FR2595981A1 - STACK OF SOLDERABLE THERMOPLASTIC MATERIAL PLATES - Google Patents

Abstract

SOLDERABLE THERMOPLASTIC PLATES, HAVING A LARGE NUMBER OF SINGLE-PIECE SINGLE-SIDED SURFACES, ARE ULTRASOUND WELDED, FRICTION WELDED OR USING HEATING FILAMENTS IN A STACK IN WHICH THE SHEET FACES ARE WELDED AT THE SPOTS OF SURFACES SURFACES PLATES NEIGHBORS AND ARE REMOTELY MAINTAINED. THE WELDED STACK IS SUCH AS THERMAL HEAT EXCHANGER BODY. FIG. 3 gives as an example several possible forms of noise 6, 7, 8.

Description

The invention relates to stacks of plastic plates which

  are suitable as accumulation material for: heat transfer between gas streams in heat exchangers. The basis of the invention is a simplified process for the manufacture of weldable plates and for their

  stacks of plates.

  International patent application WO 83/02997 discloses a plastics material which is suitable in particular for heating the boiler exhaust gases of a boiler, cleaned in a purification stage wet, by heat transfer from unpurified boiler exhaust gases, before they are directed to wet scrubbing. In this case, several stacks of plates are arranged in a rotor which enters two flue gas streams in such a way that the various plate stacks are alternately traversed by the two streams of flue gas. In this way, they receive heat from the warmer flue gas stream and return it to the cooler smoke gas stream. Between their passage through the flue gas streams, the stacks of plates are traversed by a cleaning liquid, in particular water, in order to expel solids deposited on the surface of the plates from the flue gas. Under these conditions, the plate stacks are exposed to alternating stress due to the high temperature and corrosive action of the flue gas, as well as to the mechanical load of the cleaning liquid which penetrates the machine. Polyphenylene oxide is mentioned

  as a material that is able to support these loads.

  In order to manufacture inexpensively and simply stacks of plates that serve as heat accumulator, it is proposed to weld by layers, by means of ultrasound, flat plates of plastic material with the interposition of spacers. With this method, the spacers

  must be laid individually on each plate plane.

  In order to avoid this operation, it has furthermore been proposed to make the spacer profiles from the plate storage elements in the form of partial regions thereof. This supposes an additional operation. In addition, the surface of the plate is interrupted, at each spacing member formed, by a corresponding protrusion. This embodiment has different disadvantages. Thus, the mechanical strength of the surface of the plates is reduced by these interruptions. The spacers obtained by deformation of a portion of the surface of the plates are necessarily thinner than the material of the plates and they are hollow inside. They therefore have only limited resistance. Another disadvantage is that in stacking identical plate elements, the spacers formed on one plate respectively penetrate the hollow rear sides of the spacers of the next plate, so that Prerequisites for welding at this location are unfavorable. If the spacers in the different planes are

  As a result of the shift in position relative to each other, the total plate stack is less resistant to the case where all the mutually corresponding spacers are superimposed in the manner of a continuous column.

  The object of the invention is to eliminate the disadvantages

  above. In particular, the manufacture of the weldable plate elements used for the construction of the stack of plates has to be simplified and the use of spacers made separately must be avoided.

  In addition, the purpose of the invention is to reduce the number of operations during the meeting of the plate elements.

  individual stacks of plates welded.

  The objects of the invention are achieved by the fact that the stack of plates is composed of a multipiicit% dc: plates of weldable thermoplastic material, cpor rta-nt several protrusions united in one piece to the body of the plate. The different plates are arranged parallel to each other in the stack of plates and the upper ends of the projections are welded to the surface of the adjacent plate. The projections are distributed over the

  unbroken surface of the plate.

  Figs. 1 to 12 serve to better explain the invention.

  Fig. 1 is a sectional view of a plate element with

  the projections that are arranged on it.

  Figs. 2-4 are perspective views of different

  embodiments of the plate elements.

  Fig. 5 shows how several plate plans & current trajectories in the same direction are combined into one.

heat exchanger co-current.

  Fig. 6 represents the cross arrangement of two

  plate members for forming a cross-flow heat exchanger.

  Figs. ? 9 are sectional views of different embodiments of the projections which are respectively adapted to

different welding processes.

  Fig. 10 is a sectional view of a finished welded joint. Fig. 11 is a fragmentary sectional view of a

stack of plates finished.

  Fig. 12 schematically represents a device for the

  manufacturing the plate elements according to the invention.

