Corrugated plastic pipe e.g. for use in motor vehicle has bend created by welding or sticking corrugation rings together on one side

The present invention relates to an elbow pipe which can be used, for example, to form a pipe for transporting fluids. This pipe is intended in particular for motor vehicles to equip the cooling circuit of the heat engine thereof. The subject of the invention is also an intermediate product in the form of a straight pipe and a method for bending this intermediate product.

It is known to produce fluid transport pipes in thermoplastic material from a corrugated or semi-annealed tube having sufficient flexibility to be bent in order to comply with a predefined path in the engine environment of the vehicle. These tubes are generally produced by means of an extrusion machine at the outlet of which they are in a rectilinear form before being bent and hot formed. However, these ringed tubes exhibit high elongations under the combined action of temperature and a mechanical stress such as the pressure of the fluid transported or such as traction exerted on the tube. In addition, these tubes, which are generally polyamide 12 monolayer, are relatively expensive.

According to the invention, there is provided a pipe which has great flexibility in forming to produce very tight angles and radii and which has a low elongation of the ringed zones after forming.

The pipe according to the invention comprises at least one bend, at least two adjacent rings at the bend and a means for connecting the rings to one another on an inner side of the bend.

Thus, the connection of the rings together ensures the conservation of the geometry of the elbow even when stresses are exerted on the pipe, by opposing any variation in the distance separating them.

According to a first embodiment, the rings are welded to each other on the inner side of the elbow.

The connection of the rings together can then be achieved without requiring the addition of elements external to the pipe and therefore without making it heavier. This embodiment is also particularly simple.

According to a second embodiment, the pipe comprises an outer tube extending at least over the elbow and having internal surface portions fixed to the rings.

The bond thus provided between the rings is particularly strong.

The invention further relates to intermediate products for making the above bent pipes.

The invention also relates to a method for forming an elbow on an intermediate product comprising a substantially rectilinear pipe comprising an outer layer of a material which has a predetermined softening temperature and which is capable of being welded to itself at a temperature. greater than or equal to this softening temperature, the process comprising the steps of:

- bend this pipe and heat the bent area to a surface softening temperature of the pipe to bring the adjacent corrugations into contact with each other on the side of the latter inside the elbow so that they are welded to them- same,

- cooling the pipe, the corrugations preferably being kept in contact against each other during cooling.

The combined action of the heating and the curvature of the pipe makes it possible to make the connection between the corrugations without requiring additional operations.

The subject of the invention is also a method for forming an elbow on an intermediate product comprising a substantially rectilinear pipe comprising an inner tube having coaxial corrugations and a smooth outer tube, the outer tube being of a heat-shrinkable material which is able to be welded to the outer surface of the inner tube and has in a retracted state an inner diameter at most equal to the outer diameter of the inner tube and in an expanded state an inner diameter greater than the diameter outer inner tube, the method comprising the steps of:

- bend this pipe and heat the bent area to cause retraction of the outer tube and softening of the inner surface of the outer tube so as to weld portions of the inner surface of the outer tube to the rings of the inner tube,

- cool the pipe.

Thus, the positioning of the outer tube on the inner tube prior to retraction is easy. Further, during retraction, the elasticity of the outer tube tends to press the inner surface thereof against the inner tube corrugations, which facilitates the welding of the inner surface portions to the corrugations.

Preferably, the outer tube comprises an inner layer of a material having a predetermined softening temperature and an outer layer of a material having a heat shrinkage temperature substantially equal to the softening temperature.

A single heating operation then ensures the retraction of the outer tube and the welding thereof to the rings of the inner tube.

Other characteristics and advantages of the invention will emerge on reading the following description of particular non-limiting embodiments of the invention.

Reference will be made to the accompanying drawings, among which:

- Figure 1 is a cross section of a pipe according to a first embodiment of the invention;

- Figure 2 is a longitudinal section of a bent portion of this pipe;

- Figure 3 is a cross section of the inner tube of a pipe according to a second embodiment of the invention;

- Figure 4 is a cross section of the outer tube of this pipe, in an expanded state;

- Figure 5 is a longitudinal section of a bent portion of this pipe.

In accordance with the first embodiment of the invention and with more particular reference to FIG. 1, the pipe is generally designated as 1 and is of the ring type.

