DE102013216597B4 - Process for producing a green body for a diaphragm of a valve device and device for producing the green body for a diaphragm of a valve device - Google Patents

Abstract

Method for producing a green body for a membrane of a valve device comprising a granulate (4) comprising a polymer, wherein the green compact is produced prior to sintering by means of a mold (20) by pressing the granules (4), characterized in that the mold (20) is rotated prior to pressing during introduction of the granules (4) into a cavity (8) of the mold (20) about a rotation axis (10) such that the granules (4) are compressed within the cavity (8).

Description

The invention relates to a method for producing a green compact for a diaphragm of a valve device according to the preamble of claim 1 and to an apparatus for producing the green compact for a diaphragm of a valve device according to the preamble of an independent claim.

It is known that for the production of a molded part made of polytetrafluoroethylene, the corresponding granules are manually or automatically filled and scraped by means of a slide into a cavity. In particular, in the case of fine-grained granules, the wiping causes difficulties, since the fine-grained granules are only limited free-flowing and tends to form lumps. Accordingly, there is an uneven distribution of the granules in the cavity. After the subsequent pressing and sintering process results in a molded part, which has no uniform structure and thus is of inferior quality. For example, such a molded part can break more easily, since the uneven structure leads to unequal force stresses.

From the publication DE 22 32 962 A For example, a method and a spinning mold for sintering shaped bodies of polytetrafluoroethylene is known. A compliant wall of a cylindrical metal jacket, the longitudinal edges of which overlap, can expand when a sintered mass in a mold chamber is compressed during spinning.

The object of the invention is therefore to improve the quality of the molded part to be produced. The object is achieved by a method according to claim 1 and a device according to a non-independent claim. Advantageous developments are specified in the subclaims. Features which are important for the invention can also be found in the following description and in the drawings, wherein the features, both alone and in different combinations, can be important for the invention without reference being made to it again.

Advantageously, a mold is rotated prior to pressing during introduction of a granulate into a cavity of the mold around a rotation axis in such a way that the granules are substantially uniformly compressed within the cavity. By this uniform compaction of the granules, after molding and sintering, a molded article having a substantially uniform structure can be produced. In addition, complex geometries of the molded part can be produced. In particular, a fine-grained granules, in particular a powdered granules, can be used. Furthermore, an advantageous automation for the production of the molding is possible.

In an advantageous embodiment of the invention, a rotational speed of the mold is increased with an increasing degree of filling of the cavity. This ensures that the centrifugal force, which acts in each case on the pellets located in the deposition process, can be determined in the course of substantially radial equal. The granule pieces located in the deposition phase are thus pressed with an always equal force to the already deposited granulate pieces, resulting in the substantially uniform compaction of the granules within the cavity.

In an advantageous embodiment, the granules in the region of the axis of rotation of the cavity is supplied. Through this central introduction of the granules uniform distribution within the cavity can be supported.

In an advantageous embodiment of the method, the granules store substantially in a first, in particular radial direction when introduced into the cavity. To compress the granules, a thickness of the cavity in a second direction is reduced. The second direction is substantially orthogonal to the first direction, in particular substantially parallel to the axis of rotation.

In an advantageous embodiment, a filling stop limits a thickness of the cavity for introducing the granules, wherein the filling stop for pressing the granules is removable. Advantageously, the thickness of the cavity and thus both the density and the thickness of the molded part to be produced can be influenced by the filling stop. Furthermore, this can simplify automation.

In an advantageous embodiment, the cavity extends substantially transversely to the axis of rotation. As a result, the addition of the granules is advantageously supported during the rotation of the mold.

Other features, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. Here, all features described or illustrated alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing. For functionally equivalent sizes and features In all drawings, the same reference numerals are used in different embodiments.

• 1 eine schematische Schnittansicht einer Vorrichtung zur Herstellung eines Grünlings während eines Einfüllvorgangs;
• 2 eine schematische Schnittansicht der Vorrichtung in einem befüllten Zustand; und
• 3 eine schematische Schnittansicht der Vorrichtung während eines Pressvorgangs.

