GB2108898A - A press die for making ceramic bodies - Google Patents

Abstract

The press die comprises a first mould member (16) having a first mould face which is complementary to one side of the formed body, a second mould member (36) having a second mould face (38) complementary to the opposite side of the formed body, a cavity (64) being defined by the two mould members (16, 36) when the press die is closed and into which opens a supply duct (42) for the ceramic material (10), and an elastic membrane (22) comprising a marginal bead (28) enclosing the cavity (64) annularly and adapted selectively to be engaged with the first mould face as shown or be pressed away from the same by pressure fluid supplied through passages (20). The marginal bead (28) has a depression (30) forming a bay-like radially outwardly directed enlargement of the cavity (64), the mouth (44) of the supply duct (42) being located opposite the depression (30). The marginal bead (28) is deformable by the pressure fluid into a final press position in which the depression (30) is substantially flattened, while the material (10) in the cavity (64) is compressed between the pressurized membrane (22) and the mould face (38). In this manner the depression (30) establishes communication between the mouth (44) and the cavity (64) provided the marginal bead (28) is not deformed by the pressure fluid. The communication is interrupted when the marginal bead (28) and thus the cavity (30) are deformed. <IMAGE>

Description

SPEC!FICATION A press die for making ceramic formed bodies from a pulverous mass The invention relates to a press die for making ceramic formed bodies, in particular plates, of a pulverous or granular mass, comprising a first mould member including a first mould face at least approximately complementary to one side of the formed body, particularly the underside of the plate, a second mould member including a second mould face complementary to the opposite side of the formed body, particularly the topside of the plate, and a cavity defined by the two mould members when the press die is closed and into which opens a supply duct for the mass which is adapted to be fed under the influence of gravity and/or a pressure gas.

In a known press die of this kind (DE-OS 25 25 085, Figure 7) the two mould members are displaceable in an annular female die along a common vertical axis. The cavity which is to be filled with the ceramic mass and in which the mass is pressed into a formed body is defined directly by the mould faces of both mould members and by the interior wall of the female die. The upper mould member whose mould face is complementary to the topside of a plate comprises an axial bore in which a slide member is guided which is designed like a piston rod and connected to the piston of a double-acting hydraulic piston and cylinder unit. The bore flares within the upper mould member to form an annular space to the side of which the supply duct for the ceramic mass is connected and which comprises a mouth formed at the first mould face and coaxially with the slide member.

The pulverous ceramic mass is passed from a container through a bucket wheel type gate into a pre-chamber and is then conveyed by compressed air through the supply duct whose mouth has been opened by the slide member into the cavity of the closed press die. Subsequently the slide member again is moved down by the associated piston and cylinder unit so as to close the mouth of the supply duct, pressing the ceramic mass from the lower part of the annular space and from the mouth of the supply duct into the cavity which is already filled with ceramic mass. Consequently the ceramic mass is pre-compacted in the range of the cavity close to the axis as it has only little chance to distribute radially outwardly from the mouth. This takes place prior to the pressing operation proper which is effected by relative axial movement of the two mould members toward each other.

The formed body pressed in the known press die thus is inherently inhomogeneous, and this may cause cracks in the firing. Moreover, the slide member leaves an annular trace at the top of the pressed formed body, and this cannot be removed so thoroughly, even by careful dressing, that it does not become visible again after firing. The known press die is neither intended nor suitable for isostatic pressing with a membrane. When using a membrane, the additional ceramic mass pressed into the mould cavity by the slide member would compress the membrane in its central area, leaving behind a corresponding thickening in the pressed formed body. The lacking suitability of the known press die for isostatic pressing makes it impossible to use this press die for producing high quality ceramic formed bodies of different thickness, for instance, plates having a foot edge.

It is, therefore, an object of the invention to develop a press die of the kind described initially such that it will be suitable for isostatic pressing and leave no other traces, if any, of the filling operation at the pressed formed body than those which can be removed by little work and will no longer be disturbing after the firing.

This object is met, in accordance with the invention, in a press die for making ceramic formed bodies, in particular plates of a pulverous or granular mass, comprising a first mould member including a first mould face at least approximately complementary to one side of the formed body, particularly the underside of the plate, a second mould member including a second mould face complementary to the opposite side of the formed body, particularly the topside of the plate, a cavity defined by the two mould members when the press die is closed and into which opens a supply duct for the mass which is adapted to be fed under the influence of gravity and/or a pressure gas, and a membrane comprising a marginal bead which surrounds the cavity annularly and is adapted selectively to be engaged with the first mould face or be pressed away from the same by pressure fluid, the marginal bead has a depression forming a bay-like radially outwardly directed enlargement of the cavity, the mouth of the supply duct is located opposite the depression, and the marginal bead is adapted to be deformed by the pressure fluid into a final press position at which the depression between the mouth of the supply duct and the cavity at least is flattened.

