EP0228538B1 - Method and device for the manufacture of moulded articles provided with conduits and made of a moulding powder, especially of a ceramic moulding material, catchword: honeycomb - Google Patents

Abstract

A method for producing press-molded articles having a plurality of cavities therein includes a mold cavity which can be filled with a particulate molding compound, which mold cavity contains rods sheathed with expandable tubes which can be expanded by means of a fluid under pressure conveyed into the space between the rods and the tubes: this causes compaction of the molding compound to form the pressed article, which can be removed from the mold after reduction of the fluid pressure to allow detumescence of the expandable tubes and withdrawal of these from the mold cavity so that the mold cavity can be opened to remove the shaped pressed article.

Description

The invention relates to a process for the production of channeled compacts from a molding compound, in which in a mold cavity filled with the molding compound and penetrated by bars surrounded by inflation tubes, the inflation tubes are expanded by means of fluid pressure brought to the inside thereof, compacting the molding composition to form the compact and after Depletion of the fluid pressure, the coated rods withdrawn from the compact and this is removed from the mold cavity.

Such a method is known from DE-B 1 016 178. In the known method, a plastic molding compound for the production of hollow building blocks is processed as the molding compound. When filling the plastic mass, the inflatable hoses assume their state of smallest cross-section. They have a radial distance from the bars surrounded by them.

From DE-C 882 973 a method for the production of hollow components is known, in which closed hoses protrude at their ends from one boundary wall of a mold cavity into a mold cavity. A filler-binder mixture consisting of wood shavings and cement mortar is introduced into this mold cavity until the mold cavity is completely filled, whereupon the mold cavity is closed and the hoses are filled with compressed air.

From DE-C 537 886 a device for molding hollow bodies with cavities passing through the whole molding is known. The cavities are formed by stretchable cores in the form of tubes. These tubes are arranged around bars at a radial distance from them and centered at their ends.

The invention is based on the object of specifying a method with the aid of which channels of small caliber can optionally also be produced in a form-retaining manner in the respective compact.

To achieve this object, it is proposed that a powdery molding compound be filled into the mold cavity while the inflation tubes rest on the rods on their longitudinal sections lying within the mold cavity. In the method according to the invention, the shape of the channels can be dimensioned exactly as an image of the rods, so that channels can be produced, for example, with a cross-sectional dimension of 1 mm to 10 mm, in particular 3 mm to 8 mm, the cross-sectional shape of the channels, for example can be round or polygonal, i.e. roughly square.

The compacts to be produced are intended in particular for further processing into moldings which have a large inner surface and are used in physical and chemical reactions. The shaped bodies can either be microporous, so that capillaries start from the individual channels, which in turn serve to enlarge the inner surface. But it is also conceivable that the inner surface is formed exclusively by the channels. In the respective physical or chemical processes, the molding compound can either itself be a reactant, for example a catalytic reactant. However, it is also conceivable for the molding compound to be mixed with a substance which is a reactant, for example a catalytic reactant. Finally, it is conceivable that the molded body, in particular in the region of the channels, is coated with a substance, for example by vapor deposition, and that this coating is effective as a reactant, for example a catalytic reactant, in the respective process.

In addition, it is conceivable that the moldings obtained from the compacts are used wherever large surfaces are required, for example in the heat exchange between aggressive media.

The compacts can be finished to the shaped bodies in a conventional manner by firing or sintering.

With the aid of the invention, it is possible to obtain moldings with a large inner surface which have sufficient stability to be able to be subjected to the further processing processes in question, for example burning or sintering, without the risk of substantial damage or destruction and which continue to be so stable, that they can be handled in the necessary ways from the production of moldings to further processing without the risk of substantial damage or destruction.

A ceramic molding compound is particularly suitable as the powdered molding compound. In addition, molding compositions with additions of catalytic reactants are possible, which in turn can be produced on the basis of a ceramic base substance. Spray-dried granules, as mentioned, for example, in DE-A 3 101 236, page 31, last paragraph and page 32, first paragraph, are particularly suitable for processing by the process according to the invention.

In the method according to the invention, very high pressures can be applied by expanding the inflation hoses under fluid pressure, in particular under hydraulic pressure using a liquid fluid, which lead to isostatic compaction of the material, so that its stability after pressing and even before firing, Sintering or other hardening is guaranteed. After the fluid pressure in the inflation hoses has been reduced, they immediately return to their starting position of smaller diameter due to the elasticity of the materials that are regularly used, such as rubber or other elastomers, so that it is readily possible to pull the rods back immediately after the inflation process and with it the hoses, and in this way to demold the compact. It has been shown that channels of very small caliber, for example with a diameter of 1 to 10 mm, can be obtained in this way, ie moldings with a very large specific surface area, such as, for example, in the exhaust gas detoxification of commercial systems, however are also required for exhaust gas detoxification from motor vehicles.

