EP1556314A1

EP1556314A1 - Method for manufacturing a brick, ceramic or similar article

Info

Publication number: EP1556314A1
Application number: EP03761710A
Authority: EP
Inventors: Andrew Simon Smith
Original assignee: Ceram Technology Ltd
Current assignee: Ceram Technology Ltd
Priority date: 2002-06-28
Filing date: 2003-06-30
Publication date: 2005-07-27
Also published as: AU2003251141A1; GB0215048D0; WO2004002918A1

Abstract

The invention relates to a method for manufacturing a brick, ceramic or similar article. Traditionally the manufacture of bricks, roofing tiles and pipes has been an energy intensive process. Increasing commercial and environmental demands are drivers to reduce energy requirements the generation of so-called greenhouse gasses. By the addition of finely milled glass, as a fluxing agent, the firing temperature has been reduced. This has had the added benefit of reducing fluoride emissions from the articles during firing. The invention overcomes problems associated with the prior art by providing a method for manufacturing a brick or similar article comprising the steps of: producing a clay mix by mixing milled clay with a fluxing agent, forming the mix and firing it to produce finished brick or ceramic articles, characterised in that the clay mix is capable of being fired at a lower temperature.

Description

Method for Manufacturing a Brick. Ceramic or Similar Article

Background

This invention relates to a method for manufacturing a brick, ceramic or similar article, such as pipes, ducts, slabs or tiles, formed from clay. All of the aforesaid articles are hereinafter collectively referred to as ceramic articles.

Traditionally the manufacture of heavy clay products such as bricks, roofing tiles and pipes has been an energy intensive process. Increasing commercial and environmental demands are drivers to reduce energy requirements. The tendency to try to reduce the firing temperatures of ceramic articles is also driven with the aim of trying to reduce generation of so-called greenhouse gasses, such as carbon dioxide (CO₂) and carbon monoxide (CO). Increasingly primary manufacturers are being penalised, in the form of taxes, for the production of so-called greenhouse gasses from energy intensive processes. Collectively these taxes are often referred to as carbon taxes.

Another problem associated with the manufacturing processes of bricks and ceramic articles, is that elevated manufacturing temperatures can give rise to emission of fluoride gasses from the articles during firing.

Prior Art

A typical clay brick manufacturing process can be described as follows. Seams of clay in a quarry, which is usually, but not exclusively, adjacent or close to a brick manufacturing plant, are worked. Where required, clay is formed into a compacted layered stockpile to provide a uniform blend of material for the brick making process. As required the clay is dug from the face of the stockpile and transferred to a box feeder, often via a primary crusher. From the box feeder the clay is conveyed to a pan mill. This can be a wet or dry grinding process. Dry ground clay is subsequently screened with oversize material returned to the pan mill for further grinding. Additional grinding may be carried out through the use of medium or high-speed rolls before the clay is fed to a mixer, where a controlled addition of water is introduced to provide plastic clay suitable for shaping. At the mixing stage controlled additives of body stains and anti-scumming agents may also be introduced as required. The product at this stage is referred to as tempered clay and it is then formed into bricks, either by an extrusion or soft mud moulding process. At this point variations in appearance can be obtained by texturing the face of an extruded column of clay and the application of surface sands and stains.

Extruded bricks are manufactured either solid or with body perforations, with an upper limit of around 25% of the gross volume of the unit. Soft mud moulded bricks are often produced with an indentation in a bed face referred to as a "frog". After shaping, bricks are palletised for drying in either a tunnel or chamber type dryer. Safe rates of drying will vary for different types of clay, but typically drying to less than 1% moisture content is achieved in about 48 hours. The vast majority of bricks are fired in continuous tunnel kilns although some are still fired in traditional continuous chamber kilns and others in intermittently fired chamber kilns. When firing in tunnel kilns, bricks are automatically set on kiln cars. Depending on the type of clay, bricks are fired to a top temperature in the range of 950-1200°C.

Tunnel kilns may be in excess of 50 metres long and consume in excess of several Tera joules of energy every day. The vast majority of kilns are fired by natural gas. The temperature profile varies through the kiln in a controlled way in order to provide a controlled rate of heating, soaking and cooling. One reason why this is done is due to the thermal properties of the material: namely it cannot be fired (or cooled) too quickly otherwise the bricks could undergo thermal shocks and may bloat or fracture.

Close control needs to be exercised over the firing process in terms of uniformity of temperature and airflows. Desired variations in face colour can be achieved by adjusting the kiln atmosphere during the latter stages of firing. On exiting the kiln, kiln cars are unloaded and the bricks assembled for packaging. A medium sized brick plant typically produces about 500,000 bricks per week with larger plants producing over 2 million bricks per week.

A disadvantage with the aforementioned process is that it consumes vast quantities of energy in order to make, dry and fire the bricks.

