EP0107747B1 - Method of making cylindrical ceramic tubes with localized impressions, and apparatus for carrying out this method - Google Patents

Description

The present invention relates to a method for manufacturing cylindrical ceramic tubes having imprints located on their internal face and a device for implementing this method, as well as tubes provided with said imprints and obtained by said method.

The invention further relates to devices for making localized impressions.

Even more precisely, the present invention relates to a method of producing cylindrical tubes of permeable ceramics having on their internal face localized reliefs, such as annular, helical impressions or single helices or crossed double helices or even point impressions.

Document FR-A-2 073 777 discloses a method of manufacturing pipes, the internal face of which has a helical projection, a process which consists in placing a pipe between two plates, one of which carries a projection in the form of a linear edge. oblique to the edge of the plate, and which slide in opposite directions.

Document FR-A-759 777 discloses a method of manufacturing metal pipes, the periphery of which comprises helical folds, a method which consists in clamping a pipe in a tool provided with rollers having a grooved profile, the tool being placed rotation around the pipe.

Document FR-A-1 150 246 discloses an apparatus for manufacturing tubes having a constriction, this apparatus comprising a die of which one end comprises a core in the form of a neck movable from front to rear, as well as a diaphragm which opens or closes in synchronism with the displacement of the nucleus.

It is also known that one of the techniques for separating a mixture of gases having similar molecular masses is gas diffusion. According to this technique, the gas mixture is circulated under pressure inside tubes formed by a microporous wall. These tubes, according to a known technique, consist, on the one hand, of a macroporous ceramic tube, generally called support, internally coated with a microporous layer deposited on this internal wall. The assembly constituted by the tube itself or "support and the microporous layer makes it possible to adapt the total porosity of the coated tube or" barrier in order to obtain an optimal gas separation coefficient. This technique is in particular used for the separation between two gases corresponding to different isotopes of the same simple body.

However, it has been found that, during the flow of gas inside the barriers or tubes, there is a certain accumulation of one of the phases on the internal surface of the tube. This is why, according to the invention, reliefs are formed on the inner face of the tubes to create significant turbulence of the gas inside the tubular elements in order to avoid this accumulation of one of the phases and thus increase the coefficient. separation by gas diffusion.

The invention relates exclusively to the production of the support, that is to say the production of the macroporous tube. In their most conventional form, such cylindrical tubes are produced by the usual ceramic methods, that is to say by mixing ceramic oxides, thermally removable organic binders and a liquid phase (more generally water ). After kneading of these main elements, the mixture is in the form of a plastic and deformable paste and formed into a tubular shape using a piston press or a screw extruder. The dough is placed in the press cylinder and forced under pressure through an annular space determined by an external nozzle and an internal punch, which define the external and internal diameters of the tube to be produced.

Cut to the desired length, the tube is then placed on rollers which rotate and advance in a dryer whose temperature allows the elimination of the liquid phase and leads to a non-deformable, solid tube capable of being handled or transported automatically towards the other materials which will make it undergo the following operations of pre-cooking (elimination of organic binders) and actual cooking at high temperature which gives the tube the desired properties (for example: permeability, pore dimensions) and high mechanical resistance and, possibly transport to other material processing equipment.

At the outlet of the shaping machines (die or screw extruder) the element is in the form of a deformable plastic tube but relatively resistant to elongation and tearing.

It is at this stage of the development of the tubes that the process of producing the reliefs or imprints on the internal face of the tube comes into play.

The subject of the present invention is a process for producing impressions on the internal wall of portions of a tube which is obtained by continuous forming of a paste based on ceramic and cutting of this tube, characterized in that immediately after having formed these portions of tubes which are still deformable, they are placed on drive rollers whose axes are parallel to each other and in the same horizontal plane, and which are driven by rotations around their axes, the axes of revolution of the tube portions being parallel to the axes of the rollers, and pressure means are applied to at least a portion of the tube portions so that these tube portions are sandwiched between the rollers and the pressure means, the pressure means and / or the rollers being provided with at least one impression-making tool, each tool having a main printing direction which is not confused with the direction of the axes of revolution of said tube portions , and in this that a relative movement is created between the tube portions and each tool so that there is substantially no slippage between the tube portions and each tool.

According to its main mode of implementation, the method of manufacturing cavity tubes according to the invention is based on the fact that at the outlet of the tube forming assembly, these are placed on rotary rollers ensuring a rotation of the tubes and advancing towards the dryer and that the roller turns without sliding on a real or fictitious fixed surface. A tool placed on the tubes it supports is also fixed. It is then possible to make imprints on the tubes which are still deformable by applying to them an absolutely fixed tool which will locally deform the tube and will make permanent imprints on the internal face of the tube, these imprints being of shape and profile determined by the tools. and the relative movement mode of the tubes and tools.