  What characterizes the plates of which the stack of plates is composed is a continuous plate body 1 which is not interrupted at the points of implantation of the projections and which has at most a flat recess 3 of the c-tee. opposite to the projections. Although it is possible to have projections on both sides of the plates for their assembly to other plates, it is preferable that all the projections provided for the removal of other plates are arranged on the plate. one of the face of the plate. So that the plates are arranged parallel to each other in the stack of plates, it is appropriate that all the projections used for the soda assembly have the same height h. Apart from the salllies used for welding, it may be arranged on one side or on both sides of the plates, other projections of lower height, which serve for example to direct the current or shout turbulence circulating gas. Hereinafter, the protrusions which serve the

  fixing by welding to the neighboring plate.

  These projections are conveniently arranged at distances of 20 to 200 mm from each other. For reasons of manufacture as well as to increase the strength, it is advantageous that the projections have a larger diameter at the base, where they originate from the plate body itself, than at the tip. They preferably have a wedge-shaped section which continues in the surface of the plate body by a curved transition zone. This transition zone preferably has a radius of curvature r of at least 1 mm, preferably 2 to 10 am. When spot welds are sufficient, the plates may have as shown in FIG. 2 separate projections in the form of pyramids or truncated cones 4. This arrangement gives rise to a particularly low flow resistance. It may be wise to form in the edge region a protrusion in the form of a continuous rib 5 with which the stack of plates can be sealed laterally. The projections can also be made, as shown in FIG. 3, in the form of segments of rib 6 more or less long. From the point of view of the fluid technique, it is advantageous that the ribs extend parallel to each other and that they are sharpened at the ends or rounded at the ends, in a manner favorable to the flow. Ribs 7 corrugated in the same direction or, preferably, in opposite directions or ribs 8 whose diameter varies periodically may serve to accentuate the flow turbulence. Turbulence promotes heat transmission and prevents the deposition of dust. The maximum strength of the stack of plates is obtained with continuous ribs 9 along the entire length of the plates. The plate body generally has a thickness of 0.5 to 3 mm. Apart from the projections and the transition zone at their base, the plate body preferably has a uniform thickness with, at most, variations due to manufacture. If, by exception, this should not be the case, we would take the thickness of the plate at the thinnest points as the basis for the following sizing. The invention makes it possible to form projections which are higher than the thickness of the plate. Their height h preferably amounts to more than twice the thickness of the plate, in particular to 2 to 10 times this thickness. The projections have for example a height of 1 to 10 mm, preferably 3 to 6 mm. The invention also makes it possible to form thick projections. The diameter d at half height of the projection is generally greater than the thickness of the plate and it

  is for example 1.5 to 3 times the thickness of the plate.

  The optimum shape of the head of the projections is judged from the welding process. For ultrasonic welding, a sharpened head 10 according to FIG. 7 is advantageous. The angle a of the point is conveniently between 70 and 110 '. On a rib-like projection, the head has the shape of a continuous cutting edge. For the friction welding process, a rounded head 11 according to FIG. 8. It is particularly advantageous that the friction welding connection is made between the head 11 and a flattened depression 3 formed in the surface 2 to be assembled. Since, as a rule, similar plates are joined by welding in a stack, a head 11 of a protrusion of one of the plates is in each case in contact with the back of the base surface of the corresponding projection of the plate imediately next. At this point, there is in general rule a flattened cavity. This cavity is formed by itself when the lower face 12 of the plate passes over a cooling drum or a conventional polishing cylinder devoid of recesses and the protrusion a height and / or appreciable thickness. In this case, a flattened cavity 3 is formed by thermal vibration upon cooling. When the projections are constituted by ribs 13 which extend without a solution of continuity of an edge of the 5 'plate to the opposite bors, one can apply the method of welding by heating filament. For this purpose, the heating filament 14

  is embedded in the head of the projection 13.

  The stack of plates according to the invention or the plates used for its formation are made of weldable thermoplastic material. The plastics material must be extrusion-processable and must be welded when heated to the melting temperature, if necessary under slight pressure, so that, after cooling, the assembly will the matter. As for the rest, the characteristics of the plastic material are judged according to the conditions of use. For heat exchange with air at temperatures in the range of -20 to 80 ° C, a large number of thermoplastics commonly used in the art, such as polyvinyl chloride, polystyrene, glass, can be used. acrylic or polycarbonate. For the preferred use in flue gas cleaning plants, plastics having a heat distortion temperature of more than 120 ° C, for example a polyphenylene oxide, a polyethersulfone or a polyetherimide, are used. Oxide

polyphenylene is preferred.