The pipe 1 is multilayer and comprises from the outside to the inside layers 2, 3, 4, 5 (it will be noted that these layers are not detailed in FIG. 2 for reasons of clarity thereof).

The outer layer 2 is made of a material which can be welded to itself which has a predetermined surface softening or contact welding temperature. This material may be an elastomeric thermoplastic such as a mixture of polypropylene, SEBS or SBS with parafinic oil, or any other thermoplastic material having similar weldability characteristics, for example a common polyethylene, a high density polyethylene or a low density polyethylene. . This material is here a thermoplastic elastomer such as one of those whose references follow:

- MULTIFLEX G85 or G70 from MULTIBASE,

- TEFABLOC chosen from the TO STD, TS categories

STD, TE 500, 600, 700 or 800, produced by the company LVM 'COUSIN TESSIER,

- BERGAFLEX produced by the company CTE MA HANNA

COMPANY.

Layer 3 is made of a thermoplastic material having adhesion properties with layer 2 and having a softening temperature higher than those of outer layer 2. This material may be a polyolefin such as a polypropylene, for example of the MOPLEN EPD60R type produced by MONTELL, ELTEX PHL 4 02 from SOLVAY, or BA202 from BOREALIS.

Layer 4 is made of a thermoplastic material compatible with that of layers 3 and 5 so as to ensure the cohesion of these layers. This material is for example a modified polyolefin such as a grafted polypropylene with chemical functions compatible with the layer 5. The material is here chosen from those whose references follow:

- ADMER selected in the QF550E categories,

QB510E, AT843E, AT1190E, AT1657E, AT1658E, QF551E from the company MITSUI CHEMICALS,

- GRILON XE3153 or CR8E from the company EMS CHEMIE,

- BYNEL of the 5000 series and in particular 50E571 or 50E725 from the company DUPONT DE NEMOURS.

The inner layer 5 is made of a thermoplastic material chemically resistant to the fluids conveyed, such as a polyamide 12 stabilized against glycolysis and hydrolysis, and for example one of those whose references follow:

- GRIMALID L25ANZ or XE3721 from the Company EMSCHEMIE,

- RILSAN type A MA 4650, A M-AESN P210 T6L, or A M-AESN P110 T6L from ATOFINA.

This multilayer structure makes it possible in particular to limit the quantity of polyamide used and to keep the cost of the pipe low.

The pipe 1 is produced in a manner known per se by coextrusion then molding at the outlet of the extrusion machine.

With reference also to FIG. 2, the tube is then bent and then hot formed.

The material of the outer layer 2 has a contact solder temperature less than or equal to the forming temperature of the pipe and the material of the layer 3 and preferably the materials of the other layers have a softening temperature higher than the forming temperature pipe 1.

Due to the deformation of the tube, the rings Ί of the pipe 1 come into contact with each other in the zones 6 inside the bend. The pressure resulting from the contacting of the rings and the forming temperature then allow the outer layer 3 to melt superficially and to weld to itself at the level of the zones 6. Since the layers 3, 4 and 5 are not softened at the forming temperature, they retain a sufficient modulus of elasticity to exert the pressure necessary for the welding of the rings. In addition, the modulus of elasticity being preserved, the thickness of these layers is not substantially affected by these operations.

The pipe 1 is then cooled. During the cooling, the pressure of the corrugations against each other is maintained.

The elbow is thus fixed and the welds 6 prevent the ringed zone from stretching out.

According to the second embodiment of the invention and with reference to Figures 3 to 5, the pipe 10 comprises an inner tube generally designated 11 and an outer tube generally designated 12.

With particular reference to FIG. 3, the inner tube 11 is corrugated and of the multilayer type.

The inner tube 11 comprises from the outside to the inside of the layers 13, 14, 15, 16 (it will be noted that these layers are not detailed in FIG. 5 for reasons of clarity thereof).

The outer layer 13 is made of a weldable material which has a predetermined surface softening or contact weld temperature. This material may be an elastomeric thermoplastic such as a mixture of polypropylene, SEBS or SBS with parafinic oil, or any other thermoplastic material whose weldability characteristics are similar, for example a common polyethylene, a high density polyethylene or a low polyethylene. density. This material is here a thermoplastic elastomer such as one of those whose references follow:

- MULTIFLEX G85 or G70 from MULTIBASE,

- TEFABLOC chosen from the categories TO STD, TS STD, TE 500, 600, 700 or 800, produced by the company LVM COUSIN TESSIER,

- BERGAFLEX produced by the company CTE MA HANNA

COMPANY.

