FR2589981A1 - Continuous development of cellular insulation and sheathing for pipes - Google Patents

Abstract

Thermally insulated pipe is made by introducing the core pin into a cavity defined by two opposed series of split mould tools moving as continuous loops while a foam forming mix is introduced which will develop and stiffen before emerging from between the travelling moulds. The covered pipe passes on through an extrusion coating die which applies a continuous sheath of relatively dense but pref. at least partly expanded material (II).

Description

Method and device for the continuous production of
thermally insulated pipes and pipes thus produced "
The present invention relates to a method and a device for the continuous manufacture of thermally insulated pipes comprising a protective casing of synthetic material for the transport of liquid or gaseous fluid, hot or cooled, method according to which the pipe receives a protective casing in synthetic material, expanded, if necessary with a sheet acting as a separating agent relative to the device.

 Processes are known for manufacturing both continuously and discontinuously thermally insulated pipes, which are provided on the outside with a protective covering made of synthetic material.

Different methods among the known continuous methods, consist in passing in a fixed molding tube, pipes provided with spacers, in common, axec a tube formed of a sheet of synthetic material as a protective envelope; in the molding pipe, the edges of the plastic strip are joined and welded to form the tube formed by the sheet of synthetic material,
Just before introduction into the fixed molding tube. The mixture of synthetic material to be expanded is generally applied focusing the joining and welding of the overlapping edges of the strip of plastic material shaped into a tube; this mixture of synthetic material to be expanded is applied to the plastic band. During the passage through the fixed molding tube, the annular volume between the pipe and the protective outer covering, of tubular shape, expands . Where appropriate in this process, one can use instead of the pipe consisting of a sheet of synthetic material, an aluminum sheet reïêtée on its two faces of copolymers and to extrude the protective envelope after passage of the pipe provided with its foam, through the fixed molding tube using an extruder (DE-OS 33 07 865).

 However, these continuous processes could not be imposed in practice for large diameter pipes, because the frictional forces between the envelope or outer sheath and the fixed molding tube, forces generated by the pressure of the foam which are formed, are too large to allow rapid passage through the fixed molding tube, even if an additional slip agent is introduced between the outer casing and the fixed molding tube.

 Unlike these continuous processes, in practice, discontinuous processes are applied to pipes having lengths from 6 to 12 m and diameters from 20 to 60 mm, processes according to which the pipe is first provided with organs. spacers impermeable to foam, members provided at specified intervals and coated with a relatively thick plastic tube. The structure thus prepared is then expanded - little by little in an inclined position.

The thickness of the plastic tube depends on this process on the expansion pressure, because this pressure is not only intended to form the outer shell but at the same time to serve as a "mold". For this reason, the plastic tube must be strong enough to absorb the expansion pressure of the foam. The disadvantage of this process is thus not only the necessity of using a thick plastic tube, but also the fact of not obtaining regular foam due to the expansion in the inclined position; furthermore, the foam has a relatively high density. In addition, this discontinuous process is not economical.

 The present invention thus aims to create a method and a device for manufacturing large diameter pipes, continuously, efficiently while saving material for the production of the outer envelope and forming a regular foam of low density, constituting an effective thermal insulation layer.

To this end, the invention relates to a method of the above type characterized in that a) the pipe to be surrounded is introduced with an expanded mass,
continuously in a tubular cavity formed by a
double belt conveyor molding installation
molding while inducing expansion axially at
center, b) the mixture of synthetic material likely to be
expanded, being regulated so that it is sufficiently
hardened and can exercise a support function of the
hose in case the hose could bend or bend
under the effect of its own weight, and c) at the exit of the double conveyor installation
molding strip, the pipe provided with the expanded mass,
receives by extrusion through an extru
deuse calibrated under ide if necessary cooled,
a plastic sheath, expanded using
an annular nozzle, this envelope having a density
telex.

The double molding strip installation is known per se and is used, for example, for the continuous production of foam tubes, for insulation, split longitudinally according to DE-AS 12 66 485 or for the continuous production of two semi-tubular, expanded shells, which fold down and which are connected in the manner of a hinge by an outer sheet according to
DE-A 25 03 425.

The continuous production of insulating foam tubes, split lengthwise, according to
DE-AS 12 66 485 presents particular difficulties in holding the core which extends over the entire length of the molding channel formed by the two movable chains of mold blocks, the core which is necessary to form the internal volume of the pipe. foam insulation. It has in fact been found that even if the core was fixed firmly at the two ends, the pressure generated by the foam in the molding channel was so high that the core could not be maintained in the centered position over its entire length. To avoid such shifts, the core has also been provided over its entire length with a supporting, retaining plate which penetrates radially into the molding channel between the facing mold blocks.