It is possible to form the channels completely through the compacts if, for example, a flow of gas or liquid through the finished molded article is desired. But it is also conceivable to close the channels at one end. This opens up the possibilities that do not exist in extrusion, for example, where complex sealing measures would have to be taken to achieve closed channels. Closing the channels is advantageous, for example, when the shaped body is to be used as a soot filter for diesel engines, for example.

The rods and the inflatable hoses require considerable manufacturing effort, particularly when forming channels of small caliber. On the other hand, the hoses and the channels are only subjected to relatively low loads, even at high pressures of the fluid, since the load is absorbed by the molding compound or by the guides accommodating the rods and the hoses in the boundary walls of the mold cavity. It can therefore be expected that the equipment used to manufacture the moldings will have a long service life.

The dimensions of the mold cavities can be chosen as large as desired, depending on the technique used for the filling. As a rule, the dimensioning of the mold cavity will be made dependent on the requirements for the dimensions of the molded body ultimately used. In the event that molded articles of extreme size are required, it is also possible to produce building blocks for the required molded articles by the process according to the invention and to place them on top of one another and, if necessary, to connect them to one another. On the other hand, if extremely small moldings are required, it is also conceivable that, with a view to an economical implementation of the method according to the invention, compacts are produced which are larger than the moldings ultimately required and that these compacts are subdivided, either directly after the production of the compacts or also after the production of the finished shaped body by sintering, firing or the like.

The pressing process, which is essentially based on the contribution of the inflation hoses, can also be supported by exposing a membrane, which at least partially delimits the mold cavity, to a fluid pressure on the side remote from the molding composition, in particular simultaneously with the application of fluid pressure to the inflation hoses. The proportion of contacting that is supplied by the membrane naturally depends on the overall cross section of the molded product and is smaller the larger this cross section becomes.

In order to ensure that the pressurization is as uniform as possible and in order to reduce the outlay on apparatus, it is recommended that a membrane which surrounds the mold cavity in the manner of a jacket is used with generators which are essentially parallel to the direction of the rods which are generally parallel.

After reducing the fluid pressure in the inflation hoses and, if necessary, on the outside of the membrane, it is advisable to first pull the coated rods out of the molded article in order to treat the obtained compact carefully, and then to remove the compact from the mold cavity.

With regard to a uniform pouring of the molding compound inside the mold cavity before the pressing process by inflating the hoses, it is advisable to introduce the molding compound into the mold cavity while the coated rods are already present in the mold cavity.

Furthermore, it is advisable to use a filling technique with a view to a uniform pouring and possibly pre-compression of the molding compound in the molding cavity, in which a vacuum is applied to the molding cavity and the molding compound is thereby sucked in. For details of this filling technique, reference is made to the explanations in DE-A 3 101 236. It is also recommended to apply the measures of fluidizing the supplied molding compound mentioned in that laid-open document and to ensure, at least at the beginning of the filling process, that the air extraction openings to which the vacuum is applied do not prematurely by restricting the flight speed of the molding compound particles entering the mold cavity clog and impair or prevent further filling.

It is further recommended that while a negative pressure exists in the mold cavity, a negative pressure is also maintained on the inside of the inflation hoses and possibly also on the side of the membrane remote from the molding compound, in order to keep the inflation hoses in contact with the rods and possibly the membrane to keep in contact with the molded jacket.

The invention further relates to a device for producing channeled compacts from powdered molding composition, comprising a mold cavity, a group of bars within the mold cavity, which are surrounded by inflation hoses at least over part of their length, a filling device for filling the mold cavity with the powdery Molding compound and a fluid supply device for the supply of pressure fluid to the inside of the inflation hoses.

Taking into account the above task, it is proposed for such a device that the inflation hoses in the idle state, i.e. before the application of the fluid pressure, bear against the rods with their longitudinal sections received within the mold cavity.

For the reasons given above, the mold cavity can be at least partially delimited by a pressurizable membrane in order to exert compacting pressure on the resulting compact from the outside.

With regard to the simplification of the demoulding, but also with regard to the parallel flow of the finished moldings, it is advisable to arrange the rods parallel to each other; in this case the membrane will preferably be made as a jacket membrane with generators parallel to the bars; it has been shown that optimal uniformity of density in the compact is obtained.

With a view to shaping the compact as precisely as possible, it is recommended that the bars be at least at their ends transverse to their longitudinal direction in a fixed position with respect to the mold cavity during the pressurization of the inflation hoses and possibly the membrane. It has been shown that in this way an exact distribution of the channels and an approximate cross-sectional constancy of the channels along their length is achieved, so that several molded bodies obtained from such compacts with aligned channels can be connected to one another.

