DUAL SLEEVE MOULDING METHOD AND APPARATUS

Reference to Related Application

This application is related to our earlier international patent application PCT/SG2007/000128 filed 8 May 2006 the contents of which are hereby incorporated herein by reference as if disclosed herein in their entirety.

Technical Field

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

Background

For the production of articles such as ceramics tubes and tubes with multiple holes, there is a known method using a sliding sleeve with a core. During forming, the core blocks a portion of the flow path of the material entering the mould (forming the holes), while the sliding sleeve helps to keep the core in position to minimize thermal and bending stresses within the formed tubes, reducing problems of distortion and deformation. The core can have one or many pins, depending on the number of holes to be formed, and the resultant article has good material uniformity throughout, even for articles with high aspect ratios.

Although this method is successful for producing high quality ceramic tubes with multiple holes, it is only suitable for forming homogenous articles. This method is unable to produce tubes that need to have different material properties (e.g. density) at different locations of the tube.

Summary

According to a first aspect, there is provided a method of moulding an article. The method comprises injecting a first material into the cavity to form a first portion of the article, the first material displacing a first sleeve in the cavity; and injecting a second material into the cavity to form a second portion of the article, the second material displacing a second sleeve in the cavity.

The method may further comprise placing a core in the cavity for forming at least one elongate opening in the article.

According to a second aspect, there is provided apparatus for moulding an article. The apparatus comprises a die set having a cavity; a first sleeve displaceable by a first material to form a first portion of the article; and a second sleeve displaceable by a second material to form a second portion of the article.

The apparatus may further comprise a core in the cavity for forming at least one elongate opening in the article.

For all aspects, the core may be located and supported by at least the first sleeve. The core may comprise a plurality of pins for forming a plurality of elongate openings in the article. A number of the plurality of pins may be located and supported by the first sleeve, and another number of the plurality of pins may be located and supported by the second sleeve.

The elongate opening may be selected from the group consisting of: through the article, and blind hole.

The first sleeve may slideably engage the second sleeve. The second sleeve may slideably engage the cavity. The first sleeve may slideably engage the cavity or at least a section of the first sleeve may be entirely within the second sleeve.

The first sleeve may be displaced by pressure of the first material acting on a near end of the first sleeve. The second sleeve may be displaced by pressure of the second material acting on a near end of the second sleeve.

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

have a second sleeve holder at a far end of the second sleeve, the second sleeve holder being for drawing the second sleeve along the cavity.

The first sleeve may be of a cross-sectional shape, configuration and size that may be substantially the same as the cross-sectional shape, configuration and size of the first portion of the article. The second sleeve may be of a cross-sectional shape, configuration and size that may be substantially the same as the cross-sectional shape, configuration and size of the second portion of the article.

According to a further aspect, there is provided a first sleeve and a second sleeve for use in the moulding of an article, the first sleeve and the second 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 the second sleeve; the first sleeve being displaceable by a first material to form a first portion of the article, the second sleeve being displaceable by a second material to form a second portion of the article, the first sleeve being of a cross-sectional shape, configuration and size that may be substantially the same as the cross-sectional shape, configuration and size of the first portion of the article, and the second sleeve being of a cross-sectional shape, configuration and size that may be substantially the same as the cross-sectional shape, configuration and size of the second portion of the article.

The first sleeve may be for receiving therein, locating relative to the cavity, and supporting, at least one pin for forming at least one elongate opening in the article.

The second sleeve may be for receiving therein, locating relative to the cavity, and supporting, at least one pin for forming at least one elongate opening in the article.

According to another aspect, there is provided an article produced by the method described above.

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 a schematic cross-section of a preferred embodiment during the moulding process of a first portion of the article;

Figure 2 is a schematic cross-section of the embodiment of Figure 1 during the moulding process of a second portion of the article;

Figure 3 is a schematic cross-section of an article formed by the embodiment of Figures 1 and 2;

Figure 4 is a schematic cross-section of another preferred embodiment during the moulding process of a first portion of the article;

Figure 5 is a schematic cross-section of the embodiment of Figure 4 during the moulding process of a second portion of the article; Figure 6 is a schematic cross-section of an article formed by the embodiment of Figures

4 and 5;

Figure 7 is a collage of perspective views of products able to be produced by the process; and

Figure 8 is a schematic illustration of the process steps with a preferred embodiment.

Detailed Description of the Preferred Embodiments

To refer to Figures 1 and 2, there is shown a die set 10 that form a cavity 12 in which a green article is to be formed (prior to subsequent processing such as debinding and sintering). A core 14 is placed in the cavity 12 and held in position by a core holder 16 (100, Figure 8). In the cavity are also a first movable sleeve 20 and a second movable sleeve 22. The core 14 passes into and is supported by the first sleeve 20. The first sleeve 20 is moveable with respect to the core 14, and slideably engages the second sleeve 20. In this embodiment, at least a portion of the first sleeve 20 is entirely within the second sleeve 22. The second sleeve 22 slideably engages the die set 10.

