WO2002022333A1

WO2002022333A1 - Ceramics moulding

Info

Publication number: WO2002022333A1
Application number: PCT/GB2001/004066
Authority: WO
Inventors: Francesc Gomez; Jeronimo Navidad
Original assignee: Morgan Matroc S.A.; Farwell, William, Robert
Priority date: 2000-09-12
Filing date: 2001-09-11
Publication date: 2002-03-21
Also published as: AU2001286073A1

Abstract

A method of making multiply-perforated ceramic plaques (1) by pressing a plastic ceramics mix between upper (A, B) and lower (C) mould members, wherein the upper mould member has a corresponding multiplicity of retractable pins (4) to form the perforations in the plaque (1), and the plaque (1) is made by steps of moulding the ceramics mix to form a green plaque, withdrawing the lower mould (C) member leaving the plaque (1) adhering to the upper mould member (B) and its pins (4), retracting the pins (4) from the plaque (1), and releasing the plaque (1) onto a support for drying and firing.

Description

CERAMICS MOULDING

The invention relates to perforated ceramic plaques for flame arresters, gas burners and other uses.

In a method currently in use, plaques are pressed from a plastic ceramics mix in a mould having pins to produce the perforations. These pins are in the lower half of a two-part mould, and are withdrawn after pressing to allow removal of the green plaque. With multiple perforations, the plaques in the green state are delicate and the necessary handling to remove them from the mould frequently damages them, especially if large sizes are being made. Hitherto we have made circular plaques up to 18 cm diameter but substantially larger plaques are desirable in some applications.

We have had an idea that avoids damaging handling. Specifically, we provide a method of making multiply-perforated ceramic plaques by pressing a plastic ceramics mix between upper and lower mould members, wherein it is the upper mould member that has a corresponding multiplicity of retractable pins to form the perforations in the plaque, and the plaque is made by steps of moulding the ceramics mix to form a green plaque, withdrawing the lower mould member leaving the plaque adhering to the upper mould member and its pins, retracting the pins from the plaque, and releasing the plaque onto a support for drying and firing.

Suitably the upper mould member comprises a pin carrier and below it a guide plate through which the pins pass, retraction of the pins from the plaque initially leaving the plaque adhering to the guide plate.

Suitably further the lower mould member has locating recesses receiving the ends of the pins during the moulding step.

In the prior process the plaque is produced in a tool where the pins that produce the perforations or holes in the plaque are in the bottom part of the tool, which means that the plaque remains, once pressed, in that part. With this system and with the properties of a semi-wet (soft pad) material the sizes of the plaques cannot be very great due to the problems of taking the plaque out of the cavity of the tooling, with the possibility of deformation, finger marks, cracks etc. The largest round plaque currently produced with this system has for example a diameter of 180 mm.

In the new pressing process, suited to producing plaques with larger diameters, this handling is avoided, introducing a pressing cycle where there is no need to create tensions and deformations in the plaque after pressing, during drying, and during firing. In the way the plaques are produced the idea is to use an inverse concept of the movements of the tooling. The pins that produce the holes in the plaques are in the upper part of the tool instead of having them in the bottom. That will create, once the tool opens, engagement between pins and material that will stick the plaque to the upper part of the tooling allowing the location of a tray under the plaque. Once we have this tray located under the plaque (the plaque remains in engagement with the pins), we move the pins up out of the plaque, and the plaque drops down on the tray. With this system there are no finger marks or any other handling-system marks on the plaque once it is moved out of the cavity of the tool, and subsequent to firing a perfect plaque is obtained with at most a cleaning up of the lower face that rests on the tray by, for example, grinding off a thin layer.

A round ceramic plaque obtained with this process may for example be 295 mm. in diameter, and such large plaques are new in themselves. An aspect of the invention therefore lies in pressed ceramic plaques with multiple perforations formed during the pressing, the plaques being of 20 or 25 cm or greater minimum transverse dimension.

The invention is illustrated in the following example.

The components of the ceramics mix used are:

In this mix, as will be recognised by those skilled in the art, the components are finely ground and formed into a mix sufficiently plastic for moulding, though stiff and abrasive. The organic load burns out in firing to give a porous final product. The cordierite is the main component, the wax and other conventional components giving a mouldable mix. Many different mixes can be used according to the end use of the moulded product.

The mould is broadly of known kind, with upper and lower members arranged for pressing a charge of the ceramics mix, which is loaded into the lower member, and forming the perforations in it by means of a multiple array of withdrawable pins made in chrome-molybdenum steel. Hitherto these pins have been in the lower member but in moulds for use in the method of the invention they are provided in the upper member, registering when the mould is fully closed with blind holes in the lower member, and carried on a mounting plate or carrier for withdrawal through a guide plate also forming part of the upper member, in unison. Their disposition is determined by the disposition of perforations required in the final plaque, of which an example is shown in the drawings.

In the drawings there is shown in Figure 1 in plan (Figure la) and in section on B-B (Figure lb) a flame arrester plaque 1, of 300 ± 2 mm outer diameter, having inner and outer frames 2 and 3 that are 6 mm wide, the outer diameter of the inner frame being 150 ± 1.5 mm. The finished ground plaque is 12.7 ± 1.5 mm thick, and the perforations are 1.3 mm diameter with nil positive tolerance and 0.15 mm negative tolerance. As seen in the fragmentary part-drawing of the plaque in Figure 2, the spacings of the perforations are 2.0823 mm average centre to centre at A-A and they are in staggered rows so that the centres of any group of three perforations, formed by one perforation in one row and two adjacent perforations in the next row, lie at the apices of an equilateral triangle. In all some 17200 perforations, schematically illustrated in Figure 1, are present in the plaque.

The mechanical construction of the mould to withstand pressing is broadly as in previous moulds with the pins in the lower part and is in itself no part of the invention. A schematic drawing of the mould is however given as Figure 3, with enlarged fragmentary sectional views of an upper mould member having a pin carrier 3a (showing one row of pins only), and a guide plate 3b with through holes for the pins, and a lower mould member 3c with locating depressions for the ends of the pins. The pins are seen at 4 on a mounting plate 5, with spacing corresponding to that seen in Figure 2 but of course allowing for the shrinkage of the ceramic in drying and firing of the green plaque. The pins are of a length to pass through the upper mould member B and the thickness of ceramics mix in the mould. The upper mould member has holes 6 closely sized to the diameter of the pins, and the lower mould member C has blind locating holes 7 to receive and locate the shaped ends 8 of the pins.

In its end use the plaque is fixed in a casing with gaskets in per se conventional way, which bear on the inner and outer frames, and forms a robust and functionally effective flame trap.

Claims

1. A method of making multiply-perforated ceramic plaques by pressing a plastic ceramics mix between upper and lower mould members, wherein the upper mould member has a corresponding multiplicity of retractable pins to form the perforations in the plaque, and the plaque is made by steps of moulding the ceramics mix to form a green plaque, withdrawing the lower mould member leaving the plaque adhering to the upper mould member and its pins, retracting the pins from the plaque, and releasing the plaque onto a support for drying and firing.

2. A method according to claim 1 wherein the upper mould member comprises a pin carrier and below it a guide plate through which the pins pass, retraction of the pins from the plaque initially leaving the plaque adhering to the guide plate.

3. A method according to claims 1 or 2 wherein the lower mould member has locating recesses receiving the ends of the pins during the moulding step.

4. A moulded multiply-perforated ceramic plaque of greater than 20 or 25 cm width.

5. A flame arrester or gas burner comprising a housing and, as a flame arresting or gas burning element, a plaque made by the method of claims 1, 2 or 3 or a plaque as set out in claim 4.