WO2014122461A1

WO2014122461A1 - Method and apparatus for forming a ceramic product

Info

Publication number: WO2014122461A1
Application number: PCT/GB2014/050341
Authority: WO
Inventors: Allen HANLEY; Stewart SAUNDERS; Andrew Christopher Clark
Original assignee: Mantec Technical Ceramics Limited
Priority date: 2013-02-08
Filing date: 2014-02-06
Publication date: 2014-08-14
Also published as: GB201302233D0; GB2526961A; GB201514444D0

Abstract

A method of forming a ceramic product, the method comprising producing a ceramic forming mixture in the form of a slurry, causing the slurry to foam, extruding the foamed slurry to form a product, and thereafter drying and firing the extruded product.

Description

METHOD AND APPARATUS FOR FORMING A CERAMIC PRODUCT

This invention concerns a method of forming a ceramic product, a product made by such a method, and also apparatus for forming a ceramic product.

There are two main generic products on the market for kiln refractory linings: ceramic fibre and refractory bricks. The decision to pick one product over the other is very much based on the type of product being fired, the firing cycle and the type of kiln. Fast-fired products are generally fired in fibre-lined kilns. Longer higher temperature fired products are generally fired in brick lined kilns.

Refractory brick are generally either produced via extrusion or pressing. They are pre-fired prior to sale and are then bonded together using refractory cement by refractory brick layers to form rigid fixed wall kiln linings. Once brick linings are installed, they usually last for many years if not decades. However, by virtue of them being bricks they are relatively dense and have relatively higher thermal mass/conductivity, in comparison to ceramic fibre.

High temperature ceramic fibre has a lower thermal mass/conductivity than refractory bricks. The main benefit of fibre is that it fires much more quickly than brick lined kilns. The lower thermal mass lining allows the kiln to heat up and cool down quicker than kilns lined with refractory bricks. This lends itself to lower energy costs per firing and increased capacity as the kiln can be fired quicker. However, there is a down side with ceramic fibre at high temperatures i.e. higher than 1550 °C, with it degrading/shrinking prematurely and generally not having the same working life as bricks. When it has reached the end of its life ceramic fibre has to be treated as hazardous waste requiring specialist extraction precautions and breathing apparatus. All percentages expressed in this specification are weight percentages.

According to a first aspect of the invention there is provided a method of forming a ceramic product, the method comprising producing a ceramic forming mixture in the form of a slurry, causing the slurry to foam, extruding the foamed slurry to form a product, and thereafter drying and firing the extruded product.

The ceramic product may be extruded as a continuous length, and cut into required lengths immediately following extrusion.

To cause the slurry to foam, air may be fed into the slurry, and the air and slurry mixed together to entrain the air within the slurry. The air may be fed into the slurry as compressed air, and the compressed air may be at a volume of between 0.2 and 2 litres/min.

A foaming agent may be added to the slurry to aid foaming, and the foaming agent may be an organic amine oxide. The foaming agent may be drip dosed into the slurry, and may be drip dosed at a rate of between 2 and 15ml/mins. To cause the slurry to foam, the slurry and air may be fed into a foaming unit, which unit may comprise a plurality of relatively rotating rotors and stators, which may rotate at a speed of between 200 and 500rpm.

An increased pressure will be developed in the foaming unit, which increased pressure may be between 20 and 80 psi.

A feed pipe may be provided extending from the foaming unit to an extruding unit. If the cross sectional size of the product to be formed is greater than the cross sectional size of the feed pipe, then a chamber may be provided between the feed pipe and a die of a required size and shape, which chamber is of greater cross sectional size than the die.

Following extrusion the extruded product may be fired at a temperature above 1200°C.

A setting agent may be added to the slurry. The setting agent may be any of gypsum, calcium aluminate cements, Portland cements, PVA plus cross linking polymer additives, alginates or starches.

The ceramic forming mixture may be mixed together by a high speed blunger.

The ceramic forming mixture may include:

10 - 40% water

20 - 80% of a ceramic forming material

2 - 10% of additives

The ceramic forming material may be any of alumina which may be calcined, fused or tabular, silica, magnesium oxide, silicon carbide, zirconium silicate, silliminite, mullite, steatite or cordierite.

