GB2075415A

GB2075415A - Pressing ceramic powder

Info

Publication number: GB2075415A
Application number: GB8114415A
Authority: GB
Original assignee: Erich Netzsch GmbH and Co Holding KG
Current assignee: Erich Netzsch GmbH and Co Holding KG
Priority date: 1980-05-12
Filing date: 1981-05-12
Publication date: 1981-11-18
Also published as: DE3018138A1; GB2075415B; IT1137008B; DE3018138C2; IT8121658A0

Abstract

A press tool for moulding articles such as plates from ceramic powder material comprises first 30, 32 and second 60 mould parts with a flexible membrane 24 therebetween, the membrane being deflectable by pressure medium admitted at 46. As the mould is opened, the first mould part 30, 32 is advanced plunger-like in a mould part holder 16 so as to cause a reduction in pressure in a space 40 therebetween, so drawing the membrane against the first mould part. In this manner the edge of the moulded article is freed from the edge bead 26 of the membrane so that the article may expand unhindered when the pressing pressure is relieved. <IMAGE>

Description

SPECIFICATION Press tool for producing moulded ceramic articles from powder material The invention relates to a press tool for producing moulded ceramic articles, from powder or granular material. The invention is particularly applicable to the production of plates.

Plates may be moulded in a press tool which comprises: a first mould part having a first mould face complementary to one side of the article to be moulded, in particular to the underside of the plate, as well as at least one duct leading from said first mould face to the rear of the first mould part; a second mould part having a second mould face complementary to the opposite side of the article to be moulded, in particular to the upper side of the plate; a pot-shaped mould part holder having a cylindrical inner wall surrounding the first mould part, a bottom, as well as a pressure medium connection, and, for opening and closing the press tool, as well as for pressing the material, being axially movable together with the first mould part relative to the second mould part; a membrane having an edge bead secured on the mould part holder and capable optionally of being attracted by suction up against the first mould face or of being pressed away from the first mould face by a pressure medium fed via the pressure medium connection; and an intermediate space between the bottom of the mould part holder and the rear side of the first mould part, in which space pressure below or above atmospheric pressure is likewise effective.

A press tool of this type is known, (DE-AS 26 27 160), in which the outer diameter of the first mold part devised to support the membrane is substantially larger than the inner diameter of the membrane edge bead which determines the outer diameter of the pressed moulded article. The first mould part consists of a ring-shaped insert bolted to the bottom of the pot-shaped mould part holder and an axially movable centre member guided in this insert and biassed by a spring towards the membrane. In the filling position of the known press tool (Fig. 4 of DE-AS 26 27 1 60), the membrane is in contact only with the movable centre member and is lifted by the latter off the major portion of the mould face formed on the ring-shaped insert.However, it is possible to apply a sub-atmospheric pressure at the pressure medium connection at the bottom of the mould part holder, this sub-atmospheric pressure then establishing itself throughout the interior of the pot-shaped mould part holder and thereby attracting the membrane by suction up against the ring-shaped insert, the movable centre member being pulled back simultaneously owing to the sub-atmospheric pressure acting on the membrane.

In the case of the known press tool, the subatmospheric pressure required in the pot-shaped mould part holder to attract the membrane by suction has to be produced by means of a vacuum pump separate from the tool, whereby relatively large spaces have to be evacuated, for which either a high pump output or a substantial amount of time is required. In addition, in the case of the known press tool it is difficult to remove the pressed moulded article, because in its relaxed state the membrane has the same shape and position as in the final pressing position, so that above all flat, plate-shaped moulded articles tend to jam at the edge bead of the membrane as soon as they expand when the pressing pressure is relieved; for a plate diameter of 300 mm, for instance, a one-percent expansion involves an increase of 3 mm in diameter.

The underlying problem in the invention is thus to devise a press tool of the type described at the outset in such a manner that, on the one hand, the sub-atmospheric pressure required to attract the membrane by suction up against the mould face of the first mould part needs little effort and time to produce and, on the other hand, the pressed moulded article can be easily removed.

This problem is solved in the invention, in that - the outer diameter of the first mould part is slightly smaller than the inner diameter of the membrane edge bead which determines the outer diameter of the pressed moulded article, - the first mould part in its entirety, together with its at least one duct, is movable plunger-like relative to the mould part holder, and - the first mould part has an associated mould part drive which advances the first mould part when the press tool is opened, thereby producing a sub-atmospheric pressure in the intermediate space between the first mould part and the bottom of the mould part holder to hold the membrane in contact up against the entire mould face of the advanced first mould part while the pressed moulded article is being removed and while ceramic material is subsequently being fed in.

