GB2322327A

GB2322327A - Manufacture of hollow ceramic bodies; optical ferrule sleeves

Info

Publication number: GB2322327A
Application number: GB9803649A
Authority: GB
Inventors: Chul-Ho Lee
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1997-02-24
Filing date: 1998-02-23
Publication date: 1998-08-26
Also published as: JPH10278016A; FR2760100A1; GB9803649D0; KR19980068745A; KR100288751B1; CN1199719A; DE19807055A1

Abstract

In a method of manufacture of hollow ceramic bodies, such as optical ferrule sleeves, a porous mould is formed, and a suspension containing a ceramic is poured into the mould cavity to form an adhesion moulded layer by adherence of ceramic particles to the surfaces of the mould cavity. A dry, moulded layer is formed by removing the suspension from the mould cavity after a predetermined, and drying the porous mould. A sintered body may be formed by drying and sintering the dry, moulded layer. The required ceramic body is formed by processing the sintered body, for example by cutting to length, and/or cutting a longitudinal slit to improve the elasticity of the sleeve.

Description

2322327 1 METHOD OF MANUFACMERE OF HOTIDW CERAMIC BODIES, SUCH AS OPECAT,

FERRIAE STEEM Ile present invention relates to methods of manufacture of hollow ceramic bodies, in particular, optical ferrule sleeves.

A sleeve, super precision-machined for aligning an optical ferrule used to connect optical fibres, is conventionally fabricated either by injection moulding or by extrusion moulding. These two methods involve moulding an intended shape by forcefully applying pressure to a suspension of ceramic particles, using the fluidity of an organic binder.

lle extrusion moulding process involves forming a long sleeve-shaped moulding, cutting the moulding to a required length, and further processing^the moulding to complete a sleeve. A ceramic powder and a binder are individually processed, mixed in vacuum, and extrusion-moulded. Then, the extruded moulding is forcefully dried in an oven, baked at about 200-300Q and sintered at about 150TC. Ile sintered moulding is processed lengthways, inside, and outside. The ferrule sleeve is preferably then split in one direction, to improve its elasticity. This is preferably achieved after sintering, by using a diamond saw to cut a slit in the ferrule sleeve. Thus, the sleeve is completed.

The injection moulding process involves pressurised moulding in which a highly fluid material is introduced into a predetermined mould, and a mouldshaped sleeve is obtained. In injection moulding, a sleeve material being a mixture of ceramic powder with about 50% binder is processed, mixed in vacuum, and injection-moulded. Then, the binder is removed from the mould g by degreasing the moulding by heat treatment at about 500700C The binder- free moulding is sintered, and processed lengthways, inside, and outside. The ferrule sleeve is preferably then split in one direction, to improve its elasticity. Ilds is preferably achieved after sintering, by using a diamond saw to cut a slit in the ferrule sleeve, thereby completing the sleeve.

However, the above extrusion and injection moulding processes suffer 2 from several problems. lle fabrication processes are complicated and lengthy, increased due to the heat treatment required to remove the binder added in processing sleeve materials. lle equipment required in the conventional processes is costly, resulting in high product cost. For example, a kneader, an 5 injector or extruder, and a degreasing furnace are all required respectively for Imeading the ceramic with the binder, moulding, and removing the binder. The conventional manufacturing processes are further complicated by additional processing steps such as binder adding and vacuum mixing necessary to fluidify ceramic particles. An expensive mould is required to cast the sleeve, thereby increasing product cost and lowering competitiveness in the field.

To circumvent the above problems, an object of the present invention is to provide a relatively simple method of manufacture of hollow ceramic bodies, such as optical ferrule sleeves.

An object of the present invention is to provide a method of manufacture of hollow ceramic bodies, wherein the size and shape of the hollow ceramic bodies may be simply and inexpensively modified.

An object of the present invention is to provide a method of manufacture of hollow ceramic bodies, wherein the hollow ceramic bodies are densely formed from ceramic particles.

Another object of the present invention is to provide a method of manufacture of hollow ceramic bodies, such as optical ferrule sleeves, at reduced cost, thereby reducing the cost of the finished product.

To achieve the above objects, there is provided a method of manufacture of hollow ceramic bodies comprising the steps of providing a porous mould having at least one mould cavity formed therein; pouring a suspension containing ceramic particles into the mould cavity; forming an adhesion moulded layer by adherence of ceramic particles to the surfaces of the mould cavity for a predetermined time; and forming a dry, moulded layer by removing the suspension from the mould cavity, and drying the porous mould. Ile method according to the invention may further comprise the steps of forming 3 a sintered body by drying and sintering the dry, moulded layer; and forming a hollow ceramic body by processing the sintered body.

In an embodiment of the invention, the adhesion moulded layer is formed by the ceramic particles adhering to the surface of the mould by capillary pressure.

In an embodiment of the invention, the hollow ceramic body is an optical ferrule sleeve.