The same remarks concerning the deflection of the core also apply to another known installation which uses as a core a stationary spindle which is only fixed at the entrance to the installation and penetrates freely into the external mold or fixed peripheral. In this case, the spindle fixed at one end does not have sufficient stability to absorb without bending the forces generated during the expansion. For this, reference is made to the explanations given in patent DE-A 25 03 425, column 3, line 49 and following. Due to the difficulty linked to the deflection of the spindle as indicated above, it has been proposed in another known installation according to
DE-AS 21 65 584, to control the deflection of the spindle using a laser beam and to carry out alignment corrections via adjustment and control elements, but this auxiliary installation does not makes it very difficult to achieve correct alignment of the core or internal, fixed spindle, and the entire installation is extremely complex and very unreliable.

 Based on the experience accumulated on such double-band installations forming chains of molding blocks in connection with the manufacture of foam insulation tubes, split longitudinally, it should be considered particularly surprising that with the aid of the process according to the invention using a double block molding installation of mold chains, pipes insulated by expanded synthetic material are obtained, in which the pipes themselves, of large diameter, are exactly fixed in position, coaxially in expanded foam without the need for spacers.

 The continuous process made possible by the application of the double chain belt installation of mold blocks allows continuous expansion on the pipes, offering the advantage that the foam envelope has a uniform structure over its entire length. bubble-free cells for low density; this not only guarantees regular mechanical resistance but also better lambda coefficients.

 The extruder placed downstream of the double chain installation with molding blocks and corresponding vacuum calibration devices also makes it possible to economically form the protective envelope of high density expanded synthetic material with a smooth outer film. In addition, the protective plastic cover can be made considerably thinner thanks to the invention process than in the discontinuous process set out in the preamble, because the pressure generated during the formation of the insulating foam layer thermal no longer has to be absorbed by the envelope or sheath of synthetic material.

Thus, in the method according to the invention, the functions of the envelope of synthetic material are limited to those of the density of diffusion and of protection against accidents during transport and installation. The expanded protective envelope decreases the weight, the price and increases the flexibility. This envelope is preferably made of polyethylene, polypropylene, polyvinyl chloride or the like and in particular has a density of 500 to 3800 kg / m.

 As the installation according to the invention is designed so that the pipes are centered automatically relative to the envelope or outer sheath, that is to say are concentric or coaxial, this makes it possible to dispense with all the spacing members or centering devices as they were necessary in the methods described in the prior art. This results in the advantage of eliminating the numerous thermal bridges, which considerably improves the thermally insulated pipe thus manufactured and makes it less expensive.

 The process according to the invention is suitable for all pipes which have to be thermally insulated, for example copper, steel or plastic pipes. In the case of copper or synthetic pipes, in the case of small diameters, for example diameters of 22 mm, these pipes can be unwound from a roll with a length of 50 meters or more, after having sent them appropriately to supply them practically continuously to the double-strip belt installation of molding blocks and after expansion and application of the plastic casing, they can be rewound again.

 In the case of plastic pipes of larger diameters than above, these pipes are produced in the most advantageous manner directly upstream of the device according to the invention, by extrusion so as to eliminate the handling of the pipes. At the outlet of the device according to the invention, the pipes which can no longer be wound on a roll are cut into thermally insulated pipes of appropriate length.

 Rigid pipes such as, for example, steel pipes or other metallic pipes are preferably used in the form of elements from 12 to 18 m which are connected Just before their introduction into the device according to the invention using sleeves made of material. synthetic, of a particular type to form an "endless cord" to be provided practically "continuously with a foam and to receive the same under the same conditions. After making the envelope, the pipes are cut again at the level sleeves, i.e. pipe connecting pieces using a special saw, the pipe connecting elements are designed so that after their removal when installing thermally insulated pipes, these elements free the pipe ends without foam insulation so that the pipes can be tightly and permanently connected by common pipe connecting elements, and then be insulated.

 In order to obtain the layer of thermally insulated foam, any synthetic material containing the appropriate propellants or starting elements forming the corresponding synthetic material can be used.

 Depending on the use, the layer of foam providing thermal insulation may be more or less flexible or rigid. It is for example advantageous to use flexible foams if the thermally insulated, "continuous" pipes are wound on a roll when they leave the device according to the invention. Pat against in the case of rigid pipes. it may be advantageous to form a hard foam.

 As suitable foams, there are preferably polyurethane foams, polyisocyanate foams, polyolefin foams, in particular polyethylene or polypropylene foams or also foams formed from suitable copolymers such as polystyrene foams.

