WO2013102514A1

WO2013102514A1 - Injection molding tool and method for producing a ceramic component

Info

Publication number: WO2013102514A1
Application number: PCT/EP2012/073369
Authority: WO
Inventors: Thomas Loibl; Imke Heeren
Original assignee: Robert Bosch Gmbh
Priority date: 2012-01-03
Filing date: 2012-11-22
Publication date: 2013-07-11
Also published as: DE102012200045A1; EP2800655B1; EP2800655A1

Abstract

The invention relates to a method and a ceramic injection molding tool for producing a hollow cylindrical ceramic component (20, 30) from a first and a second ceramic material (21, 22).

Description

description

title

Injection molding tool and method for producing a ceramic component prior art

The present invention relates to an injection molding tool and a method for producing a hollow cylindrical ceramic component, in particular a

Kerzensteins (insulator) for a spark plug of at least two different ceramic materials.

Spark plugs are different from the prior art

Embodiments known and have a candle on which

made especially for cost reasons of alumina ceramics. So far, the candle stones are made of spray-dried

Aluminiumoxidkeramikrohstoff semi-isostatically pressed and in one

subsequent grinding process in the typical insulator shape.

Subsequently, a sintering of the molding takes place. This was now

found that in particular in the step of powder pressing within the alumina ceramic different pore sizes and different

Form pore shapes. However, these can also be at a

Optimization of process parameters can not be reduced or avoided. Too many and too large pores in the candle stone, however, have a negative impact on the dielectric strength of the candle stone. Therefore, so far a dielectric strength of the plug stones of spark plugs is limited to a maximum of 50 kV / mm. In new, highly supercharged internal combustion engines, however, it is necessary that the candle stones significantly increased

Must have a dielectric strength of at least 75 kV / mm or more. For this purpose, however, suitable tools and manufacturing processes are still missing.

Disclosure of the invention The inventive method for producing a hollow cylindrical ceramic component having the features of claim 1 has the advantage over that the production of a ceramic component, such as a

Kerzensteins, from at least two different ceramic materials is possible. The ceramic component thus has, on the one hand, increased resistance to breakdown and, on the other hand, in addition significantly improved electromagnetic compatibility, e.g. even at very high ignition voltages (as for highly charged internal combustion engines). According to the inventive method for producing a hollow cylindrical ceramic component, the

Ceramic materials sequentially injected using a core assembly with a central core and a pressure core and a retractable split ring core (multi-part slide). The ring core ensures while spraying the first ceramic material sure that a

Ring cavity for the second, later injection process remains. Subsequently, a sprue cross section is closed by means of the central core. Then, a step of applying pressure, in which an axial force is applied by means of the pressure core on the first ceramic material, in particular the

To reduce pore sizes and to unify the pore forms as possible. After retraction of the toroidal core, the annular cavity is then filled with the second ceramic material. Here, the two ceramic materials are preferably selected such that a first permittivity of the first ceramic is smaller than a second permittivity of the second ceramic. The second ceramic preferably surrounds the ceramic component annularly and in a certain length in the axial direction of the ceramic component. This can, for example, a

Candle stone are produced, in which the second ceramic with high

Permittivity is arranged at a position of the candle stone, on which a resistance element of a spark plug is later arranged. As a result, the resistance element is covered annularly and to some extent also in the longitudinal direction of the spark plug, whereby a capacity of the candle plug in the region of the resistance element can be increased. Thereby can

Electromagnetic interference during the ignition of the spark plug can be significantly reduced.

The dependent claims show preferred developments of the invention. More preferably, the two ceramic materials are arranged such that in the radial direction of the ceramic component, at least a portion of double-layered, that is, that in the radial direction, a layer of the first

Ceramic material and a layer of the second ceramic material is present. Preferably, the two layers are substantially the same thickness or alternatively, the layer of the ceramic material with higher permittivity is thicker. Alternatively, the two ceramic materials can also follow one another in the axial direction, so that the ceramic component is essentially produced from two hollow-cylindrical elements made of different ceramic materials.

Particularly preferably, the central core of the core arrangement is at one

Gutter side tapered tapering formed. As a result, a laminar inflow of the ceramic material is ensured in the cavity in the tool. Particularly preferably, the central core is conical. More preferably, the central core is formed as a two-part core with a toroidal core and a cylindrical inner core.

