FR2467829A1 - Refractory brick mfr - by mixing refractory aggregate with aluminium phosphate binder, micronised magnesia or alumina and carboxymethyl:cellulose and pressing - Google Patents

Abstract

Refractory element such as a brick comprises 75-90% refractory aggregates of high mechanical strength, a chemical binder of aluminium monophosphate type and reactants such as micronised colloidal products and carbomethylcellulose (sic). The granulates must conform to the formula: Y=A+(100-A) square root d/D where Y is the percentage of grains in the mixt. passing through a sieve of mesh dimerisation d; A is the Bolomey coefft. for a fluid mass, and is taken as 14 in the present case, D is the dimersion of largest grain in the mixt., and must be highly homogeneous. Used in mfr. of pressed very high density refractory bricks. The sintering step of mfr. used in prior art is omitted with consequent saving of energy. Smooth flat surfaces such as are produced by pressing are retained with advantages of stocking during transport and assembly. High mechanical strengths are achieved in both the unfired bricks and the fired refractory linings formed after building, and firing the first heat in the furnace constructed. The method can be used in principle for acid or basic refractories.

Description

 The present invention relates generally to mixed compositions for the manufacture of pressed bricks at very high density.

 The refractory bricks currently used are composed of granular refractory products mixed with raw clay, tar, or other chemicals, liquids or solids, and water.

 These mixtures are kneaded, deaerated and pressed or compressed so as to form monolithic pieces, the latter then being dried and then baked.

These prefabricated parts all have various drawbacks such as:
- High cost price because their cooking at high temperature in order to obtain a material which will no longer present significant volumetric variations, requires a great debauchery of energy during cooking.

- This same firing also results in a deformation of the block which then no longer has a flat surface state X of rigorous dimensions.

The object of the invention is to remedy these drawbacks because:
- On the one hand, it recommends the use of noble materials, already stabilized and in selected particle sizes which results in the addition of an appropriate binder, reacting when cold, to suppress the baking phase while safeguarding the physical characteristics of the material.

 - On the other hand, the fact of eliminating the cooking phase makes it possible to keep the surface condition and the dimensions of the block intact.

 - Finally, the pressure of very high density bricks allows maximum compactness, minimum porosity and high density to be obtained.

 In addition, the invention makes it possible to remedy certain drawbacks presented by uncooked bricks, based on sand, containing 7 to 8% of alumina, currently commonly produced but whose major drawback is the brittleness despite all the coagulation aggregates. existing on the market.

The invention and the manufacturing process therefore relate essentially to:
- the choice of aggregates, the geological and physical nature of the products making up their particle size as well as their homogeneity
-the incorporation of suitable binders allowing cold bonding
- the use of pressing equipment of adequate density.

1.- THE CHOICE OF AGGREGATES AND THEIR GRANULOMETRY AS WELL AS
THEIR HOMOGENEITY
The aggregates which can be indifferently aluminous or basic must all be calcined at a temperature close to their temperature of use.

dans laquelle y = % de grains du mélange passant à travers la maille de
de tamis de dimension d
A = coefficient Bolomey pour une masse fluide pris égal à
14 dans le cas présent.Their particle size must be as close as possible to the curve according to the following formulation:

in which y =% of grains of the mixture passing through the mesh of
d-size sieves
A = Bolomey coefficient for a fluid mass taken equal to
14 in this case.

dn dimension of the mesh considered (valid)
D = maximum grain size of the mixture.

(d and D expressed in the same units)
Such a formulation has the advantage of producing materials having good plastic behavior during their use either in the press or in the press, while having sufficient rigidity as soon as this stress ceases, regardless of any consideration on the binder. .

As for homogeneity, it will be a determining factor in the quality of the finished product since it will condition the good distribution of the aggregates on the one hand but above all the optimum dispersion of the binder in the mass.

This can be obtained using a mixer fitted with the following accessories or working tools:
- Mixer tank fitted with a rotating floor
- Internal tooling of the tank composed of a vortex whose speed of rotation can vary from 300 to 1000 revolutions / minute and a stirrer-scraper.

The scraper agitator continuously picks up and pushes the material towards the vortex.

 These two accessories rotate in the same direction while the rotary sole rotates in the opposite direction.

2.- INCORPORATION OF A SUITABLE BINDER ALLOWING A
COLD CONNECTION
The binders we use are chemical binders from the phosphate family.

 These products, known for many years, are commonly used as binders in many refractory masses. However, when used as is, they do not allow cold bonding of aggregates.

Indeed at 180 C, the primary aluminum phosphate transforms X aluminum metaphosphate by dehydration, and the metaphosphate remains stable up to 8000C. Beyond 8200C, the aluminum metaphosphate releases P205, and we witness the reverse process of phosphate formation which gives orthophosphate from poly- and pyrophosphate. As the temperature increases and after all P205 has disappeared, there is still A1203.

ORTHOPHOSPHATE PRI
MAYOR OF ALUMINUM
ALUMI METAPHOSPHATE.

 ALUMI POLYPHOSPHATE.

ALUMI PYROPHOSPHATE.
The table above illustrates the stages of metaphosphate formation as the temperature increases.

 The invention consists in adding to it a product causing a cold bond.

 To do this, it is advisable to make a basic addition making it possible to neutralize the phosphates in the form of micronized colloidal products such as alumina or magnesia.

 The reaction will be completed by the incorporation of carbomethylcellulose intended to retain and then release the necessary humidity during the chemical setting. In addition, this agent, by its lubricating power will facilitate the pressing of the exterior and will make the extrusion of the blocks easier.