 When forming polyurethane foams, whether flexible or rigid, it is necessary to use a separating sheet which is introduced into the double chain belt installation with molding blocks at the same time as the pipe so as to be applied against the molding blocks. Then, the annular volume is made to expand between the separation sheet and the pipe.

 As separating sheets, any type of sheet can be used, for example sheets of paper, plastic or metal. To achieve good separation, it is sufficient to use paper or a sheet of synthetic material as a separation sheet. If, however, other effects are sought, such as heat reflection or a vapor effect, it is advantageous to use a metal sheet, for example an aluminum sheet, one side or both sides are coated with paper. or synthetic material.

 In addition, in certain types of foam, such as, for example, polyethylene or polystyrene foam, there may be no separating sheet, since it may be sufficient to treat the channels of molding blocks, when they are returned using of a usual separation agent. If, on the return, we also have chains with cooled molding blocks, we can, by proceeding appropriately, obtain a film with a very homogeneous and relatively solid surface, which in some cases even makes it possible not to have an envelope. protective exterior in synthetic material.

 The introduction of the mixture capable of being expanded into the annular volume between the pipe and the separating sheet or the molding block channels is carried out in the usual manner as is for example described in document DE-OS 33 07 865 already described in the preamble in that the mixture capable of expanding is applied to the separating sheet which aims to join this sheet to form a tube.

The adjustment of the composition of the synthetic material capable of expanding, preferably the components A and
B to form the polyurethane foams is done so that shortly after the entry of the separation sheet shaped into a tube and provided with the mixture capable of expanding, in the installation with a strip of double chain with molding blocks, the expanded material fills the annular volume between the pipe and the separating sheet and at the same time maintains the pipe in a concentric position by the foam which in the meantime has become load-bearing.

The means necessary for this purpose are known to the specialist or can be determined without difficulty.

 If necessary, when surrounding the pipe with foam, one or more signaling means can be fixed in the foam at a certain distance from the pipe. These warning means are used to signal and locate moisture that has entered the foam layer.

 The method according to the invention also makes it possible to simultaneously expand several pipes insulated from one another and which are surrounded by the same protective envelope of synthetic material. Preferably, two pipes are placed in a protective casing made of synthetic material and these two pipes are isolated from one another, the section of such a structure preferably being oval and not circular. This arrangement is used, for example, for branches between the main pipe and users, so that the return and return pipes can be housed in the same assembly to reduce transport and installation costs.

The present invention will be described below using preferred embodiments shown in the accompanying drawings, in which
- Figure 1 is a schematic view from above of the main part of the device according to the invention.

 - Figure 2 is a schematic cross-sectional view of the double lugs with molding blocks of the installation comprising the blocks, the section being taken along line A-A of Figure 1.

 - Figure 3 is a cross section of a thermally insulated pipe according to the invention.

 - Figure 4 is a section at a pipe connecting element.

In FIGS. 1 to 4, the following references have been used in the description 1 pipe 2 feed roller supplying the sheet of
separation 3 separation sheet 4 expansion machine 5 double chain belt installation with block
molding Sa, Sb, 5a ', 5b' the molding blocks forming the chains 6 vacuum calibrated extruder 7 thermally insulated pipe 8 molding channel formed by the molding blocks Sa,
5b 9 structure for guiding the molding block chains 10 layer of thermal insulation foam 11 protective sheath of expanded synthetic material 12 pipe connection element.

 According to FIG. 1, the double chain belt installation with molding blocks 5, shown diagrammatically, comprises two mold halves which are distributed in separate molding blocks Sa, Sb, Sa ', 5b' and which move at speed. compliant along a straight path. The different molding blocks Sa, 5b are tightly pressed against each other and constitute the necessary molding channel; outside the manufacturing area, these blocks are returned in the form of separate molding blocks Sa ', 5bl (see FIG. 2) on the guide structure 9, in a known manner by being deflected and returned. molding Sa, 5b can be replaced to adapt to any choice of diameter of the pipe or of the thermal insulation foam envelope that it is desired to produce.

 According to a preferred embodiment of the invention, a flexible copper tube or a flexible plastic tube is unwound from a roller and introduced by a supply and support installation passing over a dressing tool. in a strip installation with a double chain of molding blocks 5 at the same time as the separation sheet 3 is taken from a supply roller 2; before entering the double chain molding block belt installation 5, the sheet 3 receives from the expansion machine 4 a mixture capable of expanding and the sheet is formed into a tube. the strip installation 5, the pipe 1 provided with the foam layer 10 supplied by the extruder 6 provided with a vacuum calibration device, receives on the separation sheet 3, a protective envelope made of expanded synthetic material 11, proper high density. The thermally insulated pipe 7, thus manufactured (see FIG. 3) is then wound up on a transport roller and is supplied at the place of use to be unwound from the roller and to be installed.