The additives may include any of organic binders, methyl cellulose, starches or polyvinyl acetate.

The additives may include an organic deflocculant, which may be sodium tripolyphosphate.

The ceramic forming mixture may also include up to 50% clay to form a slurry, which may be ball or china clay. According to a second aspect of the invention there is provided a ceramic product made by a method according to any of the preceding fourteen paragraphs. According to a third aspect of the invention there is provided apparatus for forming a ceramic product, the apparatus including a mixing unit for mixing together components of a ceramic forming mixture, the mixing unit being connected to a foaming unit for causing the slurry to foam, the foaming unit connecting to a die unit for extruding foamed mixture therethrough.

A support unit may be provided arranged to receive extruded lengths of material from the die unit. The support unit may be in the form of a conveyor, which may be a roller conveyor. The mixing unit may be in the form of a high speed blunger.

A pump may be provided for pumping slurry from the mixing unit to the foaming unit, and the pump may be a fixed displacement pump. A sieve may be provided between the mixing unit and the foaming unit to remove particles above a predetermined size such as for instance 2mm.

The foaming unit may include an inlet for compressed air to be mixed with the slurry. The foaming unit may include an inlet for a foaming agent, and may permit drip dosing of the foaming agent.

The foaming unit may comprise a plurality of relatively rotating rotors and stators for entraining the air in the slurry, and the rotors and stators may rotate at a speed of between 200 and 500 rpm. A feed pipe may be provided extending from the foaming unit to the extruding unit. An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic side view of apparatus according to the invention; and

Fig. 2 is a more detailed diagrammatic side view of part of the apparatus of Fig. 1 . Fig. 1 shows an apparatus 10 according to the invention for producing ceramic products by a method of the invention. The apparatus 10 comprises a mixing unit 12 which includes a high speed blunger.

The mixing unit 12 also includes a conventional fixed displacement pump (not shown) which pumps material through a magnet and a sieve to remove any solid or unmixed particles of say greater than 2mm. The pump connects to a pipe 14 which leads to a foaming unit 16.

The foaming unit 16 includes a chamber 18 with a unit 20 connected thereto. The unit 20 permits compressed air to be fed into the slurry at a volume of between 0.2 and 2 litres/min. The unit 20 also permits a foaming agent to be dripped dosed into the mixture.

The foaming unit 16 also includes a mixing head 22 to receive the air rated slurry incorporating the foaming agent. The mixing head includes a series of relatively rotating rotors and stator blades nesting together which spin around at 200 - 500 rpm to entrain and fully mix the air into the slurry in a whisking like action. This produces foam air bubbles in the ceramic slurry which stay embedded within the slurry without bursting or slumping. The foaming agent provides temporary green strength to maintain the bubbles in the foam structure. A natural increased pressure of between 20 and 80psi will build up in the mixing head 22. This increased pressure is sufficient to push material through a feed pipe 24 into a die unit 26. The die unit 26 permits a selection of interchangeable dies 28 to be fitted of a required size and shape, to permit products of different sizes and shapes to be formed.

If the die 28 as shown in Fig. 2 is of greater cross sectional area than the feed pipe 24, a die chamber 30 is provided between the feed pipe 24 and the die 28, which chamber 30 is of greater cross sectional area than the die 28. The die chamber 30 ensures that material passes out through the die 28 consistently and at a constant speed.

The die unit 26 is located such that material 32 passing thereoutof will land on a roller conveyor 34. Where a continuous length of material is being extruded from the die unit 26, a cutting arrangement may be provided adjacent thereto to enable cutlets to be located on the conveyor 32.

In one example a high alumina ceramic with approximately 70% alumina silica and other materials is mixed in the mixing unit 12 to form a slurry with a solids content of approximately 70%. The slurry is then pumped through the pipe 14 into the foaming unit 16. Any solid or unmixed particles greater than 2mm are removed by the sieve or magnet.