Hereinafter, exemplary embodiments of the invention will be explained with reference to the drawings. In the drawing show:

• 1 a schematic sectional view of an apparatus for producing a green compact during a filling process;
• 2 a schematic sectional view of the device in a filled state; and
• 3 a schematic sectional view of the device during a pressing operation.

1 shows a schematic sectional view of a device 2 for producing a green body for a molded part. In particular, a green compact for a diaphragm of a valve device by means of the device 2 produced. The device 2 is located in 1 in a filling process. A granulate 4a is via a metering device 6 a cavity 8th fed. The metering device 6 is presently designed as a funnel whose opening 9 essentially centrally to a rotation axis 10 is arranged. This will make the granules 4a in the area of the rotation axis 10 the cavity 8th by means of the metering device 6 fed. This drops the granules 4a from the metering device 6 against the z-direction by gravity into the cavity 8th , The granules 4a Of course, it can be both coarse-grained and pulverulent. In the powdery form, the granules 4a by means of a sieve in the area of the opening 9 the metering device 6 the cavity 8th be supplied.

The cavity 8th is essentially rotationally symmetrical to the axis of rotation 10 educated. In the cross section shown, the cavity 8th from the outside to the axis of rotation 10 an outdoor section 12 , a vault section 14 , and a center section 16 on. The outer section 12 extends substantially transverse to the axis of rotation 10 and has a thickness 18 on. From the rotation axis 10 starting from a wall closes 19 the outer section 12 and thus the cavity 8th radially outward. Of course, the cavity 8th also have a different shape than shown, to produce a different shaped green body for a molded part.

The cavity 8th is part of a form 20 , Form 20 includes a first mold half 22 and a second mold half 24 , The first half of the mold 22 includes a first radially outer portion 26 and a second radially inner part 28 , Furthermore, the first mold half comprises 22 an opening 30 through which the granules 4a into the cavity 8th can be introduced. Furthermore, the wall 19 also the first half of the mold 22 assigned. Thus limits the first half of the mold 22 the cavity 8th both radially outwardly and substantially in the z-direction.

The second half of the mold 24 includes a third radially inner part 32 and a fourth radially outer part 34 , The second half of the mold 24 thus limits the cavity 8th essentially counter to the z-direction. Furthermore, the second mold half comprises 24 a recess 36 extending along the axis of rotation 10 extends. In the middle section 16 the cavity 8th there is a first stamp 38 and a second stamp 40 , The first stamp 38 and the second stamp 40 give in the middle section 16 a space of the cavity 8th free, which later represents a mounting portion for a valve rod of the membrane to be produced. The first stamp 38 and the second stamp 40 are along the axis of rotation 10 movable and fixable. During the filling process are the stamp 38 and the stamp 40 in the in 1 shown position and limit with the second mold half 24 a part of the middle section 16 ,

In z-direction is the first half of the mold 22 with a slice 46 connected. The second half of the mold 24 is opposite to the z-direction with a disc 48 connected. In the area 44 can be the first half of the mold 22 essentially free of play over the second half of the mold 24 slide. By means of a filling stop 50 becomes the movement of the first half of the mold 22 limited against the z-direction. This limits the filling stop 50 the fat 18 the cavity 8th for introducing the granules 4 into the cavity 8th in particular parallel to the axis of rotation opposite to the z-direction. For a subsequent pressing on the filling process is the filling stop 50 for pressing the granules 4 removable.

By means of a press stop 52 can after removing the filling stopper 50 the thickness during pressing against the z-direction be limited.

