DD223112A1 - Device for the crack-free pressing of molding compounds - Google Patents

Abstract

The invention relates to a device for homogeneous compression of powder mixtures having a high specific surface area, in particular of ceramic or powder metallurgical masses, wherein the pressing tool is provided with a plurality of air channels. The aim of the invention is to improve the venting of the mold cavity. It is therefore the task to perform the venting of the mold cavity and the cleaning of the air channels as a function of the compression cycle. According to the invention, a channel (11), which is covered by a filter (5) in the upper and lower dies, is connected both to a common vacuum ring pipe (3) and to a common compressed air ring pipe (8), the work of Control valves (2, 7) for the ring lines (3, 8) via a control system (4, 9) with the movement of the pressing tool (10) is coupled. Fig. 1

Description

Manfred Naumann 'P 1028

Erhard Remme IPK: B 30. B, 13/00

11.4.1984

Title of the invention

Device for rifelfree eating of molding compounds

, Field of application of the invention

The. The invention relates to a device for crack-pressing of molding compositions, in particular ceramic or powder-metallurgical compositions, the pressing tool being provided with a plurality of air channels. The device is particularly suitable for the homogeneous compaction of powder mixtures with a high specific surface area.

Characteristic of the known technical solutions

It is known. Shaped bodies of ceramic, powder metallurgical and similar masses of different density and specific surface area on mechanical, hydraulic

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Structures, and similar shaping errors that do not heal during sintering, but often emerge even more. The causes of these errors are mainly due to air pockets or uneven distribution of material. -. · ..

In order to avoid such air pockets and to facilitate material distribution within the press tool, it is known to provide the press tool with a plurality of openings for venting and with a feed opening for the molding compound. The vents are connected via channels to a large volume vacuum vessel, and the feed port is connected to a bulk reservoir. During shaping, a negative pressure is initially generated via the mold wall in the pressing tool. Due to the pressure difference occurring between the mold cavity and the outside of the feed opening (atmospheric pressure), the .Formmasse is sucked into the mold cavity and, pre-compressed under venting. . After that, the compression is performed to the desired ^end: density (LD 157,083). A disadvantage is the risk of clogging the vents, which consists of the impact of mass particles when sucking the mass. Even by a clever arrangement of the vents, which is a _s multiple reversal of the flow of For.mmasseteilchen intended to be summarized, not always be satisfying results. Rather, it turns out that for this reason: the 'molding material distribution within the' mold cavity.

• often not uniform enough.

Object of the invention ^;

Bas Z.iel the, invention is therefore to improve the venting of the mold cavity.

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Explanation of the essence of the invention

The invention has for its object to develop a device for crack-free molding of molding compounds, wherein the Pre.ßwerk- tool is provided with a plurality of air channels, in which the venting of the mold cavity and the cleaning of the air ducts takes place depending on the compression cycle. '.

According to the invention, in each case an opening in the upper and a lower punch channel, which is covered by a filter, · connected both to a common vacuum ring line and to a common compressed air ring line, the work of the control valves for the ring. 'lines via a control system with' the movement of the pressing tool coupled 1st.

It when the filter in the plunger is arranged centrally 'is advantageous. This concentrated is evacuated the Formhphl ' center.

Preferably, the upper or lower punch is further arranged in a movably mounted sealing ring. The operation of the device will become apparent from the following embodiment.

embodiment

The invention will be explained by way of example with reference to a drawing. The figure shows the device for pressing and the control of the compressed air or vacuum supply line in principle.

The hydraulic press 1 with the pressing tool 10 is provided with a path-time-dependent control for venting and Druc kluitzufuhr for the mold cavity formed by the pressing tool. The venting or .Druckluftzufuhr via one each in the top and bottom punches

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arranged channel 11, which is covered by a metal filter 5 towards the mold cavity. The channels 11 are connected both via a ring line 3 with a vacuum container and via a ring 8 with a compressed air tank. Depending on the loading _v motion sequence. of the pressing tool A 0 is triggered via the switch 4, the electrical control system for the vacuum and opened by the control valve 2, the vacuum ring line or blocked. Also depending on the movement of Preßwerk-. zeüges - takes place via the switch 9 with the corre sponding electrical control system the .Open-or '. Close the valve. 7 for the compressed air ring line 8 '. When the pressing tool Au is open, the mold cavity is filled with molding powder. After closing the press tool 1.0 by lowering the spring-mounted. Sealing ring '6, the valve 2 for the vacuum ring 3 is opened by the actuation of the switch 4 "and thus das.das located in the mold cavity .Masspulver on the two in the top and bottom punch open-vented the channels, i1 Air stored in the powder is sucked out here via the channel openings covered by filter 5. After expiration of the selected time for venting, the compression of the air-free powder in the mold cavity begins, whereby the control valve 2 for the vacuum ring line 3 initially remains open before the opening of 'press tool 1 0 -wi-rd exceeded the, control valve 2, the line to the vacuum system blockiert.- In the upper position of the upper plunger ¹ wird.der switch 9 is actuated. Thus, check valve 7 and opens the compressed air flows via the ring line 8 into the channels 11 and the filters 5- In this way, the filters of mass powder residues: freed.

At the same time, the filling process of the mold cavity is initiated, whereby a homogeneous distribution of the molding material powder is promoted by the inflowing compressed air. During commissioning ^{1 of} the upper punch iri

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Direction Pressing the supply of compressed air is blocked by the control valve 7. After closing the pressing tool by lowering the sealing ring 6, the cycle begins again with the opening of the vacuum ring line. , The pressed on the device ceramic 'body are homogeneous in their internal structure. Microcracks, voids or spalling still occur. Thus, metal oxide varistors showed that all tests were passed at currents of ^ 300 A and pulse widths of 2 ms. In contrast, a large part of the varistors produced according to the prior art was already explosively destroyed at currents of 100 to 200 A, or electrical breakdowns occurred.

Claims (3)

P 1.028 Injury claim •1 . Device for the crack-free pressing of molding compounds, ''''.'' in particular ceramic or powder metallurgical compositions ,, wherein the press tool is provided with several ". '· air ducts, characterized in that a in the upper and the lower ram opening out, ~ \ channel (1-1) supported by a filter (5) is covered, both with a common vacuum ring line (3) ^N and with a common Druckluitringleitung (8) is connected, ^ vobei the work of the control valves (2, 7) for the ring lines (3, 8) via a -... Control system (4, 9) is coupled to the movement sequence of the pressing tool (10).,. 2: device according to point T, characterized in that the filter (5) in. Stamp centric ange.ord- λ ^; . ' is net. ... '.' 3: - 'Device according to item 1, characterized by' '. The fact that the upper or lower punch is arranged in a movably mounted sealing ring (6). - For this 1 page drawings - '/,