding operation, all the elements projecting from the normal external surface of the molded part, such as lugs, supports, various reinforcements in the form ribs or extra thicknesses, etc., with the fitting of inserts of any shape and nature if necessary, crossing or not crossing the wall of the molded part.

 The plastic material used for the second molding operation can be different from the plastic material in which the half-shells 2, 3 are made: it can be different in nature, or different in its mechanical characteristics: it can then be of the same nature and have a different filler, for example a different fiber content.

 In known manner, it is possible to carry out an operation of preparing the surfaces intended to receive a new supply of plastic material, before carrying out the second molding operation on said surfaces.

 These surfaces can thus be prepared by the action of a solvent for the molded material, or of a primer: this improves the adhesion of the new addition of material. If a plastic material different from that in which the half-shells 2, 3 are used for the second molding operation, the primer is chosen so that it is suitable for the two plastics.

 It is obviously possible to check the tightness of the collector after the first or, preferably, the second molding operation.

 Generally, a structural strength calculation makes it possible to determine, according to the specifications defined for the part to be produced, the nature and the thickness of the plastic material to be used in the first molding operation. , the location of the plastic inputs to be used in the second operation, the nature of this plastic and the dimensions of these inputs.

 In the embodiment shown in Figure 3, each of the flanges 18, 19 is designed so that its outer edge has a flange 20, 21 projecting substantially in the direction away from the assembly surface of said flange with the other flange.

 A reinforcing cord 22 of substantially C-shaped section is thus formed covering the projecting flanges 20, 21 and the flanges 18, 19 up to the outer surface of the half-shells 2, 3. The cord 22 is thus firmly anchored on the two flanges 18, 19. In addition, the withdrawal of the plastic material from the cord 22 upon cooling causes said cord 22 to clamp the two flanges 18, 19 against each other, which improves the tightness of said flanges . The cord 22 has a radial protuberance 24 serving as a hooking tab.

 In the embodiment of FIG. 4, the bead 23 is molded in one piece with a peripheral transverse rib 25 of the lower half-shell 2. The upper half-shell 3 has received a section of peripheral transverse rib 26 separated from the bead 23.

 In the embodiment of FIG. 5, a two-part mold 27, 28 has been shown schematically around the flanges 18 and 19, enclosing the flanges 20, 21 and resting, above all for sealing reasons, on the inclined flats 36, 37 of the half-shells 2 and 3. Such a mold makes it possible to produce a cord 29 in the form of a C, the ends of which completely fill the space between each of the flanges 20, 21, and the outer surface of the corresponding half-shell 2, 3. . The plastic injection channel is shown diagrammatically at 30.

 In the embodiment of FIG. 6, and in a known manner, the lower flange 31 has, on its face opposite the upper flange 32, a longitudinal rib 33, while the upper flange 32 has, on its corresponding face, a groove conjugate 34 adapted to receive the rib 33. These two flanges can be assembled by vibration welding in the radial direction shown diagrammatically by the double arrow 35. It is known that such flanges are capable of constituting an assembly, by gluing or by welding, having better sealing and mechanical resistance characteristics than the assembly of ordinary flat flanges.

 We have thus described a hollow body of complicated shapes, namely an air intake manifold, which can be produced very easily from two half-shells molded from plastic and assembled along their respective flanges. The assembly zone, which constitutes a zone of least resistance of this hollow body, is reinforced by molding a reinforcement bead which can be calculated so that this assembly zone has a mechanical resistance equivalent to that of the rest of the body hollow. One can realize, in the second molding operation, all other elements serving as reinforcements, fixing lugs, bearing surfaces, etc ... allowing both the fixing of the hollow body on a support as the fixing of other elements on said hollow body.

 It is thus possible to conceive of the air intake manifold described above as a complete sub-assembly provided with elements allowing both its attachment to the engine and the attachment or support of other elements to the manifold.

The Applicant has calculated the following comparison elements for the same air intake manifold:
- a collector made by injection of plastic material with soluble or fusible core at a cost price P and can withstand a burst pressure F
- the same manifold manufactured by injection of two half-shells assembled by welding along their respective flanges at a cost price of the order of P / 2 and can withstand a burst pressure of the order of F / 3 , which is insufficient compared to the specifications of many manufacturers
- The same collector, manufactured according to the method of the present invention, has a cost price of around 6P / 10 and can withstand a burst pressure of around F, which is sufficient for said notebooks of charges.

 Of course, the invention is not limited to the embodiments which have just been described, and many changes and modifications can be made to them without departing from the scope of the invention.

 Thus, a hollow body can be produced by assembling more than two molded parts. The shape of the flanges can be any, and the choice of materials can be adapted at will to the conditions of use provided for the hollow body considered.

 It is also possible to incorporate into said hollow bodies, in any of the molding steps, a prefabricated insert of any kind and shape adapted to the conditions of use and to the functions provided for said hollow body.

 It is likewise possible to produce other hollow bodies of complicated shapes subjected to mechanical, chemical, thermal, vibratory stresses, in particular other hollow bodies intended to be housed under the hood of the engine of a motor vehicle, for example degassing boxes, these hollow bodies being designed as complete sub-assemblies.

Claims (9)

 1. Process for manufacturing a plastic body (1) intended to have a predetermined mechanical resistance, this process comprising the steps which consist in producing, by pressure plastic molding, at least two half-shells (2, 3) each provided with an assembly flange (4, 5; 18, 19 31, 32), and to assemble these half-shells (2, 3) along their respective flanges (4, 5; 18, 19 ; 31, 32), characterized in that it further comprises, after the assembly step, a step consisting in carrying out a second plastic molding operation under pressure on the hollow body (1) assembled to form a reinforcing cord (15, 22, 23, 29) covering the two assembled flanges (4, 5; 18, 19; 31, 32) along at least part of the length thereof.  2. Method according to claim 1, characterized in that, in the second molding operation, an additional quantity of plastic material is provided at places in the hollow body (1) other than the flanges themselves (4, 5; 18 , 19; 31, 32) to reinforce or complete said hollow body (1).  3. Method according to one of claims 1 or 2, characterized in that the two half-shells (2, 3) are assembled by gluing or welding their respective flanges (4, 5; 18, 19; 32, 33 ) one against the other.  4. Method according to one of claims 1 to 3, characterized in that each flange (18, 19) is formed so that its outer edge has a flange (20, 21) projecting substantially in the direction s 'moving away from the assembly surface of said flange with the other flange.  5. Method according to claim 4, characterized in that a reinforcing bead (22, 23, 29) of substantially C-shaped section is formed covering the projecting flanges (20, 21) of the two flanges (18 , 19).  6. Method according to one of claims 1 to 5, characterized in that one uses for the second molding operation a plastic material different from the plastic material in which are made the half-shells (2, 3).  7. Method according to any one of claims 1 to 6, characterized in that an operation is carried out to prepare the surfaces intended to receive a new supply of plastic material before proceeding to the second molding operation on said surfaces. .  8. Hollow body (1) made of plastic, characterized in that it is produced by implementing the method according to one of claims 1 to 7.  9. Hollow body according to claim 8, characterized in that this hollow body is a manifold (1) of air intake for internal combustion engine.