During the filling of the granules 4a into the cavity 8th the device turns 2 around the axis of rotation 10 according to the arrow 54 , The direction of rotation according to the arrow 54 can of course also be chosen opposite. Because of the shape 20 before pressing during the introduction of the granules 4 into the cavity 8th the form 20 around the axis of rotation 10 is rotated, a centrifugal force acts on individual granules 4b thus moving radially outward. Of course, also the middle section 16 with granules 4b filled. At the latest after refilling the middle section 16 with granules 4 learn the granules 4b , which is laterally from the center axis 10 a radially outwardly open space of the cavity 8th are exposed, a centrifugal force radially outward. The first granules 4b on the wall 19 impinge on the wall 19 by the centrifugal force. After attaching some granules thus forming a first compacted granule section 56 in the cavity 8th , Thus, the granules are stored 4 during insertion into the cavity 8th substantially in a first radial direction to a radially inward boundary 58 of the granule section 56 on, with the granules 4 essentially at the border 58 is compressed substantially uniformly. A following to 3 explained pressing occurs in a second direction opposite to the z-direction, wherein for pressing the granules 4 the thickness of the cavity in the second direction is reduced. The second direction is substantially orthogonal to the first direction, in particular substantially parallel to the axis of rotation.

On the granules 4b or granulated powder grains 4b act radially inward a smaller centrifugal force and radially outside a larger centrifugal force when the device 2 or the shape 20 rotates at a same rotational speed. This is the form 20 connected to a rotary drive, not shown. To a compaction of the granules 4 radially, for example in an x-direction, to keep substantially uniform, the rotational speed of the mold 20 with an increasing degree of filling of the cavity 8th elevated. The degree of filling corresponds essentially to the limit 58 , which moves radially inward during filling. The border 58 of the granule section 56 migrates with increasing degree of filling of the cavity 8th radially inward. By increasing the rotational speed with increasing degree of filling of the cavity 8th will be in the area of the border 58 ensures that over the filling process, a substantially equal centrifugal force on the granules 4b acts, which are on the border 58 to the granule section 56 attach. The relationship between degree of filling and rotational speed can be configured as a linear function.

Before the press, the shape 20 during the introduction of the granules 4 into the cavity 8th thus around the axis of rotation 10 rotates that granules 4 essentially uniform within the cavity 8th compacted. In particular, this results in a pre-compression of the granules 4 in the cavity 8th before pressing to make the green compact. The pre-compression is designed such that the uniform distribution of the granules 4 in the cavity 8th to a substantially equal material density of the granules 4 inside the cavity 8th leads. In particular, essentially the same material density of the granules results 4 inside the cavity 8th in a radial direction. The substantially uniform compaction of the granules 4 in the cavity 8th corresponds essentially to an equal density of the granules 4 in the cavity 8th in the radial direction.

The granules 4 is prior to introduction into the metering device 6 weighed. The granules 4 is a polymer and in particular polytetrafluoroethylene or modified polytetrafluoroethylene. Of course, other thermoplastics such as polyamides or polyethylenes can serve for the production of the green body.

The cavity 8th extends substantially transverse to the axis of rotation 10 , During the filling process, the shape 20 around the axis of rotation 10 moved, the metering device 6 preferably not around the axis of rotation 10 moved, but is executed fixed.

2 shows a schematic sectional view of the device 2 out 1 in a filled state. In this filled state, the granules fill up 4 the cavity 8th essentially completely. In this filled state, the shape becomes 20 no longer around the axis of rotation 10 emotional. The filling process, which in the 1 is shown in the in 2 completed filled state completed. A third stamp 60 closes the cavity in the area of the middle section 16 in z direction. Furthermore, the third stamp 60 to the first half of the mold 22 established.

3 shows a schematic sectional view of the device 2 during a pressing process. During the pressing process, the first half of the mold 22 and the second half of the mold 24 moved towards each other, so that the thickness 18 the cavity 8th reduced and the granules 4 that is in the cavity 8th is pressed in the z-dimension. The press stop 52 limits movement of the first half of the mold 22 against the z-direction. Of course, no press stop 52 be provided and the pressure is performed by a press drive, not shown by means of a defined pressing time and a defined pressing pressure.

