GB2068356A

GB2068356A - Refractory binder

Info

Publication number: GB2068356A
Application number: GB8101506A
Authority: GB
Original assignee: Steetley Refractories Ltd
Current assignee: Steetley Refractories Ltd
Priority date: 1980-02-05
Filing date: 1981-01-19
Publication date: 1981-08-12
Also published as: GB2068356B

Abstract

A method for making a refractory article comprises pressing a mixture containing one or more refractory materials, a phosphate binding agent and an organic binder which on firing leaves little or no residual carbon in the article, and optionally firing the article.

Description

SPECIFICATION Fume-free brick The present invention relates to a method of making refractory articles, such as bricks.

In one method of making refractory bricks, a mixture containing refractory particulate material and a binder is pressed to form the bricks. The binder is used to impart adequate wet and dry strength. The resulting green bricks may be used directiy in furnace construction or first fired to give ceramically bonded bricks.

The binders most frequently used as sulphite lye or tar. When green bricks containing these materials are first used or fired they give off a considerable amount of fume which pollutes the environment.

We have now found a binder system which reduces the fume problem.

Accordingly the present invention provides a method for making refractory articles such as bricks, which method comprises pressing a mixture containing one or more refractory materials, a phosphate binding agent and an organic binder which, if fired, leaves little, if any, residual carbon and optionally firing the article.

By a phosphate binding agent is meant an inorganic compound having a phosphorus pentoxide component and which is capable of developing a bond with magnesia or calcined dolomite at temperatures above 6000C. Such compounds include phosphoric oxides, phosphoric oxyacids and salts thereof, i.e. material containing both oxygen and pentavalent phosphorus.

Examples include salts and acid salts containing as the anionic component, orthophosphate, pyrophosphate, metaphosphate, polyphosphate, for example having a chain length of 5-25, and the like. Suitable cationic components for these salts include ammonium, alkali metal e.g. sodium, alkaline earth metal e.g. calcium or magnesium etc.

Specific phosphate binding agents, include sodium polyphosphate, ammonium polyphosphate, potassium phosphate, magnesium phosphate and the like. A particularly useful phosphate is the sodium polyphosphate sold as Calgon.

The organic binder is in general one where less than 10% of the carbon content of the binder is retained in a brick after firing at 10000C in a nonoxidising atmosphere. Such a non-oxidising or even reducing atmosphere may be produced by burning fuel in excess over the air supply available in the furnace. This is to be compared with conventional tar-containing binders which fume excessively and for which at least 20% of the carbon content of the tar is retained after firing at 10000C in a reducing atmosphere. Desirably the low carbon organic binder is one which is substantially oxidised to innocuous gases such as carbon dioxide and water when burnt in air.

The low carbon organic binder is preferably a wax but may also be a vegetable oil, a fatty acid pitch, a stearin pitch and the like.

The wax used in the present invention may be a natural wax or a synthetic wax. Suitable natural waxes include animal (beeswax, spermaceit, lanolin, shellac wax), vegetable (carnauba, candelilla, bayberry, sugar-cane) and mineral (ozocerite, ceresin, montan, paraffin, petroiatum).

Suitable synthetic waxes include ethylenic polymers, polyol ether-esters, chlorinated naphthalenes, etc.

The amount of organic binder in the mixture is preferably 2% to 6% by weight, preferably 2.5% to 5% by weight based on the weight of the mixture.

The amount of phosphate binder employed in the rnixture is preferably in the range 0.5% to 4% preferably in the range 1% to 2.5% as P205, the percentages being by weight based on the weight of the mixture.

The refractory particles used in making the articles e.g. brick according to the present invention are normally obtained by crushing and grading refractory materials to obtain a coarse fraction and a fine fraction suitable for compounding into articles. The fine fraction is generally prepared in a ball or tube mill and is of such a size that substantially all passes a 72 BS sieve, and has the consistency of flour. This fine fraction may contain a proportion of particles down to 1 micron mean diameter and have a specific surface area of 0.1 to 1.0 square metres per gram. Weighed proportions of the coarse graded fraction, which is preferably all retained on 72 BS sieve, and the fine fraction are mixed together.In general the proportions of the coarse fraction to the fine fraction are around 70% by weight of coarse to 30% by weight of fines but the proportions may be varied from 90:10 to 20:80 respectively with a preferred range of from 80:20 to 60:40 respectively.

