WO2013102513A1

WO2013102513A1 - Method and tool for producing a hollow cylindrical ceramic component

Info

Publication number: WO2013102513A1
Application number: PCT/EP2012/073364
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: EP2800654A1; DE102012200046A1; EP2800654B1

Abstract

The invention relates to a tool and a method for producing a hollow cylindrical ceramic component (21), in particular a spark plug insulator for a spark plug, said ceramic component (21) having a central through-opening. The method has the following steps: closing a tool which is separated in the radial direction of the ceramic component (21) and which comprises a first tool part (2) and a second tool part (3) that define a cavity (4); arranging a central core arrangement, which comprises a first core (7) and a second core (8), into the cavity (4), said first and second core being movable in the axial direction (X-X) of the tool, wherein the second core is designed as a hollow core and at least partly receives the first core (7); arranging the first core (7) on a feed side of the tool such that an annular feed cross-section (9) is formed; arranging the second core (8) at an end opposite the feed side in the axial direction (X-X), said second core (8) defining an end of the cavity; injecting a ceramic material into the cavity (4) through the annular feed cross-section (9); closing the annular feed cross-section (9) by means of the first core (7) such that the cavity (4) is enclosed by the first and second tool part (2, 3), the first core (7), and the second core (8); and moving the second core (8) in the axial direction (X-X) towards the feed side in order to exert pressure onto the injected ceramic material and compact same in the cavity (4).

Description

description

title

Method and tool for producing a hollow cylindrical

ceramic component

State of the art

The present invention relates to a method and a

Ceramic injection molding tool for producing a hollow cylindrical

Ceramic component, in particular a candle for a spark plug.

Spark plugs include an insulator (candle plug) which is usually made of alumina ceramic (Al ₂ O ₃ ). According to the current state of the art, the candle stone is brought into its typical shape by pressing the Al ₂ 0 ₃ raw material and a subsequent grinding process. This is followed by sintering, in which the compact is solidified at high temperature. A disadvantage of this method is that different pore sizes and pore shapes may be formed within the material during the step of powder pressing. However, the pore sizes and pore shapes affect a dielectric strength of the

Insulator material in a strong way, so that the dielectric strength

conventionally manufactured candle stones to a maximum of 50 kV / mm is limited. Recently, however, increasingly highly supercharged internal combustion engines are used, which leads to higher ignition voltages due to the pressure increase in the combustion chamber. Therefore, there is a need for a

Dielectric strength of the insulators must be increased to 75 kV / mm or more, to ensure a safe use even in charged

To ensure internal combustion engines.

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 a ceramic component with a uniform as possible

Pore size and can be produced with the most uniform pore shapes. In particular, the ceramic component produced according to the invention has a significantly increased dielectric strength of up to 75 kV / mm and more. This is inventively achieved in that an injection molding tool has a core arrangement with a first and second core, which in

Axial direction are displaced. The first core is at least partially disposed in the second, designed as a hollow core core. In this case, the first core is arranged in the injection mold such that an annular sprue cross-section is formed on a sprue side of the tool. In particular, this measure ensures that an injected ceramic material is forced into a controlled, rotationally symmetrical and flow-division-free block shear flow. As a result, in particular free-jet training and

Flow seams, which lead to a significant defect formation in the ceramic component, can be avoided. In particular, to such defects results in a reduced dielectric strength. Furthermore, the concentrically arranged core arrangement allows the manufacture of ceramic components with the highest rotationally symmetrical precision and absolutely uniform wall thickness over the entire cross section. After the ceramic mass has been injected into the cavity of the tool, the annular sprue cross-section is closed by means of the first core, so that the cavity is closed by the tool walls and the first and second core. Subsequently, a displacement of the second core in the axial direction against the ceramic mass, in order

Exert pressure on the injected ceramic compound and compact it. Thus, according to the invention, a re-compaction still takes place within the injection molding tool in order to achieve microstructural compaction in the cavity.

This allows a uniform compression of the injected

Ceramic material from the opposite side of the sprue are made possible. Another advantage of the method according to the invention is that by moving the first core and closing the annular core

Angular cross section also takes place a separation of the injected ceramic material of sprue areas of the tool. This can be avoided in particular that, as in the prior art after the completion of the molding, the molding is removed from the tool and from demolished so-called sprue. This leads to a

frayed edge, which is also very critical to the

Dielectric strength and the mechanical strength of the ceramic component affects. Such a frayed edge must then consuming by means

Sanding processes are smoothed, but this can be omitted in the process according to the invention.

