DE20115860U1 - Pressing device - Google Patents

Description

DE 8221 Patent Attorney

Graduate Physicist

Reinfried Frhr. &ngr;. Schorlemer

Karthäuserstr. 5A 34117 Kassel Allemagne

Telephone/Telephone (0561) 15335

(0561)780031

Fax/Telecopier (0561)780032

Harald Schneider, 34134 Kassel
Pressing device

The invention relates to a pressing device of the type specified in the preamble of claim 1.

Known pressing devices of this type are used, among other things, to produce pipes that have a bottom at one end (DE 295 00 253 Ul). The bulk material used is preferably a special mixture containing vermiculite, water glass and a silicone-containing hydrophobic agent with a grain size of e.g. 1 mm to 2 mm, in order to obtain molded parts with tubular sections that are largely insensitive to moisture and wetness.

When using such pressing devices, the tubular sections are compressed in the radial direction at a ratio of 3:1 or more, i.e. during the pressing process, the wall thickness created when filling the pressing chamber is compressed to a third in order to achieve a high level of strength. However, such pressing pressures are not always applicable, particularly when molded parts with more complicated shapes are involved. If, for example, molded parts are to be produced which have a tubular section with a radially protruding flat part attached to one end, as is the case for the heat protection housings of catalysts for household ovens, then uniform compression and strength of the bulk material can only be achieved throughout the molded part if the bulk material is compressed in a ratio of 2:1 using axial compression.

•# · φ φ φ φ φ ··■···· r

becomes.

φ φ φ φ φ

The use of such pressing pressures has the surprising result that cracks easily appear where the corner jaws of the pressing device, arranged between the pressing jaws, border on the surfaces of the molded parts, since crumbs can form here due to insufficient pressing. This is attributed to the fact that a type of laminate formation takes place in these areas during the pressing process, because the edge zones of the pressing jaws only push the bulk material in front of them in directions perpendicular to one another and therefore the bulk material particles cannot be adequately mixed. The areas compacted by adjacent pressing jaws therefore consist of separate zones pushed against one another, which are not or only incompletely connected along their interfaces.

The invention is based on the technical problem of designing the pressing device of the type described at the outset in such a way that even with compression ratios of up to approximately 2:1, cracks in the molded parts are avoided and uniform compression is achieved over the entire circumference of the tubular sections.

The characterising features of claim 1 serve to solve this problem.

The invention has the advantage that crack formation is avoided even with comparatively small compression ratios. The chambers or cavities formed according to the invention with the aid of the end surfaces and the bevelled edges, which are set back radially behind the outer surfaces of the molded parts, obviously have the effect that the bulk material can partially move sideways during the pressing process and build up a counterpressure that enables uniform mixing and compaction of the bulk material grains even in the interfaces and therefore counteracts crack formation.

Further advantageous features of the invention emerge from the subclaims.

The invention is explained in more detail below in conjunction with the accompanying drawings using an exemplary embodiment. They show:

Fig. 1 shows a vertically adjustable pressing device

-3-in
a filling position;

Fig. 2 is a slightly enlarged plan view of the pressing device according to Fig. 1 with the upper part removed, i.e. approximately as a section along a parting plane indicated by the line II-II in Fig. 1;

Fig. 3 is an enlarged detail X of Fig. 2;

Fig. 4 and 5 show two views of the pressing device according to the invention corresponding to Fig. 1, but in an intermediate and end position; and

Fig. 6, 7 or 8, 9 or 10, 11 are plan views corresponding to Fig. 2 or enlarged details X of the pressing device corresponding to Fig. 3, but in two intermediate positions and one end position corresponding to Fig. 5.

The pressing device according to the invention is explained in more detail below using a molded part 1 (Fig. 5) to be produced in one piece, which represents, for example, a housing for a catalyst and has a tubular section la, to one end of which, in Fig. 5, at least one radially projecting flat part 1b is attached. The bulk material used to produce the molded part 1 is dotted in Figs. 1 to 11 and shown in different shades of gray in order to make the gradual pressing of the molded part 1 and the resulting different degrees of compaction of the bulk material visible.

