MOULD SLEEVE AND MOULDING METHOD

Field of the Invention

This invention relates to a mould sleeve and a moulding method and refers particularly, though not exclusively, to such a sleeve and method for producing ceramic tubes.

Background to the Invention

It has been proposed to use a movable sleeve to centralize the core during the production of plastics and metal tubes. However, it has never been proposed for ceramics tubes and tubes with multiple holes. Also, the prior proposal locked the core at one end. During forming, the core will therefore block a portion of the flow path of the material entering the mould thereby causing non-uniformity in the filling of the cavity by the material thus creating thermal stress within the formed tubes leading to distortion, especially for tubes with multiple holes. Also, with the prior proposal, during filling there is a pressure applied on the core that results in a bending stress within the core. As such, as the sleeve moves the stress within the core will be released and thus cause a deformation of the hole or the tubes formed.

As shown in Figure 1 , room temperature single/double screw extrusion is a continuous commercial fabricating process to produce ceramic tubes and other relative large hollow sections. The starting raw materials are mixtures of ceramics powders and water-based binders. The mixtures are then formed into the required shapes by extrusion. The green parts are then oven or air dried prior to thermal debinding at 900 to 1000 degrees C. The debinded parts are then sintered at elevated temperature of 1400 to 1700 degrees C.

Room temperature plunger extrusion is only able to be used for batch ceramic tubes and other relative large parts. The process is the same as single/double screw extrusion with the exception of the shape forming process. In this process, the mixture is added to the extrusion chamber and then air is evacuated. After evacuation, the plunger pushes the materials out of the die to form the required shape.

These processes have been in the market for several years. However, the production yield is always low for high precision, relative large and complex components. As a result, complex and costly secondary operations are required. All these make the process an expensive fabrication process, although extrusion is considered one of the most inexpensive fabrication processes in terms of the green part forming.

There is no commercial high temperature ceramic extrusion process available using a mixture of powders and polymer binders.

The latest developed and commercially available high temperature ceramic extrusion uses a semi-solid high temperature ceramic extrusion process. In this process, the starting raw materials are mixtures of low melting point glass with ceramics powders and the extrusion is conducted at a temperature over 600 degrees C. The process is suitable for special ceramic-glass mixtures and the processing temperature is over 500 degrees C.

The commercial high temperature extrusion is available for aluminum and other metals and their alloys. The method is a batch process and the extrusion force is from a hydraulic plunger. The process is suitable metallic extrusion and the processing temperature is also over 500 degrees C.

Powder injection moulding utilizes the flow of the feedstock materials to form a complex shape by injection moulding. The green parts are then debinded and sintered through a particle diffusion process at high temperature. The process is suitable for producing small metallic, ceramic and carbide articles with a complex geometry in a large volume.

Summary of the Invention

In accordance with a first preferred aspect there is provided a method of moulding an article, the article having elongate openings therein, the method comprising:

(a) placing a core in a cavity of a die set;

(b) the core being supported at a first end by a core lock and at a second end by a movable sleeve mounted in and being movable relative to the cavity and the core;

(c) injecting material into the cavity to commence to form the article; and

(d) moving the movable sleeve along the cavity to support the core while forming the article.

According to a second preferred aspect there is provided apparatus for moulding an article with at least one elongate opening therein, the apparatus comprising:

(a) a die set having a cavity;

(b) a core for forming the at least one elongate hole and being for placement in the cavity and supportable at a first end by at least one of a core holder and at least one core lock, and at a second end by a movable sleeve mountable in and being able to move in a sliding manner relative to the cavity and the core;

(c) the sleeve being able to so move under the influence of material entering the cavity.

The core may comprise a plurality of pins. The elongate openings may be through the article, or may be blind holes. The core may be placed in the cavity by means of a core holder. The at least one core lock may be at a moulding gate. The core lock may be a fixed or sliding lock. The core may be supported at a first end by the at least one core lock at the moulding gate and at the second end by the core holder. The support by the core holder may be by a guild plate. The core may be positioned by the movable sleeve. The core holder and the at least one core lock may be at opposite ends of the core. There may be one core lock for each pin.

Pressure of the material acting on a first end of the sleeve may force the sleeve along the cavity.

The sleeve may have a sleeve holder at a second end of the sleeve, the second end being remote from the first end; the sleeve holder being for drawing the sleeve along the cavity.

The sleeve may be of a cross-sectional shape, configuration and size that is substantially the same as the cross-sectional shape, configuration and size of the article. The sleeve may be a close but sliding fit within the cavity.

