GB2273703A

GB2273703A - A process for preparing a ware

Info

Publication number: GB2273703A
Application number: GB9226991A
Authority: GB
Inventors: Michael J Kilroy; Richard Monahan
Original assignee: * R.T.
Current assignee: * R.T.
Priority date: 1992-12-24
Filing date: 1992-12-24
Publication date: 1994-06-29
Anticipated expiration: 2012-12-24
Also published as: BE1005109A6; GB2273703B; GB9226991D0

Abstract

A liquid bone china clay mixture is sieved in step 3, pressed through an electromagnet - step 4 and into a holding tank in step 5. The mixture is then delivered in step 6 to a filter press from which slabs of filter cake are removed in step 7. The cake is either formed into holloware 10 or flatware 11. In both cases moulds are used which are formed by mixing water and plaster of Paris in a weight ratio of preferably 100:72. This provides moulds which can be used for longer periods than has heretofore been possible. The holloware 10 and flatware 11 are fettled in step 13, sponged in step 14, glazed in step 19, and enamel fired in step 24 to produce chinaware 25. <IMAGE>

Description

ZA Process for Preparing a Ware" The invention relates to a process for preparing a ware, particularly to a process for preparing a chinaware.

According to the invention there is provided a process for preparing chinaware comprising the steps of: preparing a mixture of powdered animal bone, china clay, china stone and water to provide bone china clay in a liquid form; blending the mixture for a period of at least two hours; sieving the mixture through a series of vibrating screens to remove particles from the mixture above a predetermined size; passing the sieved mixture through an electromagnet to remove any particles of metal from the mixture; delivering the sieved mixture to a holding tank; pumping the mixture from the holding tank to a filter press; filtering the mixture in the filter press to reduce the water content to less than 23% by weight; removing slabs of filtered press cake from the filter press;; preparing a mould from a mixture of plaster of paris and water, the ratio of the plaster to water being from 100:70 to 100:75 by weight, delivering the filtered mixture into the mould thus formed; removing the product from the mould; fettling the product; sponging the product; loading a plurality of the products thus formed into a biscuit kiln; applying a barrier material to the products in the biscuit kiln; kilning the products in the biscuit kiln at a temperature of at least 12000C over a period of at least eight hours; removing the biscuit ware from the kiln; polishing the biscuit ware to remove barrier material; glazing the biscuit ware; firing the glazed products in a glazing kiln at a temperature of at least 19500C over a period of at least four hours; decorating the glazed ware thus formed; and enamel firing the decorated glazed ware at a temperature of at least 7000C over a period of at least four hours.

In a particularly preferred embodiment of the invention the ratio of plaster to water in the mould is approximately 100:72 by weight.

In a preferred arrangement the mould is prepared by gradually adding the plaster to the water while agitating the water.

Preferably the plaster and water mixture are blended for at least 3 minutes prior to pouring into a casing to form a mould of desired shape. Preferably the casing is of rubber-like material.

In one embodiment of the invention the process includes the steps of delivering the slabs of: delivering the slabs of filtered press cake to a holding tank; adding water and a dispersing agent to the cake; agitating the mixture in the holding tank to provide a casting slip; delivering the slip to a slip holding tank above a plurality of slip casting stations; and gravity feeding slip from the slip holding tank to the slip casting stations.

Preferably the slip in the slip holding tank is agitated without adding air to the slip.

Most preferably the slip holding tank is of generally cylindrical shape having agitating means therein.

In one embodiment of the invention the agitating means comprises a centrally disposed shaft having two longitudinally spaced-apart beater bars projecting radially outwardly from the shaft. Preferably the beater bars are offset substantially at right angles to one another.

In a particularly preferred embodiment of the invention the slip holding tank and agitating means are of stainless steel material.

In a preferred arrangement excess slip from the slip casting stations is collected and recycled to the mixture make up.