The dependent claims show preferred developments of the invention.

Preferably, the first core is tapered at one end on the sprue side, in particular formed tapered. As a result, a laminar influx is further promoted in the ring cross section and further increased a homogeneity of the molding.

Particularly preferably, the ceramic material is supplied through a hot runner of the sprue device. As a result, too fast cooling and solidification is avoided, so that after the complete injection of the

Ceramic mass and closing the sprue cross section directly in the tool still the embossing process can be made.

According to a further preferred embodiment of the present invention, a plate-shaped component with a nozzle, in particular of a heat-insulating material, is provided on the sprue side. The plate-shaped component is preferably made of a ceramic, in particular of Zr0 ₂ . As a result, in particular a too rapid cooling of the ceramic material in the

Gating area can be prevented and continue to be avoided too fast solidification of the ceramic material with thin walls.

In order to achieve the shortest possible process time, preferably the first and second core are simultaneously or substantially simultaneously in

Axial direction shifted. It should only be noted that the second core for the embossing process still remains displaceable as soon as the first core has closed the sprue cross-section.

The invention further relates to a ceramic injection molding tool for producing a hollow cylindrical ceramic component, in particular a candle block for a Spark plug, with the features of claim 6. Das

Ceramic injection molding tool comprises a first and a second tool part which divide the tool in the radial direction, so that a longitudinal seam is avoided on the later ceramic component. Further, a sprue device having a supply port for supplying a ceramic material and a

Core assembly comprising a first and second core provided. The cores are movable in the axial direction, wherein the first core is at least partially disposed in the second core. In this case, the first core can be brought into a first position, in which an annular spout cross-section is formed between the first core and the spout device in order to allow laminar inflow of a ceramic mass. Furthermore, the first core can be brought into a second position, in which the first core closes the spout cross section. This makes it possible that the second core is then moved in the axial direction and exerts pressure on the injected ceramic material from the other side of the cavity ago.

Preferably, an outer diameter of the first core corresponds to one

Diameter of a feed opening of the sprue device. In this way, a secure closing of the feed cross section through the first core can be achieved.

More preferably, the ceramic injection molding tool comprises a

A moving device that independently moves the first and second cores. In order to achieve as laminar a flow as possible of the injected ceramic material during the injection process, the first core preferably has a tapering end. Particularly preferably, the tapered end is formed as a spherical portion or conical.

According to a further preferred embodiment of the present invention, a plate-shaped component is further provided with a nozzle which is arranged between a tool part and the sprue device. The

plate-shaped component prevents in particular a too rapid cooling of the injected ceramic material. The plate-shaped component is preferably made of a good insulating material, preferably a ceramic or other hardened material. A diameter of the nozzle preferably corresponds to a diameter of the first core, so that the first core the injected mass in the region of the nozzle can shear off and close the nozzle. The use of the plate-shaped component also ensures rapid tool retrofitting by simply replacing the first core and the plate-like component and correspondingly replacing other components of other dimensions (for example, others

Diameters) can be exchanged. As a result, candle stones can be produced with different inner diameters.

In this case, a diameter of the nozzle of the plate-shaped component is particularly preferably equal to an outer diameter of the first core.

More preferably, the first core is formed in two parts with a first, central cylindrical core part and a second hollow core surrounding the first core part. The hollow core is then surrounded by the second core. The use of a two-part first core makes it possible in particular also the formation of a shoulder in the interior of the ceramic component, so that in particular when producing an insulator for a spark plug in the

Essentially step-shaped center electrode can abut an annular shoulder in the interior of the cavity.

Furthermore, the present invention relates to an insulator for a spark plug, which is produced by a method according to the invention. The insulator preferably has a dielectric strength of greater than or equal to 75 kV / mm.

drawing

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

Figure 1 is a schematic sectional view of a

Ceramic injection molding tool according to a first

Embodiment of the invention in an injection state, FIG. 2 shows a sectional view of FIG. 1 in the embossing state,

FIG. 3 is an enlarged view of a portion of the injection molding tool of FIG. 1;

Figure 4 is a schematic sectional view of a through the

inventive method produced spark plug and

Figure 5 is a two-part sectional view of a

Ceramic injection molding tool according to a second

Embodiment of the invention.