  For the economical manufacture of the new plates, it is of essential importance that they can be produced in a single operation. Suitable for this purpose the installation 30 shown schematically in FIG. 12. From an extruder 20, a plasticized molding material enters the flat die 21 and is extruded therefrom as a flat continuous web 22. The still plastic web is introduced into the plastic slot. The extrusion speed and the rotation speed of the calendering rolls are adapted to each other in such a way that before the calendering slot a bead 25 so as to melt. At least one of the calendering cylinders 23 has in its surface a number of cavities 26 for forming the projections in the extruded plate. Under the effect of the pressure in the calendering slot, the plastic wetting material penetrates into the cavities 26 and the projections 2 are thus formed. This penetration is facilitated by a conical shape of the cavities 26 and projections 2 formed. The calendering rolls are cooled below the melting temperature of the plastic so that after their formation the protrusions 2 retain the shape they have taken in the molds.

  26. The cooling of the calendering rolls 23, 24 is provided by cooling fluid lines 27 which are traversed in a manner known per se by a cooling fluid flowing through the hollow axes of the rolls.

  For the formation of conical protrusions 4, the surface of the

  cylinder 23 is provided with corresponding conical cavities 26.

  Edge ribs 5 may be produced by an annular groove hollowed out in the periphery. Correspondingly, cavities 26 may be formed in the surface of the cylinder for the formation of rib-like protrusions 6, 7. A continuous rib 5, 9 may be produced either by an annular groove formed in the periphery or by a groove dug in the surface parallel to the axis. In the first case, an endless rib is formed in the direction of extrusion, while in the second case a rib is formed perpendicular to the extrusion direction over the entire width of the plate. In either case, a heating filament 14 can be embedded in the head of the projection by inserting into the groove of the cylinder

  calendering, before entering the slot between the cylinders, a heating filament which must be located as much as possible at the bottom of the groove and which is possibly held there by means of magnet. When the groove is filled with material to be molded, the heating filament is embedded therein.

  The material necessary for filling the cavities is taken from the bead 25, which must therefore have a sufficient size for this purpose. In case of formation of ribs in the direction of passage of the extruded plate. it is advantageous to give the extruded web 22 a slightly larger thickness in the places where a rib is to be formed, by a corresponding widening of the exit slot of the die 21, in order to make available constantly the amount of material necessary for the formation of the rib. The sheet of material provided with protrusions, produced continuously, is cut, in a known manner on the ground, into individual plates.

as required.

  A stack of plates according to the invention is shown in cross section in FIG. 11. Multiple plate members (31a, 31b, 31c ...) having projections are disposed parallel to each other, the upper ends of the projections being each welded to the underside of the immediately adjacent plate. Fig. 10 is a typical sectional view of a soda assembly. The molding material, melted during the welding operation, has formed a bead 15 which joins the head of the projection by joining the material to the surface of the adjacent plate. Preferably, all the individual plates 31a, b, c ... have the same dimensions and are welded together so that the corresponding edges are in a plane. The base surface of the stack of plates is rectangular as a rule. When each plate contained in the stack comprises, on each of two opposite edges, an uninterrupted bordering rib 5, the total stack of plates is hermetic to the fluid.

flowing on these sides.

  The dimensions of the individual plates are judged by the intended application and are only limited by the width of the extrusion die. That's why

  As a rule, the width is between 0.1 and 2 μm and the length in the direction of extrusion between 0.1 and 10 μm.

  The stack of plates may for example have a height between 0.1 and 2 m, which corresponds to a number of 10 to 200 individual superposed plates. When fixing the number of plates required for a given height of the stack, it must be taken into account that the height of the projections can be reduced by up to about 1 mm when

the welding operation.

  In the case of ultrasonic welding, high frequency vibrational energy is applied under pressure to the point of contact between the tip of a protrusion and the smooth back of a plate. With a suitable form of the vibration transmitting device, it is possible to produce in one operation an entire line of weld spots or a linear weld bead along an unbroken rib. By line-by-line movement of the welding device, all the projections of a plate plane can be welded step-by-step to the adjacent plate. In this way, a stack

  of plates can be raised in layers of one plate each.

  In the case of friction welding, an entire plate is vibrated parallel to its base surface, so that all the projections are melted simultaneously by the heat of friction produced and are welded to the back of the plate placed on them. This process is therefore much faster than the ultrasonic welding process. An even higher working speed is achieved with the heating filament welding method, in which the heating filaments 14 are embedded in the tips of the unbroken ribs 13 according to FIG. 9, are heated by applying a precisely dosed electrical voltage, whereby the etched ends and the contiguous surface of the adjacent plate are melted simultaneously and are welded. With this method, a complete stack of plates can be welded in a single operation, when all the heating filaments are simultaneously connected to the heating voltage. In this process also, the individual plates are maintained under a

  slight pressure until completion of the welding operation.