In another embodiment of the invention the process includes the steps of: delivering slabs of filtered press cake to an inlet auger of a pug mill; feeding the cake to shredder blades; de-airing the shredded cake in a vacuum chamber; discharging the de-aired cake from the vacuum chamber in a long roll by means of a discharge auger; slicing the long roll of cake material into slices of desired size; delivering the slices to a mould on a flatware making machine; and forming the slices of cake into flatware.

Preferably at least the augers and shredder blades are of stainless steel construction.

In a preferred arrangement the kilning of the products in the biscuit kiln is carried out at a temperature of approximately 12400C over a period of approximately 12 hours.

In another embodiment of the invention the firing of the glazed products is carried out at a temperature of approximately 1110 C over a period of approximately 7 hours.

In a preferred arrangement the enamel firing is carried out a temperature of approximately 770"C over a period of approximately 6 hours.

In one embodiment of the invention the barrier material is aluminium oxide material which is scattered over the products in the biscuit kiln.

In one embodiment of the invention the mixture is filtered in the filter press to reduce the water content to from 20 to 22% by weight.

The invention also provides chinaware whenever produced by the process of the invention.

The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a flow diagram of the process of the invention; Figs. 2 and 3 are respectively end and side elevational views of apparatus used in sieving and magnetising process steps of the invention; Fig. 4 is a plan view of a pump and associated filter press apparatus used in the process of the invention; Fig. 5 is a perspective view of a slip holding tank used in the process of the invention; Fig. 6 is an elevational view of a pug mill used in the process of the invention; Fig. 7 is a plan view of the pug mill of Fig. 6; and Fig. 8 is an end view of the pug mill.

Referring to the drawings and initially to Fig. 1, in the process for preparing chinaware according to the invention the first step 1 is the preparation of a mixture of powdered animal bone, china clay and china stone in approximate proportions 50:25:25 with water to provide a bone china clay mixture in a liquid form. The bone china clay is then blended in step 2 for a period of at least two hours and the mixture is then sieved in step 3 through a sieve 40 (see Figs. 2 and 3) which has a plurality of screens which are vibrated to remove particles from the mixture above a predetermined size. The sieved mixture is then passed in step 4 through an electromagnet 41 which removes any particles of metal from the mixture. The mixture is then delivered in step 5 to a holding tank 42.

The sieved mixture from the holding tank 42 is pumped by a pump 45 along pipework 46 in step 6 to a filter press 47 through which the mixture is pumped to reduce the water content to less than 23% by weight, most preferably to between 20 and 22% by weight. The slabs of filtered press cake from the filter press 47 in step 1 are then removed and further processed either in a slip casting process to produce hollow ware or in a flatware making machine to produce flatware such as plates and the like. In each case a mould is used which is formed from a mixture of plaster of paris and water, the ratio of the plaster to water being from 100:70 to 100:75 by weight, most preferably approximately 100:72 by weight.

The moulds are prepared in step 12 by gradually adding the plaster to the water while agitating the water and subsequently blending the mixture for at least three minutes prior to pouring into a casing to form a mould of desired shape. The casing for the mould is made by first forming a model from solid plaster and then producing a block mould from the model from which a casing, which is preferably of rubber-like material, is made. This casing is then used to produce the moulds. The moulds have a relatively short life-span. We have surprisingly found through extensive research and development that by using a ratio of 72:100 plaster to water the mould life could be substantially increased without changing the mould characteristics. We have found that the mould life can be extended by up to 25%. On examination, the moulds are generally in a better condition than previous moulds formed with different proportions of water and plaster.

Thus not only are the moulds of longer life span but also a better quality product is produced.

The filtered mixture from the filter press is delivered into the moulds in steps 8 and 9 thus formed either in the form of holloware 10 or flatware 11 and, when formed, the products are removed from the moulds. The moulded products which at this stage are leather-hard are then fettled in step 13, i.e. various edges and openings are cleaned using a special knife. The fettled product is then sponged over with hot water in step 14 to produce a smooth surface and a plurality of the products thus formed are loaded into a biscuit kiln. A barrier material is then applied to the products in the biscuit-kiln in step 15. The barrier material is preferably an aluminium oxide material in a powder form which is scattered over the products as they are loaded into the biscuit kiln.The barrier material prevents excessive hardening of the outer skin of the product during biscuit firing.