According to a third preferred aspect there is provided a sleeve for use in the moulding of an article with at least one elongate opening therein, the sleeve being for placement in a cavity of a die set and being able to move in a sliding manner relative to the cavity and a core in the cavity; the sleeve being able to move under the influence of material entering the cavity and acting on a first end of the sleeve; the sleeve having a sleeve holder at a second end of the sleeve, the second end being remote from the first end; the sleeve holder being for drawing the sleeve along the cavity; the sleeve being of a cross-sectional shape, configuration and size that is substantially the same as the cross-sectional shape, configuration and size of the article. The sleeve may be for receiving therein, locating relative to the cavity, and supporting, the core.

According to a fourth preferred aspect there is provided a product produced by the above method.

Brief Description of the Drawings

In order that the present invention may be fully understood and readily put into practical effect, there shall now be described by way of non-limitative example only preferred embodiments of the present invention, the description being with reference to the accompanying illustrative drawings.

In the drawings:

Figure 1 is an illustration of a known, prior art process;

Figure 2 is a schematic side illustration of a preferred embodiment;

Figure 3 is a schematic illustration of the process steps with the preferred embodiment;

Figure 4 is a schematic illustration of a front view corresponding to Figure 2;

Figure 5 is a view corresponding to Figure 4 but of an alternative embodiment;

Figure 6 is a schematic illustration of the embodiment of Figures 2, 4 and 5 during the moulding process;

Figure 7 is a series of perspective views showing the process after the moulding process;

Figure 8 is a collage of perspective views of products able to be produced by the process.

Detailed Description of the Preferred Embodiments

To refer to Figures 2 to 6, there is a shown a die set 10 that form a cavity 12 in which an article is to be formed. In this embodiment, the article is to be flat surface tubes for use in fuel cells. To form the tubes, core 14 is held in the cavity by core holder 16, and sleeve 20. A core guild plate 17 may be used, if required or desired. The core 14 may have a plurality of pins 15. One or more core lockers 80 may be used, if required or desired. The core lockers 80 may be fixed or sliding lockers. If sliding lockers, they may be pin lockers. There is preferably one locker 80 for each pin 15. The material enters cavity through sprue/runner/gate 18.

Located in cavity 12 is a movable sleeve 20 which is initially near the gate. The core 14 passes into and is supported by the sleeve 20.

As shown in Figure 3, as the material 22 enters cavity 12 through sprue/ruuner/gate 18 it presses on the top 28 of moveable sleeve 20. As more material 22 enters cavity 12, the material forces sleeve 20 along the cavity 12. As sleeve 20 moves, it continues to support cores 14. The core lockers 81 , 82 and 83 hold the core 14 in position at the first or upper end. The sleeve 20 receives therein the core 14 to hold the core 14 in position relative to the cavity, and to support the core 14, until the sleeve 20 reaches the end of its movement, thereby forming the article 24 with tubes 30 formed by the core 14. The tubes 30 are elongate tubes and may be through article 24, or may be blind hole tubes. When the sleeve 20 moves sufficiently down the cavity 12, the core 14 is no longer in, located by or supported by, the sleeve 20.

In Figures 4 to 6, the sleeve 20 has a sleeve holder 26 that is able to be acted upon by a force provider or actuator (not shown) to draw sleeve 20 along cavity 12 as the material 22 advances along cavity 12. In this way the pressure in cavity 12, and hence on core 14, may be more controlled, and even reduced. Furthermore, it allows for more control of the core 14 to enable a more even wall thickness for article 24; and more even spacing, and regularity in the shape of tubes 30 formed in article 24. The sleeve 20 will be the same as, or will have a cross-sectional shape and configuration, of the article 24. Therefore, article 24 as shown in Figure 6 is also a representation of sleeve 20. The sleeve 20 will be a close but slidable fit in cavity 12. By close it means that the sleeve 20 will contact the wall 32 of cavity 12 with sufficient force to prevent material 22 from passing between sleeve 20 and

the wall 32 of cavity 12, but with sufficient freedom of movement to be able to slide as described above.

Figure 5 illustrates a different embodiment where the core 14 is held by the core holder 16 at one end - the opposite end to that of Figure 4 - and by the sleeve 20 at the other end. The sleeve 20 is initially near the gate 18. During forming, the sleeve 20 will move and the lockers 80 and holder 16 keep the core 14 at the desired position. As such there is no obstacle in the gate 18 to the entry of the material 22. Therefore, the material 22 can fill the cavity 12 more uniformly to form the article 24. Also, there is no bending pressure applied to the core 14.

As shown in Figure 7, once article 24 is moulded, the core 14 and core holder 16 are removed from cavity 12. The movable plate (10, 12, 14, 16, 34 and 36) opens and ejects the product. The pins 14 and pins holder 16 are then put back to the desired position positioned by a locker at the gate and sleeve. The mould is ready for next cycle.

Figure 8 illustrates products able to be moulded using this process. They include: ceramic tubes with through hole or blind hole, sintering tubes, other products with elongate openings therein or thereon, and so forth.

The core 14 may be a single core, a single core with a single pin, a single core with multiple pins, or multiple cores.

Whilst there has been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the present invention.