Owing to the outer diameter of the first mould part being slightly smaller than the inner diameter of the membrane edge bead, when the first mould part is advanced the membrane is inverted outwards in the zone immediately inside the edge bead, so that the edge of the moulded article is freed from the edge bead of the membrane before it can be jammed there. The entire remaining membrane surface is attracted by suction up against the mould face of the first mould part, which is formable plunger-like in its entirety, so that the moulded article is not loaded by elastic restoring forces of the membrane which might damage it. The mould part drive is basically of any desired type and at all events less expensive than a vacuum pump.Especially suitable as a mould part drive is a piston-cylinder unit feedable from the same pressure medium source required in any case for pressing away the membrane, i.e. for hydrostatic pressing of the article to be moulded.

The sub-atmospheric pressure required to attract the membrane by suction up against the first mould face results automatically from the first mould part devised plunger-like in its entirety being moved, if the pressure medium feed from the pressure medium source is shut off in the manner required in any case, e.g., by means of a three-way valve, before the press tool is opened.

Altogether, therefore, through the invention the operating expense of a press tool of this type, as well as the risk of pressed moulded articles breaking, are substantially reduced.

In the case of the press tool in the invention, the first mould part is preferably devised such that the outer diameter of the first mould face is twice to six times the thickness of the outer edge of the pressed moulded article smaller than the inner diameter of the membrane edge bead.

In the case of the known press tool which has been described, the second mould part has a cylindrical outer surface on which an axially movable sliding ring is guided, the latter assuming an advanced position when the press tool is closed and thereby sealing with its front face against the membrane edge bead and against the mould part holder, and being pushed back during pressing. These known features can also be provided in the press tool in the invention, then being expediently developed in that a sliding-ring drive is associated with the sliding ring, said drive holding the sliding ring in its pushed-back position while the press tool is being opened, in which position the moulded article pressed out of the membrane edge bead by the movement of the first mould part can expand in a radial direction without being hindered by the sliding ring.

Whereas the mentioned known press tool is arranged upright, i.e., its mould parts are movable relative to one another along a vertical axis, the last-described development of the invention is also suitable for horizontal arrangement of the press tool, in which case the sliding ring has a filling duct for the ceramic material on its upper side a short axial distance away from its front face, which seals against the membrane edge bead and/or against the mould part holder.In this embodiment of the invention, the membrane main portion, which the first mould part, movable plunger-like, has inverted as it were outwards with respect to the membrane edge bead, defines together with the second mould part a filling space geometrically similar to the pressed moulded article but disproportionately wide in the outer edge zone and in this respect, inter alia, different from the filling space of known horizontal press tools (DE-OS 24 37 852). This disproportionately wide filling space in the outer edge zone results in a certain surplus of ceramic material there when the press tool is closing up completely, this ensuring adequate compression in the edge zone, too, of the moulded article.

One embodiment of the invention is described below with the help of schematic drawings, in which Fig. 1 is a vertical-axis section through a press tool in the removing position, Fig. 2 is a corresponding section in the filling position Fig. 3 is a corresponding section in the final pressing position, Fig. 4 is a corresponding section in an intermediate position when the press tool is being opened, and Fig. 5 is the part section V-V in Fig. 1 on a larger scale.

The illustrated press tool has the purpose, on every stroke of a non-illustrated press in which it is installed, of pressing a moulded article 10' from powder or granular ceramic material 10 - in the illustrated example a soup plate is involved. The' press tool consists of two tool parts 12 and 1 4, which are devised essentially symmetrical to a common horizontal axis A. The axis A is at the same time the axis of symmetry of the moulded article 10' and indicates the direction of the stroke movements of the associated press.

The tool part 12 shown on the right in Figs. 1 to 4 has a pot-shaped mould part holder 16 comprising a cylindrical inner wall 18 and a bottom 20. At the cylindrical inner wall 1 8 a first mould part 22 is movably guided, plunger-like, along the axis A. Also belonging to the tool part 12 are a membrane 24 with a thickened edge bead 26, as well as a clamping ring 28 bolted to the mould part holder 1 6 to clamp tight the edge bead 26.

The first mould part 22 consists of two disc-like members 30 and 32 bolted together, the first member 30 of which has a first mould face 34 complementary to the underside of the article to be moulded 10'. Parallel-axis ducts 36 interconnected by distribution ducts 38between the members 30 and 32 extend through both members 30 and 32 and connect the first mould face 34 to an intermediate space 40 between the first mould part 22 and the bottom 20. The ducts 36 are also connected by radial ducts 42, only one of which is shown, to a ring groove 44 at the outer perimeter of the member 32; this ring groove is permanently connected to a pressure medium connection 46 on the mould part holder 1 6.