Compressed air is fed into the slurry at a required volume of between 0.2 and 2 litres/min, and an organic amine oxide foaming agent is drip dosed into the slurry at a rate of between 2 and 15ml/min. This mixture is then mixed at high speed in the mixing head 22 to entrain the air and create foam air bubbles in the ceramic slurry. An increased pressure of between 20 and 80 psi develops in the foaming unit 16. The foaming agent provides temporary green strength to these bubbles prior to firing. A setting agent such as gypsum, calcium aluminate cements, Portland cements, PVA plus cross linking polymer additives, alginates or starches may be injected into the slurry to aid the forming process. The setting agent may include accelerants or retardants.

The foamed mixture is then passed under pressure through the feed pipe 24 into the die unit 26 and as show in Fig 1 can be extruded into lengths 32. The lengths 32 can be cut as required to at least rough lengths, and dried and then fired at a temperature above 1200°C.

The products thus formed can be cut further if required into precise shapes for use for instance in lining a kiln or in other refractory applications. These products have a 65-75% alumina content. This method enables mixes with little or no clay to be used, which previously has not generally been possible, as a clay content has been required to give the foamed material some strength.

A wide range of modifications may be made without departing from the scope of the invention. For instance different dies can be used to produce required sizes and/or regular cross sections, to produce for instance tiles, bricks, blocks, rods or prills. Where a relatively small die is to be used which is not of greater cross sectional size than the feed pipe, then a die chamber may not be required.

This apparatus and/or method can be used with a wide range of ceramic materials, other than the above described example. For example different proportions of alumina could be used, and the alumina may be calcined, fused or tabular. Other ceramic forming materials may be used alone or in combination, such as silica, magnesium oxide, silicon carbide, zirconium silicate, silliminite, mullite, steatite or cordierite. Clay of up to 50% may be added, which may be ball or china clay. Additives in the mixture may include organic binders, methyl cellulose, starches, polyvinyl acetate or other suitable binders. The additives may include an organic deflocculant, which may be sodium tripolyphosphate.

A different mixing unit could be used to entrain the air in the slurry. The die unit may take a different form. The firing conditions for the final product will depend on the nature of the material. An after burner will generally be required in the process due to the combustion products produced from the binders.

In practice the invention has been found to produce a product with a tightly controlled pore size distribution, with a foamed ceramic micro porous internal structure. This product provides two main benefits.

Firstly, it has an intimately mixed, homogenous micro porous structure all the way through the component, and secondly it has a much lower resultant bulk density over conventional continuous manufacturing techniques for ceramic shapes. This combination of properties lends itself to superior refractory components for use inside industrial kilns and furnaces. This structure is ideal for a refractory insulating product.

This therefore provides a material which can have the rigidity and longevity of a brick, but has a much lighter bulk density and therefore provides significant energy saving. Products made with this material could be retro fitted as well as fitted in new installations.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1 . A method of forming a ceramic product, the method comprising producing a ceramic forming mixture in the form of a slurry, causing the slurry to foam, extruding the foamed slurry to form a product, and thereafter drying and firing the extruded product.

2. A method according to claim 1 , characterised in that the ceramic product is extruded as a continuous length, and cut into required lengths immediately following extrusion.

3. A method according to claim 2, characterised in that to cause the slurry to foam, air is fed into the slurry, and the air and slurry mixed together to entrain the air within the slurry.

4. A method according to claim 3, characterised in that the air is fed into the slurry as compressed air.

5. A method according to claim 4, characterised in that the compressed air is at a volume of between 0.2 and 2 litres/min.

6. A method according to any of claims 3 to 5, characterised in that a foaming agent is added to the slurry to aid foaming.

7. A method according to claim 6, characterised in that the foaming agent is an organic amine oxide.

8. A method according to claims 6 or 7, characterised in that the foaming agent is drip dosed into the slurry.

9. A method according to claim 8, characterised in that the foaming agent is drip dosed at a rate of between 2 and 15ml/mins.

10. A method according to any of claims 3 to 9, characterised in that to cause the slurry to foam, the slurry and air are fed into a foaming unit.