In this manner the depression establishes communication between the mouth of the supply duct and cavity of the press die, provided the marginal bead is not deformed by the pressure fluid into its final press position. However, this communication is interrupted at least approximately when the marginal bead adopts its final press position under the influence of the pressure fluid.

In the terminating position of the pressing operation, preferably, the depression has become so flat that in the area of the depression the formed body will receive a pressing burr at least not substantially thicker than in the remaining zones of the marginal bead.

It is convenient for the depression to widen toward the centre of the membrane when the latter is in relaxed state. This accelerates the filling process and promotes the homogeneous distribution of the ceramic mass in the cavity.

In agreement with the state of the art described, the press die according to the invention may comprise a slide member which is guided at the second mould member and movable in the supply duct towards and away from the cavity so as to close or open the mouth of the supply duct.

In a preferred embodiment of the invention the slide member is displaceable at least approximately in parallel with a surface line of the membrane extending through the centre of the depression.

An embodiment of the invention will be described below with reference to diagrammatic drawings, in which: Figure 1 is a vertical axial sectional elevation of a press die in a filling position during the filling procedure; Figure 2 is a corresponding axial sectional elevation of the press die in the filling position immediately upon termination of the filling procedure but prior to the beginning of pressing; Figure 3 is a corresponding axial sectional elevation of the press die in its final press position; Figure 4 is a sectional elevation along line lV-lV in Figure 2; Figure 5 is a sectional elevation along line V-V in Figure 2; and Figure 6 is a sectional elevation along line VI--VI in Figure 3.

The press die shown serves to press a formed body 12, this being a soup-plate in the example shown, of a pulverous or granular mass 10 during each stroke of a press (not shown) into which the press die is installed.

The press die comprises a first mould member carrier 14 and a first mould member 16 fixed to the same and having a first mould face 18 which is formed to be complementary to that side of the formed body 12 which normally is the bottom.

Pressure fluid passages 20 end at this first mould face 1 8. A membrane 22 of elastic material is associated with the first mould member 1 6 and lies in engagement with the first mould face 1 8 when it is relaxed, as shown in Figures 1 and 2. At its edge the membrane 22 has a collar 24 which is clamped in sealing fashion between the first mould member 1 6 and a clamping ring 26 in engagement by screwing means with the mould member 1 6. The membrane 22 further has a marginal bead 28 at its front side facing the observer of Figure 4. This marginal bead 28 is supported by the clamping ring 26 but is exposed at its front side when the press die is open.A depression 30 having approximately an outline of circular arc shape is formed in the front side of the marginal bead 28. In the relaxed condition of the membrane 22, shown in Figures 1,2, and 4, this depression is widened and deepened radially inwardly. Also formed in the front side of the marginal bead 28 and of the clamping ring 26 are two groove-like venting passages 32 each offset approximately by 450 with respect to the vertical plane of symmetry of the depression 30.

The press die further comprises a second mould member carrier 34 including a second mould member 36 in which a second mould face 38 is formed complementary with that side of the formed body 12 which normally is the top.

Both mould member carriers 14 and 34 and the corresponding mould members 1 6 and 36 are movable toward and away from each other along a horizontal axis A. In the embodiment shown the first mould member carrier 14 is provided to be fixed to a structural member of a press, such as a toggle lever press movable along axis A, while the second mould member carrier 34 is provided to be fixed to a stationary structural member of the same press.

In its upper range the second mould member 36 comprises an insert 40 arranged and designed to be symmetrical to an axial vertical plane V, the plane of the drawing of Figures 1 to 3, just like the depression 30 in the marginal bead 28 of the membrane 22. A supply duct 42 is formed in the insert 40 so as to extend vertically in its upper portion and obliquely downwardly in its lower portion toward the free front end face of the insert 40 where it has a mouth 44 disposed exactly opposite the depression 30.

A slide member 46 is guided in the insert 40 so as to open the supply duct 42 in its retracted position shown in Figure 1 and close the mouth 44 of the supply duct when in an advanced position shown in Figures 2 and 3. The direction of movement of the slide member 46 is at least approximately parallel to a straight line by which the surface line of the membrane 22 lying in the vertical plane V may be replaced approximately below the depression 30. The reciprocating motion of the slide member 46 is effected by a plunger 48 arranged at the second mould member carrier 34 and operable, for example, hydraulically.