The biscuit firing is carried out in step 16 in a biscuit kiln at a temperature of at least 12000C over a period of at least 8 hours, preferably at a temperature of approximately 12400C over a period of 12 hours. This brings the mixture right up to its melting point to fix it and provide good strength to the product. The aluminium oxide powder barrier prevents degradation of the outer skin at these high temperatures and allows the product to be further processed easily. The products are then removed from the biscuit kiln and the outer barrier layer is removed in step 17 by vibro polishing.

The biscuit ware is then glazed in step 18 and after glazing a plurality of glazed products are loaded into a glazing kiln and kilned in step 19 at a temperature of at least 19500C over a period of at least 4 hours, most preferably at a temperature of approximately 11100C over a period of approximately 7d hours.

The glazed ware 20 thus formed is decorated either by hand-painting in step 21 or by applying decals in step 22 and/or by gilding in step 23.

After decoration the decorated glaze ware is loaded into an enamelling kiln where the wares are kilned in step 24 at a temperature of at least 7000 over a period of at least 4 hours, most preferably at a temperature of approximately 7700C over a period of approximately 6 hours to produce chinaware 25.

If the press cake 7 from the filter press is to be used for slip casting to produce hollowware the slabs of filtered press cake are loaded into a holding tank 26 to which water and a dispersing agent are added. The dispersing agent is used to avoid the need to add excess water. The higher the water content the more difficult the product is to work. The mixture in the holding tank is then agitated to provide a casting slip in step 27 which is then delivered in step 28 to a slip holding tank 30 (see Fig. 5). As will be apparent from Fig. 5 the slip holding tank 30 is of generally cylindrical construction and is supported at a high level by means of a structural steel framework including support legs 31. The slip in the slip holding tank, by virtue of the fact that the tank is generally cylindrical, is agitated without adding air to the slip.The agitating means comprises a centrally disposed shaft 32 having two longitudinally spaced-apart beater bars 33, 34 respectively projecting radially outwardly from the shaft 32. Beater bars 33, 34 are offset substantially at right angles to one another as will be apparent from Fig. 5. The tank and the agitating means are preferably of stainless steel material.

Slip from the slip holding tank 30 falls by gravity to a plurality of slip casting stations. Because the slip falls by gravity pumping is not necessary so that excess agitation and possible addition of air is avoided.

Excess slip from the slip casting stations is collected and recycled to the mixture make up.

In the case where the press cake is to be used to produce flatware a pug mill 50, illustrated in Figs. 6 to 8, is used. In step 61 press cake is fed by an auger to be shredded in step 62, the cake thus formed being de-aired in step 63, formed into long rolls in step 64 which are cut in step 65 into slices. The pug mill comprises an inlet trough 51 which delivers the press cake to an inlet auger 52, which feeds the cake onwards to two shredder blades 53 which shred the cake prior to delivery into a vacuum chamber 55. In the vacuum chamber 55 all air is removed from the shredded cake. From the vacuum chamber 55 the de-aired cake is delivered to a discharge auger 56 which discharges a long roll of material through an outlet auger 57. The diameter of the roll may be varied by modifying the outlet end of the pug mill 50. The long roll is then cut into slices of desired size which are delivered to a mould on a flatware making machine and formed into flatware. At least the augers and shredder blades, and preferably the entire material of the pug mill, are of stainless steel construction to avoid rusting which causes contamination in the form of specking in the finished product.