According to this general mode of implementation, two preferred modes of implementation are envisaged.

According to a first mode of implementation, the rotation rollers include relief imprints and a horizontal plate is applied to the tubes to be deformed in order to exert a certain pressure of the tubes on the relief imprints of the rollers. This process makes it possible to make annular impressions. To make these impression rolls, an economical process which allows many possibilities consists in threading elastomer O-rings on the rollers. However, it is more difficult to imagine that all the rollers of the drying assembly are equipped with toroids or raised imprints. It is more economical to equip a roller element which receives the tubes at the outlet of the shaping. On this section, pressure is applied to the tubes which are then transferred to the smooth rollers of the dryer itself.

According to a second mode of implementation which allows more varied imprint configurations and which is apparently more industrial and economical, the tubes are deposited on perfectly cylindrical rollers and which can in this case be the rollers of the dryer itself and tools are applied to these tubes, the arrangement and profile of which allow the desired impressions to be made.

This tool can be a corrugated plate or a tool formed from rods or tubes fixed to a panel. If these rods or tubes are arranged perpendicular to the axis of the tubes to be formed, the impression produced is annular. This tool can also be constituted by continuous rods or tubes or by series of discontinuous tubes arranged in staggered rows so as to reduce the load distributed over the tube, this load tending to decrease its diameter so as to apply more localized pressure.

This tool can also consist of rods or tubes inclined with respect to the axis of the tubes to be marked. In this case, the imprint is a helical groove. The tool can consist of a single section to obtain a continuous helical mark over the entire length of the tube or of several tubes in order to produce tubes having marked zones alternating with zones which remain smooth.

It is also possible in the latter case to alternate the slope of the tools so as to produce helical marks in opposite directions, the pitch of which can be modified by changing the angle of the tools relative to the axis of the tube.

It is also possible to make a tool comprising a succession of parallel tubes or rods of increasing diameter so that the impression is made with a very punctual punch at the start of the operation and that it is widened by more punches large diameter in the following phases until a final impression of desired size is obtained.

Finally, it is possible to produce tubes having specific depressions. To do this, the tool which presses on the tubes can be fitted with judiciously arranged localized reliefs.

However, it has been found that, in certain cases, the method previously described according to these two main modes of implementation could have certain drawbacks. In fact, to obtain sufficiently marked or imprinted throttles, it may be necessary to locally deform the tube when passing under the imprinting tools by an amount much greater than the desired residual permanent deformation. It may also be necessary to repeat the elementary deformation operation several times to obtain a sufficient imprint depth, for example by making the tube travel along a path corresponding to a rotation of several turns under rods or tubes placed perpendicular to the axis of the tube. In these two cases, the part of the tube which does not come into contact with the impression-forming tools also undergoes deformation: its section in the vicinity of the impression-forming tool is no longer circular but more or less oval. In order for the tube to return to a circular profile after it has passed under the tubes or rods, the longitudinal profile of the latter comprises on the outlet side of the tubes a gently sloping area where the nipping of the tube between the impression tools and the tube progression rollers and therefore its ovalization gradually decrease until it cancels. More precisely, over the entire length of the rods or tubes or more generally of the impression-forming tools, the rolling of the tube to be marked which is pinched between the tools and the rollers causes it to undergo a "rolling ovalization" which is characterized by the succession of profiles shown in FIG. 17. This rolling ovalization causes the appearance of tensile stresses on the surface of the tube at points A, B ', C and D' in Figures 17a and 17c and at points A ', B , C 'and D in Figures 17b and 17d. Therefore, each region of the inner surface and the outer surface of the tube is alternately stressed in tension and compression during the passage under the tubes or impression-forming tools. This alternating stress is more or less well accepted by the paste from which the tube is made and can cause, by a phenomenon of fatigue, the appearance of cracks.

This is why the present invention also relates to two improved embodiments of the invention, which make it possible to avoid or at least reduce this introduction of constraints during the formation of imprints on the tube.

In a first preferred improved embodiment, fingerprinting tools are used which are heated. This allows the regions of the tube to be deformed to be heated by contact and selectively. We have. noted that the thermal conductivity of the ceramic pastes being low, the zone heated by the impression forming tools extends to the entire thickness of the tube if this thickness is not too high but its width remains small, this is that is, the regions of the tube which do not come into contact with the impression-forming rods remain cold. The viscosity of the liquid, glue, grease or other product used as a binder for the ceramic used to constitute the tubes, and consequently the resistance to deformation of this paste decreasing sharply when the temperature increases, the localized heating of the paste by the tools fingerprinting softens it locally and therefore allows it to be easily deformed. On the other hand, the regions of the tube which are not to be deformed remain relatively rigid.

Using these heated impression tools has the following advantages. For the same number of rotations of the tube under the tools, and for the same pinching of the tube between the tools and the rollers, imprints of greater depth can be obtained.