  The plate stacks produced according to the invention are preferably usable, in the cocurrent construction form, as heat accumulating materials in heat exchangers. exhaust gas purification sta- tions. Other applications include air conditioning installations for buildings, greenhouses, stables or bimetals, which can be reheated or cooled as needed. In this case, a heat exchange takes place between the fresh air entering and the exhaust air coming out. Under these conditions, apart from the principle of the regenerator, according to which the stack of plates collects and delivers alternately heat, it is also possible to apply the principle of the recuperator, according to which the currents which exchange heat pass simultaneously. through alternating layers of the stack of plates; cross flow recuperators constructed according to FIG. 6 10 are suitable for this purpose. Even if the heat exchange of air or flue gas is of paramount importance, such heat exchangers can also be used to

  other gaseous or liquid fluids, such as water.

  1L Plate stack, consisting of a multiplicity of plates of weldable thermoplastic material, having a large number of projections (2) which are integrally joined to the plate body (1) and which are distributed over the non-surface 5 interrupted from the plate, the faces of the plates (3Sa, b, c ...)

  being arranged parallel to each other in the stack of plates and the upper extremities of the projections (4-9) being welded to the surface of the adjacent plate.

  Plate stack according to claim 1, characterized in that all projections (4-9) of each plate

  are arranged on one side of the plate.

  Stack of plates according to claim 1 or 2, characterized in that many or all of the protrusions (49) of each individual plate have the same height.

  Do stack of plates according to any one of

  Claims 1 to 3, characterized in that the projections (4-9) of each individual plate have mutual distances of 20

at 200 mm.

  Stack of plates according to any one of claims 1 to 4, characterized in that the projections (4) have a larger diameter at the base than at the tip.

   Plate stack according to claim 5, characterized

  in that the projections <5-9) have a wedge-shaped section.

  Plate stack according to claim 5 or 6, characterized in that the faces of the plates continue in the surface of the projections by a transition zone having a

  radius of curvature of at least 1 mm, preferably 2 to 10 mm.

  And stack of plates according to any one of claims 1 to 7, characterized in that at the place where the projections of the adjacent plate are welded, the plates

  have flattened cavities (3).

  9.5 Stacking of plates according to any one of

  Claims 1 to 8, characterized in that the projections (4-9) have a height of more than one of the thickness of the lacquer,

  in particular from 2 to 10 times this thickness.

  Plate stack according to claim 9, characterized in that the projections have a height of 1 to 10 nm.

  11. stack of plates according to claim 10, characterized in that the projections have a height of 3 to 6 mm.

  12. Stack of plates according to any one of claims 1 to 11, characterized in that the projections (4) have, at mid-height, a diameter which is greater than

the thickness of the plate.

  13. Stack of plates according to claim 12, characterized in that the diameter of the projections (4) at half height amounts to

  1.5-3 times the thickness of the plate.

  L4. Stacking of plates according to any one of

  Claims 1 to 13, characterized in that the projections (4) have an approximately square or circular base area

  and have the shape of pyramids or cones.

  Plate stack according to one of Claims 1 to 14, characterized in that the projections (6-9)

  have the shape of ribs arranged approximately parallel.

  1Q. Stack of plates according to claim 15, characterized in that the ribs (8) have a diameter which varies periodically in the longitudinal direction.

  Plate stack according to Claim 15, characterized in that the ribs (7) are corrugated in

longitudinal direction.

  Stack of plates according to any one of claims 15 to 17, characterized in that the ribs (69) are separated by distances of 20 to 250 mr.

  19. Stack of plates according to any one of claims 15 to 18, characterized in that an end to

  least, the ribs (6--9) are sharpened or rounded

  in a favorable manner to the flow.

  Plate stack according to any one of Claims 15 to 19, characterized in that the ribs (75 9) extend continuously along the entire length of the

plate.

  21. Stack of plates according to claim 20, characterized in that the ribs <13> comprise a heating filament (14> at the weld bead with the adjacent plate 10.

  22, stack of plates according to any one of claims 1 to 21, consisting of a plastic material whose hot deformation temperature is greater than

  'C. Plate stack according to claim 22, consisting of polyphenylene oxide, polyethersulfone or polyetherimide. 24. Stack of plates according to claim 23, characterized in that it is composed of individual plates of 20 same dimensions, whose corresponding edges are located

respectively in the same plane.

  Plate stack according to claim 24, characterized in that at each of two opposite edges each plate contained in the stack comprises an uninterrupted bordering rib (5).

  Plate stack according to Claim 25, characterized in that the edge ribs (5) of all the plates

  individual are arranged in the same direction.

  7. A stack of plates according to claim 25, characterized in that the bordering ribs (5) of superposed plates extend at right angles to one another.