The first mould part 22 is matched up as a sliding fit inside the mould part holder 16; in this way, the member 30 has an outside diameter virtually corresponding to the diameter of the inner wall 18.

The latter outer diameter is only slightly smaller than the inner diameter of the edge bead 26, which determines the outer diameter of the moulded article 10'. In the example shown, the outer diameter of the member 30, and consequently the diameter of the first mould face 34, is about four times the thickness of the outer edge of the pressed moulded article 10' smaller than the inner diameter of the edge bead 26.

In the bottom 20 a mould part drive 50 is embedded, this being a commercially available hydraulic piston-cylinder unit in the example shown. This mould part drive 50 can be supplied via a duct 52 in a base plate 54 with pressure oil and is capable, under the effect of this pressure oil, of pushing the mould part 22 along the axis A away from the bottom 20.

The tool part 14 has a second mould part 60, on which a second mould face 62 determining the upper side of the pressed moulded article 62 is formed. The second mould part 60 is fixed, by a spigot 64 bolted to it, on a second mould part holder 66, which in turn is bolted to a second base plate 68.

The second mould part 60 has a cylindrical outer surface 70, on which a sliding ring 72 is movable along the axis A. The sliding ring 72 is bolted to a holding ring 74, which is movably guided on the likewise cylindrical outer surface of the second mould part holder 66. There is a dowel pin 76 fixed parallel to the axis in the holding ring 74, the former being guided in a slide sleeve 78 fixed in the base plate 68 and preventing the holding ring 74 together with the sliding ring 72 from turning around the axis A.

The sliding ring 72 has a flat front face 80 which, in the filling position shown in Fig. 2, seals against a likewise flat front face of the edge bead 26 of the membrane 24.

This sealing up is made possible by a sliding ring drive 82, constituted in the example shown by a plurality of piston-cylinder units distributed evenly around the perimeter of the holding ring 74. These piston-cylinder units can be fed with pressure oil through ducts 84 in the second base plate 68 and then press in each case against one settable stop screw 86 fixed in the holding ring 74, in order to push the holding ring 74 together with sliding ring 74 in the direction towards the first mould part holder 1 6.

Incorporated in the upper part of the sliding ring 72 there is a filling duct 90, which, as shown in Fig. 5, is subdivided by several vertical partitions 92 and is connected to a filling funnel 94 for the powder or granular ceramic material 10 to be pressed. To prevent this material 10 causing wear of the sealing and guide faces of the sliding ring 72 and of the holding ring 74, a ring-shaped sleeve 96 made of an elastomer is fixed to the second mould part holder 66, on one side, and to the holding ring 74, on the other side.

A work cycle of the press tool described comprises, proceeding from the removing position shown in Fig. 1, the tool parts 12 and 14 being moved towards each other along the axis A; this movement is performed by tool part 12, for instance, and ends in the filling position shown in Fig. 2, after the sliding ring drive 72 has catered for sealed contact between the front face 80 of the sliding ring 72 and the front face of the edge bead 26. In the removing position in Fig. 1 and also still in the filling position in Fig. 2, the mould part drive 50 has been run out, so that the intermediate space 40 has its maximum possible volume, and the membrane 24 in its edge zone radially immediately inside its edge bead 26 has been inverted outwards, i.e., towards the second mould part 60, the membrane 24 being in contact up against the entire first mould face 34.

In the filling position-shown in Fig. 2, the membrane 24, on the one side, and the mould face 62 of the second mould part 60, on the other side, define a filling space 98, the shape of which differs from that of the pressed moulded article 10' in that the width of the filling space is larger, by a mainly constant factor, than the thickness of the pressed moulded article 10'. An exception is a ring-shaped outer edge zone immediately inside the edge bead 26 of the membrane 24; within this edge zone 100, the filling space 98, measured parallel to the axis A, is disproportionately wide, owing to the fact that the membrane 24 is inverted outwards by the advanced first mould part 22 in the manner described.

From the filling position in Fig. 2, the two tool parts 1 2 and 1 4 are now pushed closer together; this is effected, for instance, in that the tool part 12 is maintained stationary, while the tool part 14 is pushed towards the tool part 12 by a highpower hydraulic piston-cylinder unit. In the process, the first mould part 22 is pushed towards the bottom 20 by the pressure exerted by the second mould part 60, via the material 10 and the membrane 24, on the first mould face 34. As a result, pressure oil so far contained in the intermediate space 40 is forced out through the ducts 36 and 42, the ring groove 44 and the pressure medium connection 46 into a not-illustrated oil tank, this being made possible by a likewise notillustrated three-way valve.As the movement from the filling position into the pressing position begins, the sliding ring 72 is forced in the direction towards the second base plate 68, thus cutting off the filling space 98 from the filling duct 90.