Simultaneously, the tendency to crack the tube decreases sharply and as a result its mechanical strength after sintering is no longer reduced as it was in the absence of heating. Indeed, a deeper impression being quickly obtained, the part of the tube which does not come into contact with the impression-forming tools undergoes rolling ovalization of lower intensity.

Of course, the heating of the fingerprinting tools can be obtained by various means which will be described later.

A second improved embodiment of the process which is the subject of the invention consists in the use of tools for forming fingerprints subjected to vibrations. The use of these vibrating tools has the following advantages.

For the same number of tube rotations under the tools and for the same pinching of the tube between the rods and the drive rollers, imprints of greater depth can be obtained.

Simultaneously, the tendency to crack the tube decreases sharply and as a result its mechanical resistance after sintering is no longer reduced as it is if this vibration phenomenon is not implemented. Indeed, a deeper imprint being quickly obtained, the part of the tube which does not come into contact with the rods or imprinting tools undergoes rolling ovalization of lower intensity.

Vibration of the impression-forming tools can be carried out by any appropriate means, for example by means of an electromagnet supplied by an alternating current or by means of an eccentric rotating mass rotated by a motor. fixed to the chassis which supports the impression-forming tools or by any other vibrating device disposed on this chassis. The vibration can be exerted parallel or perpendicular to the axis of the tubes to be formed or in several directions at the same time (for example rotary vibration).

It goes without saying that these two improved embodiments of the process can be combined, that is to say that it is possible to use impression tools which are heated, these tools being simultaneously subjected to vibrations as previously indicated.

The invention also relates to the various devices for implementing the method according to its different variants.

The invention also relates to the porous and permeable ceramic tube provided with the various forms of imprints which can be produced by implementing the method of the invention according to its various variants. Mention may in particular be made of annular fingerprints, helical fingerprints, localized or point fingerprints.

• sur les figures 1 à 4, des portions de tubes comportant diverses formes d'empreintes en relief ;
• sur la figure 5, un dispositif de réalisation d'empreintes, avec un seul outil porté par un plateau de pression ;
• sur les figures 6a et 6b, un dispositif de réalisation d'empreintes dans lequel les outils sont portés par les rouleaux d'avance des tubes ;
• sur les figures 6'a et 6'b, des vues en élévation et. en coupe axiale d'un mode de mise en oeuvre avec un rouleau anneleur qui exerce la pression sur la portion de tube à déformer ;
• sur les figures 6"a et 6"b, des vues en élévation et en coupe axiale d'une variante du dispositif de mise en oeuvre dans laquelle trois rouleaux anneleurs exercent la pression sur la portion du tube à déformer :
• sur les figures 7a et 7b, un dispositif dans lequel le plateau de pression comporte plusieurs outils pour réaliser des gorges annulaires ;
• sur la figure 8, une vue de dessous du plateau de pression de la figure 7a ;
• sur la figure 9, une vue de dessous du plateau de pression dans un dispositif comportant trois séries d'outils décalées ;
• sur les figures 10 et 11, des vues de dessous du plateau de pression muni d'outils pour réaliser des empreintes en forme d'hélice ;
• sur la figure 12, une vue de dessous du plateau de pression muni d'outils pour réaliser des empreintes localisées ;
• sur la figure 13, une vue d'ensemble d'un dispositif pour réaliser des empreintes ;
• sur la figure 14, une vue de dessous du plateau de pression montrant des outils pour réaliser des empreintes en forme d'hélice à l'aide d'outils ayant des épaisseurs croissantes ;
• sur la figure 15, une vue en coupe verticale d'un plateau de pression constitué par une tôle munie d'ondulations ;
• sur les figures 16, des vues en élévation et en coupe transverse d'un dispositif à outils chauffants pour la réalisation d'empreintes ;
• sur les figures 17, des schémas représentant des coupes transverses d'un tube en cours de réalisation des empreintes pour montrer les déformations que subit ce tube.
• Sur les figures 1 à 4, on a représenté en coupe verticale différentes empreintes que l'on peut obtenir à l'aide du procédé selon ses différentes variantes.
• Sur la figure 1, le tube 2a présente des empreintes annulaires E_i. Sur la figure 2, le tube 2b présente des empreintes en forme d'hélice qui sont référencées E₂. La figure 3 représente un tube 2c sur lequel sont ménagées des empreintes en forme d'hélice E₃, des espaces J étant ménagés selon l'axe du tube entre des séries de trois hélices. Sur la figure 4, on a représenté un tube 2d sur lequel sont ménagées quatre zones marquées par des hélices E4 et E5 de sens opposé.
• Sur la figure 5, on a représenté de façon schématique un dispositif pour la mise en oeuvre du procédé. Dans ce dispositif on trouve un support horizontal 4 sur lequel des rouleaux 6 peuvent rouler sans glisser selon le sens des flèches f. Le dispositif comprend également un porte-outil 8 sur lequel sont fixés des outils tels que 10 qui servent à réaliser des empreintes, comme on l'a indiqué précédemment dans les tubes 12. Le mouvement de rotation des rouleaux 6 entraîne, d'une part, un mouvement de rotation des tubes 12 autour de leur axe propre et, d'autre part, un mouvement général de translation de ces tubes selon la flèche F. Il faut comprendre que le porte-outil 8 et donc les outils 10 sont immobiles par rapport au plan support 4 et qu'ils permettent, par exemple, d'assurer une des empreintes en forme annulaire. Il est important de préciser en outre que les tubes 12 sont placés sur les rouleaux d'entraînement 8 immédiatement à la sortie de la filière servant à les former. Ainsi, le matériau céramique constituant les tubes 12 est encore relativement malléable.