With a view to rational production, it is recommended that a rod holder at one end of the rods and a linear drive for this rod holder are provided for the joint retraction and extension of the rods in or out of the mold cavity, with the press bear, for example, as a linear drive the press usual in the ceramic industry can be used, a press that is necessary anyway in order to apply the mold clamping force for the mold cavity. For the rational production of the compacts, it is also advantageous if a perforated mold wall of the mold cavity facing the rod holder and penetrated by the rods is connected to the rod holder for common movement by the linear drive. The penetrated mold end wall can form the essential part of the rod holder. When the bars are pulled, the mold end wall penetrated by the bars is also lifted. If it turns out that parts of the compact are touched by the rods during pulling and are therefore subject to the risk of destruction, it is also possible to decouple the rod holder and the end wall of the mold through which the rods move so that the rods are removed before removal the mold end wall penetrated by them can be drawn, so that the rods are in any case still guided through this mold end wall until the end of the drawing process.

If one wishes to obtain a compact whose channels have the same cross-section over their entire length, it is recommended that the inflation hoses with the end sections exposed to the fluid pressure extend beyond the mold cavity. In order to protect these end sections, the outer surface of which is then not protected against excessive inflation by the molding compound, against excessive inflation outside the mold cavity, it is necessary to accommodate these end sections in closely surrounding support channels in the respective mold end wall.

A particularly simple and, in the presence of a large number of rods and in particular in the case of small-caliber rods, a very economical measure both for fixing the rods in the respective housing and for sealing the tubes during the pressing, if appropriate also for both purposes at the same time, is that the inflatable tubes, together with the rods, pass through a squeeze plate made of elastomeric material which can be squeezed between two squeezing surfaces and which can be squeezed for the purpose of sealing the inflatable tubes in the region of the respective end and / or for fixing the tubes and rods in the region of the respective end. The squeeze plate can be enclosed between a surface of the respective perforated mold end wall remote from the mold cavity and a perforated pressure plate, this pressure plate being able to be pressed against the respective mold end wall by conventional hydraulic or pneumatic means.

With regard to a simple structure of the device, it is proposed for the supply of the inflation hoses with pressurized fluid that they are connected or connectable to at least one end to a central fluid supply chamber, this fluid supply chamber being able to be formed in the region of one mold end wall or both mold end walls and possibly with the mold end wall can be combined to form a structural unit.

The unhindered inflow of fluids to the inflation hoses can be secured according to a first possibility in such a way that the inflation hoses are open at at least one end, the open end being in communication with the fluid supply chamber. If it turns out that when the pressure is being applied, the inflation hoses are closed unintentionally, they can be expanded in a funnel shape at their open ends or the rods can be designed with fluid supply grooves on their surface and / or fluid supply channels on the inside. If one makes use of the possibility of the fluid supply channels inside the rods, there is also the possibility of closing off the inflation hoses at both ends, at least at one end through the mediation of the respective rod, and then the fluid to the inside surface of the inflation hoses to lead via the fluid supply channels within the rods, these channels in turn being connected to the fluid supply chamber.

An embodiment appears particularly promising in which a squeeze plate is provided on each of the two mold end walls, one squeeze plate being squeezed into and out of the mold cavity for releasing and retracting the rods and relieved for inflation and the other is relieved when the rods move , so that the rods can penetrate them and, on the other hand, is squeezed when the inflation hoses are inflated. In this embodiment it is possible to work with inflation hoses which are open at both ends; the holder of the rods and the inflation hoses at one end is particularly simple in that the holder is simply taken over by the one squeeze plate. The installation of the coated rods is extremely simple because the rods only need to be inserted through the squeeze plate and then when the squeeze plate is squeezed to maintain their hold in the axial and transverse directions.

It is not absolutely necessary for the hoses to be open at both ends for the inflation, but it proves to be advantageous in particular with regard to rapid emptying of the inflation hoses.

The mold cavity can be provided with air suction means and at least one molding compound filling opening if the mold closing known from DE-A 3 101 236 is to be used. It is advisable, according to DE-A 3 101 236, to design the air suction means as a circumferential gap or a circumferential row of openings along the joint between a mold end wall and a mold jacket and the at least one molding compound filling opening in the joint area between the mold jacket and an opposite one Arrange the mold end wall. In this way, the requirement already laid down in DE-A 3 101 236 is met that the air suction openings should be along at least a maximum circumference of the mold cavity and the molding material supply at one point as far as possible equidistant from the suction openings or the suction gap. For details, reference is also made to the disclosure of DE-A 3 101 236 and the corresponding US Pat. No. 4,473,526.