As soon as the pressing position in Fig. 3 is reached, the above mentioned three-way valve is switched over, so that pressure oil from a likewise not-illustrated pump is forced in through the pressure medium connection 46, the ring groove 44 and the ducts 42 and 36, and presses the membrane 24 away from the first mould face 34.

In this manner, isostatic after-pressing of the ceramic material 10 is effected, and the pressed moulded article 10' is thereby finish-pressed.

Subsequently, the mould part drive 50 is pressurized via a likewise not-illustrated threeway valve and the duct 52, and -- independently of this the tool parts 12 and 14 are moved apart. The first mould part 22 is moved, relative to the first mould part holder 16, by the mould part drive 50 in the direction towards the second mould part 60, so that the movement of the tool parts 12 and 14 away from each other initially still does not lead to a separation of the mould parts 22 and 60. In the case of the shift of the first mould part 22 effected by the mould part drive 50-in Fig. to 4 it is a shift to the leftthe 1 to4itisashifttotheleft-the entire oil which had penetrated between the first mould face 34 and the membrane 24 and had been depressurized by the three-way valve connected to the pressure medium connection being switched over, is sucked into the intermediate space 40, so that the membrane 24 is brought into contact up against the entire first mould face 34 and re-assumes simultaneously in its edge zone its outwards inverted shape, which can also be seen in Fig. 4. As it does so, that edge of the pressed moulded article 10' is freed from the edge bead 26 of the membrane 24, so that the moulded article 10' can expand unhindered.

As the tool parts 12 and 14 continue to move away from each other into the removing position shown in Fig. 1, the pressed moulded article drops on to a chute formed, for instance, by soft belts, unless it is preferred to remove the moulded article by means of, for instance, a transport device provided with suction cups.

Claims

1. A press tool for producing moulded ceramic articles, from powder or granular material, comprising a first mould part having at a front side a first mould face complementary to one side of the article to be moulded, as well as at least one duct leading from said first mould face to the rear side of the first mould part, a second mould part having a second mould face complementary to the opposite side of the article to be moulded, a potshaped mould part holder having a cylindrical inner wall surrounding the first mould part, a bottom, as well as a pressure medium connection, and, for opening and closing the press tool, as well as for pressing the material, being axially movable together with the first mould part relative to the second mould part, a membrane having an edge bead secured on the mould part holder and capable optionally of being attracted by suction up against the first mould face or of being pressed away from the first mould face by a pressure medium fed via the pressure medium connection, and an intermediate space between the bottom of the mould part holder and the rear side of the first mould part, in which space pressure below or above atmospheric pressure is likewise effective, wherein the outer diameter of the first mould part is slightly smaller than the inner diameter of the edge bead of the membrane, which edge bead determines the outer diameter of the pressed moulded article, the first mould part in its entirety, together with its at least one duct, is movable plunger-iike relative to the mould part holder and, the first mould part has an associated mould part drive which advances the first mould part when the press tool is opened, thereby producing a subatmospheric pressure in the intermediate space between said first mould part and the bottom of the mould part holder to hold the membrane in contact up against the entire mould face of the advanced first mould part while the pressed moulded article is being removed and while ceramic material is subsequently being fed in.

2. The press tool as claimed in claim 1, wherein the outer diameter of the first mould face is twice to six times the thickness of the outer edge of the pressed moulded article smaller than the inner diameter of the edge bead of the membrane.

3. The press tool as claimed in claim 1 or 2, in which the second mould part has a cylindrical outer surface on which an axially movable sliding ring is guided, the latter assuming an advanced position when the press tool is closed and thereby sealing with its front face against the membrane edge bead and/or against the mould part holder, and being pushed back during pressing, wherein a sliding ring drive is associated with the sliding ring, said drive holding the sliding ring in its pushed-back position while the press tool is being opened, in which position the moulded article pressed out of the edge bead of the membrane by the movement of the first mould part can expand in a radial direction without being hindered by the sliding ring.

4. The press tool as claimed in claim 3, wherein in the case of horizontal arrangement of the press tool, the sliding ring has a filling duct for the ceramic material on its upper side a short axial distance away from its front face, which seals against the edge bead of the membrane and/or against the mould part holder.

5. A press tool substantially as hereinbefore described with reference to the accompanying drawings.