Preferred Embodiments of the Invention Hereinafter, referring to Figs

Ceramic injection molding tool 1 according to a first preferred

Embodiment of the invention described in detail.

FIG. 4 shows an example of a use of one using the

ceramic component produced according to the invention. In Figure 4 is a

Spark plug 20 shown, wherein a candle stone (insulator) 21 of the spark plug can be produced by the inventive method. The spark plug further comprises, as known, a center electrode 22, one or more

Ground electrodes 23, a resistance fuse 24, a

Terminal bolt 25 and a housing 26. The plug 21 is made of an insulating material and has a hollow cylindrical main shape.

Figures 1 to 3 show a ceramic injection molding tool 1 for producing e.g. of the candle plug 21. The ceramic injection molding tool 1 comprises a first tool part 2 and a second tool part 3, which in the assembled

Condition define a cavity 4. Here are the first and second

Tool part 2, 3, the ceramic injection molding tool 1 such that it is divided in the radial direction R to a longitudinal axis X-X. The

Ceramic injection molding tool 1 further comprises a core assembly 6 having a first core 7 and a second core 8. As can be seen in FIG. 1, the first core 7 is partially received in the hollow, cylindrical second core 8. The shape of the first core 7 is also cylindrical, with the first core 7 having a tapered tip 70 at its free end. In this

In the embodiment, the tapered tip 70 is a hemisphere. Here, the two cores, as indicated in Figure 2 by the arrows A, B, in

Direction of the longitudinal axis X-X slidably disposed in the ceramic injection molding tool 1. Here, the first core 7 can be moved independently of the second core 8 and vice versa.

Furthermore, the ceramic injection molding tool 1 comprises a sprue device 5 with a feed channel 50. The sprue device 5 is heated and a

Ceramic material (powdered ceramic and binder) is fed in the direction of arrow C through the sprue 5 in the cavity 4.

The process according to the invention proceeds as follows. Starting from the state shown in Figure 1, in which the first core 7 and the second core 8 are arranged in their retracted positions in the ceramic injection molding tool, on the sprue side of the cavity 4 is an annular sprue 9 between the wall of the first tool part 2 and the first Core 7 available. If now ceramic material, as indicated by the arrow C, flows through the sprue device 5 in the first tool part 2, this is in the

Area of the annular sprue 9 is supplied, which is indicated in Figure 3 by the arrows D. This results in a laminar and thus error-free, annular influx of the ceramic material into the cavity. The air contained in the cavity 4 is vented through a vent passage (not shown) or a volume is applied to the cavity prior to injection. From this annular ceramic mass flow thus results in a uniform filling front in the axial direction of the ceramic injection molding tool in the direction of the second core 8. When the entire cavity 4 is filled with ceramic material, the first core 7 is advanced in the axial direction X-X in the direction of the sprue side until the first core 7 abuts against a wall region 12 with a reduced diameter.

As a result, the ceramic material contained in the cavity 4 is enclosed, that is, the connection to the feed channel 50 is interrupted, so that no further ceramic mass can flow in. It should be noted that this

Step must still take place in the plastic state of the ceramic mass. Thus is located in the cavity 4 ceramic mass of the still in the

Sprue device 5 located cleanly separated mass. In the next step, the second core 8 is moved in the direction of the arrow B (FIG. 2) and thus exerts a pressure on the ceramic mass located in the cavity 4. This results in a compaction of the ceramic mass in the cavity 4 (embossing process), whereby a porosity is reduced, pore sizes are reduced and as uniform as possible pore shapes are obtained. As can be seen from FIG. 2, practically the finished candle block can thus be put under pressure without any further post-processing of the candle block being necessary here.

After the compression process, cooling and curing of the molding and then this is removed from the ceramic injection mold 1. In a final step for the production of the candle stone, the molding is then sintered.

It should be noted that preferably during the cooling of the

Ceramic mass in the injection mold, the pressure is maintained by the second core.

FIG. 5 shows a ceramic injection molding tool 1 according to a second

Embodiment of the invention. Two states of the method are illustrated in FIG. 5, the two cores 7 and 8 being positioned in the retracted state in the state shown above the longitudinal axis X-X, and the two cores 7 being in the state shown below the longitudinal axis X-X.