1 1 . A method according to claim 10, characterised in that the foaming unit comprises a plurality of relatively rotating rotors and stators.

12. A method according to claim 1 1 , characterised in that the rotors and stators of the foaming unit may rotate at a speed of between 200 and 500rpm.

13. A method according to any of claims 3 to 12, characterised in that an increased pressure will be developed in the foaming unit.

14. A method according to claim 13, characterised in that the increased pressure is between 20 and 80 psi.

15. A method according to any of claims 3 to 14, characterised in that a feed pipe is provided extending from the foaming unit to an extruding unit.

16. A method according to claim 15, characterised in that when the cross sectional size of the product to be formed is greater than the cross sectional size of the feed pipe, a chamber is provided between the feed pipe and a die of a required size and shape, which chamber is of greater cross sectional size than the die.

17. A method according to any of claims 2 to 16, characterised in that following extrusion the extruded product is fired at a temperature above 1200°C.

18. A method according to any of the preceding claims, characterised in that the ceramic forming mixture is mixed together by a high speed blunger.

19. A method according to any of the preceding claims, in which a setting agent is added to the slurry.

20. A method according to claim 19, in which the setting agent is any of gypsum, calcium aluminate cements, Portland cements, PVA plus cross linking polymer additives, alginates or starches.

21 . A method according to any of the preceding claims, characterised in that the ceramic forming mixture includes:

10 - 40% water

20 - 80% of a ceramic forming material

2 - 10% of additives

22. A method according to claim 21 , characterised in that the ceramic forming material is any of alumina which may be calcined, fused or tabular, silica, magnesium oxide, silicon carbide, zirconium silicate, silliminite, mullite, steatite or cordierite.

23. A method according to claims 21 or 22, characterised in that the additives include any of organic binders, methyl cellulose, starches or polyvinyl acetate.

24. A method according to any of claims 21 to 22, characterised in that the additives include an organic deflocculant sodium tripolyphosphate.

25. A method according to any of claims 21 to 22, characterised in that the ceramic forming mixture also includes up to 50% clay to form a slurry.

26. A method according to claim 25, characterised in that the clay is ball or china clay.

27. A ceramic product made by a method according to any of the preceding claims.

28. Apparatus for forming a ceramic product, the apparatus including a mixing unit for mixing together components of a ceramic forming mixture, the mixing unit being connected to a foaming unit for causing the slurry to foam, the foaming unit connecting to a die unit for extruding foamed mixture therethrough.

29. Apparatus according to claim 28, characterised in that a support unit is provided arranged to receive extruded lengths of material from the die unit.

30. Apparatus according to claim 29, characterised in that the support unit is in the form of a conveyor.

31 . Apparatus according to claim 30, characterised in that the support unit is a roller conveyor.

32. Apparatus according to any of claims 28 to 31 , characterised in that the mixing unit is in the form of a high speed blunger.

33. Apparatus according to any of claims 28 to 32, characterised in that a pump is provided for pumping slurry from the mixing unit to the foaming unit.

34. Apparatus according to claim 33, characterised in that the pump is a fixed displacement pump.

35. Apparatus according to any of claims 28 to 34, characterised in that a sieve is provided between the mixing unit and the foaming unit to remove particles above a predetermined size.

36. Apparatus according to claim 35, characterised in that the predetermined size is 2mm.

37. Apparatus according to any of claims 28 to 36, characterised in that the foaming unit includes an inlet for compressed air to be mixed with the slurry.

38. Apparatus according to any of claims 28 to 37, characterised in that the foaming unit includes an inlet for a foaming agent.

39. Apparatus according to claim 38, characterised in that the foaming unit permits drip dosing of the foaming agent.

40. Apparatus according to any of claims 26 to 39, characterised in that the foaming unit comprises a plurality of relatively rotating rotors and stators for entraining the air in the slurry.

41 . Apparatus according to claim 40, characterised in that the rotors and stators of the foaming unit rotate at a speed of between 200 and 500 rpm.

42. Apparatus according to any of claims 28 to 41 , characterised in that a feed pipe is provided extending from the foaming unit to the extruding unit.