More preferably, the tool is rotated prior to the step of injecting the second ceramic material. This makes it possible that two supply areas for the two ceramic materials are present on one side of the tool, which reduces the structural complexity.

Particularly preferably, the second ceramic material is substantially in

Axial direction of the ceramic component injected into the annular cavity.

More preferably, the first and / or second ceramic material are heated during the feeding to the tool. This ensures that the ceramic materials have sufficient flowability during the spraying operations.

Furthermore, the present invention relates to a ceramic injection molding tool for producing a hollow cylindrical ceramic component. The

Ceramic injection molding tool comprises a first and a second tool part, which define a cavity, wherein the two tool parts preferably share the tool only in the radial direction and not in the axial direction share. Furthermore, a first sprue device is provided with a feed opening for feeding a first ceramic material and a core arrangement with a central core and a pressure core. The central core and the pressure core are movable independently of each other in the axial direction, wherein the central core is at least partially disposed in the pressure core. Further, one end side of the

Compressor core arranged in the axial direction at one end of the cavity, wherein the feed opening of the first sprue device is arranged at the opposite end of the cavity. In this case, the central core is designed to close the feed opening of the first sprue device in order to allow a pressure build-up by means of the pressure core. Furthermore, a split ring core (multipart

Slider) provided, which has a ring cavity for the second

Ceramic material provides. The toroidal core is arranged radially outside the central core. The second ceramic material is over a second

Sprue device supplied. Thus, according to the invention

Ceramic injection molding tool provided which allows the injection of two different ceramic materials, preferably with different permittivity, and wherein after the injection molding, a step of the pressure on the first ceramic material is possible.

The ceramic injection molding tool preferably has a central core with an outer cross section, which corresponds to an inner cross section of the feed opening of the first sprue device. As a result, a simple and secure closing of the feed opening by means of the central core can be realized by simply axially displacing the central core into the feed opening. Alternatively, the central core only closes the feed opening of the first

Sprue device, so that no ceramic material can get into the cavity. Furthermore, shearing of the ceramic material at a longitudinal end of the ceramic component is achieved by closing the supply opening, so that, in particular, a costly reworking of the longitudinal end of the ceramic component is not necessary.

More preferably, the central core has a tapered end,

in particular a conical end, on. This will be a laminar

Flow supported in the cavity of the tool. Preferably, the central core is formed in two parts. More preferably, the ceramic injection molding tool comprises a rotating device to rotate the ceramic injection molding tool, preferably by 90 °.

The invention further relates to a spark plug for a spark plug, which according to the inventive method and / or by means of the

ceramic injection molding tool according to the invention is prepared and made of at least two different ceramic materials, preferably with different permittivity. Preferably, the

Kerzenstein thereby a dielectric strength of greater than or equal to 75 kV / mm on.

Short description of the drawing

Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. The same or functionally identical parts are each provided with the same reference numerals. In the drawing is:

1 shows a schematic sectional view of an injection molding tool according to a first embodiment of the invention in a first position,

FIG. 2 shows a sectional view of the injection molding tool of FIG. 1 in a second position,

Figure 3 is a schematic sectional view of the one with

Injection molding tool made of Figures 1 and 2 ceramic component,

Figure 4 is a schematic sectional view of an injection molding tool according to a second embodiment of the invention and

FIG. 5 shows a schematic sectional view of a ceramic component,

which is manufactured by means of the second injection molding tool of FIG. Preferred embodiments of the invention

Hereinafter, with reference to Figures 1 to 3 a

Ceramic injection molding tool 1 and a method for producing a hollow cylindrical ceramic component described in detail.

As can be seen in particular from FIGS. 1 and 2, this includes

Ceramic injection mold a first tool part 2 and a second

Tool part 3, which define a cavity 4. A separation point 5 between the first and second tool parts 2, 3 extends in the radial direction to an axial direction X-X of the ceramic injection molding tool 1. In the cavity 4, a core assembly 10, comprising a central core 1 1 and a pressure core 12, arranged. Further, in the cavity 4, a split ring core 13 (multi-part slide) is arranged, which during the injection process by means of a first ceramic material, a ring cavity 14 (see Figure 2) free. The ring core 13 is, as indicated in Figure 1 by the arrows B, C, in several parts and in the radial direction in a space 15 slidably, so that a second ceramic material can be injected into the resulting annular cavity 14.