With regard to the demolding, it can be advantageous to design the mold cavity with an at least two-part mold jacket. In contrast to an extrusion process, for example, the design with a subdivided molded jacket allows molded molded parts to be molded on the outside of the molded part, which differ from the cylindrical or prismatic shape, for example mounting flanges.

If the compact is also pressed from the outside by means of a jacket membrane, a closed molded jacket can be used which supports the jacket membrane on the inside. The jacket membrane also opens up the possibility of attaching profilings to the outside of the molding, including profilings that deviate from the cylindrical or prismatic shape of the molding. The only requirement for this is that the possible retraction path of the membrane is set so that it is greater than the height of such profiles relative to the surface of the molding.

The molding compound filling opening can be implemented by a sealing stamp with an end surface adapted to the shape of the molding cavity if one wishes to avoid impressions of the molding compound at the location of the molding compound supply opening.

For handling reasons, it is recommended that the bars run essentially vertically within the mold cavity and can be pulled out of the mold cavity upwards. This is also advantageous in order to avoid bending of the bars due to their own weight when inserting them into the mold cavity and to thereby possibly avoid difficulties which could arise when the bars and inflation tubes are threaded into the openings in the opposite end wall of the mold. In such an embodiment with vertical bars, it is advisable to arrange the air suction means in the lower region and the filling opening in the upper region of the mold cavity and thus to further favor the filling of the mold cavity.

In order to avoid sealing problems when introducing pressure medium into the inflation hoses, it is proposed that the inflation hoses are integrally connected at one end to a plate made of the same material.

• Fig. 1 eine Presse mit einer erfindungsgemäßen Einrichtung, teilweise geschnitten, wobei die Stäbe aus dem Formhohlraum zurückgezogen sind und der Formhohlraum offen ist;
• Fig. 2 eine Ansicht entsprechend derjenigen der Fig. 1, wiederum teilweise im Schnitt, wobei die Stäbe in den Formhohlraum eingefahren sind und der Mantel des Formhohlraums geschlossen ist;
• Fig. 3 eine Ansicht entsprechend der Fig. 2 bei einer abgewandelten Ausführungsform;
• Fig. 4 eine Vergrößerung entsprechend Fig. 1, wobei die Stäbe bereits in den Formhohlraum eingefahren sind, der Mantel des Formhohlraums und die Stäbe aber zur vergrößerten Darstellung teilweise unterbrochen sind;
• Fig. 5 eine vergrößerte Darstellung der Stäbe und ihrer oberen Halterung im Schnitt;
• Fig. 6 einen Schnitt nach Linie VI-VI der Fig. 5;
• Fig. 7 eine vergrößerte Darstellung des oberen Blähschlauchendes an der Stelle VII der Fig. 5;
• Fig. 8 einen Stabaufbau, abweichend von demjenigen gemäß Fig. 6;
• Fig. 9 eine Einfüllöffnung zum Einfüllen der Formmasse in den Formhohlraum und
• Fig. 10 eine Darstellung entsprechend Fig. 5 bei einer abgewandelten Ausführungsform.

The accompanying figures explain the invention using exemplary embodiments. They represent:

• Figure 1 is a press with a device according to the invention, partially cut, with the rods withdrawn from the mold cavity and the mold cavity is open.
• FIG. 2 shows a view corresponding to that of FIG. 1, again partly in section, the rods being inserted into the mold cavity and the jacket of the mold cavity being closed;
• Fig. 3 is a view corresponding to Figure 2 in a modified embodiment.
• FIG. 4 shows an enlargement corresponding to FIG. 1, the rods having already been moved into the mold cavity, but the shell of the mold cavity and the rods being partially interrupted for an enlarged view;
• Figure 5 is an enlarged view of the rods and their upper bracket in section.
• Fig. 6 is a section along line VI-VI of Fig. 5;
• Fig. 7 is an enlarged view of the upper inflatable hose end at point VII of Fig. 5;
• FIG. 8 shows a rod structure which differs from that according to FIG. 6;
• 9 shows a filling opening for filling the molding compound into the mold cavity and
• Fig. 10 is an illustration corresponding to FIG. 5 in a modified embodiment.

In Fig. 1, the stand of a ceramic press is designated 10. Several tie rods 12 protrude from this stand 10. These tie rods 12 are connected to one another at their upper end by a press yoke 14. A press bear 16 is guided vertically on the tie rods 12 and can be moved up and down by a hydraulic ram 18. A lower mold end wall 20 is stretched on the press stand 10. An upper mold end wall 22 and a group of vertical, inflatable tube-covered rods 24 are arranged on the press bear 16. The bars 24 with the inflation hoses are laterally spaced apart. On the press stand 10 two mold shell halves 26a and 26b are further attached, which together form a mold shell 26. The mold shell halves 26a and 26b are adjustable by hydraulic auxiliary presses 28a and 28b between a mold opening position shown in FIG. 1 and a mold shell closing position shown in FIG. 2. Centering mandrels 30 are attached to the press bar 16 and, when the press bar 16 goes down with the mold jacket 26 closed, ends around the upper mold to place wall 22 on the molded jacket 26, engage in blind holes 32 of the molded jacket 26.