The porous mould may be composed of gypsum plaster.

Ile suspension preferably includes an organic dispersing agent to prevent attraction between the ceramic particles. The organic dispersing agent preferably has either an acid pH or an alkaline pH to prevent agglomeration of the ceramic particles. The organic dispersing agent preferably has a lowest zeta potential.

Ile ceramic may be formed of zirconia, alumina or a mixture of zirconia and alumina.

The suspension is preferably prepared in the presence of a milling means to separate the ceramic particles. The milling means may include ball media.

Preferably, the ceramic comprises 40-60WT% of the total weight of the suspension materials, and the ball media comprise 30-50% of the volume of a vessel containing the suspension, and in which the suspension is prepared.

The invention also provides a porous mould for use in the manufacture of hollow ceramic bodies, having a moulding cavity comprising a narrow neck portion, narrow such that any difference in capillary pressures of a later introduced ceramic suspension, between the open portion and the cavity bottom is minimised.

The invention also provides a suspension of 40-60WT% ceramic particles, an organic dispersing agent and water, for use in the manufacture of hollow ceramic bodies. Such a suspension may further comprise milling means.

The above objects, characteristics and advantages of the present invention, in addition to others, will become more apparent in the following description of certain embodiments thereof with reference to the attached

4 drawings in which:

figure 1 schematically illustrates a gypsum mould used to fabricate a hollow ceramic body such as an optical ferrule sleeve according to an embodiment of the present invention; and figures 2A-21) schematically illustrate a fabricating process according to the present invention, for the manufacture of hollow ceramic bodies such as optical ferrule sleeves.

Like reference numerals denote like features in the drawings. A detailed description of known function and structure of the present invention is avoided if it is deemed to obscure the subject matter of the present invention.

Figure 1 schematically illustrates a mould according to an embodiment of the present invention. Mould 10 is composed of a porous material, such as gypsum plaster. Ile mould 10 contains one or more mould cavities 12. Each moulding cavity 12 preferably has a narrow neck portion at its upper limit.

Ceramic suspension is later introduced through an opened portion, which is at the upper extremity of the narrow neck portion.

In the absence of such a narrow neck portion, different capillary pressures may act in the suspension at the cavity bottom, and at the opened portion. This difference in capillary pressures may cause a difference in the density of ceramic particles deposited on the mould wall. Such difference in density could cause a moulding to crack during later processing steps such as drying and sintering.

Ihe dimensions of the narrow neck portion must be chosen such that any difference in capillary pressures between the open portion and the cavity bottom 2 5 is minimised, but must not be so narrow that it is blocked by adhesion of suspension particles to the mould walls.

To make the mould 10, a rod is first formed of a non-porous material such as polyvinyl chloride (PVC) to have a diameter 0.5mm larger than the outer diameter of the required hollow ceramic body, such as sleeve 26 shown in figure 2D. Ilen, mould cavities 12 are formed in gypsum plaster 10 by putting the PVC rod(s) into a gelled gypsum paste, and allowing the gypsum paste to harden before removing the rod(s).

A suspension 16 is formed, such as by circulating a ceramic powder 18, an organic dispersing agent 30, a milling means such as a ball medium 28, and water in a pot 14 for 2-4 hours. The suspension should preferably have a mean particle diameter of about 0.5jim. The ceramic 18 may be formed of zirconia, alumina, or a mixture thereof.

When ceramic particles are dispersed into water, they acquire electric charge on their surface. Such charge is a characteristic of the ceramic material used. An attractive force between ceramic particles is thereby produced. This force affects the uniformity and the viscosity of the suspension. The 'zeta potential' represents this attractive force between ceramic particles in the suspension. Preferably, a dispersing agent, such as an organic dispersing agent 30, is added to the suspension, in order to reduce the zeta potential by reducing the electric charge on the ceramic particles, thereby improving dispersion of the ceramic particles, and homogeneity of the suspension.

The organic dispersing agent 30 should have an acid or alkaline pH to prevent attraction between, that is, agglomeration of, the ceramic particles. In other words, the organic dispersing agent 30 has a pH deviating from the range of 7-8, and the lowest possible zeta potential. In the pot 14, the ceramic 18 is mixed with the water at about 40-60WP% based on the total weight of suspension materials, and the ball media 28 are introduced in the pot 14 at about 30-50% of the volume of the pot 14.

Ilen, the suspension 16 is poured into the cavities 12 of the gypsum mould 10, and left for a predetermined time of, for example, about 5-20 minutes.

As illustrated in figure 2A, ceramic particles 18 adhere to the surfaces of the mould cavities 12 by the capillary pressure unique to porous materials such as gypsum, thereby forming an adhesion moulded layer 20. During the capillary pressure-induced adhesion, moisture contained in the suspension 16 is absorbed 6 into the mould 10, reducing the volume of suspension 16 in the cavities 12. To prevent this, a supply tank may be installed to automatically supply suspension 16 into the mould cavities 12.