The ceramic injection molding tool 1 further comprises a first sprue device 6 with a cylindrical feed opening 7 and a second sprue device, which in this embodiment is a feed channel 8. The second

Ceramic material is, as indicated in Figure 2 by the arrow D, fed through the supply channel 8.

The two cores of the core assembly 10 are in the axial direction X-X independently displaced. Here, the central core 1 1 is cylindrical and has a tapered end 1 1 a, which is rounded in this embodiment. The pressure core 12 is a hollow cylindrical core with a pressure surface 12 a, which limits one end of the cavity 4. The two cores of the core assembly 10 are individually displaceable in the axial direction, that is, pushed forward or pushed back.

The method according to the invention for producing a candle block 20, as shown in FIG. 3, proceeds as follows. First, the first and the second tool part 2, 3 are closed, wherein the first tool part 2 several lugs 2a and the second tool part 3 has a plurality of recesses 3a, which are formed corresponding to each other to allow easy connection and release. Previously, the ring core 13 and the core assembly 10 were arranged in the cavity 4 in the position shown in Figure 1. Here, the ring core 13 is arranged at a distance from the central core 1 1 of the core assembly. Then, a first ceramic material is supplied via the first gate device 6 through the feed opening 7, as indicated in Figure 1 by the arrow A.

As a result, the cavity 4 fills with the first ceramic material 21. The air contained in the cavity 4 can escape via ventilation channels, not shown. As soon as the cavity 4 has been completely filled with the first ceramic material 21, the central core 1 1 is advanced in the direction of the arrow E. Since an outer diameter of the central core 1 1 corresponds to an inner diameter of the central opening 7, the central opening 7 is closed by the central core 1 1, wherein the central core is inserted into the central opening. In this case, a shearing of the first ceramic material takes place at a to the first

Sprue device 6 directed end of the molding.

Subsequently, the pressure core 12 is moved in the direction of the arrows F to exert pressure on the first ceramic material 21. As a result, a pore size of the ceramic material is reduced and as uniform as possible pore shapes of

Ceramic material achieved.

Subsequently, as indicated in Figure 1 by the arrows B, C, the multi-part ring core 13 moved radially outward into the space 15 to provide the annular cavity 14, wherein individual parts of the toroidal in

Radial direction can be moved differently far, which is not shown in the figure. Then, as indicated by the arrow D in FIG. 2, the second ceramic material 22 is fed through the supply channel 8. As a result, the annular cavity 14, which has formed by the radial movement of the ring core 13 directly to the first ceramic material 21, with the second

Ceramic material 22 filled. As can be seen from FIG. 2, the second ceramic material 22 is fed into the radial cavity 14 essentially in the axial direction X-X through the feed channel 8.

After a certain time, the molding produced in this way is then removed from the ceramic injection molding tool, wherein the cores, in particular the Central core 1 1, to be withdrawn. FIG. 3 shows such a molding 20, which is then sintered in a subsequent sintering step. As shown in Figure 3, it is thus possible with the method according to the invention or the ceramic injection molding tool 1 according to the invention, a

Candle stone, which has two layers in the radial direction, namely a first layer of a first ceramic material 21 and a second layer of a second ceramic material 22. In this case, a thickness of the second ceramic material 22 in the radial direction is selected such that a minimum thickness is at least equal to a maximum thickness of the first ceramic material 21 in the two-layer region 24 of the candle block. Further, a through-hole 23 in the candle plug for receiving a center electrode and further elements of a spark plug is also provided.

Subsequently, a sintering of the molding takes place. This was the first

Ceramic material 21 compressed immediately after injection, so that the hollow cylindrical member produced has a maximum dielectric strength. FIGS. 4 and 5 show a ceramic injection molding tool 1 and a molded article produced therewith in accordance with a second exemplary embodiment, and a method for producing an alternative candle block 30 will be described. As can be seen from FIG. 5, the candle plug 30 of the second exemplary embodiment has a first region 31 from the first

Ceramic material and a second region 32 of the second

Ceramic material on. Thus, only an annular contact region 34 results between the first and second ceramic material. Furthermore, a passage opening 33 is again provided. The tool necessary for producing such a candle stone 30 is shown in FIG. The tool substantially corresponds to that of the first embodiment, wherein a significantly larger, split ring core 13 and a correspondingly larger space 15 are provided for the second ceramic injection molding tool. As can be seen from Figure 4, the ring core 13 covers in