When the mold jacket 26 is closed, the press bar 16 moves downward, so that the inflatable tube-covered rods 24 move into the mold cavity 34 formed within the mold jacket 26 (FIG. 2). Then the mold cavity 34 is filled with this molding compound by sucking in powdered molding compound. The inflation hoses, which surround the rods 24, are then inflated, so that a honeycomb-shaped compact is formed.

Further details are shown in FIGS. 4, 5 and 6.

It can be seen there that the upper mold end wall 22 is fastened to the press bear 16 by means of spacers 36. Within the spacers 36 two interconnected pressure plates 38 and 40 are attached. The centering pins 30 are connected to these pressure plates 38 and 40. The lower pressure plate 38 is perforated many times for receiving the rods 24. Likewise, as can be seen from FIG. 4, the upper mold end wall 22 is perforated many times for the passage of the rods 24. Between the pressure plate 38 and the upper mold end wall 22 there is a flat disk-shaped one Chamber formed for receiving a squeeze plate 42, which is formed between a squish surface 44 of the upper mold end wall 22 and a squish surface 38a of the pressure plate 38. A fluid supply chamber 46 is formed between the two pressure plates 38 and 40 and is connected to a fluid supply channel 48. The pressure plates 38 and 40 can be adjusted up and down by an auxiliary stamp 50.

As can be seen from FIG. 5, the rods 24 are covered by inflation hoses 52. It can be seen that the rods 24 and the tubes 52 extend to the top of the pressure plate 38, that is to say both the upper mold end wall 22 and the squeeze plate 42 and the lower pressure plate 38 pass through in bores. The inflation hose ends open at the top are in communication with the fluid supply chamber 46.

In addition, the rods 24 are provided with inner channels 54 and 54a, which are also in communication with the fluid supply chamber 46 and bring fluid to the inside of the inflation hoses 52.

In the lower mold end wall 20, which is firmly clamped onto the press frame 10, two pressure plates 56 and 58 are guided through an auxiliary stamp 60, specifically by means of mandrels 62, which can also engage in blind holes in the mold jacket when the mold jacket 26 is closed, in order to additionally press against this pressure hold together.

A squeeze plate 64 is received between the upper pressure plate 56 and the lower mold end wall 20, specifically between a squeeze surface 66 of the mold end wall 20 and a squeeze surface 56a of the pressure plate 56.

The rods and inflation tubes also penetrate the lower mold end wall 20, the lower squeeze plate 64 and the pressure plate 56; the lower ends of the channels 54 communicate with a lower fluid supply chamber 68. The fluid supply chamber 68 is connected to a fluid supply line 70.

The upper mold end wall 22 is provided with an annular seal 72 for placement on the mold jacket 26; the shaped jacket 26 is provided with sealing elements of semi-ring shape, which are denoted by 74 and rest on the lower mold end wall 20.

A vacuum line 76 is connected to the shaped jacket, in the region of the shaped jacket half 26a, which leads to an annular gap 78 or a plurality of suction openings 78 distributed in a ring. A molding material supply channel 80 is connected to the upper mold end wall 22 and is connected to a fluidizing air supply line 82 (cf. FIG. 9). The molding material supply line 80 opens into a molding material supply bore 84, which has an opening 86 in the molding cavity 34. This opening 86 can be closed by a stamp 88. Several such molding material feeds can be arranged distributed over the circumference.

The device described so far works as follows:

The device is initially in the position shown in FIG. 1. By pressing the auxiliary punches 28a and 28b, the molded jacket 26 is first closed. The pressbear 16 then moves downward, the inflatable tube-covered rods 24 passing through the perforations of the lower mold end wall 20, the squeeze plate 64 and the pressure plate 56. In the position of FIG. 1 and while the press bear 16 is moving downward, the inflatable tube-covered rods 24 are held on the bear 16 in that the squeeze plate 42 is squeezed between the squeeze surfaces 38 a and 44. At the same time, the squeeze plate 64 is relieved, so that the bars with the inflatable tubes 52 can pass through the perforations of the lower squeeze plate 64 unhindered. As soon as the device has reached the position according to FIGS. 2 and 4, the lower squeeze plate 64 is squeezed by means of the auxiliary stamp 60 and the upper squeeze plate 42 is relieved. The rods 24 are now fixed in the longitudinal direction by the lower squeeze plate 64.