8 are shown in the extended state. Furthermore, this includes

Ceramic injection molding tool 1, a plate-shaped member 15 having a nozzle 16. An inner diameter of the nozzle 16 corresponds to an outer diameter of the first core 7. Here, a sprue-side end of the first core 7 in cone form, in particular as a spray cone executed. Thus, in turn, during the inflow process, an annular cross-section 9 can be provided between the first core 7 and the tool wall, in order to achieve a laminar, swirl-free inflow into the tool. When the printing phase is to begin, in turn, the first core 7 is advanced, due to the same diameter between the core and the nozzle 16 of the first core

7, the nozzle 16 completely closes and optionally also in the Sprue device 5 can be inserted. Then, as in the first embodiment, a feeding of the second core 8, in order to pressurize the closed ceramic material located in the cavity 4. For the described embodiments, it should be noted that the first

Core 7 may be formed in two parts. More preferably, the first core is in two parts and formed with a first, central cylindrical core part and a second hollow core surrounding the first core part. The hollow core is then surrounded by the second core. The use of a two-part first core allows in particular the formation of a heel in

Interior of the ceramic component, so that in particular when producing an insulator for a spark plug, a substantially positionally shaped center electrode can abut an annular shoulder in the interior of the cavity.

Claims

claims

Method for producing a hollow cylindrical ceramic component (21), in particular a candle plug for a spark plug, wherein the

Ceramic component (21) has a central passage opening, comprising the steps:

Closing a tool divided in the radial direction of the ceramic component (21) with a first tool part (2) and a second tool part (3), which define a cavity (4),

Arranging a central core arrangement comprising a first core

(7) and a second core (8), in the cavity (4), wherein the first and second core in the axial direction (XX) of the tool are movable, wherein the second core is formed as a hollow core and the first core (7) at least partially absorbs,

Arranging the first core (7) on a sprue side of the tool such that an annular sprue cross-section (9) is formed,

Arranging the second core (8) on one of the sprue side in

Axial direction (X-X) opposite end, the second core

(8) defines an end of the cavity,

- Injecting a ceramic mass through the annular

Sprue cross-section (9) into the cavity (4),

- Closing of the annular sprue cross-section (9) by means of the first core (7), so that the cavity (4) by means of the first and second tool part (2, 3), the first core (7) and the second core (8) is included , and

- Moving the second core (8) in the axial direction (X-X) in the direction of the sprue side to exert pressure on the injected ceramic material and to compress them in the cavity (4).

2. The method according to claim 1, characterized in that the first core (7) is tapered on the sprue side, in particular is formed tapered.

Method according to one of the preceding claims, characterized

characterized in that the ceramic material is supplied via a hot runner.

Method according to one of the preceding claims, characterized

characterized in that at the sprue side of the tool a

plate-like component (15) with a nozzle (16), in particular of a heat-insulating material, is arranged.

Method according to one of the preceding claims, characterized

in that the first core (7) and the second core (8) are advanced simultaneously or substantially simultaneously in the axial direction (X-X) after the ceramic material has been injected.

Ceramic injection molding tool for producing a hollow cylindrical ceramic component (21), in particular a candle plug for a spark plug, comprising

a first tool part (2),

a second tool part (3), wherein the ceramic injection molding tool is divided by the first and second tool parts (2, 3) in the radial direction and wherein the first and second tool parts (2, 3) define a cavity (4),

- A sprue device (5) having a supply opening for supplying a ceramic material, and

- A core assembly (6) comprising a first core (7) and a second core (8), wherein the cores (7, 8) are movable in the axial direction and wherein the first core (7) at least partially in the second core (8) is arranged

- wherein the first core (7) can be brought into a first position, which is an annular sprue cross section (9) is formed and can be brought into a second position in which the first core (7) closes the annular sprue, and

- Wherein the second core (8) at one of the sprue-side axial direction (X-X) opposite end is arranged and defines an axial end of the cavity (4).

7. Tool according to claim 6, characterized in that a

Outer diameter of the first core (7) corresponds to a diameter of the feed opening of the sprue device (5).

8. Tool according to claim 6 or 7, characterized by a

A moving device which independently moves the first core (7) and the second core (8).

9. Tool according to one of claims 6 to 8, characterized in that the first core (7) has a tapered end.

10. Tool according to one of claims 6 to 9, further comprising a

plate-shaped component (15) with a nozzle (16) which is arranged between the first tool part (2) and the sprue device (5).

1 1. Insulator for a spark plug, produced by a method of

Claims 1 to 5.