Many variations on the specific embodiments of the invention described will be readily apparent and accordingly the invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims

1. A process for preparing chinaware comprising the steps of: preparing a mixture of powdered animal bone, china clay, china stone and water to provide bone china clay in a liquid form; blending the mixture for a period of at least two hours; sieving the mixture through a series of vibrating screens to remove particles from the mixture above a predetermined size; passing the sieved mixture through an electromagnet to remove any particles of metal from the mixture; delivering the sieved mixture to a holding tank; pumping the mixture from the holding tank to a filter press; filtering the mixture in the filter press to reduce the water content to less than 23% by weight; removing slabs of filtered press cake from the filter press; preparing a mould from a mixture of plaster of paris and water, the ratio of the plaster to water being from 100:70 to 100::75 by weight, delivering the filtered mixture into the mould thus formed; removing the product from the mould; fettling the product; sponging the product; loading a plurality of the products thus formed into a biscuit kiln; applying a barrier material to the products in the biscuit kiln; kilning the products in the biscuit kiln at a temperature of at least 12000C over a period of at least eight hours; removing the biscuit ware from the kiln; polishing the biscuit ware to remove barrier material; glazing the biscuit ware; firing the glazed products in a glazing kiln at a temperature of at least 19500C over a period of at least four hours; decorating the glazed ware thus formed; and enamel firing the decorated glazed ware at a temperature of at least 7000C over a period of at least four hours.

2. A process as claimed in claim 1 wherein the ratio of plaster to water in the mould is approximately 100:72 by weight.

3. A process as claimed in claim 1 or 2 wherein the mould is prepared by gradually adding the plaster to the water while agitating the water.

4. A process as claimed in claim 3 wherein the plaster and water mixture are blended for at least 3 minutes prior to pouring into a casing to form a mould of desired shape.

5. A process as claimed in claim 4 wherein the casing is of rubber-like material.

6. A process as claimed in any preceding claim including the steps of: delivering the slabs of filtered press cake to a holding tank; adding water and a dispersing agent to the cake; agitating the mixture in the holding tank to provide a casting slip; delivering the slip to a slip holding tank above a plurality of slip casting stations; and gravity feeding slip from the slip holding tank to the slip casting stations.

7. A process as claimed in claim 6 wherein the slip in the slip holding tank is agitated without adding air to the slip.

8. A process as claimed in claim 7 wherein the slip holding tank is of generally cylindrical shape having agitating means therein.

9. A process as claimed in claim 8 wherein the agitating means comprises a centrally disposed shaft having two longitudinally spaced-apart beater bars projecting radially outwardly from the shaft.

10. A process as claimed in claim 9 wherein the beater bars are offset substantially at right angles to one another.

11. A process as claimed in any of claims 8 to 10 wherein the slip holding tank and agitating means are of stainless steel material.

12. A process as claimed in any of claims 6 to 11 wherein excess slip from the slip casting stations is collected and recycled to the mixture make up.

13. A process as claimed in any of claims 1 to 5 wherein the process includes the steps of: delivering slabs of filtered press cake to an inlet auger of a pug mill; feeding the cake to shredder blades; de-airing the shredded cake in a vacuum chamber; discharging the de-aired cake from the vacuum chamber in a long roll by means of a discharge auger; slicing the long roll of cake material into slices of desired size; delivering the slices to a mould on a flatware making machine; and forming the slices of cake into flatware.

14. A process as claimed in claim 13 wherein at least the augers and shredder blades are of stainless steel construction.

15. A process as claimed in any preceding claim wherein the kilning of the products in the biscuit kiln is carried out at a temperature of approximately 1240"C over a period of approximately 12 hours.

16. A process as claimed in any preceding claim wherein the firing of the glazed products is carried out at a temperature of approximately 11100C over a period of approximately 7F hours.

17. A process as claimed in any preceding claim wherein the enamel firing is carried out a temperature of approximately 770"C over a period of approximately 6 hours.

18. A process as claimed in any preceding claim wherein the barrier material is aluminium oxide material which is scattered over the products in the biscuit kiln.

19. A process as claimed in any preceding claim wherein the mixture is filtered in the filter press to reduce the water content to from 20 to 22% by weight.

20. A process substantially as hereinbefore described with reference to the accompanying drawings.

21. Chinaware whenever produced by a process as claimed in any preceding claim.