The first and the second stamp are also used for the pressing 38 and 40 towards the third stamp 60 emotional. The pressing process follows the filled condition. The stamps 38 and 40 become so on the stamp 60 moved towards that between the stamp 38 and the stamp 60 forms a thickness that is substantially the same as a thickness between the punch 38 and 40 , each in the z dimension. Of course, different thicknesses can be provided. For this purpose, the stamp 38 and 40 depending on or independently of each other different distances on the stamp 60 be moved towards. After the first compression of the granules 4 During the filling process, a second compression is now carried out during the pressing process by pressing, wherein the first compression means an attachment in the first direction, and the pressing of the granules 4 in the cavity 8th happening in a second direction. The disc 48 is in 3 only schematically as a block without the slider 42 shown.

When the pressing process is completed, the first half of the mold will be made 22 and the second half of the mold 24 far enough away from each other so that the green compact created by the pressing of the form 20 remove and is fed to a sintering process.

The presented device 2 and the described method steps are designed for automated production. In particular, a filling station, a pressing station and a sintering station are provided for this purpose. In the filling station is in accordance with the 1 the filling process with a first compression of the granules 4 carried out. In the pressing station, the pressing process from the 3 carried out to produce the green body. The green compact produced is then fed to the sintering station. In the sintering station, the resulting green compact is heated substantially to two-thirds of the melting temperature of the polymer used, so that a solid compound of the granules 4b arises and thus the molded part is created. Of course, after the pressing process and the sintering process, a further Nachpressvorgang and another Nachsintervorgang done. Moreover, it is still possible that the molding is fed to a calibration process after the sintering operations or the sintering process is completed. Of course, further post-treatment steps are conceivable.

In the illustrated embodiment according to the 1 to 3 For example, a green sheet for a membrane is made for a valve device using granular modified polytetrafluoroethylene. Such a membrane has advantages, since an accumulation of dirt particles by the material polytetrafluoroethylene in the operation of the valve device can be prevented and the membrane further has sufficient flexibility. Thus, for example, valve devices can be created which are applicable, for example, in the field of medicine, chemistry, food industry or biotechnology.

Claims (10)

Method for producing a green body for a membrane of a valve device comprising a granulate (4) comprising a polymer, wherein the green compact is produced prior to sintering by means of a mold (20) by pressing the granules (4), characterized in that the mold (20) is rotated prior to pressing during introduction of the granules (4) into a cavity (8) of the mold (20) about a rotation axis (10) such that the granules (4) are compressed within the cavity (8). Method according to Claim 1 in that a rotational speed of the mold (20) is increased with an increasing degree of filling of the cavity (8) such that the granulate (4) compresses substantially uniformly in the cavity (8). Method according to Claim 1 or 2 , wherein the granules (4) in the region of the axis of rotation (10) of the cavity (8) is supplied. Method according to the preceding claim, wherein the granulate (4) during introduction into the cavity (8) substantially in a first particular radial direction abuts one another, and wherein for pressing the granules (4) has a thickness (18) of the cavity (4 ) is reduced in a second direction, wherein the second direction is substantially orthogonal to the first direction, in particular substantially parallel to the axis of rotation (10). A method according to any one of the preceding claims, wherein the polymer comprises polytetrafluoroethylene or modified polytetrafluoroethylene. Apparatus (2) for producing a green body for a diaphragm of a valve device comprising a granulate (4) comprising a polymer, wherein the green body can be produced prior to sintering by means of a mold (20) by pressing the granules (4), characterized in that the mold (20) is rotatable around a rotation axis (10) prior to pressing during introduction of the granulate (4) into a cavity (8) of the mold (20) such that the granulate (4) within the cavity (8 ) compacted. Device (2) according to Claim 6 in that a rotational speed of the mold (20) can be increased with an increasing degree of filling of the cavity (8) in such a way that the granulate (4) compresses substantially uniformly in the cavity (8). Device (2) according to Claim 6 or 7 , wherein the granules (4) in the region of the axis of rotation (10) of the cavity (8) by means of a metering device (6) can be fed. Device (2) according to one of Claims 6 to 8th in that a filling stop (50) limits a thickness (18) of the cavity (8) for introducing the granulate (4), wherein the filling stop (50) for pressing the granulate (4) is removable. Device (2) according to one of Claim 6 to 9 , wherein the cavity (8) extends substantially transversely to the axis of rotation (10).

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