 Finally, this agent will disappear when the refractory is put into service and will leave only a minimum of deposit after combustion.

 It should be noted that the compositions thus prepared and after incorporation of the binders must be rapidly shaped in all cases within a period which may not exceed 8 to 12 hours.

3. - THE USE OF HIGH DENSITY PRESSING EQUIPMENT:
A brick with optimum qualities, is obtained, after compliance with the recommendations of paragraphs 1 and 2 above, only after pressing under 400 atmospheres minimum.

To do this, the selected equipment must meet the following characteristics:
- Pressing force greater than 400 atmospheres
- Double compression effect
- Deaeration of the pressed block during tightening.

The shaped refractory elements will then be stored in a ventilated place and cannot be put into service until after 48 hours. This period is indeed necessary to reach the end of the chemical reaction as described in paragraph 2 above.

 We give below by way of indication a few examples of the composition of bricks prepared according to the characteristics of the invention.

a) Sand-based brick:
Raw silico-aluminous substance titrating 6 to 8% of slightly dehydrated alumina to contain only 7% of water with a particle size between 0.5 and 1.5 mm. The pyroscopic resistance of use of the brick could be improved by additions of quartz, flint, disthene, zirconium silicate, zircon oxide for example, additions which will also bring an increase in volume intended to compensate for the shrinkage of the raw clay laws of temperature rise.

 The invention will consist in supplementing this preparation with the agents described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Colloidal micronized products from 2 to 6% of the mixture - CarbomethylceLulose from 5 # to 1% of the mixture.

b) Brick at 60% of A1203
Aluminous substance titrating more or less 60% alumina with a particle size as close as possible to the curve described above composed of: - 80 to 90% andalusite, kerphalite and others - 5 to 7.5% colloidal clay.

 The invention will consist in supplementing this preparation with the additions described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Colloidal micronized products from 2 to 6% of the mixture - Carbomethylcellulose from 5Y00 to 1 % of the mixture.

c) Brick with 80% of A12O3:
Highly aluminous substance titrating more or less 80% of alumina with a grain size as close as possible to the curve described above composed of: - 80 to 90% of bauxite, gypsum and others.

- 5 to 7.5% of a colloidal clay
The invention will consist in supplementing this preparation by the additions described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Colloidal micronized products from 2 to 6% of the mixture - Carbomethylcellulose from 5 # to 1% of the mixture.

d) Brick containing 80/85% MgO
Magnesium substance titrating more or less 85% of MgO, with a particle size as close as possible to the curve described above composed of: - 85 to 95% of magnesia, chromium and others ...

- 2.5 to 5% of a colloidal clay.

The invention will consist in supplementing this preparation with the additions described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Colloidal micronized products from 2 to 6% of the mixture - Carbomethylcellulose of 0.5X 1% of the mixture e) Chromium magnesia-
Substance based on magnesia and chromium ore with a particle size as close as possible to the curve described above composed of: - 85 to 95% of chromium magnesia - 2.5 to 5% of a colloidal clay.

The invention will consist in supplementing this preparation by the additions described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Colloidal products micriples from 2 to 6% of the mixture - Carbomethylcellulose from 0.5 to 1% of the mixture.

f) Brig of silicon carbide:
Substances based on silicon carbide with a ganulometry as close as possible to the curve described above composed of: - 85 to 95% of silicon carbide - 2.5 to 5% of a colloidal clay or other colloidal products - dux.

 The invention will consist in supplementing this preparation by the additions described above in the following proportions: - Phosphates from 0.5 to 3.5% of the mixture - Micronized colloidal products from 2 to 6 t of the mixture - Carbomethylcellulose of 0.5 '' to 1 t of the mixture.

Claims (10)

"original" Claims: 1. Refractory element such as brick, characterized in that it is essentially composed of 75 to 90% of refractory aggregates with high mechanical resistance, of a chemical binder of the alumina monphosphate type and of reagents such as products micronized colloidals and carbomethyl cellulose. 2. Refractory element according to claim 1, characterized in that the aggregates must approximate in their particle size to the formulation:

 in which: Y =% grain of the mixture passing through the mesh  d dimension sieve A = Bolomey coefficient for a fluid mass taken equal to 14 in the present case. D = maximum grain size of the mixture. d = dimension of the mesh considered (variable) (d and D expressed in the same units) 3. Refractory element according to any one of claims 1 and 2, characterized by a very high homogeneity of the mass, 4. Refractory element according to one. any one of claims 1 to 3, characterized by a chemical bond using an agent of the phosphatic type chosen for its refractory qualities, its stability to freezing and its handling presenting no danger from the medical point of view. 5. Refractory element according to any one of claims 1 to 4, characterized by the versatile aspect of the phosphate chemical binders which can be indifferently used for the bonding of aluminous masses and basic masses. 6. Refractory element according to any one of claims 1 to 5, characterized by the addition of alumina or due micronized collodal magnesia intended to cause the cold reaction of the chemical binder described in claim 4. 7. Refractory element according to any one of claims 1 to 5, and 6 characterized by the addition of carbo methoxycellulose intended to release the necessary humidity during the chemical setting. 8. Refractory element according to any one of claims 1 to 7, characterized by a shaping delay which cannot exceed 8 to 12 hours. 9. Refractory element according to any one of claims 1 8, characterized by a pressing suitable to the circumstance in order to obtain the maximum compactness. 10. Refractory element according to any one of claims 1 to 9, requiring storage of at least 48 hours in a ventilated place eliminating any drying.