It is therefore desirable to reduce the amount of energy used in the firing process and also to reduce generation of greenhouse gasses, such as carbon dioxide (CO₂) and carbon monoxide (CO). Increasingly an advantage of this is to reduce so-called carbon taxes that may be levied.

The present invention arose in order to overcome the aforementioned problems.

Summary of the Invention

According to a first aspect of the present invention there is provided a method for manufacturing a brick, ceramic or similar article comprising the steps of: producing a clay mix by mixing at least 90%, by weight, of milled clay with 10% by weight, or less, of fluxing agent, the fluxing agent having a melting point less than 800°C; forming said clay mix into predetermined forms and firing said forms so as to produce finished brick or ceramic articles, characterised in that the clay mix is capable of being fired at a lower temperature without any degradation of quality in the finished brick or ceramic article.

According to a second aspect of the present invention there is provided a method for manufacturing a brick, ceramic or similar article comprising the steps of: producing a clay mix by mixing at least 90%, by weight, of clay with 10% by weight, or less, of fluxing agent, the fluxing agent having a melting point less than 800°C; milling the mix thereby formed; forming said clay mix into predetermined forms and firing said forms so as to produce finished brick or ceramic articles, characterised in that the clay mix is capable of being fired at a lower temperature without any degradation of quality in the finished brick or ceramic article.

It will be appreciated that fluxing agent may be mixed with milled clay and then mixed; or mixed with unmilled clay prior to the clay having been milled.

The introduction of a fluxing agent has been found to reduce significantly the energy requirements for firing and as a consequence reduce emissions to the atmosphere. Use of the fluxing agent therefore reduces carbon taxes that would otherwise been due.

It is important that extensive mixing of the fluxing agent is performed so that the fluxing agent is mixed intimately and dispersed throughout the clay, so as to obtain an homogenised mixture. A deflocculating agent may be used in order to assist and/or promote this mixing.

Ideally the percentage weight of the milled clay lies in the range between 90% to 95%, with a corresponding percentage weight of fluxing agent in the range from 10% to 5%.

Preferably the fluxing agent includes crushed glass. The glass is preferably glass that has been milled or ground to an average particle size of 100 μm or less. Most preferably the average particle size is 75 μm or less.

The addition of crushed glass as a fluxing agent has been found to be particularly effective at reducing the firing temperature by as much as 100°C. This substantial reduction in firing temperature has resulted in considerable savings in energy costs with a resultant reduction in greenhouse gas emission.

The addition of crushed glass as a fluxing agent has also been found to improve certain physical properties of the brick or ceramic article. One particular property is the frost resistance. This property is an extremely important property and is widely used in the brick industry as an indication to the quality of the brick.

Additives may be added to the wet clay mixture so as to remove any additional substances, such as sodium, which may leach from the crushed glass. Alternatively, or in addition to, separate specialised means may be provided for removal of excess sodium. The means for removal of excess sodium may include: chemical absorbents or electro-chemical processors.

Crushed glass may be obtained from glass recycling and recovery plants. In situations where unwanted substances may leach from a crushed glass fluxing agent, means is advantageously provided for the detection of said substances and for its automatic removal. Any additional deflocculating which may be required is felt to be more than compensated by the superior properties such as improved frost resistance, of the finished brick or ceramic article.

An unexpected benefit of using crushed glass is that the ceramic article can be fired in less time than was previously possible. Thus for particular ceramic articles, such as bricks, a faster throughput is achievable.

Another advantage of the method of manufacturing a ceramic article, in particular a brick, is that it has been found that there is reduction in emissions of gasses such as Hydrogen Fluoride (HF), when the method is compared with existing brick manufacturing processes. The reduced emissions may be a corollary of firing at lower kiln temperatures or shorter firing time.

According to another aspect of the invention there is provided a mixture suitable for producing a brick or ceramic article comprising: at least 90%, by weight, of milled clay and 10% by weight, or less, of fluxing agent.

The crushed glass may be crushed glass derived from recycled domestic or industrial waste. Brief Description of the Drawing

A preferred embodiment of the invention will now be described, with reference to the Figure, which is a diagrammatical flow diagram illustrating key steps in the manufacturing process of one way of performing the invention, namely the manufacture of bricks.

Detailed Description of Preferred Embodiments

The Figure is a simplified flow diagram illustrating key steps in brick manufacture. For ease of reference the steps are numbered.

Finely milled glass can be added into the processing stream of the clay at a number of points in the manufacturing process. The nature of where and how glass fluxing material is added, to the clay processing stream, is reflected in the methods identified below:

1. Addition of fine ground glass (fluxing material) is made as a tempered powder. The ground glass is mixed with 0-10% of ball clay, or other mineral and water, sufficient to moisten the mix and make it slightly cohesive. The fluxing material may then be added into the clay processing stream during, (a) the stockpile building stage (step 3); or (b) as a discrete layer or layers in the stockpile; or (c) proportioned into a box feeder (step 4).