The mold cavity 34 is now filled with molding compound by applying a vacuum to the mold cavity 34 through the gap 78 and the sealing die 88 being pulled.

By sucking the molding compound into the mold cavity 34, the latter is also completely filled and pre-compressed between the rods 24. As long as the vacuum is applied to the mold cavity 34 via the openings 78, a vacuum must also be applied to the inside of the inflation hoses via the pressure fluid supply lines 48 and 70, so that they do not stand out from the rods 24 under the effect of the vacuum in the mold cavity can.

The molding compound sucked into the mold cavity is already somewhat pre-compressed by the relatively high impact speed of the molded particles, although this is done by adjusting the impact points speed at least at the beginning of the filling process, care must be taken to ensure that the suction openings 78 are not blocked.

Once the mold cavity is filled, the vacuum applied to the inner surfaces of the inflation hoses 52 is turned off and then pressure is applied via lines 48 and 70 and the fluid supply chambers 46 and 68 to the inner surfaces of the inflation hoses 52, partly via the channels 54, 54a , partly over the open ends of the tubes 52. The inflatable tubes are inflated and compact the filled molding compound within the mold cavity 34. The rods 24 cannot change their position laterally since they are secured in the perforations of the end walls 20 and 22 against lateral movement are.

Inflation of the inflation hoses outside the mold cavity is not possible, since the inflation hoses in the perforations of the mold end walls 20, 22, the squeeze plates 42 and 64 and the pressure plates 38 and 56 are secured against inflation and at the same time at their ends the internal pressure and the external pressure of the Exposed to fluids.

As soon as the inflation process has led to sufficient compacting, the fluid pressure is reduced again through the two fluid lines 48 and 70, so that the inflation hoses now return to their position, which is snug against the rods 24. Now the squeeze plate 64 is relieved and the squeeze plate 42 is squeezed again. The press bear can then move upwards, taking the rods with them, which are pulled out of the perforations of the pressure plate 56, the squeeze plate 64 and the lower end wall 20 of the mold.

Finally, the mold shell halves 26a and 26b are moved apart so that the finished compact can be removed.

It is also possible to dispense with the channels within the bars 24 when pressing. The fluid supply to the inside of the inflatable tubes then takes place, for example, through the funnel-shaped upper ends 52a of the inflatable tubes 52 (FIG. 7), the filling of the inflatable tubes being made possible by relieving the pressure on the upper squeeze plate 42 and squeezing the lower squeeze plate 64. It is then only necessary to supply fluid from the line 48 via the fluid supply chamber 46, because the inflatable tubes are squeezed like a valve at their lower ends by the squeeze plate 64. In this latter embodiment, the filling of the inflation hoses can also be supported in that the rods 24 are provided with surface grooves 90, which prevent the inflation hoses from being inadvertently closed when the fluid hoses are applied by tightly fitting them against the rods 24.

In the embodiment according to FIG. 3, the mold jacket 126 is a one-piece, annularly closed mold jacket which is lined on the inside by a ring membrane 192, the ring membrane 192 being able to be subjected to a vacuum on its rear side via a fluid supply system 194 when the mold cavity is filled and can be pressurized when the molding compound is pressed. Of course, it is also possible here to form the molded jacket 126 in two parts and to divide the membrane 192 accordingly. The compact must be removed in the axial direction with the mold jacket closed in a ring.

3 corresponds to that of FIGS. 1, 2, 4, 5, 6 and 9.

In the embodiment according to FIG. 1, the mold shell halves 26a and 26b can be provided with profiles, for example profiles which result in holding elements or a holding flange for the molding. These profiles must of course be shaped so that they take into account the direction of removal. The projections can be arranged either close to the edge or between the edges of the mold shell halves 26a, 26b.

In the embodiment according to FIG. 3, profiles can be provided in the molded jacket 126 and in the membrane 192, in order to also produce profiles on the molded article. If these profilings extend parallel to the jacket axis over the entire length of the inner surface of the molded jacket 126, this does not cause any difficulties in the demolding. However, it is also possible to apply profilings to the inner surface of the molded jacket 126 and to the membrane in order to allow corresponding profilings to be formed on the molded article if these profilings do not extend over the entire height of the molded jacket 126, but for example at a distance from the upper edge and lower edge end of the molded jacket, or to provide profiles which produce ribs or the like running on the molded article in the circumferential direction. In this case, with regard to the demolding, care must be taken that either the molded jacket is divided or the return path of the membrane when releasing the pressure and, if necessary, re-applying the supporting vacuum is large enough to compensate for the profiling on the outside of the molding compared to the profiling to release the membrane and, if applicable, the shaped jacket 126.