As shown in Figure l(a), as a first material 30 is injected into the cavity 12 (102, Figure

8) via a gate, it presses on a near end 2On of the first sleeve 20. The near end 2On is the

end of the first sleeve 20 that is nearer the gate. As more first material 30 enters the cavity 12, the material 30 forces the first sleeve 20 to slide within the second sleeve 22 (104, Figure 8). As the first sleeve 20 moves, it continues to support the core 14. The core holder 16 keeps the core 14 in position with respect to the die set 10. The first sleeve 20 receives the core 14 therein to hold the core 14 in position relative to the cavity 12, and to support the core 14, until the first sleeve 20 reaches the end of its movement as shown in Figure l(b). hi this way, a first portion 40 of the article is formed. When the first sleeve 20 moves sufficiently along the cavity 12, the core 14 is no longer in, located by or supported by, the first sleeve 20. The core 14 is instead supported by the first material 30 which has displaced the first sleeve 20. Depending on the length of the pins, a blind hole could be made.

When the first portion 40 of the article is sufficiently solid, a second material 32 enters the cavity 12 as shown in Figure 2(a) (106, Figure 8). Sufficiently solid is to be taken that the first material 30 is of sufficient solidity to minimize transference at the interface of the first and second materials 30, 32. The second material 32 presses on a near end 22n of the second sleeve 22 and forces the second sleeve 22 to move along the cavity 12 (108, Figure 8). The second material 32 fills the cavity 12 between the first material 30 and the die set 10, thus coping with any irregularities in the interface surface of the two materials 30, 32. The die set 10 supports the second sleeve 22 until it reaches the end of its movement as shown in Figure 2(b). At this point, the second material 32 has displaced the second sleeve 22, forming a second portion 42 of the article.

Preferably, the sleeves 20, 22 are the same as, or have a cross-sectional shape, configuration and size, of the respective portions 40, 42 of the green article that they form. The first sleeve 20 is in a slideable fit in the second sleeve 22, while the second sleeve 22 is in a slideable fit with the die set 10.

Figure 3 shows the formed green article. The article is a cylindrical tube with a through hole 44 formed by the core 14. The formed tube could be through or blind holes depending on the position of the pins. The tube has a first portion 40 made of a first material 30 and a second portion 42 made of a second material 32. Depending on the

intended use of the article after subsequent processing such as debinding and sintering, the first material 30 and the second material 32 may be different, or they may be made of the same material but having different material properties, such as initial particle size. Material density can be controlled by varying the moulding parameters such as the material flow rate and the pressure exerted on the near ends 2On, 22n of the sleeves 20, 22. In the case of ceramic tubes, the first material 30 and the second material 32 may have different percentage volume of the same or different ceramic particles in a polymer binder. The polymer binder may provide an additional function of self lubrication of the materials 30, 32 to facilitate material flow in the cavity during moulding. Some mixing of the materials 30, 32 at the interface 41 between the first portion 40 and the second portion 42 of the green article during moulding may also be advantageous. Mixing at the interface 41 may promote better fusion of the two portions 40, 42 upon sintering.

To control the pressure, the sleeves 20, 22 can each have a sleeve holder 2Oh, 22h that is able to be acted upon by a force provider or actuator to draw the sleeves 20, 22 along the cavity 12 as each material 30, 32 advances along the cavity 12. hi this way the pressure in the cavity 12, and hence on the 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 each portion 40, 42 of the article. The sleeve holders 2Oh, 22h are preferably located at a far end 2Of, 22f of the sleeves 20, 22.

Figure 4 illustrates another embodiment where the core comprises a plurality of pins 52 that are held in position by a core holder 54 at one end. A number of pins 56 are located and supported by a first sleeve 60, while another number of pins 58 are located and supported by a second sleeve 62. The first sleeve 60 is in sliding contact with the second sleeve 62. Both the first sleeve 60 and the second sleeve 62 are side-by-side in sliding contact with the die set 64. During forming of a first portion 70 of the article, the first sleeve 60 is displaced by a first material 80 pressing on a near end 6On of the first sleeve 60 until the first sleeve 60 reaches the end of its movement as shown in Figure 4(b). Sliding movement of the first sleeve 60 is constrained by both the second sleeve 62 as well as the die set 64.

When the first portion 70 of the article is sufficiently solid, a second material 82 enters to displace the second sleeve 62 as shown in Figure 5(a). Sufficiently solid is to be taken that the first material 80 is of sufficient solidity to minimize transference at the interface of the first and second materials 80, 82.The second material 82 presses on a near end 62n of the second sleeve 62 and forces the second sleeve 62 to slide in contact with the first sleeve 60 and the die set 64. When the second sleeve 62 reaches the end of its movement as shown in Figure 5(b), the second material 82 has displaced the second sleeve 62, forming a second portion 72 of the article.

To control the pressure, the sleeves.60, 62 can each have a sleeve holder 6Oh, 62h that is able to be acted upon by a force provider or actuator to draw the sleeves 60, 62 while each material 80, 82 advances. In this way the pressure on the pins 52, may be more controlled, and even reduced. Furthermore, it allows for more control of the pins 52 to enable a more even wall thickness for each portion 70, 72 of the article. The sleeve holders 60h, 62h are preferably located at a far end 6Of, 62f of the sleeves 60, 62.

Figure 6 shows the formed green article having two portions 70, 72 made of different materials, having multiple through holes 74 formed by the plurality of pins 52. Other examples of products able to be moulded using this process are shown in Figure 7. They include: ceramic tubes with through hole or blind hole, sintering tubes, other products with elongate openings therein or thereon, and so forth, each able to be made of more than one material or to be made of the same material but having different material properties at different locations of the article.

The core 14 may be a single core, a single core with a single pin, a single core with multiple pins, or multiple cores. Alternatively, if the article is to have no elongate openings therein, there need not be any core used during moulding.

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.