According to Fig. 1 and 2, the pressing device is provided with a pressing chamber 2, in the center of which a core 3 is arranged with an axis 4 which rises vertically from a base (not shown) forming the underside of the pressing device. Alternatively, the axis 4 could also be arranged horizontally or obliquely.

Four sections 2a to 2d of the chamber 2 adjoin the core 3, whereby the sections 2a, 2b and 2c are arranged opposite one another in pairs and whereby all sections 2a to 2d are spaced apart from one another by 90° along the circumference of the core 3. The height of the

Chamber 2 uh<J ^: $Jej Ab&rHjifte.Ja to .24 .from .the .floor? .to the top depends

the length of the core 3 or of the molded part 1 to be produced. The outer contour or the outer cross section of the core 3 corresponds to the desired inner contour of the tubular section la and is cylindrical in the embodiment.

In sections 2a to 2d of the press chamber 2, a press jaw 5a to 5d is arranged which extends over the height of the chamber and is mounted so as to be displaceable in the direction of an arrow u perpendicular to the axis 4 of the core 3 and radially to the tubular section la to be produced and has a press surface 6a to 6d (Fig. 2) on its front side facing the core 3, which is provided with a profile 7 formed from recesses and projections if required. All press jaws 5a to 5d are preferably identical and adapted to the outer contour of the tubular section la in the finished state according to Fig. 5. In the case of larger cross-sectional changes in this area, the press jaws 5a to 5d are preferably divided in order to enable filling to take this circumstance into account.

According to Fig. 2, the press chamber 2 is further delimited by four identical corner jaws 8a to 8d, each of which has a corner 9a to 9d and two side walls 10 and 11 adjoining it. The arrangement is such that the side walls 10, 11 of adjacent corner jaws 8a to 8d are parallel to one another in pairs as shown in Fig. 2 and on the one hand form a guide in which an associated press jaw 5a to 5d can be displaced in the manner described, and on the other hand seal the sections 2a to 2d laterally. The corner jaws 8a to 8d can, if required, be mounted so as to be displaceable in the direction of arrows v perpendicular and radial to the core axis 4 and can be moved back and forth between the front end position shown in Fig. 2 and a retracted position used for demolding. It is understood that the displacement directions for the pressing jaws 5a to 5d (arrows u) preferably each form an angle of 45° with the displacement directions (arrows v) of the adjacent corner jaws 8a to 8d, although other angles are also possible.

As shown in particular in Fig. 1, 4 and 5, the core 3 is surrounded by a first, sleeve-shaped compensating element 12, which has an inner cross section corresponding to the outer cross section of the core 3 and a tubular section parallel to the inner cross section and the outer cross section. The compensating element 12 is on

the core 3 is mounted so as to be movable back and forth parallel to the axis 4, i.e. in the direction of a double arrow w (Fig. 1).

The compensating element 12 can in turn be surrounded by a second compensating element 14, which has an inner cross-section corresponding to the outer cross-section of the first compensating element 12 and a circular outer cross-section which corresponds approximately to the outer cross-section of the tubular section la to be produced. In this case, the compensating element 14 is mounted so that it can slide back and forth on the first compensating element 12 in the direction of a double arrow x. In addition, the compensating element 14 is mounted so that it can slide in a stationary guide body 15 which seals the press chamber 2 to the outside and guides the undersides of the press jaws 5.

On its upper side, the pressing chamber 2 is delimited by a likewise stationary bearing ring 16, in the center hole of which a pressure plate 17 is arranged which delimits the pressing chamber 2 in this area and is mounted so as to be displaceable parallel to the axis 4 (double arrow y_ in Fig. 1). The pressure plate 17 has a passage 18 which is coaxial with the core 3 and the axis 4 and has an inner cross section corresponding to the outer cross section of the core 3.

Pressing devices of this type are generally known (DE 295 00 253 Ul) and therefore need not be explained in more detail.