In any case, the invention will be better understood on reading the description which follows of the various modes of implementing the invention and of the devices for implementing these methods. The description refers to the appended figures in which there is shown:

• in FIGS. 1 to 4, portions of tubes comprising various shapes of imprints in relief;
• in Figure 5, a device for making impressions, with a single tool carried by a pressure plate;
• in FIGS. 6a and 6b, an impression-making device in which the tools are carried by the feed rollers of the tubes;
• in Figures 6'a and 6'b, elevation views and. in axial section of an embodiment with a ring roller which exerts pressure on the portion of tube to be deformed;
• in FIGS. 6 "a and 6" b, views in elevation and in axial section of a variant of the implementation device in which three annealing rollers exert pressure on the portion of the tube to be deformed:
• in FIGS. 7a and 7b, a device in which the pressure plate comprises several tools for producing annular grooves;
• in Figure 8, a bottom view of the pressure plate of Figure 7a;
• in FIG. 9, a bottom view of the pressure plate in a device comprising three series offset tools;
• in Figures 10 and 11, bottom views of the pressure plate provided with tools for making impressions in the form of a helix;
• in Figure 12, a bottom view of the pressure plate provided with tools for making localized impressions;
• in Figure 13, an overview of a device for making impressions;
• in FIG. 14, a bottom view of the pressure plate showing tools for making helical impressions using tools having increasing thicknesses;
• in Figure 15, a vertical sectional view of a pressure plate consisting of a sheet provided with corrugations;
• in FIGS. 16, views in elevation and in cross section of a heating tool device for making impressions;
• in FIGS. 17, diagrams representing cross sections of a tube in the process of making the impressions to show the deformations that this tube undergoes.
• In Figures 1 to 4, there is shown in vertical section different imprints that can be obtained using the method according to its different variants.
• In FIG. 1, the tube 2a has annular imprints E _i . In FIG. 2, the tube 2b has imprints in the form of a helix which are referenced E ₂ . FIG. 3 represents a tube 2c on which helical imprints E are formed E ₃ , spaces J being formed along the axis of the tube between series of three helices. In Figure 4, there is shown a tube 2d on which are formed four zones marked by propellers E4 and E5 in opposite directions.
• In Figure 5, there is shown schematically a device for implementing the method. In this device there is a horizontal support 4 on which rollers 6 can roll without sliding in the direction of the arrows f. The device also includes a tool holder 8 on which are fixed tools such as 10 which are used to make impressions, as indicated above in the tubes 12. The rotational movement of the rollers 6 causes, on the one hand , a rotation movement of the tubes 12 about their own axis and, on the other hand, a general movement of translation of these tubes according to arrow F. It should be understood that the tool holder 8 and therefore the tools 10 are stationary by relative to the support plane 4 and that they make it possible, for example, to provide one of the fingerprints in annular form. It is important to specify in addition that the tubes 12 are placed on the drive rollers 8 immediately at the outlet of the die used to form them. Thus, the ceramic material constituting the tubes 12 is still relatively malleable.

Figures 6a and 6b show a second device for implementing the same method according to a variant. In general, using this device, the impressions are no longer made using a tool applying pressure on the tubes driven by the rollers but by tools which are provided directly on the rollers. drive, the force applied by these tools being obtained by a piece for holding the tubes relative to the rollers. More precisely, as seen in FIGS. 6a and 6b, there is a carpet of rollers 6 ′ which, as best seen in FIG. 6b, includes toric imprints 6 "capable of defining the shape of the imprint in the The rollers realize the rotation of the tubes 12 on the one hand and, on the other hand, they are subjected to a general translational movement along the arrow F (perpendicular to the axis of the tubes 12). 'indicated, a pressure plate 14 associated for example with a spring device 16 ensures the immobilization in a vertical direction of the tubes 12 relative to the rollers 6' provided with the tools 6 ". Using such a device, it is possible, for example, to obtain the annular impressions visible in FIG. 6b.