An advantage of this method is that the fluxing material can be easily handled, without the need for specialised handling equipment. At smaller, less complex manufacturing plants the fluxing agent is handled as a tempered powder and can be handled by a front-end loader (not shown).

2. Finely milled glass can also be added in the form of pelletised granules. An organic or inorganic binder is used which is immediately disrupted on contact with water. Addition of the fluxing agent in this state is made at step 4 or thereafter. An advantage of using the material in this pelletised state is that is easily handled and dust is reduced. Once again no additional, expensive handling equipment is required. Material can be pneumatically conveyed if required. No (or very little) water needs to be added with the glass, which makes this pelletised form suitable for clays where limited water can be added, or where the clay stockpile is already too wet.

3. Finely milled crushed glass is added, with water, in the form of slurry in a mixer. A deflocculating agent is added in order to promote mixing of the finely milled crushed glass and water mixture. The deflocculating agent is needed in order to help to maintain the glass particles in a stable suspension. This process can be either on site or delivered in IBC containers or bulk.

An advantage with using a deflocculating agent is that it promotes more intimate mixing with the clay and glass fluxing agent and therefore a better dispersion of glass. By adding the deflocculating agent in a slurry form and producing an homogeneous mixture, the dispersion of dry powder is reduced and this also reduces the amount of airborne dust, because when the glass fluxing agent is wet it tends to stick together and cake.

Addition rates of the deflocculating agent can be carefully controlled, and the slurry can be added instead of adding main process water at the mixing stage (step 7). It may also be desirable to add additional quantities of water during the mixing stage to achieve the right consistency for extrusion or moulding. The slurry can be mixed locally at brickworks, to avoid shipping water.

The invention has been described by way of an exemplary example only and it will be appreciated that variation may be made to the embodiment described without departing from the scope of the invention.

Claims

1. A method for manufacturing a brick, ceramic or similar article comprising the steps of: producing a clay mix by mixing at least 90%, by weight, of milled clay with 10% by weight, or less, of fluxing agent, the fluxing agent having a melting point less than 800 °C; forming said clay mix into predetermined forms and firing said forms so as to produce finished brick or ceramic articles, characterised in that the clay mix is capable of being fired at a lower temperature or for a shorter time without any degradation of quality in the finished brick or ceramic article.

2. A method for manufacturing a brick, ceramic or similar article comprising the steps of: producing a clay mix by mixing at least 90%, by weight, of clay with 10% by weight, or less, of fluxing agent, the fluxing agent having a melting point less than 800°C; milling the mix thereby formed; forming said clay mix into predetermined forms and firing said forms so as to produce finished brick or ceramic articles, characterised in that the clay mix is capable of being fired at a lower temperature without any degradation of quality in the finished brick or ceramic article.

3. A method for manufacturing a brick, ceramic or similar article according to claim 1 or 2 wherein the percentage weight of the milled clay lies in the range between 90% to 95%, with a corresponding percentage weight of fluxing agent in the range between 10% to 5%.

4. A method for manufacturing a brick, ceramic or similar article according to any of claims 1 to 3 wherein the fluxing agent is mixed intimately and dispersed throughout the clay, so as to obtain an homogenised mixture

5. A method for manufacturing a brick, ceramic or similar article according to any of claims 1 to 4 wherein the fluxing agent includes crushed glass.

6. A method for manufacturing a brick, ceramic or similar article according to claim 5 wherein the crushed glass has been milled or ground to an average particle size of 100 μm or less

7. A method for manufacturing a brick, ceramic or similar article according to claim 5 or 6 wherein the crushed glass has been milled or ground to an average particle size of 75 μm or less.

8. A method for manufacturing a brick, ceramic or similar article according to any preceding claim wherein additives are added to the wet clay mixture in order to remove substances, such as sodium.

9. A method for manufacturing a brick, ceramic or similar article according to any of claims 5 to 7 wherein the fluxing agent includes crushed glass wherein means is provided for removal of excess sodium.

10. A method for manufacturing a brick, ceramic or similar article according to claim 9 wherein the means includes chemical absorbents or electro-chemical processors.

11. A method for manufacturing a brick, ceramic or similar article according to any of claims 5 to 10 wherein the fluxing agent includes crushed glass obtained from glass recycling and recovery plants.

12. A method for manufacturing a brick, ceramic or similar article according to any preceding claim wherein a deflocculating agent is added in order to promote mixing of the clay and fluxing agent

13. A brick, ceramic or similar article manufactured according to any of claims 1 to 12 wherein the addition of crushed glass fluxing agent has been found to improve certain physical properties of the brick or ceramic article.

14. A brick, ceramic or similar article manufactured according to claim, 13 wherein the frost resistance of the brick, ceramic or similar article is superior to existing brick, ceramic or similar articles.

15. A mixture suitable for producing a brick or ceramic article comprising: at least 90%, by weight, of milled clay and 10% by weight, or less, of fluxing agent.