The embodiment of FIG. 10 differs from that of FIG. 5 in that the inflatable hoses 52 are designed differently. In the embodiment according to FIG. 10, the inflatable hoses 52 are closed at their lower ends. The channels 54 are likewise closed at their lower ends. The decisive difference is that the inflation hoses 52 are integrally connected at their upper ends to a plate 52x made of the same material. In this way, the sealing problem for the pressure medium to be introduced into the inflation hoses 52 is solved in the simplest way.

The powdery molding compound used can in particular be a spray grain compound which has been produced as follows:

A slip containing 40% by weight water and 60% by weight solid was processed. For the preparation of the suspension, a dry mass was produced which consisted of 50% by weight kaolinite, 25% by weight feldspar and 25% by weight quartz, the percentages in each case based on the Ge velvet dry matter, consisted. The grain size of the kaolinite was max. 25 g. The grain size of feldspar and quartz was max. 63 µ. Feldspar and quartz were introduced in the form of a pegmatite, which contains both the feldspar and the quartz. The dry matter was processed into a suspension or a slip with the addition of the water. This slip was then sprayed through spray nozzles into a hot gas atmosphere. In this hot gas atmosphere, spheres with a size of 0 to 500 μ formed, with 80% of the total weight between 350 and 450 days. The beads were hollow beads that could be easily crushed between two fingers of one hand. The residual moisture of the granular material obtained in this way was approx. 3%.

Claims (31)

1. A method of making pressed mouldings provided with ducts from a moulding compound, wherein, in a mould cavity (34) filled with the moulding compound and traversed by rods (24) encased in inflatable tubes (52), the inflatable tubes (52) are expanded by means of fluid pressure applied to their inside with compaction of the moulding compound to form the blank and, after the fluid pressure has been reduced, the sheathed rods (24) are withdrawn from the blank and the latter is removed from the mould cavity (34), characterized in that the filling of the pulverulent moulding compound into the mould cavity (34) takes place while the inflatable tubes (52) bear against the rods (24) along the portions of their length situated within the mould cavity (34).

2. A method according to Claim 1, characterized in that a membrane (192), at least partly bounding the mould cavity (34), is subjected to a fluid pressure on the side remote from the moulding compound, especially simultaneously with the fluid pressure application to the inflatable tubes (52).

3. A method according to one of Claims 1 and 2, characterized in that, after the fluid pressure in the inflatable tubes (52) and, if applicable, against the membrane (192) has been reduced, the rods (24) are first pulled out and thereafter the blank is removed from the mould cavity (34).

4. A method according to one of Claims 1 to 3, characterized in that, for the introduction of the pulverulent moulding compound into the mould cavity (34), a vacuum is applied to this cavity (at 78) and the moulding compound is thereby sucked in.

5. A method according to Claim 4, characterized in that, during the existence of a sub-pressure in the mould cavity (34), a sub-pressure is also maintained at the inner face of the inflatable tubes (52) and, if applicable, also at the side of the membrane (192) remote from the moulding compound, in order to keep the inflatable tubes (52) in contact with the rods (24) and, if applicable, the membrane (192) in contact with the mould wall (126).

6. A method according to one of Claims 1 to 5, characterized in that a ceramic moulding compound is used as pulverulent moulding compound.

7. Apparatus for making blanks provided with ducts from pulverulent moulding compound, comprising a mould cavity (34), a group of rods (24) inside the mould cavity, which are surrounded over at least a part of their length by inflatable tubes (52), a filling device (78, 80, 82, 84, 86, 88) for filling the mould cavity (34) with the pulverulent moulding compound and a fluid feed device (48, 46) for the feed of pressurized fluid to the inner side of the inflatable tubes (52), characterized in that the inflatable tubes (52), in the at-rest condition, that is before the fluid pressure is applied, bear against the rods (24) with their longitudinal portions contained within the mould cavity (34).

8. Apparatus according to Claim 7, characterized in that the mould cavity (34) is bounded at least partly by a pressure-loadable membrane (192).

9. Apparatus according to one of Claims 7 and 8, characterized in that the rods (24) are disposed parallel to one another.

10. Apparatus according to Claim 9, characterized in that the membrane (192) is a side wall membrane (192) having its generatrix parallel to the rods (24).

11. Apparatus according to one of Claims 7 to 10, characterized in that the rods (24), during the pressure loading of the inflatable tubes (52) and, if applicable, of the membrane (192), are fixed at their ends at least transversely to their longitudinal direction relative to the mould cavity (34).

12. Apparatus according to one of Claims 7 to 11, characterized in that, for the joint introduction and removal of the rods (24) into and out of the mould cavity (34), a rod holder (22, 38, 40, 42, 50) and a linear drive (16, 18) for this rod holder are provided.