According to the invention, both the pressing surfaces 6a to 6d of the pressing jaws 5 and the corners 9a to 9d of the corner jaws 8a to 8d are designed in a special way, as can be seen in particular in Fig. 3, which shows a detail X of Fig. 2 in great magnification. In Fig. 3, the two adjacent pressing jaws 5a and 5b and the corner jaw 8b arranged between them are shown, although only the end sections of the pressing surfaces 6a and 6b of these pressing jaws 5a, 5b immediately adjacent to the corner jaw 8b are visible, as can easily be seen from a comparison with Fig. 2.

Deviating from the known pressing patterns, the pressing surfaces 6a, 6b are not provided with

their curvature corresponding to the outer edge ^of the

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continuously up to the side wall 10 or 11 of the adjacent corner jaw 8b. According to the invention, the pressing surfaces 6a, 6b are provided with bevels on their lateral edges. Beveled edges 20a or 20b formed in this way slope outwards, i.e. in the direction of the side walls 10, 11 of the corner jaw 8b, and therefore form angles with these that are smaller than 90°. This ensures that the bulk material coming into the effective area of the pressing surfaces 6a, 6b is not only transported in this direction when they are advanced in the direction of the axis, but also receives a movement component transverse to it, i.e. in the direction of the side walls 10, 11, as explained below. The lateral edges of the pressing surfaces 6a, 6b and the other pressing surfaces 6c, 6d, which are not visible in Fig. 3, are designed accordingly.

According to the invention, the corners 9a to 9d do not run towards each other at angles of 90° when there are four corner jaws 8a to 8d, but are also provided with bevels. According to Fig. 3, these lead, for example, to an end surface 21b that faces the core 3 and forms an angle of 90° with a radius 22 (Fig. 2) extending from the axis 4 and running through an imaginary 90° corner that would otherwise be present. However, angles other than those shown in Figs. 2 and 3 and end surfaces 21b other than flat are also possible. The corner jaws 9a, 9c and 9d are provided with end surfaces 21 in a corresponding manner.

The end surfaces 21b are arranged in the front end position of the corner jaws 8, as can be seen in particular from Fig. 10 and 11, at a greater radial distance from the axis 4 than is the case for the pressing surfaces 6a to 6d when the pressing jaws 5a to 5d are in the pressing position. The reasons for this are evident from the following description.

The production of the molded part 1 is essentially carried out as follows:

First, the corner jaws 8, if they are designed to be movable, are brought into their front end position and at the same time the pressing jaws 5 are brought into a retracted filling position, as shown in Fig. 1 and 2. In addition, the two compensating elements 12 and 1.4 are brought into the end positions retracted downwards, as shown in Fig. 1.

tion and the SQjufikplattBin.iÄ ejae njftit.represented , ^: #ach hben.»!retracted final position

-7-

tion in which the pressing chamber 2 is accessible from above.

The pressing chamber 2 is now filled with bulk material up to the level shown in Fig. 1 or slightly more, which is indicated by dotted lines. The pressure plate 17 is then pushed forward in the direction of the arrow y in the direction of the axis 4 up to the bulk material until, as shown in Fig. 1, its underside enters the center hole of the bearing ring 16 and the core 3 enters with its upper side into the passage 18 of the pressure plate 17, in order to completely close and seal the pressing chamber 2 on its upper side.

At the same time, the first compensating element 12 can be raised slightly in the direction of the arrow w, so that the bulk material is pushed together and partially compacted in an area 23 of the press chamber 2 located between the pressure plate 17 and the first compensating element 12 or the core 3. This ensures that the bulk material, where the flat part 16 is to be attached to the tubular section la, cannot escape upwards during the subsequent pressing process, but also offers a certain resistance to the bulk material fed in by means of the press jaws 5.

Furthermore, the pressing chamber 2 is limited and sealed at the sides by the pressing jaws 5 and the corner jaws 8, while at the bottom it is limited and sealed by the compensating elements 12, 14 and the guide body 15. The actual pressing process can now begin.