These tools 6 "which are cylindrical crowns can either be machined from the mass of the rollers 6, or be attached in the form of rings constituted by O-rings.

In Figures 6'a and 6'b, there is illustrated a device for a third embodiment of the method which somehow combines the embodiments of Figures 5 and 6. There are two rollers d 'drive 106 and 106' on which we place the portion of tube 12 on which we want to make the impressions. A third roller 108 said anneler can be lowered to apply pressure on the tube 12 to be deformed and this roller 108 has reliefs 110 (visible in FIG. 6'b) which make it possible to make impressions 112 of annular shape. The roller 108 can also rotate around its axis XX ′, thus obtaining a minimum of slippage and friction between the tube to be deformed 12 and the annealing roller 108.

In Figures 6 "a and 6" b, there is shown a variant of the device for the third embodiment of the method, object of the invention. According to this variant, not only the roller 108 carries reliefs 110, but also the two drive rollers. In other words, there are three identical rollers 108 provided with reliefs 110, the reliefs of course facing each other. During the rotation of the rollers 108, each imprint in the tube is formed simultaneously by the action of the reliefs of the three rollers.

The device of Figure 7 is close to that shown in Figure 5, that is to say that we find the rollers 6 but instead of finding a single tool 8 we find, as in Figure 6 , a pressure plate 14 associated with an elastic device 16 and on the underside of which are mounted impression-making tools 18. As can best be seen in FIG. 7b, these tools have for example a rounded active face 18a for make groove-shaped impressions. Of course, on this device we could have tools with different shapes to achieve an adequate shape fingerprints on the tubes 12.

Figure 8 shows a bottom view of a pressure plate 14 on which are mounted tools 20 for making annular impressions. These tools are the entire width of the pressure plate and can have, in a plane of section perpendicular to their length, a shape adapted to the section of the impression to be produced.

In Figure 9, there is shown a tool in which there are three pressure plates integral with each other, referenced 14a, 14b and 14c, each plate carrying tools for making impressions 22. The tools make a fingerprint out of three. In other words, if we call p the pitch of the final impressions to be made on the tube, the tools 22 of the same plate are offset by a length equal to 3p and a tool of a plate is offset d 'a length p of the tool of the adjacent tray.

Figure 10 shows a bottom view of a pressure plate 14 provided with impression-making tools 24 which are inclined relative to the axis of displacement of the tubes. These tools 24 make it possible to make helical impressions with a pitch p '.

In Figure 11, there is shown a plate 14 of the same type which is provided with tools 24 'allowing the production of propellers in the opposite direction.

The plate 14 in bottom view of FIG. 12 is provided with localized punches 26 which thus make it possible to make point impressions on the tubes.

In Figure 13, the installation is shown in more detail. This comprises on the one hand a loading station 30 which makes it possible to place the tubes to be formed at the outlet of the tube forming die on the rollers 6. These are driven in translation and in rotation by the assembly a belt device 32 driven in rotation by end wheels 34a and 34b which ensure the tension and the rotational drive of this carpet. The device also comprises a pressure plate 14 carrying tools 36 and a station for unloading the tubes provided with their imprint 38.

In Figure 14, there is shown another form of tool for obtaining sets of helical imprints. On the underside of the pressure plate 14, there are at the two ends two zones A ₁ and A ₂ constituted by tools of short length, five in this particular case, and two zones A ₃ and A ₄ constituted by tools inclined by relative to the axis of the plate and of greater length. These zones are each made up of five tools, the diameter of which increases from right to left.

As shown in FIG. 15, instead of having a plate 14 on which the tools capable of creating the imprint are fixed, the whole of the plate and the tools can be produced using a ribbed sheet 40 which is associated with spring pressure means 42. This makes it possible, for example, to obtain impressions with relatively large radii of curvature.

We will now describe three concrete examples of implementation of this first form of the process.

Example 1

Method for producing porous alumina tubes with an outside diameter of 20 mm, an internal diameter of 16 mm and a length of 800 mm, having annular impressions 0.4 mm deep (measured on the internal surface), and spaced 20 mm apart, over a length of 650 mm. Each end has a 75 mm smooth cylindrical area.

The tubes emerging from a piston press, still perfectly plastic and deformable, are placed on rollers 42.4 mm in diameter, spaced 8.4 mm rolling on a fixed plane which gives them a rotational movement and advancing towards a drying box at the speed of one meter per minute (see Figure 5).