Initial state of a cavity from which later for the second

Ceramic material of the second region 32 is provided. Thus, first in turn, the first ceramic material is injected via the supply opening 7 (arrow A), then the central core 1 1 is advanced in the direction of arrow E to close the central opening 7. Subsequently, a printing operation takes place in the axial direction XX by means of the pressure core 12. Then, the ring core 13 is again moved in the radial direction to a corresponding

Release ring cavity for the second ceramic material (arrows B, C). Thereafter, the injection of the second ceramic material 32 via the supply channel. 8

As described in the exemplary embodiments, hollow cylindrical ceramic components made of two different ceramic materials can thus be produced in an efficient manner according to the invention. By applying the in

In the axial direction of X-X acting pressure on the first ceramic material, pore sizes and pore shapes can be reduced and standardized, which leads to better electromagnetic results in a subsequent use of the ceramic component.

Claims

claims

1 . Method for producing a hollow cylindrical ceramic component,

in particular a candle plug for a spark plug, wherein the

Ceramic component (20; 30) has a passage opening (23; 33), comprising the steps:

Closing a tool (1) divided in the radial direction of the ceramic component with an inserted toroidal core (13) divided in the axial direction (X-X), a first tool part (2) and a second tool part (3), which define a cavity (4),

Arranging a core arrangement (10) with a central core (11) and a pressure core (12) in the cavity,

wherein the central core and the pressure core in the axial direction (X-X) are independently movable, and

wherein the pressure core defines an axial end of the cavity (4) and at least partially accommodates the central core (11),

wherein the central core (11) is arranged in the cavity (4) such that an annular sprue cross-section is formed at a free end (11a) of the central core (11),

Injecting a first ceramic material (21) through the annular sprue cross section,

Closing the sprue cross-section by means of the central core (11), moving the pressure core (12) in the axial direction (X-X) in the direction of the sprue side to apply pressure to the injected first

To apply ceramic material (21),

- Retracting the ring core (13) in the radial direction, so that a

Ring cavity (14) arises, and

Injecting a second ceramic material (22) into the annular cavity (14). A method according to claim 1, characterized in that the first ceramic material (21; 31) has a lower permittivity than the second ceramic material (22; 32).

Method according to one of the preceding claims, characterized in that the central core (1 1) is formed on the sprue side tapered to provide a laminar flow of the ceramic material.

Method according to one of the preceding claims, characterized in that the tool (1) is rotated prior to the step of injecting the second ceramic material (22; 32).

Method according to one of the preceding claims, characterized in that the second ceramic material (22; 32) in

Substantially in the axial direction (X-X) of the tool (1) in the Ringkavitat (14) is injected.

Method according to one of the preceding claims, characterized in that the first and / or second ceramic material is heated during the feeding to the tool.

Ceramic injection molding tool for producing a hollow cylindrical ceramic component (20, 30), in particular a candle plug for a spark plug

a first tool part (2),

a second tool part (3),

the first and second tool parts defining a cavity (4), a first sprue device (6) having a feed opening (7) for feeding a first ceramic material (21; 31),

a core assembly (10) comprising a central core (1 1) and a pressure core (12), wherein the central core (1 1) and the pressure core (12) are movable independently of one another in the axial direction, wherein the central core (1 1) partially in the pressure core (12) is arranged and wherein the pressure core (12) defines one end of the cavity (4) in the axial direction, an at least two-part toroidal core (13), wherein the parts of the toroidal core (13) are radially movable to release a ring cavity (14) for a second ceramic material (22; 23), and a second gate device (8) for feeding the second ceramic material (22; 32),

wherein the supply opening (7) of the first sprue device (6) by means of the central core (1 1) is closable.

8. ceramic injection molding tool according to claim 7, characterized in that an outer cross section of the central core (1 1) corresponds to an inner cross section of the supply opening (7).

9. ceramic injection molding tool according to claim 7 or 8, characterized

characterized in that the central core (1 1) has a tapered end (1 1 a).

The ceramic injection molding tool according to any one of claims 7 to 9, further comprising a rotating means for rotating the ceramic injection molding tool (1).

1 1. Candle plug (20, 30) for a spark plug, produced by a method according to claims 1 to 6.