In a first process step, the press jaws 5 are advanced in the direction of the front end position, whereby the bulk material is gradually compacted in the other sections of the chamber 2. When the press jaws 5 have already been advanced for part of their stroke, the pressure plate 17 is also moved downwards in Fig. 1 and the first compensating element 12 is moved upwards in the direction of the upper edge of the core 3 until all of these parts have reached their end position shown in Fig. 5 and have formed the molded part 1 consisting of the tubular section 1a and the flat part 16. The first compensating element 12 also serves the purpose of compacting the material evenly in order to form the flat section 16 in

an upper, circumferential, fixed ^, septum-shaped section la to be requested

by pressing the bulk material in this critical zone not only radially from the outside by means of the pressing jaws 5, but also axially from above and below by means of the first compensating element 12 and the pressure plate 17. The lengths of the strokes of the first compensating element 12 and the pressure plate 17 can be selected depending on the desired compression ratio and in such a way that essentially the same compression ratio of preferably about 2:1 is obtained throughout the entire molded part 1.

To increase the stability of the molded part 1, it may be expedient to press the tubular section 1a more strongly in its upper region 23 bordering the flat part 1b than in the other regions. To this end, while the parts 5, 12 and 17 have been brought into their final position, the second compensating element 14 is also gradually pushed forward into its upper final position shown in Fig. 5, in which it is approximately flush with the surface of the guide body 15.
15

After a preselected dwell time in the position shown in Fig. 5, all parts are retracted into the positions essentially shown in Figs. 1 and 2 so that the finished molded part 1 can be demolded and removed.

The various transition positions between the filling position according to Fig. 1 and 2 and the pressing or end position according to Fig. 5 and 10 can be seen in Fig. 4, 6 and 8. In contrast, the effect of the bevelled edges 20 of the pressing jaws 5 and the end surfaces 21 of the corner jaws 8 can be seen in Fig. 3, 7, 9 and 11. Starting from the filling position according to Fig. 3, the pressing jaws 5a, 5b are initially gradually pushed forward in the direction of the pressing position with the corner jaw 8b in the end position. The pressing surfaces 6a, 6b push the bulk material in front of them essentially in a radial direction, since the side walls 10, 11 of the corner jaw 8b still have a limiting effect here. This essentially applies until the intermediate position according to Fig. 9 is reached.

At the latest when the intermediate position of the pressing jaws 5a, 5b is reached as shown in Fig. 9, the bevelled edges 20a, 20b result in the bulk material being deflected increasingly transversely to the feed direction into a cavity 'UA' during further feed in the direction of the axis 4: the now straight edges 20a and 20b,

side surfaces of the press jaws 5 and the end surface 21b. As a result, the bulk material is pressed somewhat less strongly in this area, since the cavity 24 forms an escape chamber or a compensation and support chamber which takes up excess bulk material. On the other hand, the end surface 21b forms a counter-pressure surface which prevents further escape of the bulk material and builds up a counter-pressure. Therefore, when the press jaws 5a, 5b reach their front end or pressing position shown in Fig. 11, in which they rest against the peripheral jacket of the tubular section la (Fig. 10) of the now completely pressed molded part 1, the cavity 24 is almost closed off by the inclined edges 20a, 20b of the press jaws 5a, 5b.

The arrangement is advantageously such that in this position the edges 20a, 20b almost touch each other along their edges 25a, 25b (Fig. 11) bordering the side surfaces of the press jaws 5a, 5b. This ensures that only narrow and radially slightly protruding ridges 26 are formed on the peripheral surface of the tubular section 1b wherever a corner jaw 8 is located, which do not have a disruptive effect on the finished molded part 1. In contrast, the bulk material in the area of the remaining cavities 24 is only very slightly compacted, so that it falls off or can be easily stripped off when the molded part 1 is removed from the mold and does not contribute to the formation of the ridges 26.

The invention has the advantage that in the area of the ridges 26 no more disturbing laminate formations occur, but the tubular section la is also solid and mechanically stable in these zones, without tending to crack. This is probably a result of the fact that the bulk material is evenly mixed and compacted in the interfaces between the layers pushed radially forward by the press jaws 5 due to the lateral displacement into the cavities 24. This makes it possible to compact the bulk material in the tubular section la in a ratio of approximately 2:1, so that compaction during production of the molded part 1 can be carried out both radially and axially at a ratio of approximately 2:1, which leads to an effective overall compaction. The angles at which the edges 20a, 20b are to beveled and the depth of the cavities 24 in the radial direction, i.e. The radial distances of the end surfaces 21b from the outer surface of the molded part 1 when the pressing jaws 5 are in the pressing position can easily be determined in individual cases by means of tests.