On the sheet of tubes thus formed is applied a tool formed by a very flat, horizontal plate, 700 mm in width and about 1 meter in length, below which tubes are arranged by welding, gluing and any other process. made of stainless steel with an outside diameter of 8 mm, perpendicular to the axis of the tubes to be marked, spaced 20 mm apart, forming the impression-forming tools; the ends of these tubes being bevelled so that the deformation of the tubes is progressive at the entry of this tool and that the exit is also regular. This tool is arranged in height so that the marker tubes sink about 2 mm into the ceramic tubes. In order to avoid sticking of the tubes on the drive rollers and on the tools which cause deformation by tubes, the tubes or rollers are coated with a film of purely organic oil before the working area.

After drying and heat treatment, the tubes have annular impressions of the desired size and the process used is perfectly continuous and industrial.

It is obvious that it is easy, by modifying the distances between marker tubes to make any steps of annular impressions and that the profile and the depth of these impressions can be changed using tools of different diameters and shapes or by adjusting the height of the tool in relation to the tubes.

Example 2

Method for producing porous alumina tubes with an outside diameter of 20 mm, 16 mm outside diameter, 16 mm inside diameter and 800 mm in length, having helical imprints 0.5 mm deep (measured on the internal surface) in 20 mm steps and arranged in four distinct zones: two 70 mm zones length, the two ends of the tube being unmarked over 75 mm and two central zones of 210 mm in length.

Each ringed zone is thus separated from its neighbor by a smooth reserve of approximately 30 mm.

The tubes leaving the spinning press are arranged as in Example 1 on the rotary rollers advancing towards the dryer. On the plane of the scrolling tubes is applied a tool consisting of a perfectly flat plate on the lower surface of which are fixed tubes of 7 mm outside diameter: two tubes of 220 mm in length on the side of the plate and two rods 660 mm in length on the central parts of the tray.

These four tubes are inclined by about 15 ° relative to the axis of the tubes to be marked and are parallel to each other. Each tube marks its helix in the corresponding zone, the shorter tools leading to the shorter zones. In order to facilitate the marking of the tubes and to obtain a greater footprint depth, the marker tubes are brought to 70-80 ° C by circulation of oil heated by a thermostatic device in a closed circuit. The increase in local temperature allows a slight softening of the tube which becomes more deformable.

After this operation, drying and heat treatment, the tubes produced have well marked helical imprints according to the desired geometric arrangement.

Example 3

Process for producing porous alumina tubes 20 mm in outside diameter and 16 mm in inside diameter and 800 mm in length having helical impressions of the same depth and not the same as those of Example 2 but whose profile will be much more wide, i.e. with a much larger radius of curvature.

It is impossible, in this case, to make the propeller with a single large diameter marking tool because such a punch deforms and ovalizes the tube without marking deeply.

It is however possible to obtain such profiles by making the propeller with several parallel bars, of increasing diameters, each tool widening the more localized impression made by the previous punch.

Each propeller is marked, for example, by five cylindrical tools of diameter 8, 10, 12, 14 and 16 mm, perfectly parallel and whose spacing has been carefully calculated so that each tool falls precisely back into the mark produced by the punch preceding it.

In this case, the marker plate consists of a hollow parallelepiped frame in which the heating fluid can be circulated. One side of this frame is perfectly flat and four marking tools are attached to it. These tools consist of plates in which bars 8, 10, 12, 14 and 16 mm in diameter have been machined, each bar being offset from the previous one, of a length corresponding to one revolution (or a circumference) of the tube to be marked, the offset being measured in the direction of movement.

With this device, the propellers obtained are wide and deep and the tube has not undergone an exaggerated elongation which would have reduced its diameter in the intermediate cylindrical parts.

• à l'aide de résistances chauffantes électriques. Cela est particulièrement intéressant si l'outil de réalisation d'empreintes constitue lui-même la résistance chauffante,
• par circulation d'un liquide chaud dans des conduits aménagés dans le dispositif de formage. Un cas particulier est celui où les outils de formage se présentent sous forme de baguettes constituées par des tubes métalliques dans lesquels circule le liquide chaud. Un autre cas est celui où les tubes dans lesquels circule le liquide chaud sont soudés le long des baguettes,
• par rayonnement infrarouge dirigé sur les baguettes, la surface du tube étant protégée de ce rayonnement par des écrans.

As indicated above, it is possible to add to the mechanical deformation of the tube due to the tools a localized heating operation of the tube in line with the impressions to be made. This heating can be achieved in various ways. We can cite for example:

• using electric heating resistors. This is particularly interesting if the fingerprinting tool itself constitutes the heating resistor,
• by circulation of a hot liquid in conduits arranged in the forming device. A particular case is that where the forming tools are in the form of rods formed by metal tubes in which the hot liquid circulates. Another case is that where the tubes in which the hot liquid circulates are welded along the rods,
• by infrared radiation directed on the rods, the surface of the tube being protected from this radiation by screens.