A funnel-shaped supply vessel 50 containing a supply of ceramic mass 10 and shown on a largely reduced scale as compared to the second mould member 36, is disposed spaced above said second mould member 36. At the lower end of the supply vessel a shut-off slide 52 is guided in a mixing vessel 54 and is operable by means of a piston and cylinder unit 56. When the shut-off slide 52 is in open position, as shown in Figure 1, the supply vessel 50 of the ceramic mass communicates with a perforated pipe end 58 extending through the mixing vessel 54 and being connected to the supply duct 42 by a mass conduit 60. Outside of the perforated pipe end 58 a pressure air line 62 opens into the mixing vessel 54.

When the second mould member 36 is in filling position, the marginal bead 28 of the membrane 22 is in sealing engagement around the second mould face 38 formed at the second mould member 36, as shown in Figures 1 and 2. Yet the depression 30 leaves free an area around the mouth 44 of the supply duct 42. The membrane 22 itself is in abutment with the first mould face 1 8 when in filling position because atmospheric pressure or even low pressure prevails in the pressure fluid passages 20. In this manner a cavity 64 remains between the membrane 22 and the second mould face 38, having a cross-sectional shape similar to that of the pressed formed body 12, but of greater thickness.

Upon removal of a pressed formed body 12 each operating cycle of the press die begins with the first mould member 16 being moved into its filling position according to Figure 1. During this movement at first the slide member 46 keeps the mouth 44 closed. During the preceding operating cycle, while the shut-off slide 52 was open, a volume of ceramic mass 10 corresponding to the volume of the cavity 64 has collected above the slide member 46 in the mass conduit 60 which is shown greatly reduced and shortened.

Subsequently the shut-off slide 52 has been moved into closing position, likewise before or during the closing movement of the first mould member 1 6.

As soon as the first mould member 1 6 has reached the filling position shown in Figure 1, the slide member 46 is retracted so as to open the mouth 44 and, at the same time, compressed air is introduced by impulse through the pressure air line 62 into the mixing vessel 54 for a short period of time of, for instance, half a second. Through the perforated pipe end 58 this compressed air passes into the mass conduit 60, entraining the amount available of ceramic mass 10 into the cavity 64.

While the cavity 64 is being filled in this manner with the ceramic mass 10, the air escapes through the venting passages 32. Subsequently the slide member 46 is advanced again so that it will again close the mouth 44, as shown in Figure 2.

Subsequently a liquid pressure fluid will be introduced through the pressure fluid passages 20 so as to urge the membrane 22 away from the first mould face 18, as shown in Figure 3. This also influences the radially inner area of the marginal bead 28 which now approaches the second mould member 36 around the cavity 64 or the insert 40 in the upper range thereof. Consequently the connection between the mouth 44 and the cavity 64 is constricted substantially by a deformation of the depression 30, indicated in Figures 3 and 6. In this manner in the area of the insert 40 a pressing burr is formed which is just as thin or, at any rate, not substantially thicker than the pressing burr normally formed all around the cavity 64.

As soon as the entire ceramic mass 10 contained in cavity 64, as shown in Figure 3, has been compacted to a homogeneous formed body 12, the first mould member carrier 14, including the first mould member 1 6 is moved away from the second mould member 36 into an open position (not shown) so as to permit removal of the formed body 12. During this time the mass conduit 60 is again filled with ceramic mass 10 upon opening of the shut-off slide 52 so that subsequently a new operating cycle may begin.

Claims (5)

1. A press die for making ceramic formed bodies, in particular plates of a pulverous or granular mass, comprising a first mould member including a first mould face at least approximately complementary to one side of the formed body, particularly the underside of the plate, a second mould member including a second mould face complementary to the opposite side of the formed body, particularly the topside of the plate, a cavity defined by the two mould members when the press die is closed and into which opens a supply duct for the mass which is adapted to be fed under the influence of gravity and/or a pressure gas, and a membrane comprising a marginal bead which surrounds the cavity annularly and is adapted selectively to be engaged with the first mould face or be pressed away from the same by pressure fluid, in which the marginal bead has a depression forming a bay-like radially outwardly directed enlargement of the cavity, the mouth of the supply duct is located opposite the depression, and the marginal bead is adapted to be deformed by the pressure fluid into a final press position at which the depression between the mouth of the supply duct and the cavity at least is flattened.

2. The press die as claimed in claim 1, in which in the final press position the depression is flattened to such an extent that in the area of the depression the formed body will receive a pressing burr at least not substantially thicker than in the remaining zones of the marginal bead.

3. The press die as claimed in claim 1 or 2, in which the depression widens towards the centre of the membrane when the latter is relaxed.

4. The press die as claimed in any one of claims 1 to 3, comprising a slide member which is guided at the second mould member and movable in the supply duct towards and away from the cavity so as to close or open the mouth of the supply duct, in which the slide member is displaceable at least approximately in parallel with a surface line of the membrane extending through the centre of the depression.

5. A press die for making ceramic formed bodies substantially as described herein with reference to and as illustrated in the accompanying drawings.