The layer 14 is made of a thermoplastic material having adhesion properties with the layer 13 and having a softening temperature higher than the softening temperature of the outer layer 12. This material can be a polyolefin such as a polypropylene, for example from MOPLEN EPD60R type produced by the company MONTELL, ELTEX PHL 402 from the company SOLVAY, or BA202 from the company BOREALIS.

Layer 15 is made of a thermoplastic material compatible with layers 14 and 16 so as to ensure the cohesion of these layers. This material is for example a modified polyolefin such as a grafted polypropylene with chemical functions compatible with the layer 16. The material is here chosen from those whose references follow:

- ADMER selected in the categories QF550E, QB510E, AT843E, AT1190E, AT1657E, AT1658E, QF551E from the company MITSUI CHEMICALS,

- GRILON XE3153 or CR8E from the company EMS CHEMIE,

- BYNEL of the 5000 series and in particular 50E571 or 50E725 from the company DUPONT de NEMOURS.

Layer 16 is made of a thermoplastic material chemically resistant to the fluids conveyed, such as a polyamide 12 stabilized against glycolysis and hydrolysis, and for example one of those whose references follow:

- GRIMALID L25ANZ or XE3721 from the Company EMSCHEMIE,

- RILSAN type A MA4650, AM-AESN P210 T6L, or AM-AESN PI10 T6L from ATOFINA.

Referring more particularly to Figure 4, the outer tube 12 is smooth and comprises an outer layer 17 and an inner layer 18 (it will be noted that these layers are not detailed in Figure 5 for reasons of clarity thereof) .

The outer layer 17 is formed by a heat-shrinkable material having an olefinic base compatible in extrusion with the material of the inner layer 18.

The inner layer 18 is formed by a material compatible in coextrusion with the outer layer 17, and compatible in heat welding with the material of the outer layer 13 of the inner tube 11. The inner layer 18 may be made of a thermoplastic elastomer material. such as one of those which may constitute the outer layer 13.

The outer tube 12 has in its expanded state (visible in Figure 4) an inner diameter greater than the outer diameter of the inner tube 11 and in a retracted state an inner diameter less than the outer diameter of the inner tube 11.

The process for producing the pipe 10 consists in producing the inner 11 and outer 12 tubes separately by coextrusion. The inner tube 1 is obtained in a manner known per se by coextrusion and then molding at the outlet of the extrusion machine.

Then, the outer tube 12 is threaded over the inner tube 11. The assembly thus formed is then placed in the forming mold.

The hot forming is carried out at a temperature greater than or equal to the welding temperature of layers 13 and 18 and at a temperature greater than the heat shrinkage temperature of the outer tube 2. The material of the layer 14 and preferably the materials of the others layers 15 and 16 have a softening temperature higher than the forming temperature of pipe 10.

During forming, the outer tube 12 retracts onto the inner tube 11 (see Figure 5) and the layers 13 and 18 weld to each other by the combined effects of temperature and pressure exerted by the retraction of the outer tube 12. The rings 19 are then welded to the inner surface of the inner layer 18 of the outer tube 12.

After cooling, the assembly is bonded by welding. The outer tube 12 acts as an element for blocking the elongation of the ringed zones under the effect of the pressure of the fluid inside the pipe.

Alternatively, the outer layer 13 is made of a material weldable to itself so that the rings 19 of the inner tube 11 weld against each other during forming in a manner analogous to the first embodiment.

Of course, the invention is not limited to the embodiment described and it is possible to provide variant embodiments without departing from the scope of the invention as defined by the claims.

In particular, the term “corrugation” will be understood to mean annals extending either over the entire circumference of the pipe or over a part thereof only. Likewise, the pipe can be corrugated over its entire length or only over part of it, at the elbow.

Further, the pipe according to the invention may result from a kinematic reversal of the described embodiments, i.e. the corrugations may be connected on an outer side of the bend in order to prevent their coming together. so as to maintain the curvature of the elbow.

In addition, the rings can be glued to each other instead of being welded.

A groove bonding gutter can be used instead of the heat-shrinkable outer tube.