 According to another preferred embodiment of the invention, rigid, non-flexible pipes 1 are used, in particular pipes of larger diameter having lengths from 6 to 18 m, preferably lengths between 12 and 18 m; these pipes come from a store, not shown, to be supplied to a pipe feeding and holding installation, also not shown, and from there to the double chain belt installation of molding blocks 5 together with the sheet of separation 3 and the mixture capable of expanding, as described above.

 To allow continuous operation, the pipes 1 to be insulated are connected, using pipe connecting elements 12 such as that shown in FIG. 4 and are introduced in the form of an almost continuous bead in the tape installation 5. The pipe connecting elements 12 have an outside diameter and an inside diameter adapted to the corresponding pipe 1 as well as to the layer of foam 10 ensuring thermal insulation. At the outlet of the extruder 6 fitted with a vacuum calibration device and after the application of the protective plastic casing 11, the pipe connecting element 12 is sawn which does not appear at 1 outside using a controlled saw which cuts in the middle, transversely to the longitudinal axis. The thermally insulated pipes 7, thus separated, are supplied via a support frame to the installation of packaging and bundling. The pipe connection elements thus cut advantageously remain on the pipes 7, insulated, until these pipes are put in place and are only removed for a short time during assembly.

 It is clear that it is also possible to immediately remove the pipe connecting elements 12 from the insulated pipes 7 leaving the extruder 6 with a vacuum calibration device so that the unsawed connecting elements 12 can be used again, after removing the separating sheet 3 and the envelope of synthetic material 11 which cover them. The insulated pipes 7, from which the connecting elements 12 have been removed, can then be provided with other protective caps for their transport and this Until they are mounted, in case this is desired.

 Another characteristic arising from the use of the pipe connection element 12 used according to the invention is that after removal of this connection element 12, the pipe ends are immediately exposed or stripped to carry out the connections by standard, waterproof and permanent tube sleeves, as necessary.

Claims (7)

 10) Process for the continuous production of thermally insulated pipes provided with a protective plastic cover for transporting hot or cooled liquid or gaseous fluid, process by which a foam is expanded around the pipe if necessary using a sheet constituting a means of separation with respect to the device, and which is provided with a protective sheath of synthetic material, process characterized in that a) the pipe (1) is introduced to be surrounded by an expansive mass  placed continuously in a tubular cavity formed  by a double belt conveyor molding installation  molding (5) while inducing axial expansion  lying in the center, b) the mixture of synthetic material likely to be  expanded, being adjusted so that it is sufficiently  hardened and can exercise a support function of the  pipe (1) in case the pipe (1) could bend or get  fold under the effect of its own weight, and c) at the exit of the double conveyor installation  molding strip (5), the pipe (1) provided with the mass  expanded, receives by extrusion through  an extruder (6) calibrated under vacuum if necessary  cooled, a plastic sheath, expanded  (11) using an annular nozzle, this envelope  having a high density.  20) Method according to claim 1, characterized in that before expanding the intermediate volume between the pipe (1) and the molding blocks (5a, 5b) of the double conveyor belt molding installation (5) , is introduced at the entrance of the molding installation (5), a separation sheet (3) in the form of pipes, preferably a paper sheet or an aluminum sheet coated with synthetic material or paper or a sheet of synthetic material, then only after that the annular volume between the pipe (1) and the separation sheet (3) is expanded.  30) Method according to any one of claims 1 and 2, characterized in that expands between the pipe (1) and the separation sheet (3), a mixture forming polyurethane foam.  40) A method according to any one of claims 1 and 2, characterized in that to achieve the protective envelope of expanded synthetic material (11), using a polyolefin loaded with a propellant preferably polyethylene or polysinyl chloride.  50) Device for implementing the method according to any one of claims 1 to 4, characterized by an expansion machine (4) provided with a molding installation with a double conveyor belt, upstream of which it is provided with a pipe fitting and holding installation if necessary with a pipe straightening tool and downstream of its outlet, there is provided an extruder (6) for calibrating under ide, possibly cooled, comprising an annular nozzle to make the protective cover of expanded synthetic material (11).  60) Device according to rerendiea- tion 5, characterized in that the expansion machine (4) is a two-component mixing machine for the manufacture of polyurethane foam.  70) Pipe: (7) with thermal insulation, characterized in that the protective envelope of synthetic material (7) provided on the layer of expanded foam (10) with thermal insulation effect is a foam of high density synthetic material and with a surface formed of closed, smooth cells.