The invention is limited to the following example:

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can be modified in many ways. This applies in particular to the tube or flat part shapes shown and the compression ratios specified, which can be selected differently depending on the individual case. In particular, it is possible to produce molded parts in the manner described which are hollow cylindrical as a whole. Furthermore, only the parts absolutely necessary for understanding the function are shown in Fig. 1 to 11. The various movements can be brought about in particular with the aid of hydraulic or pneumatic cylinder-piston arrangements, servomotors or the like and by using suitable guides, as is usual in mechanical engineering for comparable purposes and is generally known to the person skilled in the art. When using materials other than those described, e.g. Styrofoam, it can also be expedient to cool or heat the core 3 and/or the press jaws 5a to 5d or their pressing surfaces 6a to 6d during the pressing process in order to influence the achievable compression ratio. It is further clear that the tubular section la could also be manufactured by means of three or more than four pressing jaws 5 and a corresponding number of corner jaws 8 distributed at corresponding angular intervals around the axis 4. The bevelled edges and end faces are then provided in a corresponding manner. Finally, it is clear that the various features can also be applied in combinations other than those described and illustrated.

Claims (8)

1. Pressing device for producing a molded part ( 1 ) having a tubular section ( 1a ) from loose material by applying pressure, comprising: a core ( 3 ) with an axis ( 4 ) and an outer cross section corresponding to the inner cross section of the tubular section ( 1a ), at least three corner and pressing jaws ( 8 and 5 ) arranged alternately one after the other, which are arranged radially outside the core ( 3 ) and surround it in a ring shape, and a pressing chamber ( 2 ) which is delimited on a radially inner side by the core ( 3 ) and on a radially outer side by the corner and pressing jaws ( 8 , 5 ), wherein at least the pressing jaws ( 5 ) are mounted so as to be able to be pushed back and forth between a radially retracted filling position and a radially advanced pressing position and facing the core ( 3 ) and in the pressing position corresponding to the outer cross section of the tubular section to be produced, tubular section ( 1a ), characterized in that the pressing surfaces ( 6 ) are provided with bevelled, outwardly sloping edges ( 20a , 20b ) on lateral edges and the corner jaws ( 8 ) are provided with end surfaces ( 21b ) on the corner regions facing the core ( 3 ), which, when the pressing jaws ( 5 ) are in the pressing position , have a greater radial distance from the axis ( 4 ) than the pressing surfaces ( 6 ) and form a compensation and support chamber ( 24 ). 2. Pressing device according to claim 1, characterized in that it contains four corner and pressing jaws ( 8 , 5 ). 3. Pressing device according to claim 1 or 2, characterized in that the stroke of the pressing jaws ( 5 ) between the filling position and the pressing position is selected such that the bulk material is compacted during the pressing process in a ratio of approximately 2:1. 4. Pressing device according to one of claims 1 to 3, characterized in that it is designed to form at least one radially extending flat part ( 1 b) arranged at one axial end of the tubular section ( 1 a). 5. Pressing device according to claim 4, characterized in that the pressing chamber ( 2 ) is delimited at the end of the tubular section ( 1a ) to be provided with the flat part ( 1b ) by a pressure plate ( 17 ) which is movable in the direction of the axis ( 4 ) and which has a passage ( 18 ) intended to receive the core ( 3 ). 6. Pressing device according to claim 4 or 5, characterized in that the pressing chamber ( 2 ) is delimited on a side facing away from the flat part ( 1b ) by a first compensating element ( 12 ) mounted axially displaceably on the core ( 3 ). 7. Pressing device according to one of claims 4 to 6, characterized in that the pressing chamber ( 2 ) is delimited on a side facing away from the flat part ( 1b ) by a second compensating element ( 14 ) displaceably mounted on the core ( 3 ) or the first compensating element ( 12 ). 8. Pressing device according to one of claims 4 to 7, characterized in that the compaction of the bulk material in the radial and axial directions takes place approximately in a ratio of 2:1.