According to this embodiment of the method, it is advantageous to heat the regions of the tube to be deformed before starting the actual deformation operations. For this, progressive profile forming tools are used, as shown in FIGS. 17. The heating tool 50 has a first region I, the heating tool 50 has in cross section the shape shown in the figure. 16a, that is to say that the tool 50 only provides heating without any mechanical deformation. In region II, the tool 50 provides progressive mechanical deformation, as shown in Figures 16b and 16c. In this region, the tool 50 of course also provides heating. In zone III, the profile decreases in thickness, as shown in FIG. 17b and this zone constitutes a clearance zone.

In fact, and although this has not been illustrated, it is clear that the tools shown in Figures 5 to 14 can be heated. Either they have a built-in heating resistance, or they are hollow and a hot liquid circulates there.

The heating of the part by the heating tools, even if it is limited to the areas to be deformed, can cause harmful volatilization of certain constituents of the dough with which the tubes are made. To avoid this evaporation, one can enclose the zone where the forming operation is carried out in an enclosure where an atmosphere saturated with the volatile compounds constituting the tube is maintained. This slows down or completely prevents vaporization. The tube can also be coated beforehand with a film of non-volatile compounds such as, for example, a paraffin oil.

Furthermore, in order to avoid the evaporation of the constituents of the paste forming the tube in line with the surface of the tube which comes into contact with the tools, these regions can be coated with a film of non-volatile liquid. In particular, this liquid can be deposited on the active face of the tools, from where it will be transferred to the tube thanks to the contact which takes place during the impression forming operation.

As has also been indicated, not only can the impression-making tools be heated, but they can also be subjected to vibrations, these two characteristics being able to be combined.

Vibration of the impression-making tools can be carried out by any suitable means. Mention may in particular be made of an electromagnet supplied by an alternating current associated with a magnetic piece integral with the plate carrying the tools for making impressions. One can also use an eccentric rotating mass rotated by a motor fixed on the plate which carries the tools. More. generally, any vibrating device fixed to the tool support plate can thus be used. The vibration can be exerted parallel or perpendicular to the axis of the tubes to be deformed or in several directions at the same time, for example by rotary vibrations.

We will now describe comparative examples which illustrate the efficiency of the process with heating and with the creation of vibrations.

The examples below relate to the forming of throttles in the inner section of tubes made of a ceramic paste with a thixotropic behavior and containing thermoplastic binders having the following characteristics:

In examples n ° 2 and n ° 4 below, there is a rotary vibration around a horizontal axis perpendicular to the axis of the tube, with a frequency of 120 Hz and a peak-to-peak amplitude of 0.2 mm.

The height of the projections obtained on the inside of the tubes is as follows:

In the four examples above, the tubes showed no cracks after drying and sintering.

Claims (31)

1. Process for making imprints in the inner wall of portions of a tube (12), obtained by the continuous shaping of a ceramic-based paste and by cutting off this tube, characterized in that immediately after these tube portions which are still deformable have been shaped, they are placed on drive rollers (6), the axes of which are parallel to one another and in one and the same horizontal plane and which are driven in rotation about their axes, the axes of revolution of the tube portions being parallel to the axes of the rollers, and pressure means (14) are applied to at least part of the tube portions, in such a way that these tube portions are gripped between the rollers and the pressure means, the pressure means and/or the rollers being equipped with at least one tool (6", 18) for making imprints, each tool having a main direction of impression not coinciding with the direction of the axes of revolution of the said tube portions, and in that a relative movement is generated between the tube portions and each tool, in such a way that there is substantially no slipping between the tube portions and each tool.

2. Process according to Claim 1, characterized in that the imprints are made by means of at least one tool (6") integral with the rollers, and in that these are subjected to a translational movement in the said plane.

3. Process according to Claim 1, characterized in that the imprints are made by means of at least one tool (18) integral with the pressure means, and in that the rollers are subjected to a translational movement in the said plane.

4. Process according to any one of Claims 1 to 3, characterized in that, at the same time as the said tube portions (12) are deformed, those regions of the tube portions which are to be deformed are heated.

5. Process according to Claim 4, characterized in that the said regions of the tube portions (12) are heated in proportion as the tube portions are deformed.

6. Process according to Claim 4, characterized in that the said regions of the tube portions (12) are heated before and during the deformation of the tube portions.

7. Process according to any one of Claims 4 to 6, characterized in that the deformation and heating of the tube portions (12) are carried out in an atmosphere which is saturated with at least one compound intended to prevent the evaporation of the materials constituting the tube when the tube portions are heated.

8. Process according to any one of claims 1 to 7, characterized in that, at the same time as the tube portions (12) are deformed, the tools are subjected to vibrations.

9. Process according to Claim 8, characterized in that the said vibrations are exerted parallel to the axis of the tube portions.

10. Process according to Claim 8, characterized in that the said vibrations are exerted perpendicularly to the axis of the tube portions.

