MOULDING CERAMIC PARTS

Technical Field

The present disclosure relates to a composition for use in forming cores for use in moulding ceramic parts. The cores have particular application for use in forming ceramic parts for pumps, such as pump impellers, but are not limited to that use.

Background of the Disclosure

Some parts for industrial machinery, such as impellers for centrifugal pumps, are formed from ceramic materials. Traditionally, ceramic parts are formed by moulding. A typical mould is formed from plaster of paris (POP) using a pre-prepared wooden pattern. Often, a wax core is also formed using a core box. The wax core is used where necessary to mould internal details in the part being moulded. A slip is prepared which is then poured into the mould and core arrangement. The slip settles in the mould and the POP material draws water out of the slip. When enough water has been removed the resultant green moulded part can be removed from the mould. This process can take around 2 to 3 days. Thereafter, the wax core is removed using a heating arrangement to melt the wax. Often, removal of the core can take a further 1 to 2 days. Following removal of the wax core the green part is surface finished and fired to produce the finished moulded part.

There remains a need to increase the rate of production of ceramic parts.

Summary of the Disclosure

In a first aspect there is provided a composition for use in forming mould for use in moulding ceramic parts including: epoxy resin; and a water absorbent material; wherein the composition includes more than 10% by weight of the water absorbent material.

In certain embodiments, the composition may include between 1% to 20% by weight of epoxy resin.

In certain embodiments, the composition may include between 5% to 10% by weight of epoxy resin.

In certain embodiments, the water absorbent material may include clay.

In certain embodiments, the composition may further include a filler material. In certain embodiments, the filler material may include rice husks.

In certain embodiments, the composition may include between 15% and 25% by weight of water absorbent material. In a second aspect, there is provided a mould core for use in moulding ceramic parts formed from a composition according to the first aspect.

In a third aspect, there is provided a method of moulding ceramic parts including the steps of: providing a mould and at least one mould core according to the second aspect; casting a slip in the mould; allowing the slip to solidify to form a green cast part; removing the green cast part from the mould; removing the core by breaking up the core; and firing the green part.

In a fourth aspect, there is provided a ceramic part formed by a method according to the third aspect.

The part may be an impeller, or part of an impeller, for use in a centrifugal pump. Other aspects, features, and advantages will become apparent from the following detailed description which illustrates, by way of example, principles of the inventions disclosed.

Detailed Description

An embodiment will now be described with reference to an example of forming an impeller for use in a centrifugal pump: Step 1

A POP mould and core are prepared. The POP mould is prepared and kept under oven at 60 degrees Celcius for 6 hours for drying. The core is moulded in a core box. The composition used to form the core comprises:

• Rice Husk 69%wt

• Bentonite clay 20%wt

• commercial grade epoxy and hardener 5%wt

• sodium silicate 2%wt

· PVA 2%wt

• PEG 2%wt

The composition is mixed and poured into the core box and allowed to set at room temperature. The core is then removed from the core box.

Step 2

The raw material to be put into the mould is crushed and mixed with suitable binders by means of a ball mill. The raw material is silicon carbide material. A slip is prepared which is sent to a laboratory to check viscosity and flow properties.

Step 3

All POP mould parts are assembled together with the core. The POP mould is provided with a casting and vent hole. Step 4

The previously prepared slip is poured into the casting hole until it fills and settles. The POP mould and core start absorbing moisture from the slip which solidifies. The top of the POP mould is released and subsequently side parts of the mould are also released and kept for open air drying. The core is removed by hand by breaking up the core.

Step 5

The moulded green part is taken for removal of extra parts of casting and to smoothen the surface. The green part is finished using emery sheet. The green part is then sent for first stage of sintering: Sintering temperature - Nitrogen atmosphere - 1440°C - Sintering time 3 days and cooling 1 day.

The partially sintered part is then sent for second stage firing: Sintering temperature - Oxidation atmosphere - 1440°C - Sintering time 3 days and cooling 1 day

Step 6

The fully sintered part is then inspected for cracks and dimensions checked.

Acceptable results have been found using the following ranges of constituents core composition:

• Rice husk - 60%wt to 70%wt

• Bentonite clay - 15%wt to 25%wt

• Epoxy and hardener - 5%wt to 10%wt

• PVA - l%wt to 2%wt

• PEG - l%wt to 2%wt

• Sodium Silicate - 2%wt to 3%wt

It can be seen that embodiments of the invention have at least the following advantages:

• Water absorbent core draws moisture from slip to reduce moulding time;

• Core material is very light and can easily be broken up and be removed from the mould by hand in as little as 1-2 hours, thereby reducing time taken to remove core from green part;

• Production process time can typically be reduced from 15 days to 10 days or less.

Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.

In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "left" and right", "front" and "rear", "above" and "below" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

In addition, the foregoing describes only some embodiments of the

invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.