When the inner diameter of the adhesion moulded layer 20 reaches a predetermined value (e.g. about 2.5mm) a predetermined time later, the remaining suspension 16 is removed from the mould cavities 12, and the gypsum plaster mould 10 is dried upside down for about 5 minutes or less. Inversion of the mould 10 serves to homogenise the inner diameter of the adhesion moulded layer 20 in the cavities 12 Iben, the gypsum plaster mould 10 is tamed upright. Thus, the adhesion moulded layer 20 becomes a dry, moulded layer 22 spaced from the inner surface of the cavity 12 by a predetermined gap 28. llien, the dry, moulded layer 22 in the cavity 12 is further dried for a predetermined time, and then sintered.

A sintered body 24 is thereby produced, as shown in figure 2C.

Protrusions 22a and 22b protruding firom both sides of the sintered body 24 are cut, and then the sintered body 24 is processed lengthways. A slit is cut into the sintered body 24, thereby completing the sleeve 26 as shown in figure 21).

As described above, the manufacturing method according to the present invention is advantageous as follows: firstly, a fabrication process and material processing steps are simplified by avoiding the use of a binder, but rather by controlling the pH of an organic dispensing agent to prevent attraction between ceramic particles; secondly, because a kneader, a moulder, and a degreasing furnace are not required, fabrication and moulding are easy and product cost is reduced; thirdly, due to the case of varying the gypsum plaster moulding cavities 12, the number of sleeves per mould, and their size and shape can be freely adjusted, thereby ensuring excellent product yield; and fourthly, since collision with milling means such as ball media individually separates agglomerated ceramic particles, and uniformly disperses the ceramic particles, a product is densely cast through deposition of individual particles, by the capillary pressure of gypsum plaster.

7 While the present invention has been described in detail with reference to the above specific embodiment, it is to be clearly understood that many variations can be made by anyone skilled in the art within the scope of the present invention. In particular, the method of the invention may be used to manufacture hollow ceramic bodies other than optical ferrule sleeves. The mould may be made of porous material other than gypsum plaster. The mould may be made by any suitable process, such as by machining a solid block of porous material.

Ilie suspension may be made in a liquid other than water.

8

Claims

CLAIMS:

I. A method of manufacture of hollow ceramic bodies comprising the steps of:

(a) providing a porous mould having at least one mould cavity formed therein; (b) pouring a suspension containing ceramic particles into the mould cavity; (c) forming an adhesion moulded layer by adherence of ceramic particles to the surfaces of the mould cavity for a predetermined time; and (d) forming a dry, moulded layer by removing the suspension firom the mould 10 cavity, and drying the porous mould.
2. A method according to claim 1, further comprising the steps of..

(e) forming a sintered body by drying and sintering the dry, moulded layer; and (f) forming a hollow ceramic body by processing the sintered body.
3. A method according to claim 1 or claim 2 wherein the hollow ceramic body is an optical ferrule sleeve.
4. A method according to any of claims 1 to 3 wherein the porous mould 20 is composed of gypsum plaster.
5. A method according to any of claims 1 to 4, wherein the suspension includes an organic dispersing agent to prevent attraction between the ceramic particles.
6. A method according to claim 5, wherein the organic dispersing agent has one of an acid pH and an ne pH to prevent agglomeration of the ceramic particles.
7.A method according to claim 5 or claim 6, wherein the organic dispersing 9 agent includes a dispersing agent having the lowest zeta potential.
8. A method according to any of claims 1 to 7, wherein the ceramic is formed of zirconia.
9. A method according to any of claims 1 to 7, wherein the ceramic is formed of alumina.
10. A method according to any of claims 1 to 7, wherein the ceramic is 10 formed of a mixture of zirconia and alumina.
11. A method as claimed in any of claims 1 to 10, wherein the suspension is prepared in the presence of a milling means to separate the ceramic particles.
12. A method according to claim 11 wherein the milling means includes ball media.
13. A method according to claim 12, wherein the ceramic comprises 406OWM based on the total weight of the suspension materials, and the ball 20 media comprise 30-50% of the volume of a vessel containing the suspension.
14. A method according to any preceding claim, wherein the ceramic particles adhere to the surface of the mould by capillary pressure in step (c).
15. A porous mould for use in the manufacture of hollow ceramic bodies, having a moulding cavity including a narrow neck portion at its upper limit, the narrow neck portion itself comprising an opened portion at its upper extremity for introduction of a ceramic suspension, whereby any difference in capillary pressures of the ceramic suspension between the open portion and the cavity 30 bottom is minimised.
16. A suspension comprising 40-606 ceramic particles, an organic dispersing agent and water, for use in the manufacture of hollow ceramic bodies.
17. A suspension according to claim 16, further comprising milling means within the suspension.
18. A method of manufacture of hollow ceramic bodies substantially as herein described, with reference to the accompanying drawings.