11. Process according to Claim 8, characterized in that the said vibrations are exerted in several directions at the same time.

12. Process according to any one of Claims 3 to 11, characterized in that the deformation of the tube portions is carried out by means of at least one tool of elongate form (18) which is arranged on the pressure means perpendicularly to the axes of the tube portions.

13. Process according to any one of Claims 1 to 11, characterized in that deformation is carried out by means of at least one tool of elongate form which is arranged on the pressure means obliquely relative to the axes of the tube portions.

14. Process according to any one of Claims 3 to 11, characterized in that the deformation of the tube portions is carried out by means of punches (26) arranged on the pressure means in order to make localized imprints in the tube portions.

15. Process according to either one of Claims 12 and 13, characterized in that the final imprint is obtained by causing several tools, designed to make imprints of increasing size, to act in succession.

16. Process according to either one of Claims 12 and 13, characterized in that several series of tools are used, each series of tools making some of the imprints.

17. Apparatus for making imprints in the inner wall of portions of a tube (12), obtained by the continuous shaping of a ceramic-based paste and by cutting off this tube, comprising a smooth horizontal platform (14) equipped with means (16) of applying the. latter to the said tube portions, characterized in that it comprises a plurality of drive rollers (6) which are intended for the tube portions (12) and the axes of which are all in one horizontal plane, means of rotating the rollers about their axes and subjecting the said rollers to a translational movement in the said horizontal plane, and annular tools (6") in the form of rings mounted on the said rollers, the drive rollers (6) and the smooth platform (14) being arranged in such a way that the tube portions are pressed against the drive rollers by the smooth platform.

18. Apparatus for making imprints in the inner wall of portions of a tube (12), obtained by the continuous shaping of a ceramic-based paste and by cutting off this tube, comprising a horizontal platform (14) equipped with means (16) of applying the latter to the said tube portions, and tools (18, 50) mounted, on the face of the said platform turned towards the said tube portions, characterized in that it comprises a plurality of drive rollers (6) which are intended for the tube portions (12) and the axes of which are all in one horizontal plane, means of rotating the rollers about their axes and of subjecting the said rollers to a translational movement in the said horizontal plane, and the said drive rollers being smooth.

19. Apparatus for making imprints in the inner wall of portions of a tube (12), obtained by the continuous shaping of a ceramic-based paste and by cutting off this tube, characterized in that it comprises two drive rollers (106, 106' ; 108) of parallel axes, equipped with means of driving them in rotation about their axes and intended for receiving a tube portion (12), a third roller (108) carrying annular tools (110) in the form of rings mounted on the said third roller, the axis of which is parallel to those of the first two rollers, and means of applying the said third roller to the said tube portion and of allowing the said third roller to rotate about its axis.

20. Apparatus according to Claim 19, characterized in that the three rollers (108) are identical, and all three carry annular tools (110), each plane perpendicular to the axes of the rollers and containing a tool of one roller likewise containing a tool mounted on the other two rollers.

21. Apparatus according to Claim 18, characterized in that the said tools (18, 50) consist of rods, tubes or bars arranged perpendicularly to the axis. of the tube portions.

22. Apparatus according to Claim 18, characterized in that the said tools (18, 50) consist of rods, tubes or bars arranged obliquely relative to the axis of the tube portions.

23. Apparatus according to Claim 21, characterized in that the said platform has several staggered series of tools, each series of tools being designed to make some of the imprints.

24. Apparatus according to either one of Claims 21 and 22, characterized in that each tool has a cross-section which increases in order to obtain progressively the desired size of imprint.

25. Apparatus according to either one of Claims 19 and 20, characterized in that the said third roller (108) has means of making it vibrate.

26. Apparatus according to any one of Claims 18, 21, 22, 23 and 24, characterized in that the platform (14) is equipped with means of making the said platform vibrate in a horizontal plane.

27. Apparatus according to any one of Claims 18, 21, 22, 23 and 24, characterized in that the platform (14) has means of making the said platform vibrate in a vertical direction.

28. Apparatus according to any one of Claims 17 to 27, characterized in that it comprises means of heating those regions of the tube portions where the imprints are to be made.

29. Apparatus according to Claim 28, characterized in that the tools themselves have a heating effect.

30. Apparatus according to either one of Claims 28 and 29, characterized in that the apparatus as a whole is placed in an enclosure having means of generating in the said enclosure a gas atmosphere intended for preventing the evaporation of the constituents of the tube portions (12) during heating.

31. Apparatus according to either one of Claims 21 and 22, characterized in that each tool (50) itself has a heating effect, in that each tool has a height in the vertical direction which increases and then decreases in the direction of translational movement of the tube portions, in such a way that only the middle part of the tube having the greatest height is capable of making an imprint.

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