The refractory material may be dead burned magnesia, dead burned limestone, dead burned dolomite or stabilised dead burned dolomite either alone or in admixture with another refractory material such as dead burned magnesia.

Stabilised dolomite is a product obtained by dead burning a mixture containing dolomite and a substance which forms an oxide capable of reacting with the calcium oxide component of the dolomite thereby substantially decreasing its reactivity with water.

Green bricks made by the process of the present invention may be used directly in furnace construction or they may be fired to a temperature in the range 6000C to 12000to give ceramically bonded bricks.

Preferably the mixture is formed at temperature in range 1 50C to 1000C.

The present invention also includes a green refractory article e.g. brick comprising refractory particles, and, as a binder, a mixture containing a phosphate binding agent and a low carbon organic binder and also includes a fired refractory article e.g. brick when produced by firing such a green refractory article.

The following examples, in which parts are by weight, are given to illustrate the present invention.

EXAMPLE 1 Dead burned dolomite was mixed with 2% sodium polyphosphate and 4% paraffin wax at 800 C. The mixture was pressed into bricks at 8 tpsi.

The grading of the dead burned dolomite was as follows: Size of mesh (mm) % retained 4 2 2.8 32 2.0 16 1.0 16 0.5 3 0.25 1 -0.25(0.4 sq m/g) 30 On first firing of a furnace lined with bricks made according to this example only a limited amount of fume was caused. It was found that the bricks were substantially carbon free after firing.

EXAMPLE 2 The bricks of example 1 obtained after pressing were fired at 1 0000C to give a ceramically bonded product from which the wax binder had been burned off. Fume emission during firing was relatively light. It was found that the fired bricks were substantially carbon free after firing.

Claims

1. A method for making a refractory article, which method comprises pressing a mixture containing one or more refractory materials, a phosphate binding agent and an organic binder which on firing leaves little or no residual carbon in the article, and optionally firing the article.

2. A method as claimed in claim 1 wherein the mixture contains as a refractory material dead burned magnesia, dead burned limestone, dead burned dolomite or stabilised dead burned dolomite.

3. A method as claimed in claim 1 or claim 2 wherein the refractory material comprises a mixture of a coarse fraction and a fine fraction in the proportions of 90:10 to 20:80 by weight, the coarse fraction being retained by a 72 BS mesh sieve and the fine fraction substantially all passing a 72 BS sieve.

4. A method as claimed in any preceding claim wherein the phosphate binding agent is an orthophosphate pyrophosphate, metaphosphate or polyphosphate.

5. A method as claimed in claim 4 wherein the phosphate binding agent is an orthophosphate, pyrophosphate, metaphosphate or polyphosphate of ammonium, an alkali metal or an alkaline earth metal.

6. A methof as claimed in claim 5 wherein the phosphate binding agent is sodium polyphosphate ammonium, polyphosphate, potassium phosphate or magnesium phosphate.

7. A method as claimed in any preceding claim wherein the organic binder is a wax, a vegetable oil, a stearin pitch or a fatty acid pitch.

8. A method as claimed in claim 7 wherein the organic binder is beeswax, spermacetiwax, lanolin, shellac wax, carnauba wax, candelilla wax, bayberry wax, sugar-cane wax, ozocerite, ceresin wax, montan wax, paraffin wax, petrolatum, or a waxy ethylemicpolymer polyol polyester or chlorinated naphthalene.

9. A method as claimed in any preceding claim wherein the amount of organic binder in the mixture is from 2 to 6% by weight.

10. A method as claimed in any preceding claim wherein the amount of phosphate binding agent in the mixture expressed as P205 is from 0.5 to 4% by weight.

11. A method as claimed in any preceding claim including the step of firing the refractory article at a temperature of from 600 to 10000 C to form a ceramic bond therein.

12. A method as claimed in any preceding claim wherein the refractory article is a brick.

13. A method for producing a refractory brick substantially as hereinbefore described in Example 1 or Example 2.

14. A green or fired refractory brick produced by a method as claimed in any preceding claim.

15. A green refractory article containing refractory material, a phosphate binder and an organic binder as defined in claim 1.

16. A fired refractory article obtained by firing an article as claimed in claim 1 5.

1 7. A furnace comprising bricks as claimed in claim 14 or bricks being articles as claimed in claim 15 or claim 16.