13. Apparatus according to Claim 12, characterized in that a perforated mould wall (22) of the mould cavity (34), facing towards the rod holder and traversed by the rods, is connected with the rod holder for the combined movement by the linear drive (16,18).

14. Apparatus according to one of Claims 7 to 13, characterized in that the inflatable tubes (52) project out beyond the mould cavity (34) with end portions subjected at one side to the fluid pressure and that these end portions are housed in the relevant mould end wall (20, 22) by support ducts closely surrounding them.

15. Apparatus according to one of Claims 7 to 14, characterized in that the inflatable tubes (52) pass, at least at one end jointly with the rods (24), through a squeeze plate (42; 64), squeezable between two squeezing surfaces (38a, 44; 56a, 66), which (squeeze plate) can be squeezed for the purpose of sealing the inflatable tubes (52) in the region of the relevant end and/or the fixing of the inflatable tubes (52) and the rods (24) in the region of their relevant end.

16. Apparatus according to Claim 15, characterized in that the squeeze plate (42, 64) is housed between a surface (44; 66) remote from the mould cavity of the relevant perforated mould end wall (22; 20) and a perforated pressure plate (38; 56).

17. Apparatus according to one of Claims 7 to 16, characterized in that the inflatable tubes (52) are or can be attached by at least one end each to a fluid supply chamber (46; 68).

18. Apparatus according to Claim 17, characterized in that the inflatable tubes (52) are open at at least one end, the open end being in communication with the fluid supply chamber (46; 68).

19. Apparatus according to Claim 18, characterized in that the inflatable tubes (52) are widened out funnel-shaped at their open ends (at 52a).

20. Apparatus according to Claim 18 or 19, characterized in that the rods (24) are formed at their surface with fluid supply grooves (90) and/or in their interior with fluid supply ducts (54, 54a).

21. Apparatus according to Claim 17, characterized in that the inflatable tubes (52) are closed at both ends, and indeed at at least one end by means of the relevant rod (24), and that the inner surfaces of the inflatable tubes (52) are in communication via fluid supply ducts (54, 54a) inside the rods (24) with the fluid supply chamber (46; 68).

22. Apparatus according to one of Claims 15 to 20, characterized in that, at each end wall (22, 20) a squeeze plate (42; 64) is provided, the one squeeze plate (42) being squeezed for the purpose of introducing and withdrawing the rods (24) into and out of the mould cavity (34) and being relieved of load for the purpose of inflation, and the other (64) being relieved of load as the rods (24) move and being squeezed as the inflatable tubes (52) are inflated.

23. Apparatus according to one of Claims 7 to 22, characterized in that the mould cavity (34) is provided with air extraction means (76, 78) and at least one moulding compound filler opening (86) and that, if applicable, for the purpose of applying the inflatable tubes (52) onto the rods (24) and the membrane (192) onto the mould wall (126), means for applying a vacuum to the inside of the inflatable tubes (52) and to the side of the membrane (192) remote from the moulding compound are provided.

24. Apparatus according to Claim 23, characterized in that the air extraction means comprise a peripheral gap or a peripheral row of openings (78) along the joint position between one mould end wall (20) and a mould side wall (26), and that at least one moulding compound filler opening (86) is disposed in the joint region between the mould side wall (26) and an opposite mould end wall (22).

25. Apparatus according to one of Claims 7 to 24, characterized in that the mould cavity (34) possesses a mould side wall (26) subdivided at least twice.

26. Apparatus according to one of Claims 7 to 24, characterized in that the mould cavity (34) comprises a closed mould side wall (126) and a side wall membrane (192) supported against the inner face of the side wall (126).

27. Apparatus according to one of Claims 23 to 26, characterized in that the moulding compound filler opening (86) is closable by a closure plunger (88) having an end face adapted to the shape of the mould cavity (34).

28. Apparatus according to one of Claims 7 to 27, characterized in that the rods (24) extend substantially vertically inside the mould cavity (34) and can be withdrawn upwards out of the mould cavity (34).

29. Apparatus according to Claim 28, characterized in that the air extraction means (78) are disposed in the lower region and the filler opening (86) in the upper region of the mould cavity (34).

30. Apparatus according to one of Claims 7 to 29, characterized in that, at the inner face of the mould cavity (34) and, if applicable, at a membrane bearing against this inner face, profilings are formed, which produce projections and/or depressions on the outer face of the moulding, especially projections or depressions which impart to the moulding a surface which differs from the cylindrical or prismatic form.

31. Apparatus according to one of Claims 7 to 30, characterized in that the inflatable tubes (52) are, at one end each, sealingly, integrally continuous with a plate (52x) of the same material.

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